JPS62206304A - Fuel controller for 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 Industrial Application] The present invention relates to a fuel control device for a boiler that requires fuel throttling accompanied by rapid burner extinguishing.

[Conventional technology]

Boilers in thermal power plants, etc., are disconnected from the plant power system in the event of a power system accident, etc., and the boiler load is rapidly reduced in order to operate the plant alone or the boiler alone.
) functionality is requested.

At the time of PCB, the boiler input water, fuel, and air must be stably throttled within a time on the order of several seconds to several tens of seconds. Among these, the fuel control system has conventionally been configured as shown in FIG.

This is a common sense control system configuration for feedback t[tlJ starvation, and is a combination of a proportional-integral regulator 6 and a function generator 7 that generates a preceding signal 8. Figure 6 shows the behavior of each part in this control system during PCB.

At the same time as the PCB, the combustion amount command 1 is lowered to the lowest fuel flow rate target value that can cover the in-house load or the boiler-only load. The rate of change limiter 2 and signal selector 3 are used to lower the fuel flow rate command 4 at a constant rate of change. The preceding signal 8 of the valve opening decreases in accordance with the fuel flow rate command 4.

Process from when the fuel flow control valve opening command (output of the automatic/manual switching station 10) operates in the closing direction until the fuel flow control valve 12 closes and the flow rate signal 14 is detected by the flow rate detector 13 There is a mechanical process delay, and generally, in order to remove noise (due to pulsation, etc.) from the comparison signal, feedback control is often performed on the fuel flow rate using a primary lag device 15. From these, since there is a delay between the fuel command 1 and the feedback signal, the deviation, which is the output of the subtractor 5 that calculates the deviation, always takes a value on the negative side (valve closing side), and this continues until the narrowing is completed. Therefore, the output of the proportional-integral regulator 6 is also set to a value on the valve-closing side, and as a result, the fuel flow rate control valve opening degree command becomes a value even smaller than the preceding signal. Therefore, it is difficult to perform optimal adjustment both during FCB and during normal operation.

Note that related known technology includes Japanese Patent Laid-Open No. 124330/1983.

[Problem that the invention seeks to solve]

In order to ensure stable combustion, the boiler must have burner header pressure above the specified value, and at 208:00, to protect the reheater piping from which steam is cut off, the fuel flow rate must be reduced to a certain level within a certain period of time. There is a boiler protection restriction called narrowing down. In the conventional method, in addition to the preceding signal, there is feedback control by a proportional-integral regulator, so it is affected by the proportional gain and integral time constant settings, which are frequently changed during operation adjustment, and the burner header is over-restricted. The pressure will drop and the fuel will become expensive due to insufficient throttling, which may exceed the limit and trip the plant.

An object of the present invention is to provide a control device that can stably perform fuel control even when a burner is quickly extinguished, without changing the constant setting of a proportional-integral regulator.

[Means for solving problems]

The above objective is achieved by controlling the fuel flow control valve, which is the large mouth valve of the burner header piping, in coordination with burner extinguishing, that is, reducing the number of burners, during burner rapid extinguishing.

[Effect]

The relationship (including dynamic characteristics) between the number of burners and the fuel flow control valve is adjusted to an arithmetic circuit that receives the burner number signal as input.

The characteristics of the burner header piping can be expressed by the following equation.

Pa=t (Qr Qs) dt - (1) where PB: Burner header pressure QF: Fuel flow rate injected from the fuel flow control valve QR: Fuel flow rate flowing out from the burner Kl: Constant The characteristics can be expressed by the following equation.

Qr=Kr-Ar-f(P+, Pa) (2
)Qi=to+s −Ai−f (PB, Po)
(8) Here APIAB: Valve opening P+: Ie Feed quantity control valve inlet pressure o: Burner outlet pressure (furnace pressure) KF, to! 1: Constant burner valve opening degree Am is the sum of the opening degrees of the individual burners because there are a plurality of burners. Burner valve is 0N10
Since it is an FF valve, the following formula may be used.

A B = Km'・Na −・ −1 −−
(Opening degree of the shaft) From (1) and (4), Qa=l(n”Na-f(Ps, Po) ---(
5). Equation (5) shows that the burner flow rate Q is proportional to the number of burners NB. Also, equation (2) is
It is shown that the flow rate Qr flowing in from the fuel flow control valve is proportional to the fuel flow control valve opening degree Ar.

From equation (1), if QF=Ql, burner header pressure Psld does not change, so from equation (2) and 5, Kr-A
r-f (P+, Pa)-Ki''-Nm・f (Pg
, Po) Therefore, the burner header pressure does not change even at 208 hours.

One of the functions of the arithmetic circuit that receives the burner number signal as input is
The coefficient of the number Nm of burners in the above equation (6) is calculated to output the fuel flow rate control valve opening Ar.

Another function of this arithmetic circuit is to compensate for this nonlinearity since the valve opening AF and the valve opening command are generally nonlinear.

If the fuel flow control valve is throttled during PCB using a signal that has all of the above two effects, the inflow and outflow amounts of the burner header become equal, so the fuel can be throttled without changing the burner header pressure.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, a function generator 22 is used as an arithmetic circuit (hereinafter referred to as a narrowing-down arithmetic circuit) 21 which receives a burner number signal 20 as an input. At all times, that is, during feedback control, the switch 23 is on the feedback control side. At the time of PCB, the switch 23 disconnects the feedback control and selects the narrowing calculation circuit 21 side, so at this time, the opening command of the flow control valve is set to the function generator when the burner is extinguished, that is, when the burner number signal 20 decreases. The results are narrowed down by the function determined in step 22. This behavior is shown in FIG. When rapidly extinguishing burners using a PCB or the like, by narrowing down the fuel flow control valve in proportion to the number of burners, the inflow and outflow amounts of the burner header can be made equal, so that the burner header pressure does not fluctuate.

The settings of the function generator 22 should be determined by the values of the number of burners and the opening degree of the fuel flow control valve before starting PCB, that is, in a static state, and the values of the number of burners and the opening degree of the fuel flow control valve after FCB. I can do it. Therefore, settings can be made using only static characteristics. The settings do not depend on the characteristics of the control loop (loop gain, loop time constant), so rather than narrowing down using the feedback control system, it is better to separate the feedback control system and narrow it down in cooperation with the number of burners, as in this example. The system is stable.

According to this embodiment, since the narrowing down calculation circuit 21 is only the function generator 22, there is an effect that adjustment is easy.

FIG. 3 shows another embodiment of the invention. The difference from FIG. 1 is that the narrowing down calculation circuit 21 performs signal correction 30 based on fuel pressure based on equation (6). This correction signal is created by a two-variable function generator 28 and a divider 29 from each signal of the fuel flow control valve front pressure 25, burner header pressure 26, and furnace draft 27 detected by the detector 32, and is generated by the multiplier 31. The burner number signal and multiplication are matched by .

According to this embodiment, there is an effect that the influence of fluctuations in the pressure in front of the fuel flow control valve and the furnace draft can be absorbed, and the fuel can be reduced while keeping the burner header pressure stable.

FIG. 4 shows another embodiment of the invention. The difference from FIG. 1 is that a time element 35 is added to the function generator 22 as the narrowing down calculation circuit 21. By adding the time element, it is possible to compensate for the time difference between the burner number signal and the actual burner valve opening. Furthermore, according to this embodiment, it is possible to delay or advance the throttling of the fuel flow control valve depending on the time element, so it is possible to adjust the burner header pressure to slightly increase or decrease it. Become.

In the figure, 9 is an adder, 11 is a converter, 24 is a valve opening command during PCB, 31 is a multiplier, and 32 is a detector.

〔Effect of the invention〕

According to the present invention, stable fuel control can be performed without changing the constant setting of the proportional-integral regulator during rapid burner extinguishing such as during PCB.

[Brief explanation of drawings]

Claims (1)

[Scope of Claims] 1. In a fuel flow rate control device, a circuit comprising an arithmetic circuit that receives a burner number signal as input, and a switch that switches between an output signal of the arithmetic circuit and a signal from a feedback control system. A boiler fuel control device comprising: