Evaluation of carbon forms and elements composition in coal gasification solid residues and their potential utilization from a view of coal geology

Abstract

As the development of coal gasification technology expands in China, the resulting solid by-products can become environmental and economic concerns. Evaluation of carbon forms and elemental composition in coal gasification solid residues from three advanced commercial-scale entrained-flow gasification plants in China related to feedstock coal properties are studied and their potential utilization is discussed in the present study. The properties of the residues of the three entrained-flow gasification processes differed as a result of the type of process applied, even though the properties of their feedstocks are similar. Eight types of carbon forms were identified. The high-inertinite feedstock resulted in a fusinite-like carbon being the primary carbon form of the residues, except for the General Electric fine residue (GE-FR) sample. The carbon contents of the coarse residues (CRs) produced from the Opposed Multi-Burner (OMB) coal-water slurry gasifier and the Gaskombiant Schwarze Pumpe (GSP) pulverized coal gasifier are comparable, lower than 2% (C_d), but a high content of carbon present as "black particles" (79.90%, C_d) was concentrated from the OMB-CR sample. Fourier transform infrared spectroscopy (FTIR) analyses indicate that the main functional group of the fusinite-like material in OMB-CR is methyl (CH₃-). From the chemical composition point of view, the high proportions of F₂O₃ and CaO in the GE residues make them potential sources of high-Fe or high-Ca material. The relatively high concentrations of In, Ga, Sb, Cs, Cr, Ba, and rare earth elements in the residues make them potential raw materials for extracting critical trace elements, especially the OMB-FR and GSP-FR samples for extracting Ga.

Keywords: Carbon forms; Chemical composition; Gasification residues; Solid waste utilization.