Environmental Effects of Fossil Fuel Use: Water Pollution Although much of the mineral matter of coal is removed at the mine mouth, coal delivered to a power plant or other facilities still contains adhering mineral matter, simply called ash The ash content can amount to anywhere between 1% and 15% of the coal weight Even oil contains ash, amounting to 0.01–0.5% by weight coal particle oil droplet After combustion of the coal particle ( 煤粉 ) or oil droplet ( 油 滴 ), the mineral matter remains uncombusted, and either falls to the bottom of the boiler or is blown out with the flue gas as fly ash pulverized-coal-fired boilers In modern pulverized-coal-fired boilers ( 煤粉锅炉 ), about 90% of the mineral matter forms fly ash, and 10% bottom ash
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