Abstract
The raw syngas effluent from a fluidized bed gasifier typically contains a large amount of fly ash having a high concentration of carbon, which is undesirable. The present work examined the newly developed entrained-flow gasification technology intended to gasify raw syngas. Simulation of gas-solid flow and reaction behavior in an industrial-scale entrained-flow gasifier applying this new technology was first performed to obtain a better understanding of the particle flow and gasification characteristics. In addition, the devolatilization and heterogeneous reactions of fly ash particles were characterized by thermogravimetric analysis and user-defined function. The predictions from the simulation showed good agreement with the results of in situ experimental measurements. The combustion reaction for raw syngas occurred in the burner jet zone. As the hot gaseous products diffused, gasification reactions dominated the other zones. When burner inclination angle was 0°, 8.5°, and 25.5°, the temperature at the bottom outlet of the gasifier was lower than the ash flow temperature with the value of 1360°C. Solid slag formed and blocked the outlet. By comparison, this gasifier with the burner inclination angle of 17° could discharge the liquid slag and function as a continuous operation. In this way, the carbon conversion in fly ash reached the maximum value of 87%.
Highlights
Coal gasification which converts elements C and H from coal into effective syngas (CO + H2) is the key technology for clean and efficient utilization of coal and production of coal-based chemicals (Chang et al, 2016)
In order to accurately describe the heterogeneous reactions of fly ash, the kinetic parameters were introduced to the non-premixed combustion model using the user-defined function (UDF)
Oxygen is consumed rapidly in the jet zone (JZ), so a high-temperature, strongly reductive environment is formed in the other zones, which favors the gasification of the fly ash entrained by the raw syngas
Summary
Coal gasification which converts elements C and H from coal into effective syngas (CO + H2) is the key technology for clean and efficient utilization of coal and production of coal-based chemicals (Chang et al, 2016). A novel technology for the purification of raw syngas has been developed in which fly ash is treated in an entrained-flow gasifier after coming directly came from a fluidized bed This process is referred to as fly ash entrained-flow gasification, and the first 80,000 Nm3/h fly ash entrained-flow gasifier was constructed in Liaoning, China in 2015 (Fang et al, 2020). Because the fine ash is rapidly heated in this system to generate molten particles, the unburned carbon is almost completely exhausted, while the remaining ash forms a liquid slag that is discharged from the gasifier In this manner, a fly ash entrained-flow gasifier effectively converts the small particles into raw syngas. A fly ash entrained-flow gasifier effectively converts the small particles into raw syngas This kind of gasifier can replace the wet removal equipment in a typical fly ash post-treatment system while removing the generation of sewage and lowering equipment costs.
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