JP2001342805A - Operation control method for water supply booster pump of steam power plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent functional loss of a water supply booster pump of a steam power plant at low cost and with good reliability. SOLUTION: The process value related to deaerator in the condensate supply system of the steam power plant, and a current value and a transition estimated value of effective NPSH of the water supply booster pump are computed and displayed on a central control board. When the effective NPSH and its transition estimated value of the water supply booster pump are below the sum of required NPSH of the water supply booster pump and a preset margin value, a target condensate flow obtained by computing and estimating a suitable condensate flow is displayed on the central control board, and an operator is forced to operate a deaerator water level control valve so that the effective NPSH of the water supply booster pump is not less than the sum of the required NPSH and the preset margin value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the operation of a pump, and more particularly to a so-called steam power plant in which steam used in a turbine is condensed and used as feed water for a steam generator, such as a thermal power plant or a nuclear power plant. The present invention relates to a method for controlling the operation of a water supply booster pump.

[0002]

2. Description of the Related Art In thermal power plants and nuclear power plants,
Boiler or reactor vessel (also called nuclear boiler)
In general, a steam turbine is driven by the steam generated in the above, and the exhaust steam is condensed in a condenser to form condensed water (condensed water), which is returned to a boiler to circulate water. FIG. 2 shows an example of a condensate water supply system of a working pressurized water nuclear power plant. In brief, the condenser 1 is a facility for condensing steam received from a steam turbine (not shown) with cooling water and returning it to water (condensation). The condensate flowing out of the condenser 1 is pressurized by the condensate pump 3 and the condensate booster pump 5. The pressurized condensate passes through a deaerator water level control valve 7 and a low-pressure feedwater heater (a plurality of stages) 9 to deaerator 11.
Flows into. In the deaerator 11, the condensate is heated by bleeding of a low-pressure steam turbine (not shown) to remove contained gas components, that is, to degas. The deaerated condensate flows down to the deaerator tank 13 below, where it is temporarily stored.
The condensed water is hereinafter referred to as water supply, and reaches the high-pressure water heater 21 through the deaerator downcomer 15, the water supply booster pump 17 and the water supply pump 19, and is further conveyed to the water supply nozzle of the steam generator 23.

More specifically, the deaerator water level control valve 7 is
The water level in the deaerator tank 13 is always maintained at a preset value, and the low-pressure feed water heater 9 is generally a shell-tube heat exchanger, and heats condensate by turbine bleed. As described above, the deaerator 11 also raises the temperature of the condensed water by direct contact heat exchange with the turbine bleed air, and removes the gas component (air) contained in the condensed water so that it can be used as water supply. The high-pressure feed water heater 21 is a shell-tube heat exchanger, and heats the feed water by extracting air from a high-pressure turbine (not shown). The water supply minimum flow valve 25 secures the minimum flow rates of the water supply booster pump 17 and the water supply pump 19 when the amount of water supplied to the steam generator 23 decreases.
In order to always maintain the flow control by the water supply pump 19 properly, it is important to secure the minimum flow rate.

In the condensate water supply system configured as described above,
The feedwater booster pump is arranged so that it can always operate normally. That is, in the normal rated operation state, the temperature of the condensate flowing into the deaerator 11 is around 160 ° C., the pressure in the deaerator 11 is 12 kg / cm ² abs, and the temperature is 190 ° C.
(Saturation temperature). On the other hand, the water level of the supply water of the deaerator tank 13 is set at a position higher than the suction port of the water supply booster pump 17, and the pressure head (effective NPSH) of the water supply booster pump 17 has a margin for the necessary NPSH of the water supply booster pump. To secure.
When the effective NPSH becomes less than the required NPSH, the water supply is flushed at the suction port of the water supply booster pump 17 and the pump function is lost, so that this is prevented.

In the above-described system, under normal operating conditions, the pressure of the deaerator and the saturation pressure of the supply water at the pump suction section are almost equal, and there is no problem. However, the power plant is disconnected from the power system due to lightning or the like. When this occurs, the turbine load drops sharply. When the load suddenly decreases, the steam flowing into the turbine is throttled by the steam control valve, the turbine bleed pressure instantaneously decreases, and the supply of the heating steam to the low-pressure feedwater heater 9 and the deaerator 11 is stopped. Therefore, the temperature of the condensate flowing into the deaerator 11 decreases, and the heating in the deaerator 11 is interrupted, so that the pressure in the deaerator 11 decreases. On the other hand, the amount of the steam generator 23 decreases even after the sudden decrease in the load, but the steam generator 23 needs water supply and continues to operate. However, the water supply to the water supply booster pump 17
Since it is supplied by flowing down the deaerator downcomer 15, it takes several tens seconds to several minutes from the deaerator tank 13 to the suction port of the water supply booster pump 17. That is, the water supply from the deaerator tank 13 (supply water having a higher temperature and a higher saturation pressure than the deaerator tank) from several tens of seconds to several minutes before flows into the suction port of the water supply booster pump 17. This will reduce the effective NPSH of the feedwater booster pump by the saturation pressure difference.

[0006] As described above, when the effective NPSH decreases and falls below the required NPSH, the function of the water supply booster pump 17 is lost as described above, and the water supply to the steam generator 23 is interrupted. That is, since the steam generator 23 trips, it takes a long time to restart the operation, and various problems occur in maintaining the power distribution network. The possibility of occurrence of such a problem has been known, and the following countermeasures have been taken. 1. The load drop is automatically detected by the plant measurement device. 2. The degree of opening of the deaerator water level control valve 7 is reduced to a preset value, the amount of condensate flowing into the deaerator 11 is limited, and the rate of decrease of the deaerator pressure is limited. 3. The deaerator pressure control valve (not shown in FIG. 2) attached for other purposes is fully opened to allow the steam retained in the plant to flow into the deaerator 11 to limit the rate of decrease in the deaerator pressure. 4. By fully opening the water supply pump minimum flow valve 25, the amount of water flowing into the water supply booster pump 17 from the deaerator tank 13 is increased, and the time delay in the deaerator downcomer 15 is reduced. In this way, the effective NPSH of the water supply booster pump 17 at the time of a sudden decrease in load is secured.

[0007]

However, as described above, the effective N of the water supply booster pump 17 conventionally used is
The measures for securing PSH are exclusively for responding to a sudden decrease in load. In other words, the set values used in the countermeasures are determined by assuming all conceivable situations when the load suddenly drops, and in order to ensure the effectiveness of the countermeasures, simulations must be performed for all those situations. And confirm the validity of the results. And the simulation is: a. Plant load before load drop, b. Opening of the deaerator water level control valve before the load drops, c. Operation of the deaerator heating steam control valve d. Operation method of feed water pump minimum flow valve, e. It is necessary to change the parameters such as the amount of water supply before and after the load suddenly decreases, etc., and the number of cases may exceed 100.
It requires a great deal of money and time. FIG. 3 shows an example of the result of the simulation. In addition, although the above simulation case assumes all states,
People are limited, and unexpected situations may occur. In such a case, it cannot be denied that an unexpected result is produced. In the above-described conventional countermeasures, it can be understood that the NPSH securing countermeasure control of the feed water booster pump at the time of a sudden decrease in the load has been activated, but it is effective for plant operators.
Since the value of PSH is not displayed, it is not possible to reliably secure the effective NPSH, and anxiety occurs. Furthermore, NPSH securing countermeasure control of the conventional water supply booster pump is necessary.
Is not directly controlled, but as a result of implementing each of the above measures, the minimum value of the effective NPSH is
It is intended to be above SH, and it is difficult to completely determine that the control is appropriate. Also, in the above measures,
Reducing the valve opening of the deaerator water level control valve when the load suddenly decreases is effective in ensuring effective NPSH, but the constant decrease in the deaerator tank water storage amount is too large in some cases. . Therefore, an object of the present invention is to provide a method for controlling the operation of a feed water booster pump of a steam power plant which does not require a large simulation cost and which can confirm the actual value of the effective NPSH during operation and does not cause anxiety about reliability. To provide.

[0008]

According to the present invention, there is provided, in accordance with the present invention, the operation of a feed water booster pump incorporated in a condensate water supply system of a steam power plant such as a thermal power plant or a nuclear power plant. At the time, deaerator pressure,
The feedwater booster pump is determined by process values including the condensate flow rate and temperature entering the deaerator, the feedwater flow rate exiting the deaerator, the water level and temperature of the water stored in the deaerator tank, and the feedwater booster pump suction feedwater temperature. The effective NPSH of the water supply booster pump and the transition of the effective NPSH of the predetermined time ahead are calculated and displayed on the central control panel, and the effective NPSH of the water supply booster pump and the predicted value thereof are set in advance as the required NPSH of the water supply booster pump. If it is less than the sum of the allowance values, the target condensate flow rate obtained by calculating and predicting the appropriate condensate flow rate is displayed on the central control panel, and the operator is allowed to manually operate the deaerator water level control valve so that the water supply booster Effective NPSH of the pump
Is set to be equal to or more than the sum of the required NPSH and a preset margin value. Also, the effective NPS of the water supply booster pump
When the load is expected to decrease sharply, a target condensate flow rate value that is an effective NPSH that does not fall below the sum of the required NPSH of the feed water booster pump and a preset margin value is obtained by repeated calculation. Is input to the deaerator water level control valve controller to maintain the effective NPSH of the feedwater booster pump in a predetermined range.

[0009]

Embodiments of the present invention will be described below. In this embodiment, the feedwater booster pump whose operation is controlled is provided in the condensate water supply system of the pressurized water nuclear power plant shown in FIG. It is needless to say that the present invention is applicable to the operation of the water supply booster pump in the water supply system. In the present embodiment, an effective NPSH calculation control device (hereinafter abbreviated as calculation control device) for calculating the effective NPSH of the water supply booster pump is used, but the following parameters are used as inputs for the calculation. i. Condensate flow rate Gc (Kg / sec) ii. Deaerator inflow condensate temperature Tc (° C.) iii. Deaerator downcomer feedwater flow rate Gf (Kg / sec) iv. Deaerator pressure Pd (Kg / m ² abs) v. Deaerator tank storage temperature Td (° C) vi. Feed water temperature Tf of feed water booster pump suction part
(° C) vii. Deaerator tank storage water level Ld (m) Since these parameters are ordinary physical quantities such as flow rate, temperature, pressure and water level, they can be detected with high reliability by arranging ordinary detectors in appropriate places. Further, in order to maintain high control reliability, a plurality of detectors may be provided so as to constitute a redundant system.

The operation of the arithmetic and control unit will be described. 1) The feed water saturation temperature and specific weight are constantly calculated from the deaerator pressure Pd. Since the feedwater in the deaerator is in a saturated state, the saturation temperature of the feedwater is calculated by storing data of a steam table and the like, and the specific weight of the feedwater is calculated from the temperature. 2) Water flow rate signal that time every time the unit flow rate flows from the Gf and deaerator pressure Pd ₁ deaerator downcomers, saturation temperature Td ₁ of the feed water, to record the specific weight Rd _1. The unit flow rate is
This is the amount obtained by dividing the internal volume of the deaerator downcomer by N. The data recorded before the _Nth deaerator pressure Pd _N , saturation temperature Td _N , and specific weight Rd _{N correspond} to the inlet of the feedwater booster pump at that time. Data. 3) From the above data, the required NPSH of the feedwater booster pump at the present time is calculated from the following equation. Effective NPSH = (Pds−Hk × Rk−Pss) / Rs (1) where Pds = Pd ₀ : deaerator internal pressure (saturation pressure) Pss = Pd _N : saturation pressure of pump suction part fluid Pk = ΣRd _N / N: average specific weight of the fluid in the deaerator downcomer Rs = Rd _N : specific weight of the fluid at the pump suction section Hk: height difference between the deaerator tank water surface and the pump suction section 4) From the deaerator tank water level Ld The water storage volume in the deaerator tank is calculated, and then the condensate water amount Wd in the deaerator tank is calculated from the specific weight Rd of the water supply in the deaerator tank. 5) The transition of the deaerator pressure is predicted by calculating the total calorific value. However, here, the condensate flow rate Gc and the deaerator downcomer down pipe feed water flow rate G
f does not change. The total heat quantity of water in the deaerator and deaerator tank at the present time is: Qd = Wd × Td The total heat quantity after unit time t seconds is Qd _t = (Qd−Gc × Tc × t−Gf × Td × t) / ( Wd + Gc × t−G
f × t) Then, the deaerator tank water temperature (saturation temperature after the unit time t seconds) _{is, Td t = Qd t / (} Wd + Gc × t-Gf × t) total heat after the next unit time t seconds Is: Qd _t1 = (Qd + Gc × Tc × t × 2-Gf × Td × t × 2) / (Wd +
Gc × t2−Gf × t2) The water supply temperature (saturation temperature) in the deaerator tank after the next unit time t seconds is: Td _t1 = Qd _t1 / (Wd + Gc × t × 2−Gf × t ×
2) The calculation of the above equation is repeated to calculate the transition of the supply water temperature in the deaerator tank. Furthermore, the transition of the deaerator pressure is calculated from the supply water temperature and the calculation formula of the steam table. 6) The effective NPSH of the feedwater booster pump is calculated by combining the transition of the deaerator pressure and the calculation of the above-mentioned items 2 and 3.
Predict the transition of. 7) If the predicted transition value of the effective NPSH obtained as described above is less than the sum of the required NPSH of the water supply booster pump and a preset margin value, the condensate flow rate lower than the actual condensate flow rate is used. The calculation of the terms 5 and 6 is repeated to calculate a condensate flow rate (target condensate flow rate) in which the minimum effective NPSH is the sum of the required NPSH and a preset margin value. The deaerator tank water storage temperature and the water supply booster pump suction part water supply temperature, which are the data not used in the calculation at the first plant input, are compared with the calculation results in the above items 1 and 2, and the apparatus is operated normally. Check if it works. FIG. 1 shows an example of a result of a simulation based on the above calculation.

Based on the above calculation results, the current effective NPSH and effective NPSH of the feed water booster pump
Is displayed on a central control panel (not shown). And the effective NPSH of the water supply booster pump is required NP
If the value is less than the sum of SH and the preset margin value, adjust the opening of the deaerator water level control valve to reduce the amount of condensate flowing into the deaerator and display the target condensate flow rate on the central control panel. Instruct the operator to manually adjust the deaerator water level control valve. Further, the target condensate flow rate is input to the deaerator water level control valve control device, and the control of the deaerator water level control valve is switched to the condensate flow rate control in response to a sudden load decrease signal. In this case, the operator need only monitor and confirm the normal operation of the device.

[0012]

As described above, according to the present invention,
The process value related to the deaerator in the condensate water supply system of the steam power plant is detected, and the current value of the effective NPSH of the water supply booster pump and the predicted transition value of the effective NPSH are displayed. Since the manual adjustment or the automatic adjustment is performed, the water supply booster pump or the condensate water supply system can be operated with high reliability. Further, when the operation method of the present invention is carried out, reliability can be secured without performing the prior simulation required conventionally, and the operation cost can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing operation control results according to an embodiment of the present invention.

FIG. 2 is a system diagram partially showing an example of a steam power plant to which the method of the present invention is applied.

FIG. 3 is a graph showing an operation control result by a conventional control device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Condenser 3 Condensate pump 5 Condensate booster pump 7 Deaerator water level control valve 9 Low pressure water heater 11 Deaerator 13 Deaerator tank 15 Deaerator downcomer 17 Water supply booster pump 19 Water pump 21 High pressure water Heater 23 Steam generator

Claims (2)

[Claims] 1. Process values including deaerator pressure of a steam power plant, condensate flow and temperature entering the deaerator, feedwater flow exiting the deaerator, and water level in the deaerator tank. The effective NPSH of the feed water booster pump and the transition of the effective NPSH at a predetermined time ahead are calculated and predicted and displayed on the central control panel, and the effective NPSH of the feed water booster pump and the predicted transition value thereof are required for the feed water booster pump. If it is less than the sum of the NPSH and the preset margin value, the target condensate flow rate obtained by calculating and predicting the appropriate condensate flow rate is displayed on the central control panel, and the operator operates the deaerator water level control valve. Operating the effective NPSH of the feed water booster pump so as to be equal to or more than the sum of the required NPSH and a preset margin value. Roll control method. 2. Process values including the deaerator pressure of the steam power plant, the condensate flow and temperature entering the deaerator, the feedwater flow exiting the deaerator, and the level of water stored in the deaerator tank. The effective NPSH of the feed water booster pump and the transition of the effective NPSH at a predetermined time ahead are calculated and predicted and displayed on the central control panel, and when the load suddenly decreases, the decrease of the effective NPSH of the feed water booster pump is repeatedly calculated. To obtain a target condensate flow rate value which is an effective NPSH not less than the sum of the required NPSH of the feed water booster pump and a preset margin value, and inputs the data of the target condensate flow rate value to the deaerator water level adjusting valve control device. And controlling the effective NPSH of the feed water booster pump within a predetermined range.