Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FREEZE-PROTECTED HEAT EXCHANGER
BACKGROUND OF THE INVENTION
1. Field of the invention:
The present invention relates to heat exchangers, and more
particularly to heat exchangers featuring anti-freeze protection of the
condensate draining path.
2. Brief description of the prior art:
Although freeze protection is an important criteria in designing
an air-cooled steam condenser, the systems of the prior art, after more
than two decades of development, still present complex and costly
solutions to that problem and/or are unable to prevent freezing under
certain operating conditions.
A typical solution to reduce the risk of freezing in the tubes of
a steam condenser is to use a bundle of more than one row of tubes
successively traversed by the air flow. The first row is struck by the
coldest air flow but only a portion of the steam supplied to the tubes can
be condensed. The outlet of the first row is connected to the inlet of the
next row which converts a further amount of steam into condensate but
is contacted by preheated air. Hence, although the steam could be totally
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reduced to cooled condensate at that stage, freezing is prevented
because of the higher temperature of the air flow striking that row.
Larinoff in US patent No 5,787,970 issued on August 4, 1998
presents an improved solution based on that concept characterized by a
mixed flow vertical tube bundle design, in which some of the tube rows
conduct counterflow steam and condensate while others have parallel
flow. The condensate is drained at the bottom of the bundle from a
header connecting a parallel flow row to a successive counterflow row in
the protected warm air zone and non-condensable gases are collected at
the outlet header of the counterflow rows.
The main drawback of the above type of systems lies in their
lower efficiency/cost ratio as the second pass tube rows provide less heat
exchange than the others for a comparable size and manufacturing cost.
Also, some risks of freezing in the condensate drain piping and in tubes
next to the edges of the bundle are still present. Moreover, circulation of
steam and condensate in counterflow may result in interaction between
the two fluids that disrupts normal flow and heat transfer. US patent No
5,056,592 (Larinoff) issued on October 15, 1991 offers a solution to that
problem by providing baffling inside some of the tubes to channel and
separate the upward bulk flow of steam and the downward flow of
condensate.
Another approach based on a similar principle is to use two
rows of U-shaped tubes connected to a common steam supply as
described in US patent No 3,705,621 (Schoonman) issued on December
12, 1972. The tubes are so disposed that the air flow is successively
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striking the hottest legs of the first and second rows and then the coldest
legs of the second and first tube rows.
Similarly, US patent No 4,926,931 (Larinoff] issued on May 22,
1990 presents a system in which the tubes are so arranged that steam
flows from the input headers to the exposed legs of the inner and outer
tube rows, and returns as condensate through the tube legs located in the
protected warm air region in the middle of the tube bundle. The air flow
thus successively strikes the hottest legs of the outer tube row, the
coldest legs of the same row, the coldest legs of the second tube row and
finally the hottest legs of that second row. Such an arrangement provides
better protection to the exposed tubes especially at the top and bottom
faces of the bundle. Moreover, the condensate drain headers extending
in the protected region parallel and next to the steam supply headers
provide some protection against freezing of the condensate by radiation
heating. However, this system has drawbacks similar to the above
concepts, as to the efficiency/cost ratio and still offers limited freezing
protection especially in the U-shaped portions connecting the two legs of
the finned tubes.
Another solution of comparable efficiency is described in US
patent No 5,765,629 delivered to Goldsmith on June 16, 1998 and uses
a second stage vent condenser disposed in the same plane as a first
stage condenser, both comprising bundles of vertically oriented tubes.
The first stage operates at a higher steam pressure and consequently is
easily drained from condensate and non-condensable gases into a lower
header with excess steam. This header is connected to the upper header
of the second stage condenser and to a hydraulically balanced common
drain pot below the lower header. Non-condensable gases from the
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second stage flow counter-currently to be vented near the upper header.
In this arrangement, freezing is controlled by continuous purging of the
tube rows to avoid steam back-flow in the tube rows thereby eliminating
trapping of condensate and non-condensable gases. However, this
system is maintaining a constant level of condensate in the drain headers
and the drain pot which are subject to freezing, particularly on the second
stage condenser side.
Some solutions of the prior art have been specifically
addressing potential freeze-up of the condensate drain lines. For
instance, US patent No 3,968,836 (Larinoff) issued on July 13, 1976
discloses a heat exchanger wherein leg seals connecting with outlets
from individual condensate outlet headers are enclosed within a drain pot
which is heated by uncondensed vapor from one of the outlet headers.
In US patent No 4,240,502 issued on December 23, 1980, Larinoff brings
some improvements to the latter system, including a small hole in the
drain pipe to purge the drain pot when the steam condensing system is
shut down and applying some insulating material on the portion of the
outlet header extending outside of the heated drain pot.
In US patent 5,145,000, (Kluppel) issued on September 8,
1992, a steam condensing system similar to the above has a tank
receiving the condensate drain line from the drain pot. A steam line from
the source of steam which also feeds the condenser, is connected to the
upper end of the tank section receiving the drain line for supplying steam
above the condensate level in the tank section. The steam heats the
condensate drain line in the tank section to avoid freezing of the
condensate.
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In US patent 5,355,943 (Gonano) issued on October 18, 1994,
steam from the source supplying the condenser is again connected to the
upper end of a tank section receiving a condensate overflow drain duct
from a drain vessel. Condensate is rain-like spread falling in the duct
while the steam supplied to the tank goes up along the duct in
5 countercurrent with the condensate, thus heating it on its passage to
finally be sucked with non-condensable gases through the top portion of
the drain vessel.
Although the latter vapor condensing system arrangements of
the prior art significantly contribute to prevent freeze-up of the heat
exchanger tube bundles or condensate drain lines, considerable
drawbacks still limit their use on the market. Principally, their relative
complexity significantly increases the system manufacturing and
maintenance costs, while some efficiency of the heat transfer is lost and
most of these systems still present risks of freezing especially if they are
operated outside of their optimal vapour pressure conditions.
There is thus a need for an improved air-cooled vapor
condensing system providing freeze protection over a wide range of
operating conditions as required in applications such as heating of
buildings.
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SUMMARY OF THE INVENTION
The present invention, as broadly claimed, is concerned with
a freeze-protected heat exchanger comprising:
a fluid supply member for connection to a source of condensable
heated fluid;
a drain chamber coextending with the fluid supply member, and
comprising a drain outlet;
a plurality of heat exchanger tubes extending from the fluid supply
member and drain chamber, each heat exchanger tube comprising:
- a first pipe having a heat-conductive wall, and a proximal
end in fluid communication with the drain chamber;
- a second pipe coextending with the first pipe, and having a
proximal end in fluid communication with the fluid supply
member; and
- at least one first orifice through which the first pipe is in fluid
communication with the second pipe; and
at least one second orifice through which the drain chamber is in
fluid communication with the fluid supply member.
In operation, heated fluid is supplied from the fluid supply member to the
second pipes, heated fluid from the second pipes is transferred to the
respective first pipes through the first orifices, heat from the heated fluid
in the first pipes is transferred to the outside of the first pipes through
the
heat-conductive walls, cooled fluid from the first pipes is collected and
drained through the drain chamber and drain outlet, and the at least one
second orifice produces a jet of heated fluid in the drain chamber to
prevent the formation of ice in said drain chamber.
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In accordance with preferred embodiments of the invention:
- the second orifice opens in the drain chamber in the area of the drain
outlet;
- the first pipe comprises an outer pipe having the heat-conductive wall
and a distal closed end, the second pipe comprises an inner pipe
having an inner pipe wall and disposed within the outer pipe with a
space between the inner and outer pipes, and the first orifice extends
through the inner pipe wall;
- the fluid supply member and the drain chamber are substantially
elongated and coaxial to each other, and the heat exchanger tubes
extend substantially radially from the fluid supply member and drain
chamber;
- the heat exchanger tubes are generally horizontal with a slight slope
toward the fluid supply member and drain chamber to enable draining
of the cooled fluid from the first pipes toward the drain chamber by
g ravity;
- each outer pipe comprises at least one outer heat-conductive fin to
enhance heat transfer from the heat-conductive wall of the outer pipe
to the outside, this fin comprising a helical extruded fin integral with
the outer pipe to further prevent dilatation of the outer pipe and thus
preventing formation of ice in the outer pipe;
- the coextending fluid supply member and drain chamber are
elongated, and the heat exchanger tubes are arranged in bundles
distributed along the length of the fluid supply member and drain
chamber, each bundle of heat exchanger tubes comprise a plurality
of rows of heat exchanger tubes, the heat exchanger tubes comprise
first and second sets of heat exchanger tubes, and these first and
second sets are diametrically opposite to each other about the fluid
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supply member and drain chamber;
- the coextending fluid supply member and the drain chamber are
substantially elongated and vertical, the drain chamber comprises a
bottom end provided with the drain outlet through which cooled fluid
collected by the drain chamber from the first pipes is drained, and the
the fluid supply member comprises a header with a closed lower end
proximate to the drain outlet, the lower end of the header being
provided with the second orifice to produce the jet of heated fluid in
view of preventing formation of ice in the region of the drain outlet of
the bottom end of the drain chamber;
- the fluid supply member comprises a heat-conductive wall located at
least in part in the drain chamber to provide for transfer of heat from
the heated fluid to the drain chamber in view of preventing formation
of ice in the drain chamber;
- each inner pipe has a distal end short of the distal closed end of the
corresponding outer pipe, and the distal end of the inner pipe is open
through at least one first orifice to transfer heated fluid from the inner
pipe to the area of the outer pipe proximate to the distal closed end of
the outer pipe; and
- a plurality of first orifices are distributed along the first and second
pipes, and the fluid supply member comprises a header provided with
a plurality of heated fluid inlets distributed along this header.
The present invention also relates to a face and by-pass heat
exchanger unit comprising:
a freeze-protected heat exchanger comprising:
an elongated, substantially vertical fluid supply member for
connection to a source of condensable heated fluid;
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an elongated, substantially vertical drain chamber coextending
with the fluid supply member, and comprising a drain outlet;
a set of bundles of heat exchanger tubes extending generally
radially from the fluid supply member and drain chamber and
distributed along the fluid supply member and drain chamber, each
heat exchanger tube comprising:
a first pipe having a heat-conductive wall, and a
proximal end in fluid communication with the drain
chamber;
a second pipe coextending with the first pipe, and
having a proximal end in fluid communication with the fluid
supply member; and
at least one first orifice through which the first pipe is in
fluid communication with the second pipe; and
at least one second orifice through which the drain
chamber is in fluid communication with the fluid supply
member, this second orifice opening in the drain chamber
in the area of the drain outlet;
whereby, in operation, heated fluid is supplied from the fluid
supply member to the second pipes, heated fluid from the
second pipes is transferred to the respective first pipes
through the first orifices, heat from the heated fluid in the
first pipes is transferred to the outside of the first pipes
through the heat-conductive walls, cooled fluid from the first
pipes is collected and drained through the drain chamber
and drain outlet, and the at least one second orifice
produce a jet of heated fluid in the drain chamber to prevent
the formation of ice in the area of the drain outlet;
i
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a housing comprising:
at least one airflow passage, the bundles of heat exchanger
tubes extending across the airflow passage whereby heat from the
heated fluid in the first pipes is transferred to the air flow through
5 the heat-conductive walls of the first pipes; and
air deflectors extending across the airflow passage to
selectively direct the airflow through the bundles of heat exchanger
tubes and/or in by-pass zones of the airflow passage between the
bundles of heat exchanger tubes.
In accordance with preferred embodiments of the face and by-
pass heat exchanger unit:
- the face and by-pass heat exchanger unit further comprises a closed
housing portion for receiving the fluid supply header and the drain
chamber;
- the closed housing portion is heat-insulated;
- the first pipe comprises an outer pipe having the heat-conductive wall
and a distal closed end, the second pipe comprises an inner pipe
having an inner pipe wall and disposed within the outer pipe with a
space between the inner and outer pipes, and the first orifice extends
through the inner pipe wall;
- the fluid supply member and the drain chamber are substantially
coaxial to each other;
- the heat exchanger tubes are generally horizontal with a slight slope
toward the fluid supply member and drain chamber to enable draining
of the cooled fluid from the first pipes toward the drain chamber by
g ravity;
- each outer pipe comprises at least one outer heat-conductive fin to
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enhance heat transfer from the heat-conductive wall of the outer pipe
to the outside, and the at least one fin comprises a helical extruded fin
integral with the outer pipe to further prevent dilatation of the outer
pipe and thus preventing formation of ice in this outer pipe;
- each bundle of heat exchanger tubes comprise a plurality of rows of
heat exchanger tubes;
- the housing comprises first and second airflow passages, and the set
of bundles of heat exchanger tubes comprise first and second subsets
of bundles of heat exchanger tubes, these first and second subsets
being diametrically opposite to each other about the fluid supply
header and drain chamber;
- the drain chamber comprises a bottom end provided with the drain
outlet through which cooled fluid collected by the drain chamber from
the first pipes is drained, and the fluid supply member comprises a
header with a closed lower end proximate to the drain outlet, the lower
end of the header being provided with the at least one second orifice
to produce the at least one jet of heated fluid in view of preventing
formation of ice in the region of the drain outlet of the bottom end of
the drain chamber;
- the fluid supply member comprises a heat-conductive wall located at
least in part in the drain chamber to provide for transfer of heat from
the heated fluid to the drain chamber in view of preventing formation
of ice in the drain chamber;
- the inner pipe has a distal end short of the distal closed end of the
outer pipe, and the distal end of the inner pipe is open through at least
one first orifice to transfer heated fluid from the inner pipe to the area
of the outer pipe proximate to the distal closed end of this outer pipe;
and
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- the face and by-pass heat exchanger unit comprises a plurality of first
orifices distributed along the first and second pipes, and the fluid
supply member comprises a header provided with a plurality of heated
fluid inlets distributed along the header.
The foregoing and other objects, advantages and features of the present
invention will become more apparent upon reading of the following non
restrictive
description of illustrative embodiments thereof, given for the purpose of
exemplification only with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the appended drawings:
Figure 1 a is an isometric front view of a face and by-pass heat
exchanger heating unit incorporating a freeze-protected heat exchanger
according to the present invention;
Figure 1 b is an isometric rear view of the face and by-pass heat
exchanger unit of Figure 1 a;
Figure 2a is an isometric front view of a freeze-protected heat
exchanger according to the present invention, in which fins of the outer tubes
are
not shown;
Figure 2b is a front elevation view of the freeze-protected heat
exchanger of Figure 2a;
Figure 2c is a top view of the freeze-protected heat exchanger of
Figure 2a;
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Figure 3 is a perspective, partly cross sectional view of an
upper portion of the freeze-protected heat exchanger of Figures 2a, 2b
and 2c, showing steam distribution and condensate return paths;
Figure 4 is a perspective, partly cross sectional view of a lower
portion of the freeze-protected heat exchanger of Figures 2a, 2b and 2c,
showing condensate drain path and the heating steam jets;
Figure 5a is a side elevational view of a preferred embodiment
of coextending steam supply header and drain chamber forming part of
the freeze-protected heat exchanger according to the invention;
Figure 5b is an elevational, end view of the coextending steam
supply header and drain chamber of Figure 5a; and
Figure 5c is a top plan view of the coextending steam supply
header and drain chamber of Figures 5a and 5b.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the appended drawings, similar reference numerals refer to
similar parts throughout the various figures.
The preferred embodiment of the freeze-protected steam
operated heat exchanger according to the present invention will now be
described in detail referring to the appended drawings.
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A face and by-pass heat exchanger unit 100 is illustrated in
Figure 1. This face and by-pass heat exchanger unit incorporates the
preferred embodiment of the freeze-protected heat exchanger 1 (Figure
2). In this preferred embodiment, the freeze-protected heat exchanger 1
is steam operated. Of course, use of any other type of condensable
heated fluid could be contemplated. The face and by-pass heat
exchanger unit (Figure 1 ) comprises a housing 10 in which the freeze-
protected heat exchanger 1 (Figure 2) is installed.
Referring to Figure 1, housing 10 defines a pair of airflow
passages 31 and 32 each provided with a remotely adjustable front set
of air deflectors 11 (Figure 1a) for:
- directing a predetermined portion of the incoming air flow (see arrow
25) through bundles 5 of heat exchanger tubes 7 forming part of the
freeze-protected heat exchanger 1 (better shown in Figures 2a, 2b
and 2c; and
- directing the remaining portion of the incoming air flow 25 toward
by-pass zones such as 27 located between the bundles 5 of heat
exchanger tubes 7;
and a remotely adjustable rear set of air deflectors 23 (Figure 1 b) for:
- blocking passage of air through the by-pass zones; or
- blocking passage of air through the bundles 5 of heat exchanger
tubes by blocking the exit downstream these bundles 5.
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Each bundle 5 comprises at least one vertical row of generally
horizontal heat exchanger tubes 7 connected at one end to generally
vertical steam supply header 3 and condensate drain chamber 4.
As better shown in Figures 2a and 3, the steam supply header
5 3 is substantially cylindrical and extends substantially vertically and
coaxially in the box-like condensate drain chamber 4. The steam supply
header 3 comprises an upper, threaded steam inlet connector 2.
Referring to Figure 1a, the steam supply header 3 and the box-like
condensate drain chamber 4 are installed in a substantially central closed
10 housing portion 12 of the face and by-pass heat exchanger unit 100.
In Figures 1a, 1b, 2a, 2b and 2c diametrically opposite sets of
superposed and substantially radially extending bundles 5 of heat
exchanger tubes 7 are illustrated. However, it shall be deemed that in
15 smaller units having less heating capacity, the housing portion 12 and the
enclosed steam supply header 3 and drain chamber 4 may be located at
one end of the unit 100 comprising a single set of superposed bundles 5
of heat exchanger tubes 7 extending substantially radially from supply
header 3. In this case, to improve distribution of the steam into the inner
pipes 13 (Figure 3) of the superposed bundles 5, a plurality of steam
inlets (not shown) can be provided in the side wall of supply header 3.
Preferably, these steam inlets will be distributed along the length of the
header 3 and disposed diametrically opposite to the single set of
superposed bundles 5 of heat exchanger tubes 7. As described
hereinafter and as illustrated in Figure 3, each heat exchanger tube 7 is
formed of an heat-conductive outer pipe 26 and an inner pipe 13.
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In this type of application, a substantially constant steam flow
is established through the steam inlet connector 2 while the temperature
of the air emerging downstream of the heat exchanger unit 100 is
modulated according to the position of the cooperating series of air
deflectors 11 and 23. Both series of air deflectors 11 and 23 are
connected together through connecting rods such as 24 and actuated
through an external actuator such as an electric motor (not shown) to
operate as follows:
- in a face mode, the defectors 11 direct the incoming air flow toward
the bundles 5 of heat exchanger tubes 7, while the deflectors 23 block
the by-pass zones; and
- in a by-pass mode, the deflectors 11 direct the incoming air toward
the by-pass zones, while the deflectors 23 block the exit downstream
the bundles 5 of heat exchanger tubes 7.
Intermediate positions of the deflectors 11 and 23 may be adopted by the
face and by-pass heat exchanger unit 100 under the control of the
external actuator so as to modulate the proportion of air flowing through
the bundles 5 of heat exchanger tubes 7 and being heated by the heat
exchanger 1, thus controlling the average temperature of the air flow
downstream the face and by-pass heat exchanger unit 100.
The housing portion 12 provides some protection of the
condensate drain chamber 4 against contact by incoming cold air and can
be filled with insulating material to further improve insulating properties.
Figures 2a and 2b illustrate a generally vertical condensate drain pipe 8
extending from the bottom of the condensate drain chamber 4. Figures
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2a and 2b also illustrate a threaded condensate outlet connector 9 of the
condensate drain pipe 8.
Figure 3 illustrates the upper portion of the freeze-protected
heat exchanger 1 showing the structure of the steam distribution and
condensate return paths. Steam is supplied through the inlet connector
2 of the steam supply header 3. The inner pipes 13 of the heat
exchanger tubes 7 are each provided with two diametrically opposite
series of orifices 14 distributed therealong. The inner pipes 13 extend
generally horizontally and radially from the steam supply header 3 and
are in fluid communication therewith (see openings such as 28). Each
inner pipe 13 therefore extends through a wall of the condensate drain
chamber 4 and is mounted in a corresponding outer pipe 26 coaxially
therewith with an annular spacing between the inner 13 and outer 26
pipes. On the other hand, each outer pipe 26 is heat-conductive and
provided with a rigid heat-conductive integral helical extruded fin 15 to
enhance heat transfer from the heat-conductive wall of the output pipe 26
to the airflow 25. Also, each outer pipe 26 has a distal closed free end 29
and a proximal end 30 opening in the condensate drain chamber 4. More
specifically, the proximal end 30 of each outer pipe 26 is connected to
and extends through a side wall of the condensate drain chamber 4, in
fluid communication therewith. As illustrated, the inner pipes 13 extend
into the respective outer pipes 26 up to a few inches short from the distal
closed free ends 29. These inner pipes 13 preferably comprise
respective axial end orifices 21 to produce axial steam jets 22 toward the
closed free ends of the respective outer pipes 26. All the inner 13 and
outer 26 pipes are slightly sloping downwardly toward the condensate
drain chamber 4 to assure proper draining of the condensate 19 from the
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outer pipes 26 in the chamber 4 by gravity. A slope of the order of 2%
fulfills this purpose.
Those of ordinary skill in the art will appreciate that the steam
supplied by a steam source (not shown) through inlet connector 2 to the
steam supply header 3 is distributed in the inner pipes 13 and
subsequently transferred to the outer pipes 26 through the orifices 14 and
21. Again, it shall be noted that in large units comprising many
superposed bundles 5 of heat exchanger tubes 7, more than one steam
inlet can be provided along steam supply header 3 to better balance the
distribution of steam into the inner pipes 13. Upon contact with the inner
side of the air-cooled wall of finned outer pipes 26, heat from the steam
is transferred to the airflow 25 through the finned outer pipes 26 and the
steam condenses and flows by gravity as condensate 19 toward the drain
chamber 4, rain-like spread falling along the walls thereof toward the
bottom 20 (Figure 4) of that chamber. Each row of heat exchanger tubes
7 in such an arrangement provides about twice the heat-transfer capacity
of a conventional U-shaped tube design, thus reducing the size and cost
for a face and by-pass heat exchanger unit 100 of given capacity.
The internal volume and the walls of the condensate drain
chamber 4 are submitted to some heating from the steam supply header
3, thus preventing sub-cooling of the condensate and formation of ice in
the chamber 4 or at the outlet (proximal ends 30) of the outer pipes 26.
Moreover, the rigid extruded fins 15 provide the outer tubes 26 with a high
resistance to dilatation which contribute to further prevent formation of
ice. Although integral, extruded fins 15 are preferred, use of some other
fin configuration such as flat or corrugated plates, or flat or corrugated
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rectangular individual fins of an overlapped or footed "L" design could be
contemplated with acceptable results.
Figure 4 illustrates the lower portion of the freeze-protected
heat exchanger 1 to show the structure of the condensate drain path.
The condensate 19 dripping along the internal walls of drain chamber 4
hits the bottom 20 and flows through an inlet 18 of the condensate drain
pipe 8 and is returned to the steam trap and remaining components of the
system (not shown) via the threaded condensate outlet connector 9. Two
jets of steam 16a and 16b are respectively escaping from two small
orifices 17a and 17b of diameter depending on the pressure of the steam
supply, preferably provided in the bottom wall 31 of the steam supply
header 3 and so positioned as to direct these steam jets 16a and 16b
preferably toward the front (cold air side) corners of the bottom 20 of the
condensate drain chamber 4 thus avoiding any build-up of ice at the
bottom 20 and at the inlet 18 of the condensate drain pipe 8. The orifices
17a and 17b also serve to drain the condensed steam from the steam
supply header 3 when the steam-producing heating device (not shown)
is shut-off and the steam flow 32 is interrupted at the steam inlet
connector 2.
Alternatively, more than two orifices such as 17a and 17b can
be provided to produce more than two corresponding jets of steam such
as 16a and 16b.
In the case of the two orifices 17a and 17b, these orifices can
be positioned at a higher level on the vertical and cylindrical wall of the
header 3 to both heat and prevent build-up of ice throughout the entire
drain chamber 4. In the case of a number of orifices larger than 2, the
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orifices can be distributed vertically on the vertical, cylindrical wall of
the
header 3 again to both heat and prevent build-up of ice throughout the
entire drain chamber 4.
Furthermore, a closure member (not shown) can be provided
5 for manually or automatically controlling the opening and closing of the
orifices as a function of different operating conditions such as external air
temperature.
Figures 5a, 5b, and 5c illustrate an alternative embodiment 50
10 of the freeze-protected heat exchanger 1 showing the structure of the
steam distribution and condensate return paths.
The embodiment 50 of Figures 5a, 5b and 5c comprises a
steam supply header 52 and a condensate drain chamber 53 formed of
15 a vertical tube 55 with a closed top end 56. A central vertical flat, heat-
conductive wall 57 separates the vertical tube 55 into two halves of which
one forms the header 52 and the other the drain chamber 53. The steam
supply header 52 has closed top and bottom ends, while the drain
chamber 53 has a closed top end but a bottom end 54 open to form a
20 drain outlet 58.
Steam is supplied through an inlet connector 51 of the steam
supply header 52. As illustrated, inlet connector 51 is threaded for
connection to a steam source (not shown). The inner pipes 13 of the
heat exchanger tubes 7 are still provided with the two diametrically
opposite series of orifices 14 (see Figures 5c) distributed therealong. The
inner pipes 13 extend generally horizontally and radially from the steam
supply header 52 and are in fluid communication therewith (see portions
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of inner pipes 13 extending through the drain chamber 53). Each inner
pipe 13 therefore extends through a wall of the condensate drain
chamber 53 and is mounted in a corresponding outer pipe 26 coaxially
therewith with an annular spacing between the inner 13 and outer 26
pipes. On the other hand, each outer pipe 26 is heat-conductive and
provided with a rigid heat-conductive integral helical extruded fin 15 to
enhance heat transfer from the heat-conductive wall of the output pipe 26
to the airflow 25. Also, each outer pipe 26 has a distal closed free end 29
and a proximal end 30 opening in the condensate drain chamber 53.
More specifically, the proximal end 30 of each outer pipe 26 is connected
to and extends through a side wall of the condensate drain chamber 53,
in fluid communication therewith. As illustrated in Figure 5c, the inner
pipes 13 extend into the respective outer pipes 26 up to a few inches
short from the distal closed free ends 29. These inner pipes 13
preferably comprise respective axial end orifices 21 to produce axial
steam jets 22 toward the closed free ends of the respective outer pipes
26. All the inner 13 and outer 26 pipes are slightly sloping downwardly
toward the condensate drain chamber 53 to assure proper draining of the
condensate from the outer pipes 26 in the chamber 53 by gravity. A
slope of the order of 2% fulfills this purpose.
Those of ordinary skill in the art will appreciate that the steam
supplied by a steam source (not shown) through the inlet connector 51 to
the steam supply header 52 is distributed in the inner pipes 13 and
subsequently transferred to the outer pipes 26 through the orifices 14 and
21. Again, it shall be noted that in large units comprising many
superposed bundles 5 of heat exchanger tubes 7, more than one steam
inlet such as 51 can be provided along steam supply header 52 to better
balance the distribution of steam into the inner pipes 13. Upon contact
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with the inner side of the air-cooled wall of finned outer pipes 26, heat
from the steam is transferred to the airflow 25 through the finned outer
pipes 26 and the steam condenses and flows by gravity as condensate
toward the drain chamber 53, rain-like spread falling along the walls
thereof toward the bottom end 54 and drain outlet 58 (Figure 5a) of that
chamber. Each row of heat exchanger tubes 7 in such an arrangement
provides about twice the heat-transfer capacity of a conventional
U-shaped tube design, thus reducing the size and cost for a face and by-
pass heat exchanger unit 100 of given capacity.
The internal volume and the walls of the condensate drain
chamber 53 are submitted to some heating through the heat-conductive
wall 57 from the steam supply header 52, thus preventing sub-cooling of
the condensate and formation of ice in the chamber 53 or at the outlet
(proximal ends 30) of the outer pipes 26. Moreover, the rigid extruded
fins 15 provide the outer tubes 26 with a high resistance to dilatation
which contribute to further prevent formation of ice. Although integral,
extruded fins 15 are preferred, use of some other fin configuration such
as flat or corrugated plates, or flat or corrugated rectangular individual
fins
of an overlapped or footed "L" design could be contemplated with
acceptable results.
The condensate dripping along the internal walls of drain
chamber 53 hits the bottom 54 and flows through the drain outlet 58 and
is returned to the steam trap or remaining components of the system (not
shown) via this drain outlet 58. Drain outlet 58 is threaded for connection
to the steam trap or remaining components of the system. At least one
jet of steam 59 escapes from a small orifice 60 of a diameter depending
on the pressure of the steam supply, preferably provided in the lower
CA 02299682 2000-02-28
23
portion of wall 57 of the steam supply header 52 and so positioned as to
direct this steam jet 59 preferably toward a cold air side corner 61 of the
bottom 54 of the condensate drain chamber 53 thus avoiding any build-up
of ice at the bottom 54 and at the drain outlet 58. The orifice 60 also
serves to drain the condensed steam from the steam supply header 52
when the steam source (not shown) is shut-off and the steam flow is
interrupted at the steam inlet 51.
Alternatively, a plurality of orifices such as 60 can be provided
to produce a plurality of corresponding jets of steam such as 59.
In the case of the single orifice 60, this orifice can be positioned
at a higher level on the wall 57 to both heat and prevent build-up of ice
throughout the entire drain chamber 53. In the case of a plurality of
orifices such as 60, the orifices can be distributed vertically on the wall 57
again to both heat and prevent build-up of ice throughout the entire drain
chamber 53.
Furthermore, a closure member (not shown) can be provided
for manually or automatically controlling the opening and closing of the
single or plurality of orifices such as 60, as a function of different
operating conditions such as external air temperature.
Therefore, it will be apparent to those of ordinary skill in the art
that the freeze-protected heat exchanger 1 of the present invention can
be advantageously used for efficiently transferring heat from a steam flow
32 to an air flow 25 potentially below the freezing point of water, without
causing damages or malfunctions due to freezing of steam condensate,
thus overcoming the drawbacks of the prior art devices.
CA 02299682 2000-02-28
24
Although the present invention has been described
hereinabove by way of a preferred embodiment thereof, this embodiment
can be modified at will, within the scope of the appended claims, without
departing from the spirit and nature of the subject invention.
For instance, it would be obvious for one of ordinary skill in the
art to use the freeze-protected heat exchanger of the present invention
with a different arrangement of bundles and rows of tubes, in a wide
range of sizes and power capacities and/or to use two units forming a
A-shaped condenser for condensing steam or other condensable heated
fluid at the outlet of turbines in power plants. Moreover, the heat
exchanger can be retrofitted into many types of existing units.
