JPH037869B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a backwash operation control device for a condenser for use in a power generation plant, etc., which has one tube bundle and has two cooling water turns.

[Technical background of the invention and its problems]

Generally, a power generation plant is provided with a condenser for the purpose of condensing turbine exhaust gas, and seawater is mostly used as cooling water for the condenser. However, this seawater contains foreign objects such as shellfish and wood chips, and since this cooling water flows through the cooling pipes, long-term operation of the condenser causes the foreign objects in the seawater to be transferred to the inlet side of the cooling pipes. They may block the pipes or become clogged in the pipes, reducing the efficiency of the condenser or causing damage to the heat exchanger pipes, etc. Therefore, in order to remove these foreign substances, a so-called backwash operation is generally performed in which a backwash valve is installed in the cooling water supply and drain pipes and the cooling water is flowed from the opposite direction of the cooling pipe to remove the attached foreign substances. It is.
Moreover, the number of times this backwash operation is performed varies depending on the amount of foreign matter, but if there is a large amount, it is performed once a day.

By the way, in the above-mentioned cooling water backwash operation system, the backwash valve is very expensive, the system is more complicated than a system without a backwash valve, and the cooling water piping sends a large amount of cooling water. From this point of view, the large diameter of 1 to 3 m poses the problem of high equipment costs, but backwashing has the advantage of increasing plant operating efficiency by eliminating clogging of cooling pipes, etc. has.

As for the cooling water system of conventional power generation plants, based on the cost comparison of the two sides mentioned above, in most cases large power plants are systems that allow backwash operation due to the merits of increased operational efficiency, while systems that allow backwash operation are used in small power plants. However, a backwash operation system was not adopted from the viewpoint of the merits of initial capital investment.

However, with the recent huge rise in the cost of fuels such as oil, operating costs account for a very large proportion of the cost of power generation plants, and small power generation plants that are recently planned are Backwash operation systems are increasingly being adopted with the aim of increasing operational efficiency.

On the other hand, condensers in small plants with small turbine displacements are configured with one tube bundle per condenser, and if the required amount of cooling water is small, the number of condenser cooling pipes is small and the length of the cooling pipes is small. Because it needs to be long, a two-pass condenser is used in which one tube bundle is divided into two sections and the cooling water reciprocates within the tube bundle. That is, mainly when the required amount of cooling water is small in a small-sized plant, a one-tube bundle, two-pass type condenser is used.

1 and 2 are schematic system diagrams of a one-tube bundle two-pass type condenser in which a backwash valve is installed in the cooling water system, and the front water chamber 2 of the condenser 1 is connected to a partition plate. The front water chamber 2 and the rear water chamber 4 are connected by a plurality of cooling pipes 5, and the cooling pipes 5 are divided into an inlet water chamber 2a and an outlet water chamber 2b. It is divided into an inlet tube bundle 5a and an outlet tube bundle 5b in terms of connections with the tubes.

Cooling water pipes 8 and 9 having stop valves 6 and 7 are connected to the inlet water chamber 2a and the outlet water chamber 2b, respectively, and the other ends of both of the cooling water pipes 8 and 9 are connected to a four-way switching valve. A cooling water supply pipe 13 having a stop valve 11 and a water intake pump 12 is connected to one of the other two ports of the backwash valve 10, and a cooling water supply pipe 13 having a stop valve 11 and a water intake pump 12 is connected to the other two ports of the backwash valve 10. A cooling water discharge pipe 15 having a stop valve 14 is connected. Note that 16 is a valve body of the backwash valve 10.

When the valve body 16 of the backwash valve 10 is rotated to the position shown in FIG. communicate. Therefore, the seawater pumped up by the water intake pump 12 flows into the condenser inlet water chamber 2a through the backwash valve 10, the cooling water pipe 8, and the stop valve 6 as cooling water. The cooling water that has flowed into the inlet water chamber 2a flows through the inlet pipe bundle 5a, the rear water chamber 4, and the outlet pipe bundle 5b in order, enters the outlet water chamber 2b, and then passes through the stop valve 7, the cooling water pipe 9, the backwash valve 10, and the cooling water It is returned to the sea via the discharge pipe 15.

On the other hand, when backwashing the condenser 1, the backwash valve 10
The valve body 16 is rotated to the state shown by the dotted line in FIG. Then, the seawater pumped up by the water intake pump 12 flows into the outlet water chamber 2b through the backwash valve 10, the cooling water pipe 9, and the stop valve 7, and then, as shown by the arrow, during the forward washing shown in FIG. Conversely, the water flows through the outlet pipe bundle 5b, the rear water chamber 4, and the inlet pipe bundle 5a in order, enters the inlet water chamber 2a, and is returned to the sea via the cooling water pipe 8, the backwash valve 10, and the cooling water discharge pipe 15.

Such backwash operation of the condenser can be performed by using the above-mentioned backwash valve, but this type of backwash valve has the following problems as its characteristics.

That is, when the valve body 16 of the backwash valve 10 moves from the forward flush state to the backwash state, as shown in FIG. The flow from the cooling water supply pipe 13 to the cooling water pipe 8 is almost eliminated because there is a resistor such as the condenser 1 on the downstream side, and the cooling water sent from the cooling water supply pipe 13 is directly discharged. It tends to flow into the pipe 15. In other words, the cooling water sent from the water intake pump 12 is transferred to the backwash valve 10 and the cooling water discharge pipe 1.
5 to the sea, and no cooling water flows into the condenser 1. FIG. 4 is a diagram showing the change in the amount of cooling water flowing toward the condenser when transitioning from the forward flushing state to the backwashing state, and shows the change in the amount of cooling water flowing toward the condenser side.
As the cooling water rotates, the cooling water that was flowing 100% forward gradually decreases, and when the valve body 16 reaches the state shown in Fig. 3, that is, the valve displacement point position, the cooling water flows toward the condenser. The flow rate becomes zero, and then gradually increases in reverse flow state.
It will increase up to 100%.

In this case, in order to prevent the occurrence of water hammer phenomenon in the valve part, the above-mentioned backwash valve is operated for 60 seconds from the normal washing state with a flow rate of 100% in the normal normal washing state to the intermediate position state with a flow rate of 0%. Flow rate 100% from state
One operation is completed in a total of 120 seconds, including 60 seconds until the backwash state.

On the other hand, condensers for power plants are operated at the design vacuum level (approximately 720 mmHg) set during normal operation, but if the condenser vacuum drops transiently for some reason, it will not have a negative impact on the power plant. As such, a turbine trip limit vacuum degree is always set. This turbine trip limit vacuum level is determined in consideration of the safety of the turbine installed in connection with the condenser, and is set at a constant value around 600 to 650 mmHg regardless of the type of plant. Ru.

Therefore, when a phenomenon occurs in the condenser where the cooling water decreases to zero as described above, the condensation capacity of the turbine exhaust decreases by an amount commensurate with the change in cooling water, and as a result, the condenser The vacuum may drop abnormally to below the trip limit value, making it impossible to handle 100% of the power generation load during backwash operation.

By the way, in large-scale power plants, the number of tube bundles is two or more due to the large amount of cooling water and the number of cooling pipes that make up a tube bundle, and as shown in Figure 5 a, b, and c, each Tube bundle 5a,
An inlet water chamber 2a and an outlet water chamber 2b are independently provided for each tube bundle, and a cooling water system is also provided independently for each tube bundle, and a backwash valve 10 is attached to each of them.

Therefore, when the tube bundle consists of two, both tube bundles 5
During forward washing operation of both tube bundles 5a and 5b, the cooling water flows as shown by the arrow in Fig. 5a, and during backwashing operation, the cooling water flows only into either one of the pipe bundles 5a and 5b as shown in Fig. 5b. As shown by the arrows in and c, the cooling water is flowed in the opposite direction to that during the normal washing operation.

Therefore, both tube bundles can be independently backwashed, and the amount of cooling water only changes in one of the plurality of tube bundles during backwash operation, while the other tube bundles are always The entire design amount of cooling water is flowing. Therefore, even if backwash operation is performed, changes in cooling water have a very small effect on the overall condenser vacuum, and generally the vacuum decreases by about 10 to 20 mmHg, which is not enough to affect the trip limit vacuum. There is almost no decline.

However, in the condenser in the small power generation plant that is the target of the present invention, as described above, the tube bundle becomes one tube bundle, so when switching to backwash operation, no cooling water is sent to the condenser tube bundle. This may result in a significant drop in vacuum in the condenser, which may cause a situation where the trip limit vacuum level is exceeded as described above.

Therefore, in order to avoid the above-mentioned situation in a condenser in a small plant that employs two passes in one tube bundle, it is necessary to prevent trips from occurring even when the flow rate is transiently zero, before starting backwashing operation. load,
For example, after setting the power plant at 30% load, it is necessary to shift to backwash operation or forward wash operation.

However, in this case, it is necessary to reduce or increase the load each time a backwash operation is performed, making plant operation complicated. In addition, the load must be reduced each time a backwash operation is performed, and the load changes. Since these operations cannot be carried out in a short time, the thermal efficiency of the plant throughout the year decreases, which goes against the current trend of increasing plant thermal efficiency. Moreover, the number of load changes will significantly increase compared to the conventional number of load changes.
There are problems such as a decrease in the reliability probability of the plant.

By the way, Figures 6a and 6b are diagrams showing the results of transient analysis obtained by computer analysis of the state of change in condenser performance due to opening and closing of the backwash valve using theoretical calculations based on test results. , Figure 6a shows the change in cooling water flow rate with time on the horizontal axis and flow rate toward the condenser on the vertical axis, and Figure 6b shows time on the horizontal axis and condenser vacuum on the vertical axis. 2 is a diagram showing how condenser performance changes, and both diagrams have the same time axis so that relative changes can be seen. In Figure 6a, curve A,
B and C each indicate the change in cooling water flow rate when the operating speed of the backwash valve changes,
Curve A corresponds to the conventional valve operation of 120 seconds, curve B corresponds to approximately 90 seconds, and curve C corresponds to approximately 60 seconds. According to this figure, the backwash valve corresponds to the case of normal flushing. As the time of backwashing progresses, the vacuum in the condenser decreases, and the lowest vacuum in the condenser occurs slightly later than when the flow rate is 0%, and then as the backwash valve operates, the vacuum in the condenser decreases. It can be seen that the vacuum will recover. Further, as can be seen from the minimum vacuum curve D connecting the minimum vacuum points of A, B, and C, the minimum vacuum value increases as the operating time of the backwash valve becomes shorter.

Therefore, in the state of curve A, which was set in consideration of the occurrence of the conventional water hammer phenomenon, the minimum vacuum value will be lower than the trip limit vacuum value E, but if the backwash valve operation time is shortened, The minimum vacuum value is higher than the trip limit vacuum value E.

However, shortening the valve operation time as described above, on the other hand, leads to the occurrence of water hammer phenomenon in the backwash valve section.

The above-mentioned water hammer phenomenon generally occurs during the opening and closing operations of a valve. During the opening operation of the valve, water that has been stationary in the pipes rapidly increases its flow velocity as the valve opens, and This is because a gas phase is generated in the pipe due to a decrease in static pressure corresponding to the increase in dynamic pressure of the water, and when the valve is closed, the flowing water is This is due to the collision effect of water associated with sudden stopping. Therefore, as the opening/closing time of the valve becomes shorter, the size of the water hammer also becomes larger.

However, unlike ordinary valves, in a backwash valve, water is flowing even before and after switching the backwash valve, so a drop in static pressure does not occur, and water hammer occurs when the backwash valve starts operating. is not a problem. Only at the end of the valve's operation does the water hammer phenomenon occur, although it is smaller than in a typical valve.

For this reason, when switching the condenser from the forward washing state to the backwashing state or vice versa,
By shortening the operation time of the backwash valve, it is possible to prevent the minimum vacuum drop in the condenser from falling below the trip limit vacuum, and furthermore, it is possible to take measures against the water hammer phenomenon only before the operation of the backwash valve ends. If this is done, the water hammer phenomenon can be prevented from occurring, and there is no need to reduce the load on the power plant each time the transition to backwash operation or forward wash operation is made, and the above-mentioned problems can be solved. It has been found.

[Purpose of the invention]

In view of these points, the present invention focuses on the relationship between the operating speed of the backwash valve and the change in condenser performance, and makes sure that the vacuum of the condenser is below the trip limit value when transitioning to backwash operation or forward wash operation. Condenser backwash operation that can reliably prevent the water from dropping to 100%, enable 100% load operation without reducing the load, and at the same time prevent the water hammer phenomenon from occurring when the backwash valve is activated. The purpose is to obtain a control device.

[Summary of the invention]

The present invention provides a backwashing operation control device for a condenser with one tube bundle and two passes of cooling water flow. A wash valve operating position detector, a signal from the operating position detector indicating that the valve displacement point of the backwash valve has been passed when switching the backwash valve, and a condenser design from the vacuum detector. The backwash valve is operated at high speed to prevent the condenser vacuum from dropping below the turbine trip limit vacuum until a signal higher than the specified vacuum level set between the vacuum level and the turbine trip limit vacuum level is received. Thereafter, a control signal generator outputs a control signal that operates at a low speed that does not cause water hammer phenomenon in the cooling water pipes, etc., and the backwash valve is operated by the output signal from the control signal generator. The device is characterized by having a backwash valve drive device, which prevents the condenser vacuum from dropping below the turbine trip limit vacuum level when switching to backwash operation, etc., and reduces the plant load. This eliminates the need for any reduction.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 7 to 11. Note that the same parts in FIG. 7 as in FIG. 1 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

FIG. 7 is a schematic system diagram of an embodiment of the control device of the present invention, in which the condenser 1 has a condenser vacuum detector 2
0 is provided, and its condenser vacuum detector 20
The output signal from the backwash valve drive device 21 is inputted to a control signal generator 22 which generates a control signal to the backwash valve driving device 21. In addition, a backwash valve operating position detector 23 is attached to the backwash valve 10, and outputs a signal when the valve body 16 of the backwash valve 10 reaches an intermediate opening or more, that is, when the valve displacement point has been passed. However, the output signal is also applied to the control signal generator 22, and the backwash valve driving device 21 is controlled by the output signal from the control signal generator 22.

That is, the above-mentioned backwash valve driving device is configured so that, during the switching operation of the backwash valve, the valve body 16 passes the intermediate opening as shown in FIG. Higher than the specified value set between the trip limit vacuum level, for example, the condenser vacuum level is higher than the vacuum value that reaches 1/4 to 1/2 of the difference between the minimum vacuum level and the design vacuum level and the minimum vacuum level. The backwash valve 10 is operated at a high speed until the condenser vacuum does not fall below the turbine trip limit vacuum level, and thereafter the backwash valve 10 is operated at a relatively low speed so that no water hammer phenomenon occurs in the condenser. The backwash valve 10 is operated. In this case, the speed of the backwash valve driving device can be changed by changing the power supply voltage supplied to the electric motor, which is the driving device, using a resistor, or by changing the speed of the electric motor using a frequency converter. It can also be done by means.

FIG. 8 is a block diagram of the control signal generator 22, which includes a control switch 31 that instructs the backwash valve to perform a forward wash operation, and a control switch 3 that instructs a backwash operation.
2. A stop switch 33 for both operations, a backwash valve position detector 34 that generates an output signal when the valve opening from the normal valve flushing operation to the backwashing operation exceeds the intermediate opening, that is, passes the intermediate opening; A backwash valve position detector 35 generates an output signal when the valve opening from the washing operation to the normal washing operation exceeds the intermediate opening, and outputs an output signal when the condenser vacuum reaches a specified vacuum. A vacuum detector 36 is provided, and control switches 31, 3
The output terminals of 2 are connected to one input terminal of OR circuits 38 and 39, respectively. In addition, both OR circuits 38,
The output terminals of self-holding circuits 40 and 41, which are opened and closed by the stop switch 33, are connected to the other input terminals of 39, respectively, and the output terminals of the OR circuits 38 and 39 are connected to one input of AND circuits 42 and 43, respectively. connected to the end.

On the other hand, the backwash valve intermediate opening degree or higher signal from the backwash valve position detector 34 and the signal from the vacuum detector 36 that is higher than the condenser vacuum standard, that is, the signal higher than the condenser vacuum standard are both input to the AND circuit 44. It was done like this,
Further, the backwash valve intermediate opening degree or more signal from the backwash valve position detector 35 and the condenser vacuum specified or more signal from the vacuum detector 36 are both input to an AND circuit 45.

The output terminals of the above AND circuits 44 and 45 are respectively
It is connected to one input terminal of AND circuits 46 and 47, and further connected to the other input terminal of AND circuits 42 and 43 via NOT circuits 48 and 49, respectively. Further, the output terminals of OR circuits 38 and 39 are connected to the other input terminals of AND circuits 46 and 47, respectively.

Therefore, the output end of the AND circuit 42 is connected to a backwash high-speed circuit 50 that performs a rotation operation of a drive device for rotating the valve body 16 of the backwash valve from the forward washing direction to the backwashing direction at high speed. The output terminal of 46 is connected to a backwash low-speed circuit 51 that rotates the drive device in the backwash direction at a low speed, while the output terminal of the AND circuit 43 rotates the drive device from the backwash direction to the forward wash direction at high speed. The output terminal of the AND circuit 47 is connected to a forward washing low speed circuit 53 which performs rotation from backwashing to forward washing at a low speed.

Therefore, when the control switch 31 is turned on when switching the backwash valve from the normal wash state to the backwash state,
This input signal is input to the OR circuit 38, and in cooperation with the self-holding circuit 440, the backwash command signal is held until the stop switch 33 is activated and is input to the AND circuit 42. By the way, at the time when the control switch 31 is turned on, since normal washing is in progress, the degree of vacuum in the condenser is sufficiently high, and naturally the opening degree of the backwash valve is also in the normal washing operation state. Therefore, the signal from the backwash valve position detector 34 that is equal to or higher than the backwash valve intermediate opening does not act on the AND circuit 44, and the AND circuit 44 does not act on it. Therefore, the AND circuit 42 to which the backwash command signal is input is operated by the output signal from the NOT circuit 48, and the command signal is input to the backwash high speed circuit to operate the drive device, causing the backwash valve 10 to operate. The valve body 16 is rapidly rotated in the backwashing direction. That is, the backwash valve 10 is rotated at a fast constant operating speed such that the minimum vacuum value of the condenser due to the decrease in the amount of cooling water due to the rotation does not fall below the turbine trip limit vacuum value specific to the plant. It will be done.

In this manner, when the backwash valve opening exceeds the intermediate opening, the degree of vacuum in the condenser, which has once decreased, begins to rise again. When the degree of vacuum reaches the specified vacuum value, the AND circuit 44 operates, and the backwash command signal is sent to the backwash low speed circuit 51 via the AND circuit 46 based on the output signals of the AND circuit 44 and the OR circuit 38. is input. On the other hand, at this time, the NOT circuit 48 ceases to operate, the AND circuit 42 becomes inactive, and the high-speed backwashing command signal is canceled. Therefore,
The backwash valve driving device is placed under the control of the backwash low-speed circuit 51, and the backwash valve 10 is rotated in the backwash direction at a low speed that does not cause water hammer phenomenon until switching is completed, and the condenser is rotated. Completely backwashed. That is, the flow of cooling water in the condenser 1 is switched from the direction shown by the solid line arrow in FIG. 7 to the direction shown by the dotted line arrow.

On the other hand, when switching from the backwash state to the normal wash state, when the control switch 32 is turned on, the AND circuits 43 and 47 operate in sequence in the same manner as described above, and the backwash valve opening becomes equal to or higher than the intermediate opening and the condensate When the chamber vacuum exceeds a specified vacuum, the operating speed of the backwash valve is changed from high speed to low speed.

In this way, when switching the backwash valve from the forward wash state to the backwash state or vice versa, the condenser vacuum is prevented from falling below the turbine trip limit vacuum, and the The water hammer phenomenon can be prevented from occurring.

FIG. 9 is a diagram showing another embodiment of the present invention, in which between the AND circuit 46 and the backwash low speed circuit 51,
Between the AND circuit 47 and the normal washing low-speed circuit 53, OR circuits 54 and 55 are interposed, respectively, and self-holding circuits 56 and 57 are connected to one input terminal of both OR circuits 54 and 55, respectively. Output end is connected.

Therefore, once the backwash valve is selected to operate at low speed, the low speed operation continues even if the degree of vacuum in the condenser decreases and the conditions for low speed operation no longer hold. Therefore, even if the degree of vacuum in the condenser suddenly decreases for some reason after switching to low-speed operation, the system will not shift to high-speed operation again, providing protection from the water hammer phenomenon caused by backwash valves, etc. be able to.

〔Effect of the invention〕

As explained above, in the present invention, with the above configuration, when switching the operating state of the backwash valve, a signal indicating that the valve displacement point of the backwash valve has been passed from the backwash valve position detector and a vacuum detection are detected. The backwash valve prevents the condenser vacuum from dropping below the turbine trip limit vacuum until it receives a signal from the condenser that is higher than the specified vacuum between the condenser's design vacuum and the turbine trip limit vacuum opening. The vacuum level of the condenser is set to the turbine trip limit vacuum level when the backwash valve is switched. It is possible to prevent the following from occurring, there is no need to reduce the load on the plant each time before starting a backwash operation, etc., and the switching time can also be shortened, making it possible to prevent a decrease in plant efficiency. Moreover, the water hammer phenomenon does not occur in the latter half of the operation of the switching valve, and the safety of the plant can also be ensured.

[Brief explanation of the drawing]

Figures 1 and 2 are diagrams for explaining the operation of a condenser cooling water system with a backwash valve, Figure 3 is a diagram for explaining the flow state of cooling water showing the intermediate opening position of the backwash valve, and Figure 4 is a diagram for explaining the flow state of the cooling water. Figures 5a, b, and c are diagrams of changes in cooling water flow rate with respect to valve displacement of the backwash valve, respectively. Figure 6a is a diagram of changes in the flow rate of cooling water to the condenser when the backwash valve is operated, Figure 6b is a diagram of changes in condenser vacuum corresponding to changes in the flow rate of cooling water, and Figure 7 is a diagram of changes in the condenser vacuum according to the present invention. A schematic system diagram of a backwash operation control device in an embodiment, FIG. 8 is a block diagram of a control signal generator in the present invention, and FIG. 9 is a block diagram of a control signal generator in another embodiment of the present invention. be. 1... Condenser, 2a... Inlet water chamber, 2b... Outlet water chamber, 5... Pipe bundle, 10... Backwash valve, 20...
Condenser vacuum detector, 21...Backwash valve drive device, 2
3...Backwash valve position detector.

Claims (1)

[Claims] 1 In a backwash operation control device for a condenser with one tube bundle and two passes of cooling water flow, a vacuum detector that detects the degree of vacuum of the condenser and a backwash valve consisting of a four-way switching valve are installed. When switching the operating position detector and the backwash valve, a signal from the operating position detector indicating that the valve displacement point of the backwash valve has been passed and a design vacuum degree of the condenser from the vacuum detector are provided. The backwash valve is operated at high speed so that the condenser vacuum does not fall below the turbine trip limit vacuum until a signal higher than the specified vacuum level set between the turbine trip limit vacuum levels is received; A control signal generator that outputs a control signal that operates at a low speed that does not cause water hammer phenomenon in cooling water pipes, etc., and a reverse valve that operates a backwash valve by the output signal from the control signal generator. 1. A backwash operation control device for a condenser, comprising a wash valve drive device.