Managing oil-contaminated soil and sludge has become a key priority for refineries, petrochemical plants, and long-operated oilfields. With environmental regulations tightening worldwide, thermal desorption is increasingly recognized as a dependable approach for soil remediation. Building on this trend, the following article presents a structured, industry-oriented comparison of in-situ and ex-situ thermal desorption, outlining their operating mechanisms, applicability, and the benefits and constraints of each method.
Thermal desorption is a physico-thermal separation technology that uses high temperatures to volatilize hydrocarbons, water, and other organic compounds in soil or sludge. Unlike incineration, its goal is not to combust contaminants but to apply controlled thermal energy to break the bond between pollutants and solids. The volatilized hydrocarbons are subsequently condensed, and the resulting condensate can be recovered as oil, thereby improving resource utilization efficiency. Based on the location of treatment activities, thermal desorption is generally classified into in-situ and ex-situ approaches.
In-situ thermal desorption refers to heating the contaminated soil without excavation. The thermal energy is delivered directly underground, raising subsurface temperatures until organic contaminants volatilize. These vapors are then extracted through a network of wells and conveyed to above-ground treatment units.
Several engineering routes are used to deliver heat into the subsurface:
Electric current is passed between electrodes, causing the soil’s natural resistance to generate heat. Effective in saturated zones and high-moisture environments.
Steel heaters are inserted into boreholes to conduct heat outward. Temperatures can exceed 300°C, enabling treatment of semi-volatile hydrocarbons.
PLH introduces alternating current at standard power-line frequencies (typically 50 or 60 Hz) to induce dielectric heating within the subsurface.
RFH applies electromagnetic waves in the radio-frequency range to heat the contaminated matrix volumetrically.
Ideal for sites where hydrocarbons extend across broad zones and penetrate several meters deep, requiring uniform thermal treatment without extensive excavation.
Applicable in oilfields, industrial pads, and pipeline corridors where physical removal of soil is unsafe, disruptive, or technically unfeasible.
Well-suited for wetlands, coastal belts, and protected habitats where conventional mechanical remediation would cause ecological stress.
Beneficial for areas where preserving existing landforms, operational facilities, or buried infrastructure is a priority during remediation.
Ex-situ thermal desorption involves excavating contaminated soil or oil sludge and transporting it to a specialized processing system. Treatment is performed inside the thermal desorption unit—usually a rotary heating reactor, indirect thermal desorption unit, or pyrolytic reactor—where temperature and residence time can be precisely controlled.
A standard ex-situ thermal desorption line operates through the following stages:
Contaminated soil or sludge is excavated and transported to the processing platform.
Screening, crushing, and moisture adjustment ensure uniform feed size for efficient heating.
Material enters a rotary dryer, indirect heating chamber, or continuous pyrolysis reactor. Temperatures typically range from 300–550°C depending on sludge complexity.
Hydrocarbon vapors are condensed into recoverable oil fractions, which can be used as industrial fuel or feedstock.
Treated solids reach regulatory thresholds for Total Petroleum Hydrocarbon (TPH).
Combustion chambers, catalytic oxidizers, or scrubbers remove organic residues and odor before discharge.
Ex-situ thermal desorption is recommended in the following scenarios:
Effective for refinery tank bottoms, separation pit oil sludge, flotation residues, and highly emulsified sludge that require aggressive heating to break down complex hydrocarbons.
Suitable for treating oil-based or synthetic-based mud cuttings that contain elevated hydrocarbon loads and demand consistent thermal processing.
Appropriate for remediation tasks operating under compressed schedules or strict regulatory timelines.
Best applied when logistics allow easy hauling with loaders and trucks, ensuring efficient feedstock delivery and continuous system operation.
Beston Group manufactures ex-situ thermal desorption units designed for contaminated soil, oil sludge, drilling cuttings, and refinery waste. The unit utilizes an indirect heating mechanism that delivers precise temperature control while preventing direct combustion, significantly reducing the generation of secondary pollutants. This technology offers an efficient resource-recovery pathway for oil-contaminated soil and sludge. Please feel free to contact us for more technical details!
Thermal desorption, whether applied in-situ or ex-situ, has proven to be a reliable and effective technology for addressing oil-contaminated soil and oil sludge. Both approaches are capable of reducing hydrocarbon concentrations to regulatory targets and restoring the usability of impacted sites. The selection of a suitable method depends on a range of project-specific factors, including site conditions, contamination depth, material properties, regulatory expectations, and available infrastructure. As remediation demands continue to tighten, thermal desorption technology is expected to play an increasingly important role in advancing cleaner and more sustainable industrial environments.