Experimental Investigation Of Coal Pyrolysis And Sulfur Transformation At Intermediate Temperature Of Coals From Western China

The pyrolysis of coal is an important process, is the essential first step in the carbonization, gasification, and combustion of coal. Coal pyrolysis is an effective method for sulfur removal before reaction. A better knowledge of the thermal decomposition of coals is necessary in order to assess their potential for being used in certain coal utilization processes. The bituminous coal sampeles from weatern China were treated with a fixed-bed reactor and a thermogravimetric analyzer at the temperature varied from 400 to 800℃.The pyrolysis kinetic parameters with the method of single reaction model and the distributed activation energy model (DAEM) were calculated. The results showed that a general activation energy range of 50-200 kJ-mol-1 was suggested for the coal pyrolysis process of MLT coal samples. Conditions of pyrolysis have a great influence on the product distribution. Temperatuere dependence was shown for different kinds of coal. The thermogracimetric analysis showed that curves of thermalgracimetric and differential thermogravimetric shifted toward the high temperature region with the increase of heating rate.The influence of temperature on the release of products was investigated. Under the atmosphere of argon (Ar), char is the main product for all temperatures. As temperature increase, the yield of gaseous increases and that of char product decreases, while the highest yield of tar was acquired at the temperature between 600 and 650℃. The yield of each gaseous product increase with the temperature increasing. Main components of gaseous product were hydrogen (H2), methane (CH4), carbon monoxide (CO) and carbon dioxide (CO2) while the content of nitrogen (N2), ethylene (C2H4), ethane (C2H6) and hydrogen sulphide (H2S) was small compared with the others. The volume fraction of H2 and CO increased with the raising temperature, while CH4、 CO2、C2H6、C2H4、N2 and H2S decreased. With the existence of H2 in the carrier gas, the yields of hydrocarbon gaseous products and tar increased obviously. Compared with the yield of tar at the atmosphere of argon, the yield at the hydrogen atmosphere increased 4.3%.The research showed that the characteristic of coal had a great influence on the release of products. Experiments of four Chinese western coals were performed on a fixed-bed. The results showed yield of hydrocarbon gaseous products increased with the mass ratio of H/C, while the yield of CO and CO2 increase with increasing mass ratio of O/C.Thus, for coals with different characteristics, it is convenient to control diversity reaction conditions and process routes to meet the purpose of efficient utilization of different coals.In this work, the sulfur transformations during pyrolysis have been also experimentally inveatigated. The results showed that the mainly existence form of sulfur is pyrite and organic sulfur. Pyrite (FeS2) in coal, during pyrolsis, transforms into ferrous sulphide (FeS) and leads to the formation of H2S. Some H2S react with the organism and form organic sulfur, such as thiophene. The release of sulfur-containing species was highly dependent on temperature and the inherent alkali mineral content of the coal. During pyrolysis, the desulfurization kept stable above 650℃. The desulfurization of MLT above 650℃ is about 46%. The desulfurization decreased with the existence do alkaline mineral. With the purpose of desulfurization by pyrolysis,650℃ is recommended. Different methods should be adapted according to the existing form of sulfur.