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Computational modeling was completed on a simplified downdraft gasifier to be implemented at the University of Iowa Oakdale Power Plant. The model was created in Gambit and exported to FLUENT, a computational fluid dynamics software program, in order to process non-premixed combustion on biomass fuels and better understand the combustion and gasification zones.
The fuels were modeled as coal particles with the empirical formula of the biomass found from off-site proximate and ultimate analyses. The coal model inherent to FLUENT contains the same chemicals (C, H, N, O, and S) as the biomass tested, so this model was determined to be accurate. The model was tested for varying packing densities, oxidizer inlet velocities and fuel type to describe the effects on the combustion zone.
It was concluded that packing densities around 0.5 with oxidizer inlet velocities less than 5 m/s would be ideal for modeling wood. The temperature distribution was the most even in this environment and produced 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 and 678K for wood), the wood showed a greater area of RFC for gasification and pyrolysis.