JP3146975B2 - Combustion control method - 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 method for a furnace or the like, and more particularly to a combustion control method using an O ₂ concentration detector.

[0002]

2. Description of the Related Art Conventionally, a combustion control method includes a method in which a solenoid valve provided in a fuel system and a solenoid valve provided in an air supply system are turned on and off to turn on and off fuel and air supply, and a fuel system and an air supply system. There is a method in which the respective supply amounts are controlled by the respective pressure control valves, the control of both pressure control valves is related, and a method in which a flow control valve is used instead of the pressure control valve.

[0003]

However, in any of the methods, if the control accuracy is to be improved, the apparatus becomes complicated and the cost increases. An attempt to raise accuracy of the control, but it is preferable to control the air ratio based on the O ₂ concentration in the exhaust gas, the conventional sensor has high cost, the sensor is unable to self-diagnose it be degradation or failure, reliability There is a problem such as a problem with the sex. The object of the present invention is to achieve low cost,
An object of the present invention is to provide a highly reliable combustion control method capable of controlling the air ratio based on the O ₂ concentration.

[0004]

The method of the present invention for achieving the above object is as follows. (1) by the current value signal from the該検Deco the O ₂ concentration may be provided detectable detectors by the output current value furnace or flue detects O ₂ concentration, based on the detected O ₂ concentration was When controlling the air ratio by using
Or combustion control method der the failure of the combustion device for self-diagnosis
Thus, the first self-diagnosis determines whether combustion is OFF.
Step: if it is determined in the first step that the combustion is not OFF,
₍₂₎ Determine whether the output current value of the sensor is larger than a predetermined value B
Second step: In the second step, the output current value of the O ₂ sensor exceeds a predetermined value B.
A third step of instructing a decrease in air supply when it is determined to be large; an output current value of the O ₂ sensor being equal to or less than a predetermined value B in the second step
A fourth step of instructing an increase in air supply when it is determined that the output current value of the O ₂ sensor is smaller than B after the fourth step.
A fifth step of determining whether the output current value of the O ₂ sensor is equal to or less than a predetermined value C in the fifth step;
The sixth step for instructing a system down when it is determined that
Extent; O ₂ sensor when the combustion is determined to OFF in the first step
The output current value of the sensor is larger than a predetermined value A which is larger than a predetermined value B
The output current value of the O ₂ sensor exceeds a predetermined value A in the seventh step.
An eighth step of instructing continuation of operation when it is determined to be large;
And, in the seventh step, the output current value of the O ₂ sensor is predetermined.
A to O ₂ sensor is deteriorated when it is determined that less value A
Display alarm and instruct system down if necessary
A combustion control method including a ninth step.

In the combustion control method (1 ), since the O ₂ concentration is detected based on the output current value, the cost can be reduced, the size can be reduced, the responsiveness can be improved, and the reliability can be improved. In addition, the self-diagnosis function allows sensor deterioration,
The self-diagnosis of the failure of the combustion device can be performed, and the reliability is improved.

[0006]

Embodiments of the present invention will be described below. FIG. 1 shows an example of an apparatus to which the method according to the embodiment of the present invention is applied. In FIG. 1, a furnace 11 includes a burner 1
3 is provided, and the burner 13 has fuel (for example,
A supply system 14 for supplying gaseous fuel) and a supply system 15 for supplying air are connected. Reference numeral 12 indicates a flame. Air supply system 15
Has a blower 16 and a control valve 17 provided in a passage connecting the blower 16 and the burner 13, and the opening of the control valve 17 is controlled by a signal from a control box 18. An O ₂ concentration detector 20 is provided in the furnace or the flue 19. The output of the detector 20 is sent to the control box 18. The control box 18 calculates the required supply amount of fuel based on the output of the detector 20, and sends the signal to the control motor of the control valve 17. , The opening of the control valve 17 is controlled so that the supplied air amount becomes the required supplied air amount.

The detector 20 comprises, for example, a detector (O ₂ sensor) of the type which detects the O ₂ concentration based on the output current value. In this case, the detector 20 has a structure shown in FIG. Detector 20
Is a zirconia solid electrolyte 21 formed into a test tube mold,
Platinum electrodes 22 and 23 provided on the inner and outer surfaces of the zirconia solid electrolyte 21; a diffusion-controlling layer 24 made of a ceramic coating provided on the outer surface of the outer electrode 23;
(A part consisting of 1, 22, 23, 24)
Heater maintained at 0 ° C or higher (for example, ceramic heater)
25, and a protective cover 26 provided outside the element. Reference numeral 27 denotes a heater lead, reference numeral 28 denotes an inner electrode lead, and reference numeral 29 denotes an outer electrode lead.

The principle of detecting the O ₂ concentration of the detector 20 which detects the O ₂ concentration based on the output current value will be described with reference to FIGS. A certain value (for example, 650 ° C)
When a voltage is applied to the zirconia solid electrolyte 21 under the above temperature conditions and a current is forced to flow, O ²⁻ ions move through the solid electrolyte 21 as shown in FIG. This O ²⁻ ion transfer amount is detected as a current value and linearly increases with an increase in applied voltage. However, when the diffusion controlling layer 24 is provided on the cathode side to control the diffusion of oxygen molecules, the output current value is saturated at a constant value even when the applied voltage is increased (see FIG. 6). Then, in the region where the output current value is saturated, when the applied voltage is constant (V ₀ ), the O ₂ concentration and the saturated output current value have a substantially linear relationship (see FIG. 6).

The output characteristic of the detector 20 as shown in FIG. 2 is as shown in FIG. 3, similarly to the relationship between the element of FIG. 5 and FIG. When the applied voltage is changed, stable saturation current characteristics can be obtained over a wide range of air-fuel ratios. FIG. 4 shows the output current characteristics at an element temperature of 700 ° C. and an applied voltage of 0.7 V, and almost linear characteristics are obtained in an air-rich combustion atmosphere.

Generally, in the case of furnace combustion in a burner, combustion is not performed in a gas-rich atmosphere, but in an air-rich atmosphere. In this case, O ₂ is burned with a surplus of at least about 0.5% to at most about 21%. Therefore, it is within the operating range of the detector 20. In this case, by performing feedback control of the O ₂ concentration in the furnace detected by the detector 20 to the control motor of the control valve 17, low O ₂ combustion near the unburned portion generation limit O ₂ concentration becomes possible.

In the combustion control method according to the embodiment of the present invention, which is carried out using the above-described apparatus, a detector 20 capable of detecting the O ₂ concentration based on an output current value is provided in a furnace or a flue. and detecting the O ₂ concentration with a current value signal, and controlling the air ratio based on the detected O ₂ concentrations were (ratio of supply air to the theoretical amount of air required in the case of complete combustion), from Become. In this combustion control method, for example, a lean mixture sensor used in an automobile or an improved version thereof can be used as the detector 20 to be used. Since there is no problem in terms of space at the time of installation, and the current output type, the responsiveness is high and the response reliability of the control is improved.

For example, the HI-
When LO-OFF combustion is performed (HI and L at the set temperature)
An example of a control method for switching O and switching between LO and OFF at the set temperature + α (α is a small positive value) will be described below. Here, HI indicates high combustion, LO indicates low combustion, and OFF indicates main fuel cut. (1) Cooling furnace startup: HI or LO combustion. The control motor is fully open. The detector 20 does not operate until a certain temperature or time. Then, at detector 20 (detector 2
Meaning by sending an output signal of 0 to the control box and sending an operation signal in the control box to the control motor,
The same applies to the following.) Control the air (supply) flow rate. (2) Switching from HI to LO: Return to LO combustion while keeping the control motor constant (CO due to incomplete combustion)
). Thereafter, the air flow rate is controlled by the detector 20. (3) Switching from LO to OFF: shut off the main fuel. Purge and purge with appropriate amount of air using the control motor. (4) Switching from OFF to LO: After the control motor is fully opened, LO combustion is ignited and LO combustion is performed (to prevent CO from being generated due to incomplete combustion). Thereafter, the air flow rate is controlled by the detector 20. (5) Switching from LO to HI: After the control motor is fully opened, HI combustion is ignited and HI combustion is performed (to prevent CO from being generated due to incomplete combustion). Thereafter, the air flow rate is controlled by the detector 20. By the above combustion, low O ₂ combustion and suppression of emission of CO into the atmosphere can be achieved.

FIG. 7 shows a combustion control method in which a self-diagnosis (self-diagnosis such as deterioration of the detector 20 and malfunction of the combustion device) can be further performed in the air ratio control step in the combustion control method. Is shown. The control routine of FIG. 7 is stored in the control box 18 (for example, a computer).

The routine of FIG. 7 is interrupted at intervals of a predetermined time ΔT (where ΔT is about 30 seconds or less). In step 101, it is determined whether or not combustion is OFF (if NO, combustion is HI or LO). (As another method, a method of forcibly blowing air to the sensor or a method of extracting the sensor from the flue and making it come into contact with the atmosphere may be adopted.) When the combustion is turned off and the blower is turned on. In this case, the furnace or the flue is air-rich (large O ₂ concentration). In the case of HI or LO, the inside of the furnace or the flue has a low O ₂ concentration.

In the case of HI or LO, step 102
And the output signal value of the detector (O ₂ sensor) is larger than the predetermined value B (for example, 3 mA) (the O ₂ amount is larger).
Is determined (O ₂ amount is small). If the value is large, it means that the air supply amount is too large. Therefore, the process proceeds to step 103, instructs to reduce the air supply, rotates the control valve to the closing side, and then proceeds to the END step. If the air supply amount is small, it means that the air supply amount is too small. Therefore, the routine proceeds to step 104, where an instruction to increase the air supply amount is issued, and the control valve is rotated to the open side. Next, the process proceeds from step 104 to step 105, where it is determined whether or not the output current value of the detector 20 is equal to or smaller than a set lower limit value C (a value smaller than B). If it is larger than the set lower limit value C, the process directly proceeds to the END step. However, if the output current value of the detector 20 is equal to or less than the set lower limit value C in step 105, it means that the air supply does not increase beyond the set lower limit value even if the increase in the air supply is instructed in step 104. This means that some failure (for example, a blower failure) has occurred in the system, and the process proceeds to step 106 to shut down the system (stop the combustion of the furnace). That is, passing through the route in step 106 means that the occurrence of an abnormality in the system has been self-detected, and that the self-diagnosis has been made.

If the combustion is OFF and the blower is ON in step 101, the air in the furnace or the flue is air-rich, and the routine proceeds to step 107, where the detector 20 (O
_It is determined whether or not the output signal of the _two sensors is larger than a predetermined value A (a value larger than the above B, for example, 35 mA). If the main fuel is OFF and air is supplied, the furnace or the flue is in an air-rich state, and if the detector 20 is normal, it naturally outputs a value equal to or larger than the predetermined value A.
If it is determined at 07 that the value is larger than A, the process proceeds to step 108 to continue the operation, and proceeds to the END step.

However, if it is determined in step 107 that the value is equal to or less than A, the output signal of the detector 20 outputs a large output corresponding to the O ₂ amount irrespective of whether the furnace or the flue is in an air-rich state. This means that the detector 20 itself has failed due to sensor deterioration or the like. Therefore, in that case, step 10
Go to 9 and issue a sensor deterioration alarm (alarm etc.)
Also, if necessary, the system will be shut down (furnace combustion stopped). However, since there is little need to shut down the system immediately after the detector 20 has deteriorated, the system may be shut down after an appropriate time has elapsed after a sensor deterioration alarm (alarm etc.) is issued, or the furnace operation may be stopped. In some cases, only the detector 20 may be replaced while continuing.
In any case, passing through the route of step 109 means that an abnormality has occurred in the detector 20 and the detector 2
Self-diagnosis of deterioration (or abnormality) of 0 (O ₂ sensor).

By providing such a self-diagnosis function, the reliability of the operation of the combustion control method according to the embodiment of the present invention is enhanced. Also, even if an abnormality occurs, it is possible to determine whether the blower is abnormal or the sensor is abnormal, so that appropriate measures can be taken. Furthermore, there is an advantage that these self-diagnosis are always performed during operation of the furnace.

[0019]

According to the combustion control method of the first aspect, since the O ₂ concentration is detected based on the output current value, the cost can be reduced, the size can be reduced, the response can be improved, and the reliability can be improved. In addition, the self-diagnosis function allows self-diagnosis of sensor deterioration and combustion device failure, thereby improving reliability.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an apparatus for performing a combustion control method according to an embodiment of the present invention.

FIG. 2 is a sectional view of a detector used in the combustion control method according to the embodiment of the present invention.

FIG. 3 is a graph showing a relationship between an output current (mA) and an applied voltage (V) by the detector of FIG. 2;

FIG. 4 is a graph showing a relationship between an output current (mA) of the detector shown in FIG. 2 and an air-fuel ratio (air / fuel).

FIG. 5 is a cross-sectional view near a solid electrolyte showing the principle of detecting the oxygen concentration of a detector used in an embodiment of the present invention.

FIG. 6 is a graph showing a relationship between an output current / applied voltage and an output current / O ₂ concentration of a detector portion in FIG. 5;

FIG. 7 is a flowchart of a control routine of a combustion control method having a self-diagnosis function according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Furnace 12 Flame 13 Burner 14 Fuel system 15 Air supply system 16 Blower 17 Control valve 18 Control box 19 Flue 20 Detector

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F23N 5/00 F23N 5/24 107 F23N 5/24 113 F23N 1/02

Claims (1)

(57) [Claims] (1) O _{2 in the} furnace or the flue depending on the output current value.
When a detector capable of detecting the concentration is provided, the O ₂ concentration is detected by a current value signal from the detector, and when the air ratio is controlled based on the detected O ₂ concentration, abnormalities of the detector and abnormalities are detected. / or failure of the combustion device to a combustion control method for self-diagnosis, the self-diagnosis, combustion first step of determining whether the OFF; O when the combustion in the first step is determined not OFF
₍₂₎ Determine whether the output current value of the sensor is larger than a predetermined value B
Second step: In the second step, the output current value of the O ₂ sensor exceeds a predetermined value B.
A third step of instructing a decrease in air supply when it is determined to be large; an output current value of the O ₂ sensor being equal to or less than a predetermined value B in the second step
A fourth step of instructing an increase in air supply when it is determined that the output current value of the O ₂ sensor is smaller than B after the fourth step.
A fifth step of determining whether the output current value of the O ₂ sensor is equal to or less than a predetermined value C in the fifth step;
The sixth step for instructing a system down when it is determined that
Extent; O ₂ sensor when the combustion is determined to OFF in the first step
The output current value of the sensor is larger than a predetermined value A which is larger than a predetermined value B
The output current value of the O ₂ sensor exceeds a predetermined value A in the seventh step.
An eighth step of instructing continuation of operation when it is determined to be large;
And the output current value of the O ₂ sensor is equal to or less than a predetermined value A in the seventh step.
Alarm when the O ₂ sensor has deteriorated
Ninth step to display and instruct system down if necessary
Combustion control method comprising extent, process.