Sulphur in fuels like natural gas, biogas, biomass, coal or fuel oil gets combusted and forms SOx. Most of this is in the form of SO2 and 2% to 4% is present as SO3. This SO3 condenses when flue gas is cooled and forms sulphuric acid (H2SO4). This leads to corrosion of metal surfaces, ducts and stacks. This condensation reaction takes place when the flue gas temperature drops below, or the flue gas comes in contact with a surface temperature below what is called the Acid Dew Point. The polymer heat exchange technology allows flue gas to be cooled without having the risk of corrosion.