Hydrodynamic Study of AR Coupling Effects on Solid Circulation and Gas Leakages in a High-Flux In Situ Gasification Chemical Looping Combustion System

Xiaojia Wang,Baosheng Jin,Xianli Liu,Decheng Wang

doi:10.3390/pr6100196

Abstract

In situ gasification chemical looping combustion (iG-CLC) is a novel and promising coal combustion technology with inherent separation of CO2. Our previous studies demonstrated the feasibility of performing iG-CLC with a high-flux circulating fluidized bed (HFCFB) riser as the fuel reactor (FR) and a counter-flow moving bed (CFMB) as the air reactor (AR). As an extension of that work, this study aims to further investigate the fundamental effects of the AR coupling on the oxygen carrier (OC) circulation and gas leakages with a cold-state experimental device of the proposed iG-CLC system. The system exhibited favorable pressure distribution characteristics and good adaptability of solid circulation flux, demonstrating the positive role of the direct coupling method of the AR in the stabilization and controllability of the whole system. The OC circulation and the gas leakages were mainly determined by the upper and lower pressure gradients of the AR. With the increase in the upper pressure gradient, the OC circulation flux increased initially and later decreased until the circulation collapsed. Besides, the upper pressure gradient exhibited a positive effect on the restraint of gas leakage from the FR to the AR, but a negative effect on the suppression of gas leakage from the AR to the FR. Moreover, the gas leakage of the J-valve to the AR, which is directly related to the solid circulation stability, was exacerbated with the increase of the lower pressure gradient of the AR. In real iG-CLC applications, the pressure gradients should be adjusted flexibly and optimally to guarantee a balanced OC circulation together with an ideal balance of all the gas leakages.

Highlights

Chemical looping combustion (CLC), which possesses an inherent feature of isolating CO2 during the combustion process, has been regarded as a promising novel combustion technology with a low energy penalty for carbon capture [1,2]
The following conclusions can be drawn from the present study: (1) The In situ gasification chemical looping combustion (iG-CLC) system exhibited favorable pressure distribution characteristics and good adaptability of solid circulation flux, demonstrating the positive role of the direct coupling method of the air reactor (AR) in the stabilization and controllability of the whole system
Applications, the upper pressure gradient of the AR should be limited within the stage of circulation strengthening in order to guarantee a balanced and adjustable oxygen carrier (OC) circulation

Summary

Introduction

Chemical looping combustion (CLC), which possesses an inherent feature of isolating CO2 during the combustion process, has been regarded as a promising novel combustion technology with a low energy penalty for carbon capture [1,2]. A conventional CLC system is mainly comprised of a fuel reactor (FR) and an air reactor (AR). The fuel introduced into the FR is oxidized to CO2 and H2 O by a solid oxygen carrier (OC). The reduced OC particles are transferred to the AR where they are re-oxidized upon contact with air. Compared to conventional combustion methods, the fuel will no longer mix with N2 in a CLC process, by means of the circulation of OC between the two reactors. The flue gas leaving the FR will only contain CO2 and H2 O with a complete conversion of the fuel, which enables efficient and energy-saving CO2 capture via the condensation of H2 O [3,4]

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