August 1, 2009

Improved FGD Dewatering Process Cuts Solid Waste

Craig Moyer, Duke Energy and Juan Fernandez and Bob Carraro, GE Water & Process Technologies

In 2007, Duke Energy’s W.H. Zimmer Station set out to advance the overall performance of its flue gas desulfurization (FGD) dewatering process. The plant implemented a variety of measures, including upgrading water-solids separation, improving polymer program effectiveness and reliability, optimizing treatment costs, reducing solid waste sent to the landfill, decreasing labor requirements, and maintaining septic-free conditions in clarifiers. The changes succeeded in greatly reducing solid waste generation and achieving total annual savings of over half a million dollars per year.

Duke Energy’s W.H. Zimmer Station (Figure 1) is a 1,300-MW coal-fired power plant located on the Ohio River at Moscow, Ohio. The unit entered commercial operation in 1991 and consumes approximately 3.8 million tons of coal annually. The U.S. Environmental Protection Agency required the Zimmer Station to remove a minimum of 91% of the sulfur dioxide (SO₂) from the flue gas while not exceeding an emission rate of 0.548 pounds of SO₂ per million Btu based on a 30-day rolling average.

1.    Powering Ohio. By making modifications in 2000 and 2007, the W.H. Zimmer Station in Moscow, Ohio, dramatically decreased the amount of scrubber by-product that has to be landfilled. Courtesy: Duke Energy

The station is equipped with a magnesium-enhanced wet flue gas desulfurization (FGD) system (scrubber) to control SO₂ emissions. In 2000, the scrubber process was modified to accommodate a gypsum conversion process system to make high-quality synthetic gypsum that is sold to a wallboard manufacturer. Prior to the scrubber modification, scrubber by-products were landfilled at an average rate of 1.7 million tons per year. The 2000 modification cut the landfill rate by 77%.

In 2007, station personnel set out to further improve the overall performance and effectiveness of the FGD dewatering process. A team consisting of station personnel, GE Water & Process Technologies, and Utter Construction worked closely throughout the year to identify potential areas of improvements and create/modify key performance objectives.