DE102014214427B4 - Method and device for removing a coating from a surface of a base material - Google Patents

Abstract

Method for removing a coating (12) containing polychlorinated biphenyls, PCB, from a surface of a base material (13), in which the coating (12) is heated to a predetermined temperature by a first laser beam (4) so that the polychlorinated biphenyls are thermally decomposed, the decomposition being monitored by laser-induced fluorescence by a zone (15) above the heated coating (12) being irradiated by a second laser beam (10) as a beam with a linear cross-section (as a lightsheet) or as a line and the second laser beam (10) has a wavelength in the range from 271 nm to 279 nm, a chemical compound formed during the thermal decomposition as a characteristic chemical intermediate product of the decomposition being excited to fluorescence in the zone (15) and the fluorescence is detected with an optical detector (11).

Description

The present invention relates to a method and a device for removing a coating containing polychlorinated biphenyls (PCB) from a surface of a base material.

Polychlorinated biphenyls were used as a component in paints until they were banned in the Federal Republic of Germany. Concrete walls were sealed with these paints to protect them against contamination. In the course of renovation or demolition work, these paints, the PCB content of which exceeds a risk limit value, must be removed from the walls, packed and disposed of in a separate work step in a hazardous waste incineration plant.

A manual-mechanical removal with subsequent thermal aftertreatment in a hazardous waste incineration plant is known from the prior art. These methods require a high level of safety-related effort to minimize or avoid secondary contamination from flying dust. Working in protective clothing with a breathing mask is an extremely high physical strain for the staff and is associated with considerable health risks. The low mechanical precision also removes concrete structures that do not have any toxic contamination, but are also sent for thermal post-treatment, which increases the costs accordingly.

Laser ablation of the paint is also known as a further method. In the utility model DE 20 2009 009 514 U1 such a laser ablation is described. A disadvantage of such methods is that the paint is indeed removed, but no monitoring is carried out for complete removal or for the formation of toxic decomposition products during the removal. Further state of the art is off DE 199 13 220 C2 , DE 102 10 518 A1 , DE 694 10 900 T2 and WO 95/27986 A1 known.

The present invention is therefore based on the object of proposing a method and a device with which the above-mentioned disadvantages are overcome, i. H. Process monitoring takes place at the same time as the removal.

This object is achieved with a method according to claim 1 and a device according to claim 7. Advantageous refinements and developments are described in the subclaims.

In a method for removing a coating containing polychlorinated biphenyls (PCB) from a surface of a base material, the coating is heated to a predetermined temperature by a first laser beam, so that the polychlorinated biphenyls are thermally decomposed. The thermal decomposition is monitored by laser-induced fluorescence (LIF) by irradiating a zone above the heated coating with a second laser beam with at least one wavelength that can excite a characteristic chemical intermediate product of the decomposition. A chemical compound formed during thermal decomposition as a characteristic chemical intermediate product is excited to fluorescence in the zone by the second laser beam and the fluorescence is detected with an optical detector.

By heating the coating to a predetermined temperature, the coating, typically a lacquer, is detached from the surface of the base material and burned. The use of laser radiation for decontamination has the advantage of being able to generate very high temperatures locally very quickly. As a result of the thermal decomposition, a reaction zone is formed that is located above the previously irradiated area and can be easily examined there with regard to the composition with the second beam. The use of laser-induced fluorescence enables fast and precise real-time investigation of the reaction zone. The second laser usually excites chemical interconnections that arise during the thermal decomposition of PCB-containing coatings to fluorescence, so that these components can be examined in a targeted manner.

The power of the first laser beam can be increased if a concentration of the chemical compound determined with the optical detector by the laser-induced fluorescence falls below a predetermined limit value. By adapting the laser power of the first laser, an energy input for the thermal decomposition of the coating can be set and controlled as a function of the determined concentration of intermediate products. An optical observation system is particularly suitable for this because of the possibility of contactless measurement. An on-line process control, in which the output is increased if the limit value for the intermediate product is not reached, so that the polychlorinated biphenyls are decomposed, unnecessary removal of material can be avoided, since only the coating, but not the uncontaminated base material, is removed will.

The second laser beam shines through as a beam with a linear cross-section, i.e. preferably as a light section with a vertically widened, horizontally focused cross-section, the zone above the heated coating. Through this cross-section of the second laser beam, also known as the “lightsheet”, only a small but meaningful area of the combustion zone or the reaction zone above the burning coating is examined, which means that the method can also be used in limited space. Alternatively, the laser beam focuses on a single point as a line method and monitors the process without realizing a spatial resolution.

The second laser beam has a wavelength in the range from 271 nm to 279 nm, since this wavelength range can be used for the reliable excitation of intermediate products that are formed.

The chemical compound formed when the thermal decomposition is complete can contain a radical, preferably CCI. The presence of this radical allows a statement to be made about a successful decontamination process. If no CCI can be detected, this is an indication that the removal process is not working properly and that the polychlorinated biphenyls are not being decomposed. Alternatively or additionally, the chemical compound formed during the thermal decomposition can be a chemical compound contained in a material, in particular concrete, on which the coating is formed, or a chemical element contained in the material. By the detection of substances that are typical for the detachment of the coating, a reliable indication of the successful detachment, i.e. H. Decontamination of the surface of the base material can be concluded.

It can be provided that the gaseous chemical components formed during the thermal decomposition are thermally quenched to temperatures of less than 250.degree. H. be cooled quickly. Alternatively or additionally, the predetermined temperature can be at least 1000 ° C. Such a high temperature with subsequent rapid cooling prevents the formation of polychlorinated dibenzodioxins (PCDD) and polychlorinated dibenzofurans (PCDF) through a recombination of decomposition products.

Typically, the first laser beam has a wavelength of 800 nm to 1100 nm, preferably 915 nm, 940 nm, 980 nm and 1030 nm and preferably a continuous wave power in the kilowatt range, i. H. of at least 3 kW, particularly preferably of at least 10 kW. This enables the coating to be reliably heated so that it evaporates and can be examined using the laser-induced fluorescence. A quarter of the four mentioned wavelengths can each be present in the first laser beam.

A device for removing a coating containing polychlorinated biphenyls (PCB) from a surface of a base material has a first laser which is designed to radiate a first laser beam onto the coating and thereby thermally decompose it. The device comprises a second laser which is set up to irradiate a zone located above the coating with a second laser beam as a beam with a linear cross section (as a lightsheet) or as a line and with a wavelength in the range from 271 nm to 279 nm and thereby a To stimulate the fluorescence of a chemical compound formed during thermal decomposition. The device also has an optical detector which is set up to detect the fluorescence.

A control unit can also be provided which increases the power of the first laser when a concentration of the chemical compound falls below a predetermined limit value.

It can also be provided that the device has a suction device which sucks off gaseous and particle-bound chemical compounds that arise during thermal decomposition. The aspirator preferably has at least one filter in order to bind toxic substances in the aspirated volume. Typically, the described cooling to temperatures of less than 200 ° C., i.e. the thermal quenching, takes place upstream of the suction device.

The first laser can produce a laser spot with a size of 45 mm by 10 mm, which is preferably rectangular. As a result, the surface of the base material can be completely and quickly traversed and, at the same time, a sufficiently homogeneous energy transfer to the coating can be guaranteed.

Alternatively or additionally, the first laser can generate at least 220 kJ / m unit energy, preferably at least 225 kJ / m unit energy, particularly preferably at least 230 kJ / m unit energy, in order to reliably ablate the polychlorinated biphenyls. The second laser is typically set up to irradiate the zone located above the coating with a second laser beam with a wavelength in the range from 271 nm to 279 nm.

The optical detector is typically set up to detect the fluorescence in a temporally and spatially resolved manner. The optical detector can also be set up to carry out point processes or line processes, for example via photomultiplier. It can also be provided that the optical detector is designed to carry out a line method without spatial resolution. The information obtained by the optical detector can be used for fine control of the first laser in order to control the removal in a defined manner.

The method described is typically carried out with the apparatus described or the apparatus described is suitable for carrying out the method described.

An embodiment of the invention is shown in the drawing and is explained below with reference to FIG 1 explained.

• 1 eine schematische Ansicht einer Vorrichtung zur Laserdekontamination PCB-haltiger Lacke mit Prozess-Monitoring.

It shows:

• 1 a schematic view of a device for laser decontamination of paints containing PCBs with process monitoring.

1 shows a schematic view of a device for laser decontamination of paints containing PCBs with process monitoring. The device comprises a high-power laser unit 1 that is via a fiber optic cable 2 with laser optics 3 connected is. The high-power laser unit is a diode laser and emits a laser beam 4th with a power of 10 kW and a wavelength of 800 nm to 1100 nm, preferably 915 nm, 940 nm, 980 nm and 1030 nm via one or more glass fibers of the optical cable 2 and the laser optics 3 on a layer of varnish 12th containing polychlorinated biphenyls (PCB) and on a base material 13th containing concrete is applied. The four mentioned wavelengths are each a quarter in the laser beam 4th available. The base material 13th can for example be a calcitic, quartzitic concrete or mixed concrete. A thickness of the varnish layer 12th is typically between 0.1 mm to 1 mm. A distance between the arbitrarily positioned laser unit 1 and laser optics 3 can be several hundred meters, thereby contaminating the laser unit 1 can be avoided. The laser optics 3 shapes the laser beam 4th into a rectangular spot measuring 45 mm by 10 mm in order to enable a corresponding removal area in the square centimeter range.

The laser beam 4th is on a laser work head 5 coupled, which ensures complete combustion through supply air nozzles as well as a controlled extraction of the flue gas that is produced through an exhaust pipe 6th . The rectangular laser spot hits a surface of the lacquer layer 12th and burns or degrades them at temperatures of more than at least 1000 ° C, which causes complete decomposition of the PCB. The hot flue gas that results from the combustion is then sucked off into a suction section, ie through the exhaust pipe 6th , one after the exhaust pipe 6th arranged filter 7th , for example a wet filter, and a suction unit arranged at the end of the suction section 8th that the flue gas through the exhaust pipe 6th and the filter 7th sucks off to avoid recombination to polychlorinated dibenzodioxins (PCDD) and dibenzofurans (PCDF). Even if the filter 7th and the aspirator 8th in 1 are shown spatially separated, the filter 7th in further exemplary embodiments also directly on the suction device 8th be arranged. The base material 13th , that is typically a concrete block, is not affected during this process, that is, when carrying out the method described.

With lacquer thicknesses between 0.1 mm and 1 mm, the lacquer layer is completely removed 12th and the decomposition of the polychlorinated biphenyls by the laser unit 1 Provided line energy of at least 225 kJ / m required.

The laser working head 5 has optical entrances, typically windows that are arranged at right angles to each other. This allows a second laser unit from the front 9 sent out laser sheet 10 , so a second laser beam with a linear cross-section, which is also referred to as a lightsheet or laser disk, with a wavelength between 271 nm and 279 nm, so that one above the current of the laser beam 5 processed area of the paint layer 12th located combustion zone 15th is irradiated. This enables laser-induced fluorescence measurement. At the specified wavelengths, the radical CCI is excited, the presence of which allows a statement to be made about the successful decontamination process. The excited CCI takes the energy from the laser sheet 10 and emits it again, emitting fluorescence. The fluorescence is determined by means of a detection system 11th detected that perpendicular to the second laser unit 9 and is sensitive to the wavelength range between 271 nm and 285 nm. This means that a statement can already be made in the process, i.e. on-line, about the decomposition of the polychlorinated biphenyls and the possible formation of toxic products, and real-time monitoring is provided.

The detection system 11th transmits the received data to a computer 14th holding the laser unit 1 controls depending on the determined concentration of CCI, i.e. increases the output if the concentration is too low, since the detection of CCI allows the statement that polychlorinated biphenyls are decomposed, and at a high concentration it lowers the output until the CCI concentration begins to decrease . If no CCI is detected, although polychlorinated biphenyls in the lacquer layer in a measurement carried out before the procedure was carried out 12th have been detected, the lack of evidence of CCI by the laser-induced fluorescence indicates that the decontamination process is not working and polychlorinated biphenyls are not incinerated.

By means of the described device or the described method, a renovation or demolition of building structures can be carried out in a resource-saving manner with high efficiency and without the risk of contamination.

Claims (10)

Method for removing a coating (12) containing polychlorinated biphenyls, PCB, from a surface of a base material (13), in which the coating (12) is heated to a predetermined temperature by a first laser beam (4) so that the polychlorinated biphenyls are thermally decomposed, the decomposition being monitored by laser-induced fluorescence by a zone (15) above the heated coating (12) being irradiated by a second laser beam (10) as a beam with a linear cross-section (as a lightsheet) or as a line and the second laser beam (10) has a wavelength in the range from 271 nm to 279 nm, a chemical compound formed during the thermal decomposition as a characteristic chemical intermediate product of the decomposition being excited to fluorescence in the zone (15) and the fluorescence is detected with an optical detector (11). Procedure according to Claim 1 , characterized in that the power of the first laser (4) is increased when a concentration of the chemical compound determined by the laser-induced fluorescence using the optical detector (11) falls below a predetermined limit value. Procedure according to Claim 1 or Claim 2 , characterized in that the chemical compound formed during thermal decomposition is a radical. Method according to one of the preceding claims, characterized in that the gaseous chemical components formed during the thermal decomposition are thermally quenched to temperatures of less than 250 ° C. Method according to one of the preceding claims, characterized in that the predetermined temperature is at least 1000 ° C. Method according to one of the preceding claims, characterized in that the first laser beam (4) is operated with wavelengths of 800 nm to 1100 nm. Device for removing a coating (12) containing polychlorinated biphenyls, PCB, from a surface of a base material (13) with a first laser (1) which is designed to radiate a first laser beam (4) onto the coating (12) and thereby thermally decomposing them, a second laser (9) which is set up, a zone (15) located above the coating (12) with a second laser beam (10) as a beam with a linear cross-section (as a lightsheet) or as a line and to shine through with a wavelength in the range from 271 nm to 279 nm and thus to stimulate fluorescence of a chemical compound formed during decomposition, and an optical detector (11) which is set up to detect the fluorescence. Device according to Claim 7 , characterized in that the device has a control unit (14) which is set up to increase a power of the first laser (1) when a concentration of the chemical compound falls below a predetermined limit value. Device according to Claim 7 or Claim 8 , characterized in that a suction device (8) is provided for suctioning off gaseous and particle-bound chemical components formed during decomposition. Device according to one of the Claims 7 until 9 , characterized in that the first laser (1) generates a line energy of at least 220 kJ / m.

Images