One dimensional steady-state circulating fluidized-bed reactor model for biomass fast pyrolysis

A one dimensional (1-D) steady-state biomass fast pyrolysis reactor model is developed for integration with a biomass pyrolysis plant system model. A state-of-the-art biomass pyrolysis kinetic mechanism is combined with the 1-D Eulerian fluid dynamics and heat transfer description. Simulations are performed for a small scale reactor (0.023 kg/s) with four different biomass feedstocks (pine, wheat straw, olive husks, organic fraction of MSW). Results show that biomass particles are heated to pyrolysis temperature of 786 K in 0.3 s and 99% biomass conversion is reached in 0.9 s from entering the reactor. Comparison of pyrolysis products yields against available literature data shows that the employed reaction mechanism generally gives good predictions. However, water yield is under predicted. Fluid dynamics and heat transfer results are compared with averaged results from a 2-D, transient reactor model developed in Multiphase Flow with Interphase eXchanges (MFIX). Comparison of the 1-D and the 2-D model results shows flow patterns and reasonably similar values of flow parameters, with the average relative error between the gas velocities of 10%. The solids velocity predictions from the 1-D model carry a larger error since particle clustering is neglected in the plug flow approximation. The 1-D model is still considered attractive because of a reasonable agreement with the averaged experimental results.