A mathematical model of R 70 self - heating test for the propensity of coal spontaneous combustion

The R70 self-heating test has been used as one of the major laboratory methods for testing the intrinsic properties of coal that influences its propensity for spontaneous combustion. The R70 test is conducted in an artificially created adiabatic environment so that only and all the heat generated by the coal sample is used to prompt the oxidation process and to increase the temperature of the sample. The key to create such an artificial adiabatic testing environment is to eliminate any heat exchange between the coal sample in the testing container and the outside environment through a precise temperature control. Even a minor of amount of heat exchange in the testing duration could produce unreliable testing results, especially for the coals having low propensity. Based on the law of energy conservation, a mathematical model has been developed to quantify the effects of any imperfection of the testing adiabatic environment on the testing results for a R70 self-heating test setup and the testing procedure. The model considers the heat losses and gains caused by coal moisture, inlet oxygen flow and exhaust air, conduction and convection between coal and outside, and heat diffusion in the sample. The mathematical model can be applied to correct the testing results in terms of the heat generation rate at a given temperature cause by the system imperfection. Coupled with the experimentally determined parameters such as the specific heat of coal, heating value of various combustibles in the coal, etc. the accuracy of the R70 methods could be greatly improved. The mathematical model also allows the determination of heating value, activation energy and pre-exponential factor from the experiment-generated temperature development curves.