PFA-linings for avoidance of dewpoint corrosion in heat-exchangers and ducts of waste-incineration power plants

The combustion of wastes of diverging qualities leads to the formation of gases with a high content of sulphur, chlorine and fluorine compounds. When the dewpoint of these gases is underrun in heat exchangers, housings and ducts in order to re-cycle more heat out of the combustion gases, this leads to a heavy condensation of hydrochloric, hydrofluoric and sulphuric acid on the involved equipment and in consequence to one of the strongest types of corrosion known, called dewpoint corrosion. The latter even corrodes the most resistant steel grades and thus requires other technical solutions. A lining of the condensing heat-exchangers, their housings and the flue gas ducts with the fully-fluorinated thermoplastic PFA (tetrafluoroethylene-perfluoroalkylvinylether) renders possible a service of the heat exchangers under condensing conditions and consequently increases the total power production efficiency of the wasteincineration plant, even having a positive environmental effect due to a positive influence on the overall energy mix. Although the suitability of this technical principle had already been demonstrated in multiple successful examples in fossil- and waste-fired power plants, constructive and technical details can have an influence on the performance of the lined equipment, such as material properties, welding of the liner, installation and sealing against the unlined parts as well as constructive aspects of the heat exchanger pipes and tubes. This will be discussed in the following.