Air heating for small incinerator waste to energy

[Impdrew]

Hi, i am designing a small scale incinerator plant for waste to energy.
Concern is over the need to preheat combustion air prior to it entering the air heat exchanges utilising exhaust flue gas. Due to the corrosive nature of the flue gas and its relatively high acidic dew points i am concerned that using air at ambient temperature at the inlet of the air heaters, with the flue gas approaching its dew point (after passing through a heat recovery boiler) will cause excessive corrosion.
I have become aware of the use of steam-air preheaters, where steam from the incinerator-boiler can be blead prior to superheating, or alternatively some of the steam exiting the turbine can be condensed for pre-heating air.
Has anyone any experience in incinerator air heating and steam air heaters.
Thanks

 

[jdbanks]

You are right to expect corrosion on the flue gas side of the preheat exchanger if the acid gas dewpoint is high enough in the flue gas. Have you calculated the dewpoint yet? Using waste steam to preheat the cold air is a good approach in this case, if maximum heat recovery is needed. Steam preheat has been used before in certain types of incinerators, but is not common. An alternate is to use an acid-proof alloy to construct the affected part of the exchanger - you may find that the extra cost for alloy is comparable to the cost for steam preheater, etc.