Liquid heaters and vaporizers – Cleaning – Fluid jet
Reissue Patent
1998-10-15
2004-07-06
Lu, Jiping (Department: 3749)
Liquid heaters and vaporizers
Cleaning
Fluid jet
C122S379000, C122S380000, C122S384000, C122S390000, C122S391000, C122S405000
Reissue Patent
active
RE038542
ABSTRACT:
FIELD OF INVENTION
This invention relates to an upper bundle cleaning system for a nuclear power plant steam generator which eliminates the need to use chemical cleaning techniques.
BACKGROUND OF INVENTION
Steam generators convert heat from the primary side of a nuclear power plant to steam on the secondary side so that the primary and secondary systems are kept separate. A typical generator is a vertical cylinder consisting of a large number of U-shaped tubes which extend from the floor or “tube sheet” of the generator. High temperature and pressure fluid from the reactor travels through the tubes giving up energy to a feed water blanket surrounding the tubes in the generator creating steam and ultimately power when later introduced to turbines.
Steam generators were designed to last upwards of forty years but in practice such reliability figures have proven not to be the case. The problem is that sludge from particulate impurities suspended in the feed water forms on the tubes which greatly affects the efficiency of the generator and can even cause the tubes to degrade to the point of causing fissures in the tubes. If radioactive primary fluid within the tubes seeps into the secondary side, the result can be disastrous. Plugging or otherwise servicing such fissures is time consuming and results in expensive down time during which power must be purchased from other sources at a great expense.
There are known methods for cleaning the tubes proximate the bottom of the steam generator using flexible lances and the like which clean the tubes using water under pressure, but since a typical steam generator can be thirty feet tall, it is difficult to reach the sludge at the upper levels of the tubes using water jets. So, chemical cleaning is used but there are several disadvantages. First, chemical cleaning is very expensive (from $5,000,000 to $10,000,000 per application) and requires an extended outage. Also, some corrosion of steam generator internals by the solvents used will occur during the cleaning. In addition, large quantities of hazardous, possibly radioactive waste may be generated. Disposal of this waste is very expensive. For these reasons, although many utilities have considered chemical cleaning, few plants have actually implemented chemical cleaning.
On the other hand, there are severe technical challenges faced when considering alternate cleaning methods. A typical steam generator has approximately 50,000 square feet of heat transfer area. The tube bundle is about 10 feet in diameter and 30 feet tall but the access alley in the middle of the tube bundle is only 3.5 inches wide and is interrupted by support plates approximately every 4 feet. There are flow slots through the support plates but they are very small in size, typically 2.75 by 15 inches. In addition, the access into the steam generator is limited to a six inch hand hole. Finally, inter tube gaps are only 0.406 wide or smaller.
Thus, the inherent design parameters of a typical steam generator make it difficult to incorporate water jet sludge lancing techniques at the upper tube bundles even though these techniques are adequate to clean the tubes at the level of the tube sheet at the bottom most portion of the steam generator. See, e.g. U.S. Pat. Nos. 4,700,662; 4,980,120; 4,887,555; 4,676,201; and 4,769,085.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide an upper bundle steam generator cleaning system.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which cleans the generator from the top down thereby flushing deposits downward during the cleaning process.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which eliminates the need to use chemical cleaning techniques and overcomes the disadvantages inherent in chemical cleaning or which can be used in conjunction with chemical cleaning.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which adequately cleans the upper bundles of the steam generator using water under pressure even within the close confines of the tubes of the steam generator.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which successfully delivers sufficient water energy to remove scale and also distributes this energy in an efficient manner throughout the tube bundle.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which accomplishes cleaning remotely thereby overcoming the access restrictions of the steam generator as well as reducing exposure of personnel to radiation.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which maximizes cleaning effectiveness with a minimum use of water.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which minimizes the number of equipment moves during the cleaning procedure thereby reducing cleaning and hence outage time.
It is a further object of this invention to provide such an upper bundle steam generator cleaning system which utilizes both a bulk cleaning head and a rigid lance for intertube inspection and cleaning.
It is a further object of this invention to provide a method for cleaning the steam generator from the top down thereby flushing deposited downward during the cleaning process using the system of this invention.
This invention results from the realization that the most effective way to clean a steam generator is from the top down thereby flushing deposits downward as the cleaning process progresses; that there is an access path to the upper regions of the steam generator and that these upper regions of the steam generator can be cleaned without chemical cleaning techniques if a cleaning head which delivers fluid under pressure about the tubes can be deployed along this access path from the bottom of the steam generator and then raised up through successive flow slots into position; and furthermore that all the tubes on one side of the steam generator at one level can be cleaned from one flow slot thereby minimizing equipment moves and cleaning time; that a mechanical swinging arm can be used for bulk cleaning; that alignment of the nozzles of the swing arm first on one side of the tube gap and then on the other side to clean all the surfaces of the tubes maximizes cleaning effectiveness with a minimum use of water; and that a rigid lance which extends between the rows of tubes accomplishes effective inter-tube cleaning.
This invention features and may suitably comprise, include, consist essentially of and/or consist of an upper bundle steam generator cleaning system. There is a cleaning head means deployment and support device receivable through a hand hole of the steam generator which includes means to position a cleaning head about a flow slot of the upper bundles of the steam generator. The cleaning head means mounted with the support device directs fluid about the tubes of the upper bundles of the steam generator for cleaning the generator from the top down thereby flushing deposits downward during the cleaning process.
The cleaning head means deployment and support device includes a translation rail extending between a hand hole of the steam generator and the center tie rod along the blow down lane. There is a rotation stage including a number of vertically extendable cylinders pivotably mounted on the translation rail.
One head means includes means for directing fluid between the tubes from a flow slot such as an arm extendable along the direction of the flow slot wherein the arm includes a plurality of nozzles alienable with the spaces between the tubes. A number of the nozzles are opposed to each other for cleaning tubes on opposite sides of a flow slot at the same time and for balancing the thrust received by the arm. There are means for changing the pitch orientation of the nozzles and for rotating the arm to s
Ashton Augustus
Fischbach Daniel L.
Lovett Timothy
Foster-Miller Inc.
Iandiorio & Teska
Lu Jiping
LandOfFree
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