BE1028862B1 - Mixed system of soil depollution by thermal desorption and production of electrical energy using solar energy - Google Patents

Abstract

The present invention consists of a method of depollution by thermal desorption using solar energy, making it possible to depollute large polluted surfaces without external energy supply, by means of a solar installation which can, after depollution, be used as a production of electrical energy or heat. The invention consists of placing a network of solar panels over the entire contaminated area, where these solar panels heat a fluid that circulates in a network of horizontal and vertical pipes. This network is controlled by automatic valves actuated by an automation device which directs the fluid towards the adequate vertical heating elements. The technique is based on a gradual distribution of heat produced by means of solar concentrators in the basement, in combination with an in situ destruction system of pollutants so as not to release toxic compounds into the atmosphere during depollution.

Description

Mixed system for soil remediation by thermal desorption and electrical energy production using solar energy BE2020/0129

DESCRIPTION FIELD OF THE INVENTION The present invention relates to a thermal rehabilitation system for contaminated land using thermal solar panels in combination with photovoltaic panels. Once the remediation is complete, the system can be converted into a renewable energy power plant; The invention relates in particular to a method and devices for remediating soils containing hydrocarbons and/or other organic contaminants, more particularly a method and devices for volatilizing contaminants from the soil by thermal conduction and for removing these contaminants from the soil. and oxidize them further in situ. The system can then be converted into a solar power plant. BACKGROUND OF THE INVENTION Contamination of surface and near-surface soils has become a matter of great concern in many places. Soil can be contaminated with contaminants — chemical, biological and/or radioactive. Material spills, storage tank leaks, and improperly disposed materials seeping into landfills are just a few examples of the many ways soil can become contaminated. If left in place, many of these contaminants will find their way into aquifers, the air or the food supply and could pose a public health hazard.

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 large areas of soil need to be treated.

One method that can be used to remove contaminants from subterranean soil is a soil vapor extraction method. In this process, a vacuum is applied to the ground to draw air and vapor through the underground soil. The vacuum can be applied to a ground/air interface, or the vacuum can be applied by vacuum wells placed in the ground. Air and steam can entrain and transport volatile contaminants to the source of the vacuum. Off-gases extracted from the ground by the vacuum, which include 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 the in-situ heating of the soil to increase its temperature while simultaneously removing off-gases from the soil. Heat added to contaminated soil can raise the temperature of the soil above the vaporization temperatures of the contaminants present in the soil and cause the contaminants to vaporize. A vacuum applied to the floor draws the vaporized contaminant out of the floor. One method of heating soil containing contaminants is to inject a heated fluid into the soil. Such a method is for example described in US Patent No. 6,000,882. The method described here consists of introducing a system of perforated pipes into the ground. A current of hot air is sent through the pipes. Hot air is injected into the ground through perforations in the pipes at the pipe perforations. Contaminating vapor is formed in the ground, which can be removed from the ground through the pipe perforations and vented to an off-gas treatment unit. A major drawback of this type of method, however, is that the injection of hot air into the ground tends to create preferential paths for the flow of steam in the ground. As a result, the hot air is not evenly distributed through the contaminated soil, but rather accumulates at the injection into the soil, i.e. in and around the pipe perforations.

Another way to heat a floor is to heat a self 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 an ancient art.

The present invention aims to provide an alternative solution for treating the soil ex situ by simplifying the method and optimizing the treatment. It consists in particular in treating the contaminated earth in an insulated container making it possible to obtain a higher temperature of the contaminated earth more quickly.

Contaminated land includes land that has been contaminated, for example by past industrial use, accidental spills or other pollution. Types of contaminants include petroleum hydrocarbons, polycyclic aromatic hydrocarbons, chlorine compounds, other miscellaneous organic substances as well as inorganic compounds and heavy metals. A specific type of contaminated land, defined as brownfield, is defined as abandoned, unused, or underutilized commercial or industrial properties where past actions have caused environmental contamination, but which still have potential for redevelopment or other opportunities economic. Other Contaminated Sites are defined as land containing contaminants that is currently used for its original purpose and/or has no intended use, i.e. land that has no significant value for any real estate development.

40 Canada's Federal Contaminated Sites Inventory currently identifies over 23,000 federal brownfield sites in Canada, including over 5,000 active contaminated sites. According to the United States Environmental Protection Agency, a brownfield is defined as a property whose expansion, redevelopment, or reuse may be complicated by the presence or potential presence of a hazardous substance, pollutant or a contaminant. It is estimated that there are currently over 450,000 brownfield sites in the United States.

It is desirable to remediate both brownfield sites and other contaminated land to enable their reuse for economic and/or societal purposes. Many governments have programs in place to promote and assist in the remediation of contaminated sites. However, particularly in the case of large sites with little or no economic value, rehabilitation costs are often prohibitive compared to the economic and/or societal benefit they can bring. Furthermore, current technologies are either affordable but not fully effective (bioremediation, phytoremediation) or effective but expensive (excavation and transport, thermal desorption). This leads, overall, to inaction and unsustainable land use.

Solar farms exist and are sometimes developed on contaminated land, in particular for a beneficial use of this land, without however the soil being treated. Solar farms are defined as large areas of photovoltaic panels installed on these lands and producing electricity.

In some cases, this electricity is used, in whole or in part, to supply energy to an inefficient remediation technique, such as bioremediation, soil vapor extraction, bioventing or even thermal desorption. electricity in situ. The overall energy balance remains mediocre because solar energy is first transformed into electricity which is then transformed into mechanical or thermal energy, which gives very low yields.

A solar thermal collector collects heat by absorbing sunlight. The term “solar collector” generally refers to a solar water heating device, but it can refer to large power generation installations such as parabolic solar pans and solar towers or devices not used for heating water, such as solar air heaters.

Solar thermal collectors are either non-concentrated or concentrated. In non-concentrating collectors, the aperture area (i.e. the area that receives solar radiation) is about the same as the absorption area (i.e. the area that absorbs radiation). This type of sensor has no additional parts except the sensor itself. Concentrating collectors have an aperture much larger than the absorption surface 40 — (additional mirrors concentrate sunlight on the absorber) and receive only the direct component of sunlight.

Non-concentrating collectors are typically used in residential and commercial buildings for space heating, while concentrator collectors in concentrating solar power plants generate electricity by heating a heat transfer fluid to drive a turbine connected to an electrical generator.

The invention makes it possible to solve essential problems of large-scale pollution, in particular in countries where the solar resource is abundant.

DETAILED DESCRIPTION OF THE INVENTION The terms "contaminated soil" and "soil containing contaminants" are used herein synonymously and should be understood to include all types of soils which may be contaminated with hydrocarbons or other organic compounds.

Heat by conduction occurs when two mediums or material objects are in direct contact, and the temperature of one is higher than that of the other.

Heat conduction consists of a transfer of kinetic energy from the hottest medium to the coldest medium.

The term "conduction" as used herein therefore refers to all types of heat transfer in which heat is moved from one (hotter) object to another (colder) object by direct contact.

It is understood that in the present invention, when it comes to heat transfer by conduction, a very small amount of heat is generally also transferred to the ground by radiation.

The present invention consists on the one hand in a network of vertical heating wells (7) installed on a ground containing volatile and/or semi-volatile pollutants, with an interdistance of 1.0 to 3.5 m, preferably between 1.5 and 2.0 m and at a variable depth to adapt to the depth of contamination (11). Each vertical heating element (7) is constructed from 2 metal tubes, coaxial, composed of an inner tube (12) and an outer tube (13) and where the hot fluid enters the central tube and rises to through the annular space between the inner tube and the outer tube.

The outer tubes have a variable diameter ranging from 20 to 250 mm and preferably between 30 to 100 mm, depending on the depth of the heating element and the calorific value of the heating fluid.

A remote-controlled electric valve (4) is placed on the inner tube and/or at the outlet of the outer tube (3) and is used to regulate the flow rate of the heating fluid passing through the vertical heating element; An individual catalytic oxidizer (9) is placed in the outer vapor tube (8), below ground level, creating a heated environment in which said catalytic oxidizer (9) can operate effectively; On the other hand, the network is made up of a set of solar panels (1), direct or concentrated, allowing the energy of solar radiation (6) to be converted into heating of a heat transfer fluid.

This fluid is then injected into the network (2) in order to heat the soil 40 — contaminated (11).

5 The network of heating elements (7) and the network of solar panels (1) are woven in such a way that the heating by solar radiation and the heating of the ground alternate and are as efficient as possible.

In a preferred embodiment, the heat transfer fluid may be directed to a pile of contaminated soil to be treated by thermal desorption, similar to that used for in-situ treatment.

In a preferred embodiment, a separate set of photovoltaic panels is installed in order to supply electricity to certain elements essential for the circulation of fluids and/or the extraction of pollutants In a preferred embodiment, the remote-controlled automatic valves (3, 4 and 5) make it possible to direct the heat transfer fluid towards certain specific zones according to their level of contamination and according to the quantity of energy available.

In a preferred embodiment, the remote-controlled automatic valves (3, 4 and 5) are closed in order to prevent the circulation of the heat transfer fluid when the solar panels do not produce heat (at night for example). In a preferred embodiment, the catalytic oxidation unit (9) is provided with an electric pre-heating device connected to photovoltaic panels.

In a preferred embodiment, the solar heating of the ground is light and makes it possible to accelerate the bio-degradation in situ; In a preferred embodiment the system activates high temperature thermal desorption for a short period of time before leaving a slight heating in the pre-treated area to activate the bio-remediation In a preferred embodiment the heating elements (7 ) are also placed in the saturated zone (aquifer) if it is polluted; The heating of the aquifer thus making it possible to trigger either in situ chemical oxidation reactions (oxidation and/or reduction) or to increase the effectiveness of natural biodegradation in the aquifer downstream of the zone (diffusion of heat and slight increase temperature up to 15 to 50°C and preferably from 25 to 35°C)

Claims (9)

1. A method of thermal desorption, the method comprising: - a solar concentration unit generating renewable heat to produce a high temperature heating fluid used to remediate contaminated sites by thermal conduction heating and which can also be used for generate electricity in a conventional turbine; - remediation of at least one area of the contaminated site, using heat from heat-generating equipment; and directing at least a portion of the heat produced for the remediation of another area of the contaminated site, based on the actual heat transfer in the subsoil achieving temperatures equal to or greater than 100°C in the contaminated soil to mobilize contaminants in the vapor phase 2. The method of claim 1, wherein the heat generating equipment comprises a solar cell and a photovoltaic cell or a wind turbine. 3. Method according to claims 1 and 2, in which the heat-generating equipment supplies heat only to a small part of the contaminated site, and in which the heat is used to increase the temperature of the subsoil in a smaller part of the contaminated site. 4. The method according to claims 1 to 3, wherein monitoring equipment is further connected to the heat generating equipment to monitor the effectiveness of the remediation on at least the area of the contaminated site. 5. The method according to claims 1 to 4, further comprising: - monitoring the effectiveness of the remediation; and - programming the heat flow in the heating sinks in order to improve the efficiency of the sanitation, on the basis of said monitoring. 6. An on-site thermal desorption system, the system comprising: - A device for inserting heating elements into a pile of excavated contaminated material - Heat generating equipment for renewable heat generation located at a contaminated site - The remediation equipment for remediating at least one area of the contaminated site, the remediation equipment using heat from the heat generating equipment to effect the remediation. 7. The system of claim 6, wherein the heat generating equipment comprises a solar cell and a photovoltaic cell or a wind turbine. 8. The system according to claims 6 and 7, wherein the heat generating equipment provides heat only to a small part of the contaminated site, and wherein the remediation equipment is located in the small part of the contaminated site. 9. The system according to claims 6 to 8, which further comprises monitoring equipment connected to the heat generating equipment to monitor the effectiveness of the remediation on at least the area of the contaminated site.