Particle segregation in spouted bed pyrolysis reactor: Sand-coconut shell and sand-cocoa shell mixtures

Abstract

The singularity of air-particle flow characteristics and segregation phenomenon are still the main obstacles for application of conical spouted bed (CSB) for fast pyrolysis. This paper aims to investigate statistically the operating parameters (minimum spouting velocity and bed pressure drop) and biomass segregation (biomass mixing index) in a CSB composed of biomass (coconut and cocoa shells) and sand mixtures. Models for the pressure drop and inlet air velocity at the minimum spouting condition and for the axial mixing index were obtained. The bed voidage does not change significantly with the increase of biomass mass fraction (coconut and cocoa shells), therefore, larger amounts of biomass can be used without greatly increasing or decreasing the inlet air velocity to stabilize the spouted regime. From the analysis of bed stability and particle segregation, significant insights were obtained for future application of the CSB for the pyrolysis of biomasses. It is recommended the use of mixtures with 40 wt% of coconut shells and 75 wt% of cocoa shells in initial pyrolysis tests in CSB reactor. The cocoa shells particles are more suitable to pyrolysis because of their higher flowability.