JPH0664000B2 - Industrial gas concentration measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an industrial gas concentration measuring device, and more specifically, it is installed on a furnace wall or exhaust gas passage wall of various combustion furnaces such as industrial furnaces and boilers. The present invention relates to an industrial gas concentration measuring device for measuring a gas concentration in a combustion exhaust gas or an atmosphere in a furnace or an exhaust gas passage.

(Prior Art) Conventionally, in an oxygen concentration detector that detects, for example, the oxygen concentration in the exhaust gas from a boiler of a thermal power plant or various combustion furnaces, for example, at an upper and lower temperatures of about 600 ° C. as a boundary, The measuring device was configured separately for low temperatures. First, in a measuring device for high temperatures of about 600 ° C or higher, since the operating temperature of the oxygen sensor element or higher is reached, a measuring element for measuring the temperature of the oxygen sensor element is arranged near the sensor element, and each temperature is measured. After the electromotive voltage of the oxygen sensor element in 1 was corrected for each temperature, it was obtained as an output signal.

Next, in a measuring device for low temperatures from less than about 600 ° C to normal temperature, since it is below the operating temperature of the oxygen sensor element, adjust the temperature in the vicinity of the oxygen sensor element with a heating element to raise the temperature above the operating temperature. The electromotive force E corresponding to the oxygen partial pressure in the measurement gas was calculated by the open logarithmic conversion circuit in the analysis unit and output as a directly readable oxygen concentration.

(Problems to be solved by the invention) However, as described above, in the oxygen concentration measuring device having a structure divided into high temperature and low temperature, when measuring an atmosphere changing from room temperature to about 1400 ° C. Depending on the region, it was necessary to replace and install both of the above-mentioned measuring devices to measure the oxygen concentration, which was inconvenient.

The present invention, for example, in a wide temperature range from room temperature to about 1400 ° C., the oxygen concentration in the exhaust gas atmosphere, an industrial gas concentration measurement that can be measured by one measuring device without the need for a separate measuring device. We will provide the equipment.

(Means for Solving Problems) An industrial gas concentration measuring device according to the present invention includes a detection unit including a sensing cell and a heating body, which are integrally formed in a plate-like laminated manner, and a temperature sensing body. An industrial gas concentration measuring device provided at the tip of a probe, at least a part of which is inserted into gas, wherein temperature correction calculation means for correcting the output of the sensing cell by the signal of the temperature detecting body, and the signal of the temperature detecting body By providing a temperature calculation processing unit having a temperature control means for controlling the heating element so that the sensing cell reaches a predetermined temperature, when the measured gas temperature is equal to or lower than the target operating temperature of the sensing cell, the sensing cell is controlled by the temperature control means. After setting a preset temperature correction temperature equal to or higher than the target operating temperature, temperature correction calculation means performs temperature correction based on this temperature correction temperature, and the measured gas temperature is the sensing cell. When the target operating temperature is exceeded, the temperature correction calculation means performs temperature correction based on a preset temperature correction temperature.

Preferably, the arithmetic processing unit has a temperature control means for controlling the heating body so that the sensing cell has a predetermined temperature by a signal from the temperature detection body.

More preferably, the sensing cell, the heating body, and the temperature detecting body are integrally laminated in a plate shape.

(Operation) With the above configuration, the detection unit becomes smaller and lighter, and by providing the temperature calculation processing unit that corrects the signal of the temperature detection body, it is possible to measure the gas concentration with higher accuracy.
Further, by providing the temperature control means for controlling the heating element based on the signal of the temperature detecting element, the gas concentration can be measured not only in the high temperature area but also in the low temperature area.

(Example) As a concrete example of the industrial gas concentration measuring device of the present invention, an industrial oxygen concentration measuring device will be described with reference to the drawings.

A cross-sectional view shown in FIG. 1 is an overall view of an industrial oxygen concentration measuring device. This is a so-called direct insertion type, and reference numeral 23 indicates a cylindrical probe for collecting the measured gas, for example, it is inserted into a hole formed in the furnace wall of the flue of the combustion furnace, and the mounting flange is attached. Held by 35. The detection unit 21 is attached to the tip end side of this probe through a disc-shaped support 22 made of alumina. It is connected to an external control circuit via a lead wire 30 connected to this detector 21.

Next, the detector will be described below.

FIGS. 2 (A), (B) and FIG. 3 show an example of the detection part, that is, the oxygen sensor element S of the industrial oxygen concentration measuring device of the present invention.

The structure of the oxygen sensor element S is as follows. First, an oxygen pump portion P including a fixed electrolyte body 40 and an upper pump electrode 41 and a lower pump electrode 42 arranged on both upper and lower sides of the solid electrolyte body 40 is provided on the upper portion. Is provided. An upper heating portion H1 is provided on the upper surface side of the oxygen pump portion P so as to surround the upper pump electrode 41.

Next, similarly to the oxygen pump section P, the solid electrolyte body 43
And the measurement electrodes arranged on the upper and lower sides of this solid electrolyte body 43.
An oxygen concentration battery section B consisting of 44 and a reference electrode 45 is provided.

It should be noted that, between the oxygen pump portion P and the oxygen concentration battery portion B, a diffusion chamber 46 having a narrow gap flat space for guiding the gas to be measured under a predetermined diffusion resistance is formed from an insulator. A space member 47 (47a, 47b) having a predetermined thickness is interposed. Further, at a position corresponding to the central portion of the diffusion chamber 46 in the oxygen pump portion P, gas introduction holes 48 (48a, 48b, 48c, 48c, 48b, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c, 48c) for communicating the diffusion chamber 46 with the space where the measured gas is present.
48d) has been formed. Therefore, this gas introduction hole 4
The gas to be measured is guided by 8 (48a, 48b, 48c, 48d), diffused in the diffusion chamber 46 under a predetermined diffusion resistance, and comes into contact with the lower pump electrode 42 of the oxygen pump section B. Further, the measurement electrode 44 of the oxygen concentration battery section B is also connected to the lower pump electrode.
Contact the measured gas near 42.

Next, below the oxygen concentration battery section B, a space member 49 made of a solid electrolyte body and a solid electrolyte body 50 are sequentially provided. As a result, an air passage 51 exposing the reference electrode 45 is formed. The air passage 51 communicates with the atmosphere at the base of the oxygen sensor element S. The reference air, which is the atmosphere, is introduced through the air passage 51 and comes into contact with the reference electrode 45.

In the air passage 51, a temperature detecting portion Th is provided on the lower surface of the solid electrolyte body 43 at a position close to both sides of the reference electrode 45.

Furthermore, a lower heating unit H2 is provided on the lower side. Therefore, the heating section H2 and the upper heating section H1 are arranged on both sides of the oxygen pump section P and the oxygen concentration battery section B so as to sandwich the oxygen pump section P and the oxygen concentration battery section B, and the predetermined temperature (for example, from both sides). It can be heated to more than 600 ℃.

The solid electrolyte bodies 40, 43, 50 and the space member 49 are composed of stabilized or partially stabilized zirconia porcelain that exhibits oxygen ion conductivity at high temperatures. As is well known, this stabilized or partially stabilized zirconia porcelain is obtained by dissolving yttrium oxide, calcium oxide or the like in zirconium oxide. The electrodes 41, 42, 44, 45 are each made of porous platinum or the like. Of these electrodes 41, 42, 44, 45, porous ceramic layers 52, 53, 54 made of alumina or the like are laminated on the upper pump electrode 41, the lower pump electrode 42, and the measurement electrode 44, which come into contact with the gas to be measured. It is provided in the state where it was opened.
Therefore, the gas to be measured comes into contact with the electrodes 41, 42, 44 through the porous ceramic layers 52, 53, 54, respectively.

On the other hand, the heating portions H1 and H2 cover the heater elements 55 and 56, which are heater elements, with porous layers 57 (57a, 57b) and 58 (58a, 58b) made of alumina or the like having electrical insulation properties. It is provided in the opened state. On these porous layers 57 (57a, 57b) and 58 (58a, 58b), airtight layers 59 and 60 made of a solid electrolyte such as zirconia are further provided. As a result, each of the heater elements 55 and 56 can be shielded or isolated from the measured gas outside. The heater elements 55, 56 are formed by a method such as printing and arranging a paste containing alumina powder and platinum powder as main components, or arranging a cermet-shaped film.

Further, the temperature detecting unit Th has a configuration including a resistor or the like having a positive or negative temperature coefficient whose electric resistance largely changes due to temperature change. The temperature detecting element 61 is embedded in a porous layer 62 made of alumina or the like having electrical insulation properties, and is electrically insulated from the surrounding solid electrolyte body 43 and the space member 49. In addition,
The temperature detecting element 61 of the resistor is 0.1 to 0.5 for a paste containing a ceramic powder such as zirconia or alumina and a platinum powder as a main component or a paste containing cermet, a ceramic powder such as zirconia or alumina and a platinum powder as a main component. % Titanium dioxide added paste or cermet,
Alternatively, such as a paste or cermet in which oxides of manganese, cobalt, nickel, etc. are added to a ceramic powder such as zirconia, alumina, etc. as a main component,
It is formed by using a technique such as printing and laminating a paste having a positively increasing temperature coefficient of resistance, or arranging a cermet-shaped film. Further, as the temperature detecting element 61 of the resistor, zirconia porcelain,
Alternatively, a platinum wire or a platinum thin film may be used. A technique such as CVD, vacuum deposition, or sputtering can be used for the print lamination of these platinum wires or platinum thin films. Further, instead of the temperature sensing element 61 of the resistor, different metals (for example, platinum and gold) or pastes or cermets containing these different metals are combined and printed and laminated as a thermocouple to form a thermocouple. The temperature detecting element 61 may be configured.

The oxygen pump portion P, the oxygen concentration battery portion B, the heating portions H1 and H2, the temperature detecting portion Th, and the space member 47 as described above are stacked as shown in FIG. A laminated structure is formed and then sintered to form an integral structure. In addition, M is a pump electrode 41,4
2, the measuring electrode 44, the reference electrode 45, the heater elements 55 and 56, and the temperature sensing element 61, which are printed electric contact terminals.

In the case of this embodiment, the oxygen pump portion P and the oxygen concentration battery portion B constitute the sensing cell of the present invention.

The oxygen concentration measurement by the oxygen sensor element S thus configured will be described below with reference to the block diagram of FIG.

The oxygen concentration battery section B allows the oxygen pump section P to be provided in the diffusion chamber 46.
From the comparison between the measured gas that has entered by diffusion through the gas introduction hole 48 and the atmosphere of the reference air, the electromotive force E generated between the measurement electrode 44 and the reference electrode 45 according to the oxygen partial pressure ratio of both is measured.
Occurs.

This electromotive force E is However, R: gas constant T: absolute temperature n: ionization number F: Faraday constant P _A : oxygen concentration of reference gas P _S : oxygen concentration of measurement gas

This generated electromotive force E is set by the subtractor 63 at the set voltage Vf (air ratio m
The difference voltage (E-Vf) between the two is taken as the oxygen pump current ( _IP ) controller.
Supplied to 64. However, as the temperature rises, the predetermined value for setting the air ratio m≈1, that is, the set voltage Vf is, for example,
Since it is reduced by about 0 mV to 100 mV (see FIG. 6 (A)), it is necessary to correct the set voltage Vf according to the temperature change. In order to correct this set voltage Vf, the temperature detection unit Th
Use the output from.

For example, when a thermistor is used for the temperature detection unit Th, the resistance R of the thermistor is It has the following characteristics. The value corresponding to the resistance R obtained from the thermistor Th is the amplifier connected to the thermistor Th.
After being amplified at 65, it is supplied to a temperature linearizer 66 connected to the amplifier 65, where the temperature-resistance characteristic having a logarithmic relationship is converted into a temperature-voltage characteristic having a direct relationship.

Further, an example of the temperature linearizer 66 will be described with reference to FIG. The value of the resistance R amplified by the amplifier 65 is converted into a relationship of Log R and 1 / T by the Log conversion circuit 67 (1 / T = A · Log R + B, where A and B are constants).
This Log conversion circuit is, for example,
It can be configured by applying a current-voltage characteristic between the bases or by using a reduction circuit (straight broken line approximation circuit) in which a resistor and a diode are combined. A voltage value corresponding to the absolute temperature 1 / T is obtained by the log conversion circuit 67, and this value becomes a voltage value proportional to the absolute temperature T by the reciprocal conversion circuit 68 of the next stage, actually a divider. As described above, temperature linearizer
At 66, a voltage proportional to absolute temperature is obtained.

One of the outputs of the temperature linearizer 66 is supplied to a reference voltage setting circuit 69 connected thereto, and the other is supplied to a coefficient correction circuit 70 also connected to the output side.

In the reference voltage setting circuit 69, for example, a function converter and a bias circuit by polygonal line approximation can be used to set the set voltage value Vf according to the change of the absolute temperature T, and the set voltage Vf is supplied to the subtractor 63. .

The temperature-compensated difference voltage (E-Vf) is calculated by the subtractor 63
A predetermined control signal for controlling the pump current (I _P ) is supplied to the PI controller 71 connected to. The PI controller 71 performs proportional and integral control so that the electromotive force of the oxygen pump portion P becomes equal to the output voltage of the reference voltage setting circuit 69, and outputs a predetermined control signal. For example, i) When E <Vf, ii) E> Vf so that oxygen in the diffusion chamber 46 is pumped out by the oxygen pump portion P, as indicated by a solid arrow in FIG. In the case of, carbon dioxide CO in the measured gas is measured by the oxygen pump P.
_2. Electrolyze the water H ₂ O to pump oxygen into the diffusion chamber 46 (in the diffusion chamber 46, H ₂ + 1 / 2O ₂ → H ₂ O, CO + 1 / 2O
₂ → Reacts with CO ₂ . ) It controls the oxygen pump current (I _P ). As a result, the oxygen concentration in the diffusion chamber 46 becomes a predetermined value.

In order to control such pump current (I _P ), PI
A voltage-current converter 72 is connected to the next stage of the controller 71 to convert the output voltage of the PI controller 71 into a pump current (I _P ).

In the method of setting the predetermined value, the oxygen concentration in the diffusion chamber 46 is set to an oxygen concentration corresponding to the air ratio m≈1, specifically, the oxygen concentration is set to 0%.

Since oxygen molecules, carbon monoxide, and hydrogen molecules in the gas to be measured have different diffusion constants with respect to nitrogen gas, the oxygen pump current (I _P ) is represented by the following equation.

I _P = K ₁ · Po ₂ −K ₂ · Pco-K ₃ · P _{H 2} where K ₁ : coefficient proportional to diffusion of oxygen molecule K ₂ : coefficient proportional to diffusion of carbon monoxide K ₃ : hydrogen molecule Coefficient proportional to the diffusion of P: The partial pressure of oxygen molecules, carbon monoxide, and hydrogen molecules.

Therefore, when the gas to be measured is in the oxidation region, the concentrations of carbon monoxide and hydrogen molecules are 0%, so that I _P = K ₁ · Po ₂ .

Further, when the gas to be measured is in the reduction region, the oxygen molecule concentration is 0%, so that I _P = ₋ [K ₂ · Pco + K ₃ · P _{H 2} ].

Output current of the voltage-current converter 72, that is, pump current ( _IP )
Is supplied to the oxygen pump unit P on the one hand, and is supplied to the output converter 74 via the multiplier 73 on the other hand.

In the multiplier 73, when the oxygen concentration is constant, the pump current (I _P ) changes with the absolute temperature T (see FIG. 6 (B)). Therefore, the output voltage corresponding to the absolute temperature of the temperature linearizer 66 is changed. Using the coefficient correction circuit 70, in the actual case, in the function converter and bias circuit by the polygonal line approximation, the function K (t) such that the pump current (I _P ) is constant with respect to the absolute temperature T is obtained. (See FIG. 6 (B)) is output, and this function K (t) is multiplied by the multiplier 73 so that the pump current I _P at a certain oxygen concentration becomes constant regardless of the absolute temperature T. I have to.

In this way, the pump current I _P and the oxygen concentration are obtained from the multiplier 73 in a one-to-one relationship, and in the output converter 74 of the next stage, a desired display format, for example, the oxygen concentration in the measured gas, It is converted into an O ₂ value signal indicating the oxygen deficiency.

By the way, in the case where the operating temperature (for example, about 600 ° C.) of the oxygen sensor element S, specifically, the oxygen pump portion P and the oxygen concentration battery portion B is lower than or equal to the temperature range from room temperature to about 1400 ° C., A heater current is applied to the heater elements 55 and 56 of the heating portions H1 and H2 so that the portions P and B are maintained at a predetermined temperature. Further, even when the oxygen pump part P and the oxygen concentration battery part B are heated to operating temperatures or higher, the heating parts H1 and H2 may continue to be heated, or the voltage from the temperature linearizer 66 is set to a predetermined value or higher. When it becomes, the heater current can be cut off by a switch in the heater temperature controller 75. In any case, the temperature is detected and the temperature correction is always calculated, so that a reliable oxygen concentration can be measured regardless of the temperature.

Next, a modified example will be described. The same parts as those in the above-described embodiment are designated by the same reference numerals, and redundant description will be omitted (first conversion example-FIG. 7). In this example, the sensing cell is oxygen. By using the oxygen sensor element S, which is composed of only the concentration battery section B, the temperature detecting section Th is provided on the upper surface of the solid electrolyte 43, and the lower heating section H2 is provided on the lower surface of the solid electrolyte 50. There is. In this case, the voltage signal from the temperature detector Th is sent to the amplifier 65.
The temperature is then input to the temperature linearizer 66, and as described above, the voltage V (t) that is linearly proportional to the absolute temperature T is output. This output voltage V (t) is input to the voltage correction circuit 76.

In this voltage correction circuit 76, the voltage E and the voltage V (t) supplied from the measurement electrode 45 through the amplifier 65 are divided, multiplied by, for example, 1000, and the electromotive force generated when the temperature is 1000 (K). Is converted to. That is, the electromotive force E corresponding to the oxygen concentration at the fictive temperature of 1000 (K) is obtained. Therefore, the oxygen concentration is virtually measured at a constant temperature.

Next, the output of the voltage correction circuit 76 is subjected to open logarithm in the open logarithm circuit 77 of the next stage, and the oxygen concentration in the measurement space is Is converted into a desired output display by the output conversion circuit 74 in the next stage.

(Second Modification-FIG. 8) In this oxygen sensor element, the sensing cell is the oxygen pump portion P.
A space member 81 made of alumina or the like is interposed as a diffusion resistance means between the oxygen pump portion P and the lower heating portion H2.
A temperature detection unit Th is provided on the upper surface of H2. The gas to be measured is also supplied to the lower surface side of the oxygen pump portion P via the porous space member 81, and thus is supplied to both surface sides of the oxygen pump portion P.

In the oxygen sensor element S thus configured, the oxygen concentration is measured by measuring the oxygen pump current (I _P ) by the oxygen pump mechanism. The oxygen pump current I _P is measured by the ammeter 82 and supplied to the multiplier 73 via the amplifier 65. Further, the multiplier 73 is input with the temperature detection unit Th, specifically, the resistance value from the resistor 61 which is made into a desired function K (t) by the coefficient correction circuit 70. And the multiplier 73
Where the pump current I _P and the function K (t) are multiplied,
A temperature-independent I _P -oxygen concentration relationship is obtained.

(Effects of the Invention) In the industrial gas concentration measuring device of the present invention, the detection unit is small and lightweight, and the temperature correction calculation unit and the temperature control unit are provided, so that a wide range of temperatures of the gas to be measured ( For example, the oxygen concentration can be measured from room temperature to 1400 ° C.

[Brief description of drawings]

FIG. 1 is an overall view of the device of the present invention, FIGS. 2 (A) and 2 (B) are an exploded perspective view and a perspective view of an integrated structure of a detection unit (oxygen sensor element) of the device of the present invention, and FIG. 1 is a horizontal cross-sectional view taken along the line III-III in FIG. 1, FIG. 4 is a block diagram for explaining temperature correction and temperature control, and FIG. 5 is a block diagram for explaining a temperature linearizer, FIG. 6 (A), (B) is over temperature, Vf, I _P and K
FIGS. 7 and 8 are graphs showing how (t) changes, and FIG. 7 and FIG. 8 are block diagrams corresponding to FIGS. 2 and 3 for explaining a modified example of the apparatus of the present invention. 21 …… Detector, 23 …… Probe 66 …… Temperature linearizer, 69 …… Reference voltage setting circuit 70 …… Coefficient correction circuit, 73 …… Multiplier B …… Oxygen concentration battery section H1, H2 …… Top and bottom Heating part P ... Oxygen pump part, Th ... Temperature detection part

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G01N 27/419 7363-2J G01N 27/58 B

Claims (2)

[Claims] 1. A detection unit comprising a sensing cell and a heating body, which are integrally laminated in a plate shape, and a temperature detection body, is provided at the tip of a probe at least a part of which is inserted into a gas to be measured. An industrial gas concentration measuring device, wherein temperature correction calculation means for correcting the output of a sensing cell according to a signal of a temperature detection body, and temperature control for controlling a heating body so that the sensing cell reaches a predetermined temperature by a signal of the temperature detection body A temperature calculation processing unit having means is provided, and when the measured gas temperature is equal to or lower than the target operating temperature of the sensing cell, after the sensing cell is set to a preset temperature correction temperature equal to or higher than the target operating temperature by the temperature control means, When the temperature of the measured gas exceeds the target operating temperature of the sensing cell, the temperature correction calculation means performs temperature correction based on this temperature correction temperature, and a preset temperature correction temperature is set. Industrial oxygen concentration measuring apparatus characterized by performing temperature correction temperature correction calculating means with respect to the. 2. The industrial gas concentration measuring device according to claim 1, wherein the sensing cell, the heating body, and the temperature detecting body are integrally laminated in a plate shape.