JPH0850109A - Gas analyzing method - Google Patents

Abstract

PURPOSE:To enable continuous analysis of respective components by analyzing the respective components from the obtained partial pressures by using a specific formula denoting the relationship between the heat conductivity of a sample gas that has been measured when a heat generating resistor is driven at a constant temperature, and the heat conductivities and the partial pressures of the respective components of the sample gas, and by analyzing the respective components from the obtained partial pressures. CONSTITUTION:The measured heat conductivity of gas passing through the feeding passage arranged in a resistance body TCD 1 is expressed by the formula lambda=lXXCx+lambdayXCy+lambdazXCz, and it is obtained by the product of the heat conductivities of the constituent components and the partial pressures of the components. Where, lambdax is the heat conductivity of gas x, lambday the heat conductivity of gas y, lambdaz the heat conductivity of gas z, Cx the partial pressure of gas x, Cy the partial pressure of gas y, and Cz the partial pressure of gas z. While changing the temperature of the TCD 1 at three points, for instance, T1 to T3, the heat conductivities are measured, and since the lambdaT1, lambdaT2, lambdaT3 are physical constants being determined by the temperature, by solving these simultaneous equations, the component ratios of Cx, Cy, Cz are determined, and the respective concentrations can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas analysis method for performing gas analysis based on a difference in thermal conductivity.

[0002]

2. Description of the Related Art As a gas analyzer for measuring gas concentration, there is a heat conduction type gas analyzer, which is used, for example, for analysis of hydrogen gas. FIG. 1 is a configuration diagram showing a schematic configuration of a main part of a heat conduction type gas analyzer driven at a constant temperature.

In FIG. 1, 1 is a resistance temperature detector (TCD) arranged in a sample gas supply passage, R1, R2 and R3 are resistors, 3 is a comparator, 5 is a thermal conductivity calculating section, and 6 is The concentration derivation unit 7 is a ROM that stores a plurality of types of calibration curves that are commonly determined for the entire analyzer according to the types of measurement target gas and coexisting gas contained in the sample gas.
A Wheatstone bridge is assembled in the constant temperature bath 8 by the resistors R1, R2 and R3. As the sample gas,
For example, it is a gas containing H ₂ gas as a measurement target gas and N ₂ gas as a coexisting gas.

In this constant temperature driven heat conduction type gas analyzer, the sample gas is fed to the TCD 1 and takes away heat in proportion to its heat conductivity. As a result, the heat generation temperature T _{Rh of the} TCD 1 which is always kept constant changes, and the resistance value Rh thereof changes. The voltage generated at the connection point between the resistors R1 and TCD1 is supplied to the inverting input of the comparator 3 as the output voltage v, and the voltage generated at the connection point between the resistors R3 and R2 is supplied to the inverting input of the comparator 3. As a result, the temperature change of TCD1
It is detected as a change Δv in the output voltage v.

The comparator 3 controls the current i flowing to the TCD 1 based on the detected change Δv in the output voltage v,
The resistance value Rh of TCD1 is constant (Rh = (R1 × R2) /
Keep on R3). As a result, the output voltage v changes and TC
The heat generation temperature _{TRh of} D1 is kept constant. It can be seen from the following equation (1) that the heat generation temperature T _{Rh of} TCD1 is kept constant. That, TCD 1 is a platinum thin-film resistor, the resistance value Rh is indicated by (1), by controlling a constant resistance value Rh of the TCD 1, is also kept constant at the same time heating temperature T _Rh.

Rh = Rh ₂₀ {1 + α ₂₀ · (T _Rh −20) + β ₂₀ · (T _Rh −20) ² } (1) In the formula (1), Rh ₂₀ is TC at 20 ° C.
Resistance value of D1 (Ω), α ₂₀ is the primary temperature coefficient of resistance of TCD1 at 20 ° C, β ₂₀ is 2 of TCD1 at 20 ° C.
Next is the temperature coefficient of resistance.

Here, the heat quantity Q transmitted from TCD1 to the surroundings
_T is represented by the following equation (2). In equation (2), Q _G is the amount of heat transferred to the sample gas by heat conduction, Q _S is the amount of heat transferred to the silicon pedestal through the diaphragm (silicon) and the resistance pattern that make up TCD1, and Q _C is convection (forced convection and natural convection). Heat quantity transferred by convection), Q
_R is the amount of heat transferred by radiation.

Q _T = Q _G + Q _S + Q _C + Q _R (2)

The heat quantity Q _T in the equation (2) is further expressed as the following equation (3). In this equation, T _RR2 is the temperature (° C.) of the constant temperature bath 8, λm is the thermal conductivity (w / k · m) of the sample gas, G is the device constant (m), and λ.
_si is the thermal conductivity (w /
k · m) and G _S are device constants (m) in the diaphragm and the resistance pattern.

Q _T = (T _Rh −T _RR2 ) · λm · G + (T _Rh −T _RR2 ) · λ _si · G _S + Q _C + Q _R (3)

In this equation (3), G and G _S do not change depending on the gas composition, Q _C and Q _R are sufficiently smaller values (or constant values) than Q _G and Q _S , and λ _si is also It is considered to be constant. Further, since T _Rh and T _RR2 are controlled to be constant, the above equation (3) is represented by the following equation (4), where A and B are unique device constants (shape factors including operating conditions). Can also be expressed by the following equation (5).

Q _T = A · λm + B (4)

Q _T = i ² · Rh = v ² / Rh (5)

Then, Q _T = A · λm + B = v ² / Rh
Therefore, the thermal conductivity λm of the sample gas is expressed by the following equation (6).

Λm = (v ² / Rh−B) / A (6)

Here, if the unique device constants A and B are known, the output voltage v is substituted into the above equation (6) to obtain
The thermal conductivity λm of the sample gas can be obtained. Therefore, in this heat conduction type gas analyzer, the above equation (6) is set in the heat conductivity calculating section 5 as an arithmetic expression, while the device constants A and B unique to this arithmetic expression are determined as follows. ing.

That is, first, a first calibration gas having a known thermal conductivity (for example, 100% N ₂ gas) is fed to the TCD 1 to measure the output voltage v (v _N2 ). Next, a second calibration gas having a known thermal conductivity (for example, 100% H ₂ gas)
To TCD1 to measure the output voltage v (v _H2 ).
Then, the measured output voltages v _N2 and v _H2 are given in (7) below.
The device constants A and B unique to each other are obtained by substituting the equations and the formula (8), and the obtained device constants A and B are set as the device constants A and B in the arithmetic expression in the thermal conductivity calculation unit 5. .

A = (v _N2 ² −v _H2 ² ) / {Rh · (λ _N2 −λ _H2 )} (7) B = (v _N2 ² · λ _H2 −v _H2 ² · λ _N2 ) / {Rh · (λ _H2 −λ _N2 )} (8) In equations (7) and (8), λ _N2 is 100% N ₂
Thermal conductivity (w / k) of gas at (T _Rh + T _RR2 ) / 2
・ M), λ _H2 is (T _Rh + T _{RR 2} ) / of 100% H ₂ gas
2 is the thermal conductivity (w / km) of 2.

The above equations (7) and (8) are
・ V ² = Rh obtained by transforming λm + B = v ² / Rh
・ V _N2 , λ _N2 , and v _H2 , λ _{H2 in} A ・ λm + Rh ・ B
It is obtained by solving the simultaneous equations of the following equations (9) and (10) obtained by substituting

V _N2 ² = Rh · A · λ _N2 + Rh · B (9) v _H2 ² = Rh · A · λ _H2 + Rh · B (10)

On the other hand, the ROM 7 stores a plurality of types of calibration curves that are commonly set for the analyzer as a whole according to the types of measurement target gas and coexisting gas contained in the sample gas. For example, the gas to be measured is H ₂ and the coexisting gas is N 2.
For the thermal conductivity λm of the sample gas when formed into a _2, H ₂
A calibration curve showing the gas concentration is stored. In addition, a calibration curve (CH ₄ -H ₂ calibration curve) showing the concentration of H ₂ gas with respect to the thermal conductivity λm of the sample gas when the measurement target gas is H ₂ and the coexisting gas is CH ₄ and , A calibration curve (CO ₂ -H ₂ calibration curve) showing the concentration of H ₂ gas with respect to the thermal conductivity λm of the sample gas when H ₂ is the measurement gas and CO ₂ is the coexisting gas. The calibration curve is stored.

Some of these calibration curves have already been obtained as physical data, but if they have not been obtained, they are created after actual measurement. Further, in this heat conduction type gas analyzer, the concentration derivation unit 6
A required calibration curve is read out from the calibration curves stored in the ROM 7. For example, if the gas to be measured is H ₂ and the coexisting gas is N ₂ , N ₂ —H ₂
Read the calibration curve. Then, the read N ₂ -H ₂
The concentration of H ₂ gas contained in the sample gas is calculated based on the thermal conductivity λm of the sample gas calculated by the thermal conductivity calculator 5 with reference to the calibration curve, and this concentration is output as the measured concentration value.

[0023]

Since the conventional structure is as described above, it is basically necessary to measure the change of one component in the gas composition consisting of two components, and one heat conduction type gas analyzer is used. However, there was a problem that multiple components could not be analyzed.

The present invention has been made in order to solve the above problems, and uses a heat conduction type gas analyzer for each component of a sample gas composed of a plurality of components. The purpose is to be able to analyze.

[0025]

The gas analysis method of the present invention is a method for measuring the heat of a sample gas, which is measured when the heating resistor is driven at a constant temperature by changing the set temperature by the number of each component constituting the sample gas. A relational expression showing the relation between the conductivity, the thermal conductivity of each component constituting the sample gas and their partial pressures is generated for each of the changed set temperatures, and the generated relational expressions are solved simultaneously. Thus, the partial pressure of each component is obtained, and each component is analyzed from these partial pressures.

[0026]

[Function] The thermal conductivity of the sample gas is equal to the sum of the products of the thermal conductivity and the partial pressure of each component, and the thermal conductivity is known in advance as a value unique to each component. If the rate is obtained by measurement, only the partial pressure of each component becomes an unknown.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below. Here, in the heat conduction type gas analyzer shown in FIG. 1 which describes the measurement of the sample gas composed of three components, the resistance temperature detector (TC
D) The measured thermal conductivity λ of the gas passing through the feed passage in which 1 is arranged is, on the other hand, the thermal conductivity of the constituent component and the partial pressure of the component as shown in the following equation (11). It is calculated by the product of

Λ = λx × Cx + λy × Cy + λz × Cz (11) In the equation (11), λ is the thermal conductivity of the mixed gas,
λx is the thermal conductivity of gas x, λy is the thermal conductivity of gas y, λ
z is the thermal conductivity of the gas z, Cx is the partial pressure of the gas x, Cy is the partial pressure of the gas y, and Cz is the partial pressure of the gas z.

Here, the temperature of TCD1 in FIG.
1, T2, T3 are changed at three points to measure the thermal conductivity. At each temperature, the following (12), (1
As shown in equations 3) and (14), simultaneous equations can be created.

Λ _T1 = λx _T1 × Cx + λy _T1 × Cy + λz _T1 × Cz ... (12) λ _T2 = λx _T2 × Cx + λy _T2 × Cy + λz _T2 × Cz (13) λ _T3 = λx _T3 × Cx + λy _T3 × Cy + λz _T3 x Cz (14)

Here, λx _T1 , λy _T1 , λz _T1 , λ
x _T2 , λy _T2 , λz _T2 , λx _T3 , λy _T3 , and λz _T3 are physical constants (known) determined by temperature. By applying these constants to the equations (12), (13), and (14) and solving these simultaneous equations, the component ratios of Cx, Cy, and Cz can be known, and the respective concentrations can be obtained.

In the above embodiment, the case where the sample gas is composed of three components has been described, but the present invention is not limited to this. Even when measuring a gas consisting of four or five components,
The same is true, for example, in the measurement of a sample gas consisting of five components, the temperature of TCD1 is changed at five points, the thermal conductivity is measured, five equations are set, and this can be solved. Further, if the temperature of TCD1 is measured while being changed in a very short time, it is possible to perform a substantially continuous multi-component gas analysis.

[0033]

As described above, according to the present invention, the set temperature of the resistance temperature detector of the heat conduction type gas analyzer driven at a constant temperature is changed and the heat conduction of the sample gas at each temperature is changed. The partial pressure of each component was obtained by establishing a simultaneous equation of the thermal conductivity and the partial pressure of each component constituting the sample gas, which was obtained by measuring the rate. Therefore, there is an effect that each of the components can be analyzed by measuring the sample gas of three or more components with one heat conduction type gas analyzer.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a schematic configuration of a main part of a heat conduction type gas analyzer driven at a constant temperature.

[Explanation of symbols]

1 ... Resistance temperature detector (TCD), R1, R2, R3 ... Resistance,
3 ... Comparator, 5 ... Thermal conductivity calculation unit, 6 ... Concentration derivation unit, 7
... ROM, 8 ... Constant temperature bath.

Claims (1)

[Claims] 1. A sample gas flowing in contact with a heating resistor that is driven at a constant temperature at a predetermined set temperature, by measuring the thermal conductivity of the sample gas by the amount of heat taken from the heating resistor. In a heat conduction type gas analyzer for analyzing a gas, the heat conduction of the sample gas measured when the heating resistor is driven at a constant temperature by changing the set temperature by the number of each component constituting the sample gas. A relational expression showing the relationship between the rate, the thermal conductivity of each component constituting the sample gas, and their partial pressures is generated for each of the changed set temperatures, and the generated relational expressions are solved simultaneously. The partial pressure of each said component is calculated | required by this, and each said component is analyzed from the said partial pressure, The gas analysis method characterized by the above-mentioned.