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30 ppd

  1. 1. Tezpur University Mechanical Engineering Down Draft Gasification Modelling of Some Indigenous Biomass for Thermal Applications Partha Pratim Dutta Assistant Professor Department of Mechanical Engineering, Tezpur University, Assam, India.)
  2. 2. Overview INTRODUCTION Biomass Gasification BIOMASS GASIFICATION REACTORS BIOMASS CLASSIFICATION AND PROPERTIES MODELLING-THERMOCHEMICAL EQUILIBRIUM APPROACH EXPERIMENTAL DEVELOPMENT AND RESULTS Fuel characteristics result Modelling result CONCLUSIONS REFERENCES
  3. 3. INTRODUCTION Biomass definition: “all organic matter produced by living organisms” Wood = complex biomass main compounds in wt % arrangement of three main organic polymers + inorganic compounds (ash) Biomass is characterized by low energy density Pratical applications require biomass trasformation into gas or liquid derived fuel mean composition of biomass in wt % volatiles ash cellulose hemi-cellulose lignine C H O N S Ash
  4. 4. GASIFICATION: It is essentially an oxygen limited thermochemical conversion of carbonaceous material to a useable gaseous fuel Biomass gasification process One of the best way to optimize the extraction of energy from biomass and to obtain a standardized gas starting from very different materials Air, Steam, CO2, and/or O2 CO, H2, CO2, H2O, CH4, C2H4 BIOMASS Low Calorific Value: Medium Calorific Value: + unconverted tars (all organic compound with mass > C6H6) 4 - 6 MJ/Nm3 12 - 18 MJ/Nm3 Using air and steam/air Using oxygen and steam
  5. 5. BIOMASS GASIFICATION REACTORS Fixed bed technology Updraft gasifier Downdraft gasifier Advantages: simple design, good maturity. Drawbacks: low calorific value gas with a high tar and fines content. Fluidized bed technology Bubbling fluidized bed Circulating fluidized bed Advantages: Good gas and solid mixing, uniform temperatures and high heating rates, greater tolerance to particle size range safer operation due to good temperature control compared to fixed bed gasification . Drawbacks: segregation of low density biomass fuel.
  6. 6. Different steps in Gasification 1. Drying 2. Pyrolysis 3. Oxidation 4. Reduction Fig.1 .A typical downdraft gasifier
  7. 7. Biomass classification and properties Biomass : wood and non woody Woody biomass is characterized by high bulk density, less void age, low ash content, low moisture content, high calorific value. Non-woody biomass is characterized by lower bulk density, higher void age, higher ash content, higher moisture content and lower calorific value Properties Bulk chemical analysis These provide information on volatility of the feedstock, elemental composition and heat content. Physical properties This provide information about shape, size, void age, thermal conductivity, heat capacity, diffusion coefficient etc. Biochemical analysis Provide information about biological degradation.
  8. 8. Modelling- thermochemical equilibrium approach The equilibrium model assumes that all the reactions are in thermodynamic equilibrium. It is expected that the pyrolysis product burns and achieves equilibrium in the reduction zone before leaving gasifier; hence an equilibrium model can be used in the downdraft gasifier. The reactions are as follows: C + 2H2 CH4 CO + H2O CO2 + H2 (+75000 J/mol) (+41200 J/mol) The equilibrium constant for methane generation (K1) is K1 P 4 CH (3.1) ( P 2 )2 H And equilibrium constant for the shift reaction (K2) is K2 P 2 PH 2 CO P PH 2O CO (3.2)
  9. 9. The global gasification reaction can be written as: CH1.65 O0.71 wH 2 O mO2 3.76 mN 2 x1 H 2 x2 CO x3CO2 x4 H 2 O x5 CH 4 3.76 mN 2 (3.3) Where w is the amount of water per kmol of wood, m is the amount of oxygen per kmol of wood, x1 to x5 are the coefficients of constituents of the products. If MC is taken to be the content of moisture per mole of biomass, then MC mass of water (100%) mass of dry biomass MC 18 w (100%) 24 18 w MC mass of water (100 %) mass of dry biomass MC 18 w (100 %) 24 18 w Then, w 26.8 MC 18 (1 MC )
  10. 10. From the global reactions, there are six unknowns x1 to x5, and T, representing the five unknown species of the product and the temperature of the reaction Carbon Balance: (3.4) 1 = x 2 + x3 + x5 Hydrogen Balance: 2w + 1.65 = 2x1 + 2x4 + 4x5 (3.5) Oxygen Balance: w + 0.71 + 2m = x2 + 2x3 + x4 (3.6) The heat balance for the gasification process (assumed to be adiabatic) is: x1 H 0 fH 2 H 0 fwood w( H 0 fH 2O (l ) 3.76mH 0 fN2 H ( vap ) ) mH 0 fO2 T '(mC p O2 3.76mC p N 2 ) x2 H 0 fCO x4 H 0 fH 2O ( vap ) x2C pCO x3C pCO2 x3 H 0 fCO2 x5 H 0 fCH 4 T ( x1C p H 2 x4C pH 2O ( vap ) x5C pCH 4 3.76mC pN2 Where ∆T = T2 ʹ T1 and ∆Tʹ T2 ʹ T1 = - T1 = temperature of the inlet T2 = temperature of the reduction zone T2ʹ air inlet temperature = (3.7)
  11. 11. From Eq. (3.4) x5 = 1 – x2 – x3 (3.8) From Eq. (3.5) x4 = w + 0.82 - x1 - 2x5 (3.9) Substituting the value of x5 from the Eq. (3.4) into Eq. (3.5) x4 = – x1 + 2x2 + 2x3 + w –1.175 (3.10) From Eq. (3.1) x12 K1 = 1 – x2 –x3 (3.11) Substituting the value of x4 from the Eq. (3.10) into Eq. (3.6) – x1 + 3x2 + 4x3 = 2m + 1.885 (3.12) Substituting the value of x4 from the Eq. (3.10) into Eq. (3.2) x1x3 = K2 x2 [ – x1 + 2x2 + 2x3 + w –1.175 ] (3.13)
  12. 12. From Eq. (3.7) H 0 fwood w( H 0 fH 2 0(l ) ) H ( vap ) ) H 0 fO2 3.76mH 0 fN2 T2 T1 T '(mC pO2 3.76mC pN2 ) x1H 0 fH 2 x2 H 0 fCO x3 H 0 fCO2 x4 H 0 fH 2O ( vap ) x5 H 0 fCH 4 ( x1C pH 2 x2C pCO x3C pCO2 x4C pH 2O (vap ) x5C pCH 4 3.76mC pN2 ) (3.14) The general equation for lnK1 is given by ln K1 7082.848 ( 6.567) ln T T 7.466 10 3 T 2 2.164 10 6 2 T 6 0.701 10 2T 2 5 32.541 (3.15) The general equation for lnK2 is given by ln K 2 5870.53 T 1.86 ln T 2.7 10 4 T 58200 T2 18.007 (3.16)
  13. 13. The set of equations (3.11) to (3.16) can be solved using the following algorithm: 1. Specify the value of m and w. 2. Assume temperature T2; find K1 & K2 using Eq. (3.15) and Eq. (3.16). 3. Find x1, x2, & x3 using Eq. (3.11), Eq. (3.12), & Eq. (3.13) respectively. 4. Find x4 & x5 using Eq. (3.8) & Eq. (3.10) respectively. 5. Calculate the new value of T2 using Eq. (3.14). 6. Repeat the above steps until successive value of T2 becomes constant.
  14. 14. Experimental development and results Feedstock: Bamboo char Bamboo Neem
  15. 15. Gulmohar Sishum Mixed
  16. 16. Gasifier system FLAME VIBRATOR MOTOR GASIFIER FILTER Cooling system CENTRIFUGAL BLOWER Figure 2 : Gasifier (10 kW) in operating condition
  17. 17. Producer gas burner
  18. 18. Producer gas burner • Partially premixed • Premixed
  19. 19. Table 1. TECHNICAL SPECIFICATION OF GASIFIER Model Gasifier Type Rated Gas flow Gasification Temperature Fuel Storage Capacity Ash Removal Start-Up Fuel type and size Permissible Moisture content in biomass Biomass charging Rated hourly consumption Rated hourly Ash discharge Typical conversion efficiency Typical gas composition „ANKUR‟ WBG-10 Scrubbed Gas Mode Downdraft 25 Nm3/hr 1050-1100 oc 85 kg Manual, Dry Ash Discharge Through Blower Wood/ woody waste with maximum dimension not exceeding diameter 25mm Less than 20% (wet basis) On-line Batch mode ,by topping up once every hour 9 to 10 kg 500 gm to 1 kg >75% CO - 16-22% H2 - 16-20% CO2 - 7-13% CH4 - upto 3% N2 - 50%
  20. 20. Fuel characteristics result Table 1: Ultimate analysis of different biomass C% by weight 48.39 44.43 45.10 44.85 45.85 Feedstock Bamboo Gulmohar Neem Dimaru Sisham H% by weight 5.86 6.16 6.00 5.98 5.80 Carbon Hydrogen Nitrogen N% by weight 2.04 1.65 1.70 1.65 1.60 O% by weight 39.21 41.90 41.50 41.84 40.25 Oxygen 50 Percentage of Elements 45 40 35 30 25 20 15 10 5 0 Bamboo Gulmohar Neem Biomass type Dimaru Sisham Figure 3: Elemental composition of different biomass
  21. 21. Table 2: Proximate analysis of different biomass Feedstock Bamboo Gulmohar Neem Dimaru Sisham Volatiles % db 80.30 81.25 81.75 82.00 80.00 Fixed Carbon % db 15.20 13.25 12.65 12.20 15.40 Ash % db Volatiles 4.50 5.50 5.60 5.80 4.60 Ash Moisture % wb 15.00 15.00 15.00 15.00 15.00 Fixed Carbon 90.00 Percentage of Elements 80.00 70.00 60.00 50.00 40.00 30.00 20.00 10.00 0.00 Bamboo Gulmohar Neem Dimaru Sisham Biomass type Figure 4: Compositional variation of different biomass
  22. 22. Table 3: Calorific value of different biomass Biomass LHV(MJ/kg) Bamboo 18.4 Neem 16.6 Shisham Gulmohar Dimaru 17.15 16.2 15.95 The following empirical relation may be used to compute theoretical GCV of a typical biomass. GCV = 0.3491XC + 1.1783XH + 0.1005XS – 0.0151XN – 0.1034XO -0.0211Xash[MJ/kg] where Xi is the contents of Carbon, Hydrogen, Sulphur, Nitrogen, Oxygen and ashes in wt % (wb) and it is clear from the formula that C, H and S contribute positively for heating value and N, O and ash contents affect negatively to the heating value. The net calorific value may be calculated from the following correlation. NCV = GCV [(1 - 𝑤 𝑤 ℎ 𝑤 )] – 2.44100 – 2.444100 8.936(1- 100 ) MJ/kg wb 100 Where w is moisture content of fuel in wt % (wb) and h is concentration of hydrogen in wt % (db).
  23. 23. Calorific values of biomasses Poly. (Calorific values of biomasses) 19 y = -1.629x2 + 53.50x - 420.8 R² = 0.998 Experimental (NCV) 18.5 18 17.5 17 16.5 16 15.5 15 15.5 16 16.5 17 Theoritical (NCV) Figure 5: Comparative studies of theoretical and experimental (NCV) Figure 12. represents variation of theoretical net heating value and experimental values for the all samples. The relationship may be best described with the curve fitting expression: [NCV] exp. = -1.692(NCV)2theor + 53.50(NCV)theor) -420.8
  24. 24. Series1 Linear (Series1) 16.6 y = 0.935x - 1.849 R² = 0.998 Net Calorific Value 16.4 16.2 16 15.8 15.6 15.4 15.2 15 18.00 18.50 19.00 19.50 20.00 Gross Calorific Value Figure 6. variation of theoretical net and theoretical gross calorific value Figure 13 shows variation of gross calorific value with net calorific value. It is clear from curve fitting that the relationship between the two variable follow liner relationships given by the equation. The relationship between net calorific value and gross calorific value is linear with slope equals to 0.935. NCV = 0.935GCV -1.849
  25. 25. Modeling result 40 Hydrogen Carbon monoxide Carbon dioxide Methane Neem (CH1.137O0.141) 35 Gas (% v/v) 30 25 20 15 10 5 0 0 5 10 15 20 25 30 35 Moisture Content (% wt basis) Gas Composition (%v/v) Figure 7: Effect of moisture content in Neem on gas composition at 850 °C 30 Neem (CH1.137O0.141) 25 20 15 10 5 0 Hydrogen Carbon monoxide Carbon dioxide Methane Syngas Component Figure 8: experimental results for Neem biomass at a gasification temperature of 850 °C.
  26. 26. 40 Bamboo (CH1.65O0.71) Gas (% v/v) 35 30 Hydrogen Carbon monoxide 25 20 15 10 5 0 0 5 10 15 20 25 30 35 Moisture Content (% wt basis) Figure 9: Effect of moisture content in Bamboo on gas composition at 850 °C 40 Sisham (CH1.132O0.18) 35 Gas (% v/v) 30 Hydrogen Carbon monoxide 25 20 15 10 5 0 0 5 10 15 20 25 Moisture Content (% wt basis) 30 35 Figure 10: Effect of moisture content in Shisham on gas composition at 850 °C
  27. 27. 40 Gulmohar (CH1.68O0.140) 35 Gas (% v/v) 30 Hydrogen Carbon monoxide Carbon dioxide Methane 25 20 15 10 5 0 0 5 10 15 20 25 Moisture Content (% wt basis) 30 35 Figure 11: Effect of moisture content in Gulmohar on gas composition at 850 °C 40 Dimaru (CH1.136O0.23) 35 Gas (% v/v) 30 Hydrogen Carbon monoxide Carbon dioxide Methane 25 20 15 10 5 0 0 5 10 15 20 25 Moisture Content (% wt basis) 30 35 Figure 12: Effect of moisture content in Dimaru on gas composition at 850 °C
  28. 28. Conclusion  It was observed that bamboo samples had highest calorific values (18.4 MJ/kg) and Dimaru had minimum (15.95 MJ/kg) for same moisture. Out four main types of woody biomass Shisham gave maximum calorific value (15.15 MJ/kg).  From modelling a gasification temperature of 850 C is reached in case of Neem which gives corresponding syngas composition as H2-16.98%, CO27.35%, CO2-8.14%, CH4-1.8%.  For all biomass sample predicted result shows that when moisture content increases H2 and CO2 composition increases and a decreasing trend is observed for CO and N2. CH4 composition is almost fixed.  In case of bamboo the increase of CO with moisture content is found to be more as compared to Neem and almost similar trend is observed for H2, CO, CO2, CH4 and N2 with moisture in case of all biomass.
  29. 29. References References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] Brown, A,. 2010 survey of energy resources. Technical report, World Energy Council, 2010. Beurskens J,. Peter AF., Ingvar F., Fridleifsson Erik Lysen-David Mills Jose Roberto Moreira Lars J. Nilsson Anton Schaap Wim C. Sinke Jose Goldemberg Amulya K.N. Reddy Kirk R. Smith Wim C. Turkenburg, John Baker and Robert H. Williams. World energy assessment. Technical report, United Nations Development Program(UNDP), United Nations Department of Economic and Social Affairs(UNDESA), and the World Energy Council(WEC), 2001. Handbook of Biomass Downdraft Gasifier Engine Systems. Kendall's Advanced Theory of Statistics Vol. 2: Interference and Relationship. Gri_n, 1972. Biomass Gasi_cation: Principles and Technology. Noyes Data Corporation, 1981. Annual energy outlook 2011. Technical report, Energy Information Administration, 2010. Biomass feedstock fuel cost comparison. Technical report, White Technology, 2010. Antal, M.J.; Varhegyi, G. (1995). “Cellulose pyrolysis kinetics: the current state of knowledge,” Ind. Eng. Chem. Res. 34, 703-717. Aznar, M. P.; Corella, J.; Gil, J.; Martin, J. A.; Caballero, M. A.; Olivares, A.; Pérez, P.; Francés, E. (1997). “Biomass gasification with steam and oxygen mixtures at pilot scale and with catalytic gas upgrading. Part I: performance of the gasifier.” from Developments in Thermochemical Biomass Conversion, Vol. 2, Eds: Bridgwater, A. V.; Boocock, D. G. B., Blackie, London, UK, 1194-1208. Beenackers, A.A.C.M.; Maniatis, K. (1996). “Gasification Technologies for Heat and Power from Biomass.” Beenackers, A.A.C.M.; Van Swaaij, W.P.M. (1984). “Gasification of Biomass, a State of the Art Review,” in Thermochemical Processing of Biomass, Bridgwater, A.V., Ed., London, UK: Butterworths, pp. 91-136.
  30. 30. …………………………..THANK YOU

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