Biomass Power

Define

Biomass is defined as any organic matter that is available on a renewable or recurring basis. It includes all plants and plant derived materials, including agricultural crops and trees, wood and wood residues, grasses, aquatic plants, animal manure, municipal residues, and other residue materials. Plants (on land or in water) use the light energy from the sun to convert water and carbon dioxide to carbohydrates, fats, and proteins along with small amounts of minerals. The carbohydrate component includes cellulose and hemi-cellulose fibers which gives strength to plant structures and lignin which binds the fibers together. Some plants store starches and fats (oils) in seeds or roots and simple sugars can be found in plant tissues.

OR

Biomass is a renewable energy resource derived from the carbonaceous waste of various human and natural activities. It is derived from numerous sources, including the by-products from the timber industry, agricultural crops, raw material from the forest, major parts of household waste and wood.

Industrial biomass can be grown from numerous types of plants including miscanthus, switchgrass, hemp, corn, poplar, willow, sorgham,  sugarcane, and a variety of tree species, ranging from eucalyptus to oil palm (palm oil). The particular plant used is usually not important to the end products, but it does affect the processing of the raw material.

Biomass is carbon, hydrogen and oxygen based. Nitrogen and small quantities of other atoms, including alkali, alkaline earth and heavy metals can be found as well. Metals are often found in functional molecules such as the porphyrins which include chlorophyll which contains magnesium.


The chemical composition of biomass varies among different species, but in general biomass consists of :

  • 25% lignin
  • 75% carbohydrates or sugars.
  • Within this range of lignin and carbohydrates most species also contain about 5% of a third portion of smaller molecular fragments called extractives.


- Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Its advantage is that it can be used to generate electricity with the same equipment or power plants that are now burning fossil fuels. Biomass is an important source of energy and the most important fuel worldwide after coal, oil and natural gas.

- Although fossil fuels have their origin in ancient biomass, they are not considered biomass by the generally accepted definition because they contain carbon that has been “out” of the carbon cycle for a very long time. Their combustion therefore disturbs the carbon dioxide content in the atmosphere

- Traditional use of biomass is more than its use in modern application. In the developed world biomass is again becoming important for applications such as combined heat and power generation. In addition, biomass energy is gaining significance as a source of clean heat for domestic heating and community heating applications. In fact in countries like Finland, USA and Sweden the per capita biomass energy used is higher than it is in India, China or in Asia.

- Instead of burning the loose biomass fuel directly, it is more practical to compress it into briquettes (compressing them through a process to form blocks of different shapes) and thereby improve its utility and convenience of use. Such biomass in the dense briquetted form can either be used directly as fuel instead of coal in the traditional chulhas and furnaces or in the gasifier. Gasifier converts solid fuel into a more convenient-to-use gaseous form of fuel called producer gas.

- Biomass is renewable, as we’re going to carry on making waste products anyway. We can always plant & grow more sugar cane and more trees, so those are renewable too.

Uses for Biomass
There are many ways we can use biomass to provide us with useful energy:

Type of Biomass What the Biomass Does
biodiesel (a fuel typically made from soybeans) a nontoxic alternative to diesel fuel with reduced air emissions
corn stover (leftover stalks, leaves, cobs) can be burned as a fuel in boilers to heat buildings
yard waste can be burned and converted into heat or electricity
unused seed corn burned to fire cement kilns (used to make ceramics)
crop residue (pieces of crop plants remaining after harvest) burned for grain-drying
switchgrass (a prairie grass typically used to make hay) reburning fuel in coal-fired cyclone burners to reduce nitrogen oxide (NO) emissions
manure converted to methane (natural gas)
landfill and wastewater methane converted to electricity

There are five fundamental forms of biomass energy use:

(1) the “traditional domestic” use in developing countries (fuelwood, charcoal and agricultural residues) for household cooking (e.g. the “three stone fire”), lighting and space-heating. In this role-the efficiency of conversion of the biomass to useful energy generally lies between 5% and 15%.

(2) the “traditional industrial” use of biomass for the processing of tobacco, tea, pig iron, bricks & tiles, etc, where the biomass feedstock is often regarded as a “free” energy source. There is generally little incentive to use the biomass efficiently so conversion of the feedstock to useful energy commonly occurs at an efficiency of 15% or less.

(3) “Modern industrial.” Industries are experimenting with technologically advanced thermal conversion technologies which are itemised below. Expected conversion efficiencies are between 30 and 55%.

(4) newer “chemical conversion” technologies (“fuel cell”) which are capable of by-passing the entropy-dictated Carnot limit which describes the maximum theoretical conversion efficiencies of thermal units.

(5) “biological conversion” techniques, including anaerobic digestion for biogas production and fermentation for alcohol.

In general, biomass-to-energy conversion technologies have to deal with a feedstock which can be highly variable in mass and energy density, size, moisture content, and intermittent supply. Therefore, modern industrial technologies are often hybrid fossil-fuel/biomass technologies which use the fossil fuel for drying, preheating and maintaining fuel supply when the biomass supply is interrupted.

Global Scenario

  • Biomass is an important energy source contributing to more than 14% of the global energy supply. About 38% of such energy is consumed in developing countries, primarily in the rural and traditional sectors of the economy.
  • In 2009, biomass production contributed 3.9 quadrillion Btu of energy to the 73.1 quadrillion Btu of energy produced in the United States or about 5.3% of total energy production.
  • The U.S. and Brazil produced about 89 percent of the world’s fuel ethanol in 2008 out of total world production of 17335MW.
  • In terms of energy content the total annual production of biomass is estimated at 2,740 Quads  (1 Quad = 10,000,000,000,000,000 Btus). Biomass production is about eight times the total annual world consumption of energy from all sources (about 340 Quads). Therefore, biomass represents a very large energy resource. At present the world population uses only about 7% of the annual production of biomass. Therefore, we are only partially exploiting nature’s abundant renewable resource.

Indian Scenario

  • Indian climatic conditions offer an ideal environment for biomass production. Bio-energy has remained critical to India’s energy mix. The current potential of surplus agro and forest residues to energy is estimated at 16,881 MW along with an additional “waste-to-energy” potential of 2,700 MW.
  • With the setting up of new sugar mills and the modernization of existing ones, the potential of Bagasse cogeneration is estimated at 5,000 MW. The cumulative installed capacity, of grid-interactive biomass and Bagasse cogeneration power was 2313.33 MW only, as on 30.10.2010.
  • In India, biomass-based power generation has attracted investments worth USD 120 million and generated more than 5,000 million units of electricity, besides providing an employment to more than 10 million man-days in rural areas. India ranks second in the world in biogas utilisation.
  • Under the 11th Plan period ( 2007-12) the Government of India plans to add as much as 1700 MW through biomass and Bagasse cogeneration in various states
  • India encourages ethanol as a fuel for automobiles and Regulations provide for the mandatory blending of 5% of ethanol with petrol (to be increased to 10%). The Government also plans to free the movement of ethanol across the country and eliminate local taxes thereby increasing its usage.
  • Close on the heels of the Kyoto protocol recommending a phased changeover to bio-diesel through blending, the Government of India has taken a number of initiatives to promote bio-fuels.
  • The availability of biomass in India is estimated at about 540 million tones per year covering residues from agriculture, forestry, and plantations. By using these surplus agriculture residues, more than 16,000 MW of grid quality power can be generated.
  • India has approximately 50 million hectares of degraded wasteland that lie outside the areas demarcated as national forests, and another 34 million hectares of protected forest area, in much of which tree cover is severely degraded.
  • In addition, about 5,000 MW of power can be produced from sugar mills residues. Thus the estimated biomass power potential is about 21,000 MW.
  • Promotional Policies:
    • Besides the Central Financial Assistance, fiscal incentives such as 80% accelerated depreciation, concessional import duty, excise duty, tax holiday for 10 years etc., are available for Biomass power projects. The benefit of concessional custom duty and excise duty exemption on equipments is also available.
    • In addition, State Electricity Regulatory Commissions have determined preferential tariffs and Renewable Purchase Standards (RPS).
    • Indian Renewable Energy Development Agency (IREDA) provides loan for setting up wind power and Bagasse cogeneration projects.
    • In addition, capital subsidies area also given for the establishment of Bagasse and Biomass based units.

Bioenergy conversion technologies

1. Direct combustion processes

Feedstocks used are often residues such as woodchips, sawdust, bark, hogfuel, black liquor, bagasse, straw, municipal solid waste (MSW), and wastes from the food industry.

Direct combustion furnaces can be divided into two broad categories and are used for producing either direct heat or steam. Dutch ovens, spreader-stoker and fuel cell furnaces employ two-stages. The first stage is for drying and possible partial gasification, and the second for complete combustion. More advanced versions of these systems use rotating or vibrating grates to facilitate ash removal, with some requiring water cooling.

The second group, include suspension and fluidised bed furnaces which are generally used with fine particle biomass feedstocks and liquids. In suspension furnaces the particles are burnt whilst being kept in suspension by the injection of turbulent preheated air which may already have the biomass particles mixed in it. In fluidised bed combustors, a boiling bed of pre-heated sand (at temperatures of 500 to 900°C) provides the combustion medium, into which the biomass fuel is either dropped (if it is dense enough to sink into the boiling sand) or injected if particulate or fluid. These systems obviate the need for grates, but require methods of preheating the air or sand, and may require water cooled injection systems for less bulky biomass feedstocks and liquids.

i) Co-firing

A modern practice which has allowed biomass feedstocks an early and cheap entry point into the energy market is the practice of co-firing a fossil-fuel (usually coal) with a biomass feedstock. Co-firing has a number of advantages, especially where electricity production is an output.

Firstly, where the conversion facility is situated near an agro-industrial or forestry product processing plant, large quantities of low cost biomass residues are available. These residues can represent a low cost fuel feedstock although there may be other opportunity costs. Secondly, it is now widely accepted that fossil-fuel power plants are usually highly polluting in terms of sulphur, CO2 and other GHGs. Using the existing equipment, perhaps with some modifications, and co-firing with biomass may represent a cost-effective means for meeting more stringent emissions targets. Biomass fuel’s low sulphur and nitrogen (relative to coal) content and nearly zero net CO2 emission levels allows biomass to offset the higher sulphur and carbon contents of the fossil fuel. Thirdly, if an agro-industrial or forestry processing plant wishes to make more efficient use of the residues generated by co-producing electricity, but has a highly seasonal component to its operating schedule, co-firing with a fossil fuel may allow the economic generation of electricity all year round. Agro-industrial processors such as the sugarcane sugar industry can produce large amounts of electricity during the harvesting and processing season, however, during the off-season the plant will remain idle. This has two drawbacks, firstly, it is an inefficient use of equipment which has a limited life-time, and secondly, electrical distribution utilities will not pay the full premium for electrical supplies which can’t be relied on for year round production. In other words the distribution utility needs to guarantee year round supply and may therefore, have to invest in its own production capacity to cover the off-season gap in supply with associated costs in equipment and fuel. If however, the agro-processor can guarantee electrical supply year-round through the burning of alternative fuel supplies then it will make efficient use of its equipment and will receive premium payments for its electricity by the distribution facility.

ii) Fluidized Bed Technology

The major portion of the coal available in India is of low quality, high ash content and low calorific value. The traditional grate fuel firing systems have got limitations and are techno-economically unviable to meet the challenges of future. Fluidized bed combustion has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse and other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr.

Mechanism of Fluidized Bed Combustion

In a fluidized-bed boiler, the fuel is fed into a solid bed, which has been fluidized, i.e., lifted off a distribution plate by blowing air or gas through the plate. The amount of bed material is very large in comparison to that of the fuel.

When an evenly distributed air or gas is passed upward through a finely divided bed of solid particles such as sand supported on a fine mesh, the particles are undisturbed at low velocity. As air velocity is gradually increased, a stage is reached when the individual particles are suspended in the air stream – the bed is called “fluidized”.

With further increase in air velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense defined bed surface. The bed of solid particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid – “bubbling fluidized bed”.

At higher velocities, bubbles disappear, and particles are blown out of the bed. Therefore, some amounts of particles have to be recirculated to maintain a stable system – “circulating fluidized bed”.

Fluidization depends largely on the particle size and the air velocity. The mean solids velocity increases at a slower rate than does the gas velocity. The difference between the mean solid velocity and mean gas velocity is called as slip velocity. Maximum slip velocity between the solids and the gas is desirable for good heat transfer and intimate contact. If sand particles in a fluidized state is heated to the ignition temperatures of coal, and coal is injected continuously into the bed, the coal will burn rapidly and bed attains a uniform temperature.


Figure: Principle of Fluidization

The fluidized bed combustion (FBC) takes place at about 840°C to 950°C. Since this temperature is much below the ash fusion temperature, melting of ash and associated problems are avoided. The lower combustion temperature is achieved because of high coefficient of heat transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed through in-bed heat transfer tubes and walls of the bed.

The gas velocity is maintained between minimum fluidization velocity and particle entrainment velocity. This ensures stable operation of the bed and avoids particle entrainment in the gas stream.

Combustion process requires the three “T”s that is Time, Temperature and Turbulence. In FBC, turbulence is promoted by fluidization. Improved mixing generates evenly distributed heat at lower temperature. Residence time is many times greater than conventional grate firing. Thus an FBC system releases heat more efficiently at lower temperatures. Since limestone is used as particle bed, control of sulfur dioxide and nitrogen oxide emissions in the combustion chamber is achieved without any additional control equipment. This is one of the major advantages over conventional boilers.

2. Thermochemical processes

These processes do not necessarily produce useful energy directly, but under controlled temperature and oxygen conditions are used to convert the original biomass feedstock into more convenient forms of energy carriers, such as producer gas, oils or methanol. These carriers are either more energy dense and therefore reduce transport costs, or have more predictable and convenient combustion characteristics allowing them to be used in internal combustion engines and gas turbine.

i)Gasification

A Biomass Gasifier converts solid fuel such as Wood Waste, Saw Dust briquettes and agro-residues converted into briquettes into a gaseous fuel through a thermo-chemical process and the resultant gas can be used for heat and power generation applications. The overall thermal efficiency of this process is more than 75%. The combustible gas mixture, known as ‘producer gas’, typically contains carbon monoxide (20% – 22%), hydrogen (12% – 15%), nitrogen (50% – 54%), carbon dioxide (9% – 11%) and methane (2% – 3%). The producer gas has relatively low calorific value, ranging from 1000 to 1100 kCal.Nm3 (5500 MJ/Nm3).

High temperatures and a controlled environment leads to virtually all the raw material being converted to gas. This takes place in two stages. In the first stage, the biomass is partially combusted to form producer gas and charcoal. In the second stage, the C02 and H2O produced in the first stage is chemically reduced by the charcoal, forming CO and H2. These stages are spatially separated in the gasifier, with gasifier design very much dependant on the feedstock characteristics. Gasification requires temperatures of about 800°C and is carried out in closed top or open top gasifiers.

A major future role is envisaged for electricity production from biomass plantations and agricultural residues using large scale gasifiers with direct coupling to gas turbines. The potential gains in efficiency using such hybrid gasifier/gas turbine systems make them extremely attractive for electricity generation once commercial viability has been demonstrated. Such systems take advantage of low grade and cheap feedstocks (residues and wood produced using short rotation techniques) and the high efficiencies of modern gas turbines to produce electricity at comparable or less cost than fossil-fuel derived electricity. Net atmospheric CO2 emissions are avoided if growth of the biomass is managed to match consumption. The use of BIG/STIG (Biomass Integrated Gasifier Steam Injected Gas turbine) initially and BIG/GTCC (Biomass integrated Gasifier Gas Turbine Combined Cycle) as the technology matures, is predicted to allow energy conversion efficiencies of 40% to 55%. Modern coal electrical plants have efficiencies of about 35% or less. Combined Heat and Power systems could eventually provide energy at efficiencies of between 50% to 80%. The use of low-grade feedstocks combined with high conversion efficiencies makes these systems economically competitive with cheap coal-based plants and energetically competitive with natural gas-based plants.

Explanations: The framed rectangles show the process steps while the arrows show the conversion stages of the fuel during the gasification. The framed rectangles below show the different technologic options for each process step.

During the thermo-chemical biomass gasification process solid biomass is cracked by thermal energy and a fumigator and converted into a product gas. The product gas is cleaned and used for the production of heat and power e.g. by gas engines (biomass CHP).

The gasification process comprises four stages:

  • Drying
  • Pyrolysis
  • Oxidation
  • Reduction

The fuel particles in fixed bed gasifiers are not moved by the gas flow and thus the fuel in the gasifier is arranged as fixed bed. The fuel feeding of most reactors is positioned above the fuel bed while the char coal and the ash are extracted from the bottom of the fuel bed. The four stages of the gasification process take place in a distinguishable drying, pyrolysis, oxidation and reduction zone. The biomass fuel moves from the top to the bottom of the fuel bed resulting in relatively long residence times of the fuel in the gasifier. A special design of fixed bed gasifiers comprises a fuel feeding from below the fuel bed. Depending on the direction of the product gas flow relative to the direction of the fuel transport the fixed bed gasifiers are classified into co-current, counter-current or cross flow gasifiers. Figure 2 shows the three basic designs of fixed bed gasifiers and the characteristic reaction zones of each gasifier.

Fluidised bed gasifiers are operated with significantly higher gas flow velocities than fixed bed gasifiers. The fuel bed and a carrier material (e.g. sand) are fluidised by the gas flow (fumigator and recirculated product gas). Thus, the gasification reaction takes place in a fluidised bed but only 5-10 wt% of the bed is fuel. Since the fluidised bed allows an intensive mixing and a good heat transfer, there are no distinguished reaction zones. Hence, drying, pyrolysis, oxidation and reduction reactions take place simultaneously. The temperature distribution in the fluidised bed is relatively constant and typically ranges between 700°C and 900°C. Since the fluidised bed causes a relatively high reaction surface, the residence time of the fuel in fluidised bed gasifieres ranges between a few seconds and a few minutes and is clearly lower than the one of fixed bed reactors. Thus, higher fuel throughput rates are achievable.

he product gas usually contains different impurities which need to be separated before further utilisation in order to avoid erosion, corrosion and deposits in plant components upstream the gasifier. Such impurities are condensable hydrocarbons (tar), particles (dust, ash, sand from fluidised beds), alkali metal compounds (mainly potassium and sodium compounds), nitrogen compounds (e.g. NH3, HCN), sulphur compounds (e.g. H2S, COS), halogen compounds (e.g. HCl) and heavy metal compounds (e.g. Cd, Zn and Hg; especially when waste wood is applied).
The concentration of these impurities in the product gas strongly depends on the gasification technology, the operation parameters and the composition of the fuel applied. The necessary product gas quality depends on the product gas utilisation. The residues from the gas cleaning process need to be disposed of adequately.

For the utilisation of the product gas different utilisation technologies are applicable in order to produce electric energy, thermal energy for space and process heating and other sources of energy (fuel, synthesis gas).
The simplest way of utilisation is burning the gas for the production of heat. In order to produce electricity and heat technologies such as gas engines, gas turbines, steam turbine processes or stirling engines are applied. Furthermore, it is possible to use the product gas for Co-Firing in fossil fired power plants.
Further utilisation possibilities include the production of standardised liquid or gaseous fuels such as Fischer-Tropsch-(FT)-Diesel or synthetic natural gas (SNG) in catalytic reactors. Moreover, the compounds CO and H2 could be used as base material to synthesise other chemicals.

The gasification of carbonaceous biomass occurs via three main reactions—partial oxidation (equation 1), complete oxidation (equation 2), and the water gas reaction (equation 3).

C + ½O2 = CO               ,H298K = -268 KJ/mol               (1)

C + O2 = CO2                 ,H298K = -406 KJ/mol               (2)

C + H2O = CO + H2 ,H298K = 118 KJ/mol                 (3)

In addition, the water gas shift reaction plays an important role in the composition of the CO, CO2, and H2 (equation 4).

CO + H2O = CO2 + H2 (4)

Syngas can also contain a number of other compounds such as methane (CH4), acetylene, ethylene, ethane, nitric oxide (NO), sulfur dioxide (SO2), tars, and ash which can have complex effects on the metal catalyst or microorganisms used. Equations 5 through 10 show some of these reactions.

The impurities differ by feedstock and gasification process. Coal gasification produces more NOx and SOx impurities, whereas biomass gasification produces more hydrocarbon impurities. Impurities are typically dealt with by including a gas clean-up process downstream of the gasifier or by modifying the design of the gasifier to produce lower levels of impurities (e.g., lower tar production). The addition of catalysts (such as CaO) can also be used to reduce tar (Corella, 2006). Research is needed to better understand how impurities affect microorganisms and their associated enzymatic functions.

The mix of gases contained in the syngas varies as a result of the feedstock type and oxidizing agent used (air, pure O2 or steam).

Air (because of the high inert N2 content) increases the volume of nitrogen in the syngas which increases the downstream cost of cleaning and storing syngas. However, the added cost of the air process must be balanced with the extra cost of using pure O2 or steam as the oxidizing agent. Steam produces a higher H2 content because of the water gas-shift reaction (equation 4), but requires more energy to create. The differences in the mixture of gases using air-steam and air-catalysts (i.e., 20-30 wt% silica sand and dolomite) for a variety of different feedstocks are shown in tables 1 and 2 respectively. The air-catalyst process produces less methane and has a lower hydrocarbon volume percentage than occurs with the air-steam process.


Types of Gassifiers

  1. Counter-current fixed bed (updraft) gasifiers consist of a fixed bed of biomass with a counter current flow of steam, oxygen and/or air flowing upward through the fuel bed. In order to form a fixed bed that is permeable to the flow of the oxygen source, the biomass fuel must have high mechanical strength and not cake into an impermeable mass. Gas exit temperatures are low, which improves thermal efficiency, but increases tar and methane impurities in the gas.
  2. Co-current fixed bed (downdraft) gasifiers are similar to updraft gasifiers except that the steam, oxygen or air flows co-currently downward with the fuel. Because the gas passes through the hot char at the bottom of the bed before exiting, some impurities such as tars are trapped in the char and the final product has a higher purity. The exit temperature of the gas is higher, resulting in a lower overall efficiency.

The fuel in a fluidized bed gasifier is gasified in an oxygen/air and steam mixture. The ash is often removed using a cyclone. Fuel throughput is higher than for fixed bed gasifiers, and has the advantage of uniform temperature distribution achieved in the gasification zone resulting in cleaner reactions. However, conversion rates are lower, requiring the recycling of part of the exit gas back to the gasifier. Fluidized beds work particularly well for biomass, as biomass resources contain higher levels of corrosive ashes that can harm fixed bed reactor.

In entrained flow gasifiers, the fuel is fed either as a dry pulverized solid or a fuel slurry in tandem with oxygen (or sometimes air). Gasification takes place in a dense cloud of fine particles and is particularly useful for coals which can be easily pulverized into fine particles. This gasifier has the highest operating temperature and pressure, which decreases the amount of tars and methane formed during gasification.

Gasifier manufacturers indicate that of the commercial gasifiers in use, 75% are co-current, 20% are fluidized beds, 2.5% are counter-current, and 2.5% are other designs.

Difference between updraft and downdraft gasifier

Updraft Gasifier:

  • It can run on higher moisture i.e. upto 20%
  • It is a multi-fuel system
  • It can work on briquettes, coal and other fuels
  • It has easy removal of ash, so it can take the raw material which contains high ash material such as coal
  • The disadvantage of updraft gasifier is that the quality of gas is comparatively low as it is having high tar and particulate matter

Downdraft Gasifier:

  • Due to high quality gas, it is suitable for power applications.
  • It is also suitable for the thermal applications where high quality of gas is required.
  • It can only undertake woody biomass & charcoal and the material should be low ash content, having low moisture and should not cripple under heat.
  • For big size gasifiers, size is a limitation in case of downdraft gasifier. We generally supply downdraft gasifier for replacement of Furnace Oil upto 400 liters.

Syngas Microbial Catalysts

The commercial production of chemicals from syngas typically uses metal catalysts, but an alternative route to produce ethanol from syngas uses microbial catalysts (e.g. bacteria). Several genera of microorganisms are capable of consuming syngas as part of their metabolism and producing chemicals such as ethanol and other products (e.g. acetic acid). The overall stoichiometry for the formation of ethanol using syngas substrates are shown in equations 11-13.

6 CO + 3 H2O ? CH3CH2OH + 4 CO2 (11)

2 CO2 + 6 H2 ? CH3CH2OH + 3 H2O                         (12)

6 CO + 6 H2 ? 2 CH3CH2OH+2 CO2 (13)

Clostridium ljungdahlii and Clostridium autoethanogenum were among the first organisms identified that convert CO, CO2 and H2(syngas) to ethanol and acetic acid. C. ljungdahlii, first isolated in 1987, is a gram-positive, rod-shaped anaerobe capable of fermenting sugars such as xylose and fructose in addition to syngas (Klasson, 1992). This organism favors the production of acetate during its active growth phase while ethanol is produced primarily as a non-growth related product. The production of acetate is favored at higher pH (5-7), whereas the production of ethanol is favored at lower values (pH 4 to 4.5).

Clostridium autoethanogenum is a strictly anaerobic, gram-positive, spore-forming, rod-like, motile bacterium which metabolizes CO to form ethanol, acetate and CO2 as end products. It is also capable of using CO2 and H2, pyruvate, xylose, arabinose, fructose, rhamnose and L-glutamate as substrates (Abrini, 1994).

Eubacterium limosum has been isolated from various habitats including the human intestine, rumen, sewage and soil. It has a high growth rate under high CO concentrations and can ferment syngas to produce acetate, ethanol, butyrate and isobutyrate (Chang 1998, 1999, 2001).

Peptostreptococcus productus is a gram-positive anaerobic coccus, found in the human bowel, and capable of metabolizing CO2, H2or CO to produce acetate(Lorowitz, 1984). Studies have shown that although acetate is one of the primary end-products of its metabolism, P. productus can also form additional products in response to CO2 limitations (Misoph, 1996).

Clostridium carboxidivorans P7T is a novel solvent-producing anaerobic microbe which was isolated from the sediment of an agricultural settling lagoon. It is motile, gram-positive, and spore-forming and forms acetate, ethanol, butyrate, and butanol as end-products. The optimum pH range for this strain is 5.0-7.0 and the optimum temperature range is 37-40 ºC (Liou, 2005).

All of these microorganisms are acetogens. Acetogens are a versatile group of microorganisms that can use gases like CO2, H2 and CO, as well as sugars and other substrates (Drake, 1994; Wood, 1986b,c). They also are anaerobic microorganisms that utilize the acetyl-CoA pathway as their predominant mechanism to produce acetyl-CoA from CO2. Acetyl-CoA is subsequently a precursor to the production of other compounds such as lipids, amino acids, nucleotides and carbohydrates

    ii) Pyrolysis

    The biomass feedstock is subjected to high temperatures at low oxygen levels, thus inhibiting complete combustion, and may be carried out under pressure. Biomass is degraded to single carbon molecules (CH4 and CO) and H2 producing a gaseous mixture called “producer gas.” Carbon dioxide may be produced as well, but under the pyrolytic conditions of the reactor it is reduced back to CO and H2O; this water further aids the reaction. Liquid phase products result from temperatures which are too low to crack all the long chain carbon molecules so resulting in the production of tars, oils, methanol, acetone, etc. Once all the volatiles have been driven off, the residual biomass is in the form of char which is virtually pure carbon.

    Pyrolysis has received attention recently for the production of liquid fuels from cellulosic feedstocks by “fast” and “flash” pyrolysis in which the biomass has a short residence time in the reactor. A more detailed understanding of the physical and chemical properties governing the pyrolytic reactions has allowed the optimisation of reactor conditions necessary for these types of pyrolysis. Further work is now concentrating on the use of high pressure reactor conditions to produce hydrogen and on low pressure catalytic techniques (requiring zeolites) for alcohol production from the pyrolytic oil.

    iii) Carbonisation

    This is an age old pyrolytic process optimised for the production of charcoal. Traditional methods of charcoal production have centred on the use of earth mounds or covered pits into which the wood is piled. Control of the reaction conditions is often crude and relies heavily on experience. The conversion efficiency using these traditional techniques is believed to be very low; on a weight basis Openshaw estimates that the wood to charcoal conversion rate for such techniques ranges from 6 to 12 tonnes of wood per tonne of charcoal. {Openshaw, 1980}.

    During carbonisation most of the volatile components of the wood are eliminated; this process is also called “dry wood distillation.” Carbon accumulates mainly due to a reduction in the levels of hydrogen and oxygen in the wood.

    The wood undergoes a number of physico-chemical changes as the temperature rises. Between 100 and 170°C most of the water is evaporated; between 170°C and 270°C gases develop containing condensible vapours, CO and CO2. These condensible vapours (long chain carbon molecules) form pyrolysis oil, which can then be used for the production of chemicals or as a fuel after cooling and scrubbing. Between 270°C and 280°C an exothermic reaction develops which can be detected by the spontaneous generation of heat {Emrich, 1985}.

    The modernisation of charcoal production has lead to large increases in production efficiencies with large-scale industrial production in Brazil now achieving efficiencies of over 30% (by weight).

    There are three basic types of charcoal-making: a) internally heated (by controlled combustion of the raw material), b) externally heated (using fuelwood or fossil fuels), and c) hot circulating gas (retort or converter gas, used for the production of chemicals).

    Internally heated charcoal kilns are the most common form of charcoal kiln. It is estimated that 10 to 20% of the wood (by weight) is sacrificed, a further 60% (by weight) is lost through the conversion to, and release of, gases to the atmosphere from these kilns. Externally heated reactors allow oxygen to be completely excluded, and thus provide better quality charcoal on a larger scale. They do, however, require the use of an external fuel source, which may be provided from the “producer gas” once pyrolysis is initiated.

    Recirculating heated gas systems offer the potential to generate large quantities of charcoal and associated by-products, but are presently limited by high investment costs for large scale plant.

    iv) Catalytic Liquefaction

    This technology has the potential to produce higher quality products of greater energy density. These products should also require less processing to produce marketable products.

    Catalytic liquefaction is a low temperature, high pressure thermochemical conversion process carried out in the liquid phase. It requires either a catalyst or a high hydrogen partial pressure. Technical problems have so far limited the opportunities of this technology.


    Fermentation Reactors
    Several reactor designs can be used for the fermentation process. Trickle-bed reactors (TBR) consist of a vertical tubular reactor, packed with solid material that the microorganisms can attach to. The direction of fluid-flow is normally counter current, with the liquid trickling downwards as the gases flow upwards (Amos, 2004; Wolfrum, 2002).

    Continuous stirred-tank reactors (CSTR) are commonly used in syngas fermentation. A CSTR has a continuous flow of gas bubbling through the liquid which typically consists of a dilute solution of essential nutrients for the microorganism to grow and survive on. The liquid is continuously added and removed from the reactor.  High agitation is needed to enhance the transfer rate of the CO, CO2, and H2 from the syngas to the organisms (Klasson, 1992). If the transfer is not fast enough, the production of cellular products will be limited to how fast the gas is transferred to the organism. Microbial cell recycle systems can be used in conjunction with the CSTR to increase cell density within the reactor. In such a system, the fermentation broth is pumped through a recycle filter and the retentate containing the microbial cells is separated from the permeate (cell-free media) and recycled back to the bioreactor. This process prevents loss of cell mass from the bioreactor during continuous operation and also allows the CSTR to be operated at dilution rates greater than the maximum growth rate of the microbial catalyst. Recycling has been shown to provide a 2.6 fold increase in cell concentration (Klasson, 1993a,b).

    Packed-bed reactors (immobilized-cell reactors) are columns packed with biocatalyst particles to which the microorganisms are immobilized (Bailey, 1986). These reactors are usually operated concurrently where the liquid and gas flow in the same direction (Klasson, 1992). Advantages of this reactor include high density of the microorganisms and easy separation of the microbial cells from the fermentation broth. However, the rate at which syngas components are transferred to the organism is usually slow.

    Commercial Production of Ethanol Via Microbial Conversion of Syngas. Ethanol is not currently produced on a commercial basis using microbial fermentation of syngas. This is a new technology still in the research phase, with most research conducted at a laboratory scale using synthetic syngas (mixed from commercial gases). As summarized in table 3, a number of research groups have reported product yields for the conversion of syngas to ethanol using microorganisms.

    Compared with metal catalytic processes, microbial ethanol from syngas processes can be operated at relatively low pressures and temperatures. Most biological enzymes operate at close to ambient temperatures which reduce costs (Wolfrum, 2002) and occur in the dark, enabling the use of closed reactors which use simpler reactor designs and have lower costs. Microbial enzymes have a higher tolerance for syngas contaminants than metal-catalysts (which are very susceptible to poisoning), and are even capable of adapting to contaminants like tar within certain limits (Ahmed, 2006; Ragauskas, 2006). The production of ethanol from biomass-derived syngas circumvents problems such as solids handling and disposal of the unconverted lignin that occur in conventional lignocellulosic fermentation processes.

    Disadvantages of microbial processes include the long reaction time of the water-gas shift reaction due to the slow cell growth of the microorganisms. Since the reaction is anaerobic, it does not provide as much energy for cellular metabolism as do photosynthetic and aerobic reactions. Syngas fermentation is often limited by low productivity and the rate at which syngas can transfer to the liquid (Worden, 1997), which places a premium on good bioreactor design and high cell-densities of the microorganism to make the process economically feasible. At high partial pressures, nitric oxide (NO) and carbon monoxide (CO) contaminants in the syngas can inhibit the hydrogenase enzyme that is involved in the conversion of syngas to ethanol (Krasna, 1954; Tibelius, 1984).


    Uses of Gasifiers


    POTENTIAL APPLICATIONS
    Petro-fuel replacement in Industrial Kilns : Presently in Industrial Kilns & Furnaces Furnace Oil/LDO/HSD/LPG etc. is being used. These fuels can be replaced by the producer gas, produced from our Gasifier system.

    Stainless Steel Re-Rolling Industries : Gasifier is being used in heating, re-heating and heat treatment furnaces.

    Steel Re-Rolling Mills : Gasifier system is being used in main heating furnace

    Lime Kilns : In Calcium Carbonate and other industries, kilns are being fired with producer gas. With the usage of Gasifier system, besides the reduction in the cost, better quality of lime is assured. Even the exhaust gases from lime kilns are being used for carbonation.

    Hot Air Generators : Gasifiers are being used for producing Hot Air in fertilizer and cement industries.

    Galvanizing Industries : Producer gas from Gasifier is used to melt the Zinc.

    Hot Water Generation : Gasifiers are used for heating water in variety of applications in industries.

    Glass Melting & Annealing : Gasifier is also used for melting the glass and also used in annealing furnace.

    Aluminum Die-Cast : Gasifier system are very efficient for Aluminum Die-Cast industries (for melting the aluminum)

    Copper / Brass Sheet industry : Gasifiers can be used for melting copper/brass and then heating the copper ingout for rolling operation.

    Resorts/Hotels/Farm Houses : Gasifier system are best suited for big Resorts/Hotels/Farm Houses having wide area for cooking, water heating and air heating applications.

    Food processing : Gasifiers can be used in food processing units for drying of vegetable and seeds etc.

    Bakeries : Gasifiers can be used in Bakeries/ Biscuit manufacturing units, for heating requirements of their Ovens etc.

    Charcoal Production : Gasifier system can also be used for the production of Charcoal.

    Gasifier can be used in any application where LPG, Diesel or any other Petro-fuel is used

    Power Application

    Gasifier system can be used for power requirements for Villages, Colonies, Farm Houses, Hotels etc.To produce power with Gasifiers ,there are two routes available :

    Dual fuel application : In this system Diesel Generation sets are used. Producer gas is fed to D.G.sets which replaces upto 70% of the diesel consumption. After modification, D.G.sets will use upto 70% gas and 30% diesel.
    100% producer gas application : In this system Spark Ignition Engines are used and the engine runs on 100% gas.

    Captive Power Generation:
    In power applications, Gasifier system are best suited for CAPTIVE POWER GENERATION . In India, presently the cost of power generated in industries, with 100% Producer Gas mode is around Rupees 3.50 to Rupees 4.50 per kW (depending on the cost of Biomass available at that place). In Dual Fuel mode, cost of power is around Rupees 4.50 to Rupees 6.50 per kW.

    Rural Electrification:
    The Governments across the globe are establishing Biomass based power plants for rural electrification. Biomass gasification technology is best option due to following advantages :

    • Cost of power is same as of grid power, but there is huge savings in erecting the wires to bring grid power to the villages and creating sub-stations.
    • Even in renewable energy, it is better than solar power, as the capital cost per kWh is less than 30%. It is also cheaper than wind energy.
    • Gasifier system is more reliable than both the Solar and Wind energy, because with the gasification, villagers can get the power at their option. They need not wait for Sunshine and wind .On one side Gasification is a cost effective technology and on the other hand the Gasifiers are easy to run and maintain.
    • The Biomass and agriculture residues are found in bulk in the rural areas, so availability of raw material is not a problem.
    • Power station based on the gasification technology, gives the sense of entrepreneurship to villagers as they learn to collect the biomass, run the power plant, to take care of the revenue received and ultimately to know the profits & losses. In brief, they get the training to run an industry.

    Type of Gas Engines used with Gasifiers :
    For generating the power through Biomass Gasification, two type of engines are used :

    • 100% Producer Gas Engines: These are Spark Ignition Gas Engines . These engines are available in the market for natural gas application. We change the air manifold gas carburization system to run the natural gas engine on Producer Gas. Number of Indian and overseas manufacturers are also offering gas engines for producer gas applications, such as Cummins, Greaves, Kohler etc.
    • Diesel Engine: The existing Diesel engine can be used for Duel Fuel applications. The Diesel engine can be operated anytime on full diesel mode. So, one can run the diesel engine on full Diesel mode or on Duel Fuel mode at his option.

    We have the results of 5000 hours of running the diesel engine on Duel Fuel mode and we found that wear & tear is less comparing to full diesel mode. Also emission is cleaner than 100% diesel option.

    Conversion of Diesel Engine into Gas Engine:
    We also undertake the work of converting the Diesel engine into Gas engine, if the rating of the standard gas engine is not suiting to the customer’s requirement.

    Subsidies From Government (MNRE)

    Capital subsidy for Biomass Gasification Plants and Coal Gasification Plants coupled with 100% producer gas engine in industry would be as follows :

    • Rs. 10.00 lakhs per 100 KWe for 100% producer gas engine with gasifier systems.
    • Rs. 8.00 lakhs per 100 KWe for 100% producer gas engine alone.

    Deployment of biomass gasification plants with 100% producer gas engines in Institutions for captive use :
    Institutions such as Engineering / Medical Colleges and Religious / Charitable institutions working purely on nonprofit basis and not registered under Companies Act will also be covered under the Scheme. Institutions that have already set up gasifier system with 100% producer gas engine under SADP programme will not be covered under this Scheme

    The capital subsidy for institutional gasifier systems would be as follows :

    • · Rs. 15.00 lakhs per 100 KWe for 100% producer gas engine coupled with gasifier system.
    • Rs. 10.00 lakhs per 100 KWe for 100% producer gas engine alone.

    The rates of subsidy indicated above would be applicable only for the projects based on spark-ignition IC engines.

    Clean Development Mechanism (CDM):


    Carbon emission is a major cause of global warming. It is due to use of fossil fuels such as coal and petroleum in thermal power plants and automobiles. Therefore any project undertaken to improve the energy efficiency in the utilities or renewable sources of energy, qualify for carbon credits.

    According to Kyoto protocol, carbon has become a tradable commodity with an associated value. One ton of CO2 reduced through a CDM project, when certified by a designated operational entity, is known as a CER(certified emission reduction), which can be traded.

    As Biomass Gasification is a renewable energy product, so user can avail the CDM benefits.

    Advantages of Biomass Gasification

    • Low cost : 4 Kg. biomass replaces 1 liter petro-fuel. You can easily find out the per day savings b installing the biomass gasifier.
    • Extremely Clean Fuel : If you compare the emissions from the petro-fuels with the emissions from producer gas, you will found SO2 free emission from gasifier.
    • Reduces wood consumption up to 50% for institutional & industrial application, where still wood is being used for thermal application
    • Environmentally sound technology
    • Easy to operate and maintain
    • Provides energy security
    • Generates local employment
    • Replace the fossil fuels.
    • Being renewable energy product, gasifiers are eligible for Carbon Credits under CDM mechanism.

    Salient Features of “CPW” Biomass Gasifier

    • Down draft, throat less design with low specific gasification rate, which facilitates smooth fuel flow and avoids bridging.
    • Multi-fuel capability
    • Air pre-heating for gasification maintains high temperatures resulting in better quality of gas
    • Insulated firebox, which maintains high temperatures resulting in better quality gas and longer service life.
    • Specially designed for rural areas
    • Reliable and rugged system
    • Do not consume diesel or any other fossil fuel for operation
    • Uses spark ignition engines
    • Efficient cleaning and cooling train

    Note : * for 100% producer gas application

    Biomass Fuels used

    • Fuel wood , wood chips
    • Agriculture stalk
    • Coconut shells
    • Briquettes of several residues
    • Mustard stalk
    • Cashew-nut shells
    • Lantana

    Biochemical processes.

    The use of micro-organisms for the production of ethanol is an ancient art. However, in more recent times such organisms have become regarded as biochemical “factories” for the treatment and conversion of most forms of human generated organic waste. Microbial engineering has encouraged the use of fermentation technologies (aerobic and anaerobic) for use in the production of energy (biogas) and fertiliser, and for the use in the removal of unwanted products from water and waste streams.

    1. 1. Anaerobic Fermentation/ Biogas

    Anaerobic reactors are generally used for the production of methane rich biogas from manure (human and animal) and crop residues. They utilise mixed methanogenic bacterial cultures which are characterised by defined optimal temperature ranges for growth. These mixed cultures allow digesters to be operated over a wide temperature range i.e. above 0°C up to 60°C.

    When functioning well, the bacteria convert about 90% of the feedstock energy content into biogas (containing about 55% methane), which is a readily useable energy source for cooking and lighting. The sludge produced after the manure has passed through the digester is non-toxic and odourless. Also, it has lost relatively little of its nitrogen or other nutrients during the digestion process thus, making a good fertiliser. In fact, compared to cattle manure left to dry in the field the digester sludge has a higher nitrogen content; many of the nitrogen compounds in fresh manure become volatised whilst drying in the sun. On the other hand, in the digested sludge little of the nitrogen is volatised, and some of the nitrogen is converted into urea. Urea is more readily accessible by plants than many of the nitrogen compounds found in dung, and thus the fertiliser value of the sludge may actually be higher than that of fresh dung.

    Anaerobic digesters of various types were widely distributed throughout India and China. Extension programmes promote biogas plants as ideal candidates for rural village use due to their energy and fertiliser production potential along with their improved health benefits. Health benefits primarily arise from the cleaner combustion products of biogas as opposed to other biomass or fossil fuels which may be used in the domestic environment, These two countries now have an estimated 5 to 6 million units in use.

    Reliability problems have arisen from a number of problems i.e. construction defects, the mixed nature of the bacterial population, the digesters requirements for water and the maintenance of the optimum nitrogen ratio of the medium. Another problem is the digester’s demand for dung, which may have alternative uses.

    Modern designs have answered many of these problems and digesters are again becoming useful, especially with regard to the potential of digesters to remove toxic nutrients such as nitrates from water supplies; levels of which are now much more stringently controlled in many industrialised countries. The combination of energy production with the ability to enhance crop yields make biogas technology a good candidate for more widespread use now that reliable operation can be demonstrated. Recent Danish commercial experience with large scale digesters provides a useful example.

    Process of Biogas Production- The process of biogas production is explained using’ gobar gas’ as an example. ‘Gobar gas’ plants are based on excreta of cattle and other farm animals, which contains about 20% inorganic dust particles. The level of dust particles is reduced to about 10% by mixing the dung with water in 1:1 ratio. The feeding rate of a typical dung based biogas plant is at the rate of 3,500 kg dung/day.

    Generally, spent slurry at about 2% (v/v) of the fresh dung slurry is added back to maintain the microbial population. Calcium ammonium nitrate at the rate of 1 % (w/w) of the dung is added to the slurry. In addition to cowdung, human excreta (up to 3% of slurry) and kitchen waste can also be used.

    Addition of human excreta markedly increases biogas output, perhaps due to its higher nitrogen content. The optimal temperatures for biogas production are between 35-38°C. Lower temperatures lead to lower gas yields, and at 15°C biogas production may come to a halt.

    Therefore, biogas production during winters and in colder regions requires thermal insulation and/or heating of the digesters. The pH of slurry should be around 7, which is not a problem when cowdung is used as substrate. Under favourable conditions, the biogas yield may be upto 60 l/kg of dung.

    The digesters in various biogas production schemes may be operated either under mesophilic (20-25°C to 40-45°C) or thermophilic (50-55°C to 60-65°C) conditions, each involving different bacterial species. Mesophilic operation is safer and more stable but, thermophilic operation is more likely to inactivate pathogens and animal parasites.

    Bio gas : Bio gas is made from organic waste matter after it is decomposed. The decomposition breaks down the organic matter, releasing various gases. The main gases released are methane, carbon dioxide, hydrogen and hydrogen sulphide. Bacteria carry out the decomposition or fermentation. The conditions for creating bio gas has to be anaerobic that is without any air and in the presence of water. The organic waste matter is generally animal or cattle dung, plant wastes, etc. These waste products contain carbohydrates, proteins and fat material that are broken down by bacteria.  The waste matter is soaked in water to give the bacteria a proper medium to grow. Absence of air or oxygen is important for decomposition because bacteria then take oxygen from the waste material itself and in the process break them down.

    There are two types of bio gas plants that are used in India. These plants mainly use cattle dung called “gobar” and are hence called gobar gas plant. Generally a slurry is made from cattle dung and water, which forms the starting material for these plants. The two types of bio gas plants are :
    1. Floating gas-holder type
    2. Fixed dome type

    Floating gas holder type of plant : The diagram below shows the details of a floating gas holder type of bio gas plant.

    A well is made out of concrete. This is called the digester tank T. It is divided into two parts. One side has the inlet, from where slurry is fed to the tank. The tank has a cylindrical dome H made of stainless steel that floats on the slurry and collects the gas generated. Hence the name given to this type of plant is floating gas holder type of bio gas plant. The slurry is made to ferment for about 50 days. As more gas is made by the bacterial fermentation, the pressure inside H increases. The gas can be taken out through outlet pipe V.  The decomposed matter expands and overflows into the next chamber in tank T.  This is then removed by the outlet pipe to the overflow tank and is used as manure for cultivation purposes.

    Fixed dome type of plant : The diagram below shows the details of a fixed dome type of bio gas plant.

    A well and a dome are made out of concrete. This is called the digester tank T. The dome is fixed and hence the name given to this type of plant is fixed dome type of bio gas plant. The function of the plant is similar to the floating holder type bio gas plant. The used slurry expands and overflows into the overflow tank F.

    Typical composition of biogas
    Compound Chem %
    Methane CH4 50–75
    Carbon dioxide CO2 25–50
    Nitrogen N2 0–10
    Hydrogen H2 0–1
    Hydrogen sulfide H2S 0–3
    Oxygen O2 0–0

    The composition of biogas varies depending upon the origin of the anaerobic digestion process. Landfill gas typically has methane concentrations around 50%. Advanced waste treatment technologies can produce biogas with 55–75% CH4 or higher using in situ purification techniques . As-produced, biogas also contains water vapor, with the fractional water vapor volume a function of biogas temperature; correction of measured volume for water vapor content and thermal expansion is easily done via algorithm.

    In some cases biogas contains siloxanes. These siloxanes are formed from the anaerobic decomposition of materials commonly found in soaps and detergents. During combustion of biogas containing siloxanes, silicon is released and can combine with free oxygen or various other elements in the combustion gas. Deposits are formed containing mostly silica (SiO2) or silicates (SixOy) and can also contain calcium, sulfur, zinc, phosphorus. Such white mineral deposits accumulate to a surface thickness of several millimeters and must be removed by chemical or mechanical means.

    Practical and cost-effective technologies to remove siloxanes and other biogas contaminants are currently available.

    1. 2. Methane Production in Landfills.

    Anaerobic digestion in landfills is brought about by the microbial decomposition of the organic matter in refuse. The levels of organic matter produced per capita vary considerably from developed to developing countries e.g. the percentage of Municipal Solid Waste (MSW) which is putrescible in Sierra Leone is about 90% {Steele, 1992}, compared to about 60% for US MSW. The reduced levels of putrescibles in US MSW are a result of the increased proportions of plastics, metals and glass, mostly from packaging {Slivka et al., 1992}. Landfill-generated gas is on average half methane and half carbon dioxide with an energy content of 18 to 19 MJ/m3. Its production does not occur under pressure, and thus recovery processes must be active.

    Commercial production of land-gas can also aid with the leaching problems now increasingly associated with landfill sites. Local communities neighbouring land fill sites are becoming more aware of the potential for heavy metals and nutrients to leach into aquifers. Landfill processing reduces the volume of sludge to be disposed of, and the nutrient content, thus facilitating proper disposal.

    Methane is a powerful greenhouse gas, with substantial amounts being derived from unutilized methane production from landfill sites. Its recovery therefore, not only results in the stabilisation of the landfill site, allowing faster reuse of the land, but also serves to lessen the impact of biospheric methane emissions on global warming.

    1. 3. Biofuels

    A variety of fuels can be produced from biomass resources including liquid fuels, such as, ethanol, methanol, biodiesel, Fischer-Tropsch diesel and gasoline, and gaseous fuels, such as hydrogen and methane. Biofuels are primarily used to fuel vehicles, but can also fuel engines or fuel cells for electricity generation.

    Fuels :

    i)Ethanol

    Ethanol is most commonly made by converting the starch from corn into sugar, which is then converted into ethanol in a fermentation process similar to brewing beer. Ethanol is the most widely used biofuel today. Ethanol produced from cellulosic biomass is currently the subject of extensive research, development and demonstration efforts.

    ii)Biodiesel

    Biodiesel is produced through a process in which organically derived oils are combined with alcohol (ethanol or methanol) in the presence of a catalyst to form ethyl or methyl ester. The biomass-derived ethyl or methyl esters can be blended with conventional diesel fuel or used as a neat fuel (100% biodiesel). Biodiesel can be made from any vegetable oil, animal fats, waste vegetable oils, or microalgae oils. Soybeans and Canola (rapeseed) oils are the most common vegetable oils used today.

    iii)Bio-oil

    A totally different process than that used for biodiesel production can be used to convert biomass into a type of fuel similar to diesel which is known as bio-oil. The process, called fast or flash pyrolysis, occurs when heating compact solid fuels at temperatures between 350 and 500 degrees Celsius for a very short period of time (less than 2 seconds). While there are several fast pyrolysis technologies under development, there are only two commercial fast pyrolysis technologies as of 2008. The bio-oils currently produced are suitable for use in boilers for electricity generation. There is currently ongoing research and development to produce bioOil of sufficient quality for transportation applications.

    iv)Other Hydrocarbon Biofuels

    Biomass can be gasified to produce a synthesis gas composed primarily of hydrogen and carbon monoxide, also called syngas or biosyngas. Syngas produced today is used directly to generate heat and power but several types of biofuels may be derived from syngas. Hydrogen can be recovered from this syngas, or it can be catalytically converted to methanol or ethanol. The gas can also be run through a biological reactor to produce ethanol or can also be converted using Fischer-Tropsch catalyst into a liquid stream with properties similar to diesel fuel, called Fischer-Tropsch diesel. However, all of these fuels can also be produced from natural gas using a similar process.  A wide range of single molecule biofuels or fuel additives can be made from lignocellulosic biomass. Such production has the advantage of being chemically essentially the same as petroleum-based fuels. Thus modifications to existing engines and fuel distribution infrastructure are not required.

    Advantages & Disadvantages of Biomass/ Bioenergy

    Advantages

    • It makes sense to use waste materials where we can.
    • The fuel tends to be cheap.
    • Less demand on the fossil fuels.
    • Waste is disposed of at the same time and in the same operation
    • Consumes methane that might otherwise leak into the atmosphere and increase the greenhouse effect.

    Disadvantages

    • Collecting or growing the fuel in sufficient quantities can be difficult.
    • We burn the biofuel, so it makes greenhouse gases just like fossil fuels do.
    • Some waste materials are not available all year round.
    • The main disadvantage is the loss of the organic waste for compost or fertilizer

    5 Responses to Biomass Power

    1. Today, biomass has become the great renewable source of energy. Through Biomass feedstock we can make Eco friendly bio fuel which is best alternative to fossil fuels.

    2. MK Reddy says:


      MK Reddy:

      Dear Sir / Madam,
      we are starting the Biogas based power generation – 250 KW per Month. (Cow dung – 70 MT per day)
      Please provide the technical information for proceeding further.

      • Noren Das says:

        Mr MK Reddy,

        We are providing EPC and O&M to Thermal (Biomass Based) Power Station, Would like to know more about your project.
        How is the present operating status of the above plant.
        Are you in any state starting a new similar project.
        Do Contact us at ibd@nsthermalenergy.com

    3. Faviola Wyandt says:

      Really nice layout and good subject material , absolutely nothing else we require : D.

    4. Lateisha says:

      Your asnwer shows real intelligence.

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