Solid electrolyte sensor and method of using solid electrolyte sensor

Abstract

To provide a solid electrolyte sensor capable of taking accurate concentration measurements by suppressing a sensor element from being damaged even when the temperature of a measurement gas is lower than a temperature range in which the concentration of a gas to be detected shows correlation with electromotive force with respect to a solid electrolyte and the measurement gas has a large flow rate.SOLUTION: A sensor probe 1b comprises: a sensor body which is provided with a first electrode 11 and a second electrode 12 on a surface of a sensor element 10, and has a first space S1 that the first electrode contacts and a second space S2 that the second electrode contacts sectioned; a casing 40 which is in a bottomed cylinder shape and supports the sensor body inside so that the space formed with the sensor body is the first space; and an introduction pipe 71b and an exhaust pipe 78 which penetrate the casing respectively and also have their ends opened inside the first space, wherein parts provided with at least the first electrode and second electrode are inserted into the atmosphere in a heating furnace 60.SELECTED DRAWING: Figure 2

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 for using the solid electrolyte sensor. [Background technology]

[0002] Various gas sensors using solid electrolytes (ion-conductive ceramics) as sensor elements to detect the concentrations of gases such as hydrogen, oxygen, and carbon dioxide have been proposed, and the present applicant has also previously proposed several potential-detection gas sensors. These gas sensors use the principle of a concentration cell, in which a potential difference occurs in a solid electrolyte due to a difference in concentration of the same ion. They measure the electromotive force generated in the sensor element when the concentrations of the target gas differ 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 determined from the measured electromotive force and the temperature of the sensor element using the Nernst equation. Alternatively, by measuring the electromotive force while keeping the gas concentration in one space constant and varying the gas concentration in the other space, the correlation between the gas concentration and the electromotive force can be determined in advance, allowing the gas concentration to be determined from the measured electromotive force when the gas concentration is unknown.

[0003] Here, the solid electrolyte is limited to a specific temperature range within which the concentration of the gas to be detected (or gas partial pressure; the same applies below) shows a correlation with electromotive force, and the lower limit is high, at several hundred degrees. When the sensor probe of a solid electrolyte sensor is inserted into an industrial furnace for the purpose of measuring the gas concentration therein, 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, this may be the case when the concentration of a specific gas in the exhaust gas emitted from a gas burner, gas turbine, engine, etc. is to be detected for the purpose of controlling combustion conditions or detecting abnormalities in the combustion state. The temperature of such exhaust gas is generally below 200°C, and currently there is no solid electrolyte that correlates the concentration of the target gas with the electromotive force at such low temperatures.

[0005] Therefore, the present applicant has previously proposed a solid electrolyte sensor with a heater (see, for example, Patent Document 1). Such heaters are broadly divided into internal 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 high, the temperature of the sensor element in a conventional solid electrolyte sensor with a heater can drop below the temperature range where the concentration of the target gas correlates with the electromotive force, making measurement impossible. This tendency becomes particularly pronounced as the concentration of hydrogen in the measurement gas increases, due to the high thermal conductivity of hydrogen gas. Furthermore, when the flow rate of the measurement gas is high, 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. This not only makes it impossible to perform accurate concentration measurement, but also causes damage such as cracks in the sensor element due to the temperature difference, making measurement impossible. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-027317 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above 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 target gas correlates 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: "A sensor probe and a heating furnace are included, 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 the surface of the sensor element in a second space partitioned from a first space in contact with the first electrode, wherein 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, so that a space between the sensor body and the casing forms 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 position 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 the 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 the first space to which the first electrode is in contact and the second space to which the second electrode is in contact are "compartmentalized" include a configuration in which the sensor element is shaped like a bottomed cylinder, and the first space and the second space are partitioned by the sensor element alone, or a configuration in which the sensor element seals the end or interior of a cylindrical holder, and the holder and sensor element form a bottomed cylindrical body, thereby partitioning the first space and the second space.

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

[0012] The atmosphere inside the heating furnace has a larger volume than the atmosphere heated by conventional external or internal heaters, and the entire sensor element, or almost the 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 high and the measurement gas is likely to take heat from the sensor element, sufficient heat 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, allowing the concentration of the target gas contained in the measurement gas to be accurately measured.

[0013] Furthermore, since the sensor probe is inserted into the heating furnace so that at least the portion of the sensor element where the first electrode and 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 has: "The inlet pipe and the outlet pipe penetrate the peripheral wall portion of the casing, The first space may further include 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.

[0015] When both the inlet pipe and the outlet pipe penetrate the peripheral wall of the casing, the measurement gas introduced into the first space from the inlet pipe may flow along the inner peripheral surface of the peripheral wall of the casing and be discharged from the outlet pipe. If an attempt is made to insert the sensor probe into the heating furnace while avoiding interference with the inlet pipe and the outlet pipe, the sensor body near the open ends of the inlet pipe and the outlet pipe may not be sufficiently heated by the heating furnace, and the portion of the sensor body near 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 the axial direction of the inlet pipe near the opening of the inlet pipe and extends toward the bottom of the casing. Therefore, the baffle plate prevents the measurement gas introduced from the inlet pipe from traveling straight ahead and guides it toward the bottom of the casing. Therefore, the measurement gas can be guided to a portion of the sensor body that is easily heated by the heating furnace, allowing the measurement gas to come into contact with the sensor element in that portion, thereby enabling accurate measurement of the concentration of the target gas contained in the measurement gas.

[0017] Next, the method of using the solid electrolyte sensor according to the present invention is as follows: "A method of 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. Currently, there are no solid electrolytes that have an operating temperature range that covers such a low temperature range. Nevertheless, as will be described in detail later, the solid electrolyte sensor having the above configuration can accurately measure the concentration of the target gas contained in the measurement gas, even when the measurement gas is in such a low temperature range, or even when the measurement gas is in such a low temperature range and has a high flow rate. [Effects of the Invention]

[0019] As described above, the present invention can provide a solid electrolyte sensor and a method for using the 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 target gas to be detected correlates with electromotive force and the flow rate of the measurement gas is high. [Brief explanation 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. [Figure 2] FIG. 4 is a longitudinal sectional view of a solid electrolyte sensor according to a second embodiment of the present invention. [Figure 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. 10 is a longitudinal sectional view of a solid electrolyte sensor according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Solid electrolyte sensors D1 to D4 according to one embodiment of the present invention and methods for using the same will now be described with reference to Figures 1 to 4. First, the configuration of the solid electrolyte sensor D1 according to the 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 main 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 a first space S1, and its internal space is a second space S2. That is, in the sensor main body of this embodiment, the first space S1 and the second space S2 are separated 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 and 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. A thermocouple 23 also passes through this protective tube 26, with its measurement contact abutting against the surface of the sensor element 10 on the second space S2 side. In addition, a reference gas inlet pipe 25 for introducing a reference gas is inserted into the second space S2. Note that when air is used as the reference gas, the second space S2 may be open to the atmosphere without using the reference gas inlet pipe 25.

[0025] The casing 40 is cylindrical and has a bottom, and is made up of a peripheral wall 41 and a bottom 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 and the inner peripheral surface of the peripheral wall 41 of the casing 40 is partially airtightly 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 an outlet 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 outlet port 46 are provided at opposing positions on the peripheral wall 41 of the casing 40.

[0027] An inlet pipe 71b for introducing the measurement gas is inserted into the inlet port 45. As a result, the inlet pipe 71b penetrates the peripheral wall portion 41 of the casing 40, with one end of the inlet pipe 71b opening inside the first space S1. The inlet pipe 71b branches off from the measurement gas inlet pipe 71, and an on-off valve 73 that opens and closes the flow of gas and adjusts the gas flow rate is provided in the measurement gas inlet pipe 71 downstream of the branch point with the inlet pipe 71b. This makes it possible to pass the entire amount of measurement gas introduced into the measurement gas inlet pipe 71 through the inlet pipe 71b, or to pass only a portion of the measurement gas introduced into the measurement gas inlet pipe 71 through the inlet pipe 71b.

[0028] The heating furnace 60 is a cylindrical shape with a bottom and is made up of a peripheral wall 61 and a bottom 62. In the sensor probe 1a, the portion on the bottom 42 side of the 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 gas partial pressure; the same applies hereinafter) of a target gas in a measurement gas, the measurement gas is introduced through the measurement gas inlet pipe 71 and then 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 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 200°C or below, and if the measurement gas inlet pipe 71 is installed outdoors, the temperature may be lower depending on the season, ranging from -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 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 portions 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 enclosed in a cylindrical casing 40 with a bottom, and a measurement gas is introduced into a first space S1, which is the space between the casing 40 and the sensor body, through an 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, the temperature of the sensor element 10 made of the solid electrolyte can be maintained within the usable temperature range, and the measurement gas can be brought into contact with the sensor element 10 maintained at such a temperature. This allows the solid electrolyte sensor D1 to measure the concentration of the target gas contained in the measurement gas even when the temperature of the measurement gas is lower than the lower limit of the usable temperature range.

[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 target gas contained in the measurement gas can be accurately measured.

[0033] Furthermore, because almost the entire sensor element 10 can be sufficiently heated to a temperature within the usable temperature range, even if the measurement gas takes heat from the sensor element 10 when the flow rate of the measurement gas is high, heat sufficient to compensate 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 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, which effectively prevents temperature distribution from occurring in the sensor element 10, thereby preventing damage such as cracks from occurring in the sensor element 10 due to 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 of 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 separated 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, which separates the first space S1, which is the outer space, from the second space S2, which is the inner space.

[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 enclosed by the casing 40. The other configurations of the solid electrolyte sensor D2 are the same as those of the solid electrolyte sensor D1, including the fact that the inlet pipe 71b and the outlet 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 having such a configuration 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 within the internal atmosphere of the heating furnace 60, and therefore the effect of using the heating furnace 60 to maintain the temperature of the sensor element 10 within the usable temperature range of the solid electrolyte 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 in the shape of a long, narrow flat plate, and is positioned in first space S1 between casing 40 and the sensor main body with a small gap between it and the inner circumferential surface of casing 40. Specifically, baffle plate 80 has a protruding portion at one end, and this portion is fixed to the inner circumferential surface of casing 40 between introduction port 45 and sealing portion 51 or sealing portion 52. One end of baffle plate 80 is perpendicular to the axial direction of introduction pipe 71b near the opening of introduction pipe 71b, and extends from there toward bottom 42 of casing 40.

[0042] In the solid electrolyte sensor D1, the inlet pipe 71b and the outlet pipe 78 penetrate the peripheral wall 41 of the casing 40, and the inlet port 45 and the outlet port 46 through which the inlet pipe 71b and the outlet pipe 78 penetrate, respectively, face each other. Therefore, 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 41 of the casing 40 or along the outer circumferential surface of the cylindrical portion of the sensor element 10 and be discharged directly from the outlet pipe 78. To avoid interference between the inlet pipe 71b and the outlet pipe 78 and the heating furnace 60, the sensor probe 1a is inserted into the heating furnace 60 at a portion closer to the bottom 42 than the position where the inlet pipe 71b and the outlet pipe 78 penetrate the casing 40. In this case, if the measurement gas flows circumferentially from the inlet pipe 71b to the outlet 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 contacting that portion of the sensor element 10, and the electromotive force may not be measured accurately.

[0043] In contrast, in solid electrolyte sensor D3, which is obtained by adding a baffle plate 80 to solid electrolyte sensor D1, when a measurement gas is introduced into first space S1 through inlet pipe 71b, the measurement gas that has flowed into first space S1 is prevented from proceeding straight 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 the portion of sensor element 10 that is sufficiently heated in heating furnace 60, allowing accurate measurement of the concentration of the target gas contained in the measurement gas. Furthermore, even when first electrode 11 and second electrode 12 are provided at the bottom of cylindrical sensor element 10 with a bottom, baffle plate 80 guides the measurement gas toward that portion. Therefore, the measurement gas can be brought into sufficient contact with the portion of sensor element 10 where first electrode 11 and second electrode 12 are provided, allowing accurate measurement of electromotive force.

[0044] Similarly, in the solid electrolyte sensor D2, the measurement gas introduced into the first space S1 from the inlet pipe 71b 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. In the solid electrolyte sensor D2, the sensor element 10 is supported by the holder 30. Therefore, if the measurement gas flows in the circumferential direction, the measurement gas is unlikely to come into contact with the sensor element 10, and 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, which is obtained by adding baffle plate 80 to solid electrolyte sensor D2, when a measurement gas is introduced into first space S1 through inlet pipe 71b, the measurement gas that has flowed into first space S1 is prevented from proceeding straight 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] Solid electrolyte sensor D4 differs from solid electrolyte sensors D1, D2, and D3 in that inlet port 45 and outlet port 46 are provided through bottom 42 rather than peripheral wall 41 of casing 40, and in that inlet pipe 71b and outlet pipe 78 penetrate bottom 42. Accordingly, in order to avoid interference between inlet pipe 71b and outlet pipe 78 and heating furnace 60, heating furnace 60 has a cylindrical configuration consisting only of peripheral wall 61 and does not have bottom 62. While FIG. 4 illustrates solid electrolyte sensor D4 in which sensor probe 1b is inserted into the internal atmosphere of heating furnace 60, solid electrolyte sensor D4 in which sensor probe 1a is inserted into the internal atmosphere of heating furnace 60 may also be used.

[0048] In the solid electrolyte sensor D4 configured as described above, when a measurement gas is introduced into the first space S1 through the inlet pipe 71b, the measurement gas fills the portion of the first space S1 close to the bottom 42 of the casing 40 and is then discharged through the outlet pipe 78. Therefore, when the sensor probe is the sensor probe 1b, the measurement gas can be brought into sufficient 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 that is 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 and 1b are inserted into the internal atmosphere of the heating furnaces 60 and 60b, and the measurement gas is circulated into the first space S1 between the casing 40 and the sensor body via the inlet pipe 71b and the outlet pipe 78 that penetrate the casing 40. This allows the sensor element 10, which is placed in the internal atmosphere of the heating furnaces 60 and 60b and is sufficiently heated, to accurately measure the concentration of the target gas contained in the measurement gas.

[0051] The internal atmosphere of the heating furnaces 60, 60b has a larger volume than the atmosphere heated by a conventional external 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 heat from the sensor element 10, sufficient heat 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, allowing the concentration of the target gas contained in the measurement gas to be accurately measured.

[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 even when the flow rate of the measurement gas is high when the temperature of the measurement gas is lower than the lower limit of the usable temperature range, and 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 AB 1-a B' a O 3-αIn the solid electrolyte sensor of this embodiment, a solid electrolyte having a composition in which A is Sr, B is Zr, B' is Yb, and a is 0.1 is used. 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. The heating furnace surrounding the sensor probe in the solid electrolyte sensor of this embodiment was adjusted so that the temperature of the internal atmosphere was maintained at 500°C.

[0054] The solid electrolyte sensor used as a comparative example was a sensor body equivalent to the sensor probe 1b minus the casing, with an internal heater added to locally heat only the sensor element from the inside. The solid electrolyte used in 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, measurement gases at temperatures lower than the lower limit of the usable temperature range of the solid electrolyte, i.e., -10°C, 25°C, and 200°C, were introduced into the first space. The flow rates (per unit time) of the measurement gas were varied to 200 ml / min, 500 ml / min, 1000 ml / min, and 2000 ml / min. The measurement gases used were four types with different hydrogen concentrations: 1% hydrogen-99% argon, 10% hydrogen-90% argon, 30% hydrogen-70% argon, and 100% hydrogen. Note that "%" here refers to 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. The hydrogen gas concentration in the measurement gas was calculated using the Nernst equation. If the calculated hydrogen gas concentration matched the actual hydrogen concentration in the measurement gas, or if the difference between the two was within a predetermined tolerance (a range determined based on the magnitude of the electromotive force and taking into account measurement error), the measurement was evaluated as accurate and a "Good" was given. If the difference between the two exceeded the predetermined tolerance but no damage occurred to the sensor element, the measurement was evaluated as accurate but not accurate and a "Good" was given. If the sensor element was damaged, such as by cracking, the measurement was evaluated as impossible and a "Bad" was given. The results are shown in Table 1.

[0057] [Table 1]

[0058] As can be seen from Table 1, when comparing the solid electrolyte sensors of the comparative example with the same flow rate of the measurement gas, the lower the temperature of the measurement gas, the more likely it was that accurate measurement would be impossible or that damage to the sensor element would occur, and this tendency became more pronounced as the hydrogen concentration in the measurement gas increased. This is thought to be because the lower the temperature of the measurement 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 its usable temperature range, and also because hydrogen gas has high thermal conductivity, the higher the hydrogen concentration of the measurement gas, the more easily the measurement gas will absorb heat from the sensor element.

[0059] Furthermore, 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 would not be possible or that damage to the sensor element would occur. This is thought to be because, as the flow rate increases, the measurement gas is more likely to absorb heat from the sensor element, causing the temperature of the sensor element to fall outside the usable temperature range, making accurate concentration measurement impossible, and the temperature distribution that occurs in the sensor element leads to damage due to the temperature difference.

[0060] In contrast, the solid electrolyte sensor of this embodiment was able to accurately measure concentrations in a temperature range of -10°C to 200°C. Although -10°C is significantly lower than the usable temperature range of solid electrolytes, placing the solid electrolyte sensor in the atmosphere inside the heating furnace ensured sufficient heating to keep the sensor element within the usable temperature range. Accurate measurements were also possible even when the flow rate of the measurement gas was increased from 200 ml / min to 2000 ml / min. This suggests that even if the low-temperature measurement gas absorbs heat from the sensor element, the high-temperature atmosphere inside the heating furnace provides sufficient heat to compensate, maintaining the sensor element temperature within the usable temperature range of the solid electrolyte. It is particularly significant that accurate concentration measurements can be performed by maintaining the sensor element temperature within the usable temperature range of the solid electrolyte, even with a very high flow rate of measurement gas, such as 1000 ml / min to 2000 ml / min. In other words, if the diameter of the pipe through which the gas flows is the same, increasing the flow rate will increase the flow rate, so by introducing the measurement gas into the solid electrolyte sensor at a high flow rate, the concentration of the target gas in the measurement gas can be measured efficiently.

[0061] In addition, accurate measurements were 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, it is thought that the temperature of the sensor element can be maintained within the usable temperature range of the solid electrolyte because heat is provided from the high-temperature atmosphere inside the heating furnace to compensate for this.

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

[0063] For example, in the sensor probe 1b in the above embodiment, the sensor element 10 has a cylindrical shape with a bottom and is fixed to the holder 30 so that its open end is located on the second space S2 side. However, the sensor element 10 may be fixed to the holder 30 so that its 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 plate shape. Furthermore, the position at which the sensor element 10 is fixed to the holder 30 is not limited to an end of the holder 30. The sensor element 10 may be configured to seal the internal space of the cylindrical holder 30 at a midpoint 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 included, 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 the surface of the sensor element in a second space partitioned from a first space in contact with the first electrode, wherein 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, so that a space between the sensor body and the casing forms 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 position 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. A solid electrolyte sensor characterized by:

2. the inlet pipe and the outlet pipe pass through 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.

2. The solid electrolyte sensor according to claim 1, wherein the solid electrolyte sensor is a silicon dioxide gas.

3. A method for using the solid electrolyte sensor according to claim 1 or 2, 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.

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