A mechanistic analysis of particle flow in a pulsatile circulating dual fluidized bed for chemical looping technology based on CDF-DEM simulation

Abstract

This paper presents a three-dimensional computational fluid dynamic–discrete element method (CFD-DEM) model using Geldart class D particles for studying the fluid flow pattern in a circulating dual fluidized bed (CDFB) for chemical looping dry reforming of methane (CLDRM). The system design comprised a high-velocity air reactor (AR) also known as riser fluidized bed, a riser tube, a cyclone chamber, a fluidizing bed fuel reactor (FR), and a connecting loop, which closes the loop between AR and FR. The particles distribution, volume fraction, flow pattern, velocity and their circulation between the AR (riser) and FR (second fluidized bed) in CDFB were deeply investigated. The results showed that the CLDRM system experiences a pressure imbalance between the reduction and oxidation zones, causing solid particles to undergo a highly intricate and turbulent pulse flow. As a result, the operation of the system is alternately governed by two flow regimes: bubbling fluidization and pulsatile circulating fluidization. The burst of a high pressure pulses provide the pressure head required for circulation of the particles. The pulses also led to the intermittent transportation of particles ― in the form of particles clusters ― from high-pressure area to the region with a lower pressure.