Three-stage model-based evaluation of a downdraft biomass gasifier

Abstract

Biomass gasification suggests several advantages toward clean environment and energy sustainability. Multi-stage gasifiers enhance the process efficiency and syngas quality. Thus, multi-stage model developments are essential to take into account separate chemical schemes for successive pyrolysis and partial oxidation reactors. The current study is contributed to develop and evaluate a conceptual three-stage biomass gasifier model. The model is built by integrating three successive sub-models for drying and pyrolysis, partial oxidation and char reduction reactors. Pyrolysis sub-model is based on kinetic rate modelling with considering biomass lingo-cellulosic structure. Partial oxidation sub-model is developed by applying axis-symmetric 2D transport equations accompanied by appropriate chemical scheme. Char reduction sub-model is extended based on axis-symmetric 2D DPM model as well as appropriate chemical kinetic scheme. Accuracy of each sub-model and also the whole three-stage gasifier model are separately verified against available experimental data. Verification analysis demonstrates high resolution agreement between the results of the developed model and available experimental data. Simulations ascertain that gasification of 24.8 kg. hr−1 hardwood with about 26.5% moisture content in presence of 7 kg. hr−1 steam and 25 kg. hr−1 air has produced syngas with the composition of 1.92% CH4, 34.02% H2, 16.77% CO, 14.63% CO2 and 32.66% N2, outlet tar concentration of 2.3439 gr. N m−3 and grate char particles concentration of 0.0397 kg. m−3.