Physicochemical transformation of gasification slags with different residue carbon contents during sintering/melting process

Abstract

The ash residue after gasification in the coal gasifier contains a certain proportion of residual carbon, which exerts a significant effect on the slag properties such as sintering, melting, and flow within the furnace. The residues discharged outside the gasifier retain the distribution patterns of ash and residual carbon under gasification conditions. This study selected coarse and fine residues generated from an entrained-flow gasifier and investigated the transformation of slags with different carbon contents during heating process. The obtained ash residues underwent characterization to determine the modes of the compositions occurrence. Subsequently, ash residues with different carbon contents were observed for the sintering-melting processes with a high-temperature confocal scanning laser microscope (CSLM). With the aid of FactSage, the physicochemical transformation of slag particles was determined. The impact of residual carbon on particle characteristics manifests in both physical structure and chemical reactions. On one hand, residue residual carbon can act as a skeleton during the melting process, causing the molten phase to enter the pores of porous carbon, intensifying particle shrinkage. After the inorganic components melt, the liquid encapsulated by carbon retains the original particle shape. On the other hand, the carbon can react with the inorganic ash components. If the carbon content is less than 6%, a new FexSi with a high ash melting point can be formed. As the carbon content increases, the carbon reacts with the Si to form SiC. This implies a reduction in the liquid content. Therefore, the flow temperature is greatly delayed by an increase in carbon content above 14%.