an euler-euler cfd model

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An Euler-Euler CFD Model for Biomass Gasication in Fluidized BedQingluan Xue and Rodney FoxAmes Laboratory, Iowa State University DE-AC02-07CH11358

NETL Conference on Multiphase Flow Science Morgantown, WV, May 22-24, 2012

Objectives

Provide MFIX-based Euler-Euler CFD models for polydisperse, reacting, variable density solid particles Facilitate the numerical simulation and scale up of energy systems such as gasier

Q. Xue & R.O. Fox (A Lab/ISU)

Polydisperse Biomass Gasication

May 22-24

2 / 19

Background: Multiphysics & Multiscales

Q. Xue & R.O. Fox (A Lab/ISU)

Polydisperse Biomass Gasication

May 22-24

3 / 19

Physical ModelsSpherical particle assumption Porosity and moisture modeled Uniform conversion model for micro-particlesConstant particle diameter (dp ) Variable particle density (p ) with increasing pores Intra-particle transport ignored for micro-particle

Couple continuity and species equation to update

pN 1

apparent

=n =1

X s ,n

(n )truePolydisperse Biomass Gasication May 22-24 4 / 19

Q. Xue & R.O. Fox (A Lab/ISU)

Chemical ModelsDevolatilization: Tar reaction: Volatile reaction: Carbon monoxide oxidation Hydrogen oxidation Methane oxidation Water-gas shift Char combustion Partial combustion Char gasication: Boudouard reaction Steam gasication Hydrogen gasication Biomass light gas (CO, CO2 , H2 , CH4 ) + tar + char + H2 O Tar (g) light gas (CO+ CO2 + H2 + CH4 + H2 O) + inert Tar CO + 1/2 O2 CO2 H2 + 1/2 O2 H2 O CH4 + 2 O2 CO2 + 2 H2 O CO + H2 O CO2 + H2 C + 1/2 O2 CO C + CO2 2 CO C + H2 O CO + H2 C + 2 H2 CH4

Reaction rate based on min[k = exp [E /RT ], C (2Sij Sij )1/2 ]

Q. Xue & R.O. Fox (A Lab/ISU)

Polydisperse Biomass Gasication

May 22-24

5 / 19

Implementation in MFIX-ContinuumTime-splitting approach coupling hydrodynamics and kinetics

(t ) (t + t ) (t + t ) Synchronized time-step for transport and reactionTime step: t n Back up variables at ttn

transport

chemical reaction

n

Transport calculation iterationReset variables values t > dt_min n to t ; reduce t No Reset variables values n-1 n to t ; reduce t t

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