Preparation Of Char Water Slurry From Lignite Char

Coal-water slurry (CWS), as a significant technology from clean coal utilities in China, has been used in coal gasification, combustion instead of oil and other fields for its less environment pollution, high efficiency, low cost and easy process. Generally, the raw material for CWS in industry is high rank coal. Lignite, for its high maximum moisture holding capacity(MHC), oxygen-bearing functional groups and other characteristics, is limited in the preparation of CWS. The lignite char, obtained from pyrolysis at low temperature, with low inherent moisture and hydrophilic groups is preferable to prepare char-water slurry. This paper was aimed to prepare lignite char water slurry (LCWS) from three kinds lignite chars with fixed bed technology, so as to extend the materials for coal water slurry and the utilities of lignite. The main results are shown as follows:The packing efficiency and particle size distribution of lignite char particles are important factors in the preparation of LCWS with high slurry concentration and well rheology. The effect of particle size distribution about lignite chars pyrolyzed at different temperature(340℃,420℃,500℃,580℃) to the properties of LCWS was investigated. The high quality LCWS can be obtained with the lignite char from pyrolysis at 420℃through 120 min grinding of 280 g lignite char. And this grinding condition is also feasible to other lignite chars.The effect of three anionic dispersants, sodium lignosulphonate (SL), sodium humicsulphonate (SH) and naphthalenesulfonate-formaldehyde condensate (NSF), on the properties of LCWS were investigated and the optimum mixture of the dispersants was obtained. The results indicate that NSF and SH have the similar effect on the properties of LCWS and are more effective than SL in decreasing apparent viscosity, but SL has better static stability on LCWS than both them. The mixture of SL and SH in the ratio of 1:1 and the dosage of 0.4 wt%(air dry basis coal) was effective for preparing LCWS with good apparent viscosity and static stability. The best static stability of LCWS was demonstrated 110 days. The mixed dispersant was also feasible to other lignite chars.To decrease the apparent viscosity of LCWS, the effect of pyrolysis methods and ultrasonic treatment on the properties of LCWS were investigated. The results indicated that the char obtained by the flash pyrolysis with solid heat carrier technology was more appropriate than that by temperature-programmed fixed-bed pyrolysis technology and that by flash pyrolysis in fixed-bed. The apparent viscosity decreased obviously when LCWM treated by ultrasonic treatment for 1 min.