Simulating volatiles conversion in dense burning coal suspensions. Part 3. Extrapolations to entrained flow gasification conditions

Abstract

This simulation study uses the reaction mechanisms from Part 1 to simulate the chemical transformations along a single coal jet from an injector in Shell and General Electric (GEPS) entrained flow gasifiers. CFD simulations in the literature determined the operating conditions along the coal jet, including coal mass loading, O2 and moisture feedrates, thermal histories, and transit times. A simplified reactor network staged the chemistry in this environment with utility grinds for dry feed and slurries of the same three diverse coal types. Disparate extents of char burnout are the distinguishing factor that interprets the much different gas compositions from the near-burner flame zones (NBFZs) in Shell and GEPS gasifiers. Progressively faster char oxidation reactivities produce more reducing gas conditions which have more CO and H2 and less CO2 and H2O in the nascent syngas. Consequently, the much finer coal grind in Shell gasifiers gives greater char burnout with the same coal, and gas compositions that are much closer to ultimate syngas compositions. Since coals of progressively higher rank have slower char oxidation reactivities, nascent syngas from NBFZs contains less CO and H2 and more CO2 and H2O with coals of progressively higher rank under both gasification conditions. Gaseous hydrocarbons were completely eliminated in NBFZs under Shell and GEPS conditions with all coals. The smallest sizes in the Shell PSD never fully ignited to a rapid-burn condition due to their relatively rapid heat loss rates. Consequently, disproportionate amounts of fine-particle residual char from NBFZs should be evaluated as potential sources of unreacted carbon from these gasifiers.