When the flow of gases to be cleaned is high and the concentration of organic compounds is very low (less than 1 g/Nm³), the treatment by thermal oxidation would suppose a very high energy cost, since the heat generated by the organic compounds would be very low and heat to get the oxidation temperature should be achieved by the burner. Therefore, in these cases, the concentration of organic compounds is used in a gas stream with a volume between 10 and 16 times lower that will be treated later.
This concentration of the gases to be purified is achieved by a zeolite rotor concentrator, which is a device capable of adsorbing on its surface the organic compounds of the gas stream to be purified. The zeolite absorber is impregnated on a corrugated mineral fiber substrate within the rotor.
The gases to be cleaned, with a low concentration of VOC's, pass through a filter in which the particles are retained, which would damage the zeolite. Once filtered, the gases pass through the rotor in which the VOC's are absorbed. The clean gases leave the wheel and are emitted into the atmosphere through a stack.
The VOC's are desorbed from the rotor by the passage of a small stream of hot gases through it and in the opposite direction to that of the process gases. The rotor cools this gas stream as the VOC's desorb and exit as a concentrate at a temperature of 50 to 60° C. Normally, the further treatment of the concentrate consists of thermal oxidation (usually in a thermoreactor).
The process gases that leave the cooling sector of the rotor are hot (at a temperature between 75 and 110 °C) and can be used as desorption air with additional heating. The use of this air preheated by the rotor in the cooling zone reduces the overall energy consumption of the system.