Simulating volatiles conversion in dense burning coal suspensions. 2. Extrapolations to commercial p.f. firing 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 a tangentially fired utility furnace. CFD simulations based on detailed engineering specifications determined the operating conditions along the coal jet, including coal mass loading, thermal histories, and transit times. A reactor network developed from the CFD results staged the chemistry in this environment with a utility grind of the same three diverse coal types in Part 1. Variations in mass loadings were then characterized to span the behavior from the commercial specification to the loading in the validation tests in Part 1.Volatiles combustion under commercial loadings in an isolated primary coal suspension alters the species concentrations but does not necessarily add or eliminate any fuel components or N-species. With all but low volatility coals, the effluents contain CH4, C2H2, H2, CO, HCN, and H2S, char, and soot. With low volatility coals, effluents have minimal or no gaseous hydrocarbons and appreciable amounts of NO. Soot burnout is negligible with all coals, and char burnout is appreciable with only low rank coals. Variations in loading do not change the dynamics of volatiles combustion or char ignition but progressively heavier loadings accelerate O2 elimination. The elimination of O2 allows gaseous reductants to accumulate along the post-flame region and drive the effluent NO concentration well below its maximum, even when extents of char and soot burnout are negligible. Coal quality primarily affects near-burner NO production via variations in char oxidation reactivity. Rapid char burning rates accelerate O2 consumption during volatiles combustion, which biases the partitioning of HCN toward N2, away from NO. The simulations also gave nearly identical tendencies for progressively greater O2 levels in the validation database in Part 1 and for progressively lighter loadings in the primary suspension simulations, provided that the thermal histories of both coal and gas are similar.