JPS6020652B2 - Combustion control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a combustion control method for various combustion furnaces such as boilers.

In general, the oxygen concentration in the exhaust gas of a combustion system is an important index for detecting the combustion state, detecting the amount of sulfuric anhydride generated, the amount of NOx generated, and the like.

Ideally, the residual oxygen concentration in the exhaust gas should be zero, but in order to ensure stable combustion and reduce black smoke generation, the concentration of residual oxygen in the exhaust gas should be reduced to 0.3%.
The lower limit is considered to be 0.6 to 0.7%. However, of course, it varies depending on the size of the burner and the combustion method. Conventionally, when attempting optimal combustion control by detecting this dissolved oxygen concentration, the reliability of the oxygen meter that detects the residual oxygen concentration was low, making it difficult to employ it in important control loops.

In other words, oxygen meters are less reliable than sensors such as pressure gauges and flow meters, and in conventional systems, upper and lower limits were set on the output of oxygen meters to prevent the system from running out of control. However, if the oxygen meter became abnormal, the output would reach the upper and lower limits within the air-fuel ratio correction control range, making it impossible to perform proper combustion control. An object of the present invention is to provide a combustion control method that can eliminate these drawbacks, accurately grasp the residual oxygen concentration, and perform optimal combustion control.

In order to achieve this object, the present invention calculates the oxygen concentration in the combustion exhaust gas from the measured fuel flow rate and the measured air flow rate, and if the difference between the calculated oxygen concentration and the measured oxygen concentration is within a predetermined allowable limit, the measured oxygen concentration If it is outside the limit, the calculated oxygen concentration is used as the oxygen concentration adjustment standard, which is a controlled amount.

Further, if it is within a predetermined allowable limit, air-fuel ratio correction control is performed using the oxygen concentration adjustment output, and if it is outside the limit, air-fuel ratio correction control is also performed using a preset air-fuel ratio.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

The figure shows one embodiment. In the diagram, a burner of a boiler 1 is connected to a heavy oil transport pipe 2 for transporting heavy oil, which is fuel, and an air transport pipe 3 for transporting air under pressure. The transport pipes 2 and 3 are provided with flowmeters 4 and 5, each of which outputs a flow rate signal proportional to the heavy oil flow rate and the air flow rate. Also, transport pipes 2 and 3
Is there a control valve 6? 7 are provided, and these control valves 6, 7'
The heavy oil flow rate to air flow rate is controlled by the adjustment output of the heavy oil flow rate controller 8 and the air flow rate controller 9.The boiler is equipped with a temperature transmitter, which transmits a signal proportional to the temperature inside the boiler. The signal is output to the temperature controller turtle 1. This temperature controller compares the predetermined temperature signal A with the measured temperature signal from the transmitting organ crab, and outputs the temperature adjustment output signal to the ratio setter '2 and the heavy oil flow rate. The controller 81 outputs a heavy oil flow rate control output that compares the temperature control output signal and the heavy oil flow rate signal of the flowmeter 4 and adjusts the opening/closing degree of the control valve 8. Next, if the fuel is heavy oil The calculation of the calculated oxygen concentration in the exhaust gas in the case will be explained.

If the excess air rate associated with combustion is assumed to be Buddha, then Yama = Kensagi Gunryo Cloud Wall Tsuba; Actual heavy oil flow rate The required amount of air is 9).

In the case of heavy oil combustion, since there is no change in volume between the amount of air supplied for combustion and the amount of combustion exhaust gas, the oxygen content of excess air remains in the exhaust gas. Therefore, excess air amount x oxygen concentration; exhaust gas amount x residual oxygen concentration (A mountain f) x21 = public x○2 (French -1) x21 = family Aox02. 、． 〇2d21(3-i)〈%) ...side ■.

Of course, for other fuels, if there is a change in customer type between the amount of exhaust gas and the combined amount, the amount of gas is expressed as KA (Keizan constant).

In order to obtain the calculated oxygen concentration in this way, a multiplier 14 is provided to multiply the heavy oil flow rate signal from the flow meter 4 by the heavy oil specific gravity from the setting device 3 x the required air amount C per unit heavy oil,
Further, a divider mechanism 5 is provided to divide the actually measured air flow rate from the flow meter 5 by the theoretical air amount from the multiplication mechanism mechanism.

The output of this divider 15 is the excess air ratio material, and a calculation glue 6 is provided to calculate the excess air ratio, that is, equation 21 (raw 1). The concentration signal is applied to comparator 171. Further, an oxygen meter 8 is installed in the bonito passage section of the boiler 1, and an actually measured residual dissolved oxygen concentration signal in the exhaust gas from the oxygen meter 18 is applied to a comparator 17. The comparator 17 compares the calculated oxygen concentration signal and the actually measured residual oxygen concentration signal. As a result of this comparison, if the difference is within a predetermined allowable range, a change-over switch is provided that transmits the actually measured residual oxygen concentration signal to the oxygen controller 2.
transmits the calculated oxygen concentration signal to the oxygen controller 2 via the comparison point 1 when the comparison result of the comparator T is outside the predetermined tolerance range. The oxygen regulator 22 compares these concentration signals with a reference oxygen concentration signal B and outputs an oxygen concentration adjustment signal. This output is added to the multiplier 2 and the temperature control signal multiplied by a predetermined constant, which is a predetermined air-fuel ratio, in the ratio setter 82. The output of the device turtle 2 is added to the switch G Ugly contact 2 fin one wing! The movable support point of the changeover switch Toha is the contact 2 turtle - lightning, 28 - 2 Nae. Switching the input added to the air flow regulator 9. This cut-off switch 20 is operated by the output of the comparator meter, and if the difference between the measured residual oxygen concentration and the calculated oxygen concentration is outside the predetermined tolerance range, the output of the ratio setter 12 is switched to the air flow rate controller. 9, and if it is within a predetermined tolerance range, the output of the multiplier Kumokame is used as the reference signal of the controller 9. Therefore, the calculated oxygen concentration from the arithmetic unit 6 and the actually measured residual oxygen concentration from the oxygen meter 18 are set to the predetermined value. If it is within the allowable range, check the actual measured residual oxygen concentration and reference oxygen concentration using the oxygen controller 22.
The output of the ratio setter is corrected by multiplying the oxygen adjustment signal by the ratio corresponding to the predetermined air-fuel ratio. Further, if the difference between the actual residual oxygen concentration measured by the oxygen meter 18 and the calculated oxygen concentration from the calculator 6 is outside the predetermined tolerance range, the comparator 171 operates the changeover switch 19 to change the calculated oxygen concentration to However, since the selector switch 20 also uses the comparator i7 to input the output of the ratio setter 12 to the air flow controller 9, no control is performed to correct the air-fuel ratio, and the calculated scheduled air-fuel ratio is used. In another embodiment of the present invention, the changeover switch 20 is not provided, and the multiplication value of the output of the ratio setter 12 and the output of the oxygen controller 22 is used as the reference input of the air flow controller 9. This can also be done by always adding it.

In this case, if the air-fuel ratio is within the predetermined allowable range, the air-fuel ratio is corrected based on the actually measured residual oxygen concentration, and if it is outside the predetermined allowable range, the air-fuel ratio is corrected based on the calculated residual oxygen concentration. In yet another embodiment, the changeover switch 19 may not be provided and the actually measured residual oxygen concentration may always be input to the oxygen controller 22.

In this case, if it is within a predetermined allowable range, the output of the ratio setter 12 is corrected using the oxygen concentration adjustment signal to perform air-fuel ratio correction control,
If it is outside the specified tolerance range, use the ratio setter! The air flow rate is adjusted based on the scheduled air-fuel ratio from 2. As described above, according to the present invention, the oxygen concentration in the combustion exhaust gas is calculated from the measured fuel flow rate and the measured air flow rate, and if the difference between the calculated oxygen concentration and the measured oxygen concentration is within a predetermined allowable limit, the measured oxygen concentration of,
If it is outside the limit, use the calculated oxygen concentration as the oxygen concentration adjustment standard,
Further, if it is within a predetermined allowable limit, air-fuel ratio correction control is performed using the oxygen concentration adjustment output, and if it is outside the limit, control is performed using a preset air-fuel ratio. Therefore, by using the residual oxygen concentration in the exhaust gas as one of the control parameters, it is possible to perform control that does not deteriorate the residual oxygen concentration. Furthermore, it prevents the oxygen meter that actually measures the residual oxygen concentration in the exhaust gas from running out of control by comparing it with the calculated oxygen concentration, resulting in highly reliable control.

[Brief explanation of the drawing]

The figure is a block diagram of one embodiment of the present invention. 1...Boiler, 4,5...Flowmeter,
6, 7...Control valve, 8...Heavy oil flow rate controller, 9...Air flow rate controller, 10...Temperature detector, 11...Temperature adjustment Meter, 12... Ratio setter, 17... Comparator 18... Oxygen meter,
19, 20...Choice switch, 22...Oxygen controller.

Claims (1)

[Scope of Claims] 1 Calculate the oxygen concentration in the combustion exhaust gas from the measured fuel flow rate and the measured air flow rate, and compare the calculated oxygen concentration with the actually measured oxygen concentration in the combustion exhaust gas to determine whether the measured oxygen concentration is reliable. Controlling the air-fuel ratio between the fuel flow rate and the air flow rate by using the measured oxygen concentration if it is within a predetermined allowable limit, and by using the calculated oxygen concentration if it is outside the predetermined allowable limit, using the oxygen concentration in the combustion exhaust gas as a controlled quantity. A combustion control method characterized by: 2 Calculate the oxygen concentration in the combustion exhaust gas from the measured fuel flow rate and the measured air flow rate, compare this calculated oxygen concentration with the actually measured oxygen concentration in the combustion exhaust gas, and determine whether the measured oxygen concentration is within a reliable predetermined allowable limit. For example, a combustion control method in which the air-fuel ratio between the fuel flow rate and the air flow rate is changed by an oxygen concentration adjustment output based on the measured oxygen concentration, and if the air-fuel ratio is outside the predetermined allowable limit, the fuel flow rate and the air flow rate are controlled at a predetermined air-fuel ratio.