JPH07107443B2 - Combustion control method - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a combustion flame whose optical power amplitude is O ₂ % in exhaust gas.
Utilizing the fact that it is proportional to, the signal related to the amplitude of the optical power obtained during operation of the combustor is compared with the signal related to the amplitude of the optical power corresponding to the appropriate O ₂ %, and combustion is performed to eliminate the deviation. The present invention relates to a combustion control method for controlling the flow rate of commercial air.

2. Description of the Related Art Conventionally, as a method for controlling combustion, Japanese Patent Laid-Open No. 59-138811
JP-A-58-146124.

The former Japanese Patent Laid-Open No. 59-138811 is arranged in a combustion sensor flame made of semiconductor, monitors the combustion state by the change of its electric resistance, and stops combustion when oxygen deficiency and misfire are detected. It is what

In the latter one of JP-A-58-146124, the emission spectrum of flames is spectroscopically analyzed by an optical measuring device to obtain temperature distributions of these flames, and this is compared with the temperature distribution of flames in the optimum combustion state. It outputs a control signal and attempts to control the flame shape constantly by this output.

However, the former only turns ON / OFF the combustion, but does not control the combustion flame itself in the furnace. Further, the latter has a drawback that the detection unit and the control unit are complicated because the emission spectrum is spectrally analyzed.

As a combustion control method that does not have such drawbacks, January 1985
Some of them are disclosed in the newspaper of the Sangyo Keizai Shimbun dated 25.

This is a zirconia O ₂ sensor installed in the flue, O ₂ % in the exhaust gas passing through this flue is measured, and the amount of forced air for combustion becomes the optimum amount according to the load conditions using this O ₂ % as an index. The rotation speed of the blower is controlled by an inverter.

Regarding the use of optical power for detecting the combustion state, JP-A-59-137719, JP-A-59-109715, and JP-A-59-12227.
No. 58-143274.

Problems to be Solved by the Invention Although the combustion control using the zirconia O ₂ sensor can easily control the combustion state in the furnace, it has the following drawbacks.

Since the sensor must be installed in the flue, the O ₂ concentration in the combustion chamber increased when outside air entered through the inspection port existing between the combustion chamber outlet and the measurement unit or the gap created by the structure. I will mistakenly judge that it is a thing.

Due to the flow of gas from the combustion chamber outlet to the measurement section,
There is a time lag.

The zirconia O ₂ sensor has a response delay of 30 to 40 seconds. For this reason, it becomes a bottleneck in performing more speedy control.

Instead of the above zirconia O ₂ sensor, the above-mentioned JP-A-59-137719 is used.
It is conceivable to use the optical sensors described in Japanese Patent No. 6-48242, but these optical sensors cannot detect the optical power immediately because they only detect optical power.

Means for Solving Problems The combustion state greatly varies depending on the mixing ratio of combustion and air, and the ratio is generally an air ratio (or O _{2 in} exhaust gas).
Concentration) is an important point in combustion management. For example, when the air ratio is made too large, exhaust gas loss increases, thermal efficiency decreases and NOx increases, resulting in a bad combustion state. On the other hand, if the air ratio is made too small, incomplete combustion results in black smoke, which also leads to misfire, which is also a bad combustion state. Therefore, a good combustion state is combustion with a minimum air ratio that does not cause incomplete combustion.

The air ratio and the O ₂ concentration in the exhaust gas have the following relationship.

By the way, in a burner of the type that retains flames by swirl force, the light intensity generated from the flame of the burner varies depending on the air ratio (or O ₂ concentration in exhaust gas) when the amount of combustion (fuel flow rate) is constant. 2 shows a change as shown by a curve I, and the optical power signal thereof exhibits a sawtooth wave shape which constantly vibrates as shown in FIGS. 3 and 4. The optical power signal level shows a mountain-shaped change as shown in FIG. ₂ , and in the region (a) where the O ₂ concentration is higher than the peak value, the optical power signal level decreases as the O ₂ concentration increases. , And in the region where the O ₂ concentration is lower than the peak value (b), O ₂
It has the characteristic that the optical power signal level also decreases as the density decreases.

However, as for the oscillation of the optical power signal, as shown in FIG. 3, the oscillation width shows a characteristic that it increases as the O ₂ concentration decreases. The above characteristics do not change even when the combustion amount is changed, but when the combustion amount is increased, the oscillation width of the optical power signal increases, and conversely, when the combustion amount is decreased, it decreases.

Looking at a burner of the type having a cone-shaped flame stabilizer, its light intensity changes as shown by the curve II in FIG. However, regarding the vibration of the optical power signal, contrary to FIG. 3, the vibration width becomes smaller as the O ₂ concentration decreases.

Based on the above findings, the present inventors obtained data as shown in FIG. 5 for a burner of the type that retains flame by a turning force.

In this figure, the vertical axis represents the value relating to the amplitude of the optical power, and the unit time Δ of the optical power signal as shown in FIG.
The differential value for each t is calculated, the average value is further calculated, and the deviation integral value with respect to the average value is calculated, and the deviation integral value thus calculated is plotted according to the scale on the vertical axis. The horizontal axis shows O ₂ % in the exhaust gas.

Curves a, b, and c respectively show the relationship between the exhaust gas O ₂ % and the deviation integral value for various combustion amounts of fuel, and the curve d shows the exhaust gas O _{2 with the} optimum air ratio at which the incomplete combustion does not occur. The relationship between% and the integral value is shown.

Therefore, for example, when the combustion amount is set to 60 / h, if the integrated value detected from the burner flame is Y, the corresponding O ₂ % (C) is appropriate O ₂ % (D). It can be read from FIG. 5 that there is a deviation (e), and this deviation (e) corresponds to the deviation B of the integrated value.

Further, the present inventors obtained the data shown in FIG. 6 for the burner of the type having a cone-shaped flame stabilizer.

The combustion control method according to the present invention utilizes the data as shown in FIG. 5 or FIG. 6, and controls for eliminating the deviation B based on the deviation B obtained from the comparison between the data and the detection signal. It is intended to output a signal.

That is, in order to solve the above problems, the present invention obtains a flow rate signal of the fuel supplied to the combustor and an O ₂ % signal in the exhaust gas of the combustor, and the O ₂ % corresponds to the flow rate of the fuel. Reasonable
In the combustion control method of calculating the deviation when it deviates from O ₂ % and performing an output for eliminating the deviation to the flow rate adjusting unit of the combustion air, an optical power signal from the flame of the combustor. Is detected and the optical power signal is differentiated at every predetermined time to calculate a differential value, and an average value of the differential values is calculated to obtain a deviation integral value with respect to the average value. Reasonable for the combustion flow rate of
It is said that the deviation is calculated by comparing with the deviation integrated value corresponding to O ₂ %, and the output for eliminating the deviation is output to the combustion air flow rate control unit to make O ₂ % in the exhaust gas appropriate. The method is adopted.

Action An optical power signal is detected from the flame formed by the combustor and this optical power signal is processed to obtain a control output.

Therefore, it is possible to control O ₂ % without directly detecting O ₂ % in the exhaust gas. As a result, a relatively inexpensive optical sensor can be used instead of an expensive zirconia O ₂ sensor.

Further, when the combustor is a burner, it is nothing but detection of the combustion state in the furnace, and therefore, combustion control can be performed without a time lag, as compared with the conventional method of detecting by a flue.

Differentiate the optical power signal every predetermined time to calculate the differential value,
Further, an average value of the differential values is calculated to obtain a deviation integral value with respect to the average value, and thereafter, this deviation is compared with a deviation integral value corresponding to a reasonable O ₂ % with respect to the present fuel flow rate, which is previously obtained, and the deviation is calculated. Calculate

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 5 and 7.

FIG. 7 shows a heat treatment furnace using the combustion control method according to the present invention.

In FIG. 7, reference numeral 1 indicates a furnace main body, and a wall of the furnace main body 1 is provided with a door 2 for loading metal products and a flue 3 for discharging exhaust gas.

In this case, the burner 4, which is a combustor provided in the furnace body 1, is of a type that retains flames by a swirling airflow.

A pipe 5 for supplying fuel and a pipe 6 for supplying combustion air are connected to the burner 4, the pipe 5 is provided with a flow control valve 7 and a flow meter 8, and the pipe 6 is provided with a flow control valve 9. ing.

The fuel flow rate control valve 7 is controlled by the fuel control device.

The apparatus comprises a temperature sensor 10 composed of a thermocouple for detecting the temperature in the furnace body 1 and a fuel control section 11.

The fuel control unit 11 is provided with a temperature converter 12 and a temperature controller 13, converts the signal from the temperature sensor 10 into a predetermined output signal by the temperature converter 12, and the temperature controller 13 receives this to output a predetermined signal. A control signal for adjusting the opening of the control valve 7 so that fuel that can maintain the set temperature reaches the burner 4 is output by performing a comparison calculation with the set temperature.

The flow rate control valve 9 for combustion air is controlled by a combustion air control device.

The device is a combustion air control unit for converting a light power emitted from the combustion flame 14 of the burner 4 into an electric signal and a control signal for receiving the signal and the like to output a control signal to the flow rate control valve 9 for the combustion air. Equipped with 16.

The optical sensor 15 consists of a Ge photodiode, Si photodiode, phototransistor, solar cell, etc.
It is fixed at the location opposite to.

The combustion air control unit 16 calculates the differential value by differentiating the A / D converter 17 for converting the analog signal from the optical sensor 15 into a digital signal and the electric signal from the converter 17 at every predetermined time,
Further, an average value of the differential values is calculated to obtain a deviation integral value with respect to the average value, and an arithmetic unit 18 for outputting the integrated value and the arithmetic unit 18
The output from the combustion air flow control valve is calculated by comparing the calculated output with a deviation integral value corresponding to a proper O ₂ % for the present fuel flow rate, which is obtained in advance, and canceling the deviation. 9 to adjust the O ₂ % in the exhaust gas to a reasonable value.

Here, the operations of the arithmetic unit 18 and the adjuster 19 will be described based on the first flowchart.

In step 1, the optical power level data is read at intervals of Δt seconds and stored in the data area of the calculator 18, and then in step 2
It is determined whether or not data has been taken in for a certain period of time, and if NO, the process returns to step 2 and is repeated until data is taken in for a certain period of time.

If YES is determined in step 2, the process proceeds to step 3, the differential value of the optical power level is calculated, the differential value is calculated in step 4, and the deviation integral value Y with respect to the average value is calculated in step 5. In step 6, the controller 19 calculates the difference B from the target O ₂ %, and in step 7, outputs the correction value of the air amount,
Return to step 1 and repeat a series of controls. Step 7
The output at is input to the control valve 9.

Thus, the exhaust gas generated in the furnace body 1 becomes a predetermined optimum O ₂ % gas and is discharged from the flue 3 to the outside of the system, and low O ₂ combustion is achieved in the furnace body.

EFFECTS OF THE INVENTION The present invention detects an optical power signal from a flame formed by a combustor as described above and processes the optical power signal to obtain a control output, so that O ₂ % in exhaust gas is not directly detected. Both O ₂ %
Can be controlled. Therefore, a relatively inexpensive optical sensor can be used as a sensor instead of an expensive O ₂ % sensor, which is useful for combustion control of furnaces, gas turbines, and the like.

Also, when the combustor is a burner, the combustion state is detected in the furnace, so compared to the conventional method of detecting exhaust gas through the flue, even if a sudden change of O ₂ % occurs due to opening and closing of the furnace, Can be dealt with, and even if air leaks from the gap in the flue, the detection result will not be affected.

[Brief description of drawings]

FIG. 1 is a flow chart showing a procedure for obtaining a control output of a fuel control method according to the present invention, FIG. 2 is a graph showing a relationship between optical power and exhaust gas O ₂ % under a constant combustion amount, and FIG. 3 is a combustion amount. Is a graph showing the relationship between the optical power and the time when O ₂ % is changed while keeping constant, FIG. 4 is an enlarged view of the IV part of FIG. 3,
FIG. 5 is a graph showing the relationship between the integrated value of deviation of optical power and O ₂ % with the combustion amount as a parameter, and FIG. 6 is a graph similar to FIG. 5 showing different types of burners, FIG. FIG. 3 is a control system diagram of a heat treatment furnace using the present invention. 1: furnace body, 4: burner, 8: fuel flow meter, 9: combustion air flow control valve, 15: optical sensor, 16: combustion air control unit, 17: A / D converter, 18: calculator, 19: Regulator.

Continuation of front page (56) References JP-A-46-6433 (JP, A) JP-A-56-151814 (JP, A) JP-B-43-20634 (JP, B1)

Claims (1)

[Claims] 1. A flow rate signal of fuel supplied to a combustor and an O ₂ % signal in exhaust gas of the combustor are obtained, and the O ₂ % deviates from a proper O ₂ % with respect to the flow rate of the fuel. In the combustion control method, in which the deviation is sometimes calculated and an output for eliminating the deviation is output to the flow rate adjusting unit of the combustion air, the optical power signal is detected from the flame of the combustor and the optical power is detected. Differentiate the signal every predetermined time to calculate the differential value,
Further, an average value of the differential values is calculated to obtain a deviation integral value with respect to the average value, and thereafter, this deviation is compared with a deviation integral value corresponding to a reasonable O ₂ % with respect to the present fuel flow rate, which is previously obtained, and the deviation is calculated. The combustion control method described above, characterized by calculating and performing an output for eliminating the deviation to the combustion air flow rate control unit to make O ₂ % in the exhaust gas appropriate.