Gas/steam power station plant

In a gas/steam power station plant, which consists essentially of at least one fossil-fired internal combustion engine (2), at least one steam circuit (1) and at least one heat exchanger (3), the heat exchanger (3) connected downstream of the internal combustion engine (2) is fed with exhaust gases (27) from the internal combustion engine (2). Together with a number of steam turbines (12, 13), the steam circuit 1 has a generator (14), a series of other auxiliary units (15, 16) and a water-cooled reactor (11) which produces an amount of saturated steam (B) from an amount of preheated feed water (C) treated in the heat exchanger (3) and fed to it. This amount of saturated steam is thereupon fed to a superheat stage (A) in the heat exchanger (3), where the actual final treatment of the steam takes place.

DESCRIPTION 
The present invention relates to a gas/steam power station plant and to 
methods of operating a plant of this kind. 
TECHNICAL FIELD AND PRIOR ART 
In the case of a nuclear power station plant having a water-cooled reactor, 
only saturated steam at modest pressure can be produced. In accordance 
with the present state of development a reactor of this kind works with 
modest steam data, for example at 63 bar and 280 degrees Celsius, and thus 
achieves a conversion efficiency of about 33% of the energy produced in 
the reactor into electric energy. 
It is obvious that a conversion efficiency of this kind is no longer able 
to satisfy the operating economy expected at the present time in the 
production of energy. 
In the case of solely fossil-fired power station plants it is the state of 
the art practice to extend a gas turbine plant with a waste-heat steam 
generator (= waste-heat boiler) and to combine it with a steam turbine 
plant connected downstream, although fossil-fired steam power stations can 
achieve efficiencies of over 40%. 
These so-called combination plants are then distinguished by very good 
conversion efficiencies, which range in order of magnitude from 50 to 52%. 
These high efficiencies result from the cooperation of a gas turbo unit 
with at least one steam turbine circuit, the gas turbine exhaust gases 
being passed through a waste-heat boiler in which the residual heat 
potential of precisely these waste gases is utilized for producing the 
steam required for feeding a steam turbine. 
In such combination plants it is found that the evaporation of the feed 
water, which proceeds isothermally, in a waste-heat boiler naturally 
occurs with declining temperature of the waste gases, while on average an 
unnecessarily high temperature difference results. This gives rise to 
undoubtedly unnecessary additional losses of energy (losses of work 
capacity of the waste gases), which, considered graphically in a T/Q 
diagram, can be represented as the area between the steep temperature fall 
curve of the waste gases in the waste-heat boiler and the flat evaporation 
curve of the feed water. 
It is true that a correction can be made by using a multipressure 
waste-heat boiler. However, more than two pressure stages are not easily 
handled either in respect of design or in respect of operation, so that 
even with the aid of a waste-heat boiler of this kind the energy losses 
cannot be reduced to the desired extent. 
Problem Underlying the Invention 
The invention seeks to provide a remedy in this connection. The problem 
underlying the invention, as the latter is characterized in the claims, is 
that of minimizing energy losses in evaporation in a gas/steam power 
station plant of the kind first mentioned above. 
The essential advantages of the invention are to be seen in that the 
evaporation process making optimum use of the energy potential of the 
thermally offered power of a nuclear reactor is backed up by feed water 
preheating and steam superheating in the waste-heat boiler of a gas 
turbine. Since both the feed water preheating and the steam superheating 
take place countercurrently to the flue gas cooling, there are in fact 
naturally no energy losses exceeding the extent necessary for heat 
transfer. All in all, over the entire range of heat supply, which is split 
up into a nuclear and a fossil part, the smallest possible energy losses, 
and therefore the smallest possible efficiency loss in the conversion of 
heat into electricity as the result of poor thermal impedance adaptation, 
will thus occur. However, the fact that this applies particularly to the 
fossil part of the energy supplied is of decisive importance because the 
environmental load through fossil fuels is thus reduced to a minimum. If 
natural gas is used, additional fossil-produced electric energy can be 
obtained with minimum emission of carbon dioxide. 
Further advantages of the invention arise in connection with an increase of 
the power of an existing nuclear power station plant if a number of 
internal combustion engines, preferably gas turbine plants, are connected 
upstream of the nuclear power station plant. 
If in the last-mentioned configuration the corrective intervention in 
respect of the absorption capacity of the steam turbines and the power 
capacity of the generator should remain slight or be completely absent, it 
is possible to provide a circuit arrangement in which the excess steam 
fraction is branched off from the superheat stage in the heat exchanger 
and passed to the circuit of the internal combustion engines, preferably 
into their combustion chambers, and it is there ensured that the resulting 
loss of power in the steam circuit of the nuclear power plant is 
approximately compensated by the increase of power of the internal 
combustion engines. 
Another advantage of the invention relates to the adaptability of the 
circuit arrangement. With a quantitatively and/or thermally reduced 
potential of the exhaust gases provided by the internal combustion 
engines, the nominal power of the reactor need not be reduced. It is in 
fact entirely possible for only a part of the feed water flow coming from 
the condenser to be preheated in the waste-heat boiler and also to 
superheat therein only a part of the steam produced in the reactor, so 
that a correspondingly smaller gas turbine plant can be installed. 
Nevertheless, the fossil part of the energy required for this purpose is 
converted with the improved efficiency prognosticated above. 
A further advantage of the invention is to be seen in the fact that the 
circuit arrangement has great expansibility and combinability, such as 
using the potential of the preheat stage in the waste-heat boiler to the 
required extent for operating an outside heat consumer. 
Advantageous and expedient further developments of the solution to the 
problem supplied by the invention are characterized in the other dependent 
claims. 
Examples of embodiment of the invention are schematically illustrated in 
the drawing and explained more fully below. All elements not necessary for 
immediate understanding of the invention have been omitted. The direction 
of flow of the media is indicated by arrows. In the various figures 
identical elements are in each case given the same references.

DESCRIPTION OF THE EXAMPLES OF EMBODIMENT 
FIG. 1 shows a circuit arrangement of a power station plant which consists 
of the cooperation of a nuclear power station plant 1 with a gas turbine 
plant 2, a waste-heat boiler 3 being interposed between the two blocks. 
The gas turbine plant 2 connected upstream of the waste-heat boiler 3 and 
of the nuclear power station plant 1 consists essentially of a compressor 
22, a gas turbine 23 preferably mounted on a common shaft with said 
compressor, a generator 21 coupled to the rotation of these two machines, 
and a combustion chamber 24. The induced air 25 is passed into the 
compressor 22, where the compression takes place, and this compressed air 
then flows into the combustion chamber 24. The fuel 26 for operating the 
combustion chamber 24 consists of gaseous and/or liquid fuels. The hot 
gases produced in the combustion chamber 24 pass in the following process 
into the gas turbine 23; after their expansion these hot gases, whose 
pressure has been consumed, flow as waste gases 27 through the waste-heat 
boiler 3, in which their residual thermal potential is further utilized. 
The nuclear power station plant 1 consists of a light water reactor 11, 
which supplies an amount of saturated steam, and further of a high 
pressure steam turbine 12 and, connected downstream thereof, a low 
pressure steam turbine 13. A generator 14 is coupled to the steam 
turbines. By way of one or more exhaust steam pipes the expanded steam 
flows out of the low pressure steam turbine 13 into a preferably water- or 
air-cooled condenser 15. The condensate formed therefrom is passed via a 
pump 16 into the waste-heat boiler 3, where via stage C it undergoes 
preheating to feed water. The next stage of the process consists in that 
the feed water is passed into the reactor 11, where the actual treatment 
of steam to form a saturated steam B takes place. After this treatment 
stage in the reactor 11 the saturated steam is passed once more into the 
waste-heat boiler 3, where via another heat transfer stage the final 
treatment of the steam to form a superheated steam A takes place. This 
steam treated with a maximized thermal potential then passes into the high 
pressure steam turbine 12 and then into the low pressure steam turbine 13, 
the two turbines producing the electric power of the generator 14 coupled 
there. After the waste gases 27 have substantially given up their heat 
potential in the waste-heat boiler 3, they flow off as flue gases 31 
through a chimney (not shown). 
Optionally, an additional furnace (not shown) may be connected upstream of 
the waste-heat boiler 3 to bring the waste gases 27 to a higher 
heat-exchangeable temperature. A measure of this kind, although it 
increases the producible electric power, nevertheless reduces conversion 
efficiency. 
As a quantitative example of embodiment, a nuclear power station plant 
containing a light water reactor 11 for a thermal power of 3000 MW will be 
considered. In order to bring the feed water preheating in stage C to 220 
degrees Celsius and the steam heating in stage A of the saturated steam 
produced in the reactor 11 at 280 degrees Celsius boiling temperature 
finally in stage B to 480 degrees Celsius, there must be in the waste-heat 
boiler 3 a flue gas mass flow which exceeds the live steam mass flow by a 
factor of 2.75. The gas turbines used in this example each have a flue gas 
mass flow of 500 kg/s and each produces 141 MWe. Their conversion 
efficiency amounts to 33.6%. In order to superheat the live steam mass 
flow from the reactor 11 of 1627 kg/s and to preheat the feed water, a 
total waste gas mass flow of 4480 kg/s is necessary. Nine gas turbines are 
required for this purpose, which together produce a power of 1269 MWe. 
Since the steam turbines 12 and 13, if necessary after appropriate 
adaptation, work with superheated steam and no further amount of steam has 
to be taken from them for feed water preheating, they produce together 
1710 MWe. The integration of the gas turbine plant 2, with its number of 
gas turbines, into the nuclear power station plant 1 thus permits a total 
power of 3000 MWe, as compared with 1000 MWe from the original nuclear 
power station plant. 
The 3779 MWth of fossile fuel expenditure for all gas turbines are 
converted into electrical energy with an efficiency of 52.4%, because: 
##EQU1## 
A single nuclear power station, correspondingly combined, would thus make 
it possible once again to achieve twice the power of the nuclear power 
station and to do this with very high conversion efficiency, which would 
mean extremely efficient and therefore environment-friendly utilization of 
the fossil fuel, preferably natural gas. A circuit arrangement of this 
kind is particularly interesting in respect of the investment aspect if it 
is conceived as a retrofit operation for an existing nuclear power station 
plant. 
Even when conceived in this way, the circuit arrangement remains very 
adaptable; if, for example, the absorption capacity of the steam turbines 
does not permit absorption of the amount of steam produced, or if the 
power capacity of the existing generator is at its limit, the excess steam 
fraction can be branched off from the superheat stage in the waste-heat 
boiler 3 and passed into the circuit of the gas turbine plants 2, 
preferably into their combustion chamber 24. The resulting loss of power 
in the steam circuit of the nuclear power station plant 1 is largely made 
good by an increase of power of the gas turbine plants 2. In addition, 
with a reduced potential of waste gases, whether quantitative and/or 
thermal, the nominal power of the reactor 11 need not be reduced; a part 
of the amount of saturated steam B from the reactor 11 which cannot be 
treated in the waste-heat boiler 3 is branched off and fed directly to the 
steam turbines of the steam circuit of the nuclear power station plant 1. 
It may then be advantageous for this excess steam fraction, which cannot 
be superheated by the waste-heat boiler 3, to be throttled and thus, 
slightly superheated, to be passed into the steam turbines at a suitable 
point. The two last-mentioned possible circuit arrangements are not shown 
in FIG. 1, since in the light of the above description they can be 
recreated without difficulty. 
In FIG. 2 the circuit arrangement shown in FIG. 1 is illustrated 
diagrammatically. In this connection the minimized energy losses during 
the evaporation process along stage B, and also during the preheating C 
and the superheating A, should be noted. Only the temperature differences 
necessary for heat transfer result therefrom. 
In FIG. 3 the energy flows are illustrated with the aid of a Sankey 
diagram. Three efficiencies of conversion of the thermal energy expended 
into electrical energy can here be distinguished: 
a) Efficiency of the nuclear part (FIG. 1, item 1) 
.eta.nuk=1000 MWe/3000 MWth=33.3%. 
b) Efficiency of the fossil part (FIG. 1, items 2, 3) 
.eta.fos=42.3%+23.7%)/126%=52.4%. 
c) Efficiency of the entire plant (FIG. 1, items 1, 2, 3) 
.eta.ges=(57%+42.3%)/(100%+126%)=43.9%. 
If a progressive, future water-cooled reactor is considered, which for 
example is able to deliver saturated steam at 340 degrees Celsius and at 
147 bar, it becomes possible to provide intermediate superheating. If, in 
addition, this reactor is paired with gas turbines of the next generation, 
it would be possible to obtain therewith a steam temperature of about 550 
degrees Celsius, with the result that the conversion efficiency of the 
plant would be substantially increased. Under these conditions the concept 
of a new plant based on the hybrid principle described could even open up 
interesting prospects. FIG. 4 shows an example of such a circuit 
arrangement. 
The following description of FIG. 4 is restricted to the construction of 
the circuit arrangement illustrated. Nothing is said regarding the power 
of the individual machines. The gas turbine plant 2 corresponds in 
construction to that shown in FIG. 1. In comparison with the latter, the 
nuclear power station plant 1a is extended in that between the high 
pressure steam turbine 12 and the low pressure steam turbine 13 a medium 
pressure steam turbine 17 is interposed. For safety reasons, between the 
reactor 11a and the waste-heat units an insulating heat exchanger 32 is 
provided, which constitutes a requirement in connection with the use of a 
future reactor. This arrangement moreover is in any case a functionally 
necessary precaution for pressurized water reactors. 
The original waste-heat boiler 3 shown in FIG. 1 is here replaced by three 
individual, independent, dedicated waste-heat units. The condensate from 
the condenser 15 flows through a preheater 3a, which is connected 
downstream of a superheater 3b and an intermediate superheater 3c and 
wherein preheating of the feed water is first effected. The feed water 
treated in this manner then flows through the previously mentioned 
insulating heat exchanger 32, which is associated with the reactor 11a and 
in which the treatment of saturated steam takes place. This medium then 
flows through the superheater 3b, which is likewise individually fed with 
waste gases 27 and in which the final thermal treatment of the steam takes 
place. The superheated steam is then fed in the first operation to the 
high pressure steam turbine 12. After expansion in this stage the steam is 
passed through the intermediate superheater 3c, which is likewise fed with 
waste gases 27 and in which the steam is again subjected to thermal 
treatment before being passed to the previously-mentioned medium pressure 
steam turbine 17 forming an intermediate unit between the high pressure 
and low pressure steam turbines. When the passage through this stage has 
been completed, the substantially expanded steam flows directly into the 
low pressure steam turbine 13, where it gives up its residual energy 
potential. The other steps of the circuit arrangement correspond to the 
operating sequence illustrated in FIG. 1. With the circuit arrangement 
assumed here, fossil energy conversion efficiencies of over 60% can be 
expected. In order to produce saturated steam at a sufficiently high 
pressure in the heat exchanger 32, such as that necessary for the 
interposition of intermediate superheating, a very high pressure level is 
required in the reactor 11a in the case of water cooling. Such a level can 
be reduced by selecting a high-boiling coolant, for example sodium, or by 
means of a suitable gas, such as CO.sub.2 or He. 
By operating the gas turbine plant 2 under nominal conditions with 
compressor preguide rows 10% closed, the shorter inspection intervals for 
gas turbines, in comparison with steam turbines, can be bridged over. 
Applied to the circuit arrangements according to FIG. 1 and possibly FIG. 
2, this would mean that for the utilization of the entire preheating and 
superheating potential ten machines would be necessary. In addition, it 
would be possible to consider equipping the waste-heat boiler 3 or the 
waste-heat units 3a, 3b, 3c, or a different configuration of waste-heat 
units, with an additional furnace, which is not illustrated. By this means 
the nominal operation of the steam part could be maintained even in the 
event of a breakdown requiring the shutting down of one or more gas 
turbine plants 2. 
It is obviously also possible in this case to provide the more extensive 
circuit facilities described in connection with FIG. 1, namely diversion 
of the excess steam fraction into the circuit of the gas turbine plant 2 
or introduction of a fraction of the saturated steam into the steam 
turbines of the steam circuit of the nuclear power station plant 1a.