Chapter -2 An Overview of Energy Resources

Chapter -2 An Overview of Energy Resources

2.1 Energy Requirements

The more energy is consumed by a nation, more developed it will be. At present India’s population is 18 % of the world population (Indian population 1.3 billion), however it consumes only 6 % of total energy produced in the world.[ India Energy Outlook, World Energy Outlook Special Report 2015]. According to International Energy Association (IEA), in 2013 total world energy consumption was 9,301 Mtoe or 3.89 X 10²⁰ Joule of energy, equivalent to 108 PWh (Petawatthour) and an average power consumption of 12.3 terawatts. [Key world Energy Statistics 2015, IEA]. Energy use in India has doubled since 2000, but energy consumption per capita is still only around one third of the global average and about 240 million people have no access of electricity [India Energy Outlook, World Energy Outlook Special Report 2015, p.19]. Annual residential electricity consumption in India in 2013 was 200 kWh per capita in comparison to world average 920 kWh per capita.

Energy is required for each and every activity. The major sectors of consumption of energy are :

i.                 Household activities- cooking, lighting, heating/cooling inside the room, electricity for household gadgets and instruments.

ii.               Transportation- Energy is needed for transportation of goods and human beings.

iii.             Industry- A major part of energy is consumed in industry to run machines for production of goods together with regular use like, lighting, heating, cooling etc.

iv.             Agriculture- Mechanised methods of agriculture and irrigation also require a large amount of energy.

v.               Miscellaneous- Like homes; offices, schools, colleges, universities, hospitals, shops need energy for lighting, heating/cooling, electricity for their gadgets and instruments.

Sector wise distribution of world energy is [Key world Energy Statistics 2015, IEA p 46]

Industry – 31.4 %

Transport – 24.6%

Building and agriculture – 34.3%

Non-energy use – 9.7%

In India Sector wise distribution of energy is [TERI]

Industry – 48%

Transport – 15%

Building and agriculture – 30 %

Non-energy use – 9%

2.2 Present Scenario of Energy Resources

At present major global energy source is fossil fuel. Fossil fuel consists of coal, oil (petroleum) and natural gas. These sources are non-renewable. These sources have been exploited excessively, so they will come to end after some years.  Besides this, burning of fossil fuel is responsible for environmental pollution, in terms of greenhouse effect, acid rain, resulting in global warming. So world must move towards other energy options. Commonly used other sources of energy are Nuclear Energy and Hydroelectricity. Again nuclear energy is non-renewable and hydroelectricity is renewable. Other new options are solar energy, hydrogen energy, wind energy, ocean energy, tidal wave and geothermal energy. All these resources are renewable, except geothermal, which is renewable up to some extent depending on the exploitation. All these sources are discussed in brief in the following:

2.2.1 Non-renewable Energy/Conventional Energy

2.2.1.1 Fossil Fuels

Fossil fuels are formed from the remains of plants and animals buried under layers of sedimentary rocks under high pressure and over large time span. Hence fossil fuels are organic in nature. The process of formation of fossil fuels is extremely slow. They are even forming today, but exploitation has been increased excessively in this century, therefore their resources are depleting at faster rate. Even today about 80% global energy need is fulfilled by fossil fuel [Key world Energy Statistics 2015, IEA]. The major fossil fuels are coal (solid), crude oil or petroleum (liquid) and natural gas (gas).

2.2.1.1 a Coal

Coal is formed primarily by dead plants. Most of the dead plants decompose into organic matter and incorporated into soil or washed away by water. Those plants which are buried in deep have no supply of oxygen. Therefore, their break down stops. These thick accumulated partially decayed brown–coloured materials are known as peat. It is rich in carbon, hydrogen and oxygen. Peat is the first stage of coal formation. As the pressure and temperature is increased due to further deposition of debris and sediments on upper layer, peat is converted into other form. As the time passes, the oxygen and hydrogen content of peat decreases and it becomes drier and rich in carbon content.  Now the colour of peat becomes dark brown and it is known as lignite (soft, dark brown). Due to increasing compression, lignite changes into bituminous coal (soft coal) and finally into anthracite (hard coal). Anthracite has maximum carbon content up to 95% and has highest calorific or heat value. The coal has been formed over a period from about 360 to 285 million years ago. The main impurity in coal is in form of sulphur, which releases sulphur dioxide (SO₂) on burning and is responsible for acid rain. The sulphur content of the coal may be generally classified as low (zero to 1 %), medium (1.1 to 3 %), or high (greater than 3 %).  The coal with minimum % of sulphur produces least pollution.

            Coal mining is done by two methods; underground method and strip mining (open-pit). Strip mining is in many cases technologically and economically more advantageous than underground method. Common methods of strip mining include area mining (on relatively flat area) and contour mining (in hilly area).  The type of mining depends on the topography of the area. Coal is used to produce electricity, to heat space in buildings, to produce heat in factories.

2.2.1.1 b Oil (Petroleum or Crude oil)

Oil is also formed from organic debris, but in ocean rather than on land. Plant litter is carried by streams and rivers to the oceans. The ocean plants and animals also sink in ocean and are accumulated on the sea bed. This organic debris buried in sediments is under compression and get heat up (50° C to 100° C). In this environment (high pressure and high temperature) the organic debris is converted to tiny droplets of liquid petroleum dispersed among the sediments. This oil is collected above the impermeable rock acting as reservoir. The oil is brought to the surface in liquid form by means of oil wells. Sometimes very heavy oil that is too thick and viscous to flow at normal surface temperatures is found in sand deposits. They are commonly known as Tar sands, occur at shallow depths and can be mined using open-pit techniques. The oil is separated from the sand as (using steam or by heating the sand) and the clean sand is returned to the pit.

            Oil is mainly used in transportation. Other uses are heating buildings and running machineries. Crude oil, when comes out of the ground is very viscous and must be refined. The crude oil varies in colour as black, brown or amber to various sheds of green. This oil is very corrosive and contains impurities like sulphur, salts and metals. In the refining process, crude oil is turned into automobile gasoline, heating oil, jet fuel, tar for roads, motor oil and other substances. Oil forms the raw materials to manufacture various plastics, fertilizers, medicines and many more products.

2.2.1.1 c Natural Gas

Natural gas is primarily composed of methane (CH₄) gas. As the petroleum is subjected to elevated temperature beneath the earth surface, it is converted to natural gas. The gas is lighter to the oil, therefore is collected at the top of oil reservoir. Many oil deposits have gas as a top layer above the liquid oil. Sometimes gas leaves the oil reservoir and is collected in a separate reservoir. The gas and oil reservoir must have cap rock otherwise it will escape.

            The methane produced below 3 to 6 km depth under high pressure and temperature, is known as thermogenic methane. At this high temperature no microorganism is alive. Within the depth of 1 to 3 km, a different reaction takes place. Microorganisms consume buried organic material and produce methane as by-product. This gas is known as biogenic gas, consisting of methane. 4H₂ + CO₂ = CH₄ + 2 H₂O. In thermogenic production no microorganism is involved, as they cannot survive at higher temperature.  About 20% natural gas is produced by biogenic method. In a swamp or marsh sometimes bubbles of gas rising to the surface of water may be seen. This may be biogenic gas.

2.2.1.2 Nuclear Energy

Nuclear Energy is non-renewable energy, as it uses radioactive elements, whose stock is fixed. Unlike fossil fuel, it does not produce greenhouse effect as environmental pollution. However, the disposal of nuclear waste is another problem related to radioactive pollution. Also, if any accidents, like leakage of radioactive radiation in atmosphere take place, it will lead to a very serious problem. About 4.8% of global energy consists of nuclear energy. In developed country this percentage is higher (> 20%) as part of their domestic energy. France has 75% share of nuclear energy in its domestic energy. Nuclear energy is produced by two methods; nuclear fission and nuclear fusion. In nuclear fission a radioactive isotope of heavy element (uranium or plutonium) split in two or more daughter products and an enormous amount of heat is released simultaneously. In nuclear fusion isotopes of lighter elements fuse to give heavier element. In this process also large amount of energy is released. All the current nuclear reactor operates by nuclear fission. In Sun energy is produced by nuclear fusion. On earth nuclear fusion in laboratory is in developmental stage.

2.2.1.2. a Nuclear Fission

The first controlled nuclear fission was demonstrated in 1942, leading the way to the use of uranium in explosives and as a heat source to provide steam for generation of electricity. Fission of 1 kg of uranium oxide releases approximately the same amount of energy as the burning of 16 metric tons of coal [E. A. Keller, Environmental Geology, Chapter 15, Page 17, Prentice – Hall, eighth edition 2000, New Jersey].

In nuclear fission one neutron is bombarded on one uranium 235 atom to produce two or more fragments, which are highly radioactive but not fissionable. In this reaction neutron is also produced, which initiate more fission reactions. In this process large amount of heat is produced. Thus the process is chain reaction. The uncontrolled chain reaction leads to concept of atomic bomb. In nuclear reactor this process occurs in controlled way. In nature uranium has three isotopes; U-238 (99.3%), U-235 (0.7%) and U-234 (0.005%). Among these only U-235 is fissionable. However U-238 converts to plutonium-239 by capturing fast neutron produced in chain reaction. Plutonium-239 is fissionable. Hence naturally occurred uranium is processed to enrich U-235. The neutrons produced in nuclear fission reactions are very fast. Fast neutrons are readily absorbed by U-238. Therefore, their speed is curtailed to convert them into slow neutron, so that they can be readily absorbed by U-235. For this purpose moderators are used in nuclear reactors. Moderators are graphite rod, beryllium or heavy water [M.L.McKinney and R.M.Schoch, Environmental Science, Chapter 8, Jones and Bartlett Publishers, Sudbury, Massachusetts, 1998].

Most reactors today consume more fissionable material than they produce and are therefore known as burner reactors. The main components of nuclear reactor are the core, control rods, coolant and reactor vessel. In the core, there is strong stainless steel reactor vessel in which chain reaction takes place. Nuclear fuel is kept in hollow tubes of about 1 cm diameter. About 40,000 such tubes are placed in a reactor. The control rods are fully inserted into core to control the speed of neutron and to slow down chain reaction. When control rod is removed completely, reaction becomes fast.  Excessive amount of heat produced during this process is removed by coolant that is water. The primary coolant transfers its heat to secondary coolant water pipe as the primary water pipe may have traces of radioactive elements. The heated water produces steam, which runs turbine to generate electricity. The reactor vessel is housed in a containment structure composed of thick steel-reinforced concrete. This containment structure protects the environment by all radioactive contaminations.

Breeder reactors take advantage of the ability of non-fissionable U-238 to be converted to fissionable Pu-239. In this way most of the non-fissionable uranium found in nature can be used as fissionable nuclear fuel.

2.2.1.2. b Nuclear Fusion

            To initiate fusion reaction extremely high temperature (40 million degree C) is needed, which is very difficult to create. On earth the first fusion reaction was attained in 1954-in the form of a successfully detonated hydrogen bomb. It is not economically feasible to produce electricity. Two basic approaches to produce such a high temperature are; (1) magnetic confinement and (2) high-energy lasers and particle beams. The fusion at room temperature known as cold fusion may open a new path of energy.

2.2.2 Limitation of fossil fuel and Nuclear Energy

Although state-of-the-art technology of energy production belongs largely to fossil fuel (coal, petroleum and natural gas) and enormous energy can be produced by nuclear plants, pollution to environment and risk associated with them together with other factors indicate the search for another form of energy. The limitations and problems associated with fossil fuel and nuclear energy are listed below:

·       Non-renewable nature

It takes million of years in formation of fossil fuels. The fast development in human society and technology needs more and more energy, which results in excessive exploitation of fossil fuels. So their stock is decreasing at faster rate than formation. Hence it will come to end one day. The major fuel of nuclear plant is also limited.

·       Environmental Pollution

As fossil fuels are organic in nature, after burning lots of carbon dioxide is released in atmosphere, which is responsible for greenhouse effect and in turn global warming. Acid rain is another big problem associated with fossil fuel. Acid rain affects agriculture very much and kills the microorganisms.

·       Radioactive Pollution

Even, if there is no leakage of radioactive radiation in atmosphere from nuclear plant, the management of nuclear waste in form of liquid and water creates radioactive pollution. The safe disposal of nuclear waste is also important as it can be further used in non-peace activity.

·       Un-even distribution around the globe

Fossil fuel and nuclear fuel both are concentrated in few patches in world. So the country which has larger stock has more opportunity to exploit. Other countries with less stock or no stock depend on import.

2.2.3 Need of Renewable Energy

In light of above discussion it is clear that growing demand of world energy for sustainable growth cannot be meet out by conventional fossil fuel and nuclear energy. World must move towards cleaner and renewable source of energy. New energy source must have following characteristics:

• Abundant availability & Renewable nature
• Environmentally clean
• High energy content
• Low cost
• Easily storable
• Economically transportable
• Conveniently usable
• Socially compatible

2.2.4 Renewable Energy/non-conventional Energy

Various types of renewable sources of energy have been discovered and are being utilized. These are discussed here.

2.2.4.1 Solar Energy

Currently humans are harnessing energy at the rate of 12.3 TW. The Sun delivers the light and heat at the rate of 80,000 TW. About 20 days solar energy is equivalent to all the energy of stored fossil fuels around the globe. Indirectly all the energy, which we use today in any form has been originated by trapping solar energy. Fossil fuels, wood and other biomass combustibles are the result of organisms that trapped the Sun’s energy into a form that can be conveniently employed. Hydropower and wind power is also derived by the Sun. Sun heats the different portion of atmosphere in different way, the reason for wind to blow.  Due to heating of atmosphere, water evaporates and causes the rain, which fills the river and other water bodies to produce hydropower.

Direct solar energy can be utilized in active and passive modes.

2.2.4.1.a Passive solar systems

It often includes architecture design, without implementation of mechanical power, to take the advantage of natural solar energy.

·       For example, south facing windows harness more solar energy in comparison to north facing windows.

·       The glasses of windows having electrochromic properties can change their optical properties in response to small electrical currents and either block or admit sunlight as necessary to maintain a comfortable interior temperature.

·       Lightpipes, mirrors and reflecting surfaces can be used to illuminate even the deep recesses of a building during the day.

·       Modern passive solar design usually stresses well-insulated buildings to keep heat in when it is cold outside and keep the interior cool when it is hot outside. In many cases, “thermal masses” are incorporated into the building to store excess heat and release it when needed. Traditional thermal masses include stone and brick walls (including interior walls), tile floors and sod or earth. This thermal mass will absorb excess heat during day time and will radiate it in cooler night to maintain inside temperature.

The cheap and easily available energy in form of electricity has stopped the use of passive solar systems in many buildings. At the time of construction of building it is easier to apply passive system.

2.2.4.1.b Active Solar Systems

These systems require mechanical power, usually pumps and other apparatus to circulate air, water or other fluids from solar collectors to a heat sink, where heat is stored until used.

·       Solar Collectors consist of a black metal plate covered by flat glass that absorbs heat from the Sun. This heat is transferred to the liquid (water or alcohol) flowing in the pipes in contact of metal plate. The heat of this liquid may be further transferred to heat the water, in heating the building or may be stored in large heat reservoir (large tank of water).

·       Parabolic dish collectors or lenses focus sunlight onto a single point, to obtain hot liquid to produce water steam to run the turbine which leads to generation of electricity. Hot molten liquid using solar energy can also produce electricity, even in the night.

·       Another useful active solar system is Solar Cell. It consists of Photovoltaic system, which utilizes semiconductor technology to convert solar energy directly into electricity. Silicon substances are used for this purpose.

At present solar energy (in form of electricity) has share of 25 % of renewable energy produced globally. This is 1.5 % of Total energy produced in world. The disadvantage of solar energy is that it needs large area to establish solar plates. The initial establishment is costly. The cost of electricity produced by solar energy is 5 to 6 times more than electricity produced through fossil fuel. The advantage of solar energy is that it can produce electricity for that area, where routine supply of electricity is not available. In satellites electricity demand is fulfilled by solar energy.

2.2.4.2 Hydrogen Energy

Electricity produced through photovoltaic may split water into hydrogen and oxygen. The hydrogen produced in this way may be utilized as fuel. This way of producing hydrogen is completely renewable with zero pollution. When hydrogen burns, the only product is water. Hence hydrogen is generated through water and after combustion again changes into water with zero pollution. Solar energy and water both have unlimited stock and may fulfil plentiful energy demand of globe.

2.2.4.3 Wind Energy

It has already been in use for the applications such as wind mills and sailing ships. Now electricity may also be produced using wind energy. For this purpose, wind turbine consisting of blades and rotor connected to an electric generator is mounted on the top of a tall tower. The electricity thus produced is fed into local grid. A typical wind form may contain thousands of wind machines.

At present the share of wind energy in total renewable energy is 58 %. This encompasses of 5.5 % total world energy. The wind energy is very safe and environmentally benign. It may be established on shore, offshore, on mountain or in forms. If established on form, the land can also be utilized simultaneously for cattle and for cultivation. The problems associated with wind energy are

·             Continuous supply of wind is interrupted. Even if a pattern of particular area is predicted, the fluctuations in speed, direction and duration of wind can break the continuous supply of wind to produce electricity.

·             Noise is produced when wind turbines operate.

·             Although no pollution is created by wind energy as in case of fossil fuel,  it creates trouble to birds. Even birth death has been noticed due to collision of birds with blades of turbines.

·             It may interfere with radio and television broadcasting.

·             It may damage scenic resources of that area.

·             Wind energy cannot be produced anywhere.

2.2.4.4 Ocean Energy

The Oceans are a vast source of energy. The various methods to exploit ocean energy have been researched and it is comparatively new area to produce electricity. One may use wave energy, tidal wave or ocean thermal energy conversion system to produce electricity. 

2.2.4.4.a Tidal Wave

The regularities of the tides can be used to drive mechanical system, which in turn may produce electricity. A tidal power station operates by allowing water at the high tide to flow into a reservoir or bay through sluice gates; then the gates are shut to form a dam. At low tide water is released through a turbine and used to generate electricity. Although there is no pollution produced by the process of generating electricity by tidal wave, the damming process disturbs the marine life very much. The tidal power is very intermittent. The height of tides must be sufficiently large and there should be difference of significant height between high and low tides to collect water inside the bay /artificial lake to produce electricity. 

2.2.4.4. b Wave Energy System

Energy can be derived from the natural movement of ocean waves through wave energy conversion (WEC) devices. These can be categorized under two operating principles: wave-activated point absorbers and Oscillating Water Columns (OWC). OWC devices use wave action to expand and compress air above a water column to rotate an air turbine generator (e.g., Oceanlinx). The wave-activated devices oscillate due to wave action relative to a fixed part of the device, and use one of  the three generation systems:

·       a hydraulic system to turn a motor generator;

·       a linear generator, which generates electricity by moving a magnetic assembly within a coil

·       direct rack and pinion mechanical coupling

Among Numerous WEC concepts some are shoreline-based, while others are seabed-mounted or moored in depths of less than 80 meters.

2.2.4.4.c Ocean Thermal Energy Conversion (OTEC)

Due to solar heating, the surface waters of the oceans in tropical latitudes are warmer than the waters at depth, creating a temperature gradient.  The surface temperature of ocean water may be as high as 28° C and the temperature at a depth of 600 m may be as low as 2° to 6° C. An OTEC plant is a giant heat engine that exploits the temperature difference to generate electricity.

Open System

In open system warm water is withdrawn from ocean and is fed to vacuum chamber. In vacuum water evaporates at the temperature of 28°C and steam is produced. This steam runs the turbine to produce electricity. The cold water is pumped from the ocean to condense the vapors into fresh water as by-product. Large amount of incoming warm water is required as only 0.5% converts into steam.

Closed System

In close system warm water is used as heat exchanger to vaporize pressurized liquid ammonia. Ammonia vapors run the turbine to produce electricity. The cold water of ocean is used to condense the ammonia vapor into normal pressurized liquid. No fresh water is produced in this process.

The system of OTEC expends   a very large amount of input energy in pumping of warm and cold water. So the net effect is that less amount of energy is produced in comparison to input energy. Hence this method is not in practice. The other disadvantages are pumping of water will change the temperature of ocean and temperature difference will get disturbed, which in turn creates problems to marine life. The large amount of water pumped by ocean may also affect the nutrients and minerals quality of ocean water. This will also disturb the life of microorganism.

An OTEC plant may be established in following manner:

·     Plant may be built on shore and water will be collected through large pipes by   pumping. Electricity generated may be utilized on land.

·     Plants may be built offshore on platforms and electricity will be generated on platforms. But this electricity has to be transferred to land for utilization by means of underground cables.

·     Plants may be built offshore on platforms and electricity will be generated on platforms. Now this electricity will not be transferred to land, but it will be stored. Electricity may also be utilized in producing hydrogen.

2.2.4.5 Geothermal energy

Geothermal energy is harnessing natural heat from the earth’s interior. The heat is primarily generated by radioactive decay within the earth. This heat reaches the surface by molten rock, erupting volcanoes, hot geysers and springs.  As the depth inside earth’s crust is increased, the temperature also increases. The increase in temperature with depth below the earth’s surface, measured in degrees per kilometer, is called the geothermal gradient. In general, steeper the gradient, the greater the heat flow to the surface. A moderate gradient belongs to 30° C to 45° C per kilometer. The heat trapped in this way may be used directly to heat buildings or to produce electricity. Electricity may be generated either by utilizing naturally vented steam directly or by heating water to produce steam for running turbine.

            There are four basic types of geothermal deposits: Hydrothermal fluid reservoirs, geopressured brines, magma (hot melted rock) and hot dry rock. Hydrothermal reservoirs are basically areas of the crust where hot rock occurs at relatively shallow depths and natural groundwater is heated, sometimes to extremely high temperatures. Such reservoirs may naturally manifest themselves on the surface as hot springs or geysers or even as direct source of steam. Geopressured brines are naturally occurring deposits of hot, salty water (brine) under pressure at depths of 3 to 6 km. Such brines may contain significant quantities of dissolved gases, including methane. The brine can be utilized for its heat content, dissolved gases and pressure. When magma reaches the surface before volcanic eruption, pipes containing water can be inserted into it to heat water and running turbines. The temperature of magma is 600 to 1300° C. In hot dry rock technology, a hole is drilled 3 to 10 km deep into the subsurface rock, until a sufficiently hot and thick layer of hard, dry rock is found. Once such a layer is located, two wells placed relatively close together are established in the rock. Next the rock between the two wells is fractured. Then cold water is pumped down one well and hot rock heats the water and it is withdrawn from the second well for use in generating electricity or for direct heating applications.

            Geothermal energy does not produce pollution to the environment as fossil fuel does. However large heat released in atmosphere may create thermal pollution. The fractures created in the rock may invite earthquake. The geothermal energy is not truly renewable. Once the heat is extracted it will not be replenished in human time frame.

2.2.4.6 Hydroelectricity

Unlike fossil fuel and nuclear energy, hydroelectricity is a renewable source of energy. In global electricity 16 % share comes from hydroelectricity. The energy of falling water is used to move turbines and thus hydroelectricity is produced. For this purpose dams are built over rivers. Although hydroelectricity is very clean and it does not produce any greenhouse gases like fossil fuel and not any hazardous radioactive materials like nuclear energy, the initial establishment and construction of dam needs heavy investment. For construction of dam large land is needed, which in turn disturbs the ecology of that area and ecology of running river. A large mass of society is needed to be shifted elsewhere, which affect their cultural and economic background. The pool of water in form of lake changes the surroundings of that area. The water evaporates regularly from lake, leaving behind higher concentration of salts and minerals in lake. It also affects the aquatic animal and flora-fauna of that area. In case of any damage, there is always risk of flood associated with large dams.

            In this context, small hydroelectric plants are more advantageous. They may feed the local area, small industry or a housing society. These micro hydroelectric power plants may be of 100 kW power. In future there may be increase in micro hydroelectric power plants. 

2.2.4.7 Biomass Energy

It is the oldest fuel used by humans. Biomass is the organic matter that can be burned directly as a fuel or converted to a more convenient form and then burned. Sources of biomass energy can be classified as: wastes, standing forests and energy crops.

·       Wastes includes wood scraps, unusable parts of trees, pulp residue, paper scraps generated by the wood and paper industry animal waste and municipal solid waste. During lumbering operations in timber forests, many sticks, branches, leaves, stumps and roots are left over. These are collected and burned for energy. Likewise agricultural wastes from food crops, such as leaves, stems, stalks and even surplus or damaged food items can serve as a source of biomass energy.

·       Natural standing forests have vast source of biomass energy, but it is not desirable to cut forest for energy needs. Forests are necessary for ecological balance.

·       Energy Crops There are some fast growing varieties of trees and grasses which can be burnt directly or can be converted into other types of fuels (such as biogas, methanol, or ethanol). Coppicing trees (once that will regenerate from stumps left in the ground) and perennial grasses may be particularly well suited to energy farming. After cutting the plants no further planting is necessary as stumps and roots are already in the ground.

            The disadvantage is that a large fertile farm is needed to plant energy crops, which would be otherwise used in food crops.

Biomass Fuels and Technologies

Raw biomass can be burnt directly or can be converted to other form of fuel like methanol, ethanol, syngas or biogas. Different technologies to utilize biomass are discussed in the following:

·       Direct burning: Biomass can be burnt directly for heat and also as fuel for electricity generation. Wood, pulp, paper by-products and waste of paper industry are used for direct burning of biomass.  Peanut shells, rice husks, peach pits, cherry pits, municipal wastes all can be used as fuel for direct burning to produce electricity.

·       Thermochemical conversion: Heating biomass in an oxygen-deficient or oxygen free atmosphere transforms the material into generally simpler substances that can be used as fuels. Classic example is charcoal prepared by wood. Modern thermochemical conversion technologies can produce petroleum and natural gas substitutes from biomass or coal as syngas and methanol. Syngas is also known as coal gas or town gas. Syngas is basically a mixture of hydrogen gas (H₂) and carbon monoxide (CO) which is produced by exposing steam (H₂O) to a heated carbon source (such as coal or biomass). Syngas or other derivatives can be subjected to liquefaction and via a series of catalytic reactions, converted to a liquid fuel, methanol (also known as methyl alcohol CH₃OH). Methanol is extremely versatile and can be burned in automobiles. Thermochemical conversion technique can be used to transform organic material into wide range of oils, lubricants and raw materials for petrochemical industry. For example oilseed crops and microalgae can be chemically converted into diesel fuel.

·       Biochemical Conversion: In this method microorganisms are used to convert biomass in fuel. From olden days biochemical conversion has been utilized by humans for fermentation of foods (such as grapes, corn and barley) by microscopic yeast cells to produce ethanol (ethyl alcohol, C₂H₅OH) which is the basis of beverage industry. Ethanol can also be used as fuel source. Ethanol can be mixed to gasoline to use in automobiles, known as gasohol.

            Besides ethanol, other commonly used fuel produced by biochemical conversion is biogas, which is mixture of methane (natural gas, CH₄) and carbon dioxide (CO₂). Biogas is often referred to as methane, swamp gas or marsh gas. Biogas is produced when anaerobic bacteria digest organic matter in the absence of oxygen. This process occurs naturally in the deep layers of organic material in the bottom of swamps or in some landfills. Special reactors known as biogas digesters can be used to promote the production of biogas. Organic material and microbes are placed in the sealed reactor from which oxygen has been removed. In this condition microbes digest the biomass and produce biogas. Biogas consists of 95% pure methane. The residue from reactor can be used as fertilizer and soil conditioner. 

            Burning of biomass contributes pollution to environment. It will be renewable only if another tree is planted for each tree which is cut down for biomass.