Ultrasonic Effect on the Extraction of Ash-free coal from Low Rank Coal

Extraction was performed to prepare ash-free coal from low rank coal under the temperature of 200-430 degrees C and initial pressure of 0.1MPa. Three kinds of coal samples with different rank were used and N-methyl-2-pyrrolidi-none(NMP,polar), 1-methyl naphthalene(1-MN, non-polar), Light Cycle Oil(LCO, non-polar) were used as solvents. Results showed that higher extraction yield could be obtained with NMP than with 1-MN and LCO, but the ash concentration shows minimun in the case of 1-MN. Three operation modes were compared, that is, idle, agitation and ultrasonic extraction mode. From the results, it was found that the extraction yield and ash concentration were 70.09% and 1.03% under the agitation mode, 80.7% and 0.76% under the ultrasonic operation mode respectively in the case of NMP used at the temperature of 350 degrees C. Similar results were obtained with 1-MN. Effect of ultrasonic on the extraction was estimated as 15-20% increase in the yields and 26% reduction in the ash concentration.