Experimental Study On Low Temperature Pyrolysis Of Lignite, Combustion Characte-Ristics And Slurryability Of Semicoke

With the increase of energy demand, the consumption of high rank coal such as anthracite and bituminous coal rises by a big margin, leading to high rank coal supply tension. In this situation, low rank coal, such as lignite, is playing more and more important role in solving the problem. Using lignite efficiently and cleanly is becoming increasingly significant to ease the tension of high quality coal and optimize the structure of energy industry.Lignite, as a low rank coal, has high moisture, high volatile content and low calorific value. It’s hard to store because it’s quite easy to be oxidized and spontaneous combustion. The unit energy cost of transport is high while the direct combustion efficiency is low. It’s quite difficult for lignite to prepare for coal water slurry (CWS) with a high concentration and low viscosity. Generally speaking, there many problems and adverse factors for direct lignite utilization. Therefore, upgrading is a necessary step in lignite utilization.Low temperature (450℃～650℃) pyrolysis was used to treat lignite in this paper. Pyrolysis temperature and retention time has been chosen as variable to observe the change of coal characteristics of lignite after modification, investigate the effect of pyrolysis temperature and retention time on lignite characteristics, tar component, gas composition, and the production rate of various components. The combustion characteristics and slurry properties of lignite semi-coke were studied in this paper in order to provide some references for the utilization of lignite semi-coke. The data were analyzed by thermal analysis method to evaluate combustion characteristics of samples. Raw lignite and semi-coke were prepared for CWS to investigate the slurry ability of lignite and semi-coke. The effects of pyrolysis temperature and retention time on slurry ability of semi-coke were studied.The result shows that low temperature pyrolysis can effectively remove the inner moisture of lignite, promote the oxygen group to decompose, reduce its volatile content and improve its coal rank. Modified lignite tends to be similar with high rank coal. High pyrolysis temperature makes this tendency be more obvious. After modification, the ignition temperature and activation energy of semi-coke increased, while combustion characteristic index and reduced, which means the thermal stability of semi-coke was improved after pyrolysis treatment, so as to the spontaneous combustion of lignite has been effectively inhibited.The slurry experiment shows that both lignite and semi-coke CWS present pseudoplastic fluid characteristics with shear thinning. The solid concentration of semi-coke CWS was effectively increased with improving pyrolysis temperature. The maximum solid concentration was increased from44.31%to a maximum of66.78%. High pyrolysis temperature is beneficial for the fluidity and stability of semi-coke CWS. Retention time has no significant influence on lignite pyrolysis, combustion and slurry performance of semi-coke.