JPH0231205B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a combined cycle power generation plant control device, and more particularly to a water pump recirculation flow rate control device that also serves as economizer inlet temperature control.

[Prior Art] When low-temperature water is supplied to an economizer, dew condensation occurs on the outer surface of the economizer tube, and the outer surface of the tube corrodes. If a deaerator is installed like in a conventional thermal power plant, the above problem does not occur because the feed water is heated in the deaerator, but in a combined cycle, deaerator is installed to simplify the system configuration. In many cases, a condenser deaeration method is used, omitting the air vent.
Measures are required to prevent corrosion on the outside surface of the tube.

[Problems to be Solved by the Invention] Conventionally, as described in, for example, Japanese Unexamined Patent Publication No. 58-190504, a system was provided to return hot water from the outlet of a circulation pump to the inlet of a economizer, and this return flow rate was saved. The temperature is controlled by a charcoal machine inlet temperature control device.

However, the method of coordinated control between ensuring the minimum flow rate of the feed water pump in the recirculation flow control system and maintaining the inlet temperature of the economizer is not always clear, and when switching between the two control systems, it is not possible to transition smoothly and the control There was a problem with disturbances (so-called bumps).

The purpose of the present invention is to maintain the inlet temperature of the economizer above a specified value while ensuring the minimum flow rate of the water pump by using a water pump recirculation flow rate control system.
It is an object of the present invention to provide a water supply pump recirculation flow rate control device capable of smoothly switching and cooperatively controlling ensuring the minimum flow rate of a water supply pump and maintaining the inlet temperature of a energy saver in a bumpless manner.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a recirculation flow rate for a portion of the water supply at the outlet of the water supply pump that pressurizes the water supply from the low-pressure economizer and sends it to the high-pressure economizer. In a water pump recirculation flow rate control device that controls a recirculation flow rate returned to the inlet side of the low pressure economizer via a control valve,
A means for calculating a recirculation flow rate to ensure a flow rate of the water supply pump at a predetermined value or higher, and a means for calculating a recirculation flow rate for maintaining the low-pressure economizer inlet temperature at a predetermined value or higher. A means for selecting a high value of the recirculation flow rate determined by the means as an opening control signal to the recirculation flow rate control valve, and two calculations using the recirculation flow rate and the opening control signal determined by the two calculation means. The present invention proposes a water pump recirculation flow rate control device comprising means for determining execution/stop of calculation of the calculation means and forcibly causing the output of the calculation means to match a selected high value while the calculation is stopped.

[Function] The original purpose of water pump recirculation flow control is to
The goal is to ensure the minimum flow rate of the water pump and prevent the pump from overheating due to insufficient flow. For this reason, a system is provided to return hot water from the water pump outlet to the energy saver inlet, and the return flow rate is regulated by a recirculation flow rate control device.

An economizer inlet temperature control loop is added to this recirculation flow rate control device, and the higher value of the recirculation flow rate calculation value to ensure the minimum flow rate and the recirculation flow rate calculation value to maintain the feed water temperature at the economizer inlet is set. When controlling the flow rate by returning priority, the present invention uses the output of the flow deviation calculation means and the temperature deviation calculation means, which stops calculation until the time of control switching and resumes calculation until then. Since the high value that has been given priority is forced to match and the calculation is started from there, there is no difference in the calculation result when switching the control, and the control can be continued smoothly.

[Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of a typical single-shaft combined power plant to which the present invention is applied. The main components are a gas turbine, waste heat boiler, steam turbine, and generator.

The compressor 102 adiabatically compresses air 101 as a working medium and sends it to the combustor 104 as compressed air 103. In this combustor 104, the fuel control valve 106
Fuel 105 and compressed air 1 sent through
03 is mixed and combusted, resulting in high energy combustion air 1
07 is generated. Combustion air 107 is supplied to turbine 1
After doing work at 08, it is led to the waste heat boiler 114.

On the other hand, steam exhausted from the steam turbine 110 is condensed in a condenser 111, and then
2, and the water is supplied to the low-pressure economizer 23. The heated water supply 24 is divided into two types: one is supplied to the low-pressure drum 27 via the low-pressure water supply control valve 25, and the other is further pressurized by the high-pressure water pump 29 and supplied to the high-pressure energy saver 119. Divided.

The feed water entering the low pressure drum 27 is sent to the low pressure evaporator 11
5, it becomes low pressure steam 116 and is sent to the steam turbine 110 via the low pressure regulating valve 117. After the low-pressure steam has done its work, it is exhausted and repeats the first cycle. A low pressure bypass valve 118 is provided for pressure control of the low pressure steam 116.

The water supply 120 from the high-pressure economizer 119 is further pressurized and is supplied to the high-pressure drum 122 via the high-pressure water supply control valve 121 . This feed water becomes high-pressure steam 124 in a high-pressure steamer 123, and after further increasing its temperature in a superheater 125, it is sent to the steam turbine 110 via a high-pressure regulating valve 126. After the high-pressure steam has done its work, it is exhausted and repeats the first cycle. High pressure bypass valve 127 controls the pressure of high pressure steam 128.

The work of gas turbine 108 and the work of steam turbine 110 are converted into electricity by generator 109.

FIG. 2 shows the system of plant parts associated with the feedwater pump recirculation flow control according to the present invention.

The feed water 22 pressurized by the condensate pump 112 in FIG. 1 is sent to the energy saver 23. The heated feed water 24 is divided into two parts as described above. In other words, the low pressure drum 27 passes through the water supply control valve 25.
and a water supply 28 to the high-pressure drum side via a water supply pump 29. This water supply 28 is further fed into a water supply 30 to the high pressure drum and a recirculated water supply 31.
Divided into. The flow rate of the water supply 31 is controlled by a recirculation flow rate control valve 32 and returned to the inlet side of the economizer.

In the present invention, in addition to the flow rate 35 of the feed water 28 detected by the flow rate detector 34, the temperature 36 of the feed water 22 measured by the temperature detector (for example, a thermocouple) 33 is input to the recirculation flow rate control device 37. There is. The control output 38 of the recirculation flow control device 37 determines the opening of the recirculation flow control valve 32. Recirculation flow control valve 3
A signal 57 confirming the fully closed position of No. 2 is in turn taken into the recirculation flow control device 37.

Next, the configuration of the recirculation flow rate control device 37 will be explained with reference to FIG.

The recirculation flow rate control device 37 has two loops: recirculation flow rate control and economizer inlet temperature control. All of these methods perform proportional/integral or proportional/integral/differential calculations on the deviation between the set value and the actual measured value. The higher value of the outputs of the two loops after calculation is selected to determine the opening degree of the recirculation flow rate control valve. Furthermore, means are provided to ensure bumpless control and quick response when switching control loops.

First, the economizer inlet temperature control loop is configured as follows. The adder 40 calculates the deviation 41 between the economizer inlet temperature set value 39 (the minimum temperature that the economizer can tolerate plus some margin) and the feed water temperature 36, and calculates this using proportional/integral or proportional/ It is output to the integral/differential calculator 43. Since the contents of the arithmetic unit 43 are a known technique, a description thereof will be omitted, but it is assumed that execution and stop of the arithmetic operation can be arbitrarily switched using a switch. The output 45 of the arithmetic unit 43 is sent to a high value priority circuit 56
is output to the calculation management logic 44. The calculation management logic 44 has a deviation 41, a control output 38, and a calculation output 4.
5 and a fully closed position confirmation signal 57 are input, and the following calculation management is executed.

That is, when the deviation 41 is positive (when the value of the water supply temperature 36 is smaller than the set value of the inlet temperature of the economizer), the calculation is performed unconditionally, and the calculation output 45 corresponding to the deviation 41 is set. If the deviation 41 is negative (when the feed water temperature is higher than the set value), the calculation is stopped until the recirculation flow rate control valve 32 is fully closed or the calculation output 45 becomes smaller than the control output 38. , the calculation output 45 is forced to match the control output 38. To force a match like this,
This is to perform so-called bumpless control in which the control target signal is smoothly switched between both control loops and continuity of control is maintained.

Next, the recirculation flow control loop is as follows. The adder 48 calculates the deviation 51 between the recirculation flow rate setting value (a value obtained by adding some margin to the minimum water flow rate that the water supply pump can tolerate) 49 and the flow rate 35 of the water supply 28 detected by the flow rate detector 34, and calculates this deviation. It is output to a proportional/integral or proportional/integral/differential calculator 53. The output 55 of the arithmetic unit 53 is output to the arithmetic management logic 54, and the output 4 for controlling the temperature at the inlet of the economizer.
Similarly to 5, it is also output to the high value priority circuit 56. The operation of the calculation management logic 54 is the same as 44 described above.

Here, the recirculation flow rate of the water pump is sufficient, but
Consider the case where the temperature at the economizer inlet is low.

Initially, the deviation 41 is positive and the arithmetic unit 43 is in the execution state.
The calculation output 45 is a positive value corresponding to the deviation, whereas the deviation 51 is negative, the calculation unit 53 is in an execution state, and the calculation output 55 is a negative value corresponding to the deviation. The output of the high value priority circuit 56 becomes the calculated output 45, which gradually opens the recirculation flow control valve 32. At the same time, the arithmetic unit 53 becomes stopped, and the arithmetic output 55 becomes equal to the control output 38.

If the recirculation flow rate of the water supply pump becomes insufficient in this state, the deviation 51 becomes positive, and the calculator 53 starts calculation using the control output 38 as an initial value. In this case, the control output 38 is the larger of the calculation outputs 45 and 55.

In this state, when the inlet temperature of the economizer becomes sufficiently high, the deviation 41 becomes negative, the arithmetic unit 43 becomes stopped, and the calculation output 45 becomes equal to the economizer output 38.

When the recirculation flow rate and the economizer inlet temperature reach sufficient values, both deviations 41 and 51 become negative, and the control output 3
8 gradually decreases, and when the recirculation flow control valve is fully closed, both the calculation units 43 and 53 stop, and the values of the calculation outputs 45 and 55 are the control outputs when the calculation is stopped (i.e., the recirculation flow control valve is fully closed). position).

FIG. 4 details the calculation management logic. Comparator 5
8 determines whether the deviation 41 or 51 is positive or negative, and when it is positive, sets the logic output 59 to "1" and outputs it to the OR gate 62. When the reset signal 65 is “0”,
The OR gate 62 self-holds and outputs its output as a switch switching signal 42 or 52 to the respective arithmetic unit 43 or 53. logic output 5
9 is "0" and the logic output 61 or the recirculation flow control valve fully closed confirmation signal 57 is "1", the hold of the OR gate 62 is reset. The condition for the logic output 59 to be "1" is when the comparator 60 detects that the calculation output 45 or 55 has become smaller than the control output 38.

Please note that there is a temperature difference of approximately 100°C between the inlet and outlet of the low-pressure economizer 23, and the low-pressure economizer 23
Considering that the ratio of the water supply sent directly to the low-pressure drum 27 and the water supply sent to the high-pressure economizer 119 via the high-pressure water pump 29 is approximately 1:7, the water supply to the high-pressure economizer 119 If about 1/3 of the water is recirculated, the temperature of the condensate will rise by about 30°C, and there will be no problem in making the water supply temperature sufficient for the low-pressure economizer 23.

However, the control of the water level in the high-pressure drum 122 must be planned in consideration of this recirculation flow rate.

[Effects of the Invention] According to the present invention, when maintaining the inlet temperature of the economizer at a specified value or higher while ensuring the minimum flow rate of the water pump by using the water pump recirculation flow rate control system,
Among the flow deviation calculation means and the temperature deviation calculation means,
The calculation is stopped until the point of control switching, and the output of the one that restarts the calculation is forced to match the high value that had been prioritized up to that point, and the calculation is started from there. A water supply pump recirculation flow rate control device is obtained that does not produce a step difference in calculation results and can smoothly switch and coordinately control ensuring the minimum flow rate of the water pump and maintaining the inlet temperature of the economizer in a bumpless manner. .

Therefore, it is possible to prevent dew condensation on the outer surface of the tube and further prevent corrosion thereof while ensuring the minimum flow rate of the water supply pump.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an example of a combined power generation plant to which the present invention is applied, FIG. FIG. 3 is a diagram showing the configuration of a recirculation flow rate control device according to the present invention, which is equipped with an economizer inlet temperature control loop and a recirculation flow rate control loop, and FIG. 4 is a diagram showing details of the calculation management logic in FIG. 3. It is. 23... Economizer, 27... Low pressure drum, 29...
...Water pump, 32...Recirculation flow control valve, 33
... Economizer inlet temperature detector, 34 ... Flow rate detector, 37 ... Recirculation flow rate control device, 39 ... Economizer inlet temperature set value, 40, 48 ... Adder, 4
3, 53... Arithmetic unit, 44, 54... Arithmetic management logic, 49... Recirculation flow rate setting value, 56... High value priority circuit, 58, 60... Comparator, 62, 64...
OR gate.

Claims (1)

[Claims] 1. A part of the water supply at the outlet of the water supply pump that pressurizes the water supply from the low-pressure economizer and sends it to the high-pressure economizer is returned to the inlet side of the low-pressure economizer via the recirculation flow rate control valve. A water supply pump recirculation flow rate control device for controlling a circulation flow rate, comprising: means for calculating a recirculation flow rate to ensure a flow rate of a predetermined value or more in the water feed pump; means for calculating a recirculation flow rate to maintain; means for selecting a higher value of the recirculation flow rates determined by the two calculation means as an opening control signal to the recirculation flow rate control valve; Based on the recirculation flow rate determined by the calculation means and the opening degree control signal, it is determined whether the calculations of the two calculation means should be executed or stopped, and the output of the calculation means while the calculations are stopped is forced to the selected high value. A water pump recirculation flow rate control device, characterized in that it comprises means for matching.