An Approach to Simulate Vapor Phase Reactions of Coal Volatiles in a Reducing Section of the Two Stage Entrained Flow Gasifier with a Detailed Chemical Kinetic Model

The present study further develops an approach in predicting reactions undergone by coal volatiles in a reducing section (reductor) of an air-blown two-stage entrained flow gasifier toward designing a better gasification process. A detailed chemical kinetic model was first applied to simulate chemical reactions of a complex molecular mixture of the coal volatiles evolved due to rapid pyrolysis of coal fed into the reductor. The composition of volatiles was determined based on pyrolysis-gas chromatography experiments, where 22 compounds including inorganic gases (H2, H2O, CO and CO2), light hydrocarbon gases (C1–C4) and aromatic hydrocarbons (benzene to pyrene) were identified. Gas composition at the reductor inlet was estimated by integrating the information on the experimentally obtained molecular composition of the volatiles, and the thermodynamically calculated composition of inorganic gases generated from the combustor and the coal feeding rates into reductor and combustor. Concentration profiles of the individual chemical species, as well as soot particles along with the flow direction of the reductor, were revealed by using an extended detailed chemical kinetic model involving 202 species, 1,351 gas-phase reactions and 101 surface reactions for soot formation and growth. The simulation highlighted that near-complete decomposition of tar (<1.5 mg/Nm3) regarded as a set of all aromatic hydrocarbons is likely to require operation temperature of the reductor at temperatures as high as 1,200°C, when the combustor is operated at 1,800°C.