Heat exchange – With cleaning means for heat exchanger
Reexamination Certificate
1999-08-19
2001-10-30
Leo, Leonard (Department: 3743)
Heat exchange
With cleaning means for heat exchanger
C015S304000, C122S379000, C134S021000, C134S022110, C134S16600C
Reexamination Certificate
active
06308774
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for the cleaning of heat exchange tubes which are led through a tube plate of a heat exchanger, in particular of a heat exchanger of a nuclear plant, in which deposits in the heat exchange tubes are released and conveyed to a respective tube end. The invention also relates to a collecting device for the collection of deposits from heat exchange tubes led through a tube plate of a heat exchanger, in particular a heat exchanger of a nuclear plant.
When a heat exchanger is in operation, deposits may form in the heat exchange tubes. The deposits reduce the thermal conductivity of the heat exchange tubes and therefore the efficiency of the heat exchanger. In addition, the deposits make it difficult to check the heat exchange tubes for possible damage. That is because, for example, test heads are introduced into the heat exchange tubes for checking purposes. In that case, the measurement signals determined by the test heads may be influenced greatly by the deposits, so that it is only possible to obtain evidence as to the state of the heat exchange tubes to a limited extent.
It is necessary to check the heat exchange tubes for safety reasons, particularly in the case of a heat exchanger used in a nuclear plant. In a heat exchanger of that type, the deposits may be contaminated radioactively. Manual cleaning, in which the operating personnel would be directly exposed to the radioactive materials, is therefore usually disregarded. The aim is to carry out the cleaning of the heat exchange tubes as automatically as possible with the aid of manipulators.
Different methods may be employed in order to clean the heat exchange tubes. For example, they may be cleaned mechanically with the aid of a brush which is led through each heat exchange tube. The deposits may also be released and removed chemically or with the aid of abrasive blasting agents through the use of a blasting method.
A blasting method, in which the heat exchange tubes are first dried and subsequently treated with a compressed air/blasting agent mixture, is described in German Published, Non-Prosecuted Patent Application DE 195 46 788 A1, corresponding to U.S. Pat. No. 5,883,512. Through the use of that cleaning method, the heat exchange tubes are prepared for eddy current integrity testing, in order to improve fault detection during such a test.
Particularly in the case of a heat exchanger used in a nuclear plant, a situation must be avoided in which the released deposits and, possibly, abrasive blasting agents enter the heat exchanger and pass from there into other parts of the nuclear plant and influence its operation. It is therefore necessary for the released deposits and the abrasive blasting agents to be removed from the heat exchanger completely.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for the cleaning of heat exchange tubes and a collecting device for the collection of deposits from heat exchange tubes, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type, in which the method provides simple measures to ensure that released deposits are collected and time spent in carrying out the method is as short as possible and in which the collecting device is simple to handle and ensures that the released deposits from the heat exchange tubes are collected, so that complete removal from the heat exchanger is possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for cleaning heat exchange tubes led through a tube plate of a heat exchanger, in particular a heat exchanger of a nuclear plant, which comprises mounting a common collecting vessel on the tube plate from below in the vicinity of the heat exchange tubes; releasing deposits in the heat exchange tubes and conveying the deposits to respective tube ends of the heat exchange tubes; and collecting the deposits from a plurality of the heat exchange tubes in the collecting vessel, without the collecting vessel changing position.
The essential advantage of the method is that the collecting vessel encloses a plurality of tube ends at the same time with its inlet orifice and, when these tubes are being cleaned, does not need to be moved from one tube end to the other. Due to the large number of heat exchange tubes in a heat exchanger, it is therefore not necessary to position the collecting vessel exactly at the tube end of the heat exchange tube which is to be cleaned. Therefore, in an automatic cleaning method, in which the heat exchange tubes are cleaned, for example through a manipulator, a complicated control for positioning the collecting vessel at the respective tube end of the heat exchange tube to be cleaned is dispensed with.
In accordance with another mode of the invention, the collecting vessel is introduced through a service orifice into the heat exchanger and is deployed there to a desired size and shape. Since the service orifice is usually very small, as compared with the area of the tube plate, what can be achieved thereby is that a very large region of the tube plate can be covered by the collecting vessel, despite a relatively small service orifice.
In accordance with a further mode of the invention, in order to ensure that the released deposits are collected completely by the collecting vessel, the collecting vessel is sealed off relative to the surroundings. In particular, its inlet orifice is sealed off, so that the released deposits pass completely into the collecting vessel.
In accordance with an added mode of the invention, in order to position the collecting vessel as simply as possible, the inlet orifice of the collecting vessel extends in one half space, in the region of the tube plate, over the entire underside of the tube plate which is present there.
As a rule, the region below the tube plate in a heat exchanger is divided into two half spaces. In this case, a heat exchanging medium flows through the first half space into the entry-side tube ends disposed in this half space. The medium subsequently flows out of the exit-side tube ends of the heat exchange tubes in the second half space. The inlet orifice therefore surrounds the exit-side tube ends of all of the heat exchange tubes simultaneously. The collecting vessel therefore only has to be mounted once on the underside of the tube plate, and individual suction extraction from the exit-side tube ends is not necessary.
In accordance with an additional mode of the invention, the inlet orifice is adapted, at least in a partial region, to a predetermined geometry, in particular to the geometry of the half space in the region of the tube plate, by the inflation of a hose, and at the same time is sealed off relative to the environment.
The inflatable hose ensures sealing off relative to the surroundings in a very simple and elegant way, specifically essentially irrespective of the geometry of the region to be sealed off. This is because the initially uninflated hose only needs to be attached approximately to the edge of the region to be sealed off. It is adapted automatically to the geometry and also seals off roundings without difficulty by being inflated. Moreover, handling is very simple, since the hose, when folded together, can easily be introduced into the heat exchanger through the service orifice.
Alternatively to sealing off through the use of the hose, an elastic material or spring elements such as, for example, helical annular springs made of metal or plastic, may also be used.
In accordance with yet another mode of the invention, the collecting vessel is positioned automatically with the aid of a positioning device, so that the collecting vessel is mounted even before the actual cleaning operation, without manual intervention of the operating personnel within the heat exchanger being necessary.
In accordance with yet a further mode of the invention, the released deposits are suction-extracted from the collecting vessel. A vacuum is
Ammann Franz
Krämer Georg
Greenberg Laurence A.
Leo Leonard
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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