JP3698494B2 - Oxygen concentration measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, a first electrode made of a material capable of ionizing oxygen gas and a second electrode are provided on a base material made of a solid electrolyte, and a regulating means for making the gas contact ratio to each electrode different is provided. A gas detection element, a voltage supply unit for applying a voltage between both electrodes of the gas detection element, a heating means for heating the gas detection element, and the gas detection element in a heated state; The oxygen concentration in the gas in contact with the electrode can be measured based on the output current that flows when a voltage is supplied to the sensing element, and the oxygen concentration in the exhaust gas of the combustion equipment of fuel gas mainly composed of methane is determined. The present invention relates to an oxygen concentration measuring apparatus for measuring.
In other words, such an oxygen concentration measurement apparatus monitors the oxygen contained in the combustion equipment exhaust gas of the fuel gas mainly composed of methane, for example, by controlling the air-fuel ratio of the combustion equipment, etc. It is used for purposes such as controlling
[0002]
[Prior art]
Conventionally, this type of oxygen concentration measuring apparatus employs a configuration that directly detects exhaust gas even when measuring the oxygen concentration in combustion exhaust gas.
[0003]
[Problems to be solved by the invention]
According to the above-described conventional oxygen concentration measuring apparatus, when measuring the oxygen concentration in the exhaust gas of combustion equipment of fuel gas mainly composed of methane, the oxygen concentration is not accurately measured, and particularly the combustion condition of excessive fuel However, there is a problem that the oxygen concentration may be measured too low, and there is a possibility that the combustion state of the combustion device may be mistakenly recognized.
[0004]
Accordingly, an object of the present invention is to provide an oxygen concentration measuring apparatus that can accurately measure the oxygen concentration regardless of the combustion conditions in view of the above-mentioned drawbacks.
[0005]
[Means for Solving the Problems]
The present inventors have found a new finding that the above problem is caused by the fact that the unburned methane gas component is contained in the exhaust gas. Such a phenomenon is caused when the temperature of the exhaust gas is usually 600. In view of the situation where the temperature also reaches 0 ° C., the unburned methane gas is oxidized on the electrode of the gas detection element in the oxygen concentration measuring device, and oxygen is consumed as the methane gas is oxidized on the electrode (CH ₄ + 2O _2). → CO ₂ + 2H ₂ O), considering the phenomenon that the output current decreases by the amount of consumed oxygen, and the conditions under which the methane gas is oxidized on the electrode were examined. The critical temperature is required due to the relationship between the methane gas and the electrode, such as when the gas temperature starts to exceed 400 ° C, and the above problems are encountered at gas temperatures below that critical temperature. To obtain a new finding that almost does not occur.
The present invention has been made based on these new findings,
In order to achieve the above object, the present invention is characterized in that a first electrode made of a material capable of ionizing oxygen gas and a second electrode are provided on a substrate made of a solid electrolyte, and gas contact with each electrode is made. A gas detecting element provided with a regulating means for varying the rate, a voltage supply section for applying a voltage between both electrodes of the gas detecting element, and a heating means for heating the gas detecting element. A fuel mainly composed of methane, which can measure the oxygen concentration in the gas in contact with the electrode based on the output current that flows when a voltage is supplied to the gas sensing element while the sensing element is heated. In the oxygen concentration measuring device that measures the oxygen concentration in the exhaust gas of gas combustion equipment,
There is a temperature maintaining mechanism for maintaining the temperature of the first electrode at a set temperature below the limit temperature at which methane gas is oxidized on the first electrode,
Preferably, an exhaust gas cooling introduction mechanism for cooling the combustion equipment exhaust gas below the set temperature and introducing it into the gas detection element is provided,
The material capable of ionizing the oxygen gas is platinum, and the set temperature may be 380 ° C. or higher and 400 ° C. or lower.
[0006]
[Function and effect]
That is, by providing a temperature maintaining mechanism for maintaining the temperature of the first electrode at a set temperature that is lower than the limit temperature at which methane gas is oxidized on the first electrode, the gas temperature is measured by the gas sensing element. Oxygen gas concentration measurement can be performed while the temperature is kept below the limit temperature. Therefore, during the measurement of the oxygen concentration, it is possible to suppress the oxidation reaction of methane contained in the gas to hardly occur, and the output current is reduced based on the oxygen consumption accompanying the oxidation of methane during the oxygen concentration measurement. Situations that would have been detected are less likely to occur. For this reason, only the output current for oxygen by the gas detection element can be accurately determined, and the oxygen concentration can be accurately determined.
Further, if the exhaust gas temperature is cooled below the set temperature as the temperature maintaining mechanism, the exhaust gas temperature only rises to the temperature of the gas detection element even when the gas detection element is heated. Without oxidizing the methane, it is possible to suppress the oxidation of the methane by a normal setting in which the temperature of the gas detection element is set to a temperature range that is equal to or lower than the limit temperature and easy to detect oxygen.
As the first electrode, a noble metal material such as platinum is generally used. However, when platinum is used, the set temperature is usually set to the gas based on the new knowledge that the limit temperature is about 400 ° C. It is desirable to set the temperature of 380 ° C. or more and 400 ° C. or less using the detection element. This is because the base material of the gas detection element is less likely to exhibit properties as a solid electrolyte at a low temperature of, for example, 380 ° C. or lower.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 2, a base electrode 10 made of a solid electrolyte is provided with a first electrode 11 and a second electrode 12 made of a material capable of ionizing oxygen, and gas contact efficiency with each of the electrodes 11 and 12. 1 is provided, and the gas detection element 1 provided with the heating means 14 for heating the electrodes 11 and 12 and the base material 10 is provided. As shown in FIG. A voltage supply unit 20 with a built-in voltage variable mechanism 21 for applying a voltage between the electrodes 11 and 12 is provided, and a bypass path 33 is provided in an exhaust gas path 32 from a gas combustion device 30 with a built-in combustion control mechanism 31. A gas detection element 1 is provided to constitute an oxygen concentration measuring device.
The bypass passage 33 is provided with a large number of fins 34 on the outer wall, and an exhaust gas cooling introduction mechanism F that cools the exhaust gas flowing through the bypass passage 33 to facilitate contact with outside air.
[0008]
The solid electrolyte is usually a zirconium oxide that is stabilized by adding about 10 mol% of magnesium oxide, calcium oxide, yttrium oxide, etc., and the first electrode and the second electrode can ionize oxygen. Of the materials, noble metals are preferably used, for example, platinum, palladium, rhodium and the like.
The regulating means includes a cover member 13a that covers the first electrode 11 side of the base material 10, and a gas flow hole 13b is provided in the cover member 13a, and the gas contact rate with respect to the first electrode 11 is set. The gas contact rate with respect to the second electrode 12 is set to be lower, and instead of such a configuration, a porous filter is provided so as to cover the first electrode 11. May be.
The heating means 14 is provided with a heating coil 14a in the vicinity of the gas detection element 1, and is configured to receive voltage supply from the voltage supply unit 20 to generate Joule heat.
[0009]
The oxygen concentration measuring device is used by being provided in an exhaust gas passage of a city gas combustion device. For example, when an exhaust gas of 450 ° C. flows into the bypass passage, the exhaust gas is cooled to 350 ° C. or lower and the gas is cooled. When the gas reaches the sensing element and the gas sensing element measures the gas concentration at 400 ° C., the methane in the exhaust gas is heated to almost 400 ° C., and is hardly oxidized on the electrode. The oxygen therein is ionized by the electrode and detected by the solid electrolyte, so that an output current based on the oxygen concentration is generated without being influenced by the methane. Therefore, it is possible to accurately measure the oxygen concentration regardless of unburned methane in the exhaust gas.
The oxygen concentration thus obtained is input to the combustion control mechanism of the gas combustion device as combustion control information of the gas combustion device and used for combustion control such as adjustment of the gas supply amount and the air supply amount.
[0010]
【Example】
The temperature dependence of the oxidation activity when methane was brought into contact with the platinum electrode was as shown in FIG. From FIG. 3, it was found that oxidation was not promoted on the platinum electrode in an environment of 400 ° C. or lower, and oxygen detection was hardly affected.
Further, when the oxygen concentration measuring device of the present invention provided with the temperature maintaining mechanism and the conventional oxygen concentration measuring device not provided with the temperature maintaining mechanism are applied to the oxygen concentration measurement in the exhaust gas of the gas engine, the The output characteristics are as shown in FIG.
As shown in FIG. 4, in the oxygen concentration measuring apparatus according to the present invention, the oxygen concentration and the output are generally proportional to each other from the low concentration region to the high concentration region. Accordingly, it is understood that the output voltage gradually decreases, and it is considered that the output voltage is observed to decrease due to the electron transfer accompanying the oxidation of the unburned methane gas accompanying the decrease in the combustion efficiency of the gas engine.
In the present invention, the exhaust gas cooling introduction mechanism and the heating means for heating the gas detection element are collectively referred to as a temperature maintenance mechanism, but the temperature maintenance mechanism is not limited to the above-described configuration. ,
In addition to providing sensors for detecting the temperature of the gas detection element, a heating means and a cooling means for the gas detection element are provided, and a control device for controlling the heating and cooling of the gas detection element to a predetermined temperature is provided. Various aspects can be employed.
[Brief description of the drawings]
FIG. 1 is a schematic view of an oxygen concentration measuring apparatus according to the present invention. FIG. 2 is a longitudinal sectional perspective view of a main part of a gas detection element. FIG. 3 is a graph showing a limit temperature by a platinum electrode. Comparison graph of long-term stability between conventional and oxygen concentration measuring device
DESCRIPTION OF SYMBOLS 1 Gas detection element 20 Voltage supply part 30 Combustion equipment F Temperature maintenance mechanism

Claims (3)

A gas detection element provided with a first electrode made of a material capable of ionizing oxygen gas and a second electrode on a substrate made of a solid electrolyte, and provided with a regulating means for varying the gas contact rate to each electrode. Provided with a voltage supply section for applying a voltage between both electrodes of the gas detection element, provided with heating means for heating the gas detection element, and in a state where the gas detection element is heated, a voltage is applied to the gas detection element. Oxygen concentration to measure the oxygen concentration in the combustion equipment exhaust gas of fuel gas mainly composed of methane based on the output current that flows when the gas is supplied A measuring device,
An oxygen concentration measurement apparatus provided with a temperature maintaining mechanism for maintaining the temperature of the first electrode at a set temperature equal to or lower than a limit temperature at which methane gas is oxidized on the first electrode. The oxygen concentration measuring device according to claim 1, further comprising an exhaust gas cooling introduction mechanism that cools the combustion equipment exhaust gas to the set temperature or less and introduces it into the gas detection element. The oxygen concentration measuring apparatus according to claim 1, wherein the material capable of ionizing the oxygen gas is platinum, and the set temperature is 380 ° C. or higher and 400 ° C. or lower.

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