US2959013A

US2959013A - Steam turbine installation

Info

Publication number: US2959013A
Application number: US667125A
Authority: US
Inventors: Ricard Pierre Jean
Original assignee: Societe des Forges et Ateliers du Creusot
Current assignee: Societe des Forges et Ateliers du Creusot
Priority date: 1956-06-30
Filing date: 1957-06-21
Publication date: 1960-11-08
Anticipated expiration: 1977-11-08

Description

Nova & 396G P. .1. Ric/Ann STEAM TURBINE INSTALLATION Filed June 21, 1957 INVENTO}? Fig.3 16 re 15 14 MMMMWL PIERRE JEAN 121cm]:

ATTORNEYS STEAM TURBINE INSTALLATION Pierre Jean Ricard, Paris, France, assignor of one-half to Societe des Forges et Ateliers du 'Creusot, Paris, France, a company of France Filed June 21, 1957, Ser. No. 667,125

Claims priority, application France June 30, 1956 4 Claims. (Cl. 60-67) In steam turbine installations, the condensed water is usually reheated in a series of water reheaters consisting of tubular heat exchangers fed by steam drawn off from the turbine. The heat given up in such a reheater by the steam drawn 01?, between the temperature at which it leaves the turbine and a temperature equal to or slightly higher than, the saturation temperature corresponding to its pressure, that is to say the reheating heat of the reheater, is given up to the water in a particular zone known as the de-superheating zone, which precedes, in the direction of flow of the steam, the so-called saturated zone, where the steam gives up its latent heat of vaporisation.

In such an installation, the heat exchange in the desuperheating zone introduces an element of irreversibility into the thermodynamic cycle because the temperature of the steam may be much higher than that of the Water,

especially in installations comprising one or more resuperheating operations.

The present invention has the purpose of increasing the efliciency of the installation by reducing the degree of irreversibility in the thermodynamic cycle.

According to the invention, the installation is characterised by the fact that it comprises means for sampling a fractional delivery of water in at least one condensed water reheater at the point where the water has finished reheating in the saturated steam zone of the reheater, a heat-exchanger being provided in order to reheat the said fractional delivery of water to a temperature slightly lower than that of the steam drawn off from the turbine,

and means being finally provided to re-introduce the said fractional delivery into the main water circuit, the point of re-introduction being situated after the first water reheater in the direction of flow, reckoning from the output of the reheater set, whereof the output temperature is lower than the temperature of the fractional delivery of reheated water.

The delivery of water drawn oif can, in certain cases, be divided into two parts after a predetermined degree of reheating, one of the said parts continuing alone to be reheated, the two parts being re-introduced into the main water circuit at two separate points suitably chosen as a function of the respective final temperatures of the two parts.

An installation according to the invention is diagrammatically illustrated in the attached drawing, and described hereinafter.

In the drawing:

Figure l is an overall diagram of the installation.

Figure 2 is a diagram of the temperatures in an installation as shown in Figure 1.

Figure 3 is a partial diagram showing a subdivided water take-0E.

Figure 4 is a diagram of the temperatures in an installation wherein the water drawn ofi is partially vaporised.

Figures 5 and 6 show two types of water reheaters incorporating the heat-exchangers used.

2,959,013 Patented Nov. 8, 1960 Figure 7 shows a variant of an embodiment of the installation in the case where the water reheater is of the mixer type.

Figure 8 is a modification of Figure 1.

The diagram in Figure 1 shows an initial water sampling system in the case of a re-superheating turbine, for which only three steam take-offs are illustrated.

In this diagram, 1 designates the high-pressure part of the turbine, 2 the re-superheater, 3 the lower pressure turbine, and 4 the condenser. Three condensed

water reheaters

5, 6 and 7 are fed by the three steam take-

offs

8, 9 and 10 respectively. The saturated zones of these reheaters are designated by 5a, 6a and 7a respectively, while the de-superheating zones are designated by 5b, 6b and 7b. The condensed water outlets of the reheaters are illustrated at 8a, 9a and 10a.

The reheater 5 is fed by water from condenser 4 through conduit 14 to reheater 5a comprises a water take-01f 11 which is reheated by the take-off 8 in the zone 5b, the heat-exchanger used replacing, in this zone, the usual de-superheating exchanger for the steam drawn off.

The delivery of reheated water 11 is conveyed at 12 to the main water delivery 14c at the outlet of the last reheater if its temperature is higher than that of the water at the outlet of the reheating set of the turbine.

In the opposite case, the delivery of reheated water 11 is conveyed at 13 in Figure 8 to the condensed water circuit 14b after the first reheater, reckoning from the outlet of the reheating set, for example 6, whereof the outlet temperature is lower than its own temperature. Water from reheater 5a is taken by conduit 14a to reheater 6a, then through heater 6b and, by conduit 14b, to

heaters

7a and 7b to water delivery conduit 140.

The water take-oils are contrived in the same fashion on each of the other reheaters; they are not illustrated for the sake of clarity in the diagram.

In the diagram in Figure 2, wherein the quantities of heat exchanged are plotted as abscissae, and the temperatures as ordinates, the curves T and 2 respectively represent the variation of steam and water temperature as a function of the quantity of heat exchanged in unit time. The two curves T and t are of the shape shown because the specific heat of water is an increasing function of temperature, and the specific heat of steam on the other hand is a decreasing function of temperature.

The point A represents the temperature of the steam and the point G the temperature of the water at the end of the de-superheating zone. The horizontal line .98 represents the saturation temperature corresponding to the steam pressure in the saturated zone, and the curve gG represents the end of water temperature variation in the said zone. The point A may possibly coincide with the point S, or be situated slightly above the point S, according to the surface area of the de-superheating exchanger. The interval 86 is generally of the order of 2 to 3 C. in an ordinary reheater.

The improvement obtained in the efiiciency of the installation becomes greater as the two curves T and t approach one another, and consequently as the delivery of water drawn off becomes smaller, but the said delivery must be fixed by a diaphragm or valve (not illustrated), in such a manner that:

(a) there is always sufficient difference in temperature between the steam and the water. Since the interval AG is small, this condition is realised if the slope of the curve t is not greater than that of'the curve T at the points G and A respectively.

(b) the difference in temperature at the end of the heat-exchanger where the fluids are hottest, represented by BC, remains sufliciently large for the area of the exchanger not to make this appliance too costly.

In the cast in which the condition (a) is determinative, the efficiency of the cycle may be increased by bypassing from the delivery ofwater drawn off, during reheating, a partial delivery which continues to be reheated alone in accordance with the curve D; theffresultbfthis is a reduction in the final temperature diifereiice,' which becomes BE instead of BC. v

This dividedtake-off, which forms a "sdpple'rrientary feature of the invention, is illustrated in thedia'gram in Figure 3.

In this diagram, 8 is the steam take-01f, 14 is'the 'r'nain water delivery,15 is the delivery'of water driawn'joif, which divides, after having been Subjected to" a' first reheating operation, into a'delivery 11 which isreturned to the circuitat a'pointchos'enin accordance'with the foregoing, for example before one of' the subsequent reheaters, and a delivery 16 'which continues to be reheated, and is then returned to the circuit at another suitably chosen point,'for example at the outlet of the last reheater.

The efiiciency of the cycle could be further increased by lay-passing, from the delivery of water drawn off, a second amount, which would be'r'eheated in accordance with the curved in the diagram in Figure 2, the final diflerence in temperature then'being represented by BF, and so forth.

Thewater take-offs do not require any pump other than the pumps normally provided in a steam turbine installation in the case of water reheaters of the so-called high-pressure type, that is to say situated on the delivery side of the pump feeding the steam generator. In fact, in this case, the water drawn off only has to pass through the exchanger which reheats it, while the main water delivery has to pass through the subsequent water reheaters, which are at least one in number. There is therefore enough pressure available to ensure circulation of the delivery drawn off.

On the other hand, a special pump is required in the case of low-pressure reheaters situated before the feed pump, if the delivery of water drawn off must be conveyed to the high-pressure circuit. However, in order to avoid having to install a low-power high-pressure pump, the delivery of water drawn off may be conveyed to the body of the reheater provided itself, where it mixes with the blow-olfs coming from the higher-pressure reheaters, instead of being conveyed to the main water delivery before it enters the reheater. The two processes are in fact substantially equivalent as regards efiiciency.

In certain cases, the temperature at which the steam is drawn off may be sufficiently high for the delivery of water drawn off to be partially vaporised. The temperatures then vary as shown in the diagram in Figure 4, wherein the curve T represents steam temperature, and the curve 1 represents water temperature, this latter curve having a horizontal portion HI during which the water becomes partially vaporised. Then either the delivery of water drawn off may be increased in order to prevent vaporisation, the temperature then varying in accordance with GK, or partial vaporisation in accordance with HI may be accepted, which increases the efliciency in so far as the condition (a) defined above does not cause any limitation in this method. The heat-exchanger then comprises a zone where partial vaporisation occurs, and the tubes must be so shaped in this zone that the steam cannot accumulate at a bend and hinder circulation.

his then advantageous to convey the mixture of water and steam leaving the exchanger either to the container of the steam generator if the temperature of the'said mixture is higher than that of the saturated steam in the last reheater, or, in the opposite case, to the saturated zone of the first reheater for which the steam temperature is higher than that of the mixture.

All kinds of construction of Water reheaters can be used for putting the invention into practice.

Figures 5 and 6 show, in more or less diagrammatic form, and by way of example, two water reheaters with heat exchanger incorporated for reheating the delivery of water drawn off.

The exchanger illustrated in Figure 5 is of the waterbox type, and that in Figure 6 of the header type.

In these two figures, 21 and 22 respectively designate the saturated zone and the heat-exchanger incorporated in order to reheat the Water drawn off, while 23 and 24 respectively designate the steam inlet and the condensed water outlet.

In the reheater shown in Figure 5, the water enters at 25, the main water delivery outlet is situated at 26, and th outlet for the water drawn off at 27.

The reheater shown in Figure 6 comprises a water inlet header 28, an intermediate header 29 and an outlet header 30 for the water drawn off.

If the water reheater is of thernixer typ'e,'which is so in the case of a degasifier, the delivery of'water drawn off can be reheated in a special exchanger. The diagram of such an exchanger is shown in Figure 7, wherein 8 is the steam take-off, 14'the main water delivery, ll the delivery of water drawn 011, 19 the pump'which'a'spirates the water leaving the reheater," and '20 the special exchanger.

What is'claimed is:

1. In a steam' turbine installation including a turbine and a turbine condenser, a plurality of feedwater heaters, a first steam zone and a second steam zone for each of said heaters, a steam path from the turbine to said first zone and then to said second Zone for each of said heaters, a feedwater path from the turbine condenser to said second zone of the first of said heaters, a tap in said first heater between said zones of said first heater dividing the reheated feedwater when the feedwater has been heated in said second steam zone of said first heater, a part of the feedwater passing through said first steam zone of said first heater for heating to a temperature less than but approximating that of the steam' from the turbine, the remainder of the feedwater passing from said tap to said second steam zone of an adjacent one of said heaters and then passing in series through said second and then said first zones of the remainder of said heaters and said part of the feedwater after heating in said first zone of said first heater entering the feedwater path downstream of the adjacent one of said feedwater heaters to said first feedwater heater.

2. In an installation as described in claim 1, a tap in said first steam zone of said first heater dividing the feedwater heated in said first steam zone into two parts one 'of which is further heated in said first steam zone, said two feedwater parts being reintroduced into the feedwater path downstream of the adjacent one of said feed water heaters to said first feedwater heater.

3. In an installation as described in claim Zysaid further heated parts of said two parts of said feedwater being introduced into the feedwater path at a point after the last of said heaters in the direction of'feedwater flow.

4. An installation as described in claim 1 in which each of said heaters is a tubular heat exchanger having a first steam zone and a second steam zone.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Apr. 6, 1955