A rapid method for determining the R70 self-heating rate of coal

A rapid, simple method was developed for the determination of R70 self-heating rate of coal. The coal samples were tested under adiabatic and programmable temperature conditions, separately. It indicates that it is a linear relationship between the differential value of oxygen concentration at 70 °C under a programmable heating condition (ΔCO2,70) and the adiabatic R70 self-heating rate. This linear relationship can be described by a fitted trendline equation R70=0.68504ΔCO2,70+0.12098. So the R70 can be determined by testing the value of ΔCO2,70. For most coals, the testing processes of ΔCO2,70 need a time less than 1.5 h. A new evaluation method for the propensity of coal to spontaneous combustion was also proposed from previous R70 method. Based on the value of ΔCO2,70, a coal with a ΔCO2,70 value below 0.55% is considered to be low risk, 0.55-1% medium risk, higher than 1% high risk. The study will be helpful for more widely and convenient use of R70 self-heating rate.