January 15, 2007

Vacuum-driven "hypo" chlorination is safer and cheaper

Tony Callery, Portacel Inc.

About two years ago, Jeff Gremelspacher —then chief chemist at Cardinal Generating Station in Brilliant, Ohio—was asked to evaluate potential replacements for the chlorine gas disinfectant system serving Units 1 and 2. The system was used to prevent the formation of microorganisms in the Ohio River water pumped through thousands of 1-inch-diameter cooling tubes in the 600-MW unit's steam condensers. Unit 1 (Figure 1) is owned by American Electric Power (AEP); Units 2 and 3 are owned by Buckeye Power, a generation and transmission cooperative established by Ohio's rural electric co-ops. Cardinal Operating Co., co-owned by AEP and Buckeye Power, operates all three units of Cardinal Generating Station.

 

 

 

Clean and lean

Chlorinating cooling water improves the efficiency of the cooling process. Without chlorination, microorganisms introduced with the water source would accumulate rapidly on the inner surfaces of condenser tubes. They excrete a sticky organic material that can coat the tubes, trapping inorganic matter such as dirt or sand particles and leading to the formation of slime. Gremelspacher explained that slime can reduce the efficiency of heat transfer and steam condensation in as few as 10 days, with potentially costly consequences.

"When condensation efficiency is reduced," said Gremelspacher, "the result is a slight increase in backpressure from the turbines. An increase in backpressure of, say, 0.1 inches Hg or a fraction of a psi may not seem like much, but any loss of condenser vacuum means that more Btus of fuel are needed to produce the same output. Because compensating for every 0.1 inch loss in condenser vacuum requires an additional 25 Btus, we've calculated that operating our unit with that pressure differential would raise our annual fuel bill by $250,000."
 

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