JP4194452B2 - Equipment for measuring oxygen concentration in high-temperature gas - Google Patents

Description

  The present invention relates to an apparatus for measuring oxygen concentration in high-temperature gas, which can directly and continuously measure the oxygen concentration in high-temperature gas, and has excellent durability and low production cost.

  For example, as a method for measuring the oxygen concentration in a high-temperature gas such as various melting furnaces and combustion furnaces, as shown in Patent Document 1 and Patent Document 2, gas is once sucked out of the furnace using a pump or the like. A method of analyzing the oxygen concentration in another place is usually adopted. However, such an oxygen concentration measuring device has a large size and high material cost, and also requires heat and corrosion resistant pumps, filters, piping, etc. that can withstand high-temperature gas, resulting in high production costs. there were.

  On the other hand, as shown in Non-Patent Document 1, it is known to use an oxygen ion conductive solid electrolyte as a principle for measuring the oxygen concentration in a high-temperature gas. If such a solid electrolyte is used, there is a possibility that a small oxygen concentration measuring device with a small heat capacity that can be sensitive to temperature changes can be put into practical use. However, in the case where a small-diameter cylindrical solid electrolyte tube is used, there are the following problems and it has not been put into practical use.

(1) The platinum electrode can be easily adhered to the outer surface of the electrolyte tube on the working electrode side, but the platinum electrode is extremely difficult to adhere to the inner surface of the electrolyte tube on the reference electrode side. (2) When the distance from the outer wall of the furnace body to the measurement site of the oxygen concentration is long, a long solid electrolyte tube is necessary and expensive. (3) Although it is desired that the expensive solid electrolyte tube has only the minimum necessary tip portion and the remaining portion is made of an inexpensive ordinary refractory, a reliable sealing method at the joint is not known. In other words, as a means for joining refractories, a method of applying and fixing alumina cement or the like is generally used, but fine shrinkage holes and cracks are generated after drying, and airtightness cannot be ensured reliably, and solids are also solid. The electrolyte tube and the refractory were subject to breakage due to differences in thermal expansion / contraction during heating / cooling, and airtightness could not be ensured.
JP-A-60-187854 Japanese Utility Model Publication No. 6-86058 Otani Masayasu, “Iron Metallurgical Thermodynamics” (Nikkan Kogyo Shimbun) 119

  The problem to be solved by the present invention is to adopt a new and inexpensive sealing method that can relax the thermal stress and ensure the airtightness between the solid electrolyte tube and the general refractory, and use a small solid electrolyte tube. This makes it possible to measure the oxygen concentration in high-temperature gas directly and continuously with high accuracy without using special equipment such as a furnace gas suction device, and has high durability and low production costs. It is to provide an oxygen concentration measuring device. In addition, the high temperature gas as used in the field of this invention means the gas of 750 degreeC or more.

An apparatus for measuring oxygen concentration in a high-temperature gas according to the present invention, which has been made to solve the above problems, provides a platinum coating layer on the inner and outer surfaces of a cylindrical solid electrolyte tube sealed at the tip, and each of the platinum coating layers An apparatus for measuring oxygen concentration in a high-temperature gas, wherein a platinum electrode is connected, the inside of the solid electrolyte tube is a reference electrode using air, and the outside of the solid electrolyte tube is in contact with the high-temperature gas, the inside of the solid electrolyte tube The tip is filled with a platinum mesh, and the tip of the platinum electrode is pressed against and brought into contact with the platinum mesh .

  The apparatus for measuring oxygen concentration in a high-temperature gas according to the present invention comprises a battery in which the inside of the solid electrolyte tube is a reference electrode using air and the outside of the solid electrolyte tube is a working electrode in contact with the high-temperature gas. The oxygen partial pressure of the working electrode can be calculated from the electromotive force of the gas and the oxygen partial pressure of the reference electrode to accurately measure the oxygen concentration in the high temperature gas. In addition, by using a small solid electrolyte tube, the oxygen concentration in the high-temperature gas can be directly and continuously measured without using special equipment such as a conventional furnace gas suction device. Moreover, it is excellent in durability and can be produced at low cost.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a front view showing an entire oxygen concentration measuring apparatus according to the present invention, and FIG. In the figure, 1 is a cylindrical solid electrolyte tube in which a tip portion made of a general stabilized zirconia system is sealed and a rear end is opened, 2 is a cylindrical support refractory made of dense alumina or the like, The solid electrolyte tube 1 and the supporting refractory 2 are attached to the tip of the probe body 3.

  The inner and outer surfaces of the solid electrolyte tube 1 are provided with platinum coating layers 4a and 4b by brushing or sponge coating, and platinum electrodes 5a and 5b are connected to the platinum coating layers 4a and 4b, respectively. 6a and 6b are cylindrical refractory tubes that insulate the platinum electrodes 5a and 5b from protection. In the present invention, a battery is constructed in which the inside of the solid electrolyte tube 1 is a reference electrode using air and the outside of the solid electrolyte tube 1 is an operating electrode in contact with a high-temperature gas.

  In the illustrated example, the inner tip of the solid electrolyte tube 1 is filled with a platinum mesh 7, and the tip of the platinum electrode 5a is mechanically pressed against the platinum mesh 7 so as to contact the platinum coating layer on the inner surface. It has become. This is because if the contact area between the inside of the solid electrolyte tube 1 and the platinum electrode 5a is small, a contact potential difference due to contact resistance may occur at the reference electrode, and an accurate oxygen concentration measurement may not be possible. This problem can be solved by filling the platinum mesh 7 on top.

In the figure, reference numerals 8a and 8b denote air suction holes and discharge holes used as reference electrodes. As the reference electrode, in addition to air, a substance in which oxygen partial pressure is fixed with pure oxygen, a mixed powder of a metal such as Ni / NiO, Fe / FeO, Cr / Cr ₂ O ₃ and its oxide is used. it can. However, in principle, air is the best method for continuously and inexpensively measuring the oxygen concentration in the gas. In the present invention, air is used as the reference electrode.

  In the illustrated example, the rear end side of the solid electrolyte tube 1 is inserted and supported by a cylindrical support refractory 2, and a ceramic yarn 8 is interposed in the support portion to interpose the solid electrolyte tube 1 and the support refractory 2. The structure is airtight. This is because only the solid electrolyte tube 1 serving as the sensor portion may be attached to the tip of the probe support jig 3, but the solid electrolyte tube is expensive, so that only the minimum tip portion is necessary to reduce the cost. is there. In particular, when the distance from the outer wall of the furnace body to the location where the oxygen concentration is to be measured is long, a long solid electrolyte tube is required, resulting in a significant increase in cost and a platinum coating layer on the inner surface of the small-diameter solid electrolyte tube. It is difficult to form uniformly and it is difficult to obtain a highly accurate electrode, and there is a possibility that the measurement accuracy of the oxygen concentration is deteriorated.

  However, when the solid electrolyte tube 1 and the supporting refractory 2 are joined, a method of applying and fixing alumina cement or the like is generally used, but minute shrinkage holes and cracks are generated after drying to ensure airtightness. In addition, there remains a problem that the solid electrolyte tube 1 and the supporting refractory 2 are easily broken due to differences in thermal expansion and contraction during heating / cooling and cannot secure airtightness. Therefore, in the present invention, the insertion support portion of the solid electrolyte tube 1 has a structure in which the solid electrolyte tube 1 and the supporting refractory 2 are kept airtight by interposing a ceramic yarn 8 having excellent heat resistance. In the illustrated example, the ceramic yarn 8 is wound around the outer periphery of the solid electrolyte tube 1 and the ceramic cement 9 is applied.

  The ceramic yarn 8 is preferably interposed in a portion of a temperature region that is 200 ° C. or more lower than the temperature at which the yarn starts to melt. This is because if the ceramic yarn 8 is melted, the airtightness is poor and the gas sealing function cannot be guaranteed. Specifically, for example, when 1 m of a 2 m long probe is inserted into an electric furnace in which a high temperature gas of 1600 ° C. exists in the center of the furnace, the tip of the solid electrolyte tube 1 exposed to the high temperature gas It is preferable to wrap around a portion that is 200 mm deeper than the portion. In many cases, the melting start temperature is not clearly shown as the characteristic display of the ceramic yarn. At this time, a temperature range lower than the complete melting temperature by 600 ° C. or more may be used as a guide.

  Next, the principle of measuring the oxygen concentration will be described. As shown in FIG. 3, the Nernst equation shown in the following chemical formula 1 is known in a concentration cell using a solid electrolyte tube.

Ｅは起電力、Ｒは気体定数、Ｔは絶対温度、Ｆはファラデー定数、Ｐｏ_１は基準極の酸素分圧、Ｐｏ_２は作動極の酸素分圧である。本発明では基準極に空気を用いるためその酸素分圧は０．２１ａｔｍである。従って、起電力（Ｅ）とプローブ先端温度（Ｔ）を測定すれば化学式１より作動極の酸素分圧（Ｐｏ_２）が連続的かつ正確に算出できることとなる。実際にはプローブ内側に熱電対を封入して同時に温度を測定できるようにすることが好ましい。

E is the electromotive force, R is the gas constant, T is the absolute temperature, F is the Faraday constant, Po ₁ is the oxygen partial pressure of the reference electrode, and Po ₂ is the oxygen partial pressure of the working electrode. In the present invention, since air is used for the reference electrode, the oxygen partial pressure is 0.21 atm. Therefore, if the electromotive force (E) and the probe tip temperature (T) are measured, the oxygen partial pressure (Po ₂ ) of the working electrode can be continuously and accurately calculated from the chemical formula 1. In practice, it is preferable to enclose a thermocouple inside the probe so that the temperature can be measured simultaneously.

ZrO ₂ .8 mol% Y ₂ O ₃ was used as a solid electrolyte tube, and an outer diameter of 8 mm, an inner diameter of 5 mm, and a length of 300 mm were prepared. A platinum coating layer was formed on the inner and outer surfaces of the tube by brushing. Moreover, the inner tip part of the solid electrolyte tube was filled with a platinum mesh having a diameter of 5 mm and 55 mesh, and a platinum electrode having a thickness of 0.5 mm was used. On the other hand, the supporting refractory was made of dense alumina, and a diameter of 15 mm, an inner diameter of 10 mm, and a length of 1000 mm were prepared. The solid electrolyte tube and the supporting refractory were combined as shown in FIG. 2 to form a sensor unit. The ceramic yarn is of the Al ₂ O ₃ .B ₂ O ₃ system, has a diameter of 0.3 mm and a melting start temperature of 1420 ° C., and is a solid electrolyte tube having a temperature range lower than this yarn melting start temperature by 200 ° C. or more. It wound around the part 250-300mm from the front-end | tip part.

The maximum temperature in the center of the Tamman furnace was set in the range of 800 to 1200 ° C., and Ar / O ₂ mixed standard gas was allowed to flow in the furnace at 5 l / min. Table 1 and FIG. 4 show the results of measuring the oxygen concentration in the gas in the center of the furnace using the oxygen concentration measuring apparatus obtained above.

上記表１、および図４に示すように、標準混合ガス中の酸素濃度と本発明の装置で測定した酸素濃度とはほぼ完全に一致しており、ガス中の酸素濃度を精度よく測定できることが確認できた。

As shown in Table 1 and FIG. 4, the oxygen concentration in the standard mixed gas and the oxygen concentration measured by the apparatus of the present invention are almost completely the same, and the oxygen concentration in the gas can be accurately measured. It could be confirmed.

  In a 30 kg melting furnace, 30 kg of electrolytic iron was melted, the components were adjusted to hot metal containing 4% C, and the hot metal temperature was adjusted to 1450 ° C. When the oxygen concentration measuring apparatus of Example 1 was set at a position where the tip sensor portion was 200 mm below the upper surface of the seal pot (approximately 20 mm above the hot metal surface) and the oxygen concentration in the gas was measured, it was 0.19%. . On the other hand, the result of measuring the oxygen concentration in the gas with the gas analyzer at the same position by sucking and collecting the gas at the same position was 0.18%, and the apparatus of the present invention accurately measured the oxygen concentration in the gas. It was confirmed that measurement was possible.

It is a front view which shows embodiment of this invention. It is sectional drawing of the principal part which shows embodiment of this invention. It is explanatory drawing which shows the measurement principle of oxygen concentration. It is a graph which shows the relationship between the oxygen concentration in a standard mixed gas, and the oxygen concentration measured by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid electrolyte pipe 2 Support refractory 3 Probe main body 4a Platinum coating layer 4b Platinum coating layer 5a Platinum electrode 5b Platinum electrode 7 Platinum mesh 8 Ceramic yarn 9 Ceramic cement 10 Voltage measuring device

Claims (3)

A platinum coating layer is provided on the inner and outer surfaces of a cylindrical solid electrolyte tube sealed at the tip, and a platinum electrode is connected to each of the platinum coating layers. The inside of the solid electrolyte tube is a reference electrode using air, and a solid electrolyte tube In the oxygen concentration measuring device in the high-temperature gas with the outside serving as the working electrode in contact with the high-temperature gas, the inner tip of the solid electrolyte tube was filled with platinum mesh, and the tip of the platinum electrode was pressed against and contacted the platinum mesh. A device for measuring oxygen concentration in a high-temperature gas. The rear end side of the solid electrolyte tube is inserted and supported by a cylindrical support refractory, and a ceramic yarn is interposed at the joint between the solid electrolyte tube and the support refractory so that the air tightness of the solid electrolyte tube and the support refractory The oxygen concentration measuring device in the high temperature gas according to claim 1, wherein 3. The oxygen concentration in the high-temperature gas according to claim 2, wherein the ceramic yarn is interposed at a portion in a temperature range that is 200 mm or more away from the tip of the solid electrolyte tube and lower than the temperature at which the yarn starts melting by 200 ° C. or more. measuring device.

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