Coal product moisture control using stockpiles

Abstract

The moisture content of product coal is a major factor influencing the efficiency of downstream coal utilization processes. Product stockpiles are often used as a control measure to regulate the moisture content of the coal by gravity drainage and evaporation. An understanding of the mechanisms of water migration and retention in coal stockpiles are required to optimise the management of these stockpiles. Apart from the process water carried over into the product after beneficiation, additional water due to rainfall can add to the total moisture contained in a stockpile. When the rain falls on the stockpile, it either runs off the surface or infiltrates the stockpile. The infiltrated water can evaporate from the surface (down to a certain depth), drain through a saturated toe, or remain within the stockpile to add to the total final moisture content. To study these mechanisms, laboratory scale experiments were designed. A drainage column was used to simulate the percolation of water in a stockpile, and the data verified that particle size, especially the -0.5 mm fraction, had the most significant influence on both the drainage rate and the water retained in the bed. The ratio between run-off water and infiltration water during rainstorms were also quantified, and it was shown that compaction of the bed had a major influence on infiltration. Evaporation from a coal bed surface was tested by measuring the mass loss from coal beds exposed to the atmosphere, while measuring weather conditions like temperature, relative humidity and wind speed. The average evaporation loss was about 0.8 L per m2 per day.