A novel two-zone sequential optimization model for pyro-oxidation and reduction reactions in a downdraft gasifier.

A robust mathematical model is developed for prediction and optimization of syngas in a downdraft gasifier. The gasifier is modelled for two distinct zones i.e. pyro-oxidation zone (zone I) and reduction zone (zone II). A thermodynamic equilibrium model is implemented for the prediction of syngas composition in zone I, while zone II is modelled by implementing a finite kinetic approach. For each zone five control parameters are identified for sequential maximization of carbon conversion efficiency (CCE). Maximization of H(2) and CO yield in syngas and minimization of char contaminants is the main objective in the present analysis. The Taguchi method is implemented for process optimization while ANOVA is used to determine the most influential parameter. The optimized model gives 17.79% improvement in calorific value of syngas, while the final CCE obtained was 96.04%. For zone I the equivalence ratio was found to be the most influential parameter with 97% contribution, while for zone II the reduction zone temperature was the most influential parameter with 88% contribution.