Effect of Peak Temperature on Biomass Pyrolysis Characteristics in Thermally Thin Regime in a Fixed-Bed Reactor

Abstract

Effect of reactor peak temperature on biomass pyrolysis in thermally thin regime with a constant heating rate of 30 K/s, reactor pressure of 1 atm and reactor peak temperature ranging from 500 to 1000 ^oC in a fixed-bed reactor has been numerically investigated. Wood samples  were modeled as two-dimensional porous solids. Transport equations, solid mass conservation equations, intra-particle pressure generation equation and energy conservation equation were coupled and simultaneously solved to simulate the pyrolysis process. First order Euler Implicit Method (EIM) was used to solve the solid mass conservation equations. The transport, energy conservation and intra-particle pressure generation equations were discretized by Finite Volume Method (FVM). The generated set of linear equations was solved by Tri-Diagonal Matrix Algorithm (TDMA). Intra-particle fluid flow velocity was estimated by Darcy’s law. Results showed that increase in reactor peak temperature from 500 to 600 ^oC slightly increased the degree of volatiles intra-particle secondary reactions and that further increase of the former has no effect on the latter. Increasing reactor peak temperature from 500 to 600 ^oC also resulted in slight increase in gas and secondary tar yield but some decrease in tar and char yield. Further increase in reactor peak temperature above 600 ^oC has no effect on products evolution and yields. The highest tar yield (45.31%) was obtained at 500 ^oC.

Keywords: Biomass, pyrolysis, intra-particle secondary reactions, thermally thin regime