AN IMPROVED METHOD OF PRESERVING AND EXTRACTING MINERAL MATTER FROM COAL BY VERY LOW-TEMPERATURE ASHING (VLTA)

Low-temperature ashing (LTA) has been used to extract mineral matter from coal. The problem has been that the ashing temperature could not be measured and consequently the ashing processes could not be controlled. The ashing temperature in this study was measured by thermographs, which indicate the highest temperature reached during ashing. Some of the disadvantages of LTA were shown to be due to the ashing temperature being too high (150-300-degrees-C). It was also confirmed that the mineral matter, especially sulphide, usually oxidizes and some is lost as SO2. To solve these problems, a new method was developed, very low-temperature ashing (VLTA), to preserve and extract mineral matter from coal without loss or damage of the original phases. It was shown that to obtain an 'in situ' ash, the ashing temperature should not exceed 60-70-degrees-C, regardless of the rank of the coal. To decrease the ashing temperature, the oxygen was diluted with helium to decrease the reaction rate. To achieve this very low temperature, the ashing atmosphere (oxygen/helium ratio) must be adjusted for coal rank and sulphur content.