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Combustion of solid biofuel

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Bioenergy system becomes more importantt as petroleum products tend o become more expensive and need to be imported.

Bioenergy system becomes more importantt as petroleum products tend o become more expensive and need to be imported.

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  • 1. COMBUSTION OF SOLID BIOFUEL Solid Bio-fuels - Characteristics - Properties - Preparation of biomass as feedstock for combustion reactorCombustion Process and equipment - Combined Cycle Operation
  • 2. 2
  • 3. Forestry in the New Millennium Tropical India, with its adequate sunlight, rainfall, land and labour, is ideally suitable for tree plantations. With the enhanced plan outlay for forestry sector and financial support from donor agencies, the country is able to march ahead towards the target of 33 percent forest cover. 3
  • 4. What is biomass? Biomass is plant matter such as trees, grasses, agricultural crops (residues), tree borne oil seeds or other biological material. It may be divided into woody, non-woody and aqueous waste with high BOD content. Fuels derived from biomass are called biofuels compared with petroleum based fuels. It can be used as a solid fuel, or converted into liquid or gaseous forms for the production of electric power, heat, chemicals, or fuels. 4
  • 5. RURAL DOMESTIC USE: FUEL FOR COOKING Cooking energy constitutes about 85 percent of our rural energy demand and has traditionally been met by biomass fuels such as firewood, agricultural residues and animal wastes. Under the National Programme on Improved Cookstoves, about 30 million cookstoves have so far been installed, which are helping to cut back and conserve fuelwood use. 5
  • 6. Can solid biofuels be used in Power Plants? Power generation plants fired solely by biomass are small compared with conventional coal, gas, oil or nuclear stations. This size depends on biomass growing capacity and delivery. Transport of biomass, a material with a low bulk energy density is expensive when conveyed over the long distances to larger plants. The traffic involved may also be a major local concern. Specific capital cost, efficiency and specific operational cost advantages of larger power plants are balanced against fuel transport issues. 6
  • 7. What inputs are needed to develop biofuels?  Biofuel as energy source of rural poor people     requires social and technical inputs to make it a modern sustainable system. Wasteland Forest wastes _ forest tree twigs, shrubs Marginal Croplands Overcome disadvantage of low bulk energy density of particulate biomass by preparatory process like briquetting. 7
  • 8. Give examples of solid bio-fuels WOOD [Forestry / agro-forestry based] BAGASSE [Agro - industry residue] RICE HUSK [Crop residue] NEEM ETC.- [Multi-purpose trees] PROSOPIS ETC.- [Energy crops] 8
  • 9. Common sources of solid bio-fuels 9
  • 10. 10
  • 11. APPLCATIONS OF BIOMASS COMBUSTION • RURAL DOMESTIC: COOKING • HEAT & STEAM FOR SMALL SCALE PROCESS • COGENERATION / COMBINED CYCLE FOR ELECTRIC POWER GENERATION 11
  • 12. What is the advantage of solid bio-fuel over coal as fuel for combustion? • For decentralized and small / medium scale operation where coal mines are remote but forest resource / woodlands are near. • Restricts the emission of green house gases and air pollutants (like SO2). •Lessens our dependence on imported hydrocarbon fuels, creates rural employment. 12
  • 13. As fuel for combustion, what are the disadvantages of solid bio-fuel over coal? • Availability is location specific and limited • Lower calorific value; variable particle size • Preparation like drying, briquetting etc. needed for wood /agro-residue • Price depends on production system like energy plantation, social forestry, saw mills, paddy processing etc. • India‟s Forest resource is highly stressed 13
  • 14. Biomass Power Potential (MW):2000 Source Potential(MW) From surplus Biomass 16000 From bagasse based co-generation in the existing sugar mills Total 3500 19500 Ref: MNES Annual Report, 1999 14
  • 15. Important Properties and Suitability as fuel MOISTURE CONTENT ELEMENTAL ANALYSIS CHEMICAL COMPOSITION PARTICLE SIZE & DISTRIBUTION SUITABLE WHERE LOCALLY AVAILABLE THROGHOUT THE YEAR AND FOR SMALL & MEDIUM SCALE OPERATION 15
  • 16. Proximate and Ultimate Analysis, and HHV Proximate Analysis: (1) Moisture, (2) Volatile, (3) Fixed carbon and (4) Ash. [Wt %] Ultimate Analysis : C, H, O, N, S. [Wt %] Higher Heating Value, MJ/Kg 16
  • 17. 17
  • 18. 18
  • 19. Providing the Draft P required to make the air flow through the fuel bed and to the flue gas discharge height is called draft of air in a furnace and is expressed in millimeters of water. Natural: by means of a chimney Artificial: The fan is used to suck the gases away from the furnace [induced draft], or to force the air required [forced draft] through the grate. 19
  • 20. COMBUSTION PROCESS 20
  • 21. Thermal decomposition steps for a biofuel: 21
  • 22. COMBUSTION REACTIONS C6n[H2O]5n = 6nC + 5nH2O Biomass C + O2 + 3.79N2 = 3.79N2 +CO2 EXOTHERMIC, 395400 KJ / KG ATOM OF CARBON 22
  • 23. COMBUSTION PROCESS • Combustion: Oxidation of reduced forms of carbon and hydrogen by free radical processes. • Chemical properties determine the higher heating value & the pathways of combustion. • Bio-fuel: A wet (50% moist), dirty, light in weight, heterogeneous in particle size, and quite reactive condition. 23
  • 24. COMBUSTION PROCESS continued Biofuel is  highly reactive,  volatile,  oxygenated  fuel of moderate heating value. Moisture content lowers the combustion efficiency and affects the economics of the fuel utilization. 24
  • 25. • Drying, • Pyrolysis, • Release of volatiles and • Formation of char are followed by • pre-combustion gas phase reactions • char oxidation reactions. Flaming combustion <> Glowing combustion 25
  • 26. 26
  • 27. Requirements of efficient combustion: Sufficient air to provide oxygen needed for complete burning; higher than theoretical air. Distribution of air supply: mix with fuel Secondary air to burn the volatile Volume of furnace; Flow path for flue gas Minimize heat losses 27
  • 28. Factors influencing thermal efficiency in wood combustion Enthalpy of the fuel Moisture content of the fuel Level of excess air employed Final stack temperature Note: Theoretical flame temperature depends on moisture content, % excess air and preheating of air 28
  • 29. Briquetting in India • Indian briquettes made from: groundnut shell, cotton stalk, saw dust, coffee husk, bagasse, mustard stalk and press mud. Whi • Southern region: groundnut shell and saw dust • Western and Northern regions: bagasse, groundnut shell, cotton stalk, mustard stalk and press mud briquettes. 29
  • 30. Briquetting continued A recent addition: Municipal solid waste densified for use as fuel in process industries (tea, tobacco, textile, chemical, paper, starch, tyre retreading, tiles, etc.) for thermal applications. 30
  • 31. Screw and Ram Press • Both the machines give briquettes with a density of 1-1.2 gm /cc, suitable as industrial solid fuels. • The screw type machines: briquettes with a concentric hole-- better combustibility- a preferred fuel. • These briquettes can also be more conveniently deployed in small furnaces and even cook-stoves than solid briquettes generated by a ram press. 31
  • 32. Screw Press for briquettes 32
  • 33. Ram press for briquettes 33
  • 34. 34
  • 35. 35
  • 36. 36
  • 37. FURNACE FOR BIOFUEL COMBUSTION Horizontal grate furnace Chain grate furnace Inclined step grate furnace Spreader-stoker system Suspension burning system Cyclone firing system Fluidized bed combustion system 37
  • 38. 38
  • 39. 39
  • 40. Inclined step grate furnace: • Fuel is fed to the top of the grate • heating and drying can occur very near to the fuel feed shoot. • Solid phase pyrolysis can occur as the fuel is sliding down the grate. 40
  • 41. 41
  • 42. Inclined step grate furnace: ….continued • Char oxidation can occur at the base of the grate and on the dumping grate. • Gas phase reactions can be controlled by over-fire air distribution and separated completely from solid phase reactions 42
  • 43. Spreader stoker • Fuel particles are fed into the firebox and flung, mechanically or pneumatically across the grate • Some heating and drying and possibly some pyrolysis occurs while the particle is in suspension • Solid phase pyrolysis and char oxidation occur on the grate. 43
  • 44. 44
  • 45. Spreader stoker …continued • Pre-combustion gas phase reactions occur between the grate and the zone where secondary air is introduced. • Gas phase oxidation occurs either throughout the firebox or in the vicinity of the zone where secondary air is introduced if the under-grate air is limited to sub-stoichiometric quantities. 45
  • 46. 46
  • 47. Suspension burning system: horizontal cyclone furnace • A horizontal or slightly inclined cylinder lined with firebricks into which air is ejected tangentially at a velocity of 6000- 7000 m/min. • The flame in the furnace revolves at a rpm of 1200 to 1800 • The fuel introduced at the cyclone tip is entrained by the revolving mass and is thrown against the cyclone walls where it burns. 47
  • 48. Horizontal cyclone furnace • The flue gases that escape at high velocities through the aperture at the other end of the cyclone are substantially free from fly ash. • The heat release rate of (2-5 )X 106 kcal/m2-hr can be achieved for pulverized coal in a cyclone furnace 48
  • 49. 49
  • 50. 50
  • 51. Circulating Fluidized bed combustion 51
  • 52. Circulating Fluidized bed combustion 52
  • 53. COMBINED HEAT & POWER • STEAM INJECTED GAS TURBINE • INTERCOOLED STEAM INJECTED GAS TURBINE • COMBINED CYCLE 53
  • 54. biofuel use in cogeneration cycle • SUITABLE FOR SMALL SCALE (<10 MW) GENERATION • PRODUCES LESS AIR POLLUTANTS AND SOLID WASTES • AUGMENTS POWER SUPPLY TO INDUSTRY 54
  • 55. BIOMASS INTEGRATED GASIFIER /GAS TURBINE (BIG/ GT) TECHNOLOGY   HIGH THERMODYNAMIC CYCLE EFFICIENCY   GAS TURBINES TECHNOLOGY IS MADE AVAILABLE NOW AT REASONABLE COSTS   LOW UNIT CAPITAL COST AT MODEST SCALES FEASIBLE   IT IS EXPECTED THAT THIS TECHNOLOGY WILL BE COMMERCIALLY SUCCESSFUL IN THE NEXT FIVE YEARS. 55
  • 56. 56
  • 57. 57
  • 58. Reference Books • • • A. Chakraverthy, “Biotechnology and Alternative Technologies for Utilisation of Biomass / Agricultural Wastes”, Oxford & IBH publishing Co., N. Delhi, 1989. Samir Sarkar, Fuels and Combustion, 2nd Edition, Orient Longman, 1990 Chapters on Combustion process Stoichiometry and Thermodynamics, Combustion Kinetics and Combustion Appliances. pages 217 to 326 58
  • 59. Reference Books / journals Journal—„Biomass and Bio-energy‟, a) 1996, 11(4): 271-281 „Biomass Combustion for power generation‟ b) 1998, 14(1): 33-56 „De-centralized biomass combustion: state of the art and future development‟ 4. Wood Combustion, Tillman, Ch. 5 „Heat production & release from wood combustion‟, 5. Progress in biomass Conversion, vol 3, Edited by K V Sarkanen, D A Tillman and. E C Jahn, Academic Press, 1982 59
  • 60. Reference Books / journals 6. Solid Fuels Combustion and Gasification, Marcio L.de Souza-Santos, MARCEL DEKKER, 2005 7. Wood Energy News, October 1999, Vol. 14, No 9, The Regional Wood Energy Development Programme in Asia (RWEDP), Email: rwedp@fao.org, „Wood energy in India‟ 60

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