JPS63687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In recent years, thermal power plants have been operated under intermediate loads, and as a result, there has been a demand for a control system that has less influence on the main engine and is easy to start and stop.
In response to this, the introduction of a microcomputer has made it possible to optimally control the main steam temperature, which until now had been a method of programmatically controlling the fuel amount using the load request signal using the operating mode as a parameter. However, there are no proactive measures to improve the reheat steam temperature control system, and as a result of the lack of optimal control of the main steam temperature, the system is in a sense uncontrolled, resulting in an increase in the reheat steam temperature at startup. is the current situation. In the present invention, without affecting the main steam temperature, that is, without changing the combustion pattern of the furnace,
Provides a control method that suppresses the rise in reheat steam temperature at startup.

FIG. 1 shows an example of a schematic configuration of a plant controlled by the present invention. In the figure, 1 is a furnace;
2 is a burner, 3 is a wind box, 4 is a wind box air volume control damper, 5 is a forced ventilation fan, 6 is an FDF inlet vane,
7 is a control valve, 8 is a control valve, 9 is a secondary superheater, 10
1 is a secondary reheater, 11 is a primary reheater, 12 is a primary superheater, 13 is an economizer, 14 is an evaporator pipe, 15 is a high pressure turbine control valve, 16 is a high pressure turbine, 17 is an intermediate pressure turbine control valve , 18 is an intermediate pressure turbine, 19 is a gas recirculation fan outlet damper, and 20 is a gas recirculation fan.

At the time of plant startup, the reheaters 10, 11
Because the main steam flow rate through the tube is small, the reheat steam temperature is dominated by the gas temperature rather than by heat exchange between the gas fluid and the pipe fluid, and the temperature tends to rise rapidly. When the condition stabilizes after the start of ramping, the temperature rises while the difference between the main steam temperature and the reheat steam temperature remains almost constant. increases, and the difference between the main steam temperature and the main steam temperature decreases. The reheat steam temperature peaks when the load is around 20%, and there is not much difference between plants. In this way, the only way to suppress the rise in reheat steam temperature near 20% load is to lower the gas temperature in the furnace. An effective way to lower the gas temperature in the furnace is to increase the amount of recirculated gas before it is added. In conventional recirculation gas amount control, the opening program is set to reduce the recirculation gas amount up to around 10% load in order to prevent a rise in reheated steam temperature during ramping. However, as mentioned above, the heat exchange pattern when the load is around 20% or less is due to the gas temperature regarding the reheat steam temperature, so with the current GRF opening program, it is not possible to suppress the reheat steam temperature rise at startup. Have difficulty.
Reduces gas temperature in the area below around 20% load,
Furthermore, in order to prevent the temperature of reheated steam from increasing during ramping at a load of 20% or more, it is considered necessary to change the load operation pattern of the GRF gas amount to a method that is compatible with the characteristics of the main engine.

That is, in the conventional control method, the reheat steam temperature is controlled using the main steam flow rate as a parameter, but in the present invention, a GRF opening program is created using a load request signal as a parameter using a function generator, and this output signal is used. This increases the amount of gas as a GRF damper opening command signal at startup, thereby achieving the effect of reducing gas temperature. Although it is effective to reduce the furnace gas temperature by injecting a large amount of recirculated gas before charging, it also reduces the amount of heat absorbed by the furnace, and the primary superheater shown in Fig. 12 This has two contradictory properties: the amount of fuel increases slightly due to inlet fluid temperature control, and the furnace gas temperature increases.
Therefore, it is necessary to determine an appropriate amount of recirculation gas from this duality. Therefore, in the current control method, the increase in main steam temperature is suppressed, that is, without changing the heat absorption amount of the existing furnace, only the increase in reheat steam temperature is suppressed by controlling the amount of recirculated gas using the GRF damper. It is thought that there are limits to things.

The present invention eliminates the above drawbacks, reduces the gas temperature at startup, and suppresses the rise in reheated steam temperature without changing the amount of heat absorption in the furnace, that is, without changing the combustion pattern in the existing furnace. It is in.

The present invention will be specifically explained below.

FIG. 2 shows examples of an air flow rate program for carrying out the present invention, a wind box air volume control damper opening degree program, and a conventional air flow program, respectively.
2 and 23. FIG. 3 shows an example of a GRF damper opening degree program for carrying out the present invention and a conventional GRF damper opening degree program at 24 and 25, respectively. Fig. 4 shows a block diagram of conventional air amount control (FDF inlet vane opening control), and Fig. 5 shows an embodiment of the present invention based on Fig. 4 with some modifications. A block diagram of air volume control is shown. FIG. 6 shows a block diagram of conventional GRF damper control, and FIG. 7 shows a block diagram of GRF damper control according to an embodiment of the present invention.

The symbols in each figure are as follows.

26 is a function generator, 27 is a multiplier, 28 is an analog memory, 29 is a proportional integrator, 30 is a minimum opening setting circuit, 31 is a high value selector, 32 is a signal generator, 33 is an analog memory, 34 is a switch 35 is a voltage/current converter, 36 is an electro-pneumatic converter, 37 is an FDF inlet vane control drive, 38 is an addition + bias device, 39 is a high value selector, 40 is an air flow transmitter, 41 is a boiler master signal , 42 is a reheat steam temperature transmitter, 43 is a function generator, 44 is a function generator, 45 is a function generator,
46 is a function generator, 47 is a proportional integrator, 48 is a low value selector, 49 is a high value selector, 50 is an analog memory, 51 is a switch, 52 is a main steam flow rate detection development signal, 53 is a total air amount Detection and development signal, 54 is a function generator, 55 is a multiplier, 56 is an analog memory, 57 is a proportional integrator, 58 is a high value selector, 59
is a signal generator, 60 is an analog memory, 61 is a function generator, 62 is a high value selector, 63 is an adder,
64 is a function generator, 65 is a function generator, 66 is a wind box air amount detection transmitter, 67 is a high value selector, 68
is a signal generator, 69 is a switch, 70 is a fuel control circuit, 71 is a load request signal, 72 is a boiler master signal, 73 is a main steam flow rate detection transmitter, 74 is a reheat steam temperature detection transmitter, 75 is a function generator, 7
6 is a function generator, 77 is a function generator, 78 is a function generator, 79 is a proportional integrator, 80 is a low value selector,
81 is a high value selector, 82 is a function generator, 83 is an analog memory, 84 is a switch, and 85 is a load request signal.

To explain the opening degree control of the FDF inlet vane, whereas in the past the air amount was increased in proportion to the increase in load as shown by curve 23 in Figure 2, in the present invention As shown by curve 21 in Figure 2, the amount of air is temporarily increased at startup. Here, the increased amount of air relative to the conventional air amount shown by curve 23 is injected into the furnace from the wind box 3 shown in FIG. Here, if the air volume is increased while the wind box 3 is held at the minimum opening as currently used,
All the increased amount of air will be injected into the furnace from the air register of the unlit burner.
Since the amount of heat absorbed by the furnace is reduced and the inlet fluid temperature of the primary superheater 12 is balanced, the amount of fuel tends to increase slightly, so it is thought that the effect of reducing the furnace gas temperature will decrease. Therefore, set the wind box air volume control damper opening degree as shown in curve 22 in Figure 2, limit it to the range where open air register control can operate normally, and adjust it so that it is the same as the current operation. .

Next, air amount control will be explained. In conventional air amount control, an air amount set value is created using a boiler master signal 72, and the deviation from the air amount, which is a feedback value, is passed through an integrator 57 and used as an opening degree command signal for the FDF inlet vane 6. In the present invention, a program is created by the function generator 61 using the load request signal 71 as a parameter, and the increased amount of air at startup is set. Here, the program by the function generator 61 is as shown by the curve 21 in FIG. 2, as described above. The signal output by the function generator 61 is in a form that is compared by the high value selector 62 with an air amount setting signal created from a conventional boiler master signal. Since the amount of air at startup is temporarily larger than the conventional amount, the output signal of the function generator 61 is larger than the output signal of the high value selector 67. Therefore, the signal for the increase in air amount at startup is sent to adder 6.
It is possible to detect it by 3. In order to inject the increased amount of air into the furnace from the wind box 3, it is sufficient to set the opening degree of the wind box air volume control damper 4 commensurate with the signal detected by the adder 63, that is, the increased amount of air. This is done by a function generator 64. The opening degree program of the wind box air volume control damper 4 is set as shown in the curve 22 shown in FIG. 64
The output signal is used as a wind box air volume control damper opening target setting signal, and the signal detected by the wind box air amount detector 66 is converted into a wind box air volume control damper opening degree by a function generator 65, and is used as a feedback signal. The deviation from the signal is taken and this signal is used as the wind box air volume control damper opening command signal. As a result, the amount of air that temporarily increased during startup is injected into the furnace from the wind box,
It becomes possible to obtain the effect of reducing the gas temperature without changing the amount of heat absorption in the furnace. Therefore, it is possible to prevent the temperature of reheated steam from increasing at around 20% load.

The concept of controlling the GRF damper opening shown in FIGS. 6 and 7 is that, as mentioned earlier, the conventional control method controls the reheat steam temperature using the main steam flow rate as a parameter, but the present invention Now, create a GRF opening program using a function generator using the load request signal as a parameter, and use this output signal to control the opening at startup.
The GRF damper opening command signal is used to increase the gas amount.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing an example of a thermal power plant to which the present invention is applied, Figures 2 and 3 are examples of program signals for a function generator, and Figures 4 and 5 are conventional examples of air volume control. , a block diagram showing an embodiment of the present invention, FIGS. 6 and 7 are conventional examples of GRF damper opening control,
1 is a block diagram showing an embodiment of the present invention. FIG. 1... Furnace, 2... Burner, 3... Wind box, 4... Wind box air volume control damper, 5... Push-in ventilation fan, 6... FDF
Inlet vane, 7... Control valve, 8... Control valve, 9... Secondary superheater, 10... Secondary reheater, 11... Primary reheater,
12... Primary superheater, 13... Economizer, 14... Evaporator, 15... High pressure turbine control valve, 16... High pressure turbine, 17... Intermediate pressure turbine control valve, 18... Intermediate pressure turbine, 19... Gas recirculation fan outlet Damper, 2
0...Gas recirculation fan.

Claims (1)

[Claims] 1 When starting up the boiler plant, the amount of air is temporarily increased in response to a load request signal, and the increased amount of air is injected from the wind box into the outer furnace, thereby reducing the gas temperature without changing the amount of heat absorption in the furnace. and a means for preventing a rise in reheat steam temperature by increasing the amount of recirculated gas and reducing the furnace gas temperature by programming a load request signal. Reheat steam temperature control device at startup.