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Mobile thermal desorption treats excavated soil on site using direct-fired or indirect-fired thermal systems. Controlled heat separates organic contaminants from the material; downstream gas treatment, recovery and verification are configured to the feed and permit.
The process
Thermal desorption uses controlled heat to drive contaminants out of soil as vapour, without combusting the soil itself. Excavated material is screened, conditioned, and fed into a rotary drum. Inside the drum the feed is raised above the boiling point of the target contaminant, which volatilizes and leaves the mineral matrix behind.
That is where most descriptions of thermal soil remediation stop, and it is why the process is so often misunderstood. Desorption on its own does not destroy anything. It moves the contaminant from a solid phase into a gas phase. Destruction happens in the next stage, when the vapour stream enters a thermal oxidiser and is held above its destruction temperature for a defined residence time. Gas handling must match the intended outcome, whether contaminant destruction or controlled recovery.
The treated soil is cooled, re-moisturised to control dust, tested against the applicable jurisdictional criteria, and returned to the excavation as engineered fill. Reuse, residual handling and any off-site movements are determined by the approved closure plan.
Treatment train
1. Feed preparationOversize screening, debris removal, and moisture conditioning. Feed consistency governs throughput more than burner capacity does.
2. Desorption drumCounter-flow rotary drum raises soil temperature above the contaminant boiling point. Residence time is tuned by drum speed and inclination, not by feed rate alone.
3. Vapour captureThe off-gas stream, carrying the volatilized contaminant plus steam from soil moisture, is drawn under negative pressure into the secondary chamber. Pressure control helps contain the vapour stream; operating checks and monitoring verify containment.
4. Thermal oxidationThe secondary combustion chamber holds the vapour above its destruction temperature for a defined residence time. This is the step that converts desorption into destruction.
5. Emissions controlQuench, acid gas scrubbing where chlorinated or fluorinated compounds are present, and baghouse particulate capture. Continuous emissions monitoring runs throughout.
6. Treated soil handlingCooling, re-moisturising, confirmation sampling, and placement back into the excavation. Sampling frequency is set by the closure plan, not by convenience.
The process follows soil through screening, the rotary desorber, cooling and discharge. Separate gas, water and dust streams show how particulate capture and thermal oxidation support the treatment train.
Direct-fired or indirect-fired
Burner flame and combustion gases contact the feed inside the rotary drum, then an oxidizer treats the liberated organics.
Feed below 5% total organics, including petroleum hydrocarbons F1 to F4, BTEX, crude, drilling waste, tank bottoms and slop oil. PCBs, legacy dioxin residues, furans and chlorinated materials may also be treated directly when loading and project conditions support it.
The flame remains outside the drum within an insulated box. Hot-fan and condensing configurations provide a smaller, concentrated off-gas stream; condensing can recover hydrocarbons for reuse or sale, while non-condensable gases continue to the oxidizer.
Feed above 5% total organics, including mill scale, biosolids and other high-organic materials. PCBs, legacy dioxin residues, furans and chlorinated materials may use either thermal route depending on loading, feed characteristics and project conditions.
Nelson uses below 5% total organics as a planning guideline for direct treatment and above 5% for indirect treatment. Final route selection depends on characterization, pilot work and permitting. Material at the boundary requires project-specific assessment.
Condensing indirect configurations can recover hydrocarbons; recovered product is separate from the non-condensable gas sent to the oxidizer. Recovery and destruction are different outcomes and are documented against the project objectives.
Mobile thermal desorption fleet configurations
Temperature by contaminant
Feed composition, moisture, particle size, contaminant loading and treatment criteria determine the operating envelope. Treatability testing and commissioning confirm temperature, residence time and production rate; a contaminant name alone does not establish a universal setpoint.
Soil heating and downstream gas treatment are separate stages. Verification may include treated-material sampling, permitted stack testing, emissions monitoring and recovery-product testing, as required by the project and regulator.
Nelson's PFAS thermal work remains at pilot and validation stage and is not offered as a commercial treatment service.
Selecting a thermal remediation contractor
Owned mobile fleet versus brokered equipmentA contractor who owns and maintains the units controls the schedule. A contractor who brokers them inherits someone else's maintenance history and availability.
Verified DRE, not claimed DREAsk for stack test records against a principal organic hazardous constituent from a comparable project, in the same contaminant class, at the same scale.
Regulatory closure history in your jurisdictionPermitting envelopes differ by province, state, and country. A contractor who has closed sites under your regulator has already solved problems the newcomer will discover during commissioning.
Mobilisation capabilityThermal treatment only competes with disposal if the plant reaches the site. Arctic winter, tropical humidity, and remote logistics are engineering problems, and they are solved before mobilisation or not at all.
See mobile thermal desorption fleet configurations
Where this sits
This page explains the method. The contaminant pages set out what the regulator expects for a specific problem, and the capabilities overview sets out the plant, crew, throughput, and verification behind the work on site.
Back to the problem
HydrocarbonsTPH, diesel, and weathered crude in soil, and the criteria a regulator closes against.
BTEXBenzene, toluene, ethylbenzene, and xylenes, including vapour risk and volatile handling.
Talk to the contractor
Tell us four things about the site and a Nelson thermal specialist will come back with an honest read on treatability, throughput, and whether our mobile fleet is the right fit. No obligation, and no pressure if it is not.
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