The stream of SO2 enters the conversion tower equipped with 3 or 4 catalyst layers (depending on the plant’s capacity) with the purpose of converting SO2 into SO3.

Considering that each catalyst bed has to be at a specific temperature in order to start conversion, there are heat exchangers which cool down the stream so as to obtain the best performance.

The hot exhaust air coming from the exchangers reaches a temperature of over 300°C. It is used for the regeneration of silica gel beds or other purposes such as steam generation.