Preparation Of Semi-coke Water Slurry Using Semi-coke From Pyrolysis Of Low Rank Coal

With the development of the economy and increasing demand of energy in China, the exploitable reserve and annual production of high rank coal, i.e., bituminous coal and anthracite, has substantially declined as a consequence of enormous coal consumption in recent years, thus the supply and demand of high rank coal is no longer balanced. To ensure the energy security, the efficient utilization of low rank coal including brown coal and long flame coal becomes an increasingly important concern for China. Semi-coke is the solid product of low rank coal pyrolysis, and there are two types of semi-coke categorized by aggregation state: lumpy semi-coke can be used as a raw material for gasification to produce methanol, fertilizer, natural gas, etc., while the utilization of semi-coke is a practical issue. Given the desirable reactivity of semi-coke from which the semi-coke water slurry is likely to be prepared, semi-coke has the potential to be a suitable raw material for gasification.In this dissertation, the slurry-ability of semi-coke derived from Inner Mongolia lignite and Shaanxi long flame coal has been studied. The additive(DCS-M) for semi-coke water slurry has been developed, and its dispersion mechanisms have been explored. The main conclusions are as follows:The integrated experimental apparatus for low temperature coal pyrolysis was employed to simulate the pyrolysis process of low rank coal in externally heated upright carbide furnace. The experimental results demonstrate that with the increase of pyrolysis temperature, the yield of tar initially increases and then falls down, the yield of semi-coke decreases significantly. The insight into the proximate analysis of resulting semi-coke indicates that the content of fixed carbon and ash increase and the volatile content decrease gradually with increasing pyrolysis temperature. The investigation of ultimate analysis sheds light on the migration behavior of various elements in terms of the low rank coal pyrolysis. The relative percentage content of carbon increases as pyrolysis temperature increases, while the hydrogen content in semi-coke decreases with increasing pyrolysis temperature. Nitrogen content in semi-coke increases first and eventually declines as pyrolysis temperature rise. The sulfur content seems insensitive to pyrolysis temperature.The slurry forming characteristic of the semi-coke derived from the pyrolysis of low rank coal was carefully explored with the help of slurry-ability experiment. The mathematical model of slurry-ability of the semi-coke attempting to correlate slurry-ability with the composition property of corresponding coal was established using Origin software. The results demonstrate that the relationship between pyrolysis conditions and slurry-ability of semi-coke varies with coal type. Furthermore, there is an apparently negative correlation between air dried basis moisture of the semi-coke(Mad,sc) and the slurry ability, Mad,sc therefore could be viewed as the key factor to evaluate the slurry ability of a specific coal. It’s also found that the volatile content as well as C/H ratio of the semi-coke is negatively correlated with slurry ability, hence these two factors are considered as secondary factors. The mathematical model quantitatively predicting the slurry ability of the semi-coke has been concluded as following: φ=72.37-0.067[Vad]-1.22[Mad]-0.0064[C/H], in which the multiple correlation coefficient was R=0.9057. The availability of this model was confirmed by the slurry-ability experiment of semi-coke from Yunnan lignite, Gansu long flame coal and Xinjiang lignite.The technological conditions for preparing additive(DCS-M) were determined through orthogonal experiment. The optimum adding amount(0.4%) of the additive for semi-coke water slurry preparation was determined through slurry performance experiment. Meanwhile, the highest slurry concentrations corresponding to Shaanxi semi-coke and Inner Mongolia semi-coke were increased from 65.3%, 63.4% to 66.3%, 64.5%, respectively. The slurryability of DCS-M proved to be much better than that of DCS, NSF and NDF.The adsorption experiment and infrared spectrometry analysis of DCS-M showed that the mechanism behind the favorable dispersion of DCS-M might be explained by the similarity of some specific functional groups contained in both semi-coke and DCS-M, which is mainly attributed to the hydrophobic functional group(=CH-、methylene、aromatic ring) and the hydrophilic functional group(phenolic hydroxyl group、sulfonic acid root).