JPH0399101A - Controller of exhaust heat recovering heat exchanger - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a control device for an exhaust heat recovery heat exchanger in a combined cycle plant that combines a gas turbine and a steam turbine.

(Prior technology) Recently, as part of high-efficiency power generation, a gas turbine is used to generate electricity, and the heat in the exhaust gas discharged from the gas turbine is recovered by an exhaust heat recovery heat exchanger, and the steam generated by the same boiler is used to generate electricity. Combined cycle plants that drive steam turbines are attracting attention.

FIG. 5 is a diagram showing a schematic configuration of the system of the above-mentioned combined cycle plant, in which the gas turbine 1 has a generator 2
and a steam turbine 3 are connected, and the exhaust gas that has done work in the gas turbine 1 is supplied to the exhaust heat recovery heat exchanger 4, and the steam generated there is introduced to the steam turbine 3, and the exhaust heat in the exhaust gas is This is to ensure maximum recovery.

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

Branch conduit 14 branched from the outlet of the low pressure economizer 9
A high-pressure water supply pump 15 is provided, and the water pressurized by the high-pressure water supply pump 15 is supplied to the high-pressure economizer 7 and further sent to the high-pressure evaporator 6 via the high-pressure drum 16. 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 evaporator 3.

However, in such a plant, at startup and in a low load area, the temperature of the boiler flowing gas is low, so the relatively low temperature heat exchanger tube group parts, that is, the low pressure economizer 9 and the high pressure economizer 7, are It has the characteristic of reducing the pressure and causing evaporation. However, if a mixed fluid of air and water occurs inside the energy saver, the control system may become unstable, making it difficult to continue operation, or water hammer may occur, resulting in equipment damage and other inconveniences. There are some problems.

Therefore, unlike conventional fire boilers, feed water flow rate control valves 17 and 18 are provided on the outlet sides of the low-pressure economizer 9 and high-pressure economizer 7, respectively, and the discharge pressure of each water pump 12, 15 is adjusted to The internal fluid pressure of 7 is maintained and the fluid temperature is maintained at a temperature below the saturation temperature at the pressure to prevent evaporation in the part. In addition, when the plant is shut down at night, one low-pressure evaporator recirculation line and one high-pressure evaporator recirculation line 20 are used to prevent self-evaporation in the economizers 9 and 7 based on pressure drop. It is designed to prevent harmful effects caused by water mixtures.

However, in such a device, when starting up, the evaporator recirculation line 19.20 is closed, the water supply pump 12.15 is started, and when it becomes possible to control the drum level of each high and low pressure drum 13, 16. Exhaust gas from the gas turbine 1 is introduced, but the canned water in the evaporator 6.8 expands due to temperature rise.
The drum water level tends to rise. For this reason, the flow rate control valve 17
, 18 are controlled to continue the closing operation for 10 to 30 minutes at the initial stage of startup. The water in the economizer 7, 9 system is thus heated in the sealed tube and the fluid volume increases by 5-6%. Therefore, although it depends on the capacity of the economizer, each economizer system usually expands by approximately 1rIt.

Therefore, in order to prevent abnormal pressure rise of the fluid in the economizer, the expanded water can be blown into the water doubler 11 via the minimum flow line 21 of the high-pressure water pump and the minimum flow line 22 of the low-pressure water pump. It has been proposed (Japanese Unexamined Patent Publication No. 61-21340).

However, when trying to start up the exhaust heat recovery heat exchanger using the system shown in FIG. Since it is not connected to the redump tank, the temperature of the fluid gradually rises during minimum flow circulation, and the low pressure economizer 9 absorbs heat from the exhaust gas, so these two effects reduce the minimum flow. During operation, the fluid mixture in the low-pressure economizer 9 exceeds the saturation temperature at that pressure, causing problems such as damage to the high-pressure water pump 15 due to generated steam bubbles.

In order to solve this problem, as shown in FIG. The economizer recirculation valves 25 and 26 installed in both economizer recirculation lines 23 and 24 are controlled by the saturation temperature of the drum pressure, or by controlling the first line water temperature to control the economizer outlet water supply. A method of blowing is used to prevent steaming from occurring due to an excessive rise in temperature (see Japanese Patent Laid-Open No. 53-8401 and Japanese Patent Publication No. 63-26801).

When adjusting the water supply temperature at the outlet of the economizer, in order to ensure stability of control and reliable operation, the temperature setting value at the outlet of the economizer should be set at the steaming start temperature at the outlet of the economizer. The control device is set to a value that is a certain deviation lower than that of the valve, and is combined with a control device having hysteresis in order to prevent the valve from opening and closing frequently.

(Problem to be solved by the invention) However, in such a device, during plant shutdown or hot banking, the canned water in the drum is at a saturation temperature, and the temperature inside the economizer is slightly lower than that of the drumned water. . Then, when the water supply pump is started and minimum flow operation starts, the economizer outlet temperature gradually rises and reaches the temperature setting value of the economizer recirculation valve 25, 26 of the economizer recirculation line.
The economizer recirculation valve is opened and blowing into the condenser begins.

On the other hand, when the gas turbine is started and the pressure increases, the temperature of the canned water in the drum is lower than the saturation temperature at the drum pressure, and the gas temperature at the evaporator outlet is almost the same as this low temperature of the canned water. The temperature of the gas at the inlet of the economizer will also be approximately the same as the temperature of the water in the drum.

Therefore, the temperature of the water supply at the outlet of the economizer is only slightly lower than the gas temperature at the inlet of the economizer, but this temperature difference is small and in reality, the temperature of the can water and the temperature of the water supply at the outlet of the economizer are almost equal. , steaming will not occur even without blowing.

However, since the economizer recirculation valve in the economizer recirculation line is controlled to open at a temperature deviation ΔT that is normally about 6°C lower than the saturation temperature, the economizer outlet temperature may reach the steaming temperature. Even if not, the economizer recirculation valves 25 and 26 of the economizer recirculation line will open, causing problems such as water in the high-pressure and low-pressure economizers being blown into the condenser.

In other words, the amount of heat absorbed by the high-pressure economizer due to the above-mentioned blowing is discarded to the condenser, increasing the startup loss, and the temperature of the gas flowing into the low-pressure evaporator 8 does not rise, and in the case of a double-pressure boiler, Even if the high-pressure boiler rises to a predetermined operating pressure, the low-pressure boiler does not rise to the predetermined operating pressure, and the steam from the high-pressure boiler must be bypassed while waiting for the pressure to rise in the low-pressure boiler (Figure 7). However, there is a problem in that the startup loss increases by the bypass of high-pressure steam, the startup time becomes longer, and the characteristics of a combined cycle plant with good load followability are lost.

In view of these points, an object of the present invention is to obtain a control device for an exhaust heat recovery heat exchanger that can reduce startup time and startup loss of a double pressure exhaust heat recovery heat exchanger. .

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a plurality of evaporators and economizers each having a different pressure in the exhaust gas discharged from a gas turbine, and connects the outlet of each economizer to each evaporator. A water pump that supplies water to other economizers is connected to the steam drum installed in the tank, and a water pump that supplies water to other economizers is installed in piping branched from the outlet of the low-pressure economizer, and the outlet side of each water pump and the condenser are connected to a minimum flow. connecting the outlet of each economizer to the condenser via an economizer recirculation line, each having an economizer recirculation valve;
Furthermore, the control circuit for the economizer recirculation valve is provided with a switching device that mutually switches the control setting signal to the economizer recirculation valve when the boiler is started and during normal operation.

(Function) When the boiler is started, the control setting value of the economizer recirculation valve is switched to the same temperature as the starting temperature setting value, for example, the saturation temperature corresponding to the pressure. Therefore, when starting the boiler, the economizer recirculation valve is not opened until the feed water temperature at the outlet of the economizer reaches the saturation temperature, and the feed water that has not reached the steaming temperature is blown into the condenser. This is definitely prevented.

Therefore, the amount of heat absorbed by the high-pressure economizer is not discarded to the condenser, and startup loss is reduced.

(Example) Hereinafter, an example of the present invention will be described 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. Inside the exhaust heat recovery heat exchanger 4, from the upstream side in the flow direction of exhaust gas, a superheater 5, a high pressure evaporator 6, a high pressure node Coal generator 7, medium pressure evaporator 31, medium pressure economizer 32,
A low-pressure evaporator 8 and a low-pressure economizer 9 are provided, and condensate condensed in a condenser 11 is supplied to the low-pressure economizer 9 by a water supply pump 12. The water that has passed through the low-pressure economizer 9 is sent to the low-pressure drum 13, heated by the low-pressure evaporator 9 connected to the low-pressure drum 13, and the steam generated there passes through the low-pressure drum 13 to form low-pressure steam (not shown). supplied to the turbine.

Branch conduit 14 branched from the outlet of the low pressure economizer 9
is further branched into two conduits 33, 34, each conduit 3
3. The water heated by the medium-pressure water pump 35 and high-pressure water pump 15 provided at
, the high-pressure economizer 7, and further sent to the medium-pressure evaporator 31 and high-pressure evaporator 6 via the medium-pressure drum 36 and high-pressure drum 16, respectively. The steam generated in the intermediate pressure evaporator 31 passes through the intermediate pressure drum 36 to an intermediate pressure steam turbine (not shown), and the steam generated in the high pressure evaporator 6 passes through the high pressure drum 16 and is further superheated in the superheater 5. sent to a high pressure turbine.

In addition, the reference numeral 37 in the figure is a flow rate control valve provided in a conduit connecting the outlet of the medium pressure economizer 32 to the medium pressure drum 36.

By the way, economizer recirculation lines 23, 38, and 24 connected to the condenser 11 are branched out from each outlet of the high-pressure economizer 7, medium-pressure economizer 32, and low-pressure economizer 9. Each economizer recirculation line 2B, 38.24 is provided with an economizer recirculation valve 25, 29.26.

On the other hand, minimum flow lines 22 and 40.41 are connected to the outlet portions of the low pressure water supply pump 22, medium pressure water supply pump 35, and 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, Figure 1 shows the economizer recirculation valves 25, 39.2.
6, each drum 16, 36, 13 is provided with a pressure detector 42, and when the pressure signal detected from the pressure detector 42 exceeds a predetermined value, the signal is ANDed. It is input to the circuit 43. On the other hand, the gas turbine 1 is provided with a rotation speed detector 44, and when the gas turbine rotation speed exceeds a predetermined value, a signal thereof is input to the AND circuit 43. When the drum pressure exceeds a predetermined value and the rotational speed of the gas turbine exceeds a predetermined value, the switch 45 is activated by the output signal from the AND circuit 43, and the starting temperature deviation setting signal is changed from, for example, 0°C to normal. During operation, the temperature deviation setting signal is switched to, for example, 6° C., and the temperature deviation signal is input to the subtracter 47 via the amplifier 46.

On the other hand, the drum pressure signal is also input to a function generator 48, which calculates the saturation temperature corresponding to the pressure, and inputs the saturation temperature signal to the subtracter 47. Then, from the saturation temperature signal outputted from the function generator 48, the subtracter 47 converts the saturation temperature signal to the amplifier 4.
The temperature deviation setting signal output from 6 is subtracted, and the deviation signal is inputted to four comparators as a temperature setting signal.

The actual temperature signal from the economizer outlet temperature detector 50 is also input to the four comparators, and the actual temperature signal and the temperature setting signal are compared, and the deviation signal is sent to the proportional integrator 51. The opening of the economizer recirculation valves 25, 39, 26 is controlled.

Therefore, when starting up the plant, the water supply pumps are started in the order of low pressure water supply pump 12, medium pressure water supply pump 35, and high pressure water supply pump 15, and each pump is operated in minimum flow mode using minimum flow lines 22, 40 and 41. do.

So, when the gas turbine is started, the pressures in the high, medium, and low pressure drums begin to rise.

By the way, in this case, since the drum pressure is below a predetermined value and the rotational speed of the gas turbine is also below a predetermined value, the AND
The output signal from the circuit 43 is 0, and the switching device 45 outputs a starting temperature deviation setting signal, for example, 0°C. Therefore, the subtracter 47 outputs the saturation temperature signal output from the function generator 48, and the four comparators compare the actual temperature signal at the outlet of the economizer with the saturation temperature signal. Therefore, the economizer recirculation valve is kept fully open until the actual temperature at the economizer outlet reaches the saturation temperature.

Therefore, the rise in fluid temperature inside 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 water supply inside the economizer is at a pressure close to the pump's cut-off pressure. steaming does not occur.

In this case, the high pressure economizer 7 and the intermediate pressure economizer 32
Since there is no flow of feed water inside the evaporator, there is nothing other than the high-pressure evaporator 6 and the intermediate-pressure evaporator 31 to absorb heat on the gas upstream side of the low-pressure evaporator 8, and the pressures of the evaporator and drum rapidly rise. At the same time, the temperature of the gas also rises, causing thermal expansion of the water supply trapped in the economizer, but the volume increase due to this thermal expansion is discharged to the condenser through the minimum flow line of the pump. , no excessive pressure will be generated within the economizer.

In this way, when the drum pressure reaches a predetermined value and the rotational speed of the gas turbine, the switching device 45 is activated.
The temperature deviation setting signal is switched from the startup temperature deviation setting signal to the normal operation temperature deviation signal, for example, 6°C. Therefore, the comparator 49 has a temperature of 6°C below the saturation temperature at the relevant pressure.
When the temperature signal lower than the saturation temperature is inputted as a setting signal, and the economizer outlet temperature becomes 6 degrees Celsius lower than the saturation temperature, the economizer recirculation valve is controlled in the opening direction, and the economizer recirculation valve 25 is controlled to open.
．． 39.26 is now controlled by the temperature at the outlet of the economizer (Figure 3).

In this way, during startup, the drum pressure can be raised to the specified value while suppressing the exhaust of heat due to heat absorption by the energy saver, making it possible to increase the pressure faster and shorten the startup time. .

FIG. 4 is a diagram showing another embodiment of the present invention, in which the setting signal from the temperature deviation setting device 53 is subtracted by the subtracter 54 from the saturation temperature signal output from the function generator 48, and the setting signal is set from the saturation temperature. A set temperature signal that is lower by the value is input to four comparators. The economizer outlet temperature signal is also input to the four comparators, and the difference signal between the two is input to the gate circuit 55. The gate circuit 55 is an AN
When the drum pressure is above a predetermined value and the rotational speed of the gas turbine is above a predetermined value, a control signal is manually inputted to the gate circuit 55 via the D circuit 43, the gate is opened, and the four comparators Control signals from the economizer recirculation valves 25, 39 . are applied to the actuator 52 via the proportional integrator 51.
26 is controlled in the opening direction.

Thus, in this case, at start-up, no control signal from the comparator 49 is applied to the economizer recirculation valve, and the economizer recirculation valve is held fully open.

Therefore, when the gas turbine is completely started and the drum pressure reaches a predetermined value during normal operation, the gate circuit 55 is opened, and the deviation signal from the comparator 49 is applied as a control signal to the actuating device to restart the economizer. The circulation valve is switched to control by the economizer outlet temperature.

Therefore, this embodiment also performs the same function as the first length embodiment.

〔Effect of the invention〕

As explained above, in the present invention, when the exhaust heat recovery heat exchanger is started, the control temperature set value of the economizer recirculation valve can be changed to a higher temperature than that during normal operation.
The economizer recirculation valve does not open too early during startup.
Heat is no longer discharged due to heat absorption in the economizer, and heat is absorbed only by the evaporator, which contributes to the rise in drum pressure. This allows the drum pressure to rise faster, shortening start-up time and reducing start-up loss. It has the following effects:

[Brief explanation of drawings]

FIG. 1 is a control system diagram of the economizer recirculation valve in the present invention,
FIG. 2 is a schematic system diagram of the combined cycle plant according to the present invention, FIG. 3 is a diagram explaining the startup state, and FIG. 4 is a control system diagram of the economizer recirculation valve in another embodiment of the present invention.
FIGS. 5 and 6 are system diagrams of conventional combined cycle plants, and FIG. 7 is a diagram showing a starting line for 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 energy saver, 8...Low pressure evaporator, 9...
...Low pressure energy saver, 12...Low pressure water pump, 13...
・Low pressure drum, 15... High pressure water pump, 16...
High pressure drum, 25, 26. 39... economizer recirculation valve,
31... Medium pressure evaporator, 32... Medium pressure economizer, 35.
...Medium pressure water pump, 45...Switcher, 47...Subtractor, 48...Function generator, 4...Comparator, 52
...actuating device.

Claims (1)

[Claims] In addition to arranging multiple evaporators and economizers with different pressures in the exhaust gas discharged from the gas turbine,
The outlet of each economizer is connected to the steam drum provided in each evaporator, and a water pump that supplies water to other economizers is installed in piping branched from the low-pressure economizer outlet. The outlet side and the condenser are connected by a minimum flow line, and the outlet of each economizer is connected to the condenser via a economizer recirculation line each having an economizer recirculation valve, and further, the above-mentioned An exhaust heat recovery heat exchanger characterized in that the control circuit of the economizer recirculation valve is provided with a switching device that mutually switches the control setting signal of the economizer recirculation valve during boiler startup and during normal operation. control device.