During adsorptive concentration a VOC containing air is introduced to a solid. At the surface of the solid the VOC is bonded. In most cases adsorption wheels consisting of zeolite as contact material are used. The adsorption wheel extend into the air stream so the VOC can accumulate at the contacting surface. By rotation the area with high concentration of VOC is turned into the desorption area where hot air flows through the rotor. The hot air removes the VOC from the surface of the rotor be desorption. The rotor turns further into a cooling zone. For this typically a part of the exhaust air is used. At the same time the air is heated and can be reused as regeneration/desorption air (heating) of the rotor.