Computational modeling was completed on a simplified downdraft gasifier being installed at the University of Iowa Oakdale Power Plant. The model was created in Gambit and simulated in ANSYS Fluent. The process modeled was non-premixed combustion on biomass fuel with a fixed-bed. The Fluent coal model was modified based on (off-site) proximate and ultimate analyses of the biomass. Varying packing densities, oxidizer inlet velocities and fuel types were simulated and the impact on the combustion zone was assessed. It was found that packing densities around 0.5 with oxidizer inlet velocities less than 5m/s were ideal for modeling wood gasification and produced a temperature distribution that was the most analogous to previous experimental measurements. The resulting reaction field was mainly a large rich fuel combustion (RFC) zone where gasification and pyrolysis could occur. The different fuels were found to have similar temperature and mean mixture fraction patterns, although the maximum temperatures attained were very different (1080K for seed corn versus 678K for wood), with the wood showing a greater area of RFC for gasification and pyrolysis. The temperature contour corresponded to the mixture fraction figure perfectly and well explained the stable asymmetric combustion in a downdraft gasifier.

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