REMOVING CONTAMINATION

Abstract: A method of removing from the surface of an object a contaminating substance buried in an organic substance on the surface of the object, the method including directing a laser beam at the organic substance to cause chemical change of the organic material or direct removal of the organic material by laser generated chemical change.

Description: REMOVING CONTAMINATION The present invention relates to removing contaminating substances from surfaces such as those of buildings, structure, industrial plants, vessels, cabins and the like. According to the present invention there is provided a method of removing from the surface of an object a contaminating substance buried in an organic substance on the surface of the object which includes directing a laser beam at the organic substances to cause chemical change of the organic material or direct removal of the organic material by laser generated chemical change. The said object may be the surface of a building, structure, industrial plant, vessel, cabin or the like. The said contaminating substance may be a radioactive, biological or chemical contaminant. The said organic substance in which the contamination is embedded may include one or more of paint, epoxy resin, sealant, adhesive, plastics, cloth, moss, lichen, fungus or other plants. The said surface to be treated may be the surface of a substrate comprising a building material such as concrete, mortar, rendering, cement, brick, tiles, plaster, stainless steels, mild steels, alloying materials or the like. The said laser beam may be of ultraviolet, visible or infrared wavelength. The laser beam may be generated by a laser generator such as a gas laser, eg a" C0 2 gas laser or a CO gas laser, a solid state laser, eg a Nd-YAG (Neodymium-Yttrium- Aluminium-Garnet) or a Ti-Sapphire laser, an Excimer laser, a dye laser, a free electron laser or a semiconductor laser. The laser beam may be either pulsed or continuous. The laser beam which preferably produces high power is used to generate photothermal energy at the surface to be treated. After absorption of such energy by the organic substance a series of chemical changes will occur to the organic substance in the following temperature ranges: At 200 - 700°C, wate ' r and hydraulic bonds in organic materials will be driven out or broken and decomposition of C-H chains will result, forming charred material - carbon. At 700 - 1000°C carbonaceous materials will be oxidised - forming C0 2 and CO gases through combustion, leaving ashes of other oxides. Flames can be seen at this stage if not controlled with additional gas(es). Carbon rich contamination like soot found on the surface of most buildings in industrial cities can be removed this way. Under these applied temperatures the substrate material (inorganic) may not be melted, or damaged but certain heat effects may be caused. By careful control of the laser parameters this effect on the substrate can be minimised to an acceptable level. When the laser beam has a wavelength in the ultraviolet range, direct photo-induced chemical change, such a bond breaking, may occur with organic materials, which may result in ablation. The typical operating conditions and procedures are described below and illustrated in the embodiment described below. The invention provides an efficient and effective method for treating contaminated surfaces, eg in the decommissioning of buildings or industrial plant facilities. Preferably, at least one gas may be delivered to a treatment region of the surface being treated. The gas may desirably be compressed air. The gas provides removal of ashes formed by blowing them off the surface, controls any flames formed in the chemical reactions and provides oxygen to the treatment region to assist the chemical reaction occurring. The laser beam and gas may be delivered to the treatment region via an inner nozzle or shroud and waste materials formed may be extracted by an extraction arrangement comprising an outer nozzle or shroud. The waste materials may be extracted by suction. Conveniently the laser beam may be provided from a laser source arranged on a mobile carrying means, eg trolley, which may be transported to a site of use. A supply of gas and a pump reguired for extraction of waste materials may both be carried on the said mobile carrying means, eg trolley. The laser beam may be applied from the laser source to the region of the surface to be treated via an operator handset which may be moved by a human or robotic operator to guide the beam to the reguired part of the surface to be treated. The beam may be delivered from the laser source to the handset by a flexible beam delivering system, eg one or more optical fibre guides or cables, or by optical mirrors which reflect the beam or by a hollow waveguide all in a known way. The handset may include a scanning means which sweeps the laser beam over the surface to be treated with a controlled sweep speed, pattern and rate. The laser power density of the laser beam may be between 200 - 250 W/cm 2 depending on materials to be treated, although higher power densities may be used, especially with lasers operating in the ultraviolet range. Thus focusing of laser beam may or may not be needed depending on the raw beam diameter. Paint and epoxies are easier to remove whereas wet moss is most difficult because some energy has to be used to vaporise the free water retained by the moss. Removal of contaminated organic substances on non-metallic substrates requires much less energy than on metal substrates because of higher thermal loss which occurs with the conductive metals. The laser beam scanning speed may be between 1 - 1000 mm/sec depending on the materials' thickness and properties. An embodiment of the present invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 is a side view of an arrangement for treating a building wall having contaminated organic material on its surface. A laser source 1 provides a laser beam 2. The laser beam 2 exits from a laser output window la of the source 1 and is guided to an operator handset 4 by a flexible beam delivering system 3. At -the handset 4 the laser beam 3 is focused by a lens 4a and is directed by a beam scanning means 5 onto the surface of the wall to be treated, indicated in Figure 1 by reference numeral 12. The scanning means 5 controls the laser beam sweep speed, pattern and rate. Windows 6 transparent to the laser beam 2 are used to isolate the laser optics from the downstream environment. An internal nozzle 7 with a suitable exit end shape such as a rectangular shape is used to pass the laser beam 2 and gas from a gas supply 8 to an interaction zone 9 on the surface 12. An external nozzle 10 with a similar end shape to the internal nozzle surrounds the internal nozzle 7. An extraction unit 11 is connected to the external nozzle 10 to collect the removed waste. An operator handle 14 is connected to the handset 4. Control switches and " adjustments are mounted on an operating control box 15 located near the operator on a trolley 16. The laser generator 1 and waste collection unit 11 and gas supply unit 8 can be mounted on the trolley 16. Materials removal rate for most organic materials is between 2000 and 5000 cm 3 /kWhr. Removal depth increases with laser power density and reduces with scanning speed. The main advantage of the method according to the invention is the removal of surface and embedded contamination without generating serious damage or removal of the underlying materials, although a higher intensity of laser beam can be used, in appropriate circumstances, to further melt and glaze the underlying surface for subsequent sealing.

Claims: Claims 1. A method of removing from the surface of an object a contaminating substance buried in an organic substance on the surface of the object, the method including directing a laser beam at the organic substance to cause chemical change of the organic material or direct removal of the organic material by laser generated chemical change. 2. A method as in Claim 1 and wherein the said object is the surface of a building, structure, industrial plant, vessel, cabin or the like. 3. A method as in Claim 1 or Claim 2 and wherein the said contaminating substance is a radioactive, biological or chemical contaminant. 4. A method as in any one of the preceding Claims and wherein the said organic substance in which the contaminating substance is embedded includes one or more of paint, epoxy resin, sealant, adhesive, plastics, cloth, moss, lichen, fungus or other plants. 5. A method as in any one of the preceding Claims and wherein the said surface to be treated is the surface of a substrate comprising a building material including concrete, mortar, rendering, cement, brick, tiles, plaster, stainless steels, mild steels, alloying materials or the like. 6. A method as in any one of the preceding Claims and wherein the said laser beam is of ultraviolet, visible or infrared wavelength. 7. A method as in any one of the preceding Claims and wherein the laser beam is generated by a laser generator selected from a gas laser, a solid state laser, an excimer laser, a dye laser, a free electron laser or a semiconductor laser. 8. A method as in any one of the preceding Claims and wherein the laser beam is either pulsed or continuous. 9. A method as in any one of the preceding Claims and wherein the laser power density of the laser beam is between 200 W/cm 2 to 250 W/cm 2 , the laser beam intensity is from 150 W/cm 2 to 10 kW/cm 2 and the beam is scanned at a scanning speed of from 1 mm/sec to 1000 mm/sec. 10. A method as in any one of the preceding Claims and wherein at least one gas is delivered to a treatment region of the surface to be treated. 11. A method as in Claim 10 and wherein the gas comprises compressed air. 12. A method as in Claim 10 or Claim 11 and wherein the laser beam and the gas are delivered to the treatment region by means of an inner nozzle or shroud and waste materials formed are extracted by an extraction arrangement comprising an outer nozzle or shroud, the waste materials being extracted by suction. 13. A method as in any one of the preceding Claims and wherein the laser beam is provided from a laser source arranged on a mobile carrying means including a trolley, the mobile carrying means being transported to a site of use. 14. A method as in any one of Claims 10 to 13 and wherein a supply of the gas and a suction pump for the extraction of the waste materials are both carried on the said mobile carrying means. 15. A method as in any one of the preceding Claims and wherein the laser beam is applied from the laser source to the region of the surface to be treated via an operator handset which is moved by a human or a robotic operator to guide the beam to the required part of the surface to be treated, the beam being delivered from the laser source to the handset by a flexible beam delivering system, the handset including a scanning means which sweeps the laser beam over the surface to be treated with a controlled sweep speed, pattern and rate. 16. A method as in Claim 15 and wherein the beam delivering system comprises one or more optical fibres or cables. 17. A method as in Claim 15 and wherein the beam delivering system comprises mirrors which reflect the beam. 18. A method as in Claim 15 and wherein the beam delivering system comprises a hollow waveguide.

Inventors: LI LIN, SPENCER JULIAN TIMOTHY, LI, LIN, SPENCER, JULIAN, TIMOTHY
Applicants: BRITISH NUCLEAR FUELS PLC, LI LIN, SPENCER JULIAN TIMOTHY, LI, LIN, SPENCER, JULIAN, TIMOTHY
Application year: 1995
Main classification: G21F9
IPC codes: A01G7, A47L11, A62D3, B01J19, B08B7, B63B59, C08J3, G21F9