Three

摘要

Exhaust air containing a number of volatile organic compounds is purified in a 3 - stage catalytic after-burning system in which 3 types of catalyst are provided in spatially separate zones, to allow use of a suitable type of catalyst for each stage. Preferably, the reaction temperature for each stage can be individually adjusted by use of a burner between stages 1 and 2 or between stages 2 and 3, operating in combination with an exhaust air preheater, comprising an air - air heat exchanger. Catalyst poisons are separated in the first stage and oxidation is carried out in all stages.