BE1030543B1 - IN-SITU OR ON-SITE HYBRID THERMAL DESORPTION: COMBINATION OF THERMAL DESORPTION AND SKIMMING - Google Patents

Abstract

The present invention relates to a method for remediating soil and groundwater containing contaminants with a density less than 1g/cm³, such as hydrocarbons. The present invention provides a method for cleaning contaminated soils based on In-Situ thermal desorption technology. Contaminated areas are heated to the required temperatures for the time necessary for the volatile and semi-volatile compounds to vaporize. Skimming technology focuses on recovering the floating layer. The present invention deals with the combination of in situ thermal desorption and skimming in order to treat all layers present in the subsoil and optimize the treatment time of the saturated zone by heating the contaminant and making it thus more mobile.

Description

1 BE2022/5382

HYBRID THERMAL DESORPTION IN SITU OR ON SITE: COMBINATION

THERMAL DESORPTION AND SKIMMING

FIELD OF THE INVENTION

The present invention relates to a system for combining groundwater and contaminated soil remediation technologies. In particular, the invention relates to a method for coupling thermal desorption and skimming technologies for pollution by light non-aqueous phase liquids (LNAPL) such as petroleum hydrocarbons.

In a second aspect, the present invention also relates to the remediation of both a floating layer in the saturated zone and the soil in the unsaturated zone below. Heating makes it possible to mobilize the floating layer towards the skimmers by reducing the viscosity of the pollutant and also to vaporize the pollutant present in the unsaturated layer and to direct this vapor towards the steam extraction tubes.

CONTEXT

Contamination of soil and groundwater is an issue of great importance in a world where the environment and sustainable development are becoming increasingly important. This often invisible problem can be caused by a wide variety of chemical, biological or even radioactive contaminants and an equally wide range of pollution sources. If nothing is done, contamination can spread and end up in other resources essential to the surrounding flora and fauna. It is therefore important, for environmental and public health purposes, to eliminate these contaminants before they have too much impact.

Soil and groundwater remediation technologies are numerous and can be separated into three main categories: thermal, biological and physico-chemical. The choice of technique depends on several parameters such as the nature of the contamination, the properties of the soil, the physical constraints of the site and the total cost of the project. The present invention combines two soil remediation technologies: thermal desorption and In Situ skimming.

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Thermal desorption

According to the present invention, said materials are first heated by thermal conduction and under a slight vacuum to a temperature and vacuum sufficient to cause vaporization of said contaminants. The materials are heated by thermal conduction through heating elements introduced into said materials. In addition to allowing greater removal of contaminants from soils, increased heat in the soil can cause contaminants to chemically change before they are removed. WO2016062757A1 and US7618215B2 are recognized as prior art to the invention.

In particular, thermal desorption is a technology that relies on heating the ground so that contaminants volatilize. Once in the vapor phase, the contaminants can be extracted from the ground to be destroyed or recovered after condensation. Thermal desorption is effective against all organic contaminants, as well as some inorganic pollutants such as cyanides and mercury. It is effective against all compounds whose boiling point at atmospheric pressure is less than 550°C.

Heating by thermal conduction is one of the ways to implement thermal desorption. In this application, thermal energy from the heating tubes propagates radially into the ground. This technique has several advantages over other soil treatment approaches. It is capable of reaching ground temperatures above 350°C (which is, for example, not possible with resistive electric heating - as in the document

US9347302B2), which allows a large number of contaminants to be quickly cleaned, regardless of the heterogeneity of the soil. It is applicable both ex-situ and in-situ. In ex-situ thermal desorption (ESTD), soil is excavated and placed in a pile, which is then treated. In the case of in situ thermal desorption (ISTD), heating tubes are inserted directly into the polluted area. This avoids excavation and transport of soil, and makes it possible to treat soils with limited space and/or access, such as remote or urban sites, underground construction, etc. Overall, this saves considerable time, reduces energy consumption and minimizes the environmental impact of processing.

One process that can be used to remove contaminants from underground soil is a soil vapor extraction process. In such a process, a vacuum is applied to the ground to draw air and vapor through the underground soil. Vacuum can be applied to a ground/air interface, or vacuum can be applied through vacuum wells placed in the ground. Air and steam can carry volatile contaminants into

3 BE2022/5382 the vacuum source. The gaseous effluent removed from the ground by vacuum, which includes contaminants that were in the ground, is then transported to a treatment facility where it is treated to remove or reduce the contaminants to acceptable levels. In-situ thermal desorption can be used to increase the efficiency of a soil vapor extraction process. In-situ thermal desorption involves the in-situ heating of the soil to increase the soil temperature while simultaneously removing residual gases from the soil. Heat transferred to contaminated soil can raise soil temperatures above the vaporization temperatures of contaminants in the soil and cause vaporization of contaminants. A vacuum applied to the ground removes the vaporized contaminant from the ground.

Heating by thermal conduction combined with the application of a vacuum into the contaminated soil to remove the contaminant is an old technique.

Limits of thermal desorption

Thermal treatment consists of heating contaminated materials to extract volatile and semi-volatile pollutants in the form of vapors. Due to the presence of water, thermal desorption consumes a lot of energy. Therefore, heat treatment is very suitable for remediation of the vadose zone (unsaturated) but less so for groundwater (saturated zone).

Removal of pollutants in groundwater

One of the techniques for eliminating the floating layer in the saturated zone is skimming. The purpose of the present invention is to provide a device for skimming LNAPL pollution, particularly petroleum hydrocarbons above groundwater, which is capable of precisely positioning itself at the hydrocarbon-water interface based on buoyancy in water.

The device of the present invention, installed in a well previously drilled to reach the level of the water table, must make it possible to skim the upper part of the underground water tables and thus ensure total recovery of the supernatant liquid, even if the thickness is small and whatever the variation in the water table level.

In particular, it aims to propose a process capable of skimming floating layers of hydrocarbons with a thickness of less than 1 mm in an industrial environment, such as oil ports or petrochemical complexes where the extent of the floating layer d Hydrocarbons can reach areas of several hectares. These areas are generally located near large rivers or near the sea, where the water table can vary significantly in

4 BE2022/5382 due to tides or locks, and the invention, in a preferred embodiment, aims to take this particularity into account.

EP1334780A2 and EP1518614A1 are recognized as prior art to the invention.

The present invention discloses a device for skimming pollutants such as a floating layer of hydrocarbons on a water table comprising at least one float and at least one pollutant suction pipe, characterized in that the latter also comprises at least a collection orifice and at least one groove on the upper part, allowing access of said pollutants to said collection orifice and in that said float has an intermediate density between the density of the water and the density of the pollutants to be recovered allowing it to be positioned at the interface between water and the pollutants floating there.

According to the invention, the device further comprises at least one water suction pipe to form a folding cone.

An essential characteristic of the present invention is that the pollutant suction and water suction pipes simultaneously serve as a slide for said float.

The invention also discloses a method for cleaning bodies of water characterized in that a hydrocarbon floating on a body of water is sucked towards a central collection unit via a pipe connected to a device comprising a float comprising a groove and a collection orifice, the upper part of said float remaining at the hydrocarbon/water interface by being guided on the slides and, conveying said hydrocarbons via a collection pipe connected to a suction pipe through a transfer channel in a assembly profile. …Limits of skimming

The effectiveness of groundwater treatment by skimming is dictated by the movement of the pollutant to the pumping wells which is directly related to the viscosity of the floating layer product. Therefore, the greater the viscosity of the pollutant, the longer the pumping time.

SUMMARY OF THE INVENTION

The present invention and its embodiments serve to provide a solution to one or more of the aforementioned drawbacks. To this end, the present invention relates to — hot skimming which reduces the viscosity of the pollutants which make up the floating layer to be treated by heating the saturated and unsaturated zone.

Thermal desorption can be used in both saturated and unsaturated soil layers. Skimming is used for processing floating layers. The combination of the two techniques makes it possible to cover all layers in the sites of interest. One of the main innovations of the invention is to treat contamination at the source, both in the vadose zone and in the saturated zone, with the elimination of all pollution.

The invention is further described by the following non-limiting examples which further illustrate the invention, and are not intended to, nor should be construed as, limiting the scope of the invention.

The present invention is described in more detail below, with reference to examples which are not limiting.

The present invention discloses a pollutant skimming device combined with a heating system. The device for skimming pollutants such as a floating layer of hydrocarbons on a water table comprises at least one float and at least one hydrocarbon suction pipe, characterized in that the latter further comprises at least one orifice collection and at least one groove on the upper part, allowing access of said hydrocarbon to said collection orifice and in that said float has an intermediate density between the density of the water and the density of the hydrocarbons to be recovered allowing it to be position at the interface between water and floating hydrocarbons.

According to the invention, the device further comprises at least one water suction pipe to form a folding cone.

An essential characteristic of the present invention is that the hydrocarbon suction and water suction pipes simultaneously serve as a slide for said float.

Furthermore, according to the invention, the float is essentially made of high density polyethylene (HDPE) whose density can vary in the range of 0.94 to 0.97 g/cm? .

Advantageously, the suction pipe communicates via a lower connection part with a collection pipe communicating with the collection orifice and constitutes an assembly for the suction of hydrocarbons.

Another characteristic of the invention is that the float is made up of modular elements.

The invention also discloses a method for cleaning bodies of water characterized in that a pollutant floating on a body of water is sucked towards a central collection unit via a pipe connected to a device comprising a float comprising a groove and a collection orifice, the upper part of said float

6 BE2022/5382 clinging to the hydrocarbon/water interface while being guided on the slides and, conveying said hydrocarbons via a collection pipe connected to a suction pipe through a transfer channel in an assembly profile.

In a particular embodiment of the invention, water is sucked up by a water suction pipe to form a drawdown cone in order to facilitate the collection of hydrocarbons.

Finally, the invention describes the use of the skimming device for the recovery of hydrocarbons infiltrated in groundwater.

In a first aspect, the present invention provides a method for heating the floating layer and recovering pollutants. Thus, in a preferred embodiment, the system comprises: - at least one heating element to be inserted into the ground, said heating element comprises a non-perforated outer tube having an open end and a closed end and a non-perforated inner tube having the two open ends, the inner tube is inserted into the outer tube thus forming an internal space between the two tubes, the open ends of the tubes and the internal space can be connected to a heat source to heat the soil thus transforming the contaminants present in the soil in contaminant vapor; -at least one metal mass element insertable in the annular space formed between the outer and inner tubes connected to one of the ends of the tubes by a rod whose height is adjustable; - at least one combustion chamber consisting of two concentric cylinders, the inner cylinder of which is made of refractory material, thus constituting an annular part through which secondary air is introduced by means of a separate air inlet, in order to cooling the exterior of said combustion chamber and providing additional combustion air to oxidize gaseous pollutants introduced into said combustion chamber through the inlet; - at least one control box for the heat source, said box being able to be connected to the end of the heating element, in the direct extension of the combustion chamber; - at least one means for measuring the temperature of the soil, said means is inserted into the contaminated soil; - at least one means for measuring the temperature of the combustion fluids of the heating element, said means being able to be connected to the heating element;

7 BE2022/5382 - at least one heating box connected to the end of the combustion chamber is regulated according to the temperatures measured by the three elements described above;

In a second aspect, the invention provides a system for treating the floating layer and for treating the vadose zone. Thus, in a preferred embodiment, the system comprises the aforementioned elements and: - at least one perforated steam tube which can be connected to a suction means for extracting the contaminating vapor from the ground, the diameter of the tube steam is between 25 mm and 60 mm, - at least one means of measuring the pressure of the soil inserted in the contaminated soil, - at least one means of measuring the pressure of the soil which can be connected to the steam tube.

DESCRIPTION OF FIGURES

The following description of the figures of specific embodiments of the invention is merely exemplary in nature and is not intended to limit the present teachings, their application or their uses. In all drawings, corresponding reference numerals indicate similar or corresponding parts and features.

Figure 1 shows a perspective view of the device of the invention.

Figure 2 represents a schematic view of the operation of a remediation process using the device according to Figure 1 installed in a borehole.

Figure 3 illustrates thermal desorption by the action of the heating tubes equipped with burners and the vapor extraction system.

Figure 4 is an illustration of the first configuration of the combination of in situ thermal desorption and skimming technologies for the treatment of the floating layer.

Figure 5 is an illustration of the second configuration combining in situ thermal desorption and skimming technologies for the treatment of the floating layer and the vadose zone.

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Definitions

The terms "contaminated soil" and "contaminated material" are used herein synonymously and should be understood to include all types of soil, sludge or other materials that may be contaminated by any cocktail of pollutants, such as contaminants organic, for example hydrocarbons, and inorganic contaminants, with a boiling point at atmospheric pressure of 550°C or more and/or heavy metals.

Conductive heat occurs when two materials or material objects are in direct contact and the temperature of one is higher than the other. Thermal conduction is the transfer of kinetic energy from the hottest medium to the coldest medium. The term "conduction" as used here is therefore intended to refer to all types of heat transfer in which heat is moved from one (hotter) object to another (colder) by direct contact. It should be understood that in the present invention, when heat transfer by conduction is mentioned, a very small amount of heat is also transferred to the ground by radiation.

The term groundwater (or water table) refers to the water-saturated zone of the contaminated soil.

The term "floating layer" refers to a certain quantity of liquid pollutants, very poorly soluble in water, and lighter than water (LNAPL) which have reached the water table. In such a context, the liquid accumulates in the capillary fringe, just above the upper level of the water table. The floating (or supernatant) layer forms when this accumulation reaches a critical value.

Reference throughout this specification to "an embodiment" or "an embodiment" means that a particular feature, structure or element described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the expressions "in one embodiment" or "in an embodiment" appearing in various places throughout this specification do not necessarily refer to the same embodiment, but may do so. Further, the particular features, structures or features may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more modes of

9 BE2022/5382 realization. Additionally, although some embodiments described herein include some, but not others, features included in other embodiments, combinations of features of different embodiments are intended to be within the scope of application of the invention and form different embodiments, as would be understood by a person skilled in the art. For example, in the following claims, any of the claimed embodiments may be used in any combination.

The invention

The invention relates to a method for treating soil and groundwater comprising alternatively heating the soil and pumping the floating layer comprising: -a set of at least one heating well in the vadose zone, in the floating layer or in the groundwater combined with a pumping well in which the skimming system is installed; -at least one system of perforated tubes added in the heating well near the heating element in the case of treatment in a vadose zone and/or to recover the contaminated steam produced during the treatment.

In one embodiment, said heating element comprises: -at least one system of internal and external tubes connected to a heat source to heat the ground, thus transforming the contaminants present in the ground into contaminant vapors; and at least one control unit controlling the heat source, said control unit being connectable to or remote from the end of the heating element.

The water table skimmer is used to recover a layer of polluting supernatants in general and hydrocarbons in particular, from a water table or underground, this floating layer being observed beforehand by a control piezometer in an equipped drilled well of a mesh tube (20).

The device of the present invention shown in Figures 1 and 2 comprises a cylindrical profile in high density polyethylene called float (5), the specific weight of which is such that the upper part will be positioned at the interface between the layer of hydrocarbons ( 15) insoluble in water and groundwater. — Generally, the specific weight of the "high density" polyethylene used varies depending on the catalysts used from 0.94 to 0.97 g/cm3 but is preferably around 0.96 g/cm3, that of hydrocarbons around 0 .8 g/cm and that of water of approximately 1

10 BE2022/5382 g/cm3. Another resin with similar specific gravity and good strength properties may also be suitable.

The float (5) is provided with two external guide grooves (10) and a collection hole (3) passing through the float along its diameter. The dimensions of the float (5) must be less than the diameter of the receiving well (20), which can be, for example, a 4 inch (114 mm) well (figure 2, 3 and 4).

Two slides formed by the water (9) and oil (2) suction pipes or equivalent means guide the float (5) which can follow local variations in the water level in the well (20). High density polyethylene is the ideal material for this type of float because, in addition to its intermediate density between pollutants and water, it resists well to the attacks (dissolution, softening, swelling) of most hydrocarbons, which is why it is used, like polypropylene, in the manufacture of automobile tanks.

The float (5) is preferably constructed in a modular manner, so that the length of the device can be significantly changed by stacking the modules.

The same applies to the length of the guides formed by the water suction (9) and oil suction (2) pipes, because the device must be able to automatically adapt to extreme fluctuations in height of the groundwater for months without any control. As mentioned above, the water table level can vary significantly from place to place and from time to time, for example due to tidal precipitation or nearby locks.

The two tubes also serving as guides (2) and (9) are connected at the head and at the base respectively by an upper (1) and lower (7) connecting profile, with in the center of the lower connecting piece (7) a suction tube (6) whose length corresponds approximately to half the sliding height on the guides.

The head piece (1) is provided with a suitable means such as an orifice (11) which will be used to hang the skimmer on a chain in order to maintain it in the well at a median height between the maximum and minimum level of the water table, thus making it possible to integrate variations in the level of the latter over time.

Initially, it is therefore appropriate to choose a skimming device whose diameter is slightly smaller than the diameter of the drilled well (20). One of the two slides of the shape shown serves as a transfer tube (2) by sucking the product through the collection orifice (3) of the float. This product will be conveyed via the collection tube (6) and the channel (8) to the suction tube (2) which is connected by a flexible tube (12) to a central collection unit (16). The entire device is then lowered into the well by a chain holding it in position (13) until it is in position.

11 BE2022/5382 contact with the water level. The necessary distance has usually been measured beforehand. The device, thanks to its float (5), follows variations in the level of the water-pollutant interface and therefore the level of the local water table. The float (5) is perfectly capable of adapting to this level because it is held and guided by the two slides (2) and (9). It is also possible to drill several wells and install a device according to the invention in each of them.

If a floating layer of hydrocarbons (15) is present, the float (5) of the device of the invention will stabilize at the water-hydrocarbon interface due to its density and its profile.

By means of a suitable pumping unit (16), the product will thus be sucked through the device of the invention.

The present invention also relates to a system comprising a number of perforated and non-perforated thermally conductive pipes placed in a floor. The tube (25) is in communication with a heat source (21) which circulates a heated fluid within the tube, causing a rise in the temperature of the surrounding medium (18)(15)(19). Perforated tubes (27) are placed around the heating tubes when treating the vadose zone. In certain stages of the application plan (Figure 5), the perforated tubes (27) are evacuated, transporting the contaminated vapors to a treatment system. In other stages of the application plan (Figure 4), these perforated tubes (27) are not necessary.

Heating tubes (25) are placed in contaminated material, for example contaminated soil (18)(15)(19). A heated fluid, preferably high temperature air/gas heated to a temperature between 300 and 800°C, and more preferably between 500 and 750°C, circulates in the tubes (25). Heat (28) is transferred to the materials by thermal conduction and gradually increases the temperature of the ground, the floating layer (15) and a certain part of the aquifer (19) (and the vadose zone (18)) . The elevated ground temperature causes mobilization of the floating layer toward the pumping wells and volatilization of contaminants from the vadose zone, producing contaminated vapor that is collected from the ground (18) via the steam tubes (27). Vaporized soil contaminants (5) are mobilized into the perforated tubes (27) by imposing negative pressure in the perforated tubes (27), for example by connecting the tubes to a vacuum system. Contaminated vapors travel through the perforated tubes (27) and may be collected by a vapor collection pipe system carrying the contaminated fluid to a processing unit and/or are injected and destroyed in the burner flame therein. of the combustion chamber (22).

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The vacuum is maintained throughout the heating period and for a sufficient time after heating to prevent loss or dispersion of contaminants.

The vacuum system must be capable of drawing a vacuum appropriate to the combination of soil permeability and perforated tubes in a treatment system. The vacuum system (27) may be capable of drawing a vacuum in the range of 50 Pa to 5000 Pa. The vacuum system may be a fan or a sealed pump. In a preferred embodiment, a drainage pack is placed around the perforated tube (22) to ensure even suction.

In a preferred embodiment, the heating system is centralized on the saturated zone of the ground in order to heat the water table and mobilize the pollutants towards the skimmer (figure 4).

In another preferred embodiment, when for example the pollution extends from the vadose zone to the water table, the heating system is applied to the saturated and unsaturated zone (figure 5): the pollutants from the unsaturated zone of the soil are treated by thermal desorption and recovered by the extraction system while the floating layer in the water table is mobilized towards the skimmer.

The pipes (25)(20) are arranged in a pattern in the contaminated soil so that the most uniform heating is achieved along the pattern. A regular pattern of pipes can be used, such as triangular, square, rectangular, hexagonal, etc. chosen to substantially cover the contaminated area. Triangular models are preferred because they offer the best thermal efficiency. The ground temperature is increased by circulating heated fluid through the pipes (25). Superposition of heat flow from all pipes results in a more uniform increase in temperature throughout the pattern. It will be appreciated that the number of pipes (25)(20) applied in the ground, the spacing, the relative position of the pipes, may vary depending on the degree of contamination and/or the time desired to complete the process and/or the soil type and/or economic considerations. In a preferred embodiment, the distance between two adjacent pipes is between 1m and 1.8m.

All the metal parts used in the device of the present invention are made of stainless steel for obvious reasons of resistance to corrosion and heat over time.

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The device can be operated continuously or intermittently by a control unit which is controlled by different measuring devices, in particular by the level and importance of the audible or visual alarm devices and by the remote control.

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LEGEND

1. Upper assembly profile 2. Floating layer suction tube also serving as a slide for the float 3. Float port for oil recovery 4. Connection groove on the top of the float, positioned at the oil/water interface. 5. Float 6. Floating layer collector tube 7. Lower assembly profile including the transfer channel to the floating layer collector tube 8. Transfer channel to the central suction tube 9. Suction tube water to create an additional drawdown also serving as a slide for the float. 10. Diameter slot for float guide 11. Hole for attaching the device to a chain 12. Flexible suction tube 13. Chain for maintaining position in the well 14. Water level 15. Floating layer of hydrocarbons 16. Central collection unit with vacuum tank 17. Ground level 18. Unsaturated zone 19. Saturated zone 20. Casing installed in a borehole. 21. Burner 22. Burner body 23. Flexible return 24. Make-up valve 25. Heating tube 26. Polluted vadose zone 27. Steam tube 28. Heat conduction

Claims (7)

15 BE2022/5382 CLAIMS 1. A soil and groundwater treatment system adapted to alternately heat the soil and pump the floating layer comprising: - at least one heating well with a heating element in the vadose zone, in the floating layer or in the groundwater, combined with a pumping well in which a skimming device suitable for skimming pollutants is installed; - at least one system of perforated tubes, suitable for recovering the contaminated steam produced by the heating element, in which the system of perforated tubes is added in the heating well near the heating element. 2. System according to claim 1, said heating element comprising: - at least one system of internal and external tubes connected to a heat source for heating the ground so as to transform the contaminants present in the ground into contaminant vapors; and at least one control unit suitable for controlling the heat source, said control unit being connectable to or remote from the end of the heating element. 3. System according to claim 1, in which a hydrocarbon skimming device for groundwater installed in the pumping well comprises a float, which has the following characteristics: - a density which is between the density of the water (1 g/cm? at 20°C) and the density of the hydrocarbons (<1 g/cm°) to be recovered; - a high density polyethylene (HDPE) material whose density can vary in the range of 0.94 to 0.97 g/cm? . 4. System according to claim 1, said perforated tube system being characterized by: at least one perforated tube (steam tube) connectable to a vacuum unit to extract the contaminating vapor from the contaminated soil; and the diameter of the steam tube is between 25mm and 60mm. 5. System according to claims 1 to 4 where the distance between the heating wells is between 1m and 20m. 16 BE2022/5382 6. System according to claims 1 to 5 where the distance between the pumping wells is between 1m and 20m. 7. System according to claims 1 to 6 where the heating zone can be limited to the floating layer by moving the heat source in the internal tube to the desired depth.