Coal, Petroleum and other form of fuels for energy conversion

Genuinely ‘Clean Coal’ - Solution for Reliable and Cheap Energy Source of Future

2010-09-18T02:53:00.000-07:00

Genuinely ‘Clean Coal’ - Solution for Reliable and Cheap Energy Source of Future

Partha Das Sharma, B.Tech(Hons.),
E.mail: sharmapd1@gmail.com
Blog/Website: http://saferenvironment.wordpress.com, www.coalandfuel.blogspot.com

Introduction:
Sufficient, reliable sources of energy are a necessity for industrialized nations. With global energy demand rising at an unprecedented rate, the world's vast coal reserves are attracting growing interest. Despite its low cost and abundance, increasing concerns over greenhouse gases and other emissions from fossil fuels are altering the technological and regulatory environment for coal. Programs are underway to limit, reduce, and capture emissions from coal plants. This may result in the emergence of new generation technologies and the increased use of advanced emissions control technologies. In so doing, the costs and economics of coal use may change.

Environmental Factors:
Coal combustion produces emissions of air pollutants including sulfur dioxide (SO2), nitrogen oxides (NOx), particulate matter (PM), carbon dioxide (CO2), and mercury (Hg). SO2, NOx, and PM emissions are associated with air quality impacts and acidification of water resources, or acid rain. CO2 emissions contribute to global climate change. Mercury, which can move in multiple environmental pathways, is a neurological toxin in humans and wildlife.

A wide range of control technologies can be employed to reduce emissions of particulates, mercury, sulfur dioxide, and oxides of nitrogen.

Particulates are captured with baghouses (BH), electrostatic precipitators (ESP), and multiclones (MC). Nitrogen oxides (NOx) compliance actions may include a mix of combustion control technologies, such as low-NOx burners (LNB) and overfire air (OFA), and end-of-pipe emission control technologies, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR).

Sulfur dioxide (SO2) compliance actions may include switching to lower-sulfur coal, retirements, and installation of various scrubber technologies, such as flue gas desulfurization (FGD), dry lime injection (DLI), and spray dry injector (SDI). Burning low-sulfur coal can reduce SO2 emissions from an uncontrolled plant by two-thirds; installing a scrubber can reduce emissions by 90 percent or more. Mercury can be reduced to a limited extent by conventional SO2 scrubbers; more advanced controls specifically designed to reduce mercury include carbon injection (CI) and baghouse (BH) equipment.

Carbon capture and sequestration (CCS) technologies are under evaluation for their potential for removing the CO2 emissions from coal-fired power plants. The commercially available method for capturing CO2 from a conventional pulverized coal-fired boiler is the use of an amine-based system to absorb CO2 from the flue gas stream, and its subsequent regeneration to produce a nearly pure product stream. An alternative method, known as oxy-combustion, to capture CO2 is to use oxygen rather than air as the oxidant in the combustion process that yields a flue gas stream comprised primarily of CO2 and H2O. By removing the water, a nearly pure CO2 stream can be produced.

Coal combustion produces significant quantities of solid waste by-products that can be put to beneficial use. Coal combustion waste products can be used as an ingredient in the manufacture of cement, asphalt, roofing shingles, gypsum, calcium chloride, lightweight aggregate, lightweight block, and low-strength backfill.

Emerging Coal Generation Technologies:
Pulverized coal system (PC) is the conventional coal burning technology used in most of the cases. In this, finely ground coal is combusted to make steam that turns turbines and generates electricity. The raw coal is fed into the pulverizer along with air heated to approximately 650˚F from the boiler. As the coal is pulverized, the hot air dries it and blows the usable fine coal powder out to be used as fuel. The powdered coal is then blown directly to a burner in the boiler. The burner mixes the powdered coal in the air suspension with additional pre-heated combustion air and forces it out of a nozzle similar in action to fuel being atomized by an automotive fuel injector. Under normal operating conditions, there is enough heat in the combustion zone to ignite all the incoming fuel.

As environmental emission regulations have been tightened, many coal plants have employed a range of operational modifications and capital equipment investments. In addition to fuel switching, i.e., low-sulfur coal, technologies are available and emerging to reduce emissions from coal burning at three different stages: pre-combustion, combustion, and post-combustion. Pre-combustion cleaning involves the removal of impurities from coal with physical, chemical or biological processes. Advanced combustion processes include improvements in existing coal combustion processes and new processes that remove pollutants from coal as it is burned. Post-combustion cleaning involves the removal of pollutants from the downstream flue gas after combustion and before exiting the stack. Many of the post-combustion pollution control technologies have been widely commercialized and have evolved into proven, mature technologies.

In recent years, technological advancements have led to substantial reductions in the cost of controlling SO2 and NOx emissions. Some of the most successful advancements are low-NOx burners, Selective Catalytic Reduction (SCR), Selective Non-Catalytic Reduction (SNCR), and scrubbers. Advanced pollution controls installed on existing power plants or engineered into new facilities can provide effective and low cost ways to reduce sulfur dioxide and nitrogen emissions.

Advanced power generation technologies are complete electric power generating systems that offer superior efficiency and environmental performance over conventional coal-burning systems. These new processes, such as circulating fluidized bed (CFB) combustion, can improve both efficiency and emission control. Another category of advanced coal technologies involves the conversion of coal into another form of fuel, e.g., gas or liquid. In most of these cases, the new fuel form provides both energy and environmental benefits by reducing the pollutants emitted from combusting the new fuel as compared to coal. Integrated gasification combined cycle (IGCC) is an example of this type of technology.

a. Circulating Fluidized Bed (CFB) - CFB combustion evolved from efforts to control pollutant emissions without external emission controls, such as scrubbers. The CFB technology suspends solid fuels on upward-blowing jets of air during the combustion process, resulting in a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer. The technology allows burning at temperatures well below the threshold where NOx form. In addition, the mixing action of CFB brings the flue gases into contact with a sulfur-absorbing chemical, such as limestone or dolomite, capturing more than 95 percent of the sulfur pollutants inside the boiler. The popularity of fluidized bed combustion is due not only to its capability of meeting SO2 and NOx emission standards without the need for expensive add-on controls but also technology's fuel flexibility. Almost any combustible material, from coal to municipal waste, can be used for fuel.

b. Integrated Gasification Combined Cycle - Another emerging combustion technology, integrated gasification combined cycle (IGCC), converts coal to a gaseous form similar to natural gas before being burned. This advanced technology converts coal into a combustible synthetic gas by reaction with oxygen and heat/steam. Emissions from these plants are very low compared to other coal technologies because the gas is cleaned prior to combustion, burned in a gas turbine, and the resulting exhaust gases are used to produce steam that then drives a steam turbine. Typically 60 to 70 percent of the power comes from the gas turbine with IGCC. The result is an IGCC configuration that provides ultra-low pollution levels and, in addition, carbon-capture technologies can more readily be built on to the back end of IGCC plants than traditional pulverized coal combustion technologies.

On the front end of IGCC is a gasification technology. Worldwide, there are 117 operating plants that include 385 gasifiers. Products from the syn-gas produced from gasification include chemicals, liquid fuels, and electric power.

c. Super Critical Steam - The use of supercritical (SC) and ultra-supercritical (USC) steam, heated to a higher temperature than conventional boilers, has the potential to achieve greater generation efficiency, resulting in more output per unit of fuel as well as fewer pollutants. Efficiencies of 40 percent and higher have been demonstrated. SC and USC plants require the use of more durable metals and alloys in order to withstand the higher operating temperatures. Although several SC and USC coal plants have been constructed and operated in the United States, some have experienced operating difficulties due to the high tolerances required. In more recently constructed plants in Japan and elsewhere, anecdotal reports indicate that SC and USC plants have operated more reliably with fewer outages than earlier designs.

d. Oxy-combustion (Oxy-Coal) – Oxy-combustion, or oxy-coal involves the combustion of coal in a mixture of oxygen and re-circulated flue gas. The main benefits of oxy-combustion technology with CCS are:
* Reduction of carbon dioxide emissions up to nearly 96.9 percent removal
* Reduction of SO2
* Potential for enhancement of mercury removal in the baghouse and advanced SO2 controls

Because it uses conventional equipment already proven in the power generation industry, the oxy-combustion technology can readily be applied to new coal-fired power plants. Plant control during startup, shutdown, and load following is very similar to a conventional PC plant. Finally, the key process principles have been proven in the past including air separation and flue gas recycle (FGR).

However, several challenges to oxy-combustion have also been identified:
* Air infiltration into the boiler dilutes the resulting flue gases. This could potentially be minimized by improved boiler materials, sealants, control technologies, and membranes.
* Combustion of fuels in a purified oxygen stream would occur at temperatures too high for existing boiler or turbine materials. This issue is being addressed by diluting the oxygen via the FGR, which results in an increase of the auxiliary power load and decreases efficiency. Further developments aim at increasing the efficiency of the FGR and improved boiler materials.
* The current capital and operating costs of specialized components are high.
* Plant efficiency is reduced by the use of the auxiliary load of FGR and air separation equipment.

Conclusion:
With introduction of improved and emerging technology, the efficiency and cleanliness of coal-fired power stations is improving. Genuinely clean coal - i.e.: one that emits close to zero CO2 thanks to carbon capture and storage technology - is not expected to become economically viable before twenty years, are now viable. Thus, coal is making a comeback as a cheap and reliable source of energy.

Important Fuels and their Energy content

2009-05-07T05:22:00.000-07:00

Important Fuels and their Energy content:

1. Coal –

Coal is a rock formed from ancient plants that have been decomposed and heated under pressure underground. This process is called metamorphism. Coal varies widely in its composition, as it is a complicated mixture of hydrocarbons and carbohydrates, with small amounts of nitrogen, sulphur, water and minerals. It must be mined from the ground, either from deep mines (which creates spoil heaps), or by open-cast surface mining (which devastates the landscape). There are enough reserves for 200–250 years at the present rate of consumption.

Coal burns in air with a yellow smoky flame, leaving ash behind. The energy content of coal depends upon its type. The heat of combustion of brown coal or lignite is about 25 kJ/g, but the heat of combustion of bituminous coal (used in industry) and anthracite (used in homes) is about 32 kJ/g. When coal burns, it produces water and carbon dioxide. It also produces harmful sulphur dioxide, carbon monoxide, oxides of nitrogen (known as NOx), hydrocarbons and soot.

Coal cannot be used in cars and aircraft, but it can be converted into gaseous or liquid fuel. This fuel can be used to power diesel engines, and German aircraft flew using it in the Second World War. The“liquefaction plants” needed to make it produce carcinogenic (cancer-causing) hydrocarbons.

2. Natural Gas –

Natural gas is nearly always found associated with oil (see the Oil sheet). It consists almost entirely of methane. For example, the Frigg gas field in the North Sea produces gas which is 95% methane and 4% ethane, with only traces of other hydrocarbons. It has no smell and does not contain carbon monoxide, so it is not poisonous. However, it can asphyxiate (suffocate), and so an artificial smell is added before it is distributed so that leaks can be detected.

Natural gas ignites easily, and will cause explosions if sufficiently large quantities escape. It is a relatively clean fuel, and produces only carbon dioxide and water when it burns completely. Its heat of combustion is –890.3 kJ/mol, equivalent to an energy content of 55.6 kJ/g. There are sufficient reserves of natural gas for only 20 years at the present rate of consumption. However, rotting rubbish in landfill sites generates it, and some companies are now pumping it out for sale. It also can be produced by deliberate production of “biogas”, which is about 50% methane. Biogas is produced from decaying organic matter in biogas digesters, and is particularly popular in India and China.

Natural gas is not very portable, and is usually delivered to the customer through underground pipes. It can be liquefied to form NGL (natural gas liquid). This is different from LPG (liquid petroleum gas), which is a liquefied by-product of oil refineries). NGL (and LPG) can be used to power vehicles, and some experimental aircraft.

3. Ethanol –

Ethanol is a member of a large class of compounds called alcohols. It is a colourless liquid (boiling point 78ºC) which will mix with water. It can be made by reacting ethene (a product of crude oil) and water at 300ºC and high pressure with phosphoric acid as a catalyst. It can also be produced from carbohydrates, such as sugar, by fermentation using yeast. This is the method of choice for producing alcoholic drinks.

Ethanol burns very easily with a pale yellow flame to form carbon dioxide and water. Its heat of combustion is –1367.3 kJ/mol, which is equivalent to an energy content of 29.6 kJ/g. Alcohol has been used as a fuel for a long time, for example in spirit lamps and as methylated spirits. It is relatively safe and easy to transport, as it is a liquid. Petrol can be blended with up to 20% ethanol for use in an ordinary car engine without adjustment. Recently, ethanol has been produced by fermentation in industrial quantities to power vehicles. Brazil, in its Proalcohol programme, produces 3,200 million litres of ethanol (“Gasohol”) per year from crops such as sugar cane, sorghum and cassava. Brazil has also designed and manufactured cars to run on pure ethanol. The fuel is more expensive than petrol, but effectively is a renewable energy source and does not have to be imported. However, it is doubtful that hungry people see this as a benefit.

4. Hydrogen –

Hydrogen is the most abundant element in the Universe, but on Earth free hydrogen is less than one part per million of the atmosphere. However, it is abundant on Earth in the form of water, which is an almost inexhaustible supply of the element.

Several million tonnes of hydrogen are manufactured in the world each year, including 500,000 tonnes per year in the U.K. It can be made by the electrolysis of brine (sodium chloride solution), but this process is expensive and inefficient. Other methods include passing steam over white-hot coke (the Bosch or Water Gas Process), and the oxidation of natural gas using a catalyst. It is also found as a by-product in oil refineries.

When hydrogen burns completely, the only product is water. The heat of combustion for hydrogen is –285.8 kJ/mol, which is equivalent to an energy content of 142.9 kJ/g. Hydrogen is very easy to ignite, and caused dreadful accidents (such as the famous “Hindenburg” disaster) when used to lift airships in the days before helium became plentiful. Hydrogen is stored in gas cylinders or liquid containers, allowing it to be used in some domestic or industrial situations where natural gas might be used. It would be difficult to use in cars or aircraft in this way, but large quantities can be absorbed by expensive metals such as palladium, and released later by warming.

5. Summary - Average energy content of coal, oil and natural gas:

Crude Oil - 47.9 kJ/g

Natural Gas - 55.6 kJ/g

Lignite Coal - 25 kJ/g

Bituminous and Anthracite coal - 32 kJ/g

Underground coal gasification (UCG) - Potential to increase coal reserve worldwide:

2008-09-29T01:48:00.000-07:00

Underground coal gasification (UCG) - Potential to increase coal reserve worldwide:

Introduction: Worldwide, coal reserves are quite vast - over 10 trillion tonnes. However, unless cleaner and cheaper ways can be found to convert coal to gas or liquid fuels, coal is unlikely to become an acceptable replacement for dwindling and uncertain supplies of oil and natural gas. Mining coal is dangerous work. Coal is dirty to burn and much of the coal in the ground is too deep or too low in quality to be mined economically. Today, less than one sixth of the world’s coal is economically accessible. However, there is a renewed interest world over to revive the old technology that offers promise to substantially increase usable coal reserves and make coal a clean and economic alternative fuel. Known as underground coal gasification (UCG), this technology converts coal to a combustible gas underground.

Underground Coal Gasification (UCG) is the process by which coal is converted in situ into a combustible gas that can be used as a fuel or chemical feedstock. It is a process to convert unminable underground coal/lignite into combustible gases (i.e., combustible syngas – a combination of hydrogen and carbon monoxide) by gasifying. UCG uses a similar process to surface gasification. The main difference between both gasification processes is that in UCG the cavity itself becomes the reactor so that the gasification of the coal takes place underground instead of at the surface.

Despite considerable research and testing, no commercially viable project has yet been demonstrated anywhere. Research has been conducted principally in Western Europe, USA, China, the former Soviet Union and Australia.

Benefits of UCG - As a method of exploiting coal, UCG represents an environmental improvement on the combination of coal mining and surface combustion of coal. It is also safer and intuitively more efficient.

Environmental benefits of UCG over underground coal mining for fuelling power generation include:

(i) Lower fugitive dust, noise and visual impact on the surface

(ii) Lower water consumption

(iii) Low risk of surface water pollution

(iv) Reduced methane emissions

(v) No dirt handling and disposal at mine sites

(vi) No coal washing and fines disposal at mine sites

(vii) No ash handling and disposal at power station sites

(viii) No coal stocking and transport

(ix) Smaller surface footprints at power stations

(x) No mine water recovery and significant surface hazard liabilities on abandonment.

Additional benefits include:

(i) Health and safety

(ii) Potentially lower overall capital and operating costs

(iii) Flexibility of access to mineral

(iv) Larger coal resource exploitable

Note: At present, natural gas offers attractions as a clean fuel that UCG may find difficult to compete.

Process of Underground Coal Gasification (UCG):

The basic UCG process involves drilling two wells into the coal, one for injection of the oxidants (water/air or water/oxygen mixtures) and another well some distance away to bring the product gas to the surface. Coal is gasified underground by creating a linkage through the coal seam between the injection and production wells and injecting air (or oxygen) and water (or steam) into the underground reaction zone. The injected gases react with coal to form a combustible gas which is brought to the surface in a production well, cleaned and used as a fuel or chemical feedstock. A cavity is formed as the coal burns and the roof collapses. This results in lateral growth and is allowed to continue until the product gas quality deteriorates. The greater the lateral growth, the longer the life of a gasifier and the more cost-effective the operation. When the quality of the product gas falls, fresh coal is ignited further along the injection well. Once the coal within the underground gasifier has been exhausted, new injection and production wells are drilled and the process is repeated.

Injecting oxygen rather than air reduces the nitrogen content and raises the heating value of the produced gas to the ‘medium-Btu’ gas range – of heating value roughly one-fourth of natural gas. If the goal is high-Btu gas (also called as substitute natural gas or SNG), the percentage of methane in the produced gases needs to be boosted. For methane formation in UCG, two additional steps are required. First, some of the carbon monoxide made in the gasification process is reacted with steam to form additional hydrogen. This step, called shift conversion, sets up the proper ratio of gases for the next step called methanation. The hot gas thus produced is allowed to pass through the coal seam to the exit boreholes and is carried to the surface where it is cleaned and upgraded for use. The whole aspect is elaborated in next paragraphs.

In fact, gasification differs from combustion which takes place when coal is burned in excess oxygen to produce carbon dioxide and water. Another important difference between coal combustion and coal gasification is in pollutant formation. The reducing atmosphere in gasification converts sulphur (S) from coal to hydrogen sulphide (H2S) and nitrogen (N) to ammonia (NH3), whereas combustion (oxidation) produces sulphur dioxide (SO2) and oxides of nitrogen (NOx).

The principal processes can be divided into two stages, namely (i) pyrolysis (also known as carbonisation, devolatilisation or thermal decomposition) and (ii) gasification. During pyrolysis coal is converted to a char releasing tars, oils, low molecular hydrocarbons and other gases. Gasification occurs when water, oxygen, carbon oxide and hydrogen react with the char.

The main gases produced are carbon dioxide, methane (CH4), hydrogen and carbon monoxide (CO) and oxygen. CH4 is essentially a product of pyrolysis, rather than gasification. Its formation is favoured by low temperature and high pressure.

In a theoretical appraisal of the gasification process, the Autothermal Chemical Equilibrium (ACE) condition exists. This is a condition at which the heat value of the product gas and the conversion efficiency of the gasified coal (chemical energy of product gas/chemical energy of gasified coal) is a maximum. At high temperatures and pressures (say 5MPa, 900°C), ACE conditions are approached rapidly but at lower temperatures and pressures the time to attain equilibrium greatly exceed the residence time of the gases in the gasifier and therefore ACE will not be attained.

The basic reactions can be generalised to a simple empirical form:

C + O2 → CO2 (+heat)

C + CO2 (+heat) → 2CO

C + H2O (+heat) → H2 + CO

C + 2H2 → CH4 (+heat)

During pyrolysis coal, subjected to high temperatures, yields higher heat value gases than ACE gasification products for a relatively small consumption of O2. Pressure increases the proportion of coal pyrolysed to form methane thus raising the heat value of the product gases. There is also some evidence to suggest that elevated pressures cause pyrolysis processes to penetrate in situ coal, further enhancing the gasifier yield.

Gasification circuit and Cavity behaviour: The gasification circuit requires a flow link to be achieved between an injection and a production well. Methods of achieving the link are:

* Accurate drilling assisted by a target device in the vertical well if necessary.

* Reverse combustion, involving ignition at the base of the production well.

Initially, channel created in coal seam using special drilling techniques. As reaction proceeds, channel grows, creating underground ‘cavity’. Volume of cavity increases progressively with progress of reaction.

Installation of well pairs (injection and production wells) is costly and therefore it is desirable to gasify the maximum volume of coal between a well pair. As gasification proceeds, a cavity is formed which will extend until the roof collapses. This roof collapse is important as it aids the lateral growth of the gasifier. Where the roof is strong and fails to break, or where the broken ground is blocky and poorly consolidated, some fluid reactants will by-pass the coal and the reactor efficiency could decline rapidly.

The most successful gasifier or reactor control process, developed in the USA, involves the use of a burner attached to coiled tubing. The device is used to burn through the borehole casing and ignite the coal. The ignition system can be moved to any desired location in the injection well. This ‘controlled retraction of ignition point’ (CRIP) technique enables a new reactor to be started at any chosen upstream location after a declining reactor has been abandoned.

Carbon capture and sequestration (CCS): If the CO2is to be captured at the surface and sequestered, it must be separated from the syngas. At a UCG production site, a significant percentage of the CO2would likely be sequestered in the void left by the burned coal seam. Ideally, remaining CO2can be sequestered in deep geologic formations nearby.

If the CO2is not sequestered in place, it can be piped to oil fields. Oil companies can then inject it underground to increase production from oil and natural gas wells, a process called enhanced oil recovery. This represents an opportunity to sequester carbon at a lower cost compared with storing it in geologic repositories.

Monitoring and Control: In order for the gasification process to be controlled, it is essential that continuous analytical measurement of the product gas stream is available.

Injection flow rate and composition, temperature and pressure were measured at various parts of the circuit to facilitate control of the gasifier and to ensure pressure and temperature design limits of system components were not exceeded. The manipulation of the following variables allowed the reaction rate and the gas quality to be adjusted within certain limits:

(i) Injected gas flow rate and composition

(ii) Reactor back pressure

(iii) Production well base temperature

(iv) Safety monitoring and alarm control

Technical requirements: Important technical requirements and considerations in designing a commercial gas production scheme:

(i) A cost-effective means of acquiring high-resolution coal seam geological data

(ii) Reproducible drilling accuracy

(iii) Multiple, independent gasifier units (with separate injection and production wells) to ensure systems failures do not totally halt gas production

(iv) Integrated surface plant using readily available off-the-shelf equipment wherever practicable.

The most critical element of deep UCG is arguably the directional drilling. Technologies exist which are capable of achieving the required precision but there is considerable uncertainty about the general drillability of coal seams in other than ideal conditions.

Environmental Impact and its Control: The main environmental issues concerning UCG are:

(i) Atmospheric emissions;

(ii) Surface water;

(iii) Drinking water pollutants;

(iv) Noise;

(v) Site operations;

(vi) Groundwater;

(vii) Subsidence.

Conclusion: Today, high prices of oil and gas and uncertainties about political stability in most of oil producing countries, have renewed interest in all kinds of fuel. A renewed interest in coal gasification is therefore not surprising. Further-more, hydrogen is now a welcome by-product because of the current interest in alternatively fuelled vehicles. UCG is potentially the most important clean coal technology of the future with worldwide application. Ultimately, it could be a substitute for deep mining coal for power generation use.

Applying improved UCG technology to gasify deep, thin, and low grade coal seams could vastly increase the amount of exploitable reserves. The coal could be converted to gas for a variety of uses and emissions of sulphur, nitrous oxides and mercury could be dramatically reduced. UCG could increase recoverable coal reserves by as much as 300 to 400 percent. Another benefit of UCG is that hydrogen accounts for nearly half the total gas product which can be separated and actively used as automotive fuel or as feed-stock for the Chemical Industry.

Countries are turning to UCG to fully utilize their coal resources in an economically viable and environmentally acceptable manner. Using UCG technology even without a carbon-capture-and-sequestration plan could also be eligible for carbon credits.

Summary: Underground coal gasification (UCG) involves injecting steam and air or oxygen (O2) into a coal seam from a surface well. The injected gases react with coal to form a combustible gas which is brought to the surface in a production well, cleaned and used as a fuel or chemical feedstock. A cavity is formed as the coal burns and the roof is allowed to collapse. This process results in lateral growth of the gasifier in the seam and is allowed to continue until the quality of the product gas declines. When this occurs the seam is re-ignited at a new location further along the gasifier. Once the coal within the underground gasifier has been exhausted, new injection and production wells are drilled alongside the exhausted gasifier and the process is repeated.

UCG has the potential to exploit coal resources which are either uneconomic to work by conventional underground coal extraction, or inaccessible due to depth, geology or other mining and safety considerations. The successful development of UCG will not only depend on advances in the use of technology but also on demonstrating that a clean energy can be produced without detriment to the environment. As a method of exploiting coal, UCG represents a substantial environmental improvement on the combination of coal mining and surface combustion of coal.

Energy Mix Strategies for oil importing country – Important in the scenario of energy security and global warming:

2008-08-05T23:30:00.000-07:00

Energy Mix Strategies for oil importing country – Important in the scenario of energy security and global warming:

A. We are aware of the problems of environmental pollution and the adverse consequences of global warming causing due to CO2 emission. To restrict environmental pollution, to mitigate the CO2 emission and rate of increase of CO₂ concentration in the atmosphere, responsive long term energy mix strategies exploiting the maximum potential of non-greenhouse gas emitting energy sources need to be developed and implemented as rapidly as possible. The future energy mix will not only depend on environmental issues, but also will depend on technological, economic, supply, logistics and political factors. It is generally accepted that for many decades fossil fuels will continue to be the major energy source world over. Natural gas being the lowest fossil fuel greenhouse gas emitter will increase the share in energy scenario world over. Countries having or exporting fossil fuels cannot easily turn away from their use and likewise the industrially & economically dynamic countries of Asia such as China, Japan and India cannot radically shift from fossil fuels towards uncertain and currently costly renewable for their growing power needs.

B. National and regional factors are the most important in guiding country's energy mix. Percentage share of energy differ considerably today and they will in the future. For example, today China is more than 90% dependent on various forms of fossil fuels. On the other hand, France and Sweden have reduced their dependence on fossil fuels to less than 50% and 35% respectively by using nuclear and hydro-power to a great extent. Moreover, out of all the fossil fuels coal is the workhorse of global electric power sector and is used to generate more than half of the electricity world consumes. Coal is also world’s most abundant fossil fuel, with supplies projected to last almost 250 years or more. As coal-fired power plants generally produce the lowest-cost electricity and coal is abundant, most of the country’s economic and energy security depend on the continued use of the fuel.

C. Therefore, on the global level, it is difficult to make a policy decisions to foster a reduced reliance on fossil fuel. Decision makers are confused on how to proceed for country’s energy mix for the future as there is general support for cost effective energy efficiency techniques and on the supply side an endorsement of an increased use of renewable and sustainable energy sources. In fact, both the efforts are necessary at present; but ‘renewable and sustainable energy sources’ have limited potential over the near term. However, in the developed and industrialized countries, the significant energy efficiency gains and use of renewable energy sources have been seen over the past two decades, that changed the dependence on fossil fuels and energy scenario to a great extent on their industrial and residential front.

D. The supply potential from renewable energy sources, at present, is difficult to assess since they are only emerging technologies and currently not suitable for meeting large energy demand of a country. With differing relevance for the various renewable energy sources, technological improvements are needed and basic challenges exist in reducing costs, improving efficiency and reliability, solving energy storage problems and integrating the technologies into existing energy systems. In most of the developed countries many decision makers in the opinion that, non-hydroelectric renewable energy sources, such as solar and wind will not be economically competitive for large scale production in the foreseeable future and that they will play no more than a limited role in the decades to come. They opine that, even with adequate support and subsidies the share of such renewable energy sources could reach only 5-8% (including about 3% non-commercial energy share) of primary energy supply by 2020.

E. Fortunately, hydroelectric has already been extensively developed and in use in Europe and North America (some 50% of the estimated maximum economic potential). Its greatest potential lies primarily in Asia, South America and Africa, where the trend will likely be towards small capacity units as concerns grow about the damaging environmental and social impacts of large dams.

F. Energy security and implementing proper energy mix strategies for oil importing countries are very much crucial especially in the scenario of rapid industrialization. For those countries, in my opinion, renewable energy must be developed in parallel with nuclear power and a clean-up of coal-fired power station technology, if these nations are to meet increasing demand without relying on enormous and potentially debilitating natural gas imports. For a nation the provision of sufficient, affordable and secure energy is crucial for any modern economy. Many countries are facing the challenge of bridging the widening gap between energy supply and demand. At the same time, across the globe, those same economies are facing challenges such as climate change, limited resources and rising costs. Therefore, for oil importing countries, energy mix should shift more towards, nuclear power and clean coal technology.

G. There are very large amounts of remaining oil, gas and coal left in the world and in the absence of concerted government initiatives, it may take many years before alternative energy sources such as wind and solar become a significant part of the world’s energy mix. It is true that some renewable sources such as bio-fuels and wind have attained ten-fold production increases throughout the past ten years. However, global energy demand is increasing at such a rate that, if we ignore hydro-electricity, renewable energy - as a proportion of total energy supply - may well remain at less than 2 per cent of the total market for many years to come. It may be noted here that, global climate change may be best addressed in the short term by energy conservation, by increasing fuel efficiency, and by subsurface storage of the carbon dioxide that results from burning fossil fuels. At the same time, the greatest advantages of nuclear power is that it avoids the wide variety of environmental problems arising from burning fossil fuels, apart from economically generating a high amount of electrical energy in one single plant using small amount of fuel.

H. Therefore, concerted efforts by such economies, in order to have secured energy for their sustainable developments, should involve large scale nuclear expansion, the development of clean coal-fired power stations, implementation of hydro-electric power to maximum potential and a increase in renewable energy sources such as solar and wind.

Energy security – ‘Clean Coal’ has potential to change the world from pariah to paragon of virtue in high oil price regime:

2008-07-04T22:53:00.000-07:00

Energy security – ‘Clean Coal’ has potential to change the world from pariah to paragon of virtue in high oil price regime:

A. The thirst of populous emerging economies for energy and the industrial countries’ sustained need for energy will ensure a further rise in demand. However, it looks as if the supply of oil, and later also natural gas, will not keep pace with this demand. Only by leveraging every possible means will it be possible to compensate the imbalances emerging on the horizon. However, during the transition to the renewable sources of energy such as wind and solar age, an energy gap will have to be filled.

B. With oil currently trading at around USD 140/bbl, coal-to-liquid technology is already an interesting alternative from a purely commercial point of view. Coal offers great potential as a substitute for oil and natural gas in the medium term, but so far its versatility has been underestimated. Going forward, coal could attract more attention in all three major energy sectors – power generation, the heating market and transport – provided that the right technologies delivering higher efficiency and lower environmental burdens take root. Environmental risks emphasize need for “clean coal”. Global warming is one of the biggest dangers facing human existence on earth, and combating this danger is therefore one of the greatest challenges. Since coal causes 40% of global CO2 emissions, only advanced technology can pave the way to a better future. The required quantum leaps in technology could, however, open the doors to the global mass markets. The need for investment is very high not only in emerging economies like China and India but also in US and Europe. CO2-free coal-fired power plants could become a milestone on the way to a better energy future in spite of their additional fuel consumption.

C. Worldwide prospects for energy is actually quite good, but only if all possible levers are used. These include steps – apart from urgently needed conservation and efficiency-enhancing strategies – to diversify the range of energy carriers with an even greater drive to mobilize renewable energies and to continue developing potential alternative technologies. In public debate about our energy options after the petroleum age virtually no consideration is given to coal or else it gets very bad reviews. In the developed countries, coal is usually considered synonymous with a dangerous climate killer; in the developing countries, for inhuman labor conditions in the mining industry, the talk is of ‘blood coal’. At best, coal is given credit for its valuable contribution to energy security during the industrialization era.

D. Today, coal is used in the industrial countries above all as a source of fuel for generating electricity, for the heating market and for metal production. In some of the emerging economies, coal is still used in some places to fire steam engines. Going forward, coal could attract much more attention in all three major energy sectors – power generation, heating and transport – provided that the right technologies with higher efficiency levels and a low environmental impact take root. In this sense, the versatility of coal has been underestimated. As a substitute for the hydrocarbon fuels oil and natural gas, which will become increasingly scarce in the relatively near future, coal offers considerable potential for improving our energy structures in future. However, only advanced technologies and innovations will be able to pave the way for coal into a better future.

E. As mentioned above, environmental risk emphasizes need for “clean coal”. Global warming is one of the biggest dangers facing human existence on earth, and combating this danger is therefore one of the greatest challenges facing mankind. Fossil fuels, especially those that pose the greatest threat to the earth’s climate, will only have a future if they can be reinvented from an ecological standpoint. Coal accounts for 40% of global output of carbon dioxide (CO2). The ‘bridge to the future’ must therefore lead to ‘clean coal’, which if possible has to be climate neutral and thus acceptable to the public at large. If ‘King Coal’, the mythical figure of the coalmining saga, stops wearing a black robe in future and instead dons an environmentally-friendly white robe, his days will not be numbered and he may go on to prosper the second time round. Until renewable sources of energy are finally mature and established enough to shoulder the burden of the world energy supply largely on their own, the purified ‘clean coal’ may develop into one of the biggest sources of hope for a more secure energy supply.

F. One advantage of coal is that it offers the greatest range of global reserves among the fossil fuels. Plenty of coal reserve, up to about more than 200 years worth, is readily available, almost all over the world. By contrast, the ranges for oil (42 years) and natural gas (63 years) are much smaller.

G. The search for alternatives to conventional fuels did not seem to be an urgent task in late 1998 when a barrel of oil cost less than USD 10. Not quite 10 years later, with oil going for an annual average price of USD 65 in 2006. The most prominent participants in the contest for the fuels of the future are:

(i) First-generation bio-fuels are increasing in popularity in the most diverse countries of the world, such as Brazil, the US and Germany. In Brazil, they have long since become commercially competitive. Research on the second generation, the synthetic bio-fuels (biomass-to-liquids, or BTL), is continuing briskly.

(ii) Natural gas has been a common fuel in some countries for years. More appears to be possible if the catalytic conversion of natural gas proves able to secure the availability of a synthetic fuel, so called GTL (gas-to-liquids), on an industrial scale. GTL and BTL will mean fewer emissions and higher efficiency.

(iii) By means of liquefaction (coal-to-liquids, CTL), coal may directly replace oil even as a fuel. Thanks to higher reserve and resource ranges, coal as a substitute would clearly have an advantage over fuels based on natural gas.

(iv) Nuclear energy will be one of the major contributors to the world energy sources. Although, there is furious opposition against nuclear energy in some part of the world, the advantage of its potential of delivery of clean energy is the major plus point makes it better option.

H. A total of USD 10 trillion is expected to be invested in power generating plants around the globe up to 2030, with over USD 2 trillion being invested in China alone. The need for investment is very high all over the world. For investments, not only the direct costs but also the implications for the world climate will increasingly gain importance. This holds all the more so as over the past 30 years the share of CO2 emissions from coal has risen from 35% to 40% – with total emissions rising by 70% globally. One much more revolutionary project is a plan to develop emission-free coal-fired generating plants. Upstream and downstream CO2 sequestration, for which there are several different methods, aims for climate conservation. Thus, new power generation technology for fewer emissions will become the backbone of industrialization.

Green coal for power - To take care of post-Kyoto issues from energy security point-of-view:

2008-06-26T23:21:00.000-07:00

Green coal for power - To take care of post-Kyoto issues from energy security point-of-view: a. Coal is the world’s most abundant and important source of primary energy. Turning a potential pollutant into a clean, green fuel for economical power production has become a matter for concern on a global scale. Coal continues to dominate the energy industries as the single most important and widely-used fuel. Delivering around 27 per cent of the world’s consumption of primary energy, almost half of which is used for electricity generation; reserves of coal are spread worldwide throughout some 100 developed and developing countries, sufficient to meet global needs for the next 250 years. b. Although a combination of economic and environmental pressures has forced the closure of older, inefficient, fossil fuelled thermal stations, the massive growth in power demand on a world scale will continue to be met predominantly by coal-fired plant for the foreseeable future. In many of the rapidly developing and industrializing regions of the world the rate of consumption of coal as a primary fuel for electricity generation is actually increasing. In energy-hungry India alone, coal-burn for power generation is forecast to more than double in the next few years to 350 million tonnes per year. Annual coal production in China, the world’s largest producer, has rocketed to over 1,500 million tonnes. Nevertheless, post-Kyoto issues have heightened environmental awareness, forcing the pace of technological change in the use of this abundant but potentially polluting fuel for power generation. The environmental threat posed by the release of even more millions of tonnes of toxic pollutants, acidic and greenhouse gases from both new and existing coal-burning power stations is widely accepted. Currently, signatories to the Kyoto Protocol are focusing on solutions to the problem of global warming, including the reduction of CO2 and other ‘greenhouse’ gases. In many other non- signatory countries, major programmes have been implemented by utilities and power producers to reduce SOx, NOx and CO2 emissions. Additional environmental concerns have also emerged, including the potential health impacts of trace emissions of mercury and the effects of particulate matter on people with respiratory problems. c. In contrast with both natural gas and LPG, hard coal can contain a wide range of compounds including sulfur in addition to useful hydrocarbons. The percentage of sulfur can vary widely, with relatively low concentrations in the highest quality anthracite and very high amounts in lignite, generating large volumes of SOx. As well as the need to treat the fuel prior to firing and control closely the combustion process itself to limit the production of nitrogen oxides, coal-fired stations based on conventional pulverized coal technology can only reduce SOx emissions through the use of post-combustion treatments. Further problems still remain through the safe disposal of fly ash which can contain high levels of toxic compounds including heavy metals. d. Enormous environmental problems faced by operators of older, coal-fired generating plants all over the world, plants were forced to take drastic action after various public protests about the deadly effects of SOx emissions and other emissions. Emissions from coal and lignite-fired units at various power generating stations caused widespread damage, killing livestock and crops downwind of the plant and causing respiratory illness in the population in many countries. The plants were forced to cut output. This tends to place an unacceptably high strain on the commercial viability of an existing power station in many of the developing nations and represents a completely uneconomic option for the majority of obsolescent installations. Power producers in industrialized developed countries are therefore adopting a variety of leading-edge clean-coal technologies for electricity generation. e. New clean coal technologies are providing an attractive and economically viable option to post-combustion systems. Applying the latest combustion, steam and process technologies in new power plant or upgrading existing coal-fired generating facilities provides significant improvements in thermal efficiency, reducing environmental impact and energy costs to the consumer. At the same time, higher thermal efficiencies result directly in reduced fuel costs, improving profitability and market position for the independent power producer. (i) For new and smaller coal-fuelled generating plant, boilers using well-proven circulating fluidized-bed CFB technology provide a cost-effective and efficient system capable of meeting current and future environmental standards. They are now being widely used and successfully operated in coal-fired generating units, burning a very wide range of coal and other fuels with widely differing heat values and mineral content. These can typically include anthracite, semi-anthracite, bituminous and sub-bituminous coal, lignite and even ‘gob’ – a form of high-ash bituminous coal waste. (ii) As an alternative to direct combustion based systems, coal gasification is becoming increasingly attractive, with Integrated Gasification Combined Cycle (IGCC) technology offering one of the best ‘clean’ options for effective power production. Gasification systems use steam and controlled amounts of air or oxygen under high temperatures and pressures to react with coal to form clean synthetic gas or ‘syngas’. Current systems provide efficient clean-up of the gas-stream to produce a mixture of carbon monoxide and hydrogen which can be used subsequently as a ‘clean’ fuel or a basic feedstock for liquefaction. f. Used as a fuel for power generation in a typical IGCC generating plant, a syngas-fired gas turbine drives a generator, with exhaust heat from the gas turbine recovered to produce steam to power a steam turbine in conventional ‘combined cycle’. IGCC power generating systems are presently being developed and operated in Europe and the US, with commercial systems capable of operating at thermal efficiencies approaching 50 per cent. NOx and Sox emissions levels are minimized with the potential for carbon-capture and sequestration of the CO in the sysngas stream being actively researched as design strategies for near-term and future coal-based IGCC plants. Elemental sulfur is removed from the syngas before combustion and is a highly saleable commercial byproduct. If the gasifier is fed with oxygen rather than air, the flue gas contains highly concentrated CO2 which can readily be captured, at about half the cost of that from conventional plants. g. As an alternative to the direct use of syngas as a fuel for electricity generation, it can also be processed using modern gas-to-liquids (GTL) technologies to produce a wide range of liquid hydrocarbon fuels such as gasoline and diesel oil. Coal-to-oil is a long-established technology in coal-rich South Africa. h. Nevertheless, clean coal technology is moving very rapidly in the direction of coal gasification, with a second stage designed to produce a concentrated and pressurized carbon dioxide stream followed by separation and geological storage. This has the potential to provide extremely low emissions of conventional coal pollutants, and as low-as-engineered carbon dioxide emissions – a vital step in the fight to prevent irreversible climate change.

Coal is Essential for Energy Security for many – Strategies to enlarge supply base and reduce environmental impacts are the prerequisites:

2008-06-16T22:57:00.000-07:00

Coal is Essential for Energy Security for many – Strategies to enlarge supply base and reduce environmental impacts are the prerequisites:

A. More and more frequent environmental problems and disasters – floods, forest fires, tornados, air pollution in big cities – cause growing concerns everywhere. Energy harvesting, conversion, production and use contribute to these environmental burdens.

Hence, improving the environmental performance of the energy sector is of paramount importance. Thus, wider application of cleaner fuels and conversion technologies is a key element in the strategy to improve the environmental performance of the energy sector. Further, the lower price of coal as compare to petroleum based fuels; the interest in coal is renewed because of the more even geopolitical distribution of coal reserves and of larger supply bases of coal allover the world.

In fact, the environmental concerns about coal are not associated with coal itself, but with its utilization in different stages of the energy chain. Novel and more environmentally friendly technologies for coal utilization, commonly known as “Clean Coal Technologies” (CCT), are believed to be able to bring coal back into the picture. Hence, CCT recently enjoy a growing interest almost all parts of the world. At present, this interest mostly focuses on cleaner coal conversion through increased efficiency and CO2 capture technologies, for which large R&D efforts are ongoing worldwide.

B. Market implementation of CCT is expected to cause an increase in coal use. Coal demand could also rise significantly because the recent sharp increase in oil prices has a lower impact on coal than on gas prices. This is explained by the more favorable geopolitical distribution of coal reserves compared to that of gas. As a result, coal has become cheaper in relative terms than oil and gas. All in all, in a scenario of soaring oil & gas prices, coal is predicted to be the energy source with the fastest growing demand. The expected increase in coal demand for power generation raises the question of its secure availability in the future. Thus, enlargement of the coal supply base is essential throughout the world, with adoption of cleaner technology.

C. The enlargement of the coal supply base can take place in four main directions:

(a) More powerful mapping techniques for coal reserves - Modern geophysics and seismic techniques, improve mine planning and exploitation by reducing geological uncertainties and increasing extraction efficiencies. At the same time, they can reduce environmental externalities and energy use for coal extraction.

(b) Improvement of existing under-ground mining technologies - Underground (deep) coal mining accounts for about 60% of world coal production. Current best coal recovery rates for underground mining are 50-60% for the “room-and-pillar” technology and about 75% for “longwall” mining. The implementation of modern automated and computerized mining technologies can increase these recovery rates.

(c) Research and development for underground coal gasification - Underground gasification of coal deposits which are not technically or economically exploitable (anymore) with conventional mining technologies, can add enormous coal supply potential in Europe and worldwide. At present underground coal gasification is at an experimental stage. Significant further efforts are necessary to make it technically and economically viable. In many of the countries like India etc., commercialization of underground gasification technologies may reduce the energy import dependence and enhance energy security scenario, apart from creating new employment.

(d) Utilization of coalmine methane (CMM) gas - Methane gas, released from coalmines, has always raised serious safety and environmental concerns. Methane is highly explosive when accumulated in confined areas. It is also a powerful greenhouse gas with 20- times stronger global warming potential than carbon dioxide. On the other hand, CMM, which consists mainly of natural gas, is a suitable clean fuel. The capture and useful utilization of CMM can bring important synergy benefits in terms of enhanced security of supply and better environmental and safety performance of coal mining.

D. Therefore, for realizing the full potential of CCT, coal is sufficiently

(a) Abundant… only if we keep working on the enhancement of coal reserves,

(b) Cheap… as long as the supply continues to match the demand,

To reach market maturity, clean coal technologies, covering extraction, preparation and conversion, need a long term vision and investment security. In the present pre-commercial stage they need firm political commitment and further R&D support.

‘Carbon sequestration’ - Greatest challenge of clean coal technology to deliver "zero emissions" in reality:

2008-06-13T22:09:00.000-07:00

‘Carbon sequestration’ - Greatest challenge of clean coal technology to deliver "zero emissions" in reality:

A present trend of clean coal technology is moving rapidly towards a very interesting phase, realizing efficiency improvements of coal. In fact, this clean coal technology together with the use of natural gas and renewables such as wind will not provide the deep cuts in greenhouse gas emissions necessary to meet future national targets. Naturally, a plant to produce hydrogen from coal and sequester emissions will be the world’s zero emission coal-fired plant – as envisaged for ‘FutureGen’ project.

As discussed earlier, the clean coal technology field is moving in the direction of coal gasification with a second stage so as to produce a concentrated and pressurized carbon dioxide stream followed by its separation and geological storage. This technology has the potential to provide what may be called "zero emissions" - in reality, extremely low emissions of the conventional coal pollutants, and as low-as-engineered carbon dioxide emissions.

A. The greatest challenge now is to sequester emissions by carbon capture and geological storage technology. The technology, known as carbon sequestration, has attracted global attention from industries and governments that are eager to capture and bottle up the gas that can linger in the atmosphere for decades.

B. Carbon capture and sequestration begins with the separation and capture of CO₂ from power plant flue gas and other stationary CO₂ sources. At present, this process is costly and energy intensive, accounting for the majority of the cost of sequestration. However, analysis shows the potential for cost reductions of 30–45 percent for CO₂ capture. Post-combustion, pre-combustion, and oxy-combustion capture systems being developed are expected to be capable of capturing more than 90 percent of flue gas CO₂.

C. The primary function of carbon sequestration research and development (R&D) objectives are:

(1) lowering the cost and energy penalty associated with CO₂ capture from large point sources; and

(2) improving the understanding of factors affecting CO₂ storage permanence, capacity, and safety in geologic formations and terrestrial ecosystems.

D. After capturing of carbon the next step is to sequester (store) the CO_2; which has mainly two processes - (i) The primary means for carbon storage are injecting CO₂ into geologic formations or (ii) using terrestrial applications.

(i) Geologic sequestration involves taking the CO₂ that has been captured from power plants and other stationary sources and storing it in deep underground geologic formations in such a way that CO₂ will remain permanently stored. Geologic formations such as oil and gas reservoirs, unmineable coal seams, and underground saline formations are potential options for storing CO₂. Storage in basalt formations and organic rich shales is also being investigated.

(ii) Another form of sequestration is ‘terrestrial sequestration’, which involves the net removal of CO₂ from the atmosphere by plants and microorganisms that use CO₂ in their natural cycles. Terrestrial sequestration requires the development of technologies to quantify with a high degree of precision and reliability the amount of carbon stored in a given ecosystem.

E. Any carbon sequestration program should involve (a) Core R&D, and (b) Demonstration & Deployment.

(a) Core R&D – Core R&D accomplished through laboratory and pilot-scale research, develops new technologies and systems for reducing greenhouse gas emissions from industrial sources. Core R&D integrates basic research and computational sciences to study advanced materials and energy systems. It focuses on few major areas for technology development: (i) CO₂ Capture, (ii) Carbon Storage, (iii) Monitoring, Mitigation, and Verification, (iv) Non-CO₂ Greenhouse Gas Control, and (v) Breakthrough Concepts.

(b) Demonstration & Deployment – It speeds the development of new technologies through commercial opportunities and collaboration with Govt. departments. Core R&D scientists also learn practical lessons from these demonstration projects and are helpful to develop further technology solutions and innovations.

As mentioned above, this system along with use of natural gas and renewable energy sources such as wind, solar etc., will be advantageous in order to mitigate to a great extent in greenhouse gas emissions necessary to meet future national targets. Many countries see "zero emissions" coal technology as a core element of its future energy supply in a carbon-constrained world. They have program to develop and demonstrate the technology and have commercial designs for plants with an electricity cost of only 10% greater than conventional coal plants available by 2012. Australia is very well endowed with carbon dioxide storage sites near major carbon dioxide sources, but as elsewhere, demonstration plants will be needed to gain public acceptance and show that the storage is permanent. In general, "zero emissions" technology seems to have the potential for low avoided cost for greenhouse gas emissions.

‘FutureGen’ project - to design, build and operate a nearly emission-free coal-based electricity and hydrogen:

2008-06-11T22:06:00.000-07:00

‘FutureGen’ project - to design, build and operate a nearly emission-free coal-based electricity and hydrogen:

The clean coal technology field is moving very rapidly in the direction of coal gasification with a second stage so as to produce a concentrated and pressurised carbon dioxide stream followed by its separation and geological storage. At present the high cost of carbon capture and storage renders the option uneconomic. But a lot of work is being done by many of the research institutes, to improve the economic viability of this system.

More recently department of energy (DOE) of Federal Govt. of the USA has announced ‘FutureGen’ project to design, build and operate a nearly emission-free coal-based electricity and hydrogen production plant. It will use cutting-edge technologies to generate electricity while capturing and permanently storing carbon dioxide deep beneath the earth. The integration of these technologies is what makes FutureGen unique. Researchers and industry have made great progress advancing technologies for coal gasification, electricity generation, emissions control, carbon dioxide capture and storage, and hydrogen production. But these technologies have yet to be put together and tested at a single plant - an essential step for technical and commercial viability.

Therefore, the FutureGen initiative would have comprised a coal gasification plant with additional water-shift reactor, to produce hydrogen and carbon dioxide. About one million tones of CO₂ would then be separated by membrane technology and sequestered geologically. The hydrogen would have been be burned in a power generating plant and in fuel cells. The project was designed to validate the technical feasibility and economic viability of near-zero emission coal-based generation. Construction of FutureGen was due to start in 2009, for operation in 2012.

Coal gasification processes –

(a) In conventional plants coal, often pulverised, is burned with excess air (to give complete combustion), resulting in very dilute carbon dioxide at the rate of 800 to 1200 g/kWh.

(b) Gasification converts the coal to burnable gas with the maximum amount of potential energy from the coal being in the gas.

(c) In Integrated Gasification Combined Cycle (IGCC) the first gasification step is pyrolysis, from 400°C up, where the coal in the absence of oxygen rapidly gives carbon-rich char and hydrogen-rich volatiles.

(d) In the second step the char is gasified from 700°C up to yield gas, leaving ash. With oxygen feed, the gas is not diluted with nitrogen.

(e) The key reactions today are C + O₂ to CO, and the water gas reaction: C + H₂O (steam) to CO & H₂ - syngas, which reaction is endothermic.

(f) In gasification, including that using oxygen, the O₂ supply is much less than required for full combustion, so as to yield CO and H₂.

(g) The hydrogen has a heat value of 121 MJ/kg - about five times that of the coal, so it is a very energy-dense fuel.

(h) However, the air separation plant to produce oxygen consumes up to 20% of the gross power of the whole IGCC plant system.

(i) This syngas can then be burned in a gas turbine, the exhaust gas from which can then be used to raise steam for a steam turbine, hence the "combined cycle" in IGCC.

(j) To achieve a much fuller clean coal technology in the future, the water-shift reaction will become a key part of the process so that:

(i) C + O₂ gives CO, and

(ii) C + H₂O gives CO & H₂, then the

(iii) CO + H₂O gives CO₂ & H₂ (the water-shift reaction).

(k) The products are then concentrated CO₂ which can be captured, and hydrogen. (There is also some hydrogen from the coal pyrolysis), which is the final fuel for the gas turbine.

(k) Overall thermal efficiency for oxygen-blown coal gasification, including carbon dioxide capture and sequestration, is about 73%.

(l) Using the hydrogen in a gas turbine for electricity generation is efficient, so the overall system has long-term potential to achieve an efficiency of up to 60%.

‘Clean Coal Technology (CCT)’ – methods to remove pollutants from coal.

2008-06-09T22:30:00.000-07:00

‘Clean Coal Technology (CCT)’ – methods to remove pollutants from coal.

Carbon dioxide from burning coal is the main focus of attention today, since it is implicated in global warming, and the Kyoto Protocol requires that emissions decline, notwithstanding increasing energy demand.

A. Capture & separation of Carbon dioxide - A number of means exist to capture carbon dioxide from gas streams, but they have not yet been optimised for the scale required in coal-burning power plants. The focus has often been on obtaining pure CO₂ for industrial purposes rather than reducing CO₂ levels in power plant emissions. Capture of carbon dioxide from flue gas streams following combustion in air is expensive as the carbon dioxide concentration is only about 14% at best. This treats carbon dioxide like any other pollutant and as flue gases are passed through an amine solution the CO₂ is absorbed. It can later be released by heating the solution. This amine scrubbing process is also used for taking CO₂ out of natural gas. There is an energy cost involved. Captured carbon dioxide gas can be put to good use, even on a commercial basis, for enhanced oil recovery. Injecting carbon dioxide into deep, unmineable coal seams where it is adsorbed to displace methane (effectively: natural gas) is another potential use or disposal strategy.

B. Coal arriving at a power plant contains mineral content that needs to be removed, in order to make it clean, before it is burnt. A number of processes are available to remove unwanted matter and make the coal burn more efficiently.

(a) Coal cleaning by washing - Coal washing involves grinding the coal into smaller pieces and passing it through a process called gravity separation. One technique involves feeding the coal into barrels containing a fluid that has a density which causes the coal to float, while unwanted material sinks and is removed from the fuel mix. The coal is then pulverised and prepared for burning.

(b) Gasification of coal – The Integrated Gasification Combined Cycle (IGCC) plant is a means of using coal and steam to produce hydrogen and carbon monoxide (CO) which are then burned in a gas turbine with secondary steam turbine (ie combined cycle) to produce electricity.

Coal gasification plants are favoured by some because they are flexible and have high levels of efficiency. The gas can be used to power electricity generators, or it can be used elsewhere, i.e. in transportation or the chemical industry. In Integrated Gasification Combined Cycle (IGCC) systems, coal is not combusted directly but reacts with oxygen and steam to form a "syngas" (primarily hydrogen). After being cleaned, it is burned in a gas turbine to generate electricity and to produce steam to power a steam turbine. Coal gasification plants are seen as a primary component of a zero-emissions system. However, the technology remains unproven on a widespread commercial scale.

(c) Removing pollutants from coal - Burning coal produces a range of pollutants that harm the environment: Sulphur dioxide (acid rain); nitrogen oxides (ground-level ozone) and particulates (affects people's respiratory systems). There are a number of options to reduce these emissions:

(i) Sulphur dioxide (SO2) - Flue gas desulphursation (FGD) systems are used to remove sulphur dioxide. "Wet scrubbers" are the most widespread method and can be up to 99% effective. A mixture of limestone and water is sprayed over the flue gas and this mixture reacts with the SO2 to form gypsum (a calcium sulphate), which is removed and used in the construction industry.

(ii) Nitrogen oxides (NOx) - NOx reduction methods include the use of "low NOx burners". These specially designed burners restrict the amount of oxygen available in the hottest part of the combustion chamber where the coal is burned. This minimises the formation of the gas and requires less post-combustion treatment.

(iii) Particulates emissions - Electrostatic precipitators can remove more than 99% of particulates from the flue gas. The system works by creating an electrical field to create a charge on particles which are then attracted by collection plates. Other removal methods include fabric filters and wet particulate scrubbers.

Clean coal technology (CCT) - A discussion

2008-06-09T02:00:00.000-07:00

Clean coal technology (CCT) - A discussion

Coal when burned is the dirtiest of all fossil fuels. A range of technologies are being used and developed to reduce the environmental impact of coal-fired power stations. Thus, clean coal technology (CCT) is the name attributed to coal chemically washed of minerals and impurities, sometimes gasified, burned and the resulting flue gases treated with steam with the purpose of removing sulfur dioxide, and reburned so as to make the carbon dioxide in the flue gas economically recoverable.

A. It is a known fact that, the burning of coal, a fossil fuel, is the principal causes of anthropogenic climate change and global warming. In fact, the byproducts of coal combustion are very hazardous to the environment if not properly contained. This is seen to be the technology's largest challenge, both from the practical and public relations perspectives. While it is possible to remove most of the sulfur dioxide (SO2), nitrogen oxides (NOx) and particulate (PM) emissions from the coal-burning process, carbon dioxide (CO2) emissions will be more difficult to address. Therefore, fact regarding the coal remains:

(a) Coal is a vital fuel in most parts of the world.

(b) Burning coal without adding to global carbon dioxide levels is a major technological challenge which is being addressed.

(c) The most promising "clean coal" technology involves using the coal to make hydrogen from water, then burying the resultant carbon dioxide by-product and burning the hydrogen.

(d) The greatest challenge is bringing the cost of this down sufficiently for "clean coal" to compete with nuclear power on the basis of near-zero emissions for base-load power.

B. In relation to clean coal technology, a terminology ‘carbon capture and storage’ (CCS) is being discussed. CCS is nothing but method of capturing the carbon dioxide, preventing the greenhouse gas entering the atmosphere, and storing it deep underground by various ways, such as

(a) CO2 pumped into disused coal fields displaces methane which can be used as fuel,

(b) CO2 may be pumped into and stored safely in saline aquifers, or

A range of approaches of CCS have been developed and have proved to be technically feasible. They have yet to be made available on a large-scale commercial basis because of the costs involved.

C. Clean coal technologies are continually developing. Today, efficiencies of 46% can be achieved by implementing the best available technology. With further research into techniques such as Ultra-supercritical combustion, efficiencies above 50% are envisaged in the near future. Work is underway to exploit the opportunities of capturing and storing CO2, which is an inevitable by-product of the thermal use of all fossil fuels. Coupled with integrated gasification, coal could in this way provide a source of low-carbon hydrogen for fuelling transport without producing local emissions. There will be challenges in bringing these technologies to market, but with the right mix of research investment and market incentives, coal may stake a place in a sustainable and secure energy future.

D. To summarise, burning coal, such as for power generation, gives rise to a variety of wastes which must be controlled or at least accounted for. So-called "clean coal" technologies are a variety of evolving responses to late 20th century environmental concerns, including that of global warming due to carbon dioxide releases to the atmosphere. However, many of the elements have in fact been applied for many years, and they will be only briefly mentioned here:

(i) Coal cleaning by 'washing' has been standard practice in developed countries for some time. It reduces emissions of ash and sulfur dioxide when the coal is burned.

(ii) Electrostatic precipitators and fabric filters can remove 99% of the fly ash from the flue gases - these technologies are in widespread use.

(iii) Flue gas desulfurisation reduces the output of sulfur dioxide to the atmosphere by up to 97%, the task depending on the level of sulfur in the coal and the extent of the reduction. It is widely used where needed in developed countries.

(iv) Low-NOx burners allow coal-fired plants to reduce nitrogen oxide emissions by up to 40%. Coupled with re-burning techniques NOx can be reduced 70% and selective catalytic reduction can clean up 90% of NOx emissions.

(v) Increased efficiency of plant - up to 45% thermal efficiency now (and 50% expected in future) means that newer plants create less emissions per kWh than older ones.

(vi) Advanced technologies such as Integrated Gasification Combined Cycle (IGCC) and Pressurised Fluidised Bed Combustion (PFBC) will enable higher thermal efficiencies still - up to 50% in the future.

(vii) Ultra-clean coal from new processing technologies which reduce ash below 0.25% and sulfur to very low levels mean that pulverised coal might be fed directly into gas turbines with combined cycle and burned at high thermal efficiency.

(viii) Gasification, including underground gasification in situ, uses steam and oxygen to turn the coal into carbon monoxide and hydrogen.

(ix) Sequestration refers to disposal of liquid carbon dioxide, once captured, into deep geological strata.

E. Discussion - Many experts think, the concept of clean coal is said to be a solution to climate change and global warming. Whereas, environmental groups believe it is nothing but another way of making everybody fool, in other words, it is ‘green-wash’. Environmentalists say, with this technology emission and wastes are not avoided, but are transferred from one waste stream to another. They opine that, coal can never be clean. Critics of the planned power plants assert that there is no such thing as "clean coal" and that the plant will still release large amounts of pollutants compared to renewable energy sources such as wind power and solar power. A good deal of investment in research and development and also in implementation of pollutant free renewable energy (such as wind power and solar power) has to augmented, to make the world very clean, to make the required electricity generation fully green.

Classification of coal based on volatile matter and coking power of clean material

2008-04-21T22:34:00.000-07:00

Classification of coal based on volatile matter and coking power of clean material

Coal is a readily combustible rock containing more than 50 percent by weight of carbonaceous material, formed from compaction and indurations of variously altered plant remains similar to those in peat.

After a considerable amount of time, heat, and burial pressure, it is metamorphosed from peat to lignite. Lignite is considered to be "immature" coal at this stage of development because it is still somewhat light in color and it remains soft.

Lignite increases in maturity by becoming darker and harder and is then classified as sub-bituminous coal. After a continuous process of burial and alteration, chemical and physical changes occur until the coal is classified as bituminous - dark and hard coal.

Bituminous coal ignites easily and burns long with a relatively long flame. If improperly fired bituminous coal is characterized with excess smoke and soot.

Anthracite coal is the last classification, the ultimate maturation. Anthracite coal is very hard and shiny.

Class	Volatile matter (weight %)	General description
101	<>	Anthracites
102	3.1 - 9.0	Anthracites
201	9.1 - 13.5	Dry steam coals	Low volatile steam coals
202	13.6 - 15.0
203	15.1 - 17.0	Coking steams coals
204	17.1 - 19.5
206	19.1 - 19.5	Heat altered low volatile steam coals
301	19.6 - 32.0	Prime coking coals	Medium volatile coals
305	19.6 - 32.0	Mainly heat altered coals
306	19.6 - 32.0	Mainly heat altered coals
401	32.1 - 36.0	Very strongly coking coals	High volatile coals
402	> 36.0	Very strongly coking coals
501	32.1 - 36.0	Strongly coking coals
502	> 36.0	Strongly coking coals
601	32.1 - 36.0	Medium coking coals
602	> 36.0	Medium coking coals
701	32.1	Weakly coking coals
702	> 36.0	Weakly coking coals
801	32.1 - 36.0	Very weakly coking coals
802	> 36.0	Very weakly coking coals
901	32.1 - 36.0	Non-coking coals
902	> 36.0	Non-coking coals

Volatile matter - dry mineral matter free basis. In coal, those products, exclusive of moisture, given off as gas and vapor determined analytically.

Anthracite coal creates a steady and clean flame and is preferred for domestic heating. Furthermore it burn longer with more heat than the other types.

Typical Sulfur Content in Coal

Anthracite Coal : 0.6 - 0.77 weight %

Bituminous Coal : 0.7 - 4.0 weight %

Lignite Coal : 0.4 weight %

Typical Moisture Content in Coal

Anthracite Coal : 2.8 - 16.3 weight %

Bituminous Coal : 2.2 - 15.9 weight %

Lignite Coal : 39 weight %

Typical Fixed Carbon Content in Coal

Anthracite Coal : 80.5 - 85.7 weight %

Bituminous Coal : 44.9-78.2 weight %

Lignite Coal : 31.4 weight %

Typical Bulk Density of Coal

Anthracite Coal : 50 - 58 (lb/ft³), 800 - 929 (kg/m³)

Bituminous Coal : 42 - 57 (lb/ft³), 673 - 913 (kg/m³)

Lignite Coal : 40 - 54 (lb/ft³), 641 - 865 (kg/m³)

Typical Ash Content in Coal

Anthracite Coal : 9.7 - 20.2 weight %

Bituminous Coal : 3.3-11.7 weight %

Lignite Coal : 4.2 weight %

Chemical compositions of some common gaseous fuels:

2008-04-18T01:15:00.000-07:00

Chemical compositions of some common gaseous fuels are indicated in the table below:

Composition (%)
Fuel	Carbon Dioxide (CO2)	Carbon Monoxide (CO)	Methane (CH4)	Butane (C4H10)	Ethane (C2H6)	Propane (C3H8)	Hydrogen (H2)	Hydrogen Sulfide (H2S)	Oxygen (O2)	Nitrogen (N2)
Carbon Monoxide		100
Coal Gas	3.8	28.4	0.2				17.0			50.6
Coke Oven Gas	2.0	5.5	32				51.9		0.3	4.8
Digester Gas	30		64				0.7	0.8		2.0
Hydrogen							100
Landfill Gas	47	0.1	47				0.1	0.01	0.8	3.7
Natural Gas	0 - 0.8	0 - 0.45	82 - 93		0 - 15.8		0-1.8	0 - 0.18	0 - 0.35	0.5 - 8.4
Propane Gas				0.5 - 0.8	2.0 - 2.2	73 - 97

Environmental pollution in coal mining and mitigation measures

2008-04-14T22:15:00.000-07:00

Environmental pollution in coal mining and mitigation measures:

The environmental related issues in coal mines (both in opencast and underground) have been discussed. As coal is very important fossil fuel and its importance has been more prominent after tremendous increase in international price of crude oil; coal mining is now essential part of civilization.

A. In number of ways coal mining projects pollute environment. Environment problems related to coal mines are discussed below:

(1) Air pollution: Air pollution in coal mines is mainly due to the fugitive emission of particulate matter and gases including methane (CH4), sulphur dioxide (SO2) and oxides of nitrogen (NOx). The mining operations like drilling, blasting, movement of the heavy earth moving machinery on haul roads, collection, transportation and handling of coal, screening, sizing and segregation units are the major sources of such emissions. Under-ground mine fire is also a major source of air pollution in some of the coal fields.

High levels of suspended particulate matter increase respiratory diseases such as chronic bronchitis and asthma cases while gaseous emissions contribute towards global warming besides causing health hazards to the exposed population.

Methane emission from coal mining depends on the mining methods, depth of coal mining, coal quality and entrapped gas content in coal seams.

(2) Water pollution: The major source of water pollution in the coal mines is the carry over of the suspended solids in the drainage system of the mine sump water and storm water drainage. In some of the coal mines, acidic water is also found in the underground aquifers. In addition, waste water from coal preparation plant and mine water are other sources of water pollution.

(3) Land degradation: The opencast coal mines are developed at the surface, because of that these mines are also called surface coal mines. The overburden, i.e., the rock or soil overlaid the coal seam, are removed before extraction of coal. This overburden is dumped on surface, preferably on mined-out or decoaled area. Therefore, this type of mining requires quite large area on surface. Many a times, large forest areas are transferred for coal mining purpose. The land degradation is the result of creation and expansion of opencast coal mines. The aspect of land degradation in underground coal mines is due to subsidence over the underground cavity resulted from underground caving.

(4) Noise pollution: Main sources of noise pollution are blasting, movement of heavy earth moving machines, drilling and coal handling plants etc.

(5) Solid waste: Major source of solid waste in a coal mine is the overburden. Segregation of the stones in the coal handling plants and the coal breeze also contribute to the solid waste generation. Over-burden to coal ratio in the open cast mining is about 2 m³/tonne of coal or sometime more. Therefore, the quantum of overburden generated and its proper management is the main concern area in dealing with the environmental issue of opencast coal mines.

(6) Deforestation: As explained, the requirement of land for a big opencast coal projects are quite large. Many of the forest area, many a times, are converted to mining field. Therefore, large forest areas are deforested to make a way for large opencast coal mines.

B. The unscientific mining practices undertaken result in large degradation of land in the form of subsidence, underground goaf filled with water, mine fires, destruction of vegetation, generation of wind blow dust etc. To mitigate above environmental problems several control measures, generally, are adopted. Some of the control measures are discussed below:

(1) Subsidence: Subsidence of surface takes place due to extraction of coal by underground mining. Subsidence is exhibited by cracks on surface and lowering of land in the worked out areas compared to surroundings. The surface is rehabilitated by dozing and sealing of cracks followed by plantation of trees. The subsided areas with medium-sized depressions are ideal for developing water pools and sustain green vegetation and also to meet the water needs of local people.

(2) Abandoned mines: The mined-out areas are to be backfilled and then rehabilitated for development of vegetation. In the quarried areas water reservoir is developed for water harvesting. The big voids created by open-pit mining cause land degradation. These voids can be gainfully utilized to serve as water reservoirs. This water provides moisture for vegetation in the surroundings areas. The water is used for domestic supply after necessary treatment. Irrigation to nearby agricultural land also may be thought off.

(3) External overburden dump: The external dump area presents an unaesthetic appearance unless rehabilitated. Vegetative rehabilitation of these dumps prevents erosion and also improves aesthetics.

(4) Mine fire: The measures for controlling the mine fires, include dozing, levelling and blanketing with soil to prevent the entry of oxygen and to stabilize the land for vegetal growth.

(5) Water and air pollution control: Mine water is pumped to a lagoon, which acts as a sedimentation pond. The overflow water, which is fairly clean, is drained out to natural drain or used for dust suppression activities. Similarly, washery effluent is re-circulated through thickener and slime ponds. For reducing air pollution, water spraying and sprinkling is done on the haul /transport roads to suppress the dust generation.

Coke making process and its environmental impacts:

2008-04-09T22:42:00.000-07:00

Coke making process and its environmental impacts:

Coke is a solid carbon fuel and carbon source used to melt and reduce iron ore. Coke and coke by-products, including coke oven gas, are produced by the pyrolysis (heating in the absence of air) of suitable grades of coal. The process also includes the processing of coke oven gas to remove tar, ammonia (usually recovered as ammonium sulfate), phenol, naphthalene, light oil, and sulfur before the gas is used as fuel for heating the ovens.

A. Coke making process: In the coke-making process, bituminous coal is fed (usually after processing operations to control the size and quality of the feed) into a series of ovens, which are sealed and heated at high temperatures in the absence of oxygen, typically in cycles lasting 14 to 36 hours. Volatile compounds that are driven off the coal are collected and processed to recover combustible gases and other by-products. The solid carbon remaining in the oven is coke. It is taken to the quench tower, where it is cooled with a water spray or by circulating an inert gas (nitrogen), a process known as dry quenching. The coke is screened and sent to a blast furnace or to storage. Coke oven gas is cooled, and by-products are recovered. Flushing liquor, formed from the cooling of coke oven gas, and liquor from primary coolers contain tar and are sent to a tar decanter. An electrostatic precipitator is used to remove more tar from coke oven gas. The tar is then sent to storage. Ammonia liquor is also separated from the tar decanter and sent to wastewater treatment after ammonia recovery. Coke oven gas is further cooled in a final cooler. Naphthalene is removed in the separator on the final cooler. Light oil is then removed from the coke oven gas and is fractionated to recover benzene, toluene, and xylene. During the coke quenching, handling, and screening operation, coke breeze is produced. It is either reused on site (e.g., in the sinter plant) or sold off site as a by-product.

B. Pollution during coke making process:

The coke oven is a major source of fugitive air emissions. The coking process emits particulate matter (PM); volatile organic compounds (VOCs); polynuclear aromatic hydrocarbons (PAHs); methane, at approximately 100 grams per metric ton (g/t) of coke; ammonia; carbon monoxide; hydrogen sulfide (50–80 g/t of coke from pushing operations); hydrogen cyanide; and sulfur oxides, SOx (releasing 30% of sulfur in the feed). Significant amount of VOCs may also be released in by- product recovery operations. For every ton of coke produced, approximately 0.7 to 7.4 kilograms (kg) of PM, 2.9 kg of SOx (ranging from 0.2 to 6.5 kg), 1.4 kg of nitrogen oxides (NOx), 0.1 kg of ammonia, and 3 kg of VOCs (including 2 kg of benzene) may be released into the atmosphere if there is no vapor recovery system. Coal-handling operations may account for about 10% of the particulate load. Coal charging, coke pushing, and quenching are major sources of dust emissions.

Wastewater is generated at an average rate ranging from 0.3 to 4 cubic meters (m3) per ton of coke processed. Major wastewater streams are generated from the cooling of the coke oven gas and the processing of ammonia, tar, naphthalene, phenol, and light oil. Process wastewater may contain 10 milligrams per liter (mg/l) of benzene, 1,000 mg/l of biochemical oxygen demand (BOD) (4 kg/t of coke), 1,500–6,000 mg/l of chemical oxygen demand (COD), 200 mg/l of total suspended solids, and 150–2,000 mg/l of phenols (0.3–12 kg/t of coke). Wastewaters also contain PAHs at significant concentrations (up to 30 mg/ l), ammonia (0.1–2 kg nitrogen/t of coke), and cyanides (0.1–0.6 kg/t of coke). Coke production facilities generate process solid wastes other than coke breeze (which averages 1 kg/t of product). Most of the solid wastes contain hazardous components such as benzene and PAHs. Waste streams of concern include residues from coal tar recovery (typically 0.1 kg/t of coke), the tar decanter (0.2 kg/t of coke), tar storage (0.4 kg/t of coke), light oil processing (0.2 kg/t of coke), wastewater treatment (0.1 kg/t of coke), naphthalene collection and recovery (0.02 kg/t of coke), tar distillation (0.01 kg/t of coke), and sludges from biological treatment of wastewaters.

C. Pollution Prevention and Control: Pollution prevention in coke making is focused on reducing coke oven emissions and developing coke-less iron & steel-making techniques. The following pollution prevention and control measures should be considered.

1. General -

(a) Use cokeless iron- and steel-making processes, (b) such as the direct reduction process, to eliminate the need to manufacture coke. (c) Use beneficiation (preferably at the coal mine) and blending processes that improve the quality of coal feed to produce coke of desired quality and reduce emissions of sulfur oxides and other pollutants. (d) Use enclosed conveyors and sieves for coal and coke handling. Use sprinklers and plastic emulsions to suppress dust formation. Provide windbreaks where feasible. Store materials in bunkers or warehouses. Reduce drop distances. (e) Use and preheat high-grade coal to reduce coking time, increase throughput, reduce fuel consumption, and minimize thermal shock to refractory bricks.

2. Coke Oven Emissions –

(a) Charging: dust particles from coal charging should be evacuated by the use of jumper-pipe systems and steam injection into the ascension pipe or controlled by fabric filters.

(b) Coking: use large ovens to increase batch size and reduce the number of chargings and pushings, thereby reducing the associated emissions. Reduce fluctuations in coking conditions, including temperature. Clean and seal coke oven openings to minimize emissions. Use mechanical cleaning devices (preferably automatic) for cleaning doors, door frames, and hole lids. Seal lids, using a slurry. Use low-leakage door construction, preferably with gas sealing.

(c) Pushing: emissions from coke pushing can be reduced by maintaining a sufficient coking time, thus avoiding “green push.” Use sheds and enclosed cars, or consider use of traveling hoods. The gases released should be removed and passed through fabric filters.

(d) Quenching: where feasible, use dry instead of wet quenching. Filter all gases extracted from the dry quenching unit. If wet quenching, is used, provide interceptors (baffles) to remove coarse dust. When wastewater is used for quenching, the process transfers pollutants from the wastewater to the air, requiring subsequent removal. Reuse quench water.

(e) Conveying and sieving: enclose potential dust sources, and filter evacuated gases.

Carbon Dioxide Emission by Combustion Fuels:

2008-04-05T04:10:00.000-07:00

Carbon Dioxide Emission by Combustion Fuels:

Environmental emission of carbon dioxide - CO2 - from fuels like coal, oil, natural gas, LPG and bio energy

To calculate the CO₂ emission from a fuel, the carbon content of the fuel are multiplied by the ratio of the molecular weight of CO₂(44) to the molecular weight of carbon (12) -> 44/12 = 3.7.

Approximately environmental emission of Carbon Dioxide - CO₂ - from the combustion of different fuels can be approximated from the table below:

Fuel	Carbon Content (kg C/kg fuel)	Energy Content (kWh/kg)	Emission of CO₂ (kg CO₂/kWh)
Coal (bituminous/anthracite)	0.75	7.5	0.37
Gasoline	0.9	12.5	0.27
Diesel	0.86	11.8	0.24
Light Oil	0.7	11.7	0.26
Natural Gas, Methane	0.75	12	0.23
LPG - Liquid Petroleum Gas	0.82	12.3	0.24
Bioenergy	0	-	0

Bioenergy is produced from biomass derived from any renewable organic plant, including

· dedicated energy crops and trees

· agricultural food and feed crops

· agricultural crop wastes and residues

· wood wastes

· aquatic plants

· animal wastes

· municipal wastes and other waste materials

Emissions of CO2 can contribute to climate change. Combustion of bioenergy don't add to the total emission of carbon dioxide as long as the burned biomass don't exceed the renewed production. (Emission of CO₂ from combusting wood is in reality approximately 0.18 kg/hWh)

A variety of biofuels can be made from biomass resources, including

ethanol

methanol

biodiesel

Fischer-Tropsch diesel

gaseous fuels like hydrogen or methane

Solar Cell – Clean Energy Source:

2008-04-04T05:38:00.000-07:00

Solar Cell – Clean Energy Source:

Solar cell is a semiconductor device that converts the energy of sunlight into electric energy. These are also called ‘photovoltaic cell’. Solar cells do not use chemical reactions to produce electric power, and they have no moving parts.

Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. These disks act as energy sources for a wide variety of uses, including: calculators and other small devices; telecommunications; rooftop panels on individual houses; and for lighting, pumping, and medical refrigeration for villages in developing countries. In large arrays, which may contain many thousands of individual cells, they can function as central electric power stations analogous to nuclear, coal-, or oil-fired power plants. Arrays of solar cells are also used to power satellites; because they have no moving parts that could require service or fuels that would require replenishment, solar cells are ideal for providing power in space.

A. Most photovoltaic cells consist of a semiconductor pn junction, in which electron-hole pairs produced by absorbed radiation are separated by the internal electric field in the junction to generate a current, a voltage, or both, at the device terminals. Under open-circuit conditions (current I = 0) the terminal voltage increases with increasing light intensity, and under short-circuit conditions (voltage V = 0) the magnitude of the current increases with increasing light intensity. When the current is negative and the voltage is positive, the photovoltaic cell delivers power to the external circuit.

The mechanism of producing electricity from light is:

(a) Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon;

(b) Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. The complementary positive charges that are also created (like bubbles) are called holes and flow in the direction opposite of the electrons in a silicon solar panel;

B. Characteristics of a Solar Cell - The usable voltage from solar cells depends on the semiconductor material. In silicon it amounts to approximately 0.5 V. Terminal voltages is only weakly dependent on light radiation, while the current intensity increases with higher luminosity. A 100 cm² silicon cell, for example, reaches a maximum current intensity of approximately 2 A when radiated by 1000 W/m². The output (product of electricity and voltage) of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy.

C. Cell Types: One can distinguish three cell types according to the type of crystal: monocrystalline, polycrystalline and amorphous. To produce a monocrystalline silicon cell, absolutely pure semiconducting material is necessary. Monocrystalline rods are extracted from melted silicon and then sawed into thin plates. This production process guarantees a relatively high level of efficiency.

The production of polycrystalline cells is more cost-efficient. In this process, liquid silicon is poured into blocks that are subsequently sawed into plates. During solidification of the material, crystal structures of varying sizes are formed, at whose borders defects emerge. As a result of this crystal defect, the solar cell is less efficient.
If a silicon film is deposited on glass or another substrate material, this is a so-called amorphous or thin layer cell. The layer thickness amounts to less than 1µm (thickness of a human hair: 50-100 µm), so the production costs are lower due to the low material costs. However, the efficiency of amorphous cells is much lower than that of the other two cell types. Because of this, they are primarily used in low power equipment (watches, pocket calculators) or as facade elements.

D. Efficiency: Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 42.8% with multiple-junction research lab cells. Solar cell energy conversion efficiencies for commercially available multicrystalline Si solar cells are around 14-16%. The highest efficiency cells have not always been the most economical — for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide and produced in low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass production, while only delivering about four times the electrical power.

To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected PV systems); in stand alone systems, batteries are used to store the energy that is not needed immediately.

E. Advantages of solar energy: Solar cells are long lasting sources of energy which can be used almost anywhere. They are particularly useful where there is no national grid and also where there are no people such as remote site water pumping or in space. Solar cells provide cost effective solutions to energy problems in places where there is no mains electricity. Solar cells are also totally silent and non-polluting. As they have no moving parts they require little maintenance and have a long lifetime. Compared to other renewable sources they also possess many advantages; wind and water power rely on turbines which are noisy, expensive and liable to breaking down.

Rooftop power is a good way of supplying energy to a growing community. More cells can be added to homes and businesses as the community grows so that energy generation is in line with demand. Many large scale systems currently end up over generating to ensure that everyone has enough. Solar cells can also be installed in a distributed fashion, i.e. they don't need large scale installations. Solar cells can easily be installed on roofs, which mean no new space is needed and each user can quietly generate their own energy.

F. Disadvantages of solar cells: The main disadvantage of solar energy is the initial cost. Most types of solar cell require large areas of land to achieve average efficiency. Air pollution and weather can also have a large effect on the efficiency of the cells. The silicon used is also very expensive and the problem of nocturnal down times means solar cells can only ever generate during the daytime. Solar energy is currently thought to cost about twice as much as traditional sources (coal, oil etc). Obviously, as fossil fuel reserves become depleted, their cost will rise until a point is reached where solar cells become an economically viable source of energy. When this occurs, massive investment will be able to further increase their efficiency and lower their cost.

Electric cell or battery and their recent breakthrough:

2008-03-31T04:17:00.001-07:00

Electric cell or battery and their recent breakthrough:

Electric cell is a device that stores electric energy in the form of chemical energy and delivers electric energy when needed. The electric energy is released when a conductor is connected between the terminals of the cell. All cells consist of an electrolyte, i.e., solution containing ions, a positive electrode and a negative electrode. During energy release stage the negative electrode (cathode) reacts with the electrolyte to release electrons and positive electrode (anode) acquiring these electrons; thereby electricity is generated. When the cell has no power to release electricity, or in other words, electrolyte has reacted fully, the cell is said to be dead or discharged.

On the other hand, some types of cell can be recharged, i.e., the condition of electrolyte can be returned to the original state by passing a current in reverse direction. This type of rechargeable cell is also called storage cell or secondary cell. Primary cell can not be recharged. Following are the list of common type of cells used and also new developments made in storage of electricity:

(i) Alkaline dry cells - One of the commonest and quite old types of primary cell used today is alkaline dry cell. This type of cell consists of a positive electrode made from manganese oxide and a negative electrode made of zinc. Potassium hydroxide as the electrolyte is used. Alkaline cells are used widely in radios, personal stereos, and torches as they can supply quite large currents for long periods.

(ii) Mercury cells - Another major primary cell used is the mercury cell. It can be made in the shape of a small disc to use in small, portable electronic devices. These are so small these can be used very comfortably in hearing aids, wristwatches, calculators etc. In these cells the negative electrode consists of zinc, while the positive electrode is made of mercuric oxide. The electrolyte is a solution of potassium hydroxide.

(iii) Silver oxide primary cells – Silver oxide cells are also primary cell similar to the mercury cell. In silver oxide primary cell negative electrode is made of zinc with potassium hydroxide as the electrolyte. Silver oxide positive electrode in the cell delivers better voltage than mercury cells. These are also often made in the shape of a small disc.

(iv) Lead-acid battery – This is a secondary cell, i.e., it can be recharged when it is discharged fully. It generally consists of three or six cells connected in series. The electrolyte used is a dilute solution of sulfuric acid (H2SO4), the negative electrode consists of lead (Pb) and the positive electrode is made of lead dioxide (PbO2). This type of battery is used mostly in cars, trucks, aircraft, and other vehicles. Its major advantage is that it can deliver a strong current of electricity for starting an engine; however, it runs down very quickly.

A lead-acid storage cell runs down when sulfuric acid is gradually converted into water and the electrodes are converted into lead sulfate. When the lead-acid battery is recharged, these chemical reactions are reversed until the chemicals have been restored to their original condition. A lead-acid battery has a useful life of about two to three years and they produce about 2 V per cell.

(v) Nickel-iron battery (Alkaline cell) - Another widely used secondary cell in heavy industry is the alkaline cell, or nickel-iron battery. The principle of operation is the same as in the lead-acid cell. The only exception is that the negative electrode consists of iron and the positive electrode is made of nickel oxide. The electrolyte used is a solution of potassium hydroxide. The nickel-iron cell has the disadvantage of giving off hydrogen gas during charging.

(vi) Cadmium battery (Nickel-cadmium cell) – This is also very similar to Nickel-iron battery. Here negative iron electrode is replaced by one consisting of cadmium. The positive electrode remains same of nickel oxide. Certain Nickel-cadmium batteries gradually lose their maximum energy capacity if they are repeatedly recharged after being only partially discharged – this phenomenon of losing energy capacity exists in some battery, is called ‘Memory effect’ or ‘Lazy memory effect’.

(vii) Lithium-ion batteries (sometimes abbreviated Li-ion batteries) – This is a rechargeable type battery in which a lithium ion moves between the anode and the cathode. This type of battery is very commonly used in consumer electronics, laptop computers, cell phones, video games etc. Because of the benefits like, one of the best energy-to-weight ratios, no memory effect, and a slow loss of charge when not in use, they are currently one of the most popular types of battery found for portable electronics.

(viii) Nanowire lithium-ion battery – Recently, researchers have found a way to use silicon nanowires to reinvent the rechargeable lithium-ion batteries that power laptops, iPods, video cameras, cell phones, and countless other devices. The new technology produces 10 times the amount of electricity of existing lithium-ion, known as Li-ion, batteries. A laptop that now runs on battery for two hours could operate for 20 hours, a boon to ocean-hopping business travelers.

(ix) Ultra capacitor - A Texas company says recently that, it can make a new ultra-capacitor power system to replace the electrochemical batteries in everything from cars to laptops. Company’s claim that, it is a kind of battery-ultra-capacitor hybrid based on barium-titanate powders, will dramatically outperform the best lithium-ion batteries on the market in terms of energy density, price, charge time, and safety. Much like capacitors, ultra-capacitors store energy in an electrical field between two closely spaced conductors, or plates. When voltage is applied, an electric charge builds up on each plate. Ultra-capacitors have many advantages over traditional electrochemical batteries. Unlike batteries, "ultracaps" can completely absorb and release a charge at high rates and in a virtually endless cycle with little degradation.

(x) Sodium-sulfur (NaS) battery - Until recently, large amounts of electricity could not be efficiently stored. Thus, when you turn on the living-room light, power is instantly drawn from a generator. A new type of a room-size battery, however, may be poised to store energy for the nation's vast electric grid almost as easily as reservoir stockpiles water, transforming the way power is delivered to homes and businesses. Compared with other utility-scale batteries plagued by limited life spans or unwieldy bulk, the sodium-sulfur battery is compact, long-lasting and efficient.

Fischer-Tropsch process to produce synthetic liquid hydrocarbons from coal and natural gas:

2008-03-28T05:37:00.000-07:00

Fischer-Tropsch process to produce synthetic liquid hydrocarbons from coal and natural gas:

Fischer-Tropsch (F-T) technology converts coal, natural gas, and low-value refinery products into a high-value, comparatively cleaner burning fuel. The resultant fuel is colorless, odorless, and low in toxicity. In addition, it is virtually interchangeable with conventional diesel fuels and can be blended with diesel at any ratio with little to no modification. Currently, several oil companies are researching large-scale production of Fischer- Tropsch fuels.

For the past 50 years, Fischer-Tropsch fuels have powered all of South Africa’s vehicles—from buses to trucks to taxicabs. The fuel is primarily supplied by Sasol, a world leader in Fischer-Tropsch technologies. Sasol’s South African facility produces more than 150,000 barrels of high quality fuel from domestic low-grade coal daily.

The Fischer-Tropsch process is a catalyzed chemical reaction in which carbon monoxide and hydrogen are converted into liquid hydrocarbons of various forms. Typical catalysts used are based on iron and cobalt. Synthesis gas, a mixture of hydrogen and carbon monoxide, is reacted in the presence of an iron or cobalt catalyst; much heat is evolved, and such products as methane, synthetic gasoline and waxes, and alcohols are made, with water or carbon dioxide produced as a byproduct. The catalyst is usually supported on carbon or silicon dioxide to optimize its activity. An important source of the hydrogen-carbon monoxide gas mixture (known as water gas) is obtained by the gasification of coal (manufacturing process of water gas involves treating white-hot hard coal or coke with a blast of steam; carbon monoxide and hydrogen are formed). Thus, gasification is the first step of coal liquefication or production of Fischer-Tropsch fuels from biomass such as corn stover (corn stalks), wood or switch grass. The feed gas is produced in a gasifire by heating the gas to a temperature greater than 700^oC. By carefully controlling the oxygen content the hydrocarbons in the feedstock are broken down to carbon monoxide and hydrogen. The temperature, pressure and catalyst determine whether a light or heavy syncrude is produced.

The principal purpose of this process is to produce a synthetic petroleum substitute, typically from coal, natural gas or biomass, for use as synthetic lubrication oil or as synthetic fuel.

There are mainly two types of F-T reactors. The vertical fixed tube type has the catalyst in tubes that are cooled externally by pressurized boiling water. For a large plant, several reactors in parallel may be used presenting energy savings. The other process uses a slurry reactor in which pre-heated synthesis gas is fed to the bottom of the reactor and distributed into the slurry consisting of liquid wax and catalyst particles. As the gas bubbles upwards through the slurry, it is diffused and converted into more wax by the F-T reaction. The heat generated is removed through the reactor's cooling coils where steam is generated for use in the process.

The resulting organic compounds are a synthetic form of petroleum, analogous to a crude oil, and can be converted into many petroleum products including diesel and gasoline. Alternatively hydrogen can be recovered by further processing, resulting in only carbon dioxide and hydrogen with no hydrocarbons in the product stream. The primary interest at the present time is to produce low sulfur diesel fuel. Production of diesel fuel requires little processing from the F-T crude, has low sulfur and aromatic content, high cetane number and it burns exceptionally clean in a diesel engine.

Based on available research, there are no significant differences in Fischer- Tropsch fuel’s performance versus petro-diesel fuels. In fact, the higher cetane number of Fischer-Tropsch diesel fuel might result in improved combustion; the cetane number is a primary measure of diesel fuel quality. In addition, many alternative fuels require major changes in vehicle engines, but Fischer-Tropsch fuels require no engine modifications. Fischer-Tropsch fuels, however, are slightly less energy dense than petrodiesel, which might result in lower fuel economy and power. Further investigations of fuel compatibility issues need to take place, as well.

Advantages of Nuclear power:

2008-03-27T00:25:00.000-07:00

Advantages of Nuclear power:

Power from nuclear energy can prevent many of the environmental consequences arising out of the use of fossil fuels. Below we discuss advantages of nuclear power vis-a-vis other energy options, especially fossil fuel.

1. One of the greatest advantages of nuclear power is that it avoids the wide variety of environmental problems arising from burning fossil fuels - coal, oil, and gas. Nuclear energy does not produce smoke or carbon dioxide, so it does not contribute to the greenhouse effect. Thus ‘global warming’ process can be minimized - changing the earth's climate, acid rain, which is destroying forests and killing fish; air pollution etc. It checks degrading our quality of life; i.e., the destructive effects of massive mining for coal; and oil spills which do great harm to ecological systems can be prevented.

2. It is possible to generate a high amount of electrical energy in one single plant using small amount of fuel.

3. Nuclear power is reliable. This technology is readily available; it does not have to be developed first.

4. Produces small amounts of waste. The disposal of radio-active waste which nuclear power plant generates, can be effectively organized as our technology is improving at a fast pace. Moreover, the quality of radio-active waste improved if we go for reprocessing of spent fuel.

5. Nuclear power is also not so expensive as compare to power from coal. Reprocessing and reuse of plutonium from spent fuel makes it even cheaper than coal based power plant. The concern about proliferation should be taken out of mind as there are much easier, faster, and cheaper ways for a nation to develop nuclear weapons than through a nuclear power programme.

Some facts about nuclear reactor for power generation:

2008-03-26T02:01:00.000-07:00

Some facts about nuclear reactor for power generation:

A. Understanding running of nuclear reactor (fission) for power generation –

i. Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. Today it is almost all uranium. The fission of an atom of uranium produces few million times the energy produced by the combustion of an atom of carbon from coal.

ii. Natural uranium is almost entirely a mixture of two isotopes, U-235 and U-238. Today’s commercial nuclear reactor uses U-235 for fission reaction. Natural uranium has 99.3 percent of U-238 and only 0.7 percent of U-235.

iii. Most nuclear power plants today use enriched uranium in which the concentration of U-235 is increased from 0.7 percent to (nowadays) about 4 to 5 percent.

iv. The U-238 "tails" are left over for eventual use in "breeder reactors". The Canadian CANDU reactors don't require enriched fuel, but since they use expensive heavy water instead of ordinary water, their energy cost is about the same.

v. Present reactors that use only the U-235 in natural uranium are very likely good for some hundreds of years.

vi. A power reactor contains a core with a large number of fuel rods. Each rod is full of pellets of uranium oxide. An atom of U-235 fissions when it absorbs a neutron. The fission produces two fission fragments and other particles that fly off at high velocity. When they stop the kinetic energy is converted to heat.

vii. The steam withdrawn and run through the turbines controls the power level of the reactor. The heat from the fuel rods is absorbed by water which is used to generate steam to drive the turbines that generate the electricity.

viii. After about two years, when enough U-235 is converted to fission products and the fission products have built up enough so that the fuel rods must be removed and replaced by new ones.

ix. Besides fission products, spent fuel rods contain some plutonium produced by the U-238 in the reactor absorbing a neutron. This plutonium and leftover uranium can be separated in a reprocessing plant and used as reactor fuel.

x. Thus running a reactor for four years produces enough plutonium (about 1/4 as much as the U-235 that was in the fuel rods) to run it for one more year provided the plutonium is extracted and put into new fuel rods. Newer designs with higher "burnup ratios" get more of their energy from plutonium.

B. Understanding nuclear waste –

i. After the fuel has been in the reactor for about 18 months, much of the uranium has already fissioned.

ii. A considerable quantity of fission products also have built up in the fuel.

iii. The reactor is then refueled by replacing about 1/3 of the fuel rods. This generally takes one or two months. Canadian CANDU reactors replace fuel continuously.

iv. When fuel rods are removed from the reactor they contain large quantities of highly radioactive fission products and are generating heat at a high rate.

v. They are then put in a large tank of water about the size of a swimming pool. There they become less radioactive as the more highly radioactive isotopes decay and also generate less and less heat.

vi. The fuel rods should then be chemically reprocessed. Reprocessing removes any leftover uranium and the plutonium that has been formed.

vii. The fission products are then put in a form for long term storage.

viii. A large reactor produces about 1.5 tonnes of fission products per year.

ix. Economic advantages of reprocessing are great. If we do not reprocess, we lose the economic benefit of the plutonium.

x. At the same time, the spent fuel remains radioactive for longer duration and has to be better guarded, because it contains plutonium.

C. Understanding of future nuclear reactor - ‘breeder reactor’ -

i. If the design of reactor is such that, enough U-238 can also be converted to plutonium so that after a fuel cycle there is more fissionable material than there was in the original fuel rods in the reactor. This system is more economical.

ii. Such a design is called a ‘breeder reactor’.

iii. Breeder reactors essentially use U-238 as fuel. Therefore, it is more advantageous and it is estimated that, there is 140 times more beneficial than the conventional reactor.

iv. They are more expensive than present reactors.

v. Breeder reactor will be reprocessing on site, so no plutonium will ever become externally available.

vi. It is much safer system than the present one. It is hoped that it wiould address the proliferation concerns of the anti-nukes.

Oil from coal:

2008-03-24T03:48:00.000-07:00

Oil from coal:

As petroleum price is increasing due to various reasons, the alternative methods of producing oil gained much importance. The most widely known alternatives involve in extracting oil from sources such as Natural gas (methane), coal, oil shale and tar sands. Though some these sources exist in large quantities, it has become a challenge to extract oil economically and without excessively harming environment. Therefore, in this respect, extraction of oil from coal or from natural gas has been significant.

In fact, technology to extract oil from natural gas or from coal was available since the world war – II; but it was not so much significant until the exorbitant hike in international crude oil prices in last decade. During the World war – II, Germany produced some quantity of oil from coal and there after, South Africa (Sasol) was the major country to produce oil from coal, to meet its energy needs during its isolation under Apartheid. As crude oil prices increase, the cost of coal to oil conversion becomes comparatively cheaper. Now, many countries like China, whose coal production is quite substantial but have less reserve of crude oil, have started producing oil from coal. Recently, India has also started thinking of such conversion of their coal to synthetic oil. This conversion process produces low sulfur diesel fuel but also produces large amounts of greenhouse gases.

The Fischer-Tropsch process is well known for conversion of coal to oil. It is a catalyzed chemical reaction in which carbon monoxide (CO) and hydrogen (H2) are converted into liquid hydrocarbons of various forms. Typical catalysts used are based on iron and cobalt. The principal purpose of this process is to produce a synthetic petroleum substitute, typically from coal, natural gas or biomass.

There is another process called Karrick process for conversion of coal to synthetic oil. It is a low temperature carbonization (LTC) of coal, shale, lignite or any carbonaceous materials. These are heated at 360 degree Celsius to 749 degree Celsius, in the absence of air to distill out oil and gas. Recently, China has announced high volume commercial coal liquefaction production by this method.

Fluidized Bed Combustion (FBC) technology uses coal washery rejects / fines for power supply

2008-03-23T08:22:00.000-07:00

Fluidized Bed Combustion (FBC) technology uses coal washery rejects / fines for power supply:

In developing countries, most of energy is generated by coal fired power plants. For quality purpose, coals are washed. Disposal of huge rejects and fines obtained from coal washery are a problem everywhere. Fludised Bed Combustion (FBD) technology as the renewable source of energy generates eco-friendly power supply using washery rejects and washery fines.

The objectives of coal-fired power generation is to have (1) power generation at a economical cost; (2) to improve thermal efficiency; (3) to comply with current and future environmental standards. Many of these objectives may be gained by the FBC technology based plants, with incorporation of supercritical steam cycles together with some form of flue gas desulfurization and low NOx measures.

Advanced FBC system represents significant advantages over conventional coal combustion system. This technology uses a more compact boiler and very high rate of heat transfer to the tube surfaces in the bubbling bed; thus, level of NOx and SOx generated is much less, which is a good indication of pollution control. Generation of particulates is also less as compare to the conventional system.

Above all, it can utilize effectively coal washery rejects, coal washery fines, lignite etc. Utilizing coal washery rejects and coal washery fines means easing pressure for disposal problem of these materials.

Coal bed methane (CBM) drainage - Potential uses of coal mines methane:

2008-03-20T23:36:00.000-07:00

Coal bed methane (CBM) drainage - Potential uses of coal mines methane:

One of the major decisions facing a mine owner, when considering the implementation of a CBM drainage program is the potential use for the gas. The gas is a clean energy resource. However, the location of the mine and the ability to convert the gas into a marketable product may severely test the mine planners’ perseverance in finding an economic way of using the gas and producing the accompanying reduction in greenhouse gases. Here we would try to outline some possibilities for the gas whether it is a high-Btu, medium-Btu, or low-Btu product.

(1) High-Btu Gas (> 950 Btu/scf) - High-Btu gas is generally defined as having enough heat content to be used in a natural gas pipeline. Several potential uses exist for high-Btu gas. If the drainage system provides primarily CH4 and little in the way of inert gas, the product may be gathered, compressed, and marketed to a pipeline company. This is one of the most desirable options if natural gas pipelines are located near the mine. Thus, marketing of coal mines methane to a pipeline company would be a very desirable goal.

In case, pipelines are not readily available or the pipeline companies are not ready to buy coal mines methane, several other options are available for high-Btu gas. The first of these would be to use the gas as a feedstock to produce ammonia, methanol, or acetic acid. Currently, these chemicals are produced from natural gas, but coal-bed methane would be equally useful if it is available in sufficient quantities and if the chemical plants were in a favorable location. Another potential method of using CBM would be to compress or liquefy it for use in buses, trucks, and automobiles. This implementation has been successfully used in many of the CIS countries like Ukraine, Czech Republic etc.

(2) Medium-Btu Gas (300 to 950 Btu/scf) - There are many possible uses for medium-Btu gas. If the gas is at the high end of the heat content scale, enrichment by blending with a higher-quality gas or ‘spiking’ of the gas to produce a gas of pipeline quality is possible. Enrichment is the removal of gases like nitrogen, oxygen, and carbon dioxide to improve the heat content of the gas. ‘Spiking’ is the process of combining another fuel gas (like propane) with the methane to increase the heat content. Spiking will normally be economic only if the supplement gas is available cheaply in the area. A major and growing use of medium-Btu gas is as a substitute for other fuels in space heating and other applications where natural gas, fuel oil, or coal is normally used. For example, CBM can be used for heating mine facilities, heating mine intake air, heating greenhouses and institutional facilities, as a heat source in a thermal dryer and as a heat source for treating brine water.

Another use for medium-Btu methane is in electric power production. Using methane in coal-fired utility and industrial boilers and as a supplement to natural gas in blast furnaces is common where methane is extracted from coal mines.

(3) Low-Btu Gas (<>

Summery of specific options for utilization of Coal-bed methane from mines:

a. Power Generation - CBM can be ideal fuel for co-generation Power plants to bring in higher efficiency and is preferred fuel for new thermal power plant on count of lower capital investment and higher operational efficiency.

b. Auto Fuel in form of Compressed Natural Gas (CNG) - CNG is already an established clean and environment friendly fuel. Depending upon the availability of CBM, this could be a good end use. Utilization of recovered CBM as fuel in form of CNG for mine dump truck is a good option.

c. Feed stock for Fertilizer – Many of the fertilizer plants in the vicinity of coal mines where coal-bed methane is drained, have started utilizing fuel oil as feedstock for its cracker complex.

d. Use of CBM at Steel Plants - Blast furnace operations use metallurgical coke to produce most of the energy required to melt the iron ore to iron. Since coke is becoming increasingly expensive, in the countries where CBM is available, the steel industry is seeking low-capital options that reduce coke consumption, increase productivity and reduce operating costs.

e. Fuel for Industrial Use - It may provide an economical fuel for a number of industries like cement plant, refractory, steel rolling mills etc.

f. CBM use in Methanol production - Methanol is a key component of many products. Methanol and gasoline blends are common in many countries for use in road vehicles. Formaldehyde resins and acetic acid are the major raw material in the chemical industry, manufactured from methanol.

g. Other uses - Besides above, option for linkages of coal-bed methane produced by coal mines, through cross country pipe lines may be considered.

Economic benefits of coal-bed methane (CBM) drainage:

2008-03-20T01:01:00.000-07:00

Economic benefits of coal-bed methane (CBM) drainage:

There are many mining benefits that accrue from a methane drainage system. Coal-bed methane drainage systems can: (1) enhance coal productivity because of less frequent downtime or production slowdowns caused by gas; (2) decrease fan operating costs because of reduced air requirements for methane dilution; (3) reduce shaft sizes and number of entries required in the mains, (4) increase tonnage extracted from a fixed-size reserve as a result of shifts of tonnage from development sections to production sections; (5) decrease dust concentrations due to reduction of velocities at the working face; (6) improve mine safety resulting from lower methane contents in the face, returns, gobs and bleeders; (7) reduce problems with water; (8) improve worker comfort through reduction of velocities in the working faces; and (9) provide miscellaneous other benefits. Other benefits, such as reduced dust concentration, improved safety, or improved worker comfort, are difficult to estimate; while they constitute a real and significant benefit.

(1) Reduced Downtime - Enhanced coal productivity is probably the most significant benefit to be obtained from methane pre-drainage systems where coal-bed methane is encountered in significant quantities. The benefits come in the form of added production that occurs when downtimes or slowdowns resulting from high methane occurrences are avoided using methane drainage.

(2) Ventilation Power Cost Savings - The power costs associated with the mine ventilation system will ordinarily be the second most significant benefit associated with the addition of a methane drainage effort. In many mines, ventilation to ensure continuous production is quite expensive. Methane drainage would normally be used instead of increased ventilation because the overall costs associated with drainage will be lower than the costs associated with ventilation.

(3) Reduced Development Costs- Another important issue in assessing the costs and benefits associated with mining is the possibility that a reduction in the ventilation requirements will result in a reduced requirement for development openings. This can result in two types of cost benefits. The first benefit is the reduction in the size and number of shafts and other development openings connecting the coal seam to the surface. This can at times result in a significant level of economic savings. The second benefit results if the coal from the development entries of a mine is more costly on a cost/ton basis than that in the production sections. In a longwall mining operation, the coal produced from development openings will be much more costly than that produced in a longwall panel.

(4) Increased Reserve - The benefit of an increased reserve is also provided in a mining operation when a gas drainage system allows for a reduced number of entries in the development of mains, submains, headgates, and tailgates of mining layouts. This results in an increased number of tons of coal that can be extracted from a fixed-size coal block. The extra tonnage is derived from the fact that only about 50% of the coal in development sections is extracted while production sections may extract 85% to 95% of the coal under good conditions. The extra coal extracted when this occurs is an economic benefit of significant value under many conditions. Thus, it should be evaluated as a potential benefit in every operation where degasification is considered.

(5) Mine Safety - The effect of a methane drainage system on the safety of a mining system will certainly result in positive benefits. Any high-methane operation will incur a higher level of hazardous operating conditions than an equivalent mine with a methane drainage system in place.

(6) Reduced Dust Problems - The relationship between gas drainage activities and the costs of providing proper dust control in a mining section is another possible source of cost benefits from gas drainage.

(7) Reduced Water Problems - The presence of water in coal mine roof strata can be a costly source of delays in some underground mining operations. The most sizeable delays will ordinarily be encountered in the development sections of the mine and will be quite variable depending upon the geologic parameters of the roof strata. The water in the roof, when occurring in conjunction with high methane contents, can be mitigated by a methane drainage system.

(8) Worker Comfort - The level of comfort of work in a mining environment deteriorates if high air velocities are required to keep methane contents below the regulatory limits. The difficulty of working in an air velocity above 600 ft/min is that ordinary tasks become more difficult and the high velocities will generate more dust.

Thus, extraction of coal-bed methane provide lot of economical benefits in running coal mines, apart from providing cleaner environment by preventing release of major greenhouse gas, methane, in the atmosphere and recovering extra energy source as well.

Coal-bed Methane (CBM) Drainage from Underground Coal Mines:

2008-03-19T01:30:00.000-07:00

Coal-bed Methane (CBM) Drainage from Underground Coal Mines:

Coal mine methane, a byproduct of mining operations, can be recovered to provide various types of benefits to a mining company. These benefits include, but are not limited to, reduced ventilation costs, downtime costs, and production costs; and the ability to use the recovered gas as an energy source, either at or near the mine site or by injecting it into a commercial gas pipeline system. There are many variables that play a part in the decision to implement a coal mine methane drainage project. Mining companies can employ basic decision-making logic to determine the feasibility of draining and/or using methane at specific coal mines.

Over the past few decades, emissions of methane from coal mines have increased significantly because of higher productivity, greater comminution of the coal product, and the trend towards recovery from deeper coal seams. Under current coal mine regulations of many countries, methane must be controlled at the working faces and at other points in the mine layout. This has traditionally been performed using a well-designed ventilation system. However, this task is becoming more difficult to achieve economically in modern coal mines. In addition, scientists have established that methane released to the atmosphere is a major greenhouse gas, second only to carbon dioxide in its contribution to potential global warming. In order to improve mine safety and decrease downtime as a result of methane in the mine openings, many mines are now using a degasification system to extract much of the coalbed methane from their seams before or during mining. Methane drainage offers the added advantages of reducing the ventilation costs, reducing the development costs of the mine, reducing the global warming threat, and allowing a waste product to be productively utilized.

This byproduct can be gathered to produce three levels of benefits to a mining company, depending on the market potential of the methane. The benefit levels are as follows:

(1) The methane is gathered from the coal seam to reduce ventilation costs, downtime costs, production costs, and shaft development costs or to benefit from increased coal resources. All of these benefits are achieved internal to the mining operation and can be easily analyzed by the mining company.

(2) The coalbed methane is extracted from the seams to be mined and is utilized as a local energy resource to heat buildings, dry coal output from the coal preparation facility, generate electrical power, power vehicles by compressing the gas, or other local uses.

(3) The extracted methane can be upgraded, if necessary, or immediately compressed and introduced into a commercial gas pipeline system. This may provide the highest possible benefit to the mining company providing that the methane is of high quality and the mine location is near a gas pipeline. With this option, the value of the methane as an energy resource may be very large and it can make a significant contribution to profits.

Methane degasification methods: With the increasing coal production and depth of coal mines, traditional ventilation methods are not always the most economical methods of handling methane in the coal seam. Degasification systems have been developed that recover the gas before, during, or after mining. The degasification methods, coupled with mine ventilation, may be the most economical method of keeping methane concentrations low in many mines.

Degasification methods that have been used in the U.S. include vertical wells, gob wells, horizontal boreholes, and cross-measure boreholes.

(1) Vertical wells method - The term “vertical well” is generally applied to a well drilled through a coal seam or seams and cased to pre-drain the methane prior to mining. The wells are normally placed in operation 2 to 7 years ahead of mining and the coal seam is hydraulically fractured to remove much of the methane from the seam. The water in the coal seams must be removed to provide better flow of gas. This water is separated and must then be treated and/or disposed of in an environmentally acceptable manner. To enhance the flow of gas from a vertical well, either hydraulic fracturing or open-hole cavity completions are generally used.

Vertical wells recover high-quality gas from the coal seam and the surrounding strata. The gas quality is ensured in most cases because the methane will not be diluted by ventilation from the mine. The total amount of methane recovered depends on site-specific conditions such as the gas content of the coal seams and surrounding strata, permeability of the geologic materials, the drainage time, the amount of negative head applied, and other variables of the geologic and extractive systems. Vertical wells can recover 50% to 90% of the gas content of the coal and are normally placed in operation two to seven years before mining commences.

Vertical wells offer an advantage over other methods because they can be applied to multiple coal seams simultaneously. These wells produce greater gas yields that can make them commercially economic as well as further reduce the potential for gas influx into the operating mine.

(2) Gob Wells - The designation “gob well” refers to the type of coalbed methane (CBM) recovery well that extracts methane from the gob areas of a mine after the mining has caved the overlying strata. Gob wells differ from vertical wells in the sense that they are normally drilled to a point 10 to 50 feet above the target seam prior to mining, but are operated only after mining fractures the strata around the wellbore. The methane emitted from the fractured strata then flows into the well and up to the surface. The flow rates are mainly controlled by the natural head created by the low-density methane gas or can be stimulated by blowers on the surface. Gob wells can recover 30% to 70% of methane emissions depending on geologic conditions and the number of gob wells within the panel.

(3) Horizontal Boreholes - Horizontal holes are drilled into the coal seam from development entries in the mine. They drain methane from the unmined areas of the coal seam shortly before mining, reducing the flow of methane into the mining section. Because methane drainage occurs only from the mined coal seam and the period of drainage is relatively short, the recovery efficiency of this technique is low.

(4) Cross-Measure Boreholes - Cross-measure boreholes are drilled at an angle to the strata, normally from existing mine entries. The boreholes are strategically placed above areas to be mined with the goal of pre-draining the overlying strata and exhausting gas from the gob area. Like horizontal borehole systems, the individual holes must be connected to a main pipeline which ordinarily is coursed through a vertical borehole to the surface.

Carbon emission from bio-fuels:

2008-03-18T00:30:00.000-07:00

Carbon emission from bio-fuels:

Bio-fuels are the fuels of solid, liquid or gaseous in nature, which has been derived from bio-mass – recently living organisms or their metabolic byproducts. Thus, it could be oils from plants, manure from cows, wood from trees etc. For example, bio-gas (i.e., gas produced by the biological breakdown of organic matter in the absence of oxygen); bio-ethanol; bio-diesel; straight vegetable oil etc., are the bio-fuels. It is a renewable energy source, mostly have agricultural based, unlike other natural resources such as petroleum, coal and nuclear fuels.

It has been seen that certain social and environmental benefits bio-fuels has as compare to use of fossil fuels, such as reduction of greenhouse gas emission, increased national energy security, increased rural earnings and development and above all, reduction of use of fossil fuel.

Bio-fuels and other forms of renewable energy are thought to be ‘carbon neutral’ or ‘carbon negative’. Carbon neutral or carbon negative is the difference of quantum of carbon produced and emitted to the atmosphere when these are used as fuels and the quantum of carbon absorbed in the process of their growth. If both are same, is called carbon neutral or if quantum of carbon absorbed through photo-synthesis is more than the emission is called carbon negative. Both the cases are advantageous towards environment point of view and reduction of global warming.

Strictly speaking, bio-fuels are neither carbon neutral nor carbon negative. This is because extra energy is required to grow crops and process them into fuel. This extra energy releases extra carbon to atmosphere as emission. For example, plants require fertilizer to grow, requires energy for transportation and processing; this extra energy releases carbon to the atmosphere as emission. Therefore, this emission aspect is to be debated, whether we are really gaining in respect of carbon emission, by using bio-fuel. However, the arable lands can be better utilized if people shift towards bio-fuels; so the rural earnings. The poorly irrigated land mass also can be taken up for cultivation.

Pollution from Oil refineries:

2008-03-17T03:59:00.000-07:00

Pollution from Oil refineries:

Oil refineries pollute our air, water, and land. Oil refineries cause smog and air pollution. Almost all refineries in every country currently pollute at unacceptable, unhealthy levels. Oil refineries emit about 100 chemicals everyday. These include metals like lead which makes it hard for children to learn. They also include very smaller size dust particles that get deep into our lungs and harm our ability to breathe. Finally, refineries emit many gases like sulfur dioxide (SO2), nitrogen oxide (NO2), carbon dioxide, carbon monoxide, methane, dioxins, hydrogen fluoride, chlorine, benzene and others.

Many of the gases emitted by refineries are harmful to humans, and can cause permanent damage and even death. They can cause respiratory problems (such as asthma, coughing, chest pain, choking, bronchitis), skin irritations, nausea, eye problems, headaches, birth defects, leukemia, and cancers. Young children and the elderly are the worst affected.

Sulfur dioxide (SO2): Crude oil and coal both contain relatively high quantities of sulfur. (Natural gases contain much less sulfur and therefore are safer.) When crude oil or coal is heated at the refinery to produce fuel, the sulfur is converted into a gas called sulfur dioxide. This is a colourless gas with a very strong smell, like rotten eggs.

Bad effects of Sulfur dioxide: Exposure to very high concentrations of SO2 can result in painful irritation of the eyes, nose, mouth and throat, difficulty in breathing, nausea, vomiting, headaches and even death. Some of the health effects from daily exposure to outdoor levels of SO₂are tight chests, worsening of asthma and lung disease, and narrowing of air passages in the throat and chest. People with asthma are more sensitive to SO2. Exposure to SO2 can provoke asthma attacks. SO2 mixes easily in water, including moisture in the air to form an acid. Acid rain and early morning dew causes much damage to metals, stones, and the environment.

Fugitive emissions are the air pollution which escapes through leaks in the equipment. Very often the amount of pollution coming from fugitive emissions is higher than the amount coming out of the stacks.

Many of the refineries often use low quality crude oil that has high levels of sulfur. When this is refined it produces higher levels of SO2 pollution.

Accidental fires, explosions, and chemical and gas leaks are common at refineries. Such accidents cause higher than usual amounts of pollution, which may result in more acute exposure to pollutants and greater health impacts.

Chemical processing of crude oil:

2008-03-13T23:20:00.000-07:00

Chemical processing of crude oil:

Crude oil is a mixture of thousands of different hydrocarbons (compounds of hydrogen and carbon). There are four primary activities that occur in crude refinery processes: (a) Separating hydrocarbons (e.g., distillation), (b) Creating hydrocarbons (e.g., cracking/coking), (c) Blending hydrocarbons, (d) Removing impurities (e.g., sulfur removal).
A. Chemical processing is nothing but changing one fraction into another. Chemical process generally has three methods, such as, (i) Breaking large hydrocarbons into smaller pieces (i.e., cracking); (ii) Combining smaller pieces to make larger ones (i.e., unification); (iii) Rearranging various pieces to make desired hydrocarbons (i.e., alteration).
(i) Cracking: Cracking takes large hydrocarbons and breaks them into smaller ones. Generally, there are two types of cracking; Thermal and Catalytic. In thermal cracking, you heat large hydrocarbons at high temperatures (sometimes high pressures as well) until they break apart. In catalytic cracking, a catalyst is used to speed up the cracking reaction. Catalysts include zeolite, aluminum hydrosilicate, bauxite and silica-alumina. After various hydrocarbons are cracked into smaller hydrocarbons, the products go through another fractional distillation column to separate them.
(ii) Unification: To combine smaller hydrocarbons to make larger ones is called unification. The major unification process is called catalytic reforming and uses a catalyst (platinum, platinum-rhenium mix) to combine low weight naphtha into aromatics, which are used in making chemicals and in blending gasoline. A significant by-product of this reaction is hydrogen gas, which is then either used for hydrocracking or sold.
(iii) Alteration: Sometimes, the structures of molecules in one fraction are rearranged to produce another. Commonly, this is done using a process called alkylation. In alkylation, low molecular weight compounds, such as propylene and butylene, are mixed in the presence of a catalyst such as hydrofluoric acid or sulfuric acid. The products of alkylation are high octane hydrocarbons, which are used in gasoline blends to reduce knocking.

B. Treating and blending the fractions: Distillated and chemically processed fractions are treated to remove impurities, such as organic compounds containing sulfur, nitrogen, oxygen, water, dissolved metals and inorganic salts. Treating is usually done by passing the fractions through: (i) a column of sulfuric acid which removes unsaturated hydrocarbons (those with carbon-carbon double-bonds), nitrogen compounds, oxygen compounds and residual solids (tars, asphalt); (ii) an absorption column filled with drying agents to remove water; (iii) sulfur treatment and hydrogen-sulfide scrubbers to remove sulfur and sulfur compounds. After the fractions have been treated, they are cooled and then blended together to make various products, such as:
(a) Gasoline of various grades, with or without additives;
(b) Lubricating oils of various weights and grades;
(c) Kerosene of various grades;
(d) Jet fuel;
(e) Diesel fuel;
(f) Chemicals of various grades for making plastics and other polymers.

Bio-diesel - an effective renewable alternative fuel to petro-diesel:

2008-03-04T23:48:00.000-08:00

Bio-diesel is an effective renewable alternative fuel to petro-diesel:

Bio-diesel is a renewable alternative fuel generally used in place of petro-diesel in the engines. It is a fuel made from various vegetable oils, vegetable and animal fats etc. Bio-diesel fuels can be used in diesel engines without changing them. It is the fastest growing alternative fuel in many countries. Bio-diesel, a renewable fuel, is safe, biodegradable, and reduces the emissions of most air pollutants.

Most bio-diesel today is made from oil produced from soybean, palm and jatropha seeds. Bio-diesel is most often blended with petroleum diesel in ratios ranging from 2 percent to 20 percent. It can also be used as pure bio-diesel Bio-diesel fuels can be used in regular diesel vehicles without making any changes to the engines. It can also be stored and transported using diesel tanks and equipment.

Bio-diesel and the environment:

(i) Bio-diesel is renewable, nontoxic, and biodegradable. Compared to diesel, bio-diesel is significantly cleaner burning. It produces fewer air pollutants, like particulates, carbon monoxide, hydrocarbons, and air toxics. It does slightly increase emissions of nitrogen oxides, though. Bio-diesel produces less black smoke.

(ii) Regular petro-diesel fuel contains sulfur. Sulfur can cause damage to the environment when it is burned in fuels. New environmental laws will require the amount of sulfur in diesel fuel to be dramatically reduced over the next few years. When sulfur is removed from regular diesel fuel, the fuel doesn't work as well. Adding a small amount of bio-diesel can fix the problem. Bio-diesel has no sulfur, so it can reduce sulfur levels in the nation's diesel fuel supply while making engines run more smoothly.

(iii) Bio-diesel has a higher cetane rating than petro-diesel, which can improve performance and clean up emissions compared to crude petro-diesel.

(iv) Bio-diesel can reduce by as much as 20% the direct (tailpipe) emission of particulates, compared to low-sulfur diesel.

(v) Bio-diesel is biodegradable under ideal conditions and non-toxic.

BIO-DIESEL FROM ALGAE

While a number of bio-feedstock is currently being experimented for bio-diesel production, algae have emerged as one of the most promising sources for bio-diesel production. The current oil crises and fast depleting fossil oil reserves have made it imperative to invest more into research on suitable renewable feedstock such as algae.

It is widely believed that, petroleum had its origins in kerogen, which was converted to an oily substance under conditions of high pressure and temperature. Kerogen is formed from algae, biodegraded organic compounds of plankton, bacteria and plant materials. Several studies have been conducted to simulate petroleum formation by pyrolysis. On the basis of these findings, it can be inferred that algae grown in carbon dioxide rich air can be converted to oily substances. Such an approach can contribute to solving two major problems: (a) air pollution resulting from carbon dioxide evolution, (b) future crises due to a shortage of energy sources.

Therefore, it is believed that, algae are one of the most promising feedstocks for future bio-diesel production. The advantegeous points about algae are their widespread availability, higher oil yields and pressure on cultivated land for production of bio-diesel is reduced.