bout Thermal Desorption

DEEP GREEN's installation are built to treat contaminated soils with organic pollutants, mostly petroleum products (PAH, TPH, BTEX...), such as gasoline, diesel fuel, jet fuel, lubricating oils, crude oil, fuel oils and petroleum by-products, as well as chlorinated solvents, the halogenous pollutants and cyanides.

After adequate pre-screening, blending and soil preparation, an inclined conveyor feeds and meters the material to the Primary Treatment Unit (rotary kiln).

The PTU heats contaminated material to evaporate hydrocarbon contaminants and water. This process is known as low temperature thermal desorption. It is a controlled evaporation process.

Typically, materials are treated at temperatures of 340 °C to 680°C then discharged from the rotary kiln. The heat removes compounds by changing them from liquid to vapour. The vapour becomes part of the exhaust gas stream controlled by the draft system. The gas stream, which also carries combustion products from the burner, is controlled to a temperature of 370°C to 560°C exiting the rotary kiln.

The treated soil is fed into a cooling unit. Water is added for cooling and dust control. The material exits the cooling unit as a remediated material, ready for testing, subsequent reuse and recycling.

The gas stream from the rotary kiln requires further treatment before it is released into the atmosphere. First, it typically goes into a primary dust collector.

The Secondar y Treatment Unit (afterburner) oxidizes hydrocarbon contaminants from the gas stream by heating to temperatures above those required for auto-ignition. Typically, treatment temperatures range from 850°C to 1090°C, depending upon the type of contaminant. Most hydrocarbon contaminants are converted into carbon dioxide and water by the high temperature oxidation reaction. The hydrocarbon contaminants released in the remediation process are eliminated by conversion to inert compounds.

After leaving the afterburner, the gas stream is usually cooled in a gas-cooling unit to a temperature usually about 230°C. The gas stream then passes through the fabric filter where remaining particulate is removed. The gases are then exhausted into the atmosphere, or treated further in a scrubber if chlorinated or sulfonated constituents are involved.

Benefits of Thermal desorption

Release of environmental liability

The most important benefit from thermal desorption is its ability to clean soils up to natural levels. Thermal desorption enable our clients to get rid off their environmental liabilities through an in-depth decontamination of their soils, i.e. a full destruction of organic pollutants contained in the soils.

Control of the costs on the long run

The destruction of pollutants contained in the soils remains the most effective way to minimise the long-term cost of soils decontamination operations, preventing for example the consequences of legislation changes that would potentially imply a second decontamination process. The need for recurring control of a partially decontaminated site also disappears as well as the costs attached. No risk either to support part of the costs for the rehabilitation of a landfill that collected contaminated soils.

Suitable for Sustainable Development

This environment friendly process allows a reuse of the treated soils on-site or in another location instead of storing them in landfills, thereby complying with the European environmental laws.

Technical guarantee

The residual contamination in the soils after treatment is daily checked and operators do control every day if analysis of the clean soils are in accordance with decontamination objectives. All operational parameters of thermal desorption are under control. Operators may quickly adapt operational parameters in case of need. There is no room for uncertainty in thermal desorption.

Guarantee on deadline

The daily capacity of each unit is known. A ton per month quantity of soils treated may be guarantee by Deep Green.

Payment when treatment is completed

Our clients receive an invoice when a certain amount of soils is effectively cleaned and when they receive soils analysis as an evidence of the success of treatment. The financial exposure of our client is quite limited.

Limits of Thermal desorption

Thermal desorption only applies to organic pollutants as well as to cyanides. Thermal desorption has no impact on the concentration of heavy metals in the soils as these pollutants are not transformed into a gaze phase at temperatures under 600°C. They remain in the soils after thermal treatment. Their presence is however not a technical issue for thermal desorption.
It is often not cost efficient to perform thermal on-site treatment of low volume due to mobilisation costs of thermal desorption units. Once can expect that on-site thermal treatment become cost efficient for projects above 5.000 tons for TPH contaminations and 10 to 15.000 tons for PAH contaminations.

Type of contaminants treated

Thermal desorption applies to various organic pollutants as well as to cyanides. Amongst treated contaminants, we can find:

Mineral oils / TPH
Aromatic hydrocarbons / BTEX & PAH
Chlorinated materials / EOX, Solvents
Cyanides
Explosives
And other specific stuffs as Phenols, Cresote, .

Typically, Thermal Desorption is efficient for the treatment of materials (soils, blocks and concrete) contaminated with pollutants having a volatilisation temperature under 550°C.