Note: Descriptions are shown in the official language in which they were submitted.
Case 4214
106~430
BACKGRCUND OF THE INVENTION
~ield of the Invention
This invention relates to pressurized heat exchangers
and more specifically to an arrangement for relieving excessive
pressure differentials within the heat exchanger in the event of
a failure in the secondary coolant supply system.
Description of the Prior Art
The use of heat exchangers in conjunction with pres- -
surized water reactors is well kncwn. Typically, the heat ex-
changer takes the forn of a vertically oriented elongated
cylindrical pressure vessel containing a plurality of closely
spaced tubes extending throughout the entire length of the vessel
forming a tube bundle.
At both ends of the tube bundle a horizontally trans-
posed tubesheet holds the tubes in position. A cylindrical tube
shroud surrounds the tube bundle, and cooperates with the vessel
wall to form an annular passage therebetween. A horizontally
oriented partition wall circumscribes the tube shroud and divides
the annular space into a fluid inlet compartment and fluid out-
let compartment.
In this particular arrangement, a hot primary coolant
enters the pressure vessel through an inlet nozzle, located at
the base of the vessel, travels up through the tubes housed within
the vessel, and exits through an outlet nozzle located at the
head of the vessel. Simultaneously, secondary fee~water enters
through a feedwateT inlet nozzle, passes through the inlet
compartment and is vaporized as it travels upwardly and around the
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tubes, and is then redirected downwardly through the fluid outletcompartment for discharge through the steam outlet noz21e.
During normal operating conditions, the shell side
pressure may be in the order of 1085 psi. However, if either the
secondary feedwater line or the main steam line should rupture,
the pressure will quickly drop in the compartment connected with
the ruptured line causing a large pressure differential across
the two compartments. Such a pressure drop may cause extensive
damage to the internal components of the vessel.
It is obvious that a reliable pressure equalization
mechanism is therefore necessary to relieve the resulting pressure
differential between the two compartments before serious damage
occurs.
SUMMARY OF THE INVENTION
The present invention achieves pressure equalization
in a pressurized heat exchanger in the event of a failure within
either the main steam piping system or the secondary feedwater
piping system.
In the main embodiment of the invention, there is
provided a pressure vessel comprising a tube bundle. The tube
bundle is surrounded by a cylindrical shroud forming an annular
space with the vessel w~ll. The space is divided by a partition
wall into a fluid inlet compartment and a fluid outlet compartment.
The partition wall includes a plurality of openings; each being
noTmally closed by a flap valve.
Each flap valve is made to open whenever the pressure
differential between the inlet and outlet compartments attains
a predetermined value, e.g., 14~ psi. Selected valves will open
depending o~ their orientation vis a vis the pressure differential.
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Case 4214
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Some of the valves can only open into the fluid inlet c~mpartment
whereas the remaining valves can only open into the fluid outlet
compartment. The valves which open into the inlet compartment
are closed by resilient means whereas the valves which open into
the outlet compartment gravitate to their normally closed position
by virtue of their own weight. Of course, the latter valves may
also be equipped with resilient means.
In an alternate embodiment of the invention, the fluid
inlet and outlet compartments are connected by longitudinally
situated ducts extending between two axially spaced annular plates
comprising the partition wall. The ducts which serve as openings
in the partition wall can either be closed by flap valves or rupture
discs,
In a further embodiment of the invention, the flap
valves are replaced by rupture discs designed to burst whenever the
pressure differential exceeds the predetermined value.
BRIEF DESCRIPTION OF THE DRAWING
Fig. 1 is a cross sectional elevation of a pressure
vessel embodying the invention;
Fig. 2 is an alternate embodiment ofthe invention in
partial cross sectional elevation;
Fig. 3 is a cross sectional plan view taken along line
3-3 of Fig. l;
Fig. 4 is a detail view of an open flap valve;
Fig. 5 is a detail view of a closed flap valve; and
Fig. 6 shows a further embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
Fig. 1 shows an upright pressure vessel 10. The primary
coolant enters the vessel through inlet nozzle 12, flows through
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tubes 16, of which only one is depicted and exits throu~h out-
let nozzle 18. The tubes 16 are grouped to form a tube bundle
14, and the latter is surrounded by a cylindrical shroud 20
which cooperates with the vessel wall 22 to define an annular
passage 21 therebetween. A partition wall 26 is disposed between
the wall 22 and the shroud 20. The partition wall 26 is in the
form of an annular plate circumscribing the shroud 20. As a
result of this construction, the annular passage 21 is divided
into a lower fluid inlet compartment 28 and an upper fluid
outlet compartment 30. The feedwater enters the inlet ccmpartment
28 through the feedwater inlet nozzle 34 as indicated by directional
arrow 32. The water is vaporized as it passes up and around tube
bundle 14 and leaves the outlet compartment 30 as indicated by
directional arrow 36 through the main steam outlet nozzle 38 for
delivery to a turbine, not shown.
The partition wall 26 contains a plurality of openings
40 and 40a which are normally closed by hinged flaps 42 and 44
of flap valves 43 and 45, respectively. The flaps 42 open into
the fluid outlet compartment 30 as shown in dotted line at 42a,
whereas flaps 44 open into the fluid inlet ccmpartment 28 as
shown in dotted line at 44a.
A tension spring 46 keeps each flap 44 closed. The
flaps 42 do not require a tension spring since they will close of
their own accord due to their weight. All of the valves 43 or 45
are designed to open whenever the pressure differential across com-
partments 28 and 30 attains a predetermined differential~ e.g.,
140 psi. Depending on the location of the pressure loss, flaps 44
will assume position 44a whereas flap 42 will assume position 42a.
When the pressure differential falls below the predetermined
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value, all open valves will return to their normally closed
positions. Handholes 48, which are normally sealed by plates
50, allow for periodic inspection of valves 43 and 45.
Assuming that a rupture occurs in the feedwater piping
system, not shown, the inlet compartment 28 will experience a
large pressure loss thereby resulting in an excessive pressure
differential between it and the outlet compartment 30. This
condition will cause all of the flaps 44 to open to position 44a,
as indicated in Figure 1 thereby reducing the pressure differential
between the inlet and outlet c~mpartments 28 and 30. It should
be recog~ized that flaps 42 will remain closed.
Assuming that a rupture occurs in the main steam piping
system, not shcwn, the outlet compartment 30 will experience a
large pressure loss thereby resulting in a differential between
it and the inlet compartment 28. If this pressure differential
attains the predete~mined value, all of the flaps 42 will swing
open to position 42a, reducing the pressure differential between
the inlet and outlet compartments 28 and 30. It should be recog-
nized that flaps 44 will remain closed.
According to an alternate embodiment of the invention,
as shown in Fig. 2, the partition wall 26 is foTmed by two
axially spaced annular plates 26a and 26b circumscribing the
shroud 20 and defining an annular chamber 52. A plurality of
ducts 54 ex~end between the annular plates 26a and 26b to form
the openings 40 and 40a through partition wall 26. The interiors
of ducts 54 which form the openings 40 and 40a are normally
closed by hinged flaps 42 and 44 of flap valves 43 and 45.
Fig. 3 is a cross sectional plan view taken along line
3-3 in Fig. 1 showing the partition wall 26 disposed between the
shroud 20 and the vessel wall 22. The partition wall includes
alternately disposed openings 40 and 40a and the valves 43 and
45 with the flaps 42 and 44 in theiT closed position.
Case 4214
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Figure 4 sh~s opening 40a and flap valve 45 with its
hinged flap 44 in the open position whereas Fig. S shcws the
flap 44 in its normally closed position. Both the opening 40a
and the hinged flap 44 have beveled seating surfaces 60A and
60B, respectively, for tight seating. Flap 44 is hinged and
supported from a support member 56 which is connected to the
partition wall 26. In its fully open position, flap 44 will
rest on a stop bar 58 which is connected to shroud 20. The
spring 46 acts to close the flap 44 whenever the pressure
differential between the inlet and outlet compartments 28 and
30 falls below the predetermined value and maintains the flap
44 in its closed position during normal operating conditions.
Figure 6 is directed to a further embodiment of the
invention which employs rupture discs in lieu of flap valves
and depicts one such disc 62 which is sized to cover the opening
40 or 40a, not shown, and is suitably attached to the partition
wall 26. The disc 62 is designed to burst whenever the pressure
differential between the inlet and outlet compartment 28 and 30
attains the predetermined value.
While in accordance with the provisions of the statutes
there is illustrated and described herein a specific embodiment
of the invention, those skilled in the art will understand that
changes may be made in the form of the invention covered by the
claims and that certain features of the invention may sometimes
be used to advantage without a corresponding use of the other
features.
