Gasification of Mixed Biomass: Analysis Using Equilibrium, Semi-equilibrium, and Kinetic Models

Abstract

Biomass gasifiers with capacities exceeding 1 MW have large biomass consumption, and mixture of biomasses need to be used as feedstock in these gasifiers. In this chapter, we have presented a review of our studies in gasification of biomass blends using approaches of non-stoichiometric equilibrium, semi-equilibrium, and kinetic models. Initially, gasification of biomass mixtures has been assessed using thermodynamic equilibrium and semi-equilibrium (with limited carbon conversion) model employing Gibbs energy minimization. Influence of operating parameters such as equivalence ratio, temperature of gasification, and composition of the biomass mixture has been evaluated using two criteria, viz net yield and LHV of the producer gas. Interestingly, optimum operating conditions for all biomass mixtures have been established as equivalence ratio ~0.3 and gasification temperature ~800 °C. The kinetic model analysis of gasification of biomass based on a circulating fluidized bed gasifier. A series of chemical reactions was considered for obtaining complete mass balance. Although the profiles of molar composition, net yield and LHV of the producer gas predicted by kinetic model matched with equilibrium models qualitatively, significant quantitative difference was evident. The processes of char gasification and tar oxidation have slow kinetics that adversely affects the carbon conversion in the riser of the circulating fluidized bed gasifier.