DETAILED KINETICS OF SOLID FUEL GASIFIERS. COMPARISONS BETWEEN BIOMASS AND COAL PERFORMANCES

摘要

Gasification is a thermo-chemical process aiming at the production of high heating value syngas,rnstarting from biomass, coal, or refuse derived fuels. Depending on the solid fuel and on the operating parameters ofrnthe process, the quality and the chemical composition of the produced syngas is differently affected. The finalrnapplications of syngas include the power generation and the production of chemicals, with special reference tornmethanol/ammonia synthesis and Gas-to-Liquid technologies. The aim of this work is to propose a comprehensivernmathematical model of a biomass and coal gasifier. The first complexity relies in the characterization of the solidrnfuels and their pyrolysis and devolatilization process. The pyrolysis of the different solid fuels is characterized by arnmultistep kinetic model, with a detailed characterization of gas, tar and solid residue. The secondary gas phasernreactions describe the successive evolution of the released gas and tar components, while heterogeneous gasificationrnand combustion reactions allow to account for the evolution of the solid residue. Moreover, the mathematical modelrnof the gasifier requires a comprehensive description of the coupled transport and kinetic processes, both at the particlernand the reactor scale. The complexity of the resulting numerical problem is due both to the dimension of therndifferential algebraic system and to the stiffness of radical reactions. A validation example of the overall model withrnproper experimental data supports the reliability of the comprehensive approach here discussed. Comparisonsrnbetween the performances of a countercurrent coal and biomass gasifier are proposed.