Scale conditioning agents and treatment method

Abstract

An improved scale conditioning composition and method is disclosed that results in improved dissolution and disruption of tube scale, hardened sludge and other deposits composed primarily of highly densified magnetite such as those found in heat exchange vessels, particularly steam generators. After treatment with the advanced scale conditioning composition, these magnetite rich deposits are more easily removed using known and commercially available high pressure hydro-mechanical cleaning techniques. The present invention further provides effective cleaning in a short period of time and at relatively low temperatures, while reducing the amount of waste produced and reducing the resulting corrosion of carbon and low alloy steel components within the steam generator during the cleaning process.

1 . A method of conditioning and removing scale and deposits within a heat exchange system that utilizes at least one heat transfer liquid comprising:
 taking the heat exchange system out of service;   removing at least a portion of the heat transfer liquid from the heat exchange system;   introducing an aqueous cleaning solution of a scale conditioning agent into the heat exchange system, wherein the scale conditioning agent comprising a chelant, the chelant being present in the aqueous cleaning solution at a treatment concentration that is higher than 1 weight percent and less than or equal to about 2 weight percent;   maintaining the aqueous cleaning solution at a treatment temperature;   maintaining the aqueous cleaning solution at a treatment pH that is higher than 9.0 and less than or equal to 11.0;   removing substantially all of the aqueous cleaning solution from the heat exchange system;   introducing replacement heat transfer liquid; and   returning the heat exchange system to service,   wherein the heat exchange system comprises a steam generator of a nuclear power plant.   
     
     
         2 . The method according to  claim 1 , wherein the chelant comprises at least one chelant selected from a group consisting of EDTA, HEDTA, lauryl substituted EDTA, and polyaspartic acid with imminodisuccinate; and
 the scale conditioning agent further comprises a pH control agent; and   the pH control agent is a nitrogen containing aliphatic compound having fewer than 10 carbons such as triethanolamine, dimethylamine, ethylamine, 1,2-diaminoethane, diaminopropane, ethanolamine, diethanolamine, 2-methyl-2-amono-1-propanol, 5-aminopentanol, or methoxypropylamine.   
     
     
         3 . The method of  claim 1 , wherein:
 the method comprises conditioning and removing scale and deposits from free span tube surfaces within the heat exchange system;   the heat exchange system is configured and arranged to transfer heat to the heat transfer liquid via the free span tube surfaces;   the scale conditioning agent comprises a reducing agent; and   the free span tube surfaces have scale and deposits accumulated thereon when the aqueous cleaning solution is introduced into the heat exchange system.   
     
     
         4 . The method of  claim 1 , wherein the method further comprises, between taking the heat exchange system out of service and returning the heat exchange system to service, increasing the porosity of magnetite scale disposed on surfaces of tubes of the steam generator. 
     
     
         5 . The method according to  claim 1 , wherein the scale conditioning agent further comprising a reducing agent, wherein the reducing agent is selected from the group comprising: ascorbic acid, citric acid, hydrazine, catalyzed hydrazine, carbohydrazide, and isomeric forms of ascorbic acid, citric acid, hydrazine, catalyzed hydrazine, and carbohydrazide. 
     
     
         6 . The method according to  claim 1 , further comprising introducing additional scale conditioning agent before removing substantially all of the aqueous cleaning solution from the heat exchange system, wherein the additional scale conditioning agent is introduced into the heat exchange system as a concentrated premix solution, the introduction of the additional scale conditioning agent being sufficient to maintain the scale conditioning agent at the treatment concentration. 
     
     
         7 . A method of conditioning and removing scale and deposits within a heat exchange system that utilizes at least one heat transfer liquid comprising:
 taking the heat exchange system out of service;   providing within the heat exchange system an aqueous cleaning solution of a scale conditioning agent, the scale conditioning agent comprising a chelating agent, the chelating agent being present in the aqueous cleaning solution at a treatment concentration range higher than 1 weight percent and less than or equal to 2 weight percent,   circulating the aqueous cleaning solution throughout the heat exchange system during a treatment period and, while circulating the aqueous cleaning solution;   maintaining the temperature of the aqueous cleaning solution within a treatment temperature range;   maintaining the pH of the aqueous cleaning solution within a treatment pH range that is higher than 9.0 and less than or equal to 11.0; and   agitating the aqueous cleaning solution as it circulates through the heat exchange system during a least a portion of the treatment period;   removing substantially all of the aqueous cleaning solution from the heat exchange system at the end of the treatment period;   introducing replacement heat transfer liquid; and   returning the heat exchange system to service,   wherein the heat exchange system comprises a steam generator of a nuclear power plant.   
     
     
         8 . The method according to  claim 7 , wherein forming the aqueous cleaning solution further comprises:
 introducing a predetermined amount of an aqueous premix solution into the heat exchange system,   the aqueous premix solution comprising a concentrated solution of the scale conditioning agent,   wherein the predetermined amount of the aqueous premix solution being sufficient, when combined with the heat exchange liquid, to form an aqueous cleaning solution such that the concentration of scale conditioning agent is within the treatment concentration range.   
     
     
         9 . The method according to  claim 7 , wherein the combination of the treatment temperature, the treatment pH, and the treatment period are sufficient both to increase the porosity and dissolution of magnetite scale, and further wherein this combination of the treatment temperature, the treatment pH, and the treatment period induce corrosion of less than 0.001 inch per application in carbon and low alloy steels. 
     
     
         10 . A method of conditioning and removing scale and deposits within a heat exchange system that utilizes at least one heat transfer liquid comprising, in sequence, the steps of:
 taking the heat exchange system out of service;   providing an aqueous cleaning solution of a scale conditioning agent within the heat exchange system, the scale conditioning agent comprising a chelant, a treatment concentration of the chelant in the aqueous cleaning solution in the heat exchange system being higher than 1 weight percent and less than or equal to about 2 weight percent, the aqueous cleaning solution having a pH higher than 9.0 and less than or equal to 11.0;   removing substantially all of the aqueous cleaning solution from the heat exchange system;   returning the heat exchange system to service,   wherein the heat exchange system comprises a steam generator of a nuclear power plant.   
     
     
         11 . The method of  claim 10 , further comprising:
 before providing the aqueous cleaning solution of the scale conditioning agent within the heat exchange system, removing at least a portion of the heat transfer liquid from the heat exchange system; and   after removing substantially all of the aqueous cleaning solution from the heat exchange system, introducing replacement heat transfer liquid.   
     
     
         12 . The method of  claim 10 , wherein said providing within the heat exchange system the aqueous cleaning solution comprises introducing the aqueous cleaning solution into the heat exchange system. 
     
     
         13 . The method of  claim 10 , wherein said providing within the heat exchange system the aqueous cleaning solution comprises forming the aqueous cleaning solution in the heat exchange system. 
     
     
         14 . The method of  claim 10 , wherein the method further comprises, between taking the heat exchange system out of service and returning the heat exchange system to service, inducing corrosion of less than 0.001 inch in carbon and low alloy steels. 
     
     
         15 . The method of  claim 10 , wherein the aqueous cleaning solution has a pH that is between 9 and 11. 
     
     
         16 . The method of  claim 10 , wherein:
 the method comprises conditioning and removing scale and deposits from free span tube surfaces within the heat exchange system;   the heat exchange system is configured and arranged to transfer heat to the heat transfer liquid via the free span tube surfaces;   the scale conditioning agent comprises a reducing agent; and   the free span tube surfaces have scale and deposits accumulated thereon when the aqueous cleaning solution is provided within the heat exchange system.   
     
     
         17 . The method of  claim 10 , wherein the method further comprises, between taking the heat exchange system out of service and returning the heat exchange system to service, increasing the porosity of magnetite scale disposed on surfaces of tubes of the steam generator. 
     
     
         18 . A method of conditioning and removing scale and deposits within a heat exchange system that utilizes at least one heat transfer liquid comprising, in sequence, the steps of:
 taking the heat exchange system out of service;   providing within the heat exchange system an aqueous cleaning solution of a scale conditioning agent, the scale conditioning agent comprising a chelant at a concentration in the aqueous cleaning solution that is higher than 0.034 moles per liter and less than or equal to 0.068 moles per liter, the aqueous cleaning solution having a pH that is higher than 9.0 and less than or equal to 11.0;   removing substantially all of the aqueous cleaning solution from the heat exchange system;   returning the heat exchange system to service,   wherein the heat exchange system comprises a steam generator of a nuclear power plant.   
     
     
         19 . The method of  claim 18 , wherein the chelant is present in the aqueous cleaning solution at a concentration that is less than or equal to 2 weight percent. 
     
     
         20 . The method of  claim 19 , wherein the chelant is present in the aqueous cleaning solution at a treatment concentration higher than 1 weight percent. 
     
     
         21 . The method of  claim 20 , wherein the method further comprises, between taking the heat exchange system out of service and returning the heat exchange system to service, inducing corrosion of less than 0.001 inch in carbon and low alloy steels. 
     
     
         22 . The method of  claim 18 , wherein the method further comprises, between taking the heat exchange system out of service and returning the heat exchange system to service, increasing the porosity of magnetite scale disposed on surfaces of tubes of the steam generator.