Modelling and simulation of a downdraft gasifier using agricultural wastes
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In this study a thermodynamic equilibrium model based on integrating stoichiometric and nonstoichiometric equations was structured in order to predict the exit gas composition, heating value, as well as the mass and energy balances. The model also predicts the exit gas temperature basing on the energy balance formulations for heat energy changes in the downdraft gasifier fed by different agricultural wastes. The model equations are solved using Engineering Equation Solver (EES) software basing on initial values and lower/upper limits for the solution. Various gasification parameters were simulated by the EES program in order to study their effect on the determined model parameters for five selected biomass feedstock which include groundnut shells, coffee husks, rice husks, maize cobs and sugarcane bagasse. Groundnut shells had the best performance in the present model among the examined five agricultural feedstocks with a maximum heating value of 4.87 MJ/Nm3. The model findings were also validated by comparing them with gasification experimental data for the selected agricultural feedstock and other gasification models developed by several authors. The producer gas compositions and heating values for the various agricultural feedstock predicted by the model were close to those obtained from various gasification experiments and other developed models in literature.