Form Sulfur Transformation During Coal Pyrolysis At Various Gas Atmospheres

In this paper, the sulfur release characteristic of five bituminous coals undergoing the process of the temperature programmed pyrolysis at the H2, N2,CO and air atmosphere respectively were studied used the fixed-bed quartz reactor, and the quantity of sulfur in the pyrolysis gas and char were measured carefully used the coulometric titration apparatus and chemical analysis. Based on the comparison of the variation of the sulfur forms in the coal before and after pyrolysis experiments, the experimental results have been listed as follow: The product distribution regularities of coal pyrolysis were summarized.The product distribution of pyrolysis and hypyrolysis of coal was not significantly different, while the low-temperature oxidation of relative content of volatile matter increased in varying degrees. Temperature is the main factor to influence the coal pyrolysis. Increases with temperature, the weight loss rate of all the atmosphere increases.The migration regularities of gas phase sulfur of coal during pyrolysis were summarized.(1) Improving the final temperature and using reductive atmosphere can promote the release of volatile matter, thus contributing to the escape of sulfur in gas phase. The relationship between volatile matter and total sulfur in gas phase of coal pyrolysis process was related to the rule of form sulfur transformation.(2) Peaks of sulfur in the gas phase during pyrolysis process of coal separately in two ranges: the first peak at about 300℃, and the second peak at 600~750℃. The first peak should belong to the unstable organic sulphur, is aliphatic mercaptan, polyethylene sulfide, aromatic sulfide and disulfide. The second peak should belong to be part of a stable sulfur organic sulfur is pyrite, diaryl disulfide, and thiophene sulfur compounds.(3) When the relative content of total sulfur gas escaping less than or equal to the relative content of volatile matter releasing, the content of sulfur in coke is greater than or equal to the total amount of sulfur in raw coal, And when the relative of the total sulfur gas escaping is greater than or equal to the relative content of volatile matter, the content of sulfur in coke less than or equal to the total amount of sulfur in raw coal.The migration regularities of solid phase sulfur form of coal during pyrolysis were summarized.(1) The migration regularities of sulfur form during low-temperature pyrolysis process of coal were summarized. The pyrite sulfur transform was related to the atmosphere, that the pyritic sulfur will easily react with the reductive atmosphere and air atmosphere under the pyrolysis process, led the the transform of pyrite will more easily under reductive atmospherethan air atmosphere. The organic sulfur transform was related to the atmosphere, that the organic sulfur will easily react with the reductive atmosphere and air atmosphere under the pyrolysis process, led the the transform of pyrite will more easily under air atmosphere than reductive atmosphere.(2) The migration regularities of sulfur form in the pyrolysis process of coal were summarized. The pyrite sulfur has begun to decompose at 400℃, and the reductive atmosphere including CO and H2 can promote its decomposition. While decomposition of pyrite sulfur completed at 600℃. (3) Under 600℃, the different types of organic sulfur in the coal will causative different decomposition effects. When the temperature was more than 800℃, the decomposition of organic sulfur can be promoted only under the H2 atmosphere. The sulfur in the gas phase is mainly from thermal decomposition of the organic sulfur of coal, and has not affected nearly with the decomposition of pyritic sulfur.(4) The initial decomposition reaction temperatures of ferrous sulfate, copper sulfate, magnesium sulfate and calcium sulfate are about 500℃, 600℃, 850℃and 1000℃respectively. Added 17% (wt) Fe2O3 can significantly improve the conversion rate of CaSO4 and reduce its decomposition onset temperature, while adding 17% (wt) CuCl2 is not obvious. The iron oxide and activated carbon can used as co-reactant promote the thermal decomposition of calcium sulfate at 1000℃to mainly form the calcium sulfide, but the effect of iron oxide should be under reductive atmosphere, however the activated carbon can affect under the both the reductive and the inert atmosphere.