Note: Descriptions are shown in the official language in which they were submitted.
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Description
Methods for cooling a carrier fluid of an electric power
plant, electric power plants and cooling system
The present invention concerns methods for cooling a carrier
fluid, which carrier fluid is used to drive a turbine in an
electric power plant. The invention also concerns electric
power plants with a carrier circuit with a carrier fluid
which carrier fluid in operation drives a turbine of the
power plant. Furthermore, the invention concerns a cooling
system for such power plants
In electric power plants a typical way of how to generate
power out of heat is to bring a carrier fluid to a certain
heat level and thus to provide it with a certain level of ki-
netic energy. The carrier fluid, such as water, evaporates
and becomes vapour. The water, which is put under a consider-
able pressure of about 270 bar, is converted into vapour,
which means additionally increasing the volume of the carrier
fluid. Thus, the vapour has enough energy to drive a large
turbine the movement of which will then move the generator.
After driving the turbine this steam has to be cooled down,
which is usually done in a condenser. Such condenser is often
a heat exchanger with a cooling circuit along which a carrier
circuit with the carrier fluid is led. Thus, the carrier cir-
cuit is a pipe system which is connected to the turbine, the
cooling circuit is filled with cooling liquid which is
brought into indirect contact with the carrier fluid and
which is considerably cooler than the carrier fluid before
condensation. Part of the heat of the carrier fluid, i.e. the
steam, is thus transferred to the cooling liquid in the cool-
ing circuit so that the steam becomes water again.
In today's power plants using such technology, in order to
cool down the temperature within the cooling circuit, use is
made of wet cooling towers or of dry cooling towers. In wet
cooling towers part of the cooling liquid, again typically
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water, will be evaporated and released into the air. The
other part of the cooling fluid may either be reused within
the cooling circuit or released into a river from which even
colder water is extracted in return in order to feed the
cooling circuit again with fresh cooling water at river tem-
perature.
Such a power plant according to the state of the art is de-
picted in Fig. 1. A power plant 2 some components of which
are schematically shown in this figure has a carrier circuit
1 and a cooling circuit 11. In the carrier circuit 1 carrier
fluid 5, in this case water 5, respectably water vapour is
pumped through a pipe system. by means of a carrier circuit
pump 3. In order to cool the water vapour 5 down to a consid-
erably lower temperature in order to transform it into liquid
water 5 again, a heat exchanger 9 is used. The condensated
water is pumped off by a carrier circuit pump 3. The heat ex-
changer 9 is also connected to the cooling circuit 11 with
cooling fluid 13, namely cooling water 13. The cooling water
13 is extracted from a river 27 and pumped by a cooling cir-
cuit pump 23 to the heat exchanger 9. Before reaching the
heat exchanger 9 the cooling water 13 has about the tempera-
ture of the river 27. After leaving the heat exchanger 9 the
cooling water 13 has extracted a lot of heat from the water
vapour 5 in the carrier circuit 1. It is therefore considera-
bly hotter than before and also needs to be cooled down in
order to be led back into the river 27. For that purpose a
wet cooling tower 19 is used. Here the hot cooling water 13
from the cooling circuit 11 is sprayed into the tower whilst
air 17 is ventilated in the cooling tower 19. Steam clouds 21
result from this process while the rest 25 of the cooling wa-
ter 13 is led back into the river 27 at a considerably lower
temperature level than before entering the wet cooling tower
19.
According to that principle, the a considerable "" ? portion
of cooling water 13 that was used to condense the water va-
pour 5 in the heat exchanger 9 will evaporate into the air in
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the wet cooling tower 19. This provides for a very high cool-
ing efficiency as there result considerably lower tempera-
tures of the remaining rest 25 of the cooling water 13. As
the efficiency of the power plant 2 depends directly on the
ability of this cooling system to cool down the carrier fluid
5, this kind of condenser system provides for a high power
plant efficiency overall. However, wet cooling towers consume
large quantities of water. Depending on the ambient condi-
tions that consumption reaches values well above 500 kg/s of
water for a 500 MW power plant.
Therefore, an alternative to wet cooling towers are a so-
called dry cooling towers the principle of which will be de-
scribed with reference to Fig. 2. A dry cooling tower 33 di-
rectly cools down a carrier fluid 5 within a carrier circuit
1. The carrier fluid 5 comes from a turbine 29 in a power
plant 2. The turbine 29 drives a generator 31 which generates
electric power from the rotation of the turbine 29. Within
the dry cooling tower 33 the water 5 is led through a pipe
system 37, which functions as a fin-tube heat exchanger. In
order to cool the pipe system 37, a ventilator 35 provides
for fresh air which is ventilated around the pipe system 37
so that a constant stream of air 17 is led around the pipe
system 37. The carrier fluid 5 thus slowly cools down in the
pipe system 37 and can be pumped back to a heating unit (not
shown) by means of a carrier circuit pump 3. Such heating
unit may comprise a heating chamber in which substances (oil,
coal, waste and other burnable materials) are burnt or may
comprise a nuclear reactor or a solar-thermal field.
Dry cooling towers 35 do not necessarily require water sup-
ply, however they are limited in their effectivity by the am-
bient temperature. High ambient temperature will result in a
less efficient thermodynamic process as the condenser tem-
perature in the dry cooling tower 35 and thus the respective
pressure at the turbine 29 exit will increase.
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It is also possible to combine both a wet cooling tower 19
and a dry cooling tower 35 within one power plant. However,
there is still a certain dilemma for the operation of any
power plants based on either or both cooling technologies. In
some regions water is scarce and/or the air is very hot at
peak times. Usually both these effects can be found at the
same time. These arid places, such as deserts, however have
the advantage that usually a lot of solar energy is readily
available. Thus, it proves to be a major problem to provide
for an effective cooling system while enough heating energy
would theoretically be available at very low costs.
It is the object of the invention to optimise further the
cooling processes for condensation power plants. In particu-
lar, it is the object of the invention to preferably reduce
the consumption of water or indeed any other cooling fluid
during such process.
This object is met by a method according to claim 1, by a
method according to claim 7, by an electric power plant ac-
cording to claim 13 and also according to claim 14.
According to a first embodiment of the invention, the method
of the above-mentioned kind is enhanced by the fact that at
least part of a cooling process is realized by leading the
carrier fluid and/or a cooling fluid for cooling the carrier
fluid underground a soil to a depth in which the soil is sub-
stantially cooler than the ambient air. In other words, use
is made of an underground region where the carrier fluid
and/or the cooling fluid is cooled. The thermal intertia of
the underground soil are thus used. Even in deserts, the un-
derground soil is relatively cold in comparison with daytime
ambient temperature above ground which is mainly due to a
strong cooling effect at night times.
Two principles may be used in the context of this embodiment:
Direct cooling of the carrier fluid can be realized by rout-
ing the carrier circuit of this carrier fluid through the un-
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derground region. Indirect cooling means that a cooling fluid
such as water or another fluid with a high heat capacity is
routed through pipes in the underground. This cooling fluid
then cools the carrier fluid in a heat exchanger.
5
The method according to the invention may be realized instead
of using evaporation or ventilation techniques as described
above or in addition to using any of such techniques. Thus,
an underground region below the surface level of the soil in
the area of the power plant is used as a cooling region in
which the carrier fluid and/or the cooling fluid is cooled at
least partially.
As for the definition of "underground", essentially any re-
gion below the surface of the soil can be considered to be
underground. For the purpose of the invention it is necessary
to cool the carrier fluid and/or the cooling fluid so that
the underground region must be substantially cooler than the
ambient air, i.e. the air above ground. That means that there
is at least a temperature difference of 10 C, more preferably
20 C between the ambient air and the underground region in
which the cooling takes place. It is further preferred to
lead the carrier fluid and/or the cooling fluid in an under-
ground region which is at least 0.5 m, more preferably at
least 1 m below the surface level of the soil. In this region
pipes for transporting the fluid are led along a certain
length so that the temperature of the underground region will
absorb effectively some of the higher temperature of the
fluid. Such length of pipes is preferably at least 10m, more
preferably at least 20m, but the pipes need not necessarily
be led in only direction but may comprise turns and windings
for example in the way of a typical heat exchanger. As for
the carrier fluid as well as for the cooling fluid, they may
comprise a liquid such as water and/or a gas such as air.
They may comprise the same material but may also comprise
different materials, for instance water as the carrier fluid
and oil as the cooling fluid. The cooling circuit in which
the cooling fluid is transported may also comprise several
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separate cooling sub-circuits so that for instance a first
cooling fluid is cooled down by a second cooling fluid in a
heat exchanger or the like.
According to a second embodiment of the invention such cool-
ing effect may also be achieved by means of a method of the
above-mentioned kind, whereby at least part of a cooling
process is realized by supplying at least some of the carrier
fluid, and/or at least some of a cooling fluid used to cool
the carrier fluid, from a cold storage which stores fluid at
a significantly lower temperature than the temperature of the
carrier fluid in the turbine. Such cold storage may be situ-
ated underground as described above, but may also be above
ground level and then preferably comprise a thermally iso-
lated container. This container is preferably fed with a liq-
uid or gas which has been cooled underneath the soil. How-
ever, it is also possible to have a cold storage which re-
ceives fluid at a low temperature level at night time and
then stores the cold temperature during daytime. For in-
stance, such cold storage may be realized as a large basin
which is opened at night so that its content (i.e. the fluid)
becomes cold and which is closed and thermally isolated dur-
ing daytime in order to maintain the low temperature level
for as long a time as possible. The cold storage can also be
fed with fluid which has been cooled down by a cooling proc-
ess above ground (e.g. by air to liquide heat exchange, which
means using dry cooling techniques) and/or underground (i.e.
according to the first embodiment of the invention).
Both principal embodiments of the method according to the in-
vention have one uniting principle: low temperature is stored
or provided in a certain place. In the first embodiment, the
low temperature is stored in the underground region due to
the low underground temperatures which are available anyway.
In the second embodiment the invention makes use of a spe-
cially designated container in which the low temperature is
artificially preserved. In both embodiments of the invention
no evaporation techniques are necessary and the loss of water
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due to cooling and condensation is considerably reduced. A
ventilation technique is also not essential, although such
technology can be used in addition to the cooling technology
according to the invention.
Accordingly, depending on the use of either of the embodi-
ments described above, an electric power plant of the above-
mentioned kind can be realised in two different ways, which
may be combined or used separately.
In accordance with the first embodiment of the method accord-
ing to the invention, an electric power plant of the above-
mentioned kind can be enhanced by the fact that at least part
of the carrier circuit and/or part of at least one cooling
circuit with a cooling fluid used to cool the carrier fluid
is led underground to a depth that is substantially cooler
than the ambient air.
For that purpose the power plant preferably comprises under-
ground pipes and/or tanks. The underground region serves as a
"heat sink" or as a kind of low temperature reservoir. Such
pipes or tanks are preferably made of a material with a high
heat transfer coefficient so that transfer of heat from the
fluid into the underground region outside the pipe or tank is
as effective as possible. Therefore, the heat transfer coef-
ficient of such pipe or tank is preferably above 15 W/mK,
most preferably above 100 W/mK, i.e. at least in the range of
the transfer coefficient of metals such as stainless steel or
above. It is thus most preferred to use thermally unisolated
pipes or tanks. The heat transfer can further be even en-
hanced by heat transfer enhancement means such as fin tubes.
Secondly, i.e. additionally or alternatively an electric
power plant of the above-mentioned kind can be enhanced by
the fact that at least part of the carrier fluid and/or at
least part of a cooling fluid used to cool the carrier fluid
is stored in a cold storage at a significantly lower tempera-
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ture than the temperature of the carrier fluid in the tur-
bine.
Such cold storage may be realised as a container or tank
above ground or below ground level. It may be incorporated
into buildings of the power plant in order to reduce the need
for thermal isolation but may also be situated outside such
buildings in order to be further away from the heating proc-
ess. Such container is preferably thermally isolated so that
little heat will be transferred into the inside of the con-
tainer which in return means that the low temperature inside
the cold storage is maintained as long as possible. Espe-
cially it is preferred that the cold storage will keep the
temperature of its contents at a certain level which does not
exceed 20 C above its lowest level during the course of one
day. This is the preferred value for the cold storage in a
state in which it is filled with the designated fluid during
a day on which no fluids are inserted or taken out of the
cold storage.
As outlined above, both embodiments of the power plant ac-
cording to the invention also follow the common principle
which has been described with reference to the two embodi-
ments of methods according to the invention. In a combination
of these embodiments, the cold storage is supplied under-
ground under the surface of the soil and thus need not neces-
sarily be equipped with isolating means because the isolation
is actually realised by the surrounding soil instead of addi-
tional isolating material.
Lastly, the invention also concerns a cooling system for an
electric power plant in which at least part of a carrier cir-
cuit with a carrier fluid and/or part of at least one cooling
circuit with a cooling fluid used to cool the carrier fluid
is led underground to a depth that is substantially cooler
than the ambient air and/or in which cooling system at least
part of the carrier fluid and/or at least part of the cooling
fluid is stored in a cold storage at a significantly lower
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temperature than the temperature of the carrier fluid in the
turbine.
With such a cooling system according to the invention, power
plants can be re-equipped so as to become a power plant ac-
cording to the invention of either of the embodiments de-
scribed above.
Particularly advantageous embodiments and features of the in-
vention are given by the dependent claims, as revealed in the
following description. Thereby, features revealed in the con-
text of one of the methods may also be realized in the con-
text of the respective other method and/or in the context of
any one of the embodiments of the electric power plant ac-
cording to the invention unless the contrary is explicitly
stated.
It is particularly preferred that the cooling is carried out
in an electric power plant in a hot environment. Such a hot
environment is particularly given in desert surroundings or
in similarly arid environments. They can be characterised by
the fact that during at least 100 days of the year a top tem-
perature of 40 C is reached. In such circumstances water is
particularly scarce. This implies that the water consumption
of power plants directly competes with water needs for food
production and urban life so that it is likely that local
life and food production will have the highest priority over
power generation. Therefore, power plants in such regions can
only be successfully operated if they have a very low water
consumption foot print, i.e. as little water losses in opera-
tion as possible. Using the methods according to the inven-
tion is particularly helpful in order not to waste valuable
water for power generation. Such water can now be saved for
other purposes such as agriculture and home use.
At the same time solar impact in such regions is at a par-
ticularly high level. Therefore, such arid environments offer
the possibility to operate solar power plants, however, up to
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now there was the dilemma concerning efficient cooling as de-
scribed in the introductory paragraphs. It is therefore pre-
ferred that the cooling is performed for a carrier fluid in a
solar power plant, in particular in a concentrated solar
5 power plant. Firstly such solar power plants are often situ-
ated in arid zones as described above. Secondly, such power
plants, in particular concentrated solar power plants, pro-
duce carrier fluids with very high temperatures. Concentrated
solar power plants are characterised by the fact that light
10 rays from the sun are concentrated onto small spots so that
they produce very high temperatures in these spots. The re-
sult is that the temperatures generated by concentrated solar
power plants are particularly high and sufficient for power
plant cycle. However the efficiency of the cycle is deter-
mined by the lower temperature of the cold end (condensa-
tion). This temperature defines the achievable lowest pres-
sure at the turbine exit. The lower it is the higher the ef-
ficiency and therefore the extracted power output of the
power plant. This can be enhanced by the methods according to
the invention.
In order to further cool down any of the fluids additional
cooling apart from the cooling realised by the method accord-
ing to the invention may be necessary. A first possibility is
that the cooling according to the invention is performed for
a carrier fluid in a power plant comprising an air cooled
condenser or dry cooling tower which carries out part of the
cooling. As shown before, dry cooling towers with ventilators
have the advantage that, again, essentially no cooling fluid
is lost into the air. The combination of the cooling method
according to the invention with a cooling method using air
cooled condenser makes possible a closed cooling circuit or a
closed carrier circuit in which no fluid is lost to the ambi-
ent environment.
A second possibility which also includes additional cooling
is that the cooling according to the invention is performed
in a power plant comprising a wet cooling system which car-
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ries out part of the cooling. The first and the second possi-
bility may be combined so that in fact three cooling systems
together provide for the overall cooling effect of the car-
rier fluid and/or the cooling fluid. However, the cooling
method according to the invention may also be combined with a
wet cooling system only. This means that a wet cooling tower
takes over some of the cooling while the rest of the cooling
is performed by the cooling system according to the inven-
tion. As outlined above, wet cooling provides for the most
effective cooling overall so that a particularly effective
system is realized whereby the methods according to the in-
vention help to reduce fluid consumption. Whether the wet
cooling tower is situated upstream or downstream the cooling
system according to the invention can be chosen according to
both technical preferences and according to the availability
of space as well as in dependence of other pre-assumptions.
In some special cases, however, tt is preferred to place to
wet cooling tower downstream the cooling system according to
the invention. This is particularly the case when the water
losses of the wet cooling tower are to be reduced by the
cooling system, which can be enhanced by such arrangement of
the two cooling systems.
To sum up, combining such different cooling systems with the
method according to the invention provides for a system with
increased efficiency. It also makes possible the temporary
use of either cooling methods at different times. For in-
stance, a main cooling circuit may comprise an dry cooling
tower system while only in peak times there is operated a
cooling system according to the invention.
Whereas it is possible to simply lead the carrier fluid
and/or the cooling fluid through a pipe system underground,
it is preferred that the carrier fluid and/or the cooling
fluid is cooled in a heat exchanger connected to a cooling
circuit. Such cooling circuit contains a cooling fluid. The
carrier fluid may be cooled directly in the heat exchanger or
cooling fluid is cooled in the heat exchanger by a second
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cooling fluid circulating in the cooling circuit. The latter
means that two cooling circuits altogether are used, both
containing cooling fluid, whereby the cooling fluids in the
different cooling circuits may be different in kind but need
not necessarily be.
As for the method according to the second embodiment of the
invention (i.e. employing a cold storage), the cold storage
is preferably situated underground at a depth that is sub-
stantially cooler than the ambient air. This in fact means
that both embodiments of methods according to the invention
are combined so that the cooling takes place underground in
an underground cold storage. This is particularly advanta-
geous for example because no isolation means for firmly iso-
lating the cold storage are needed as would usually be the
case if the cold storage was above ground.
It is particularly preferred that such cold storage is re-
plenished with fluid at night time which fluid is then sup-
plied during daytime. That means that the carrier fluid
and/or the cooling fluid are a cooled down at night time and
collected in the cold storage so that they can be supplied
during daytime, in particular during those times of the day
when the weather is particularly hot.
Additionally, some of the carrier fluid and/or some of the
cooling fluid can be stored in a plurality of cold storages.
For instance, there may be one main cold storage for what may
be labelled "normal operation" and a second additional cold
storage for operation times under severe conditions such as
very hot weather or a times of peak power consumption. How-
ever, different cold storages may also be used at different
time, e.g. on different days, so that the time to recover the
low temperature in each of the cold storages is longer. Also,
all cold storages may be used in parallel at any given time
in order to provide for a combined cooling effect.
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The cooling methods according to the invention are particu-
larly useful for those times in which cooling of the carrier
fluid is particularly necessary. Therefore, they are most
preferably applied under extreme heat conditions and/or dur-
ing times of peak power consumption.
For such extreme conditions it is further preferred that use
of the cooling method is initiated by a driving unit accord-
ing to variable input data pertaining to temperature informa-
tion and/or power consumption information. Such a driving
unit receives information about ambient temperature and/or
information about the current power consumption within the
power supply network and therefrom derives orders to activate
or de-activate those parts of the power plant which will op-
erate the cooling system according to the invention. For in-
stance valves into and/or out of the cooling system according
to the invention can be opened and closed depending on such
orders of the driving unit. This means that the cooling sys-
tem can be opened and closed off according to current need.
Other objects and features of the present invention will be-
come apparent from the following detailed descriptions con-
sidered in conjunction with the accompanying drawings. It is
to be understood, however, that the drawings are designed
solely for the purposes of illustration and not as a defini-
tion of the limits of the invention.
In the drawings, like reference numbers refer to like objects
throughout. Objects in the diagrams are not necessarily drawn
to scale.
Fig. 1 shows a schematic view of a power plant with a first
cooling system according to the state of the art,
Fig. 2 shows a schematic view of a power plant with a second
cooling system according to the state of the art,
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Fig. 3 shows a schematic view of a power plant with a cooling
system according to a first embodiment of the invention,
Fig. 4 shows a schematic view of a power plant with a cooling
system according to a second embodiment of the invention,
Fig. 5 shows a schematic view of a power plant with a cooling
system according to a third embodiment of the invention,
Figure 6 shows a detailed view of a part of the cooling sys-
tem of Fig. 5.
Figs. 1 and 2 have been described above in the context of the
description of the state of the art
Figure 3 shows a power plant 2' according to a first embodi-
ment of the invention. In this and the following figures, the
other components of the power plant 2' such as the heating
chamber, the turbine, the generator and the power system are
not shown for reasons of clarity.
In a cooling circuit 11 cooling fluid 13, here cooling water
13, is pumped through a pipe system by a cooling circuit pump
3. First it passes a dry cooling tower 33 of the kind which
has been described in the context of Fig. 2. Then the cooling
water 13 is led further below the ground into the soil into
an underground depth 41. Part of the cooling circuit 11 is
thus an underground pipe 40, in which the cooling water 13
can be cooled down by the low temperatures in the underground
depth 41. The underground pipe 40 thus constitutes a cooling
system 4. The cooling water 13 is further led into a wet
cooling tower 19 of the kind described in Fig. 1. Water va-
pour leaves the wet cooling tower 19 in the form of steam
clouds 21. The rest of the cooling water 13 is then collected
and pumped to a heat exchanger (not shown) to cool a carrier
fluid of the power plant 2'.
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The underground pipe 40 and thus the cooling system 4 can be
fed with cooling water 13 via a first valve 59, whereas a di-
rect connection 60 circumventing the underground pipe 40 can
be opened and closed by a second valve 61. If the cooling wa-
5 ter 13 is to be cooled in the underground tube 41 the first
valve 59 is opened whereas the second valve 61 is preferably
closed. On the other hand, if the cooling by the dry cooling
tower 33 and the wet cooling tower 19 is sufficient in itself
to cool down the cooling water 13 to the desired low tempera-
10 ture, the second valve 61 can be opened while the first valve
59 can be closed in order to cut off the connection into the
underground pipe 40. For that purpose a control unit 63 gives
orders SB to both the first valve 59 and the second valve 61
by which orders the two valves are operated. The control unit
15 63 comprises an input interface 64 for information data ID,
for example information about the ambient temperature of the
power plant 2' and/or about current power consumption of the
power network which is fed by the power plant 2'. A driving
unit 57 derives from these information data ID the orders SB
which will close and open the first valve 59 and the second
valve 61. Therefore opening and closing the valves 59, 61 is
dependent on those information data ID supplied via the in-
terface is 64. In other words, the underground tube 40 can be
cut off or given access to in dependence of the information
data ID. For instance, during day time under hot weather con-
ditions the information data ID will contain information
about high temperatures. The information data may also com-
prise date and time information from which there can be ex-
tracted in arid zones a certain expected temperature level.
For instance, the information that it is midday will suffice
in deserts as an indication of very hot ambient temperatures
without an extra measurement of the temperatures. From the
information data ID the driving unit 57 derives orders SB to
open the first valve 59 and to close the second valve 61 so
that additional cooling in the underground tube 40 is made
available. The same may be the case in times of extremely
high power consumption in the power supply network.
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Such control unit 63 can be used in any of the following em-
bodiments as described with reference to Figs. 4 and 5. It is
therefore not shown in the following figures.
Figure 4 shows a power plant 2' according to a second embodi-
ment of the invention. Again cooling water 13 is pumped
through a cooling circuit 11 by a pump 3. It passes a dry
cooling tower 33 as described before before entering an un-
derground depth 41 in which a heat exchanger 45 is situated.
In the heat exchanger 45 the cooling water 13 is cooled down
and led further into a wet cooling tower 19 as described with
reference to Fig. 3. The heat exchanger 45 is supplied with a
second cooling liquid 46 which is led through a second cool-
ing circuit 47 by a second cooling circuit pump 49. This sec-
and cooling circuit 47 is in the underground depth 41 so that
it is cooled by the underground soil. The second cooling cir-
cuit 47 together with the heat exchanger 45 and the second
cooling circuit pump 49 therefore constitutes a cooling sys-
tem 4 according to a second embodiment of the invention.
Figure 5 shows a power plant 2' according to a third embodi-
ment of the invention. For the sake of clarity common fea-
tures with Figs. 3 and 4 are not mentioned again. After leav-
ing the dry cooling tower 33, the cooling water 13 is led
again into an underground depth 41 in which a cold storage 51
is situated. It may be noted that such cold storage 51 can
also be situated above ground in which case it is preferably
thermally isolated from the outside.
The cold storage 51 is shown in more detail in Fig. 6. It is
realized as a basin in which the cooling water 13 is stored
in great amount. For the purpose of cooling the cooling water
13 an additional pipe system 53 with a pump 55 is led under-
ground so that the cooling water 13 is cooled underground and
led back into the cold storage 51. From the cold storage 51
the cooling water 13 goes back into the cooling circuit 11 as
shown in Fig. 5.
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Although the present invention has been disclosed in the form
of preferred embodiments and variations thereon, it will be
understood that numerous additional modifications and varia-
tions could be made thereto without departing from the scope
of the invention. As mentioned above, the cold storage can
also be positioned above ground and it is not absolutely nec-
essary to use dry cooling towers and/or wet cooling towers in
addition to the cooling system used to realize the method ac-
cording to the invention.
For the sake of clarity, it is to be understood that the use
of "a" or "an" throughout this application does not exclude a
plurality, and "comprising" does not exclude other steps or
elements.
