Four Zones Modeling of the Downdraft Biomass Gasification Process: Effects of Moisture Content and Air to Fuel Ratio

A mathematical model of a biomass downdraft gasification process has been developed. The model was considered to be four modules that are drying, pyrolysis, oxidation, and reduction which the products of upper module will be the reactants of the next. The one-dimensional kinetic finite rate models were applied to drying and reduction modules. The pyrolysis model took place when drying temperature reached 473 K. The equilibrium sequence model was used to describe the oxidation process by considering the sequence of order of reaction rates. For the model validation the comparison showed a good agreement. In the parametric study the moisture content increasing affected the height of drying, and pyrolysis zones increasing while the critical char bed length of reduction zone decreased from 0.53 to 0.25 m. The height of these zones decreased along A/F increasing. The results of this study can be used in the reactor design evaluation.