Etude de la combustion de gaz de synthèse issus d'un processus de ...

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Chapter 2 Table 2.8 shows a comparison performed by Javier et al. (1999) based on results from Herguido et al. (1992), Javier et al. (1997) and Narváez et al. (1996) in order to determine the effect of gasifying agent on other results like tar content in the produced gas. Three basic ratios were used for comparison of results using different gasifying agents in a bubbling fluidized bed gasifier running with small chips of pine: - Equivalence ratio (φ) for air; - Gasifying ratio (GR) [(H 2 O+O 2 )/Biomass (kg/h)/(kg dry-ash free/h)], for steam- O 2 mixtures; - Steam to biomass ratio (SB) [H 2 O/Biomass (kg/h)/(kg dry-ash free/h). Table 2.8 – Effect of gasifying agent on syngas composition Parameter Air (φ=0.3) Steam/O 2 GR = 0.9 Steam SB=0.90 tel-00623090, version 1 - 13 Sep 2011 H 2 (vol.% dry basis) 8-10 25-30 53-54 CO (vol.% dry basis) 16-18 43-47 21-22 LHV (MJ/m 3 , dry basis) 4.5-6.5 12.5-13.0 12.7-13.3 Ygas (m 3 , dry basis/kg daf) 1.7-2.0 1.0-1.1 1.3-1.4 Y tar (g/kg daf) 6-30 8-40 70 Tar (g/m 3 ) 2-20 4-30 30-80 Gasification with air produces a higher syngas yield. Tar yields are quite different between the gasifying agents being the lowest values obtained with air. 2.4. Concluding remarks about biomass gasification Gasification is a versatile thermochemical conversion process which produces a gas mixture of H 2 , CO and CH 4 the proportions being determined by the use of air, oxygen or steam as the gasification medium, with a concomitant range of heat values, low (4–6 MJ/Nm 3 ), medium (12–18 MJ/Nm 3 ) and high (40 MJ/Nm 3 ). Key parameters for successful gasification are the feedstock properties (moisture, ash, alkalis and volatiles) and feedstock pre-treatment (drying, particle size, fractionation and leaching). Gasifiers are of two main types, fixed bed and fluidized bed, with variations within each type and specific characteristics which determine the need for and extent of feedstock preparation/pre-treatment. For use in gas engines gas produced from a fixed bed, downdraft gasifier provides a low tar gas, with a high particulates loading: as tar is a major contaminant for engine operation and particulates can be relatively easily removed, this system is considered best for fuelling gas engines. Extensive development of wood gas-fuelled IC engines, 39
Bibliographic revision suggests that diesel-based engines, with large cylinder volumes/valve areas, operating at constant load and low rpm, provide optimum power output. Regarding the influence of various parameters involved in the process of gasification in the final features of syngas, there is some discrepancy in the values given by various authors. This highlights the strong dependence on the final composition of the syngas on condition of biomass used, the type of gasifier and conditions of pressure and temperature. Thus, in order to make precise studies on the use of syngas it will be necessary to consider that its composition will be very difficult to maintain constant. The development of mathematical models for numerical simulation fully validated experimentally may be a very useful tool to determine the final composition of syngas by changes in initial conditions without laborious and expensive experimental tests. tel-00623090, version 1 - 13 Sep 2011 2.5. Laminar premixed flames A flame may be described as a reaction zone that moves with respect to the initial mixture. In practice the term is usually reserved for fast exothermic reactions of this type, and these are often also accompanied by emission of light. Flames may be either stationary flames on a burner and propagating into a flow of gas from a burner tube, or they may be freely propagating flames travelling in a gas mixture. There are two types of stationary flames: - Premixed flames where the reactants are mixed before approaching the flame region. These flames can only be obtained if the initial fuel and oxidant mixture lies between certain composition limits called the composition limits of flammability. - Diffusion flames where both fuel and air are separated and the combustion occur at the interface. For defined thermodynamic starting conditions, the premixed system has a defined equilibrium adiabatic flame temperature and for the idealized situation of planar flame in a one-dimensional flow field, premixed flame has a defined adiabatic burning velocity or equivalent mass flux in a direction normal to its surface. An unstrained diffusion flame has no such simply defined parameters. Many practical combustion problems are concerned with turbulent combustion, but laminar flame must firstly be well controlled. In premixed flames, the laminar burning velocity and flame structure data can be extremely useful in the analysis of 40
Page 1 and 2: THÈSE Pour l’obtention du Grade
Page 3 and 4: Acknowledgements Acknowledgements T
Page 5 and 6: Résumé __________________________
Page 7 and 8: Nomenclature Nomenclature Roman tel
Page 9 and 10: Nomenclature Subscripts tel-0062309
Page 11 and 12: Contents tel-00623090, version 1 -
Page 13 and 14: Contents 6.4. SYNGAS FUELLED-ENGINE
Page 15 and 16: Introduction CHAPTER 1 INTRODUCTION
Page 17 and 18: Introduction proves to have higher
Page 19 and 20: Introduction Chapter 3 - Experiment
Page 21 and 22: Bibliographic revision CHAPTER 2 BI
Page 23 and 24: Bibliographic revision point today
Page 25 and 26: Bibliographic revision - Boudouard
Page 27 and 28: Bibliographic revision Table 2.1 -
Page 29 and 30: Bibliographic revision Biomass Dryi
Page 31 and 32: Bibliographic revision Circulating
Page 33 and 34: Bibliographic revision or eliminate
Page 35 and 36: Bibliographic revision established
Page 37 and 38: Bibliographic revision Hydrogen Hyd
Page 39 and 40: Bibliographic revision of low moist
Page 41: Bibliographic revision scrubbing an
Page 45 and 46: Bibliographic revision 1 d( δ A) 1
Page 47 and 48: Bibliographic revision Since n is
Page 49 and 50: Bibliographic revision 2 ( rsr ) 2
Page 51 and 52: Bibliographic revision This evoluti
Page 53 and 54: Bibliographic revision The burning
Page 55 and 56: Bibliographic revision δVG = − a
Page 57 and 58: Bibliographic revision 2 1 − −
Page 59 and 60: Bibliographic revision where the su
Page 61 and 62: Bibliographic revision the stretche
Page 63 and 64: Bibliographic revision burning velo
Page 65 and 66: Experimental set ups and diagnostic
Page 89 and 90: Chapter 4 CHAPTER 4 EXPERIMENTAL AN
Page 91 and 92: Chapter 4 4.1 Laminar burning veloc
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Chapter 4 4.1.1.1 Flame morphology
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Chapter 4 P i = 1.0 bar, Ti = 293 K
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Chapter 4 Figure 4.5 shows schliere
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Chapter 4 P i = 2.0 bar, T i = 293
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Chapter 4 Sn (m/s) 3.0 2.5 2.0 1.5
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Chapter 4 5 ms 10 ms 15 ms 20 ms 25
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Chapter 4 behaviour of the curves r
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Chapter 4 1.50 Sn (m/s) 1.25 1.00 0
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Chapter 4 0.5 0.4 φ =1.0 Su (m/s)
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Chapter 4 variation of the normaliz
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Chapter 4 4.1.1.6 Comparison with o
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Chapter 4 The values of laminar bur
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Chapter 4 Pressure (bar) 7 6 5 4 3
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Chapter 4 0.5 0.4 φ=1.2 Su (m/s) 0
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Chapter 4 0.3 φ=0.8 Su (m/s) 0.2 0
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Chapter 4 a minimum pressure to exp
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Chapter 4 Notice the similar behavi
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Chapter 4 A very good agreement bet
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Chapter 4 ( ) Q = h T − T (4.21)
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Chapter 4 tel-00623090, version 1 -
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Chapter 4 are tested and discussed.
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Chapter 4 7 500 Pressure (bar) 6 5
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Chapter 4 Pressure (bar) 7 6 5 4 3
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Chapter 4 4.2.3.4 Quenching distanc
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Chapter 4 10000 Quenching distance
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Chapter 5 CHAPTER 5 EXPERIMENTAL ST
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Chapter 5 30 10 25 8 Pressure (bar)
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Chapter 5 30 Piston position (mm) 2
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Chapter 5 5.1.1.4 In-cylinder press
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Chapter 5 estimation of various par
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Chapter 5 TDC 1.25 ms 2.5 ms 3.75 m
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Chapter 5 Piston position (mm) 500
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Chapter 5 From figure 5.15 is possi
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Chapter 5 From figure 5.16 is obser
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Chapter 5 80 Pressure (bar) 70 60 5
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Chapter 5 80 10 Pmax (bar) 70 60 50
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Chapter 5 -5.0 ms -3.75 ms -2.5 ms
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Chapter 5 observation emphasis the
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Chapter 6 CHAPTER 6 NUMERICAL SIMUL
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Chapter 6 centered at the spark plu
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Chapter 6 H 2 O, (3) N 2 , (4) O 2
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Chapter 6 For all the above express
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Chapter 6 motions within the cylind
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Chapter 6 Heat transfer Wei et al.,
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Chapter 6 The calibration coefficie
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Chapter 6 6.3.2.2 In-cylinder volum
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Chapter 6 40 Experimental 30 Numeri
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Chapter 6 80 70 60 Numerical Experi
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Chapter 6 downdraft syngas than for
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Chapter 6 80 23º BTDC 60 29.5º BT
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Chapter 6 with experimental results
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Conclusions CHAPTER 7 CONCLUSIONS 7
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Conclusions radius and time for syn
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Conclusions conditions, therefore s
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Conclusions tel-00623090, version 1
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References References tel-00623090,
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References tel-00623090, version 1
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Appendix A - Overdetermined linear
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Appendix A - Overdetermined linear
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Appendix B- Syngas-air mixtures pro
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Appendix C -Rivère model Heat flux
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Appendix C -Rivère model The work
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tel-00623090, version 1 - 13 Sep 20
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