CFD Modelling of Plasma Downdraft Coal Gasification Process: Effect of Throat Diameter on the Produced Syngas Composition

Abstract

Plasma gasification is a high purity reaction which resulted on the conversion of carbon containing feedstock into syngas with extreme low tar content. Despite the advantages of low tar syngas, achieving high combustible component in syngas (H2 and CO) via plasma gasification method through the modification of reactor was still unclear. Hence, the present study aims to investigate the effect of throat size of the plasma downdraft gasifier on the quality of produced syngas using Computational Fluid Dynamics (CFD) modelling. The effect of different sizes of reactor throat diameter on the temperature and produced syngas composition was systematically investigated and validated with previous study. The model geometry was developed by SolidWorks software package and simulation work was performed using Ansys Fluent software package. The design geometry of plasma throated downdraft gasifier involved a throat diameter of 201 mm, 164 mm, and 238 mm. The simulation model in this work was using the combustion, mixing and turbulent model of non-premixed combustion, Euler-Lagrangian method, and the K- turbulence model respectively. The Air, coal and plasma inlet temperature was set at 673 K, 293 K, and 1173 K, respectively. Whereas the air, feedstock and plasma gas flowrate were set at 0.0029 kg/s, 0.029 kg/s, and 0.0438 kg/s respectively. The results revealed that the throat diameter had a significant effect on the properties of the gas and temperature profile. This study reported that the temperature distribution at the centerline of reactor decreased with the increase of throat diameter. This result consequently caused the increase of the concentration of H2, CO, and CH4 by 8%, 12% and 6% due to the occurrence of endothermic reaction rather than exothermic reaction as complete combustion process is hindered.