EP0424865B1 - Removal of dioxins and furans - Google Patents

Abstract

The invention relates to a process for the removal of dioxins and/or furans from layers close to the surface, in which especially the contaminated layers close to the surface are isolated from the surrounding room air and, by passing air and/or an exchange gas over the layers, a gas stream is generated on the layers close to the surface and, before or after it has swept over the layers close to the surface, is passed over a surface-active adsorbent and exposed to an ionising radiation. In a further embodiment, the layer which is close to the surface and is to be decontaminated is exposed before, during and/or after the treatment by the gas stream to artificial irradiation by UV-C light.

Description

The present invention relates to a method for removing dioxins and / or furans from layers near the surface, in particular from surfaces contaminated by fire damage.

From Alfons Weiss, "Versicherungswirtschaft" 11/1987, it is known, for example, that fires in which the askarels present as a coolant and dielectric in electrical equipment and systems have overheated result in polychlorinated dibenzofurans and polychlorinated dibenzo-p-dioxins. Traces of dioxins can also occur when products that contain polyfluorinated phenols are burned or burned. Many foamed and non-foamed plastics also contain polybrominated biphenyls and polybrominated diphenyl ethers as flame retardants, which are potential dioxin suppliers. Practically all substances that release a hydrogen halide or the corresponding halogen radical when charred or burned represent at least one of the two components for the formation of halogenated dioxins and furans. The combustion of PVC-containing materials has proven to be a particular problem. In addition, for example, also count the chlorinated hydrocarbons used in large quantities as degreasing and cleaning agents in industry as well as the chlorofluorocarbons and the halons used as extinguishing agents for the problematic dioxin and furan formers.

Of all the dioxins, the most toxic one by far, the four-chlorinated 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), has been best studied. The toxicity data of various dioxins are approximately based on 2,3,7,8-TCDD equivalents. This means that all other dioxins are converted into 2,3,7,8-TCDD quantities or equivalents in relation to their lower toxicity compared to 2,3,7,8-TCDD with the help of (partially estimated) toxicity factors.

Acceptable limit and guideline values for surface contamination by dioxins and / or furans for office and living rooms of 10 ng / m² TCDD or 50 ng / m² polychlorinated dibenzo-p-furans / dioxins (PCDF / PCDD).

In the case of fires of chlorinated plastic materials and / or chlorinated solvents, it can be expected that the limit values will be exceeded by a factor of 1000 in the areas with the greatest exposure. In the case of fire damage with Chlophen-filled transformers, far higher levels of dioxin have also been determined.

For the partial elimination of such dioxin-containing fire gas condensates, methods known in the prior art can be carried out, which have been used in fire rehabilitation for a long time anyway. These include, in particular, steam jet cleaning, hot water high pressure cleaning, sandblasting cleaning or the removal of contaminated material. In the event of fire damage, the dioxins and furans formed are almost always bound to the soot also formed during the fire, which more or less adheres to the surface, so that when the soot is removed, the dioxins are largely removed. However, wet cleaning does not usually lead to a reduction in contamination below the required guide values. In addition, the disposal of the now contaminated cleaning agents, in particular the washing water, the removal and the sandblasting material, presents considerable problems.

If the structural requirements for collecting the waste water are met, wet cleaning (high-pressure hot washing with the addition of a wetting agent) or treatment of the surfaces with solvents such as toluene can be considered according to the prior art. If further cleaning is required, unsatisfactory results with manual wet cleaning are not available, especially for uncoated surfaces, for example metal surfaces.

In addition, it is known to reduce the concentration of dioxins and furans in the ambient air to acceptable values in rooms contaminated with dioxin with the aid of suction devices while the air flow is adsorbed on activated carbon filters. However, a sufficient reduction in the dioxins and furans is not observed in the adjacent surfaces of the contaminated materials.

From "Insurance industry" 11/1987, page 704 it is known to carry out the actual building cleaning after a fire in the event of intensive dry cleaning with high-performance vacuum cleaners which are equipped with activated carbon filters for the exhaust air. However, this does not lead to satisfactory results since the dioxins are suitable due to their molecular nature to diffuse into deeper layers.

The photochemical degradation of polychlorinated di-benzo-p-dioxins in solution is known from reports 5/85 of the Federal Environment Agency from November 1984, pages 94-97.

EP-A 0 257 170 discloses a process for the decontamination of surfaces and liquids, in which UV radiation, if appropriate in the presence of hydrogen atoms, when using special reagents for reaction with the dioxins and / or furans, namely wetting agents, alcoholates and / or Radical formers, halogenated and polyhalogenated organic compounds are broken down.

WO 79/00835 describes the dehalogenation of halogenated compounds in solution by means of UV radiation under the action of oxidizing gases such as oxygen, air or ozone as prior art. (U.S. Patent 3,977,952), however, uses UV radiation in the presence of hydrogen gas in the absence of oxidizing agents.

From the journal "The Science of the Total Environment", Volume 10, 1978, pages 97-104, A. LIBERTI et al., A method for removing toxins from near-surface layers is known, whereby - among other things - the contaminated near-surface layers transferred to a plastic drum, whereupon the drum is sealed [ie, the contaminated near-surface layers are isolated from the ambient air]; After rotating the drum for the purpose of homogenizing the material, open cans are filled with the homogenized material, sprayed with a 1: 1 (vol.) xylene / ethyl oleate activation solution and finally exposed to solar radiation.

The object of the present invention is to remove dioxins and / or furans from layers near the surface, in particular in the event of fire. Of particular importance is the fact that it is desirable, for example when decontaminating control cabinets or other machine systems, to keep them in operation during the renovation.

It is a further object of the present invention to prepare contaminated layers close to the surface in such a way that the systems, devices or components can be used effectively during and after decontamination.

The object according to the invention is achieved by a method for removing dioxins and / or furans from layers near the surface, the contaminated, solid surfaces optionally being suctioned off dry first, the suction material on one Substrate adsorbed and disposed of, characterized in that the contaminated layers near the surface are isolated from the ambient room air and by passing air and / or an exchange gas over the layers, a gas flow is generated at the layers near the surface, which before or after painting over the layers near the surface is passed over a surface-active adsorbent and the gas stream is exposed to ionizing radiation.

The term "near-surface layer" within the meaning of the invention naturally includes the actual solid surface and in particular the visible solid surface.

When the gas stream is treated with ionizing radiation, ionic molecules or particles naturally arise which also act on the contaminated surface if the ionization stage is carried out before being transferred to the contaminated surface.

In the event that the ionizing radiation only acts on the gas stream after it has been passed over the contaminated surface, a reduction in the dioxin and / or furan values in the exhaust air can be observed.

The contaminated layers near the surface can be isolated from the ambient air, for example by partitioning them off with a film, it being possible to generate a gas stream on the contaminated surface which is isolated from the surrounding ambient air.

With the help of the present invention it is thus possible to reduce the concentrations of dioxins and furans in contaminated, solid surfaces to acceptable values. In the treatment of loose goods such as building rubble, scrap or goods and inventories, ie especially moving goods The method according to the invention leads to a reduction in the amount of highly contaminated waste, as a result of which high landfill costs are reduced, and the overloaded incineration plants can be relieved.

Devices for sucking in room air from dioxin-contaminated rooms are known per se. Here, the ambient air is adsorbed on a substrate, in particular through a filter system consisting of a prefilter and a special activated carbon filter, and then passed through an ionization stage in which existing gaseous components or aerosols can be split.

Surprisingly, it was found that even when air and / or an exchange gas was passed over the layers near the surface, a reduction in the concentration of dioxins and / or furans in the layers near the surface could also be registered if the gas flow was over before contact with the layers near the surface a surface-active adsorbent is passed and exposed to ionizing radiation. In principle, all protective gases that are gaseous at room temperature are suitable as exchange gases for air. However, non-combustible gases such as nitrogen or carbon dioxide are preferred. These allow working in fire risk areas. In the prior art, reactive exchange gases such as oxygen, ozone or hydrogen are also known per se, which may also be used in the context of the invention.

The method according to the invention is particularly suitable for near-surface layers such as floors, wall surfaces, ceilings, building rubble, scrap, soil, means of transport, in particular vehicles or ships, technical systems, electronic devices, machines, transport containers and / or control cabinets. Switching off the devices which are contaminated by dioxins and / or furans is not absolutely necessary during the implementation of the method according to the invention, since there is no wet cleaning stage is necessary, which was previously considered necessary in the prior art. In addition to reducing the concentration of dioxins and / or furans, the typical fire smell that practically always occurs after fire damage is also eliminated.

The treatment of building rubble can be carried out, for example, in such a way that it is exposed to the gas flow from top to bottom or vice versa on a perforated, air-permeable surface and, if appropriate, is exposed to radiation with artificial UV radiation.

In a particular embodiment of the present invention, the method is carried out in a closed system. This can be done, for example, by first isolating the contaminated surface from the room air in a control cabinet after opening the doors by inserting a partition with a lock, for example using a cover film, and creating a closed system. An air filter device known per se is flanged to this system with the aid of air channels or hoses and a gas stream is cyclically circulated in the system with the aid of a blower until the content of dioxins and / or furans is reduced to the desired values. Here, the gas flow sweeps over the sometimes difficult to access surfaces of the electrical components of the control cabinet. It was observed that the concentration of dioxins and / or furans on the surfaces was also significantly reduced if the surface was not suctioned dry before the method according to the invention was carried out. This fact was surprising insofar as it was previously assumed in the prior art that the poorly soluble dioxins and furans would adhere particularly well to the surfaces and could therefore not be subjected to such stripping. In the same way, it was observed that the soot which occurs in the event of fire damage and usually adheres firmly to the surface also does so it was decontaminated that the dioxins and / or furans were broken down on the spot into harmless compounds. When using a closed system, it is particularly prevented that insufficiently decontaminated room air is released to the outside, which ultimately reduces the concentration of dioxins and / or furans in the contaminated surface in question, but would contaminate the environment.

1 shows a partial view of a preferred embodiment of the present invention. The contaminated wall surface (1) is isolated from the ambient air by a sealing film (2). In the illustrated embodiment, the UV lamp (4), (4 ′) and (4˝) as well as tubular air inlet openings (5) and air intake openings (6), to which a filter unit (7) is located, are located in the cavity (3) thus created. is flanged, which contains a blower for generating a gas stream, an activated carbon filter and an ionization device. The cavity (3) between the wall surface (1) and the film is laterally isolated from the surrounding room air by sealing measures - not shown. After contact with the filter, the gas flow is subjected to ionization and circulated until the decontamination gives acceptable values. Of course, the gas flow direction can also be set against the direction of the arrow.

Fig. 2 shows a perspective view along the viewing angle (II) of Fig. 1 and shows that practically the entire wall surface is irradiated by the UV lamps (4), (4 ') and (4˝). With the help of the separation devices (8) and (9) a system is created that is sealed off from the ambient air.

3 shows a preferred embodiment of the filter device (7) to be used according to the invention in a closed system using the example of a control cabinet (10). With the aid of the blower (11), a gas flow is generated along the direction of the arrow, which reaches the ionization stage (14) after contact with the prefilter (12) and then the main filter (13). The gas stream is then passed through the post-filter (15). When the method according to the invention is carried out in a closed system, the gas stream is circulated until the contamination of dioxin and / or furans is reduced to acceptable values.

FIG. 4 shows a special embodiment of a non-closed system for removing dioxins and / or furans according to the present invention. The fan (11) generates a gas stream which is passed over the contaminated surfaces and then, after painting over the contaminated surface, reaches the filter unit (7) (not shown), the gas stream passing through a pre-filter (12), a main filter (13) and a subsequent ionization stage (14) is guided. This is followed by a post-filter stage (15). To increase the gas flow rate or to set a desired pressure in the system, the pressure and / or the gas flow rate in the incomplete system can be set as desired by varying the suction power of the blower (16) in conjunction with the blower (11). In the same way, it is possible according to the invention to let the gas flow flow against the direction of the arrow. It may be necessary here to reverse the order in the filter unit (7) in order to obtain the order of the prefilter (12), main filter (13), ionization stage (14) and postfilter (15). In this case, the gas stream is first passed through the prefilter (12) and the main filter (13) in the same way as above, before the gas stream passes through the ionization stage (14). The presence of the post-filter (15) is usually of minor importance. After contact with the ionization stage (14), the gas flow is directed here against the direction of the arrow onto the contaminated surface - not shown - and extracted with the aid of the blower (11).

One way of creating a closed system is for the gas flow to be introduced and carried out through the ventilation slots in a closed control cabinet. In addition, in the case of immovable objects, such as machines, there is also the possibility of producing a complete system by airtight partitioning of the objects, to which the cleaning elements are flanged via hose lines. Foreclosure can be done, for example, by placing a tent over the object to be decontaminated, under which the objects to be treated and any equipment required are to be placed. It is possible to remove contaminations inside the machines or systems without the need for a wet treatment which is hazardous to corrosion. It is also possible to create stationary facilities into which objects to be decontaminated are placed.

In principle, the pressure prevailing in the system can be freely selected. This can therefore be lower, equal or higher than the external air pressure and, of course, can also be varied once or several times during the treatment time of the contaminated surface.

In addition to the pressure, it is also possible to set the gas flow rate. An increased gas flow rate causes a faster removal of the dioxins and / or furans from the contaminated surfaces to be treated. The influence of the temperature of the gas stream and the relative humidity is also of some importance. It is readily possible to carry out the treatment of the surfaces at temperatures which are increased or decreased compared to room temperature. The increase in temperature with a simultaneous lowering of the air humidity leads, in particular if the layers near the surface are wetted beforehand due to the good ones Aerosol binding of the dioxins and / or furans so that they are highlighted from deeper layers and brought to the surface. This allows the contamination to be removed beyond the visible surface in the layers near the surface. The dioxins and / or furans to be broken down then get into the gas stream by evaporation on the surface.

In principle, all substances which have sufficient adsorption capacity for the dioxins and / or furans can be used as surface-active adsorbents. For the purposes of the present invention, activated carbon is particularly preferably used as the surface-active adsorbent. It is also possible to use filter systems which, for example, consist of a pre-filter, a chemical main filter - in particular specially doped activated carbon of high weight - and a post-filter. While the pre-filter is intended to trap visible particles in the air, the chemical filter reacts with the dioxins or furans and binds these substances. For example, activated carbon Variosorb ^R A is suitable for this.

Finally, the post-filter filters out residual particles and keeps the cleaning stage inside and the blower clean.

The ionizing radiation acting on the gas stream can be generated by methods known per se. Vacuum UV tubes are particularly suitable. The task of the ionization stage in the remediation is to neutralize gas molecules by micro-oxidation by producing energy-charged atoms, for example oxygen atoms, to accelerate the removal and / or the chemical conversion of the dioxins and / or furans into harmless compounds and thus also to increase the lifespan of the extend chemical filter. As a side effect, most of the osmogens (gas of organic origin) are neutralized by the ionization and usually the typical smell of fire is eliminated. When using a closed Systems does not release any noticeable ozone concentration.

For example, in order to reduce a dioxin or furan concentration from health-endangering 1 µg / m³ to a relatively harmless level of 10⁻⁵ µg / m³, only about 15 air changes with a filter efficiency of 50% are required with known indoor air filter devices.

The remaining filters can be disposed of in a known manner by catalytic combustion.

Another embodiment of the present invention consists in exposing the near-surface layers to ultraviolet radiation before, during or after the treatment by the gas stream. From “reports” 5/85, the photo-degradation of polychlorinated dibenzo-p-dioxins on a laboratory scale is known in principle, but no degradation could be detected when irradiating 2,3,7,8-TCDD suspended in crystalline form in distilled water.

Likewise, only slight decreases (t 1/2> 14 days) could be observed with pure 2,3,7,8-TCDD, which was adsorbed on soil samples and irradiated with UV light. Influences of temperatures and / or air humidity have not been investigated. By adding solvents for the dioxins and / or furans, the photolysis rate could be increased considerably. However, the contamination may have penetrated into deeper layers. Although the radiation can normally only be effective on the direct surface of the soil, it has been described that considerably better degradation rates could be achieved by dissolving the 2,3,7,8-TCDD. However, a large-scale application of this principle for decontamination was not carried out because of the fear of the penetration of 2,3,7,8-TCDD into even greater depths. When irradiating soil samples, it was found that the concentration of dioxins and / or furans could be considerably reduced to a depth of 3 cm without these areas being exposed to direct radiation.

According to the invention, it was found that, in particular at a slightly higher temperature than room temperature, for example 30 to 40 ° C. and dehumidification of the air, even without the use of solvents for the dioxins and / or furans, an acceptable reduction in the concentration of dioxins in the process described here and / or furans considerable degradation rates can be achieved in the deeper surface layers. For example, there was an acceptable rate of degradation when ethanol (non-solvent) was applied to the surfaces.

For the purposes of the present invention, however, it can be advantageous to apply liquid, non-reactive media to the layers near the surface before and / or during the irradiation in the region of room temperature.

A further embodiment of the present invention is characterized in that the applied non-reactive medium is selected from solvents or preferably non-solvents for dioxins and furans. For the purposes of the present invention, it is also possible initially to work without the action of a liquid, non-reactive medium and to use it only in the course of the irradiation.

Thus, in particular, liquid aliphatic, aromatic-aliphatic and / or aromatic hydrocarbons, halogenated hydrocarbons, glycols, ethers, glycol ethers, ketones and / or esters can be used as solvents in the region of room temperature will. In the case of a strongly absorbent substrate, however, there is the possibility that the dioxins and / or furans diffuse into deeper, unreachable layers.

Due to the extremely low water solubility of the dioxins and / or furans, the application of water to the contaminated surfaces to be treated is particularly preferred, since this prevents the dioxins and furans from penetrating into even deeper layers. The liquid, non-reactive media can, for example, be sprayed or painted onto the surfaces before the treatment. Suitable objects can also be immersed directly in the media. In addition, the liquid, non-reactive media can be added to the gas stream.

When water evaporates from deeper layers to the surface, dioxins and / or furans can be carried along, for example, as a suspension, solution or aerosol and exposed to the radiation on the surface. In addition, low-boiling solvents or non-solvents such as alcohols, in particular methanol, ethanol, propanols and / or butanols can also be used.

If necessary, a wetting agent can also be added to the aforementioned media. The task of the wetting agent is, according to the invention, to introduce the solvent and / or the non-solvent for dioxins and furans into the contaminated areas.

By suitable selection of the radiation intensity and the duration of the artificial UV radiation, the contamination of dioxins and furans can be removed practically quantitatively in the layers near the surface. For this purpose, ultraviolet radiation in the range from 200 to 280 nm, ie UV-C radiation, is preferably used.

Examples example 1

A low-voltage distribution cabinet with painted surfaces in a building that was contaminated by an obvious fire with dioxins and furans was sealed off with a plastic film (2) after opening the doors. A decontamination system consisting of a filter unit (7), a vacuum UV radiation source (14) and a blower (11) was flanged onto it via two air channels (5) and (6). Variosorb ^R A activated carbon was used as filter material (13) in an amount of about 8 kg, 5 IRE tubes in the blow-out stream as ionization stage and a radial fan with a pump capacity of about 1000 m³ / h. Over the course of 21 days, the contamination determined by wiping test was reduced from 104 ng / m² of polychlorinated dibenzofurans to 9 ng / m². This corresponds to an efficiency of 91%. The TCDD equivalents were 2.6 ng / m² before exposure and 0.22 ng / m² after treatment. Based on the TCDD equivalents, this corresponds to an efficiency of 91%.

Example 2

A wall surface (1) made of exposed concrete, which was contaminated by a close fire with dioxins and furans, was covered with a device according to FIG. 1 in a closed system with a filter unit (7) according to Example 1 and three UV tubes (4), (4 ') and (4˝) treated with a radiation maximum in the range of 270 to 280 nm at a distance of 50 cm for 8 days.

The size of the wall area was 8.2 m². A black plastic film was used as the cover film (2) to enable further work in the contaminated room. Over the course of 8 days, the contamination determined by means of a wipe test was reduced from 80 ng / m² of polychlorinated dibenzofurans to 2.8 ng / m². This corresponds to an efficiency of 96%.

Claims (16)

1. A process for removing dioxins and/or furans from layers adjacent to the surface, wherein the contaminated solid surfaces optionally are first exhausted by suction while dry, the withdrawn material is adsorbed onto a substrate and is then disposed of, characterized in that the contaminated layers adjacent to the surface are isolated from the ambient air in the room and a gas stream is generated on the layers adjacent to the surface by passing air and/or an exchanging gas thereover, which gas stream, prior to or subsequently to being passed over the layers adjacent to the surface, is passed over a surface-active adsorbent and is exposed to an ionizing radiation.
2. The process according to claim 1, characterized in that layers adjacent to the surfaces of floors, wall areas, ceilings, building rubble, scrap metal, soil, means of transport, in particular vehicles and ships, technical installations, electronic equipment, machines, transport containers and/or switch cabinets are treated.
3. The process according to claims 1 or 2, characterized in that layers adjacent to the surfaces within a sealed system are subjected to the treatment.
4. The process according to claim 3, characterized in that a gas pressure is employed which has been reduced or elevated over the atmospheric pressure.
5. The process according to claim 4, characterized in that the gas pressure of the system is changed once or several times in the course of the period of the treatment.
6. The process according to claims 1 to 5, characterized in that the velocity of the gas stream is varied in the course of the treatment.
7. The process according to claims 1 to 6, characterized in that activated carbon is used as the surface-active adsorbent.
8. The process according to claims 1 to 7, characterized in that the ionizing radiation is generated by means of vacuum-ultraviolet tubes.
9. The process according to claims 1 to 8, characterized in that the layers adjacent to the surfaces are additionally exposed to an artificial ultraviolet radiation prior to, during or after the treatment.
10. The process according to claim 9, characterized in that the layers adjacent to the surfaces are exposed to a UV radiation having wavelengths of from 200 to 280 nm.
11. The process according to claims 9 or 10, characterized in that the temperature of the surface to be treated is increased over room temperature and/or the humidity of the air is reduced during the treatment.
12. The process according to claims 9 to 11, characterized in that liquid non-reactive media are applied onto the layers adjacent to the surfaces prior to and/or during the irradiation within the range of room temperature.
13. The process according to claim 12, characterized in that media are applied which have been selected from solvents and/or non-solvents for dioxins and furans.
14. The process according to claim 13, characterized in that liquid aliphatic, aromatic-aliphatic and/or aromatic hydrocarbons, halogenated hyrocarbons, glycols, ethers, glycol ethers, ketones and/or esters are employed as solvents within the range of room temperature.
15. The process according to claim 13, characterized in that water, alcohols, especially methanol, ethanol, propanols and/or butanols are employed as non-solvents.
16. The process according to claims 13 to 14, characterized in that wetting agents are added to the liquid medium.

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