BE1027833B1 - SLUDGE AND SOIL CLEANING SYSTEM WITH CONTAMINANT RECOVERY - Google Patents

Abstract

The present invention relates to a method and system for cleaning mud or soil containing contaminants. According to the present invention, said materials are heated by thermal conduction under the action of heating tubes placed in said sludge/soil at a temperature and pressure sufficient to cause the vaporization of said contaminants. This pressure is preferably obtained by imposing a vacuum on the ground to thereby extract the contaminants from the contaminated ground. The combined efficiency of heat and steam flow results in 100% sweeping efficiency, leaving no areas untreated, and removal efficiency approaching 100%. The present invention requires less energy input compared to traditional methods because it allows the recovery of contaminated vapors and their reinjection into the heating system. The present method is therefore more efficient from an energy point of view and entails less operating costs. The temperature reached by the ground is an important parameter for evaluating the cleaning potential of this method, since it is a determining factor in the decomposition of pollutants. For this, the present invention proposes a method which comprises monitoring the temperature in the ground at different places in the system. The method and system described herein are intended to clean both volatile and semi-volatile contaminants, particularly for hydrocarbons.

Description

Sludge and soil cleaning system with contaminant recovery

DESCRIPTION FIELD OF THE INVENTION The present invention relates to a thermal pollution control system for sludge and contaminated soil in a closed environment. In particular, the invention relates to a method and devices for cleaning floors containing hydrocarbons and/or other organic contaminants, more particularly a method and devices for volatilizing contaminants in sludge or soil by thermal conduction and elimination of these contaminants from the sludge or soil to recover if and when they are recoverable or destroy them if and when they are not. BACKGROUND OF THE INVENTION Soil contamination has become a matter of great concern in many places. Soil may be contaminated with chemical, biological and/or radioactive contaminants. Material spills, leaking storage tanks, and seepage in material landfills are just a few examples of the many ways soil can become contaminated. If left in place, many of these — contaminants will end up in aquifers, the air, or the food supply and could pose public health risks.

There are many methods proposed to remove surface contaminants, such as excavation followed by incineration, in situ vitrification, biological treatment, chemical additives for deactivation, radio frequency heating, etc. Although effective in some applications, these methods can be very expensive and impractical if many tons of soil need to be treated.

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. The vacuum can be applied at a ground/air interface, or the vacuum can be applied through vacuum wells placed in the ground. Air and steam can entrain and transport volatile contaminants to the source of the vacuum. The off-gas removed from the ground by the vacuum which includes the contaminants that were in the ground are then transported to a treatment facility where they are 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 in-situ heating of soil to raise soil temperature while simultaneously removing off-gas from the soil. Heat added to contaminated soil can raise the soil temperature above the vaporization temperatures of contaminants in the soil and cause the contaminants to vaporize. A vacuum applied to the floor extracts the vaporized contaminant from the floor.

A method of heating soil containing contaminants includes injecting a heated fluid into the soil. Such a method is for example described in U.S. Patent No. 6000882. The method described here consists of introducing a system of perforated pipes into the ground. A stream of hot air is sent through the pipes. Hot air is injected into the ground through perforations in the pipes at the pipe perforations. A contaminant vapor forms in the ground, which can be removed from the ground through the pipe perforations and vented to an off-gas treatment unit. However, a major drawback of this type of method is that injecting hot air into the ground is prone to creating vapor flow paths in the ground. As a result, the hot air is not evenly distributed in the contaminated soil, but rather accumulates at its level of injection into the soil; i.e. in and around the pipe perforations. Another way to heat a floor is to heat a floor by thermal conduction. The thermal conduction heating of contaminated soil in combination with the removal of contaminating gases from the soil using a vapor extraction system is old in the art. During ex situ thermal desorption, the soil is excavated and the heating elements are then placed in the excavated soil, arranged in a pyramidal configuration. All surfaces in contact with the atmosphere are covered with concrete and the top has an insulation layer after the concrete layer. In ex situ treatment, the heat losses are not negligible, especially on the lateral sides of the pyramid without insulation, leading to a reduction in the efficiency of the treatment.

The present invention aims to provide an alternative solution for treating the soil ex situ by simplifying the process and optimizing the treatment. In particular, it consists of treating the contaminated soil in an isothermal container comprising at least one heating element inside the sludge or soil allowing a higher temperature of the contaminated soil to be obtained more quickly. At least one of the heating elements can be powered in part by reinjecting the energy recovered from the vapors of the contaminants of the present invention also comprises a separate device inserted into the ground in said materials making it possible to create a controlled vacuum in the container.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate the invention: FIG. 1: Detailed illustration of the system in a double dome arrangement. Fig. 2: Illustration of the principle of reburn in heating tubes equipped with burners Fig. 3: Illustration of a heating container made up of sheet piles 40 FIG. 4: Illustration of the lower part of containers or encapsulations

DETAILED DESCRIPTION OF THE INVENTION The terms “contaminated soil” and “materials or sludges containing contaminants” are used herein as synonyms and should be understood to include all types of soils, sludges or other materials which may be contaminated with hydrocarbons. or any other organic or inorganic contaminant whose boiling point at atmospheric pressure is less than 650°C.

The propagation of heat by conduction takes place 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 consists of a transfer of kinetic energy from the hottest medium to the coldest.

The term "conduction" as used herein is therefore intended to refer to all types of heat transfer in which heat is moved from one (hotter) object to another (colder) object by direct contact. || should be understood that in the present invention, when heat transfer by conduction is mentioned, also a very small amount of heat is generally also transferred to the ground by radiation.

In particular, the present invention proposes a method for remediating soil comprising contaminants, comprising the step of reinjecting the contaminated vapors into the system by a method called “reburn” (14)(15)(21). The present invention relates to a nearly closed loop system with a number of perforated or non-thermally conductive pipes (18) placed in the ground which has previously been placed in a container (16). The perforated pipes (18) are in communication with a heat source (14)(15)(21)(12) which circulates heated fluid through the pipes (18). The method — includes the steps of placing the two types of perforated pipes (18)(21) in the tank containing the contaminated soil (16), circulating a heated fluid through the pipes (18), raising the temperature surrounding soil (24) at a temperature sufficient to cause soil contaminants to vaporize; mobilizing the vaporized contaminants from the soil into the perforated pipes (21); and reinjecting the vaporized soil contaminants into the heating tubes (18). Contaminants are attracted to the perforated pipes (21) by imposing a negative pressure within these pipes (18)(21), e.g. by connecting the hoses to a vacuum system.

The pipes (18) are arranged in a pattern in the contaminated soil to provide the most uniform heating throughout the pattern.

A regular pattern of pipes (18) can be used, such as triangular, square, rectangular, hexagonal, etc. selected to substantially cover the contaminated area (24). In a rectangular tank (16), rectangular patterns are preferred because they provide the best thermal efficiency.

The temperature in the ground is increased by circulating a heated fluid through the pipes (18). The overlapping heat flow of all the pipes (18) results in a more uniform temperature rise in the pattern.

It is clear that the number of pipes (18)(21) applied in the container (16), the spacing, the relative position of the pipes (18)(21), the distance between the base and the pipes (18) (23) and the distance between the pipes (18)(21) and the lateral sides (22) of a pile of soil can 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 the base of the container (23) containing the contaminated soil and the pipes (18) is equal to 0.35 m, the distance between two adjacent pipes (18) in a layer is between 0.8 and 1 m, the distance between the pipes (18) of two superposed layers is between 0.8 and 1 m.

In this preferred embodiment, the distance between the top of the tank (20) and the last layer of pipes (18) is between 0.35 and 0.5 m and the distance between the side sides (22) of the tank ( 16) and the pipes (18) is between 0.35 and 0.6 m.

The pipes (18)(21)(14) preferably comprise pipes of a heat resistant material such as, but not limited to, steel, metal or ceramic.

The pipes (18)(21)(14) can have any desired cross-sectional shape, including, but not limited to, triangular, rectangular, square, hexagonal, ellipsoidal, round, or oval.

Preferably, the pipes (18)(21)(14) have a substantially ellipsoidal, round or oval cross-sectional shape.

In a particularly preferred embodiment, the pipes (18)(21)(14) have a substantially round transverse shape and have a diameter which is between 50 and 200 mm and preferably between 80 and 180 mm.

The pipes (18) (21) have a length of between 3 and 30 m meter, and preferably between 6 and 18 m.

The perforations in the steam pipes (21) can be, but are not limited to, holes and/or slots.

Preferably, between 5% and 50% of the surface of a pipe (21) is provided with holes and/or slots. it is particularly preferred that a large number of small perforations be provided on the pipe (21). The pipes (21) may have several perforated areas at different positions along a length of the pipe (21). When the pipes (21) are inserted into the ground, the perforated areas may be located adjacent to contaminated soil layers.

Alternatively, the perforations can be provided over the entire length of the pipes (21). The pipes (18) are heated by sending and circulating a heated fluid such as air and/or high temperature gas through these pipes (18). Preferably, the high temperature air/gas is heated to a temperature between 300 and 800°C, and more preferably between 500 and 750°C.

Extremely high temperatures can also be used, mainly depending on the temperature limits of the perforated pipes (21). Thus, in cases where perforated pipes (21) are used which can withstand extremely high temperatures, i.e. 1000 to 1500°C, a corresponding extremely high temperature air/gas supply can be used.

The heat is transferred to the ground by thermal conduction and gradually raises the temperature of the ground.

A very small amount of heat will also be transferred to the ground by radiation.

The high soil temperature causes the contaminants located in the contaminated soil to volatilize, thereby producing contaminated vapor.

According to the present invention, the ground is heated by conductive heating, which is particularly advantageous because the temperatures obtainable by such heating are not limited by the amount of water present in the ground.

Soil temperatures significantly above the boiling point of water can be achieved by using thermally conductive heating.

Soil temperatures of at least about 100°C, 125°C, 150°C, 200°C, 400°C, 500°C, 600°C, 700°C, 800°C or more can be achieved by using heat conduction heating.

A vacuum system is connected to the pipes (18) to place them under negative pressure.

The vacuum system must be capable of drawing a vacuum appropriate to the particular combination of soil permeability and perforated pipes (21) in a treatment system.

The vacuum system may be capable of pulling a vacuum in the range of 50 Pa to 5000 Pa.

The vacuum system can be a fan or a waterproof pump.

Due to the pressure difference imposed in the ground, the heated fluid which is sent through the pipes (18) will not be injected into the ground through the perforations of the pipes (21) but will remain in the piping system.

Therefore, there will be no mixing of the heated fluid with the contaminant vapor in the soil and the formation of vapor flow paths in the soil is minimized.

Unlike fluid injection into the floor, conductive heating will be very even in its vertical and horizontal sweep and will cause heat to disperse evenly across the floor.

Indeed, the thermal energy injected into the ground by the pipes (18) is uniform on each pipe (18). Additionally, conductive heating — creates permeability due to the drying and shrinking of the superheated (i.e. >100°C) soil that develops around each pipe (18). Closely spaced vapor flow paths are created even in narrow layers of silt and clay.

By placing the perforated pipes (21) under negative pressure, vaporized contaminants are drawn from the ground into the piping system (21). The contaminated vapors do not travel — through the floor to the top of the floor but rather into the perforated pipes (21) and are injected into the flame of the heating tubes (14)(15)(18). However, some vapors can travel across the floor surface into a vapor retention chamber that is formed between the floor and a coating, applied on top of the floor surface (24). The vacuum is maintained throughout the heating period and for a sufficient time after heating to prevent loss or dispersion of contaminants.

The vacuum will lower the vapor pressure of the water in the ground and cause it to boil at a temperature below the normal boiling point at atmospheric pressure.

At the same time, high boiling point contaminants will be removed by steam distillation in the presence of water vapor at a temperature well below the normal boiling point of the contaminants.

This will happen for all contaminants that are nearly immiscible in water, because the boiling point of the mixture of two immiscible fluids will always be lower than the boiling point of either component by itself. same.

In a preferred embodiment, all surfaces (20)(22) of the tank are sealed with an insulating layer (26). Creating a vacuum under the insulation layer (26) may cause the insulation layer (26) to be drawn to the floor surface, but in any case will reduce the amount of air/ gas drawn into the piping system (21)(18) from the atmosphere.

Thus, essentially only air, soil moisture and contaminants in the soil will be evacuated through the perforated pipes (21) embedded in the soil. By attracting moisture and contaminants to the pipes (21), the risk of spreading contaminants is greatly reduced. The insulating layer (26) also reduces heat loss. An insulating layer (ie concrete) may also be provided under the soil pile (24) to be treated to reduce heat loss to the underlying soil.

When the contaminated vapor is removed from the soil, the moisture level in the contaminated soil is substantially reduced, preferably to an average moisture level below about 5% by weight, more preferably to an average moisture level below about 2% by weight, and most - preferably at an average moisture content of less than about 1% by weight.

In another preferred embodiment, the present system also includes a vapor collection piping system (21) that carries the heated fluid out of the heating tubes to a processing facility. In a preferred embodiment, this treatment installation comprises a condenser (10), a demister (8), an activated carbon column (4), a post-combustion (7), etc. The current system is designed to allow the treatment of 20 to 100 m° of soil. The entire system can be loaded onto a trailer to be transported from site to site.

In another preferred embodiment, the tank would be in an inert atmosphere by recovering at the outlet of the burner body (13), the carbon dioxide produced during the process and reinjecting it into the tank (16). For this reason, it is possible to heat copper cables to recover the copper while controlling the level of oxygen inside the container (16).

In another preferred embodiment, the system is made up of one or more specially designed 40' metal containers (2) which can be adapted according to the amount of soil to be treated. The metal container can be buried or placed directly on the ground or any combination thereof.

Added to this is a heated container (1) that fits perfectly into the metal containers (2), which can be moved from one container to another when it has been processed. This container (1) is bottomless and all the treatment networks (heating pipes (18), gas, air, steam (21)) are installed inside. In addition, this heating container (1) is covered with a thermal insulation layer and a smooth steel layer, which makes the interlocking of the container and the swimming pool easier and hermetic. The tip of the heating pipes are pointed in shape to facilitate placement of the tank in the pool. In a preferred but not limited embodiment, these pipes are 2.35m long. In order to facilitate the movement of the container, handles are placed at the corners of the container. In another preferred embodiment, the heating elements are placed vertically, in particular when the insulated tank is built into the ground (2). In this preferred embodiment, the vertical heating elements are then attached together and form a dome (1) placed above the contaminated materials. By proceeding in this way, all of the heating elements (18)(21) can sink into viscous materials, while guaranteeing mechanical strength and sealing of the entire device.

In another preferred embodiment, the dome system (1) is coupled to other buried tanks (2), so as to allow continuous treatment, always feeding an open tank (2) while at least another tank is available to be in the heating phase (1).

In another preferred embodiment, the tank is constructed with metal sheet piles (19) as the core and smooth metal sheets (17)(20)(22) as the wall. Thus the device allows flexible sizing, depending on the quantities of materials to be processed, while guaranteeing good mechanical strength and the possibility of inserting insulating material (26) between the two metal walls (20)(22) . These materials are also readily available at many sites, which allows the assembly of the processing units on site and reduces the problems associated with transporting the processing unit.

In another preferred embodiment, the containers (1) or the domes (2) are placed side by side and the treated vapors leaving the containers and/or domes being treated can be used as heat transfer fluid to preheat the containers awaiting start-up.

In another preferred embodiment, the tanks are equipped, below the contaminated material placement zone, with a filtering grid (25) made up of filtering materials (25) resistant to temperatures of at least 250°C but preferably between 200°C and 400°C, and which allow the mechanical flow of free liquids present at start-up or forming during heating.

1. Heated container

2. Metallic container

3. Condensate tank

4. Hydrocarbon tank

5. Clean water tank

6. Activated carbon filter

7. Afterburner

8. Heat exchanger

9. Pump

10. Knockout

11. Cooler

12. Burner

13. Burner body

14. Flexible reburn

15. Reburn valve

16. Container

17. Container outer wall

18. Heating tube inside the container

19. Sheet pile

20. Container top surface

21. Steam tubes

22. Metal container

23. Filtration system

24. Contaminated soil

25. Filter grid

26. Insulation

Claims (5)

1. Apparatus for removing organic contamination from sludge or soil comprising: - A thermally insulated closed encapsulation containing the materials to be treated - At least 1 heating element inside the sludge or soil heating said materials by conduction - A separate device inserted into the materials and creating a controlled vacuum in the encapsulation - At least 1 heating element that can be powered in part by the energy contained in the contaminants extracted through said vacuum device 2. Apparatus according to one of the preceding claims wherein a liquid filtration system is placed under the contaminated materials 3. Apparatus according to one of the preceding claims wherein the heating elements are placed in a fixed manner and attached to the structure, in order to constitute an integral assembly which can be placed and lifted at once 4. Apparatus according to one of the preceding claims wherein the dome placed above the contaminated materials physically rests on the latter, thus making it possible to avoid the formation of a vacuum between the materials and the ground during the retraction following heating. of these 5. Device according to one of the preceding claims, in which a secondary network of orifices connected to the vacuum keeps the space created between the materials and the top of the dome or container under vacuum.