JPS63105315A - Combustion control method - Google Patents

Abstract

PURPOSE:To enable the control to be performed with a superior response by a method wherein a mean amplitude of an optical power signal within a desired period of time is calculated from a flame of a combustion unit and an output for eliminating a difference in respect to the mean amplitude corresponding to a suitable O2% to a fuel flow rate is carried out. CONSTITUTION:An optical signal from an optical sensor 15 is read into a combustion air flow rate corrector 10 through A/D converter 17 in a combustion air control part 16. an upper peak value Y and a lower peak value Z are detected from all signals with DELTAt second, each of mean values Y and Z is calculated to attain a mean amplitude A. Then, a mean amplitude B in respect to the most suitable O2% is calculated in reference to a curve line corresponding to a flow rate signal Q of a fuel flow meter. Then, a difference C between the mean amplitudes A and B is calculated, and a control amount D added with a control amount proportional to a multiplied value of a controlled amount proportional to C and C is calculated in such a way as C becomes O. In case that the most suitable air flow rate in respect to a present fuel flow rate Q is to be calculated, an air flow rate adjusting signal E is calculated by a combustion amount adjustment unit 13, and D and B are calculated by a combustion air flow rate corrector 10, an air flow rate adjusting signal F is calculated and outputted to a valve 9 and its degree of opening is adjusted.

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. 5g-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 a flame, determine the temperature distribution of the flame from this, and compare this with the temperature distribution of 0<flame under optimal combustion conditions. This output outputs a control signal that attempts to control the shape of the flame in a constant manner.However, the former only controls the ON/OFF state of combustion, and does not control the smoldering flame itself in the furnace. It's not something you do. 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 0□ sensor in the flue to measure 0% of the exhaust gas passing through the flue, and using this 0% as an indicator, 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 so that the

Regarding the use of optical power to detect the combustion state, see JP-A-59-137719 and JP-A-59-109715.
No. 59712227 and 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 in the structure between the combustion chamber outlet and the measurement part, the 00□ concentration inside the combustion chamber will increase. I mistakenly think that it is.

■ Due to the gas flow from the baking 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 02 sensor, use the above JP-A-59
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 0□ concentration in exhaust gas) and is an important point in combustion management. ing.

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 02'Ijk degree 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 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 constantly oscillates as shown in Figure 3. Shows a sawtooth wave shape. The optical power signal level shows a mountain-shaped change as shown in Fig. 2, and in the region (a) where the 02 concentration is higher than the peak value, the optical power signal level decreases as the 02 concentration increases, and the peak value In the region (b) where the 02 concentration is lower than the value, the optical power signal level also decreases as the 0□ 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 increases as a whole, and conversely, when the combustion amount is decreased, it becomes smaller.

Furthermore, when looking at a type of burner with a cone-shaped flame holder, its light intensity changes as shown by curve H in FIG. 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 Figure 4 regarding a type of burner that holds flame by swirling force.◇ In this figure, the vertical axis represents the value related to the amplitude of optical power. As shown in FIG. 3(D), the average Y of the upper peak value Y and the lower peak value Z within the unit time Δ of the optical power signal
The average amplitude A, which is the difference from the average Z of , is calibrated. The horizontal axis shows 02% in the exhaust gas.

Curves a, b, and c are exhaust gas 0 for various combustion amounts of fuel.
2% and the average amplitude, and the curve d shows the relationship between the average amplitude and the exhaust gas O2% at the optimum air ratio at which the aforementioned incomplete combustion does not occur.

Therefore, for example, the combustion amount is 607! If the average amplitude of the optical power signal detected from the burner flame is set to It can be seen from the above figure that this deviation (E) corresponds to the deviation C of the average amplitude.

Further, the present inventors obtained data shown in FIG. 5 regarding 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 FIG. 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 a reasonable 02% for the combustion flow rate. %, the deviation is calculated, and an optical power signal is detected from the flame of the combustor. At the same time, the upper peak value and the lower peak value within a predetermined time are detected from there, and then the average of the upper peak value and the lower peak value is calculated, and the average amplitude is calculated as the difference between them. A reasonable zero for the fuel flow rate whose average amplitude was determined in advance.
A method is adopted in which the deviation is calculated by comparing it with the average amplitude corresponding to 2%, and an output to eliminate the deviation is sent to the combustion air flow rate regulator to make the 02% in the exhaust gas appropriate. ing.

An optical power signal is detected from the flame formed in the working combustor, and the optical power signal is processed to obtain 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 02 sensor.

In addition, when the combustor is a burner, the combustion state is detected in the furnace, so compared to the conventional method of detecting in the flue, combustion can be controlled without causing a time lag. .

To obtain the above control output, detect the upper peak value and lower peak value within a predetermined time from the optical power signal, calculate the average of the upper peak value and lower peak value in the next step, and calculate the average of the upper peak value and lower peak value. The average amplitude that is the difference is determined, and the read-back average amplitude is compared with the average amplitude corresponding to a reasonable 02% of the fuel flow rate determined in advance to calculate the deviation.

In this way, since the calculation is performed using the average amplitude of the optical power signal, 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 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 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 an amount of 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.

This 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 sensor 15 that receives the signal, generates a rust control signal, and outputs it to the combustion air flow control valve 9. A control section 16 is provided.

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 the converter 1
Detect the upper peak value and lower peak value within a unit time from the electrical signal from 7, then calculate the average of each of the upper peak value and lower peak value, calculate the average amplitude that is the difference between them, and then The average amplitude of the hind limbs is compared with the average amplitude corresponding to an appropriate O2% for the fuel flow rate determined in advance, a deviation is calculated, and an output to eliminate the deviation is sent to the combustion air flow control valve 9. Air flow compensator 1
It consists of 9.

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

Optical power signal X from A/D converter 17. is loaded into the combustion air flow rate corrector 19 (step 1), and then the upper peak value Y and the lower peak value Z are detected from the entire signal of Δ in seconds (step 2.5), and the respective averages Y and Z are obtained. (Step 3.4.6.7).

Then, the average amplitude A is determined (step 8).

The next step is to read the flow rate signal Q of the fuel flow meter (
Step 9) Select a curve corresponding to Q from the data in FIG. 4, and find the average amplitude for 02% that is optimal for Q (Step 10).

For example, if Q=6 (Hl/h), select curve a, and from the intersection of a and d, 02% (d) is optimal, and the average amplitude at that time is B.

Then, a deviation C, which is the difference between the current average amplitude A and the above B, is determined (step 11).

After that, the control amount proportional to C and C so that C becomes O
A control amount is calculated by adding a control amount proportional to the integral value of (step 12).

The optimum 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 E is determined as to whether the valve 9 should be opened or closed more than the current degree and to what degree. E is determined by the combustion amount regulator 13 and output to the combustion air flow rate corrector 19 (step 13).

The corrector 19 obtains E and obtains an air flow rate adjustment signal F from the following correction equation (step 14), outputs this to the valve 9, and adjusts its opening degree (step 15).

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

When D=O~50%, the valve opening degree decreases, D=50~10
When it is 0%, the valve opening degree is increased. For example, when D = 40%, F = 0.8E, and when D = 60%, F = 1.2.
It becomes E.

As a result, the calculated E is corrected to increase or decrease by D and is output as F to the valve 9.

By repeating such operations, the air flow control signal from the combustion amount controller 13 is corrected and the opening degree of the air flow control valve 9 is adjusted.

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.
Since a 2% change is immediately detected by the optical sensor 15, the control valve 9 is immediately adjusted to quickly return to the appropriate 0%.

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 combustion control section 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 an optical power signal from a flame formed in a combustor such as a burner, and processes this optical power signal to obtain a control output, so that 0.2% of exhaust gas can be directly detected. 02% control is possible without doing anything. Therefore,
Rather than an expensive 0° sensor, a relatively inexpensive optical sensor can be used as a sensor, which is beneficial for combustion control in furnaces, gas turbines, and the like.

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 0.2% due to opening and closing of the furnace, it can be detected quickly. 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 (type devices, ladle preheating devices, etc.).

Furthermore, since the control output is calculated using the upper and lower peak values of the optical power signal, the storage capacity is also small, and therefore control can be performed easily.

[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 the optical power signal and exhaust gas O2% under a constant combustion amount, and Fig. 3
The figure is a graph showing the relationship between the optical power signal and time when the combustion amount is kept constant and 02% is varied. Figure 4 shows the relationship between the average amplitude of the optical power signal and 02%, with the combustion amount as a parameter. The graphs shown in FIG. 5 are similar to FIG. 4 for different types of burners, and FIG. 6 is a control system diagram 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 unit, 17: A/D converter, 19:
Combustion air flow compensator. Applicant: Toyota Motor Corporation Representative: Ichikawa Burial (1 other person) Figure 1 Figure 2 pF η' 02 (%) Figure 3 Figure 4

Claims (1)

[Claims] When a flow rate signal of fuel supplied to a combustor and an O_2% signal in the exhaust gas of the combustor are obtained, and the O_2% deviates from an appropriate O_2% for the combustion flow rate, In a combustion control method that calculates the deviation and outputs an output for eliminating the deviation to the combustion air flow rate adjusting section, an optical power signal is detected from the flame of the combustor and within a predetermined time from there. The upper peak value and the lower peak value are detected, and then the average of the upper peak value and the lower peak value is calculated to obtain the average amplitude, which is the difference between them, and then the average amplitude is determined in advance. calculating a deviation compared to an average amplitude corresponding to a reasonable O_2% for the fuel flow;
The combustion control method described above is characterized in that an output for eliminating the deviation is applied to the combustion air flow rate adjusting section to make O_2% in the exhaust gas appropriate.