JP4017712B2 - Method and apparatus for controlling temperature of feed water in exhaust heat recovery boiler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for controlling a feed water temperature of an exhaust heat recovery boiler in a combined power plant.
[0002]
[Prior art]
There is a combined power plant as a plant optimal for high-efficiency power generation and intermediate load operation. This plant generates power by a gas turbine and includes a heat recovery steam generator that recovers the heat of exhaust gas discharged from the gas turbine, and generates power by driving the steam turbine with steam generated in the heat recovery steam generator. It is. Such an exhaust heat recovery boiler will be described with reference to the drawings.
[0003]
FIG. 7 is a system diagram of a conventional combined power plant. The generator 2 is driven by the gas turbine 1, and the exhaust gas G of the gas turbine (GT) 1 is introduced into the exhaust heat recovery boiler (HRSG) 3, and the heat is recovered. A superheater 4, a high-pressure evaporator 5, a high-pressure economizer 6, a low-pressure evaporator 7 and a low-pressure economizer 8 are arranged in the gas flow path of the exhaust heat recovery boiler 3 in order from the high temperature side to the low temperature side. A low-pressure drum 9 and a high-pressure drum 10 are disposed outside the gas flow path. The water supply to the exhaust heat recovery boiler 3 is finally discharged as steam from the superheater 4 and used to drive the steam turbine 12 connected to the generator 2.
[0004]
The steam used in the steam turbine 12 is condensed in the condenser 13, and the water in the condenser 13 is supplied to the low-pressure economizer 8 from the water supply channel 19 by the condensate pump 14. The heated feed water at the outlet of the low-pressure economizer 8 is guided to the high-pressure economizer 6 by the high-pressure feed pump 15 and mixed with the feed water W to the low-pressure economizer 8 through the circulation feed water channel 20. The feed water temperature T _S1 at the inlet of the low pressure economizer 8 is detected by the temperature detector 17, and the low pressure economizer is based on the feed water flow rate at the feed water flow rate detector 21 provided in the feed water flow channel 19 by the temperature / flow rate controller 18. The opening degree of the flow rate adjustment valve 16 provided in the circulation water supply flow path 20 to the low pressure economizer 8 of the heated water supply at the outlet of the vessel 8 is adjusted.
[0005]
The reason why the feed water at the outlet of the low-pressure economizer 8 of the combined power plant configured as described above is mixed with the feed water at the inlet will be described.
In recent combined power plants, a condenser deaeration method is adopted in which the installation of a deaerator is omitted and the condenser 13 has a deaeration function for reasons such as reducing equipment costs and simplifying the system. Has been. In the case of this method, the feed water temperature T _S1 at the inlet of the low pressure economizer 8 of the boiler 3 is as low as about 30 ° C. Therefore, when the water is fed to the low pressure economizer 8 at the same temperature, the low pressure economizer 8 Cold corrosion occurs. As a countermeasure, as shown in the drawing, the heated feed water at the outlet of the low pressure economizer 8 is mixed with the boiler feed water W (the feed water at the inlet of the low pressure economizer 8) via the high pressure feed pump 15 to cause low temperature corrosion. Means for raising the temperature to a non-temperature is adopted. The temperature is set to about 50 ° C., which is a temperature at which low-temperature corrosion does not occur during rated operation, and this temperature is the feed water flow upstream of the junction between the temperature detected by the temperature detector 17 and the circulating feed water flow path 20. The flow rate adjusting valve 16 is controlled by the temperature / flow rate controller 18 based on the feed water flow rate at the feed water flow rate detector 21 provided in the passage 19 and is kept constant.
[0006]
[Problems to be solved by the invention]
Conventionally, the low temperature corrosion prevention temperature for raising the temperature of the boiler feed water W (feed water at the inlet of the low pressure economizer 8) is a constant value from the time of start-up to a predetermined load, for example, 20-30% which is the minimum load. (About 50 ° C.).
[0007]
However, since the exhaust gas temperature introduced into the exhaust heat recovery boiler is low when the boiler is started, the amount of heat recovered in the low pressure economizer 8 is small, the feed water temperature T _{S2 at the} outlet of the low pressure economizer 8 is low, and the temperature is about When the temperature is 50 ° C. or lower, it is impossible to raise the feed water temperature T _S1 at the inlet of the low pressure economizer 8 to the set temperature (about 50 ° C.). Condensation is inevitable (condensation time from water vapor is about 1 hour from the start of the boiler), and this dew condensation water is after the feed water temperature T _S1 at the low pressure economizer 8 inlet rises to about 50 ° C. However, since it takes a long time (about 3 hours or more) to complete evaporation, the heat transfer boiler of the low-pressure economizer 8 that has many operations that are repeatedly started and stopped has the disadvantage of low-temperature corrosion. It was.
[0008]
An object of the present invention, except for the disadvantages of the prior art, waste heat can reduce the low-temperature corrosion of the low pressure economizer by evaporation in a short time dew condensation water in the boiler during start-up Oite low pressure economizer The object is to provide a method and an apparatus for controlling the feed water temperature of a recovery boiler.
[0009]
[Means for Solving the Problems]
The present invention employs the following configuration in order to solve the above problems.
That is, the invention described in claim 1 is used in the steam turbine (12) at the inlet of the low pressure economizer (8) provided in the gas flow path (3) into which the exhaust gas from the gas turbine (1) is introduced. steam was supplied as feed water after condensed in condenser (13), a low-pressure economizer part of the heated feed water in the heat recovery by the low-pressure economizer (8) from the exhaust gas (8 from the outlet of) via the circulation water supply path (20) and only recycled to the inlet of the low pressure economizer (8), a low-pressure economizer by mixing with inlet feed water of low pressure economizer (8) A method for controlling the feed water temperature of the exhaust heat recovery boiler for controlling the inlet feed water temperature of (8) , wherein the control temperature of the inlet feed water temperature of the low pressure economizer (8) is prevented from low temperature corrosion of the low pressure economizer (8). The predetermined high temperature side that is sufficient to evaporate the temperature and condensation water and the low temperature of the low pressure economizer (8) Set to a predetermined low temperature side is a food-out prevention temperature, the boiler start early after starting the gas turbine (1), the boiler load signal, the physical quantity or low intermediate pressure economizer that correlate with boiler load signal (8 water supply inlet) until the predetermined value, the predetermined temperature at the inlet of the feed water of the low-pressure economizer (8) by increasing the flow rate of water to be recycled to the inlet of the low pressure economizer (8) Controlled to the high temperature side temperature to evaporate the condensed water of the low pressure economizer (8), and then the boiler load signal, the physical quantity correlated with the boiler load signal, or the amount of water supplied to the inlet of the low pressure economizer (8) When the value reaches a predetermined value, the flow rate of the feed water to be recirculated to the inlet of the low pressure economizer (8) is reduced to control the predetermined temperature of the feed water at the inlet of the low pressure economizer (8) to the low temperature side temperature. It is the feed water temperature control method of a recovery boiler.
[0010]
The invention described in claim 2 is the steam utilized in the steam turbine (12) at the inlet of the low pressure economizer (8) provided in the gas flow path (3) into which the exhaust gas from the gas turbine (1) is introduced. the condenser and the water supply system to supply a feed water after condensed in (13) (19), the low pressure economizer part of the feed water heated in the low-pressure economizer (8) by heat recovery from the flue gas A circulating water supply system (20) for recirculation only from the outlet of the vessel (8) to the inlet of the low pressure economizer (8), and a recirculation flow rate adjustment for adjusting the recirculation water flow rate to the recirculation water system (20) a heat recovery boiler and means (16),
There is a correlation between the feed water temperature detecting means (17) at the inlet of the low pressure economizer (8), the feed water flow rate detecting means (21) at the inlet of the low pressure economizer (8), and the boiler load value or the boiler load value. The physical quantity detection means and the control temperature of the inlet water supply temperature of the low-pressure economizer (8) are the low temperature corrosion prevention temperature of the low-pressure economizer (8) and a predetermined high temperature that is sufficient to evaporate the condensed water. And the boiler load value or the correlation with the boiler load value at the initial stage of the boiler start after the gas turbine (1) is started. Until the detected value of the feed water flow rate detection means (21) at the entrance of the physical quantity or the low pressure economizer (8) reaches a predetermined value, the low pressure economizer (8 ) Increase the flow rate of the feed water recirculated to the inlet Thus, the predetermined temperature of the feed water at the inlet of the low pressure economizer (8) is controlled to the high temperature side to evaporate the condensed water of the low pressure economizer (8), and then correlated with the boiler load signal and the boiler load signal. When the relevant physical quantity or the amount of feed water at the inlet of the low pressure economizer (8) reaches a predetermined value, the flow rate of the feed water recirculated to the inlet of the low pressure economizer (8) is reduced to reduce the low pressure economizer (8). A recirculation flow rate control device (18) for controlling a predetermined temperature of the feed water at the inlet to the low temperature side temperature .
[0013]
The present invention can also be applied to an exhaust heat recovery boiler that does not omit the installation of a deaerator.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described based on the following embodiments.
Although the system diagram of the combined power plant to which the present invention is applied is the same as that shown in FIG. 7, the configuration of the temperature / flow rate controller 18 is different from that of the prior art, and FIG. The configuration of the vessel 18 is shown along with that of the prior art.
[0015]
The configuration of the temperature / flow rate controller 18 in the prior art is a configuration in which the opening degree of the flow rate adjustment valve 16 is controlled so that the inlet feed water temperature of the low pressure economizer 8 becomes 50 ° C. when the high pressure feed pump 15 is started. However, in the present invention, the inlet water supply temperature of the low-pressure economizer 8 is set to two types, a relatively high temperature side temperature and a relatively low temperature side temperature, depending on the load.
[0016]
In the example shown in FIGS. 1 to 4, the relatively high temperature side water supply temperature is set to 80 ° C., and the relatively low temperature side temperature is set to 50 ° C. The reason for setting the high-temperature side water supply temperature to 80 ° C. is that, as shown in FIG. 3, if the temperature is 80 ° C. or higher, the condensation completion time of the condensed water in the exhaust gas to the heat transfer pipe of the low-pressure economizer 8 This is because the difference is small, and if the temperature is set to 90 to 100 ° C., the recirculation flow rate from the circulation feed water flow path 20 to the inlet of the low pressure economizer 8 increases accordingly, and the capacity of the high pressure feed pump 15 is exceeded. It is necessary to use a high-pressure feed pump 15 having a large capacity. Moreover, by setting the feed water temperature at the low pressure economizer 8 at 80 ° C., the heat of vaporization of the moisture once condensed can be sufficiently supplied.
[0017]
The reason why the inlet water supply temperature of the low-pressure economizer 8 is set to 50 ° C. is that the dew point temperature of water in the exhaust gas is about 45 ° C. even if the load of the gas turbine 1 is 100% load. This is because the low temperature corrosion of the economizer 8 does not occur when the temperature is set to 50 ° C.
[0018]
The time change characteristics of the low pressure economizer 8 outlet water supply temperature and the inlet water supply temperature after the boiler 3 is started, that is, after the gas turbine (GT) 1 is started, are shown in FIGS. 2 (a) and 2 (b), respectively. Show. FIG. 2C shows changes over time in the boiler load, the gas turbine rotational speed, the amount of gas introduced into the boiler, and the boiler outlet gas temperature.
[0019]
Since the exhaust gas temperature is low at the initial stage of boiler activation, the amount of heat recovered in the economizer 8 is small, and the feed water temperature at the outlet of the low-pressure economizer 8 is 50 ° C. or lower. The feed water temperature at the entrance of the economizer 8 is also 50 ° C. or less. Therefore, in this case, since the dew point temperature is not more than that shown in FIG. 2, moisture in the exhaust gas is condensed in the low pressure economizer 8. Conventionally, as the low-pressure economizer 8 outlet feed water temperature rises, the recirculation flow rate to the low-pressure economizer 8 inlet is adjusted by the flow rate adjusting valve 16, while the low-pressure economizer 8 inlet feed water temperature is 50 ° C. I was in control.
[0020]
In FIG. 2 (b), the dew point temperature increases as the boiler load increases, but this increases the fuel combustion amount of the gas turbine and increases the fuel combustion amount as the boiler load increases. This is because the amount of water in the exhaust gas increases and the dew point temperature also rises.
[0021]
In addition, according to FIG. 2, in the prior art, after the low-pressure economizer 8 outlet water supply temperature has reached 150 ° C. and has passed for a while, the dew condensation is completed for the first time. This is because condensed water present in a local portion near the feed water inlet of the low economizer 8 evaporates.
[0022]
FIG. 3 shows the relationship between the feed water temperature and the condensation completion time of the condensed water. If the feed water temperature is set to 50 ° C. as in the prior art, it takes about 3 hours until the condensation water generated at the start of the evaporation is completed. Although it turns out that it is necessary, if the feed water temperature at the inlet of the low pressure economizer 8 is once raised to 80 ° C. from the start of the boiler as in the present invention, the evaporation completion time of condensed water at 80 ° C. is 0.15 hours. I know it ’s good.
[0023]
In one embodiment of the present invention, as shown in FIG. 2, the low-pressure economizer is increased by increasing the recirculation flow rate of feed water to the low-pressure economizer 8 by adjusting the opening degree of the flow rate adjustment valve 16 from the start of the boiler. The feed water temperature at the 8 inlet is once raised to 80 ° C., and this temperature is maintained for 0.15 hours or more in order to complete the evaporation of condensed water at 80 ° C., and then the feed water temperature at the low pressure economizer 8 entrance is set to a predetermined value. It returns to control maintained at 50 degreeC.
[0024]
Here, since the value of the boiler load (according to the load signal of the gas turbine 1) when the feed water temperature at the inlet of the low pressure economizer 8 reaches 80 ° C. corresponds to β, the opening degree of the flow rate adjustment valve 16 from the time of boiler startup. By increasing the recirculation flow rate of the feed water to the low pressure economizer 8 by adjustment and maintaining the recirculation flow rate of the feed water for 0.15 hours or more after reaching the boiler load β, the condensation water is evaporated. It can also be completed.
Further, instead of the boiler load β, it is also possible to use a high-pressure or low-pressure steam flow rate or a high-pressure main steam temperature having a correlation with the water supply amount W or the boiler load β at the inlet of the low-pressure economizer 8.
[0025]
When the present invention and the prior art are compared in terms of the generation time of condensed water and the wet time of the economizer 8 until the completion of evaporation (condensation time + completion time of evaporation), the wet time is 1 hour in the case of the present invention. The total time of evaporation is 0.15 hours, which is 1.15 hours, whereas in the case of the prior art, the wetting time is 4 hours, which is a condensation time of 1 hour and an evaporation completion time of 3 hours.
[0026]
Therefore, the present invention reduces the wetting time by about 30% compared to the prior art, thereby extending the life of the low pressure economizer 8 to low temperature corrosion by about three times. In the present invention, a steel sheet having a thickness of 3 mm as a corrosion allowance can be used in the present invention, and the thickness of the heat transfer tube of the economizer 8 can be reduced.
[0027]
Further, the evaporation completion time of 0.15 hours cannot be uniquely determined due to the difference in exhaust gas conditions and the combined power plant, but if the exhaust gas temperature of the exhaust heat recovery boiler 3 is about 100 ° C., the low pressure of the feed water temperature of 50 ° C. Since the condensed water adhering to the surface of the heat transfer tube of the economizer 8 is completed in 0.15 hours, if the gas temperature is 100 ° C. or higher, the evaporation completion time is shorter than 0.15 hours.
[0028]
Here, after increasing the recirculation flow rate to the inlet side of the low pressure economizer 8 to a predetermined temperature (80 ° C.), the timing for returning to the normal control of the predetermined temperature (50 ° C.) is as follows. As shown in FIG. 4, a method of changing the set value of the feed water temperature at the low pressure economizer 8 inlet according to the boiler load α or the feed water amount W at the low pressure economizer 8 inlet can be used.
[0029]
As can be seen from FIGS. 2 (b) and 2 (c), the dew condensation water at the inlet of the low pressure economizer 8 until the boiler load in this case becomes a predetermined value α (α> β) from the start-up. The evaporation of is complete.
[0030]
Further, as shown in FIG. 5, the feed water recirculation flow rate to the low pressure economizer 8 inlet is adjusted by dividing the opening of the flow rate adjustment valve 16 into two types according to the boiler load α or the water supply amount W at the low pressure economizer 8 inlet. There is a way to do it.
In the method shown in FIG. 5, when the boiler load is equal to or less than a predetermined value α from the time of starting the boiler, the flow rate adjusting valve 16 is opened to a predetermined temperature so that the inlet water supply temperature of the low pressure economizer 8 becomes a predetermined temperature (80 ° C.). After that, the normal flow rate control valve 16 is returned to the opening control so that the feed water temperature at the inlet of the low pressure economizer 8 becomes a predetermined value (50 ° C.).
[0031]
Further, instead of the feed water amount W to the boiler load α or the low-pressure economizer 8 inlet of FIGS. 4 and 5, it is possible to use a high-pressure or low-pressure steam flow rate or a high-pressure main steam temperature correlated with the boiler load α. It is.
[0032]
In each of the above examples, the control from the start of the boiler has been described. However, the present invention is not limited to the start of the boiler, but is also applied to a case where the boiler load decreases and the exhaust gas inlet portion of the low-pressure economizer 8 may be subject to low-temperature corrosion. it can.
Although FIG. 1 has been described by taking a double pressure exhaust heat recovery boiler having a high pressure and a low pressure drum as an example, it can be applied to a single pressure or triple pressure as a matter of course.
[0033]
Further, instead of the method of adjusting the feed water recirculation flow rate to the inlet of the low pressure economizer 8 by the opening of the flow rate adjusting valve 16, the variable flow pump 22 is used as shown in FIG. Control for adjusting the feed water recirculation flow rate may be performed.
[0034]
【The invention's effect】
The present invention is performed in a state of supplying water to a normal boiler, can start up at a steep angle after starting the gas turbine, and can greatly suppress low-temperature corrosion of the heat transfer tubes of the low-pressure economizer. .
[Brief description of the drawings]
FIG. 1 is a diagram for explaining the operation of a temperature / flow rate controller at the inlet of a low-pressure economizer after starting an exhaust heat recovery boiler to which the present invention and the prior art are applied.
[Fig. 2] Time-varying characteristics of the low-pressure economizer outlet feed water temperature after the start-up of the exhaust heat recovery boiler to which the present invention is applied (Fig. 2 (a)) and low-pressure economizer inlet feed water temperature varying characteristics FIG. 2 (c) is a diagram showing temporal changes in the boiler load, the gas turbine rotational speed, the amount of gas introduced into the boiler, and the boiler outlet gas temperature.
FIG. 3 is a diagram showing the relationship between the temperature of water supplied to the economizer of the exhaust heat recovery boiler to which the present invention is applied and the completion time of evaporation of condensed water.
FIG. 4 is a diagram showing a method of changing a set value of the feed water temperature at the inlet of the low-pressure economizer according to the load of the exhaust heat recovery boiler to which the present invention is applied or the amount of feed water.
FIG. 5 is a diagram showing a method for defining the opening of the flow rate adjustment valve according to the load of the exhaust heat recovery boiler to which the present invention is applied or the amount of water supply.
FIG. 6 is a system diagram of a combined power plant to which the present invention is applied.
FIG. 7 is a system diagram of a combined power plant to which the present invention is applied.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Gas turbine 2 Generator 3 Waste heat recovery boiler 4 Superheater 5 High pressure evaporator 6 High pressure economizer 7 Low pressure evaporator 8 Low pressure economizer 9 Low pressure drum 10 High pressure drum 12 Steam turbine 13 Condenser 14 Condensate pump 15 High-pressure feed pump 16 Flow rate adjustment valve 17 Low-pressure economizer inlet feed water temperature detector 18 Temperature / flow rate controller 19 Feed water passage 20 Circulating feed water passage 21 Feed water flow detector 22 Variable flow pump

Claims (2)

The steam exhaust is utilized in a steam turbine (12) to the inlet of the gas flow path to be introduced (3) low-pressure economizer provided in the (8) from the gas turbine (1) with condenser (13) It supplied as feed water after condensate, circulating water flow path from the outlet of the low pressure economizer part of the heated feed water in the low pressure economizer by heat recovery (8) from the exhaust gas (8) (20 ) via only recycled to the inlet of the low pressure economizer (8), to control the inlet feedwater temperature of the low-pressure economizer (8) by mixing with an inlet feed water of the low-pressure economizer (8) A method for controlling a feed water temperature of an exhaust heat recovery boiler ,
The control temperature of the inlet water supply temperature of the low-pressure economizer (8) is a predetermined high-temperature side and a low-pressure economizer that is a low-temperature corrosion prevention temperature of the low-pressure economizer and a temperature sufficient to evaporate condensed water. Set to the predetermined low temperature side which is the low temperature corrosion prevention temperature of (8),
The boiler start early after starting the gas turbine (1), until the boiler load signal, or a physical quantity that correlate with the boiler load signal is water supply inlet of the low-intermediate pressure economizer (8) reaches a predetermined value, the low pressure economizer (8) of the low pressure economizer by increasing the flow rate of water to be recycled to the inlet (8) of the predetermined temperature of the feed water inlet to control the upper temperature low-pressure economizer ( When the condensed water of 8) evaporates, and then the boiler load signal, the physical quantity correlated with the boiler load signal or the amount of water supplied to the inlet of the low pressure economizer (8) reaches a predetermined value, the low pressure economizer (8) A method for controlling a feed water temperature of an exhaust heat recovery boiler, wherein a predetermined temperature of feed water at an inlet of a low-pressure economizer (8) is controlled to the low temperature side temperature by reducing a flow rate of feed water recirculated to the inlet of the exhaust gas. Steam used in the steam turbine (12) is fed into the condenser (13) at the inlet of the low-pressure economizer (8) provided in the gas flow path (3) into which the exhaust gas from the gas turbine (1) is introduced. a water supply system to supply a feed water after condensate (19), the low pressure part of the water supply to the heated low-pressure economizer (8) by heat recovery from the flue gas from the outlet of the low pressure economizer (8) A circulation water supply system (20) for recirculation only at the inlet of the economizer (8) and a recirculation flow rate adjusting means (16) for adjusting the recirculation water flow rate to the recirculation water system (20) are provided. a heat recovery steam generator,
Feed water temperature detection means (17) at the inlet of the low pressure economizer (8);
Feed water flow rate detecting means (21) at the inlet of the low pressure economizer (8);
Boiler load value or physical quantity detection means correlated with boiler load value;
The control temperature of the inlet water supply temperature of the low-pressure economizer (8) is a predetermined high-temperature side and a low-pressure economizer that is a low-temperature corrosion prevention temperature of the low-pressure economizer and a temperature sufficient to evaporate condensed water. (8) The low temperature corrosion prevention temperature is set to a predetermined low temperature side, and the boiler load value or the physical quantity detecting means correlated with the boiler load value at the initial stage of boiler startup after starting the gas turbine (1) Alternatively, the recirculation flow rate adjusting means (16) recirculates to the low pressure economizer (8) inlet until the detected value of the feed water flow rate detecting means (21) at the inlet of the low pressure economizer (8) reaches a predetermined value. By increasing the flow rate of the feed water to be supplied, the predetermined temperature of the feed water at the inlet of the low pressure economizer (8) is controlled to the high temperature side temperature to evaporate the condensed water of the low pressure economizer (8), and then the boiler Physical quantity correlated with load signal and boiler load signal When the water supply amount at the inlet of the low-pressure economizer (8) reaches a predetermined value, the flow rate of the water to be recirculated to the inlet of the low-pressure economizer (8) is decreased to supply water at the inlet of the low-pressure economizer (8). And a recirculation flow rate control device (18) for controlling the predetermined temperature to the low temperature side temperature, a feed water temperature control device for an exhaust heat recovery boiler.

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