JPS63105321A - Combustion control - Google Patents

Abstract

PURPOSE:To permit combustion control prominent in response property, by a method wherein the difference of the average values of upward and downward movements during a predetermined time is obtained from the light power of the flame of a burner and the obtained difference is compared with a difference with respect to a proper O2 %, obtained previously, to operate a deviation therebetween. CONSTITUTION:An A/D converter 17 converts a light signal from a light sensor 15, converting a light power emitted from the flame 14 of combustion into the light signal, into digital. A combustion air corrector 19 integrates electric signals from the converter 17 for an unit time to obtain the average value of movement and obtains the average value of upward movements, which is upper than the average value of movement, as well as the average value of downward movement, which is lower than the average value of upper movement. Subsequently, a difference between the average values of upward and downward movements is operated to compare it with a deviation with respect to the optimum O2 %, previously obtained, then, an output for eliminating the deviation is outputted to a combustion air flow rate regulating valve 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to a method in which the amplitude of the optical power of a combustion flame is 0.0000000000000000000000000000000000000000000000000000000.
96, the signal related to the amplitude of the optical power obtained during operation of the combustor can be adjusted to an appropriate O! The present invention relates to a combustion control method in which the flow rate of combustion air is controlled so as to eliminate the deviation by comparing a signal regarding the amplitude of optical power corresponding to %.

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 achieved by installing a zirconia O sensor in the flue and measuring 0.96 in the exhaust gas passing through the flue, and using this O2% as an index, the amount of forced air for combustion is determined to be the optimal amount according to the load conditions. The rotation speed of the blower 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. 5B-143274.

Problems to be Solved by the Invention Although combustion control using the zirconia O2 sensor described above allows easy control of 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 structural gap between the combustion chamber outlet and the measurement part, the α concentration inside the combustion chamber will increase. I mistakenly think that it is.

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

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

The above zirconia 0. Instead of a sensor, the above-mentioned Japanese Patent Application Laid-open No. 1983
Although it is conceivable to use the optical sensors described in Japanese Patent Application 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 03 concentration in exhaust gas) and 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 NO! This results in an increase in combustion conditions, resulting in poor combustion conditions. On the other hand, if the air ratio is made too small, incomplete combustion will occur, producing black smoke, and may also lead to misfire, which is also not a good combustion condition. Therefore, good combustion state means incomplete,
This is combustion at the lowest air ratio that does not result in total combustion.

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

((02 concentration in combustion air) - (α concentration in exhaust gas)
) By the way, in a type of burner that holds the flame by swirling force, the light intensity generated by the flame of the burner will vary depending on the difference in air ratio (or O1 concentration in exhaust gas) when the combustion amount (fuel flow rate) is constant. It shows a change as shown in the curved line in the figure, and the optical power signal shows a constantly vibrating sawtooth waveform as shown in Fig. 3. The optical power signal level shows a mountain-shaped change as shown in FIG. 2, with 0. In the high concentration region (A), the optical power signal level decreases as the O2 concentration increases, and in the region (B) where the O3 concentration is lower than the peak value, the optical power signal level decreases to 0. It has a characteristic that the optical power signal level also decreases as the concentration decreases.

However, as for the vibration of the optical power signal, as shown in FIG. 3, the width of the vibration 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 increases (on the contrary, when the combustion amount is decreased, it becomes smaller).

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 is 0. As the concentration decreases, the vibration amplitude becomes smaller.

Based on the above findings, the present inventors obtained data as shown in FIG. 4 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 as shown in FIG. The moving average difference B of optical power, which is the difference between the upper moving average value 2 of the lower value and the lower value, is graduated. The horizontal axis indicates o, 96 in the exhaust gas.

The curve a r b + C shows the relationship between the exhaust gas O8% and the moving average difference for various combustion amounts of fuel, respectively.
Curve d shows the relationship between the moving average difference and the optimum air ratio of 08% for the exhaust gas at which incomplete combustion does not occur.

Therefore, for example, if the combustion amount is set to 6OA'/h and the moving average difference in optical power detected from the burner flame is B, then the corresponding ot% (c) is a reasonable O
,% (d) and deviation (e), and this deviation (e)
It can be read from the above figure that corresponds to the shift D of the moving average difference.

In addition, the present invention obtained the data shown in FIG. 5 for a type of burner having a cone-shaped flame holder.

The combustion control method according to the present invention utilizes data as shown in FIG. 4 or 5 above, and performs control to eliminate the deviation based on the deviation 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 the flow rate signal of the fuel supplied to the combustor and the 0.96 signal in the exhaust gas of the combustor, and determines that the α% is appropriate for the flow rate of the fuel. In a combustion control method in which the deviation is calculated when there is a deviation from O2%, and an output for eliminating the deviation is provided to the combustion air flow rate adjustment section, the O2% in the exhaust gas is
1% is detected from the flame of the combustor as optical power, and the moving average value is determined from the optical power, and the upper moving average value of the values above it and the upper moving average value of the values below it are determined. The difference between the upper and lower moving average values is calculated, and this is compared with the difference corresponding to the appropriate O2% for the fuel flow rate determined in advance. We have adopted methods to do so.

Optical power is detected from the flame formed in the active combustor and processed to provide a control output.

Therefore, without directly detecting 0.96 in exhaust gas, 0.9
6 controls are possible. As a result, a relatively inexpensive optical sensor can be used instead of the expensive zirconia 08 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.

To obtain the above control output, find the moving average value within a predetermined time from the optical power, find the upper moving average value of the values above the moving average value, and the upper moving average value of the values below the moving average value, and then The difference between the two moving average values is determined and compared with a predetermined reasonable difference of 01% to calculate the deviation.

Since the calculation is performed using the difference between the upper and lower moving average values in this way, an appropriate control output can be obtained, and therefore combustion control with excellent responsiveness can be performed.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 to 4 and FIG. 6.

FIG. 6 shows a heat treatment furnace using the combustion control method according to the present invention.

In FIG. 6, reference numeral 1 indicates a furnace main body, and the furnace, main body 1
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 chamber.

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 flow rate control valve 9. ing.

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 Ge photodiode, a Si 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 the optical signal from the optical sensor 15 into a digital signal, and an A/D converter 17 that integrates the electric signal from the converter 17 over a unit time to obtain a moving average value. Find the upper moving average value of the upper value and the upper moving average value of the lower value, then find the difference between the upper and lower moving average values, compare this with the difference related to the optimal 02% found in advance, and calculate the deviation. The combustion air flow rate corrector 19 provides an output to the combustion air flow rate control valve 9 to eliminate the problem.

The operation of this combustion air control section 16 will be explained based on the flowchart shown in FIG.

The optical power signal Xo from the A/D converter 17 is read into the combustion air flow rate corrector 19 (Step E), and then △ is calculated as the moving average X of all the signals per second (Steps 2 and 3).
.

That is, in step 2, the oldest data Xn of the n pieces of data measured in the past Δ per second is deleted, and the current signal Xo is input in its place. Then, in step 3, the moving average X is calculated by dividing the sum of n pieces of data from X□ to Xn by n.

Next, the difference A between the current optical power signal x0 and the moving average X is determined (step 4).

Then, depending on whether the sign of the difference A is 10 or -, XO
It is also determined whether the value is larger or smaller (step 5). When A is 10, find the upward moving average Y of the values above X (step 6.7), and when it is -, find the upward moving average 2 of the values smaller than X (step 8.9). .

Next, a moving average difference B, which is the difference between Y and 2, is determined (step 10).

The steps up to this point (steps 1 to 10) are the processing procedure for handling the optical power signal as a control signal.

In the next step, the output signal Q of the fuel flow meter 8 (for example, 6
01/h) (Step 11), select a curve (for example, a) corresponding to Q, and find the moving average difference C corresponding to (d)02%, which is optimal for Q (Step 12).
), and further, the deviation, which is the difference between the current moving average difference B and the above C, is determined (step 13).

After that, the control amount proportional to D and D so that D becomes 0
A control amount E is calculated by adding a control amount proportional to the integral value of (step 14).

The optimal air flow rate for the current fuel flow rate Q is determined, and the opening degree of the valve 9 in that case is compared with the current opening degree, and the air flow rate adjustment signal F is determined as to whether the valve 9 should be opened or closed more than the current degree and to what degree. F is determined by the combustion amount regulator 13 and output to the combustion air flow rate corrector 19 (step 15).

The corrector 19 obtains E and F and obtains an air flow rate adjustment signal G from the following correction equation (step 16), outputs this to the valve 9, and adjusts its opening degree (step 17).

In this formula, E is % data and is a value within the range of 0 to 100%.

When E=O~50%, the valve opening degree decreases, E=50~10
096 is considered as an increase in the valve opening degree, for example, E=409
When 6, G = 0.8F, when E = 6096, G =
1.2 F.

As a result, F obtained by calculation 1 is corrected by E to increase or decrease, and is output as G to the valve 9.

In this way, the furnace 1 is constantly operated in the optimum combustion state, and 02% of the exhaust gas (d) (FIG. 4) is discharged from the flue 3 to the outside of the furnace.

Note that 02% may temporarily increase due to new material being taken in and taken out from door 2, but that 02% may increase temporarily.
, 96 is immediately detected by the optical sensor 15, so that the control valve 9 is immediately adjusted to quickly return to the proper o96.

Although the above embodiment is intended for a heat treatment furnace, if the target is a boiler or the like, a pressure sensor may be provided in place of the temperature sensor 10 of the fuel control unit 11, and the combustion amount regulator 13 may be replaced with a steam pressure setting method. It's good.

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, O! is expensive as a sensor! It is possible to use a relatively inexpensive optical sensor (without a sensor), which is useful for combustion control in furnaces, gas turbines, etc.

In addition, when the combustor is a burner, the combustion state is detected in the furnace, so compared to the conventional method of detecting exhaust gas while passing it through the flue, even if there is a sudden change of 0.1% due to opening and closing of the furnace, it can be detected quickly. Moreover, even if air leaks from the gap in the flue, the detection results will not be affected. Therefore, it is also possible to manage the combustion of combustion devices that are open to the atmosphere (mold heating device, ladle preheating device, etc.).

Furthermore, since the output is calculated by calculating the difference between the running averages from the optical power, an appropriate control output can be obtained.

[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 0296 under a constant combustion amount, and Fig. 3 is a graph showing the relationship between the optical power and exhaust gas 0296 under a constant combustion amount. Figure 4 is a graph showing the relationship between optical power and time when changing O, L The figure is a graph similar to FIG. 4 for different types of burners, and FIG. 6 is a diagram of a control system for 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 section, 17: A/D converter, 19
:Combustion air flow compensator.

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. Find the moving average value, find the upper moving average value of the value above it, and the lower moving average value of the lower value, then find the difference between the upper and lower moving average values, and calculate this as appropriate for the fuel flow rate found in advance. O_2%
The above-mentioned combustion control method is characterized in that the deviation is calculated by comparing it with the difference corresponding to the above, and an output for eliminating the deviation is provided to the combustion air flow rate adjusting section.