Study on dominant structural factors and laws of combustion performance of acidified coal

Abstract

The application of acidification technology changes the pore structure and microcrystalline structure of coal, which affects the combustion characteristics of coal products. In this study, three inorganic acids (HF, HCl, and HNO3) were used to treat bituminous coal, and low-temperature nitrogen adsorption tests, X-ray diffraction analysis (XRD), and simultaneous thermal analysis (STA) were carried out. Fractal dimension theory, microcrystalline structure analysis theory, and thermal analysis kinetic theory analyze the pores, crystallites, and combustion characteristics of raw coal and acidified coal, respectively. The correlation between variables can be judged by the Pearson correlation coefficient. The research results show that compared with the microcrystalline structure, the pores determine the acidified coal's synthetical combustion index S, maximum value of differential thermal analysis DTAtop and maximum mass loss rate dW/dtmax to a greater extent. Hydrofluoric acid increased the average pore size of the raw coal by 38.66%, resulting in an 11.60% increase in dW/dtmax. The ignition temperature T5 is the composite performance of the aromatic structure's thermal stability and the microcrystalline structure's ordering. The aromaticity fa determines the reaction in the oxidation weight gain stage to a greater extent and can be used as a new indicator to characterise the spontaneous combustion tendency of coal. The pore and microcrystalline structures jointly determine the activation energy E3 in the combustion stage.