Solid electrolyte sensor and method for using the solid electrolyte sensor

Abstract

Provided is a solid electrolyte sensor that can suppress damage to a sensor element and perform accurate concentration measurement, even when the temperature of the measurement gas is lower than the temperature range in which the concentration of a detection target gas shows a correlation with electromotive force in a solid electrolyte and the flow rate of the measurement gas is high. [Solution] In a sensor probe 1b comprising a sensor body having a first electrode 11 and a second electrode 12 provided on the surface of a sensor element 10, partitioned into a first space S1 in contact with the first electrode and a second space S2 in contact with the second electrode, a casing 40 which is cylindrical with a bottom and supports the sensor body inside, such that the space between the sensor body and the casing forms a first space, and an inlet pipe 71b and an outlet pipe 78 which each penetrate the casing and have their ends opening inside the first space, at least the portion in which the first electrode and the second electrode are provided is inserted into the internal atmosphere of a heating furnace 60.

Description

[Technical field]

[0001] The present invention relates to a solid electrolyte sensor that uses a solid electrolyte as a sensor element, and a method of using the solid electrolyte sensor. [Background technology]

[0002] Various gas sensors have been proposed that use a solid electrolyte (ion conductive ceramics) as a sensor element to detect the concentration of gases such as hydrogen gas, oxygen gas, and carbon dioxide gas, and the present applicant has also proposed several potential detection type gas sensors in the past. These gas sensors use the principle of a concentration cell in which a potential difference occurs in a solid electrolyte due to a concentration difference of the same ion, and measure the electromotive force generated in the sensor element when the concentration of the target gas differs between two spaces sandwiching the sensor element. If the concentration of the target gas in one of the two spaces is known, the gas concentration in the other space can be known from the measured electromotive force and the temperature of the sensor element using the Nernst equation. Alternatively, the correlation between the gas concentration and the electromotive force can be investigated in advance by measuring the electromotive force while changing the gas concentration in the other space while keeping the gas concentration in one space constant, and then the gas concentration can be known from the measured electromotive force when the gas concentration is unknown.

[0003] Here, the solid electrolyte is limited to a certain temperature range within which the concentration of the gas to be detected (or the partial pressure of the gas; the same applies below) shows a correlation with the electromotive force, and the lower limit is high at several hundred degrees. When the sensor probe of the solid electrolyte sensor is inserted into an industrial furnace for the purpose of measuring the gas concentration in the furnace, there is no problem because the solid electrolyte sensor is present in a high-temperature atmosphere that exceeds the lower limit.

[0004] However, there are cases where the temperature of the measurement gas in which the concentration of the target gas is to be detected is lower than the temperature range in which the concentration of the target gas correlates with the electromotive force in a solid electrolyte. For example, there are cases where the concentration of a specific gas in exhaust gas emitted from a gas burner, a gas turbine, an engine, etc. is to be detected for the purpose of controlling the combustion conditions or detecting abnormalities in the combustion state. The temperature of such exhaust gas is generally 200°C or lower, and currently there is no solid electrolyte in which the concentration of the target gas correlates with the electromotive force at such a low temperature.

[0005] Therefore, the present applicant has previously proposed a solid electrolyte sensor with a heater (for example, see Patent Document 1). Such heaters are roughly divided into built-in heaters that locally heat the sensor element from the inside, and external heaters that locally surround the outside of the sensor element.

[0006] However, when the flow rate of the measurement gas is large, the temperature of the sensor element of a conventional solid electrolyte sensor with a heater becomes low and falls outside the temperature range in which the concentration of the detection target gas correlates with the electromotive force, making measurement impossible. In particular, since hydrogen gas has a high thermal conductivity, this tendency becomes more pronounced when the concentration of hydrogen in the measurement gas increases. In addition, when the flow rate of the measurement gas is large, a temperature distribution occurs in which the temperature of the outer surface of the sensor element is lower than the internal temperature of the sensor element, making it impossible to perform accurate concentration measurement. In addition, there is a problem that the sensor element is damaged, such as cracked, due to the temperature difference, making the measurement itself impossible. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2016-027317 A Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above-mentioned circumstances, an object of the present invention is to provide a solid electrolyte sensor that can suppress damage to the sensor element and perform accurate concentration measurement even when the temperature of the measurement gas is lower than the temperature range in the solid electrolyte where the concentration of the detection target gas shows a correlation with electromotive force and the flow rate of the measurement gas is high, and a method for using the solid electrolyte sensor. [Means for solving the problem]

[0009] In order to solve the above problems, the solid electrolyte sensor according to the present invention comprises: "Equipped with a sensor probe and a heating furnace, The sensor probe includes: a sensor body including a sensor element formed of a solid electrolyte, a first electrode provided on a surface of the sensor element, and a second electrode provided on a surface of the sensor element in a second space partitioned from a first space in contact with the first electrode, and in which an electromotive force generated between the first electrode and the second electrode is measured; a casing having a bottomed cylindrical shape including a peripheral wall portion and a bottom portion, the casing supporting the sensor body therein, such that a space between the sensor body and the casing constitutes the first space; an introduction pipe that passes through the casing and has an end that opens inside the first space; a discharge pipe that penetrates the casing at a location different from the introduction pipe and has an end that opens inside the first space, The sensor probe is inserted into the heating furnace so that at least a portion of the sensor element where the first electrode and the second electrode are provided is located in the internal atmosphere of the heating furnace.

[0010] Here, examples of the configuration of the sensor body in which a first space to which the first electrode is in contact and a second space to which the second electrode is in contact are "partitioned" include a configuration in which the sensor element is shaped like a bottomed cylinder, and the first space and the second space are partitioned solely by the sensor element, or a configuration in which the sensor element seals the end or interior of a cylindrical holder, and the holder and the sensor element form a bottomed cylindrical body to partition the first space and the second space.

[0011] According to the solid electrolyte sensor of this configuration, the sensor probe is inserted into the atmosphere inside the heating furnace, and the measurement gas is circulated through the first space between the casing and the sensor body via the inlet pipe and the outlet pipe that penetrate the casing. This allows the concentration of the target gas contained in the measurement gas to be accurately measured by the sensor element that is placed in the atmosphere inside the heating furnace and sufficiently heated to a temperature within a temperature range (hereinafter referred to as the "usable temperature range") in which the concentration of the target gas correlates with the electromotive force in the solid electrolyte.

[0012] The atmosphere inside the heating furnace has a larger volume than the atmosphere heated by a conventional external heater or internal heater, and the entire or almost entire sensor element is placed in the atmosphere inside the heating furnace and is sufficiently heated. Therefore, even if the flow rate of the measurement gas introduced into the first space is large and the measurement gas is likely to take heat from the sensor element, heat that can compensate for this can be provided to the sensor element from the atmosphere inside the heating furnace. Therefore, the temperature of the sensor element can be maintained within the usable temperature range, and the concentration of the target gas contained in the measurement gas can be accurately measured.

[0013] In addition, since the sensor probe is inserted into the heating furnace so that at least the portion of the sensor element in which the first electrode and the second electrode are provided is located in the internal atmosphere of the heating furnace, temperature distribution is less likely to occur in the sensor element, and damage such as cracks to the sensor element due to temperature differences is suppressed.

[0014] In addition to the above configuration, the solid electrolyte sensor according to the present invention further comprises: "The inlet pipe and the outlet pipe penetrate the peripheral wall of the casing, The first space further includes a flat baffle plate that intersects with the axial direction of the introduction pipe near the opening of the introduction pipe and extends toward the bottom. Yes do.

[0015] When both the inlet pipe and the exhaust pipe penetrate the peripheral wall of the casing, the measurement gas introduced from the inlet pipe into the first space may flow along the inner peripheral surface of the peripheral wall of the casing and be exhausted from the exhaust pipe. If an attempt is made to insert the sensor probe into the heating furnace while avoiding interference with the inlet pipe and the exhaust pipe, the sensor body near the open ends of the inlet pipe and the exhaust pipe may not be sufficiently heated by the heating furnace, and the part of the sensor body close to the bottom of the casing is likely to be sufficiently heated by the heating furnace.

[0016] In this configuration, the first space is provided with a flat baffle plate, which intersects with the axial direction of the inlet pipe near the opening of the inlet pipe and extends toward the bottom of the casing. Therefore, the measurement gas introduced from the inlet pipe is prevented from proceeding straight by the baffle plate, and is further guided toward the bottom of the casing by the baffle plate. Therefore, the measurement gas can be guided to a portion of the sensor body that is easily heated by the heating furnace and can be brought into contact with the sensor element in that portion, so that the concentration of the target gas contained in the measurement gas can be accurately measured.

[0017] Next, a method of using the solid electrolyte sensor according to the present invention includes the steps of: "A method for using the solid electrolyte sensor described above, A measurement gas having a temperature of −10° C. to 200° C. is introduced into the first space through the introduction pipe.

[0018] This is a method of using the solid electrolyte sensor having the above configuration, in which a low-temperature gas of -10°C to 200°C is used as the measurement gas. At present, there are no solid electrolytes that have such a low temperature range in their usable temperature range. Nevertheless, according to the solid electrolyte sensor having the above configuration, as will be described in detail later, it is possible to accurately measure the concentration of the detection target gas contained in the measurement gas, even if the measurement gas is in such a low temperature range, or even if the measurement gas is in such a low temperature range and has a large flow rate. Effect of the Invention

[0019] As described above, according to the present invention, it is possible to provide a solid electrolyte sensor that can suppress damage to the sensor element and perform accurate concentration measurement even when the temperature of the measurement gas is lower than the temperature range in the solid electrolyte where the concentration of the detection target gas shows a correlation with electromotive force and the flow rate of the measurement gas is high, and a method of using the solid electrolyte sensor can be provided. [Brief description of the drawings]

[0020] [Figure 1] 1 is a longitudinal sectional view of a solid electrolyte sensor according to a first embodiment of the present invention. [Diagram 2] FIG. 4 is a longitudinal sectional view of a solid electrolyte sensor according to a second embodiment of the present invention. [Diagram 3] FIG. 4 is a longitudinal sectional view of a solid electrolyte sensor according to a third embodiment of the present invention. [Figure 4] FIG. 11 is a longitudinal sectional view of a solid electrolyte sensor according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, solid electrolyte sensors D1 to D4 according to one embodiment of the present invention and a method of using the same will be described with reference to Figures 1 to 4. First, the configuration of a solid electrolyte sensor D1 according to a first embodiment will be described with reference to Figure 1.

[0022] The solid electrolyte sensor D1 includes a sensor probe 1a and a heating furnace 60. The sensor probe 1a includes a sensor body, a casing 40, an inlet pipe 71b, and an outlet pipe 78.

[0023] The sensor body mainly includes a sensor element 10, a first electrode 11, a second electrode 12, and a thermocouple 23. The sensor element 10 is cylindrical with a bottom, and its external space is the first space S1 and its internal space is the second space S2. That is, in the sensor body of this embodiment, the first space S1 and the second space S2 are partitioned only by the sensor element 10. The first electrode 11 is provided on a surface of the sensor element 10 that contacts the first space S1, and the second electrode 12 is provided on a surface of the sensor element 10 that contacts the second space S2.

[0024] Lead wires 21, 22 are connected to the first electrode 11 and the second electrode 12, respectively, for electrical connection to an electrometer (not shown). Here, the lead wire 22 connecting the second electrode 12 and the electrometer passes through a ceramic protective tube 26 inserted into the second space S2. The thermocouple 23 also passes through this protective tube 26, and its measurement contact is abutted against the surface of the sensor element 10 on the second space S2 side. In addition, a reference gas introduction tube 25 for introducing a reference gas is inserted into the second space S2. When the atmosphere is used as the reference gas, the second space S2 may be opened to the atmosphere without using the reference gas introduction tube 25.

[0025] The casing 40 is a cylindrical casing with a bottom, which is made up of a peripheral wall portion 41 and a bottom portion 42. The casing 40 supports the sensor body with the sensor body positioned therein. Specifically, the space between the outer peripheral surface of the cylindrical portion of the sensor element 10 with a bottom and the inner peripheral surface of the peripheral wall portion 41 of the casing 40 is partially hermetically sealed by a sealing portion 51. As a result, a first space S1, which is the external space of the sensor element 10, is surrounded by the casing 40. In other words, the space between the casing 40 and the sensor body becomes the first space S1.

[0026] An inlet port 45 and a discharge port 46 are provided at different positions on the peripheral wall 41 of the casing 40, closer to the bottom 42 than the sealing portion 51. In this embodiment, the inlet port 45 and the discharge port 46 are provided at opposing positions on the peripheral wall 41 of the casing 40.

[0027] An introduction pipe 71b for introducing the measurement gas is inserted into the introduction port 45. As a result, the introduction pipe 71b penetrates the peripheral wall portion 41 of the casing 40, and an end of the introduction pipe 71b is open inside the first space S1. The introduction pipe 71b is a pipe branched off from the middle of the measurement gas introduction pipe 71, and an on-off valve 73 capable of opening and closing the flow of gas and adjusting the flow rate of gas is provided downstream of the branch point with the introduction pipe 71b in the measurement gas introduction pipe 71. As a result, it is possible to cause the entire amount of the measurement gas introduced into the measurement gas introduction pipe 71 to flow through the introduction pipe 71b, or to cause only a part of the measurement gas introduced into the measurement gas introduction pipe 71 to flow through the introduction pipe 71b.

[0028] The heating furnace 60 is a bottomed cylinder consisting of a peripheral wall 61 and a bottom 62. In the sensor probe 1a, a portion on the bottom 42 side from a position where the inlet pipe 71b and the outlet pipe 78 penetrate the peripheral wall 41 of the casing 40 is inserted into the heating furnace 60. Therefore, in the sensor probe 1a, almost the entire sensor element 10 including the portion where the first electrode 11 and the second electrode 12 are provided is placed in the internal atmosphere of the heating furnace 60.

[0029] When the solid electrolyte sensor D1 having the above configuration is used to detect the concentration (or partial pressure of gas; the same applies below) of a gas to be detected in a measurement gas, the measurement gas is introduced from the measurement gas inlet pipe 71 and introduced into the first space S1 of the sensor probe 1a via the inlet pipe 71b. The measurement gas can be introduced into the first space S1 by connecting a suction pump to the exhaust pipe 78 side. Alternatively, the measurement gas can be introduced into the first space S1 by connecting a blower for pressurizing the gas to the measurement gas inlet pipe 71 side.

[0030] The measurement gas is a gas such as exhaust gas that is at 200° C. or less, and when the measurement gas introduction pipe 71 is installed outdoors, the temperature may be lower depending on the season, and is in the temperature range of −10° C. to 200° C. When a measurement gas in such a low temperature range is brought into contact with the sensor element 10, if the temperature of the sensor element 10 is outside the usable temperature range of the solid electrolyte used in the sensor element 10, the concentration of the detection target gas cannot be measured.

[0031] In contrast, in the solid electrolyte sensor D1 of this embodiment, almost the entire sensor element 10 including the portion where the first electrode 11 and the second electrode 12 are provided is placed in the internal atmosphere of the heating furnace 60. In the sensor probe 1a, the sensor body is surrounded by a cylindrical casing 40 with a bottom, and the measurement gas is introduced into the first space S1, which is the space between the casing 40 and the sensor body, through the introduction pipe 71b penetrating the casing 40. Therefore, by setting the temperature of the internal atmosphere of the heating furnace 60 higher than the lower limit of the usable temperature range of the solid electrolyte used in the sensor element 10, it is possible to maintain the temperature of the sensor element 10 formed of the solid electrolyte within the usable temperature range, and the measurement gas can be brought into contact with the sensor element 10 maintained at such a temperature. As a result, even if the temperature of the measurement gas is lower than the lower limit of the usable temperature range, the concentration of the detection target gas contained in the measurement gas can be measured by the solid electrolyte sensor D1.

[0032] In this embodiment, almost the entire sensor element 10 is placed in the high-temperature atmosphere inside the heating furnace 60, and the volume of the atmosphere that can be heated to a high temperature is larger than when the sensor element 10 is locally heated by a conventional internal or external heater. Therefore, almost the entire sensor element 10 can be sufficiently heated to a temperature within the usable temperature range, and the concentration of the detection target gas contained in the measurement gas can be accurately measured.

[0033] Furthermore, since almost the entire sensor element 10 can be sufficiently heated to a temperature within the usable temperature range, even if the flow rate of the measurement gas is high and heat is taken from the sensor element 10 by the measurement gas, heat capable of compensating for this can be provided to the sensor element 10 from the surrounding high-temperature atmosphere. Therefore, even when the flow rate of the measurement gas is high, the temperature of the sensor element 10 can be maintained within the usable temperature range, and the concentration of the detection target gas contained in the measurement gas can be accurately measured.

[0034] In addition, almost the entire sensor element 10 is placed in the internal atmosphere of the heating furnace 60, effectively suppressing the occurrence of temperature distribution in the sensor element 10, thereby suppressing damage such as cracks in the sensor element 10 caused by temperature differences.

[0035] Next, a solid electrolyte sensor D2 of a second embodiment will be described with reference to Fig. 2. In the configuration of the solid electrolyte sensor D2, the same components as those in the solid electrolyte sensor D1 of the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0036] The solid electrolyte sensor D2 differs from the solid electrolyte sensor D1 in the configuration of the sensor probe 1b. In the sensor probe 1a of the solid electrolyte sensor D1, the sensor element 10 is cylindrical with a bottom, and the first space S1 and the second space S2 are partitioned only by the sensor element 10. In contrast, in the sensor main body of the sensor probe 1b of the solid electrolyte sensor D2, the sensor element 10 is fixed to one end of a cylindrical holder 30 by a sealing portion 56, so that the holder 30 and the sensor element 10 form a cylindrical body with a bottom, and the first space S1, which is the outer space, and the second space S2, which is the inner space, are partitioned.

[0037] In the sensor probe 1a, the gap between the cylindrical portion of the sensor element 10 and the peripheral wall 41 of the casing 40 is sealed by a sealing portion 51, whereas in the sensor probe 1b, the gap between the outer peripheral surface of the holder 30 and the inner peripheral surface of the peripheral wall 41 of the casing 40 is partially sealed airtight by a sealing portion 52. As a result, a first space S1, which is the external space of the sensor main body, is surrounded by the casing 40. The other configurations of the solid electrolyte sensor D2 are similar to those of the solid electrolyte sensor D1, including the fact that the introduction pipe 71b and the discharge pipe 78 penetrate the peripheral wall 41 of the casing 40 on the bottom surface 42 side of the sealing portion 52 and that the space between the casing 40 and the sensor main body is the first space S1.

[0038] The solid electrolyte sensor D2 thus configured can be used in the same manner as the solid electrolyte sensor D1 by introducing a measurement gas into the first space S1 through the introduction pipe 71b, and similar effects can be achieved. In particular, in the solid electrolyte sensor D2, the entire sensor element 10 is located entirely in the internal atmosphere of the heating furnace 60, and therefore the effect of maintaining the temperature of the sensor element 10 within the usable temperature range of the solid electrolyte by the heating furnace 60 can be more effectively achieved.

[0039] Next, a solid electrolyte sensor D3 of a third embodiment will be described with reference to Fig. 3. In the configuration of the solid electrolyte sensor D3, the same components as those of the solid electrolyte sensor D1 of the first embodiment and the solid electrolyte sensor D2 of the second embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0040] The configuration of the solid electrolyte sensor D3 corresponds to a configuration in which a baffle plate 80 is added to the solid electrolyte sensor D2 equipped with the sensor probe 1b, or a configuration in which a baffle plate 80 is added to the solid electrolyte sensor D1 equipped with the sensor probe 1a. Fig. 3 illustrates a configuration in which a baffle plate 80 is added to the solid electrolyte sensor D2.

[0041] Baffle plate 80 is an elongated flat plate, and is located in first space S1 between casing 40 and the sensor main body with a small gap between it and the inner peripheral surface of casing 40. Specifically, baffle plate 80 has a protruding portion at one end, and this portion is fixed to the inner peripheral surface of casing 40 between introduction port 45 and sealing portion 51 or sealing portion 52. Baffle plate 80 is perpendicular to the axial direction of introduction pipe 71b near the opening of introduction pipe 71b at one end side, and extends from there toward bottom portion 42 of casing 40.

[0042] In the solid electrolyte sensor D1, the inlet pipe 71b and the exhaust pipe 78 penetrate the peripheral wall portion 41 of the casing 40, and the inlet port 45 and the exhaust port 46 through which the inlet pipe 71b and the exhaust pipe 78 penetrate, respectively, face each other. Therefore, the measurement gas introduced from the inlet pipe 71b into the first space S1 may flow around in the circumferential direction along the inner circumferential surface of the peripheral wall portion 41 of the casing 40 or along the outer circumferential surface of the cylindrical portion of the sensor element 10, and may be discharged from the exhaust pipe 78 as it is. In order to avoid interference between the inlet pipe 71b and the exhaust pipe 78 and the heating furnace 60, in the sensor probe 1a, a portion on the bottom 42 side from the position where the inlet pipe 71b and the exhaust pipe 78 penetrate the casing 40 is inserted into the heating furnace 60. In this case, if the measurement gas flows while flowing around in the circumferential direction from the inlet pipe 71b to the exhaust pipe 78, the portion of the sensor element 10 that comes into contact with the measurement gas may not be sufficiently heated by the heating furnace 60. Furthermore, as illustrated in FIG. 1, if the first electrode 11 and the second electrode 12 are provided at the bottom of the cylindrical sensor element 10 with a bottom, that portion is sufficiently heated by the heating furnace 60, but the measurement gas may be discharged without sufficiently coming into contact with that portion of the sensor element 10, and the electromotive force may not be measured accurately.

[0043] In contrast, in the solid electrolyte sensor D3 in which the baffle plate 80 is added to the solid electrolyte sensor D1, when the measurement gas is introduced into the first space S1 through the introduction pipe 71b, the measurement gas that has flowed into the first space S1 is prevented from proceeding straight by the baffle plate 80, and is further guided along the baffle plate 80 toward the bottom 42 of the casing 40. Therefore, the measurement gas can be sufficiently brought into contact with the portion of the sensor element 10 that is sufficiently heated in the heating furnace 60, and the concentration of the detection target gas contained in the measurement gas can be accurately measured. Even if the first electrode 11 and the second electrode 12 are provided at the bottom of the cylindrical sensor element 10 with a bottom, the measurement gas is guided by the baffle plate 80 so that it flows toward the portion, and therefore the measurement gas can be sufficiently brought into contact with the portion of the sensor element 10 in which the first electrode 11 and the second electrode 12 are provided, and the electromotive force can be accurately measured.

[0044] Similarly, in the solid electrolyte sensor D2, the measurement gas introduced from the inlet pipe 71b into the first space S1 may flow circumferentially along the inner circumferential surface of the peripheral wall portion 41 of the casing 40 or along the outer circumferential surface of the holder 30, and may be discharged directly from the exhaust pipe 78. Since the sensor element 10 is supported by the holder 30 in the solid electrolyte sensor D2, if the measurement gas flows in the circumferential direction, the measurement gas will not easily come into contact with the sensor element 10, and there is a risk that accurate measurement may not be possible even if the sensor element 10 is sufficiently heated in the heating furnace 60.

[0045] In contrast, in solid electrolyte sensor D3, in which a baffle plate 80 is added to solid electrolyte sensor D2, when a measurement gas is introduced into first space S1 through introduction pipe 71b, the measurement gas that has flowed into first space S1 is prevented from proceeding straight ahead by baffle plate 80, and is further guided along baffle plate 80 toward bottom 42 of casing 40. Therefore, the measurement gas can be brought into sufficient contact with sensor element 10 supported by holder 30, and sensor element 10 is sufficiently heated by heating furnace 60, so that the concentration of the target gas contained in the measurement gas can be accurately measured.

[0046] Next, a solid electrolyte sensor D4 of a fourth embodiment will be described with reference to Fig. 4. In the configuration of the solid electrolyte sensor D4, the same components as those of the solid electrolyte sensor D1 of the first embodiment, the solid electrolyte sensor D2 of the second embodiment, and the solid electrolyte sensor D3 of the third embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0047] The solid electrolyte sensor D4 differs from the solid electrolyte sensors D1, D2, and D3 in that the inlet port 45 and the outlet port 46 are provided through the bottom 42 of the casing 40, not through the peripheral wall 41, and the inlet pipe 71b and the outlet pipe 78 penetrate the bottom 42. Accordingly, in order to avoid interference between the inlet pipe 71b and the outlet pipe 78 and the furnace 60, the furnace 60 has a cylindrical configuration consisting of only the peripheral wall 61 and does not have a bottom 62. While FIG. 4 illustrates the solid electrolyte sensor D4 in which the sensor probe inserted into the internal atmosphere of the furnace 60 is the sensor probe 1b, the solid electrolyte sensor D4 may also have a configuration in which the sensor probe 1a is inserted into the internal atmosphere of the furnace 60.

[0048] In the solid electrolyte sensor D4 having such a configuration, when a measurement gas is introduced into the first space S1 through the inlet pipe 71b, the measurement gas fills a portion of the first space S1 close to the bottom 42 of the casing 40 and is then discharged through the exhaust pipe 78. Therefore, when the sensor probe is the sensor probe 1b, the measurement gas can be sufficiently brought into contact with the sensor element 10 supported on the end of the holder 30, and the concentration of the target gas contained in the measurement gas can be accurately measured by the sensor element 10 sufficiently heated by the heating furnace 60.

[0049] Furthermore, when the sensor probe is the sensor probe 1a, even if the first electrode 11 and the second electrode 12 are provided at the bottom of the cylindrical sensor element 10 with a bottom, the measurement gas can be brought into sufficient contact with that part of the sensor element 10, so that the electromotive force can be accurately measured and the concentration of the target gas contained in the measurement gas can be accurately measured.

[0050] As described above, according to the solid electrolyte sensors D1 to D4 of this embodiment, the sensor probes 1a, 1b are inserted into the internal atmosphere of the heating furnaces 60, 60b, and the measurement gas is caused to flow into the first space S1 between the casing 40 and the sensor body via the inlet pipe 71b and the outlet pipe 78 which penetrate the casing 40. This allows the concentration of the target gas contained in the measurement gas to be accurately measured by the sensor element 10 which is placed in the internal atmosphere of the heating furnaces 60, 60b and is sufficiently heated.

[0051] The internal atmosphere of the heating furnaces 60, 60b has a larger volume than the atmosphere heated by a conventional external heater or internal heater, and the entire or almost entire sensor element 10 is placed in the internal atmosphere of the heating furnaces 60, 60b and is sufficiently heated. Therefore, even if the flow rate of the measurement gas introduced into the first space S1 is large and the measurement gas takes away heat from the sensor element 10, heat sufficient to compensate for this can be provided to the sensor element 10 from the internal atmosphere of the heating furnaces 60, 60b, and the temperature of the sensor element 10 can be maintained within the usable temperature range of the solid electrolyte, thereby making it possible to accurately measure the concentration of the target gas contained in the measurement gas.

[0052] In fact, a test was conducted to confirm whether the solid electrolyte sensor of this embodiment can accurately measure the concentration of the target gas contained in the measurement gas when the temperature of the measurement gas is lower than the lower limit of the usable temperature range, even when the flow rate of the measurement gas is high. The results are compared with those of a comparative example, which is a conventional solid electrolyte sensor.

[0053] The solid electrolyte sensor of this embodiment has the configuration of solid electrolyte sensor D2. The gas to be detected is hydrogen gas, and the sensor element has a chemical formula of AB 1-a B' a O 3-αIn the solid electrolyte, A is Sr, B is Zr, B' is Yb, and a is 0.1. The usable temperature range of this solid electrolyte is 380°C to 650°C. α is an oxygen vacancy, and is a value that changes depending on the atomic species of A, B, and B', the value of a, the temperature and oxygen partial pressure of the measurement atmosphere, etc. In the solid electrolyte sensor of this embodiment, the heating furnace surrounding the sensor probe was adjusted so that the temperature of the internal atmosphere was maintained at 500°C.

[0054] The solid electrolyte sensor of the comparative example was a sensor body equivalent to the sensor probe 1b without the casing, to which an internal heater was added to locally heat only the sensor element from the inside. The solid electrolyte of the sensor element was the same as that described above.

[0055] For both the solid electrolyte sensor of this embodiment and the solid electrolyte sensor of the comparative example, a measurement gas having a temperature lower than the lower limit of the usable temperature range of the solid electrolyte, i.e., -10°C, 25°C, and 200°C, was introduced into the first space. The flow rate (per unit time) of the measurement gas was changed to 200 ml / min, 500 ml / min, 1000 ml / min, and 2000 ml / min. The measurement gas was of four types with different hydrogen concentrations: 1% hydrogen-99% argon, 10% hydrogen-90% argon, 30% hydrogen-70% argon, and 100% hydrogen. Note that "%" here is volume percentage.

[0056] A reference gas with a known hydrogen concentration was introduced into the second space, and the electromotive force generated between the first and second electrodes and the temperature of the sensor element were measured, and the hydrogen gas concentration in the measurement gas was calculated using the Nernst equation. When the calculated hydrogen gas concentration matched the actual hydrogen concentration in the measurement gas, or when the difference between the two was within a predetermined allowable range (a range determined in consideration of the measurement error depending on the magnitude of the electromotive force), the measurement was evaluated as being accurate and was marked with a "◯". When the difference between the two exceeded the predetermined allowable range but no damage was caused to the sensor element, the measurement was evaluated as being possible but not accurate and was marked with a "△". When damage such as cracks occurred in the sensor element, the measurement itself was evaluated as being impossible and marked with a "X". The results are shown in Table 1.

[0057] [Table 1]

[0058] As can be seen from Table 1, in the solid electrolyte sensor of the comparative example, when comparing at the same flow rate of the measured gas, the lower the temperature of the measured gas, the more likely it was that accurate measurement would not be possible or that damage to the sensor element would occur, and this tendency was more pronounced as the hydrogen concentration in the measured gas increased. This is thought to be because the lower the temperature of the measured gas, the more difficult it becomes for an internal heater that locally heats the sensor element to maintain the temperature of the sensor element within the usable temperature range, and also because hydrogen gas has a high thermal conductivity, so the higher the hydrogen concentration of the measured gas, the more easily the measured gas will take away heat from the sensor element.

[0059] In addition, when comparing the solid electrolyte sensor of the comparative example with the same temperature and hydrogen concentration of the measurement gas, the greater the flow rate of the measurement gas, the more likely it was that accurate measurement could not be performed or that damage to the sensor element occurred. This was thought to be because, as the flow rate increases, the measurement gas is more likely to take away heat from the sensor element, causing the temperature of the sensor element to fall outside the usable temperature range and making it impossible to perform accurate concentration measurement, and a temperature distribution occurs in the sensor element, leading to damage due to the temperature difference.

[0060] In contrast, the solid electrolyte sensor of this embodiment was able to accurately measure the concentration in the temperature range of -10°C to 200°C. Although -10°C is a temperature considerably lower than the usable temperature range of the solid electrolyte, it can be seen that by placing the solid electrolyte sensor in the internal atmosphere of the heating furnace, the temperature of the sensor element is sufficiently heated to be within the usable temperature range. In addition, even if the flow rate of the measurement gas was increased from 200 ml / min to 2000 ml / min, accurate measurement was possible. From this, it was considered that even if the heat of the sensor element is taken away by the low-temperature measurement gas, heat capable of compensating for it is provided from the high-temperature atmosphere inside the heating furnace, so that the temperature of the sensor element can be maintained within the usable temperature range of the solid electrolyte. In particular, it is significant that the temperature of the sensor element can be maintained within the usable temperature range of the solid electrolyte and accurate concentration measurement can be performed even with a measurement gas with a very large flow rate of 1000 ml / min to 2000 ml / min. In other words, if the diameter of the pipe through which the gas flows is the same, the flow rate will increase if the flow velocity is increased, so by introducing the measurement gas into the solid electrolyte sensor at a high flow velocity, the concentration of the target gas in the measurement gas can be measured efficiently.

[0061] In addition, accurate measurement was possible even when the hydrogen concentration of the measurement gas was increased to 100%. Although it is rare for the hydrogen concentration in the measurement gas to reach 100% in an actual measurement site, even if the heat of the sensor element is taken away by the measurement gas containing a large amount of gas with high thermal conductivity, the heat that can compensate for this is provided from the high-temperature atmosphere inside the heating furnace, so it is thought that the temperature of the sensor element can be maintained within the usable temperature range of the solid electrolyte.

[0062] The present invention has been described above with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various improvements and design changes are possible without departing from the spirit of the present invention, as described below.

[0063] For example, in the sensor probe 1b in the above embodiment, the sensor element 10 is cylindrical with a bottom and is fixed to the holder 30 so that the open end is located on the second space S2 side. However, the sensor element 10 may be fixed to the holder 30 so that the open end is located on the first space S1 side. The shape of the sensor element 10 is not limited to a cylindrical shape with a bottom, and may be a columnar or flat shape. Furthermore, the position where the sensor element 10 is fixed to the holder 30 is not limited to an end of the holder 30, and the sensor element 10 may be configured to seal the internal space of the cylindrical holder 30 at a midway position on the inner circumferential surface of the holder 30. Even in these configurations, the first space S1 and the second space S2 are partitioned by the holder 30 and the sensor element 10. [Explanation of symbols]

[0064] 1a,1b Sensor probe 10 Sensor element 11 First electrode 12 Second electrode 40 Casing 41 Peripheral wall section 42 Bottom 60 Furnace 71b Inlet pipe 78 Exhaust pipe 80 Baffle Plate D1,D2,D3,D4 solid electrolyte electrolyte S1 First Space S2 Second Space

Claims

1. A sensor probe and a heating furnace are provided. The sensor probe includes: a sensor body including a sensor element formed of a solid electrolyte, a first electrode provided on a surface of the sensor element, and a second electrode provided on a surface of the sensor element in a second space partitioned from a first space in contact with the first electrode, and in which an electromotive force generated between the first electrode and the second electrode is measured; a casing having a bottomed cylindrical shape including a peripheral wall portion and a bottom portion, the casing supporting the sensor body therein, such that a space between the sensor body and the casing constitutes the first space; an introduction pipe that passes through the casing and has an end that opens inside the first space; a discharge pipe that penetrates the casing at a location different from the introduction pipe and has an end that opens inside the first space, the sensor probe is inserted into the heating furnace so that a portion of the sensor element where at least the first electrode and the second electrode are provided is located in an internal atmosphere of the heating furnace; the inlet pipe and the outlet pipe penetrate the peripheral wall portion of the casing, The first space further includes a flat baffle plate that intersects with the axial direction of the introduction pipe near the opening of the introduction pipe and extends toward the bottom. A solid electrolyte sensor comprising:

2. A method for using the solid electrolyte sensor according to claim 1, comprising: A measurement gas having a temperature of −10° C. to 200° C. is introduced into the first space through the introduction pipe. A method for using a solid electrolyte sensor comprising the steps of:

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