(108b) Multi-Phase CFD Simulation of a Downdraft Biomass Gasifier

Authors: 
Boravelli, T., Missouri University of Science and Tech
Smith, J. D., Idaho National Laboratory
A reliable, affordable clean energy supply is of primary importance for the economy and the environment and will prove to be pivotal in the 21st century. Biomass energy which is now accepted as a propitious alternative includes a widely available, sustainable and as a neutral CO2 resource, suited for modern applications for electricity generation and production of fuels and chemicals.

An advanced multi-dimensional mathematical model has been developed to understand the configuration and operation of a fixed bed biomass gasifier considering drying, pyrolysis, combustion and gasification reactions.  The Computational Fluid Dynamics (CFD) simulation is based on the down draft biomass gasifier design operated by the Energy Research and Development center at Missouri University and Science and Technology in Rolla, Missouri.  The multi-phase CFD model has been developed and verified with results from the experimental work. The flow model assumes an Eulerian –Eulerian formulation of the multi-phase system and uses kinetic theory of granular flow as the basis for the approximation to the turbulence flow in the solid phases with the standard к-ε turbulence model used for the gas phase.

Results illustrate the influence the air ratio has on gasification performance in terms of the production of syn gas and the amount of char produced. Predictions of gas temperature distribution through the gasifier and product gas composition are also compared to experimental results. Comparisons between the simulation and experimental results have been used to evaluate the validity of the CFD based gasification model.