CN113607882B - Ultralow-concentration flowing gas distribution system and gas distribution method - Google Patents
Ultralow-concentration flowing gas distribution system and gas distribution method Download PDFInfo
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- G01N33/007—Arrangements to check the analyser
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Abstract
The invention discloses an ultralow-concentration flowing gas distribution system and a gas distribution method, which are characterized in that: the device comprises a gas mass flow control module, a gas mass flow control module and a gas mass flow control module, wherein the gas mass flow control module is used for controlling background gas and test gas to enter a system at a certain mass flow; the Volatile Organic Compounds (VOCs) injection control module is used for realizing that liquid VOCs are injected into the pipeline at a certain flow rate; the gas distribution control module comprises a heating device for vaporizing the liquid VOCs, a constant temperature device for keeping temperature and a secondary gas distribution device for testing gas; the main control module is connected with the gas mass flow control module and used for controlling the mass flow of the background gas and the test gas, is connected with the VOCs injection control module and used for controlling the opening, closing and flow rate of the injection of the liquid VOCs, and is connected with the gas distribution control module and used for controlling heating, constant temperature, receiving feedback data and controlling the concentration of secondary gas distribution; the advantages are that: the gas, the gas and the liquid can be mixed into the testing gas with any ppb level ultra-low concentration value, the gas can flow in real time, the control is accurate, the gas distribution is accurate, and the stability is good.
Description
Technical Field
The invention relates to the field of ultralow-concentration gas distribution devices, in particular to an ultralow-concentration flowing gas distribution system and a gas distribution method.
Background
The gas distribution device is widely applied to the fields of production and life, industrial testing, experimental and scientific research and the like, and is a core device for calibrating and regulating gas concentration. For example, in the testing process of the sensitive materials such as the sensor, background gas and test gas with different concentration values need to be dynamically introduced into the testing cavity of the sensitive materials such as the sensor in real time along with the change of time. The concentration of the background gas is generally on the ppm (parts per million) level, and can be generally achieved by gas distribution through a Mass Flow Controller (MFC). However, the concentration of the test gas is often required to reach ppb (parts per billion) level, and if the gas distribution accuracy is not enough by only relying on MFC, the gas distribution effect is poor.
When test gas is introduced in the test process of sensitive materials such as a sensor, the existing standard gas needs to be diluted to obtain the test gas containing a certain amount of certain components. While some of the ingredients, particularly organic substances, are usually present in liquid form at normal temperature and pressure, such as VOCs (volatile organic compounds) such as methanol, ethanol, diethyl ether, benzene, cyclopentane, ethylene oxide, acetone, etc. The components existing in liquid form need to be accurately prepared into ppb level ultra-low concentration test gas which is required by people, and the liquid-gas proportioning technology is difficult at home and abroad. Low concentration gas distribution devices have been developed and reported in media at home and abroad to some extent, but it is rare to realize ultra-low concentration flow gas distribution devices and systems of ppb or lower.
For some gas distribution devices on the existing market which can purportedly prepare ppb level gas concentration, the gas distribution devices actually depend on the gas distribution precision of an MFC machine and the concentration of a used gas source or liquid source, accurate gas distribution is difficult to realize in practical application, the gas distribution effect is poor, and the gas distribution devices are not systematic.
Therefore, a ppb-level ultralow-concentration flowing air distribution system which does not depend on MFC precision and air source concentration, and has high precision, high quality, systematization and good stability is needed.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides an ultralow-concentration flowing gas distribution system and a gas distribution method, which can be used for preparing gas, liquid and test gas with an ultralow concentration value at any ppb level, can be used for realizing real-time flowing gas distribution, and has the advantages of accurate control, accurate gas distribution and good stability.
The technical scheme adopted by the invention for solving the technical problems is as follows: an ultra-low concentration flow gas distribution system comprising:
the gas mass flow control module is used for controlling background gas and test gas to enter the gas distribution system at a certain mass and flow;
the VOCs injection control module is used for realizing that liquid VOCs are injected into the pipeline at a certain flow rate;
the gas distribution control module comprises a heating device for vaporizing the liquid injected by the VOCs injection control module, a constant temperature device for maintaining the temperature of the vaporized VOCs and a secondary gas distribution device for performing secondary concentration distribution on the test gas;
the main control module is connected with the gas mass flow control module and used for controlling the mass and the flow of background gas and test gas, connected with the VOCs injection control module and used for controlling the opening, the closing and the flow rate of the injection of liquid VOCs, and connected with the gas distribution control module and used for controlling the heating and the constant temperature and receiving feedback data and controlling the concentration of secondary gas distribution.
In some embodiments, the gas mass flow control module includes a background gas path, a test gas path, and a first mass flow controller for controlling flow values of the respective gas paths, the first mass flow controller is connected to the main control module, and the background gas path includes at least three paths: the air inlet end of each background air path is connected with a background air source, the air inlet end of the test air path is connected with a test air source, and the test air path and the first path of dilution background air are mixed to form mixed air and enter the air distribution control module for secondary concentration distribution; the second path of dilution background gas enters the gas distribution control module to be used as dilution gas; and the third path of dilution background gas is connected with the test cavity and used as the test background gas.
In some embodiments, the VOCs injection control module includes a liquid VOCs source, a power thruster, a cylinder and a three-way valve, the liquid VOCs source is connected with one end of the three-way valve through the cylinder, the other two ends of the three-way valve are respectively connected to the first path of diluted background gas, and the power thruster is connected with the main control module and is used for controlling the liquid VOCs to be injected into the first path of diluted background gas at a certain flow rate and mixed with the background gas to form a liquid-gas mixing path.
In some embodiments, the power propeller is a syringe pump or a peristaltic pump, and a sealing ring for ensuring sample tightness is arranged between the syringe and one end of the three-way valve.
In some embodiments, two groups of heating devices are provided, each group comprises a heater and a thermocouple, the first group is arranged on the liquid-gas mixing path and at the front end of the three-way valve and used for controlling the vaporization temperature of the liquid VOCs, the second group is arranged in the constant temperature device and used for controlling the constant temperature, a temperature control table and a thyristor are arranged in the main control module, PID closed-loop control is formed among the heater, the thermocouple, the temperature control table and the thyristor, the conduction angle of the thyristor is adjusted through the temperature control table, so that the current temperature output of electricity loaded on the heater is changed, and the real-time temperature of the corresponding measuring end of the thermocouple is read back and fed back to the temperature control table; the secondary gas distribution device comprises a secondary dilution gas path, and a needle valve and a second mass flow controller which are sequentially arranged on the secondary dilution gas path, wherein the gas inlet end of the secondary dilution gas path is connected with the liquid-gas mixing path, the gas outlet end of the secondary dilution gas path is connected with the test chamber, the gas outlet end of the second path of dilution background gas is connected between the second mass flow controller and the test chamber, the needle valve is connected with the main control module and used for controlling the release and release amount of the gas in the gas path, and the second mass flow controller is connected with the main control module and used for controlling the flow of the gas in the secondary dilution gas path; the constant temperature device comprises a constant temperature cavity which coats the liquid-gas mixing circuit and the secondary dilution gas circuit, the constant temperature cavity is made of heat insulation materials, and the second group of heating devices are arranged in the constant temperature cavity.
In some embodiments, the apparatus further comprises a buffer region, the buffer region is disposed between the liquid-gas mixing path and the secondary dilution gas path, the vaporized VOCs and the background gas enter the buffer region together and are uniformly mixed therein, and then flow into the secondary dilution gas path, and the volume of the buffer region is 0.5-1.0L.
In some embodiments, the air outlet of the third diluted background gas is connected to the front end of the test chamber, the air distribution system further includes a first electromagnetic valve and a second electromagnetic valve connected to the main control module, the first electromagnetic valve is disposed on the secondary diluted background gas path and located between the air outlet of the second diluted background gas path and the air outlet of the third diluted background gas path, the second electromagnetic valve is disposed on the third diluted background gas path, and the first electromagnetic valve and the second electromagnetic valve are respectively connected to the exhaust gas path.
In some embodiments, the background gas source includes a nitrogen source and an oxygen source, the nitrogen source is respectively connected to each of the background gas paths, and the oxygen source is respectively connected to each of the background gas paths; the test air source comprises one or more test air sources, and the test air sources are respectively connected to the test air paths.
Another technical solution adopted by the present invention to solve the above technical problems is: an ultra-low concentration flow gas distribution method comprises the following steps:
dividing a background gas source into at least three paths: diluting the background gas in the first path, the diluting background gas in the second path and the diluting background gas in the third path for one time by a gas mass flow controller;
selecting a test gas source to sample or a liquid VOCs source, and if the test gas source is used for sample injection, adopting a gas mass flow controller to perform primary dilution and then accessing a first path of dilution background gas to form a mixed gas; if the sample is injected through the liquid VOCs source, controlling the flow of the liquid VOCs by adopting a power propeller, accessing the flow into the first path of diluted background gas, and heating the background gas at an inlet until the background gas is vaporized to form mixed gas;
and (3) secondary dilution: discharging a set amount of gas from the mixed gas through a needle valve, uniformly mixing the mixed gas with a second path of dilution background gas through a gas mass and flow controller, and finishing secondary dilution of the test gas, namely the ultralow-concentration test gas;
using the third path of dilution background gas as a test background gas;
the ultra-low concentration test gas pipeline and the test background gas pipeline are respectively provided with an electromagnetic valve, and the ultra-low concentration test gas and the test background gas are conveyed to the test cavity by switching on and off the two electromagnetic valves in turn.
In some embodiments, before accessing the background gas and the test gas, the method further comprises:
adjusting the opening of the needle valve: calculating the volume of gas to be discharged at the needle valve according to the concentration value of the gas to be tested, and adjusting the opening size of the needle valve;
setting parameters of a gas mass flow controller, and controlling the mass flow of gas flowing through each path;
setting parameters of a power propeller, and controlling the sampling rate of the liquid VOCs per minute;
and setting the vaporization temperature at the inlet of the liquid VOCs and the holding temperature of the constant-temperature area, wherein the vaporization temperature is determined by the boiling point of the VOCs, and the holding temperature is slightly lower than the vaporization temperature.
Compared with the prior art, the invention has the advantages that:
(1) Dynamic gas distribution at ppb level or lower is realized: the device can reduce the concentration of the common measured gas by 4 orders of magnitude (the measured gas is diluted by more than ten thousand times) through a two-stage gas distribution system, for example, when ppb-level gas is configured, the used test gas source or liquid source only needs to be 10 ppm-level or less, and the ppb-level gas is diluted by more than ten thousand times after secondary dilution, thereby achieving ppb level or even lower; if the testing gas source is 0.1ppm grade gas, the invention can easily prepare ppt grade atmosphere; meanwhile, the device can control the total flow at a certain value, such as 200sccm, through the MFC gas mass flow controller to realize controllability, and obtain ultralow-concentration and stable dynamic gas flow after secondary dilution;
(2) Volatile Organic Compounds (VOCs) liquid vaporization followed by gas distribution: in practical application, the problems that the concentration of VOCs gas purchased on the market is inaccurate, the VOCs gas is difficult to transport and the like exist, so that the structure adopts a mode of simultaneously meeting the requirement of liquid VOCs sample introduction to carry out autonomous gas distribution so as to improve the defects; the device is provided with a power propeller for controlling the flow of the liquid VOCs, for example, an injection pump and a peristaltic pump are selected and used in different occasions respectively; on the basis of the liquid sample introduction, a buffer device is additionally arranged to solve the problem that the concentration of the gas which is prepared is not uniform enough in the liquid sample introduction process and improve the gas preparation effect;
(3) The distribution control module realizes the uniform and stable output of liquefied gas: the gas distribution control module consists of a heating device, a constant temperature device and a secondary gas distribution device, wherein the buffer device is placed in the constant temperature device to obtain a constant temperature buffer cavity (the temperature is ensured to be controllable), the volatile liquid output by the power propeller is instantly vaporized by the heating device and flows into the constant temperature buffer cavity, and the volatile liquid and the constant temperature buffer cavity give a certain buffer time to the gas flow for fully mixing, so that mixed gas flow with uniform concentration is obtained; reuse the accurate exhaust control of needle valve, cooperation mass flow controller carries out secondary dynamic distribution, if do not have the needle valve setting, gas can remain the gathering in the pipeline, causes the distribution inaccurate or pipeline pressure too big damage that causes equipment, and just can guarantee through setting up of needle valve that gas does not detain in the pipeline, and the distribution forms a dynamic process, and the effect of secondary distribution is also more accurate, and the response is faster, and the error is little.
(4) Realize two kinds of gas and switch in twinkling of an eye: the existing gas distribution device has the condition that different gases are slowly switched, which is very unfavorable for a test scene needing to instantly switch the gases, for example, in the test process of the sensor response time, if the gases are slowly switched, the sensor response time is prolonged, and the judgment of the sensor performance is influenced; on the other hand, some gases which are easy to react in the pipeline before being switched to use, so that the gases deteriorate during use, the testing process and the result are seriously influenced, and inconvenience is brought. Aiming at the problems, the electromagnetic valves are respectively arranged on the ultra-low concentration test air pipeline and the test background air pipeline in the device, the two electromagnetic valves are sequentially opened and closed in turn to switch to convey ultra-low concentration test air and background air to the test cavity, when one path of air enters the test cavity, the other path of air is in a flowing state at any moment or in advance, and the two paths of air are switched instantly at a certain moment through manual or automatic control, so that the problems are improved, the response is rapid, the test interference of the sensor is reduced, and the test result is more accurate.
Drawings
FIG. 1 is a schematic diagram of an embodiment of an ultra low concentration flow gas distribution system of the present invention.
The system comprises a first path of dilution background gas 1, a second path of dilution background gas 2, a third path of dilution background gas 3, a nitrogen source 4, an oxygen source 5, test gas sources 6 and 7, a first mass flow controller 8, a liquid VOCs source 9, a power propeller 10, a three-way valve 11, a liquid-gas mixing path 12, a secondary dilution gas path 13, a needle valve 14, a second mass flow controller 15, a test cavity 16, a constant temperature cavity 17, a heating device 18, a buffer area 19, a first electromagnetic valve 20, a second electromagnetic valve 21 and an exhaust gas pipeline 22.
Detailed Description
The present invention is further described in detail with reference to the drawings and examples, but the present invention is not limited thereto.
Example one
As shown in the figure, an ultra-low concentration flow gas distribution system includes:
the gas mass flow control module is used for controlling background gas and test gas to enter the gas distribution system at a certain mass and flow;
the VOCs injection control module is used for realizing that liquid VOCs are injected into the pipeline at a certain flow rate;
the gas distribution control module comprises a heating device for vaporizing the liquid VOCs injected by the VOCs injection control module, a constant temperature device for maintaining the temperature and a secondary gas distribution device for performing secondary concentration distribution on the test gas;
the main control module is connected with the gas mass flow control module and used for controlling the mass and the flow of background gas and test gas, is connected with the VOCs injection control module and used for controlling the opening, the closing and the flow velocity of the injection of liquid VOCs, and is connected with the gas distribution control module and used for controlling the heating and the constant temperature and receiving feedback data and controlling the concentration of secondary gas distribution.
Example two
In the ultra-low concentration flow gas distribution system provided in this embodiment, a specific structure of the gas mass flow control module is further described on the basis of the first embodiment. In this embodiment, the gas mass flow control module includes a background gas path, a test gas path and a first mass flow controller for respectively controlling flow values of the gas paths, the first mass flow controller is connected with the main control module, and the background gas path includes at least three paths: the method comprises the following steps that a first path of dilution background gas 1, a second path of dilution background gas 2 and a third path of dilution background gas 3 are adopted, the air inlet end of each background air path is connected with a background air source, the air inlet end of a testing air path is connected with a testing air source, and the testing air path and the first path of dilution background gas are mixed to form a mixed gas and enter a gas distribution control module to carry out secondary concentration distribution; the second path of diluted background gas enters the gas distribution control module to be used as the diluent gas; and the third path of dilution background gas is connected with the test cavity and used as the test background gas. The trace gas as the test gas has less content and smaller flow speed compared with the standard gas as the background gas, so that the test gas circuit is arranged in front of the first path of diluted background gas, the test gas is taken away by the background gas to enter a pipeline during mixing, and no residue or blockage phenomenon is caused.
In the embodiment, the background gas source comprises a nitrogen source 4 and an oxygen source 5, wherein the nitrogen source is respectively connected to the three background gas paths, and the oxygen source is also respectively connected to the three background gas paths; the test air sources 6 and 7 comprise two (VOCs 1 and VOCs 2), and the test air sources are respectively connected into two test air paths. In this embodiment, the number of the first mass flow controllers 8 is eight, six of which are used for respectively controlling the mass flow of the nitrogen source and the oxygen source in the background gas path.
EXAMPLE III
The present embodiment provides an ultra-low concentration flow gas distribution system, which further illustrates the specific structure of the VOCs injection control module on the basis of the above embodiments. In this embodiment, the VOCs injection control module includes a liquid VOCs source 9, a power thruster 10, a syringe (not shown) and a three-way valve 11, the liquid VOCs source is connected with one end of the three-way valve 11 through the syringe, the other two ends of the three-way valve 11 are respectively connected to the first path of dilution background gas 1, the power thruster 10 is connected with the main control module, and is configured to control the liquid VOCs to be injected into the first path of dilution background gas 1 at a certain flow rate, and to be mixed with the background gas to form a liquid-gas mixing path 12.VOCs injects control module can realize that VOCs evenly injects the pipeline with the form of liquid to make VOCs reach the rapid vaporization of boiling point in the pipeline, VOCs after the vaporization can with the background gas flash mixed in the pipeline. The straight-through two ends of the three-way valve are connected with the first path of dilution background gas for ventilation, a rubber ring is arranged inside the third end of the three-way valve, and the needle head of the needle cylinder is inserted into the rubber ring from the third end of the three-way valve, so that the injection and sealing of VOCs are realized.
Example four
The specific structure of the gas distribution control module is further explained based on the above embodiments in the ultra-low concentration flow gas distribution system provided in this embodiment. In this embodiment, the heating devices are provided in two groups, each group includes a heater and a thermocouple, the first group is provided on the liquid-gas mixing path 12 and located at the front end (not shown) of the three-way valve 11 for controlling the heating temperature to vaporize the liquid VOCs, the second group of heating devices 18 is provided in the thermostat for controlling the thermostat temperature, and the setting position is not limited thereto. Be provided with temperature control table and controlled silicon (not shown) among the main control module, the heater, thermocouple and temperature control table, form PID closed-loop control between the controlled silicon, adjust the size of controlled silicon conduction angle through the temperature control table, thereby change the voltage size of loading to the heater and realize temperature output, read the real-time actual temperature of corresponding measuring terminal back through the thermocouple and feed back to the temperature control table after the temperature output, the temperature control table utilizes PID closed-loop control to realize the accurate control of temperature, practical application shows when heating to thousand degrees, the heating effect is still good, control accuracy is very high.
The secondary gas distribution device comprises a secondary dilution gas path 13, and a needle valve 14 and a second mass flow controller 15 which are sequentially arranged on the secondary dilution gas path 13, wherein the gas inlet end of the secondary dilution gas path 13 is connected with a liquid-gas mixing path 12, the gas outlet end of the secondary dilution gas path 13 is connected with a test cavity 16, a gas outlet end of the second dilution background gas 2 is connected between the second mass flow controller 15 and the test cavity 16, the needle valve 14 is connected with a main control module and used for controlling the release of gas in the gas path, and the second mass flow controller 15 is connected with the main control module and used for controlling the flow of the gas in the secondary dilution gas path.
Constant temperature equipment includes constant temperature chamber 17 including mixing way 12 of liquid-gas and the equal cladding of secondary dilution gas circuit 13, and the constant temperature chamber is made by the heat preservation material, and second group heating device 18 sets up in constant temperature chamber 17 for the temperature that maintains the constant temperature intracavity guarantees that VOCs distributes for the gaseous state all the time, and the thermocouple records constant temperature intracavity actual temperature and feeds back to main control module.
Therefore, the design of the needle valve can enable most of the mixed gas to be discharged out of the pipeline so as to release the stock and the pressure of the mixed gas in the pipeline and avoid the interference on secondary gas distribution; the dynamic secondary gas distribution and even multiple gas distribution can be possible through the emptying operation of the needle valve. The second mass flow controller is matched with a needle valve to realize that a small amount of mixed gas left in a pipeline passes through the MFC according to the set gas flow to be mixed with the second path of dilution background gas, the proportion of the mixed trace gas can be as low as one part per billion, and the aim of ppb-level ultralow-concentration flowing gas distribution is fulfilled.
The secondary gas distribution in the constant temperature area can accurately match the ppb level ultra-low concentration atmosphere, and the flowing gas distribution of any ppb level ultra-low concentration value can be realized by combining with a main control module and adopting STM32 software setting, for example; in addition, if the requirement on the atmosphere concentration is lower, the secondary gas distribution unit can be repeated to perform gas distribution for three times and four times. The control module can realize automatic control of parameters including MFC parameters, peristaltic pump parameters, injection pump parameters, constant temperature area temperature and the like, and is convenient for control operation of experimenters on atmosphere and temperature environment.
In this embodiment, the gas distribution control module further includes a buffer area 19, the buffer area 19 is disposed between the liquid-gas mixing path 12 and the secondary dilution gas path 13, the vaporized VOCs and the background gas enter the buffer area 19 and are uniformly mixed therein, and then flow into the secondary dilution gas path 13, and the volume of the buffer area 19 is 0.5-1.0L. Buffer zone can adopt the cushion flask, and this structure can make the VOCs after the vaporization more even abundant with the background gas mixture in the pipeline to no longer liquefy under the constant temperature condition, promote the distribution effect.
EXAMPLE five
The present embodiment provides an ultra-low concentration flow gas distribution system, which further describes a specific structure of a gas path based on the above embodiments. In this embodiment, the air outlet end of the third dilution background gas 3 is connected to the front end of the test chamber 16, the air distribution system further includes a first electromagnetic valve 20 and a second electromagnetic valve 21 connected to the main control module, the first electromagnetic valve 20 is disposed on the secondary dilution air channel 13 and located between the air outlet end of the second dilution background gas 2 and the air outlet end of the third dilution background gas 3, the second electromagnetic valve 21 is disposed on the third dilution background gas 3, and the first electromagnetic valve 20 and the second electromagnetic valve 21 are respectively connected to the exhaust gas pipeline 22. The design of the two electromagnetic valves can ensure that the third path of diluted background gas can be quickly switched with the prepared ppb-level ultralow-concentration atmosphere, so that different responses of the sensitive material to the test gas and the background gas during quick switching can be achieved during testing, and the testing requirement can be met. When one path of gas enters the test cavity, the other path of gas is in a flowing state at any moment or in advance, and the two paths of gas are switched instantly at a certain moment through manual or automatic control, so that the problems that the gas switching response is slow and the gas in a pipeline is easy to deteriorate in the conventional gas distribution device are solved.
Example six
In this embodiment, the power propeller 10 is an injection pump or a peristaltic pump,
when the injection pump is adopted, the output is uniform and stable, but the injection pump needs to be replaced after each use, and the injection pump can be used for short-time gas testing.
The peristaltic pump can continuously output, but the concentration of the gas to be distributed is uneven due to the output mode (alternate extrusion and release of the elastic conveying hose), so that the problem of uneven gas distribution can be solved due to the arrangement of the buffer device, the vaporized VOCs and the background gas in the pipeline are mixed more uniformly and sufficiently, and the gas distribution effect is improved.
In the aspect of liquid vaporization, the gas distribution system only needs to adopt an injection pump or a peristaltic pump, a constant-temperature heating device and a buffer cavity, has simple and reliable equipment and short vaporization channel, and has simpler and more reliable vaporization mode and lower cost on the premise of ensuring the precision and the stability.
EXAMPLE seven
The gas distribution method of the ultralow-concentration flowing gas distribution system adopting any one of the embodiments comprises the following steps:
dividing a background gas source into at least three paths: diluting background gas in a first path, diluting background gas in a second path and diluting background gas in a third path, and diluting each background gas in each path once through a gas mass flow controller;
selecting a test gas source to sample or a liquid VOCs source, and if the test gas source is used for sample injection, adopting a gas mass flow controller to perform primary dilution and then accessing a first path of dilution background gas to form mixed gas; if the sample is injected through the liquid VOCs source, controlling the flow of the liquid VOCs by adopting a power propeller, accessing the flow into the first path of diluted background gas, and heating the background gas at an inlet until the background gas is vaporized to form mixed gas;
and (3) secondary dilution: discharging a set amount of gas from the mixed gas through a needle valve, uniformly mixing the mixed gas with the second path of dilution background gas through a gas mass flow controller, and finishing secondary dilution of the test gas, namely the ultralow-concentration test gas;
using the third path of dilution background gas as a test background gas;
the ultra-low concentration test gas pipeline and the test background gas pipeline are respectively provided with an electromagnetic valve, and the ultra-low concentration test gas and the test background gas are conveyed to the test cavity by switching on and off the two electromagnetic valves in turn.
As shown in the figure, the first solenoid valve 20 and the second solenoid valve 21 both use three-way valves, and three ports are labeled as a, b, and c, with 20a and 21a being air inlets and 20b, 21b,20c, and 21c being air outlets. The initial state of the first electromagnetic valve 20 is that 20a, 20b are passages, 20a, 20c are closed circuits, 20a, 20c are passages after electrification, 20a, 20b are closed circuits, and 20b, 20c are closed circuits all the time. The principle of the second solenoid valve 21 is the same. When the test chamber works, the first electromagnetic valve 20 and the second electromagnetic valve 21 are sequentially switched to work states in turn, when the first electromagnetic valve 20 is electrified, the second electromagnetic valve 21 is in an initial state, at this time, 20a and 20c are passages, 20a and 20b are closed circuits, 21a and 21b are passages, 21a and 21c are closed circuits, and the test chamber 16 is indicated that ultra-low-concentration test gas enters and test background gas is exhausted as waste gas. Then, the second electromagnetic valve 21 is switched to be electrified under the control of the control module, the first electromagnetic valve 20 is in an initial state, at this time, 20a and 20b are passages, 20a and 20c are closed circuits, 21a and 21c are passages, 21a and 21b are closed circuits, the test background gas enters the test cavity 16, and the ultralow-concentration test gas is discharged as waste gas. The gas distribution device combines a gas distribution method to realize that test gas and background gas are alternately switched into a subsequent test fixture so as to finish sensor response. The quick switching of gas concentration when having guaranteed the test to guarantee the quick response of sensor, can not cause gaseous delay, greatly promoted test effect and performance. And the flow of the discharged gas is very small compared with that of the gas for testing, but the testing performance is greatly improved. The invention can match and use different test fixtures such as test cavities according to different test requirements, and is more convenient and wider in applicability.
In this embodiment, before the background gas and the test gas are accessed, the method further includes:
adjusting the opening of the needle valve: calculating the volume of gas to be discharged at the needle valve according to the concentration value of the gas to be tested, and adjusting the opening size of the needle valve;
setting parameters of a gas mass flow controller, and controlling the mass flow of gas flowing through each path;
setting parameters of a power propeller, and controlling the sampling rate of the liquid VOCs per minute;
and setting the vaporization temperature at the inlet of the liquid VOCs and the holding temperature of the constant-temperature area, wherein the vaporization temperature is determined by the boiling point of the VOCs, and the holding temperature is slightly lower than the vaporization temperature.
The invention relates to an ultralow-concentration flowing gas distribution system, which has the working principle as follows:
(1) Gas distribution principle: after the valve switch of the gas cylinder of the nitrogen and the oxygen is opened, the nitrogen and the oxygen enter the MFC module through the gas channel. And opening the gas cylinder valve switches of the micro gases (VOCs 1 and VOCs 2) to be tested, and allowing one or two kinds of micro gases to be tested to enter the MFC module after passing through the gas passage. MFC carries on the distribution according to the gas velocity and the proportion that set for, and nitrogen gas, oxygen and the micro-gas that awaits measuring mix in the pipeline, form the first way and dilute the background gas. At the moment, three paths of primary dilution background gas with different proportions are conveyed to a subsequent air passage, wherein the first path of primary dilution background gas contains the trace gas to be tested, and the second path of primary dilution background gas and the third path of primary dilution background gas do not contain the trace gas to be tested. The VOCs injection module is not operated at this time. The first path of primary dilution background gas enters the constant-temperature buffer area after being conveyed to a subsequent air passage, a large amount of primary dilution background gas is discharged at the needle valve, a small part of primary dilution background gas passes through the MFC module in the constant-temperature area according to a set flow speed, the first path of dilution background gas containing trace gas to be tested and the second path of dilution background gas are matched again to form secondary dilution background gas, and the dilution proportion and the dilution multiple can be accurately adjusted through the needle valve and the MFC. The secondary dilution background gas reaches ppb level, namely, the secondary dilution background gas is an ultra-low concentration test gas, a third path of dilution background gas is used as the test background gas, and then the two paths of dilution background gas are respectively controlled by two electromagnetic valve modules and are sequentially and alternately conveyed to a test cavity or a high-temperature furnace to carry out response test on the test gas and the background gas.
(2) Liquid gas distribution principle: the difference from gas distribution is that after the cylinder valve switches of nitrogen and oxygen are opened, the first and second cylinder valve switches of the trace gas to be tested are kept closed. A power propeller (an injection pump or a peristaltic pump) is turned on, one or two trace samples to be tested are controlled to be injected into a gas circuit in a liquid form, the liquid is vaporized after being heated in a constant temperature area and mixed with a first path of dilution background gas, and the mixed gas is uniformly mixed through a buffer area and then is discharged in a large quantity at a needle valve.
(3) Gas and liquid mixing and gas distribution principle: different from the method, a gas cylinder valve switch of the trace gas to be tested and a switch of a power propeller (an injection pump or a peristaltic pump) are opened simultaneously for sample injection.
The ultralow-concentration flowing gas distribution system can realize ppb-level ultralow-concentration flowing gas distribution, can realize the test of sensitive materials in an ultralow-concentration atmosphere, can realize the quick switching or maintenance of the test atmosphere by the flowing gas distribution, and ensures the stability and consistency of the test environment. The system is matched with an in-situ test cavity to realize the characterization of the in-situ reaction kinetic process in a high-temperature environment by using infrared spectrum or Raman spectrum.
The MFC with 9 different ranges of the MFC flow rate control module enables the content of each path of gas in the pipeline to be controlled more accurately. The design of the first 8 mass flow controllers in the front of the MFC flow rate control module can prepare three paths of same or different primary dilution background gases, simultaneously can provide two paths of trace test gases for the system, and can increase or reduce the number of MFCs according to actual requirements, so that the test conditions and atmosphere can meet personalized requirements; the 9 th second mass flow controller can realize the mass flow of the mixed primary dilution background gas and VOCs to realize the secondary dilution gas distribution.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and do not limit the scope of the present invention, and the present invention may be modified in materials and structures, or replaced with technical equivalents. Therefore, all structural equivalents to which the disclosure and drawings pertain, whether direct or indirect, are intended to be covered by the present invention.
Claims (4)
1. An ultra-low concentration flow gas distribution system, comprising:
the gas mass flow control module is used for controlling background gas and test gas to enter the gas distribution system at a certain mass and flow;
the VOCs injection control module is used for realizing that liquid VOCs are injected into the pipeline at a certain flow rate; the VOCs injection control module comprises a liquid VOCs source, a power propeller, a needle cylinder and a three-way valve, the liquid VOCs source is connected with one end of the three-way valve through the needle cylinder, the other two ends of the three-way valve are respectively connected to a first path of dilution background gas, and the power propeller is connected with the main control module and is used for controlling the liquid VOCs to be injected into the first path of dilution background gas at a certain flow speed and mixed with the background gas to form a liquid-gas mixed path;
the gas distribution control module comprises a heating device for vaporizing the liquid VOCs injected by the VOCs injection control module, a constant temperature device for maintaining the temperature of the vaporized VOCs and a secondary gas distribution device for performing secondary concentration distribution on the test gas; the heating device is provided with two groups, each group comprises a heater and a thermocouple, the first group is arranged on the liquid-gas mixing path and is positioned at the front end of the three-way valve and used for controlling the vaporization temperature of liquid VOCs, the second group is arranged in the constant temperature device and is used for controlling the constant temperature, a temperature control table and a controllable silicon are arranged in the main control module, PID control is formed among the heater, the thermocouple, the temperature control table and the controllable silicon, the size of a conduction angle of the controllable silicon is adjusted through the temperature control table, so that the current output of electricity pressure loaded on the heater is changed, and the real-time temperature of the corresponding measuring end is read back through the thermocouple and is fed back to the temperature control table; the secondary gas distribution device comprises a secondary dilution gas path, and a needle valve and a second mass flow controller which are sequentially arranged on the secondary dilution gas path, wherein the gas inlet end of the secondary dilution gas path is connected with the liquid-gas mixing path, the gas outlet end of the secondary dilution gas path is connected with the test cavity, a second path of gas outlet end for diluting background gas is connected between the second mass flow controller and the test cavity, the needle valve is connected with the main control module and used for controlling the release and release amount of gas in the gas path, and the second mass flow controller is connected with the main control module and used for controlling the flow of the gas in the secondary dilution gas path; the constant temperature device comprises a constant temperature cavity which covers the liquid-gas mixing circuit and the secondary dilution gas circuit, the constant temperature cavity is made of heat insulation materials, and the second group of heating devices are arranged in the constant temperature cavity;
the main control module is connected with the gas mass flow control module and used for controlling the mass and the flow of background gas and test gas, is connected with the VOCs injection control module and used for controlling the opening, the closing and the flow rate of the injection of liquid VOCs, and is connected with the gas distribution control module and used for controlling the heating and constant temperature, receiving feedback data and controlling the concentration of secondary gas distribution;
the gas mass flow control module comprises a background gas circuit, a test gas circuit and first mass flow controllers for respectively controlling the flow values of the gas circuits, the first mass flow controllers are connected with the main control module, and the background gas circuit comprises at least three paths: the air inlet end of each background air path is connected with a background air source, the air inlet end of the test air path is connected with a test air source, and the test air path and the first path of dilution background air are mixed to form mixed air and enter the air distribution control module for secondary concentration distribution; the second path of dilution background gas enters the gas distribution control module to be used as dilution gas; the third path of dilution background gas is connected with the test cavity and used as the test background gas;
the secondary dilution gas path is arranged between the liquid-gas mixing path and the secondary dilution gas path, vaporized VOCs and background gas enter the buffer area together and are uniformly mixed in the buffer area, and then the mixture flows into the secondary dilution gas path, wherein the volume of the buffer area is 0.5-1.0L;
the air distribution system further comprises a first electromagnetic valve and a second electromagnetic valve which are connected with the main control module, wherein the first electromagnetic valve is arranged on the secondary dilution air path and is positioned between the air outlet end of the second path of dilution background air and the air outlet end of the third path of dilution background air, the second electromagnetic valve is arranged on the third path of dilution background air, and the first electromagnetic valve and the second electromagnetic valve are respectively connected with an exhaust gas pipeline.
2. The ultra-low concentration flow gas distribution system according to claim 1, wherein the power thruster adopts an injection pump or a peristaltic pump, and a sealing ring for ensuring sample tightness is arranged between the needle cylinder and one end of the three-way valve.
3. An ultra-low concentration flow gas distribution system according to claim 1, wherein the background gas source comprises a nitrogen source and an oxygen source, the nitrogen source is connected to each of the background gas paths, and the oxygen source is connected to each of the background gas paths; the test gas source comprises one or more than one test gas source, and the test gas sources are respectively connected to the test gas circuit.
4. An ultra low concentration flow gas distribution method of an ultra low concentration flow gas distribution system according to any one of claims 1 to 3, comprising the steps of:
dividing a background gas source into at least three paths: diluting the background gas in the first path, the diluting background gas in the second path and the diluting background gas in the third path for one time by a gas mass flow controller;
selecting a test gas source to sample or a liquid VOCs source, and if the test gas source is used for sample injection, adopting a gas mass flow controller to perform primary dilution and then accessing a first path of dilution background gas to form mixed gas; if the sample is injected through the liquid VOCs source, controlling the flow of the liquid VOCs by adopting a power propeller, accessing the flow into the first path of diluted background gas, and heating the background gas at an inlet until the background gas is vaporized to form mixed gas;
and (3) secondary dilution: discharging a set amount of gas from the mixed gas through a needle valve, uniformly mixing the mixed gas with a second path of dilution background gas through a gas mass and flow controller, and finishing secondary dilution of the test gas, namely the ultralow-concentration test gas;
using the third path of diluted background gas as a test background gas;
respectively arranging electromagnetic valves on the ultra-low concentration test air pipeline and the test background air pipeline, and switching to convey ultra-low concentration test air and test background air to the test cavity by sequentially opening and closing the two electromagnetic valves in turn;
before the background gas and the test gas are accessed, the method further comprises the following steps:
adjusting the opening of the needle valve: calculating the volume of gas to be discharged at the needle valve according to the concentration value of the gas to be tested, and adjusting the opening size of the needle valve;
setting parameters of the gas mass flow controller, and controlling the mass flow of each path of gas flowing through;
setting parameters of a power propeller, and controlling the sampling rate of the liquid VOCs per minute;
and setting the vaporization temperature at the inlet of the liquid VOCs and the holding temperature of the constant-temperature area, wherein the vaporization temperature is determined by the boiling point of the VOCs, and the holding temperature is slightly lower than the vaporization temperature.
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| CN203422675U (en) * | 2013-07-25 | 2014-02-05 | 上海上计群力分析仪器有限公司 | Dynamic trace gas concentration distributing apparatus |
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