Under the legislation organic hydrocarbons that can be treated or used in such a manner that they are not released into the environment are exempt from the incentive tax.

Previously, Rotoflex’s exhaust air containing VOCs was filter-cleaned and released into the atmosphere. So the first step to reduce the VOC load in production rooms and minimise the volume of exhaust air to be purified was to, according to consultants Weyer und Partner AG, collect the contaminated exhaust air as closely to the source as possible and to enclose the previously open processes. Then exhaust air flows with low emissions were collected and extracted separately from the exhaust air that required treatment.

The second step was to evaluate which was the most suitable air purification system with the regenerative thermal oxidiser (RTO) chosen. Due to its energy efficiency and flexible handling of fluctuating exhaust flows and hydrocarbon concentrations, the RTO is currently considered state-of-the-art in the field of air purification across industry. This type of air purification system is typically available as a 3-canister version.

In this context, the word "regenerative" refers to the (almost complete) internal heat recovery achieved using the ceramic heat exchanger: during the heat exchange with the ceramic packing material contained in one of the three system canisters, the process stream containing contaminants is initially preheated to temperatures of approx. 30 to 50 Kelvin below the oxidisation temperature. In the combustion chamber of the RTO, the VOCs are then almost completely converted into carbon dioxide and water at approx. 820°C. The oxidatively cleaned air then flows through the other two heat exchanger canisters and the heat is dissipated on the ceramic media.

The principle of the KBA RTO design is three separate heat exchanger canisters. This design means that the hot area of the system has no metallic parts which, taking into account the high temperatures within the system, would be subject to thermal stress and thus, high levels of wear and tear.

The system concept needed to be able to handle a wide range of concentration levels, i.e. it needed to be able to ensure low-energy operation in the case of low ingoing solvent concentration, as well as stable operation in the case of maximum concentrations.

Depending on the level of VOC concentration in the exhaust air, oxidation does not take place in the actual combustion chamber, but within the ceramic heat exchanger. Due to the exothermic nature of the reactions, a dynamic temperature profile is formed within the ceramic, which can lead to undesirable effects such as excessive temperatures, unbalanced energy profiles or local "hot spots". The special KBA control modules XtraControl™ and XtraBalance© take these exothermic effects into account, thus ensuring safe, stable and efficient system operation.

In order to also ensure minimum energy requirements even when handling low concentrations of noxious substances, the system is also equipped with the patented KBA burner control with direct gas injection, which enables the infinitely variable scaling of burner performance from virtually 0 to 100 %. Combined with XtraControl™ and XtraBalance© control concepts, this produces an intelligent burner control, which takes into account not only the current combustion chamber temperature, but also the overall energy content of the individual heat exchanger beds, thus ensuring that only the energy actually required to maintain the necessary reaction temperature level is consumed.

Another key requirement for the system manufacturer was compliant with a sound pressure level of maximum 65 dB (A) at a distance of one meter. This roughly corresponds to the noise level of a normal conversation. Without additional measures, the relevant sound pressure level of the system components is approx. 85 dB(A), i.e., to comply with the required value it was necessary to reduce the level by approx. 20 dB (A). The main sources of noise on regenerative thermal oxidisers are the fans, the RTO flaps (pneumatic cylinder) and the pipelines. Soundproof hoods/noise suppression cabins, silencers and additional sound insulation, were used to reduce and attenuate the sound.