FIELD OF THE INVENTION

The present invention consists of a heating system designed to improve the thermal treatment of contaminated materials by means of conductive steel supports increasing the exchange surface between the heating tube and its environment. The invention relates in particular to a heating system suitable for ex-situ thermal desorption treatment (excavated contaminated materials) to remediate materials containing hydrocarbons and/or other organic contaminants.

BACKGROUND OF THE INVENTION

Soil contamination is a problem of great importance in a world where the environment and sustainable development are becoming more and more important. This often invisible problem can be caused by a wide variety of chemical, biological or even radioactive contaminants and an equally wide range of pollution sources. Left unchecked, contamination can spread to other resources essential to the surrounding flora and fauna. It is therefore important, in the interest of environmental protection 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 the technique depends on several parameters such as the nature of the contamination, the soil properties, the physical constraints of the site and the total cost of the project.

One of these techniques, thermal desorption, is based on heating the soil 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 (W02001078914A8). With this technique, energy from heating tubes is propagated radially through the soil by conduction. This has several advantages over other soil remediation options because thermal conduction allows soil to be heated to temperatures in excess of 350°C (which is not possible, for example, with resistive electric heating (US5656239A)) and to easily and quickly treat soils contaminated with a wide variety of contaminants, regardless of soil heterogeneity. Indeed, thermal conductivity has the particularity of not fluctuating by large orders of magnitude with the materials present in the soil. Therefore, thermal conduction is much more efficient than other heat transfer methods in heterogeneous soils.

This technique is applicable both ex-situ and in-situ. With ex-situ thermal desorption (ESTD), contaminated soil is excavated and used to form piles or placed in containers that are thermally treated. With in-situ thermal desorption, the heating tubes are inserted directly into the contaminated soil, thus avoiding excavation and transport of soil. This also allows the treatment of soils in restricted areas 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 metal tubes (BE1024596B1).

The present invention presents a heating system for improving the thermal treatment of contaminated materials by means of steel conductive supports increasing the exchange surface between the heating tube and its environment.

The present invention also relates to a heating system for improving the thermal treatment of contaminated materials by means of cast-iron conductive supports increasing the exchange surface between the heating tube and its environment.

In particular, in an ESTD mode, the heating tubes are placed horizontally between layers of contaminated materials. These tubes can be up to 20 meters long and the volume of said contaminated materials around the last few meters of the heating tube, which are the furthest away from the heat source, rises in temperature slower than the rest of the stack due to uneven heat distribution along the heating tubes. In addition, current processes do not allow the heat to be voluntary directed to selected portions of the heating tube, which is useful when certain zones of the contaminated material volume contain more moisture or require higher treatment temperatures than the remaining zones. The present invention presents a solution to correct this heating offset by increasing the exchange surface between this portion of the heating tube and the contaminated materials surrounding it by means of conductive supports, known as "fins". This invention also makes it possible to modulate, according to external parameters, the heating within the volume to be treated and to bring enough energy to the required zones, thus avoiding important energy losses.

CN110295588A and US20080069640A1 aim to increase the contact area of the heating tube and the soil, in order to improve efficiency of the heating tube in heating the soil.

The present invention improves the application with 2 advantages over the prior art. The first advantage is the independence of the fins from the heating tube, it allows the user to select where on the heating tube the heat transfer surface must be augmented and by how much. The second advantage is the simple shape of the fins, this makes their manufacturing easier and thus cheaper; this causes less friction when initiating and ending; and reduces the chance of having air pockets.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 : Example of a portion of a heating tube with 4 fins

Figure 2a : Zoom on a fin below the heating tube

Figure 2b: Zoom on a single fin

Figure 3: Example of several heating tubes with fins in ex-situ mode

The legend of the figures is as follows:

1. heating tube

2. minimum wingspan

3. maximum wingspan

4. pile of contaminated materials

DETAILED DESCRIPTION OF THE INVENTION

The terms "contaminated soil" and "contaminated material" are used here synonymously 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 contaminants, e.g. hydrocarbons, and inorganic contaminants, whose boiling temperature, Tb, at atmospheric pressure is less than 600°C 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 consists of a transfer of kinetic energy from the hotter 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 (cooler) object by direct contact. It should be understood that in the present invention, when heat transfer by conduction is mentioned, a very small amount of heat is usually also transferred to the contaminated material by means of radiation.

The present invention relates to a system having a number of thermally conductive tubes each made of 2 pipes, inner and outer, placed in contaminated soil (the outer pipe is in direct contact with the soil). The pipes are in communication with a heat source causing a heated fluid to flow through the pipes from the inner to the outer, causing the temperature of the surrounding soil to rise. The invention is intended to increase the exchange surface between the heating tube and the surrounding soil volume by using steel or cast-iron plates, hereinafter referred to as "fins", placed on the outer pipe of the heating tube.

In a preferred embodiment, the contaminated soil is excavated and then treated on site or moved to a designated cleanup site. The soil is then used to form piles or placed in containers for batch processing (ex-situ, ESTD). The heating tubes are inserted horizontally in rows through the pile in a way that the entire volume of contaminated soil is heated.

The present invention concerns fins (2) (3) placed or welded directly below or above each heating tube (1) (Figure 2a). Since steel or cast-iron have a thermal conductivity that is tens of times higher than that of various soil types, the heat is transferred quicker to the volume of contaminated soil (4) (figure 3) surrounding a heating tube with fins. As a result, the heating time is accelerated and the treatment time is decreased, resulting in a treatment with higher energy efficiency..

In a preferred embodiment, the fins are not attached or welded to the heating tubes, but simply placed on or under them.

In a preferred embodiment the fins are made of any grade of steel or cast-iron having a heat conductivity higher than 14 W/mK at 25°C and a density higher than 7.6 g/cm ³ . Thus, the material choice is abundant and can be adapted in case of acidic contaminants. In a preferred embodiment the fins are made of malleable and conductive metal, different from steel. Thus, they can be lighter and easier to place.

The number of fins to be placed and their size depends on the total length of the heating tube.

In a preferred embodiment, the position and size of the fins depend on the quality of the materials to be treated, particularly their moisture content and/or their concentration of pollutants.

In a preferred embodiment, the heating tubes have one large fin. In another preferred embodiment, the heating tubes have a plurality of small sized fins (Figure 1). The fins on a single heating tube are spaced a few tens of centimeters apart and can be of different sizes: with the one with the largest surface area (3) placed at the end of the tube and the smallest surface area (2) moving away from the end of the tube.

In the present invention, the thickness of the fins is between 1mm and 20mm and preferably between 2 and 10mm. The shape of the fin is rectangular on the sides and semicircular in the middle between the two rectangular parts (Figure 2b).

The shape of the fin is rectangular on the sides and semicircular in the middle between the two rectangular parts to match the shape of the heating tube and to maximize contact.

The length of the fin is between 350mm and 1500mm and preferably between 500 and 1200mm. The width of the fin (wingspan) is between 400mm and 1000mm and preferably between 500 and 800mm. The fins are oriented parallel to the layers of material to be treated.

The invention relates to the usage of a fin for the treatment of contaminated materials, wherein the fin is connected to a heating pipe for a distance, measured over the cross section of the heating pipe, of at least the outer radius and maximally 90% of the outer circumference of the heating pipe, preferably 40-60% of the outer circumference of the heating pipe.

In an embodiment, the wingspan of the fin is between 2 and 100 times the outer diameter of the heating tube. In an embodiment, the wingspan of the fin is between 5 and 25 times the outer diameter of the heating tube. The wingspan is the maximum distance of the fin, measured from tip to tip in the axial plane. The axial plane is the plane extending radially from the longitudinal axis of the pipe.