JPH04143405A - Auxiliary steam supplying method in combined cycle power plant - Google Patents

Abstract

PURPOSE:To uniformize the steam feeding quantity in each shaft without giving any large fluctuations to pressure in an auxiliary steam base pipe by installing a flow sensor, detecting the supply steam quantity at each shaft, and a measuring instrument detecting the full-open of an outflow valve as well as installing a general control unit inputting each signal of these elements. CONSTITUTION:Each shaft of a combined cycle power plant is provided with a sensor 17 detecting the steam feeding quantity and a measuring instrument 18 detecting the full-open state of an outflow valve 11, and each signal of these elements is inputted into a general control unit 19 which outputs a bias command (a) at each shaft by means of a judging circuit, inputting it into an each shaft control unit 13 which controls a control valve 12 so as to make auxiliary steam base pipe pressure come to the specified value. Since the bias command (a) is outputted as a certain cyclic pulse, the control valve 12 is operated to open little by little. Thus, such a gentle uniformization that there is no sudden fluctuation in the auxiliary steam base pipe pressure is carried out.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to a combined cycle power generation plant in which a plurality of generator shafts are installed, each of which is a combination of a gas turbine, an exhaust heat recovery boiler, and a steam turbine. This invention relates to an auxiliary steam supply method.

(Conventional technology) When starting up a combined cycle power plant, deaeration steam and steam turbine gland seal steam are required, and before sufficient steam is supplied from the heat recovery boiler, auxiliary steam for this purpose must be provided. Must be supplied from other equipment.

When any shaft in a multi-shaft combined cycle power plant is in operation, the auxiliary steam required when starting up the other shafts is supplied from the operating shaft.

FIG. 4 shows an example of such a conventional auxiliary steam supply method, and for the sake of simplicity, shows the case of a three-shaft combined cycle power plant.

In FIG. 4, one shaft 1 of the combined cycle power plant is activated as follows. That is, an auxiliary boiler 3 is connected to the auxiliary steam pipe 2, and at startup, the inflow valve 4 is opened to supply auxiliary steam from the auxiliary boiler 3, and this is used as deaerated steam and ground steam for the steam turbine 9. Start the gas turbine 5.

The exhaust gas from the gas turbine 5 enters the waste heat circuit boiler 6, heats the feed water sent from the condenser 7 by the feed water pump 8, and generates steam, which drives the steam turbine 9, which connects the gas turbine 5 and the steam turbine. Both of the power generators 9 drive the generator 10 to generate electric power.

As the pressure of the gas turbine 5 increases, the amount of generated steam also increases, and auxiliary steam is no longer needed, so the inflow valve 4 is closed. When the amount of steam generated further increases, it becomes possible to supply steam to other shafts, so the outflow valve 11 is opened and auxiliary steam (hereinafter referred to as supply steam) is supplied to the auxiliary steam main pipe 2 through the control valve 12.

Each axis control device [13 inputs a pressure signal from a pressure sensor 14 that detects the pressure of the auxiliary steam main pipe, and controls the opening and closing of the joints 12 so that a predetermined pressure is achieved.

In this way, when one shaft of the combined cycle power plant is operated and begins producing feed steam, the auxiliary boiler 3 is shut down.

When starting up the other shafts 15, 16 of the combined cycle power plant, the feed steam from shaft 1 is used to start up, and the other shafts likewise give out feed steam by increasing their output.

Thereafter, when one shaft of the combined cycle power plant is stopped, the outflow valve 11 is closed and the inflow valve 4 is opened to supply auxiliary steam using the steam supplied from the other shaft in operation of the combined cycle power plant. After securing, the gas turbine 5 and the steam turbine 9 are stopped.

(Problems to be Solved by the Invention) In the conventional auxiliary steam supply method described above, the control valve is opened and closed to keep the auxiliary steam main pipe pressure constant. Once pressure is established,
The pressure control valve of the shaft that is started next remains closed, and therefore the burden of supply steam is concentrated only on the shaft that is started first, and a phenomenon occurs in which no supply steam comes out from the shafts that are started afterward.

If the supply steam concentrates on a specific shaft in this way, a large load will be placed on that shaft, and a large amount of make-up water will have to be received to replenish this outflow, which will not only lead to a decrease in efficiency, but also lead to a worst-case scenario. may cause problems with driving.

Additionally, combined cycle power plants are inherently characterized by high thermal efficiency, and therefore it is desirable that each shaft supply effluent steam as evenly as possible.

The present invention aims to provide a method for supplying auxiliary steam in which the steam supplied to each shaft is equalized, and particularly takes the following matters into consideration.

■ It is necessary to avoid sudden fluctuations in the pressure of the auxiliary steam pipe due to equalization correction. In addition, the shafts that are started later and have just become capable of supplying steam have a smaller amount of steam generation and pressure than the shafts that started earlier, so it would be more inconvenient to equalize them immediately. Therefore, it is desirable to perform equalization slowly over a relatively long period of time.

■ If strict equalization is performed, the control valves on all shafts will constantly make small opening and closing operations, and the pressure in the auxiliary steam main pipe will fluctuate accordingly. It is necessary to stabilize the pressure in the main pipe, and therefore it is desirable to use a method that stabilizes the behavior of the control valve after the equalization target has been set and equalization has been achieved.

■ When all shafts of the power plant are in operation, the amount of auxiliary steam consumed by the entire power plant is close to zero. If the amount of supplied steam is distributed equally to each shaft in such a state, the 11-section valve of each shaft will open slightly, which will have a negative effect on the valve body.
When the amount of auxiliary steam consumed is small, it is desirable to avoid excessive opening operation.

(b) In order to achieve equalization, the easiest method is to unify the pressure sensor and the control device and control the pressure force WiUWi valve of each axis with the same control command, but this method prevents failure in one location. This affects the entire power plant, and does not take advantage of the characteristics of a combined cycle power plant, which is composed of multiple shafts and aims to distribute risks. If an accident such as a failure of the control device or sensor is assumed, it is desirable to perform pressure control with the control device of each axis and provide the equalization correction signal as a separate bias signal.

That is, the present invention takes these points into consideration and aims to provide an auxiliary steam supply method for a combined cycle power plant in which the steam supplied to each shaft is equalized.

[Structure of the invention]

(Means and effects for solving the problem) The present invention provides a flow rate sensor for detecting the amount of steam supplied for each axis and a meter for detecting full opening of the outflow valve, and also includes an integrated control device for inputting these signals. , bias commands for each axis are output to each axis control device according to predetermined calculations.

The central control device is equipped with a selection circuit that selects the axis with the least amount of steam supplied from among each axis, and a pulse generator corresponding to each axis, which increases the opening degree of the control valve of the selected axis. A means for generating a pulse signal, a means for calculating the maximum difference in the supply steam difference between each shaft, a means for calculating the total amount of supplied steam for each shaft, and dividing that value by the number of shafts whose outflow valves are fully open. and means for generating the pulse signal when the maximum difference and the average steam supply amount are equal to or greater than a predetermined value, and the pulse signal is used to open the control valve. It is used as a bias command.

In addition, when the above average supplied steam amount is less than a predetermined value, it is determined whether the supplied steam amount of each axis is greater than or equal to the predetermined value, and the least amount of supplied steam is determined among the axes that are equal to or greater than the predetermined value. A selector that selects the desired axis, a pulse generator corresponding to each axis, and a detection circuit that detects that the control valve is slightly open are provided. When the output of this detection circuit is established, a pulse signal is generated. This pulse signal is used as a bias command to open the control valve. Select the axis with the least amount of supplied steam, and send a pulse signal to each axis control device of that axis to open the control valve. When a bias command is given at , each shaft control device opens the control valve and increases the steam supplied to that shaft.

As a result, the auxiliary steam header pressure temporarily increases, and as a result, the control valves of the other shafts close and the supplied steam decreases. Since the bias command is a pulse that is repeated at a predetermined period, by repeating such correction, the amount of steam supplied to each axis is equalized.

Achievement of equalization is determined by calculating the maximum value of the amount of steam supplied between each axis and determining that the value becomes less than a predetermined margin, and when this is achieved, no bias command is output. In addition, from the total amount of steam supplied throughout the power plant, the average amount of steam supplied is calculated by distributing it to each axis, and if the value is less than the allowable value of the control valve, equalization is performed and the control valve itself Bias commands should not be issued because they have an adverse effect on

Furthermore, in order to reduce the negative effect on the control valve, select a shaft with a supplied steam amount above a predetermined value, and select a shaft with a small amount of supplied steam among them to open the control valve, thereby making it slightly open. fully close the control valve to prevent adverse effects on the valve body. This operation continues as long as even one control valve that is slightly open is detected, and eventually equalization is achieved between the shafts with a large amount of supplied steam, and the control valves of the other shafts are fully closed. becomes.

(Example) An embodiment of the present invention is shown in FIG.

In FIG. 1, each axis of the combined cycle power plant is provided with a sensor 17 that detects the amount of steam supplied and an instrument 18 that detects the fully open state of the outflow valve 11, and these signals are transmitted through the integrated control system! 19 is input.

The overall control device 19 outputs a bias command a for each axis using a judgment circuit described later, and inputs the bias command a to each axis control device 13.

FIG. 2 shows an example of a judgment circuit configured inside the overall control device 19.

In FIG. 2, the general control device 19 includes an adder 20 that inputs the amount of steam supplied to each axis from each sensor 17 and calculates the total amount of steam supplied to all the axes, and an outflow valve of each axis that is fully opened with each meter 18. an adder 21 that calculates the number of axes C that can supply auxiliary steam by inputting the contact point; a divider 22 that divides the total amount of steam to be supplied by the number of axes C to calculate an average amount of supplied steam d; A comparator 23 which compares a predetermined limit value e and an average supplied steam amount d, and outputs a contact output f when d) e, and inputs the supplied steam amount of each axis and selects the maximum value g. A maximum value selector 24, a minimum value selector 25 that also selects the minimum value, a subtractor 26 that subtracts the minimum value from the maximum value g to calculate the maximum deviation j, and a maximum deviation i and a predetermined margin. A selector 28 that compares the amount of steam supplied to each axis with the degree j, selects the axis with the smallest value, and outputs the contact output Q of only this axis, and the selector 28 that outputs the contact output Q of only this axis, and the AND circuit 29, 30, 31 that detects the output and outputs the contact output m for each axis, and each axis that outputs a constant cycle pulse as the bias command a while the contact output m is being output. Each pulse generator is equipped with a pulse generator 32.33°34.

In FIGS. 1 and 2, each shaft control device 13 controls the control valve 12 to bring the auxiliary steam header pressure to a predetermined value, as in the conventional case.

In order to equalize the amount of steam supplied between the shafts, the central control device 19 outputs a bias command a so as to increase the opening degree of the control valve for the shaft having a small amount of steam supplied.

In response to this bias command a, each axis control device f[13 increases the opening degree of the control valve 12, and as a result, the auxiliary steam main pipe pressure increases, and in response, the control valve 12 of the other axis increases the opening degree. This makes the amount of steam supplied between the shafts uniform.

Since the bias command a is output as a pulse with a certain period from the pulse generator 32, 33, 34, the control valve 12 is opened little by little, and the auxiliary steam main pipe pressure is gradually and evenly controlled without sudden fluctuations. conversion is carried out.

Bias command a selects the axis with the least amount of steam supplied by selector 2.
8 and the contact output Q is applied only to the axis to which the contact output Q is output. Therefore, the bias command a is given with the highest priority to the axis that supplies the least amount of steam, that is, the axis that is started the latest.

Furthermore, since the bias command a is not output to multiple axes at the same time, it does not cause a large disturbance to the main tube pressure.

If a correction is made and as a result of an increase in the amount of steam supplied to one axis, the amount of steam supplied to another axis is decreased, a similar correction is made to this axis.

Further, the maximum value g and the minimum value are determined by the maximum value selector 24 and the minimum value selector 25, and only when the maximum deviation i is larger than the tolerance j, the contact output k is output from the comparator 27, and only then the bias Since command a is allowed, equalization correction is performed until the deviation in the amount of steam supplied to each axis reaches the predetermined margin, and a certain degree of equalization is achieved and the deviation falls below the tolerance. When this happens, correction is stopped and the main pipe pressure is stabilized.

Also, use the adder 20.21 and the divider 22 to find the total amount of steam supplied for the entire power plant, and divide this by the number of shafts C producing supplied steam to calculate the average amount of supplied steam d. This average supplied steam amount d is the supplied steam amount shared by each shaft when equalization is performed, but since the control valve 12 has a minimum flow rate limit value, it is not possible to supply steam amount smaller than this. Then there is a problem.

Therefore, the comparator 23 compares the limit value e and the average supplied steam amount d, and when die, the contact output f is not output, so equalization is not performed, and the control valve 12 of each shaft is adjusted to the current opening degree. Since the valve body is maintained, adverse effects on the valve body can be avoided.

If the amount of auxiliary steam consumed by the entire power plant is large due to the above operations, and there is no problem in distributing it to each axis, the amount of auxiliary steam supplied between each axis may be distributed evenly so that the difference is within a certain margin. conversion is carried out. Furthermore, even if the overall control device fails, the bias command is not output (11), and each axis control device continues its own pressure control, so the reliability of the entire system will not be reduced.

Another example of the judgment circuit in the general control device 119 used in the present invention is shown in FIG.

In FIG. 3, the general control device 19 outputs a bias command n for each axis, and the bias command a for each axis shown in FIG. It is output to.

That is, the amount of supplied steam detected by the sensor 17 is compared with a predetermined limit value e, and when the amount of supplied steam is larger than the limit value e and the contact output O is not output, the amount of supplied steam p a switch 41, 42, 43 that does not output;
A selector 44 that compares the supplied steam amount p of each axis and outputs the contact output q of only the axis showing the lowest /J1 value, and outputs the contact output r when the supplied steam amount is greater than or equal to zero and less than or equal to the limit value e. The comparator 45.46°47 and the contact output r of each axis are O
an OR circuit 48 that detects with R and outputs a contact output S, a maximum value selector 49 that outputs a contact output t when the maximum deviation within the supplied steam amount p is larger than a predetermined margin j, and a minimum value selection 50, subtractor 51, comparator 52 and contact output S
and contact output t are detected by OR and output contact output U.
R circuit 53, AND circuits 54, 55, and 56 that output contact output U when all the negative conditions of contact output q, contact output U, and contact output f are satisfied, and , a pulse generator 57, 58, 59 that generates a pulse at a constant period and outputs it as a bias command n, and an OR circuit 35, 36 that outputs the bias commands a and n by ORing.
．． 37 is provided, and the outputs of the OR circuits 35, 36, 37 are outputted to each axis control device as a bias command.

The example shown in FIG. 2 is a case where the average supplied steam amount d is large, so when the contact output f is output, the bias command a
However, in the example shown in FIG. 3, the bias command n is output even when the contact output f is not established.

For this reason, comparators 41, 42, and 43 are provided to input the supplied steam amount p of only those axes whose supplied steam amount is larger than the limit value e into the selector 44, and input the supplied steam amount p of other axes to the selector 44. 4
4, the selector 44 selects the axis with the smallest value among the axes where the amount of supplied steam is greater than the limit value e, outputs the contact output q, and issues a bias command n to this axis. is given, and the control valve 12 is closed in the same manner as in the case of FIG.
is gradually opened, and equalization correction is performed between the axes where the amount of supplied steam is greater than the limit value e. Since the control valves 12 are gradually opened, the equalization operation is performed even for control valves whose supplied steam amount is less than the limit value e.

The condition for achieving equalization is determined by the fact that the maximum deviation of the amount of steam supplied between the shafts is smaller than the margin j, as in the case of FIG. 2, but in FIG. is provided, and the contact output r detects the state in which the amount of supplied steam is greater than zero and less than the limit value e, that is, the control valve 12 is held in a slightly open state, and even one shaft is operated in this state. is determined, and the contact output r of each axis is detected by OR and set as the contact output S, and as long as this contact output S is established, equalization correction is continued. The contact output r does not hold true when the control valve 12 is fully closed because the amount of supplied steam becomes zero.

As a result, equalization correction is performed until the slightly open control valves on all shafts are fully closed, and it becomes possible to allocate the amount of supplied steam that was burdened by these control valves to the control valves with a large opening. Operation in a slightly open state that would have an adverse effect on the valve body of the control valve is prevented, and equalization between the shafts that supply a large amount of supply steam can be safely performed.

〔Effect of the invention〕

As explained above, according to the present invention, the central control device selects the axis with the least amount of steam supplied, gives a bias command to that axis by repeating short pulse signals, and gradually opens the control valve. This makes it possible to equalize the amount of steam supplied to each shaft without causing large fluctuations in the pressure of the auxiliary steam main pipe.

The goal of achieving this equalization is to calculate the maximum deviation of the amount of steam supplied between each axis using the maximum value selector and minimum value selector, and then apply the above bias command until the deviation falls within a certain tolerance. This equalizes the difference in the amount of steam supplied so that it is within tolerance. Since no bias command is issued after equalization is achieved, it is possible to stabilize the auxiliary steam header pressure.

In addition, the amount of steam supplied from each shaft is added to obtain the total sum for the entire power plant, and this is divided by the number of shafts producing supplied steam to calculate the average amount of steam supplied, and this value is determined by the amount of steam supplied to the control valve. If the flow rate is less than the allowable flow rate, the equalization operation of the shaft is not performed, so that the adverse effect on the control valve due to slight opening can be avoided.

Furthermore, by selecting the axis with a large amount of supplied steam, giving a bias command to the axis with the least amount of supplied steam, and continuing to do so while there is a control valve that is operating slightly open, It is also possible to fully close the open control valve and equalize the other shafts with a large amount of steam.

The above-described operation eliminates the inconvenience of supply steam concentrating on a specific shaft, making it possible to safely and reliably supply auxiliary steam to a combined cycle power plant.

[Brief explanation of the drawing]

Fig. 1 is a system diagram showing one embodiment of the present invention, and Fig. 2 is a system diagram showing an embodiment of the present invention.
The circuit diagram showing the first example of the integrated control device in the figure, the third example
The same figure is a circuit diagram showing the second example, and FIG. 4 is a system diagram showing an example of an auxiliary steam supply method for a conventional combined cycle power plant. 1.15.16... Power plant shaft 2... Auxiliary steam main pipe 3... Auxiliary boiler 4... Inflow valve 5... Gas turbine 6... Exhaust recovery boiler 7... Condensate Equipment 8... Water pump 9... Steam turbine 10... Generator 11
...Outflow valve 12...Control valve 13.
...Each axis control device 14...Pressure sensor 17
... Steam amount sensor 18 ... Instrument 19 ...
・General control device 20.21...Adder 22
...divider 23.27, 38, 39, 40, 41, 42, 43, 4
5, 46, 47.52...Comparator 24.49...Maximum value selector 24.49...Maximum value selector 25.
50...Minimum value selector 26.51...Subtractor 28.44...Selector 29, 30, 31
, 54, 55, 56...AND circuit 32, 33, 34
, 57, 58, 59...Pulse generator 41, 42, 4
3...Switcher 35, 36, 37, 48, 5
3...OR circuit (8733) Agent Patent attorney Yoshiaki Inomata (and 1 other person)

Claims (1)

[Claims] Each waste heat recovery boiler in a combined cycle power plant consists of multiple power generation shafts, each of which has a gas turbine, steam turbine, generator, and waste heat recovery boiler as main components, connected to a common auxiliary steam main pipe through each control valve. A combined cycle power generation system that supplies steam generated in the heat recovery boiler to other power generation shafts as auxiliary steam through respective control valves controlled by each shaft control device and a common auxiliary steam main pipe. In the auxiliary steam supply method of the plant, a steam amount sensor that detects the amount of auxiliary steam supplied for each power generation axis and a meter that detects the auxiliary steam supply operation state are installed, and the detection signals of each axis are inputted. death,
A common integrated control device is provided that outputs a pulse-like bias signal for each axis, which is added to the control valve opening operation signal output by each axis control device based on a predetermined calculation. The steam supply amount of each axis is compared, and a bias signal is calculated so that the steam supply amount from each axis is equalized in accordance with the maximum deviation, average value, and each predetermined allowable operation control value. Auxiliary steam supply method for a combined cycle power plant featuring features.