Information
-
Patent Grant
-
6498827
-
Patent Number
6,498,827
-
Date Filed
Monday, November 1, 199925 years ago
-
Date Issued
Tuesday, December 24, 200222 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Carone; Michael J.
- Richardson; John
Agents
- Grant; Kathryn W.
- Marich; Eric
- Edwards; Robert J.
-
CPC
-
US Classifications
Field of Search
US
- 376 402
- 376 404
- 376 405
- 376 406
- 376 441
- 376 442
- 122 32
- 122 510
- 165 158
- 165 159
- 165 161
- 165 162
-
International Classifications
-
Abstract
A support plate for retaining tube array spacing within a heat exchanger tube and shell structure. The support plate having a plurality of individual tube receiving apertures formed therein. Each apertures has at least three inwardly protruding members and bights are formed therebetween when the tube associated therewith is lodged in place to establish secondary fluid flow through the support plate. The inwardly protruding members terminate in flat lands that restrain but do not all contact the outer surface of the respective tube. These flat lands minimize fretting wear and eliminate potential gouging of the outer wall of the tube. The plate wall forming each aperture has an hourglass configuration which, inter alia, reduces pressure drop, turbulence and local deposition of magnetite and other particulates on the support plates.
Description
FIELD AND BACKGROUND OF THE INVENTION
The invention relates generally to heat exchanger construction and more particularly to support plates for retaining tube array spacing within the heat exchanger.
DESCRIPTION OF THE PRIOR ART
The pressurized water vapor generators or heat exchangers, associated with nuclear power stations and which transfer the reactor-produced heat from the primary coolant to the secondary coolant that drives the plant turbines may be as long as 75 feet and have an outside diameter of about 12 feet. Within one of these heat exchangers, straight tubes through which the primary coolant flows may be no more than ⅝ inch in outside diameter, but have an effective length of as long as 52 feet between the tube-end mountings and the imposing faces of the tube sheets. Typically, there may be a bundle of more than 15,000 tubes in one of these heat exchangers. It is clear that there is a need to provide structural support for these tubes in the span between the tube sheet faces to ensure tube separation, adequate rigidity, and the like.
The tube support problem has led to the development of a drilled support plate structure of the type described in U.S. Pat. No. 4,120,350. This support system consists of an array of flat plates that is arranged in the heat exchanger with the planes of the individual plates lined transverse to the longitudinal axes of the tubes in the bundle. Holes or apertures are drilled and broached in each of the flat support plates to accommodate the tubes. Each aperture has at least three inwardly protruding members that restrain but do not all engage or contact the outer surface of the respective tube. Bights that are intermediate of these inwardly protruding members are formed in the individual support plate apertures when the tube associated therewith is lodged in place to establish secondary fluid flow through the plate. The inwardly protruding members terminate in arcs that define a circle of a diameter that is only slightly greater than the outside diameter of the associated tube. The broached support plates are made of SA-212 Gr.B, a carbon material, and may include tube free lanes with unblocked broached holes which detrimentally allow low steam quality secondary fluid flow to pass through the unblocked holes.
It has been found, after long periods of operation, that deposits consisting primarily of magnetite are formed at the tube support plates. These deposits block the bights formed between protruding members and thus cause undesirable increases in pressure drop which will in turn result in an increase in the secondary water level in the downcomer. If corrective actions are not taken, the rising water level could potentially flood the steam bleed ports and the main feed water nozzles and result in a malfunction of the steam bleeding and the main feed water systems.
Corrective actions such as power derating, chemical cleaning or water slap are costly. Moreover, the removal of deposits by chemical cleaning or water slap could damage the support plates.
Accordingly, there is a need for a tube support plate which minimizes pressure drop and deposit blockage while providing adequate structural strength.
BRIEF SUMMARY OF THE INVENTION
The problems associated with the prior art tube support plates are largely overcome by the present invention which resorts to a stronger more corrosive resistant plate material such as stainless steel and by forming hourglass shaped tube holes in the support plates which minimize pressure drop by reducing local turbulence and are less likely to cause the deposition of magnetite and other particles on the surface of the support plates.
In view of the foregoing it will be seen that one aspect of the invention is to manufacture the tube support plates out of a stronger more corrosion resistant material such as stainless steel.
Another aspect of this invention is to have the protruding members of the broached holes terminate in flat lands.
A further aspect of the present invention is to provide hourglass shaped broached holes in the tube support plates.
These and other aspects of the present invention will be more fully understood after a review of the following description of the preferred embodiment along with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a vertical elevation view in full section of a once-through vapor generator embodying the principles of the invention;
FIG. 2
is a plan view of a portion of a prior art support plate;
FIG. 3
is a plan view of one of the broached holes in the prior art support plate shown in
FIG. 2
with a tube inserted therethrough;
FIG. 4
is a detail view of a portion of the tube abutting one of the protruding members of the prior art broached hole shown in
FIG. 3
;
FIG. 5
is a plan view of a portion of a support plate and tube assembly that embodies principles of the invention for use with a heat exchanger of the type shown in
FIG. 1
;
FIG. 6
is a plan view of one of the broached holes in the support plate shown in
FIG. 5
with a tube inserted therethrough;
FIG. 7
is a detail view of a portion of the tube abutting one of the protruding members of the broached hole shown in
FIG. 6
;
FIG. 8
is a plan view of one of the broached holes in the support plate shown in
FIG. 5
with the tube removed; and
FIG. 9
is a cross-sectional view taken along lines A—A of
FIG. 8
showing the hourglass feature of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is described in connection with a once-through steam generator for a nuclear power plant, although these principles are generally applicable to shell and tube heat exchangers in any number of diverse fields of activities. Thus, as shown in
FIG. 1
for the purpose of illustration, a once-through steam generator unit
10
comprising a vertically elongated cylindrical pressure vessel or shell
11
closed at its opposite ends by an upper head member
12
and a lower head member
13
.
The upper head includes an upper tube sheet
14
, a primary coolant inlet
15
, a manway
16
and a handhole
17
. The manway
16
and the handhole
17
are used for inspection and repair during times when the vapor generator unit
10
is not in operation. The lower head
13
includes drain
18
, a coolant outlet
20
, a handhole
21
, a manway
22
and a lower tube sheet
23
.
The vapor generator
10
is supported on a conical or cylindrical skirt
24
which engages the outer surface of the lower head
13
in order to support the vapor generator unit
10
above structural flooring
25
.
As hereinbefore mentioned, the overall length of a typical vapor generator unit of the sort under consideration is about 75 feet between the flooring
25
and the upper extreme end of the primary coolant inlet
15
. The overall diameter of the unit
10
moreover, is in excess of 12 feet.
Within the pressure vessel
11
, a lower cylindrical tube shroud wrapper or baffle
26
encloses a bundle of heat exchanger tubes
27
, a portion of which is shown illustratively in FIG.
1
. In a vapor generator unit of the type under consideration moreover, the number of tubes enclosed within the baffle
26
is in excess of 15,000, each of the tubes having an outside diameter of ⅝ inch. It has been found that Alloy 690 is a preferred tube material for use in vapor generators of the type described. The individual tubes in the bundle
27
each are anchored in respective holes formed in the upper and lower tube sheets
14
and
23
through belling, expanding or seal welding the tube ends within the tubesheets.
The lower baffle or wrapper
26
is aligned within the pressure vessel
11
by means of pins (not shown). The lower baffle
26
is secured by bolts (not shown) to the lower tubesheet
23
or by welding to lugs (not shown) projecting from the lower end of the pressure vessel
11
. The lower edge of the baffle
26
has a group of rectangular water ports
30
or, alternatively, a single full circumferential opening (not shown) to accommodate the inlet feedwater flow to the riser chamber
19
. The upper end of the baffle
26
also establishes fluid communication between the riser chamber
19
within the baffle
26
and annular downcomer space
31
that is formed between the outer surface of the lower baffle
26
and the inner surface of the cylindrical pressure vessel
11
through a gap or steam bleed port
32
.
A support rod system
28
is secured at the uppermost support plate
45
B, and consists of threaded segments spanning between the lower tubesheet
23
and the lowest support plate
45
A and thereafter between all support plates
45
up to the uppermost support plate
45
B.
A hollow toroid shaped secondary coolant feedwater inlet header
34
circumscribes the outer surface of the pressure vessel
11
. The header
34
is in fluid communication with the annular downcomer space
31
35
through an array of radially disposed feedwater inlet nozzles
35
. As shown by the direction of the
FIG. 1
arrows, feedwater flows from the header
34
into the vapor generating unit
10
by way of the nozzles
35
and
36
. The feedwater is discharged from the nozzles downwardly through the annular downcomer
31
and through the water ports
30
into the riser chamber
19
. Within the riser chamber
19
, the secondary coolant feedwater flows upwardly within the baffle
26
in a direction that is counter to the downward flow of the primary coolant within the tubes
27
. An annular plate
37
, welded between the inner surface of the pressure vessel
11
and the outer surface of the bottom edge of an upper cylindrical baffle or wrapper
33
insures that feedwater entering the downcomer
31
will flow downwardly toward the water ports
30
in the direction indicated by the arrows. The secondary fluid absorbs heat from the primary fluid through the tubes in the bundle
27
and rises to steam within the chamber
19
that is defined by the baffles
26
and
33
.
The upper baffle
33
, also aligned with the pressure vessel
11
by means of alignment pins (not shown), is fixed in an appropriate position because it is welded to the pressure vessel
11
through the plate
37
, immediately below steam outlet nozzles
40
. The upper baffle
33
, furthermore, enshrouds about one third of the tube bundle
27
.
An auxiliary feedwater header
41
is in fluid communication with the upper portion of the tube bundle
27
through one or more nozzles
42
that penetrate the pressure vessel
11
and the upper baffle
33
. This auxiliary feedwater system is used, for example, to fill the vapor generator
10
in the unlikely event that there is an interruption in the feedwater flow from the header
34
. As hereinbefore mentioned, the feedwater, or secondary coolant that flows upwardly through the tube bank
27
in the direction shown by the arrows rises into steam. In the illustrative embodiment, moreover, this steam is superheated before it reaches the top edge of the upper baffle
33
. This superheated steam flows in the direction shown by the arrow, over the top of the baffle
33
and downwardly through an annular outlet passageway
43
that is formed between the outer surface of the upper cylindrical baffle
33
and the inner surface of the pressure vessel
11
. The steam in the passageway
43
leaves the vapor generating unit
10
through steam outlet nozzles
40
which are in communication with the passageway
43
. In this foregoing manner, the secondary coolant is raised from the feed water inlet temperature through to a superheated steam temperature at the outlet nozzles
40
. The annular plate
37
prevents the steam from mixing with the incoming feedwater in the downcomer
31
. The primary coolant, in giving up this heat to the secondary coolant, flows from a nuclear reactor (not shown) to the primary coolant inlet
15
in the upper head
12
, through individual tubes in the heat exchanger tube bundle
27
, into the lower head
13
and is discharged through the outlet
20
to complete a loop back to the nuclear reactor which generates the heat from which useful work is ultimately extracted.
Referring now to
FIG. 2
, there is shown a plan view of a portion of a prior art support plate
45
characterized by holes or apertures
46
, each of which has at least three inwardly protruding members
47
that restrain but do not all engage or contact the outer surface of the tube
48
extending through the hole
46
. Bights
49
that are intermediate of these inwardly protruding members
47
are formed in the individual support plate holes
46
when the associated tube
48
is lodged in place to establish fluid passage through the plate
45
. The inwardly protruding members
47
terminate in arcs or arcuate lands
51
that define a circle of a diameter that is only slightly greater than the outside diameter of the associated tube
48
.
Turning now to prior art
FIG. 3
, there is shown a plan view of one of the broached holes
46
and a portion of the surrounding support plate
45
of
FIG. 2
with a tube
48
inserted through the broached hole
46
. A detail of
FIG. 3
is shown at
FIG. 4
which depicts a problem encountered with this prior art broached hole
46
whereby the sharp edges
50
formed along the vertical sides of the arcuate land
51
of the inwardly protruding member
47
can potentially gouge the outer wall of tube
48
thereby resulting in a faster increase in the depth rate at which through-wall tube wear occurs for a given volume loss. This prior art support plate
45
also allows for a small annular space between the arcuate land
51
and the outer wall of tube
48
and, due to the associated flow restrictions, results in rapidly accumulating detrimental deposits for at least some of the support plates
52
.
Referring now to
FIG. 5
, there is shown a plan view of a portion of support plate
52
characterized by holes or apertures
53
, each of which has at least three inwardly protruding members
54
that restrain but do not all engage or contact the outer surface of the tube
55
extending through the hole
53
. Bights
56
that are intermediate of these inwardly protruding members
54
are formed in the individual support plate holes
53
when the associated tube
55
is lodged in place to establish fluid passage through the plate
52
. In accordance with the present invention, the inwardly protruding members
54
terminate in flat lands
57
.
Turning now to
FIG. 6
, there is shown a plan view of one of the broached holes
53
of
FIG. 5 and a
portion of the surrounding support plate
52
. A tube
55
extends through the broached hole
53
. A detail of
FIG. 6
is shown at
FIG. 7
where the flat land
57
of the inwardly protruding member
54
provides sufficient tube contact length to lower contact stress thereby minimizing fretting-wear of the tube
55
. The flat land configuration also eliminates the potential gouging of the outer wall of tube
55
thus decreasing the depth rate at which through-wall wear occurs for a given volume loss. Moreover, the space between the flat land
57
and the outer wall of tube
55
is increased to reduce deposition accumulation.
Referring to
FIG. 8
, there is shown a plan view of one of the broached holes
53
of
FIG. 5 and a
portion of the surrounding support plate
52
. As shown in FIG.
8
and in
FIG. 9
which is a cross-sectional view taken along lines A—A of
FIG. 8
, the inner wall
58
forming the protruding member
54
in the support plate
52
has an hourglass configuration comprised of a tube contact section
59
with beveled end sections
60
. In a tube support plate of the type under consideration, the thickness of the broached plate is 1.5 inches, the length of the tube contact section
59
is 0.75 inches, and the chamfer angle of the beveled end section
60
is 11 degrees.
The beveled end sections
60
of the broached holes
53
improve the local fluid flow patterns and reduce the deposition of magnetite and other particles on the support plate
52
due to a decrease in hydraulic shock losses. Computational fluid dynamic modelling of the flow paths through an hourglassed broached hole
53
and experimental testing have confirmed that the gradual contraction and expansion of the fluid flow therethrough effectively reduces pressure drop which contributes to the greater margin for system pressure drop increases. Furthermore, as a result of a reduction in the hydraulic loss coefficient, the hourglassed configured broached holes
53
contribute to greater margins for water level problems such as water level instability and high water levels resulting from high pressure drops. The hourglass configuration reduces fluid turbulence in the area of contact between tube
55
and the protruding member
54
of support plate
52
thereby reducing local deposition of magnetite and other particles on the support plate
52
. The hourglass configuration also allows for greater rotational motions between tubes
55
and the protruding members
54
before experiencing binding due to a moment couple from opposing forces at the top and bottom edges of the tube support plate
52
.
According to the present invention, the tube support plate
52
is made of stainless SA-240 410S material with a specified high yield of 50 ksi or above and ultimate tensile strength (UTS) of 80 ksi or above.
The following chart shows the superiority of the SA-240 410S stainless steel material of the present invention when compared to the SA-212 Gr.B carbon steel used to make the prior art tube support plates
47
.
|
Material Specification
Chemical
Yield (ksi)
UTS (ksi)
|
|
SA-212 GrB
C-Si
38 ksi (min)
70 ksi (min)
|
SA-240 410S
13 Cr
50 ksi (min)
80 ksi (min)
|
|
From the foregoing it is thus seen that the tube support plates
52
made with SA-240 410S stainless material provide (1) improved corrosion resitance; (2) higher strength; and (3) improved compatibility to minimize fretting wear with the tubes
55
which are made of Alloy 690 material.
While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.
Claims
- 1. In a heat exchanger tube and shell structure, a generally flat support plate having a plurality of individual tube receiving apertures formed therein, at least three members integral with the plate defining each of the apertures, the integral members protruding inwardly toward the center of the respective aperture and forming bights between at least adiacent pairs of the members in order to provide a predetermined flow area when the tube that is individual to the respective aperture is lodged in place, the flow area having an inlet and an outlet, the members having beveled and sections at the inlet and the outlet, the inwardmost end of each of the integral members forming a flat land, said protruding integral member flat lands restraining but not all contacting the outer surface of the individual tube that is to be received within the respective aperture.
- 2. A heat exchanger tube and shell structure according to claim 1 wherein each of the apertures has an hourglass configuration.
- 3. A heat exchanger tube and shell structure according to claim 1 wherein the beveled end sections have a chamfer angle of about 11 degrees.
- 4. A heat exchanger tube and shell structure according to claim 1 wherein the inwardmost end of each of the integral members includes a tube contact section formed between the beveled end sections.
- 5. A heat exchanger tube and shell structure according to claim 4 wherein the tube contact section is about 0.75 inches in length.
- 6. A heat exchanger tube and shell structure according to claim 1 wherein the plate is formed from SA-240 410S stainless steel material.
US Referenced Citations (14)
Foreign Referenced Citations (2)
Number |
Date |
Country |
3008455 |
Sep 1981 |
DE |
0296018 |
Dec 1988 |
EP |