Model predictions and experimental results on self-heating prevention of stockpiled coals

Abstract

The spontaneous combustion of coal stockpiles is a serious economic and safety problem. This phenomenon is herein analysed using a TNO-model modified to predict the spontaneous heating behaviour of coal piles built with “Mezcla”, a mixture of low rank coals from Teruel (Spain). The simulation carried out with the mathematical model for this coal showed that the pile porosity or voidage and wind speed play an important role, although voidage is decisive and controls the effect of the wind velocity. To reduce the negative effects of both factors, five test coal piles (2000–3000 t) were built and several measures were applied to four of them: periodic compaction, use of a low angle slope, protection of the stockpiled coal with an artificial wind barrier and covering it with an ash–water slurry. The heat losses were experimentally determined and it was found that the mathematical model gave predictions of the right order of magnitude of time, site of spontaneous combustion and magnitude of calorific losses. All the methods of protection applied to decrease the self-heating of coal were effective, but the experimental results indicate that the most economical way to avoid the heat losses is the use of an ash–water slurry to cover the coal pile.