Effect of water vapor on sulfur migration during pyrolysis of semi-coke in oven for dry distillation

The semi-coke used in metallurgical production will be affected by the water vapor generated by wet coke quenching and the combustion of returned furnace gas in the oven for dry distillation.In order to clarify the effect of water vapor on the pore structure and sulfur content of semi-coke, a low-rank coal was selected for pyrolysis experiments under different pyrolysis conditions, the effects of different final pyrolysis temperatures (500-900 ℃) and water vapor input rates (0, 20%, 40%, 60%) on the sulfur content in low-rank coal pyrolysis products were investigated. The change of pore structure and total sulfur relative content of semi-coke was analyzed by specific surface and pore size analyzer and sulfur determination instrument, and the occurrence form of sulfur-containing functional groups on the surface of semi-coke was analyzed by X-ray photoelectron spectroscopy. The experimental results showed that in an inert atmosphere, when the temperature becomes the limiting link, the sulfur removal effect is better at medium and low temperatures (500-700 ℃), and the further increase of the final pyrolysis temperature is not conducive to the sulfur removal. When water vapor is introduced into the pyrolysis process, at low temperature (500-600 ℃), a small amount (20%) of water vapor desulfurization is significant, and a large amount (40%-60%) of water vapor is not conducive to desulfurization. At this time, different forms of sulfur will be transformed into each other, and water vapor promotes sulfur to precipitate mainly in the form of gas phase. Under higher temperature conditions (700-800 ℃), although water vapor promotes the development of pore structure, sulfur cannot be precipitated in the form of gas phase. Under the combined action of water vapor and polycondensation, sulfur is mainly converted in the solid phase, resulting in a decrease in desulfurization rate.Under the condition of high temperature (900 ℃), water vapor seriously destroys the pore structure and makes sulfur mainly precipitate in the form of gas phase, which significantly improves the desulfurization rate, but it will generate some inorganic sulfur and organic sulfur which is difficult to decompose. Therefore, in the process of producing semi-coke in the oven for dry distillation, the production process in the middle and high temperature region should be strictly controlled, the entry of water vapor should be avoided, and the water vapor addition content in the low temperature region should be controlled below 20 % as far as possible.