JP2540383B2 - Combustion control device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to a combustion control device for controlling a combustion device used in a water heater or the like so as to reduce NOx concentration in exhaust gas and perform stable combustion.

[Prior art]

Since the combustor generates NOx gas when incompletely combusted, it is necessary to carry out NOx combustion as low as possible. As a conventional combustion control method, the flame current flowing through the flame of the combustion device is detected, and when the detected value is less than or equal to the set value, it is considered that incomplete combustion has occurred, the combustion is stopped, and the exhaust gas is sampled. There has been a method in which the NOx sensor using a semiconductor sensor or the like is used for analysis after adjusting the moisture and temperature conditions.

[Problems to be Solved by the Invention]

However, the method of detecting the flame current is simply to stop the combustion when the incomplete combustion is detected, it is not possible to perform the combustion while maintaining a constant low NOx state, and the NOx The method using the sensor is NOx
There is a problem that the sensor is very expensive and is unsuitable for household devices. The present invention has been made to solve the above problems, and an object thereof is to provide a combustion control device capable of obtaining a stable combustion state with low NOx.

[Means for Solving the Problems]

The combustion apparatus according to the present invention has a storage unit that stores a relationship between a flame current and a concentration of NOx components contained in exhaust gas at a predetermined combustion amount and a predetermined air ratio, and a detection unit that detects the flame current. , Based on the contents stored in the storage means, while calculating the flame current target value to obtain the optimum value of the concentration of the NOx component, comparing the flame current target value and the detection value of the detection means, Accordingly, a control means for controlling the amount of air or the amount of combustion supplied to the combustion device is provided.

[Action]

The low NOx control target value is replaced with the flame current target value, and the low NOx operation of the combustion device is controlled by controlling the air amount or the combustion supply amount so that the detected value of the flame current becomes the flame current target value. Done.

【Example】

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a combustion device, 2 is a sensor as a detection means for detecting the flame current flowing through the flame of the combustion device 1,
For example, a current flowing through the flame is detected when a predetermined DC or AC voltage is applied between the probe arranged in the flame and the burner flame hole. Reference numeral 3 denotes an A / D converter that converts the detection signal of the sensor 2 into a digital detection value, and 4 performs a predetermined arithmetic processing based on the detection value from the A / D converter 3 and outputs a control signal. A control device including a microcomputer and the like, 5 is a memory as a storage means for storing data etc. showing a relationship between a flame current and a NOx concentration, which will be described later,
Reference numeral 6 denotes a blower for sending air for mixing with combustion gas to the combustion device 1, and the amount of air is controlled by a control signal output from the control device 4. Reference numeral 8 is a valve device including an electromagnetic valve or the like for supplying combustion gas to the combustion device 1, and the valve opening thereof is controlled by the control device. 9 is a temperature sensor for detecting the ambient temperature. FIG. 2 (A) is a characteristic diagram showing the relationship between the amount of air (air ratio) supplied to the combustion device 1 and the NOx concentration. The characteristic a shows the case where the combustion amount is 10,000 Kcal / h, and the characteristic b shows Burning amount is 2
The case of 0000 Kcal / h is shown. FIG. 2B is a characteristic diagram showing the relationship between the air amount and the flame current, and the characteristics a and b correspond to the characteristics a and b in FIG. I ₁ indicated by the point x indicates the flame current target value corresponding to the low NOx control target value when low NOx combustion is performed. The characteristics c and d shown by the dotted lines are characteristics for obtaining the above I ₁ for the characteristics a and b, respectively. In this embodiment, the control device 4 extracts the NOx concentration based on a predetermined combustion amount from the memory 5 in which the data corresponding to the characteristics shown in FIGS. 2A and 2B are stored. Further, as shown in FIG. 2 (C), the flame current and the flame current at a predetermined combustion amount are shown in FIGS. 2 (A) and (B).
Relationship with NOx concentration is required. That is, the characteristics e and f are the second
It corresponds to the characteristics a and b of the combustion amount in the graphs (A) and (B). The characteristics e and f coincide with the flame current target value I _{1 in} FIG. 2 (B). That is, FIG. 2C means that the flame current target value I ₁ is determined when the NOx concentration target value is determined. Note that the relationship between the flame current and NOx concentration is
If the Ox concentration is ρ and the flame current is Ix, the flame current target value I ₁
Can be expressed as Ix = 18 × (1/1000) × ρ × Q + 100. This flame current Ix is the flame current target value.
I will be ₁ . In this embodiment, the above calculation is performed from the predetermined combustion amount Q and the NOx concentration ρ extracted from the memory 5 to obtain the flame current target value I ₁ . FIG. 6 is a side view showing an example of the combustion device 1, 10 is a ceramic burner with a metal coating, 11 is a water distribution pipe for distributing water from the water inlet 11a to the ceramic burner 10, and 12 is the ceramic burner 10 Heat exchanger, through which the generated hot water passes, 13
Is a hot water supply pipe for supplying hot water from the hot water supply port 13a, and 14 is the sensor 2 arranged in the flame (not shown) of the ceramic burner 10.
It is a probe that constitutes. The probe 14 or the heat exchanger 12 serves as a positive electrode, and the ceramic burner 10 side serves as a negative electrode. 1 indicates the distance between the positive electrode and the negative electrode. Reference numeral 15 is an exhaust port, and 16 is a premixed gas inlet. Next, the operation of the above configuration will be described with reference to the flowchart of FIG. In the state where the combustion device 1 is burning with the characteristic a or b in FIG. 2, first, the flow rate of the gas supplied to the combustion device 1 in step ST1 is detected from the valve opening of the valve device 8 and the detected value is detected. Is input to the control device 4. Next, in step ST2, the control device 4 determines each combustion amount from the characteristics c and d of FIG. 2B according to the conditions such as the ambient temperature detected by the temperature sensor 9 as shown in FIG. decide. Then, the determined combustion amount, for example, the flame current target value I ₁ in the characteristic a is calculated. The flame current target value I ₁ is a target value for causing the combustion device 1 to perform combustion in a low NOx and stable flame state, and is obtained by substantially replacing the low NOx control target value with the flame current target value. Becomes Next, in step ST3, the sensor 2 detects the flame current, and the detected value Ix is input. Then, this Ix is compared with the flame current target value I ₁ in step ST4, and I ₁ > Ix
If so, the blower is controlled to reduce the air amount in step ST5, and if I ₁ <Ix (the blower is controlled to increase the air amount in step ST6. Through the above steps ST1 to ST6, the flame current Ix is changed to the flame current Ix. It is controlled to the target current value I1, which causes NOx
The concentration becomes the low NOx control target value. Next, in step ST7, the variation width ΔIx of Ix is compared with a predetermined amplitude limit value I ₃ . When ΔI ₃ ≧ ΔIx, the flame is considered to be stable and the process returns to step ST1. When the [Delta] I ₃ rather DerutaIx, after increasing the amount of air in the step ST8, the elapsed time Tx from step ST7 it is checked whether only the predetermined time T _o in step ST9. When T _o ≧ Yx, the process returns to step ST1. When T _o <Tx, the combustion is unstable, and in step ST10 the valve device 8 is shut off to stop the gas supply and stop the combustion. Above steps ST
According to 7 to ST10, for example, when the flame becomes unstable such as lift and back, Ix is disturbed, and the time Tx when the change width ΔIx exceeds the amplitude limit value ΔI ₃ is predetermined as shown in FIG. when preceded by time T _o, because the combustion is stopped, the safety is maintained. In the example of FIG. 4, time Tx is measured from time t ₁ . Incidentally, by where the ΔIx is to monitor the time beyond the [Delta] I _3, but detects the unstable combustion, the number of times ΔIx a predetermined time (e.g. 1 sec) exceeds [Delta] I ₃ exceeds a predetermined number of times At this time, the combustion may be stopped as unstable combustion. Further, as shown in FIG. 5, sets the predetermined lower limit target value I ₂ with respect to I _1, and thus to comparing the I ₂ and Ix, as shown in the figure, at time t ₂ I _2> Ix by now, the time when Tx exceeds a predetermined time T _o from the time t _2, the or a predetermined time (e.g., 1
When the number of times I2> Ix exceeds a predetermined value in (second), the combustion may be stopped as unstable combustion. Furthermore, in steps ST5, ST6 and ST8, the blower is controlled to adjust the air amount, but the valve opening of the valve device 8 may be controlled to adjust the gas flow rate. Further, I ₁ and I ₂ are changed depending on the conditions such as the ambient temperature. Furthermore, the accuracy of control and the time to reach the target value can be shortened according to the gas flow rate and the air flow rate.

【The invention's effect】

According to the present invention, data indicating the relationship between the flame current and the NOx concentration is stored in advance, and the flame current target value corresponding to the low NOx control target value is calculated based on this data, and the flame current target value and the flame current are calculated. Since the amount of air or the amount of fuel supplied to the combustion device is controlled by comparing with the detected value of the electric current, the following effects can be obtained. (1) A combustion control device capable of obtaining a stable combustion state with low NOx can be provided at low cost. (2) The area where both the low NOx area and the stable combustion area overlap is narrow, or both areas are detected by one sensor.
It becomes possible to control. (3) Both a ceramic burner (all premixed burner) and a Bunsen burner can be used.

[Brief description of drawings]

FIG. 1 is a block diagram showing a combustion control device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing respective relationships of NOx concentration and air ratio, and flame current and air ratio, and FIG. 3 is a flow chart showing operation, 4 and 5 are characteristic diagrams for explaining detection of unstable combustion, and FIG. 6 is a side view showing an example of a combustion device. 1 is a combustion device, 2 is a sensor, 4 is a control device, 5 is a memory, 7 is a blower, 8 is a valve device, and 17 is an electrode. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (3)

(57) [Claims] 1. A relationship between a combustion device (1) that performs combustion at a predetermined combustion amount, a flame current flowing through a flame at a predetermined combustion amount of the combustion device, and a concentration of NOx components contained in exhaust gas. A storage means (5) for storing data, a detection means (2) for detecting the flame current, and a concentration of NOx component in the predetermined combustion amount are extracted from the storage means,
The flame current target value corresponding to the optimum value of the concentration of the NOx component is calculated, and the flame current target value obtained by this calculation is compared with the detection value of the detection means, and based on the difference between the two, A combustion control device comprising: a control means for controlling the amount of air supplied to the combustion device or the amount of combustion supply. 2. Whether the supply of fuel to the combustion device is stopped when the time or frequency at which the variation width of the detection value of the detection means exceeds a predetermined upper limit value or lower limit value exceeds a preset value. Alternatively, the combustion control device according to claim 1, wherein a predetermined offset value is given to the flame current target value. 3. When the time or frequency at which the detection value of the detection means exceeds a predetermined lower limit target value becomes equal to or greater than a set value, the supply of fuel to the combustion device is stopped or the flame current target value is set. The combustion control device according to claim 1, wherein a predetermined offset value is given.