The afterburner chamber is the central element of exhaust gas purification in thermal desorption. It completely combusts the pollutants released in the rotary kiln at temperatures of at least 850 °C before the exhaust gas enters further purification stages. The following sections explain how this component works technically, what legal requirements apply, and why it is indispensable in thermal soil treatment.
How does the afterburner chamber work technically?
The afterburner chamber is a thermal combustion unit connected downstream of the rotary kiln. It heats the raw gas flowing out of the kiln to temperatures of at least 850 °C and maintains it there for a legally prescribed minimum period. In the process, organic pollutants that were transferred into the gas phase during the desorption step are thermally destroyed.
Technically, the raw gas from the rotary kiln is fed directly into the afterburner chamber. Burners generate the necessary temperature, which is continuously monitored by measurement systems. The chamber is dimensioned so that the gas remains at the prescribed temperature long enough to ensure complete oxidation of the pollutants. Only after this stage does the treated exhaust gas leave the afterburner chamber and enter the subsequent purification stages.
What pollutants are destroyed in the afterburner chamber?
In the afterburner chamber, organic pollutants that were converted into a gaseous state in the rotary kiln during thermal desorption are destroyed. These include mineral oil hydrocarbons (MOH), BTEX compounds, phenols, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), cyanides, nitroaromatics, and chlorinated hydrocarbons.
Of particular relevance is the destruction of PCDD and PCDF, the so-called dioxins and furans. These highly toxic compounds form during incomplete combustion and must be safely eliminated through sufficiently high temperatures and residence times. PFAS and PFOS, known as persistent organic pollutants, can also be thermally degraded at correspondingly high temperatures. The thermal soil treatment at ARE Deutzen is approved for all of these pollutant classes.
Why is the minimum residence time in the afterburner chamber legally prescribed?
The minimum residence time is legally prescribed because complete thermal destruction of organic pollutants depends not only on temperature but also on exposure time. In accordance with the 17th Federal Immission Control Ordinance (17. BImSchV), exhaust gases must remain in the afterburner chamber at a minimum of 850 °C for at least two seconds.
The reason lies in reaction kinetics: even at high temperatures, complex pollutant molecules require a certain amount of time to fully oxidize. If the gas is cooled or diverted too early, pollutants can pass through the afterburner chamber undestrayed. The combination of temperature and time is therefore the decisive factor for the effectiveness of pollutant combustion. The legal requirement establishes a binding minimum standard that must be met regardless of the pollutant mixture.
What happens to the exhaust gas after the afterburner chamber?
After the afterburner chamber, the exhaust gas passes through a multi-stage exhaust gas purification process before being released into the atmosphere. This typically includes dust removal, flue gas scrubbing to remove acidic gas components, and an activated carbon filter that adsorbs remaining trace substances.
Dust removal eliminates particles generated during the combustion process. Flue gas scrubbing neutralizes acidic components such as hydrochloric acid or sulfur dioxide, which can form during the combustion of chlorine- or sulfur-containing pollutants. The final activated carbon filter ensures that heavy metal compounds and organic residual traces are also retained. Only after all these purification stages is the cleaned exhaust gas discharged via the chimney. Compliance with the statutory emission limit values is monitored through continuous measurement.
How does the afterburner chamber differ from a conventional waste incineration plant?
The key difference lies in the process objective: in thermal desorption in the rotary kiln, the soil itself is not incinerated — only the pollutants contained within it are vaporized. The afterburner chamber burns exclusively the pollutant-laden exhaust gas, not the mineral material. A waste incineration plant, by contrast, burns the waste itself as fuel.
This has practical consequences: the treated soil is preserved as a mineral material and can often be reused after treatment. The afterburner chamber is therefore a pure exhaust gas purification element that does not interrupt the material cycle of the mineral carrier. Waste incineration plants, on the other hand, produce slags and ashes as residues of the incinerated material. Thermal soil treatment pursues the goal of pollutant destruction while simultaneously recovering the mineral raw material.
When is an afterburner chamber absolutely required in thermal soil remediation?
An afterburner chamber is always required when organic pollutants are transferred into the gas phase during thermal soil treatment. This is the case for virtually all relevant contaminations treated in a rotary kiln. The legal requirements of the 17. BImSchV make afterburning mandatory for licensed facilities.
Specifically, this applies to soils contaminated with MOH, PAH, BTEX, phenols, PCB, PCDD/PCDF, PFAS, or chlorinated hydrocarbons. Without an afterburner chamber, these compounds would be released uncontrolled into the ambient air. A facility operated without a functioning afterburner chamber cannot obtain approval under the Federal Immission Control Act. For clients, the afterburner chamber is therefore also a quality indicator: it demonstrates that the facility is designed for the safe and legally compliant treatment of complex contaminations.
Anyone who needs to dispose of contaminated soil or remediate a contaminated site should verify whether the contracted facility has a properly operated afterburning system and can demonstrate the corresponding immission control approvals. The quality management of a certified facility provides reliable information on this.
How ARE Deutzen GmbH supports thermal soil treatment
ARE Deutzen has been operating a thermal soil treatment facility at the Deutzen site in western Saxony since 1994, equipped with a complete and continuously monitored exhaust gas purification chain, including an afterburner chamber, flue gas scrubbing, and an activated carbon filter. As a certified waste management company, ARE Deutzen offers the following services:
- Thermal desorption of contaminated soils, construction rubble, and mineral waste in the rotary kiln at temperatures of up to approximately 600 °C, depending on the material and pollutant load
- Safe pollutant combustion in the afterburner chamber at legally prescribed temperatures and residence times
- Multi-stage exhaust gas purification with dust removal, flue gas scrubbing, and activated carbon filter
- Treatment of a broad spectrum of pollutants: MOH, PAH, BTEX, PCB, PFAS, PCDD/PCDF, and others
- Material flow management for soils, dredged material, sludges, and process residues
- Approvals under BImSchG as well as certifications to ISO 9001, 14001, 50001, and 18001
For questions about your remediation project or the delivery of contaminated materials, the ARE Deutzen team is available to assist you directly. Get in touch now and receive an expert assessment of your specific needs.