Gas-Gas heat exchanger for flue gas treatment (duty 1400 kW) of dirty and cleaned flue gasses. Dirty flue gas is flowing vertically in 2 passes through the tubes. The cleaned flue gas is flowing around the tubes in a straight horizontal line. Stainless steel material is chosen for the tubes in the first pass due to the composition of the dirty flue gas. Carbon steel is chosen for the tubes in the second pass because the temperature is higher and acid condensation is not to be expected. To compensate for differences between tube side and casing side a compensator is installed internally. This heat exchanger will be installed at a cold rolling mill that supplies stainless steel cladding for decorative surfaces on the façades of world-famous buildings.