Mitigating Bed Agglomeration in a Fluidized Bed Gasifier

Mitigating Bed Agglomeration in a Fluidized Bed Gasifier Operating on Rice Straw Presenter: Jurarat Nisamaneenate Advisor: Assoc. Prof. Dr. Viboon Sricharoenchaikul Co Advisor: Dr. Duangduen Atong

Introduction Renewable energy Biomass Thermochemical conversion process Combustion Gasification Pyrolysis

Biomass Introduction Rice Straw Fluidized bed § § Suitable for low-grade material fuels Highly efficient heat transfer Excellent gas-solid contact Temperature distribution in the reactor

Introduction Fluidized bed reactor Agglomerated Deposition Sintering Fluidized Bed Reactor (Source: Andrew J. Hughes, 2007) Bed agglomeration mechanism

Introduction Agglomerated Coating induces (K /Ca ) Ash Melt induces (K /Ca/ Si) Alumina § Mitigated agglomerate problem and extend defluidization time. § Optimize the alumina ratio, used to reduce cost and increase the efficiency of biomass conversion. Visser et al. , 2008

Introduction Objective § To study the effect of the silica to alumina ratio, equivalence ratio and reaction temperature on the defluidization time and bed agglomeration. § To study SEM/EDS techniques on surface, necks and cross section of spent bed materials to allow an understanding of the chemistry behind this phenomenon.

Experimental Procedure : Preparation of material Rice straw 425 -850 µm Proximate analysis (wt%) Volatile Fixed carbon Ash Moisture LHV (MJ/Kg) Ultimate analysis (wt%) 66. 56 12. 31 11. 84 9. 30 16. 09 Inorganic Si. O 2 Al 2 O 3 wt% 60. 30 0. 24 K 2 O Carbon Hydrogen Oxygena Nitrogen 44. 00 7. 64 48. 25 0. 11 a By difference Ca. O Na 2 O Mg. O P 2 O 5 Other 18. 46 7. 62 1. 82 1. 56 1. 02 8. 98 Bed Ash Biomass Rice straw Silica 425 -500 µm Alumina 250 -425 µm

Experimental Set-up Cyclone Monometer Feeder system Condenser Unit Gas Cleaner Flow Controller Feeder Carrier Gas (N 2) Gas analyzer 2 Temp Controller Gas Analyzer Gas cleaner system Gasifier Tube Reactor & Heater Schematic diagram of fluidized bed gasification system. § Effect of the percentage ratio of silica: alumina as 0: 100, 25: 75, 50: 50, 75: 25, 100: 0 § Effect of temperature as 700 to 900°C § Equivalence ratio as 0. 2 and 0. 4

Results and Discussions Effect of Gasification § The pressure drop suddenly decreased under combustion conditions. § The gasification process can reduce bed material accumulation and extend the defluidization time.

Results and Discussions Effect of Temperature, The percentage ratio of Silica: Alumina 0% 25% 50% 75% 100% § The temperature was increased from 700°C to 900°C, the defluidization times for all ratios decreased. § 700°C, Increasing the alumina ratio led to an extension of the defluidization time. § Due to high alumina and low silica, reduced the substances of a low melting point (K 2 O-Ca. O-Si. O 2).

Results and Discussions Effect of ER 60 700°C 60 800°C 60 900°C Ratio of alumina 0% 50 40 40 30 30 30 50% 20 20 20 10 10 10 75% 0 0 0 Defluidization time (min) 50 Equivalence ratio 50 25% 40 Equivalence ratio 100% Equivalence ratio § The defluidization times from 700°C and 800°C, with respect to equivalent ratios, were not significantly different at the level of 0. 05. § The effect of equivalence ratio on bed agglomeration apparently became heightened at 900°C.

Results and Discussions Characteristics of Agglomerates ER 0. 2 Si 62% Si 55% Al 40% 50% Al 2 O 3 at 700°C 55% Si 87% Al 70% Si 60% Si 75% Al 2 O 3 at 800°C Composition (wt. %) 86% Al 100 1 2 3 4 50 0 Si Si-surface Al K Ca Na Al-surface Mg P Necks

90% Si 81% Si 36% Si 81% Al 60% Si Composition (wt. %) Results and Discussions ER 0. 2 100 1 2 3 4 5 80 60 40 20 0 Si 25% Al 2 O 3 at 900°C Al K Ca Na Mg P 91% Al 77% Al 60% Si 65% Si 74% Al Composition (wt. %) 100 1 2 3 4 5 80 60 40 20 0 Si 80% Si 65% Si 73% Al 92% Si 65% Si Composition (wt. %) 50% Al 2 O 3 at 900°C K Ca Na Mg P 100 1 2 3 4 5 80 60 40 20 0 Si 100% Al 2 O 3 at 900°C Al Al Si-surface K Ca Na Mg Al-surface P Necks

Results and Discussions Characteristics of Agglomerates 50% Si 66% Al 59% Si 52% Si Composition (wt. %) 100 1 2 3 4 5 6 7 80 60 40 20 0 Si Al K Ca Na Mg P 50% Al 2 O 3 at 700°C 78% Al 38% Si 50% Si 45% Al 75% Al 2 O 3 at 800°C Composition (wt. %) 69% Si 100 1 2 3 4 5 80 60 40 20 0 Si Al Si-surface K Ca Na Al-surface Mg P Necks ER 0. 4

Results and Discussions Syngas composition Component ER Carbon or Hydrogen Conversion % 0. 4 0. 2 7– 11 H 2 5– 17 CO 24– 34 2433– CO 2 11– 30 1932– C-CH 4 8– 11 811– H-CH 4 15– 21 14 -21 15

Results and Discussions K 2 O-Ca. O-Si. O 2 The eutectic melting point of ternary 16

Conclusion § The operating temperature significantly affects bed agglomeration due to interaction of rice straw ash with silicate in silica forming K 2 O-Ca. OSi. O 2 system. § Increasing the alumina ratio led to an extension of the defluidization time. § The effect of equivalence ratio on bed agglomeration apparently heightened at 900°C. § At linkage point of agglomerated and silica surface bed: Found high contents of Si K and Ca compounds (K 2 O-Ca. O-Si. O 2 system) but low contents at surface of Al 2 O 3. § Gas product mainly consisted of CO, H 2 and CH 4 which can be used in engines, steam turbines, as well as in other processes. § The results from this investigation can be applied to biomass-fluidized bed gasification, where bed agglomeration entails a plant shutdown and is expensive in terms of maintenance 17

Acknowledgements This research project is supported by the Second Century Fund (C 2 F), Chulalongkorn University. Authors thank for the assistance from the Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University and National Metal and Materials Technology Center for their assistance on material analysis and laboratory space. 18

Thank you 19