JPH0784921B2 - Combustion control method - Google Patents

Description

Description: INDUSTRIAL APPLICABILITY The present invention relates to a combustion flame having an optical power amplitude of O ₂ % in non-gas.
By utilizing the fact that it is proportional to the signal of the amplitude of the optical power obtained during the operation of the combustor, it is compared with the signal of the amplitude of the optical power corresponding to the appropriate O ₂ % 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.

In the former Japanese Patent Laid-Open No. 59-138811, a combustion sensor made of a semiconductor is arranged in a flame, the combustion state is monitored by a change in its electric resistance, and the combustion is stopped when an oxygen deficiency or a misfire is detected. It is something to try.

In the latter one of JP-A-58-146124, the emission spectrum of the flame is spectroscopically analyzed by an optical measuring device, the temperature distribution of the flame is obtained from this, and this is compared with the temperature distribution of the flame 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 25th.

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 The combustion control using the zirconia O ₂ sensor can easily control the combustion state in the furnace, but 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.
Although it is possible to use the optical sensors described in the publication No. etc., these optical sensors merely detect optical power and cannot be applied immediately.

Means for Solving Problems The combustion state greatly changes depending on the mixing ratio of fuel and air, and the ratio is generally an air ratio (or O _{2 in} exhaust gas).
It is an important point in combustion control as concentration. 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 at the minimum air ratio at which incomplete combustion does not occur.

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 the burner of the type having a cone-shaped flame stabilizer, the 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 related to the amplitude of the optical power, and the integrated value of the deviation of the moving average value with respect to the average value of the moving average value of the optical power signal at unit time Δt as shown in FIG. It is graduated. Horizontal axis shows O ₂ % in exhaust gas
Is shown.

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. And the moving average value is obtained from the optical power signal, the integrated value of the deviation of the moving average value with respect to the average value of the moving average value within a predetermined time is obtained, and then the present fuel is obtained in advance. The deviation is calculated by comparing it with a deviation integral value corresponding to a reasonable O ₂ % with respect to the flow rate, and an output that eliminates the deviation is output to the combustion air flow rate control unit to reduce the O ₂ % in the exhaust gas to a reasonable value. The method of assuming 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.

In order to obtain the control output, the moving average value is obtained from the optical power signal, the integrated value of the deviation of the moving average value with respect to the average value of the moving average value within a predetermined time is obtained, and then it is obtained in advance. The deviation is calculated by comparing it with the deviation integral value corresponding to a reasonable O ₂ % with respect to the current fuel flow rate.

Since the deviation integral value of the moving average value is obtained in this way, the transient oscillation of the optical power level is corrected to a smooth curve, the transient response disappears, and the control becomes stable.

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, and the signal from the temperature sensor 10 is converted into a predetermined output signal by the temperature converter 12, and this is received by the temperature controller 13 and received by the temperature controller 13. 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 processes the electric signal from 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 to obtain the moving average value, and the moving average. An arithmetic unit 18 for obtaining an integrated value of deviations of the moving average value with respect to an average value within a predetermined time, and outputting the integrated value,
The output from the calculator 18 is received, and this is calculated in advance to compare the deviation integral value corresponding to a reasonable O ₂ % with respect to the current fuel flow rate, the deviation is calculated, and an output for eliminating the deviation is obtained. The exhaust air flow control valve 9
It consists of a regulator 19 which makes O ₂ % reasonable.

Here, the operation of the arithmetic unit 18 will be described with reference to the flowchart of FIG.

In step 1, the initial setting values of the microcomputer (optical power level measurement period Δt, moving average time t ₁ second, etc.) are fetched, and in step 2, the optical power level is fetched and data is set in the data area. At t, it is judged whether the data is taken for ₁ second. If it is NO, it returns to step 2 and the data is repeatedly taken. At step 4, it is judged as YES, the total value of the data is calculated, and at step 5, the average value is calculated. Calculate the value.

In step 6, the data of the next optical power level is fetched, in step 7, the first data is deleted and the (n + 1) th data is added to calculate the moving average value, and in step 8, The total value is calculated, the moving average value is calculated in step 9, and it is determined in step 10 whether the average time t seconds have been fetched. If NO, the process returns to step 6 and is repeated until a predetermined time is fetched. If YES is determined in step 10, the deviation integrated value is calculated in step 11, and step 12
The correction value corresponding to that value is output at, the data area of the time counter correction value is reset at step 13, and the process returns to step 2 and is repeated. The correction value output in step 12 is input to the controller 19.

The controller 19 receives the flow rate signal Q output from the fuel flow meter 8, selects a curve (FIG. 5) corresponding to Q, finds the optimum deviation integral value of O ₂ % for Q, and obtains the current value. And the optimum value.

For example, when Q = 60 / h, the a curve is selected. Optimal O ₂
% Is (d), and the difference between the deviation integral values for obtaining (d) is B.

Then, the controller 19 corrects the above B to calculate the air amount for obtaining the optimum combustion state, and outputs it 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.

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.

Furthermore, the moving average value of the optical power level is calculated during the calculation process, the deviation integrated value for this average value is output, and the control amount is calculated based on this deviation integrated value. It can be corrected to a smooth curve to eliminate transient response. Therefore, the control becomes stable.

[Brief description of drawings]

FIG. 1 is a flowchart showing a main part of 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. Is a graph showing the relationship between light power and time when the amount of combustion is constant and O ₂ % is changed. Fig. 4 is an enlarged view of the IV part in Fig. 3, Fig. 5 is the integrated value of the deviation of light power. and the relationship between the O _2%, the graph showing the combustion rate as a parameter, FIG. 6 is a fifth diagram similar graph of the different types of burners, Figure 7 is a control of the heat treatment furnace using the present invention It is a system diagram. 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.

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. Searching for the moving average value from the signal, obtains an integrated value of the deviation of the moving average value to the average value in a predetermined time period of the moving average, reasonable O _2% with respect to the fuel flow rate of the previously determined current and thereafter this Comparing the deviation integrated value corresponding to the above, calculating the deviation, and performing an output for eliminating the deviation to the combustion air flow rate control unit to make O ₂ % in the exhaust gas reasonable. The above combustion control method.