Regenerative photooxidation for the removal of VOC from exhaust air

The reduction of VOCs (volatile organic compounds) in exhaust air streams presents many companies with special challenges. Cleaning with conventional methods can be expensive, especially with large volume flows and low pollutant concentrations.
The process of regenerative photooxidation offers a cost-effective and safe alternative to activated carbon filters, RTO systems, and other conventional exhaust air purification systems. In the following, find out more about regenerative photooxidation, how the process of adsorption increases energy efficiency, and what other advantages the use of UV light offers.

The elimination of the volatile organic constituents from exhaust air in the regenerative photooxidation process is based on the combination of an adsorber and a downstream UV reactor.

First, the loaded raw gas stream is passed through a particle filter and, if necessary, through a droplet separator, after which the exhaust air passes to the adsorber. Zeolite or special activated carbon is used as an adsorbent. The adsorber can be designed as a fixed-bed reactor with discontinuous regeneration or as an adsorption wheel with continuous regeneration.

After this treatment stage, the purified exhaust air is discharged to the environment via a chimney, which complies with the legal requirements of the TA-Luft and the BImSchV.

The actual degradation of the pollutants takes place by desorption and subsequent oxidation in the UV reactor. In the case of fixed-bed filters, the pollutants are desorbed discontinuously, while when an adsorption wheel is used, the desorption takes place continuously in a segment of the rotating wheel.

In the secondary regeneration cycle, the pollutants are concentrated by a factor of 10–20 and pass first into the UV reactor and then into the catalytic oxidation, where they are ideally broken down to carbon dioxide (CO2) and water (H2O). The significantly lower volume flow of the secondary circuit and the higher concentration of the pollutants compared to the raw gas flow enable a more compact design of the subsequent oxidation processes. Compared to conventional systems, both the investment costs and the costs for operation and maintenance can be significantly reduced as a result.

The reaction energy released during the oxidation is used to heat the desorption air with the aid of a heat exchanger. Excess reaction heat can be decoupled by means of a further heat exchanger and used as process heat, which further increases the efficiency of the overall system.

The main advantages of regenerative photo oxidation over conventional methods are:

• Lower investment costs
• Lower operating costs
• Safe pollutant removal even with changing volume flow or fluctuating pollutant cargo (dynamic driving style)

Another advantage of regenerative photo oxidation is the scalability of the system. The system can be expanded and retrofitted modularly in the event of production-related growing volume flows or increasing pollutant concentrations.

Regenerative photooxidation is particularly suitable for exhaust air flows from the chemical and petrochemical industry, from paint processing processes, the pharmaceutical industry and contaminated site remediation with bottom air extraction.