JP5370319B2 - Infrared absorption gas analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared absorption type gas analyzer using variations of gas pressure associated with IR spectral absorption, in which corrosion of a Ni element of a flow sensor used for detecting SO<SB POS="POST">2</SB>is prevented and a durable period of the flow sensor can be extended. <P>SOLUTION: It is supposed that NiSO<SB POS="POST">4</SB>is deposited only on a surface in a normal side face of a Ni element while NiS<SB POS="POST">2</SB>is produced to a deep portion in a corroded portion. Therefore, when Ni is sulfurized by SO<SB POS="POST">2</SB>to produce NiS<SB POS="POST">2</SB>, Ni corrodes the element into a deep portion to cut lines, but even when Ni is sulfurized, if Ni remains as NiSO<SB POS="POST">4</SB>and stays on only the surface and does not intrude into a deep portion, no problem is caused about disconnection. It is found that Ni is present as NiSO<SB POS="POST">4</SB>at 100&deg;C or lower, and NiS<SB POS="POST">2</SB>is produced at 100 or higher. Thus, by controlling the temperature of a resistance metal foil of the flow sensor to 100&deg;C or lower, production of NiS<SB POS="POST">2</SB>can be prevented. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

The present invention relates to an infrared absorption type gas analyzer that measures the concentration of a specific gas species by using a gas pressure fluctuation accompanying infrared spectrum absorption of an infrared active component gas.

Conventional technology

The flow sensor used for the quantitative analysis of gas components is a temperature-sensitive metal foil with a large temperature coefficient of resistance placed before and after the gas flow, and these temperature-sensitive metal foils are bridge-connected to change the resistance of these metal foils. Quantitative analysis of gas components in the flow. A flow sensor used in a conventional non-dispersive infrared analyzer is generated by arranging a comb resistor having a large temperature coefficient of resistance on both sides of a sensor chip in a gas flow and transferring heat from the flow. The flow is detected by detecting the deviation of the resistance values of the comb resistors on the front and back surfaces by a bridge circuit, and quantitative analysis of gas components in the flow is performed. As shown in Patent Document 1, nickel (Ni), which is a metal having a large temperature coefficient of resistance, is used for the comb resistor.

The flow sensor is installed in a room made of metal such as aluminum, and the room is divided into a front room and a rear room, and both chambers are filled with the component gas to be measured. For example, when detecting sulfur dioxide (SO ₂ ), it is filled with SO _{2. In} this case, it is preferable to dilute with an inert gas such as argon (Ar) rather than 100% SO _2. In order to improve detection sensitivity, the filling gas is a mixed gas of SO ₂ and Ar.

Japanese Patent Laid-Open No. 2003-099788

When an infrared absorption gas analyzer is used for the purpose of detecting SO ₂ , SO ₂ is enclosed in the detector chamber. In this case, Ni having a large resistance change due to temperature is used as an element of the flow sensor. When SO ₂ reacts with Ni, Ni corrodes and the flow sensor element is disconnected in several years. In this case, it is conceivable to increase the corrosion resistance by gold-plating Ni and covering the surface of Ni with metal, but this increases the cost. Therefore, the present invention provides an infrared absorption gas analyzer using an Ni element for the flow sensor, and prevents corrosion of the Ni element of the flow sensor and extends the useful life of the flow sensor with a simple configuration that does not increase the cost. With the goal.

In order to solve the above problems, the present invention includes a light source that emits infrared light, a measurement cell that introduces a sample gas, and a detection unit that detects the intensity of infrared light that has passed through the measurement cell. The part is equipped with a flow sensor and SO ₂ is enclosed, and the material of the comb resistor of the flow sensor is Ni. In an infrared absorption gas analyzer, the temperature of the comb resistor reacts between Ni and SO _2. Thus, the temperature is such that nickel sulfide (NiS ₂ ) is not generated.

When Ni comb resistor of the flow sensor is sulfurized by SO ₂ enclosed in detector NiS ₂ generates, although disconnection of the comb resistor occurs, Ni is NiS ₂ to produce sulfurized by SO ₂ This is the case above a specific temperature. That is, when the temperature is lower than the specific temperature, Ni on the surface exists as nickel sulfate (NiSO ₄ ), so the reaction does not proceed to the deep part, and when NiS ₂ is generated at the specific temperature or higher, the reaction proceeds to the deep part. If the temperature of the mold resistor is kept below a specific temperature, sulfidation corrosion due to NiS ₂ can be prevented.

Further, the voltage applied to the comb resistor can be set so that the temperature of the comb resistor becomes a temperature at which NiS ₂ is not generated. Since the temperature of the comb resistor increases as the voltage applied to the comb resistor increases, the temperature of the comb resistor increases so that the voltage applied to the comb resistor is a low voltage that NiS ₂ does not generate. Thus, sulfide corrosion due to NiS ₂ can be prevented.

Further, as a configuration for setting the temperature of the comb resistor to a temperature at which NiS ₂ is not generated, a comb circuit, a voltage source, and a fixed resistor are connected to form a bridge circuit. The voltage value of the voltage source and the resistance value of the fixed resistor can be selected so that the temperature does not generate ₂ . Since the temperature of the comb resistor increases as the voltage applied to the comb resistor increases, the temperature of the comb resistor increases so that the temperature of the comb resistor does not generate NiS _2. The voltage to be applied to the mold resistor should be set, and there are the following methods for setting the voltage. The signal processing unit of the infrared absorption gas analyzer forms a bridge circuit by combining two comb resistors and two fixed resistors. If the voltage of the voltage source supplied to the bridge circuit is changed, Accordingly, the voltage applied to the comb resistor also changes, so that the voltage value of the voltage source can be set to a specific value. Alternatively, even if the voltage value of the voltage source remains the same, changing the resistance value of the fixed resistor changes the voltage value applied to the fixed resistor, and the voltage value applied to the comb resistor changes. It can also be set to a value.

Then, by calculating a condition that minimizes the total Gibbs energy of the system including Ni, SO ₂ , and Ar with a thermodynamic calculation program, Ni is sulfided by SO ₂ and NiS ₂ is generated at approximately 100 degrees. Since it is calculated | required above, it is good to set the comb-type resistor to a temperature of approximately 100 degrees or less at which NiS ₂ is not generated.

According to the present invention, without changing the material of the flow sensor element from Ni, the temperature of the element is set to approximately 100 degrees or less, thereby preventing breakage due to corrosion of the flow sensor element and extending the lifetime of the flow sensor. be able to. In order to adjust the temperature of the flow sensor element, it is possible to easily adjust the temperature by adjusting the voltage applied to the flow sensor element. In this case, the power supply voltage value or the fixed resistance value of the bridge circuit is conventionally adjusted. The temperature of the flow sensor element can be adjusted with the components that have been used.

1 is a schematic configuration diagram of an infrared absorption gas analyzer to which the present invention is applied. The schematic block diagram of the detection part of the infrared absorption type gas analyzer to which this invention is applied. The front schematic diagram of the flow sensor to which the present invention is applied. The side schematic diagram of the flow sensor to which the present invention is applied. The schematic diagram of the bridge circuit of the flow sensor to which the present invention is applied. The composition measurement result of the corrosion part.

The configuration of a single beam infrared absorption gas analyzer equipped with a flow sensor as a detector is shown in FIG. As shown in the figure, this type of infrared absorption gas analyzer generally passes through a light source unit 1 for generating infrared light, a cell unit 2 into which a gas to be measured (sample gas) is introduced, and the cell unit 2. It comprises three units of the detector unit 3 that finally measures the sample concentration by measuring the intensity of the infrared light. The light source unit 1 is responsible for generation of infrared light, a heater 4 that is a generation source for generating infrared light, and a chopper 5 for intermittently inputting infrared light into the cell unit 2 and the detector unit 3. It consists of and.

The chopper 5 rotates, for example, a two-bladed rotating disc 6 formed with a notch part of which is cut out so as to allow passage of light from the light source 4 and the rotating disc 6. When the rotating disk 6 is rotated by the motor 7 and the non-notched part (light-shielding part) of the rotating disk 6 is positioned in front of the light source 4, the light source 4. Infrared light from the light source 4 is shielded, and when the notch is positioned in front of the light source 4, the infrared light from the light source 4 passes through and is irradiated to the cell unit 2.

The cell part 2 is a part into which a sample gas is introduced, and infrared transmissive glass or calcium fluoride (CaF ₂ ) capable of transmitting infrared rays in a wide spectral range before and after the pipe 8.
And a gas inlet / outlet hole 10 is provided on the side surface of the pipe 8 so that the gas can flow from one end to the other end. The inner surface of the pipe 8 has a mirror surface to efficiently reflect infrared light. Finish and gold coating are applied.

As shown in FIG. 2, the detector unit 3 is generally composed of a front block 11 serving as a front chamber made of metal such as aluminum and a rear block 12 serving as a rear chamber. For convenience of explanation, the front block 11 and the rear block 12 are called, but both blocks are joined and integrated later. The front block 11 and the rear block 12 are based on the principle of an infrared absorption gas analyzer, so that the detection unit allows the infrared light to be measured that has passed through the cell into which the component gas to be measured (sample gas) is introduced. In addition, a sensor such as a flow sensor for detecting the pressure difference between the front and rear chambers is disposed in the communication path communicating with the front and rear chambers in order to form two front and rear chambers for increasing the pressure of the enclosed sensitive gas. Used for.

The front and rear blocks 11 and 12 are formed with through holes having the same diameter, and both ends of the through holes of the front block 11 and one end of the through holes on the opposite side of the joint surface of the front block 11 of the rear block 12 are formed. It is sealed with a window plate 13 that transmits infrared light, and a window plate 14 facing the rear block 12 that seals the through hole of the front block 11 serves as a partition wall, and the front chamber 15 and the rear chamber 16 A room.

Further, the front block 11 and the rear block 12 are formed with tunnels 18 and 19 which are connected when the both blocks are joined and integrated to form the communication path 17, and the tunnel formed in the front block 11 is formed. 18 is connected to the tunnel 19 from the front chamber 15, and a space in which the sensor 20 can be arranged is provided in a narrow hole portion connected to the front chamber 15.

Further, in these two chambers 15 and 16, only a chemical species such as carbon dioxide (CO ₂ ) or the like to be measured by the infrared gas analyzer, or this chemical species is Ar, helium (He).
A gas diluted with an inert gas such as is filled (enclosed). The sensor 20 disposed in the communication path 17 may be any sensor 20 as long as it can detect the pressure difference between the front and rear chambers. In the case of a flow sensor that detects a gas flow, a thin film type hot-wire flow sensor manufactured by a thin and highly accurate thin film technology is generally used.

The flow sensor used for the infrared gas analyzer is configured as shown in FIGS. In the flow sensor, temperature-sensitive metal foils with a large temperature coefficient of resistance are arranged before and after the gas flow, and the temperature-sensitive metal foils are bridge-connected to change the resistance of the metal foils to change the gas components in the flow. Perform quantitative analysis.

In the flow sensor configuration, resistance metal foils 23 and 24 are arranged on both front and back surfaces of a spacer 22 having a gas flow hole 21 in the center, and sandwiched between heat insulating plates 25 and 26, thereby fixing the resistance metal foils 23 and 24. To do. Similar gas flow holes 27 and 28 are also provided in the heat insulating plates 25 and 26. Comb resistors 29 and 30 connected in series are formed on the resistance metal foils 23 and 24, and the portions of the comb resistors 29 and 30 are exposed in the gas flow holes 21, 27 and 28. Yes. Wires 31, 32, 33, and 34 are connected to the pads at both ends of the resistive metal foils 23 and 24, and lateral holes 35, 36, 37, and 38 are provided in the heat insulating plates 25 and 26 to guide them to the outside. It is done.

As the resistance metal foils 23 and 24, Ni which is a metal having a large temperature coefficient of resistance is used. Glass or ceramic is used for the heat insulating plates 25 and 26 and the spacer 22.

With such a configuration, the infrared light emitted from the light source unit 1 passes through the cell unit 2 and enters the detector unit 3. At this time, if the component gas to be measured exists in the cell, a part of the incident infrared light is absorbed by the gas in the cell according to the gas concentration in the cell, and the remaining infrared light is absorbed by the detector unit 3. Incident. Infrared light incident from the front of the front chamber 15 of the detector unit 3 is absorbed by the front chamber 15 and the rear chamber 16, but most of the infrared light is absorbed by the front chamber 15. The absorbed light energy is converted into the translational movement of the molecule, and a pressure difference is generated between the front and rear chambers 15 and 16, thereby generating a flow of the enclosed gas in the communication passage 17 that communicates both chambers. The Since the flow velocity of this gas flow depends on the intensity of incident light to the detector unit 3, the change in the resistance value of the hot wire resistance element of the thin film type hot wire flow sensor 20 disposed in the communication passage 17 of the front and rear chambers 15 and 16 is achieved. By measuring as above, it is possible to measure the infrared light intensity before and after incidence on the detector unit 3, that is, the concentration of the component gas to be measured in the cell.

Here, when detecting SO ₂ , the front chamber 15 and the rear chamber 16 are filled with SO _{2. In} this case, if Ni is used as the material of the resistance metal foils 23 and 24 of the flow sensor, SO ₂ is used. ₂ NiS ₂ is generated by Ni is sulfidation corrosion by, in some cases problems that disconnection and resistance metal foil 23, 24 the degree of sulfide proceeds occurs. Therefore, when the component structure per mol of the corroded portion of the element disconnected during energization was measured with an electron beam microanalyzer (EPMA), as shown in FIG. 6, the sulfur (S) and oxygen ( Since the ratio of O) is about 1: 4, it is estimated that NiSO ₄ is attached to the surface of Ni, and the corrosion part is NiS ₂ because the ratio of S is higher than the ratio of the side surface of the normal part. It is estimated that there is. Therefore, when Ni is sulfided with SO ₂ and NiS ₂ is generated, Ni corrodes to the deep part and breaks. However, even if Ni reacts with SO ₂ , if NiSO ₄ stops only on the surface, the problem of breakage occurs. I can say no.

Therefore, in order to examine the conditions under which NiS ₂ and NiSO ₄ generates, Ni, was calculated the conditions Gibbs energy of total system including _SO 2, Ar is minimized, at the 100 ° C. or less, NiSO ₄ generates It was found that NiS ₂ was produced at 100 ° C. or higher. Therefore, the generation of NiS ₂ can be prevented by setting the temperature of the comb resistors 29 and 30 to 100 ° C. or lower.

A configuration in which the temperature of the comb resistors 29 and 30 is set to 100 ° C. or lower using a bridge circuit to which the comb resistors 29 and 30 shown in FIG. 5 are connected will be described. In order to adjust the temperature of the comb resistors 29 and 30 to 100 ° C. or less, it is necessary to suppress the amount of heat generated in the comb resistors 29 and 30. Here, if the calorific value K (J) is electric power P (W) and time t (seconds), K = P · t, and electric power P (W) is current I (A) and voltage E (V). When resistance R (Ω), P = I · E = E ² / R, and therefore, the voltage applied to the comb resistors 29, 30 is required to adjust the amount of heat generated by the comb resistors 29, 30. Need to be adjusted. For this purpose, it is necessary to adjust the applied voltage of the voltage source 40 or to adjust the resistance values of the fixed resistors 41 and 42 of the bridge circuit to a specific value. When the voltage value of the voltage source 40 is lowered, the applied voltage at each of the resistors of the comb resistors 29 and 30 and the fixed resistors 41 and 42 is reduced, so that the amount of heat generated in the comb resistor is reduced. Even if the voltage value of the voltage source 40 is not adjusted, if the value of the fixed resistors 41 and 42 is increased, the voltage drop in the fixed resistor increases, so the voltage drop in the comb resistor decreases and the comb resistor The calorific value is reduced. Therefore, by adjusting the value of the voltage source 40 or the fixed resistors 41 and 42, the amount of heat generated in the comb resistors 29 and 30 can be reduced, and the temperature of the comb resistors 29 and 30 can be adjusted to 100 ° C. or lower. it can.

Further, when the resistance R is length l (m), cross-sectional area A (m ² ), and volume resistivity ρ (Ω · m), R = ρ · l / A, and the electric resistance of the metal increases with temperature. The volume resistivity at a specific temperature is also known (for example, the volume resistivity of Ni at 100 ° C. is known to be 10.3). Therefore, the amount of heat generated in the comb resistors 29 and 30 can also be adjusted by adjusting the resistance by adjusting the length and cross-sectional area of the comb resistors 29 and 30.

Thus, by reducing the voltage at the comb resistors 29 and 30, the temperature of the comb resistors 29 and 30 can be reduced to 100 ° C. or lower. However, when the voltage is reduced, the sensitivity of the flow sensor is reduced. In view of the sensitivity of the flow sensor, it is not preferable in terms of performance to reduce the voltage more than necessary. Therefore, adjusting to the maximum voltage value at which the temperature satisfies 100 ° C. or lower is a condition that maximizes the sensitivity of the flow sensor under the condition that NiS ₂ is not generated.

By making the temperature of the comb resistors 29 and 30 100 degrees or less as described above, the comb resistors 29 and 30 can be prevented from being broken by corrosion of Ni, and the service life of the flow sensor can be extended.

DESCRIPTION OF SYMBOLS 1 Light source part 2 Cell part 3 Detector part 4 Heater 5 Chopper 6 Rotating disk 7 Motor 8 Pipe 9 Window plate 10 Gas lead-in / out hole 11 Front block 12 Rear block 13 Window plate 14 Window plate 15 Front chamber 16 Rear chamber 17 Communication path 18, 19 Tunnel 20 Sensor 21, 27, 28 Gas flow hole 22 Spacer 23, 24 Resistance metal foil 25, 26 Thermal insulation plate 29, 30 Comb resistor 31, 32, 33, 34 Wire 35, 36, 37 , 38 Side hole 40 Voltage source 41, 42 Fixed resistance

Claims (4)

A light source that emits infrared light; a measurement cell that introduces a sample gas; and a detection unit that detects the intensity of infrared light that has passed through the measurement cell. The detection unit includes a flow sensor and is filled with sulfur dioxide. are those, in the infrared absorption gas analyzer material of the comb resistor is nickel of the flow sensor, the temperature of the comb-shaped resistor to a temperature at which the nickel of the comb resistor surface is present as nickel sulfate An infrared absorption gas analyzer characterized by The infrared absorption gas analyzer according to claim 1, wherein a voltage applied to the comb resistor is set to a temperature at which nickel on the surface of the comb resistor exists as nickel sulfate . The comb resistor, the voltage source, and a fixed resistor are connected to form a bridge circuit, and the voltage value of the voltage source and the fixed resistor are set at a temperature at which nickel on the surface of the comb resistor exists as nickel sulfate . The infrared absorption gas analyzer according to claim 2, wherein a resistance value is selected. 4. The infrared absorption gas analyzer according to claim 1, wherein the temperature at which nickel on the surface of the comb resistor exists as nickel sulfate is 100 degrees Celsius or less. 5.

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