FIELD OF THE INVENTION:
The invention relates to a steam condenser for condensing steam in a power plant
or in a chemical plant application. The present invention, in particular allows
optimization of tube arrangement of both first pass and second pass sections with a well-
defined connectivity between them. More particularly, the present invention relates to a
compact two-pass steam condenser having atleast one improved tube nest configuration
for reducing loss of steam pressure.
BACKGROUND OF THE INVENTION
A steam-condenser consists of a large number of tubes configured in a nest shape. The
number of tubes can be as high as 30,000 in a large power plant condenser. Thermal
performance of a condenser is highly dependent on the arrangement of these tubes. This
tube nest arrangement shall be capable of reducing the loss of steam side pressure and of
removing efficiently the non-condensable gas in the steam. Two-pass condensers are
generally used to limit the condenser length. Thermal hydraulics are more complex in a
two-pass condenser as approximately two-thirds of total steam condenses on the tubes in
the first pass wherein the temperature of the coolant passing through the tubes is
comparatively low and the rest of the steam condenses on the tubes in the second pass.
U.S patent No.5,649,590 describes a tube layout in the form of radiating spikes. Some of
the spikes split into branches. The branching spikes comprise a base trunk which flares
and splits into two branches of equal thickness as soon as the thickness of the trunk of the
spike reached between one-and-a-half and two times the thickness of its base. This form
of layout makes it possible to install a greater number of tubes in a given area of the tube
plate.

Another version of tube nest layout has been disclosed in U.S. patent No. 5,960,867. The
tube nest is spaced from the bottom surface and the side walls of the vessel so that steam
is able to flow from every direction into the tube nest at a reduced velocity. The
extracting opening is disposed between the centre of gravity of the outer circumference
and the width of each flow passage increases toward the open outer end. The area ratio
and the length of flow passage increase toward the center axis of the tube nest. The
advantage claimed is a compact condenser capable of reducing pressure loss and
efficiently removing non-condensable gas.
U.S patent No. 6,269, 867B1 describes a tube nest which has a massed region of
cooling tubes and a plurality of tube bundles with flow passages. A non-condensable gas
extracting tube is arranged in the massed region. A discharge flow passage if formed at
least partially in the tube nest to enable non-condensable gases from the cooling unit or
the steam condensing chamber to be discharged outside of the condenser whereby
condensing efficiency of the steam contained in the non-condensable gases which flow
into the cooling unit or the steam condensing chamber is improved.
A condenser tube nest layout based on church window principle is described in
U.S patent Application publication No. US 2001/0025703A1. The condenser consists of
at least one bundle with multiplicity of tubes arranged parallel to one another, the bundle
sub-divided into an upper sector and lower sector. A condensate discharge element is
arranged in the bundle between the upper sector and the lower sector. This arrangement
helps in preventing excessive blockage of steam paths due to condensate raining down.
However, all the prior art tube nest configurations are evolved mainly for single pass
steam condensers and these configurations cannot be optimally used for two-pass
condensers. Although US 5649590 adapts branching spikes concept, the condenser has
the disadvantage of possible air pockets formation in spikes as steam enters from both
sides of the spike.

The tube nest of US 5960867, in which a plurality of flow passages extend from
outer circumference towards the extracting opening, suffers from lack of vent lanes.
The tube nest developed based on church window concept and as disclosed in US
2001/0025703, has thick bundle width which results in higher steam side pressure drop.
In a two pass condenser, the available average temperature potential between
steam and cooling water is drastically different between the tubes in the first pass and in
the second pass . Due to this phenomenon, steam condensation in the first pass is nearly
66% and that in the second pass is 34%. None of the above prior art has considered this
phenomenon and hence they are basically applicable to single pass condenser
OBJECTS OF THE INVENTION:
It is, therefore an object of this invention to propose a compact two pass steam
condenser having atleast one improved tube-nest configuration for reducing loss of
steam pressure by allowing uniform steam distribution around the tube nest including
better accessibility of steam to all the tubes.
Another object of the invention is to propose a compact two pass steam condenser
having atleast one improved tube-nest configuration for reducing loss of steam pressure
which eliminates the disadvantages of prior art devices.
Yet another object of this invention is to propose a compact two pass steam
condenser having atleast one improved tube-nest configuration for reducing loss of steam
pressure which provides proper venting of non-condensables including effective
discharge of the non-condensables through an air cooling section.

A further object of the invention is to propose a compact two pass steam
condenser having atleast one improved tube-nest configuration for reducing loss
of steam pressure which promotes better deaeration of condensate
A Still further object of the invention is to propose a compact two pass steam
condenser having atleast one improved tube-nest configuration for reducing loss
of steam pressure in which the tube sheet area is optimally utilized.
SUMMARY OF THE INVENTION :
Accordingly, there is provided a two-pass steam condenser for condensing steam
in power/chemical plants, the condenser comprising, a steam inlet through which
steam is received; atleast one tube nest consisting of two distinct bundles
disposed one above the other, each bundle comprising a plurality of cooling
tubes for condensing the steam received through the steam inlet ; the top
bundle forming a vertical finger type of configuration with converging steam flow
passages in between the fingers and diverging non-condensable flow passages
within the fingers and the bottom bundle forming a horizontal finger type of
configuration and representing respectively a second pass and a first pass, the
second pass being enabled to maintain a higher temperature for the cooling
water flowing through the tubes of the condenser; at least one non-condensable
gas extracting tube connected to a suction pump through which non-
condensable gas contained in the steam is extracted; a condensate outlet
through which condensate condensed by the cooling tubes is discharged and a
vessel surrounding the tube nest. The cooling tubes are arranged in two distinct
bundles separated by a pass-partition to form converging flow passages for the
steam; the top bundle having vertical flow passages and the bottom bundle
horizontal flow passages; the top bundle receives steam directly from the inlet

and the bottom bundle , in case of a double section receives steam from the inlet
at a first phase through a central zone , and through a passage between the
vessel and the atleast one tube nest at a second phase, in case of a single
section type of condenser, the steam being received from a passage between the
vessel and at least one tube nest; at least two steam lanes each having width
selected based on the steam quantity to maintain a comparable velocity in the
steam lanes which in the second and first passes gradually decreases with the
steam flowing into the tube regional of the nest; 5 to 10% of the cooling tubes
are arranged in a zone located in the bottom bundle to form an air cooling zone
for cooling the non condensable gases from a main cooling unit.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS.
Figure 1 - Shows a schematic diagram depicting a compact steam condenser,
indicating configuration of the cooling tubes on a tube plate, according to the
present invention.
Figure 2 - Shows the streamlines of steam flow in a condenser in accordance
with the invention.
Figure 3 - Shows the flow of steam with high concentration of non-condensables
according to the invention.
Figure 4 - Shows horizontal segments of the tube nest in a compact condenser
according to the invention.
Figure 5 - Shows a condensate outlet (hot-well)

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION:
As shown in figure-1, a plurality of cooling tubes (1) is arranged on a tube plate (2) in
two bundles, a top bundle (3) which represents a second pass with relatively higher
temperature of cooling water flowing through the tubes (1) of the condenser,
accommodates 50% of total number of the tubes (1) of the tube nest, and the remaining
tubes (1) are arranged in a bottom bundle (10) which represents a first pass (10) with
relatively lower temperature of cooling water flowing through the tubes (1) of the
condenser. A pass partition (9) separates the first (10) and the second passes (3). An air
cooling zone (11) is located in the first pass (10). Atleast two steam lanes (4,12) are
provided, the width of the atleast two steam lanes (4,12) in the second and first passes
(10,3) decrease gradually as steam flows into the tubed region of the nest. A contour of
the steam lanes is such that uniform velocity is maintained in the steam lanes (4,12). The
widths of the steam lanes (4,12)) are selected based on the steam quantity so as to
maintain comparable velocities in the steam lanes (4,12) of the first and second passes
(10,3). Steam enters the first pass (10) through a central lane (6). A plurality of Vent
lanes (5 & 13) are provided in the first and second passes (10,3) which guide the steam
with high concentration of non-condensables to the air cooling zone (11). A first baffle
plate (7) provided to prevent direct steam entry to the air cooling zone (11) from the top.
A plurality of second baffle plate (8) disposed in the pass partition (9) to prevefit the
steam having direct access through the pass partition (9) to the air cooling zone (11). A
plurality of third baffle plates (14) provided to direct the non-condensables into the
tubed regions of an air-cooler and restrict a bypassing of the non-condensables directly
to a suction pump(18). A fourth baffle plate (15) restricts the passage of the steam from
the bottom of the tube nest (1) to the air cooling zone (11).

• Streamlines of steam flow are shown in Fig.2. The nest configuration allows uniform
steam distribution around the tube nest (3,10) and provides an improved accessibility of
steam to all the tubes (1) and thus the steam pressure loss is minimised. The number of
rows of the tubes (1) crossed by steam is also selected based on steam quantity entering
the bundles (3,10). As the steam quantity to the first pass (10) is approximately 66% of
total steam, the number of tubes (1) crossed in the first pass (10) are selected less
compared to the number of tubes (1) in the second pass(3). Thus pressure balance
including low steam pressure loss are achieved by the invention. A vessel (17) surrounds
the tube nest (3,10).
Fig. 3 shows the flow of steam with high concentration of non-
condensables.Steam enters through inlet(19) and as it passes through tubes (1), steam gets
condensed and concentration of non-condensables increases. By provision of the
plurality of vent lanes (5,13), the steam with high conentration of non-condensables from
all parts of the nest are directed towards the air cooling zone (11). The air cooling zone
(11) is located in the first pass (10) as the cooling of the non-condensabies and the
condensation of steam in the non-condensable mixture are more effective in the first pass
(10). A condensate outlet (16) is provided via which condensate condensed by the
cooling tube is discharged. The converging configuration of the air cooling zone (11)
towards the exit provides better connective heat tranasfer and aids improved cooling of
non-condensable mixture. Proper cooling of the non-condensabks helps in reduction in
their volume flow and ensures effective discharg by a suction pump (18) or sn ejector
connected to the exit of the air cooling zone (11)

Streamlines of steam flow are shown in Fig.2. The nest configuration allows uniform
steam distribution around the tube nest (3,10) and provides an improved accessibility of
steam to all the tubes (1) and thus the steam pressure loss is minimised. The number of
rows of the tubes (1) crossed by steam is also selected based on steam quantity entering
the bundles (3,10). As the steam quantity to the first pass (10) is approximately 66% of
total steam, the number of tubes (1) crossed in the first pass (10) are selected less
compared to the number of tubes (1) in the second pass(3). Thus pressure balance
including low steam pressure loss are achieved by the invention. A vessel (17) surrounds
the tube nest (3,10).
Fig. 3 shows the flow of steam with high concentration of non-
condensables. Steam enters through inlet(19) and as it passes through tubes (1), steam gets
condensed and concentration of non-condensables increases. By provision of the
plurality of vent lanes (5,13), the steam with high conentration of non-condensables from
all parts of the nest are directed towards the air cooling zone (11). The air cooling zone
(11) is located in the first pass (10) as the cooling of the non-condensables and the
condensation of steam in the non-condensable mixture are more effective in the first pass
(10). A condensate outlet (16) is provided via which condensate condensed by the
cooling tube is discharged. The converging configuration of the air cooling zone (11)
towards the exit provides better connective heat transfer and aids improved cooling of
non-condensable mixture. Proper cooling of the non-condensables helps in reduction in
their volume flow and ensures effective discharge by a suction pump (18) or an ejector
connected to the exit of the air cooling zone (11).

The present invention has features, which promote better deaeration in the steam
condenser. A plurality of the tubes (1) of said tube nest, is configured as horizontal
segments as indicated in Fig.4 have counter flow steam path with respect to the
condensate flow. This feature helps in condensate heating and consequent liberation of
dissolved oxygen from the condensate. The direct impingement of live steam on hot-well
surface through the central steam lane (6) helps in promoting better deaeration. The
positive discharge of non-condensables through the vent lanes (5,13) as described above
contributes in improving deaeration of steam.
One tube nest can be used in a single section condenser and two tube nests as
mirror images to each other, as shown in Fig. 5 can be used in a double section
condenser.
A typical power plant condenser with the present invention gives an improvement
of 15% in heat flux compared to conventional designs due to reduced steam pressure loss
and improved venting system. This leads to a reduction in exhaust pressure of turbine and
consequent improvement in power generation. Alternatively, for the same exhaust
pressure of steam turbine, the number of cooling tubes can be reduced with the present
invention and achieve savings in material cost.

WE CLAIM :
1. A two-pass steam condenser for condensing steam in power/chemical
plants, the condenser comprising, a steam inlet (19) through which steam
is received;
atleast one tube nest consisting of two distinct bundles (3,10) disposed
one above the other, each bundle (3,10) comprising a plurality of cooling
tubes (1) for condensing the steam received through the steam inlet (19);
the top bundle (3) forming a vertical finger type of configuration with
converging steam flow passages (4) in between the fingers and diverging
non-condensable flow passages (5) within the fingers and the bottom bundle
(10) forming a horizontal finger type of configuration and representing
respectively a second pass and a first pass, the second pass being enabled to
maintain a higher temperature for the cooling water flowing through the
tubes of the condensor;
at least one non-condensable gas extracting tube connected to a suction
pump (18) through which non-condensable gas contained in the steam is
extracted; a condensate outlet (16) through which condensate condensed by
the cooling tubes (1) is discharged and a vessel (17) surrounding the tube
nest (3,10), characterized in that:
the cooling tubes (1) are arranged in two distinct bundles (3,10)
separated by a pass-partition (9) to form converging flow passages for
the steam; the top bundle (3) having vertical flow passages and the
bottom bundle (10) horizontal flow passages;
the top bundle (3) receives steam directly from the inlet (19) and the
bottom bundle (10), in case of a double section receives steam from
the inlet (19) at a first phase through a central zone (6), and through a
passage between the vessel (17) and the atleast one tube nest (3,10)
at a second phase, incase of a single section type of condenser, the
steam being received from a passage between the vessel (17) and at
least one tube nest (3,10);

at least two steam lanes (4,12) each having width selected based on
the steam quantity to maintain a comparable velocity in the steam
lanes (4,12) which in the second and first passes gradually decreases
with the steam flowing into the tube regional of the nest;
5 to 10% of the cooling tubes are arranged in a zone located in the
bottom bundle (10) to form an air cooling zone (11) for cooling the
non condensable gases from a main cooling unit.
2. The condenser as claimed in claim 1, wherein the steam with high
concentration of non-condensate gases is guided by a plurality of
diverging passages (5,13) created in the tube nest (3,10) from different
zones of the cooling unit to the air cooling zone (11), the air cooling zone
(11) converging in the steam flow direction so as to achieve an effective
cooling of the non-condensable gases.
3. The condenser as claimed in claim 1, wherein a plurality of baffle plates
(14) is provided between the side walls of the vessel (17) and on the air-
cooling zone (11) to direct non-condensables into tubed regions of air-
cooling zone and thus preventing non-condensable gases bypassing the
air cooling zone and directly entering suction pump (18).
4. The condenser as claimed in claim 1, wherein the pass-partition (9) is
utilized as the steam passage (4,12).

5. The condenser as claimed in claim 1, wherein a plurality of baffles
(7,8,15) at selected locations is provided to restrict steam bypassing to
the air cooling zone (11).
6. The condenser as claimed in any of the preceding claims, wherein a
plurality of the cooling tubes (1) arranged in horizontal configuration to
provide better interaction of steam and condensate due to counter flow
conditions of steam and condensate falling down from the top tubes of
the tube nest (3,10) thereby promoting effective deaeration of
condensate.
7. A two-pass steam condenser for condensing steam in power and
chemical plants as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to a two-pass steam condenser for condensing steam in
power/chemical plants, the condenser comprising, a steam inlet (19) through
which steam is received; atleast one tube nest consisting of two distinct
bundles (3,10) disposed one above the other, each bundle (3,10) comprising
a plurality of cooling tubes (1) for condensing the steam received through the
steam inlet (19); the top bundle (3) forming a vertical finger type of
configuration with converging steam flow passages (4) in between the fingers
and diverging non-condensable flow passages (5) within the fingers and the
bottom bundle (10) forming a horizontal finger type of configuration and
representing respectively a second pass and a first pass, the second pass
being enabled to maintain a higher temperature for the cooling water flowing
through the tubes of the condensor; at least one non-condensable gas
extracting tube connected to a suction pump (18) through which non-
condensable gas contained in the steam is extracted; a condensate outlet
(16) through which condensate condensed by the cooling tubes (1) is
discharged and a vessel (17) surrounding the tube nest (3,10). The cooling
tubes (1) are arranged in two distinct bundles (3,10) separated by a pass-
partition (9) to form converging flow passages for the steam; the top bundle
(3) having vertical flow passages and the bottom bundle (10) horizontal flow
passages; the top bundle (3) receives steam directly from the inlet (19) and
the bottom bundle (10), in case of a double section receives steam from the
inlet (19) at a first phase through a central zone (6), and through a passage
between the vessel (17) and the atleast one tube nest (3,10) at a second
phase, incase of a single section type of condenser, the steam being received

from a passage between the vessel (17) and at least one tube nest (3,10); at
least two steam lanes (4,12) each having width selected based on the steam
quantity to maintain a comparable velocity in the steam lanes (4,12) which in
the second and first passes gradually decreases with the steam flowing into
the tube regional of the nest; 5 to 10% of the cooling tubes are arranged in a
zone located in the bottom bundle (10) to form an air cooling zone (11) for
cooling the non condensable gases from a main cooling unit.