Carbon emission from bio-fuels:

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:

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 SO₂ are 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:

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:

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.

Understanding fuel combustion process:

Understanding fuel combustion process:

(a) Fuels are chemical substances which may be burned in presence of oxygen to generate energy in the form of mostly heat. They mainly consist of carbon and hydrogen. Small quantity of sulfur is also present in fuel as contamination. Solid, liquid and gaseous fuels are used by various systems. Coke and coal are solid fuels, petrol, diesel, kerosene is liquid and LPG, CNG are the example of gaseous fuel.

C + O2 = CO2, (here C and O2 are reactants and CO2 is the product of burning fuel)

(b) Each fuel burn at a particular temperature, called ignition temperature. For starting the combustion process each fuel should be brought above its ignition temperature. An appropriate air-fuel ratio is also necessary to maintain in order to get desired result. The minimum ignition temperature at atmospheric pressure for some fuel is: (i) Carbon is 400 degree Celsius; (ii) Hydrogen is 580 degree Celsius; (iii) Carbon monoxide (CO) is 610 degree Celsius; (iv) Methane (CH4) is 630 degree Celsius; (v) Gasoline is 260 degree Celsius.

(c) As air is the major ingredient in any burning process, the air-fuel ratio is the term frequently used in the analysis of combustion process for any fuel. It is usually expressed on a mass basis, i.e., Mass of air required / mass of fuel burnt.

(d) Fuel combustion process is the process when a particular fuel is burnt completely, i.e., all carbon present in the fuel converts into carbon dioxide (CO2), all hydrogen converts into water (H2O) and all sulfur converts to sulfur dioxide (SO2). Theoretically, in completely burnt process, no un-burned residue of carbon, hydrogen should be present and process should not produce any carbon monoxide (CO). For any internal combustion engine, complete combustion is desirable, as energy conversion is maximized and exhaust gas characteristics is improved, thereby engine efficiency and less pollution.

(e) It is desirable to use more air than the actual requirement for the complete combustion of any fuel; to prevent chance of any incomplete combustion. Excess air is also needed to control rise in temperature of the combustion chamber.

(f) Energy is an inherent property of a system by which work is done. Any system at a given set of conditions has certain energy content. The concept of energy is derived to describe a number of processes such as conversion of work to heat. Joule (J) is the unit in SI system. Other units of energy / heat are: (i) 1 cal (calorie)= 4.1868 J; (ii) 1 kcal= 4186.8 J; (iii) 1 Btu (British thermal unit)= 1055.05 J; (iv) 1 ft.lbf= 1.35582 J; (v) 1 kJ= 1000 J; (vi) 1 hp.h (horsepower.hour)= 2,684,520 J; (vii) 1 kWh= 3,600,000 J.

(g) For any combustion energy is transferred to heat and heating value for any system is the amount of energy released when a fuel is burned completely.

Conservation of fossil fuels Fossil fuels take millions of years to make. We are using up the fuels that were made more than 300 million years ago. Once they are gone they are gone. It is best not to waste fossil fuels. They are not renewable; they can not be made again. We can save fossil fuels by conserving energy.

Ethanol as fuel:

Ethanol as fuel:

Ethanol or alcohol can be used as fuel very effectively, as a bio-fuel alternative to gasoline. In many of the countries it is used in running vehicles. As it is easier to manufacture and process, it is steadily becoming a promising alternative to gasoline almost throughout the world. It is mainly processed from sugar cane – a very common agricultural produce. Anhydrous ethanol, i.e., ethanol having less than 1% of water, can be blended very effectively with gasoline in varying proportion. 10% ethanol blended gasoline is common in most of the countries for running motor vehicles.

Current interest in ethanol mainly lies in ‘bio-ethanol’ that is produced from agricultural based starch or sugar. Basically, carbon-based feedstocks are used for bio-ethanol production. Agricultural feedstocks are considered renewable. Feedstock such as sugar cane, bagasse, miscanthus, sugar beet, sorghum, grain sorghum, switch-grass, barley, hemp, kenaf, potatoes, sweet potatoes, cassava, sunflower, fruit, molasses, corn, stover, grain, wheat, straw, cotton and other biomass can be used for production of bio-ethanol.

The basic steps for large scale production of bio-ethanol are: (a) microbial (yeast), i.e., fermentation of sugars; (b) distillation; (c) dehydration and (d) denaturing.

There has been considerable debate about actual usefulness of bio-fuel like bio-ethanol. Replacing fossil fuels by bio-ethanol take large area of arable land mass, which would have been cultivated for food crops. Moreover, the energy and pollution balance of the whole cycle of ethanol production is also not known.

Use of methane as a fuel and for other purposes:

Use of methane as a fuel and for other purposes:

Methane (CH4) is the simplest alkane, used as a fuel for various use. Apart from methane being principal constituent of natural gas, it is obtained from coal seams (as coal bed methane, CBM) and also it is obtained from bio-mass. At room temperature, methane is a gas less dense than air. Methane's relative abundance and clean burning process makes it a very attractive fuel. Burning one molecule of methane in the presence of O2 (oxygen) releases one molecule of CO2 (carbon dioxide) and two molecules of H2O (water). Methane being gas in ordinary temperature, its transportation and storage is difficult. Methane is a powerful greenhouse gas. Methane is over 20 times more effective in trapping heat in the atmosphere than carbon dioxide (CO₂)

Some methane is manufactured synthetically by the distillation of coal. Coal also contains hydrogen and oxygen, with small concentrations of nitrogen, chlorine, sulfur, and several metals. Coals are classified by the amount of volatile material they contain. Volatile substances released from coal when it is distilled, in addition to methane, include water, carbon dioxide, ammonia, benzene, toluene, naphthalene, and anthracene. In addition, the distillation also yields oils, tars, and sulfur-containing products. The non-volatile component of coal, which remains after distillation, is coke.

At high temperatures (700 to 1100 degree Celsius) in the presence of nickel catalyst, steam reacts with methane to yield CO (carbon monoxide) and H2 (hydrogen). This hydrogen is used for manufacturing of ammonia (NH3). In near future, one of the greatest uses of hydrogen would be for running vehicle by using environment-friendly hydrogen cell technology.

Methane is important for electrical generation by burning it as a fuel in a gas turbine or steam boiler. Compared to other hydrocarbon fuels, burning methane produces less carbon dioxide for each unit of heat released. In many cities, methane is piped into homes for domestic heating and cooking purposes. Methane in the form of compressed natural gas (CNG) is used as a fuel for vehicles, and is claimed to be more environmentally friendly than alternatives such as gasoline/petrol and diesel.

Note: NASA is developing LOX/methane engines as an option for the future rocket engine, as methane is abundant in the outer solar system.