Numerical modeling of a downdraft plasma gasification reactor

Gasification, a method of producing hydrogen, is an alternative way to obtain clean, sustainable, and domestic energy using coal and biomass resources. Gasification can be achieved with several methods or using various reactor designs, and plasma gasification is one of these methods. Plasma gasification has advantages compared to conventional gasification systems regarding syngas cleaning and gasification rates. Tar production, the greatest problem in fixed bed gasifiers, can be reduced and higher carbon conversion rates can be achieved with plasma gasification systems. In this study, a 10 kW microwave plasma-integrated down-draft coal gasifier was modeled with ANSYS FLUENT. A novel design is simulated in order to obtain the swirl effect and observe the increase in the residence time for coal particles inside the reactor. Plasma ionization is ignored due to the overlapping of the MHD (MagnetoHydroDynamics) module and combustion models. Therefore, plasma inlet conditions are determined via experimental studies instead of activating the MHD module in Fluent. SIMPLE algorithm is selected for pressure velocity coupling. Turbulence variables are calculated with the k-epsilon turbulence model. The interaction between gas phase and discrete phase is followed by Eularian-Lagrangian approach and 10 injection time steps are chosen for the continuity of the reactions. The Finite Rate Chemistry/Eddy Dissipation model is selected for both combustion and gasification models. DO radiation model is used for radiation modeling. Temperature, species (CO, H-2, CO2, H2O), and velocity results on different planes are obtained. According to the results, approximately 1350 K average temperature is obtained inside the reactor. Grid independency study is also performed. The results show that it is possible to obtain a syngas with 18.4% H-2 and 37.2% CO mole fractions, respectively. The cold gas efficiency of the gasifier is found to be 55.3%. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.