Acid dew point corrosion in marine uptakes
Sulphuric acid condenses on uptake and economiser surfaces below the acid dew point, which rises with fuel sulphur and limits waste heat recovery depth.
Acid dew point corrosion is the constraint that sets how much heat a ship can take out of its exhaust. A small fraction of the sulphur dioxide in the exhaust oxidises to sulphur trioxide, which combines with water vapour to form sulphuric acid. That acid condenses on any surface below its dew point, and the dew point rises with the sulphur content of the fuel burned.
The consequence is a direct trade against waste heat recovery . Deeper recovery means a lower economiser exit temperature, which means a lower exhaust gas cleaning system inlet temperature and less quench duty, but going too deep on high-sulphur fuel puts economiser tube surfaces below the acid dew point, with corrosion and soot fire risk following. The same mechanism drives cold corrosion on cylinder liners and sets the cylinder oil base number an engine needs.
The full article will cover the sulphur trioxide conversion fraction, the dew point relationship and its published correlations, protective measures including surface material selection and minimum feedwater temperature, and the economiser soot fire chain.