The growing need to improve energy efficiency and meet climate targets has implications for the selection of exhaust air purification methods in the chemical industry. Decision-makers and professionals are faced with the challenge of finding sustainable and energy-optimised solutions that meet the new requirements. Sustainable exhaust air treatment is a clear must in the future.
The following exhaust air purification processes are currently in use:
Thermal Exhaust Air Purification and its Adaptation to Current Conditions.
Thermal afterburners are traditionally used technologies in exhaust air purification. At temperatures between 750 and 1,000 °C, they oxidise pollutants and odours contained in the exhaust air. A wide range of plant types such as regenerative thermal oxidisers (RTO), recuperative thermal oxidisers, catalytic afterburners (KNV) and combustion chambers are used. RTO plants have gained particular importance, as they can achieve heat recovery of up to 98 per cent if properly designed.
However, the use of natural gas as an energy source for the operation of these plants is now no longer always economically viable in view of rising costs and CO2 emission taxes. Therefore, electrically powered post-combustion plants are increasingly being considered, which have a better carbon footprint and are more cost-effective under current conditions. However, the prolonged start-up and shut-down processes as well as special protective measures for corrosive exhaust air need to be taken into account.
Adsorption Technologies as Efficient Solutions
Adsorption systems offer an efficient way to filter volatile organic compounds (VOCs) and other pollutants from exhaust air. Continuous further development of the adsorbents used, such as various activated carbons and zeolites, means that inorganic components can also be reliably separated.
This technology offers advantages for low to medium pollutant concentrations and is characterised by its flexibility, as adsorbers can be easily switched on and off. In addition, there is the possibility of recovering and reusing concentrated solvents with the help of other technologies. In terms of CO2 balances, the adsorption process is attractive because no energy sources are required for operation.
Biological Exhaust Air Treatment as a Sustainable Alternative
The demand for biological processes in sustainable exhaust air treatment has risen steadily in recent years. Bioscrubbers and biofilters offer solutions for various requirements, from VOC separation to pollutant and odour removal to the treatment of highly fluctuating values.
Particularly noteworthy is the excellent CO2 balance of these systems and the low secondary emissions. Bioscrubbers, despite the use of pumps and a large number of secondary systems, have lower power consumption due to their low pressure drop. In addition, the lower CO2 emission compared to thermal systems makes biological exhaust air purification economically and ecologically attractive.
(Source: Andreas Breeger, Wessel-Umwelttechnik in an article in “Verfahrenstechnik 2022/08”)