Enrichment of residual carbon from coal gasification fine slag in an inflatable-inclined liquid–solid fluidized bed

The recovery and utilization of the fine slag obtained from coal gasification is of great significance to reduce environmental pollution and improve resource utilization. An inflatable-inclined liquid–solid fluidized bed was used to enrich and recover residual carbon from coal gasification fine slag, and the separation principles and influencing factors were investigated by numerical simulation and experiments. The results showed that light and heavy particles were initially separated by increasing the water flow in the vertical section of the bed when the slag entered the liquid–solid fluidized bed. Subsequently, a secondary air flow further separated light particles from heavy ones on the inclined section of the bed, which strengthened the overall separation effect of the liquid–solid fluidized bed for gasification fine slag. During the separation process, the loss-on-ignition and residual carbon recovery percentage of the concentrate first increased and then decreased; they increased with the increase in rising water velocity (and secondary air velocity) but decreased with the increase in feed quantity. The influence of these factors on the loss-on-ignition and residual carbon recovery percentage of the concentrate was as follows: water velocity (vw) > feed quantity (m) > secondary air velocity (vf). Under suitable operating conditions (m = 200 g, vw = 0.042 m/s, vf = 2.12 m/s), the loss-on-ignition of the concentrate reached 66.38%, which represents a high carbon content, thereby indicating that the liquid–solid fluidized bed efficiently enriched the residual carbon in the fine slag. According to loss-on-ignition of the concentrate and product characteristics through scanning electron microscope and thermogravimetric analysis, the concentrate has a high carbon content (loss-on-ignition of 66.38%) and high reactivity, which can be used as fuel. The findings of this study will provide a theoretical and technical basis for the resource utilization of coal gasification fine slag.