JPS625001A - Variable pressure operation method of once-through boiler - 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 [Field of Application of the Invention] The present invention relates to a method for operating a once-through boiler, and particularly to a method for operating a superheater portion under variable voltage.

[Background of the invention]

Originally, a once-through boiler was a constant pressure boiler, but in recent years.

It began to be used as a medium-load boiler.

Once-through boilers are designed to operate at variable pressure in order to improve thermal efficiency.

FIG. 3 is a schematic system diagram of an existing constant pressure once-through boiler modified for variable pressure operation.

In the diagram, 1 is the boiler feed water pump, 2 is the high pressure water heater, and 3
is a coal saver, 4 is a furnace, and 5 is a primary superheater.

6 is a superheater pressure reducing valve, 7 is a superheater stop valve, 8 is a secondary superheater,
9 is a turbine bypass valve, 10 is a turbine control valve, 1
1 is a primary superheater bypass valve, 12 is a secondary superheater bypass valve, 13 is a superheater vent valve, 14 is a flash tank,
15 is a deaerator, 16 is a high pressure turbine, 17 is a reheater,
18 is a medium and low pressure turbine, 19 is a condenser, and 20 is a condensate pump.

How to perform variable pressure operation in this once-through boiler.

The furnace is designed to be at constant pressure, so the figure is busy.
5, it is necessary to install a pressure reducing valve 6 between the primary superheater 5 and the secondary superheater 8 to reduce the pressure on the inlet sides of the secondary superheater 8 and the high pressure turbine 16.

FIG. 4 is a pressure transformation pattern diagram in the variable pressure operation of a single once-through boiler. Conventionally, as shown in the straight line ■ in the same figure, the load was 7%.
The turbine inlet steam pressure (main steam pressure) was increased by operating the superheater pressure reducing valve 6, which is called a ramping operation, from to 25% load.

That is, next week, the pressure reducing valve 6 is throttled only during startup bypass operation when the heating device piebus valve 11 is open.

When switching from start-up bypass operation to once-through operation at a load of 25%, the superheater pressure reducing valve 6 is fully opened, and when constant pressure operation is achieved, the large capacity superheater stop valve 7 is also fully opened.

The problem with conventional superheater transformer operation is that, especially at low load, since the pressure of the fluid is reduced by the superheater pressure reducing valve 6, the pressure reducing valve outlet fluid (superheater inlet fluid) approaches the saturation region. An example of this is shown in the enthalpy pressure diagram of FIG.

The curve X in the figure is a saturation curve, and the broken line Y is a line connecting the enthalpy pressure characteristic values at each location at a low load of 25%.
Point A on the broken line Y is the inlet point of the economizer, B is the outlet point of the primary superheater, and C is the characteristic point of the inlet of the secondary superheater, and the pressure reduction from point B to point C is the superheater pressure reduction. The pressure reduction by valve 6 is shown.

As shown in this figure, at 25% load, the inlet steam temperature of the secondary superheater has almost no margin with respect to the saturation temperature (curve X), and operation is restricted if load changes and the like are taken into account. In other words, there is a high possibility that the gas-liquid mixed fluid will flow into the secondary superheater, and there is a concern that the temperature of the pipe metal will rise abnormally due to the gas-liquid mixed fluid, especially near the pipe bends of the secondary superheater. When pressure is reduced using one pressure reducing valve 6.

Especially when the load is low, the superheater pressure reducing valve 6 is subjected to a height difference ring, causing a problem of valve erosion.

[Purpose of the invention]

The purpose of the present invention is to eliminate such drawbacks of the prior art,
It is an object of the present invention to provide a method for stable variable voltage operation of a once-through boiler without problems such as abnormal rise of superheater tube metal and erosion of pressure reducing valve.

[Summary of the invention]

In order to achieve the above-mentioned object, one aspect of the present invention is that at least a first superheater and a second superheater are arranged in series along the flow direction of steam, and on the upstream side of the first superheater. A first pressure reducing valve is provided, and a second pressure reducing valve is provided on the upstream side of the @2 superheater.

The first pressure reducing valve performs isenthalpic pressure reduction to a predetermined steam pressure according to the load, the first superheater superheats the steam, and then the second pressure reducing valve demands steam pressure on the turbine side. It is characterized in that after isenthalpic reduction is carried out so that the vapor pressure reaches a vapor pressure of

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic system diagram for explaining variable pressure operation of a once-through boiler according to a first embodiment of the present invention. In the figure, 1 is the boiler feed water pump, and 2 is the high pressure water heater.

3 is a coal saver, 4 is a furnace, 5 is a primary superheater, 6a is a first superheater pressure reducing valve, and 6b is a second superheater pressure reducing valve.

7 is a superheater stop valve, 8a is a first secondary superheater, and 8b is a second
9 is a secondary superheater, and 9 is a turbine bypass valve.

10 is a turbine control valve, and 12 is a secondary superheater bypass valve.

13 is a superheater vent valve, 14 is a flash tank, 15
1 is a deaerator, 16 is a high pressure turbine, and 19 is a condenser.

As shown in this figure, the secondary superheater 8 is
a and a second secondary superheater 8b and connect them in series, and furthermore, the first pressure reducing valve 6a is installed on the upstream side of the first secondary superheater 8a, and the secondary superheater m2 is connected in series. A second pressure reducing valve 6b is arranged upstream of the pressure reducing valve 8b.

First, let's talk about the operation when starting up a once-through boiler with this configuration □
I will explain. After securing the minimum water supply flow rate with the boiler feed water pump 1, ignition is performed. At that time, since the fluid temperature is low, the superheater stop valve 7 and the ml superheater pressure reducing valve 6a are fully closed, and the fluid bypasses the secondary superheater and is dumped into the flash tank 14. As the bypass fluid temperature rises, the flash tank pressure rises and reaches approximately 85 kg/cm"y. At this time, the second superheater pressure reducing valve 6b is fully opened to superheat the saturated steam in the flash tank 14. Vent valve 13. Ventilates the secondary superheaters 8a and 8b through the second superheater pressure reducing valve 6b and the turbine bypass valve 9, and also warms the main steam pipe.When the steam conditions for turbine ventilation are established, the high pressure turbine 16, and close the turbine bypass valve 9. When the turbine rotational speed increases to a specified rotational speed, the generator is synchronized with the grid and the load is taken.

The turbine control valve 10 is gradually opened to increase the load, and when the load reaches about 25%, the steam passing through the flash tank 14 becomes superheated steam due to the characteristics of the boiler.

When the load reaches 25%, the first superheater pressure reducing valve 6a is fully closed, and the pressure on the inlet side of this valve 6a is about 250
1j5. The outlet side pressure is about 85 ky/cm"y, and the valve differential pressure is about 165 kiz'y. On the other hand, since the second superheater pressure reducing valve 6b is fully open, the valve differential pressure is approximately zero. However, as mentioned above, since the first superheater pressure reducing valve 6a is fully closed, there is no need to worry about valve erosion.

When increasing the load from 25% load, the first superheater pressure reducing valve 6
By opening K, the pressure will increase according to the main steam pressure curve (3) shown in Fig. 4, but at this point, at the same time as opening the first superheater pressure reducing valve 6a, closing the second superheater pressure reducing valve 6b. The load is increased while controlling the differential pressures of the respective valves 6a and 6b to be approximately equal.

When the load is lowered, the operation is reversed, but the valve differential pressure is half that of when reducing pressure with only one valve, so erosion resistance is greatly strengthened, and the valve,
This leads to improved reliability.

In the main steam pressure curve shown in Fig. 4, curve 1 is the pressure transformation curve due to conventional ramping operation. Curve 1 - ■ is the transformation curve taking boiler efficiency into consideration, and curve 1 is the 40% pressure transformation curve.
1 shows a 75% transformation curve, and curve 1 shows a 95% transformation curve. In the case of the present invention, for example, variable pressure operation as shown in curves (1) to (2) is possible, thereby increasing the efficiency of the boiler.

Figure 2 shows the enthalpy pressure diagram of each part at 25% load. In the figure, X is the saturation curve. Point A is the energy saver inlet. Point B is the primary superheater outlet (the inlet of the first superheater pressure reducing valve). Point C is the first secondary superheater inlet (the first superheater pressure reducing valve inlet. Superheater pressure reducing valve outlet) 1
Point E is the second secondary superheater inlet (outlet of the second superheater pressure reducing valve).

Point F is the characteristic value of the second secondary superheater outlet.

The pressure is isenthalpiically reduced from the inlet of the first superheater pressure reducing valve (point B) to the first superheater pressure reducing valve, and the main steam pressure is approximately 165 kp/cm at the inlet of the first secondary superheater (point C). ``g, which allows a larger margin than the saturation point at this time.The enthalpy of the inlet steam of the second secondary superheater increases due to heat absorption in the first secondary superheater (point C Point D), even if the pressure is isenthalpic reduced by the second superheater pressure reducing valve, there is no fear of entering the saturation region (there is sufficient margin).

Figure 5 is an explanatory diagram showing the pressure setting values of each superheater pressure reducing valve.
In the figure, ■ is the main steam pressure setting value, ■ is the outlet side pressure setting value of the first secondary superheater, ■ is the burden differential pressure value at the first superheater pressure reducing valve, and ■ is the second superheater pressure reduction value. This is the burden differential pressure value at the valve. In this embodiment, the differential pressure borne by the first superheater pressure reducing valve and the differential pressure borne by the second superheater pressure reducing valve are divided equally; however, this is not necessarily limited to this, and there is a certain predetermined value. It is also possible to share in any ratio depending on the ratio or the surrounding boiler conditions.

Next, a method of controlling the first and second superheater pressure reducing valves will be explained using the control block diagram shown in FIG. 3. Reference numeral 21 in the figure is a first secondary superheater inlet side pressure detector.

22 is the first secondary superheater inlet side temperature detector, 23 is the first
, 24 is the main steam pressure detector, 25 is the load request command device, 26 is the second secondary superheater inlet temperature detector, and 27 is the second secondary superheater. An inlet side pressure detector, 28 a function generator, 29 and 30 a subtractor,
31 is a PI regulator, and 32 is a high signal selector.

33 and 34 are function generators, 35 is a subtracter, 36 is a P controller, 37 is a high signal selector, 38 is a subtracter, 39
is a function generator, 40 is a first secondary superheater inlet side saturation temperature deviation value signal, 41 is a second secondary superheater inlet side saturation temperature deviation value signal, and 42 is a first superheater pressure reducing valve pressure setting. value signal,
43 is a second superheater pressure reducing valve pressure setting value signal, 44 is a main steam pressure control signal, and 45 is a second secondary superheater inlet side saturation temperature deviation signal.

A first secondary superheater outlet side pressure setting value signal 42 obtained by the function generator 23 in response to a load signal from the load request command device 25 and a first secondary superheater outlet side pressure detector 23
Subtractor 3 the deviation from the actual pressure signal detected by
It is calculated with 0 and passed through the PI regulator 31 as a pressure control signal.

On the other hand, the first secondary superheater inlet side saturation temperature deviation value signal 40 is calculated by the function generator 28 based on the inlet side pressure detected by the first secondary superheater inlet side pressure detector 21. A subtracter 29 calculates the deviation between the actual inlet temperature signal detected by the first secondary superheater inlet temperature detector 22 .

A high signal selector 32 selects this deviation signal and the pressure control signal.
The opening degree of the first superheater pressure reducing valve 6a is adjusted by the control signal outputted from the control signal, thereby maintaining the pressure of the secondary superheater while ensuring the degree of superheating of the inlet side fluid in the first secondary superheater. can be controlled.

The same applies to the second superheater pressure reducing valve 6b.

The opening degree is adjusted by a control signal outputted by passing the main steam pressure control signal 44 and the second secondary superheater inlet side saturation temperature deviation signal 45 through the high signal selector 37.

Here, the saturation temperature control circuit may be omitted if the inlet side temperature of each secondary superheater ensures the degree of superheating in all load zones. Further, the set values of the function generator 33 for the first secondary superheater outlet side pressure and the function generator 34 for the main steam pressure are as follows:
first and second superheater pressure reducing valves 6a at each load;
The load differential pressure of 6b is set to be approximately equal (see FIG. 5).

FIG. 6 is a system diagram for explaining a second embodiment of the present invention. In this embodiment, in addition to the first embodiment, a third superheater pressure reducing valve 8 is also provided on the upstream side of the primary superheater 5.
c is installed. And this third superheater pressure reducing valve 8
C, the first superheater pressure reducing valve 8a, and the second superheater pressure reducing valve 3b
Since there is a system in which pressure is reduced in multiple stages using three pressure reducing valves, the differential pressure burden for one pressure reducing valve can be further reduced.

FIG. 7 is a system diagram for explaining a third embodiment of the present invention. This embodiment differs from the second embodiment in that it has a second superheater pressure reducing valve 6b and a second secondary superheater 8b.
is omitted.

〔Effect of the invention〕

This is because the present invention has the configuration as described above.

It is possible to improve the erosion resistance of multiple installed pressure reducing valves, and as shown in Figure 2, the steam on the inlet side of the secondary superheater does not enter the saturated region, which allows for boiler transformation with a margin. Able to drive.

[Brief explanation of the drawing]

FIG. 1 is a system diagram for explaining the variable pressure operation of a once-through boiler related to the 1% reduction of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between steam pressure and enthalpy in the variable pressure operation.
FIG. 3 is a block 1m showing an example of the i11 control method for variable pressure operation, and FIG. 4 is a characteristic diagram showing the relationship between load and main steam pressure during variable pressure operation. Fig. 5 is an explanatory diagram showing the pressure setting values of each superheater pressure reducing valve, Fig. 6 and Ic@7 are system diagrams for explaining the second embodiment, w, and third embodiment, and Fig. 8 is a conventional diagram. FIG. 9 is a characteristic diagram showing the relationship between steam pressure and enthalpy in the variable pressure operation of a once-through boiler. 5...-Next week's heater, 6a...First superheater pressure reducing valve, 6b...Second superheater pressure reducing valve, 6
C...Third superheater pressure reducing valve, 8a...
@1 secondary superheater, 8b...2nd secondary superheater. 1""l,", / W'+i'!+=- Fig. 2 Pressure (atal Fig. 3 Horse Fig. 4 Negative part (%) Fig. 5 Fig. 6 Fig. 9 Pressure (ata)

Claims (1)

[Claims] At least a first superheater and a second superheater are arranged in series along the flow direction of steam, a first pressure reducing valve is provided upstream of the first superheater, and a first pressure reducing valve is provided upstream of the first superheater, and a first pressure reducing valve is provided upstream of the first superheater. A second pressure reducing valve is provided on the upstream side of the superheater, and after the first pressure reducing valve performs isenthalpic reduction so that the steam pressure reaches a predetermined steam pressure according to the load, the first pressure reducing valve performs isenthalpic pressure reduction. A variable pressure operating method for a once-through boiler, characterized in that the steam is overheated, and then isenthalpic reduced by the second pressure reducing valve so that the steam pressure reaches the required steam pressure on the turbine side, and then superheated by the second superheater. .