Liquid heaters and vaporizers – Cleaning – Blow off
Reexamination Certificate
2001-09-28
2003-02-04
Wilson, Gregory (Department: 3749)
Liquid heaters and vaporizers
Cleaning
Blow off
C122S390000, C376S316000
Reexamination Certificate
active
06513462
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a removing device for removing sludge or scale, for example, on a tube plate and a tube nest of a heat exchanger such as a steam generator used in a nuclear power plant or the like.
BACKGROUND ART
In order to understand the present invention, a description of a steam generator used in a nuclear power plant or the like is necessary. Thus, such a steam generator will be briefly described with reference to FIG.
10
.
In
FIG. 10
, numeral
1
indicates a steam generating portion of a steam generator. The steam generating portion
1
has a substantially cylindrical body portion
2
in which hand holes or inspection holes (only one of which is indicated at numeral
17
) are diametrically opposed to each other. In the lower portion of the body portion
2
, there is arranged a tube plate
3
, which defines, together with a bottom portion
2
a
of the body portion
2
, a water chamber
4
. Above this tube plate
3
, a large number of normally U-shaped heat-transfer tubes
5
are arranged so as to communicate with the water chamber
4
. Further, a plurality of tube support plates
6
a
,
6
b
, . . . ,
6
f
are horizontally arranged so as to traverse the large number of heat-transfer tubes
5
and laterally support them. Each of the heat-transfer tubes
5
extends vertically through oddly shaped holes usually called BEC (Broached Egg Crate) holes formed in the tube support plates
6
a
,
6
b
. . . ,
6
f
. In
FIG. 10
, some of the BEC holes formed in the tube support plate
6
a
are schematically shown and indicated by numeral
7
.
The space in the water chamber
4
is divided into a hot leg portion
4
a
and a cold leg portion
4
b
by a partition
8
. One end of each U-shaped heat-transfer tube
5
communicates with the hot leg portion
4
a
, and the other end thereof communicates with the cold leg portion
4
b
. Thus, the tube plate
3
also has a large number of holes which are schematically indicated by numeral
3
a
and which serve to receive the end portions of each of the heat-transfer tubes.
Further, in
FIG. 10
, numeral
9
indicates a man-hole which enables an operator to enter the water chamber
4
, numeral
10
indicates a coolant inlet nozzle communicating with the hot leg portion
4
a
, numeral
11
indicates a coolant outlet nozzle communicating with the cold leg portion
4
b
, and numeral
12
indicates trunnions for suspending the steam generator. Though not shown, a steam outlet is formed at the top of the steam generator. Further, above the steam generating portion
1
, there is provided a water supply nozzle (not shown) for introducing supply water into the body portion.
In the case, for example, of a steam generator of a nuclear power plant, coolant at high temperature and high pressure supplied from the nuclear reactor enters the hot leg portion
4
a
of the water chamber
4
through the coolant inlet nozzle
10
and flows through the heat-transfer tubes
5
to reach the cold leg portion
4
b
before it is returned to the nuclear reactor by way of the coolant outlet nozzle
11
. Supply water from the water supply nozzle is supplied into the body portion
2
to fill the periphery of the heat-transfer tubes
5
. This supply water is heated by the high-temperature/high-pressure coolant flowing through the heat-transfer tubes
5
to become steam, which goes out through the steam outlet and is supplied to a steam turbine (not shown) for power generation.
As a result of the conversion of supply water into steam, impurities called scale are likely to adhere to the top surface of the tube plate
3
, in particular, to the portions of the top surface of the tube plate
3
in the vicinity of the holes
3
a
into which the end portions of the heat-transfer tubes
5
are inserted and to the peripheral surfaces of the lower portions of the heat-transfer tubes
5
embedded in the tube plate
3
. In this specification, these regions will be referred to as “the portion centered about the tube plate”. Further, scale is likely to adhere to the upper and lower surfaces of each tube support plate, the regions near the portions directly below the BEC holes
7
. In this specification, these regions will be referred to as “the portions centered about the tube support plates”. If neglected, this scale will lead to corrosion of the heat-transfer tubes, etc. Thus, it must be periodically removed.
In this way, steam generators, which find relatively wide use in various fields of industry, involve, as they are used, the generation of impurities called scale on the heat-transfer tubes
5
, the tube plate
3
, the tube support plates
6
a
,
6
b
, . . . ,
6
f
, etc. To maintain the performance of the steam generator and to prevent corrosion or the like due to scale, it is necessary to remove this scale.
For this purpose, various scale removing devices have been developed and proposed. In the case of a steam generator for a nuclear power plant, care must be taken, from a health care perspective, that an operator is not exposed to a dose of radiation greater than a predetermined level. Further, despite the fact that a steam generator is an apparatus of a considerably large size, the very large number of heat-transfer tubes are packed very tight. Furthermore, each heat-transfer tube has a diameter as small as approximately 20 mm, and is relatively thin-walled. Thus, the heat-transfer tubes are subject to damage if a heavy impact is applied thereto. In addition, a plurality of tube support plates are provided in the steam generator, and the distance between adjacent tube support plates is short in comparison to the height of the entire steam generator. These conditions have to be taken into account when developing a scale removing device.
As described above, a steam generator has only one tube plate, whereas it has a plurality of tube support plates. Thus, to clean the areas centered about the tube support plates, the cleaning head of a scale removing device has to ascend and descend through flow slots formed in the tube support plates (e.g., thin and narrow slots
13
formed in the tube support plate
6
a
shown in FIG.
10
). In view of this, a scale removing device for cleaning the portion centered about the tube plate and a scale removing device for cleaning the portions centered about the tube support plates have been separately developed.
FIG. 11
shows a typical scale removing device for cleaning the portion centered about the tube plate, as disclosed in Japanese Patent Application Laid-Open No. 4-503564. The scale removing device, generally indicated at
15
, is laterally inserted into a tube lane
16
directly above the tube plate
3
of a steam generator through a hand hole or inspection hole
17
. The device includes a transporter
20
adapted to move along a support rail
18
. A flexible lance
19
extends through this transporter
20
to a desired cleaning position between tube rows.
FIG. 12
shows in detail the flexible lance
19
and, in particular, a cleaning head
26
provided at the forward end thereof. The flexible lance
19
includes four high-pressure hoses
22
fixed together by a member
25
called a hose bar structure, a nitrogen purge line
23
, and a video probe optical fiber cable
24
, the forward ends of these components being connected to the cleaning head
26
. Provided at the forward end of the cleaning head
26
are a plurality of nozzles
27
communicating with the high-pressure hoses
22
. During cleaning, water
28
is jetted out from these nozzles (See FIG.
11
).
FIG. 14
shows a typical example of a scale removing device for cleaning the portions centered about the tube support plates, as disclosed in Japanese Patent Application Laid-Open No. 9-026107 by the present applicant. This scale removing device, generally indicated at
30
in
FIG. 14
, is provided with an insertion mechanism
31
and a guide mechanism
32
. The insertion mechanism
31
has on the operator side a driving device
33
. Further, it has a fixation plate
34
at its forward end, which is fixed in position by the operation of a second j
Ichioka Takehiko
Kinugasa Toshiyuki
Nakao Fumitoshi
Okada Hideya
Shiraishi Tadashi
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
Wilson Gregory
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