NL8201589A - METHOD FOR CLEANING POLLUTED SUBSTRATE AND APPARATUS FOR APPLICATION OF THE METHOD - Google Patents

Description

* i / - 1 - K 5896

METHOD FOR CLEANING CONTAMINATED SUBSTRATE AND APPARATUS FOR APPLICATION OF THE METHOD

Recently, problems have arisen increasingly in industrial areas where harmful liquids can be released that pollute the soil.

The majority of these released liquids fortunately only contaminate the surface layer, which is the top layer of earth in which small plants (whose roots do not reach a great depth) grow. The amount of these released liquids is often relatively small. However, they should be removed as soon as possible, as otherwise the liquids will penetrate deeper into the soil and reach the substrate under the surface layer. Most of these released liquids give off a very unpleasant odor or even harmful vapors, which is all the more reason to quickly remove such liquids from the ground.

Small amounts of escaped liquid, initially contaminating only the surface layer, can be removed simply by excavating the contaminated portion of the surface layer and heat-treating the contaminated soil in an oven. As a result, the polluting liquid is burned or evaporated, while the cleaned soil can be returned to the original location if desired.

When relatively large amounts of noxious liquid have escaped and / or when liquid has leaked from underground storage tanks in the past, the contaminated area is at a relatively great depth below the earth's surface. Such contamination of the subsoil - that is the part of the soil that lies under the top layer of earth in which the plants grow - can only be removed at an astronomically high cost by using the cleaning method described above 8201589. as very large amounts of soil have to be dug out to be treated in ovens.

Since the latter type of contamination has been discovered quite frequently in recent times, it is important to design a good and relatively inexpensive cleaning method for this type of contamination.

The object of the invention is to provide a method for cleaning contaminated substrate in a relatively inexpensive and simple manner, wherein the zones located above the contaminated area are not removed or only partly removed.

To this end, the method according to the invention is characterized in that steam is injected into the pore space of the substrate in order to displace fluids present in the pore space in an upward direction through the pore space to the earth's surface and the injection of steam is at least continued until vapor from takes off the ground.

The device according to the invention comprises a steam generator and a number of pipes placed in the ground, the inner sides of the pipes communicating with the pore space of the substrate and with the steam outlet of the steam generator.

The invention is now further described by way of example with reference to the drawing, which shows a vertical section of a contaminated part of the substrate and the surface layer above it.

The drawing shows an area 1 contaminated by escaped liquid hydrocarbon (such as kerosene). This area 1 lies partly in the surface layer 2 and for the most part in the substrate 3. Pipes 4 are placed vertically in the surface layer 2 and the substrate 3, the open bottom ends 5 of the pipes being below the lowest level of the contaminated area 1. The pipes are placed in a suitable 8201589 * 5-3 way, for example by drilling or driving. The outer surface of each pipe must fit snugly into the hole in which the pipe is located in order to avoid short-circuiting of the steam injected at a later stage of the process.

In the event of a mismatched pipe, this short would occur through the space between the outer wall of the pipe and the wall of the hole in which the pipe is located.

The upper ends of the pipes 4 communicate via suitable pipes 7 with a manifold 6. The manifold 6 communicates via 10 a pipe 8 and a valve 9 with the steam outlet of a steam generator 11 located at some distance from the ground surface 12 is above the contaminated area 1.

Over a part of the ground surface 12, a hood 13 is placed, wherein, if conditions allow, the bottom edge of the hood is placed in the surface layer 2 in order to seal the interior of the hood from the atmosphere.

A condenser 14 is placed inside the hood 13. Below this condenser is arranged a collection container 15 which is connected to a tank truck 19 via a pipe 16, a pump 17 and a hose 18.

Coolant is circulated through condenser 14 by means of a pump 20, lines 21, 22 and a heat exchanger 23.

The contaminating liquid is in the space between the grains of the surface layer 2 and the substrate 3.

The part of this space (also called pore space) that is contaminated by the liquid is located in the area 1. The contaminating liquid is driven from the pore space of area 1 to the surface. To this end, steam is generated in the steam generator 11 and is fed via the steam outlet 10, the valve 9 and the pipe 8 to the steam manifold 6, and then passed from this manifold via the pipes 7 to the pipes 4.

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Initially, the steam will condense in the pipes 4, but after these pipes have been heated, the steam will flow from the lower ends 5 of the pipes 4 into the pore space of the substrate 3 and the grains of the substrate as well as into the pore space of the substrate 5. heat any liquid hydrocarbon present. The liquid hydrocarbon evaporates as the temperature rises in the lower layers of the contaminated area and the evaporated hydrocarbon will flow upwards along with the injected steam (see arrows 24). In the initial phase, the vapors will condense in the higher parts of the polluted area 1, but as the injection of steam continues, the temperature in these parts will gradually rise to a value at which steam or hydrocarbon vapor no longer condenses.

The vapors then flow upwards through the pore space of the substrate 3 and the surface layer 2 and flow out of the surface of the part of the area 12 located under the cap 13. Within the hood 13, the vapors condense on the surface of the condenser pipes 14 which are continuously cooled by the cooling liquid circulating through the said pipes and through the heat exchanger 23 through the action of the pump 20.

The condensed vapors form a mixture of water and liquid hydrocarbon that is collected in the tank 15 and then pumped into the tanker 19 by means of the pump 17. The liquid mixture is then transported to a refinery or other suitable destination where the components of the mixture can be separated.

The speed at which the steam flows into the subsurface 3 is of course chosen such that the flutum pressure in the contaminated area 1 remains lower than the pressure at which craters 30 or fractures in the ground are created. In crater formation, a conical part of the soil is lifted by the flutdum pressure in the pore space of the soil, whereby steam escapes between the lifted part and the remaining soil. When a fracture occurs, the soil breaks horizontally because the fluid pressure at the lower ends 5 of the pipes 4 rises. The steam flows into this fracture, as a result of which a large part of the soil is lifted as a whole. The steam continues to flow into the fracture without rising upward to the surface.

The above-mentioned phenomena will not take place if the speed at which the steam is injected is kept so low that the pressure at the lower ends of the pipes 4 remains lower than the pressure at which fractures or craters occur, at which the lowest pressure is maintained. This speed cannot be given exactly in numbers, since this speed is highly dependent on the properties of the substrate, such as permeability and injectivity of the pore space of the substrate. In general, however, it can be stated that the rate at which the steam is injected should be chosen such that the upward flow rate of the steam in the pore space of the substrate is approximately midway between the lower ends of the pipes 4 and the earth's surface between 0.02 tons / m2 / day and 2 tons / m2 / day.

If the injectivity of the substrate is rather low and steam does not flow upwards through the pore space, the steam pressure at the lower ends 5 of the pipes A must be gradually increased. However, care must be taken to ensure that the pressure does not exceed the pressure at which craters and fractures occur. If this situation could arise, a number of pipes (not shown) must be placed parallel to the pipes 4 and distributed over the ground surface 12 under the hood 13. The open bottom ends of these additional pipes should be above the open bottom ends 5 of pipes 4. Furthermore, the upper ends of the additional pipes should be in open communication with the interior of hood 13. By means of these additional pipes, the contaminating liquid present between the open lower ends of the pipes 4 and that of the added pipes evaporates by steam. is supplied at a relatively low pressure, since the evaporated liquid and steam need not flow through the entire height of the pore space of the contaminated area 1, but the interior of the cap via the short path of the added pipes can reach. When pure steam starts to flow from the added pipes, these must be closed and an additional number of pipes must be placed, which end at an increasingly higher level in the contaminated area 1, until finally the entire area has been steamed and the vapors flow into hood 13 directly from the ground 2.

When the contaminated area 1 extends far in a horizontal direction, this area must be cleaned in parts. In the embodiment of the invention shown in the drawing, the pipes 4 are then removed from the cleaned part of the area 12 and placed in an adjacent part of this area. The hood 13 is also moved to this adjacent part and the cleaning treatment is then repeated in the manner already described above. If desired, further parts are also cleaned in the same way.

In the embodiment of the invention described above with reference to the drawing, the pore space of the region 1 was not completely saturated with liquid (s). As a result, steam and condensed water were allowed to flow upward through the pore space and removal of the evaporable noxious liquid (s) could begin after the temperature of the substrate had risen to such an extent that the noxious liquid (s) evaporated.

In other locations, however, the pore space of the contaminated areas may be completely saturated with liquid. The liquid in the pore space can be the contaminating liquid or consist of ground water and the contaminating liquid. When this type of contamination is removed by the method of the present invention, steam and condensed water will displace the liquid (s) present in the pore space to the surface and measures should be taken to prevent flooding of the soil surface 12. To this end, a dam or a small dike can be constructed around this area (or parts thereof) and the surface liquid (s) can be pumped to a suitable storage location or to a separating device where the harmful liquid is separated. of the groundwater which is then returned to a location outside the area 12. To collect the displaced liquids, holes can also be dug in the ground from which the liquids are then transported to a place where they can be further treated. When the contaminated area 1 is heated sufficiently, a mixture of steam and evaporated contaminating liquid begins to flow from the surface 12, which vapor mixture is condensed in the hood 13, as described above with reference to the drawing.

If after the above-mentioned treatments of the contaminated area 1 it appears that an amount of the harmful liquids or of the solids dissolved therein has remained in the pore space of the contaminated area, these residual solids or liquids can be removed from the area by to disassemble all material shown in the drawing, except all or any specimens of the pipes 4. Clean water is then supplied to the surface which is above the area 1 and a pump is connected to the pipes 4 in such a way that the water flowing down through the pore space of the area 1 is recycled via these pipes. The water thus recovered is mixed with the liquids and solids left in the area 1 after the steam treatment. After these liquids and solids have been separated from the reclaimed water, the water can be used again. The use of small dikes is recommended when parts of the earth's surface above area 1 are flooded.

8201589 - 8 -

In an area which has an originally high groundwater level, the above-mentioned rinsing treatment, which is applied after the steam treatment, can be carried out in another way by the rinsing water through the pipes 4 (after these have been disconnected from the steam generator 11) to the lower levels of area 1. The water will fill the pore space of this area and displace liquids or soluble solids left in the pore space after the steam treatment. Rinse water and any other liquids (along with solids dissolved therein) are collected on the surface and then removed for further treatment.

In the above treatments, it can sometimes be advantageous to prevent horizontal movement of liquids between the pore space of the contaminated area 1 and the pore space of the soil around the contaminated area. This displacement can be prevented by placing a barrier in the ground such as a cofferdam or a frozen zone, or by means of water wells that locally lower the groundwater level. A combination of these measures can also be used.

The contaminated area 1 can also be at least partially enclosed in order to prevent horizontal displacement of the liquid between the enclosed portion and the rest of the soil, after which the groundwater level in the enclosed portion is lowered through wells extending over the enclosed portion are divided. Groundwater pumped to the earth's surface is treated, if necessary, to remove any contaminants contained therein. After the ground-water level has been lowered, the steam treatment described with reference to the drawing is carried out. The groundwater level is regulated if necessary and kept at a desired level.

When a hood is used to collect the vapors flowing from the earth's surface when the underlying surface layer and substrate are steam-treated, any suitable type of hood may be used. The same goes for the condenser. If the vapors condense against the walls of the hood, appropriate gutters should be fitted to prevent the condensation products from entering the surface layer 2.

Although the pipes 4 shown in the drawing are arranged vertically in the ground, the invention is not limited thereto. If it is necessary, for example when cleaning a contaminated area that is wholly or partly located under an inaccessible earth surface (for example a residential area), the pipes can be driven into the ground in an oblique position, the upper ends of the pipes extending outside the inaccessible surface, but the lower ends of the pipes are below this surface. If possible, a hood should be used and it should cover the earth's surface from which the vapors rise.

The pipes 4 can further be provided with openings in the pipe walls, optionally in combination with open bottom ends, in order to obtain a large number of outflow openings for the steam.

An attractive way of placing the pipes is as follows. The bottom end of each pipe is closed with a streamlined cap, after which the pipe is driven into the ground. The sealing cap reduces friction when the pipe is driven into the ground and also prevents soil granules from entering the pipe. Moreover, in this method of placement, the pipe is fitted snugly into the hole, which offers advantages during the subsequent steam treatment, since no steam can escape through the space between the outer wall of the pipe and the wall of the hole. After the pipe is placed, some openings (also called perforations) are shot into the sidewall of the pipe at a location below the lowest level of the contaminated area. These openings are fired with an 8201589-10 firing perforator which is known in the oil extraction art and therefore does not need to be described in detail. The openings can also be drilled into the pipe before it is placed in the ground. Although some grains can penetrate the latter openings when the pipe is driven into the ground, these grains will not block the openings and will not interfere with the steam flowing through the openings.

Although wet steam can be used in the present process, it is preferred because of the high calorific value of dry steam and even superheated steam.

The interior of the hood 13 must of course be closed off from the atmosphere in order to prevent escape of vapors into the atmosphere. If the bottom edge of the cap cannot be closed with the ground, other suitable sealants can be used.

When contaminated areas extending to a very great depth in the substrate are cleaned, the vertical flow resistance experienced by the steam in the substrate often becomes very high, so that a high steam pressure is required at the places where steam is in the pore space of the substrate is being fed. However, this can lead to crater or fracture in the ground. This problem can be solved by initially placing the steam pipes such that the steam is injected into the contaminated area at a relatively shallow depth. After the surface layer and the part of the substrate located between the surface layer and the steam injection level have been cleaned, the steam pipes are driven deeper into the polluted area, after which the part of the substrate 30 located between the new steam injection level and the already cleaned soil by means of is cleaned of steam. This treatment is repeated until the bottom layer of the contaminated area is reached. The steam pipes are then placed in an adjacent zone, which is then cleaned in the same way.

Although crater formation in the ground must be avoided during the steam treatment in order to prevent short-circuiting of steam between the lower ends of the steam pipes and the earth's surface, crater formation before the start of steam treatment can be advantageous if one or more relatively impermeable interlayers are located in the substrate at a depth above the steam injection level. In such a case, steam or other fluid (gas or liquid) is conducted at high pressure into the pore space of the substrate at a depth below the interlayer / layers that would allow the passage of the steam upwardly through the pore space of the substrate. / would obstruct. The high fluid pressure will break open the subsurface 15, which may create a crater towards the earth's surface. By subsequently injecting steam into the pipes at reduced pressure, the crater will collapse, but the steam will be able to flow upwards through the fractured intermediate layer (s) with a relatively small loss of pressure, in order to expel the contaminating liquid.

When a contaminated area is treated in parts, steam in the treated zone may be short-circuited by steam escaping through the gas-filled pore space of an adjacent zone that has already been cleaned. Such a short circuit can be prevented by placing a cofferdam between the two zones, or by introducing liquid into the pore space of the cleaned zone in order to obtain a liquid saturation therein which is at least equal to the liquid saturation of the pore space of the cleaning zone.

In summary, it can be noted that the method and device according to the invention make it possible to clean earth layers at a relatively great depth (for instance below 1-2 meters and depths of several tens of meters), when these layers are contaminated with liquids which can be evaporated by steam. There are no restrictions on the extent of the contaminated area, but it is clear that very large areas in sections 5 need to be cleaned. This spot cleaning of the soil is particularly intended for cleaning contaminated soil, that is the soil that lies below the surface layer, the latter layer being the part of the soil in which small plants (i.e. no trees and large shrubs) are located. rooted. The thickness of the surface layer can be set at about one meter.

A contaminated surface layer can be cleaned relatively cheaply by replacing the contaminated soil with clean soil and heat-treating the contaminated soil in an oven. However, this method is too expensive to clean contaminated surfaces. Since the present method makes it possible to clean the substrate on site, it is relatively inexpensive and little time-consuming.

8201589

Claims (12)

1. A method for cleaning a contaminating substrate, characterized in that steam is injected into the pore space of the substrate in order to displace fluids present in the pore space upwardly through the pore space to the earth's surface, and the injection of steam to least continue until vapor rises from the ground. 2. Method according to claim 1, characterized in that the steam is injected into the pore space of the substrate through a large number of pipes, the inner sides of which communicate with the pore space of the substrate. Method according to claim 2, characterized in that the upper ends of the pipes are above the earth's surface and the inner sides of the pipes at or at the lower ends of the pipes communicate with the pore space of the substrate. Method according to one or more of claims 1 to 3, characterized in that the injection of steam is stopped when pure steam rises from the ground. Method according to one or more of claims 1-4, characterized in that the level at which steam is injected into the pore space is lowered at least once. 6. Method according to one or more of claims 1-5, characterized in that vapors are allowed to rise from the substrate by means of pipes, which pipes communicate with the pore space of the substrate at a level above that where the steam is injected into the pore space of the subsoil, while the pipes are further connected to a space above the earth's surface. 8201589 - 14 - Method according to claim 6, characterized in that the level at which the vapors can rise from the underground is increased at least once. 8. Method according to one or more of claims 1-7, characterized in that the method also comprises a step in which the fluids displaced in vapor form by the injected steam to the earth's surface are condensed at a location above the earth's surface . 9. Device for cleaning contaminated substrate, characterized in that the device comprises a steam generator and a number of pipes placed in the ground, the inner sides of the pipes communicating with the pore space of the substrate and with the steam outlet of the steam generator. Device according to claim 9, characterized in that the device on the surface of the earth comprises means for rendering harmless the fluids which have been expelled from the ground by the action of the steam. 11. Device as claimed in claim 10, characterized in that it comprises a cap and a condenser for condensing the fluids, the condenser being placed inside the cap and communicating with a condensed fluid storage tank. 12. Device according to one or more of claims 9-11, characterized in that it comprises additional pipes placed close to the original number of pipes, the insides of said additional pipes communicating with a space located above the earth's surface. as well as the pore space of the substrate at a level above that where the original number of pipes communicates with the pore space. 8201589