Study On The Characteristics Of Sulfur Migration In Coal Pyrolysis Under Different Atmospheres

In the process of coal utilization,sulfur in coal will become harmful gases such as SO₂ and H₂S,causing serious pollution to the atmospheric environment.The characteristics of sulfur migration during coal pyrolysis was investigated to reveal the important theoretical and practical significance of different factors influencing the sulfur migration laws for developing high-efficiency desulfurization technology and realizing the efficient and clean coal utilization.(1)This paper investigated the sulfur migration characteristics of Guizhou high-sulfur coal and Ningdong coal during rapid pyrolysis process under different pyrolysis atmospheres(nitrogen atmosphere:100%N₂,lean-oxygen atmosphere:5%O+95%N₂,weak reducing atmosphere 20%H₂+80%N₂)and pyrolysis temperatures(300°C?800°C).The main contents are as follow:(2)The total sulfur content of Guizhou high sulfur coal and Ningdong coal is4.09%and 0.58%respectively.Based on the X-ray photoelectron spectroscopy(XPS)method,six forms of sulfur in the two coal samples including pyrite sulfur and sulfide.Sulfur,thiophene sulfur,sulfoxide sulfur,sulfone-type sulfur and sulfate sulfur were obtained.Organic sulfur was the main existence state of sulfur.The content of organic sulfur in Guizhou high-sulfur coal and Ningdong coal were 68.77%and 52.85%,respectively.Thiophene sulfur in high-sulfur coal accounted for 51.90%,and sulfoxide sulfur in Ningdong coal accounted for 19.73%.In addition,Fourier infrared spectroscopy(FTIR)was used to obtain the structural characteristics of the surface functional groups of coal samples.The results showed that the types and contents of aromatic structure and oxygen-containing functional groups on the surface of Guizhou high-sulfur coal were more than those of Ningdong coal.(3)Under the nitrogen atmosphere,high-sulfur coal and Ningdong coal reached the maximum desulfurization rate at 600°C,which were 38.00%and 47.99%,respectively.The higher pyrolysis temperature cannot effectively promote the precipitation of sulfur in the coal.Under the lean-oxygen atmosphere,high-sulfur coal reached the maximum desulfurization rate of 44.62%at 500°C.However,due to the massive generation of thiophene sulfur,higher temperature will reduce the desulfurization rate of high-sulfur coal.Sulfur can be effectively removed in the pyrolysis process,and its desulfurization rate increased with the rising temperature,and the final desulfurization rate reaches 57.07%.The weak reducing atmosphere can promote each sulfur content in high-sulfur coal.The cracking of the components increased the maximum desulfurization rate to 49.32%,which was higher than the other two atmospheres,and the maximum desulfurization rate reached 49.32%.While the maximum desulfurization rate of Ningdong coal in a weak reducing atmosphere was 51.04%,lower than that in the lean-oxygen atmosphere.(4)When pyrolyzing in different atmospheres,the temperature has a great difference in the influence of the relative content of various forms of sulfur in the two coal chars.The overall performance is:the relative content of various forms of sulfur in the high-sulfur coal char is more likely to change greatly with the increase of temperature.With the increase of temperature,the content of thiophene sulfur in high-sulfur coal coke always increases,while the content of sulfone type sulfur continues to decrease.After pyrolysis treatment,most of the sulfur in Ningdong coal can be removed well,while the removal effect of sulfur in high-sulfur coal is not obvious.(5)Under the lean-oxygen atmosphere,the highest yield of high-sulfur coal at the temperature range of 300°C to 500°C was only 0.30 m L/g,and the H₂S yield of Ningdong coal was only 0.21 m L/g.When the temperature reached 600°C,the H₂S yield of high-sulfur coal rose to 2.02 m L/g,and the H₂S yield of Ningdong coal rose to 0.53 m L/g.Under the nitrogen atmosphere and a weak reducing atmosphere,the H₂S yield of the two coals can be divided into three stages according to the temperatures.In the low yield section of 300°C?400°C,H₂S yield kept at a low level.In the rapid rise section of 400°C?600°C,the increasing temperature showed a very obvious promotion effect on the H₂S yield.In the yield decrease section of600°C?800°C,the increasing trend of H₂S yield of high-sulfur coal slowed down,while the H₂S production rate of Ningdong coal showed a downward trend.Compared with the lean-oxygen atmosphere,pyrolysis in a nitrogen atmosphere and a weak reducing atmosphere can reduce the initial temperature of the rapid increase of H₂S section yield to 400°C.