JP2531801B2 - Exhaust heat recovery heat exchanger controller - Google Patents

Description

The present invention relates to a control device for an exhaust heat recovery heat exchanger in a combined cycle plant in which a gas turbine and a steam turbine are combined.

(Prior art) Recently, as part of high-efficiency power generation, power is generated by a gas turbine, and heat in exhaust gas discharged from the gas turbine is recovered by an exhaust heat recovery heat exchanger to generate steam in the boiler. Has attracted attention for a combined cycle plant that drives a steam turbine.

FIG. 5 is a diagram showing a schematic configuration of the system of the combined cycle plant, in which the generator 2 and the steam turbine 3 are connected to the gas turbine 1, and the exhaust gas working in the gas turbine 1 is exhausted. Heat recovery heat exchanger 4
The steam generated there is introduced into the steam turbine 3 so that the exhaust heat in the exhaust gas is recovered to the maximum extent.

In the exhaust heat recovery heat exchanger 4, the superheater 5, the high pressure evaporator 6, the high pressure economizer 7, the low pressure evaporator 8 and the low pressure economizer are arranged from the upstream side in the flow direction of the exhaust gas discharged from the gas turbine 1. The condenser 9 is provided, and the condensate condensed by the condenser 11 is supplied to the low pressure economizer 9 by the water supply pump 12.
Then, the feed water that has passed through the low pressure economizer 9 is fed to the low pressure drum 13, and the low pressure evaporator 9 connected to the low pressure drum 13
The steam generated in the steam generator is supplied to a low pressure steam turbine (not shown) through the low pressure drum 13.

Branch conduit 14 branched from the outlet of the low-pressure economizer 9
Is provided with a high-pressure water supply pump 15, and the water supplied by the high-pressure water supply pump 15 is supplied to the high-pressure economizer 7.
Further, it is sent to the high pressure evaporator 6 via the high pressure drum 16.
Then, the steam generated in the high-pressure evaporator 6 is sent to the superheater 5 via the high-pressure drum 16 and then to the steam turbine 3.

However, in such a plant, at startup and in a low load region, the boiler inflow gas temperature is low, so that the relatively low temperature heat transfer tube group portion, that is, the low-pressure economizer 9 and the high-pressure economizer 7 is depressurized. However, there is a characteristic that an evaporation phenomenon occurs there. However, when a mixed fluid of steam and water is generated in the economizer in this way, the control system becomes unstable, making it difficult to continue operation, and causing various inconveniences such as water hammer and equipment damage. There are some problems.

Therefore, unlike the conventional thermal power boiler, the feed water flow rate control valves 17 and 18 are provided on the outlet side of the low pressure economizer 9 and the high pressure economizer 7, respectively, and the economizers 9 and 9 are supplied at the discharge pressures of the feed pumps 12 and 15, 7
The internal fluid pressure is maintained and the fluid temperature is maintained at a temperature below the saturation temperature at the pressure to prevent evaporation at this portion. When the plant is stopped at night, the low pressure evaporator recirculation line 19, for the purpose of preventing self-evaporation in the economizers 9 and 7 based on the pressure drop,
The high pressure evaporator recirculation line 20 is used to prevent the harmful effects caused by the steam-water mixture.

However, in such a device, at the time of start-up, the evaporator recirculation lines 19 and 20 were closed, the feed water pumps 12 and 15 were started, and the drum level control of the high and low pressure drums 13 and 16 became possible. Although the exhaust gas from the gas turbine 1 is introduced, the can water in the evaporators 6 and 8 expands due to the temperature rise, and the drum water level tends to rise. Therefore, the flow rate control valves 17 and 18 are controlled to continue the closing operation for 10 to 30 minutes in the initial stage of activation. Then, the water in the economizer 7, 9 system is heated in the closed pipe, and the fluid volume increases by 5 to 6%. Therefore, although it depends on the capacity of the economizer, it usually expands by about 1 m ³ in each economizer system.

Therefore, in order to prevent abnormal pressurization of the fluid in this economizer, the expanded water is treated by the minimum flow line 21 of the high-pressure water supply pump and the minimum flow line of the low-pressure water supply pump.
It has been proposed to blow to the condenser 11 via 22 (Japanese Patent Laid-Open No. 61-213401).

However, when the exhaust heat recovery heat exchanger is started up by the system shown in FIG. 5, the minimum flow line 21 of the high-pressure water feed pump is connected from the high-pressure water feed pump to the inlet of the low-pressure economizer 9. Since it is not connected to the dump tank, the temperature of the fluid gradually rises during circulation of the minimum flow, and the low pressure economizer 9 absorbs heat of the exhaust gas. During the flow operation, the fluid temperature of the low-pressure coal economizer 9 exceeds the saturation temperature at that pressure, which causes a problem that the high-pressure feed pump 15 is damaged by the generated vapor bubbles.

In order to solve this problem, as shown in FIG. 6, the economizer recirculation lines 23 and 24 connecting the outlets of the economizers 7 and 9 to the condenser 11 are provided. Both economizer economizer recirculation lines 23 and 24 are equipped with economizer economizer recirculation valves 25 and 26, respectively, which are controlled by the saturation temperature of the drum pressure or the can water temperature to control the economizer outlet feed water temperature. Is blown so that steaming does not occur too much (see Japanese Patent Laid-Open No. 53-8401 and Japanese Patent Publication No. 63-26801).

When adjusting the feed water temperature at the outlet of the economizer,
To ensure control stability and reliable operation, the temperature setting value at the economizer outlet is set to a value that is lower than the steaming start temperature at the economizer outlet by a certain deviation, and the valve is opened / closed. Controllers with hysteresis are combined to prevent frequent movements.

(Problems to be solved by the invention) However, in such an apparatus, the temperature of the can water in the drum is saturated and the temperature in the economizer is slightly lower than that of the drum water during the plant shutdown and hot banking. .
Therefore, when the water supply pump is started and the minimum flow operation is started, the outlet temperature of the economizer gradually rises and reaches the temperature set value of the economizer recirculation valves 25 and 26 of the economizer recirculation line, The charcoal recirculation valve is opened and the blow to the condenser begins.

On the other hand, in the process of starting the gas turbine and increasing the pressure, the temperature of the can water in the drum is lower than the saturation temperature at the pressure of the drum, and the gas temperature at the evaporator outlet is almost the same as the temperature of the can water at this low temperature. Since the temperature is high, the gas temperature at the inlet of the economizer is almost the same as the temperature of the water in the drum.

The feed water temperature at the outlet of the economizer is slightly lower than the gas temperature at the inlet of the economizer, but this temperature difference is small and the can water temperature and the feed water temperature of the economizer outlet are almost equal. , Steaming does not occur without blowing.

However, since the control of the economizer recirculation valve of the economizer recirculation line is made to open at a temperature deviation ΔT which is usually about 6 ° C. lower than the saturation temperature, the economizer exit temperature reaches the steaming temperature. Even if not, the economizer recirculation valves 25 and 26 of the economizer recirculation line are opened, and there is a problem that the water in the high pressure and low pressure economizers is blown to the condenser.

That is, the amount of heat absorbed in the high-pressure coal economizer by the above-mentioned blow is passed to the condenser, the start-up loss increases, the temperature of the gas flowing into the low-pressure evaporator 8 does not rise, and in the double-pressure boiler, Even if the high-pressure boiler rises to a predetermined operating pressure, the low-pressure boiler does not rise to a predetermined operating pressure, and the pressure of the low-pressure boiler must wait while bypassing the steam of the high-pressure boiler (Fig. 7). However, there is a problem that the start-up loss is increased by the amount of bypass of the high-pressure steam, the start-up time is lengthened, and the characteristic of the combined cycle plant with good load following performance is lost.

The present invention has been made in view of the above circumstances, and an object thereof is to obtain a control device for an exhaust heat recovery heat exchanger that can reduce the startup time and startup loss of the compound pressure exhaust heat recovery heat exchanger. .

[Structure of Invention]

(Means for Solving the Problems) According to the present invention, a plurality of evaporators and economizers having different pressures are provided in exhaust gas discharged from a gas turbine, and the outlets of the economizers are connected to the evaporators. It is connected to the steam drum provided in the, and a water supply pump for supplying water to other economizers is installed in the pipe branched from the low pressure economizer outlet, and the outlet side of each water supply pump and the condenser are minimum flow. Connected by a line, the outlet of each economizer is connected to the condenser via a economizer recirculation line having a economizer recirculation valve, and further to the control circuit of the economizer recirculation valve. When the boiler is started, a full-closed control signal is output to the economizer recirculation valve, and during normal operation, the economizer recirculation valve control signal is set to a temperature setting signal that is lower than the saturation temperature corresponding to the drum pressure by a preset temperature. From the deviation signal from the economizer outlet temperature It is characterized in that a switching device for switching to the control signal is provided.

(Operation) When the boiler is started, the economizer recirculation valve is maintained in a fully closed state, and the economizer economizer recirculation valve will not be opened until the boiler is in the normal operating state, and the steaming temperature will not rise. The unreachable water supply is reliably prevented from being blown into the condenser. Therefore, the amount of heat absorbed by the high pressure economizer is not discarded in the condenser, and the starting loss is reduced.

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 2 is a diagram showing a schematic configuration of a combined cycle plant according to the present invention. In the exhaust heat recovery heat exchanger 4, a superheater 5, a high pressure evaporator 6 and a high pressure node are arranged from the upstream side in the exhaust gas flow direction. A charcoal device 7, a medium-pressure evaporator 31, a medium-pressure economizer 32, a low-pressure evaporator 8 and a low-pressure economizer 9 are provided, and the condensate condensed by the condenser 11 is supplied by the feed pump 12. It is supplied to the low-pressure economizer 9. Then, the feed water that has passed through the low-pressure economizer 9 is sent to the low-pressure drum 13 and heated by the low-pressure evaporator 8 connected to the low-pressure drum 13, and the steam generated there passes through the low-pressure drum 13 and the low-pressure steam turbine (not shown). Is supplied to.

Branch conduit 14 branched from the outlet of the low-pressure economizer 9
Is further branched into two conduits 33, 34, each conduit 33, 34
The medium-pressure water pump 35 and the high-pressure water pump 15 provided in the water supply water supply the medium-pressure economizer 32 and the high-pressure economizer 7, respectively.
The medium pressure drum 36 and high pressure drum respectively
It is sent to the medium pressure evaporator 31 and the high pressure evaporator 6 via 16. Then, the steam generated in the medium pressure evaporator 31 passes through the medium pressure drum 36 to a medium pressure steam turbine (not shown), and the high pressure evaporator 6
The steam generated in 1) passes through the high-pressure drum 16, is further superheated in the superheater 5, and is sent to the high-pressure turbine.

The reference numeral 37 in the figure indicates the outlet of the medium-pressure economizer 32 to the medium-pressure drum.
A flow control valve provided in a conduit connected to 36.

By the way, from the outlets of the high-pressure economizer 7, the medium-pressure economizer 32, and the low-pressure economizer 9, the economizer recirculation lines 23, 38, 24 connected to the condenser 11 are branched and led out. Has been done,
Each economizer recirculation line 23, 38, 24 has a economizer recirculation valve 25, 2
9,26 are provided.

On the other hand, minimum flow lines 22, 40, 41 are connected to the outlets of the low-pressure water supply pump 12, the medium-pressure water supply pump 35, and the high-pressure water supply pump 15, respectively, and the tip of each minimum flow line is connected to the condenser 11. It is connected.

By the way, FIG. 1 is a control system diagram of the economizer recirculation valves 25, 39, and 26. Each drum 16, 36, 13 is provided with a pressure detector 42, and the pressure detector 42 is provided. When the pressure signal detected from the signal exceeds a predetermined value, the signal is
Is input to On the other hand, the gas turbine 1 has a rotation speed detector.
44 is provided, and the signal is input to the AND circuit 43 when the number of revolutions of the gas turbine exceeds a predetermined value. When the drum pressure becomes equal to or higher than the predetermined value and the number of revolutions of the gas turbine becomes equal to or higher than the predetermined value, the switch 45 is operated by the output signal from the AND circuit 43, and the starting temperature deviation setting signal, for example, 0 ° C to normal. The operating temperature deviation setting signal is switched to, for example, 6 ° C., and the temperature deviation setting signal is input to the subtractor 47 via the amplifier 46.

On the other hand, the pressure signal of the drum is also inputted to the function generator 48, the saturation temperature corresponding to the pressure is calculated in the function generator 48, and the saturation temperature signal is calculated by the subtractor 47.
Is input to Then, the function generator
The temperature deviation setting signal output from the amplifier 46 is subtracted from the saturation temperature signal output from 48, and the deviation signal is input to the comparator 49 as a temperature setting signal.

The actual temperature signal from the economizer outlet temperature detector 50 is also input to the comparator 49, where the actual temperature signal and the temperature setting signal are compared, and the deviation signal is proportional to the proportional integrator.
Added to actuator 52 via 51, economizer recirculation valve 25,3
The opening of 9,26 is controlled.

Then, at the time of starting the plant, the water supply pump is a low pressure water supply pump 12, a medium pressure water supply pump 35, and a high pressure water supply pump.
Start in order of 15 and set each pump to minimum flow line 2
Use 2,40,41 for minimum flow operation.

Then, when the gas turbine is started, the pressures of the high, medium, and low pressure drums start to rise.

By the way, in this case, since the drum pressure is less than or equal to a predetermined value and the rotational speed of the gas turbine is less than or equal to a predetermined value, AND
The output signal from the circuit 43 is 0, and the starter temperature deviation setting signal, for example, 0 ° C. is output from the switch 45. Therefore, the subtractor 47 outputs the saturation temperature signal output from the function generator 48, and the comparator 49 compares the actual temperature signal at the outlet of the economizer with the saturation temperature signal. Therefore, the economizer recirculation valve is kept fully closed until the actual temperature at the economizer outlet reaches the saturation temperature. Then, the rise of the fluid temperature in the economizer is almost the same as the gas temperature, but the gas temperature is almost equal to the temperature of the canned water, and the feedwater in the economizer is under a pressure close to the cutoff pressure of the pump. Therefore, steaming does not occur.

In this case, the high pressure economizer 7 and the medium pressure economizer 32
Since there is no flow of feed water inside, there is nothing that absorbs heat other than the high pressure evaporator 6 and the intermediate pressure evaporator 31 on the gas upstream side of the low pressure evaporator 8, and the pressures of the evaporator and the drum rise rapidly. Since the temperature of the gas also rises with this, the feedwater trapped in the economizer causes thermal expansion, but the volumetric increase due to this thermal expansion is discharged to the condenser via the minimum flow line of the pump. No excessive pressure is generated in the economizer.

In this way, when the drum pressure reaches the predetermined value and the number of revolutions of the gas turbine is reached, the switch 45 operates,
The temperature deviation setting signal is switched from the startup temperature deviation setting signal to the normal operation temperature deviation setting signal, for example, 6 ° C. Therefore, the comparator 49 has 6
A temperature signal lower by ℃ is input as a setting signal, and when the outlet temperature of the economizer is 6 ° C lower than the saturation temperature, the economizer recirculation valve is controlled to open and the economizer recirculation valve 2
5,39,26 will be controlled by the temperature of the economizer outlet (Fig. 3).

In this way, the drum pressure can be raised to the specified value while suppressing the heat discharge due to the heat absorption in the economizer at the time of start-up, and the rise of the pressure can be accelerated to shorten the start-up time. .

FIG. 4 is a diagram showing another embodiment of the present invention, in which a temperature deviation setter from the saturation temperature signal output from the function generator 48 is used.
The set signal from 53 is subtracted by the subtractor 54, and the set temperature signal lower than the saturation temperature by the set value is input to the comparator 49.
The comparator 49 also receives an outlet temperature signal of the economizer, and the deviation signal between the two is input to the gate circuit 55. The gate circuit 55 inputs a control signal to the gate circuit 55 via the AND circuit 43 when the drum pressure is equal to or higher than a predetermined value and the number of revolutions of the gas turbine is equal to or higher than the predetermined value, and the gate is opened. Then, the control signal from the comparator 49 is applied to the actuator 52 via the proportional integrator 51, and the economizer recirculation valves 25, 39, 26 are controlled in the opening direction.

In this case, however, the control signal from the comparator 49 is not applied to the economizer recirculation valve at the time of start-up, and the economizer recirculation valve is held in the fully closed state. Therefore, at the time of normal operation when the gas turbine is completely started and the drum pressure reaches a predetermined value, the gate circuit 55 is opened, the deviation signal from the comparator 49 is added to the operating device as a control signal, and the economizer is reactivated. The circulation valve is switched to control by the outlet temperature of the economizer.

Therefore, also in this embodiment, the same operation as in the first embodiment is performed.

〔The invention's effect〕

As described above, in the present invention, when the exhaust heat recovery heat exchanger is started, it is possible to switch the control temperature set value of the economizer recirculation valve to be higher than that during normal operation. The economizer recirculation valve will not open early and the heat quantity will not be discharged due to the endothermic absorption of the economizer, and heat will be absorbed only by the evaporator that contributes to the increase in drum pressure, which will increase the drum pressure. This has the effect of speeding up the process, reducing the startup time, and reducing the startup loss.

[Brief description of drawings]

FIG. 1 is a control system diagram of a economizer recirculation valve according to the present invention,
FIG. 2 is a schematic system diagram of a combined cycle plant according to the present invention, FIG. 3 is a starting state explanatory diagram, and FIG. 4 is a control system diagram of a economizer recirculation valve according to another embodiment of the present invention.
5 and 6 are system diagrams of a conventional combined cycle plant, and FIG. 7 is a diagram showing a starting curve of a conventional exhaust heat recovery heat exchanger. 1 ... Gas turbine, 3 ... Steam turbine, 4 ... Exhaust heat recovery heat exchanger, 5 ... Superheater, 6 ... High-pressure evaporator, 7 ...
… High-pressure economizer, 8 …… Low-pressure evaporator, 9 …… Low-pressure economizer,
12 …… Low-pressure feed pump, 13 …… Low-pressure drum, 15 …… High-pressure feed pump, 16 …… High-pressure drum, 25,26,39 …… Coal economizer recirculation valve, 31 …… Medium-pressure evaporator, 32… … Medium pressure economizer, 35 ……
Medium pressure water supply pump, 45 …… Switcher, 47 …… Subtractor, 48 ……
Function generator, 49 ... Comparator, 52 ... Actuator.

Claims (1)

(57) [Claims] 1. A plurality of evaporators and economizers having different pressures are arranged in exhaust gas discharged from a gas turbine, and an outlet of each economizer is provided to each evaporator via a flow rate control valve. It is connected to the steam drum that is connected to each of the low-pressure coal economizer outlets, and a water supply pump that supplies water to other economizers is installed in the pipes branched from the low-pressure economizer outlets.The outlet side of each water supply pump and the condenser are connected by a minimum flow line. In addition, the control circuit of the economizer recirculation valve outputs a fully closed control signal to the economizer recirculation valve when the boiler is started, and the economizer recirculation valve control signal is applied to the drum pressure during normal operation. A control device for an exhaust heat recovery heat exchanger, characterized in that a switching device for switching to a control signal consisting of a deviation signal between a temperature setting signal lower than the saturation temperature by a predetermined set temperature and the outlet temperature of the economizer is provided. .