BE1028845B1 - Heating system for soils and contaminated materials - Google Patents

Abstract

The present invention relates to a new generation of sealed heating unit (or heating system) making it possible to decontaminate the ground via thermal desorption while maintaining high thermal efficiency. This invention comprises three major modifications compared to the old heating system making it possible to reduce heat losses and therefore to increase the efficiency of the installation. The first modification consists of placing a heat exchanger between the combustion gas outlet and the primary air inlet to extract the heat contained in the combustion gases. This heat will be used to preheat the air entering the combustion chamber. The second modification focuses on the burner body of the current technology which is replaced by a stainless steel tube containing a refractory ceramic tube. This combustion chamber is directly inserted into the heating tube and has no visible element. The third modification concerns the elimination of the current secondary air inlet and the use of a single inlet for the primary air and secondary air assembly. The primary air and secondary air separation of the new system is done at the level of the internal tube. These modifications make it possible to reduce the thermal losses which amount to 45-60% in the state of the art in the field of thermal desorption and to facilitate the adjustment of the heating.

Description

a 1 Heating system for soils and contaminated materials BE2020/0125

DESCRIPTION FIELD OF THE INVENTION The invention consists of a heating system consisting of a new generation of heating units that can be used in the field of soil remediation by thermal desorption. The invention makes it possible to significantly increase the thermal efficiency of the traditional thermal units currently used.

BACKGROUND OF THE INVENTION Soil contamination is a problem of great importance in a world where the environment and sustainable development are becoming increasingly important. This problem, often invisible, can be caused by a wide variety of chemical, biological or even radioactive contaminants and an equally wide range of pollution sources. Left as it is, the contamination can spread and end up in other resources essential to the surrounding flora and fauna. It is therefore important, in order to protect the environment and public health, to eliminate these contaminants before they have too great an impact.

Soil remediation technologies are multiple and can be separated into three main categories: thermal, biological and physicochemical. 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.

One of these techniques, thermal desorption, is based on heating the ground to volatilize the contaminants and allow their extraction and destruction/reuse after condensation. Thermal desorption is effective against organic contaminants, cyanides, mercury and any other component that can be volatilized at temperatures below 550°C. Heating via thermal conduction is one of the techniques used in the field of thermal desorption (WO2001078914A8). With this technique, the energy coming from the heating tubes propagates radially in the ground by conduction. This has several advantages vis-à-vis the other possibilities of soil remediation because thermal conduction; makes it possible to heat the ground to temperatures exceeding 350°C (which is not possible, for example, with resistive electric heating (US5656239A) and to easily and quickly treat soils contaminated by a wide variety of contaminants, little matter the heterogeneity of the soil. Indeed, the thermal conductivity has the particularity of not fluctuating by large orders of magnitude with the materials present in the soil. As a result, thermal conduction is much more effective than other methods of heat transfer in the case of heterogeneous soils.

This technique is applicable ex situ and in situ. In ex-situ thermal desorption, excavated soil is used to form piles or placed in containers which are heat treated. With in-situ thermal desorption, the heating tubes are directly . \nserated in the polluted soil thus making it possible to avoid the excavation and the transport of the earth. This also makes it possible to treat soils in restricted places and/or with limited access such as remote sites, sites in urban areas, basements of houses, etc. In general, this technique is faster and has a reduced environmental impact. Current techniques increase the temperature of the heating tube by circulating hot gases (combustion gases), coming from a burner, in two concentric tubes (BE1024596B1). The total process makes it possible to provide, during the complete treatment period, an average power of 1.5 kW per meter of tube. Unfortunately, the thermal efficiency of the latter is estimated to be around 35%, which considerably increases the cost of treatment compared to an ideal (but unrealistic) treatment situation. A large part of the thermal energy (40-50%) is lost in the combustion gases leaving the device at the exit of the heating tube, so it is interesting to concentrate on recovering this energy to improve the efficiency of the system. |

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an illustration of the complete heating system including the burner, the energy recovery system and the heating tube. Figure 2 is an illustration of the combustion head and the air and vapor compartments. Figure 3 is an illustration of the components present in the combustion head. Figure 4 is an illustration of a section of the heating system with the combustion head and the heating tubes. DETAILED DESCRIPTION OF THE INVENTION The invention is a new generation of soil depollution technology via thermal desorption. Said system was designed with the primary objective of significantly reducing the heat losses of the current system and therefore increasing the thermal efficiency of the process. - To do this, three improvements are made to the prior art. A heat exchanger (3) is placed at the outlet of the heating tube (1) to recover a significant part (up to 80%) of the energy usually lost in the combustion gases. This passage through the heat exchanger makes it possible to use the energy of the combustion gases to preheat the air necessary for combustion (air entering the combustion chamber). The second modification focuses 40 on the current burner body which, being outside the ground, results in heat losses of 5-10% of the total energy supplied by the burner. The invention consists in replacing the current burner body with a flame protection tube (11) containing a refractory ceramic tube (12). These are then placed inside the current heating tube. (1). This positioning of the combustion chamber makes it possible to contain the flame entirely in the ground and therefore to concentrate its heat there. The third modification concerns the elimination of the current secondary air inlet and the use of a single inlet for the primary air and secondary air assembly. The primary air and secondary air separation of the new system takes place at the level of the internal tube (13).

This new system makes it possible to obtain a wide range of power ranging from 2.2 to 80 kW, preheating of the combustion air up to 400°C and a total thermal efficiency exceeding 80%. With this invention, the total consumption of a project would be reduced by 70%, compared to the consumption of current technology, thus reducing the cost and the ecological impact of the process. This new device therefore does not require a burner body or a secondary air inlet, which is the case with current technology. The new system is composed of 5 independent parts:

1. The combustion head (2)

2. The heating tube (1)

3. The combustion gas evacuation network

4. The heat recovery unit (3)

5. The command and control panel (5) The combustion head (2), in a preferred embodiment, is composed of a main flange (21), an air compartment (18), an air compartment steam (19) (if the "rebum" mode is used) and a combustion chamber. The fuel used by the burner is routed through a feed tube (24) to the burner head (2). If the fuel is liquid, a solenoid valve will be placed between the supply tube (24) and the main flange (21) to prevent the arrival of fuel in the heating tube when the burner is off. The burner head — consists of a main flange to which several important elements are attached. . In a preferred embodiment, the main flange includes an ignition and flame detection electrode (16), a flame sight glass (17), a pressure switch outlet (22) and a gas injector (15). The main flange is fixed on the air intake compartment (18) by means of 4 to 10 fixings of 6 to 10 mm in diameter.

The air inlet compartment (18) supplies the burner with air. It is made up of a metal tube, preferably cylindrical and made of stainless steel, and with a diameter between 2” and 6”, preferably 4”. In a preferred embodiment, the tube has two openings. A side opening allowing the use of the gas injector adjustment handle (15) and an opening via a threaded connection, preferably in stainless steel, with a diameter between 1” and 40 3”, preferably 2”. This last opening serves as an air inlet into the combustion chamber (25). The air compartment (18) has two metal flanges, preferably stainless steel, welded to the ends of the tube, allowing the air compartment (18) to be fixed to the burner head (2) and to the combustion chamber (25). The fuel is mixed with part of the preheated air by means of a mixer (20) located at the outlet of the gas injector (15) and the air compartment (18). In a preferred embodiment, the gas injector (15) is formed by two concentric metal tubes.

Each tube is fitted with a disc drilled with 2 to 8 holes of 2 to 6 mm in diameter.

The outer tube pivots; freely around the inner tube to allow modification of the passage section by moving the two drilled discs.

In a preferred embodiment, the gas injector (15) is provided with an adjustment handle allowing modification of the passage section and therefore of the flow of fuel in the burner.

Combustion is triggered when the ignition electrode (16), fixed to the main flange (21), produces a spark.

This electrode can also be used to detect the presence of a flame in the burner just like the flame sight glass (17) fixed on the main flange (21). | When the contaminant contained in the polluted soil can be used as fuel, a mode of operation called "reburn" can be implemented.

This mode consists of reinjecting the contaminant vapors coming out of the ground into the combustion chamber to use it as fuel in the burner.

To do this, the vapors are conveyed via a vapor tube (26), placed next to the heating tube (1), and connected via a vapor hose (10) to the vapor compartment (19). This reduces the total consumption of the operation and offers a direct method of treating pollutants to produce only combustion products at the outlet.

For this mode of operation, it is necessary to add a steam compartment (19) between the air compartment (18) and the combustion chamber (25). The steam compartment (19) is a tube, preferably cylindrical and made of stainless steel.

It is provided with 1 to 6 threaded connections, preferably in stainless steel and with a diameter between 1” and 3”, preferably with a diameter of 1”. These threaded connections allow the steam compartment (19) to be connected to the steam tube (10). In a preferred embodiment, this compartment is fixed to the air compartment (18) and to the combustion chamber (25) via two metal flanges, preferably of stainless steel, and provided with 4 to 10 holes for the fixings.

It is in this compartment that the contaminant vapors coming from the ground are injected as fuel into the combustion chamber (25). The heating tube is composed of four parts: a flame protection tube (11), a refractory ceramic tube (12), an internal heating tube (13) and an external heating tube (14). ; The flame protection tube (11) and the ceramic tube (12) constitute the combustion chamber (25) of the heating device and replace the burner body present on current technology.

In a preferred embodiment, the flame protection tube (11) “is a metal cylinder, preferably of stainless steel, placed at the outlet of the mixer (20). 40 This cylinder has a perforated collar, also preferably made of stainless steel, | welded at its highest point to allow a secondary air supply in the tube of

5 heaters (1). The ceramic tube (12) is placed in the flame protection tube (11) and fixed with metal wedges welded to the base of the flame protection tube.

This tube: protects the other surrounding components from the high temperatures encountered near the flame.

The flame protection tube (11) is attached to the combustion head (2) and inserted into the internal heating tube (13). Additional perforations can be placed on the two tubes forming the combustion chamber (25) to promote mixing between secondary air and the combustion gases.

The two heating tubes are concentric and preferably cylindrical.

They are inserted into the polluted area with the outer tube (14) in direct contact with the ground.

In a preferred embodiment, the inner tube (13), preferably of stainless steel, has the smaller diameter of the two tubes and is open at its lower end.

It is contained in the outer cylinder (14), made of steel, thus allowing the hot gas to circulate in the inner cylinder (13) to its lowest point.

The hot gas leaving the internal cylinder (13) rises towards the surface by circulating in the zone located between the two heating tubes to heat, by thermal conduction, the surrounding ground.

In a preferred embodiment, the inner tube (13) has a diameter between 2” and 6”, preferably 4”, and the outer tube (14) has a diameter between 4” and 8”, preferably 6”. The hot gases have a temperature between 200 and 600° C., preferably between 300 and 500° C., and finally leave the heating tube via the combustion gas outlet located at the top of the heating tube (1). In a preferred embodiment and when deemed necessary, a solid catalyst (for example in the form of a honeycomb or in the form of a fixed bed of grains) can be added at the outlet of the heating tube (1) or at the inlet the heat exchanger (3), on the hot gas side, to complete the combustion and thus reduce harmful and dangerous gas emissions (CO, VOC, unburned gases, etc.). The outlet of the combustion gases from the heating tube (1) is connected to a heat exchanger (3) via, preferably, a fixing hose, preferably made of stainless steel (6), serving as an expansion compensator for the installation.

The heat exchanger (3) is mounted between the air inlet and the flue gas outlet.

In a preferred embodiment, a compact, lightweight exchanger with an exchange surface of at least 4 m° is preferred.

It is also important that it be resistant to temperatures of more than 500°C, generating a reasonable total pressure drop (<35mbar) and able to operate under these conditions in transient — as well as in steady state.

In a preferred embodiment, the installation of the heat exchanger (3) is done by means of threaded connections or flanges making it possible to connect the inputs/outputs to the rest of the heating system.

In a preferred embodiment, the exchanger is a spiral plate exchanger allowing optimum flow distribution.

The position of the heat recovery system (3) relative to the heating tube (1) can be adapted to reduce the size and maintain the integrity of the structure.

In a preferred embodiment, a uniaxial positioning of the exchanger will be favored due to the balance

{ BE2020/0125 structural that this positioning provides.

This positioning also makes it possible to reduce the number of visible elements and therefore to reduce the associated heat losses.

The entire heating system must be well sealed to prevent any air intake from the outside.

By circulating in the heat exchanger, the combustion gases will transmit up to 80% of their energy to the air entering the heat exchanger via the air intake valve (7). This heat exchange makes it possible to preheat the air before it is injected into the combustion chamber and therefore to considerably reduce the heat losses associated with this part of the device.

The combustion gases leave the heat exchanger (3) with a temperature below 110°C.

To reduce the temperature to a point below 80°C, a dilution tube is added between the outlet of the exchanger (3) and the fan (4). This dilution tube is composed, in a preferred embodiment, of a first metal tube perforated with 1 to 6 holes of 2 to 8 mm in diameter and covered with a second metal tube also perforated with 1 to 6 holes of 2 8mm in diameter.

By moving the perforations of the outer tube in relation to those of the inner tube, the flow of fresh air admitted for the dilution of the flue gases can be adjusted.

Once diluted with air, the combustion gases are evacuated via a smoke extractor or fan (4) and a chimney (9). To increase the thermal efficiency of the system, thermal insulation adapted to the device is installed.

In a preferred embodiment, a layer of concrete is poured over the floor to secure the heater tubes and burners in place.

A layer of insulation (23) is then applied to this layer of concrete to limit heat loss from the ground.

The visible parts of the heating system are also covered with a layer of insulation to further reduce heat loss to the outside.

In this way, the total heat losses of the system are greatly reduced and most of the energy will be used only for heating the floor.

In a preferred embodiment, the use of custom-made reusable insulation blankets can be considered for the exposed parts of the heating system.

Each heating unit (or heating system) is accompanied by a control box (5) comprising all the components and sensors necessary for ignition, flame monitoring and treatment monitoring.

To do this, several devices for measuring temperature, flow, pressure and gas concentration are placed at different strategic points on the burner.

In a preferred embodiment, 5 measurement points are defined: A point at the air inlet of — the combustion head (2), a point at the hot gas outlet of the heating tube (1), a point at the hot gas from the recuperator (3), a point at the outlet of the chimney (9) and a point at the steam inlet of the combustion head (2) (if the reburn mode is used). Each point is equipped with the sensors needed to monitor the desired variables.

In a preferred embodiment, the measurement points are integrated into the device via threaded connections to guarantee the tightness of the assembly.

All these measurements allow for better monitoring of system performance and combustion in the burner.

The number of control boxes can also be adapted according to the project.

Indeed, it is possible to have one control box per heating system or, in a preferred embodiment, a single central control box making it possible to control the entire site from a single location.

This second type of device makes it possible to reduce the size that several control boxes provide and therefore to allow the use of such technology on closed, restricted and difficult-to-access sites.

It also reduces the costs associated with the purchase of several boxes.

In-situ operation (ISTD) | In ISTD operating mode, no earth excavation is required and the remediation technology is directly integrated into the volume of polluted earth.

A drilling of the required depth is performed to be able to insert the heating tubes into the ground.

The distribution of the heating tubes as well as the distance between them is variable and chosen to optimize the heating of the floor.

Once in the ground, the heating tubes are surmounted by a combustion head and connected to the fuel network and the electricity network.

In a preferred embodiment and for safety reasons, the fuel and electricity supply circuits are fixed on high supports, thus freeing up floor space and facilitating movement on site.

Each heating system is equipped with a chimney and therefore the system does not require a combustion gas evacuation circuit.

In the situation where this system is used in a confined space, an additional central circuit for the collection of flue gases and ventilation is necessary. | 25 Ex-situ operation (ESTD) In ESTD operation mode, the polluted soil is excavated and then treated on site or moved to a site designated as a depollution site.

The earth is then used to form mounds, piles or placed in containers allowing treatment of the pollution by “batch”. The heating tubes are inserted in a horizontal position in rows through the pile with, again, a distribution allowing the best possible heating of the entire volume of soil.

In a preferred embodiment, the piles of earth will be covered with a layer of concrete and a layer of insulation to consolidate the pile and limit losses of | heat.

Current technology uses exchanger tubes placed in the stack between two rows of burners.

These tubes make it possible to use the heat of the combustion gases to reinforce the heat exchange by thermal conduction with the ground.

The presence of a heat exchanger on this new technology makes it possible to eliminate the exchanger tubes used by current technology in ESTD treatments.

This mode of operation is for the most part used in open places and therefore a system where each burner has its own extractor and its own chimney can be used.

In a preferred embodiment, the fuel and electricity supply circuits are fixed on a metal support in height.

If the device has several control boxes, they will be attached to the same metal support and aligned to facilitate the work of the operator. Additional metal brackets may be required to support the heater tubes and support the overall installation. . In a preferred embodiment, the heat exchanger (3) consists of plates in a spiral format and is located in the annular zone between the internal tube (13) and the external tube (1), in order to avoid a loss surface energy; In a preferred embodiment, the control box (5) is divided into two parts, a first part of which is kept in the immediate vicinity of the combustion head (2) and the other part is centralized and integrated into the management of several burners, in order to optimize the heating of a larger area containing heterogeneous soils; In a preferred embodiment, the steam hose (10) comprises a catalytic oxidation unit in which the oxidizable organic compounds can be oxidized and generate an immediately recoverable temperature rise; In a preferred embodiment, the entry of the vapors (19) takes place radially;

LEGEND OF FIGURES

1. Heating tube

2. Combustion head

3. Heat exchanger

4. Fan

5. Control box

6. Stainless steel hose

7. Air suction valve

8. Combustion gas suction valve

9. Exhaust line

10. Steam hose |

11. Flame protection tube |

12. Refractory ceramic tube

13. Inner tube | : 40 14. Outer tube

15. Fuel injector

16. Ignition and flame control electrode

17. Flame Gaze,

18. Air compartment 45 19. Steam compartment

20. Mixer.

21. Main flange;

22. Pressure switch output

23. Floor insulation

9; BE2020/0125.

24. Fuel inlet

25. Combustion chamber

26. Steam pipe

Claims (7)

‘a 10 BE2020/0125 CLAIMS 1. A heating system used in soil depollution by thermal desorption comprising: - A heat exchanger making it possible to recover the heat contained in the combustion gases and to use it to preheat the incoming air used in the combustion chamber. - A heat production unit (burner) having a combustion chamber | placed inside the heating tube. - Depollution of a site by thermal desorption using the heat produced by the burner and maintaining a thermal efficiency of more than 80%. | 2. A system as in claim 1, where the current technology burner body is replaced by a stainless steel tube and a refractory ceramic tube inserted into the heating tube. 3. A system as in claim 1 to 2, wherein a heat exchanger is | placed between the combustion gas outlet and the primary air inlet allowing; 20 preheat it to 400°C. ; 4. A system as in claim 1 to 3, in which each heating system “is provided with a smoke extractor and an individual chimney making it possible to avoid the use of a gas evacuation circuit. combustion with central extractor. 5, A system as in claim 1 to 4, in which the monitoring and control of the heating is done from a control box comprising sensors and components necessary for the proper functioning and monitoring of the combustion. This control box is physically separated from the heating system. 6. A system as in claim 1 to 5, wherein the current secondary air inlet is eliminated in favor of a single inlet for both primary and secondary air. The separation between the two occurs at the inner tube. 7. A system as in claim 1 to 6, in which a suitable insulating layer will be applied to the visible parts of the device to limit thermal losses.