Experimental investigation of thermal effect in coal pyrolysis process

The thermal effects of five coal types' pyrolysis processes at heating rates of 5, 10, 15, 20, and 30 °C/min in the temperature range of 30–1000 °C were systemically investigated by thermogravimetric - differential scanning calorimetry. The experimental results show that coal pyrolysis process can be roughly divided into four stages, namely the drying and dehydration stage S1, the degassing stage S2, the pyrolysis stage S3, and the polycondensation stage S4. S1, S2, and S3 are endothermic and S4 is exothermic. For a given coal, the temperature at which the process shifts from the endothermic stages (S1 + S2 + S3) to the exothermic stage (S4) increases with increasing heating rate. The heat absorbed in endothermic stages keeps invariable basically, while heat released in exothermic stage decreases with increasing heating rate. The entire pyrolysis process is exothermic when the heating rates are lower than 10 or 15 °C/min, and endothermic at heating rates higher than 15 or 20 °C/min. The temperature corresponding to the peak in the weight loss curve does not correspond to that in the heat flow curve. Therefore, the characterizations of the coal pyrolysis reaction process by weight loss and heat flow are inconsistent with each other.