LOW-TEMPERATURE CORROSION IN FEED-HEATERS HEATED BY FLUE GAS.

In a steam generating plant an increase in efficiency can be obtained by improved utilization of the waste heat of the flue gas and by a reduction in the outlet temperature of the flue gas as it leaves the boiler. Flue gas originating from fuels containing sulfur must not, however, be allowed to cool to the water vapor dewpoint, since even at 20 to 120 K above this temperature a condensate containing sulfuric acid precipitates on the heating surfaces and leads to corrosion. To reduce the risk of corrosion, an endeavor is usually made to keep the temperature from falling below the acid dewpoint. In specific cases other preventive measures may be suitable, but their general application is usually uneconomical or proves not very effective.