JPS63105316A - Combustion control method - Google Patents

Abstract

PURPOSE:To provide stable control by a less-expensive optical sensor by a method wherein an integral value of differences in respect to a mean value within a desired time of a moving mean value calculated from an optical power signal is calculated and an output for eliminating a difference in respect to a differential integral value corresponding to a suitable O2% for a present fuel flow rate is given. CONSTITUTION:Initial set values (a measuring period DELTAt of an optical power level, a moving mean time t1 second and the like) are inputted, a total value of data is calculated to calculate a mean value. Next optical power level data is taken, and a moving mean value is calculated. Integrated difference value is calculated, a correction for the difference value is outputted, a data area for the time counter correction is reset and this processing is repeated. The correction is inputted to an adjusting unit 19. The adjustor 19 receives a flow rate signal Q to be outputted from a fuel flow meter 8, calculates a corresponding difference integral value of the most suitable O2% and calculates a difference B between the present value and the most suitable value. Further, the adjustor 19 corrects the above B, calculates an amount of air getting the most suitable combustion state and outputs it to an adjusting valve 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a method in which the amplitude of the optical power of a combustion flame is
Taking advantage of the fact that there is a proportional relationship with 0.2%, the signal regarding the amplitude of optical power obtained during operation of the combustor is compared with the signal regarding the amplitude of optical power corresponding to the appropriate 0.2% to eliminate the deviation. The present invention relates to a combustion control method for controlling the flow rate of combustion air.

Conventional technology Conventionally, a method for controlling combustion has been disclosed in Japanese Patent Application Laid-open No. 59-13.
Some of these are disclosed in Japanese Patent No. 8811 and Japanese Patent No. 58-146124.

The former, JP-A No. 59-138811, places a combustion sensor made of a semiconductor in the flame, monitors the combustion state based on changes in its electrical resistance, and stops combustion when oxygen deficiency or misfire is detected. This is what we are trying to do.

The latter, published in JP-A No. 58-146124, uses an optical measuring device to spectrally analyze the emission spectrum of the flame, determine the temperature distribution of the flame from this, and compare this with the temperature distribution of the flame under optimal combustion conditions. It outputs a control signal, and uses this output to control the shape of the flame.

However, the former only turns combustion ON and OFF, but does not control the combustion flame itself in the furnace, and the latter spectroscopically analyzes the emission spectrum, so the detection and control parts are complicated. be.

In 1985, 1 was developed as a combustion control method that does not have such drawbacks.
There is something disclosed in the Netsu Sangyo Keizai Shimbun dated February 25th.

This is done by installing a zirconia 02 sensor in the flue and measuring 02% of the exhaust gas passing through the flue.

Using this 0.2% as an index, the rotational speed of the blower is controlled by an inverter so that the amount of forced air for combustion becomes the optimum amount according to the load conditions.

Regarding the use of optical power to detect the combustion state, see JP-A-59-137719 and JP-A-59-109715.
No. 59-12227.

It is disclosed in No. 58-143274.

Problems to be Solved by the Invention Although combustion control using the zirconia 02 sensor described above can easily control the combustion state in the furnace, it has the following drawbacks.

■ Since the sensor must be installed in the flue, if outside air enters through the inspection port or gap created by structure 1 between the combustion chamber outlet and the measurement part, the 02 concentration in the combustion chamber will increase. I mistakenly judge it as something.

■ Due to the flow of gas from the combustion chamber outlet to the measuring section,
A time lag occurs.

■ Zirconia 02 sensor has a response delay of 30 to 40 seconds. This becomes a bottleneck in performing faster control.

In place of the zirconia 02 sensor, the JP-A-TMS9-
Although it is conceivable to use the optical sensors described in No. 137719, etc., these optical sensors simply detect optical power and cannot be immediately applied.

Means for solving the problem Combustion conditions vary greatly depending on the mixing ratio of fuel and air, and that ratio is generally determined by the air ratio (or zero in the exhaust gas).
2 concentration) is an important point in combustion management.For example, if the air ratio is made too large, exhaust gas loss increases, thermal efficiency decreases and NOx increases, and the combustion state The situation is not good. Conversely, if the air ratio is made too small.

Incomplete combustion results in black smoke, which also leads to misfires, which is also not a good combustion condition. Therefore, a good combustion condition is combustion at the lowest air ratio that does not cause incomplete combustion.

Note that the air ratio and the 02 concentration in the exhaust gas have the following relationship.

By the way, in a type of burner whose flame is held by swirling force, the light intensity generated from the flame of the burner is determined by the combustion amount (
When the fuel flow rate (fuel flow rate) is held constant, changes will occur depending on the air ratio (or 0□ concentration in exhaust gas) as shown in the curved line in Figure 2, and the optical power signal will be shown in Figures 3 and 4. As shown in Figure 2, the optical power signal level exhibits a sawtooth waveform that constantly oscillates, and the optical power signal level exhibits a mountain-shaped change as shown in Figure 2.
In this case, the optical power signal level decreases as the 02c degree increases, and in the desired range (b) where the 02 concentration is lower than the peak value, the optical power signal level also decreases as the 02 concentration decreases. .

However, as shown in Figure 3, the oscillation of the optical power signal exhibits a characteristic in which the oscillation width increases as the 02 concentration decreases, and the above characteristics also persist when the combustion amount is changed. It doesn't change, but if you increase the amount of combustion,
The oscillation width of the optical power signal increases, and conversely decreases as the combustion amount decreases.

In addition, when looking at a type of burner with a cone-shaped flame holder, its light intensity changes as shown by curve 2 in Figure 2. However, regarding the vibration of the optical power signal, contrary to FIG. 3, the vibration width becomes smaller as the 02 concentration decreases.

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

In this figure, the vertical axis indicates the value related to the amplitude of the optical power, and the scale is the integral value of the deviation of the moving average value from the average value in unit time Δt of the moving average value of the optical power signal as shown in FIG. It is being The horizontal axis is 02 in exhaust gas.
% is shown.

Curves a, b, and c show the relationship between the exhaust gas 02% and the deviation integral value for various combustion amounts of fuel, and the curve klAd shows the relationship between the exhaust gas 02% and the deviation integral value at the optimal air ratio that does not cause the aforementioned incomplete combustion. It shows the relationship between the integral value and

Therefore, for example, if the combustion rate is set to 601/h and the integral value detected from the burner flame is Y, the corresponding 02% (c) will deviate from the appropriate 02% (d) ( E), and this deviation (E) is the deviation B of the integral value.
It can be read from FIG. 5 that this corresponds to .

In addition, the present inventors obtained data shown in FIG. 6 regarding a type of burner having a cone-shaped flame holder.

The combustion control method according to the present invention utilizes data such as shown in FIG. 5 or 6 above, and performs control to eliminate the deviation B based on the deviation B obtained by comparing this data with 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 fuel supplied to a combustor and a 02% signal in the exhaust gas of the combustor, and determines that the 02% is appropriate for the flow rate of the fuel. In a combustion control method in which the deviation is calculated when the deviation is from 0°%, and an output to eliminate the deviation is provided to the combustion air flow rate adjustment section, an optical power signal is generated from the flame of the combustor. is detected and its moving average value is determined from the optical power signal.

Calculate the integral value of the deviation of the moving average value from the average value within a predetermined time period of the moving average value, and then compare this with the deviation integral value corresponding to a reasonable 0.2% of the current fuel flow rate determined in advance. A method is adopted in which the deviation is calculated and an output to eliminate the deviation is sent to the combustion air flow rate adjusting section to make 0.2% of the exhaust gas appropriate.

An optical power signal is detected from the flame formed in the working combustor and the optical power signal is processed to provide a control output.

Therefore, it is possible to control 02% without directly detecting 02% in the exhaust gas. As a result, a relatively inexpensive optical sensor can be used instead of the expensive zirconia 0 2 sensor.

Furthermore, when the combustor is a burner, the combustion state is detected in the furnace, so combustion control can be performed without a time lag compared to the conventional method of detecting in the flue.

In order to obtain the above control output, the moving average value is obtained from the optical power signal, the integral value of the deviation of the moving average value from the average value within a predetermined time of the moving average value is obtained, and then this is obtained in advance. Reasonable 0.2% for current fuel flow rate
The deviation is calculated by comparing it with the deviation integral value corresponding to .

Since the deviation integral value of the moving average value is determined in this way, transient vibrations in the optical power level are corrected to a smooth curve, transient responses are eliminated, and control is stabilized.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 5 and FIG. 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 body, and the wall of the furnace body 1 is provided with a door 2 for charging metal products, etc., 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 maintains flame by 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 m:Aw valve 7 and a flow meter 8, and the pipe 6 is provided with a flow rate y1 regulating valve 9. is provided.

The fuel flow control valve 7 is controlled by a fuel control device.

The device is equipped with a temperature sensor 10 consisting of a thermocouple that detects the temperature inside the furnace body 1, and a fuel control section 11.

The fuel control unit 11 includes a temperature converter 12 and a temperature regulator 13.
The signal from the temperature sensor 10 is converted into a predetermined output signal by the temperature converter 12, and this is converted into the temperature WAt! g
The temperature is received by a device 13 and compared with a predetermined set temperature, and a control signal is output for adjusting the opening degree of the control valve 7 so that fuel that can maintain the set temperature reaches the burner 4.

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

The device includes an optical sensor 15 that converts the optical power emitted from the combustion flame 14 of the burner 4 into an electrical signal, and a combustion air control section that receives the signal, generates a control signal, and outputs it to the combustion air flow control valve 9. It is equipped with 16.

The optical sensor 15 is composed of a Ge photodiode, an S1 photodiode, a phototransistor, a solar cell, etc., and is fixed at a location facing the flame 14.

The combustion air control unit 16 includes an A/D converter 17 that converts an analog signal from the optical sensor 15 into a digital signal, and processes the electric signal from the converter 17 to obtain a moving average value. A calculator 18 that calculates and outputs the integrated value of the deviation of the moving average value from the average value within a predetermined time period, and a current fuel that receives the output from the calculator 18 and calculates this in advance. The deviation integral value corresponding to a reasonable 02% of the flow rate is compared, the deviation is calculated, and an output to eliminate the deviation is sent to the combustion air flow rate control valve 9 to make the 02% of the exhaust gas a reasonable value. Adjuster 19
It consists of

Here, the operation of the arithmetic unit 18 will be explained based on the flowchart of FIG.

In step 1, the initial setting values of the microcomputer, etc. (optical power level measurement period Δt, moving average time t1 seconds, etc.) are imported, in step 2 the optical power level is imported and data is set in the data area, and in step 3 Determine whether data has been imported for t1 seconds, and if NO, return to step 2 and repeatedly import the data.If YES is determined in step 3, calculate the total value of the data in step 4, and calculate the average value in step 5. calculate.

In step 6, the data of the next optical power level is taken in. In step 7, the first data is deleted and finally the n+1th data is added, and in step 8, the moving average value is calculated. Calculate the total value, calculate the moving average value in step 9, determine whether the average time has been captured in seconds in step 10, and if NO, return to step 6 and repeat until the predetermined time has been captured, determine YES in step lO. Then, in step 1, calculate the deviation integral value,
In step 12, a correction value for that value is output, and in step 13, the data area of the time counter correction value is reset, and the process is repeated by returning to step 2.The correction value output in step 2 is input to the regulator 19. Ru.

The regulator 19 receives the flow rate signal Q output from the fuel flow meter 8.
Then, select the curve corresponding to Q (Fig. 5), find the optimal corresponding deviation integral value of 02% for Q, and find the difference between the current value and the optimal value.

For example, when Q=601/h, 3 curves are selected. The optimum 02% is (d), and the difference in the deviation integral value to obtain (d) is B.

Then, the vA moderator 19 corrects the above B to calculate the amount of air to obtain the optimum combustion state, and outputs it to the control valve 9.

In this way, the exhaust gas generated within the furnace body 1 is reduced to a predetermined optimum value of 0.2%.
This gas is discharged from the flue 3 to the outside of the system, and a low 0.2% combustion is achieved in the furnace.

Effects of the Invention As described above, the present invention detects an optical power signal from the flame formed in the combustor and processes this optical power signal to obtain a control output. 0
2% control becomes possible. Therefore, instead of the expensive 02 sensor, a relatively inexpensive optical sensor can be used as a sensor, which is beneficial for combustion control of furnaces, gas turbines, and the like.

In addition, since the combustion state is detected in the furnace when the combustor is a burner, compared to the conventional method of detecting exhaust gas while passing it through the flue, it can be detected quickly even if there is a sudden change of 0.2% due to opening and closing of the furnace. Moreover, even if air leaks from the gap in the flue, the detection results will not be affected.

Furthermore, during calculation processing, the moving average value of the optical power level is obtained, the integrated deviation value from this average value is obtained, and the control amount is obtained based on this integrated deviation value, so transient fluctuations in the optical power level are calculated. It is possible to correct to a smooth curve and eliminate transient response. Therefore, control becomes stable.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing the main part of the procedure for obtaining the control output of the fuel control method according to the present invention, Fig. 2 is a graph showing the relationship between optical power and exhaust gas 02% under a constant combustion amount, and Fig. 3 Figure 4 is a graph showing the relationship between optical power and time when the combustion amount is constant and 02% is varied, and Figure 4 is the graph shown in Figure 3.
Figure 5 is a graph showing the relationship between the deviation integral value of optical power and 02% using combustion amount as a parameter. Figure 6 is a graph similar to Figure 5 that shows different types of burners. , FIG. 7 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 rate control valve, 15: Optical sensor, 16: Combustion air control section, 17: A/D converter, 18: Calculator , 19:
regulator.

Claims (1)

[Claims] Obtaining the flow rate signal of fuel supplied to the combustor and the O_2% signal in the exhaust gas of the combustor, and calculating the deviation when the O_2% deviates from a reasonable O_2% with respect to the flow rate of the fuel, In a combustion control method in which an output for eliminating the deviation is provided to the combustion air flow rate adjusting section,
An optical power signal is detected from the flame of the combustor, and a moving average value thereof is determined from the optical power signal, and an integral value of the deviation of the moving average value from the average value within a predetermined time period of the moving average value is determined. Then, the deviation is calculated by comparing this with the deviation integral value corresponding to the appropriate O_2% for the current fuel flow rate calculated in advance, and an output to eliminate the deviation is sent to the combustion air flow rate adjustment unit to adjust the exhaust gas. O_ inside
The combustion control method described above is characterized in that 2% is appropriate.