JP2004226077A - Gas dilution system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a great change of a dilution ratio caused by fluctuation of the pressure applied to a capillary. <P>SOLUTION: Indoor air is taken, and refined air refined by an adsorbent 20 and silica gel 22 which is used as zero gas is pressurized by a pump 26 and sent to a zero gas pressure governor 30. The zero gas is adjusted to have a prescribed pressure by the pressure governor 30, and adjusted to have the flow rate of about 1 L/min by zero gas capillaries formed by connecting in parallel a plurality of capillaries 34-1 to 34-6. On the other hand, standard gas filled in a container is sent to a standard gas pressure governor 8 through a solenoid valve 4, supplied similarly to a capillary 12 with a prescribed pressure, and adjusted to have the flow rate of about 10 mL/min. The refined gas and the standard gas are mixed together in a gas mixing part 16, and thereby span gas having the objective concentration is acquired and supplied from a span gas outlet 18. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a gas diluting device for diluting a high-concentration gas to a target concentration with a diluting gas such as nitrogen or purified air.
Such a gas diluting device is, for example, a standard gas supply device that supplies a standard gas for calibrating an analyzer that measures air pollutants such as nitrogen oxides, or a dilution gas that dilutes a sample gas and supplies it to the analyzer. It can be used as a sampling device.
[0002]
[Prior art]
As a standard gas preparation device for producing a standard gas, there is one that dilutes cylinder gas as a gas to be diluted and purified air as a diluent gas (see Patent Document 1). In the standard gas preparation device, air is sent to an air purification mechanism by an air pump, purified, and sent to a mixer through a mass flow meter. On the other hand, the cylinder gas is sent to the mixer through another mass flow meter while adjusting the flow rate from the gas cylinder by a capillary, and is mixed with purified air to become a standard gas. At this time, the output of the mass flow meter obtained by the flow rate of the purified air and the output of the other mass flow meter obtained by the flow rate of the cylinder gas are sent to the control mechanism, and the flow rate of the air pump that sends air based on those outputs is controlled. A standard gas having a target concentration is created and supplied to the measuring device.
[0003]
In such a standard gas preparation apparatus, an expensive apparatus called a mass flow meter is provided in each flow path in order to adjust the flow rate of the purified air and the flow rate of the cylinder gas.
[0004]
As a simple structure without using a mass flow meter, a standard gas preparation device has been proposed in which capillaries are provided in each flow path of the gas to be diluted and the dilution gas, and the respective flow rates are adjusted by the pressure applied to the capillaries. ing.
[0005]
One example of such a standard gas conditioner is shown in FIG. In order to use purified air as a diluent gas, an adsorbent 20 and silica gel 22 for removing moisture are arranged at an inlet of a flow path of a pump 26 for taking in air. The pressure of the air taken in is adjusted by the zero gas pressure regulator 30 through the filters 24 and 28, and the air is guided to the gas mixing section 16 through the capillary 34. A pressure sensor 32 is disposed between the zero gas pressure regulator 30 and the capillary 34 and detects a pressure applied to the capillary 34.
[0006]
On the other hand, a cylinder gas is supplied from a gas cylinder to the inlet 2 as a standard gas to be diluted, the pressure is made constant by the standard gas pressure regulator 8 through the filter 6 from the solenoid valve 4, and the gas is supplied to the gas mixing section 16 through the capillary 12. Be guided. A pressure sensor 10 is also arranged between the standard gas pressure regulator 8 and the capillary 12 in the flow path of the standard gas, and detects the pressure applied to the capillary 12. A branch flow path is provided between the standard gas pressure regulator 8 and the capillary 12, and the branch flow path is guided to the exhaust port via the capillary 14. This capillary 14 is for accelerating gas exchange in the standard gas flow path.
[0007]
The gas diluting device as the standard gas preparation device shown in FIG. 2 includes one capillary having a different flow path resistance on each of the dilution side and the diluting side, and has pressure gauges on both flow paths.
[0008]
[Patent Document 1]
JP 10-274604 A
[Problems to be solved by the invention]
When the dilution ratio is 100 times, the apparatus shown in FIG. 2 uses a capillary whose flow path resistance is different by 100 times between the dilution side and the dilution side by selecting the diameter or adjusting the length. Further, a pressure regulator and a pressure gauge for adjusting the pressure applied to these capillaries are provided.
[0010]
If the relationship between the pressure P, the flow path resistance R, and the flow rate F is simply F∝P / R, as long as the pressure applied to both capillaries is equal, the flow rate ratio is independent of the absolute value of the pressure. And the dilution ratio should be determined.
[0011]
However, in practice, the above-described simple relationship does not hold, and the dilution ratio changes due to a change in pressure, so that the dilution ratio becomes unstable during use. In order to eliminate such instability, the apparatus becomes expensive due to precise temperature control for keeping the set pressure of the pressure regulator constant.
[0012]
Therefore, in the present invention, the dilution gas flow path and the dilution gas flow path are connected to a mixer, each flow path is provided with a capillary, and the flow rate of each flow path is adjusted by the pressure applied to those capillaries. In a gas diluting device in which a mixed gas having a desired dilution ratio is supplied from the mixer, a large change in the dilution ratio due to fluctuations in pressure applied to the capillary is suppressed, thereby increasing the cost for precise temperature control and the like. It is intended to eliminate the need for a simple device.
[0013]
[Means for Solving the Problems]
In a flow path provided with capillaries, if the diameters of the capillaries differ by about 2 to 3 times, capillaries having the same length and a flow path resistance different by about 100 times can be obtained. For example, if the capillary diameter on the dilution side is set to 100 μm and the flow rate is set to 10 mL / min, and the capillary diameter on the dilution side is set to 300 μm and the flow rate is set to 1000 mL / min, the flow path resistance can be made 100 times different. . However, in this case, as described above, the flow rate ratio greatly changed with respect to the pressure fluctuation, and according to the experiment of the present inventor, a 10% pressure fluctuation caused a change in the dilution ratio of about 7%.
[0014]
As a result of studying the cause, in the case of the above example, the Reynolds number (Re = UD / ν: where U is the flow velocity, D is the diameter, and ν is the viscosity coefficient) indicating the state of the flow is to be diluted. The side was found to be laminar at 140 and the dilution side was turbulent at 4700. Because of the different flow conditions, the rate of change of the flow rate with respect to the change of the pressure was different.
[0015]
To solve this problem, either the turbulent flow on the dilution side or the laminar flow on the dilution side is required. However, since the flow rate on the dilution side is small, no matter how small the capillary diameter, the flow velocity reaches the sonic velocity before the turbulent flow occurs, and the turbulent flow cannot be achieved. Therefore, the only solution is to make the dilution side also laminar.
[0016]
Generally, the boundary between laminar flow and turbulent flow is around Reynolds number 2300. In experiments conducted by the present inventor, it has been found that the Reynolds number on the dilution side is desirably 1000 or less in order to make the characteristics with respect to the pressure change closer to the dilution side.
[0017]
In order to reduce the Reynolds number, there is a method of reducing the flow velocity by increasing the capillary diameter. However, as can be seen from the definition equation, the effect of decreasing the flow velocity U cancels the effect of increasing the diameter D, and the efficiency is poor. In order to obtain the same flow resistance as a thin capillary with a thick capillary, a long capillary is required, which is disadvantageous in terms of cost.
[0018]
Therefore, the Reynolds number was reduced by reducing the flow rate per tube without changing the capillary diameter.
That is, in the present invention, a plurality of capillaries are used in parallel as a capillary on the dilution gas side.
[0019]
More preferably, the conditions including the flow velocity and the capillary diameter are set so that the gas flow becomes laminar in all capillaries.
As described above, by using a plurality of capillaries in parallel, it is possible to suppress a change in dilution rate with respect to a change in pressure applied to the capillaries.
[0020]
And, by establishing a method that is stable with respect to the set pressure change of the pressure regulator in this way, it is not essential to measure the individual pressures of both flow paths and strictly adjust them. By simply measuring, monitoring and adjusting the differential pressure, a predetermined dilution factor can be obtained.
[0021]
One example to which the gas dilution device of the present invention is applied is a reference gas supply device that supplies a zero gas and a span gas to an analyzer. In that case, in addition to the span gas outlet that supplies the mixed gas as the span gas from the mixer, a zero gas outlet that is provided upstream of the mixer in the dilution gas flow path and supplies the dilution gas as the zero gas may be provided. preferable. This can prevent the zero gas purity from being reduced.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described with reference to FIG.
This embodiment shows a reference gas supply device for calibrating a device for measuring air pollutants such as nitrogen oxides as an application of the present invention.
[0023]
In order to use purified air as a diluent gas, an adsorbent 20 and silica gel 22 for removing moisture are arranged at an inlet of a flow path of a pump 26 for taking in air. The pressure of the taken-in air is adjusted by the zero gas pressure regulator 30 through the filters 24 and 28, and the air is guided from the solenoid valve 42 to the gas mixing section 16 through the parallel flow paths of the capillaries 34-1 to 34-6. The gas mixing section 16 is connected to a span gas outlet 18 for supplying a mixed gas as a span gas.
[0024]
In the solenoid valve 42, the capillaries 34-1 to 34-6 are input ports, the gas mixing unit 16 side is a normally open (NO) port, and the normally closed (NC) port is connected to a zero gas outlet 44. . The electromagnetic valve 42 is connected to a flow path so that purified air that has normally passed through the capillaries 34-1 to 34-6 is led to the gas mixing unit 16, and the capillaries 34-1 to 34-6 are set to zero gas by switching. By connecting to the outlet 44, purified air can be supplied as zero gas.
[0025]
A cylinder gas is supplied from a gas cylinder to the inlet 2 as a standard gas to be diluted, the pressure is made constant by a standard gas pressure regulator 8 through a filter 6 from a solenoid valve 4, and is guided to a gas mixing section 16 through a capillary 12. . As a channel for accelerating gas exchange in the standard gas channel, a branch channel is provided between the standard gas pressure regulator 8 and the capillary 12, and the branch channel is led to the exhaust port via the capillary 14. ing.
[0026]
In order to detect the pressure difference between the dilution side and the dilution side, between the dilution side zero gas pressure regulator 30 and the capillaries 34-1 to 34-6 and between the dilution side standard gas pressure regulator 8 and the capillary 12 Is provided with a differential pressure sensor 40. Reference numeral 41 denotes a display unit for displaying the indicated value of the differential pressure sensor 40. By including the differential pressure sensor 40 and the display unit 41, it is possible to know whether or not the differential pressure between the two flow paths is within a predetermined range. If the pressure is out of the range, the pressure difference can be returned to the predetermined dilution ratio by operating the pressure regulators 8 and 30 to adjust the differential pressure. It is possible to avoid such a situation that the dilution ratio is shifted without noticing the problem.
[0027]
Next, the operation of this embodiment will be described.
Room air is taken in, and purified air purified by the adsorbent 20 and the silica gel 22 is pressurized by a pump 26 as a zero gas and sent to a zero gas pressure regulator 30. The zero gas is set to a predetermined pressure by the pressure regulator 30, and is adjusted to a flow rate of about 1 L / min by a capillary for zero gas in which a plurality of capillaries 34-1 to 34-6 are connected in parallel.
[0028]
On the other hand, the container-filled standard gas is sent to the standard gas pressure regulator 8 via the electromagnetic valve 4, and is similarly supplied to the capillary 12 at a predetermined pressure and adjusted to a flow rate of about 10 mL / min.
[0029]
In the gas mixing unit 16, the purified gas and the standard gas are mixed to obtain a span gas having a target concentration, which is supplied from the span gas outlet 18.
[0030]
When the capillary on the dilution side is one, the flow rate is set to 10 mL / min with the capillary diameter on the dilution side set to 100 μm, and the flow rate is set to 1000 mL / min with the capillary diameter on the dilution side set to 300 μm. The resistance could be varied by a factor of 100, but a 10% pressure change resulted in approximately a 7% dilution change. On the other hand, in this embodiment, when the same capillary having an inner diameter of 300 μm is used, if the capillary is divided into six and the flow rate per one is reduced to 170 mL / min, the Reynolds number becomes about 800 and the pressure change by 10% The change in the dilution ratio could be improved to 2% or less.
[0031]
Since the apparatus of the embodiment is a gas generator for calibrating a measuring apparatus for measuring air pollutants, it also has a function of supplying zero gas for zero point calibration. The zero gas outlet 44 and the span gas outlet 18 can be made common, but if they are made common, contamination from the span gas occurs in the pipe from the reference gas supply device to the measurement device, and the zero gas purity may be reduced, The zero gas outlet 44 and the span gas outlet 18 are separate.
[0032]
In the embodiment, the six capillaries 34-1 to 34-6 are arranged in parallel in the dilution-side flow path, but in the present invention, the number of dilution-side capillaries arranged in parallel is limited. Instead, various combinations are possible by selecting the flow rate and the capillary diameter.
[0033]
Instead of providing the pressure regulators 8 and 30 on the dilution side and the dilution side as in the embodiment, it is also possible to use an "equal pressure valve" that refers to one pressure and controls the other pressure to be the same.
[0034]
In the embodiment, only the differential pressure detected by the differential pressure sensor 40 is displayed, and the adjustment operation is left to the operator. However, the present invention is not limited to this, and the automatic adjustment is performed by feedback control or the like. You may.
[0035]
【The invention's effect】
In the present invention, the gas flow path to be diluted and the dilution gas flow path are connected to the mixer, each flow path has a capillary, and the flow rate of each flow path is adjusted by the pressure applied to those capillaries. In a gas diluting apparatus in which a mixed gas having a dilution ratio of is supplied from the mixer, a plurality of capillaries of a dilution gas flow path are connected in parallel with each other, so that one capillary is connected to the dilution gas flow path. The gas diluting device is more stable against pressure changes than when the capillary is provided.
In addition, when a differential pressure sensor for detecting a pressure difference between the pressure applied to the capillary of the gas passage to be diluted and the pressure applied to the capillary of the dilution gas passage is provided, even if the pressure changes, the predetermined pressure can be easily determined. Can be adjusted to the dilution ratio.
Further, when the gas diluting device of the present invention is applied to a reference gas supply device of a measuring device, a more reliable measured value can be obtained.
[Brief description of the drawings]
FIG. 1 is a flow chart showing one embodiment.
FIG. 2 is a flow chart showing a reference gas supply device under consideration.
[Explanation of symbols]
2 cylinder gas inlet 4 solenoid valve 8 pressure regulator for standard gas 12 capillary 16 gas mixing section 18 span gas outlet 20 adsorbent 22 silica gel 26 pump 30 pressure regulator for zero gas 34-1 to 34-6 capillary 40 differential pressure sensor 41 display section 42 electromagnetic Valve 44 zero gas outlet

Claims (4)

The gas flow path to be diluted and the dilution gas flow path are connected to the mixer, and each flow path has a capillary, and the flow rate of each flow path is adjusted by the pressure applied to those capillaries, so that the desired dilution ratio and In a gas diluting device in which the mixed gas is supplied from the mixer,
A gas diluting apparatus, wherein a plurality of capillaries of the dilution gas flow path are connected in parallel with each other. The gas diluting apparatus according to claim 1, wherein conditions including a flow velocity and a capillary diameter are set such that a gas flow becomes laminar in all capillaries. The gas diluting device according to claim 1, further comprising a differential pressure sensor that detects a differential pressure between a pressure applied to a capillary of the diluted gas flow channel and a pressure applied to a capillary of the diluted gas flow channel. This gas dilution device is a reference gas supply device that supplies zero gas and span gas to the analyzer,
In addition to the span gas outlet that supplies the mixed gas as the span gas from the mixer, a zero gas outlet that is provided on the dilution gas flow path upstream of the mixer and that supplies the dilution gas as a zero gas is provided. 4. The gas diluting device according to any one of 1 to 3.

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