Influence of rainfall events on coal moisture content in mine stockpiles

Moisture is one of the most important indexes upon which a coal product is graded. The removal of moisture from coal is essential to minimize economic loss, handling, and transportation problems and to maximize the calorific value of coal. Apart from the process water carried over into the mine and mineral processing final product, extra water after rainfall can increase the total moisture in a coal stockpile. The coal moisture content can be adjusted by way of the natural drainage and evaporation. When the rain falls on the stockpile, it either runs off the surface or infiltrates. The infiltrated water can evaporate, drain or stay within the stockpile. To investigate these mechanisms, an experimental large stockpile (9 tonne) was created and shielded from rain and wind. An artificial rain sprinkler system was set up on the top of stockpile to simulate the rainfall. Also, the lab-scale drainage and evaporation tests in surface and different depths were designed to simulate the water movement in a large stockpile. The results showed that the rate of infiltration was independent of the rainfall intensity. In all rainfall conditions, drainage stopped after 2-3 days, but evaporation continued, albeit at a low rate. Evaporation helped to dewatering at rates that relied on temperature, wind and humidity circumstances. The large stockpile bed revealed a cyclic behavior of adsorbing moisture overnight and desorbing the moisture during the day. The lowest section of the stockpile contained the highest moisture and fine particles contents, whereas the outskirts section of the stockpile contained the lowest moisture and fine particles contents. Drainage and coal bed evaporation lab tests were representative of the way by which moisture moved or remained in a large coal stockpile whereas evaporation depth experiments did not accurately represent the depth to which evaporation was occurred within the coal stockpile.