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Wet Scrubbing Coal Emissions With Limestone


Wet scrubbing is the dominant method for flue gas desulfurization (FGD), a technology that removes the sulfur dioxide in the emissions of power plants.

Wet scrubbing is the dominant method for flue gas desulfurization (FGD), a technology that removes the sulfur dioxide in the emissions of power plants. It can be employed at both coal- and oil-fired power plants, according to the paper, Flue Gas Desulfurization Technologies for Coal Fired Power Plants, prepared by Paul S. Nolan of energy producer Babcock & Wilcox Co.

The average-sized power plants that employ this method will consume millions of tons of crushed stone every year, providing a constant market for a limestone producer. But this scrubber stone must contain high levels of calcium carbonate, the essential chemical that naturally absorbs the dangerous chemicals. Without this filtration, the sulfur dioxide would be released into the atmosphere and later turn into acid rain.

Energy producer Duke Energy provides a good description of this technology on www.duke-energy.com. First, the limestone dust is conveyor-fed into a huge chamber and mixed with water to create a slurry. The flue-gas exhaust created by the combustion process is then combined with this slurry, which is recirculated to create giant ìwater fallsî inside the chamber. The sulfur dioxide adheres to calcium carbonate, creating calcium sulfate, or gypsum, which is captured by a scrubber and discharged onto a conveyor.

ìThe inherent simplicity, the availability of limestone, and the high removal efficiencies required by the law quickly advanced the popularity of this system,î Nolan writes. Most wet scrubbers will recover more than 90% of the harmful chemical.

The byproduct of this process can be sold for wallboard, an agricultural soil amendment or as an ingredient for cement. Nolan writes that the material also is a stable landfill material if it cannot be sold.