Air cooled condenser

A method for uniformly distributing the vapor conducted from a parallel flow condenser section of an air cooled condenser into the dephlegmator cubes of a subsequently arranged countercurrent condenser includes throttling gaseous fluids present at the ends of the dephlegmator tubes on the collector side when the gaseous fluids are withdrawn from the dephlegmator tubes. In the air cooled condenser for carrying out the method, at least the predominant majority of the dephlegmator tubes has resistance elements at or near where they connect to the gas collector.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for uniformly distributing the 
vapors leaving the parallel flow condensing section of an air cooled 
condenser into the dephlegmator tubes of a subsequently arranged 
countercurrent condensing section. The present invention also relates to 
an air cooled condenser for carrying out the method. 
2. Description of the Related Prior Art 
The use of air for the condensation of turbine vapor has long been known in 
the art. In the case of direct air condensation, the turbine vapor is 
condensed in fin tube elements arranged in parallel followed by the 
condensate being returned to the feed water cycle. The interior of the fin 
tube elements is under negative pressure, and entrained gases which cannot 
be condensed are withdrawn. The cooling air flow is generally produced by 
means of fans or, less frequently, by natural draft. 
The air cooled condensers are arranged in modular fashion with the fin tube 
elements arranged vertically, horizontally or in an inclined A-like or 
V-like configuration, 
The roof-like or A-like configuration is widely used. In that case, the fin 
tube elements form two legs of a triangle and the fans form the third leg 
at the base of the triangle. 
A major problem in air cooled condensers is the fact that freezing of the 
fin tube elements must be prevented during the winter months, particularly 
during operation with partial load, and the danger of freezing must be 
reliably eliminated with the use of apparatus which is as simple as 
possible and inexpensive. 
Two configurations of air cooled condensers are common. They are the 
parallel flow condenser configuration and the countercurrent condenser 
configuration, also referred to as a dephlegmator. 
In the case of the parallel flow condenser, the vapor flows downwardly in 
fin tubes fed from an upper distribution duct. The pressure drop in the 
fin tubes causes a temperature drop of the saturated vapor. 
This temperature reduction essentially results in a drop of the operative 
temperature difference between the vapor and the cooling air, so that the 
efficiency of heat removal of the condenser is reduced. 
Another more serious consequence is the fact that vapor in the fin tubes is 
completely condensed before it reaches the tube ends. This may occur in 
the case of low air temperatures or when operating under partial load. In 
that case, the condensate subcools very quickly and gases which cannot be 
condensed collect in the remaining tube sections in which no vapor is 
present. This leads to an increase of the oxygen absorption of the 
condensate which, in turn, may lead to corrosion problems. Moreover, 
subcooling of the condensate may result in freezing of the condensate when 
the air temperature is below 0.degree. C., so that there is the danger 
that the cooling tubes are damaged or that they burst. 
DE-AS 10 44 125 already discloses a proposal which has the purpose of 
preventing the freezing of the condensate in parallel air cooled 
condensers. In that case, the heat exchanger surfaces of the fin tubes are 
adjusted to the available temperature drop between the vapor entry 
temperature and the cooling air temperature in such a way that the 
condensation is concluded as uniformly as possible in all tube rows at a 
small distance from the ends of the tube rows where they connect to the 
condensate collection manifold. In order to achieve this vapor 
distribution, devices for throttling the vapor intake in the form of 
nozzles or shields are provided at the inlet side of the fin tubes. 
It is a disadvantage that these shields are arranged at the inlet side 
because the entire vapor to be condensed in the condenser must flow 
through these shields and is distributed with a pressure loss into the fin 
tubes which are arranged one behind the other on the air side. 
In addition, the disadvantages resulting from subcooling of the condensate 
can be prevented by using the above-mentioned countercurrent condenser 
configuration. 
In that type of operation, the vapor is introduced from below into the fin 
tubes and is conducted in a countercurrent flow against the condensate 
which is draining off. Since the vapor continuously transfers heat to the 
condensate draining in the opposite direction, there is the advantage that 
subcooling of the condensate cannot occur when the apparatus is correctly 
dimensioned. 
The countercurrent condenser configuration has the disadvantage of 
operating at a reduced heat transfer coefficient. Moreover, the possible 
condensation rate of a countercurrent condenser can be reduced if slug 
flow conditions exist which produce a holdup of the condensate in the fin 
tubes. Slug flow conditions are that state of operation in which the vapor 
introduced from below into the dephlegmator tubes and flowing upwardly can 
no longer flow against the mass of the downwardly flowing condensate. This 
causes a condensation holdup in the fin tubes. 
A solution which has proved successful in practice is the combination of a 
parallel flow condenser and a countercurrent condenser, as disclosed, for 
example, in DE-PS 11 88 629. 
In that case, fin tube elements operating as dephlegmators are arranged 
downstream of the fin tube elements operating as parallel flow condensers. 
The fin tube elements operating as dephlegmators are simultaneously 
arranged in groups in cooling sectors in such a way that, when operating 
under partial load and at external air temperatures below the freezing 
point during the winter months, at least a portion of the element groups 
operating as parallel flow condensers can be switched off on the vapor 
side as well as on the air side, so that the vapor is condensed 
predominantly in the element groups operating as dephlegmators. While the 
countercurrent condensers have a poorer efficiency as compared to the 
parallel flow condensers, they have the advantage that they do not freeze 
even when operating under partial load because of the continuous contact 
of the downwardly flowing condensate with the upwardly flowing vapor. 
The so called condensation end of the vapor is then located in the 
countercurrent condenser, so that subcooling of the condensate is 
generally avoided. The system is regulated by switching off individual 
cooling sectors or by changing the cooling air flow. 
In order to achieve a uniform distribution of the vapor flow introduced 
into the vapor distribution chamber of a countercurrent condenser with a 
relatively low flow speed, it is additionally known from DE-GM 18 73 644 
to provide an intermediate sheet with openings in the vapor distribution 
chamber. The entire cross sectional area of the openings is smaller than 
the total cross sectional area of the condenser tubes. 
This solution also has the purpose of regulating and uniformly distributing 
the vapor entering the individual condenser tubes. 
The combined arrangement of fin tube elements as condensers and 
dephlegmators has proved successful in operation. However, in order to be 
able to handle very large load variations, particularly low vapor 
quantities during the winter months, without the danger of subcooling or 
freezing, it is also necessary in this arrangement to provide additional 
means for regulating and controlling the flow and quantity of the cooling 
air and the exhaust vapor. 
It must be taken into consideration in this connection that, due to the 
parallel arrangement of all fin tube elements on the vapor side as well as 
on the condensate side, and in the case of admitting varying quantities of 
cooling air to the various groups, the pressure loss of the vapor flow is 
equal in all fin tube elements. This has the consequence that more vapor 
flows through the less strongly cooled group than could be condensed in 
this group, while simultaneously less vapor flows through the more 
strongly cooled groups than could be condensed in those groups. While the 
effect mentioned first has the disadvantage that excess vapor is withdrawn 
through the exhaust line to the vacuum system and, thus, the vacuum is 
negatively affected, the effect mentioned last has the disadvantage that 
the vapor is not admitted fully over the entire length of the fin tube 
elements and, consequently, there is still the danger of freezing in the 
case of very low ambient air temperatures. 
In addition, particularly in the case of high loads, a condensate holdup 
may occur in the cooling tubes of the counterparallel flow condenser, with 
the result that vapor penetrates into the upper non-condensible gas 
collector and then enters the fin tubes from above producing so called 
cold pockets in the fin tubes in which inert gases collect, so that the 
efficiency of the countercurrent condenser is reduced. 
SUMMARY OF THE INVENTION 
Therefore, it is the primary object of the present invention to provide a 
method of operating an air cooled condenser with at least one parallel 
flow condenser and a countercurrent condenser arranged downstream of the 
parallel flow condenser, and to improve such an air cooled cooler in a 
simple manner in such a way that, while achieving a high total efficiency, 
an adaptation to strongly varying exhaust vapor quantities and large 
temperature differences of the cooling air is possible, wherein especially 
the inflow of vapor into the vacuum system (non-condensibles ejection 
system) is reduced and a uniform and complete flow into the dephlegmator 
tubes is achieved. 
In accordance with the present invention, any gaseous fluids present at the 
ends of the dephlegmator tubes on the collector side are throttled when 
they are withdrawn from the dephlegmator tubes. 
In the air cooled condenser according to the present invention, at least 
the predominant majority of the dephlegmator tubes has resistance elements 
in the areas of their ends at the gas collector side. 
Accordingly, it is the essence of the present invention to prevent large 
quantities of gaseous fluids from entering the gas collection chamber in 
unimpeded fashion from any fin tube. Since the flow is throttled, the 
fluid is uniformly distributed over all dephlegmator tubes, so that the 
entire heat transfer surface area is utilized for condensation. Cold 
pockets or dead zones in which exhaust vapor or condensate could be 
present are avoided. 
The provision of resistance elements at the gas collector ends of at least 
the predominant number of dephlegmator tubes presents an obstacle to the 
exhaust vapor, particularly when excess vapor is present. Consequently, 
the vapor entering the individual dephlegmator tubes from below is 
distributed uniformly. 
The resistance elements may have different shapes and dimensions. For 
example, conically shaped or round bodies are conceivable, as well as 
cap-shaped or plug-shaped structures. However, the use of shields has been 
found practical. The dimensions of the apertures of the shields are always 
selected in such a way that their cross sectional areas are smaller than 
the inner cross sectional areas of the dephlegmator tubes. 
In the case of perforated shields, the size and shape of apertures can 
vary. It is also conceivable that the individual resistance elements 
within a countercurrent condenser are constructed differently. It is 
basically also possible not to equip all fin tubes with resistance 
elements 
The resistance elements can be secured by welded connections, soldered 
connections or adhesive connections. However, other connections are also 
conceivable, for example, a connection by frictional engagement. 
It is advantageous if the same resistance elements are arranged near the 
ends of all cooling tubes. The resistance elements then present an 
obstacle only to the remaining inert gas or the excess vapor. 
Consequently, the transverse distribution of the exhaust vapor in the 
condenser is rendered uniform not only in fin tube elements which are 
composed of only one row of tubes, but also in fin tube elements which 
have a plurality of tube rows. 
However, the resistance elements have the uniformly distributing effect 
only when larger quantities of vapor or inert gas are conducted to the 
upper ends of the tubes of the countercurrent condenser. During normal 
operation, i.e., when the condensation is concluded at the upper ends of 
the tubes, the pressure conditions in the countercurrent condenser are not 
changed by the resistance elements because of the small quantity of inert 
gas to be withdrawn. 
The resistance elements have the purpose of preventing excess quantities of 
vapor from being conducted from the countercurrent condenser into the air 
withdrawal system which would cause overloading of the ejection equipment. 
Accordingly, the resistance elements act only as obstacles to the flow when 
the exhaust vapor reaches the upper ends of the tubes. Consequently, it is 
not the purpose of the resistance elements to regulate the entry of the 
vapor into the individual cooling tubes, but to ensure that the withdrawal 
is carried out uniformly. 
In addition, the resistance elements are capable of preventing return flow 
of the vapor from the upper collection chamber of the countercurrent 
condenser back into the cooling tubes from above. 
One of the significant advantages of the condenser according to the present 
invention is its behavior during regulation, particularly in the case of 
partial load. 
This is because, in the case of partial load, it is not necessary to lock 
and render inoperative entire groups of parallel flow condensers and 
countercurrent condensers by means of appropriate features; rather, it is 
only necessary to switch off the cooling air fans of individual condenser 
groups. This means that a switched-off condenser group remains filled with 
vapor. Only a slight cooling takes place in this condenser group because 
the fans are switched off. In this situation, the resistance elements 
prevent an overload of the ejection equipment which continues to withdraw 
inert gas from the remaining condenser groups which operate under load, 
while vapor is withdrawn from the condenser groups which have been 
switched off. As a result, the vacuum in the air cooled condenser 
continues to be maintained. 
In the case of a change of the load and a consequently required change of 
the condenser output, this change of the condenser output can be carried 
out by switching fans on or off or by regulating the rate of rotation or 
the angle of the blades of the fans. Such a regulation can also be carried 
out in the case of a possible increase of the condenser pressure. In the 
case of a rise of the condenser pressure, more condenser groups can be 
operated or the output of the fans can be increased. On the other hand, 
when the condenser pressure drops, the output of the fans is lowered. 
In accordance with another advantageous embodiment of the present 
invention, the resistance elements are not arranged immediately at the 
ends of the cooling tubes, but rather a short distance from the collector 
ends of the dephlegmator tubes. This creates a separate fin tube section 
downstream of the resistance element. A small amount of fluid continuously 
passes through the resistance element entering the separate fin tube 
section where it is cooled to temperature levels closely approaching the 
temperature of the air entering this section. The fluids passing through 
the resistance element can be water vapor saturated non-condensible gases, 
or a combination of the above, plus pure steam. If only saturated 
non-condensible gases are flowing through the resistance element, the 
vapor fraction of these gases is partially condensed, reducing the load on 
the ejection equipment. If a combination of non-condensible gases plus 
pure steam is flowing through the resistance element, then the steam is 
condense and the vapor fraction in the non-condensibles is partially 
condensed, once again reducing the load on the ejection equipment. 
Therefore, the cooling of the fluids in the separate fin tube section 
downstream of the resistance element has the effect of greatly increasing 
the efficiency of non-condensible gas withdrawal. 
In accordance with a further development of the present invention, the 
resistance elements form at least part of a sheet arranged above the ends 
of the dephlegmator tubes. It is also conceivable to arrange several 
sheets, wherein these sheets may also be displacable relative to each 
other. In this manner, the cross sectional size of the openings is 
adjustable. 
It is also possible to construct the resistance elements in the form of 
nets. The resistance elements can then be part of a net arranged in the 
area of the ends of the dephlegmator tubes or individual net or screen 
inserts may be arranged at the tube ends. Because of the adhesion forces 
acting between the webs of the net and 6he exhaust gas, a self-regulation 
of the shield function and of the flow resistance is possible. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of the disclosure. For a better understanding of the invention, its 
operating advantages, specific objects attained by its use, reference 
should be had to the drawing and descriptive matter in which there are 
illustrated and described preferred embodiments of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 of the drawing show a countercurrent condenser 1 with a lower 
vapor distribution chamber 2 and an upper gas collector 2. The steam 
distribution chamber 2 and the gas collector 3 are connected to each other 
through dephlegmator tubes 4. 
The exhaust vapor A is conducted into the vapor distribution chamber 2 and 
is distributed over the individual dephlegmator tubes 4. Cooling air flows 
transversely against the dephlegmator tubes 4 in the direction denoted by 
L. The exhaust vapor A rises in the dephlegmator tubes 4 and condenses as 
a result of the continuous transfer of heat. The condensate then flows 
downwardly against the upwardly flowing exhaust vapor A. 
The air collected in the gas collecting chamber is withdrawn by means of a 
vacuum system, not shown. 
Because of the different cooling and flow conditions in the dephlegmator 
tubes 4, it is possible that exhaust vapor A and/or saturated inert gas 
can flow into the gas collection chamber 3, wherein the exhaust vapor A 
then partially flows from above into those dephlegmator tubes 4 to which 
less exhaust vapor has been admitted. Consequently, so called cold pockets 
6 are formed in which inert gas is present, so that the efficiency of the 
countercurrent condenser is reduced. 
FIGS. 1a and 2a show the flow directions of the exhaust vapor A and the 
condensate K in the countercurrent condenser 1. The exhaust vapor A flows 
upwardly from the vapor distribution chamber 2 into the dephlegmator tubes 
4. This causes the exhaust vapor A to be cooled and condensed. The 
condensate K produced in this manner then flows downwardly against the 
upwardly flowing exhaust vapor A and is collected at the bottom of the 
vapor distribution chamber 2. 
FIG. 3 of the drawing shows the ends 7a through 7c of three dephlegmator 
tubes 4a through 4c on the side of the gas collection chamber. 
A resistance element in the form of a shield with an aperture 9 is arranged 
above the end 7a of the dephlegmator tube 4a. The aperture 9 has a 
significantly smaller diameter than the diameter Q of the dephlegmator 
tube 4a. 
Another embodiment of a resistance element is illustrated in FIG. 3 in the 
form of a shield 10 at the end 7b of the dephlegmator tube 4b. In this 
case, the shield 10 has two apertures 11 and 12 which are located next to 
each other. 
A resistance element in the form of a shield 13 is inserted into the end 7c 
of the dephlegmator tube 4c. The shield 13 again has only one aperture 14. 
FIG. 4 of the drawing shows a shield plate 15 which is placed directly onto 
a tubesheet 16. Above the ends 7d through 7f of the dephlegmator tubes 4d 
through 4f, resistance elements in form of apertures 17 are provided in 
the shield plate 15. 
FIG. 5 of the drawing again shows the ends 7g through 7i of three 
dephlegmator tubes 4g through 4i having different resistance elements. 
In the dephlegmator tube 4g, a shield 18 incorporating aperture 19 is 
mounted at a short distance away from its end. This produces a subcooling 
section behind the shield 18 which increases the effect of the air 
withdrawal. 
The dephlegmator tube 4h has a resistance element 20 in the form of a 
plug-like insert 22 with an aperture 21. 
In the dephlegmator tube 4i, the resistance element 23 has the form of a 
net insert 24. This net insert 24 may be arranged at the end of the 
dephlegmator tube 4i as shown in the drawing, or the net insert 24 may be 
inserted and arranged a distance away from the end, so that a subcooling 
stretch is also formed in this case. 
FIG. 6 is a perspective illustration of a branch of an air cooled 
condenser. A number of such branches are usually arranged next to one 
another, wherein exhaust vapor is admitted parallel to each of the 
branches. A typical branch is composed of three groups G1, G1 and G3 of 
fin tubes 25 which operate as parallel flow condensers and a group G4 with 
fin tubes 26 which operate as dephlegmators, i.e., countercurrent 
condensers. Fans 27 for producing the cooling air flow are arranged 
underneath the fin tubes 25, 26. 
The steam exhausting from a turbine is transported through a distributing 
line 28 to the fin tubes 25 which operate as parallel flow condensers. In 
the fin tubes 25, the exhaust steam flows downwardly from the distributing 
line 28 in the direction of arrow PF1 and partially condenses. A 
condensate collecting line 29 is arranged at the lower end of the fin 
tubes 25. The exhaust vapor which has not yet been condensed also is 
conducted into the condensate collecting line 29 and is conducted through 
the condensate collecting line 29 to the fin tubes 26 which operate as 
dephlegmators and is conducted from below into the fin tubes in the 
direction of arrow PF2. The upwardly flowing exhaust vapor is conducted 
against condensate flowing downwardly in the direction of arrow PF3. 
A gas collector 30 is provided at the upper end of the fin tube elements 
26. The resistance elements 8, 10, 13, 15, 18, 20, 23 described in 
connection with FIGS. 3, 4 and 5 are installed in the area of the ends of 
the tubes near gas collector 30. 
The gases which cannot be condensed enter the gas collector 30 and are 
suctioned away through a pipe line 31 by a vacuum system. 
The entire condensate produced in the fin tube elements 25 and 26 operating 
as parallel flow condensers and dephlegmators is collected in the 
condensate collecting line 29 and is conducted through a pipe line 32 to a 
condensate collecting tank 33. From the condensate collecting tank 33, the 
condensate is returned into the feed water cycle. 
The resistance elements 8, 10, 13, 15, 18, 20, 23 at the ends 7a through 7i 
of the dephlegmator tubes 4a through 4i at the side of the gas collector 
have the purpose of preventing excess quantities of vapor from reaching 
the air withdrawal system. Consequently, the resistance elements 8, 10, 
13, 15, 18, 20, 23 act as flow limiting means. However, these resistance 
elements become only effective when a certain minimum quantity of exhaust 
vapor A reaches the upper ends 7a through 7i of the dephlegmator tubes 4a 
through 4i. In that situation, the resistance elements 8, 10, 13, 15, 18, 
20, 23 ensure a uniform distribution of the exhaust vapor A which enters 
the individual dephlegmator tubes 4a through 4i from below. 
This uniform distribution positively influences the regulation behavior of 
the condenser, particularly when operating under partial load. It is now 
no longer necessary to switch off entire branches of parallel flow 
condensers and countercurrent condensers. Rather, it is sufficient to 
switch off or lower the output of the cooling air fans 27 of individual 
branches. While the tubes of these branches remain filled with vapor, a 
reduced heat transfer takes place. This prevents the danger of freezing 
and of overloading of the vacuum system. Consequently, the parallel flow 
condenser groups of the air cooled condenser can be regulated without 
requiring additional control and isolation features. A reduced condenser 
output takes place depending on the operational requirements. This makes 
possible a simple regulation and control which can be incorporated in 
existing plants. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the inventive principles, it will be understood 
that the invention may be embodied otherwise without departing from such 
principles.