Frequently Asked Questions
The principle is a two phase process:
• The soil is heated up to a temperature where contaminants vaporize.
• The polluted gases are extracted and the contaminants are destroyed on high temperature through oxidization (and eventually reuse of their energetic content) or collected separately through condensation.
The result is clean soil, that can be re-used and no other contamination left. The Smart Burners system consists of small heating units (burners) connected to steel tubes that serve as heating elements. Each burner and tube can be considered to be a thermal unit. This makes the system very flexible and easy to transport, install and demobilize. The soil is heated by stainless steel heating tubes that are put into the soil, through which hot air is circulating. The airflow is generated by a proprietary individual burner and is running through the pipes at a temperature between 600°C and 900°C. The soil is heated up to the temperature needed to vaporize all contaminants (typically from 90°C to 250°C depending on the contaminant).
Unlike most other in-situ thermal remediation technologies, Smart Burners heats the subsurface by conduction. Conductive heating is a much more uniform method of heat transport regardless of soil type, stratigraphy, or heterogeneity, relative to other methods of subsurface heating (e.g., steam, electrical resistance heating, radio frequency heating, hot water or hot air injection). This is because the thermal conductivity of the full range of soil types ranges only over a factor of < 5. By contrast, fluid conductivities at a given site often range over several orders of magnitude (a hundred or a thousand-fold). Thus, Smart Burners can reliably sweep 100% of the target zone, and do so in a highly predictable timeframe (typically 30-45 days). Smart Burners use of conductive heating means that the targeted treatment zone in the subsurface can be heated, if desired, past the boiling point of water, to vaporize volatile, semi-volatile, and even non-volatile contaminants wherever they might reside. No other in-situ thermal remediation technology can accomplish this cost-effectively. No fluids are injected in the soil during the Smart Burners process. Meanwhile, the boundaries of the treatment zone and the air pollution control system are maintained under a net negative pressure throughout the operation period, so that fugitive emissions are avoided.
Treatment periods depend on a number of factors: depth of contamination, soil moisture and contaminant types. In general, treatment times are greatly accelerated relative to conventional methods, and can require as few as a couple of weeks, and more commonly 1-2 months. Those durations relate to each batch, not the full site.
The temperature of the soil can reach 80 to 500°C, depending on the exact location as well as the nature of the contaminant.
As extraction is based on fluid convection, preferential paths are created to improve the extraction of the desorbed gasses. The heat conduction is not dependent on those preferential paths and therefore the heating itself is working indifferently in all types of soils and combinations thereof.
There are no lower size limits for ISTD. The smallest ISTD project zone so far was 3,5 m² (9 m deep). Governing factors for cost effectiveness include site geometry, type of contaminant, emission standards, and operational requirements. As the site volume increases, the base costs of design, mobilization, installation, and operation can be borne by a larger treatment volume, reducing unit costs accordingly. The deeper the problem, the more attractive the Smart Burners technology solution.
Contaminants extending no more than 1-2 m in depth may be difficult to treat cost-effectively in-situ. In such cases, it may be more cost-effective to consolidate the material and treat it in aboveground piles using Smart Burners on site (ESTD) or to design a horizontal well system.
Can the entire thermal well field be installed below ground surface, to allow existing facility activities to continue?
Yes, it is possible to install the wellheads, electrical cable, collection piping, and instrumentation in below-ground vaults and utility corridors, at additional cost. A period of time would be required for their installation, when sections of the facility will be temporarily cordoned off.
Many types of buried utilities, such as concrete stormwater lines and steel water lines can be left in place and/or protected during heating through appropriate placement of heaters and insulation. Some utilities (e.g., gas lines, PVC pipe) may need to be rerouted or decommissioned.
Yes. Since the heat front drops off sharply adjacent to the heated zone (typically within 1-2 m), experience has shown that heating adjacent to foundations typically has no effect on the foundations. Measures can be taken to further protect structures if necessary (for example in historic buildings).
This distance may vary from 1 to 2,5 meters, in function of the expected or required duration of the project and the related economics.
Currently the maximal depth achieved in a project has been 20 meters. But there is no reason why it could not be deeper. When depth increases the tubes will have a larger section to secure the whole pipe is heated up sufficiently.
Volumes greater than about 750,000 m³ are usually not realistically addressed by this means. However, given that the unit costs diminish as the scale of the project increases, it would be advisable to consult us for a site-specific evaluation.
There is no minimum nor a maximum for Smart Burners in-situ. The limits are mostly economical (for small quantities) or related to duration (for very large quantities and multiple batches).
The heating elements are installed on equidistance of 1 to 2,5 meter (standard 1,5 meter). The placement is done dependent on depth with various means of drilling equipment.
Between 2 and 6 weeks, dependent on the complexity of the site and project.
Working in the subsurface can be uncertain regardless of the in-situ technology. The Smart Burners process is quite robust, but at each project site we attempt to avoid overdesigning the system by sizing it to the mass estimated to be in the ground, based on pre-existing site data. If unexpectedly high contaminant mass is encountered, additional time and/or costs may be entailed to address it. Similarly, we design the system to address the estimated water content in the ground; if much greater amounts of moisture are encountered than expected based on pre-existing data, the time and/or cost to address it can be significant. This is true for other in-situ thermal technologies as well.
Other potential risks, such as electrical hazards, are dealt with using sound work practices and experienced personnel.
Air emissions are treated using off-the-shelf conventional treatment components, such as heat exchangers, chillers, thermal oxidizers and granular activated carbon filter, designed on a site-specific basis to address each of the constituents as cost-effectively as possible. Experience shows that any contaminant emissions are quite low, and that we consistently perform much better than established standards. The principal substances released to the air are carbon dioxide and water vapor.
The Smart Burners Technology is quite different from ex-situ thermal desorption or incineration. With these aboveground thermal technologies, the soil or sludge being treated is exposed to high temperatures only briefly – typically for seconds or minutes. Thus, there can be cool spots where the soil does not get fully treated and where compounds such as dioxins and furans can sometimes be created. By contrast, with Smart Burners the entire treatment zone is heated to target temperatures for days, at a minimum. Most (> 95-99%) of the organic contaminants are destroyed in-situ. Not only are dioxins and furans not created, treatability and field data indicate they too are destroyed, typically to below background levels. Dioxins and furans that are extracted are treated in the air pollution control system.
It is avoided through the proper placement of the thermal well field. All locations targeted for treatment are thereby heated to the desired temperature, while the boundaries of the treatment zone are maintained at a negative pressure. Thus contaminant movement is toward the vacuum collection points, and condensation of contaminants in cool zones is prevented.
Not at all. Since there is no excavating or hauling, the soil is not disturbed during treatment. Also, since there is no earth moving equipment or soil transport on site, there is no dust created, other than during drilling and heater installation activities. Simple dust control measures are applied.
Source zones heated to temperatures at and above the boiling point of water will be sterilized, but upon cooling will undergo repopulation by indigenous microorganisms. Microbiota residing in locations in the downgradient dissolved plume (i.e., outside the target treatment zone) may see mildly elevated temperatures, which are likely to promote rather than hinder their growth and attenuative capacity. Thus, natural attenuation can be enhanced by heating within the source zone.
No. Immediately after treatment by Smart Burners, the soil is sterile, but experience shows that recovery will be rapid. After the soil is fertilized, and seeded following normal revegetation practices, regrowth during the first growing season after treatment should be as good as with original soil. One example in France even showed that weeds, moss, and other vegetation can naturally cover a treated area within one growing season, even without any fertilization or other intervention.
The heating of the unsaturated soil has no notable effect on the stability of the soil. The (temporary) decrease of density takes place because of vaporization of water and pollutants, but does not substantially modify the volume, nor the structure.
Thermal treatment as such does not notably affect stability properties of the soil in the unsaturated zone, as experience has shown in several urban projects where we applied Smart Burners at various depths (up to 16 m). The main reasons lie in the fact that the evaporation of the water (in the non-saturated zone) do not disturb soil aggregates. Therefore no significant physical displacement of soil particles occurs. Additionally, the drying only occurs during Smart Burners treatment zone and eventual settings are compensated by the dense network of steel pipes in the soil (average interdistance is 1,5 m) that keep the whole area stable.
The situation can be different when groundwater lowering is involved, in which case no difference exists with traditional groundwater lowering issues towards stability.
Peat and severely clay soils are, however, to be handled specifically as they might behave difficultly.
These are continuously monitored (CO, CO2, O2, SOx, NOx). Particulates, HCl, HBr, HF and Hg can also be continuously monitored on request.
Heavy metals, dioxins and furans are controlled by external sampling on request of the authorities and following their specific procedures.
Smart Burners will treat just about any organic compound, including:
• Polychlorinated biphenyls (PCBs), dioxins and dibenzofuran
• Polycyclic aromatic hydrocarbons (PAHs), often present in creosote at wood treatment sites, and coal tar at former Manufactured Gas Plant sites
• Trichloroethene (TCE), tetrachloroethene (PCE), 1,2-dichloroethene (1,2-DCE), trichloroethanes (TCA), and other halogenated hydrocarbons, often referred to as chlorinated solvents
• Pesticides and herbicides
• Petroleum, petroleum products and their volatile constituents including benzene, toluene, ethylbenzene, xylenes (BTEX), and methyl tertiary butyl ether (MTBE)
• Any other volatile or semi-volatile hydrocarbon
• Light non-aqueous phase liquids (LNAPLs)
• Nearly any other organic compounds or combination of organic compounds
Then also treat the following inorganic components:
Usually, the low residual organic contaminant concentrations left behind are significantly lower than regulatory cleanup levels.
High soil moisture does not necessarily preclude the use of Smart Burners. However, the energy cost to complete in situ thermal remediation of any type rises with the amount of water that must be vaporized during treatment.
The treatment takes some 30 – 45 days per batch for the vadose zone. Then goes to 120 days for the saturated zone, excl. mobilisation and demobilisation.
These particles are pyrolised, but remain in place; they are inert after treatment. The soil contains not enough oxygen to assure a complete combustion of these elements.
No. However, we can use it to treat the soil under those transfills once we have removed the waste.
- 150 to 200°C between the soil and the gravel underlay
- 50°C between the under layer and the concrete