Investigation On The Sulfur Occurrence And Transformation During Pyrolysis Of The Flotation Fraction Of High Organic Sulfur Coals

High-quality coking coal plays a crucial role in the blast furnace smelting industry because of its good caking and coking properties.However,with the large-scale exploitation and long-term unreasonable utilization of coal resources,the reserves of high-quality coking coal resources have declined sharply.Meanwhile,the proportion of high sulfur coking coal has increased gradually.The main form of sulfur in these high sulfur coals is organic sulfur,which is difficult to be removed by coal preparation.If the problem of sulfur in coking coals can be solved the amount of high sulfur coking coal can be increased in the process of coal blending coking,which can effectively reduce the cost of coal blending and improve the efficiency of coking enterprises as well as protect high quality coking coal resources.It has important practical significance for the sustainable development of coking industry.Experimental and industrial practices show that it is technically feasible to use high sulfur coal partly to replace high quality coking coal for coking,but there is a problem that the amount of high sulfur coal is limited.With the development and application of coal-rock blending theories,different maceral in high-sulfur coking coal are separated and enriched by means of maceral separation technology,the active components with better caking property are used for coal blending coking.On the premise of considering coking property,the sulfur content in coke will not exceed the standard.Consequently,an important means to increase the blending quantity of high sulfur coking coal will be obtained.As a kind of heterogeneous organic rock,the distribution and occurrence of organic sulfur in different maceral of high organic sulfur coal are different.Therefore,based on the density difference of coal maceral,the organic part of coal can be separated from minerals by heavy medium separation,which can separate inorganic and organic sulfur and the effect of inorganic sulfur and minerals on the transformation of organic sulfur during pyrolysis can be effectively eliminated.Accordingly,the occurrence and thermal transformation behavior of sulfur in the flotation fraction of high organic sulfur coals were investigated.It is helpful to accurately understand the whole situation of coal pyrolysis and desulfurization,to understand and master the mechanism of the thermal transition of organic sulfur in a deeper level.It is of great theoretical significance for the application of high organic sulfur coking coal during coal blending coking.In this paper,two kinds of high organic sulfur coking coal with different sulfur contents were selected and separated into five fractions with different density ranges by heavy medium separation.The distribution and occurrence of sulfur in different fractions were investigated by X-ray photoelectron spectroscopy?XPS?and solid state ¹³C nuclear magnetic resonance(¹³C NMR),the fixed-bed pyrolysis reactor and mass spectrometry?Py-MS?were used to investigate the release characteristics of sulfur-containing gases during pyrolysis of fractions.And the relationship between desulfurization efficiency and thermal transition behavior of sulfur was investigated.These practices provide a theoretical basis for the directional removal and control of sulfur during coal blending coking with high sulfur coal.The main research results are as follows:?1?The yield of fractions decreases with the increase of the density.The yield of D1?<1.30 g/cm³?is the highest and that of D4?1.40-1.45 g/cm³?is the lowest among the two coals.The yield of the fractions of Liuwan coal?LW?varies little,and the distribution of organic matter in the fractions is relatively uniform,the variation ranges of in Linfen coal?LF?are larger,and its organic matter is mainly enriched in LF-D1.As the increase of density of coal fractions,the proportion of aliphatic carbon(f_al)decreases,the aromatic carbon?f_a?increases,and the molecular arrangement of organic matter is regular and the structure become more compact.The high density fraction?D5?has higher degree of aromatization.The weight loss and the maximum devolatilization rate decreases with the increase of density of coal fractions.?2?As the increase of density of coal fractions,the sulfur content of the fractions decreases firstly and then increases.The sulfur content of D1 is the highest and that of D4 is the lowest.Moreover,the distribution and occurrence of sulfur in different fractions are significantly different.Organic sulfur is mainly distributed in the low density fraction?D1?and exists in the form of thiophene,while inorganic sulfur is mainly distributed in high density fraction?D5?and exists in the form of pyrite.Compared with raw coal,the proportion of aliphatic carbon in D1 increases,which increases the content of aliphatic sulfides such as mercaptans and thioethers in this fraction.These aliphatic sulfides are easily decomposed during pyrolysis,resulting in the better desulfurization efficiency of D1 compared with raw coal.The desulfurization efficiency of LW-D1 and LF-D1 is increased by 4.0%and 1.4%,respectively.The aromatization degree of the D5 is relatively high,and the thermal stability of organic sulfur is higher.It is not easy to decompose during pyrolysis,the desulfurization efficiency of D5 is lower.?3?The formation temperature of H₂S?300 ^oC?during pyrolysis of D1 is the lowest,the release temperature range is the widest and H₂S is still generated above 700 ^oC.On the one hand,the aliphatic organic sulfur in D1 is easy to decompose and produces H₂S at lower temperature;on the other hand,thiophene sulfur in D1 decomposes to produce H₂S at higher temperature,which widens the temperature range of H₂S release.The difference pyrite sulfur content and mineral composition results in significant differences in sulfur gas release and desulfurization efficiency during pyrolysis of LW-D5 and LF-D5.The effects of hydrogen content gases?H₂,CH₄?and oxygen content gases?CO,CO₂?on sulfur content gases are different during pyrolysis of fractions.The release temperature range of H₂S is different from that of H₂,but basically coincides with that of CH₄.The release of H₂S increases with the increase of CH₄ release,which indicates that hydrogen free radicals generated during pyrolysis of aliphatic side chains can induce and activate sulfur content groups,and promote the release of H₂S,which is also one of the reasons for the higher desulfurization efficiency of D1.