A method for dynamic dilution of standard gases

Abstract

This invention relates to a method for dynamic dilution of standard gases. In the apparatus used in this method, the entire standard gas pipeline does not have any valves or other switching devices. Only through the ingenious combination of components and pipelines, the flow control of the standard gas during the dilution and mixing stage is achieved, as well as the control of purging and standard gas on / off during the purging stage. The dynamic dilution method of standard gases of this invention solves the technical problem that existing standard gas pipelines cannot achieve the inertia requirement at high temperatures, and effectively prevents problems such as standard gas loss or contaminant residue caused by adsorption in the standard gas pipeline.

Description

Technical Field

[0001] This invention relates to a method for dynamic dilution of standard gases, belonging to the field of atmospheric environmental monitoring technology. Background Technology

[0002] The standard for continuous automatic detection systems of volatile organic compounds in ambient air stipulates that the analytical instruments in the detection system should be calibrated and verified periodically using standard gases of "specified concentrations". The "specified concentration" standard gas refers to a high-concentration standard gas diluted to the required low-concentration standard gas for calibration according to the dilution ratio set in the standard.

[0003] Continuous automatic monitoring systems require large quantities of standard gas with a wide concentration range during automatic calibration. To ensure a continuous, stable, and flexible output of standard gas, continuous automatic monitoring systems are typically equipped with a dynamic dilution device to prepare standard gas and dilution gas of known concentration in real time at a specific concentration ratio. During the calibration and verification process of the continuous automatic monitoring system, the dynamic dilution device continuously provides standard gas.

[0004] Dynamic dilution apparatuses typically use mass flow meters (MFCs) to separately control the injection flow rates of standard gas and dilution gas. The two gases are mixed in a mixing chamber according to the required dilution ratio. The concentration of the diluted standard gas can be determined based on the dilution factor of the two gases. After dilution, the pipeline through which the standard gas flows needs to be purged with dilution gas to remove residual standard gas and reduce its impact on dilution accuracy. In existing technologies, solenoid valves are generally used to control the switching of gas paths during dilution and purging, while the flow rate is dynamically controlled using a mass flow meter in conjunction with a proportional valve.

[0005] In practical use, due to the special nature of standard gases, there are strict inert requirements for the pipelines through which they flow. For example, it is necessary to avoid adverse reactions that affect the concentration and purity of the standard gas, such as chemical reactions, physical adsorption, condensation of high-boiling-point compounds, and introduction of other impurities during the flow process.

[0006] Currently, for the material of the standard gas flow pipeline, "silanized stainless steel" (a widely recognized inert material in the industry) can be used to meet the above requirements; however, it is difficult to use fully inert materials to manufacture various valves on the pipeline, such as proportional valves and solenoid valves. In particular, conventional dynamic dilution devices also involve high-temperature heat tracing (usually above 120°C) of the standard gas flow pipeline.

[0007] The proportional valves and solenoid valves commonly used in this field generally have an operating temperature tolerance below 50°C. Even if there are high-temperature customized versions of valves, the flexible sealing materials used inside the valves are prone to releasing organic pollutants at high temperatures, making them unsuitable for use in standard gas dilution devices. Therefore, to date, there are no inert dynamic dilution devices on the market that can withstand temperatures above 100°C for the entire sample gas path.

[0008] Therefore, those skilled in the art urgently need to develop a new method for dynamic dilution of standard gases to solve the technical problem that existing standard gas pipelines cannot achieve the inertness requirement at high temperatures. Summary of the Invention

[0009] To address the aforementioned technical problems, the present invention provides a method for dynamic dilution of a standard gas, wherein the method includes a dilution and mixing stage and a purging stage;

[0010] The apparatus used in the standard gas dynamic dilution method includes: a standard gas source, a dilution gas source, a standard gas buffer chamber, a sonic nozzle flow meter, a gas mixing chamber, a standard gas main pipeline, a dilution gas main pipeline, a branch pipeline, and a dilution gas purging branch pipeline.

[0011] The standard gas source is connected in sequence to the standard gas buffer chamber, the sonic nozzle flow meter, and the inlet of the gas mixing chamber via the standard gas main pipeline.

[0012] The standard gas buffer chamber is equipped with a device for monitoring the gas pressure inside the chamber;

[0013] The diversion branch is connected to the standard gas buffer chamber to realize the diversion of gas in the standard gas buffer chamber, and a proportional valve is provided on the diversion branch.

[0014] The dilution gas source is connected to the inlet of the gas mixing chamber via the dilution gas main pipeline; and a mass flow meter is provided on the dilution gas main pipeline.

[0015] The upstream end of the dilution gas purging branch is connected to the main dilution gas pipeline, and the downstream end is connected to the main standard gas pipeline, and is connected between the standard gas buffer chamber and the sonic nozzle flow meter; a switching valve is provided on the dilution gas purging branch.

[0016] During the dilution and mixing stage, the switch valve on the dilution gas purging branch is closed; standard gas enters the standard gas main pipeline, and the flow rate of the standard gas entering the gas mixing chamber is controlled by the sonic nozzle flow meter. Furthermore, based on the gas pressure inside the standard gas buffer chamber, the proportional valve on the branch is adjusted to regulate the branch flow rate, thereby controlling the input gas pressure of the sonic nozzle flow meter; dilution gas enters the dilution gas main pipeline, and the flow rate of the dilution gas entering the gas mixing chamber is controlled by the mass flow meter on the dilution gas main pipeline.

[0017] During the purging phase, the switch valve on the dilution gas purging branch is opened; the dilution gas enters the dilution gas purging branch and splits into two paths at the connection between the dilution gas purging branch and the standard gas main branch. One path of dilution gas enters the gas mixing chamber through the sonic nozzle flow meter for purging, while the other path reduces the gas pressure inside the standard gas buffer chamber by adjusting the proportional valve on the split branch, allowing the dilution gas to enter the standard gas buffer chamber and blocking the flow of standard gas into the gas mixing chamber. The mixed gas in the standard gas buffer chamber then flows out through the split branch.

[0018] Preferably, during the dilution and mixing stage and the purging stage, the standard gas main pipeline and the gas mixing chamber are in a state of high-temperature heating.

[0019] Preferably, the upstream end of the standard gas main pipeline, which is connected to the standard gas source, is provided with a fixed flow-limiting gas resistor.

[0020] Preferably, a pressure regulating valve is provided on the upstream side of the mass flow meter on the main dilution gas pipeline.

[0021] Preferably, the upstream end of the dilution gas purging branch is connected to the upstream side of the pressure regulating valve.

[0022] Preferably, the standard gas buffer chamber is equipped with a pressure sensor to monitor the gas pressure inside the chamber.

[0023] Preferably, the gas mixing chamber has a water injection channel for injecting liquid water into the gas mixing chamber on the side near the inlet, and an electroosmosis pump is provided on the water injection channel.

[0024] Preferably, during the dilution and mixing stage, the electroosmotic pump is adjusted to control the water injection volume of the water injection channel by monitoring the relative humidity of the gas flowing out of the gas mixing chamber.

[0025] This invention provides a method for dynamic dilution of standard gas. In the device used in this method, the entire standard gas pipeline does not have any valves or other switching devices. Only through the ingenious combination of components and pipelines, the flow control of standard gas during the dilution and mixing stage is achieved, as well as the control of purging and standard gas on / off during the purging stage. The dynamic dilution method of standard gas of this invention solves the technical problem that existing standard gas pipelines cannot achieve the inertia requirement at high temperatures, and effectively prevents problems such as standard gas loss or contaminant residue caused by adsorption in the standard gas pipeline. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the apparatus used in the standard gas dynamic dilution method of Embodiment 1 of the present invention;

[0027] Figure 2 This is a schematic diagram of the dynamic airflow during the dilution and mixing stage of the standard gas dynamic dilution method in Embodiment 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the dynamic airflow during the purging stage of the standard gas dynamic dilution method in Embodiment 1 of the present invention. Detailed Implementation

[0029] The present invention will be further illustrated by the following examples, but the present invention is not limited to these specific embodiments.

[0030] Example 1

[0031] The standard gas dynamic dilution method of Example 1 includes a dilution and mixing stage and a purging stage.

[0032] A schematic diagram of the device 100 used in this standard gas dynamic dilution method is shown below. Figure 1 See the schematic diagram of the dynamic gas flow during the dilution and mixing stage of the standard gas dynamic dilution method. Figure 2 See the schematic diagram of the dynamic airflow during the purging phase. Figure 3 .

[0033] like Figure 1-3 As shown, the standard gas dynamic dilution device 100 includes a standard gas source 10, a dilution gas source 20, a standard gas buffer chamber 30, a sonic nozzle flow meter 40, a gas mixing chamber 50, a standard gas main line A, a dilution gas main line B, a branch line C, and a dilution gas purging branch line D.

[0034] Specifically, such as Figure 1-3 As shown, the standard gas source 10 is connected in sequence to the standard gas buffer chamber 30, the sonic nozzle flow meter 40, and the inlet of the gas mixing chamber 50 through the standard gas main pipeline A.

[0035] Preferably, in this embodiment, a fixed flow-limiting gas resistance A1 is provided at the upstream end of the standard gas main pipeline A, which is connected to the standard gas source 10.

[0036] The standard gas buffer chamber 30 is equipped with a device 31 for monitoring the gas pressure inside the chamber. Specifically, in this embodiment, the device for monitoring the gas pressure is a gas pressure sensor 31. Of course, a conventional barometer in the art can also be used.

[0037] The diversion branch C is connected to the standard gas buffer chamber 30 to realize the diversion of gas in the standard gas buffer chamber 30, and a proportional valve C1 is provided on the diversion branch C.

[0038] Preferably, the outlet of the branch line C can also be connected to a dedicated standard gas emission channel (not shown in the figure).

[0039] A dilution gas source 20 is connected to the inlet of the gas mixing chamber 50 via a dilution gas main pipeline B; and a mass flow meter B1 is provided on the dilution gas main pipeline B. Preferably, in this embodiment, a pressure regulating valve B2 is provided on the upstream side of the mass flow meter B1 on the dilution gas main pipeline B.

[0040] The upstream end of the dilution gas purging branch D is connected to the main dilution gas line B, and the downstream end is connected to the main standard gas line A, and is connected between the standard gas buffer chamber 30 and the sonic nozzle flow meter 40; a switch valve D1 is provided on the dilution gas purging branch D.

[0041] Preferably, in this embodiment, the upstream end of the dilution gas purging branch D is connected to the upstream side of the pressure regulating valve B2.

[0042] Preferably, in this embodiment, the gas mixing chamber 50 is provided with a water injection channel 51 for injecting liquid water into the gas mixing chamber 50 on the side near the inlet, and an electroosmosis pump 52 is provided on the water injection channel 51.

[0043] During the dilution and mixing stages and the purging stage, the standard gas main line A and the gas mixing chamber 50 are both under high-temperature heating; as... Figure 2 and 3 The dashed area X shown represents the high-temperature heat tracing area.

[0044] During the dilution and mixing stage, such as Figure 2 As shown, the switch valve D1 on the dilution gas purging branch D is closed. Standard gas enters the standard gas main line A, and the flow rate of standard gas into the gas mixing chamber 50 is controlled by the sonic nozzle flow meter 40; this standard gas flow rate is also the output flow rate of the sonic nozzle flow meter 40.

[0045] Regarding the "output flow rate of the sonic nozzle flow meter 40", it has a linear relationship with the input gas pressure (within a range greater than twice the output gas pressure). Therefore, the output flow rate of the sonic nozzle flow meter 40 can be precisely controlled by precisely controlling the standard gas pressure (input gas pressure) input to the sonic nozzle flow meter 40.

[0046] Regarding the method of controlling the standard gas pressure of the input sonic nozzle flow meter 40, in the prior art, a proportional valve or solenoid valve or other switching device is generally installed on the upstream side of the sonic nozzle flow meter 40 on the standard gas main line A. However, the standard gas main line A is in a high-temperature heat tracing state, and the valve components are prone to volatilizing organic pollutants at high temperatures, causing pollution of the standard gas. Therefore, the use of valve components cannot meet the inertia requirement of the standard gas main line A.

[0047] To solve the aforementioned technical problems, the inventors of this application have changed their thinking. Instead of directly adjusting the gas pressure by setting a switching device on the standard gas main line A (as is the common thinking of those skilled in the art), they have set a standard gas buffer chamber 30 on the standard gas main line A (upstream of the sonic nozzle flow meter 40) and a branch line C on the standard gas buffer chamber 30. By adjusting the branch flow rate (back pressure branch pressure control), they indirectly control the gas pressure in the standard gas buffer chamber 30 and the standard gas pressure input to the sonic nozzle flow meter 40, thereby controlling the standard gas flow rate entering the gas mixing chamber 50.

[0048] Therefore, there is no need to install valves or other switching devices on the standard gas main pipeline A to control the flow rate of the standard gas, and the pipeline structure is simple and reliable.

[0049] Preferably, in this embodiment, the upstream end of the standard gas main pipeline A, which is connected to the standard gas source 10, is provided with a fixed flow-limiting gas resistor A1 to limit the flow rate of standard gas entering the standard gas buffer chamber 30.

[0050] Specifically, the standard gas passes through a fixed flow-limiting gas resistance A1 and enters the standard gas buffer chamber 30. The pressure value inside the chamber is fed back by the pressure sensor 31 of the standard gas buffer chamber 30, and the proportional valve C1 on the diversion branch C is adjusted to regulate the diversion flow rate of the diversion branch C in real time. The standard gas that needs to be diverted flows out from the outlet of the diversion branch C through the proportional valve C1, and the standard gas that is not diverted enters the gas mixing chamber 50 through the sonic nozzle flow meter 40.

[0051] During the dilution and mixing stage, such as Figure 2As shown, the dilution gas enters the main dilution gas pipeline B. Since the dilution gas does not require inertia in the pipeline before entering the gas mixing chamber 50, the flow rate of the dilution gas into the gas mixing chamber 50 is controlled by installing a mass flow meter B1 on the main dilution gas pipeline B. Specifically, the flow rate of the dilution gas is controlled according to a set dilution ratio. Preferably, a pressure regulating valve B2 is also installed upstream of the mass flow meter B1 on the main dilution gas pipeline B.

[0052] A standard gas at a specific flow rate and a dilution gas at a specific flow rate are uniformly mixed in a gas mixing chamber 50 to obtain a diluted standard gas at a specific concentration (the desired concentration). The diluted gas is discharged through the outlet of the gas mixing chamber 50 and enters the downstream detection device (the detection device of the ambient gas detection system, not shown in the figure).

[0053] Preferably, in the standard gas dynamic dilution device 100 of this embodiment, the gas mixing chamber 50 is provided with a water injection channel 51 for injecting liquid water into the gas mixing chamber 50 on the side near the inlet, and an electroosmosis pump 52 is provided on the water injection channel 51.

[0054] During the dilution and mixing stage, the water injection volume of the water injection channel 51 is controlled by adjusting the electroosmotic pump 52 by monitoring the relative humidity of the gas flowing out of the gas mixing chamber 50.

[0055] During the purging phase, such as Figure 3 As shown, the switch valve D1 on the dilution gas purging branch D is opened; thus, the dilution gas enters the dilution gas purging branch D, and splits into two paths at the connection between the dilution gas purging branch D and the standard gas main line A (located between the standard gas buffer chamber 30 and the sonic nozzle flow meter 40); one path of dilution gas enters the gas mixing chamber 50 through the sonic nozzle flow meter 40 for purging, and the other path reduces the gas pressure inside the standard gas buffer chamber 30 (the dilution gas pressure is greater than the standard gas pressure) by adjusting the proportional valve C1 on the split branch C, so that the dilution gas enters the standard gas buffer chamber 30 and blocks the flow of standard gas into the gas mixing chamber 50; after the standard gas and dilution gas meet and the pressure is balanced in the standard gas buffer chamber 30, the excess mixture of standard gas and dilution gas flows out through the split branch C.

[0056] During this process, the dilution gas not only completes the purging from the standard gas buffer chamber 30 to the gas mixing chamber 50, but also blocks the standard gas from entering the gas mixing chamber 50. The purging and standard gas on / off control are achieved simultaneously through the pressure difference control in the gas circuit. There is no need to install valves or other switching devices in the standard gas main pipeline A. The entire pipeline structure is simple and reliable.

[0057] In summary, in the device 100 used in the standard gas dynamic dilution method of the present invention, the entire standard gas main pipeline A is not equipped with any valves or other switching devices (avoiding the use of non-inert materials due to the inability of switching devices to withstand high temperatures). Only through the ingenious combination of components and pipelines, the standard gas flow control in the dilution and mixing stage is realized, as well as the control of purging and standard gas on / off in the purging stage. The standard gas dynamic dilution method of the present invention solves the technical problem that existing standard gas pipelines cannot achieve inertness requirements at high temperatures, and effectively prevents standard gas loss or contaminant residue (affecting the accuracy of dynamic dilution) caused by adsorption in the standard gas pipeline.

[0058] Those skilled in the art, upon learning of the standard gas dynamic dilution method of this application, can apply it to an environmental gas detection system, for example, by combining the standard gas dynamic dilution device with an environmental detection device.

[0059] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0060] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for dynamic dilution of a standard gas, characterized in that: The standard gas dynamic dilution method includes a dilution and mixing stage and a purging stage; The apparatus used in the standard gas dynamic dilution method includes: a standard gas source, a dilution gas source, a standard gas buffer chamber, a sonic nozzle flow meter, a gas mixing chamber, a standard gas main pipeline, a dilution gas main pipeline, a branch pipeline, and a dilution gas purging branch pipeline. The standard gas source is connected in sequence to the standard gas buffer chamber, the sonic nozzle flow meter, and the inlet of the gas mixing chamber via the standard gas main pipeline. The standard gas buffer chamber is equipped with a device for monitoring the gas pressure inside the chamber; The diversion branch is connected to the standard gas buffer chamber to realize the diversion of gas in the standard gas buffer chamber, and a proportional valve is provided on the diversion branch. The dilution gas source is connected to the inlet of the gas mixing chamber via the dilution gas main pipeline; and a mass flow meter is provided on the dilution gas main pipeline. The upstream end of the dilution gas purging branch is connected to the main dilution gas pipeline, and the downstream end is connected to the main standard gas pipeline, and is connected between the standard gas buffer chamber and the sonic nozzle flow meter; a switching valve is provided on the dilution gas purging branch. During the dilution and mixing stage, the switch valve on the dilution gas purging branch is closed; standard gas enters the standard gas main pipeline, and the flow rate of the standard gas entering the gas mixing chamber is controlled by the sonic nozzle flow meter. Furthermore, based on the gas pressure inside the standard gas buffer chamber, the proportional valve on the branch is adjusted to regulate the branch flow rate, thereby controlling the input gas pressure of the sonic nozzle flow meter; dilution gas enters the dilution gas main pipeline, and the flow rate of the dilution gas entering the gas mixing chamber is controlled by the mass flow meter on the dilution gas main pipeline. During the purging phase, the switch valve on the dilution gas purging branch is opened; the dilution gas enters the dilution gas purging branch and splits into two paths at the connection between the dilution gas purging branch and the standard gas main branch. One path of dilution gas enters the gas mixing chamber through the sonic nozzle flow meter for purging, while the other path reduces the gas pressure inside the standard gas buffer chamber by adjusting the proportional valve on the split branch, allowing the dilution gas to enter the standard gas buffer chamber and blocking the flow of standard gas into the gas mixing chamber. The mixed gas in the standard gas buffer chamber then flows out through the split branch. During the dilution and mixing and purging phases, the standard gas main pipeline and the gas mixing chamber are in a state of high-temperature heating.

2. The standard gas dynamic dilution method as described in claim 1, characterized in that: The upstream end of the standard gas main pipeline, which is connected to the standard gas source, is provided with a fixed flow-limiting gas resistor.

3. The standard gas dynamic dilution method of claim 1, wherein: A pressure regulating valve is provided on the upstream side of the mass flow meter on the main dilution gas pipeline.

4. The standard gas dynamic dilution method as described in claim 3, characterized in that: The upstream end of the dilution gas purging branch is connected to the upstream side of the pressure regulating valve.

5. The standard gas dynamic dilution method as described in claim 1, characterized in that: The standard gas buffer chamber is equipped with a pressure sensor to monitor the gas pressure inside the chamber.

6. The standard gas dynamic dilution method as described in claim 1, characterized in that: The gas mixing chamber has a water injection channel on the side near the inlet for injecting liquid water into the gas mixing chamber, and an electroosmosis pump is installed on the water injection channel.

7. The standard gas dynamic dilution method as described in claim 6, characterized in that: During the dilution and mixing stage, the relative humidity of the gas flowing out of the gas mixing chamber is monitored to adjust the water injection volume of the water injection channel by the electroosmosis pump.

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