When contaminants in the rotary kiln transition into the gas phase, they are subsequently treated in a multi-stage exhaust gas purification system and largely destroyed. The cleaned exhaust gas stream only leaves the facility after passing through dust removal, thermal post-combustion, flue gas scrubbing, and activated carbon filters. The following sections answer the most important questions about this process in detail.
How are contaminants transferred into the gas phase in the rotary kiln?
In the rotary kiln, contaminated soils and mineral waste are heated at temperatures of up to approximately 600 °C under oxygen exclusion. This thermal desorption releases organic contaminants such as TPH, BTEX, PAH, PCB, PFAS, and chlorinated hydrocarbon compounds from solid particles and converts them into a gaseous state, without uncontrolled combustion taking place.
The exclusion of oxygen is crucial: it prevents contaminants from burning uncontrollably within the kiln itself, which could potentially generate new pollutants such as dioxins or furans. Instead, the volatile compounds are discharged together with the process gas from the rotary kiln and directed specifically to the downstream exhaust gas treatment system. The treated solid leaves the kiln as a mineral product that meets the statutory limit values for proper disposal or recovery.
What happens to the contaminant-laden exhaust gas after desorption?
The contaminant-laden exhaust gas from the rotary kiln is immediately fed into a multi-stage exhaust gas purification system. This typically comprises mechanical dust removal, thermal post-combustion at very high temperatures, flue gas scrubbing, and an activated carbon filter as the final purification stage.
In the dust removal stage, fine particles and dusts are separated from the gas stream before the gas enters the post-combustion chamber. There, the contaminant-laden process gas is thermally treated at temperatures exceeding 850 °C. This post-combustion destroys organic contaminants that left the desorption stage as gaseous compounds. The flue gas then cools and passes through the scrubber stage, where acidic gas components and water-soluble compounds are removed from the exhaust gas stream. The process concludes with the activated carbon filter, which adsorbs remaining trace substances before the cleaned gas is released into the atmosphere via the stack.
Are contaminants completely destroyed or merely relocated?
Organic contaminants such as PAH, TPH, BTEX, PCB, and PFAS are largely destroyed — not merely relocated — through the combination of thermal desorption and subsequent post-combustion. The high-temperature treatment in the post-combustion chamber breaks the chemical bonds of these compounds and converts them into combustion products such as carbon dioxide and water.
Nevertheless, residual materials are generated during exhaust gas treatment that require separate disposal. These include the separated dusts from the dust removal stage, the wash water from flue gas scrubbing, and the spent activated carbon from the filter. These residual materials are not simply disposed of, but are classified and subjected to proper recovery or disposal as part of a structured material flow management process. The key difference from mere relocation lies in the fact that the quantity and volume of contaminants are significantly reduced through thermal treatment.
How are mercury and other volatile heavy metals removed from the exhaust gas?
Mercury and other volatile heavy metals place particular demands on exhaust gas purification because they remain gaseous even at high temperatures and cannot be separated by simple dust removal. They are primarily removed from the exhaust gas stream by adsorption onto activated carbon.
Mercury (Hg) is one of the most challenging contaminants in thermal soil treatment because it evaporates at comparatively low temperatures and can be present in the gas stream as elemental mercury or in organic compounds. Flue gas scrubbing can partially remove water-soluble mercury compounds from the gas stream. Elemental mercury, however, is primarily bound by the downstream activated carbon filter. The activated carbon is disposed of as hazardous waste after saturation. For soils with high mercury content, specific operating parameters and close-meshed monitoring of exhaust gas values are therefore necessary.
What emissions still leave the facility after exhaust gas purification?
After complete exhaust gas purification, essentially combustion products such as carbon dioxide, water vapor, and nitrogen oxides leave the facility via the stack. The concentrations of all relevant contaminants must comply with the legally defined emission limit values of the 17th Federal Immission Control Ordinance (17. BImSchV).
Continuous emission measurements monitor the exhaust gas stream in real time. Parameters measured include dust content, carbon monoxide, nitrogen oxides, sulfur dioxide, hydrogen chloride, organic compounds, and heavy metals. If a measured value exceeds a limit, the plant control system intervenes automatically. The permit under the Federal Immission Control Act obliges the plant operator to carry out regular individual measurements by accredited measurement institutes and to document all operating data. This comprehensive monitoring is the foundation that enables the plant to operate safely and in compliance with regulations on a permanent basis, despite the complex input streams of contaminated soils and mineral waste. Information on quality management and the certifications in use provides further insight into operating standards.
How ARE Deutzen GmbH helps with safe contaminant treatment
ARE Deutzen GmbH has operated a licensed thermal soil treatment facility in western Saxony since 1994 and has more than 30 years of experience in treating complexly contaminated mineral waste. The company assumes full responsibility for the contaminant stream, from delivery through to verified disposal of residual materials.
Specifically, ARE Deutzen offers the following services:
- Thermal desorption in the rotary kiln at up to approximately 600 °C under oxygen exclusion, depending on the material and contaminant load
- Approval for a broad spectrum of contaminants: Hg, TPH, BTEX, PAH, PCB, PFAS/PFOS, PCDD/PCDF, cyanides, nitroaromatics, and chlorinated hydrocarbons
- Multi-stage exhaust gas purification with dust removal, post-combustion, flue gas scrubbing, and activated carbon filter
- Continuous emission monitoring and documentation in accordance with BImSchG
- Material flow management for residual materials from the purification process
- Certification as a specialist waste management company (EfB) as well as to ISO 9001, 14001, 50001, and 18001
If you wish to remediate a contaminated site or safely dispose of mineral waste, contact ARE Deutzen directly. The contact persons will advise you on delivery conditions, approved waste types, and the next steps.