JPH03207902A - Control device for temperature rise at the time of starting boiler - Google Patents

Abstract

PURPOSE:To dispense with the use of an SH spray valve, to prevent an excess rise of the main steam temp. and to suppress the rise of NOX at the time of starting by a method wherein, at the time of starting, fresh air is supplied from an after-air port damper, while as a countermeasure for the NOX rise, fresh air is supplied with combustion gas through a GM damper. CONSTITUTION:At the time of starting a boiler, an SH spray valve 17 is in the state of full close, because an opening degree setter 116 has been selected for that mode. An after-air port damper 10 is controlled by the opening degree instruction signal in which the main steam temp. deviation signal has been operated by a proportional integrator 108. In other words, when the main steam temp. rises excessively, the after-air port moves toward an opening direction, and works in such a manner that the fresh air suppresses the heat absorption of a secondary superheater 7. In addition to the above, using the NOX signal 21 and power generator output signal 18 as base signals, a normal NOX value is set by a function generator 117, while the obtained data are arithmetically calculated by the adding machine 118 and the proportional integrator 119, and the opening instruction of the GM damper 20 is formulated. By the abovementioned processes, the excessive rise of the main steam temp. at the time of starting the boiler can be restrained, and the NOX value can be restricted within a normal value.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a boiler automatic control device in a thermal power plant, etc., and is particularly suitable for controlling the main steam temperature increase at the time of plant startup. Regarding the control device. [Prior art] As described in Japanese Patent Application Laid-Open No. 63-271002, a conventional device has two types of SH spray valves, one large capacity and one small capacity, in parallel, and switches from small to large as the boiler load increases. The system switches control to

[Problem to be solved by the invention]

In the above conventional technology, when the boiler is started, the flow rate of steam flowing to the boiler side is less than 30% of the rated value, so even if SH spray water is input, it is poorly dispersed in the steam and becomes water droplets, resulting in a decrease in SH. This caused premature fatigue of the warmer and the spray nozzle of the SH spray.

Furthermore, when the boiler is started, the differential pressure across the SH spray valve becomes 80 kg or more, as shown in FIG. 4, which requires a high differential pressure type valve, resulting in poor controllability.

The purpose of the present invention is to suppress an excessive rise in main steam temperature without using an SH spray valve, and furthermore, to suppress the rise in NOx during startup, thereby facilitating smooth plant operation. It is said that

[Means to solve the problem]

In order to achieve the above object, fresh air is introduced from an after-air port damper at startup.

Additionally, to counter the rise in NOx, combustion gas was injected into the fresh air from the GM damper.

[Effect]

Injecting fresh air from the after air port damper reduces heat absorption by the 2SH.

As a result, excessive rise in the main steam temperature can be suppressed, and more heat is absorbed in the ISH, so the degree of excess of the ISH outlet temperature increases, creating a margin for the saturation temperature, and eliminating the need to use the SH soubre valve. The main steam temperature can be controlled by the fuel flow control valve and after-air port damper.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 1, the overall structure of the present invention will be explained.

First, in boiler 2, the feed water pump (hereinafter abbreviated as BFP)
Water is supplied from 15, energy saver 3, furnace wood pipe (hereinafter abbreviated as ECO) 4, primary superheater (hereinafter abbreviated as 1sH) 5, desuperheater 6
, a secondary superheater (hereinafter abbreviated as 28H), combustion is carried out by the fuel flow control valve 12 in order to send the rated superheated steam to the turbine.
This is done by adjusting the forced draft fan (hereinafter abbreviated as FDP) inlet damper.

Furthermore, in terms of plant startup, the amount of bypass steam is returned to the condenser from the ISH5 population through the IsH bypass valve 6, and the steam pressure is limited to 84 kg by the SH pressure reducing valve 21.

The steam temperature is controlled by the SH spray valve 7. BF
This is done by injecting water from the P15 outlet into the desuperheater 6. Furthermore, recirculating gas fan (hereinafter abbreviated as GRF) 1
4 and the GRF inlet damper 13, the combustion gas is transferred to the boiler 2.
(7) Adjust the amount of heat absorption with 4JECO4, ISH5, and 2SH7.

Further, there are an after air port damper 10 and a gas mixing damper (hereinafter abbreviated as GM damper) 20 for NOx suppression. Note that l indicates a boiler automatic control device.

Next, a control circuit to which the present invention is applied will be explained with reference to FIG.

First, the air flow rate control is performed by controlling the set value of the air flow rate using the function generator 101 using the generator output signal 18 as a base signal. This signal is combined with the signal of the air flow rate transmitter 8 to adder 02.
A proportional integrator 105 calculates the deviation signal calculated in , and creates an opening degree command for the FDP inlet damper 9 .

Next, the fuel flow rate control is performed using the fuel flow rate setting value and fuel flow rate 11 generated by the function generator 109 using the generator output signal 18 as a base signal, and the function generator 103 using the generator output signal as the base signal. The adder 113 calculates the main steam temperature set value created in The opening command for the fuel flow control valve 12 is calculated by the device 111.

Furthermore, the main steam temperature is controlled by an after-air port damper 10 at startup and by an SH spray valve 17 at normal times. That is, at startup, the SH spray valve 17 is fully open because the signal switch 115 selects the fully open degree generator 116, and does not contribute to main steam temperature control. On the other hand, the after air port damper 10 converts the main steam temperature deviation signal into a proportional integrator 108.
Adjust using the opening command signal calculated in . That is, if the main steam temperature rises excessively, the after air port moves in the opening direction and fresh air acts to suppress heat absorption by the 2SH7. On the other hand, under normal conditions, the SH spray valve 17 is adjusted by the opening command signal calculated by the proportional integrator 114 based on the main steam temperature deviation signal. Of course, signal switch 1
15 selects the integrator 114 side. Further, the after air port damper 10 side does not perform main steam temperature control, but is adjusted by an opening degree program set by a function generator 106 based on the generator output signal 8. This is because the after air port is normally controlled by a program for NOx control.

Next, FIG. 2 shows a control circuit when a GM damper 20 is used, which is another method of suppressing excessive rise in main steam temperature of the present invention.

The only difference from Fig. 1 is that in Fig. 1, the control circuit that adjusted the after-air port damper 10 to suppress an excessive rise in main steam temperature is now used to control the GM damper 20; the other circuits are The result is the same as in Figure 1 using the Abtar Airport Damper. Note that the set values of the function generator 106 and the proportional integrator 108 are naturally different when the after air port damper 10 and the GM damper 20 are used.

Furthermore, in Fig. 3, the main steam temperature overrise is suppressed at the after air port in exactly the same way as in Fig. 1, but in addition to this. GM damper 20. Using the NOX signal 21 and the generator output signal 18 as base signals, the function generator 117 sets the NOX specified value, and adds this to the adder 1.
The proportional integrator 119 is operated using the deviation signal calculated in step 18. This is to create an opening command for the GM damper 20. FIG. 6 shows the behavior of the main process according to the conventional control method, and FIG. 7 shows the behavior of the main process when the present invention is applied.

As is clear from FIGS. 6 and 7, the injection of fresh air from the after-air port damper suppresses an excessive rise in the main steam temperature, and also has a suppressive effect on the NOx value.

FIG. 5 shows the functional flow of the present invention.

First, a calculation block 51 determines whether the plant is starting up. If it is running, the calculation block 52
Proceed to.

In calculation block 52, a control mode is selected in which fresh air is introduced through the after air port in order to suppress an excessive rise in main steam temperature. Next, during this control mode, NOX
A calculation block 54 determines whether the value is within a specified value. If the value exceeds the specified value, the process proceeds to calculation block 55.

In the calculation block 55, GM is injected into the GM damper to suppress NOX. Furthermore, calculation block 53 indicates that the after air port damper selects the NOX control mode when the plant is not in the startup mode. [Effects of the Invention] According to the present invention, it is possible to suppress an excessive rise in the main steam temperature and to suppress the NOx value within a specified value in temperature increase control at the time of boiler startup in a thermal power plant, thereby improving plant operability. Improvements can be made.

In addition, when the steam flow rate to the turbine is 30% or less, S
Since H spray is not used, it is effective to extend the life of the SH spray nozzle and desuperheater.

Furthermore, the decrease in heat absorption at 28H becomes heat absorption by the ISH, and the degree of superheating of the ISH outlet temperature increases, which has the effect of increasing fuel control capacity and stabilizing plant operation.

[Brief explanation of drawings]

1, 2, and 3 are diagrams showing one embodiment of the present invention,
Fig. 4 is a differential pressure characteristic diagram before and after the SH spray valve, Fig. 5 is a functional flow diagram of the present invention, Fig. 6 is a diagram showing the main process of startup temperature rise control using the conventional control method, and Fig. 7 is a diagram of the present invention. It is a figure which shows the main process of temperature rise control at the time of startup by the control method by. 1... Boiler automatic control device, 2... Boiler, 10.
...After air port damper, 17...SH spray valve, Fig. 1 Fig. 2 Fig. 3 Fig. 4 BFF is output pressure n Fig. 5 Fig. 6

Claims (1)

[Claims] 1. In a boiler having an after-air port that injects fresh air from the top of the boiler in order to suppress NOx during normal operation of the boiler, at plant start-up, in order to suppress excessive rise in main steam temperature, A boiler startup temperature increase control device characterized by having a control circuit for injecting fresh air. 2. In the device according to claim 1, in a case where the NOx exceeds the specified value at startup, the O_2 concentration in the combustion air is reduced by injecting combustion gas into the fresh air from the GM damper. That's NOX
What is claimed is: 1. A boiler start-up temperature increase control device, comprising a control circuit that suppresses excessive rise in main steam temperature by reducing combustion gas temperature. 3. The apparatus according to claim 1 is characterized in that a control circuit is provided for controlling excessive rise in main steam temperature by an after-air port damper and for controlling NOx exceeding a specified value by a GM damper. Temperature rise control device for boiler startup.