JPS5928862B2 - gas detection device - 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.

[I] 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. Π 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 a temperature compensation element based on Π, since the gas detection element and the temperature compensation element are exposed to the ambient atmosphere under the same conditions, the pixel element easily follows the temperature change of the ambient atmosphere, and therefore the temperature dependence of the zero point is reduced. Due to its small size, it is widely used in household liquefied petroleum gas leak alarms.

By the way, as a result of various studies and numerous experiments by the present inventor, when the catalytic combustion type thermal linear gas detection device using the above-mentioned [I] and l(7) temperature compensation elements is applied to a city gas leak alarm, It has become clear that the warning concentration varies greatly depending on the type of city gas.

In particular, city gas mainly composed of liquefied natural gas LNG and liquefied petroleum gas LP made from petroleum produced using conventional methods.
The difference in alarm concentration between city gas and city gas whose main component is G is so large that it cannot be ignored, creating the problem 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. The reason for this is that methane, the main component of liquefied natural gas, has a lower molecular combustion heat than other hydrocarbon gases and is chemically stable, so the output from the catalytic combustion thermal linear gas detection device is lower than that of other hydrocarbon gases. This is because it is smaller than gas. The present invention improves these problems by (a) reducing the difference in alarm concentration even if the types of city gas are different, and using LPG, which is mainly composed of liquefied petroleum gas (LPG) and city gas, especially liquefied natural gas (LNG); The present invention aims to provide a temperature compensation element for a gas detection device that can be used for both city gas and city gas. According to the present invention, the present invention is an element whose activity differs depending on the type of hydrocarbon gas, that is, it does not cause catalytic combustion for methane, but it does not cause catalytic combustion for hydrocarbon gases other than methane. This is achieved by using an element that causes catalytic combustion as a temperature compensation element.

According to one advantageous embodiment of the present invention, the temperature compensation element comprises an element in which a metal oxide having oxidation catalytic properties is deposited on a carrier which is deposited on a thermal wire for temperature compensation.

In this case, in the present invention, manganese oxide, iron oxide, or a mixture thereof is selected as the metal oxide. However, according to the experiments of the present inventors,
Although such a temperature compensation element does not cause catalytic combustion with methane, which is the main component of liquefied natural gas LNG, it does not cause catalytic combustion with hydrocarbon gases other than methane, such as isobutane, which is the main component of liquefied petroleum gas LPG. will result in some degree of catalytic combustion.

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 experience a large resistance change ΔR when using isobutane, but not much when using methane. Does not produce R2. These resistance changes △R1 to △R2 of the gas detection element are taken out based on the resistance value of the temperature compensation element, but conventionally, this temperature compensation element does not cause a resistance change with respect to the detection gas (methane, isobutane, etc.). element is used. Therefore, from the conventional bridge circuit in which these gas detection elements and temperature compensation elements are incorporated, the resistance changes ΔRl, ΔR2 of the gas detection elements themselves are
An output voltage related to is extracted. 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, the alarm will not be activated if the isobutane comes into contact even if the concentration is the same. However, it also means that no alarm will be triggered if methane comes into contact with the device. Therefore, as a result of various research and experiments, the present inventors changed the conventional idea of configuring the temperature compensation element so as not to cause a change in resistance with respect to the detected gas, and developed the above-mentioned method. It has been found that the temperature compensating element may be configured so that catalytic combustion does not occur for methane, but catalytic combustion occurs for 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 equal to that of the conventional gas detection described above. Similar to the device, it appears in relation only to the resistance change ΔR1 of the gas detection element. On the other hand, when isobutane comes into contact with this temperature compensation element, this temperature compensation element also causes catalytic combustion, so the output voltage of the bridge circuit is the difference between the resistance change ΔR2 of the gas detection element and the resistance change ΔR3 of the temperature compensation element. It appears in relation to the difference ΔR (=ΔR2−ΔR3). Therefore, the difference ΔR, that is, the resistance change of the temperature compensation element ΔR, is adjusted so that the resistance change ΔR1 of the gas detection element for methane and the difference ΔR of the resistance change of the gas detection element and temperature compensation element for isobutane are approximately equal. By setting R3, an alarm can be issued for detected gases of the same concentration regardless of the type of gas. 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 consists of fixed resistors R, ,R
2. Consisting of a resistance bridge circuit B consisting of a gas detection element M and a temperature compensation element K, a power supply E that supplies power to this bridge circuit B, and a load V (for example, an alarm) connected to the output side of the bridge circuit B. has been done. Gas detection element M
The structure is such that 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 manganese oxide or the like is supported on the carrier 5, and is heated to about 350° C. like 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 manganese oxide 6 attached to the carrier 5 differs depending on the type of hydrocarbon gas. The gas detection element M is fixed to the substrate D by lead rods Fl, F2, and the temperature compensation element K is fixed to the substrate D by lead rods Hl, F2.
Similarly, it is fixed to the substrate D in close proximity to the gas detection element M by H2. Thus, when hydrocarbon gas comes into contact with the gas detection device, the gas detection element M and the temperature compensation element K each produce a temperature change, and therefore the resistance values of the platinum filament 1 and the platinum filament 4 change, and the bridge circuit B output voltage changes. This activates a load, for example an alarm device. Next, a method of manufacturing the gas detection element M and the temperature compensation element K will be explained.

Regarding the gas detection element, first use a platinum wire with a diameter of 0.06 mm to measure an outer diameter of 0.6 mm.
A platinum wire with a winding count of 10 turns and a length of 1.5 mm is manufactured using a special winding machine.

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. Further, as the oxidation catalyst, although the use of a palladium catalyst has been described, a rhodium catalyst and a mixed catalyst thereof can also be used. Moreover, a catalyst obtained by adding platinum to these catalysts can also be used. Example 1 about temperature compensation element First, like the gas detection element, the diameter is 0.06m7! A platinum wire having an outer diameter of 0.6 mm, a number of windings of 10 turns, and a length of 1.5 mm is manufactured using L platinum wire.

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 carrier was impregnated with a manganese nitrate aqueous solution with a manganese concentration of 2%,
Manganese oxide is attached to the alumina support by thermal decomposition at 500°C. In this example, manganese nitrate was used as the starting material for manganese oxide, but water-soluble manganese compounds such as manganese sulfate or manganese chloride may also be used.

Example 2 The procedure is the same as Example 1 until the alumina carrier is fixed to the platinum wire.

Thereafter, the alumina carrier is impregnated with a ferric nitrate aqueous solution having an iron concentration of 2%, and the alumina carrier is thermally decomposed at 5002C to adhere iron oxide to the alumina carrier. In this example, ferric nitrate has been described as the starting material for iron oxide, but water-soluble iron compounds such as ferrous nitrate or ferric chloride can also be used.

The temperature compensation elements described in Examples 1 and 2 exhibit high activity in catalytic combustion reactions with hydrocarbon gases other than methane, but are characterized by having no activity in catalytic combustion reactions with methane. be.

Next, an example of the experimental results will be explained using drawings.

FIG. 3 shows that a palladium catalyst-alumina carrier element is used as the gas detection element M, and an element that has been inactivated by depositing lead oxide on its surface by a conventional method is used as the temperature compensation element K. The bridge circuit B is configured to supply a power supply voltage E=1.8V, and the hydrocarbon gas isobutane, n
- Output voltage characteristics of bridge circuit B when butane, propane, propylene, ethane, ethylene and methane are brought into contact.

Isobutane and n-butane are shown by characteristic line A, fukomapan and propylene are shown by characteristic line C, ethane and ethylene are shown by characteristic line C, and methane is shown by characteristic line II. 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 is activated when the output voltage of the bridge circuit reaches 10 mV, the voltage of isobutane and n-butane is approximately 0.
．． Alarms are raised at around 13%, while for methane around 4%
An alarm will not be issued unless this occurs. FIG. 4 shows the output voltage characteristics when a hydrocarbon gas is brought into contact with the temperature compensating element K under the same conditions as in FIG. 3 using an element in which manganese oxide is attached to a carrier according to the present invention.

That is, isobutane and n-butane have characteristic line A,
Propylene and propylene are shown by characteristic line 1, ethane and ethylene by characteristic line C, and methane by characteristic line 2. 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 should be set at approximately 0.34 to 0.
．． It can be kept within the range of 4%. Similar to manganese oxide, it was confirmed that iron oxide and a mixture of manganese oxide and iron oxide also have the above effects.

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 manganese oxide or the like is attached to a carrier is used as a temperature compensation element as in the present invention, since manganese oxide or the like has catalytic activity, isobutane gas is released on the surface of the carrier of the temperature compensation element. Catalytic combustion occurs in easily combustible hydrocarbon gases such as . Furthermore, since the alumina carrier is porous, hydrocarbon gas such as isobutane gas diffuses into the carrier, and a portion of it also reaches the platinum hot wire and burns on its surface. Due to these causes, as shown in FIG. 4, 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 and does not cause catalytic combustion even with manganese oxide. As explained above, according to the present invention, by using an element as a temperature compensation element that does not cause catalytic combustion for methane but causes catalytic combustion for hydrocarbon gases other than methane. , 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. Since isobutane is the main component of liquefied petroleum gas LPG, and methane is the main component of liquefied natural gas LNG used for city gas, a general household gas leak alarm consisting of the gas detection device of the present invention , liquefied petroleum gas (LPG) and city gas (LNG) can be used in common.

[Brief explanation of drawings]

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. FIG. 4 is a characteristic diagram 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 Article 6... Manganese 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 platinum wire 1 for gas detection, and these gas detection elements and temperature compensation element are connected in a bridge circuit. In the structure in which the load is connected to the output side of the bridge circuit, the temperature compensating element includes at least manganese oxide and iron oxide on a carrier 5 attached to the temperature compensating platinum wire 4. A gas detection device characterized by using a device to which one side is attached.