EP0032641B1 - Reheating system for a steam-turbine power plant - Google Patents

Abstract

The system comprises a series of heaters arranged in cascade and fed with steam from drawoffs at pressures which progressively decrease from the steam boiler side to the condenser side of the plant. In order to improve the efficiency of the plant with which the system is associated, the system comprises a plurality of biphase turbines arranged in cascade. The first of the turbines is fed from the drain of the heater at the highest pressure and the following turbines are each fed at least in part with the outlet liquid of the biphase turbine preceding it. These biphase turbines produce mechanical energy by recovery of the kinetic energy of the condensates of the heaters feeding them.

Description

The present invention relates to condensed water heating systems used in steam turbine power generation installations such as power plants.

These reheating systems generally comprise a certain number of reheaters arranged between the condenser and the steam generator of the installation for reheating the water condensed in the condenser and supplied with steam at different pressures by respective withdrawals on the turbine. Between some of the heaters and the immediately adjacent heater supplied by a steam extraction at a lower pressure is disposed a phase separator receiving the water-steam mixture of the heater purge associated with the higher pressure withdrawal and supplying the heater associated with the withdrawal at lower pressure, in parallel with this drawing off at lower pressure, with steam separated from said mixture in the phase separator device. Furthermore, in pressurized water nuclear power stations, a superheater is provided, the condensates of which are sent to the heater associated with the highest pressure withdrawal via a phase separator.

Thanks to this arrangement, part of the energy of the water-steam mixture of the purge of some of the condensing exchangers, superheaters or heaters, is used to contribute to the heating of the fluid of the condenser-turbine circuit in a condensing exchanger supplied with steam at lower pressure. However, part of this energy is lost in thermal form in the main control valve provided in the purge pipe upstream of the phase separator, as well as in the latter.

In CH-A-320 887 a system has been described for heating the condensates of a steam turbine of an energy production installation comprising at least one condensing exchanger whose condensates are expanded to a water tank d 'supply, said system comprising at least one turbine disposed between said condensing exchanger and said tank and supplied by the condensates of said condensing exchanger. Said turbine operates with a mixture of liquid and steam, however an effort is made to limit the rate of steam.

The invention therefore aims to provide a heating system which makes it possible to use part of the energy lost in the heating systems of the prior art so as to increase the overall energy efficiency of the energy production installation. with which the heating system is associated.

The invention also aims to provide a heating system for a steam turbine power generation installation which, while having better efficiency than the heating systems of the prior art, is of simpler construction than the latter.

Finally, another object of the invention is to provide a heating system for a steam turbine energy production installation which at least partially avoids the erosion phenomena which are encountered in heating systems. classics with main control valve and phase separator in which the phenomenon of erosion is due to the high speed of the water-vapor mixture at the outlet of the main control valve.

The invention, as characterized in the claims, achieves these goals thanks to the fact that the two-phase turbine produces mechanical energy by recovering the kinetic energy of the condensers of the exchanger by condensation which l 'feeds. This results in an increase in the energy efficiency of the installation with which the heating system according to the invention is associated and the elimination of erosion phenomena in the main control valve and the phase separator since these are eliminated at the profit from the biphasic turbine.

• la Figure 1 est un schéma d'un système de réchauffage conventionnel pour centrale électrique à combustible fossile ;
• la Figure 2 est un schéma d'un système de réchauffage suivant l'invention pour centrale électrique à combustible fossile ;
• la Figure 3 est un schéma d'un système de réchauffage conventionnel pour centrale électrique nucléaire ; et
• la Figure 4 est un schéma d'un système de réchauffage suivant l'invention pour centrale électrique nucléaire.

Other characteristics and advantages of the invention will emerge from the description which follows of two particular examples of its embodiment illustrated by the appended drawings in which:

• Figure 1 is a diagram of a conventional heating system for a fossil fuel power plant;
• Figure 2 is a diagram of a heating system according to the invention for a fossil fuel power plant;
• Figure 3 is a diagram of a conventional heating system for a nuclear power plant; and
• Figure 4 is a diagram of a heating system according to the invention for nuclear power plant.

Referring to FIG. 1, there is shown the diagram of a conventional heating system with seven heaters R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ and R ₇ . The heaters R ₁ to R ₇ heat the condensed water and taken up by an extraction pump PE in the condenser (not shown) of the fossil-fuel power station and steam turbine with which this heating system is associated.

The heater R ₁ is supplied from a racking Si with steam at 0.3 bar and at a flow rate representing 4.5% by weight of the total flow rate (100% by weight) supplied by the heater R ₇ to the generator. steam (not shown) from the installation. The steam condensed in the heater R ₁ is returned by a drain pipe P _o to the condenser. The second heater R ₂ disposed in series in the main circuit CP of condensed water, downstream of the heater R _{1 ′} is supplied from a withdrawal S ₂ with steam at a pressure of 1 bar, with a flow rate of 4, 5% in weight. The third heater R ₃ , arranged downstream relative to R ₂ on the circuit CP, is supplied from a racking S ₃ with steam at a pressure of 2 bars, with a flow rate representing 3% by weight of the total flow rate.

The flow rate of the main circuit CP at the outlet of the heater R ₃ , which represents 75% by weight of the total flow rate at the outlet of the heater R ₇ , is sent to a heater by mixing or degassing tank R ₄ which is supplied from a racking S ₄ with steam at a pressure of 4 bars and at a flow rate representing 3.5% by weight of the total flow rate. The water coming from the heater R ₃ and the steam coming from the racking S ₄ are mixed in the heater by mixing R ₄ and this mixture is taken up by a food pump PA which sends it to the heater R ₅ , which is supplied, at from a S ₅ racking with steam at a pressure of 9 bars and at a flow rate representing 7% of the total flow rate. The water leaving the heater R ₅ is then sent to a heater R ₆ which is supplied, from a racking S ₆ , with steam at a pressure of 18 bars and at a flow rate representing 7% of the total flow rate.

Finally, the water leaving the heater R ₆ is further heated in the last heater R ₇ which is supplied, from a racking S ₇ , with steam at a pressure of 36 bars and at a flow rate representing 7.5 % by weight of the total flow. The condensed water leaving the heater R ₇ therefore represents, as indicated above, 100% of the total flow rate which is sent under a pressure of the order of 200 to 220 bars to the steam generator GV (not shown) of the installation where this water is vaporized to be returned to the turbine (not shown).

The vapor from the racking S ₇ condenses in the heater R ₇ and the condensates of this vapor thus formed are discharged from the heater R ₇ by a drain pipe P ₁ connected to a first phase separator SP ₁ via a main control valve SR ₁ . A motorized emergency control valve V ₁ is connected as a bypass with respect to the main control valve SR ₁ on the drain pipe P ₁ to return, if necessary, the condensate from the drain pipe P ₁ directly to the condenser. The regulation valves SR ₁ and V ₁ are controlled by a level regulator RN ₁ intended to regulate the water level in the heater R ₇ . The mixture at 244 ° C of the purge line P ₁ is sent via the main control valve SR ₁ into the phase separator SP ₁ which separates the water from the steam resulting from the expansion, the latter being sent by a CV ₁ pipe on the steam side in the R ₆ heater and the water being sent by a CE ₁ pipe on the water side in the R ₆ heater.

The condensates collected in the heater R _e are sent by a drain pipe P ₂ to a phase separator SP ₂ via a main control valve SR ₂ with which is connected in parallel a motorized emergency control valve V ₂ . The condensates at 207 ° C of the drain pipe P ₂ are separated in the phase separator SP ₂ and the steam is sent by a pipe CV ₂ on the steam side of the heater R ₅ , while the water is sent by a pipe CE ₂ water side of heater R ₅ . The phase separator SP ₂ , as well as the regulation valves SR ₂ and V ₂ which are controlled by a level regulator RN ₂ which regulates the water level in the heater R ₆ , operate in the same way and play the same role as the phase separator SP ₁ and the regulation valves SR ₁ and V ₁ described above.

The condensates at 175 ° C collected in the heater R ₅ are sent by a drain pipe P ₃ to the heater by mixing R ₄ , via a main regulating valve SR ₃ with which a bypass valve is connected. motorized emergency control V ₃ . The valves SR ₃ and V ₃ are controlled by a level regulator RN ₃ which regulates the level in the heater R ₅ . The mixture circulating in the drain pipe P ₃ , which represents 21.5% by weight of the total flow rate, is mixed in the degassing tank R ₄ with the water coming from the heater R ₃ and the steam coming from the drawing off S ₄ so that the food pump PA has a flow rate representing 100% of the total flow rate.

The condensates collected in the heater R ₃ are sent by means of a drain pipe P ₄ to a phase separator SP ₃ , by means of a main regulating valve SR ₄ with which a bypass valve is connected. motorized emergency regulation V ₄ which, like the valves V ₁ , V ₂ and V ₃ , returns condensates directly to the condenser in the event of an incident. The regulation valves SR ₄ and V ₄ are controlled by a level regulator RN ₄ which regulates the water level in the heater R ₃ . The condensates at 120 ° C of the drain pipe P ₄ are divided in the phase separator SP ₃ , from where the steam is sent to the steam side of the heater R ₂ by a pipe CV ₃ while the water is sent to the water side of the heater R ₂ by a pipe CE3.

Finally, the drain pipe P ₅ which collects the condensates at 100 ° C. from the heater R ₂ is connected in RA to a branch pipe CD which is connected between, on the one hand, the condenser and, on the other hand, the main line CP, between the heaters R ₂ and R ₃ . A motorized emergency control valve V5 is arranged in the bypass line CD between the RA connection and the condenser, and a main control valve SR _S is arranged in the line CD between the RA connection and the line connection CD with the main pipeline CP. The regulation valves SR ₅ and V5 are controlled by a level regulator RN ₅ which regulates the water level in the heater R ₂ . A PR pump from condensate recovery is arranged in the line CD between the connection RA and the regulating valve SR ₅ to reinject the condensates from the drain line P5 into the main line CP. If the PR pump stops, the condensate is returned to the condenser by the emergency control valve V5.

In operation, part of the heat energy of the mixture from the heaters R ₇ , R ₆ , R ₅ , R ₃ and R ₂ is used to heat the water in the main circuit, either by direct reinjection into the latter from the heaters R ₅ and R ₂ , either by sending to the following heater after separation of the liquid phase and the vapor phase in the phase separators SP ₁ , SP ₂ and SP ₃ . However, part of the energy of this mixture present in the form of pressure is lost in the phase separators which, moreover, have the drawback of being subject to strong erosion due to the high speed of the mixing at the regulating valve outlet.

These drawbacks are eliminated thanks to the heating system according to the invention, the diagram of which is shown in FIG. 2 on which the same reference numbers as those used in FIG. 1 were used to designate similar elements. It will also be noted that the flow rates, pressures and temperatures at different points of the circuit according to the invention are substantially the same as those indicated with reference to FIG. 1 and they will not be specified again. The heating system according to the invention of FIG. 2 differs essentially from that of FIG. 1 in that the main control valves SR ₁ , SR ₂ , SR ₃ and SR ₄ , as well as the phase separators SP ,, SP ₂ and SP ₃ have been eliminated and replaced by two-phase turbines. This is how the two-phase turbine TB replaces the regulating valve SR ₁ and the phase separator SP ₁ , the two-phase turbine TB ₂ replaces the regulating valve SR ₂ and the phase separator SP ₂ , the two-phase turbine TB ₃ replaces the control valve SR ₃ , the two-phase turbine TB ₅ replaces the control valve SR ₄ and the phase separator SP ₃ and an additional two-phase turbine TB ₄ is placed between the two-phase turbines TB ₃ and TBs.

Biphasic turbines are turbines of a particular design which are fed by means of a mixture of a liquid and a gas or vapor to drive in rotation a shaft, thus providing a mechanical work, while ensuring a separation of the liquid and gas, so that these can be collected separately at the outlet of the turbine. Since this type of turbine is known, in particular from US Pat. Nos. 3,879,949, 3,972,195 and 4,087,261 to which reference may be made, no detailed description will be given in this specification.

The condensates of the heater R ₇ are introduced into the two-phase turbine TB, as a function of the level in this heater by adjusting the position of the moderator V ', of the two-phase turbine TB, controlled by the level regulator RN ,. These condensates are directed to the condenser by the emergency control valve V, in the event of the unavailability of the two-phase turbine TB,. The vapor separated therein is directed to the steam zone of the heater R _s , while the separated water joins the condensates of the heater R ₆ . This mixture is introduced into the following two-phase turbine TB ₂ as a function of the level in the heater R _s , by adjusting the position of its moderator V ' ₂ controlled by the level regulator RN ₂ . If the TB ₂ two-phase turbine is not available, the mixture is directed to the condenser by the emergency control valve V ₂ . The steam separated in the two-phase turbine TB ₂ is directed to the steam zone of the heater R ₅ , while the separated water joins the condensates of this heater. Again, this mixture is introduced into the next two-phase turbine TB ₃ as a function of the level in the heater R ₅ , by adjusting its moderator V ' ₃ controlled by the level regulator RN ₃ . If the TB ₃ two-phase turbine is not available, the mixture is directed to the condenser by the emergency control valve V ₃ . The vapor separated in the two-phase turbine TB ₃ is directed to the heater by mixing R ₄ , while the separated water is sent directly to the next two-phase turbine TB ₄ . The vapor separated therein is directed to the vapor zone of the heater R ₃ , while the separated water joins the condensates of this heater. Finally, this mixture is introduced into the last two-phase turbine TB _S as a function of the level in the heater R ₃ , by adjusting its moderator V ' ₄ controlled by the level regulator RN ₄ . If the TB _S two-phase turbine is unavailable, the mixture is directed to the condenser by the emergency control valve V ₄ . The steam separated in the two-phase turbine TB ₅ is directed to the steam zone of the heater R ₂ , while the separated water joins the condensates of this heater in RA. The more downstream part of this system then functions as the corresponding part of the conventional heating system of FIG. 1.

In operation, the energy of the mixture of water and steam in each of the two-phase turbines is collected on a common shaft A to drive an auxiliary alternator, a pump or the like. Alternatively, the two-phase turbines may not be coupled on the same shaft.

We will now refer to FIG. 3 which shows a conventional heating system for a nuclear power plant and on which the same reference letters as those used in FIGS. 1 and 2 have been used to designate similar elements. Since the heating system of FIG. 3 is conventional and also has many similarities with that of FIG. 1, it will be described more succinctly than this.

This heating system comprises, on the main circuit CP, a sub-cooler SOR and six heaters R ₁₁ to R ₁₆ supplied with steam by withdrawals S ₁₁ to S, ₆ respectively. The heater R, ₆ is also supplied by steam separated by a phase separator SP ₁₁ from the condensates of a superheater SU (not shown) producing steam condensates at an even higher pressure than that of the heater R ₁₆ . Main regulation valves SR ₁₁ and relief valves V ₁₁ controlled as a function of the level in the superheater make it possible to direct the condensates from the latter to the phase separator SP ₁₁ or to the condenser as required, as described above. The following heater R, ₅ is supplied with steam separated from the condensates of the heater R ₁₆ by a phase separator SP ₁₂ . Main regulation valves SR ₁₂ and emergency valves V ₁₂ controlled by a level regulator RN ₁₁ are provided.

The condensates of the heater R, ₅ are sent to a recovery tank for the DRT purges via a main regulation valve SR ₁₃ . In the event of an incident, an emergency regulating valve V ₁₃ allows these condensates to be sent directly to the condenser. The DRT tank also receives condensate from a SE dryer (not shown) via a main regulation valve SR ₁₅ . An emergency regulating valve V ₁₅ , controlled like the SR ₁₅ valve depending on the level in the dryer, makes it possible to direct these condensates directly to the condenser if necessary. The DRT tank finally receives the condensates from the heater R ₁₄ , an emergency regulation valve V ₁₄ controlled by the level regulator R ₁₄ being however provided to send them to the condenser if necessary.

The content of the DRT tank is reinjected by a condensate recovery pump PR into the main circuit CP, between the feed pump PA and the heater R ₁₄ , via a main control valve SR ₁₆ controlled by a RN ₁₃ level regulator associated with the DRT tank. This regulator RN ₁₃ also controls an emergency regulation valve V, ₆ making it possible to return the condensates from the DRT tank to the condenser.

The condensates from the heater R ₁₃ are sent either to a phase separator SP ₁₃ via a main control valve SR ₁₇ or to the condenser via an emergency control valve V ₁₇ , in function of the level regulator RN ₁₅ of the heater R ₁₃ . Finally, the condensates from the heater R ₁₂ are sent, either directly to the sub-heater SOR and, from there, to the condenser via a main regulating valve SR ₁₈ , or directly to the condenser via a emergency control valve V ₁₈ , depending on the control of the level regulator RN ₁₆ of the heater R ₁₂ .

In the heating system according to the invention for a nuclear power station, as shown in FIG. 4, two-phase turbines TB ₁₁ , TB ₁₂ , TB ₁₃ , TB ₁₄ and TB ₁₅ are substituted respectively for the main control valves SR ₁₁ , SR ₁₂ , SR ₁₃ , SR ₁₇ and SR ₁₈ , and 'for the phase separators SP ₁₁ , SP ₁₂ and SP ₁₃ deleted.

The steam separated by the turbines TB ₁₁ and TB ₁₂ feeds the heaters R ₁₆ and R _{15 respectively} , while the water joins the respective condensates of these heaters to feed the following turbines TB ₁₂ and TB ₁₃ respectively. The vapor separated by the two-phase turbine TB _i3 is directed to the DRT tank, while the water is sent upstream from the condensate recovery pump PR to be reinjected with the purges from the DRT tank in the main circuit CP.

The two-phase turbine TB ₁₄ separates the steam from the condensates of the heater R ₁₃ and sends it on the steam side of the heater R ₁₂ , while the water joins the condensates of this heater. This mixture is introduced into the two-phase turbine TB ₁₅ and the vapor separated therein is directed to the steam zone of the heater R ₁₁ . The water joins the condensates of this heater and the mixture thus formed feeds the SOR sub-cooler.

Of course, as in the case of FIG. 2, the turbine biphasic TB ₁₁ to TB ₁₅ are supplied to the level in the heat exchanger by condensation from which they receive the condensate by adjusting the position of their respective moderator V _'11, V' _12, V _'13, V _'14 and V' ₁₅ . Also also, in this example, the energy of the mixture of water and steam in each of the turbines is collected on a common shaft A to drive auxiliary members or individually on the shaft of each turbine.

Thus, the two-phase turbine heating system according to the invention makes it possible both to supply the heaters in cascade with steam drawn from the condensates of a previous heater or of a superheater and to provide mechanical power additional. This therefore makes it possible to increase the overall yield of the energy production installation with which the heating system is associated.

In addition to this advantage in terms of efficiency, which can amount to an additional power supply of 0.5 to 0.8%, the heating system according to the invention makes it possible to eliminate the static phase separators from the heating systems of the prior art since it is the two-phase turbines themselves which carry out the separation. This therefore results in the elimination of the aforementioned erosion phenomena in the phase separators and a simplification of the pipeline diagram.

Claims (7)

1. A system for heating condensates of a steam turbine of an energy producing plant, comprising a series of heaters disposed in cascade and fed with steam from drawoffs at pressures which progressively increase and at least one biphase turbine fed with the condensates of a heater, characterized in that it comprises at least two biphase turbines (TB,, TB₂; TB₁₂, TB₁₃) disposed in cascade, the first turbine (TB₁ ; TB₁₂) being fed with the condensates of the heater (R₇ ; R₁₆) fed with the steam at the highest pressure, and the first biphase turbine (TB₁ ; TB₁₂) separates a steam phase which is sent to the preceding heater (R₆ ; R₁₅) fed with steam at lower pressure and a liquid phase which is sent with the condensates of the preceding heater (R₆ ; R₁₅) to the second biphase turbine (TB₂ ; TB₁₃).

2. A system as claimed in claim 1, characterized it comprises several biphase turbines (TB₁, TB₂, TB₃) disposed in cascade, each of these turbines being fed with condensates of a heater (R₇, R_e, R₅) and separating a steam phase which is sent to the preceding heater (R₆, R_s) at lower pressure, from a liquid phase which is sent with the condensates of the preceding heater (R_e, R_s) to the following biphase turbine (TB₂, TB₃).

3. A system as claimed in claim 1 or 2, comprising an intermediate mixing heater, characterized in that it comprises a biphase turbine (TB₄) associated with the heater (R₃). disposed immediatly upstream of the mixing heater (R₄) which is fed solely with the outlet liquid of the biphase turbine (TB₃) feeding the mixing heater (R₄).

4. A system as claimed in claim 1 or 2 for heating condensates in a nuclear energy producing plant, comprising downstream of the heater having the highest pressure a superheater producing steam condensates at a pressure even higher than the pressure of this last heater, characterized in that it comprises a biphase turbine (TB₁₁) between said superheater (SU) and said heater (R₁₆).

5. A system as claimed in any one of the claims 1 to 4, characterized in that it comprises a biphase turbine associated with each of a plurality of consecutive heaters.

6. A system as claimed in any one of the claims 1 to 5, characterized in that it comprises several biphase turbines (TB₁, TB₅ ; TB₁₁, TB₁₅) coupled to a common shaft (A).

7. A system as claimed in any one of the claims 1 to 6, wherein said biphase turbine comprises a regulator regulating the feed thereto, characterized in that said regulator (V₁, V'₄ ; V'₁₁, V'₁₅) is controlled by a regulator (RN₁, RN₄; RN₁₁, RN₁₅, RN₁₀) regulating the level of the condensates in said condensation exchanger.

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