JPS63123921A - Combustion control method - Google Patents

Abstract

PURPOSE:To simplify constitution, by a method wherein O2% in exhaust gas is detected as a light power from flame, the amplitude of the light power is determined by given computation, and an air flow rate for combustion is controlled by a deviation on the amplitude of the light available when O2% is a proper value. CONSTITUTION:A light power emitted from a combustion flame 14 by means of a photo sensor 15 is detected as an electric signal to input it to a combustion air control part 16. In the combustion air control part 16 an air-for-combustion flow rate corrector 19 determines a difference between adjoining upper and lower peak values according to a given program, and determines a product of the difference and an elapse time between the upper and the lower peak. Thereafter, an average value in a given time of the product is determined. Meanwhile, an average value responding to an optimum O2% is determined by means of a fuel flow rate signal from a fuel flow meter 8. In order to eliminate a deviation between an actual average value and an optimum average value, an air-for-combustion flow rate regulating valve 9 is controlled. This constitution enables execution of control by means of a simple photo sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is characterized in that the amplitude of the optical power of a combustion flame is
Using the fact that there is a proportional relationship with %, 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 02%, and the combustion is performed to eliminate the deviation. The present invention relates to a combustion control method for controlling the flow rate of air for use.

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. Furthermore, since the latter spectroscopically analyzes the emission spectrum, it has the disadvantage that the detection section and control section become complicated.

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 O2 sensor in the flue to measure 02% of the exhaust gas passing through the flue, and using this 02% as an index, the blower is set to the optimum amount of forced air for combustion according to the load conditions. The rotation speed of the motor is controlled by an inverter.

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

Problems to be Solved by the Invention Although combustion control using the zirconia 0° sensor described above allows the combustion state in the furnace to be easily controlled, it has the following drawbacks.

■ Since the sensor must be installed in the flue, if outside air enters through the inspection hole or structural gap 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 0° sensor has a response delay of 30 to 40 seconds. This becomes a bottleneck in performing faster control.

Instead of the above zirconia 0° sensor, the above JP-A-59-
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 to solve the problem Combustion conditions vary greatly depending on the mixture ratio of fuel and air, and that ratio is generally referred to as the air ratio (or 02 concentration in exhaust gas) and is an important point in combustion management. . For example, if the air ratio is increased too much, exhaust gas loss increases, thermal efficiency decreases and NOx increases, resulting in poor combustion conditions. On the other hand, if the air ratio is too small, incomplete combustion will occur and black smoke will be generated.
It also leads to misfire, which is also a bad 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 O2 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 kept constant, the difference in air ratio (or 02 concentration in exhaust gas) causes changes as shown in curve I in Figure 2, and the optical power signal is shown in Figures 3 and 4. It shows a sawtooth waveform that constantly vibrates. The optical power signal level shows a mountain-shaped change as shown in Figure 2, and in the region (A) where the O2 concentration is higher than the peak value, it reaches 0.
The optical power signal level decreases as the 02 concentration increases, and in the region (b) where the 02 concentration is lower than the peak value, the 02
It has a characteristic that the optical power signal level also decreases as the concentration decreases.

However, as shown in FIG. 3, the oscillation of the optical power signal exhibits a characteristic in which the width of the oscillation increases as the 02 concentration decreases.

Further, the characteristics described above 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 becomes larger, and conversely, when the combustion amount is decreased, the oscillation width of the optical power signal becomes smaller.

When looking at a type of burner with a cone-shaped flame holder, its light intensity changes as shown in curve II 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 product of the difference F between the adjacent upper and lower peak values and the elapsed time t between the upper and lower peaks as shown in Fig. 4 is calculated for a predetermined amount of time. In addition, the average value M, which is calculated by dividing this by time, is displayed on the scale. The horizontal axis shows 02% in the exhaust gas.

Curves a, b, and c are exhaust gas 0 for various combustion amounts of fuel.
The relationship between 2% and the above average value M is shown, and the curve d
is the exhaust gas 02 with the optimal air ratio that does not cause incomplete combustion as described above.
It shows the relationship between % and average value.

Therefore, for example, if the combustion rate is set to 606/h and the average value detected from the burner flame is M, 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 the above figure that it corresponds to .

Further, 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 the data shown in FIG. 5 or 6 above, and performs control to eliminate the deviation B based on the deviation B obtained from 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 that calculates the deviation when it deviates from O2% and provides an output to the combustion air flow rate adjustment section to eliminate the deviation, 02% of the exhaust gas is used as optical power. Detected from the flame of the above combustor,
Determining the difference between the adjacent upper and lower peak values from the optical power, and determining the product of the difference and the elapsed time between the upper and lower peaks, and then determining the average value of the product for a plurality of values within a predetermined time, Thereafter, this is compared with a predetermined average value corresponding to a reasonable 0.2% of the current fuel flow rate, the deviation is calculated, and an output to eliminate the deviation is sent to the combustion air flow rate adjustment section. procedures are adopted.

Optical power is detected from the flame formed in the working combustor and this optical bar is processed to obtain a control output.

Therefore, it is possible to control O2% without directly detecting O2% in the exhaust gas. As a result, it is possible to use a relatively inexpensive optical sensor instead of the expensive Zilfnia O2 sensor.In addition, when the combustor is a burner, it is nothing but detecting the combustion state in the furnace. Compared to methods that detect it on the road, combustion control can be performed without any time lag.

To obtain the above control output, calculate the difference between the adjacent upper and lower peak values from the optical power, calculate the product of the difference and the elapsed time between the upper and lower peaks, and then This is done by determining the average value for the current fuel flow rate, and then comparing this with a previously determined average value corresponding to a reasonable 0.2% of the current fuel flow rate to calculate the deviation.

In this way, since the calculation is performed using a relatively simple calculation formula in which the product of the upper and lower peak value difference and time is added and divided by a constant value, the control output can be obtained easily and quickly.

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 a door 2 for charging metal products and the like and a flue 3 for discharging exhaust gas are provided on the wall of the furnace body 1, respectively.

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 rate control valve 7 and a flow meter 8, and the pipe 6 is provided with a combustion air flow rate control section. A flow control valve 9 is provided.

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

The device includes a temperature sensor 10 consisting of a thermocouple that detects the temperature inside the furnace 1 and a fuel control section 11.

The fuel control unit 11 includes a temperature converter 12 and a combustion amount regulator 13.
The signal from the temperature sensor 10 is converted into a predetermined output signal by the temperature converter 12, and this is sent to the combustion amount regulator 1.
3, the temperature is compared with a predetermined set temperature, and a control signal is output for adjusting the opening degree of the control valve 7 so that the 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 device that receives the signal, generates a control signal, and outputs it to the combustion air flow control valve 9. 16.

The optical sensor 15 is composed of a G photodiode, an S photodiode, a phototransistor, a solar cell, etc.
It is fixed at a location opposite to 4.

The combustion air control unit 16 includes an A/D converter 17 that converts the optical signal from the optical sensor 15 into a digital signal, and the converter 1
Obtain the electrical signal from 7, find the difference between the adjacent upper and lower peak values, find the product of the difference and the elapsed time between the upper and lower peaks, and then average the above product for multiple values within a predetermined time. The fuel flow rate signal from the fuel flow meter 8 is then received to determine the average value corresponding to the optimum 0.2%, and the output to eliminate the deviation is determined by the combustion air flow control valve 9. and a combustion air flow rate corrector 19 for the combustion air.

The operation of this combustion air control section L6 will be explained based on the flowchart of FIG.

In step 51, the value of the optical power level is fetched, and compared with the data previously fetched in step S2. If it is in an upward trend, step S3 determines whether the data has changed from a downward trend to an upward trend. If YES, the value of the optical power level is fetched. Step S
4, data is set as the lower peak value, step S5 calculates the upper and lower peak difference, step S6 calculates the product of the peak difference X and the time between the upper and lower peaks, and resets the time counter.

On the other hand, if it is determined No in step S2, it is determined in step $7 whether the data is in a downward trend, and YES is determined.
If it is determined that the data has reversed from an upward trend to a downward trend, it is checked in step S8,
If it is determined to be ES, the data is set as the upper peak value in step S9, the upper and lower peak differences are calculated in step SIO, and the product of the peak difference x the time between the upper and lower peaks is calculated in step Stt. Calculate and reset the time counter.

If the determination in step S3 is NO (if the data is reversed from rising to falling),
If the determination is No (if the data reverses from falling to rising), step 7'S6. After performing SIL, a predetermined constant time T is counted in step SL2, and step S
If NO is determined in step 7 and after step SL2 is performed, it is determined in step SL3 whether a certain period of time T has elapsed, and if YES, in step 514, within a certain period of time T of the product of amplitude x time. Calculate the average value M in step S1
In step 5, the difference B between the optical power A and the optical power corresponding to the target 02% (d) is determined, and in step S16, a correction value for the combustion air flow rate is calculated and output, and the process returns to step S1 to repeat the series of processes.

Note that how to obtain the above correction value will be described below.

First, a controlled amount C is calculated by adding a controlled amount proportional to B and a controlled amount proportional to the integral value of B so that B becomes 0.

The optimum air flow rate for the current fuel flow rate Q is determined, the opening degree of the valve 9 in that case is compared with the current opening degree, and whether the valve 9 is opened or closed more than the current degree and the degree thereof are determined as an air flow rate adjustment signal. D is determined by the combustion amount regulator 13 and output to the combustion air flow rate corrector 19.

The corrector 19 obtains the CSD, calculates the air flow rate adjustment signal E from the following correction equation, outputs this to the valve 9, and adjusts its opening degree.

In this formula, C is % data and is a value within the range of 0 to 100%. When C=O~50%, the valve opening degree decreases, and when C=50~100%, the valve opening degree increases.For example, when C=40%, E=0.8D, and C=60%. Then, E = 1.2D.

From this, the calculated D is corrected by C to increase or decrease and is output as E to the valve 9.

In this way, the furnace 1 is constantly operated in the optimal combustion state, and the exhaust gas with an O2% of (d) is discharged from the flue 3 to the outside of the furnace.

Note that O2% may temporarily increase due to new material being taken in and out from door 2, but the O2% may increase temporarily.
Since a change of 2% is immediately detected by the optical sensor 15, the control valve 9 is immediately adjusted to quickly return to the appropriate 02%.

Although the above embodiment is intended for a heat treatment furnace, if a boiler or the like is used, a pressure sensor may be provided in place of the temperature sensor 1 of the fuel control unit 11, and the combustion amount regulator L3 may be replaced with a steam pressure setting method. It's a good thing.

Effects of the Invention As described above, the present invention detects optical power from the flame formed in the combustor and processes this optical power to obtain a control output. % control becomes possible. Therefore, 0 is expensive as a sensor.
It is possible to use a relatively inexpensive optical sensor instead of two sensors, which is useful for combustion control of furnaces, gas turbines, etc.

In addition, since the combustion state can be detected in the furnace, compared to the conventional method of detecting exhaust gas while passing it through the flue, even if a sudden change of 0.2% occurs due to the opening and closing of the five furnaces, it can be quickly dealt with.
Furthermore, even if air leaks from the gap in the flue, the detection results will not be affected.

Furthermore, the present invention calculates the difference between the upper and lower peak values from the optical power,
Since the calculation is performed using a simple formula of multiplying this by time, adding the products, and dividing by a constant value, the control output can be obtained easily and quickly, and the configuration of the corrector can be simplified. It is possible.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing the procedure for obtaining the control output of the combustion 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 is a graph showing the relationship between the combustion amount and the exhaust gas 02%. A graph showing the relationship between optical power and time when keeping it constant and changing 02%. Figure 4 is an enlarged view of part ■ in Figure 3. Figure 5 shows the relationship between the predetermined average value of optical power and 02%. The sixth graph shows the relationship between the two using the amount of combustion as a parameter.
The figure is a graph similar to FIG. 5, showing different types of burners, and FIG. 7 is a control system diagram of a heat treatment furnace using the present invention. 1: Furnace, 4: Burner, 8: Fuel flow meter, 9: Combustion air flow control valve, 13: Combustion amount regulator, 15: Optical sensor, 1
6: Combustion air control unit, 17: A/D converter, 19: Combustion air flow rate corrector.

Claims (1)

[Claims] Obtaining the flow rate signal of the 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 that outputs an output to the combustion air flow rate adjustment section to eliminate the deviation, O_2% in the exhaust gas is detected from the flame of the combustor as optical power, and the O_2% in the exhaust gas is detected from the flame of the combustor from the optical power. Calculate the difference between the adjacent upper and lower peak values, calculate the product of this difference and the elapsed time between the upper and lower peaks, then calculate the average value of the above product for a plurality of values within a predetermined time, and then calculate this in advance. The above method is characterized in that the deviation is calculated by comparing it with an average value corresponding to a reasonable O_2% for the obtained current fuel flow rate, and an output for eliminating the deviation is sent to the combustion air flow rate adjustment section. Combustion control method.