Optimization of Kazakhstan Coals Gasification Process in the Circulating Fluidized Bed Gasification Process

Abstract

Coal, coke, and semi-coke are critical feedstock for the production of iron and steel. For over a century coke and semi-coke has been produced from coal using the slow pyrolysis thermal treatment process in fixed bed coke ovens. The coke-oven slow pyrolysis process produces vast quantities of gaseous and liquid emissions associated with coal tar which are not and sometimes cannot be always captured and recycled. Contrary to this, fast pyrolysis associated with gasification processes produces less tar. In this work a novel method incorporating fast pyrolysis to produce semi-coke using circulating fluidized bed partial coal gasification is experimentally studied. The present study includes an investigation of coal fast devolatilization properties, a pilot scale experimental proof of concept, and optimization of the process. Fast pyrolysis characteristics are explored using a wire mesh reactor and a thermobalance reactor experiments, and semi-coke is produced using a high-volatile Shubarkol coal in a custom-built atmospheric lab-scale reactor comprising a riser, a cyclone, a loop seal, and fitted with mechanized systems for semi-coke retrieval. The reactor is operated autothermally, at temperatures varying from 700 to 1000oC. The experimental results indicate the operating conditions for maximum product output. The product characterization revealed that semi-coke gains distinctive characteristics, including lower density, lower volatile matter content, lower ash content, higher porosity, and higher crystallinity of the carbon matrix. In addition, a Computational Fluid Dynamics simulation employing the Eulerian-Lagrangian multiphase particle-in-cell approach reveals fluidization properties and further optimization opportunities.