Ash And Slag Formation In Opposed Multi-burner Coal-water Slurry Gasifier

Mineral is non-uniformly distributed in coal and can be divided into included mineral and excluded mineral. Ash formation of excluded mineral and included mineral is different. This difference may affect char-ash deposition behavior in gasifier, and could influence slag composition and slag flow property in the gasifier. Based on a bench-scale Opposed Multi-burner gasifier, flyash and slag in the gasifier were characterized by SEM, EDS, XRD, XRF and PSD, and ash formation mechanism and slag flow property were also analyzed.For coal-water slurry gasification, the flame is restricted within the gasifier center, and the flame dose not collide the gasifier wall. The total content of CO and H2 from the gasifier outlet is different at different oxygen to carbon ratio, and the optimized oxygen to carbon ratio was 1.0.Particle size distribution and composition of flyash are significantly different between flyash at impinging zone and flyash at gasifier outlet. Particle size distribution of flyash at impinging zone is slightly finer than that of raw coal, and composition of flyash at impinging zone are quartz, calcite and FeS. Particle size distribution of flyash at gasifier outlet dramatically decreased comparing to that of flyash at impinging zone, and composition of flyash at gasifier outlet are quartz, calcite, FeS, mullite, anorthite, gehlenite and calcium oxide. Ash formation mechanisms at different gasification stages are also different. Part of fixed-carbon combustion and excluded mineral transformation are the mechanisms of ash formation at combustion stage. Char fragmentation and included mineral liberation and transformation are the mechanisms of ash formation at char gasification stage.At the burner-plane zone, included mineral is still not liberated and the gasifier wall mainly captures excluded mineral. Viscosity-temperature curves of slag on this wall locate between the curve of excluded mineral and the curve of bulk ash. At the gasifier dome, carbon conversion increases and the gasifier wall captures more char than gasifier wall at burner-plane. Slag from the gasifier dome contains more included mineral than slag from the burner-plane. Composition of slag from the gasifier dome is still mainly comprised of excluded mineral and slag flow property is determined by the composition of excluded mineral. Due to the gasifier wall above burner-plane mainly captures excluded mineral, slag flow property is determined by the composition of excluded mineral. Consequently, the viscosity necessary for the slag to flow down would therefore always not be estimated by the viscosity of the slag forms from the bulk coal ash.