Fl ELD OF THE I NVENTI ON

The present invention relates to a system for combining technologies for the remediation of contaminated groundwater and soil. I n particular, the invention relates to a process for coupling thermal desorption and skimm ing technologies for light non-aqueous phase liquid (LNAPL) pollution such as petroleum hydrocarbons.

I n a second aspect, the present invention also relates to clean up both a floating layer in the saturated zone and the soil in the unsaturated zone underneath. Heating 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 vapor extraction tubes.

BACKGROUND

Soil and groundwater contam ination 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 chem ical, biological or even radioactive contaminants and an equally wide range of pollution sources. Left unchecked, contam ination can spread and end up in other resources that are essential to the surrounding fauna and flora. It is therefore important, for environmental and public health purposes, to remove these contam inants before they have too much impact.

Soil and groundwater remediation technologies are m ultiple and can be separated into three main categories: thermal, biological and physicochem ical. The choice of technique depends on several parameters such as the nature of the contam ination, the soil properties, the physical constraints of the site and the total cost of the project. The present invention combines two technologies for soil remediation : thermal desorption and I n Situ skimm ing.

Thermal Desorption

According to the present invention, said materials are first heated by thermal conduction and under slight vacuum to a temperature and vacuum sufficient to cause vaporization of said contam inants. The materials are heated by thermal conduction through heating elements introduced into said materials. I n addition to allowing greater removal of contam inants from soils, the increased heat in the soil can cause chemical change of the contam inants prior to removal. WO2016062757A1 and

US7618215B2 are recognized as prior art to the invention.

I n particular, thermal desorption is a technology that relies on heating the soil so that the contam inants are volatilized. Once in a vapor phase, the contaminants can be extracted from the soil for destruction or recovery 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 with a boiling point at atmospheric pressure below 550°C.

Thermal conductive heating is one of the ways to implement thermal desorption. I n this application, the thermal energy from the heating tubes propagates radially through the soil. This technique has several advantages over other soil treatment approaches. It is capable of reaching soil temperatures in excess of 350°C (which is for example not possible with resistive electric heating - as in US9347302B2) , allowing rapid clean-up of a large number of contaminants, regardless of soil heterogeneity. It is applicable both ex-situ and in-situ. I n ex-situ thermal desorption (ESTD) , the soil is excavated and placed in a pile, which is then treated. I n in situ thermal desorption (ISTD) , heating tubes are inserted directly into the polluted area. This avoids excavation and transport of the soil, and allows treatment of soils with lim ited space and/or access, such as remote or urban sites, underground construction, etc. Overall, this saves significant time, reduces energy consumption and minim izes the environmental impact of the treatment.

One process that can be used to remove contaminants from underground soil is a soil vapor extraction process. I n such a process, a vacuum is applied to the soil to draw air and vapor through the subsurface soil. The vacuum can be applied at a soil/air interface, or the vacuum can be applied through vacuum wells placed in the soil. Air and vapor can drive volatile contaminants to the vacuum source. Gaseous effluents removed from the soil by the vacuum , which include contam inants that were in the soil, are then transported to a treatment facility where they are treated to remove or reduce the contam inants to acceptable levels. I n-situ thermal desorption can be used to increase the efficiency of a soil vapor extraction process. I n-situ thermal desorption involves in-situ heating of the soil to raise the soil temperature while simultaneously removing soil off-gases. The heat transferred to the contam inated soil can raise the soil temperature above the vaporization temperatures of the contam inants in the soil and cause the contaminants to vaporize. A vacuum applied to the soil removes the vaporized contam inant from the soil. Thermal conductive heating in combination with vacuum applied into contam inated soil to remove the contaminant is old in the art.

Lim itations of thermal desorption

Thermal treatment involves heating contam inated materials to extract volatile and sem i-volatile pollutants in the form of vapors. Due to the presence of water, the thermal desorption is very energy-consuming. Therefore, the thermal treatment is very appropriate for the remediation of the vadose (unsaturated) zone but less for the groundwater (saturated zone) .

Pollutant removal for groundwater

One of the techniques for removing the floating layer in the saturated zone is skim m ing. The purpose of the present invention is to provide a device for skim ming LNAPL pollution, in particular petroleum hydrocarbons above groundwater, which is able to position itself precisely at the hydrocarbon-water interface based on buoyancy in the water.

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

I n particular, it aims to propose a process capable of skimm ing 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 of hydrocarbons can reach surfaces of several hectares. These areas are generally located near major rivers or near the sea, where the water table can vary significantly due to tides or locks, and the invention, in a preferred embodiment, is intended to take account of this particularity.

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

The present invention discloses a device for skim m ing pollutants such as a floating layer of hydrocarbons on groundwater comprising at least one float and at least one pipe for sucking up pollutants, characterized in that the latter also comprises at least one 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 the water and the pollutants floating thereon. According to the invention, the device further comprises at least one water suction pipe to form a drawdown cone.

It is a key feature of the present invention that the pollutants suction and water suction pipes simultaneously serve as a slide for said float.

The invention further discloses a method for cleaning up water bodies characterized in that a hydrocarbon floating on a water body is sucked to a central collection unit via a hose connected to a device comprising a float comprising a groove and a collection port, the upper part of said float holding on to the hydrocarbon/water interface by being guided on the slides and, conveying said hydrocarbons via a collection hose connected to a suction hose through a transfer channel in an assembly profile.

Lim itations of skim m ing

The effectiveness of skim ming groundwater treatment 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 I NVENTI ON

The present invention and embodiments thereof serve to provide a solution to one or more of above-mentioned disadvantages. To this end, the present invention relates to hot skimm ing which reduces the viscosity of the pollutants that make up the floating layer to be treated by heating the saturated and non-saturated zone.

Thermal desorption can be used in both saturated and unsaturated soil layers. Skim ming is used for the treatment of floating layers. The combination of the two techniques allows coverage of all layers in the sites of interest. One of the main innovations of the invention is to treat the contamination at the source, both in the vadose zone and in the saturated zone, with the removal 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 they be interpreted to, lim it the scope of the invention.

The present invention is described in more details hereinafter, with reference to examples that are not limitative.

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

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

It is a key feature of the present invention that the hydrocarbons suction and water suction pipes simultaneously serve as a slide for said float.

Also, according to the invention, the float is made essentially of high-density polyethylene (HDPE) with a density that can vary in the range of 0.94 to 0.97 g/cm ³ . Advantageously, the suction pipe comm unicates via a lower connecting piece with a collection pipe comm unicating with the collection port and constitutes an assembly for the suction of hydrocarbons.

A further feature of the invention is that the float is constituted by modular elements. The invention further discloses a method for cleaning up water bodies characterized in that a pollutant floating on a water body is sucked to a central collection unit through a hose connected to a device comprising a float comprising a groove and a collection port, the upper part of said float holding on to the hydrocarbon/water interface by being guided on the slides and, conveying said hydrocarbons via a collection hose connected to a suction hose through a transfer channel in an assembly profile.

I n a particular embodiment of the invention, water is drawn through a water suction pipe to form a cone of drawdown to facilitate the collection of hydrocarbons.

Finally, the invention describes the use of the skimm ing device for the recovery of hydrocarbons seeped into groundwater.

I n a first aspect, the present invention provides a method to heat the floating layer and recover the pollutants. Therefore, in a preferred embodiment, the system comprises:

- at least one heating element for insertion into the soil, said heating element comprises an imperforate outer tube having an open end and a closed end and an imperforate inner tube having both ends open, the inner tube is inserted into the outer tube thereby form ing an internal space between the two tubes, the open ends of the tubes and the internal space are connectable to a heat source for heating the soil thereby transform ing contam inants present in the soil into contam inant vapour;

- at least one metallic mass element insertable into the annular space formed between the outer and inner tubes connected to one of the ends of the tubes by a rod whose height can be adj usted;

- 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 cool the outside of said combustion chamber and to provide additional combustion air to oxidise the gaseous pollutants introduced into said combustion chamber through the inlet;

- at least one heat source control box, said box is connectable to the end of the heating element, in 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 is connectable to the heating element;

- 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;

I n a second aspect, the invention provides a system to treat the floating layer and to treat the vadose zone. Therefore, in a preferred embodiment, the system includes the above-mentioned elements and:

- at least one vapor tube perforated and connectable to a suction means for the extraction of contaminant steam from the soil, the diameter of the steam tube is between 25mm and 60m m ,

- at least one soil pressure measuring means inserted in the contaminated soil, - at least one soil pressure measuring means connectable to the vapor tube.

DESCRI PTI ON OF Fl GURES

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 uses. Throughout the drawings, corresponding reference numerals indicate like 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 through the action of heating tubes equipped with burners and the vapor extraction system .

Figure 4 is an illustration of the first configuration in combining I n-Situ thermal desorption and skim ming technologies for the treatment of the floating layer.

Figure 5 is an illustration of the second configuration in combining I n Situ thermal desorption and skim ming technologies for the treatment of the floating layer and the vadose zone.

DETAI LED DESCRI PTI ON OF THE I NVENTI ON

Definitions

The terms "contam inated soil" and "contam inated material" are used here as synonyms and should be understood to include all types of soil, sludge or other materials that may be contaminated with any cocktail of pollutants, such as organic contam inants, e.g. 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 temperature of the other. Thermal conduction is the transfer of kinetic energy from the warmer medium to the colder one. The term "conduction" as used herein is therefore intended to refer to all types of heat transfer in which heat is moved from one (warmer) object to another (colder) object by direct contact. It should be understood that in the present invention, when heat transfer by conduction is mentioned, also a very small amount of heat is usually also transferred to the ground by means of radiation.

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

The term "floating layer" refers to a certain amount of liquid pollutants, with very low solubility in water, and lighter-than-water (LNAPL) that have reached the groundwater table. I n such a context, the liquid accumulates in the capillary fringe, j ust above the upper level of the water table. The floating (or supernatant) layer is formed when this accum ulation reaches a critical value.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment but may. Furthermore, the particular features, structures or characteristics 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 embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

The invention

The invention relates to a method of treating soil and groundwater comprising alternately 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 skimm ing system is installed; at least one perforated tube system added in heating well close to heating element in the case of vadose zone treatment and/or to recover the contaminated vapor produced during treatment.

I n an embodiment, said heating element comprising: at least one system of internal and external tubes connected to a heat source for heating the soil thereby transform ing contaminants present in the soil into contam inant vapors; and at least one control unit controlling the heat source, said control unit being connectable or remote from the end of the heating element.

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

The device of the present invention shown in figures 1 and 2 comprises a cylindrical profile made of high-density polyethylene called a 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 the water table. Generally, the specific weight of the "high-density" polyethylene used varies according to the catalysts used from 0.94 to 0.97 g/cm ³ but is preferably about 0.96 g/cm ³ , that of the hydrocarbons about 0.8 g/cm ³ and that of the water about 1 g/cm ³ . Another resin with a 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) should be smaller than the diameter of the receiving well (20) , which can be, for example, a 4 inch (114m m) 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 will be able to follow the local water level variations in the well (20) . High-density polyethylene is the ideal material for this type of float because, apart from its intermediate density between pollutants and water, it resists well to the aggressions (dissolution, softening, swelling) of most hydrocarbons, which is why it is used, like polypropylene, in the manufacture of car tanks.

The float (5) is preferably constructed in a modular manner so that the length of the device can be varied considerably by stacking modules. The same applies to the length of the guides formed by the water suction (9) and oil suction (2) pipes, as the device must be able to adapt automatically to extreme fluctuations in the height of the water table over months without any monitoring. As mentioned above, the level of the water table can vary considerably from place to place and from time to time, e.g. due to tidal precipitation or to nearby locks.

The two tubes also serving as guides (2) and (9) are connected at the head and base respectively by means of an upper (1 ) and a lower (7) connecting profile, with a suction tube (6) in the centre of the lower connecting piece (7), the length of which corresponds approximately to half the sliding height on the guides. The head piece (1 ) is provided with an appropriate means such as an orifice (1 1 ) which will serve to hook the skimm ing device to a chain in order to keep it in the well at a median height between the maximum and m inimum level of the water table, thus allowing to integrate the variations of the level of the latter in time.

I nitially, therefore, a skim ming device with a diameter slightly smaller than the diameter of the drilled well (20) should be chosen. One of the two slides in the form shown serves as a transfer tube (2) by sucking in the product from the collection opening (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 whole device is then lowered into the well via a position-keeping chain (13) until it is in contact with the water level. The necessary distance has usually been measured beforehand. The device, thanks to its float (5) , follows the level variations of the water-pollutant interface and thus the level of the local water table. The float (5) is perfectly capable of adapting to this level as 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 stabilise at the water-hydrocarbon interface due to its density and profile.

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

The present invention relates also to a system with a number of perforated and nonperforated thermally conductive pipes placed in a soil. The pipe (25) is in com m unication with a heat source (21 ) which circulates a heated fluid through the pipe causing the temperature of the surrounding environment (18)(15)(19) to rise. Perforated tubes (27) are placed around the heating tubes when treating the vadose zone. I n some steps of the application plan (figure 5) the perforated tubes (27) are evacuated, conveying the contaminated vapours to a treatment system . I n other steps of the application plan (figure 4) , these perforated tubes (27) are not necessary.

Heating tubes (25) are placed in a contam inated material, for example a contam inated 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, flows through the tubes (25) . The heat (28) is transferred to the materials by thermal conduction and gradually raises the temperature of the soil, and the floating layer (15) and of a certain portion of the aquifer (19) (and of the vadose zone (18)) . The elevated soil temperature causes the mobilisation of the floating layer to the pumping wells and the volatilization of the contam inants from the vadose zone, producing a contaminated vapour which are recovered from the soil (18) via the vapour tubes (27). The vaporised contaminants (5) from the soil are mobilised in the perforated tubes (27) by imposing a negative pressure in the perforated tubes (27) , e.g. by connecting the pipes to a vacuum system . The contaminated vapours move into the perforated tubes (27) and can be collected by a vapour collection pipe system transporting the contam inated fluid to a treatment unit and/or are injected and destroyed into the burner flame inside the combustion chamber (22) . 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 m ust be capable of drawing a vacuum appropriate to the combination of soil permeability and perforated tubes in a process 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 watertight pump. I n a preferred embodiment, a drain pack is placed around the perforated tube (22) to ensure a homogeneous suction.

I n a preferred embodiment, the heating system is centralized on the saturated zone of the soil in order to heat the water table and mobilize the pollutants towards the skim mer (figure 4) .

I n another preferred embodiment, when for example the pollution extends from the vadose zone to the water table, the heating system is applied on the saturated and unsaturated zone (figure 5) : the pollutants of 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 contam inated 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 contam inated area. Triangular patterns are preferred as they offer the best thermal efficiency. The temperature in the soil is increased by circulating a heated fluid through the pipes (25) . The superimposition of the heat flow from all the pipes results in a more uniform temperature increase in the pattern. It will be appreciated that the number of pipes (25)(20) applied in the soil, the spacing, the relative position of the pipes, may vary according to the degree of contam ination and/or the desired time to complete the process and/or the type of soil and/or economic considerations. I n a preferred embodiment, the distance between two adjacent pipes is between 1 m and 1.8m .

All the metal parts used in the device of the present invention are stainless for obvious reasons of resistance to corrosion and heat over time. The device can be operated both continuously and interm ittently by a control unit which is controlled by various measuring devices, in particular by level and importance of audible or visual alarm devices and remote control.

LEGEND

1 . Upper assembly profile

2. Floating layer suction tube also serving as a slide for the float

3. Float port for oil collection

4. Connecting groove on top of the float positioned at the oil/water interface

5. Float

6. Floating layer collection tube

7. Lower assembly profile comprising the transfer channel to the collection tube of floating layer

8. Transfer channel to central suction tube

9. Water suction tube to create an additional drawdown also serving as a slide for the float

10. Diameter slot for float guide

1 1 . Hole for attaching the device to a chain

12. Flexible suction tube

13. Chain for maintaining position in 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. Borehole casing installed in a borehole

21 . Burner

22. Burner body

23. Flexible reburn

24. Reburn valve

25. Heating tube

26. Polluted vadose zone

27. Vapor tube

28. Heat conduction