JPS61142305A - Steam turbine plant - Google Patents

Abstract

PURPOSE:To promote the improvement of efficiency, by providing the second scavenge steam flow pipe, which both connects with a feed water heater in a lower pressure stage than the high pressure feed water heater connecting said pipe and has a selector valve, in the case of a steam turbine plant having a reheat device. CONSTITUTION:A steam turbine plant introduces steam, generated in a steam generating device 1, successively in the order of a high pressure turbine 2, wetness separator device 3, reheat device 4 and a low pressure turbine 5, and the steam, after it performs work, is condensed in a condenser 7. Condensed water is returned to the steam generating device 1 via low pressure feed water heaters 8, 9, supply water pump 10 and high pressure feed water heaters 11, 12. In the above, a scavenge steam flow pipe 14 connects the reheat device 4 with the high pressure feed water heater 12, and the pipe 14 connects in its half way one end of the second scavenge steam flow pipe 28 having a selector valve 26 and an orifice 27. And the other end is connected with the high pressure feed water heater 11 being in a lower pressure stage than the high pressure feed water heater 12. And the plant, when it is partly loaded, controls the selector valve 26 so as to be opened.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a steam turbine plant, and in particular to a reheating plant in which reheating is performed using oil steam from a high pressure turbine or steam generated in a steam generator. The present invention relates to a steam turbine plant having an apparatus.

[Technical backbone of the invention and its problems] Generally, in a turbine plant using a boiling water type or pressurized wood type nuclear reactor, the steam fed to the turbine is not supplied with ordinary fuel such as coal. Compared to the steam in the thermal turbine plant used, the steam contains much more moisture and is in a so-called wet steam state.

Therefore, in nuclear power turbine plants, high-humidity steam leaves the high-pressure turbine and uses a moisture separator to remove moisture before leading to the low-pressure turbine, a so-called non-reheat cycle. A so-called reheat cycle is employed in which steam is reheated using extracted steam from a high-pressure turbine or steam generated by a steam generator and then guided to a low-pressure turbine.

The reheat cycle for this scale is a first-stage reheat cycle in which reheat is performed using oil steam from a high-pressure turbine or steam generated by a steam generator, and a first-stage reheat cycle in which steam is extracted from the high-pressure turbine. There is a two-stage reheat cycle in which heat is generated and second stage reheat is performed using steam generated by a steam generator.

FIG. 3 is a system diagram showing an embodiment of a conventional nuclear turbine plant having a one-stage reheat cycle, in which most of the steam generated in the steam generator 1 passes through the main steam pipe to the high-pressure turbine 2. It will be introduced and work will be carried out there. The steam that has completed its work in the high pressure turbine 2 and has reached a humidity of approximately 12% has its moisture removed in the moisture separator @ 3, is guided to the reheating device 4, where it is heated, and is then sent to the low pressure turbine 5. It is introduced and performs work, drives power generation 816 connected to high pressure turbine 2 and low pressure turbine 5, and is converted into electrical energy.

On the other hand, the steam that has performed work in the low pressure turbine 5 is condensed in a condenser 7, heated in low pressure feed water heaters 8 and 9, and then passed through a feed water pump 10 and high pressure feed water heaters 11 and 12 to generate steam. It is refluxed to vessel 1.

By the way, a part of the steam generated in the steam generator 1 is supplied to the reheating device 4 for heating, and this heated steam gives latent heat to the steam outside the heat transfer tube (steam to be heated) in the reheating device 4. Most of the water becomes condensed condensate as it flows through the heat exchanger tube while being reheated, and is recovered by the high-pressure feedwater heater 12 via the drain tube 13. Further, a part of the heated steam does not condense during the process of flowing through the heat transfer tube, and is recovered to the high-pressure feed water heater 12 through the air-saving steam conduit 14 while maintaining the gas phase.

In other words, in the above-mentioned reheating device in which heated steam flows inside the heat transfer tube and reheats the steam outside the heat transfer tube by imparting its latent heat, the heated steam flowing into the heat transfer tube is condensed inside the tube. If all of the condensate is completely condensed in the region inside the heat exchanger tube before the outlet end of the heat exchanger tube, the inside of the heat exchanger tube will be filled with condensed condensate and become closed. However, although the heat transfer coefficient with the heat exchanger tube wall during condensation is high, the heat transfer coefficient with the condensate after condensation is low, so when the steam is filled with condensate as described above, it flows outside the heat exchanger tube. The temperature of the heated steam is not sufficiently increased, resulting in a decrease in turbine efficiency.

Furthermore, when the number of heat exchanger tubes filled with condensate reaches a certain limit, the pressure balance between the inlet end and outlet end of the heat exchanger tubes causes the condensate in all the heat exchanger tubes to synchronously flow. It is pushed out by steam, and due to the so-called hunting phenomenon, severe pressure fluctuations and unstable heat load fluctuations occur within the heat transfer tubes. As a result, the lifespan of the reheating device is significantly reduced.

For this reason, a method is generally used to increase the steam ω flowing inside the heat transfer tube to increase the flow velocity inside the tube, and to remove the condensate accumulated in the heat transfer tube with a high-speed steam flow. The used steam is recovered to the high pressure feed water heater 12 via the air saving steam conduit 14 as described above.

FIG. 4 is a configuration diagram of the heat exchanger tube section of the reheating device, and the heated steam flowing into the inlet header 21 from the heated steam inlet 20 is
After flowing through the U-shaped heat transfer tube 22 and exchanging heat with the heated steam flowing outside the heat transfer tube 22, the outlet header 2
Most of the water is discharged as drain into the drain 3, and then discharged from the drain outlet 24. Further, approximately 5 to 10% of the heated steam that has flowed into the outlet header 23 without being condensed as scavenging steam in the heat transfer tube is discharged from the scavenging steam outlet 25 and guided to the high-pressure feedwater heater.

However, from a thermodynamic point of view, the more scavenging steam m required to remove the condensate accumulated in the heat transfer tubes, the lower the thermal efficiency of the turbine cycle becomes, increasing the operating cost and increasing the It is a flow. For this reason, the air saving steam conduit 14 from the reheating device 4 is usually provided with an orifice 15 for restricting the flow rate (FIG. 3) to prevent the amount of scavenging steam from becoming more than necessary.

However, since the specifications of the orifice 15 are generally determined so that the amount of scavenging steam is appropriate when the plant is operating at rated load, the pressure, temperature, etc. on the heated steam side may change when the plant is operating at partial load. Therefore, the scavenging steam of the reheating device 4 may not perform its function sufficiently.

In other words, when the plant is operating at partial load, the amount of steam at the inlet of the turbine is small and the operation is restricted by the steam control valve, so the inlet pressure and temperature of the reheating device 4 are significantly lower than during rated load operation. ing. For example, in a typical boiling water nuclear turbine plant, 1
At 00% load operation, the inlet pressure of the reheating device 4 is approximately 14.9/cda.

The inlet temperature is about 190℃, but at 25% load operation, the inlet pressure is about 4 Kg/cm a, and the inlet temperature is about 1
It becomes 40℃. For this reason, at the outlet end of the heat transfer tube that exchanges heat with the steam on the inlet side of the heated steam of the reheating device 4, the reduced ambient temperature creates a condition where the heated steam is likely to condense.
As mentioned above, blockage due to drains inside the heat transfer tubes is likely to occur. Therefore, in order to prevent this, it is necessary to increase the scavenging steam more than during rated load operation and promptly discharge the condensate accumulated in the heat exchanger tubes.

However, as mentioned above, the orifice 15 provided in the scavenging steam 1 pipe 14 is designed to provide the optimum scavenging steam flow rate during rated load operation, so the scavenging steam flow rate hardly changes even during partial load operation. . For this reason, when a plant is started or stopped during partial load operation, the necessary scavenging steam flow rate cannot be secured, and condensate blockage or hunting occurs in the heat transfer tubes, reducing the life of the reheating equipment. In addition, there are other problems such as serious hindrance to the safe operation of turbine plants.

[Purpose of the invention]

In view of these points, the present invention can ensure the required scavenging steam flow rate even during partial pipe operation of a turbine plant,
An object of the present invention is to obtain a steam turbine plant capable of preventing clogging due to drain and hunting phenomenon in heat transfer tubes.

[Summary of the invention]

The present invention provides a steam turbine plant having a reheating device that performs reheating using extracted steam from a high-pressure turbine or steam generated by a steam generator, in which scavenging steam is transferred from the reheating device to a high-pressure feedwater heater. A second scavenging steam conduit is provided for guiding a part of the scavenging steam in the reheating device to a feed water heater at a lower pressure stage than the high pressure feed water heater through a coarse cutting valve. It is characterized by having been established.

[Embodiments of the invention]

FIG. 1 is a schematic system diagram of a steam turbine plant according to the present invention, in which steam generated in a steam generator 1 is introduced into a high-pressure turbine 2 through a main steam pipe, and the steam that has finished its work there is sent to a moisture separator. Moisture is removed in step 3 and then reheated @4
After being reheated at , it is introduced into the low pressure turbine 5. The steam that has been introduced into the low pressure turbine 5 and has done work is condensed in the condenser 7, heated up in the low pressure feed water heaters 8 and 9, and then passed through the feed water pump 10 and high pressure feed water heaters 11 and 12 into steam. It is refluxed to the generator 1.

On the other hand, the heated steam supplied to the reheating device 4 exchanges heat with the steam supplied to the low-pressure turbine 5 there, and the condensed drain therein is recovered to the high-pressure feedwater heater 12 via the drain pipe 13. Further, the scavenging steam that is not condensed in the reheating device 4 and remains in the gas phase is recovered to the high-pressure feed water heater 12 via the scavenging steam conduit 14.

Incidentally, one end of a second scavenging steam conduit 28 having a switching valve 26 and an orifice 27 is connected in the middle of the scavenging steam conduit 14 connecting the reheating device 4 and the high-pressure feed water heater 12. A second scavenging steam conduit 28 is branched out from 14, and the other end of the second scavenging steam conduit 28 is connected to the high pressure feed water heater 11 which is a lower pressure stage than the high pressure feed water heater 12.

Thus, during rated load operation of the plant, the switching valve 26 is closed, and the Y1 steam generated in the reheating device 4 is sent only to the high-pressure feedwater heater 12 via the orifice 15.

Here, when the plant is under partial load, for example, 50% load or less, the switching valve 26 is interrupted, and the scavenging steam is sent not only to the high-pressure feedwater heater 12 but also to the high-pressure feedwater heater, which is a low-pressure stage, via the orifice 27. 11 will also be sent. That is, since the pressure of the high pressure feed water heater 11 is lower than that of the high pressure feed water heater 12, a larger amount of scavenging steam type can be extracted, and in the end, the conventional 2 (8 or more) steam is used as the scavenging steam of the reheating device. Therefore, even during partial load, drain clogging and hunting phenomena in the heat transfer tubes in the reheating device are prevented.

Note that the second scavenging steam conduit 28 does not necessarily need to be connected to the high-pressure feedwater heater 11, and may be connected to, for example, the low-pressure feedwater heater 9 depending on the required length of the scavenging steam.

Further, as shown in FIG. 2, a third scavenging steam conduit 29 connected to the condenser 7 is branched from the scavenging steam conduit 14- of the reheating device 4, and the third scavenging steam conduit 29 The switching valve 30 and orifice 31 may also be provided. However, in this case, the switching valves 26 and 30 are closed when the plant is under high pressure load, the switching valve 26 is opened when the plant load is a medium load of, for example, 50 to 25%, and the switching valve 26 is opened when the plant is under a low load of 25% or less. By also monitoring the valve 30, the scavenging steam m of the reheating device can be avoided to increase significantly depending on the load.

〔Effect of the invention〕

As explained above, in the present invention, the second scavenging steam conduit is connected to the feed water heater of the lower pressure stage than the high pressure feed water heater to which the scavenging steam conduit is connected, and has a switching valve. By opening the switching valve when the load is low, the scavenging steam m can be increased, preventing drain clogging and hunting phenomena in the heat transfer tubes due to lack of scavenging steam in the reheating device, and improving plant efficiency. At the same time, its reliability can be made high.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are system diagrams showing embodiments of the present invention, respectively, FIG. 3 is a schematic system diagram of a conventional turbine plant,
FIG. 4 is a diagram showing the configuration of the heat exchanger tube section of the reheating device. 1...Hot air generator, 2...High pressure turbine, 4...
・Reheating device, 5...Low pressure turbine, 8.9...Low pressure feed water heater, 11.12...High pressure feed water heater, 14.
...Scavenging steam pipe, 26.30...Switching valve, 28.
...Second scavenging steam conduit. Applicant's agent Kiyoshi Inomata 51 Sono

Claims (1)

[Scope of Claims] 1. In a steam turbine plant having a reheating device that performs reheating using extracted steam from a high-pressure turbine or steam generated by a steam generator, a steam turbine plant having a reheating device that performs reheating using steam extracted from a high-pressure turbine or steam generated by a steam generator, in which the reheating device is connected to a high-pressure feed water heater. A scavenging steam conduit is provided to guide the scavenging steam, and a second scavenging steam conduit further guides a portion of the scavenging steam in the reheating device to a feed water heater at a lower pressure stage than the high pressure feed water heater via a switching valve. A steam turbine plant characterized by being equipped with. 2. The steam turbine plant 3 according to claim 1, wherein the second scavenging steam conduit is branched from the scavenging steam conduit connecting the reheating device and the high-pressure feed water heater; 2. The steam turbine plant according to claim 1, wherein the switching valve is opened when the load of the plant is low.