Production of low ash coal by thermal extraction with N-methyl-2-pyrrolidinone

Present study was conducted for the purpose of producing low ash coal from LRC (low rank coals) such as lignite and sub-bituminous coal through thermal extraction using polar solvent. Extraction from bituminous coal was also investigated for comparison. NMP as a polar solvent was used. The ratio of coal to solvent was adjusted as 1: 10. Experimental conditions were established which include the extraction temperature of 200–430 °C, initial applied pressure of 1–20 bar and extraction time of 0.5–2 hr were used. Extraction yield and ash content of extracted and residual coal were measured. The extraction yield increased with the increase of extraction temperature, and the ash content of extracted coal decreased below 0.4% at 400 °C from the raw coal samples that have the ash contents of 4–6%. According to the analysis of experiments results, fixed carbon and calorific value increased, and H/C and O/C decreased.