A coal preparation plant removes impurities from coal to increase its value and reduce shipping costs. The process involves crushing, separating impurities from coal, drying and forming it into a transportable solid. The water containing impurities is often toxic and hazardous. Maintaining a stockpile ensures a constant flow of material for processing.
A coal preparation plant takes coal from a mine and cleans it for transportation. When coal comes out of a mine, it’s full of impurities. These impurities reduce its overall value, reduce its usefulness, and increase shipping costs. Because impure coal is so detrimental to its use, most coal mining companies own or operate a coal preparation plant. In most cases, these plants remove impurities and process the coal into standard size and quality for shipment.
Coal that comes directly from a mine is called run-of-mine (ROM) coal. This is a very impure substance. Most ROM coal has other minerals mined along with the coal such as worthless rock, chemicals, and explosive residue. Process contaminants consist of broken pieces of equipment, fabric, paper, or any other material that entered the cargo via a miner or processor. All of these non-coal items add to the weight of the coal, which increases its transportation costs and, consequently, reduces its market value.
The first step in most coal preparation processes is crushing. The charcoal, along with all the various impurities, is reduced to a powder. Crushed coal is extremely light and will naturally try to separate itself from the crushed material. When crushed ROM is placed in water, much of the heavier material will sink to the bottom, but the lighter carbon will float to the surface. Water also releases chemicals from coal dust.
The next step is to remove the carbon from the water. After the two are separated, the charcoal is dried and formed into a transportable solid. At this point, the charcoal is in a usable form and is ready to be shipped to market or transferred to a cooking station for use.
The water containing the impurities and the water removed from the dried coal is combined into coal slurry. This mixture is often highly toxic and dangerous. Most of the time, a coal preparation plant will have some method of storing or purifying this water, often through evaporation. Hazardous material is a common talking point when discussing the dangers of coal mining processes.
Most of the time, a coal preparation plant will maintain a stock of coal ready for processing. This is more of a technological problem than a financial one. The machinery used to purify and separate the coal benefits from a slow and constant flow of material. By maintaining a stockpile, the coal preparation plant is able to keep production at the exact level desired, even when there are major disruptions between deliveries.
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