JPH0942606A - Once-through boiler steam temperature control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a once-through boiler steam temperature control device to suppress the fluctuation in a steam temperature at the furnace water-cooled wall-outlet during lowering of a load. SOLUTION: Feed water from a boiler feed water pump 2 is fed to a furnace water-cooled wall 1 through a high pressure feed water heater 3 and an economizer 4. Steam of the furnace water-cooled wall 1 is fed through a flue vaporizer 5 and a superheated to a high pressure turbine, where a part of steam completing a work heats the heater 3 through the flow of it through a high-pressure turbine steam extraction line 10a. During fallout of a load, heat accumulation of a furnace water-cooled wall is about to increase an outlet steam temperature but a high pressure steam extraction bypass valve 10c of a high pressure turbine steam extraction bypass line 10b is regulated based on a load demand signal and a detected value a steam temperature detector 19 at a furnace water-cooled wall outlet, and by bypassing high pressure turbine steam extraction, a feed water temperature is lowered to prevent the fluctuation in the steam temperature at the furnace water-cooled wall outlet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a once-through boiler steam temperature control device suitable for controlling the temperature of steam exiting a water wall of a furnace when a load load on a transformer Benson boiler or the like is reduced.

[0002]

2. Description of the Related Art A variable pressure Benson boiler is a boiler that changes the boiler pressure according to the load. This transformation Benson boiler will be described with reference to FIG. FIG. 3 is a system diagram of a conventional transformer Benson boiler. In this figure, 1 is the water wall of the furnace,
Reference numeral 2 is a boiler water supply pump for supplying water to the furnace water cooling wall 1, 3 is a water supply heater for heating water supply from the boiler water supply pump 2, 4
Is a economizer, 5 is a flue evaporator for preventing steaming of the outlet fluid of the economizer 4, 6 is a steam separator, 7 is a steam separator 6
The primary superheater superheats the steam separated in 1., the secondary superheater 9, the tertiary superheater 10 and the high pressure turbine driven by the steam from the tertiary superheater 9. 11 is a water storage tank for storing the water separated by the steam separator 5, and 12 is a water storage tank 1.
A recirculation pump for recirculating the water No. 1 to the furnace water cooling wall 1,
Reference numeral 3 is a boiler recirculation flow rate adjusting valve for adjusting the flow rate from the recirculation pump 12. Reference numeral 14 is a primary spray valve that supplies a part of the feed water from the heater 3 to the inlet of the secondary superheater 8 to adjust the outlet steam temperature, and 15 is the feed water from the heater 3 to the inlet of the tertiary superheater 9. It is a secondary spray valve that supplies part of it and adjusts its outlet steam temperature. 10a is a high-pressure turbine 10
This is a high-pressure turbine extraction line that extracts a part of the steam that has worked in 1. and guides it to the heater 3. The heater 3 heats the feed water by the high-pressure turbine extraction. The operation of such a transformer Benson boiler is well known, and therefore its explanation is omitted.

[0003]

While the boiler is operating,
Even if the spray amount is increased by adjusting the primary spray valve 14 and the secondary spray valve 15, the superheater outlet temperature becomes a constant value in the static state in view of heat balance, and the steam temperature control is effective only in the transient state. It is clear that they have.

On the other hand, in the above-mentioned transformer Benson boiler, in order to improve the plant efficiency under low load, so-called transformer operation is performed in which the steam pressure is changed according to the load. This is shown in FIG. FIG. 4 is a diagram showing an example of changes in the steam pressure with respect to the load in the transformer Benson boiler, wherein the horizontal axis represents the load and the vertical axis represents the steam pressure. When the load drops, the steam pressure also decreases as the load decreases, so the outlet steam temperature of the furnace water cooling wall 1 also decreases. In this case, since the heat transfer tube temperature of the furnace water cooling wall 1 has a large heat capacity, the temperature decrease is delayed with respect to the decrease of the steam temperature. For this reason, the temperature difference between the heat transfer tube temperature of the furnace water cooling wall 1 and the water / steam temperature becomes large, and the heat storage amount of the heat transfer tube is released to the steam side. Therefore, the outlet steam temperature of the furnace water cooling wall 1 temporarily changes. To rise. This temperature rise becomes a large disturbance to the steam temperature control of the downstream superheater, and makes it difficult to control the steam temperature of the superheater. In this case, the furnace water cooling wall 1 occupies most of the heat absorption amount of the economizer 4, the furnace water cooling wall 1, and the superheaters 7, 8 and 9.

As a means for suppressing the rise in the outlet steam temperature of the water cooling wall 1 of the furnace when the load drops, a method of increasing the gas recirculation flow rate to lower the temperature inside the furnace, and a fuel-fuel ratio, that is, fuel for the amount of water supplied A method of reducing the ratio of the amount of fuel (narrowing the amount of fuel) is adopted. However, the former is not preferable because it requires a large gas recirculation fan, its driving power is large, and its installation area is also large, and it is in the direction of not adopting it.

On the other hand, in the latter case, when the fuel amount is reduced, the furnace outlet gas temperature is lowered and the combustion gas amount is also lowered, so that the heat absorption amount of the contact heat transfer portion is lowered. FIG. 5 is a layout of the contact heat transfer parts. In this figure, the same parts as those shown in FIG. 3 are designated by the same reference numerals. Reference numeral 17 is a reheater, and 18 is a parallel damper. As shown in the figure, a coal economizer 4, a flue vaporizer 5, a primary superheater 7, a secondary superheater 8, a tertiary superheater 9, and each reheater 17 are arranged at the exit of the furnace. It is obvious that the heat absorption amount of these contact heat transfer parts is reduced by reducing the amount. And, of these contact heat transfer parts, it is convenient for each superheater and the flue evaporator 5 to reduce the heat absorption amount, but the reduction of the heat absorption amount of the reheater 17 is due to the outlet steam of the reheater 17. There is a problem that the temperature is lowered.
That is, the outlet steam temperature of the reheater 17 depends exclusively on the furnace outlet gas temperature, and the temperature cannot be controlled by other control means. Therefore, the decrease in the heat absorption amount of the reheater 17 immediately results in a decrease in the outlet steam temperature. This will cause a drop and will not be able to supply the required temperature to the medium pressure turbine.

An object of the present invention is to solve the above problems in the prior art and to provide a once-through boiler steam temperature control device capable of suppressing fluctuations in the steam temperature at the outlet of the water cooling wall of the furnace when the load is lowered.

[0008]

In order to achieve the above object, the present invention provides a feed water pump, a heater for heating feed water from the feed water pump to the water wall of the furnace, and a high pressure turbine bleed air for the heater. In a boiler with a guiding line,
A temperature detector that detects the outlet steam temperature of the furnace water cooling wall, a bypass line that bypasses the line, a bypass valve installed in this bypass line, and a bypass valve based on the detection value of the temperature detector. A control unit for controlling the opening is provided.

[0009]

The feed water supplied to the cold water wall of the furnace is heated by the high pressure turbine extraction air in the heater. When the load decreases, the heat storage amount of the heat transfer tube of the reactor water cooling wall is released to the steam side, and the outlet steam temperature of the furnace water cooling wall tends to rise temporarily,
The bypass valve is adjusted according to the decrease of the load request signal and the temperature of the steam at the outlet of the water cooling wall of the furnace, and the high-pressure turbine extraction air is bypassed from the bypass line. Suppress the rise in steam temperature at the water cooling wall outlet.

[0010]

The present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a system diagram of a main part of a boiler steam temperature control device according to an embodiment of the present invention. In this figure, the same or equivalent parts as those shown in FIG. Reference numeral 10b is a high pressure turbine extraction line that bypasses the high pressure turbine extraction line 10a and the heater 3, and 10c is a high pressure turbine extraction bypass valve that is interposed in the high pressure turbine extraction line 10b. Reference numeral 19 is a furnace water cooling wall outlet steam temperature detector for detecting the furnace water cooling wall outlet steam temperature, and 20 is a control unit for controlling the high pressure turbine extraction air bypass valve 10c. In FIG. 1, the steam separator 6, each superheater 7, 8, 9 shown in FIG. 3, the high pressure turbine 10, the water storage tank 11, the boiler recirculation pump 12, the boiler recirculation flow rate adjustment valve 13, the primary spray valve 14, Illustration of the secondary spray valve 15 is omitted.

FIG. 2 is a block diagram of the control unit 20 shown in FIG. In this figure, 21 is a load request signal, and 22 is a detection signal of the furnace water cooling wall outlet steam temperature detector 19. 23 is a differentiator, 24 is a coefficient unit, 25 is a function generator, 26 is a subtractor, 27 is a controller, and 28 is an adder.

Next, the operation of this embodiment will be described. The load request signal 21 is input to the differentiator 23, and the output signal of the differentiator 23 increases as the load request signal 21 changes (decreases) rapidly. The signal of the differentiator 23 is input to the coefficient unit 24, is multiplied by a predetermined coefficient (control gain), and is added by the adder 28.
Is output to On the other hand, the load request signal 21 is the function generator 2
5, the function generator 25 outputs the load request signal 21
Create a furnace water cooling wall outlet steam temperature setting value signal corresponding to. The subtractor 26 is a furnace water cooling wall outlet steam temperature detector 19
The difference between the furnace water cooling wall outlet steam temperature signal detected in step S4 and the furnace water cooling wall outlet steam temperature set value signal created by the function generator 25 is calculated, and the difference signal is passed through the controller 27 as a correction signal. It is input to the adder 28. The adder 28 corrects the signal from the coefficient unit 24 by adding the signal of the difference from the controller 27 to this, and outputs the corrected signal to the high-pressure turbine extraction air bypass valve 10c.

With the configuration of the present embodiment, the opening degree of the high-pressure turbine extraction bypass valve 10c increases as the degree of decrease of the load request signal 21 increases and the furnace water cooling wall outlet steam temperature increases. It increases, and the bypass flow rate of the high pressure turbine extraction air bypass line 10b is increased to lower the outlet feed water temperature of the heater 3. Therefore, especially when the load rapidly drops, the heat storage amount of the heat transfer tube is released to the steam side as described above, and even if the heat absorption amount of water / steam in the furnace water cooling wall 1 is increased from the static characteristic value, Since the outlet water supply temperature of the heater 3 is lower than the temperature at the static characteristic, it is possible to suppress the fluctuation of the furnace water cooling wall outlet steam temperature and maintain it near the set value. The behavior (change) of is maintained in the range close to the static characteristic, and it is possible to reduce the life consumption of the turbine and various parts of the boiler.

Further, as a result, the steaming of the outlet fluid of the economizer 4 can be prevented, so that the flow instability in the water wall of the furnace can be prevented and the heat transfer area of the flue evaporator can be prevented. Can also be reduced. Further, the heat absorption amount of the superheater and the reheater can be reduced by maintaining the steam temperature at the outlet of the water cooling wall of the furnace near the set value.
Superheater spray flow rate by 4 and 15 and parallel damper 20
Can be controlled more easily.

In the description of the above embodiment, the transformer Benson boiler has been described, but the present invention is not limited to this.
It is obvious that the present invention can be applied to once-through boilers in general. Further, in the description of the above-mentioned embodiments, when the load of the boiler is decreased, but when the load is increased, a part of the heat quantity supplied to the furnace is used for raising the temperature of the furnace water cooling wall 1, so that Although there is a delay in the rise of the outlet steam temperature, the water vapor ratio is decreased (the amount of fuel is increased) to accelerate the temperature rise of the furnace water cooling wall outlet steam temperature while the parallel damper 20 is used. By reducing the gas flow rate distribution on the reheater side in the parallel gas path, it is possible to cope with the increase in the reheater outlet steam temperature due to the increase in the fuel amount.

[0016]

As described above, in the present invention, the bypass line for bypassing the line for introducing the high pressure turbine bleed air is provided, and the flow rate of this bypass line is controlled. Therefore, when the load drops, the heater By lowering the outlet water temperature, fluctuations in the furnace water cooling wall outlet steam temperature can be suppressed and maintained near the set value, which in turn maintains the behavior (change) of steam temperature in each part within a range close to static characteristics. Therefore, it is possible to reduce the life consumption of the turbine and other parts of the boiler. Also, by this, the economizer 4
Since it is also possible to prevent steaming of the outlet fluid of (1), it is possible to prevent flow instability in the water wall of the furnace, and it is also possible to reduce the heat transfer area of the flue evaporator. Further, since the furnace water cooling wall outlet steam temperature is maintained near the set value, the heat absorption amount of the superheater and the reheater can be easily controlled by the superheater spray flow rate by the spray valve and the parallel damper 20. it can.

[Brief description of drawings]

FIG. 1 is a system diagram of a main part of a boiler steam temperature control device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a control unit shown in FIG.

FIG. 3 is a system diagram of a conventional boiler steam temperature control device.

FIG. 4 is a diagram showing an example of changes in steam pressure with respect to load in a transformer Benson boiler.

FIG. 5 is a layout view of each contact heat transfer section.

[Explanation of symbols]

 1 furnace water cold wall 2 boiler feed water pump 3 high pressure feed water superheater 4 coal economizer 5 flue evaporator 10a high pressure turbine extraction line 10b high pressure turbine extraction bypass line 10c high pressure turbine extraction bypass valve 19 furnace water cooling wall outlet steam temperature detector 20 control Department

Claims (2)

[Claims] 1. A boiler provided with a feed water pump, a heater for heating feed water from the feed water pump to a water wall of a furnace, and a line for introducing high-pressure turbine bleed air to the heater,
A temperature detector that detects the outlet steam temperature of the furnace water cooling wall, a bypass line that bypasses the line, a bypass valve installed in the bypass line, a load request signal, and a detection value of the temperature detector based on A once-through boiler steam temperature control device comprising: a control unit that controls the opening degree of the bypass valve. 2. The differentiating device according to claim 1, wherein the control unit differentiates the load request signal and outputs a value corresponding to a speed of change of the load request signal; Set value creating means for creating a set value of the outlet steam temperature of the furnace water cooling wall, and a first for calculating a deviation between the set value created by the set value creating means and the detected value detected by the temperature detector. And a second calculating means for correcting the value output from the differentiating means with the deviation calculated by the first calculating means and outputting the corrected value to the bypass valve. Once-through boiler steam temperature control device.