# Problems bout CFD model of biomass gasification, Downdraft gasifier

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 November 17, 2009, 21:50 Problems bout CFD model of biomass gasification, Downdraft gasifier #1 New Member   Wang Long Join Date: Sep 2009 Posts: 5 Rep Power: 16 I am a Master student study in biomass gasification in Korea. I am trying to make a CFD model of downdraft gasifier using FLUENT 6.3. I have lot problems. I hope you give me some advice about it. Thank you very much. I tried 2 ways to simulate this gasification process: one phase and multiphase. In one phase case, wood determined as very small carbon particles. So the carbon particles and air determined as fluid phase. The details you can see in the fluent case file. The model was run in a computer which has 3G RAM and Q6600 cpu for more than 12 hours and iterated about 26,000 times. The problem is: 1.The simulated result presented that nearly no reactions occurred in the gasifier. 2.If I use a injection of wood inlet, the injection rate will be very small because the wood is drop down very slowly, I cannot simulate the right case use a injection. In 2 phase case, carbon determined as solid phase and details of model setting as below: The problem is : 1.In the simulated result, temperature is too high (highest is 5000K), the temperature range in experiment is from 293K~1600K. 2.No reactions occurred in the gasifier as the simulated results. **Setting of Multiphase (2 phase) Slover Slover -Pressure Based Formulation -implicit Space -3D Velocity Formulation -Absolute Gradient Option -Green-Gauss Cell Based Porous Formulation -Superficial Velocity Multiphase Multiphase Model -Eulerian Number of phase -2 Energy -Energy Equation Viscous Model Model -k-epsilon (2 eqn) k-epsilon Model -Realizable Near-Wall Treatment -Standard Wall Functions k-epsilon Multiphase Model -Mixture Model Constants C2-Epsilon: 1.9, TKE Prandtl Number: 1, TDR Prandtl Number: 1.2, Disperion Prandtl number: 0.75, Energy Prandtl Number: 0.85, Turb. Schmidt Number: 0.7, Species Model Model -Species Transport Reactions -Volumetric & Particle Surface Options -Inlet Diffusion & Diffusion Energy Source Turbulent -Chemistry Interaction -Finite-Rate/Eddy-Dissipation Operation Condition Pressure: Operating Pressure(pascal)-101325 Gravity: Gravity- Gravitational Acceleration Z(m/s2)=-9.8 Boussinesq Parameters: Operating Temperature (k)=288.16 maleyue likes this.

 November 20, 2009, 16:45 #2 New Member   ANKW Join Date: Nov 2009 Posts: 4 Rep Power: 16 Dear, some more informations about your case are required 1) Drag Model? 2) Granular Temperature Model: which of the following you have used (Phase Property or Partial Differential Equation)? If Partial Differential equation then which model for GT 3)Granular Viscosity, Granular Bulk Viscosity and Frictional Viscosities Models

November 25, 2009, 23:27
#3
New Member

Wang Long
Join Date: Sep 2009
Posts: 5
Rep Power: 16
Quote:
 Originally Posted by ANKW Dear, some more informations about your case are required 1) Drag Model? 2) Granular Temperature Model: which of the following you have used (Phase Property or Partial Differential Equation)? If Partial Differential equation then which model for GT 3)Granular Viscosity, Granular Bulk Viscosity and Frictional Viscosities Models
Dear ANKW:

Thank you for your help. I am fresh in using FLUENT, just more than 1 month. I am sorry I am not very understand you.

1) drag model.... I think I did not set drag model, what about the drag model of downdreft gasifier?
2) 6 reaction formulas and Arrhenius equation were used in the model
3 particle-surface reactions
2C+O2=2CO
C+H2O=CO+H2
C+CO2=2CO
3 volumetric reactions
2CO+O2=2CO2
CO+H2O<=>CO2+H2
3) Granular Viscosity: I am not clear Granular Viscosity in this model.

Can you give me more advice ? Thank you!

YOURS,
WANG

 Tags biomass gasification, cfd model, downdraft gasifier