FIELD OF THE INVENTION

The present invention is intended for the thermal treatment of certain industrial and domestic wastes in order to allow their recycling, such as electrical cables, coffee capsules, sludge contaminated by hydrocarbons or steel straws contaminated by heavy mineral oils. The present invention can also be used for the thermal treatment of highly contaminated products or products containing highly toxic compounds where the good sealing of the system is a determining parameter. It can also be used in the context of a test aimed at demonstrating the effectiveness of a treatment by thermal desorption of polluted soils. The special feature of the system is that it guarantees a tight seal against the external environment, rapid assembly and easy loading/unloading of the materials to be recycled.

CONTEXT OF THE INVENTION

Faced with the tightening of admission requirements in most of the disposal channels and in front of an inevitable and constantly increasing production, the dispersion of waste is becoming a serious problem. We can consider as waste any material rejected as not having an immediate value or left as residues of a process or operation. Electrical cables, coffee capsules, sludge contaminated with hydrocarbons or steel straws contaminated with heavy mineral oils are some examples of common waste. Recycling (the operation that consists of recovering the raw materials contained in these wastes and reintroducing them into the production cycle of a product) at a reasonable cost from an energetic or economic point of view, makes it possible to satisfactorily resolve the problem of their elimination.

Recycling technologies are beginning to emerge for this type of waste, but they are generally quite complex and their cost is still high. For example, the recycling of electrical cables requires several operations. Pre-shredding is an operation that consists in reducing the size of the cables to 10 millimeters. To do this, a special machine is used: the pre-shredder. In concrete terms, the cables are loaded into the machine and the product obtained passes through several magnetic separators which allow the iron contained in the mixture to be extracted. Granulation is nothing more than the separation of conductive metals from insulators. More precisely, we speak of granulation by densimetry, blowing and suction. During this last phase of cable grinding, the metal is separated from its plastic sheath, which allows the extraction of homogeneous copper granules. Depending on the performance of the machine used, the shredder can process several tons of cable in one hour. After the granulation, we move on to the sieving. Several successive sieves are carried out to group together copper granules of the same size. The resulting batches are finally stored and then sent to smelters or refineries. There, they are transformed into secondary raw materials used for the manufacture of new cables.

Once the aluminum coffee capsules have been disposed of in the selective waste garbage can, they are sent to a sorting center. Thanks to a specific machine (the eddy current machine), the coffee capsules are separated from other recyclable waste. They are then sent to a pyrolysis center where the coffee grounds are burned and the aluminum is melted. This operation consumes a lot of energy.

Waste sludge is another example of industrial waste. It is classified according to the nature of the solid matter (organic or mineral) that makes it up and according to the affinity of this solid matter with the water it contains (hydrophilic or hydrophobic). This classification is important because the nature of the sludge conditions the choice of the processes to be implemented during the treatment of the effluent as well as during the dehydration phase.

Hydrophilic organic sludge is the most common type of sludge. They are mainly sludges from the food industry, organic chemical industry, textile industry and urban sludge. The difficulty in dewatering these sludges is due to the presence of colloids, such as hydroxides and hydrocarbons, which are very hydrophilic. Hydrophilic mineral sludges are sludges that come from mineral chemistry, dyeing, tanning and surface treatment industries. These sludges mainly contain metal hydroxides formed during physicochemical treatments by precipitation of metal ions present in the water to be treated. Hydrophobic mineral sludges come mainly from the steel industry. They are mainly composed of particles such as sands, silts and crystallized salts. Hydrophilic oily sludges are produced in the refining industries or in mechanical workshops. These sludges are characterized by the presence of small quantities of oils or fats. These oils are in emulsion or adsorbed to the particles contained in the sludge. Hydrophobic oily sludges come from the rolling mill industry and are characterized by dense dry materials that settle well (e.g. iron oxide and slag) and by the presence of a high proportion of mineral oils and greases. Finally, Jibreous sludge is generally easy to dewater. It comes from the paper, pulp and cardboard industries. The main objective of sludge treatment is to reduce the volume of sludge in order to limit the quantities to be stored (or even spread), and to stabilize it in order to improve its physical characteristics (improvement of its heap behaviour). The dryness is a fundamental parameter of the sludge characteristics.

Thickening is the first stage of sludge treatment, which is generally carried out before the mixing of sludge from the different stages of wastewater treatment (primary, secondary, and possibly tertiary sludge). This step can be preceded by the addition of synthetic organic flocculants (polyelectrolytes) or mineral flocculants (lime, iron or aluminium salts), in order to facilitate the separation of the solid and liquid phases of the sludge.

The second step is dewatering. It consists in letting the sludge flow by gravity through a silo placed above a draining table or a semi-permeable cloth. Another concentration technique is flotation, based on the injection of gas into the sludge, which separates the liquid and solid phases by density difference. At the outlet, the sludge is still liquid with a dryness of 4 to 6%. The dewatering operation reduces the water content of the sludge and achieves a dryness of 15 to 40%, which varies according to the water treatment process, the type of sludge and the dewatering technique used. It operates on a mixture of primary, secondary and tertiary sludge. Mechanical dewatering is carried out by centrifugation or filtration. Centrifugation consists in separating the water from the thickened sludge by the centrifugal force developed in a cylinder rotating at high speed. At the outlet, the sludge is pasty with a dryness of 18 to 20% for the first generation of equipment, and 20 to 25% dryness for the second. For a long time, this technique was mainly used for plants of more than 10,000 p.e.; today, solutions exist for smaller plants (p.e. corresponds to "people equivalent", a unit of measurement aimed at determining the capacity of a treatment plant based on the quantity of pollution emitted per inhabitant per day). Belt filter filtration consists of compressing and shearing the sludge between two cloths. The first models (low and medium pressure) could only reach 15 to 17% dryness. More recent models (high pressure) allow to reach 18 to 20%. At the outlet, the sludge is in the form of small plates. The filtration by filter presses with plates (commonly called filter presses) consists of a compression of the sludge between two plates equipped with filtering cloths. At the outlet, the sludge is in the form of solid "cakes" with a dryness of around 30 to 35%. While centrifugation allows continuous dewatering in a closed circuit (automated), with filter presses it is discontinuous. With belt filters, it takes place in open circuits (with production of aerosols, composed of air and water), which often requires the equipment to be covered to avoid the dispersion of bad odors. Mechanical dewatering is mainly used in large plants (several tens or hundreds of thousands of PE). Since recently, it has been developed in medium-sized plants (from 3,000 to 10,000 p.e.). In very large plants, it is most often a matter of filter presses (because they are more expensive in terms of investment and operation), and in small plants (1000 to 2000 p.e.) of band filters. Belt filters would still be the most used equipment for dewatering, the most sold centrifuges on the market today. Another dewatering technique that has recently appeared with the development of membranes is geomembrane dewatering. This dewatering technique consists of placing the sludge in geotubes with tiny pores, which allow water to pass through little by little and concentrate the matter. Once full, these geotubes contain dewatered sludge up to 15 to 25% dryness. The geotubes are then either opened and the sludge shipped to another destination, or transported as is to a Class II landfill.

Sludge drying is a quasi-total dehydration of the sludge by evaporation of the water it contains; the resulting volume reduction is significant. Thermal drying is based on two methods: direct and indirect. Direct drying consists of evaporation by convection, via a heat transfer fluid. Indirect drying is based on heat exchange by conduction, via a wall heated by a heat transfer fluid. At the outlet, the sludge is in the form of powders or granules, with a dryness rate of up to 90-95%.

Thermal desorption is one of the thermal techniques used for the treatment of polluted soils and certain recyclable wastes. It is based on heating, evaporation, extraction and destruction or reuse of contaminants after recovery.

Heating via thermal conduction is one of the techniques used in the field of thermal desorption. With this technique, the energy coming from a heating element (heat source) propagates in the material to be treated by conduction regardless of the heterogeneity of the medium.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is an illustration of the container dedicated to the heating and treatment of waste, contaminated sludge and any other contaminated materials.

Figure 2 is an illustration of the rectangular or square hot plate with burner and steam tubes.

Figure 3 is an illustration of the complete system after assembly.

Figure 4 is an illustration of the system assembly and contaminated material loading phase.

Figure 5 is an illustration of the dismantling of the system and extraction of the materials after treatment.

Figure 6 is an illustration of an example of the internal design of the rectangular or square heating plate. LEGEND OF THE FIGURES

1. Container

2. Thermal insulation

3. Fixing rails (heating plates)

4. Burner location

5. Hole for placing the tube for measuring probes

6. Tube holder for measuring probes

7. Container door

8. Rectangular or square hot plate

9. Burner

10. Steam tube

11. Openings on the steam tube

12. Flue gas outlet

13. Air intake for the burner

14. Lifting ring

15. Ceramic protection tube - flameproof tube

16. Flue gas distribution tube

17. Inner tube

18. partition plate between compartments

19. Separating sheets between internal tubes

20. Combustion gas exhaust ports

21. Material to be heated/treated

22. Extraction and loading machine

23. Tube for measuring probes

24. Container lid

25. Steam outlet

DETAILED DESCRIPTION OF THE INVENTION

The invention concerns a sealed system for the thermal treatment of sludge contaminated with hydrocarbons and certain waste materials (industrial or household) prior to their recycling, such as electrical cables, coffee capsules or any similar material. It can also be used (several units) for the thermal desorption of excavated soil. The system allows the treatment of contaminated materials that cannot be shoveled with a quick assembly and above all an easy loading and unloading of the materials. It also guarantees a perfect seal against the external environment. The system includes removable rectangular or square heating plates placed in a standard 20 or 40 feet container.

In a preferred embodiment, the standard container (1) is suitable for heat treatment of the above mentioned materials (Figure 1). It is thermally insulated (2) on all its inner walls. Seven vertical rails (3) are welded on both sides along the 40 feet long container (1) with an equal distance between rails. These rails serve as mounting brackets for the heating plates (8). On one of the two longitudinal sides of the container (1), seven rectangular openings (4) are created to pass the burner (9), the combustion gas outlet (12) and the steam tube outlet (25). Each opening (4) is located just above the vertical rails (3). The container (1) is equipped with a door (7), a separate thermally insulated cover (24) (2) and several lifting rings (14). On one of its two longitudinal sides, the container (1) is pierced on two levels at several places. Each hole (5) allows the sliding of a tube (23) to the support (6). The tube (23) is used for placing the measuring probes. The container (1) adapted in this way can withstand temperatures of up to 500 °C.

In a preferred embodiment, the heating of the mass (material to be treated) is done mainly by thermal conduction, thanks to rectangular or square heating plates (8) placed vertically inside the container (1). All heating plates (8) are made of steel or a similar material allowing heat conduction. The heating of a plate is done by direct contact between the hot combustion gases produced by the gas or liquid fuel burner (9) and the inner walls of the heating plate (8). The air required for combustion enters the burner (9) through the duct (13). The combustion gases leave the heating plate (8) through the outlet (12). Each heating plate is equipped with two steel lifting rings (14). The extraction of the vapors produced during the treatment is done through the two U-tubes (10). Each tube is equipped with several openings (11) along its length. The U-tubes (10) are attached (one on each side) to the heating plate (8). The steam outlet (25) is located on the burner side (9).

In a preferred embodiment, for monitoring the treatment, several steel tubes (23) for measurement probes will be fixed at different locations in the mass to be treated (Figure 3). Each tube (23) can contain several measuring probes for temperature, pressure and/or sampling and analysis of gas samples. Some tubes (23) can even be used during the heat treatment to take solid samples. Each tube (23) is placed in the container (1) through the opening (5). The holder (6) is used to fix the tube (23) in the container (1).

Figure (4) illustrates the loading step of the container (1). In a preferred embodiment, loading begins by closing the door (7) of the container (1) and placing the heating plates (8) into the container (1). By means of the lifting rings (14), a lifting device (22) can be used for handling the heating plate (8). Once the two heating plates (8) of one compartment of the container (1) are placed, the steel tubes (23) for the measuring probes are inserted and the material to be treated (21) is loaded. Once the container (1) is completely filled, the lid (24) is replaced. The thermal treatment of the contaminated material (21) can start after the connection of the fuel and electricity supply lines to the burners, the connection of the steam line, the connection of the flue gas discharge line and finally the connection of the various measuring and monitoring instruments.

In a preferred embodiment, once the treatment is completed, the unloading step begins (Figure 5) by disconnecting all the supply, discharge and monitoring lines, followed by dismantling the lid (24) and the steel tubes (23) for the measurement probes. Once the door (7) of the container (1) is opened, the first heating plate (8) is removed and the treated material (21) is recovered from the first compartment. The operation continues until the last compartment at the bottom.

In a preferred embodiment (Figure 6), the heating plate (8) consists of a steel flame arrestor tube (15) equipped with a refractory material. It serves to shape the flame so that it does not deform uncontrollably and also to protect the flue gas distribution tube (16) from the flame. The combustion gases produced by the burner (9) leave the distribution tube (16) and are fed evenly to the inner tubes (17) through the compartment separator plate (18). The combustion gases flow through the inner tubes (17) and then up into the annular space between the inner tube separator plates (19), then through the opening (20) in each compartment, before leaving the heating plate (8) through the gas outlet (12).

In a preferred embodiment, the heating plates (8) can be placed along the inner walls of the container (1). In this case, the burner (9), the flue gas outlet (12) and the steam outlet (25) will be installed on top of the heating plate (8).

In a preferred embodiment, the flue gas distribution tube (16) and the inner tubes (17) are made of stainless steel and are cylindrical or rectangular in shape and range in size from 1" to 4". In a preferred embodiment, the inter-compartment divider plate (18) and the inner tube divider plates (19) are made of steel or stainless steel and vary in thickness from 1 to 3mm. In a preferred embodiment, the outer walls of the heating plate (8) are made of steel or stainless steel and have a thickness between 3 and 5mm. In a preferred embodiment, the perforations or openings (11) on the U-shaped steam tube (10) are circular in size between 1 and 3mm or rectangular in length between 20 and 100mm and will not exceed 3mm in thickness. In a preferred embodiment, the distribution of the openings (11) along the U-tube (10) may be uniform or random.

In a preferred embodiment, the thermal insulation (2) of the inner walls of the container (1) and the lid (24) can be made with rock wool, glass wool (in rigid panels or in rolls) or any other material with very low thermal conductivity such as expanded clay beads. In a preferred embodiment, the thermal insulation (2) is held in place by metal panels attached to the walls of the container (1). In a preferred embodiment, the thickness of the thermal insulation varies between 50 and 100mm and that of the metal panels varies between 1 and 3mm.

In a preferred embodiment, the internal tubes (17) and the burner (9) of the heating plate (8) will be replaced by electrical resistors and a solid (granular) or liquid conductive material. The latter will serve as an intermediary to transfer heat between the heating resistors and the material to be treated.

In a preferred embodiment, the tube (23) used for the placement of the measurement probes and for the collection of the solid samples during and after processing are made of stainless steel and are cylindrical or rectangular in shape and vary in size from 1/2" to 3'.

In another embodiment, several containers (1) can be used simultaneously on site.

In another embodiment, each heating plate is equipped with a gaseous or liquid fuel burner or electric heating resistors immersed in a solid (granular) or liquid conductive material.