Insight into the spatial distribution of sulfur during pyrolysis of coal with high organic sulfur

Abstract

The complicated mass transfer during coke making process leads to the uneven spatial distribution of sulfur forms in coke, which is of great importance for the sulfur transformation and desulfurization efficiency. In this work, Yanjiahe (YJH) coal with high sulfur content was selected to investigate the spatial distribution and conversion of different sulfur forms during the high temperature coking process by sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In consideration of volatile matters evolution pathway, the content and transformation of different sulfur forms at different positions of the coke during pyrolysis were determined. The results show that the desulfurization rate of coke obtained at 500 °C gradually increases with the migration direction of volatiles. The sulfur-containing gases generated at the bottom of coke is difficult to escape due to the resistance of coke at the top, so the secondary reaction with coke in the bottom causes the increase of total sulfur content. In addition, the thiophenic sulfur content at the top is lower than that of bottom or center. This indicates that the volatiles generated by the decomposition of thiophenic sulfur at the top more easily escape from coke than that of bottom or center. When the pyrolysis temperature continues to rise, the desulfurization rate decreases with the migration direction of volatiles. The sulfoxide at the top can be converted into sulfonate and sulfate, so the sulfoxide content at the top is less than that in the bottom while the sulfonate and sulfate content is the highest at the top than that in the bottom. High temperature is promotive to the decomposition of organic sulfur or inorganic sulfur, and to promote the combination of the –OH groups or -H groups and sulfur radicals, which results in release of SO2 or H2S. The various sulfur forms perform different migration pathway with temperatures from the bottom to the top of the coke.