JPS637244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control method and a control device for controlling heating steam, etc. of a brackish water separation and reheating device in a nuclear power plant or the like.

In general, steam generated from a boiling water type or pressurized water type light water reactor is at a lower pressure and temperature than steam generated from a boiler using fossil fuels, and is under saturated steam conditions. For this reason, a large amount of moisture is generated during the expansion process in the high-pressure turbine, and if this steam is directly led to the low-pressure turbine, the moisture will cause a decrease in the turbine's internal efficiency and damage to the blades due to erosion. Therefore, conventionally, a brackish water separation and reheating device is disposed in the middle of the pipeline between the high-pressure turbine and the low-pressure turbine, and the brackish water is changed into a superheated steam state before being led to the low-pressure turbine. The brackish water separation and reheating device 2 is composed of a brackish water separation device, a first stage reheating device, and a second stage reheating device.
The heating steam of the stage reheating device uses steam extracted from the middle of the high-pressure turbine, and the heating steam of the second stage reheating device uses steam branched from the main steam from the nuclear reactor. Each heated steam exchanges heat with the heated steam through a tube bundle made up of a plurality of heat transfer tube groups, and most of the steam becomes condensed liquid, which is then supplied to water from the brackish water separation and reheating device via a drain pipe. guided to a heater.

In the above-mentioned brackish water separation and reheating apparatus, since the heat transfer tubes constituting the tube bundle are long and large, in certain operating conditions, a considerable amount of heated steam may condense inside the tubes with the largest heat load. Furthermore, if the heated steam flowing into these heat transfer tubes is completely condensed before the outlet end of the heat transfer tubes, there is a risk that a pool of supercooled condensate may form. The disadvantageous problems associated with this phenomenon of supercooling of condensate are localized thermal stress and thermal deformation in the heat exchanger tube, or instability of the two-phase flow of steam and condensate flowing inside the heat exchanger tube. ,
There is a possibility that the reliability of the heat exchanger tubes will be significantly impaired. In order to alleviate this problem, it has been proposed that it would be effective to provide an orifice at the inlet end of the heat exchanger tube or to add steam to scavenge the inside of the heat exchanger tube. However, the orifice provision method and its alternatives typically do not provide a complete solution to the problem of condensate subcooling and associated instability in brackish water separation and reheat devices. One reason that orifices are not a perfect solution is that any given orifice will direct the steam flow to meet the theoretical heat transfer demands for a given operating condition and Even if it is implemented to distribute the load, it is difficult to create an ideal design under all operating conditions, especially when the load changes rapidly.
Furthermore, in reality, since a tube bundle is composed of an extremely large number of heat transfer tubes, it is extremely difficult to design an orifice so as to optimize the flow state of each tube.

On the other hand, simply adding scavenging steam to the heating steam to prevent the flow in the heat transfer tubes from becoming unstable wastes a considerable amount of steam, resulting in a decrease in the thermal efficiency of the plant.

The purpose of the present invention is to avoid the flow instability phenomenon inside the heat transfer tube of the reheater that constitutes the brackish water separation and reheating device of a nuclear power plant, and to prevent malfunctions caused by overcooling problems, thereby improving the reliability of the reheater. An object of the present invention is to provide a control method and a control device for a brackish water separation and reheating device that improve performance.

The feature of the present invention is to detect the amount of heated steam and condensate that are heated fluids that have passed through a reheater, and the amount of condensed liquid, determine the flow state inside the heat transfer tube based on the respective flow rates, and further detect the amount of condensed liquid. The present invention provides a control method and a control device for a brackish water separation and reheating device that controls the flow rate of heated steam flowing down a reheater so as to select a flow state that does not cause supercooling of the liquid or unstable flow. .

Hereinafter, specific contents of the present invention will be explained in detail using Examples. As shown in FIG. 1, a brackish water separation and reheating device 2 is installed in the middle of pipes 17 and 18 between the high-pressure turbine 1 and the low-pressure turbine 6, and the brackish water is changed into a superheated steam state before being introduced to the low-pressure turbine 6. There is. The brackish water separation and reheating device 2 is composed of a brackish water separating device 3, a first reheating device 4, and a second stage reheating device 5, and is led to the heated steam piping 20 of the first stage reheating device 4. Steam extracted from the middle of the high-pressure turbine 1 is used as the heating steam, and steam branched from the main steam pipe 15 from the nuclear reactor is used as the heating steam led to the heating steam pipe 19 of the second stage reheating device 5. Each heated steam is delivered to the steam pipe 17 via tube bundles 31 and 32 constituted by a plurality of heat transfer tube groups (not shown).
The steam is introduced into the reserve tanks 33, 73 after exchanging heat with the heated steam guided through the steam. The steam from these reserve tanks 33, 73 flows through valves 38, 7.
The condensed condensate is passed through the steam pipes 39, 79 with valves 35, 75 to the drain pipe 34, with valves 35, 75.
74, and are led to the feed water heaters 13 and 14, respectively. In addition, the heating steam pipes 19, 2
0 is provided with valves 77 and 67. In a brackish water separation and reheating device with such a configuration, the flow inside the reheater heat exchanger tube when the heated steam is condensed is as follows:
Normally, as shown in Figure 4, the dryness x of the heated steam decreases almost linearly from the tube inlet end to the tube outlet end with respect to the tube length of the heat exchanger tube, and conversely, the internal cross-sectional area of the heat exchanger tube is condensed. The area occupied by the liquid tends to increase. However, the flow pattern of this two-phase flow of the vapor phase and the condensed liquid phase changes depending on the flow rate ratio of the gas phase side and the liquid phase side, resulting in a complicated flow pattern map as shown in Figure 2. Accordingly, the flow patterns are classified.
In Figure 2, the horizontal axis shows G _l /G _g ...ψ, and the vertical axis shows G _g /, where G _g is the steam flow rate G _l is the condensate flow rate, and ψ is a characteristic value that depends on the physical properties of the fluid. It is a quantity that changes accordingly, and can be expressed in units of (F _t −l _b ) by the following formula.

= [(γ _g /0.075) (γ _l /62.3)] ^1/2 ψ=73/σ [μ _l (62.3/γ _l ) ² ] ^1/3 γ _g : Specific weight of steam γ _l : Specific weight of condensate Specific weight σ: Surface tension μ _l : Viscosity coefficient of condensate As is clear from this figure, depending on the flow rates of the gas phase and liquid phase, there is laminar flow, wavy flow, annular flow, spray flow, spiral flow, and slag flow. , divided into seven regions of bubble flow. As is clear from the sketch diagrams of each flow pattern shown in Figure 3, laminar flow, annular flow, and spray flow are stable flow states, but wavy flow, spiral flow, and slug flow are extremely unstable. In a fluid style,
Water hammer due to condensate blockage is likely to occur, leading to unsteady flow phenomena with large pressure fluctuations and supercooling phenomena. Therefore, the stability of the two-phase flow with condensation, such as the flow inside the heat exchanger tube of a brackish water separation and reheating device, is established, and the thermal stress, thermal deformation, and flow instability of the heat exchanger tube due to supercooling of the condensate are established. In order to eliminate stability, the most effective method is to select a stable flow pattern as described above. For this purpose, a means for accurately detecting and controlling the flow rates on the liquid phase side and the gas phase side is required. The present invention captures the flow phenomenon of the gas-liquid two-phase flow as described above, and the flow rate of each,
It provides a control means that detects the flow rate ratio, state quantity, etc. as the amount of information and corrects the flow pattern to an appropriate flow pattern.

FIG. 5 shows the heating steam amount control means of the brackish water separation and reheating device to which the present invention is applied. In this figure, for the sake of simplicity, the brackish water separation and reheating device 2 includes only the first stage reheating device 4. However, this control technique can of course be applied even when the reheating device is composed of multiple stages. Also in FIG. 5, exhaust steam from the high-pressure turbine 1 flows into the brackish water separation and reheating device 2 through the steam pipe 17, and the brackish water separation and reheating device 2 is composed of a brackish water separation device 3 and a reheating device 4. It is shaped like a cylindrical shell. The steam from which moisture has been separated and removed by the brackish water separator 3 flows into the reheating device 4 and is converted into heating-side steam by passing through the outside of the tube bundle 31 consisting of a plurality of heat transfer tube groups. After heat exchange, the superheated steam changes state and is led to the following low pressure turbine through the low pressure turbine inlet pipe 18. A heating steam amount control valve 67 is arranged at the inlet of the heating steam pipe 20 into the reheating device 4 . The heating steam amount control valve 67 inputs a control signal from the load change rate calculator 55 to the temperature setting device 54 which sets the heated steam temperature at the outlet of the reheating device 4 in response to a change in the turbine load. Control output signal 7 from the temperature setting device 54
0 and a detection signal 71 obtained by detecting the temperature of the heated steam at the outlet of the reheating device 4 by the temperature detector 48. The comparator 53 compares the difference between the set temperature and the detected temperature, and a control signal from the comparator 53 is input to the opening degree setting means 49 of the heating steam control valve 67. The control valve opening setting means 49 includes a variable temperature calculator 50 and a variable flow rate calculator 5.
1. Consists of a variable valve opening computing unit 52.
Based on the deviation between the set temperature and the detected temperature from the comparator 53, a temperature amount for correcting the heated steam temperature according to the turbine output is calculated. Then,
The variable flow rate calculator 51 calculates the corrected amount of heating steam to achieve the corrected temperature. Furthermore, by inputting the heated steam correction amount from the variable flow rate calculator 51 to the variable valve opening calculator 52, the corrected valve opening of the heating steam amount control valve 67 is determined, and the variable valve opening is calculated. The control signal 66 from the device 52 is input to the heating steam amount control valve 67, the opening degree of the control valve 67 is corrected, and the appropriate heating steam amount is determined.

On the other hand, the heated steam of the reheating device 4 of the brackish water separation and reheating device 2 is partially condensed by heat exchange with the heated steam inside the heat exchanger tubes constituting the tube bundle 31, and is partially condensed at the outlet of the heat exchanger tubes. Then, it becomes a two-phase flow of steam and condensate and flows into the reserve tank 33 via the drain pipe 68. Inside the reserve tank 33, condensed drain 73 and vent steam 72 are separated. Vent steam 72 is stored in reserve tank 33
The steam is led to a vent steam amount control valve 38 via a vent steam pipe 37 connected to the upper steam chamber of the steam chamber. A flow rate detector 42 for detecting the amount of vent steam is arranged in the middle of the vent steam pipe 37, and a vent steam amount detection signal 43 is inputted to the flow rate calculator 57. In addition, the drain 73 at the bottom of the reserve tank 33 is connected to the drain pipe 3.
4 to the drain amount control valve 35. A flow rate detector 45 for detecting the amount of drain is placed in the middle of the drain pipe 34, and a drain amount detection signal 46 from the flow rate detector 45 is input to a flow rate calculator 57.
The flow rate calculator 57 is a vent steam amount calculator 58.
and a drain amount calculator 59, and the vent steam amount and drain amount are inputted to the flow pattern determining means 60 as output signals of the flow rate calculator 57. The flow pattern determining means 60 is composed of a flow pattern determining device 61 and a vent steam amount corrector 62.
Using G _g and the drain amount G _l , determine G _l /G _g and the above characteristic parameter, ψ, and (G _l /G _g )...ψ
The flow pattern of the two-phase flow inside the heat exchanger tube is determined from the flow pattern map shown in Figure 2, which shows the correlation between G g and G _g /. If the flow pattern is in the shaded area in Figure 2, that is, laminar flow, annular flow, or spray flow, operation is possible without modifying the vent steam amount. If the region exhibits an unstable flow phenomenon such as a flow, the vent steam amount corrector 6 is used to shift the flow to a stable region.
2, and sends a control signal to the vent steam amount corrector 62.
The amount of correction of the vent steam amount is determined by
The opening degree of the control valve 38 is adjusted so that the flow rate is appropriate.

In the actual operating state, the heating steam amount control valve 67 and the heating steam amount control valve 67, which are controlled by the aforementioned load change rate calculator 55, temperature setting device 54, detection signal from the reheating device outlet temperature detector 48, and control signal, There may be a time delay in adjusting the opening of the vent steam amount control valve 38. Therefore, in this case, it may become difficult to accurately control the flow pattern inside the heat exchanger tube using the vent steam amount control valve 38 alone. In order to avoid and eliminate this inconvenience, the control signal 63 from the variable flow rate calculator 51 incorporated in the opening setting means 49 of the heating steam amount control valve 67 that operates in response to load changes is transmitted to the flow rate change rate calculator 56.
By inputting the control signal 64 from the flow rate change rate calculator 56 to the vent steam amount corrector 62, the relationship between the vent steam amount control valve 38 and the heating steam amount control valve 67 is predicted. A means is used to control the operating state of the reheating device 4 to optimal conditions. on the other hand,
In response to the control signal 64, the flow pattern determining means 60 repeatedly controls the flow pattern determining device 61 and the vent steam amount corrector 62 to determine whether or not the corrected vent steam amount provides an appropriate flow pattern (61 and 62). 62) can be implemented.

In the above control method, when there is no load change, there is no need to use the flow rate change rate calculator 56, and the vent steam control valve 38 is directly controlled by bypassing the flow rate change rate calculator 56 depending on the magnitude of the load change rate. do. Therefore, when the load is steady, the internal flow of the heat transfer tube is stabilized in response to the heat transfer performance in the reheating device 4, changes in the state of the steam on the heated side (for example, changes in the humidity at the inlet), etc. Control to maintain the flow pattern becomes possible.

FIG. 6 and FIG. 7 show the steam temperature on the heated side of the reheating device, the venting steam amount, This is a comparison of how the amount of condensed liquid changes with respect to load changes. As before,
When the amount of heated steam is not controlled, the relationship between the amount of condensate G _l and the amount of vent steam G _g is determined primarily by the heat transfer performance of the reheating device, and the ratio of G _l /G _g changes as the load increases. This tends to increase, the flow pattern tends to become unstable, and furthermore, the change in the steam temperature T on the heated side becomes large. However, if the control according to the present invention is implemented, it is possible to minimize the amount of heating steam that does not participate in heating the steam to be heated on the low load side, and it is possible to significantly contribute to improving the thermal efficiency of the plant. Since the ratio between the condensate amount G _l ′ and the vent steam amount G _g ′ does not change significantly with respect to load changes, the flow inside the tube bundle 31 of the reheating device 4 can be stabilized. Further, as shown in FIG. 5, the vent steam is led to the subsequent feed water heater (not shown) via the control valve 38 and steam pipe 39, but the feed water is heated only by the extracted steam from inside the turbine. Compared to cycles, it is possible to improve the thermal efficiency of the plant.

The embodiments of the present invention have been specifically described above, and the effects obtained by the present invention are as follows.

(1) A highly reliable control method for a brackish water separation and reheating device that eliminates the flow instability of the gaseous two-phase flow inside the heat transfer tube of the reheating device and prevents problems associated with overcooling of the condensate. A control device can be realized.

[Brief explanation of the drawing]

Fig. 1 is a cycle configuration diagram of a nuclear power plant equipped with a brackish water separation and reheating device, which is the subject of the present invention, Fig. 2 is a map diagram for determining the flow pattern inside the heat transfer tube, and Fig. 3 is a diagram showing the flow pattern. FIG. 4 is a schematic diagram showing changes in wetness of heated steam when condensation is involved. FIG. 5 is a control system diagram showing a control device for a brackish water separation and reheating device to which the present invention is applied. 7 and 7 are diagrams showing changes in the amount of steam and the amount of condensed liquid with respect to the load when the present invention is applied. 2...Brackish water separation reheater, 3...Brackish water separation device,
4... Reheating device, 48... Temperature detector, 31...
Heat exchanger tube bundle, 38...Vent steam amount control valve, 49
...Control valve opening degree setting means, 50...Variable temperature calculator, 51...Variable flow rate calculator, 52...Variable valve opening degree calculator, 53...Comparator, 54...Temperature setting device, 55... ...Load change rate calculator, 56...Flow rate change rate calculator, 57...Flow rate calculator, 58...Vent steam calculator, 59...Drain amount calculator, 60...
... Flow pattern determination means, 61 ... Flow pattern determination device, 62 ... Vent steam amount corrector, 67
... Heating steam amount control valve.

Claims (1)

[Claims] 1. A method for controlling a brackish water separation and reheating device equipped with a reheater, which includes detecting the flow rates of steam and condensate in which the state of the heating fluid has changed after passing through the reheater,
From these flow rates, the flow condition of the gas-liquid two-phase flow of the heating fluid flowing down the heat transfer tube of the reheater is estimated by calculation, and based on the estimation result, the amount of vent steam flowing down the heat transfer tube of the reheater is calculated. 1. A method for controlling a brackish water separation and reheating device, characterized in that: 2. In a control device for a brackish water separation and reheating device equipped with a reheater, a flow rate detector is provided in each of the steam piping and the drain piping from which steam and drain, which are heated fluids that have passed through the reheater, are drawn out, and the flow rate detector A flow pattern calculation device is provided that calculates the flow condition of the gas-liquid two-phase flow of the heating fluid flowing down the heat transfer tube of the reheater based on the detected value from the steam pipe, and 1. A control device for a brackish water separation and reheating device, comprising a flow rate control device that controls the opening degree of a control valve installed in the control valve.