JP5292014B2 - Cross-flow type exhaust heat recovery boiler and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an once-through exhaust heat recovery boiler capable of stably controlling degree of superheat and starting at a high speed. <P>SOLUTION: In the control method of the once-through exhaust heat recovery boiler in which the mixed fluid of steam and water is produced by heating the water supplied from a water supply pump by an exhaust gas from a gas turbine in an evaporator, the mixed fluid is separated into steam and water by a steam separator, and the separated steam is superheated by the exhaust gas in a superheater, a value determined on the basis of a load signal of the gas turbine is added as a leading value of a supply water flow rate determined on the basis of the load signal of the gas turbine, in controlling the degree of superheat of outlet steam of the steam separator on the basis of the flow rate of supply water. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a once-through exhaust heat recovery boiler, and more particularly to control of a once-through exhaust heat recovery boiler suitable for performing stable superheat control.

  A natural circulation type and a once-through type are known as exhaust heat recovery boilers, and an outline of a conventional natural circulation type exhaust heat recovery boiler will be described with reference to FIGS. 7 and 8. FIG. 7 is a schematic configuration diagram of a natural circulation type exhaust heat recovery boiler described in Patent Document 1 and the like, and FIG. 8 is a system diagram of drum water level control in the exhaust heat recovery boiler.

  As shown in FIG. 7, the natural circulation type exhaust heat recovery boiler includes a superheater 50, an evaporator 49, and an inside of the flue 70 through which the high-temperature exhaust gas G flows from the upstream side to the downstream side in the flow direction of the exhaust gas G. A economizer 47 is installed.

  The water supplied by the feed water pump 46 passes through the economizer 47 and is sent to the evaporator 49 through the steam drum 48. Thereafter, the supplied drum water naturally circulates in the steam drum 48 and the evaporator 49, and the steam separated by the steam drum 48 is sent to the superheater 50, where the superheated steam is sent to the steam turbine 51. Further, the high-temperature exhaust gas G from the gas turbine 52 is supplied to the flue 70 of the exhaust heat recovery boiler, the steam is superheated by the superheater 50, the boiler water is evaporated by the evaporator 49, and further the economizer 47 It is configured to heat water. As shown in FIG. 7, a feed water flow rate adjustment valve 37 is installed between the feed water pump 46 and the economizer 47.

  Next, the water level control of the steam drum 48 in the starting process in the natural circulation type exhaust heat recovery boiler will be described with reference to FIG.

  A difference between a drum water level measurement value detected by a drum water level transmitter 29 installed in the steam drum 48 and a preset drum specified water level 31 is obtained by a subtractor 32, and a water level control deviation value output therefrom is proportionally integrated. The differential controller 33 performs proportional / integral / differential processing. The processed water level control deviation value adds the main steam flow detected by the steam flow meter 30 in the adder 34 and outputs the result to the subtractor 35.

The subtractor 35 receives the feed water flow rate measurement value detected by the feed water flow meter 28, obtains a deviation value from the output from the adder 34, and outputs a feed water flow rate control deviation value. The feed water flow rate control deviation value is proportionally / integrated by the proportional integral controller 36 and then input to the feed water flow rate adjustment valve 37 as a control command. The water level was controlled.
JP 2000-146108 A

  As described above, the conventional natural circulation type exhaust heat recovery boiler controls the feed water flow rate so as to keep the water level of the steam drum stable by using the main steam flow rate measurement value as the preceding value of the feed water flow rate command. Since the main steam flow rate of the natural circulation type exhaust heat recovery boiler is determined by the heat input from the gas turbine and is not affected by the feed water flow rate, there is no strong correlation between the feed water flow rate and the main steam flow rate.

  On the other hand, the once-through exhaust heat recovery boiler has a feature that the plant start-up stop time can be shortened as compared with the natural circulation exhaust heat recovery boiler. This is because the use of a thin brackish water separator instead of the thick steam drum used in natural circulation heat recovery steam generators eases restrictions on the rate of increase in load. It leads to shortening.

  In the once-through type exhaust heat recovery boiler, the water level control is performed in the process of starting the plant and then the superheat control is performed. However, if the superheat control is unstable, the start-up time is also affected.

  In the once-through exhaust heat recovery boiler, the evaporator outlet superheat degree control is performed to control the degree of superheat according to the once-through operation, that is, the feed water flow rate. During the once-through operation, the feed water completely evaporates while passing through the evaporator to become steam, so there is a strong correlation from the feed water flow rate to the main steam flow rate. When the main steam flow rate measurement value used for the drum water level control of the natural circulation heat recovery steam generator is used as the preceding value of the feed water flow rate command during the once-through operation, the following cycle is performed on the controller side and machine body side. A loop is formed.

  That is, on the control device side, the feed water flow command value is calculated from the main steam flow rate measurement value (preceding value of the feed water flow command) and the feed water flow command correction by the superheat degree control unit output, and based on the feed water flow command value, the machine Adjust the water supply flow rate on the main unit side. The feed water flow rate becomes steam (main steam flow rate) due to heat input from the gas turbine, forming a series of loops. In this loop, when the main steam flow rate increases, the feed water flow rate command value also increases, and the main steam flow rate also increases due to the increased feed water flow rate. In this way, when the steam flow rate measurement value is used as the preceding value of the feed water flow rate command, the addition or subtraction is repeated every calculation cycle on the control device side, the value runs in one direction, and the control becomes unstable.

  As a feature of the once-through type exhaust heat recovery boiler, high-speed start / stop is mentioned, but if the superheat degree control becomes unstable as described above, the superheat degree cannot be secured and there is a risk of shifting to the water level control. There is a concern that the start-up time may be adversely affected, and there is a drawback that the features of the once-through exhaust heat recovery boiler are not fully exhibited.

  An object of the present invention is to provide a once-through exhaust heat recovery boiler that eliminates the disadvantages of the prior art, can perform stable superheat control, and can be started at high speed, and a control method therefor.

In order to achieve the above object, the first means of the present invention is as follows:
A superheater is disposed upstream of the exhaust gas flow direction in the flue through which the exhaust gas from the gas turbine flows, and an evaporator is disposed downstream of the superheater in the exhaust gas flow direction,
Feed water supplied by a feed water pump is heated by the exhaust gas in the evaporator to produce a mixed fluid of steam and water, the mixed fluid is separated into steam and water by a brackish water separator, and the separated steam is In the once-through type exhaust heat recovery boiler that is heated by the exhaust gas in the superheater,
Control deviation value calculating means for calculating a control deviation value for controlling the superheat degree of the outlet steam of the brackish water separator by the flow rate of the feed water;
A leading value calculating means for calculating a leading value of the feed water flow rate from the load signal of the gas turbine and the atmospheric temperature, or calculating a leading value of the feed water flow rate from the fuel amount command signal of the gas turbine and the atmospheric temperature ;
Adding means for adding a preceding value of the feed water flow rate to the control deviation value and outputting a feed water flow rate command signal at the time of superheat control;
A feed water flow meter for measuring the feed water flow rate during superheat control,
An opening degree adjusting means for adjusting the opening degree of the feed water flow rate control valve based on the measured feed water flow rate and the deviation value of the feed water flow rate command signal is provided.

The second means of the present invention is characterized in that, in the first means, means for adding a value including a heat transfer time delay time constant of the exhaust heat recovery boiler to the preceding value of the feed water flow rate is provided. To do.

The third means of the present invention is:
The feed water supplied by the feed water pump is heated by the exhaust gas from the gas turbine in the evaporator to produce a mixed fluid of steam and water, and the mixed fluid is separated into steam and water by the brackish water separator, and the separated steam In the control method of the once-through type exhaust heat recovery boiler in which the exhaust gas is superheated by the exhaust gas in a superheater,
When the superheat degree of the outlet steam of the brackish water separator is controlled by the flow rate of the feed water, a value obtained from the load signal and the atmospheric temperature of the gas turbine is used as a preceding value of the feed water flow rate or the fuel amount command signal of the gas turbine And the value obtained from the atmospheric temperature is added as the preceding value of the feed water flow rate .

According to a fourth means of the present invention, in the third means,
A value including a heat transfer time delay time constant of the exhaust heat recovery boiler is added to the preceding value of the feed water flow rate .

  In a once-through type exhaust heat recovery boiler, a once-through operation is performed during superheat control. In this case, there is a strong coupling from the feed water flow rate to the main steam flow rate, and the main steam flow rate may vary depending on the feed water flow rate.

  In the present invention, the preceding value of the feed water flow rate command that does not depend on the main steam flow rate is obtained as described above, and by controlling the superheat degree based on this, stable superheat degree control can be performed and high-speed startup is possible. A once-through exhaust heat recovery boiler and its control method can be provided.

  The superheat degree control of the once-through type exhaust heat recovery boiler according to the embodiment of the present invention will be described in detail below with reference to the drawings. 1 to 3 are control system diagrams of the once-through exhaust heat recovery boiler according to the first embodiment, and FIG. 4 is a schematic configuration diagram of the once-through exhaust heat recovery boiler according to each embodiment of the present invention.

  First, a schematic configuration of a once-through exhaust heat recovery boiler according to an embodiment of the present invention will be described with reference to FIG. As shown in the figure, in the flue 70 through which the exhaust gas G from the gas turbine 38 circulates, the superheater 44, the evaporator 41 and the economizer 40 are installed from the upstream side to the downstream side in the flow direction of the exhaust gas G. Has been. The water supplied by the feed pump 39 passes through the economizer 40 and is sent to the evaporator 41, and a mixed fluid of water and steam is generated in the evaporator 41 by the high temperature exhaust gas G and supplied to the brackish water separator 42. The

  The steam separated by the brackish water separator 42 is sent to the superheater 44, and the superheated steam is supplied to the steam turbine 45. The hot exhaust gas G from the gas turbine 38 is recovered by the superheater 44, the evaporator 41 and the economizer 40 while passing through the flue 70.

  In addition, as shown with the broken line in the figure, the recirculation line 43 is provided toward the inlet side of the evaporator 41 from the brackish water separator 42. As shown in FIG. This recirculation line 43 is a line that is used when the through-flow operation is not being performed, and is a system in which saturated water separated by the brackish water separator 42 is circulated to the evaporator 41.

  As shown in the figure, a feed water flow rate adjusting valve 27 and a feed water flow meter 23 are provided between the feed water pump 39 and the economizer 40, and the brackish water separator outlet pressure is provided at the outlet side of the brackish water separator 42. A total 2 and a steam separator outlet steam thermometer 3 are attached.

  The configuration of the once-through type exhaust heat recovery boiler shown in FIG. 4 is also applied to other embodiments of the present invention described below.

  Next, the control system according to the first embodiment will be described. FIG. 3 is a block diagram of the overall control system for controlling the feed water flow rate. As shown in the figure, this control block is mainly composed of a superheat degree control unit 100, a water level control unit 200, and a control switching unit 300 which are the subject of the present invention.

  The general control method of the once-through type exhaust heat recovery boiler according to the present invention is that the water level control unit 200 controls the water level of the brackish water separator 42 at the initial stage of startup, and then the control switching unit 300 when the switching conditions are met. Therefore, the superheat degree control unit 100 is switched to the once-through operation to control the superheat degree at the outlet of the evaporator.

First, the function of the water level control unit 200 will be described with reference to FIG.
The water level setting value 81 set by the water level setting device 80 of the water separator 42 and the water level setting bias value 83 set by the water level setting device 82 are added by the adder 84. The added value passes through the analog switch 85 and is input to the change rate limiter 86. The change rate limiter 86 outputs a corrected water level set value 87 with the change rate limited.

  On the other hand, the brackish water separator 42 is provided with a water level measuring device 88, and the brackish water separator water level measurement value 89 and the corrected water level set value 87 outputted therefrom are compared by the subtractor 90, and the comparison result is the water level. A deviation value 91 is output. The water level deviation value 91 is subjected to proportional / integral / differential processing in the proportional-integral-derivative controller 93 using the control gain correction means 92 based on the gas turbine load, and the proportional-integral-derivative controller 93 outputs a control deviation value 94.

  The control deviation value 94 is added by the adder 97 with the steam flow 96 measured by the steam flow meter 95, and the adder 97 constitutes the control switching unit 300 as the feed water flow command signal 20 at the time of water level control. It is applied as a signal b to the analog switch 21 (see FIG. 1).

Next, the function of the superheat degree control unit 100 will be described with reference to FIG.
The pressure gauge 2 is installed on the outlet side of the brackish water separator 42 (see FIG. 4), and the brackish water separator outlet pressure measurement value 60 measured by the pressure gauge 2 is input to the function generator 4, and the pressure is A corresponding saturated steam temperature 7 is calculated. The saturated steam temperature 7 is added to the superheat setting value 5 by the adder 6, and the obtained steam temperature value 61 is input to the analog switch 8 as a signal a.

  In the analog switch 8, the signal a (steam temperature value 61) is selected at the time of superheat control, the rate of change is limited by the rate of change limiter 9 which becomes effective at the time of superheat control, and the steam temperature value 61 is subtracted. 10 is input.

  A thermometer 3 is installed on the outlet side of the brackish water separator 42 (see FIG. 4), and a brackish water separator outlet temperature measurement value 62 measured by the thermometer 3 is input to the subtractor 10, and the steam temperature value 61 and Based on the brackish water separator outlet temperature measurement value 62, a temperature control deviation value 63 is output from the subtractor 10. The temperature control deviation value 63 is proportionally / integrated / differentiated by the proportional-integral-derivative controller 14 and then output as a control deviation value 64. The preceding value 15 of the feed water flow rate command and the control deviation value 64 at the time of superheat control are obtained. The signal is added by the adder 16 and output as a signal a to the analog switch 21 as a feed water flow rate command value 17 at the time of superheat control.

  The proportional integral derivative controller 14 performs processing using the control gain correction means 13 with the preceding value 15 of the feed water flow rate command at the time of superheat control as an input signal. As a method of calculating the leading value 15 of the feed water flow command at the time of superheat control, a signal is generated by the function generator 11 based on the load command signal or the combustion amount command signal 1 of the gas turbine, and a first order lag is generated from the signal. The element (function generator) 12 is operated to set the leading value 15 of the feed water flow rate command at the time of superheat control. A function generator 18 is provided between the function generator 11 and the first-order lag element 12, and the signal generated by the function generator 18 is used as the time constant 57 of the preceding value of the feed water flow rate during superheat control. .

  During the superheat control, the analog switch 21 selects the signal a, and the upper and lower limit values of the feed water flow rate command value 17 during the superheat control are limited by the feed water flow upper / lower limiter 22.

  A feed water flow meter 23 is installed on the outlet side of the feed water pump 39 (see FIG. 4). A feed water flow rate measurement value 65 by the feed water flow meter 23 and a superheat degree control feed water flow rate command value 17 are subtracted by a subtractor 24. The comparison subtraction is performed, and the feed water flow rate deviation value 66 is output from the subtracter 24. This feed water flow rate deviation value 66 is subjected to proportional integral processing by the proportional integral controller 25, then passes through the automatic / manual switch 26, and is input to the feed water flow rate control valve 27 as a feed water flow rate command signal 67, and the valve opening degree. The feed water flow rate is adjusted during superheat control based on the adjustment.

  The control deviation value calculating means for calculating the control deviation value for controlling the superheat degree of the outlet steam of the brackish water separator described in the claims by the flow rate of the feed water is specifically the brackish water separator in the present embodiment. It comprises an outlet pressure gauge 2, a function generator 4, an adder 6, an analog switch 8, a change limiter 9, a brackish water separator outlet thermometer 3, a subtractor 10, a proportional integral derivative controller 14, and the like.

  Further, the preceding value calculation means for calculating the preceding value of the feed water flow rate from the load signal of the gas turbine specifically includes a function generator 11, a function generator 18, a function generator (first-order lag element) 12, and the like. Furthermore, the opening degree adjusting means for adjusting the opening degree of the feed water flow rate adjustment valve is specifically constituted by a proportional-plus-integral controller 25.

  FIG. 5 is a control system diagram of the once-through exhaust heat recovery boiler according to the second embodiment. In the first embodiment, as shown in FIG. 1, the leading value 15 of the feed water flow rate at the time of superheat control is calculated based on the load command signal or the combustion amount command signal 1 of the gas turbine.

  In the second embodiment, as shown in FIG. 5, based on the load command signal or combustion amount command signal 1 of the gas turbine and the atmospheric temperature measurement value 58 from the thermometer 19, the function generator 53 and the superheat degree control time are controlled. The function generator 18 that generates the time constant 57 of the preceding value of the feed water flow rate and the primary delay element 12 calculate the preceding value 15 of the feed water flow rate during the superheat control.

  FIG. 6 is a control system diagram of the once-through exhaust heat recovery boiler according to the third embodiment. In the present embodiment, based on the gas turbine exhaust gas flow rate 54 and the gas turbine outlet or exhaust heat recovery boiler inlet gas temperature 55 obtained by measurement or calculation, the function generator 56, the preceding value of the feed water flow rate at the time of superheat control. The leading value 15 of the feed water flow rate at the time of superheat control is calculated by the function generator 18 that generates the time constant 57 and the primary delay element 12.

  5 and 6, the system is the same as the control system shown in FIGS. 1 to 3 described above except for the system that calculates the leading value 15 of the superheat degree control feed water flow rate command. Is omitted.

1 is a control system diagram of a once-through exhaust heat recovery boiler according to a first embodiment of the present invention. It is a control system diagram of a water level control unit according to an embodiment of the present invention. It is a block diagram of the whole control system concerning the embodiment of the present invention. It is a schematic structure figure of a once-through type exhaust heat recovery boiler concerning an embodiment of the present invention. It is a control system figure of the once-through type exhaust heat recovery boiler concerning a 2nd embodiment of the present invention. It is a control system diagram of a once-through type exhaust heat recovery boiler concerning a 3rd embodiment of the present invention. It is a schematic block diagram of the conventional natural circulation type waste heat recovery boiler. It is a control system diagram of the exhaust heat recovery boiler.

Explanation of symbols

  1: Gas turbine load command signal or combustion amount command signal, 2: brackish water separator outlet pressure gauge, 3: brackish water separator outlet steam thermometer, 4: function generator, 5: superheat setting value, 6: adder 7: saturated steam temperature, 8: analog switch, 9: change rate limiter, 10: subtractor, 11: function generator, 12: first-order lag element 12, 13: control gain correction means, 14: proportional integral differential adjustment 15: Feed water flow command leading value, 16: Adder, 17: Feed water flow command value during superheat control, 18: Function generator, 19: Thermometer, 20: Feed water flow command value during water level control, 21 : Analog switch, 22: Feed water flow up / down limiter, 23: Feed water flow meter, 24: Subtractor, 25: Proportional integral regulator, 26: Automatic / manual switch, 27: Water feed water flow control valve, 28: Water feed Flow meter, 29: Drum water level oscillator, 30: Main steam Flow meter, 31: Drum specified water level, 32: Subtractor, 33: Proportional integral derivative controller, 34: Adder, 35: Subtractor, 36: Proportional integral controller, 37: Feed water flow control valve, 38: Gas turbine 39: feed pump, 40: economizer, 41: evaporator, 42: brackish water separator, 43: recirculation line, 44: superheater, 45: steam turbine, 46: feed pump, 47: economizer 48: Steam drum, 49: Evaporator, 50: Superheater, 51: Steam turbine, 52: Gas turbine, 53: Function generator, 54: Gas turbine exhaust gas flow rate, 55: Gas turbine outlet or exhaust heat recovery boiler inlet gas Temperature, 58: Function generator, 57: Time constant of preceding value of feed water flow rate during superheat control, 58: Air temperature measured value, 60: Steam separator outlet pressure measured value, 61: Steam temperature value, 62: Brack water separation Unit outlet temperature measurement, 3: temperature control deviation value, 64: control deviation value, 65: feed water flow rate measurement value, 66: feed water flow rate deviation value, 67: feed water flow rate command signal, 70: flue, 100: superheat control unit, 200: water level control Part, 300: control switching part, G: exhaust gas.

Claims (4)

A superheater is disposed upstream of the exhaust gas flow direction in the flue through which the exhaust gas from the gas turbine flows, and an evaporator is disposed downstream of the superheater in the exhaust gas flow direction,
Feed water supplied by a feed water pump is heated by the exhaust gas in the evaporator to produce a mixed fluid of steam and water, the mixed fluid is separated into steam and water by a brackish water separator, and the separated steam is In a once-through exhaust heat recovery boiler that is heated by the exhaust gas in a superheater,
Control deviation value calculating means for calculating a control deviation value for controlling the superheat degree of the outlet steam of the brackish water separator by the flow rate of the feed water;
A leading value calculating means for calculating a leading value of the feed water flow rate from the load signal of the gas turbine and the atmospheric temperature, or calculating a leading value of the feed water flow rate from the fuel amount command signal of the gas turbine and the atmospheric temperature ;
Adding means for adding a preceding value of the feed water flow rate to the control deviation value and outputting a feed water flow rate command signal at the time of superheat control;
A feed water flow meter for measuring the feed water flow rate during superheat control,
An once-through exhaust heat recovery boiler, comprising: an opening degree adjusting means for adjusting an opening degree of the feed water flow rate control valve based on a deviation value between the measured feed water flow rate and the feed water flow rate command signal. 2. The once-through exhaust heat recovery boiler according to claim 1, wherein means for adding a value including a heat transfer time delay time constant of the exhaust heat recovery boiler to the preceding value of the feed water flow rate is provided. A once-through exhaust heat recovery boiler. The feed water supplied by the feed water pump is heated by the exhaust gas from the gas turbine in the evaporator to produce a mixed fluid of steam and water, and the mixed fluid is separated into steam and water by the brackish water separator, and the separated steam In the control method of the once-through type exhaust heat recovery boiler in which the exhaust gas is superheated by the exhaust gas in a superheater,
When the superheat degree of the outlet steam of the brackish water separator is controlled by the flow rate of the feed water, a value obtained from the load signal and the atmospheric temperature of the gas turbine is used as a preceding value of the feed water flow rate or the fuel amount command signal of the gas turbine And a value obtained from the atmospheric temperature is added as a preceding value of the feed water flow rate . The flow-through exhaust heat recovery boiler control method according to claim 3, wherein a value including a heat transfer time delay time constant of the exhaust heat recovery boiler is added to the preceding value of the feed water flow rate. Control method for the type exhaust heat recovery boiler .

Images