Optimization of heating rate of crossing point temperature apparatus

Abstract

A further understanding of the heating rate of crossing point temperature apparatus was obtained by investigating the crossing point temperature (CPT) of different ranks of coal. The test was carried out using a designed experimental system for self-heating of coal. 4 gm. of coal sample of -100+200 mesh size were put into a copper reaction vessel place inside the spiral glass tube. The spiral glass tube is attached at the center of the furnace equipped with temperature controller. The temperature controller increases the temperature at different heating rates. Oxygen was permitted to flow into the coal reaction vessel at 80ml/min. The furnace temperature and the coal temperature were monitored by a temperature logger. The results indicate the CPT values affected by coal rank, moisture, sulphur and the experimental conditions. Higher rank coal show higher CPT values. A high moisture content causes a delay phenomenon during the self-heating of the coal. Drying at 40˚C decreases the effects of moisture. The flow rate of oxygen, and the heating rate of the furnace, also affects the spontaneous combustion of coal. The most appropriate experimental conditions for coal samples of a given weight and particle size were determined through contrastive analysis. For the evaluation of optimum heating rate a number of coal samples were tested at different heating rates (0.8, 1, 1.6 and 2˚C/min.) keeping the other experimental condition same or nearly same and comparing the obtained result with the standard heating rate (1˚C/min.) taking into account the degree of proneness of coal sample to spontaneous heating the optimum heating rate is decided. Correlation has been drawn between proximate analysis parameters and CPT. It is seen that CPT decreases with increase of moisture, volatile matter and fixed carbon. On the other hand it increases with increase of ash. It was also found that CPT at 1˚C/min. has better correlation with proximate analysis parameter than 2˚C/min (optimum heating rate).