Detailed Modeling of Biomass Gasification in Dual Fluidized Bed Reactors under Aspen Plus

The modeling of biomass gasification processes by simulators such as Aspen Plus is a powerful tool to assess mass and energy balances and to optimize process designs. A detailed model of the gasification reactor is one of the key points to achieve an accurate process description. A model for biomass gasification in dual fluidized bed (DFB) reactors by coupling Aspen Plus and dedicated Fortran files is presented. The DFB is divided into three modules according to the main chemical phenomena: biomass pyrolysis, secondary reactions, and char combustion. Mass yields of permanent gases, water, 10 tar species, and char are modeled with respect to the reactor temperature by a pyrolysis correlation. The secondary reactions are modeled by a semidetailed kinetic mechanism that handles gas-phase and catalytic conversions over char of CH4 and lumped tar species (phenol, naphthalene, benzene, and toluene), gas-phase water gas shift reaction (WGSR), char, and soot steam gasification. The calculated compositions of permanent gases and tars, flow rates, and lower heating values are compared with experimental data for two DFB technologies (Tunzini Nessi Equipment Companies (TNEE) and Battelle High Throughput Gasification Process (FERCO)). The syngas composition and flow rate are very sensitive to the WGSR kinetic. The rate laws for WGSR are reviewed. An optimized kinetic law for WGSR is given.