The paper gives results of pilot plant experiments to investigate the feasibility of replacing makeup water in limestone flue gas desulfurization (FGD) scrubbers with a simulated cooling tower blowdown. Tests were conducted while forcing the oxidation of the scrubber slurry to gypsum and maintaining Cl(-) concentrations at levels expected with the use of high-sulfur coals of moderate chloride content. Results show that all of the makeup water could be replaced with blowdown containing up to 690 ppm Na(+) when operating at SO2 make-per-pass below 8 mmol/L and a tightly closed scrubber loop. Material balances indicate that the uncontrolled discharge of soluble salts and trace elements from a power plant can be markedly reduced by application of water treatment units such as vapor-compression/evaporation as an integral part of the FGD scrubber. Such systems should be more effective in maximizing water reuse and should have lower energy requirements than the direct application of water treatment to blowdown streams.
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