Adiabatic testing procedures for determining the self-heating propensity of coal and sample ageing effects

An adiabatic testing procedure for determining the self-heating propensity of coal has been evaluated using New Zealand coals. Repeatability of the self-heating rate (R70), obtained by the method, is less than ±5% of the average value for tests performed consecutively over 3–4 days. For longer time periods, even using samples under controlled storage, the self-heating rate value decreases noticeably due to pre-oxidation effects. This pre-oxidation effect can be described by the equation R70(t)=atb, where t is the time in days, b a constant dependent on storage method and particle size and a the R70 value of fresh coal. When stored samples are used for analysis, knowledge of this relationship can be used to extrapolate a fresh coal R70 value by doing repeated tests over time.