Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
  • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
  • F28F13/182—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing especially adapted for evaporator or condenser surfaces
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/24—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing hexavalent chromium compounds
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/48—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
  • C23C22/63—Treatment of copper or alloys based thereon
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
  • F28F2245/00—Coatings; Surface treatments
  • F28F2245/04—Coatings; Surface treatments hydrophobic

Definitions

• the present invention relates to condenser tubes such as those used in power station condenser plants. More particularly, it relates to the chemical treatment of such tubes to improve the operational thermal efficiency thereof.
• the present invention is based on the discovery that by treating the external surfaces of the condenser tube with certain inorganic substances, it is possible to impart to those surfaces a degree of water-­repellency sufficient to prevent the formation thereon of condensate films.
• condensation instead of condensation forming on such a treated tube surface in a "film-wise” manner, it forms thereon as discrete droplets of water (i.e. as “drop-wise”, condensation) which, under gravity, run down and/or drip off the tube without forming any condensate film thereon. Since no continuous condensate film forms on the treated condenser tube surface, the working efficiency of the condenser plant can be maintained at higher levels than previously achieved.
• the present invention provides a method of improving the working efficiency of condenser tubing suitable for use in a power generating plant which comprises treating the external surface of the condenser tubing, or a part thereof, which surface has been previously cleaned and degreased, with an acidic aqueous solution of hexavalent chromium anions.
• an acidic aqueous solution of hexavalent chromium anions is a aqueous solution of chromic acid although acidic solutions of other chromates, such as potassium dichromate, may be used.
• chromic acid When chromic acid is used, it is typically used at a concentration in the range of from 0.0025% to 10% by weight corresponding approximately to a CrO3 concentration of from 0.025 to 10 0 gl ⁇ 1. Concentrations of greater than 10% by weight of chromic acid can be used in the practice of the present invention although because of the hazardous nature of chromic acid they are not preferred. At CrO3 concentrations below about 0.0025% by weight, the treatment in general is somewhat limited in usefulness since condenser tube surfaces treated at such low CrO3 concentrations tend to experience, during operation of the condenser, only small patches of "drop-wise" condensation.
• the present invention provides a method of improving the working efficiency of condenser tubing suitable for use in a power generating plant which comprises treating the external surface of the condenser tubing, or a part thereof, which surface has been previously cleaned and degreased, with an aqueous acidic treatment solution comprising Cr3+ ions and an oxidising agent to depolarize the surface of the condenser tubing.
• an aqueous acidic treatment solution comprising Cr3+ ions and an oxidising agent to depolarize the surface of the condenser tubing.
• the concentration of the Cr3+ ions in the treatment solution will be in the range of from 1.6 to 50 gl ⁇ 1, as the metal ion, and preferably in the range of from 1.6 to 10 gl ⁇ 1, as the metal ion.
• the source of Cr3+ ions is not believed to be critical provided that the anion in the salt does not interfere with the reaction.
• chrometan a commercially available basic chromic sulphate having the approximate stoichiometric formula 3Na2SO4. 2 Cr2(SO4)3.Cr2O3.nH2O where n ⁇ 1 and which yields 1g ⁇ 1 chromic ion per 6.25 gl ⁇ 1.
• a typical treatment solution for use in this aspect will contain from 10 to 60 gl ⁇ 1 of chrometan. It is essential that the Cr3+ treatment solution contains an oxidising agent to depolarize the surface of the condenser tubing being treated. Oxidising agents that are suitable will be ones that are stable in acidic conditions and which do not, of course, interfere with the reaction.
• the oxidising agent in the treatment solution.
• concentration of hydrogen peroxide used is typically in the range from 10 to 30 ml l ⁇ 1.
• the aqueous treatment solution comprising Cr3+ ions and the oxidising agent is acidic.
• the pH of this treatment solution will be in the range of from 2.5 to 4.
• the present invention provides a method of improving the working efficiency of condenser tubing suitable for use in a power generating plant which comprises treating the external surface of the condenser tubing, or a part thereof, which surface has been previously cleaned and degreased, with an aqueous solution, having a pH of not less than about 7, of a compound selected from alkali metal tungstates and alkali metal molybdates.
• an aqueous solution having a pH of not less than about 7, of a compound selected from alkali metal tungstates and alkali metal molybdates.
• the aqueous treatment solution should have a pH of not less than about 8.1.
• the sodium salts as the alkali metal salts above.
• Typical concentrations of sodium tungstate, sodium molybdate and sodium metavanadate useful in carrying out the invention according to this aspect are in the range of from 30 to 100 gl ⁇ 1.
• the condenser tubing can be anodically charged while being immersed in the treatment solution according to a modification of the above-described method.
• Condenser tubing that can advantageously be treated according to the present invention includes tubing formed of alloys commonly used for the purpose such as cupronickel alloys (eg 90/10 and 70/30) and aluminium brasses and also tubing formed of less frequently used materials such as stainless steel (eg 316 stainless steel),titanium, and the alloy designated 72200 (ASTM) which consists of 15-18% Ni, about 0.4% Cr, about 0.5% Fe, about 0.5% Mn, about 0.006%C, up to 0.002% Si with the balance being Cu.
• alloys commonly used for the purpose such as cupronickel alloys (eg 90/10 and 70/30) and aluminium brasses and also tubing formed of less frequently used materials such as stainless steel (eg 316 stainless steel),titanium, and the alloy designated 72200 (ASTM) which consists of 15-18% Ni, about 0.4% Cr, about 0.5% Fe, about 0.5% Mn, about 0.006%C, up to 0.002% Si with the balance being Cu.
• treatment solutions according to the various aspects and modifications described above are conveniently carried out by immersing a section of tubing in the treatment solution for a period of time typically not less than 1 hour, unless stated otherwise, to ensure that a reasonably long lasting surface effect on the condenser tubing is obtained.
• treatment times of less than 1 hour can be employed, especially in cases where high concentrations of Cr VI are used.
• the surface or surfaces of the condenser tubing to be treated Prior to immersion in the treatment solution, the surface or surfaces of the condenser tubing to be treated require cleaning and degreasing. In this respect, we have found that a light abrasion of the surface followed by degreasing with a suitable organic solvent such as acetone will, in general, suffice. However, better results are obtained if, after degreasing, the surface or surfaces to be treated are further cleaned with dilute hydrochloric acid, such as by immersion for up to about 30 minutes, before the tubing is transferred into the treatment solution.
• a suitable organic solvent such as acetone
• the temperature of the treatment solution during immersion therein of the condenser tubing is not critical. Generally the treatment solution during immersion of the condenser tubing will be maintained at a temperature within the range of from about 5° to about 70°C. In most cases, however, the treatment solution will be used at room temperature since any advantages achieved by operation at higher temperatures are not particularly significant when the costs of heating treatment solutions above room temperature are taken into account.
• the treatment solution is acidic.
• the source of Cr VI anions is chromic acid itself in which case there is no need to adjust the pH of the solution.
• the treatment solution is preferably a solution of chrometan and hydrogen peroxide
• the solution pH is preferably maintained at a value of from about 2.5 to about 4.
• the solution pH is maintained at a value not less than about 7 in the case of tungstates and molybdates and at a value of not less than 8.1 in the case of vanadates since simple immersion of the condenser tubing in treatment solutions having lower pH value does not give the desired results.
• the tungstate, molybdate or vanadate solution is prepared by dissolving the salt into a caustic soda solution having a pH value of about 13 and then, if desired, adjusting the pH of the treatment solution to a value of not lower than the above defined minimum values.
• the present invention provides a method of improving the working efficiency of a section of condenser tubing suitable for use in a power generating plant which comprises immersing the section of condenser tubing, the surface of which has been previously cleaned and degreased, in an aqueous solution of a compound selected from alkali metal tungstates and alkali metal molybdates having a pH of from about 4 to about 7, providing an anode and, as cathode, the section of condenser tubing, and passing an electric current between the anode and the condenser tubing.
• composition of the treatment solution, the temperature of the solution during treatment and time of treatment according to this aspect will typically be as described above in respect of the other aspects and embodiments of the invention.
• the external surface of the section of tubing is abraded, degreased with acetone and then cleaned in 25% HCl after which it is cathodically charged at - 800 mV (Pt) for a period of from 1 to 6 hours at room temperature.
• the chemical or electrochemical treatment of the condenser tubing surface is believed to result in the deposition thereon of a mixed metal oxide layer containing metal oxide derived from the metal ions in the treatment solution (i.e. Cr, W, Mo or V) and metal oxide derived from the metal(s) of which the condenser tubing is formed.
• the mixed metal oxide layer is believed to have a thickness of less than about 0.1 ⁇ and does not, therefore, significantly affect the thermal conductivity of the wall of the condenser tubing on which it has been deposited.
• the mixed metal oxide layers have the property inducing the formation of condensation of steam on its surface in a "drop-wise" manner although the surface effects that give rise to this phenomenon are not understood.
• the metal oxide layers deposited according to the invention impart corrosion resistance to the condenser tubing while being, themselves, resistant to corrosion over long periods of exposure to steam.
• the deposited oxide layers are sufficiently resistant to prevent the formation on the tubing surface of cupric oxide which does not have the property of inducing condensation from steam in a "drop-wise" manner.
• the deposited oxide layers are also capable of withstanding the thermal shock that occurs as steam condenses. This property is believed to result from an impregnation of the metal oxide into the metal surface of the condenser tubing.
• a tube of an alloy comprising 90% Cu 10% Hi (90/10) was prepared by subjecting the external surface to light abrasion followed by degreasing with acetone. The tube was then immersed in a 2% solution of chromic acid for 1 hour at room temperature. After treatment the tube was rinsed with water. After 3 hours of operation in a condenser unit, steam was still condensing onto the surface of the treated tube in a "drop-wise" manner. Similar sections of tube that had not been treated were covered with a condensate film.
• a tube formed of 90/10 alloy was prepared as in Example 1 and then immersed in 10% chromic acid at room temperature for 5 minutes.
• the tube, without any rising step, was operated in a condenser unit for 3 hours after which time, condensation was still formed in a drop-wise manner on the tube surface although some areas of film-wise condensation also occurred.
• a tube of 90/10 alloy was treated as in Example 1 except that the chromic acid solution had a concentration of 0.0025% by weight of CrO3.
• the treated tube when operated in a condensation unit was found to have some areas of drop-wise condensation and some areas of film-wise condensation on its surface.
• a tube of 90/10 alloy was lightly abraided, degreased with acetone and then immersed in 25% HCl for 30 secs.
• the tube was then anodically charged at a current density of 15mA/cm ⁇ 2 in a solution of 1g/l NaVO3 and 15Og/l NaOH (pH ⁇ 13) at 85°C for 4 mins.
• the tube was operated in a condenser unit for 3 hours after which time, some areas of dropwise condensation and some areas of filmwise condensation occurred on its surface.
• a tube of 90/10 alloy was lightly abraided, degreased in acetone and then immersed in 25% HCl.
• the tube was then cathodically charged at -800mV (Pt) in 110g/l Na2WO4pH4 for 1 hour at room temperature. After 21 ⁇ 4 hours there occurred a patch of dropwise condensation and filmwise condensation on the tube surface.
• a tube of 70/30 Cu/Ni alloy was lightly abraided, degreased in acetone and then immersed in Chrometan Solution (10gl ⁇ 1 with 10ml/l of H2O2) at 70°C for four hours. After several hours, some areas of dropwise and some areas of filmwise condensation occurred on its surface.
• a coating solution of 60g/l of chrometan was raised to pH 2.5 by the addition of small quantities of NaOH with stirring. 10ml of H2O2 were added to 1 litre of this solution.
• a tube formed of 90/10 Cu/Ni alloy was abraided, degreased with acetone and then cleaned in 10% HCl for 30 minutes. The cleaned and degreased alloy tube was then immersed in the above chrometan solution for 3 hours at room temperature. The tube when operated in a condenser unit was found to have some areas of dropwise condensation on its surface.
• a tube formed of 90/10 Cu/Ni alloy was abraided, degreased with acetone and cleaned with 10% HCl for 30 minutes.
• the tube was then immersed in a solution containing 0.1M NaVO3, pH 8.1 for 1 hour at 40°C. After treatment, the tube was operated in a condenser unit for 43 ⁇ 4 hours. After this operation, some condensation was still forming in a dropwise manner on the surface of the tube.
• a tube formed of 90/10 Cu/Ni was abraided, degreased with acetone and then cleaned in 25% HCl. It was then treated by immersion in a solution containing 0.1M Na2WO4, pH 7 at room temperature for 1 hour. Under test in a condenser unit, the treated tube was found to have on its surface a mixture of filmwise and dropwise condensation.
• a tube formed of 90/10 Cu/Ni was cleaned and degreased in accordance with the procedure in Example 9.
• the tube was then immersed in a solution containing 0.1M sodium molybdate, pH 7 at room temperature for 1 hour. After being tested for two hours in a condensation unit, the treated tube still had some dropwise condensation on its surface.
• a tube formed of 90/10 Cu/Ni alloy was cleaned and degreased according to the procedure of Example 9.
• the tube was then immersed in a solution containing 1 g/l of sodium molybdate and 150 g/l NaOH (pH 13) and anodically charged with a current density of 15 mA cm ⁇ 2 in the solution at a temperature of 85°C for 4 minutes.
• the tube under operation in the condenser unit was found to have some areas of dropwise condensation on its surface.
• Example 11 The procedure of Example 11 was repeated except that the treatment solution contained 1 g/l of sodium tungstate instead of the molybdate.
• the treated tube after testing in the condenser unit, was found to have dropwise condensation over most of its surface.
• Example 5 The procedure of Example 5 was repeated except that the treatment solution contained 110 g/l of sodium molybdate instead of the tungstate. Patches of dropwise condensation formed on the surface of the treated tube on testing.

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Citations (11)

• 1987
  • 1987-04-28 GB GB878710011A patent/GB8710011D0/en active Pending
• 1988
  • 1988-04-28 GB GB8810083A patent/GB2204249B/en not_active Expired - Fee Related
  • 1988-10-12 EP EP88309565A patent/EP0363536A1/de not_active Ceased

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