JP3318244B2 - Combustion control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion control apparatus capable of avoiding a situation in which combustion continues while generating a large amount of carbon monoxide even if an oxygen sensor for detecting the oxygen concentration in exhaust gas fails. It is about.

[0002]

2. Description of the Related Art In recent years, there has been provided a so-called regenerative burner system capable of obtaining high energy efficiency by utilizing heat of exhaust gas for preheating combustion air (for example,
Nikkei Mechanical, 1997.3.31, No. 50
3). In other words, this regenerative burner system mixes air preheated to a high temperature with fuel gas and burns it.After combustion, the heat is temporarily absorbed by a heat storage unit in the process of exhausting exhaust gas in the furnace, and then the air supply At this time, the combustion air is preheated by passing the combustion air through the heat storage body, which has become high in temperature, so that the heat storage body is easily burnt in advance. As described above, the combustion control device using the regenerative burner system obtains high energy efficiency by effectively utilizing the heat in the furnace, which was discarded together with the exhaust gas in the case of a normal furnace, for combustion.
In this regenerative burner system, the one in which the air supply path and the exhaust path are formed by one burner is called a “single type regenerative burner system”, and the air supply path and the exhaust path are formed by two burners.
The one formed by switching between book burners is called a "twin-type regenerative burner system".

As described above, the combustion control apparatus using the regenerative burner system has high energy efficiency, but has the following disadvantages. Here, FIG. 6 is a graph showing the characteristics of the combustible region, and FIG. 7 is a graph showing the output characteristics of the oxygen sensor. In FIG. 7, the solid line shows the output characteristics of the oxygen sensor in a normal state, and the broken line shows the output characteristics in an abnormal state.
Shows the output characteristics. A is a constant sensor output at the time of abnormality. As shown in FIG. 6, when air at normal temperature is used as combustion air, if the air ratio (the ratio between the actual air amount and the theoretical air amount) is outside the range of about 0.8 to 2.0, Combustion cannot be continued. But,
When high-temperature air is used as combustion air, the combustible region is widened, and in particular, combustion can be continued with an air amount much smaller than the theoretical air amount. this is,
This means that carbon monoxide may be generated in large quantities and continue to burn. Therefore, an oxygen sensor that measures the oxygen concentration of the exhaust gas is provided in the exhaust passage and monitored, and the supply of combustion air is controlled so that the oxygen concentration is optimal, thereby preventing the generation of carbon monoxide. Means are provided for doing so. In addition, as a method of detecting an abnormality of the oxygen sensor, for example, it is also performed to diagnose an operation abnormality by causing the oxygen sensor to periodically detect a known oxygen concentration in the atmosphere (about 21%). I have.

An air-fuel ratio control technique using an oxygen sensor, which is not a regenerative burner system, is disclosed in, for example, Japanese Patent Application Laid-Open No. 7-12333.

[0005]

Since the conventional combustion control apparatus is configured as described above, if the failure is such that the entire output of the oxygen sensor drifts (abnormal state in FIG. 7), the sensor concerned Abnormalities can be detected by measuring the known oxygen concentration in the atmosphere and checking the output, but no abnormalities in the output are observed near this concentration (about 21%) even when the oxygen concentration in the atmosphere is measured. In the case of a failure in which the output becomes abnormal in another concentration range (at the time of abnormality in FIG. 7), there is a problem that the abnormality of the sensor cannot be detected. Therefore, the oxygen concentration in the exhaust gas during optimal combustion is 4 to 5%. Therefore, if a failure occurs in the oxygen sensor as shown in FIG. There is a problem that a high value is output and the combustion control works in a direction to reduce the amount of air to generate a large amount of carbon monoxide.

[0006] Further, if a system for immediately stopping combustion when an oxygen sensor failure is found is adopted,
There is also a problem that it cannot be used in a metal melting furnace or the like in which a great deal of damage occurs before restarting, and it has been desired to provide a combustion control device that can effectively cope with such a case.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem. When the oxygen sensor fails, the combustion is forcibly terminated, so that the combustion is continued while generating a large amount of carbon monoxide. It is an object of the present invention to obtain a combustion control device capable of realizing safe and optimal combustion while avoiding the above problem.

Another object of the present invention is to provide a combustion control device capable of continuing combustion while avoiding a situation in which a large amount of carbon monoxide is generated and burned even if an oxygen sensor fails. I do.

[0009]

A combustion control apparatus according to the present invention controls an air amount adjusting means based on a fuel amount sent to a combustor and a detection signal of an oxygen detector so as to obtain a good air-fuel ratio. And determination control means for determining abnormality of the oxygen detector based on a detection signal of the minimum air amount detection means, and shutting off fuel sent to the combustor to terminate combustion when the abnormality is detected. is there.

A combustion control device according to the present invention controls an air amount adjusting means based on a fuel amount sent to a combustor and a detection signal of an oxygen detector so as to obtain a good air-fuel ratio, and also controls a minimum air amount. Judgment control for judging abnormality of the oxygen detector based on a detection signal of the detection means and controlling the air amount adjustment means so that the amount of the air sent to the combustor becomes a predetermined amount at the time of the abnormality. Means.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a system schematic diagram showing a combustion control apparatus according to Embodiment 1 of the present invention, FIG. 2 is a sectional view showing an air amount adjusting means, FIG. 3 is a perspective view showing the configuration of a cam and a micro switch, and FIG. 5 is a flowchart showing a control example of the above. In FIG. 1, 1 is a combustion furnace (combustor), 2 is a fuel nozzle having a shut-off valve 3 for injecting fuel into the combustion furnace 1, 4 is an air supply path for supplying combustion air to the combustion furnace 1 by a blower 5, Reference numeral 6 denotes an exhaust passage for discharging exhaust gas from the combustion furnace 1 to the outside, reference numeral 7 denotes a regenerator (air preheating means) provided in the air supply passage 4 for preheating combustion air to a high temperature, and reference numeral 8 denotes an exhaust passage. It is a heat storage that takes away the heat of exhaust gas. Well-known and common techniques can be used for the heat storage bodies 7 and 8. Reference numeral 9 denotes a switching device for switching and using the roles of the heat storage elements 7 and 8 at predetermined intervals. That is, the air supply passage 4 is used in advance as an exhaust passage,
Switch device 9 at the stage where heat is taken from exhaust gas and stored.
Thus, the air is switched to the air supply path, and the heat of the heat storage body 7 can be used for preheating the combustion air. Therefore, the heat storage body 7 and the heat storage body 8 can alternately absorb heat from exhaust gas and release heat to combustion air by the switching device 9.

Reference numeral 10 denotes an oxygen sensor (oxygen detector) provided in the exhaust passage 6 for detecting oxygen concentration in exhaust gas, and 11 denotes a butterfly valve (air amount adjusting means) provided in the air supply passage 4.
This is an air amount adjusting means for adjusting the amount of combustion air by controlling the opening of 12. Reference numeral 13 denotes an oxygen sensor output signal (detection signal) which is an output signal from the oxygen sensor 10;
Reference numeral 4 denotes a fuel amount control signal for controlling the opening of the shut-off valve 3, and reference numeral 15 denotes a butterfly valve opening / closing instruction signal for controlling the air amount adjusting means 11 and controlling the opening of the butterfly valve 12. Reference numeral 16 denotes an air amount adjusting means 1 when the butterfly valve 12 operates in the closing direction and the opening degree of the butterfly valve 12 reaches a preset limit value (for example, when the butterfly valve 12 is fully closed).
1 is a close-side limit signal (detection signal) output from the control unit 1.

A reference numeral 17 outputs a fuel amount control signal 14 to operate the shut-off valve 3 and outputs a butterfly valve opening / closing instruction signal 15 in response to the closing-side limit signal 16 and the oxygen sensor output signal 13, which will be described later. By operating the motor and the train wheel 22 and adjusting the opening of the butterfly valve 12,
It is a controller (judgment control means) that controls combustion optimally. In the controller 17, the oxygen concentration of the exhaust gas when the optimal combustion is performed is set in advance.
Further, the controller 17 is configured to optimally control the combustion when the oxygen sensor 10 determines that the oxygen sensor 10 has failed based on the oxygen sensor output signal 13 and to output a predetermined alarm signal.

Although illustrations are omitted, other components normally required for the combustion apparatus include, for example, an exhaust temperature sensor for detecting the temperature of exhaust gas, a high voltage generator for ignition, and the like. I have.

Next, the air amount adjusting means 11 will be described in more detail. 2 and 3, reference numeral 18 is provided in the air supply passage 4 by a pipe connection screw 18a.
And a valve shaft (air amount adjusting means) 19 having the butterfly valve 12 is rotatably provided. Reference numeral 20 denotes an actuator shaft (air amount adjusting means) which is connected to the valve shaft 19 by a joint 21 and is rotated by a motor and a train (air amount adjusting means) 22. Reference numeral 20a denotes an actuator shaft head. Reference numeral 23 denotes a cam (minimum air amount detecting means) for outputting the above-mentioned closing limit signal 16 by operating a micro switch (minimum air amount detecting means) 25 when the butterfly valve 12 is fully closed, for example. The cam 23 is fixed to the actuator shaft head 20a so as to be freely positioned by an adjusting screw 24 inserted into the adjusting hole 23a, and can be arbitrarily set by a user to realize safe and optimal combustion. In addition,
The cam 23 can be formed, for example, by sheet metal bending. 25a turns on the micro switch 25
The turning-off lever 25b is a roller rotatably supported by the lever 25a and in contact with the cam 23. The actuator shaft 20, the cam 23, the microswitch 25, and the like are provided in a case 26.

Next, the operation will be described. In FIG. 1, it is assumed that the heat storage body 7 has sufficiently absorbed heat from the exhaust gas by the switching device 9 described above. The combustion air generated by the blower 5 is preheated by the regenerator 7 and discharged into the combustion furnace 1 as high-temperature preheated air. The high-temperature preheated air and the fuel gas discharged from the fuel nozzle 2 are mixed and burned in the combustion furnace 1. Then, the exhaust gas in the combustion furnace 1 is absorbed by the heat storage body 8 in the exhaust path 6 and then discharged to the outside. At that time, the oxygen concentration of the exhaust gas is measured by the oxygen sensor 10, and the oxygen sensor output signal 13 is input to the controller 17, so that the oxygen concentration is obtained. Since the controller 17 presets the oxygen concentration of the exhaust gas at the time of performing the optimal combustion, the controller 17 compares this set value with the actually measured value from the oxygen sensor 10 and determines the actual measured value as the set value. A predetermined butterfly valve opening / closing instruction signal 15 is output to the air amount adjusting means 11 so that the amount of combustion air is controlled so as to coincide with the above. Then, it is assumed that a failure occurs in the oxygen sensor 10 as shown in FIG. At this time, when the oxygen concentration falls below a certain concentration, the oxygen sensor 10 continues to output the constant value A as the actually measured value, so that the oxygen sensor 10 outputs a concentration higher than the actual oxygen concentration. Therefore, the controller 17
Determines that the amount of combustion air being supplied is excessive,
In order to bring the measured value A closer to the set value, the butterfly valve 1
2 outputs a butterfly valve opening / closing instruction signal 15 so that 2 operates in the closing direction. When the butterfly valve 12 operates in the closing direction and is fully closed, the cam 23 turns on the microswitch 25 and the closing limit signal 16 is output to the controller 17.

Thereafter, the controller 17 performs the control shown in FIG. That is, if the butterfly valve 12 is fully closed in step ST30, the process proceeds to the next step ST33. If the butterfly valve 12 is fully closed for a predetermined time in this step ST33, it is determined that the oxygen sensor 10 has failed in step ST34. In step ST35, an alarm signal is output, and in step ST36, the fuel shutoff valve 3 is closed to forcibly terminate combustion. Thereby, incomplete combustion due to insufficient supply of combustion air can be prevented. On the other hand, if the butterfly valve 12 is not fully closed in step ST30 or if it is not fully closed for a predetermined time in step ST33, it is determined in step ST31 that the oxygen sensor 10 is normal, and step ST3 is performed.
At 2, normal combustion control is performed. In addition,
As long as the combustion is continued, the process returns to step ST30 to continue the combustion control. Therefore, even if the oxygen sensor 10 fails, it is possible to avoid a situation in which combustion is continued while generating a large amount of carbon monoxide, and safe and optimal combustion is realized.

As described above, according to the first embodiment, when the oxygen sensor 10 fails, the combustion is forcibly terminated, so that the situation of continuing the combustion while generating a large amount of carbon monoxide can be avoided. The effect that safe and optimal combustion can be realized is obtained.

In the first embodiment, the description has been made assuming that the regenerators 7 and 8 are used as the preheating means for the combustion air. However, the present invention is not limited to this. For example, the preheating means may be directly heated by another combustion means. It can be preheated. Also, as means for adjusting the supply amount of combustion air, it has been described that the butterfly valve 12 is provided in the air supply passage 4, but the present invention is not limited to this. For example, a rotational speed variable control system is used for the blower 5. In addition, the generated air volume itself can be adjusted. Further, the means for detecting the supply amount of the combustion air has been described as using the cam 23 and the micro switch 25. However, the present invention is not limited to this. For example, a potentiometer whose resistance value changes in proportion to the valve opening may be used. By using this, the opening of the butterfly valve 12 can be continuously detected. In addition, when using a variable rotation speed control system as the blower 5, the minimum rotation speed can be detected by voltage or frequency. Further, a flow meter can be provided in the air supply passage 4 to directly measure the air amount. Also, the combustion control device has been described as being used for a so-called single type regenerative burner, but the present invention is not limited to this, and may be used for a so-called twin type regenerative burner.

Embodiment 2 In the first embodiment, when the controller 17 determines that the oxygen sensor 10 has failed, the shutoff valve 3 is closed to forcibly terminate the combustion. However, in the second embodiment, the combustion is not forcibly terminated. , Only the feedback control by the oxygen sensor 10 is stopped,
The control is performed so that the opening of the butterfly valve 12 is kept constant and the combustion is continued.

FIG. 5 is a flowchart showing a control example of the controller of the combustion control device according to the second embodiment of the present invention. Since the configuration is almost the same as that of the first embodiment, the same components are denoted by the same reference numerals, and only different portions will be described. An opening degree of the butterfly valve 12 is determined in advance so that optimal combustion is obtained when the feedback control by the oxygen sensor 10 is not performed, and when the opening degree is reached, the opening operation of the butterfly valve 12 is stopped. The second cam and the second microswitch are provided on the actuator shaft head 20a. That is, the cam 23 and the micro switch 25 shown in the first embodiment are provided to detect the fully closed state of the butterfly valve 12, but these are not shown in the second drawing.
Of the cam and the second micro switch are the butterfly valve 12
Is provided to detect when a predetermined opening degree is reached. The detection signal of the second microswitch (not shown) is configured to be input to the controller 17.

Next, the operation will be described with reference to FIGS. 1 to 3 and FIG.
It will be described based on. Step ST30 to step S
The operation up to T35 is the same as in the first embodiment, and a description thereof will not be repeated. If the controller 17 determines that the oxygen sensor 10 has failed, the controller 17 proceeds to step ST3.
At 7, the feedback control by the oxygen sensor 10 is stopped. Then, in step ST38, the butterfly valve 12 is operated in the opening direction, and the opening is fixed to a previously determined opening degree so that optimal combustion is obtained when the feedback control by the oxygen sensor 10 is not performed. At this time, the controller 17 determines whether or not the butterfly valve 12 has reached a predetermined opening based on a detection signal from a second microswitch (not shown). After the opening of the butterfly valve 12 is fixed, the controller 17 continues the combustion as it is. This makes it impossible to perform optimal combustion as in the case where feedback control is performed using the normal oxygen sensor 10, but continues combustion for the time being while preventing incomplete combustion due to the use of the failed oxygen sensor 10. be able to.

As described above, according to the second embodiment, even if the oxygen sensor 10 fails, the combustion can be continued for the time being while avoiding the situation of burning while generating a large amount of carbon monoxide. The effect that can be obtained is obtained. For example, in a metal melting furnace or the like, if the combustion is stopped, the molten metal solidifies, and the damage increases before the melting furnace is operated again, so it is important to continue the combustion. . Therefore, the present combustion control device is particularly effective when used in such a system.

In the second embodiment, the second cam (not shown) and the second microswitch (not shown) are used as means for detecting the opening of the butterfly valve 12, that is, the supply amount of combustion air. However, the present invention is not limited to this. For example, the opening of the butterfly valve 12 can be continuously detected by using a potentiometer whose resistance value changes in proportion to the valve opening.

[0025]

As described above, according to the present invention, the air amount adjusting means is controlled based on the amount of fuel sent to the combustor and the detection signal of the oxygen detector so as to obtain a good air-fuel ratio. A determination control unit that determines an abnormality of the oxygen detector based on a detection signal of the minimum air amount detection unit, and shuts off fuel sent to the combustor to terminate combustion when the abnormality is detected. By forcibly terminating the combustion when the oxygen detector fails, it is possible to avoid a situation in which the combustion is continued while generating a large amount of carbon monoxide, and there is an effect that safe and optimal combustion can be realized.

According to the present invention, the air amount adjusting means is controlled based on the fuel amount sent to the combustor and the detection signal of the oxygen detector so as to obtain a good air-fuel ratio, and the minimum air amount detecting means is controlled. A determination control unit that determines an abnormality of the oxygen detector based on the detection signal and controls the air amount adjustment unit so that the amount of the air sent to the combustor becomes a predetermined amount at the time of the abnormality. With this configuration, even if the oxygen detector fails, there is an effect that the combustion can be continued for the time being while avoiding a situation in which a large amount of carbon monoxide is generated and burned. For example, in a metal melting furnace or the like, if the combustion is stopped, the molten metal solidifies and the damage is increased before the melting furnace is operated again, so it is important to continue the combustion. Therefore, it is particularly effective when used in such a system.

[Brief description of the drawings]

FIG. 1 is a system schematic diagram showing a combustion control device according to Embodiment 1 of the present invention.

FIG. 2 is a sectional view showing an air amount adjusting means.

FIG. 3 is a perspective view showing a configuration of a cam and a micro switch.

FIG. 4 is a flowchart illustrating a control example of a controller.

FIG. 5 is a flowchart showing a control example of a controller of a combustion control device according to Embodiment 2 of the present invention.

FIG. 6 is a graph showing characteristics of a combustible region.

FIG. 7 is a graph showing output characteristics of the oxygen sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion furnace (combustor) 7 Heat storage body (air preheating means) 10 Oxygen sensor (oxygen detector) 11 Air amount adjusting means 12 Butterfly valve (air amount adjusting means) 13 Oxygen sensor output signal (detection signal) 16 Close limit Signal (detection signal) 17 Controller (judgment control means) 19 Valve shaft (air amount adjustment means) 20 Actuator shaft (air amount adjustment means) 22 Motor and wheel train (air amount adjustment means) 23 Cam (minimum air amount detection means) 25 Micro switch (minimum air amount detection means)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F23N 5/24 108

Claims (2)

(57) [Claims] 1. An air amount adjusting means for adjusting an amount of air sent to a combustor, an air preheating means for preheating the air sent to the combustor, and a minimum amount of air sent to the combustor. In a combustion control device including a minimum air amount detecting means for detecting that the amount of oxygen has reached and an oxygen detector for detecting the concentration of oxygen contained in exhaust gas from the combustor, the amount of fuel sent to the combustor The air amount adjusting means is controlled so as to obtain a good air-fuel ratio based on the detection signal of the oxygen detector, and abnormality of the oxygen detector is determined based on the detection signal of the minimum air amount detecting means. A combustion control device comprising: a determination control unit that shuts off fuel sent to the combustor and terminates combustion when the abnormality occurs. 2. An air amount adjusting means for adjusting an amount of air sent to the combustor, an air preheating means for preheating the air sent to the combustor, and a minimum amount of air sent to the combustor. In a combustion control device including a minimum air amount detecting means for detecting that the amount of oxygen has reached and an oxygen detector for detecting the concentration of oxygen contained in exhaust gas from the combustor, the amount of fuel sent to the combustor The air amount adjusting means is controlled so as to obtain a good air-fuel ratio based on the detection signal of the oxygen detector, and abnormality of the oxygen detector is determined based on the detection signal of the minimum air amount detecting means. A combustion control device comprising: a determination control unit that controls the air amount adjustment unit so that the amount of the air sent to the combustor at the time of the abnormality is a predetermined amount.