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The pore structures and chemical composition features of two kinds of tri-high coal and their char samples prepared at a 750 °C temperature were analyzed. The results showed that the pyrolysis process has a great influence on the pore structure and the chemical composition of the char, and the influence is highly related to the coal ranks. The gasification kinetics of the two chars in pure CO2 atmosphere was also studied. The results indicated that the classical random pore model (RPM) cannot be used to explain the gasification kinetics throughout the char gasification. A modified RPM, considering the inhibitory effect of ash on the gasification kinetics, was adopted to estimate the kinetics, and the kinetic constants and the corresponding activation energies were calculated. It was observed that it was necessary to include the effect of ash on the variations of char structures during the char gasification to get an accurate description of reaction rate versus carbon conversion throughout the gasification of the tri-high coal chars.

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Two kinds of tri-high coals were selected to determine the influences of ash-existing environments and coal structures on CO2 gasification characteristics. The TGA results showed that the gasification of ash-free coal (AFC) chars was more efficient than that of corresponding raw coal (RC) chars. To uncover the reasons, the structures of RCs and AFCs, and their char samples prepared at elevated temperatures were investigated with SEM, BET, XRD, Raman and FTIR. The BET, SEM and XRD results showed that the Ash/mineral matter is associated with coal, carbon forms the main structural framework and mineral matters are found embedded in the coal structure in the low-rank tri-high coal. The Raman and FTIR results show that the ash can hinder volatile matters from exposing to the coal particles. Those results indicate that the surface of AFC chars has more free active carbon sites than raw coal chars, which are favorable for mass transfer between C and CO2, thereby improving reactivity of the AFC chars. However, the gasification reactivity was dominated by pore structure at elevated gasification temperatures, even though the microcrystalline structure, functional group structure, and increase in the disorder carbon were improved by acid pickling.

The separation of sulfur from the wet limestone fuel gas desulfurization (FGD) gypsum using oxalic acid solution was studied. Optimal separation conditions and a separation mechanism of sulfur were investigated. The obtained results indicate that the sulfur in FGD gypsum can be separated efficiently by oxalic acid solution. When separating under the optimal experimental conditions of 0.3 mol/L oxalic acid solution, 30 °C, and a 5/150 g/mL solid to liquid ratio for 8 min, the separation rate reached 97.0 wt %. Besides, the Avrami equation is more suitable for the kinetic analysis of the sulfur separation reaction than the unreacted shrinking core model. When the reaction temperature is less than or equal to 20 °C, the mechanism of the sulfur separation process is chemical-reaction-controlled; otherwise, it is diffusion-controlled. The activation energy E a of the sulfur separation reaction is 34.84 kJ/mol. During the separation process, the pH of the solution gradually decreased due to the conversion of oxalic acid to sulfuric acid, so the liquid obtained after the sulfur separation of FGD gypsum can be recycled as industrial sulfuric acid. Nearly 1 mol of sulfuric acid can be obtained for every mole of oxalic acid consumption.