Biomass ENERGY 12.1 INTRODUCTION Biomass refers to solid carbonaceous material derived from plants and animals. These include residues of agriculture and forestry, animal waste and discarded material from food processing plants. Biomass being organic matter from terrestrial and marine vegetation, renews naturally in a short span of time, thus, classified as a renewable source of energy. It is a derivative of solar energy as plants grow by the process of photosynthesis by absorbing CO, from the atmosphere to form hexose (dextrose, glucose, etc.) expressed by the reaction 6CO, + H20 ett CoHy20, + 60, Biomass does not add CO, to the atmosphere as it absorbs the same amount of carbon in growing, the plants asit releases when consumed as fuel. It is a superior fuel as the energy produced from biomass is ‘carbon cycle neutral’, Biomass fuel is used in over 90% of rural hou: Agriculture products rich produce ethanol (C;HsOH). seholds and in about 15% urban dwellings. starch and sugar like wheat, maize, sugarcane can be fermented (0 Methanol (CH;OH) is also Produced by distillation of biomass that Contains cellulose like wood and bagasse. Both these alcohols can be used to fuel vehicles and can be mixed with diesel to make biodiesel. S22 BIOMASS RESOURCES Biomass resources for energy production are widely available in forest areas, rural farms, urban refuse and organic waste from _agro-industries. Biomass classification’ is. illustrated. 1 3 tomass classification _is_illustrate® Figure 12.1. India produces over 550 million tonnes of agricultural and _agro-industrial residues eve" year. Similarly, 290 _million cattle population produces about 438 millior ynnes of dunk, annuall oo r ly. Prime biomass sources are discussed below: 296Biomass Energy * 297 Biomass Energy crops Natural veg ral vegetable Organic wastes {arid area plantation “growth * aquaiiccacny and residues Forest Agricultural Animal Urban waste Industrial residue crop waste waste residues - Municipal Sewage solid waste —_ liquid waste. : Figure 12.1. Biomass classification. : Forests Forests, naturgl_or cultivated are_a rich source of timber, fuel wood, charcoal and_raw matérial_for_paper_mills and other industries. Fast growing trees like Eucalyptus, Neem, Kikar and Gulmohar are grown along canals, railway tracks and on lands of marginal quality. Wood, saw dust, and bark residue are generated in sawmills. Forests also provide foliage ‘and logging residues. An important characteristic of forest residue is its calorific 2, Which is 4399 to 4977 kcal/kg for softwood foliage and 3888 to 5219 kcal/kg for hard wood species. Agricultural crop residues Crop residues are avail are, rice husk, wheat st able in abundance as natural resource, easily collected and stored. These v, corn obs, cotton sticks, sugarcane bagasse, groundnut and coconut shells. These are converted into briquettes or pellets for_use_as clean fu ‘biofuels’ which are high efficiency solid fuels. |. These_are called Energy crops Energy farming refers to the cultivation of fast growing plants which supply fuel wood, biomass jhat_can be converted into into gaseous and liquid fuels like biogas, vegetable oil and alcohol. To harvest biomass for power generation, ener; eiBy plantation is done on degraded or wastelands which. xded Jands in arid areas and water-logged lands. — which are saline, wind eroded lands i Energy farming is promoted by MNRE_in nine different agro-climate regions, namely, Gachwal (U.P.), Gwalpahar (Haryana), Udaipur (Rajasthan) and Shantiniketan (West Bengal). The other four centres are Madurai (Tamil Nadu), Calicut (Kerala), Raipur (Chhattisgarh), Bhubaneswar (Orissa). These centres produce quality seedlings of about 35 tree species through clonal ropagation. These fast growing fuel wood species produce 20-25 tonnes of biomass per he hectare ‘per_yet are per_year. The Biomass Reseat ntre Lucknow found the “Kubabul’ tree that grows well on saline and_rocky soils, provides wood of high caloi SP wood of high_calor (4500 kcal/kg),jogies 298 + Renewable Energy Sources and Emerging Technologi Vegetable oil crops sunflower, cotton seed, groundnut, rapeseed, i stile area crops such as, ton seed, groun Oil can be extracted from fet aie purification can be blended with diesel oil suitable as engine after purification can be blencec its seeds provide oil is an important renewable Rajasthan, Guj ind Orissa under hot-arid conditions, t is an ideal plant for areas of scanty rain with low fertility soil and produces up to 2000 ke of good insulating property can_be used as dry seed per hectire_annually. Jajoba_oil_havin su : transformer oil, Its, productsare high quality lubricants and_waxes, suitable for industry and good raw material for paints and vamishes, ¢ "There i Aquatic crop — Aquatic crop constitutes three water plants, namely algae, water hyacinth and sea weed. These plants grow abundantly in water bodies and provide organic matter for_biogas_plants, Energy plantation programme is directed _to_bring_sub-standard_soil_under_cultivation. It \d, halts desertification, prevents soil erosion, reduces flooding and restores the fertility of | improves microclimate. Animal waste Animal waste, an organic material with combustible property, is a rich source of fuel, Dung cakes prepared with animal waste are used for cool ra a raw material for biogas pl Urban waste Urban waste is of two types: (i) Municipal Solid Waste (MSW) which includes human excreta, household garbage and commercial waste, (ii) Liquid Waste from domestic sewage and effluents from institutional activities. As per MNRE estimate about 42 million tonnes of solid waste (1.15 lakh tonnes per day) and 6000 million cubic metres of liquid waste are generated every year in urban areas. At present MSW is dumped int sanitary landfills, where fuel ges is produced which is a valuabie source of renewable energy. Sewage is suit ed 10 produce biogas. ene Sewage Is suitably proce Industrial waste m : al as up in 1994. Projects are implemented with technical assistance of national laboratori jee i i ee onmeal assistance oF national laboratories. Projects developed under this programm? Pulp and Paper Industry Effluent, Starch and Glu i} Indust | luent, 3 icose Industry Waste, Palm Oil Indust): Distillary Waste and Tanneries Waste, Each project is aimed to treat its waste forthe product —— ee — —=simed to treat Tee: ae of bio-energy which can be used for power generation,= Biomass Energy + 299 123 BIOFUELS Biomass is an organic carbon-based matter obtained froin plants. Biomass is a source of energy and 40% of the total energy consumed in India comes from wood, crop residues, cov dung, etc. for cooking and various domestic uses. Dry biomass gives heat energy by direct combustion. Direct burning of firewood in traditional chulhas utilises only 10% heat. Besides inefficient burning, smoke discharge in Kitchens is a health hazard. To hamess fuel value, technologies are required to convert biomass into a high quality usable solid, liquid and gaseous fuels called ‘biofuels’. Such fuels are discussed below. Charcoal Charcoal is a smokeless dry solid fuel with high energy density, Modem charcoal retorts fumaces) operate at about 600°C 10 produce charcoal from 25-35% of dry biomass feed. It contains 75-80% carbon and is useful as a compact fuel. It can be burnt to provide heat for domestic, commercial and industrial applications. Briquetting Biomass briquetting is densification of loose biomass into a high density solid fuel. Biomass of any form such as cotton sticks, rice husk, coconut shells, saw dust and wood chips can be converted into briquets. It reduces the volume-to-weight ratio, thus making transportation easy ‘or efficient commercial and industrial use. The calorific value is about 3500 kcal/kg, Biomass briquettes can replace ‘C* grade coal used in industrial boilers. Vegetable oil Vegetable oils such as rapeseed, palm, coconut and cotton seed oil can substitute diesel fuel. Jajoba trees cultivated in marginal lands produce oil seeds. Jajoba oil is conside gold like crude oil as it can be processed into a wide range of products like motor oil, | mono-unsaturated alcohols and oil of cosmetic value, Eu after water removal give light hydrocarbon oil as engine red liquid lubricants, phorbia species produce latex which 12.4 BIOGAS Biogas can be produced by digestion of animal, plant and human waste. Digestion is a biological Tem yan takes place in a digester with anaerobic organism in absence of oxygen at weaezutute between 35°C and 70°C. In rural areas, household biogas plants operate from cow and buffalo dung which provide gas for cooking and lighting, Biogas is a mixture of CH, OS% to 65%), COs (30% to 40%). Ha, HyS and Ny (< 10%) having a calorific value between 5000 and $500 kcal/kg, 12.5 PRODUCER GAS Producer gas is obtained by , Tg a Partial combustion of wood or any cellulose organic material of Plant origin. I is a°mixture of a few gases and its constituems are CO, (19%), CHy (1%), 7300 + Renewable Energy Sources and Emerging Technologies Hydrogen and methane keep heating value between ° fi the volume of its constituents. Producer gas can be 4.5 Mi/m? and 6 MJ/m° depending upon f i ducer § burnt in a boiler to generate steam. It is used as fuel in IC engines used for irrigation pumps, in spark ignition engines and gas turbines for power generation. Hy (18%), CO, (11%) and No (45-60%). 12.6 LIQUID FUEL (ETHANOL) Ethanol (C)HsOH) is a flammable colourless biofuel. It can be produced by fermentation of any feedstock which contains sugar or starch and even cellulose material. Biomass containing sugar are: sugar-beets, sugarcane, sweet sorghum; starch crop covers corn, wheat, cassava and Potato. Cellulose is found in all plant tissues, is available in wood, solid waste and agriculture residues. Ethanol is suitably used as a fuel additive to cut down a vehicle’s carbon monoxide and other smog-causing emissions. In nine sugar producing Indian states, petrol blended with 5% ethanol is supplied. Lis BIOMASS CONVERSION TECHNOLOGIES Biomass material from a variety of sources can be utilised optimally by adopting efficient and state-of-the-art conversion technologies such as: 1. Densification of biomass 2. Combustion and incineration 3. Thermo-chemical conversion 4. Bio-chemical conversion Densification Bulky biomass is reduced to a better volume-to-weight ratio by compressing. in a die at a high ‘emperature and pressure. Itis shaped into briquettes or pellels to make a more compact source of energy, which is easier to transport and store than the natural biomass. Pel can be used as clean fuel in domestic chulhas, bakeries and hotels, lets and briquettes Combustion Direct combustion is the main process adopted for util ising biomass energy. It is bumt to produce heat utilised for cooking, space heating, industrial processes and for electricity generation. This utilisation method is very inefficient with heat transfer losses of 30-90% of the original energy contained in efficient cook-stove. biomass. The problem is addressed through the use of more @ Incineration Incineration i burning completely the solid biomass to ashi i of bum te es by high temperature oxigation. The terms _incineration and combustion _are _synonynio he pe eee ; asuon mus, But the process of combustion is applicable to all fuels, i.e., solid, liquid and gaseous. Incineration is a special = i gaseous. Incineration is a specialBiomass Energy * 301 process where the dry Municipal Solid Waste (MSW) is incinerated to reduce the volume of solid refuse.(90%) and to produce heat, steam and electicity. 7 ‘Waste incineration plants are installed in large cities to ispose off urban refuse and generate energy. It constitutes a furnace with adequaie supply of air to ensure complete combustion up to a capacity of 1000 tonnes/day. 2 Thermo-chemical conversion Thermo-chemical temperatures and_pressure: various combinations of Pyrolysis _ Biomass is heated in absence of oxygen, or partially combusted in a limited oxygen supply, to produce a hydrocarbon, rich in gas mixture (Hy, CO», CO CH, and lower hydrocarbons), an oil like Jiquid anda carbon rich solid residue (charcoal). The pyrolitic or il’ produced can easily be transported and refined into a products similar to refining crude oil. There is no waste product, the i high (82%) depending upon the feedstock used, the process temperature in re a zi air ratio during combustion: ~ Gasification Gasification is conversion of a sol gaseous fuel. The output gas CO (10-20%), CH, (1-5%), CO (9-12%) and Np (45-55%) more versatile than the solid biomass, it can be burnt to prodiice process heat and steam, or used in internal combustioi engines or gas turbines to generate electricity. The gasification process renders the use of biomass which is relatively clean and acceptable in environmental terms. 7 6 iquefaction Liquefaction of biomass can be processed through ‘fast’ or ‘flash’ pyrolysis, called ‘pyrolytic oil’ which is a dark brown liquid of low viscosity and a mixture of hydrocarbons. Pyrolysis liquid is a good substitute for heating oil, Another liquefaction method is through methanol synthesis. Gasification of biomass produces synthetic gas containing a mixture of H and CO. The gas is purified by adjusting the hydrogen and carbon monoxide composition. Finally, the purified gas is subjected to liquefaction Process, converted to methanol over a zinc chromium calatyst. Methanol can be used as liquid fuel. 7 A28 BIOCHEMICAL CONVERSION biochemical conversions: There are two forms of 1. Anaerobic digestion : = 2. Ethanol fermentation302 * Renewable Energy Sources ‘and Emerging Technologies 12.8.1 Anaerobic Digestion (Anaerobic Fermentation), This process converts the cattle dung, hurman wastes and other organic waste with high moisture rover into biogas (gobar gas) through anaerobic fermentation in absence of air. Fermentation senures in two stages by two different metabolic groups of bacteria. Initially the organic material ie hydrolyzed into fatty acids, alcohol, sugars, Hy and CO, Methane forming bacteria then converts the products of the first stage to CH, and COz, in the temperature rane 30-55°C. Biogas produced can be used for heating, or for operating engine driven generators fo produce electricity. Fermentation occurs in a sealed tank called ‘digester’ where the sludge left behind is used as enriched fertilizer. 12.8.2 Ethanol Fermentation Ethanol can be produced by decomposition of biomass containing sugar like sugarcane, cassava sweet sorghum, beet, potato, com, grape, etc. into sugar molecules such as glucose (CgH}20.) and sucrose (CjpH»20}1). : Ethanol fermentation involves biological conversion of sugar into ethanol and COs. CygHy:0,, + HO > 2CgHy20¢ Fermentation CoH 1205 ==", 2C,H,OH + 2CO, Ethanol has emerged as the major alcohol fuel and is blended with petrol. 12.9 BIOMASS GASIFICATION Biomass gasification is thermo-chemical conversi i ii i ‘hermo-chemical conversion of solid biomass into a combustible gas fue through partial combustion with no solid carb Soarbustible ans fuel agriculture resi a 12.9.1 Gasifiers Gasifiers (fixed bed type) can be of ‘updraft’ or of the air flow. The working of biomass gasificat eae) type depeding upon the direction downdraft gasifier (Figure 12.2) where fuel and ai move in ago ene eestaerng 2 ical 4 : ir move in a.¢o~ asifier, fuel . current manner. p g Land air move in a cauntercurent manner. However, the besio ees ee eee the same. ', the basic reaction zones remain Fuel is loaded in the reactor fr f © ‘200 and then pyrobee one, eS ts fe moves down itis subjected to drying vapour are produced. Descending volatiles and char a the oxida nel injected to complete the combustion. It isthe reaction zone This helps in breaking down the heavier hydrocarbons and t As these products move downwards, they enté¥ the"! a + the 2 being endothiermic) where producer gas is formed by the Eee pape Gearon hot charcoal aidetailed below: ~ ~~ ee on ECO) and water vapour on redBiomass Energy * 303 Biomass feed Pel +—— Drying zone (120°C) ++ Pyrolysis zone (200°C - 600°C) (Oxidation zone dation 2 —+ Gas out Fie Gi ae ae a {— Reduction zone (800°C - 600°C) 1— Fire grate Figure 12.2 Downdraft gasifier. Dry biomass + Water vapour CO, + 393.8 kJ/mole (combustion) CO + H; - 131.4 kJ/mole (water gas reaction) CO; + Hz + 41.2 kJ/mole (water shift reaction) 2CO - 172.6 kJ/mole Heb dib sid CH, + 75.0 ki/mole (hydrogenation reaction) Producer gas formed. ion zone contains combustible productsWike CO, Hy and CH. Hot gas flowing out is usually polluied with soot, tar and vapour. For purifying, it is passed through coolers, tar is removed by condensation, whereas Soot _and ash are removed by centrifugal separation. 7, Clean producer gas provides the process heat to operate stoves (for cooking), boilers, driers, ovens and furnaces. The major application is in area of electric power generation either through dual-fuel IC engines s (where diesel oil is replaced to an extent of 60%-80%), or through 100% gas-fired sparl ines, gasifier-based electricity generation system costs from %4.0 crores to 4.5 crores/MW and the power generation cost is between % 2.50 and % 3.50 per kWh. Fixed bed gasifiers can attain efficiency up to 75% for conversion of solid biomass to gaseous fuel. However, the performance depends on fuel size and moisture content, volatiles and ash content, ignition304 +» Renewable Energy Sources and Emerging Technologies 12.9.2 Fluidized Bed Gasifier Fluidized Bed Combustion (FBC) is a better option to use than the problematic biomass of ay i i i dustrial waste such as saw dus ry dues like rice husk (high ash content), bagasse, industria such a effluents sewage sludge etc. FBC constitutes a hot bed of inert solid particles of sand ea ae refractory support on a fine mesh or grid. The bed material is fluidized by an upward curren of air as shown in Figure 12.3. —> Fuel gas outlet Biomass inlet —> + Fluidized inert bed Air distribution grid eye Combustion air . Figure 12.3. Fluidized bed ga: Pressurized air starts bubbling through the bed and the pa les attain i turbulence, and the bed exhibits fluid like properties. A uniform temperature sities of 850-1050°C is maintained. Large surface area is created in the fluidized bed id the constantly chaiiging area per whit volume provides a higher conversion efficiency at Tow operatirig temperatures compared to the fixed beds. High heating capacity of san erating temperatures com sand_and_the uniform temperature of fluidized bed makes possible to gasify low-grade fuels of even uniform size and high moisture content, . ’ When the gasifier is put in use, the bed material is h i : n the gat in use, t material is heated to ignition temperat biomass is then injected causing rapid oxidaiion and ; era ofthe uch biomass a gasification. Fuel gas so produce impurities, dust, char particles and tar. It needs ¢ Pr aiees onditioning and cleaning for utiliz an utilization as an 12.10 BIOGAS Biogas is a renewable energy derived from organic wastes such as cattle dung, Itis a safe fuel for cooking and lighting. Left-over digested slurry is used a in agriculture lands. human waste, etc. 's enriched manureBiomass Energy _* 305° 12.10.1 Biogas Technology Biogas is produced from wet biomass through a biological conversion process that involves bacterial breakdown of organic matter by micro-organisms to produce CHy, CO; and HO. The process is known as ‘anaerobic digestion’ which proceeds in three steps. 1. Hydrolysis 2. Acid formation 3. Methane formation Hydrolysis Organic waste of animal and plants contains carbohydrates in the form of cellulose, hemicellulose and lignin, A group of anaerobic micro-organisms (celluolytic bacteria/hydrobytic bacteria) breaks down complex organic material into simple and soluble organic components, primarily acetates. The rate of hydrolysis depends on bacterial concentration, quality of substrate, pH (between 6 and 7) and temperature (30°C-40°C) of digester contents. Acid formation Decomposed simple organic material is acted upon by acctogenic bacteria and converted into simple acetic acid. Methane formation Acetic acid so formed becomes the substrate strictly for anaerobic methanogeric bacteria, which ferment acetic acid to methane and CO». Gas production is stable for pH between 6.6 and 7.6. Biogas consists of CH,, CO and traces of other gases such as Hz, CO, N, O, and H,S. Gas mixture is saturated with water vapour. The methane content of biogas is about 60% which provides a high calorific value to find use in cooking, lighting and power generation. 1210.2 Factors Affecting Biogas Production There are eight major factors which affect the quality and quantity of biogas. Solid-to-water ratio Cattle dung (gobar) contains about 18% solid matter and the remaining 82% is water. Anaerobic fermentation proceeds at a faster rate if the slurry contains about 9% solid matter. Digester feed is prepared by mixing water in the ratio 1 : 1 by weight to reduce the solid content. To increase the solid matter, crop residues and weed plants may be mixed with the feed stock. Volumetric loading rate It is expressed as the quantity of organic waste fed into the digester per day per unit Volume. In general, the municipal sewage treatment plants operate at a loading rate of 1.0 to 15 kg/m*/day, Overloading and underloading reduce the biogas production with a fixed Tetention time. For a desired retention period of 30 days, a quantity equal to 1/30th of digester Volume needs to be fed daily.306 Renewable Energy Sources and Emerging Technologies 306_+ Renewable Energy Sources and Emerging Technologies Temperature ‘ion i it i ‘ature range ‘Temperature affects bacterial activity; methane formation is esa lie ae rane 35°-38°C. Biogas production decreases below 20°C and Bates gions, another micro-organism lic’ is utilis | i eee temperature range 55°C—60°C. Gas production rises ae the ae average ambient air temperature. As the temperature increases, the total retention perio. decreases and vice-versa. However, the total gas production remains practically the same. Seeding Cattle dung contains both acid forming bacteria and methane forming bacteria. Acid forming bacteria multiply fat, while the methane forming bacteria grow slowly. To start and accelerate fermentation, seeding of methane forming bacteria is required. Accordingly, a small quantity of digested slurry rich in methane-forming bacteria is added to freshly charged digester. PH value Measure of pH value indicates the concentration of hydrogen ions, Micro-organisms are Sensitive to pH of the digested slurry. For optimum biogas production, pH can be varied between 68 and 7.8. At pH of 6.2, acid conditions prevail which restrain the growth of methanogenic bacteria. Control on pH should be exercised by adding alkali when it drops below 6.6. Carbon-to-nitrogen (C/N) ratio ~ Methanogenic bacteria needs carbon and nitrogen for its survival, Carbon is required for energy ‘hile nitrogen for building cell protein. The consumption of earbon ie 30 to 35 times faster than that of nitrogen, A favourable ratio of C : N can be taken as 30 1. Any deviation from this ratio lowers the biogas production. A proper balance of C N tatio ic maintained either by adding saw dust having a high C : N ratio or by poultry waste having alow ©: Natio Retention time retention period is d detailed in Table 12.1 Ps Table 12.1 Retention time i States Mean ambient temp (°C) | Kerala, TN, A.P., Andaman, Kamataka, Maharashtra >20 lI WB. Bihar, Orissa, MP, UP, Rajasthan, Haryana, Punjab t¢-90 Ill North-eastern region, Sikkim, Uttarakhand, Himachat, J&K and areas with long winter Retention time (in days) 30 40 10-15, 50Biomass Energy + 307 Stirring digester contents Stirring the contents of the digester is necessary to mix the bacteria rich fluid in the slurry. It provides better contact between micro-organism and the substrate and uniformly distributes the volatile solids in the slurry. Gas production improves by 15% over the full cycle. va BIOGAS PLANTS — The biogas plant is a device that converts cattle dung and other organic matter into inflammable gas called biogas and into a good quality organic manure under anaerobic conditions. There are two popular designs of biogas plants: (i) Floating drum (constant pressure) type and (ii) Fixed % dome (constant volume) type. 12.11.1 Floating Drum Type Biogas Plant A popular model developed by Khadi Village Industries Commission (KVIC) was standardized in 1961. It comprises an underground cylindrical masonary digester having an inlet pipe for feeding animal dung slurry and an outlet pipe for sludge. There is a steel dome for gas collection which floats over the slurry. It moves up and down depending upon accumulation ai of gas guided by the dome guide shaft (Figure 12.4). Mixing pit Floating S28 PIPE gas holder Spent slury Ground level Outlet tank \ / Inlet pi ee Outlet pipe Slurry Partition wall Support Ma cumat ssonary work Figure 12.4 Floating drum biogas plant (KVIC model).308 + Renewable Energy Sources and Emerging Technologies A partition wall is provided in the digester to improve circulation, necessary. for fermentation. The floating gas holder builds gas pressure of about 10 cm of water column, sufficient to supply gas up to 100 metre, Gas pressure also forces out the spent slurry through a sludge pipe. 12.112 Fixed Dome Type Biogas Plant Ics an economical design where the digester is combined with a dome-shaped gas holder (Figure 12.5). It is known as Janata model; the composite unit is made of brick and cement ‘masonary having no moving pars, thus ensuring no wear and tear and longer working life. When fs produced, the pressure inthe dome changes from 0 to 100 em of water column, It regulates 28 distribution and outflow of spent slurry. Gas pipe Removable man hole cover lI a seated with clay’ Figure 12.5. Fixed dome biogas plant (Janata model) 12.113 Deenbandhu Biogas Plant (DBP) This i pat () 2 8 3600 kg/h & |g | Husk Deaerator - > > > A £ ir Air Airheater | preheater [* Blower {___, To water treatment plant Figure 12.11 Cogeneration plant in a rice mill (50 tonnes capacity). Steam pressure after expanding in turbine 3.5 kg/cm? is utilised for three processes (i) Soaking (ii) Parboiling and (iii) Drying. Pressurized deaerator supplies water at 6000 kg/h to the boiler. Make-up water 3600 kg/h at 30°C is added into deaerator besides 3000 kg/h of hot water received from turbine exhaust after the drying process. Excess steam from parboiling process is fed into an air preheater and the hot air is further heated to maintain 80°C before feeding into the boiler. Thus, a 50 tonne/batch capacity rice mill generates 350 kW from rice husk which is normally dumped and wasted. At present 47% rice husk is used as energy source. Cogeneration in India excluding sugar industry has a potential of 10,000 MW from rice mills, distillaries, paper mills, petrochemicals and fertilizer plants. fis ETHANOL FROM BIOMASS = Ethanol is ethyl alcohol (CzHsOH), a colourless flammable liquid. It is.a renewable energ source which can substitute petroleum products. Ethanol can be produced from a vatiely of biomass materials, containing sugar, starch and cellulose. The best-known feedstock under three categories are: Sugars: sugarcane, sugar beet, sweet sorghum, grap potatoes, c: Starches: maize, wheat, barleBiomass Energy * 315 Production process Sugar rich crops, especially the sugarcane which contains the valuable raw material for crystal sugar, and by-products from sugar mills are molasses that contain 50% to 55% sugar content. It is monosaccharide form of sugar which refers to the glucose (CsHj,0,) and, fructose (CHi2Og) content in cane. Sweet fruits like ripe grape, mangoes, etc. contain glucose in natural form. Juice containing sugar can easily be fermented into ethanol by_adding yeast. Yeasts are micro-organisms called Saccharomyees Cerevisiae which produce enzymes, that convert sugar to ethanol. — CoH 105 > 2C,H,OH + 2CO, Molasses also contain fermentable sugar comprising glucose, sucrose and fructose which are converied into alcohol. One tonne of sugarcane with average sugar content of 12.5% yields 70 litres of ethanol by direct fermentation of juice. One tonne of molasses yields nearly 230 litres of ethanol. Directly fermented sugarcane juice yields much higher ethanol compared to molasses. ‘Starch crops constitute grains which are rich in carbohydrates. Starch (CgHo03)q has_a. complicated structure having many glucose molecules linked together in a long chain called disaccharide forms_of sugar. It requires’ starch chain_to_be converted into sugar_prior to done either by hydrolysis of starch with dilute HO, or through enzymatic method. Starch is se and glucose prior to initiating ethanol production. 2(CoHj0Os)q + HHO PES nC yHs2011 (Starch) Maltose CygHy20)1 + HO ——> 2CoHi20¢ CeBlyp0e FMB 2C;H,OH + 200, Cellulosic material comprises dry biomass abundantly available, but_difficult to_utilise carbohydrate in cellulose. Cellulose contained in wood, grasses and crop res residue contain a lot and lignin available in plants which hinders hydrolysis to sugars. This complex I is ealled “polysaccharides in which breaking the chemical bond of cellulose is not as casy as that of a starch to simple sugars. The conversion of cellulosic material is carried out by special hydrolysis with dilute HoSO, re 180°-200°C, which causes the product sugar to decompose into glucose. aL high temperature, (CoH10Os)y + HHO ——> nCgH)206 (Cellulose) (Glucose) Optimum glucose production is achieved by adjusting three variables, i.e., acid_concentration, Qperating temperature and reaction time. Finally, ethanol is obtained by fermentation of glucose Sugars, aa CoHi20, Femenation BIC, 20,0 + 2C0 . eGiievss) (Ethanol)316 » Renewable Energy Sources and Emerging Technologies Ethanol production from various biomass crops is given in Table 12.4. Table 12.4 Ethanol production from biomass crops a Raw material Ethanol (litre) per tonne of crop (Vi) Ethanol (litre) per hectare per year (Via) Sugar beet 90-100 3800-4800 Sugarcane 60-80 3500-7000 Sweet sorghum 80-90 2500-3500 Potato 100-120 2200-3300 Maize 360-400 1500-3000 Cassava 175-190 2200-2300 Wheat 370-420 800-2000 Barley 310-350 700-1300 Soft wood (hydraulic 190-220 1800-3100 agent dilute acid) Hard wood (dilute acid) 160-180 1500-2500 Straw (dilute acid) 140-160 200-500 Source: Internet Alternate Energy Development Board (Biomass Energy Systems) Microbial growth and conversion of sugars to ethanol is best af its 10% concentration as the fermentation process, drops down (micro-organism in the yeast is poisoned) with increase-in alcohol concentration. Concentration of ethanol can be increased to 95% by volume by suveessive fractional distillation. The product is called hydrated ethanol and used as fuel in modified IC engines. / Removal of balance 5% water from 95% ethanol concentration is not possible by simple distillation as'a constant boiling mixture (azeotrope) is formed which prevents further separatign die to the absence of differential vaporization. An hydrous ethanol is produced with azeotropic removal of water by co-distillation using benzene as solvent. Production of ethanol from three biomass resources is given in Figure 12.12. Natural sugars Sugars cane juice, molasses, beet Fermentation | —» 10% ethanol | Fractional |__, 95% ethanol hyd S ydrous ezaileon commercial ethanol | Special |__, 99,794 anhydrous ethanol ciation blended with petrol - Starches grains maize barley |—») Hydrolysis roots-potatoes Cellulose o| Hydrolysis wood, straw difficult Figure 12.12 Ethanol production from biomass.Biomass Energy * 317 aba Ethanol as Fuel In the USA, anhydrous ethanol (10%) is blended with petrol (90%) to produce ‘gasohol’ a good substitute for petrol in automobiles without any engine modifications, Ethanol being a high cctane fuel raises the octane rating of the mixture, Octane rating is explained as the fuel’s quality to increase its antiknock property. Considering the advantage, Canada and Sweden also utilise 10%.ethanol blended petrol. Brazil, the leader in ethanol production enhanced ethanol doping to 25-26% with petrol to tide over the soaring oil prices. The level of sugar production in India is 18 million tonnes per year, ensuring ethanol production to 1700 million litres. It is assessed that the requirement for potable purpose and chemical sector shall consume 1200 million litres—leaving a clear balance of 500 million litres, sufficient for 5% blending with petrol in the country. Molasses is a residue of sugar factory from which balance 40-47% sugar cannot be obtained by conventional methods. But molasses are fermented with a yeast (saccharomyces cerevisiac) and alcohol is separated in a distillation column. In Indian conditions, alcohol recovery from molasses is about 230 litres from one tonne of molasses. Ethanol yield is 6 times higher if the sugarcane juice is directly fermented instead of molasses, One tonne of sugarcane with sugar content of 13% yields about 70 litres of ethanol through direct fermentation of juice. Sugar content in molasses is only 2%, The Reliance group of industries is venturing for such.a project in Maharashtra to reduce crude oil import. As 7 BIODIESEL Biodiesel is a liquid fuel produced from non-edible oil seeds such as Jatropha, Pongamia pinata (Karanja), etc. which can be grown on wasteland. However, the oil extracted from these seeds has high viscosity (20 times that of diesel) which causes serious lubrication, oil contimination and injecior choking problems. These problems are solved through trans-esterification, a process Where the Taw vegetables oils are treated with alcohol (methanol or ethanol with a catalyst) to form methyl or ethyl esters. The_monoesters produced by trans-esterifying vegetable oil called ‘biodiesel’ having low fuel_viscosity with high octane number and _heatin; Endurance tests show that biodiesel can be adopted as an alter engines without modifications an and cotton seed, with a number of non-edible vegetable oil Producing trees which thriv. soils, a renewable resource Biodiesel is the name of. dates back to 1885, when Dr. Ru udolf newable fuel to compete with petroleum legradable and produces 80% less CO» ine number, (iv) canbe used as neat liesel, and (iv) has a higher flash point was proposed during 1980. ——} The advantages of biodiesel as engine fuel and 100% less SO, emissions, (ii) renewable, (i fuel (100% biodiesel) or mixed in any ratio with od318 + Renewable Energy Sources and Emerging Technologies making it safe to transport. Selected fuel properties of biodiesel and petrodiesel Table 12.5. Table 12.5 Properties of biodiesel and petrodiesel Properties Petrodiesel Biodiesel Boiling point, °C 188-343 182-338 Viscosity at 40°C 13-44 1.9-6.0 Carbon, wt% 87 7 Hydrogen, wt%. 13 12 Oxygen, wt% 0 1" Sulphur, wt% 0.05 max 0.0-0.0024 Heating value, kcallitre 7278 6491 1217.1 Production of Biodiesel from Jatropha Jatropha curcas drought resistant perennial shrub with 4-5 metre height is ideally suited to green up the wastelands in arid areas. Commercial seed production commences from the 6th year onwards with yield of 6000 kg/ha under rain-fed conditions and 12000 kg/ha in irrigated areas. The average oil production is 0.25 kg oil/kg seed. The oil cake is used as organic fertilizer. Scientists of Central Salt & Marine Chemical Research Institure (CSMCRD Bhavnagar (Gujarat) have confirmed the use of Jatropha curcas and Jojoba seed oil as promising substitutes for diesel. The yield of Jojoba seed is 0.5 kg per plant after 10 years of plantation, Jojoba seed costs € 200/kg, so presently it is uneconomical as feedstock for engine oil. The characteristics of four biodiesels obtained from vegetable oils of peanut, soyabean, sunflower Jatropha and diesel are given in Table 12.6 Table 12.6 Characteristics of four biodiesels Name Flash point Density at Viscosity Octane Heating value (°C) 20/40°C number (Mullitee) Diesel 32 0.82-0.86 20-75 42 34.5—36.0 Biodiesel (Jatropha) 161 0.878 4.54 65 33.7 Biodiesel (Sunflower) 183 0.880 4.60 49 33.5 Biodiesel Soyabean 178 0.885 4.50 45 33.5 Biodiesel Peanut 176 0.883 4.90 54 33.6 The heat of combustion for biodiesel is up to 95% by volume of conventional diesel, but biodiesel being oxygenated provides the same fuel value as the diesel. The parameters in Table 12.5 justify Jatropha seed (cost % 5.0/kg) as an economically favourable feedstock to produce biodiesel. Oil is extracted from Jatropha seeds in an oil press. It is treated with methanol (CH;OH) to produce three methyl ester molecules and one glycerol molecule. Alkalis like NaOH or KOH are used to catalyze the reaction having the following constituents: 1000 litre Jatropha oil + 400 litre are given in |Biomass Energy + 319 (CH;OH) + 10 litre catalyst. The reaction process is complet: i erol is separated a ‘methyl ester is obtained as biodiesel. mpleted rapidly, glycerol is separated and, The Ministry of Petroleum and Natural Gas has opened a biofuel centre in Delhi to build 8 of importance of Jatropha curcas cultivation and manufacture of biodiesel. The Indian Oil Corporation (IOC) has already established a biodiesel plant at Faridabad and another one being established in Panipat refinery to prepare 30,000 litres of biodiesel daily by crushing a iesel shall be blended with diesel to the extent of 5% in different \dian climatic conditions. Approximately, 40 million tonnes of HSD is consume ually in India, thus, only 5% replacement of petroleum fuel by biodiesel would save the country approximately € 4000 crores in foreign exchange yearly. 12.18 BIOFUEL PETROL Shell oi] company started selling petrol containing 10% cellulosic ethanol in Ottawa. Biofuel is produced from wheat straw. Logen’s process converts biomass into cellulostic ethanol using a ethanol is 340 combination of thermal, chemical and biochemical techniques. Yield of cellulos Titres per tonne of fibre. Lignin is the plant fibre is used to drive the process by generating and electricity, thus, eliminating the need of coal or natural gas. Cellulosic ethanol is ident to ethanol, but produces up to 90% less CO} than petrol. 12.19 BIOMASS RESOURCE DEVELOPMENT IN INDIA ‘The energy scenario in India indicates that ‘biomass’ is a promising form of renewable energy Matching with the agricultural base in rural areas and industrial development in urban set-ups. The estimated potential and physical achievement of biopower are given in Table 12.7. Table 12.7 Potential vis-a-vis achievement in the field of biopower Resource Estimated potential Achievement up to co) January 2009 (in MW) Blopower (woody biomass) 52000 683 5000 34.95 50,000 41.03 Rural-30,000 MW (Captive generation-industrial 20,000 MW) oe 87 5000 1034 120 lakhs 99.8 lakhs320 »* Renewable Energy Sources and Emerging Technologies + Process heat applications in industries generating biomass waste. * Cooking energy in domestic and commercial sectors (through charcoal and briquetts) © Electricity generation and © Transportation sector with liquid fuels. Future of biomass energy lies in its use with modern technologies. 12.21 GLOBAL SCENE vehicles. Biomass supports 66000 jobs in the US. In Sweden, biomass and peat contribute 12% of total energy while in Austria this-figures is 13%. World wide biomass contributes 14% of total energy and it is 38% in developing countries especially in rural sector. 12.22 ENVIRONMENTAL BENEFITS 7 Biomass energy brings several environmental benefits—reduces air and water pollution, increases soil quantity and reduces erosion, and improve wildlife habitat. Biomass reduces air pollution by being a part of carbon cycle. Actually, carbon cycle is nature’s way of moving carbon around to support life on the earth, CO, is common vehicle for carbon. Plant photosynthesis breaks CO, in two, keeping carbon to form carbohydrates that make the plant, releasing oxygen into air. When plant is burnt, it gives its carbon back to air, which is reabsorbed by other plants. On the other hand, when fossil fuels are burnt, there is no extra plant to absorb that carbon, so, the cycle becomes out of balance. There are two different carbon cycles in operation now; / the natural one between plants and air, which is in balance, and man made cycle, where carbon is pulled from the earth (fossil fuel) and emitted into the atmosphere. Thus, biomass use for ions by 90% compared with fossil fuel. stilizers and pesticides are used to grow energy crops. runoff from com field is captured, making energy reduces CO) emi Water pollution is reduced, as little fer Planting poplar trees in buffers along water ways, streams cleaner. High-yield food crops pi Prairie grasses, with their det the ground. , | ; ; Finally, biomass crops create better wildlife habitat than food crops, being native plants which attract birds and small mammals. Tn addition to above, biomass offers economic and energy security benefits. By growing our fuel at home, oil import is reduced and farmers get money for their products. Keeping in view above, Ministry of Environment and Forest (MOEF) in December 2009, exempted biomass and nonhazardous municipal water power plants up to 15 MW from environmental clearance. If planned well, our capital requirement for pellitser machines, biomass fuel fired stoves and agroprocessing industries can be financed by earning large carbon credits. ull nutrients from the soil, while energy crops improve soil quality. ep roots, build up top soil, putting nitrogen and other nutrients into