This study proposes an analysis of biomass gasification using two mathematical models: one equilibrium model and one kinetic model based on the level of details and input data. After validation with data from literature, the models were applied for analysis of a combined gasifier-combustor unit for processing of solid wastes (biomass) of footwear industries. The gas product predicted by the models was indirectly validated with experimental data. For this, the adiabatic flame temperature estimated from the gas product was confronted to experimental temperature of the combustor unit, showing the accuracy of each model. Sensitivity analyses of the models were carried out regarding to the feed air flow rate. The responses to parametric changes were observed in major output parameters: low heating value (LHV) of gas product, and cold gas efficiency, which are important measures to quantify the performance of the system.