An integrated kinetic model for downdraft gasifier based on a novel approach that optimises the reduction zone of gasifier

A kinetic model was built to estimate the optimum working parameters of a downdraft gasifier, in which a set of chemical kinetics at each zone of the gasifier was described. The model deals with a wide range of biomass types with elemental composition ranges of (38 ≤ C ≤ 52) %, (5.5 ≤ H ≤ 7) %, and (36 ≤ O ≤ 45) %. This model is able to predict gas composition, tar content, temperature and height of each zone, as well as temperature, velocity and pressure distribution at reduction zone with heating value of product gas. The model also gives full design dimensions of a downdraft gasifier. The final results, which proved to be in a good agreement with experimental works under different working conditions of biomass type, moisture content, and air-to-fuel ratio, are based on a new approach that includes calculation of the optimum height of the reduction zone. Calculation based on the optimum height ensures that all the char produced is consumed in the reduction zone, thus leading to the production of the maximum amount of gases. Results conclude that biomass with a moisture content less than 10% and equivalence ratio of 0.3-0.35 leads to the production of higher yield of syngas with low tar content. In particular, woody biomass materials are found to give the higher heating value for producer gas with a reasonable amount of tar.