JPS6122902B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature compensation element for a catalytic combustion thermal linear gas detection device in which a gas detection element and a temperature compensation element are incorporated in a branch of a bridge circuit.

Temperature compensating elements in catalytic combustion thermal linear gas detection devices have conventionally been roughly classified into the following two types.

[] An element manufactured by the same manufacturing method as the gas detection element is sealed with a metal cap and used as a temperature compensation element.

[] An element in which the surface of a carrier attached to a hot wire is coated with an inert substance such as lead oxide is used as a temperature compensation element.

In particular, in the case of the temperature compensation element according to [], since the gas detection element and the temperature compensation element are exposed to the ambient atmosphere under the same conditions, both elements tend to follow the temperature change of the ambient atmosphere, and therefore the temperature dependence of the zero point is Due to its low resistance, it is widely used in household liquefied petroleum gas leak alarms.

By the way, as a result of various studies and numerous experiments conducted by the present inventors, it has been found that when the catalytic combustion thermal linear gas detection device using the temperature compensation elements described in [] and [] above is applied to a city gas leak alarm, the city gas It has become clear that the alarm concentration varies greatly depending on the type of In particular, the difference in alarm concentration between city gas whose main component is liquefied natural gas (LNG) and city gas whose main component is liquefied petroleum gas (LPG) made from petroleum produced using conventional methods is so large that it cannot be ignored. This creates a problem in that the specifications of the city gas leak alarm must be changed depending on the type of city gas. Furthermore, it has become difficult to use liquefied petroleum gas leak alarms, which are already used in general households, for city gas.
This is because methane, the main component of liquefied natural gas, has a lower molecular combustion heat than other hydrocarbon gases and is chemically stable. This is because it is smaller than gas.

Furthermore, recently, gas leak alarms used in general household kitchens have been installed to prevent gas leakage alarms from being used when heating sake or while cooking dishes using mirin or sake.
A problem arose in that evaporated ethyl alcohol caused false alarms. The ethyl alcohol concentration at this time may exceed 1000 ppm.

The present invention improves these problems and
[B] The difference in alarm concentration is small even if the types of city gas are different, and [B] It can be used for both liquefied petroleum gas (LPG) and city gas, especially city gas whose main component is liquefied natural gas (LNG). [C] An object of the present invention is to provide a temperature compensation element for a gas detection device that can prevent false alarms caused by ethyl alcohol.

According to the present invention, such an object is achieved by using, as a temperature compensation element, an element in which iridium oxide having oxidation catalytic performance is deposited on a carrier which is deposited on a thermal wire for temperature compensation.

According to experiments conducted by the present inventors, such a temperature compensation element does not cause catalytic combustion with methane, which is the main component of liquefied natural gas (LNG), but with hydrocarbon gases other than methane. For example, catalytic combustion occurs to some extent with isobutane, which is the main component of liquefied petroleum gas (LPG). In addition, high catalytic combustion occurs with ethyl alcohol. The present invention using such a temperature compensation element is based on the following technical idea.

That is, as mentioned above, methane has a smaller heat of molecular combustion than other hydrocarbons, such as isobutane. This means that when methane and isobutane at the same concentration come into contact with a gas detection element, the gas detection element will produce a large resistance change (△R ₁₎ for isobutane, but will not show much resistance for methane. These resistance changes △R ₁ and △R ₂ of the gas detection element are extracted based on the resistance value of the temperature compensation element, but conventionally this temperature _compensation element Therefore, in the conventional bridge circuit in which these gas detection elements and temperature compensation elements are incorporated, the resistance change of the gas detection element itself is △R ₁ , △ The output voltage related to R ₂ will be taken out. Therefore, if the gas detection device is configured so that the alarm is activated when the output voltage of the bridge circuit exceeds a predetermined voltage, , even if the concentration is the same, an alarm will be issued when isobutane comes into contact, but an alarm will not be issued when methane comes into contact.
As a result of various research and experiments, the inventors of the present invention have changed from the conventional idea of configuring the temperature compensation element and the detection gas so that no resistance change occurs. It has been found that the temperature compensating element may be configured so that catalytic combustion does not occur for ethyl alcohol or hydrocarbons other than methane, such as isobutane. In other words, when such a temperature compensation element is used, when methane comes into contact with this temperature compensation element, this temperature compensation element does not cause catalytic combustion, so the output voltage of the bridge circuit is the same as that of the above-mentioned conventional temperature compensation element. Similar to the gas detection device, it appears in relation only to the resistance change ΔR ₁ of the gas detection element. On the other hand, when isobutane or ethyl alcohol comes into contact with this temperature compensation element, this temperature compensation element also causes contact combustion, so the output voltage of the bridge circuit is determined by the resistance change △R ₂ of the gas detection element and the resistance of the temperature compensation element. Difference from change △R ₃ △R=(=△
R ₂ −△R ₃ ). Therefore, the difference △R ₁ between the resistance change of the gas detection element for methane and the resistance change of the gas detection element and temperature compensation element for isobutane or ethyl alcohol is calculated.
By setting this difference △R, that is, the resistance change △R ₃ of the temperature compensation element, so that the be able to utter.

Next, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 is an assembly diagram of its main parts. The gas detection device according to the present invention mainly includes a resistance bridge circuit B consisting of fixed resistors R ₁ and R ₂ , a gas detection element M, and a temperature compensation element K, a power supply E that supplies power to this bridge circuit B, and an output side of the bridge circuit B. and a load V (for example, an alarm device) connected to. The gas detection element M has a structure in which an alumina carrier 2 is attached to a platinum filament 1, and a palladium catalyst 3 is supported on the alumina carrier 2, and is heated to about 350°C. When a hydrocarbon gas comes into contact with this gas detection element M, the resistance value of the platinum filament 1 changes due to a temperature change due to its combustion.

The temperature compensation element K has a structure in which an alumina carrier 5 is attached to a platinum filament 4, and iridium oxide 6 is supported on the carrier 5, and is heated to about 350°C similarly to the gas detection element M. . When a hydrocarbon gas other than methane comes into contact with this temperature compensation element K, combustion occurs depending on the type of hydrocarbon gas, and the resistance value of the platinum filament 4 changes due to the temperature change. This is because the surface activity of the iridium oxide 6 adhering to the carrier 5 differs depending on the type of hydrocarbon gas. The gas detection element M has lead wires F ₁ ,
It is fixed to the substrate D by F ₂ , and the temperature compensation element K is similarly fixed to the substrate D in the vicinity of the gas detection element M by lead rods H ₁ and H ₂ . Thus, when hydrocarbon gas comes into contact with the gas detection device, the gas detection element M and the temperature compensation element K each undergo a temperature change, and therefore the low resistance values of the platinum filament 1 and the platinum filament 4 change, and the bridge circuit B output voltage changes.
This activates the load V, for example an alarm device.

Next, a method of manufacturing the gas detection element M and the temperature compensation element K will be explained.

About the gas detection element First, a platinum wire with an outer diameter of 0.6 mm and a
A special winding machine is used to manufacture platinum wire with a winding count of 10 turns and a length of 1.5 mm.

Next, a mixed paste of alumina powder and alumina sol is applied to the platinum wire and fired at 800°C to fix the alumina carrier to the platinum wire. Thereafter, the alumina carrier is impregnated with an aqueous palladium chloride solution and thermally decomposed at 500°C to support the palladium catalyst on the alumina carrier. Note that a silica carrier or an alumina-silica mixed carrier can also be used as the carrier. In addition, as an oxidation catalyst,
Although I mentioned using a palladium catalyst,
Rhodium catalysts and mixed catalysts thereof can also be used. Moreover, a catalyst obtained by adding platinum to these catalysts can also be used.

About the temperature compensation element First, like the gas detection element, it is made of platinum wire with a diameter of 0.06 mm, with an outer diameter of 0.6 mm, number of turns of 10 turns, and length of 1.5 mm.
Produce platinum filaments of mm. Next, a mixed paste of alumina powder and alumina sol is applied to the platinum wire and fired at 800° C. to fix the alumina carrier to the platinum wire. After that, the alumina support was impregnated with an aqueous solution of hexachloroiridic acid, and
The iridium oxide is deposited on the alumina support by thermal decomposition at °C.

The concentration of the hexachloroiridic acid aqueous solution is preferably from 0.025% to 0.075% in terms of iridium concentration. When the iridium concentration is lower than 0.025%, the effect of the present invention becomes smaller, and on the other hand, when the iridium concentration is higher than 0.075%, the output of isobutane gas becomes smaller. Therefore, a gas leak alarm can be configured with the gas detection device according to the present invention. becomes difficult.

In this example, hexachloroiridic acid was used as the starting material for iridium oxide, but other water-soluble iridium compounds such as ammonium hexachloroiridate can also be used.

The temperature compensating element described above exhibits some degree of activity in catalytic combustion reactions with hydrocarbon gases other than methane, but is characterized by having no activity in catalytic combustion reactions with methane.

It is also characterized by high activity in catalytic combustion reactions with ethyl alcohol.

Next, a series of experimental results will be explained using drawings.

In FIG. 3, a palladium catalyst-alumina carrier element is used as the gas detection element M, and a temperature compensation element K is used.
The bridge circuit B of Fig. 1 is constructed using an element inactivated by attaching lead oxide to the surface by a conventional method, and a power supply voltage E = 1.8V is supplied, and hydrocarbon gas isobutane, This is the output voltage characteristic of bridge circuit B when n-butane, propane, propylene, ethane, ethylene, and methane are brought into contact. Isobutane and n-butane are shown by characteristic line A, propane and propylene by characteristic line B, ethane and ethylene by characteristic line C, and methane by characteristic line D. In this way, the output voltage varies greatly depending on the type of hydrocarbon gas. Therefore, in a gas leak alarm configured to operate a load V, for example, an alarm device, with the output voltage of the bridge circuit B shown in FIG. 1, the alarm concentration will vary greatly depending on the type of hydrocarbon gas.
In other words, if the alarm device is activated when the output voltage of the bridge circuit reaches 10 mV, an alarm will be issued for isobutane and n-butane at about 0.13%, while for methane, the alarm will not be issued until it reaches about 0.4%. I can't utter it.

FIG. 4 shows a temperature compensating element K according to the present invention.
This is the output voltage characteristic when a hydrocarbon gas is brought into contact with a device having iridium oxide attached to a carrier under the same conditions as in FIG. 3. That is, isobutane and n-butane are shown by characteristic line A, propane and propylene by characteristic line B, ethane and ethylene by characteristic line C, and methane by characteristic line D. As is clear from FIG. 4, regardless of the type of hydrocarbon gas, the output voltage is almost the same as that of methane. Therefore, in a gas leak alarm, the alarm concentration is the same regardless of the type of hydrocarbon gas. In other words, regardless of the type of hydrocarbon gas, the alarm concentration can be kept within the range of approximately 0.34 to 0.4%.

FIG. 5 configures the bridge circuit B of FIG. 1,
This is the output voltage characteristic of the bridge circuit B when the power supply voltage E=0.8V is supplied and ethyl alcohol is brought into contact. Characteristic line E shows the case where an element inactivated by attaching lead oxide to the surface by a conventional method is used as a temperature compensation element, and the characteristic line E shows the case where an element with iridium oxide attached to the carrier according to the present invention is used. It is shown by the characteristic line. Compared to the temperature compensation element according to the conventional method, when the temperature compensation element according to the present invention is used, the output of ethyl alcohol is reduced to one-third or more, and false alarms due to ethyl alcohol can be almost prevented.

The reason for the effect of the present invention using such a temperature compensating element is considered to be as follows. In other words, when an element in which the surface of an alumina carrier is inertly treated with lead oxide or the like is used as a temperature compensation element as in the past, the alumina and platinum hot wires are covered with an inert substance, so the surface of the temperature compensation element is In this case, catalytic combustion does not occur, and the output of the bridge circuit becomes a value according to the molecular combustion heat and oxidation reactivity of the hydrocarbon gas. On the other hand, when an element in which iridium oxide is attached to a carrier is used as a temperature compensation element as in the present invention, since iridium oxide has catalytic activity, the surface of the carrier of the temperature compensation element acts like isobutane gas. Catalytic combustion occurs in hydrocarbon gases that are easily combustible. Ethyl alcohol is also easily combustible, so catalytic combustion occurs. Due to such causes, as shown in FIGS. 4 and 5, the gas detection sensitivity decreases and the output voltage of the bridge circuit becomes a small value. However, for methane gas, the output voltage of the bridge circuit exhibits the same value as when using an element treated with lead oxide as a temperature compensation element. This is thought to be because methane gas is chemically stable, so iridium oxide hardly causes catalytic combustion.

As explained above, according to the present invention, an element that does not cause catalytic combustion for methane but causes catalytic combustion for hydrocarbon gases other than methane and ethyl alcohol is used as a temperature compensation element. By doing so, it is possible to provide a gas detection device in which the output voltages of hydrocarbon gases, such as isobutane and methane, are the same in a simple manner.

Isobutane is the main component of liquefied petroleum gas (LPG), while methane is the main component of liquefied natural gas (LNG) used for city gas. Leak alarms can be shared between liquefied petroleum gas (LPG) and city gas (LNG).

Further, by using the gas detection device of the present invention, it is possible to construct a gas leak alarm for general household use that hardly generates false alarms due to ethyl alcohol.

[Brief explanation of the drawing]

1 and 2 are schematic configuration diagrams of an embodiment of the present invention, and FIG. 3 shows the relationship between the hydrocarbon gas concentration and the bridge circuit output voltage when using a temperature compensation element inactivated by a conventional method. The relationship diagrams, FIGS. 4 and 5, are characteristic diagrams for explaining experimental results according to an embodiment of the present invention. M...Gas detection element, K...Temperature compensation element, B
...Bridge circuit, V...Load, 4...Platinum wire, 6...Iridium oxide.

Claims (1)

[Claims] 1 Equipped with a gas detection element M and a temperature compensation element K in which a catalyst 3 is attached on a carrier 2 attached to a hot wire 1 for gas detection, and these gas detection elements and temperature compensation element are connected to a branch of a bridge circuit. In this bridge circuit, in which a load is connected to the output side of the bridge circuit, iridium 6, which has oxidation catalytic performance, is attached to a carrier 5 attached to a temperature compensating hot wire 4 as the temperature compensating element. A gas detection device characterized by using an attached element.