Stack Gas Reheating with Prime Surface Heat Exchanger Minimizes Vapor Plume And Helps Disperse Moisture
Scrubbed gas from a Midwest power station had a high moisture content and thus a relatively low dew point, resulting in condensation shortly after leaving the stack. This resulted in a significant vapor plume at lower ambient temperatures and formation of mildly acidic mist in the vicinity of the stack.
To prevent this local misting effect, the power station is using specially designed Tranter PLATECOIL® Prime Surface Heat Exchanger stack gas reheater banks. These units heat 25,485 m3/m (900,000 SCFM) of flue gas from 52°C to 77°C (125°F to 170°F) using 3.4 bar (50 psi) steam. Flue gas reheating delays condensation until the gases rise higher into the atmosphere before they condense for better dilution and dispersion of the trace acidity and particulates from the scrubber.
Composed of 7 Style 73D panels, these “boiler header” panels have 17 parallel passes with 2 return passes. This pass design promotes good steam flow and heat transfer without blocking and stalling. The panels, headers and piping are made from 317L SS to withstand the long-term corrosive effects of the hot, moist flue gas. Depending on the application, other materials are available.
The banked panel configuration presents a multiple corrugated surface to the gas flow for good heat transfer without excessive pressure drop that could degrade the performance of upstream components. The banked panel design is also easier to clean and maintain than either tubular or finned tube exchangers would be. The design includes a mounting plate and rails to aid installation, removal and maintenance.
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PLATECOIL® Prime Surface Heat Exchanger banks mounted downstream of the scrubber raise gas temperature by 22°C (40°F) for better moisture dispersion from the stack.