Study On Hydro-Pyrolysis Of Shuicheng Lignite In Fixed-bed Reactor

The present energy situation of rich coal and lack of oil and gas forced us to optimize the use of coal. As a low-rank coal, lignite has low carbon content and high oxygen content, which leads to an unfavorable use of direct combustion and needs to develop high-effective thermal conversion process. Pyrolysis is regarded as a promoting process to utilize lignite, in which tar, char and gas are major productsas raw materials or fuels. In this paper, we studied the pyrolysis of Shuicheng lignite on a self-designed fixed bed reactor and especially focused on its hydro-pyrolysis.Firstly,the basicpyrolysis characteristics and features ofShuichenglignitewereanalysed. Then the isothermal mass loss characteristicsexperiments were conducted on the macro-TGA and the completingpyrolysis time at different temperature was obtained as well as the char yield. Furthermore, the influence of reaction temperature on pyrolysis products distribution andcomponents of products was investigated. The impact of hydrogenconcentration, gas residence time and particle size were also considered. Thehydro-pyrolysis characteristics and mechanism of coal pyrolysis were clarifiedas possible.The main results wereas follows:The isothermal mass loss experiments on Micro-TGA showed that the higher the react temperaturewas, the faster the pyrolysis ratewas. Based on the quality changing rate per minuteless than 5%, the completing pyrolysis timeat700 °C wassupposed to be 7minutes. The char yield decreased with the increasing temperature, and it was 52.9% at700 °C.The react temperature was one of the most important factors influencing products of the Shuicheng lignite pyrolysis, and the tar yield reachedthe maximum at 700 °C both inN2 atmosphere and 15% H2 atmosphere. The increase of hydrogen concentrationledto the increase of tar yield monotonously. With the experimental range of gas residence time(6-16 s), the increasing gas residence time increasedthe tar yield.The particle size showed little impact on the tar yield, and the large particlewas inclined to against the formation of tar.The lignite pyrolysis process was mainly composed of firstly reaction and the secondary reaction. Hydrogenation couldincrease thetar yield, because the provided H free radicals changed the secondary reaction and the synthetic function promotedthe formation of tar. The increasing H partial pressure could enhance the hydrogenation synthetic function. In the hydrogenation CO2 participatedin the reaction, and with the increase of hydrogen gas there was more BTX(benzene, toluene and xylenes) and PCX(phenol, cresols and xylenols), as the result of the transformation of oxygen functional groups.