Study on the flow characteristics of heterogeneous particles in three types of biomass fast pyrolysis down-tube reactors

Abstract

A novel staircase down-tube reactor has been developed to solve the problem of the short residence time of ceramic balls in a vertical down-tube reactor and flow separation of biochar powder and ceramic balls in a V-shaped down-tube reactor. Numerical simulation was performed using a coupled approach that combined the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD) to simulate the mixing flow of heterogeneous particles (biochar powder and ceramic balls) in three types of down-tube reactors: staircase, vertical, and V-shaped structure. The results show that at an equivalent vertical height. The average residence time for ceramic ball in a staircase down-tube reactor is longer than that of the other two types (tstaircase structure = 1.6 s > tV-shaped structure = 1.0 s > tvertical structure = 0.6 s). The average residence time of biochar powder in three types of down-tube reactors can be classified as follows: tV-shaped structure = tstaircase structure = 1.2 s > tvertical structure = 1.1 s. The flow separation and centripetal motion of heterogeneous particles were observed in V-shaped down-tube reactor. A distinct periodic motion is exhibited in staircase down-tube reactor, it has great significance for exploring the flow and heat transfer regularity of heterogeneous particles. Eccentric distance (E.d) was proposed as a measure of the spatial utilization efficiency of the device. While the degree of coherence (D.c) was used to assess the degree of flow separation among heterogeneous particles.