JP2001194356A - Gas component detecting method, and detector therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas component detecting method to improve the measurement accuracy. SOLUTION: Each flow rate of the fuel gas and the supporting gas to form a hydrogen flame and the correlation of the flow rate of the sample gas with the detection sensitivity are obtained in advance, and the flow rate of each gas is set based on the correlation. For example, when the hydrogen gas of the same quantity as the fuel gas is contained in the sample gas, the flow rate of the fuel gas is set to the flow rate corresponding to the peak zone on the sensitivity curve, and the flow rate of the sample gas is measured under the flow rate condition set so that the sum of the quantity of the hydrogen gas in the sample gas and the flow rate of the fuel gas is within the peak zone. Even when the concentration of the hydrogen gas in the sample gas is fluctuated, the detecting condition at the peak sensitivity is maintained, and the measurement of excellent accuracy can be implemented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas component detecting method and a detector used for analyzing components in a sample gas.

[0002]

2. Description of the Related Art In a gas chromatograph, while a sample is carried through a column by a carrier gas, each component of the sample is separated and eluted from a column outlet. The sample gas from the column outlet is sent to the detector, and each component in the sample gas is detected by the detector. The elution curve (chromatogram) is plotted with the detected value on the vertical axis and time on the horizontal axis. Gas analysis is performed. In this case, a flame ionization detector capable of detecting almost all hydrocarbons is used. Also, for example, when analyzing hydrocarbons in automobile exhaust gas, without passing through a chromatographic column,
Since the hydrocarbon can be continuously measured by directly introducing the sample gas into the flame ionization detector, the flame ionization detector is also used as such a continuous measurement detector.

[0003] The hydrogen flame ionization detection method is a method in which a sample gas is introduced into a hydrogen flame, ionized by the heat of combustion, and the generated carbon ions are collected to amplify an ion current generated and detected and recorded. A combustion chamber is provided. Hydrogen as a fuel gas and air as an auxiliary gas are supplied to the combustion chamber to form a hydrogen flame. Then, by injecting the sample gas into the fuel gas, the hydrocarbons in the sample gas are burned and ionized in the hydrogen flame. This is captured by the collector electrode disposed around the hydrogen flame formation region, and an ion current is generated, thereby performing the above-described gas analysis.

In such a flame ionization detector, in order to improve the measurement accuracy, conventionally, for example, various shapes such as a collector electrode shape and a nozzle shape for injecting a fuel gas and a sample gas into a combustion chamber are used. Attempts have been made to improve the relative positional relationship between the hydrogen flame formed at the nozzle tip and the collector electrode by making improvements. In other words, improvements have been made such that the efficiency of capturing ions generated around the hydrogen flame by the collector electrode that captures the ions can be increased to enable more sensitive detection.

[0005]

By the way, the flow rates of the fuel gas and the auxiliary gas supplied to the hydrogen flame ionization detector as described above are set, for example, from the viewpoint of minimizing the consumption of these gases. An operation of forming a hydrogen flame based on such a premise and injecting an appropriate amount of sample gas into the flame is performed. However, these fuel gas and auxiliary gas
In a measurement state based on the above viewpoints for each flow rate of the sample gas, sufficiently good measurement accuracy cannot always be obtained.

That is, the relative positional relationship between the hydrogen flame and the collector electrode largely depends on the shape of the hydrogen flame itself, and the shape of the hydrogen flame changes depending on the flow rate ratio between the fuel gas and the auxiliary gas. Therefore, even though the detection sensitivity greatly changes due to such adjustment of the flow rate ratio, sufficient measurement accuracy cannot be obtained because the flow rate is not set from this viewpoint.

In particular, for example, when performing a component analysis in the exhaust gas of a fuel cell electric vehicle, the exhaust gas contains hydrogen gas. In such a case, the hydrogen gas in the exhaust gas also acts as a fuel gas, and as a result, the total amount of the fuel gas fluctuates. Such flow rate fluctuations may cause a decrease in measurement accuracy. The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a gas component detection method and a detector capable of improving measurement accuracy.

[0008]

SUMMARY OF THE INVENTION Therefore, claim 1 of the present invention is provided.
The gas component detection method is a gas component detection method for detecting a change when a component to be measured contained in a sample gas burns in a hydrogen flame, and includes a fuel gas and an auxiliary gas for forming a hydrogen flame. The correlation between each flow rate with the sample gas and the detection sensitivity is obtained in advance, and each flow rate is set based on this correlation.

That is, for example, if the flow rates of the fuel gas and the auxiliary gas and the flow rate of the sample gas are set to the flow rates at which the maximum sensitivity is obtained when these flow rates are respectively changed, As a result, gas detection with the total sensitivity further increased is performed, and more accurate measurement can be performed.

In addition, even when there are restrictions such as minimizing the consumption of fuel gas and the like, the flow rates that can increase the detection sensitivity are selected and set within the restrictions, and in this case, However, since gas detection with increased sensitivity can be performed by setting these gas flow rates, more accurate analysis can be performed.

According to a third aspect of the present invention, there is provided a gas component detecting method.
In the method, when the sample gas contains the same common gas component as one of the fuel gas and the auxiliary gas, the one flow rate of the fuel gas and the auxiliary gas is changed. The flow rate of the sample gas is set to the flow rate corresponding to the peak area on the sensitivity curve, and the amount obtained by adding the amount of the common gas component to the one flow rate of the fuel gas and the auxiliary gas is within the peak area. It is characterized in that it is set so that

According to this method, when the sample gas contains, for example, hydrogen gas constituting the fuel gas, the fuel gas flow rate at this time is set to the flow rate corresponding to the peak region on the sensitivity curve. Is done. That is, such a sensitivity curve generally has an upwardly convex shape, and has a gently curved shape such that the peak sensitivity is substantially maintained even when the flow rate varies in the peak region. Therefore, as described above, the fuel gas flow rate is set in the peak region, and the flow rate of the sample gas is set so that the amount obtained by adding the amount of hydrogen gas contained therein to the fuel gas flow rate falls within the peak region. Thereby, even if the amount of hydrogen gas in the sample gas fluctuates, the detection state of the gas component at the peak sensitivity is maintained, so that the measurement accuracy is improved.

In this case, even if the sensitivity itself based on the sample gas flow rate is reduced by setting the sample gas flow rate to be small, as described above, the sensitivity based on the fuel gas flow rate is higher. , The total sensitivity is improved, and gas analysis with good accuracy can be performed. On the other hand, for example, when the sample gas contains, for example, oxygen gas that constitutes the auxiliary gas, gas detection with good total sensitivity can be performed by setting the auxiliary gas flow rate and the sample gas in the same manner as described above. The measurement accuracy can be improved.

According to a fourth aspect of the present invention, there is provided a gas component detector, wherein a combustion chamber is provided in which supply pipes for a fuel gas, an auxiliary combustion gas, and a sample gas are connected to form a hydrogen flame. Flow rate control means for individually setting the flow rate of each gas based on the correlation with the detection sensitivity.

As described above, the apparatus according to the present invention is provided with the flow rate control means for individually setting each gas flow rate based on the correlation with the detection sensitivity. , And an analysis result with good measurement accuracy can be obtained.

[0016]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic diagram of a flame ionization detector according to the present embodiment. This flame ionization detector is formed by providing a combustion chamber 1 surrounded by a cylindrical surrounding wall 1a. A mixed gas supply nozzle 2 is provided upright on a bottom wall in the combustion chamber 1, and a substantially cylindrical collector electrode 3 is provided so as to surround a space slightly above the upper end surface of the nozzle 2. Have been. The mixed gas supply nozzle 2 is connected to a high voltage cable 4 for applying a predetermined high voltage DC voltage thereto. The collector electrode 3 is connected to a signal cable 5 for guiding an ion current to be described later to the outside.

In order to form a hydrogen flame in the combustion chamber 1, first, a fuel gas supply pipe 6 for supplying hydrogen gas (hereinafter referred to as fuel gas) is connected to the bottom wall of the combustion chamber 1. ing. A sample gas supply pipe 7 (not shown) extending from, for example, a column of a gas chromatograph is connected to an intermediate position of the fuel gas supply pipe 6. Thus, the sample gas supplied through the sample gas supply pipe 7 is mixed with the fuel gas supplied through the fuel gas supply pipe 6, and the mixed gas is passed through the mixed gas supply nozzle 2 from the upper end of the nozzle 2. It is configured to spout out.

On the other hand, an auxiliary gas supply pipe 8 for supplying air (hereinafter referred to as auxiliary gas) is connected to the outer periphery of the bottom of the surrounding wall 1a in the combustion chamber 1. The auxiliary gas supplied through the pipe 8 is supplied around the bottom of the mixed gas supply nozzle 2. Note that an exhaust port 1b is formed on the upper wall surface of the combustion chamber 1. Accordingly, the auxiliary combustion gas supplied as described above flows upward in the combustion chamber 1, and is not shown in the region of the nozzle tip where the auxiliary combustion gas and the mixed gas supplied through the mixed gas supply nozzle 2 are mixed. The hydrogen flame 9 is formed by operating the ignition device.

Each of the gas supply pipes 6, 7, 8 has a pressure regulator 6a, 7a, 8 for adjusting the flow rate of the fuel gas, the sample gas, and the auxiliary gas, respectively.
a and the throttles 6b, 7b, 8b are interposed, and these constitute a flow rate control means for individually setting the flow rate of each gas based on the correlation with the detection sensitivity as described later. .

When analyzing a hydrocarbon gas, for example, with the hydrogen flame ionization detector having the above-described configuration, a mixed gas of a sample gas and a fuel gas is supplied to the combustion chamber 1 through the mixed gas supply nozzle 2 as described above. , Which burn above the nozzle 2 to form a hydrogen flame 9. The hydrocarbon contained in the sample gas is ionized by the thermal energy of the hydrogen flame 9 and collected by the collector electrode 3 surrounding the hydrogen flame 9. At the collector electrode 3, electrons are transferred due to the discharge of ions, and an ion current is generated. Then, the ionization current is guided to the outside through the signal cable 5, amplified by a signal amplifier (not shown), converted into a voltage, recorded by a recorder, and analyzed for hydrocarbon gas.

Incidentally, the measurement accuracy of the hydrogen flame ionization detector as described above largely depends on the flow ratio of the fuel gas, the auxiliary gas and the sample gas. That is, the shape of the hydrogen flame 9 changes according to these flow ratios, and the ionization rate generated around the hydrogen flame 9 changes. As a result, the collector electrode 3
As a result, the ionization current from the detector changes and the detection sensitivity changes. Therefore, in the present embodiment, the correlation between the respective flow rates of the fuel gas, the auxiliary combustion gas, and the sample gas and the detection sensitivity is obtained in advance, and the respective flow rates are set based on the correlation to perform the gas analysis.

FIGS. 3 to 5 show examples of sensitivity curves showing the correlation between each gas flow rate and sensitivity. FIG. 3 shows that the auxiliary gas flow rate is 200 ml / min and the sample gas flow rate is 5 to 20 ml / min.
At the time of changing the fuel gas flow rate (Fuel flow rate), FIG. 4 shows the supporting gas flow rate (A) when the fuel gas flow rate is 120 ml / min and the sample gas flow rate is 5 to 20 ml / min.
(ir flow rate) is changed. FIG.
Means that the fuel gas flow rate is 120 ml / min and the auxiliary combustion gas flow rate is 20
It is a sensitivity curve when the sample gas flow rate (sample flow rate) is changed at 0 ml / min. In each of these sensitivity curves, each peak sensitivity is set to “1”, and the sensitivity ratio to the peak sensitivity is set to the vertical axis.

Each gas flow rate is set based on such a sensitivity curve. For example, in the case of analyzing hydrocarbon gas in automobile exhaust gas, if an example of the set flow rate of each gas is shown, the fuel gas flow rate 120 ml / min,
Supporting gas flow rate 200ml / min, sample gas flow rate 5-20ml / m
in (hereinafter, a combination of these flow rates is referred to as a normal flow rate condition).

At this time, the fuel gas flow rate and the auxiliary gas flow rate are each in a region where sensitivity is peaked (the fuel gas flow rate is in the range of 100 to 110 ml / min, and the auxiliary gas flow rate is in the vicinity of 350 ml / min). The flow rate is slightly out of the range. This is set in consideration of, for example, minimizing the consumption of the auxiliary combustion gas (purified air). On the other hand, the sample gas flow rate is set to a flow rate smaller than the peak region. This is set to the above flow rate in order to suppress interference with gas components other than the hydrocarbon gas as the component to be measured contained in the sample gas, for example, gas components such as carbon monoxide, carbon dioxide, and oxygen. ing.

Even with such a setting, each fuel gas flow rate and each auxiliary gas flow rate are set in a flow rate range in which a sensitivity close to the peak sensitivity can be obtained. Gas detection can be performed, thereby performing more accurate analysis. For example, when performing component analysis without restriction such as suppressing the flow rate of the assisting gas as described above, or interference, etc., each flow rate of the fuel gas, the assisting gas, and the sample gas is changed. If the flow rate is set so that the maximum sensitivity can be obtained at this time, gas detection with a further increased total sensitivity can be performed, thereby enabling more accurate measurement.

By the way, for example, in the case of performing gas analysis of exhaust gas from a fuel cell electric vehicle, hydrogen gas is contained in the sample gas. For this reason, when performing gas analysis by setting the gas flow rate of the fuel gas (hydrogen gas) to the same flow rate as described above, the hydrogen gas in the sample gas also acts as the fuel gas. fluctuate.
That is, in the sensitivity curve shown in FIG. 3, the fuel gas flow rate was increased to 120 ml / min over the peak region as described above.
When the hydrogen gas in the sample gas is added to the above flow rate condition, the sensitivity is reduced based on the fuel gas flow rate. As a result, the measurement accuracy is reduced under the normal flow rate condition.

Therefore, in the present embodiment, in the gas analysis when the hydrogen gas is contained in the sample gas as described above, the sensitivity is almost the highest when the gas flow rate of the fuel gas (hydrogen gas) is changed. And the sample gas flow rate is set so that its flow rate range is smaller than the above-mentioned normal flow rate condition (hereinafter, such a flow rate setting condition is referred to as a contained component corresponding flow rate condition). ).
Next, the reason why such a flow rate condition is set will be described with reference to FIG.

As shown in the figure, the sensitivity curve when the fuel gas flow rate (Fuel flow rate) is changed has an upwardly convex shape, and its peak region, that is, in this case, the flow rate is almost 100%.
In the region from ml / min to 110 ml / min, the gently curved shape is such that the peak sensitivity is almost maintained even if the flow rate changes. Then, even if the flow rate decreases from this peak sensitivity region or increases, the sensitivity decreases in each case.

Therefore, when hydrogen of the same component as the fuel gas is contained in the sample gas, and this causes a total flow rate change as the fuel gas, the fuel gas flow rate corresponds to the peak region as described above. Area, eg 100ml
By setting to / min, even if the concentration of hydrogen contained in the sample gas fluctuates, the total flow rate as the fuel gas can be prevented from largely deviating from the above-mentioned peak region. As a result, the measurement state at almost the peak sensitivity is maintained.

Actually, when the fuel gas flow rate is changed as described above, the sensitivity curve for the auxiliary combustion gas flow rate at this time is as shown in FIG. 4 (when the fuel gas flow rate is 120 ml / m2).
(sensitivity curve when in). Therefore, according to the change in the fuel gas flow rate as described above, from the sensitivity curve for the auxiliary gas flow rate at this time, a flow rate at which the sensitivity based on the auxiliary gas flow rate is also increased, for example, 300 ml
The auxiliary combustion gas flow rate is also changed to / min.

On the other hand, the sample gas is set, for example, at 3 to 10 ml / min so that the sum of the hydrogen gas amount and the fuel gas flow rate in the sample gas falls within the above-mentioned peak region. In this case, the flow rate range (5
２０20 ml / min), a smaller flow rate will be set. Therefore, the sensitivity based on the sample gas flow rate in this case is lower. However, by setting the fuel gas flow rate in the peak sensitivity region as described above, the total sensitivity is maintained at a higher level even if the sensitivity based on the sample gas flow rate is low, and the change in the hydrogen concentration in the sample gas is suppressed. The effect is small. Moreover, by reducing the flow rate of the sample gas in this way, the influence of the fluctuation in the concentration of hydrogen contained therein is further reduced. As a result, by setting the sample gas flow rate as described above, a state in which the total sensitivity is higher is reliably maintained.

FIG. 1 shows an example of a change in the total sensitivity under the above-mentioned normal flow rate conditions when the hydrogen gas concentration in the sample gas (sample) was changed. An example of the change is indicated by ▲. These are plotted by setting the sensitivity when the hydrogen gas concentration is zero under normal flow rate conditions to “1” and calculating the sensitivity ratio with respect to this. Under normal flow conditions, the sensitivity decreases with an increase in the hydrogen gas concentration.

On the other hand, the sensitivity under the flow rate condition corresponding to the contained component, for example, under the flow rate condition in which the fuel gas flow rate is reduced from about 120 ml / min under the normal flow rate condition to about 100 ml / min as described above, the sensitivity of the hydrogen gas concentration is reduced. The decrease in sensitivity due to the increase is kept small.

As described above, in this embodiment, when the sample gas contains hydrogen of the same component as the fuel gas, the fuel gas flow rate is changed to a flow rate at which peak sensitivity is obtained when the fuel gas flow rate is changed. Set to. Then, gas analysis is performed such that the amount obtained by adding the amount of hydrogen gas included in the sample gas flow rate to the fuel gas flow rate is within the peak sensitivity region. As a result, the gas analysis of the exhaust gas of the fuel cell vehicle can be performed with higher accuracy without being affected by the fluctuation of the hydrogen concentration in the sample gas.

Although the specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various changes can be made within the scope of the present invention.
For example, in the above description, the case where the gas analysis is performed when the sample gas contains hydrogen gas of the same component as the fuel gas has been described as an example, but when the sample gas contains, for example, oxygen, the flow rate of the auxiliary combustion gas is Is set to a flow rate corresponding to the peak sensitivity region, similarly to the above, it is possible to perform the gas analysis with high accuracy by minimizing the influence of the fluctuation of the oxygen concentration in the sample gas.

In the above description, the hydrogen flame ionization detector (F
For example, a flame photometric detector (FPD) or a frame thermo-onic detector (FT)
The present invention can be applied to a case where a gas component is detected by another detector such as D).

[0038]

As described above, in the gas component detecting method according to the first aspect of the present invention, the correlation between the respective flow rates of the fuel gas and the auxiliary gas for forming the hydrogen flame, the flow rates of the sample gas, and the detection sensitivity. Then, based on these correlations, the gas components are detected by setting each gas flow rate to a flow rate at which the maximum sensitivity is obtained, for example, as in claim 2. Therefore, based on such a flow rate setting, gas detection with further increased total sensitivity is performed, and more accurate measurement can be performed.

In the gas component detecting method according to the third aspect,
When the same common gas component as one of the fuel gas and the auxiliary gas is included in the sample gas, the one gas flow rate is set to a flow rate corresponding to a peak region on the sensitivity curve, and the sample The flow rate of the gas is set so that the amount obtained by adding the amount of the common gas component to the flow rate of the one gas is within the peak region. Thus, even if the amount of the common gas component in the sample gas fluctuates, the detection state at the peak sensitivity described above is maintained, so that accurate measurement can be performed.

According to a fourth aspect of the present invention, the gas component detector individually sets a flow rate of each gas supplied to the combustion chamber through each supply pipe of the fuel gas, the auxiliary gas, and the sample gas based on the correlation with the detection sensitivity. Is provided, a highly sensitive gas detection based on the method of the above claims 1 to 3 can be performed, whereby an analysis result with good measurement accuracy can be obtained. .

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a measurement result of a relationship between a concentration of hydrogen gas contained in a sample gas and a detection sensitivity when performing a gas analysis according to a gas component detection method of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a flame ionization detector according to an embodiment of the present invention.

FIG. 3 is a graph showing an example of a sensitivity curve when a fuel gas flow rate is changed.

FIG. 4 is a graph showing an example of a sensitivity curve when the flow rate of the auxiliary combustion gas is changed.

FIG. 5 is a graph showing an example of a sensitivity curve when a sample gas flow rate is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Combustion chamber 2 Mixed gas supply nozzle 3 Collector electrode 4 High voltage cable 5 Signal cable 6 Fuel gas supply pipe 7 Sample gas supply pipe 8 Combustion gas supply pipe 6a ・ 7a ・ 8a Pressure regulator (flow control means) 6b ・ 7b ・ 8b Restrictor (flow control means) 9 Hydrogen flame

Claims (4)

[Claims] 1. A gas component detecting method for detecting a change when a component to be measured contained in a sample gas burns in a hydrogen flame, comprising: a fuel gas for forming a hydrogen flame; A gas component detection method, wherein a correlation between each flow rate with a gas and detection sensitivity is determined in advance, and each flow rate is set based on the correlation. 2. The gas according to claim 1, wherein each flow rate of the fuel gas and the auxiliary combustion gas and the flow rate of the sample gas are set to flow rates at which almost the highest sensitivity is obtained when the flow rates are changed. Component detection method. 3. When the sample gas contains the same common gas component as one of the components of the fuel gas and the auxiliary gas,
The flow rate of one of the fuel gas and the auxiliary gas is set to a flow rate corresponding to a peak area on a sensitivity curve when the flow rates are changed, and the flow rate of the sample gas is set to the fuel amount by the amount of the common gas component. 2. The gas component detection method according to claim 1, wherein an amount added to the one flow rate of the gas and the auxiliary gas is set to be within the peak region. 4. A combustion chamber in which a supply line for a fuel gas, an auxiliary gas and a sample gas is connected to form a hydrogen flame is provided. A flow rate control means for individually setting based on the correlation of the gas component detector.