Regenerative thermal oxidation (RTO)

Regenerative thermal oxidation (RTO)

Regenerative thermal oxidation (RTO), also called regenerative post-combustion, is a form of thermal afterburning. The aim of RTO is to reduce the consumption of fossil fuels of regenerative thermal oxidation plants through heat recovery. RTO systems are primarily used in the food industry, e.g. in smoking, frying and deep-frying plants.

The regenerative thermal oxidation is based on a multi-stage system, which extracts impurities contained in the exhaust air stream by transferring the air flow through several chambers. In a first step, the contaminated exhaust air is transferred into a reactor chamber. An RTO system can consist of several reactor chambers, which are connected to an oxidation chamber above. Each reactor chamber is equipped with a ceramic heat exchanger, a so-called reactor bed. As the exhaust air flows through the reactor chamber, its thermal energy is transferred to the reactor bed. The exhaust air then is led into the oxidation chamber, where a gas burner heats the exhaust air stream up to 860°C. During this step, the contained impurities oxidize and are then extracted. The exhaust air flow then splits and flows through the remaining reactor chambers. Inside these reactor chambers its thermal energy is transferred to the respective reactor beds. Once the reactor beds inside these reactor chambers reach a specified temperature, the exhaust air stream is diverted through flaps to flow into these newly heated chambers. Then, the purification process begins anew.

To optimize the use of RTO systems, the exhaust air stream always flows alternately through the different reactor chambers. The aim of regenerative thermal oxidation is to decrease the consumption of external fuels as much as possible. This form of post-combustion is particularly suitable to extract and remove intensive VOCs in exhaust air. The separation efficiency achieved by RTO systems is comparable to thermal oxidation systems during continuous operation. Regenerative post-combustion can achieve a thermal COP of up to 97%, making it, when compared to other systems, the most energy-efficient thermal oxidation system.

However, compared to electrostatic exhaust air purification systems, RTO systems require large amounts of fossil energy sources. This continuous use of fossil fuels, such as natural gas, has a negative effect on the life cycle assessment and the carbon footprint of production plants despite the high regeneration of thermal energy. RTO systems achieve a pure air quality of about 5 mg carbon per cubic meter (m3) of air.

The modern exhaust air filtration systems of KMA Umwelttechnik offer an energy-efficient alternative. KMA filtration systems reduce the energy requirement for operating the filter plant by more than 90% compared to thermal oxidation. Despite the low energy consumption, the separation efficiency is up to 99.8%. The energy consumption of an electrostatic precipitator cell corresponds to that of a 100 W light bulb – with an average exhaust air volume of 5000 m3/h. If the exhaust air filtration system is additionally combined with a heat recovery system consisting of a heat exchanger and heat pump, additional energy can be recovered from the exhaust air treatment which would have previously remained unused. The recovered energy can be used for subsequent processes, to further reduce the energy consumption of the production.