JP2006138641A - Gas component analyzer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately and continuously measure a sample gas containing a mixture of a plurality of components different in molecular weight or viscosity. <P>SOLUTION: This gas component analyzer is equipped with a sample gas introducing part 1 for introducing the sample gas G, the mass analyzer 3 connected to the sample gas introducing part 1 through an throttle 2, the exhaust system 4 connected to the mass analyzer 3, a pressure gauge 5 for detecting the pressure on the downstream side of the throttle 2 and a data processing part 6 for correcting the analytic result of the sample gas G obtained by the mass analyzer 3 using the pressure detected by the pressure gauge 5 to calculate the concentrations of the components of the sample gas G on the basis of the analytic result after correction. By this constitution, the respective components can be continuously analyzed without impairing the measurement precision of the sample gas G even if the mixture ratio of the respective components in the sample gas G, containing a mixture of a plurality of the components different in molecular weight or viscosity, is varied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas component analyzer for analyzing a component of a sample gas, and in particular, even when the mixing ratio of each component in a sample gas in which a plurality of components having different molecular weights and viscosities are mixed fluctuates, the measurement accuracy of the sample gas is measured. The present invention relates to a gas component analyzer that can continuously analyze each component without impairing the above.

A conventional gas component analyzer includes a heated sample gas inlet, a mass spectrometer connected to the sample gas inlet via a valve, an exhaust system connected to the mass spectrometer, And a data processing unit that processes data output from the mass spectrometer. In such a conventional gas component analyzer, a low-vacuum chamber is provided between the sample gas introduction unit and the mass spectrometer, and the low-vacuum chamber and the mass spectrometer are separated by a thin tube or a nozzle. The sample gas was introduced into the mass spectrometer by the differential pressure (see Patent Document 1).
Japanese Patent Laid-Open No. 2-141655

  However, in the prior art described in Patent Document 1, a low vacuum chamber regulated in a reduced pressure state and a mass spectrometer are connected so as to be separated by a thin tube or nozzle. If there is a gas with a relatively low molecular weight or viscosity, such as a gas, the flow rate of the sample gas introduced into the mass spectrometer will fluctuate even if the pressure in the low vacuum chamber is adjusted. There was a problem that it was not possible.

In addition, by providing a low vacuum chamber between the sample gas introduction part and the mass spectrometer, a diffusion rate such as hydrogen is large in this part, and a component with a low exhaust rate is selectively retained. When the mixing ratio of each gas in the sample gas varies, there is a problem that the variation cannot be followed.
Therefore, the present invention addresses such problems and does not impair the measurement accuracy of the sample gas even when the mixing ratio of each component in the sample gas in which a plurality of components having different molecular weights and viscosities are mixed varies. Another object of the present invention is to provide a gas component analyzer capable of continuously analyzing each component.

  In order to achieve the above object, a gas component analyzer according to the present invention introduces a sample gas to be measured from a sample gas introduction unit into a mass spectrometer through a restriction, and detects the pressure downstream of the restriction. The analysis result of the sample gas is corrected using the detected pressure, and the component concentration of the sample gas is calculated based on the corrected analysis result.

  According to the present invention, the gas introduction part for introducing the sample gas and the mass spectrometer part are directly connected via the restriction, and the pressure detection means is arranged downstream of the restriction of the sample gas introduction part. Therefore, the variation in the amount of sample gas introduced into the mass spectrometer can be detected, and the analysis result of the sample gas obtained by the mass spectrometer can be corrected. Therefore, even when the mixing ratio of each gas in the sample gas in which a plurality of components having different molecular weights and viscosities are mixed, measurement can be continuously performed without impairing the measurement accuracy of the sample gas.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing an embodiment of a gas component analyzer according to the present invention. This gas component analyzer is an apparatus for analyzing a component of a sample gas G in which a plurality of components are mixed, and includes a sample gas introduction unit 1, a throttle 2, a mass spectrometer 3, an exhaust system 4, and a pressure gauge. 5 and a data processing unit 6.

  The sample gas introduction unit 1 is a pipe line for introducing a sample gas G to be measured, and a throttle 2 for restricting the flow rate of the sample gas G is inserted in the middle thereof. A mass spectrometer 3 is directly connected to the exhaust gas downstream side of the sample gas introduction unit 1 via a restriction 2. This mass spectrometer 3 is composed of, for example, a magnetic field deflection type mass spectrometer or a quadrupole mass spectrometer, and obtains a mass spectrum of the introduced sample gas G to accurately measure atomic mass and the presence of an isotope. The ratio is measured and elemental analysis is performed. The analysis result obtained here is processed by the data processing unit 6 described later.

  An exhaust system 4 is connected to the mass spectrometer 3. The exhaust system 4 includes at least one vacuum pump such as a turbo pump (TP) or a rotary pump (RP), and adjusts the inside of the mass spectrometer 3 to a high vacuum. It has become. Since the mass spectrometer 3 and the sample gas introduction unit 1 are in such a structure that they are directly communicated with each other through the restriction 2, the sample gas G passes from the sample gas introduction part 1 through the restriction 2 and is connected to the mass spectrometer 3 Even when the mixing ratio of each component of the sample gas G varies, the followability to the variation can be maintained.

  A pressure gauge 5 is attached between the throttle 2 and the mass spectrometer 3 in the middle of the sample gas introduction pipe 1. The pressure gauge 5 serves as a pressure detection means for detecting the pressure on the downstream side of the throttle 2, and is composed of, for example, a total pressure vacuum gauge using a diaphragm. The pressure gauge 5 continuously monitors the pressure change of the sample gas G introduced downstream of the throttle 2. Then, the data processing unit 6 corrects the analysis result of the sample gas G obtained by the mass spectrometer 3 using the signal of the pressure value detected by the pressure gauge 5.

Next, a specific configuration of the sample gas introduction unit 1 will be described with reference to FIG. In FIG. 2, a first sample gas introduction pipe 8 and a second sample gas introduction pipe 9 are connected to an abdomen of a pipe 7 that is a flow path for the sample gas G. A partition wall 10 is provided between the first sample gas introduction tube 8 and the second sample gas introduction tube 9, and a narrow tube 11 is disposed through the partition wall 10. The narrow tube 11 corresponds to the throttle 2, and has an inner diameter of about 10 μm and a length of about 30 mm, for example, and separates the pressure on the upstream side and the downstream side of the narrow tube 11. Thereby, when the pressure inside the mass spectrometer 3 is adjusted to a high vacuum (for example, about 10 ⁻³ Pa) by the exhaust system 4, a differential pressure is generated between the upstream side and the downstream side of the thin tube 11. Therefore, the high-pressure (for example, about 100 kPa) sample gas G flowing through the pipe 7 passes through the thin tube 11 from the sample gas introduction pipe 8 and is introduced into the sample gas introduction pipe 9 and sucked into the mass spectrometer 3. At this time, the flow rate of the sample gas G sucked into the mass spectrometer 3 is about 5 μL / min.

Note that a heater 12 is attached around the first sample gas introduction pipe 8 and the second sample gas introduction pipe 9, and condensation occurs when the sample gas G contains water vapor. It comes to prevent. The heater 12 is kept at a temperature at which the water vapor is not condensed in order to prevent the influence of the temperature fluctuation of the sample gas G. In the above description, the pressure of the mass spectrometer 3 is always about 10 ⁻³ Pa and the pressure in the pipe 7 for collecting the sample gas G is about 100 kPa. However, the present invention is not limited to this, It may have a certain width. The capillaries 11 are not limited to those having an inner diameter of 10 μm and a length of about 30 mm, and the size and shape are not limited as long as the same narrowing effect can be obtained.

Here, strictly speaking, the flow rate of the sample gas G sucked into the mass spectrometer 3 shown in FIG. 2 depends on the pressure at both ends of the narrow tube 11, the viscosity, average molecular weight, and temperature of the sample gas G. The pressure on the downstream side of the narrow tube 11 substantially depends on the flow rate of the sample gas G passing through the narrow tube 11 and the exhaust amount of the exhaust system 4. Since the inside of the mass spectrometer 3 is constantly evacuated while detecting the fluctuation, the value is constantly maintained at about 10 ⁻³ Pa.

Therefore, the flow rate F of the sample gas G is as follows. The viscosity coefficient of the sample gas G is h _mix , the average molecular weight is M, the temperature is T, the inner diameter of the capillary tube 11 is a, and the length is L.
F = A / h _mix・ a ⁴ / L ・ P _ave + B ・ Z ・ a ³ / L ・ (T / M) ^0.5・ ・ ・ (1)
It is expressed by the following formula. The symbols A and B are constants.
Here, the symbol Z in the above equation (1) is:
Z = (1 + C ・ a ・ P _ave ) / (1 + D ・ a ・ P _ave ) ・ ・ ・ （２）
It is expressed. The symbols C and D are constants.

Here, the symbol P _ave in the above equation (2) indicates the average pressure at both ends of the thin tube 11. As described above, the pressure P _u in the upstream side of the capillary 11 is set to about 100 kPa, since the pressure P _d at the downstream side is held at about 10 ^-3 Pa, the average pressure across the capillary 11 _Pave
P _ave = (P _u + P _d ) / 2 ≒ 0.5 P _u (3)
And can be approximated.

Therefore, the above (1) to (3), the flow rate F of the sample gas G is seen to be dependent on the pressure P _u in the upstream side of the capillary 11.
Here, when the viscosity coefficient h _mix and the average molecular weight M of the sample gas G are substantially uniform, for example, when measuring the sample gas G in which most of the components are composed of air, nitrogen or the like, the above-mentioned Patent Document 1 is used. Can be measured by the conventional apparatus described in the above, but when the gas having a relatively small average molecular weight and viscosity coefficient exists in the sample gas G and the mixing ratio of the gas varies, the sample gas G The flow rate F changes. Therefore, even though keeping only the constant pressure P _u in the upstream side of the capillary 11, the flow rate F of the sample gas G, so fluctuates depending on its composition change, accurate measurements in the conventional apparatus It becomes difficult.

FIG. 3 is a graph showing the output value of hydrogen gas measured by the mass spectrometer 3 when the mixing ratio of nitrogen gas (N ₂ ) and hydrogen gas (H ₂ ) is changed. Originally, as shown in the graph a, it is ideal that the output value of the mass spectrometer 3 increases linearly as the ratio of hydrogen gas in the nitrogen gas increases from 0 to 100 (vol%). is there. However, in actuality, the curve b tends to increase as shown in the graph b, and the fluctuation error ΔC of the gas flow rate increases as the mixing ratio of the hydrogen gas increases. This is due to the fact that the molecular weight and viscosity of hydrogen gas are very small compared to nitrogen gas.

  As an example of such a sample gas, a fuel gas used in a fuel cell can be considered. In a fuel cell, a fuel cell structure constituted by sandwiching a solid polymer electrolyte membrane between a fuel electrode and an oxidant electrode is sandwiched by separators, and a plurality of these are laminated. Hydrogen is used as the fuel gas supplied to the fuel electrode, and air is used as the oxidant supplied to the oxidant electrode. The sample gas used in such fuel cells is characterized by the fact that hydrogen gas with a very low molecular weight and viscosity varies in a large proportion, specifically from 0% to 100% in volume ratio. Where accurate measurement is difficult with this device, this is possible with the present invention.

  Next, measurement of the sample gas G by the gas component analyzer having the above-described configuration will be described. First, in FIG. 1, as a sample gas G, a gas A (for example, hydrogen gas) having a relatively low viscosity and molecular weight, a gas B (for example, nitrogen gas) having a relatively high viscosity and molecular weight, and a gas having a viscosity and molecular weight in between. Assume that a gas mixed with C (for example, water vapor) is measured. When measuring such a sample gas G, either a gas A having a low viscosity and a low molecular weight or a gas B having a high viscosity and a high molecular weight is selected as a reference gas.

Here, the component of such a pure reference gas is measured by the mass spectrometer 3, and the pressure of the reference gas is previously measured by the pressure gauge 5 as the reference pressure P _S , and the value is obtained as a reference pressure recording unit. Record in advance in 6a. When the gas A having the smallest molecular weight is used as the reference gas, the pressure of the gas A corresponds to the maximum value of the pressure that can be taken during the measurement. Conversely, when the gas B having the largest molecular weight is used as the reference gas, The pressure of the gas B corresponds to the minimum pressure that can be taken during the measurement.

  Next, by adjusting the inside of the mass spectrometer 3 to a high vacuum with the exhaust system 4, the sample gas G mixed with the plurality of components is transferred from the sample gas introduction unit 1 to the mass spectrometer 3 through the restriction 2. Sucked. Then, the elemental analysis of the sample gas G is performed by the mass spectrometer 3 and the result is input to the analysis result input unit 6b. At the same time, the pressure Pm on the downstream side of the throttle 2 is measured by the pressure gauge 5, and the value is input to the pressure detector 6c. Then, in the coefficient calculation unit 6d, a coefficient α (= Pm / Pm) is obtained from the ratio between the measured pressure Pm of the sample gas G input to the pressure detection unit 6c and the reference pressure Ps recorded in advance in the reference pressure recording unit 6a. Ps). This coefficient α is equal to the ratio of the fluctuation amount of the flow rate of the sample gas G due to the change in the composition of the hydrogen gas. Therefore, the analysis result of the sample gas G obtained by the mass spectrometer 3 can be corrected using this coefficient α.

FIG. 4 shows an example in which nitrogen gas is selected as a reference gas when the mixing ratio of nitrogen gas and hydrogen gas in the sample gas G changes. In FIG. 4B, when the composition ratio of hydrogen gas in nitrogen gas is a predetermined ratio k (vol%), the ratio of the measured pressure Pm to the reference pressure Ps is α (= Pm / Ps). Then, as shown in FIG. 4A, the actual output value C _A of the mass spectrometer 3 has a relationship of α times the ideal value C _B.

  Therefore, as shown in FIG. 5, the output result of the mass spectrometer 3 is corrected by continuously multiplying the uncorrected analysis result A obtained by the mass spectrometer 3 by the reciprocal of α, and originally shown. The power value B can be obtained. From this, in the gas composition output correction unit 6e shown in FIG. 1, the value B to be originally shown is obtained by continuously multiplying the value of the analysis result of the sample gas G by the reciprocal of the coefficient α. The value B obtained in this way is output to the corrected concentration output unit 6f as a correction value of the analysis result obtained by the mass spectrometer 3, and displayed on the screen, for example. Further, this value B may be recorded in other recording means (not shown). In FIG. 4, the sample gas G in which two components of nitrogen gas and hydrogen gas are mixed has been described. However, the present invention can also be applied to a sample gas in which three or more components are mixed.

FIG. 6 is a graph showing the relationship between before and after correction of the analysis result of the sample gas G in which three components of hydrogen gas, nitrogen gas and water vapor are mixed. Here, when the water vapor concentration is constant and the ratio of nitrogen gas to hydrogen gas is changed, the coefficient α and the values before and after correction of the analysis results of each gas obtained by the mass spectrometer 3 are as follows. Show the relationship. Even in this case, as the ratio of hydrogen gas in the nitrogen gas increases to 0 to 100 (vol%), as shown in the thick line graph plotting the corrected value Δ of H ₂ for hydrogen gas, as shown in FIG. , Will increase linearly. Further, the nitrogen gas decreases linearly as shown by the thick line graph in which the corrected value O of N ₂ is plotted. And, for the steam, as shown in the thick line of the plot of the value □ after correction H ₂ O, the value is constant.

  Here, in FIG. 1, for example, when the rotational speed of the vacuum pump constituting the exhaust system 4 connected to the mass spectrometer 3 fluctuates for some reason, the value Pm detected by the pressure gauge 5 fluctuates. The signal from the mass spectrometer 3 is affected by that. However, as described above, when the detected pressure Pm on the downstream side of the throttle 2 fluctuates due to fluctuations in the exhaust capacity of the exhaust system 4 communicated with the mass spectrometer 3, the fluctuation amount is also simultaneously measured by the pressure gauge 5. Detected continuously. Since the fluctuation amount is transferred to the coefficient α, the value of the analysis result obtained by the mass spectrometer 3 is continuously corrected during the measurement even for the influence of the fluctuation of the exhaust capacity of the exhaust system 4. be able to.

  Further, when the reference pressure Ps at the time of measuring the reference gas is recorded in the reference pressure recording unit 6a, if the difference from the value of the reference pressure Ps recorded at the previous measurement exceeds a predetermined error range, this time This means that the reference pressure Ps has changed greatly. In this case, since it can be determined that the mass spectrometer 3 or the exhaust system 4 has changed over time or the pressure gauge 5 has changed over time, there is a problem with any of the mass spectrometer 3, the exhaust system 4 and the pressure gauge 5. An error message can be displayed.

Furthermore, in the embodiment shown in FIG. 1, when all the components constituting the sample gas G are detected by the mass spectrometer 3, all the component concentrations of each gas of the sample gas G obtained by the mass spectrometer 3 are obtained. The added value must be 100Vol%. That is, the concentration value of each gas component output to the correction density output section 6f the _{(vol%), C 1,} C 2 , respectively, placing a · · · C _n,
C ₁ + C ₂ + ... + C _n = 100 (vol%) (4)
Must satisfy the relationship. Therefore, the correction coefficient β is set to β = (C ₁ + C ₂ +... + Cn) / 100 (5)
Then, usually β = 1. However, if a problem such as drift occurs in the pressure gauge 5 during the measurement, for example, the value obtained by correcting the output obtained by the mass spectrometer 3 is affected by this. The value will not be 1. Therefore, the influence of such a defect is corrected by multiplying the value obtained by correcting the component concentration of each gas from the analysis result of the mass spectrometer 3 by the reciprocal of the correction coefficient β.

That is, the correction value a value (vol%) of the component concentration of the gas, C ₁ respectively ', C _2', putting the · · · C _n ',
C ₁ ′ = C ₁ / β, C ₂ ′ = C ₂ / β,..., C _n ′ = C _n / β (6)
It becomes.
Here, a predetermined threshold is set for the fluctuation amount Δβ from the normal correction coefficient β value (β = 1), and when the fluctuation amount Δβ exceeds the predetermined threshold value, the pressure gauge 5 has a drift or the like. It is possible to determine that a problem has occurred and display an error message to that effect. If the variation Δβ always exceeds the threshold value regardless of the passage of time, the relationship shown in the equation (4) is not established, and unknown gas components other than the n gas components are not sampled. Since it can be determined that it is contained in the gas G, an error can be displayed. In this way, the error factor of the component concentration of the sample gas G can be obtained from the value of the correction coefficient β obtained at the time of the correction calculation or the fluctuation amount Δβ thereof.

FIG. 7 is a schematic diagram showing a second embodiment of the present invention. In this embodiment, a second pressure gauge (pressure detection means) 13 is arranged on the upstream side of the throttle 2 of the sample gas introduction unit 1. In this case, the data processor 6 further uses the pressure detected by the second pressure gauge 13 to correct the analysis result of the sample gas G obtained by the mass spectrometer 3.
As shown in FIG. 8A, the output value b of the hydrogen gas (H ₂ ) obtained by the mass spectrometer on the upstream side of the aperture 2 has an error from the value a that should be originally shown due to the flow rate fluctuation of the sample gas G. . The same applies to the nitrogen gas (N ₂ ) in the sample gas G (see FIG. 8B).

Therefore, by disposing the pressure gauge 13 also upstream of the throttle 2 shown in FIG. 7, the component concentration can be calculated in consideration of the flow rate fluctuation of the sample gas G introduced from the sample gas introduction unit 1. . Specifically, the reference pressure Ps on the downstream side of the throttle of the reference gas is sampled, and at the same time, the pressure Ps ′ on the upstream side of the throttle 2 at that time is measured by the second pressure gauge 13, and the value is used as the reference pressure P _S ′. Is recorded in the reference pressure recording section 6g.

  Next, simultaneously with the measurement of the sample gas G on the downstream side of the throttle 2, the second pressure gauge 13 continuously measures the pressure Pm 'on the upstream side of the throttle 2, and the value is obtained as the throttle upstream pressure detector 6h. To enter. A ratio γ (= Pm ′ / Ps ′) between the input pressure Pm ′ and the reference pressure Ps ′ on the upstream side of the throttle is obtained by the coefficient calculation unit 6i, and the coefficient x is obtained based on γ thus obtained. Then, the second gas composition output correction unit 6j continuously multiplies the corrected value obtained by the first gas composition output correction unit 6e by the coefficient x, thereby changing the pressure of the sample gas introduction unit 1. The influence can be corrected. The coefficient x depends on the value of γ, but this is done by creating a map or the like representing the relationship between the coefficient x and γ in advance using the reference gas, and obtaining the coefficient x from γ using this map. It is like that.

It is a schematic diagram which shows the Example form of the gas component analyzer by this invention. It is sectional drawing which shows the specific structure of the sample gas introduction part shown in FIG. It is a graph which shows the output error of hydrogen with respect to the change of the mixing ratio of nitrogen and hydrogen. It is a graph which shows the relationship between coefficient (alpha) and the value before correction | amendment of the output obtained with the mass spectrometer. It is explanatory drawing which correct | amends the value of the analysis result obtained with the mass spectrometer, and obtains the component concentration of sample gas. It is a graph which shows the relationship before correction | amendment about three components which comprise sample gas before correction | amendment. It is a schematic diagram which shows the 2nd Example of this invention. It is a graph which shows the output error of hydrogen and nitrogen by the flow volume fluctuation | variation of sample gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Sample gas introduction part 2 ... Restriction 3 ... Mass spectrometer 4 ... Exhaust system 5 ... Pressure gauge (pressure detection means)
6 ... Data processing unit 7 ... Sample gas flow path 8, 9 ... Sample gas introduction tube 10 ... Partition 11 ... Narrow tube 12 ... Heater 13 ... Pressure gauge (pressure detection means)

Claims (5)

A sample gas introduction part;
A mass spectrometer connected to the sample gas inlet through a restriction,
An exhaust system coupled to the mass spectrometer;
Pressure detecting means for detecting pressure downstream of the throttle;
Correction means for correcting the analysis result of the sample gas obtained by the mass spectrometer using the pressure detected by the pressure detection means,
A gas component analyzer that calculates a component concentration of a sample gas based on the corrected analysis result.   The sample gas is sucked into the mass spectrometer by the differential pressure between the pressure upstream of the throttle of the sample gas introduction unit and the pressure of the mass spectrometer that is evacuated by the exhaust system, and the pressure detection means The gas component analyzer according to claim 1, wherein the pressure downstream of the throttle is continuously detected.   The pressure of the gas component serving as a reference is obtained in advance as a reference pressure, and the value of the analysis result obtained by the mass spectrometer is calculated using the ratio of the pressure of the sample gas detected by the pressure detection means and the reference pressure. The gas component analyzer according to claim 1 or 2, wherein the component concentration of the sample gas is calculated after correction.   The gas component analyzer according to claim 1, wherein the correction by the correction unit is also performed with respect to an influence caused by a change in exhaust capacity of the exhaust system.   The gas component according to any one of claims 1 to 3, wherein an error factor of the component concentration of the sample gas is obtained from a correction value at the time of calculating the component concentration of the sample gas or a variation amount thereof. Analysis equipment.

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