JPH0625730B2 - Analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] Hydrogen gas has a much larger diffusion coefficient than other gases except helium gas. The present invention relates to an analyzer that determines the concentration of hydrogen gas by utilizing such a difference in diffusion coefficient.

[Prior Art] Conventionally, as an analyzer capable of measuring the concentration of hydrogen gas, there is, for example, a gas chromatograph.

[Problems to be Solved by the Invention] However, in a gas chromatograph, there are problems that continuous measurement is impossible and the structure becomes complicated when a wide measurement range is attempted.

The present invention has been made to eliminate the above-mentioned problems, and an object thereof is to realize an analyzer capable of continuously measuring the concentration of hydrogen in a measurement gas in a wide range with a simple configuration.

[Means for Solving Problems] According to the present invention, a constant flow rate of a specific gas flows in a fixed direction, and at one end on the downstream side, the specific gas is mixed with a measurement gas containing hydrogen, and hydrogen is supplied to the specific gas. Measurement tube that diffuses in the direction opposite to the flow of the gas, a sensor that detects the hydrogen concentration at a predetermined position of this measurement tube, and the detection signal of this sensor that determines the diffusion rate of hydrogen and other components in the measurement gas. The analyzer is provided with a calculation unit for obtaining the concentration of hydrogen in the measurement gas based on the difference.

[Examples] The present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the analyzer according to the present invention.

In the figure, reference numeral 1 is a measuring tube, through which a specific gas supplied by a gas supplier 2 flows in a constant direction (direction A) at a constant speed. The specific gas has a known component, and is, for example, air, oxygen, nitrogen gas or the like. At one end 11 of the measuring tube 1, the specific gas and the measuring gas are mixed.

A detector 3 is provided in the flow path of the measuring tube 1 and detects the concentration of hydrogen at the installation position. As the sensor 3, for example, a zirconia element is used.

A calculation unit 4 calculates the concentration of hydrogen in the measurement gas from the detection signal of the sensor 3 by utilizing the difference in diffusion rate between hydrogen and another gas.

Next, the measurement principle of such an analyzer will be described.

The one end 11 of the measuring tube 1 is set to the 0 position, and the X axis is taken with the direction opposite to the flow of the specific gas as the positive direction. The concentrations of the components of the measurement gas at the position of x = 0 are C ₁₀ , C ₂₀ , ... C, respectively.
The concentration of each component of the measurement gas at _{N 0} and the position x is C ₁
(X), C ₂ (x), ... C _N (x).

Here, the distribution of the concentration C _N (x) of the gas N (one component in the measurement gas) at the position x is obtained.

If the diffusion coefficient of the gas N in the specific gas is D _N , the amount J _N of the gas N carried in the x direction by diffusion is calculated by the following equation if the gas N is not flowed at this position. It is the concentration gradient times the diffusion coefficient.

Since the specific gas is flowing at a constant flow rate now, the concentration C
The gas of _N (x) is carried at a flow velocity v in the direction opposite to the direction of diffusion, and the net flow amount K of the gas N is Becomes The concentration C _N (x) becomes thinner toward the upstream of the flow of the specific gas, so that the diffusion amount of the gas N and the flow amount thereof are in equilibrium at each position. When in equilibrium, K = 0, so Therefore, the concentration C _N (x) is given by the following equation.

An example of the calculation result of the formula is shown in FIG. In the graph of FIG. 2, the vertical axis is l _n {C _N (x)}, the horizontal axis is the position x (1 _n is a natural logarithm), and the diffusion coefficient D _N is used as a parameter.

In this figure, a ₁ , a ₂ , and a ₃ are H ₂ (hydrogen),
It is a graph of CH ₄ (methane) and CO (carbon monoxide).

From such a result, an analyzer as an H ₂ gas meter will be considered. Assuming that the sensor used has sensitivity to combustible gas, interference due to CO, CH _4, etc. becomes a problem. Diffusion counts, to _{H 2} is 0.611, CH ₄ is so 0.196, a flow rate is 5cm / _{sec, H 2,} C
Assuming that the initial concentration of H ₄ is 10%, the concentrations of H ₂ and CH ₄ at each position and the concentration ratio of these gases are as shown in FIG.

Since the diffusion coefficient of CH ₄ gas is smaller than that of H ₂ gas, the concentration of CH ₄ is sufficiently smaller than the concentration of H ₂ at the position of x = 5,10 mm as shown in the figure. Therefore, the interference error is not a problem.

Further, since the diffusion coefficient of CO is smaller than the diffusion coefficient of CH ₄ , the interference error becomes smaller.

In the actual measurement, v, x, D _N are known in the equation, and C
_{Since N} (x) is obtained as a measurement value, the hydrogen concentration C _N0 in the measurement gas is obtained from these.

If a zirconia element is used as the sensor 3, 1 ppb
Since it is possible to measure even below (parts per billion), it is possible to realize an H ₂ gas meter that can be used in a wide concentration range from a very small amount to 100%.

The analyzer may be a gas that has a large diffusion coefficient other than H ₂ gas, such as He (helium) gas.

[Effect] According to such an analyzer, the concentration is measured by utilizing the fact that the diffusion coefficient of hydrogen is larger than that of other gases.
The interference error is reduced, and a wide range of measurement is possible with a simple configuration. For example, in the example of FIG. 2, when x = 5 mm is selected, if the sensor can measure up to 10 ppb, 1 ppm
It is possible to measure in a dynamic range of 10 ⁶ from 10 to 100%.

In addition to this, since the sensor 3 constantly detects the concentration, continuous measurement is possible.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the analyzer according to the present invention, and FIGS. 2 and 3 are diagrams showing an example of measurement results of the apparatus of FIG. 1 ... Measuring tube, 11 ... One end, 2 ... Gas supply device, 3 ...
... Sensor, 4 ... Calculator.

Claims (1)

[Claims] 1. A measurement in which a constant flow rate of a specific gas flows in a fixed direction, and a measurement gas containing hydrogen is mixed with this specific gas at one end on the downstream side to diffuse hydrogen in the direction opposite to the flow of the specific gas. A tube, a sensor that detects the hydrogen concentration at a predetermined position of this measuring tube, and the detection signal of this sensor, which is used to measure the concentration of hydrogen in the measuring gas based on the difference in the diffusion rates of hydrogen and other components. An analyzer equipped with a calculation unit for determining the hydrogen concentration of.