Important Fuels and their Energy content

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

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

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.