BE1029844B1 - SYSTEM FOR DEPOLLUTION OF CONTAMINATED MATERIALS BY MEANS OF HEATING TUBES WITH CONDUCTIVE SUPPORTS - Google Patents

Abstract

The present invention relates to a system for the heat treatment of materials contaminated with hydrocarbons and/or other volatile organic or inorganic pollutants at 600°C. The present invention proposes a system for treating said contaminated materials via thermally conductive tubes equipped with conductive steel supports, called "fins", locally increasing their thermal conductivity.

Description

1 BE2021/5796

DEPOLLUTION SYSTEM FOR CONTAMINATED MATERIALS BY MEANS OF

HEATING TUBES WITH CONDUCTIVE SUPPORTS

FIELD OF THE INVENTION

The present invention consists of a heating system intended to improve the heat 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 treatment by ex-situ thermal desorption (excavated contaminated materials) to clean up 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 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 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 (WO2001078914A8). With this technique, the energy coming from the heating tubes propagates radially in the ground by conduction.

This has several advantages over other remedial options.

2 BE2021/5796 from the ground 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 treat easily and quickly soils contaminated with a wide variety of contaminants, regardless of the heterogeneity of the

Floor. Indeed, the 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 methods of heat transfer in the case of heterogeneous soils.

This technique is applicable ex-situ and in-situ. In Ex-Situ Thermal Desorption (ESTD), contaminated soil is excavated and used to form piles or placed in containers that are heat-treated. With in-situ thermal desorption, the heating tubes are directly inserted into the polluted soil, thus avoiding excavation and transport of soil. 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 metal tubes (BE1024596B1).

The present invention presents a heating system intended to improve the heat treatment of contaminated materials by means of conductive steel supports increasing the exchange surface between the heating tube and its environment.

In particular, in the context of an ESTD mode, the heating tubes are placed horizontally between layers of contaminated materials. These tubes can be up to 20 meters in length and the volume of said contaminated material around the last few meters of the heater tube heats up more slowly than the rest of the stack due to uneven heat distribution along the heater tubes. . Moreover, the current methods do not make it possible to direct the heat to the places chosen, for example because they contain more humidity or require higher temperatures.

The present invention presents a solution for correcting this heating offset by - increasing the exchange surface between this portion of the heating tube and the contaminated materials which surround it by means of conductive supports, called "fins", This invention also allows to modulate, according to external parameters, the

3 BE2021/5796 heating within the volume to be treated and to bring energy to the required places, thus avoiding significant energy losses.

BRIEF DESCRIPTION OF DRAWINGS

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 span fin 3. Maximum span fin 4. Pile of contaminated materials

DETAILED DESCRIPTION OF THE INVENTION

The terms “contaminated soil” and “contaminated material” are used herein as — synonyms and should be understood to include all types of soil, sludge or other material which may be contaminated with any cocktail of pollutants, such as organic contaminants, for example hydrocarbons, and inorganic ones, whose boiling point, Teb, at atmospheric pressure is less than 600° C. and/or heavy metals.

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. It 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 means of radiation.

The present invention relates to a system with a number of thermally conductive tubes placed in contaminated soil. The pipes are in communication with

4 BE2021/5796 a heat source causing the circulation of a heated fluid through the tubes: from the internal heating tube to the external heating tube, causing the temperature of the surrounding ground to rise. The invention is intended to increase the exchange surface between the heating tube and the volume of earth which surrounds it by using steel plates hereinafter called "fins", placed on the external heating tubes.

In a preferred embodiment, the contaminated soil is excavated and then treated on site or else moved to a site designated as a depollution site. The earth is then used to form piles or placed in containers allowing “batch” treatment (ex-situ, ESTD). The heating tubes are inserted in a horizontal position in rows through the pile with a distribution allowing the best possible heating of the entire volume of contaminated soil.

The present invention relates to steel fins (2) (3) placed or welded directly below or above each heating tube (1) (Figure 2a).

Since steel has a thermal conductivity tens of times higher than that of the different types of soil, the heat is distributed more quickly to the volume of contaminated soil (4) (figure 3) surrounding a heating tube with fins. Consequently, the heating time is accelerated and the treatment time reduced, resulting in better energy efficiency of the treatment.

In a preferred embodiment, the fins are not attached or welded to the heating tubes, but simply placed above or below.

In a preferred embodiment, the fins are made of malleable and conductive metal, different from steel. So they can be lighter and easier to place.

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

In a preferred embodiment, the position and the size of the fins depend on the quality of the materials to be treated, in particular their humidity level and/or their concentration of pollutants.

In a preferred embodiment, the heating tubes have a large fin. In another preferred embodiment, the heating tubes are provided with several fins of small sizes (FIG. 1). The fins on the same heating tube are separated by a few tens of centimeters and can have different sizes: with the one with the largest surface (3) placed at the end of the tube and the smallest surface (2) moving away from the end of the tube.

5 In the present invention, the thickness of the fins is between 1 mm and 20 mm and preferably between 2 and 10 mm.

The shape of the fin is rectangular on the sides and in a semicircle in the middle between the two rectangular parts (figure 2b). The length of the fin is between 350mm and 1500mm and preferably between 500 and 1200mm.

The width of the fin is between 400mm and 1000mm and preferably between 500 and 800mm.

The fins are oriented parallel to the layers of materials to be treated.

Claims (1)

6 BE2021/5796 CLAIMS 1. System for treating contaminated materials via thermally conductive tubes fitted with conductive steel supports, locally increasing their thermal conductivity.