Chemical Cleaning Method and System with Steam Injection

• US 20110209730A1
• Filed: 12/03/2009
• Published: 09/01/2011
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: Dominion Engineering, Inc.
• Original Assignee: Dominion Engineering, Inc.
• Inventors: Little, Michael J., Varrin, Robert D. JR.
• Granted Patent: US 8,459,277 B2
• Time in Patent Office: Days
• US Class Current: 134/22.19
• CPC Class Codes: B08B 2230/01 Cleaning with steam
• CPC Class Codes: B08B 3/00 Cleaning by methods involving the use or presence of liquid or steam B08B9/00 takes precedence
• CPC Class Codes: B08B 9/00 Cleaning hollow articles by methods or apparatus specially adapted thereto B08B6/00 takes precedence
• CPC Class Codes: C23G 5/00 Cleaning or de-greasing metallic material by other methods; Apparatus for cleaning or de-greasing metallic material with organic solvents
• CPC Class Codes: F22B 37/002 specially adapted for nuclear steam generators, e.g. maintenance, repairing or inspecting equipment not otherwise provided for
• CPC Class Codes: F22B 37/486 Devices for removing water, salt, or sludge from boilers F22B37/483, F22B37/50, F22B37/52 and F22B37/54 take precedence
• CPC Class Codes: F28G 9/00 Cleaning by flushing or washing, e.g. with chemical solvents appliances using jets of fluid for removing debris F28G1/16, F28G3/16
• CPC Class Codes: G21F 9/002 Decontamination of the surface of objects with chemical or electrochemical processes
• CPC Class Codes: G21F 9/28 Treating solids
• CPC Class Codes: G21F 9/30 Processing separating different isotopes of the same chemical element B01D59/00

Abstract

Disclosed are methods and apparatus for cleaning heat exchangers and similar vessels by introducing chemical cleaning solutions and/or solvents while maintaining a target temperature range by direct steam injection into the cleaning solution. The steam may be injected directly into the heat exchanger or into a temporary side stream loop for recirculating the cleaning solution or admixed with fluids being injected to the heat exchanger. The disclosed methods are suitable for removing metallic oxides from a heat exchanger under chemically reducing conditions or metallic species such as copper under chemically oxidizing conditions. In order to further enhance the heat transfer efficiency of heating cleaning solvents by direct steam injection, mixing on the secondary side of the heat exchanger can be enhanced by gas sparging or by transferring liquid between heat exchangers when more than one heat exchanger is being cleaned at the same time.

Claims

1. A method for removing deposits and impurities from the secondary side of a heat exchanger comprising:

removing a volume of working fluid from the secondary side of the heat exchanger sufficient to expose an access penetration;

installing a temporary adapter in the exposed access penetration, the adapter being configured for direct steam injection;

introducing a volume of water into the secondary side of the heat exchanger;

introducing a predetermined quantity of a chemical cleaning reagent into the water to form a cleaning solution on the secondary side of the heat exchanger, the chemical cleaning reagent selected from a group consisting of chelants, complexing agents, oxidizing agents, reducing agents and mixtures thereof;

injecting steam through the temporary adapter and into the secondary side of the heat exchanger to heat the heat exchanger and residual fluid to a target cleaning temperature range; and

maintaining the heat exchanger and the residual fluid within the cleaning target temperature range during a cleaning period using the injected steam.

2. The method according to claim 1, wherein the residual fluid includes a component selected from a group consisting of working fluid, chemical cleaning compounds, chemical cleaning solutions, chemical cleaning solvents, water and mixtures thereof.

3. The method according to claim 1, further comprising:

injecting a gas into the residual fluid at a rate sufficient to induce gas sparging within the residual fluid, the gas being selected from a group consisting of steam, non-condensible gases and mixtures thereof.

4. The method according to claim 3, wherein the gas is injected into the residual fluid through an inlet selected from a group consisting of a vessel blowdown system and the temporary adapter.

6. The method according to claim 1, further comprising;

introducing an additional quantity of the chemical cleaning reagent during the cleaning period.

7. The method according to claim 1, wherein the volume of water introduced is selected whereby the addition of steam condensate and the chemical cleaning reagent will not exceed a predetermined secondary side volume.

8. The method according to claim 1, further comprising:

controlling a steam injection rate to produce a predetermined heating profile in the residual fluid.

9. The method according to claim 1, wherein the steam is selected from a group consisting of saturated steam, superheated steam and mixtures thereof.

10. The method according to claim 1, further comprising:

controlling steam temperature and steam pressure of the injected steam to compensate for variations in liquid static head pressure range within the heat exchanger during the cleaning period.

14. The method according to claim 1, wherein the complexing agent is selected from a group consisting of EDTA, NTA, organic acids and mixtures thereof.

20. The method according to claim 1, wherein the heat exchanger is a steam generator of a nuclear pressurized water reactor.

23. The method according to claim 1, wherein the steam is injected at a rate greater than 200 pounds per hour.

24. The method according to claim 23, wherein the steam is injected at a rate greater than 1000 pounds per hour.

25. The method according to claim 24, wherein the steam is injected at a rate of about 2000 pounds per hour.

5. (canceled)

11. A method for removing deposits and impurities from the secondary side of a heat exchanger comprising:

removing a volume of working fluid from the secondary side of the heat exchanger sufficient to expose an access penetration;

installing a temporary adapter in the exposed access penetration, the adapter being configured for direct steam injection;

admixing a gas with steam to form a combined gas stream for injection into the secondary side of the heat exchanger,

injecting the combined gas steam through the temporary adapter and into the secondary side of the heat exchanger, wherein the injected steam heats the heat exchanger and residual fluid to a target cleaning temperature range; and

maintaining the heat exchanger and the residual fluid within the cleaning target temperature range during a cleaning period,

wherein said gas that is admixed with the steam does not condense during the cleaning period.

12. The method according to claim 11, wherein the gas comprises between 0.01 and 3% of the combined gas stream.

21. The method according to claim 11, wherein the heat exchanger is a steam generator of a nuclear pressurized water reactor.

26. The method according to claim 11, wherein the gas includes nitrogen, argon, or mixtures thereof, or air, oxygen, ozone or mixtures thereof.

27. The method according to claim 11, wherein the residual fluid includes a chemical cleaning reagent selected from a group consisting of chelants, complexing agents, oxidizing agents, reducing agents and mixtures thereof.

28. The method according to claim 11, wherein the gas reduces the potential for the injected steam to cause cavitation damage within the heat exchanger during the cleaning period.

13. (canceled)

15. A system for removing deposits and impurities from a secondary side of a heat exchanger comprising:

a first adapter configured for temporary installation on a first conventional access penetration, the first adapter further comprising

a flange configured for mating to the access penetration;

means for securing the adapter to the access penetration;

a conduit for introducing or removing fluid through the access penetration; and

an opening provided within the secondary side of the heat exchanger;

a steam source configured for connection to the conduit,

a gas source configured for connection to the conduit; and

a controller configured for controlling the steam injection into the secondary side of heat exchanger through the adapter,

wherein, in use, said system is adapted to admix a gas supplied by the gas source with the steam supplied by the steam source to form a combined gas stream in the conduit for injection in the secondary side of the heat exchanger and wherein said gas that is admixed with the steam does not condense during use of said system.

16. The system according to claim 15 wherein the opening is configured as an eductor.

17. The system according to claim 15 wherein the opening is configured as multiple eductors.

18. The system according to claim 15 wherein the opening is selected from a group consisting of regulator direct steam nozzles, spargers, eductors and combinations thereof.

19. The system according to claim 15, further comprising:

a second adapter configured for temporary installation on a second conventional access penetration, wherein the first and second adapters are configured for inducing fluid flow within the secondary side of the heat exchanger from the first adapter to the second adapter.

22. The system of claim 15, wherein the heat exchanger is a steam generator of a nuclear pressurized water reactor.

29. The system according to claim 15, wherein a concentration of the gas is selected to reduce the potential for cavitation damage within the conduit and/or at the opening.

30. The system according to claim 29, wherein the gas comprises between 0.01 and 3% of the combined gas stream.

31. The system according to claim 15, wherein the conduit comprises a steam injection nozzle configured to, in use, entrain a bulk fluid present in the steam generator during injection in the secondary side of the heat exchanger of the combined gas stream through the steam injection nozzle, such that entrainment of said bulk fluid promotes mixing of the combined gas stream with the bulk fluid and ensures that the combined gas stream ejected from the steam nozzle is substantially in thermal equilibrium with the bulk fluid.

32. A method for removing deposits and impurities from the secondary side of a heat exchanger comprising:

removing a volume of working fluid from the secondary side of the heat exchanger sufficient to expose an access penetration;

installing a temporary adapter in the exposed access penetration, the adapter being configured for direct steam injection;

admixing a gas with the steam to form a combined gas stream comprising the gas and the steam;

injecting the combined gas steam through the temporary adapter and into the secondary side of the heat exchanger, wherein the injected steam heats the heat exchanger and residual fluid to a target cleaning temperature range; and

maintaining the heat exchanger and the residual fluid within the cleaning target temperature range during a cleaning period,

wherein the gas in the combined gas stream reduces a potential for the injected steam to cause cavitation damage in the heat exchanger during the cleaning period.

33. A method for removing deposits and impurities from the secondary side of a steam generator of a nuclear pressurized water reactor, the method comprising:

removing a volume of working fluid from the secondary side of the heat exchanger sufficient to expose an access penetration;

installing a temporary adapter in the exposed access penetration, the adapter being configured for direct steam injection and including

a flange configured for mating, to the access penetration;

a conduit for introducing or removing fluid through the access penetration; and

an opening provided within the secondary side of the heat exchanger, wherein said conduit is in communication with a steam source configured to supply steam and a gas source configured to supply a gas;

introducing a volume of water into the secondary side of the heat exchanger;

introducing a predetermined quantity of a chemical cleaning reagent into the water to form a cleaning solution on the secondary side of the heat exchanger, wherein the chemical cleaning reagent is selected from a group consisting of chelants, complexing agents, oxidizing agents, reducing agents and mixtures thereof;

admixing the gas with the steam to form a combined gas stream for injection into the secondary side of the heat exchanger, wherein the gas comprises between 0.01 and 3% of the combined gas stream and does not condense during a cleaning period;

injecting the combined gas stream through the temporary adapter and into the secondary side of the heat exchanger, wherein the injected steam heats the heat exchanger and cleaning solution to a target cleaning temperature range, and wherein the steam is injected at a rate greater than 200 pounds per hour; and

maintaining the heat exchanger and the cleaning solution within the cleaning target temperature range during the cleaning period,

wherein a temperature and a pressure of the injected steam is controlled to compensate for variations in liquid static head pressure range within the heat exchanger during the cleaning period,

wherein the gas in the combined gas stream reduces a potential for the injected steam to cause cavitation damage in the heat exchanger during the cleaning period.

34. The method according to claim 33, wherein the steam is injected at a rate greater than 1000 pounds per hour.

35. The method according to claim 34, wherein the steam is injected at a rate of about 2000 pounds per hour.

36. The method according to claim 33, wherein the gas includes nitrogen, argon, or mixtures thereof, or air, oxygen, ozone or mixtures thereof.