This research was conducted to develop a detailed gasifier modeling program for co-current moving bed (down-draft) reactors fed carbonaceous materials. The model development consisted of formulating a non-isothermal particle model and applying the principles of thermodynamics, transport processes, hydrodynamics of solid and gas flows, and the mass and energy balances. The Fredholm integral equation technique, converting the resultant energy and mass differential equations into a nonlinear algebraic equation system, was applied to facilitate the particle model solving process. The completed gasifier modeling program was used to simulate the reactor performance and to evolve the design criterion, specifically the dimension of the gasification zone.; The particle model indicated the intra-particle gradients of the gas concentration, temperature, and carbon conversion profiles become more pronounced as the particle size and/or the bulk fluid temperature increase due to the effect of diffusional limitations. The carbon conversion is volumetric with a higher fractional conversion at the surface and decreasing towards the center at all time.; The gasifier model was validated using literature data. The dependence of reactor performance on operating variables (such as feedstock moisture contents, particle sizes, reactor insulation, input air temperatures, and gasifier loads) has been studied with poplar as a feedstock. An increasing moisture content causes the feedstock conversion efficiency to decrease because of lower oxidation temperatures. Smaller particle size (not less than 0.5 cm), reactor insulation, and high input air temperature were all proved beneficial to gasifier operation. An increase of reactor load, causing a reduced residence time, resulted in declined efficiencies. However, the reactor can meet the demand variation by varying the air input rates. As for the design of the reactor dimension, a length of 100 cm below the primary air inlet is recommended for various gasifier operating and feedstock conditions.
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