Simulation of biomass gasification in bubbling fluidized bed reactor using aspen plus®

Abstract

The direct (with air) gasification process of biomass in bubbling fluidized bed reactor was simulated using Aspen Plus®. The reactor was divided in three parts: the pyrolysis zone, combustion zone and reduction zone. The pyrolysis process simulation was supported by an external MS-Excel® subroutine to define the yield and composition of the main components, namely, char, gas and tar. Whereas the combustion and reduction processes were simulated using a kinetic model. These models were calibrated and thereafter validated with a set of distinct results from gasification of four different types of biomass using a pilot-scale bubbling fluidized bed reactor, with different equivalence ratio (from 0.17 to 0.35) and temperature (from 709 °C to 859 °C). The results obtained from the simulation, namely the concentration of CO, CO2, H2, CH4, C2H4 in the producer gas, were in good agreement with the experimental ones for a set of biomass types and operating conditions. Amongst the gases analysed, H2 gas was predicted with the lowest accuracy, always being overestimated; despite that, the highest absolute error obtained for H2 was only 4.4%. Finally, the tar concentration predicted was between 20 and 42 g/Nm3 and it decreased with the increase of equivalence ratio, temperature and biomass particle size.