VOCs gas generating device with stable concentration

Abstract

The utility model relates to a VOCs gas generating device with stable concentration. The VOCs gas generating device comprises a sample injection assembly, a gas source assembly, a gasification assembly, a pressure control assembly and a mixer, the sample injection assembly comprises a precise injection pump, a micro-injection needle and a capillary injection pipeline. The gasification assembly comprises a shell, a quartz liner tube, a heater and a quartz capillary column. The VOCs solution is gasified in the quartz liner tube and diluted for the first time. And the VOCs gas is diluted for the second time in the mixer. The pressure control assembly comprises a pressure stabilizing valve and a needle valve. The pressure stabilizing valve is used for adjusting the flow of diluent gas released by the diluent gas source flowing into the quartz liner tube and stabilizing the pressure of the gas flowing into the quartz capillary column. The needle valve is used for adjusting the flow of gas flowing out of the flow dividing opening, and then the flow of gas flowing into the quartz capillary column in the quartz liner tube is adjusted. According to the utility model, the defects of non-uniform gasification, unstable gasification process, high possibility of pulsation and discontinuous gasification of liquid in the conventional dynamic generator method are overcome from three directions of a liquid source, a gas source and a gasification process.

Description

Technical Field

[0001] This utility model relates to the technical field of VOCs gas generating devices, and in particular to a VOCs gas generating device with stable concentration. Background Technology

[0002] VOCs (volatile organic compounds) are important precursors to O3 and secondary organic aerosols. Prolonged exposure can have direct negative impacts on human health, and is associated with PM2.5 emissions. 2.5 With the further development of synergistic control with ozone, a large number of VOCs monitoring devices and purification technologies have emerged. Performance evaluation of these technologies is fundamental for subsequent applied research. The gas source, as a crucial component of performance evaluation, directly impacts the results of performance tests for monitoring devices and purification technologies. Currently, commonly used VOCs loading methods include bubbling, diffuser / permeable tube, volume ratio, and dynamic generator methods.

[0003] Among these methods, the bubbling method suffers from poor stability and low accuracy in total volume control. The diffuser / permeabilizer method has extremely high requirements for temperature control, diffusion rate, and weighing accuracy; in actual operation, it has many sources of error, is easily affected by the environment, and the measurement results are highly unstable. The volume ratio method requires multi-component VOCs standard gas cylinders with a concentration range that are difficult to obtain, and its stability during long-term use is hard to guarantee. The dynamic generator method results in uneven vaporization, especially at low concentrations, where the vaporization process is unstable and prone to pulsation and intermittent liquid vaporization. Utility Model Content

[0004] To solve the above-mentioned technical problems, this utility model provides a VOCs gas generator with stable concentration.

[0005] The VOCs gas generator with stable concentration provided by this utility model adopts the following technical solution:

[0006] A stable concentration VOCs gas generator includes a sample injection component, a vaporization component, a gas source component, a mixer, and a pressure control component. The sample injection component includes a precision injection pump, a micro-injection needle, and a capillary injection line. One end of the capillary injection line is connected to the micro-injection needle, and the other end is connected to the vaporization component. The precision injection pump is connected to the micro-injection needle to drive it, injecting a VOCs solution contained within the micro-injection needle into the injection line. The vaporization component includes a shell, a quartz liner, a heater, a quartz capillary column, and a vaporization channel. The vaporization channel is disposed inside the shell. The quartz liner is disposed within the vaporization channel. The quartz capillary column is located outside the shell. A flow divider is provided on the side wall of the vaporization channel. The quartz liner is connected to the capillary injection line, the quartz capillary column, and the flow divider to allow the VOCs to be injected. The solution vaporizes within the quartz liner and flows to the quartz capillary column and the diversion port, respectively. The quartz liner is filled with glass wool. The gas source assembly includes a dilution gas source, which is connected to the quartz liner. The mixer has a first inlet, a second inlet, and a first outlet. The first inlet is connected to the dilution gas source; the second inlet is connected to the quartz capillary column; the first outlet is used to discharge gas from the mixer. The pressure control assembly includes a pressure regulating valve and a needle valve. The pressure regulating valve is located between the dilution gas source and the outer casing. The needle valve is located downstream of the diversion port. The pressure regulating valve regulates the flow rate of the dilution gas released from the dilution gas source into the quartz liner and stabilizes the pressure of the gas flowing into the quartz capillary column. The needle valve regulates the flow rate of the gas flowing out of the diversion port, thereby regulating the flow rate of the gas from the quartz liner into the quartz capillary column.

[0007] Optionally, the pressure control assembly further includes a back pressure valve; the back pressure valve is connected to the mixer and is used to stabilize the gas pressure discharged from the mixer and eliminate fluctuations in flow and pressure at the mixer outlet.

[0008] Optionally, the gas source assembly further includes a pressure reducing valve; the pressure reducing valve is connected to the dilution gas source and is used to adjust the output pressure of the output gas source.

[0009] Optionally, the pressure control component further includes a mass flow meter; the mass flow meter is disposed between the dilution gas source and the mixer, and is used to control the flow rate of the dilution gas input from the dilution gas source into the mixer.

[0010] Optionally, the injection assembly further includes a contaminant solution bottle and a three-way inlet valve; the contaminant solution bottle is used to hold a VOCs solution; the two inlets of the three-way inlet valve are respectively connected to the micro-injection needle and the contaminant solution bottle, and the outlet is connected to the capillary injection line; the three-way inlet valve is used to control the connection between the micro-injection needle and the capillary injection line to inject the VOCs solution into the quartz liner, or to control the connection between the micro-injection needle and the contaminant solution bottle so that the micro-injection needle can draw up the VOCs solution in the contaminant solution bottle.

[0011] Optionally, it also includes a waste gas treatment component; the waste gas treatment component includes an adsorbent tube; the front end of the adsorbent tube is connected to the outlet of the needle valve and the first outlet, for treating unused VOCs gas.

[0012] Optionally, the waste gas treatment assembly further includes a VOCs sensor; the VOCs sensor is disposed at the end of the adsorbent tube and is used to monitor the VOCs content in the gas discharged from the end of the adsorbent tube.

[0013] Optionally, all components in the VOCs gas generator that come into contact with VOCs are subjected to silanization treatment.

[0014] As described above, the VOCs gas generator with stable concentration of this invention has at least the following beneficial effects:

[0015] This invention employs a precision injection pump to inject VOCs solution, allowing for precise control of the micro-injection needle's advance speed. Furthermore, the capillary injection system utilizes micro-pores in the capillary column for liquid inlet, ensuring continuous and stable liquid intake. This effectively solves the problems of unstable vaporization, pulsation, and intermittent liquid vaporization, guaranteeing a stable VOCs solution source. The flow rate and pressure of the dilution gas from the dilution gas source are controlled through a pressure reducing valve, a pressure regulating valve, a needle valve, and a mass flow meter, ensuring a stable dilution gas source. VOCs solution vaporization occurs within a quartz-lined tube filled with glass wool, resulting in uniform vaporization and ensuring a stable vaporization process. Therefore, this invention addresses the shortcomings of existing dynamic generator methods—uniform vaporization, unstable vaporization, and pulsation / intermittent liquid vaporization—from three aspects: liquid source, gas source, and vaporization process. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a VOCs gas generator with stable concentration.

[0017] Figure 2 This is a schematic diagram of the gasification component structure.

[0018] Reference numerals: 1. Precision injection pump; 2. Micro-injection needle; 3. Capillary injection tubing; 4. Contaminant liquid bottle; 41. Three-way inlet valve; 5. Housing; 51. Quartz liner; 52. Heater; 53. Quartz capillary column; 54. Vaporization channel; 6. Diverter; 7. Mixer; 8. Pressure regulator; 9. Pressure reducing valve; 10. Needle valve; 11. Back pressure valve; 12. Mass flow meter; 13. Dilution gas source; 14. Adsorbent tube; 15. VOCs sensor. Detailed Implementation

[0019] The following specific examples illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. This utility model can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this utility model. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. It should also be understood that the terminology used in the embodiments of this utility model is for describing specific implementation schemes and not for limiting the scope of protection of this utility model. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0020] It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings of this specification are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the scope of implementation of this utility model. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of this utility model, should still fall within the scope of the technical content disclosed in this utility model. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity of description and are not intended to limit the scope of implementation of this utility model. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of implementation of this utility model.

[0021] Please refer to Figure 1 , 2 This utility model discloses a VOCs gas generator with stable concentration, which includes: a sample injection component, a gasification component, a gas source component, a mixer 7, and a pressure control component.

[0022] The injection assembly includes a precision injection pump 1, a micro-injection needle 2, and a capillary injection line 3. One end of the capillary injection line 3 is connected to the micro-injection needle 2, and the other end is connected to the vaporization assembly. The precision injection pump 1 is connected to the micro-injection needle 2 and is used to drive the micro-injection needle 2 to inject the VOCs solution contained in the micro-injection needle 2 into the injection line.

[0023] Specifically, the precision injection pump 1 has a micro-injection needle 2 and a capillary injection line 3. One end of the micro-injection needle 2 is located inside the precision injection pump 1, and the other end is connected to the capillary injection line 3. The precision injection pump 1 drives the micro-injection needle 2 to pump out the VOCs solution, which is then injected into the quartz liner tube 51 through the capillary injection line 3. The precision injection pump 1 can precisely control the advancement speed of the injection needle, ensuring that the VOCs solution can be accurately, uniformly, and continuously output.

[0024] In a preferred embodiment of this invention, the minimum linear velocity of the micro-injection needle 2 is 3 μm / min, and the control error is ≤ ±0.4% when >30% of the full stroke. Each microstep distance is 0.05 μm, and each microstep injection volume is 0.01 nL (using a 10 μL micro-injection needle 2). A Luer connector is provided at the end of the micro-injection needle 2 connected to the capillary injection line 3. The micro-injection needle 2 can be airtightly connected to the capillary injection line 3 via the Luer connector. The capillary injection line 3 uses a quartz capillary column 53 or a stainless steel capillary column with micropores for liquid inlet, thereby ensuring a continuous and stable liquid inlet process.

[0025] In other embodiments of this invention, the micro-injection needle 2 may be of other specifications, such as 25μL or 100μL.

[0026] By using a precision injection pump 1 to inject VOCs solution, the advancement speed of the micro-injection needle 2 can be precisely controlled, and the capillary injection line 3 uses capillary column micropores for liquid inlet, which can ensure the continuous and stable liquid inlet process and effectively solve the problems of unstable vaporization process, pulsation and intermittent liquid vaporization.

[0027] In a preferred embodiment of this invention, the sample injection assembly further includes a contaminant solution bottle 4 and a three-way inlet valve 41. The contaminant solution bottle 4 is used to hold a VOCs solution. The two inlets of the three-way inlet valve 41 are respectively connected to the micro-injection needle 2 and the contaminant solution bottle 4, and the outlet is connected to the capillary injection line 3. The three-way inlet valve 41 is used to control the connection between the micro-injection needle 2 and the capillary injection line 3 to inject the VOCs solution into the quartz liner tube 51, or to control the connection between the micro-injection needle 2 and the contaminant solution bottle 4 so that the micro-injection needle 2 can draw the VOCs solution from the contaminant solution bottle 4.

[0028] When the micro-injection needle 2 injects VOCs solution into the quartz liner tube 51, the micro-injection needle 2 is connected to the capillary injection line 3. When the VOCs solution in the micro-injection needle 2 is used up, the three-way inlet valve 41 is switched to connect the micro-injection needle 2 to the contaminant liquid bottle 4. Driven by the precision injection pump 1, the micro-injection needle 2 draws VOCs solution from the contaminant liquid bottle 4. After drawing, the three-way inlet valve 41 is switched back to connect the micro-injection needle 2 to the capillary injection line 3, allowing VOCs solution to continue being injected into the quartz liner tube 51. By controlling the precision injection pump 1, the micro-injection needle 2, and the three-way inlet valve through a computer program, the micro-injection needle 2 automatically draws VOCs solution from the contaminant liquid bottle 4 to replenish its VOCs solution when it is insufficient, thereby significantly extending the continuous working time of the stable concentration VOCs gas generator of this invention.

[0029] Furthermore, the contaminant liquid bottle 4 can store one or more VOCs solutions. The micro-injection needle 2 can draw different types of VOCs solutions to meet the requirements of different VOCs gas generation processes without having to replace the micro-injection needle 2, which helps to improve the working efficiency of the VOCs gas generator with stable concentration of this invention.

[0030] Please continue to refer to Figure 1 The gas source assembly includes a dilution gas source 13. The dilution gas source 13 is connected to a quartz liner 51. The dilution gas source 13 can be a gas cylinder or other suitable device for storing dilution gas. The dilution gas can be nitrogen or other suitable gases. In a preferred embodiment of this invention, the dilution gas source 13 is a steel cylinder, and the dilution gas is nitrogen. Furthermore, the pressure and flow rate of the gas released from the steel cylinder are controlled by a pressure reducing valve 9 at the cylinder's outlet.

[0031] The vaporization assembly includes a housing 5, a quartz liner 51, a heater 52, a quartz capillary column 53, and a vaporization channel 54. The vaporization channel 54 is located inside the housing 5. The quartz liner 51 is located inside the vaporization channel. The quartz capillary column 53 is located outside the housing 5. A flow divider 6 is provided on the side wall of the vaporization channel 54. The quartz liner 51 is connected to the capillary injection line 3, the quartz capillary column 53, and the flow divider 6, so that the VOCs solution, after vaporization within the quartz liner 51, flows to the quartz capillary column 53 and the flow divider 6, respectively. The quartz liner 51 is filled with glass wool.

[0032] For details, please refer to Figure 1 , 2The outer shell 5 of the vaporization component is rectangular and made of aluminum alloy or 316L stainless steel. The vaporization channel 54 is cylindrical and made of stainless steel. Its function is to ensure the sealing of the quartz liner 51 and facilitate the exhaust of gas inside the quartz liner 51 or the introduction of external gas or liquid into the quartz liner 51. The quartz liner 51 has a hollow structure, forming a chamber for the vaporization of the VOCs solution. A heater 52 mounting hole is provided on the side wall of the outer shell 5, through which the heater 52 extends into the outer shell 5. The heater 52 can be cylindrical (e.g., ...). Figure 2 As shown, it can also be spiral-shaped, coiled around the inner wall of the outer shell 5, to heat the outer shell 5, and then heat the VOCs solution inside the quartz liner 51, ensuring the speed of VOCs solution vaporization.

[0033] After the liquid inlet assembly injects the VOCs solution into the quartz liner tube 51, the VOCs solution is heated and vaporized. It is then diluted for the first time after mixing with the dilution gas from the gas source assembly. The VOCs gas after the first dilution is divided into two paths. The first path is discharged from the splitter port 6, and the second path flows into the quartz capillary column 53 and then into the mixer 7.

[0034] The quartz liner 51 has a limited inner surface area. To increase the vaporization surface area of ​​the heated VOCs solution, glass wool is filled inside the quartz liner 51. The glass wool increases the vaporization surface area of ​​the VOCs solution, promoting its vaporization. Under stable pressure, with a continuous and stable inflow of liquid into the quartz liner 51, VOCs gas will be output stably and quantitatively, effectively reducing uneven vaporization.

[0035] The mixer 7 has a first inlet, a second inlet, and a first outlet. The first inlet is connected to the dilution gas source 13. The second inlet is connected to the quartz capillary column 53. The first outlet is used to discharge the gas inside the mixer 7. The VOCs gas, which has been diluted for the first time in the vaporization assembly, enters the mixer 7 through the quartz capillary column 53 and the second inlet. At the same time, the dilution gas released from the dilution gas source 13 enters the mixer 7 through the first inlet. The VOCs gas is diluted a second time in the mixer 7, and its concentration is further reduced. The mixer 7 can adopt various components with two inlets and one outlet. Preferably, in this embodiment, the mixer 7 adopts a three-way valve.

[0036] A certain concentration of VOCs gas can be generated through the gasification component and dilution with dilution gas. However, the limited volume of the gasification component restricts the minimum concentration of VOCs gas that can be obtained through it. It is impossible to obtain VOCs gas with a lower concentration through the gasification component alone. However, by setting up the mixer 7, the VOCs gas generator of this invention can stably obtain VOCs gas with a lower concentration.

[0037] The pressure control assembly includes a pressure regulating valve 8, a needle valve 10, a back pressure valve 11, and a mass flow meter 12. The pressure regulating valve 8 is located between the dilution gas source 13 and the housing 5. The needle valve 10 is located downstream of the diversion port 6. The pressure regulating valve 8 regulates the flow rate of the dilution gas released from the dilution gas source 13 into the quartz liner 51 and stabilizes the pressure of the gas flowing into the quartz capillary column 53. The needle valve 10 regulates the flow rate of the gas flowing out of the diversion port 6, thereby regulating the flow rate of the gas flowing from the quartz liner 51 into the quartz capillary column 53.

[0038] Specifically, the amount of VOCs gas vaporized per unit time within the quartz liner 51 is constant. Therefore, the gas flow rate into the quartz capillary column 53 mainly depends on the flow rate of the dilution gas flowing into the quartz liner 51 and the flow rate of the gas flowing to the diversion port 6. Thus, by controlling the flow rate of the dilution gas flowing into the quartz liner 51 through the pressure regulating valve 8 and controlling the flow rate of the gas flowing to the diversion port 6 through the needle valve 10, the gas flow rate within the quartz capillary column 53 is controlled.

[0039] Because the inner diameter of the quartz capillary column 53 is extremely small, the flow resistance within the quartz capillary column 53 can be controlled by adjusting its length. Furthermore, by adjusting the length of the quartz capillary column 53, in conjunction with the pressure regulating valve 8 and the needle valve 10, the gas flow rate within the quartz capillary column 53 can be stably controlled.

[0040] One reason why a pressure regulating valve 8 is installed between the dilution gas source 13 and the outer casing 5 instead of a mass flow meter is that the mass flow meter controls the flow rate based on the temperature changes at its inlet and outlet. Since different gases have different specific heat capacities, the mass flow meter needs to be calibrated with different correction coefficients when controlling the flow of different gases, which is inconvenient, especially when the gas passing through it contains multiple components; calibration becomes even more difficult, and measurement errors may occur.

[0041] Another reason is that the pressure regulating valve 8, together with the needle valve 10, controls the gas flow rate inside the quartz capillary column 53. The needle valve 10 is a flow-regulating valve; in a mechanical flow path control system, the working mechanism of a flow-regulating valve requires stable pressure before its inlet to ensure constant outlet flow control. Therefore, the pressure regulating valve 8 helps improve the stability of the flow control by the needle valve 10.

[0042] More specifically, the pressure regulating valve 8 is located on the pipeline connecting the dilution gas source 13 and the quartz liner 51. The pressure regulating valve 8 can adjust the flow rate of the dilution gas by controlling the opening degree of the valve body's opening and closing element, and keep the pressure downstream of the valve stable. In a preferred embodiment of this utility model, the pressure regulating valve 8 is made of stainless steel, with a maximum output pressure of 550 kPa and an output flow rate of 0-1000 mL / min.

[0043] The needle valve 10 ensures that even with changes in gas flow rate or pressure within the quartz liner 51, the gas, initially diluted within the quartz liner 51, can still stably flow through the quartz capillary column 53 into the mixer 7. In a preferred embodiment of this invention, the needle valve 1010 is made of stainless steel, with a maximum input pressure of 750 kPa and an output flow rate of 0-1000 mL / min.

[0044] Back pressure valve 11 is connected to mixer 7 and is used to stabilize the gas pressure discharged from quartz liner 51 and eliminate flow and pressure fluctuations at the outlet of mixer 7. The back pressure valve 11 facilitates the subsequent collection and utilization of VOCs generated within the device. Back pressure valve 11 can be made of stainless steel. Back pressure valve 11 has two switchable outlets; VOCs gas with the required concentration is discharged from one outlet for collection and utilization, while VOCs gas with the required concentration is discharged from the other outlet.

[0045] A mass flow meter 12 is positioned between the dilution gas source 13 and the mixer 7. Its function is to precisely control the flow rate of the dilution gas flowing to the mixer 7 according to the gas distribution requirements of VOCs. In a preferred embodiment of this invention, the flow rate range of the mass flow meter 12 is 0-10 L / min.

[0046] The pressure control component enables the dilution gas source 13 to stably dilute VOCs gas to the required concentration, and also enables the stable output of VOCs gas generated in the device, facilitating subsequent collection and utilization.

[0047] When VOCs begin to form but are not yet stable, their concentration does not meet the requirements and cannot be collected and utilized. However, they also cannot be directly released into the atmosphere, otherwise they will harm human health and the environment.

[0048] Therefore, the VOCs gas generating device with stable concentration of this invention also includes a waste gas treatment component. The waste gas treatment component includes an adsorbent tube 14 and a VOCs sensor 15. The front end of the adsorbent tube 14 is connected to the back pressure valve 11 and the needle valve 10, and is used to adsorb VOCs in the waste gas during the VOCs gas generation process.

[0049] The waste gas generated during the VOCs process includes: VOCs gas that is first diluted in the quartz liner 51 and discharged from the diversion port 6 and needle valve 10 in order to adjust the gas flow rate in the quartz capillary column 53; and VOCs gas that is second diluted in the mixer 7 but whose concentration does not meet the requirements.

[0050] The adsorbent tube 14 uses one or more adsorbents, including activated carbon, silica gel, and molecular sieves. A VOCs sensor 15 is located at the end of the adsorbent tube 14 to monitor its VOCs adsorption efficiency. When the adsorbent tube 14 detects a decrease in its VOCs adsorption efficiency, it indicates that the adsorbent in the tube has reached saturation, thus reminding staff to replace the adsorbent promptly.

[0051] More specifically, in the VOCs gas generator with stable concentration of this invention, all components in contact with VOCs undergo silanization treatment, such as the valve bodies of the mixer 7, pressure regulating valve 8, back pressure valve 11, and needle valve 10. Silanization treatment can form a mesh-like silane film on the surface of the components, enhancing their wear resistance and corrosion resistance.

[0052] The principle of this invention for a stable VOCs gas generator is as follows: A precision injection pump 1 pushes a micro-injection needle 2 to inject the VOCs solution into a quartz liner tube 51 at a certain speed. The liquid entering the quartz liner tube 51 rapidly vaporizes and mixes with the dilution gas output from the dilution gas source 13, completing the first dilution. Afterward, the gas in the quartz liner tube 51 is divided into two paths: one is discharged, and the other enters a split pipe, simultaneously entering the mixer 7 with the dilution gas output from the dilution gas source 13, completing the second dilution. The gas in the mixer 7 is output stably at a constant pressure and flow rate through a back pressure valve 11. Excess gas and the gas directly diverted from the quartz liner tube 51 enter the adsorbent tube 14 for adsorption and recovery, while a VOCs sensor 15 monitors whether the adsorbent has reached adsorption saturation.

[0053] It should be noted that when a high concentration of VOCs gas is required, and the desired concentration can be achieved after the first dilution in the quartz liner 51, a second dilution using the mixer 7 is unnecessary. The gas, after the first dilution in the quartz liner 51, can be directly taken out from the needle valve 10 for use. Therefore, the VOCs gas generator with stable concentration of this invention can switch between high and low concentrations according to the required VOCs gas concentration, thereby increasing the range of VOCs gas concentrations that can be generated and thus helping to enrich the application scenarios of this device.

[0054] The following uses gaseous toluene, a VOCs gas, as an example to illustrate the implementation principle of this invention in detail:

[0055] The required concentration of gaseous toluene is calculated based on the volume of liquid toluene used. When using a micro-needle 2 with a specific inner diameter, the delivery rate of liquid toluene is controlled by adjusting the propulsion speed of the precision injection pump 1. In practical applications, the delivery rate is related to the inner diameter of the micro-needle 2 and the propulsion speed of the precision injection pump 1. The pump delivery rate is calculated based on the desired concentration of the target substance. By changing to different specifications of injection needles and adjusting the propulsion speed of the injection pump, the desired concentration of the target substance can be achieved. For example, if the desired toluene concentration is 10 nmol·mol⁻¹... -1 A 25 μL micro-injection needle 2 with an inner diameter of 0.73 mm was used. When using this micro-injection needle 2, the delivery rate of the precision injection pump 1 was 0.047 μL / min, and the injection speed was 112.8 μm / min.

[0056] The heating temperature of heater 52 is set. After the temperature is set, heater 52 begins to heat the outer shell 5 of the vaporization device, entering the preheating process. Heater 52 has a temperature control module, which controls the start and stop of heater 52 based on the temperature feedback from the temperature sensor, maintaining the set heating temperature. The heating temperature must ensure that the inner wall temperature of the quartz liner tube 51 in the vaporization chamber is higher than the boiling point of toluene. If it is used to generate other single VOCs or complex VOCs such as benzene and xylene, the temperature setting is generally selected to be 30-50°C higher than the highest boiling point of the target component, which can ensure the vaporization of the target component.

[0057] After preheating, the precision injection pump 1 is started, and the micro-injection needle 2 is driven by the precision injection pump 1 at a speed of 112.8 μm / min to inject VOCs liquid into the quartz liner tube 51. The liquid entering the quartz liner tube 51 is rapidly vaporized and mixed with the dilution gas output at a flow rate of 1000 mL / min through the pressure reducing valve 9 and the pressure regulating valve 8 to complete the first dilution. Then it is divided into two streams. One stream is discharged through the needle valve 10 at a flow rate of 999 mL / min and enters the adsorbent tube 14 for adsorption and recovery. The other stream is split into the quartz capillary column 53 at a flow rate of 1 mL / min and enters the mixer 7 at a flow rate of 1000 mL / min controlled by the mass flow meter 12 to complete the second dilution. After that, the gas is output stably at a constant pressure and flow rate through the back pressure valve 11. The excess gas enters the adsorbent tube 14 for adsorption and recovery.

[0058] The concentration of toluene generated during the process can be controlled by adjusting the first and second dilution flow rates. The concentration of gaseous toluene generated is calculated using the following formula:

[0059]

[0060] In the formula: C i The calculated concentration of the target compound toluene is given in nmol·mol⁻¹. -1D is the inner diameter of the injection needle, in mm; V is the injection speed, in mm·min. -1 ;ρ i The liquid density of the target compound is given in mg·μL. -1 Q1 First dilution flow rate, mL·min -1 Q2 is the output flow rate after the first dilution, in mL·min. -1 Q3 represents the second dilution gas flow rate, in mL·min. -1 M i The molar mass of the target compound toluene is given in g·mol⁻¹. -1 22.4 is the molar volume of an ideal gas, in L·mol⁻¹. -1 .

[0061] It should be noted that the concentration of gaseous components can be controlled by adjusting the concentration of the liquid component in the pollutant bottle 4, thereby controlling the concentration of the gaseous target component. This can also be achieved by adjusting the output flow rates of the pressure regulating valve 8, the needle valve 10, or the mass flow meter 12.

[0062] The VOCs gas generator with stable concentration of this invention is suitable for generating toluene and other volatile organic pollutants such as benzene, ethylbenzene, xylene, n-hexane, ethyl acetate, etc. When it is used to generate other volatile organic compounds besides toluene, the above implementation principle can be referred to, and the adjustment can be made according to the properties of the organic compounds to be generated.

[0063] Compared with the prior art, the VOCs gas generator with stable concentration of this invention has the following advantages:

[0064] This invention employs a precision injection pump 1 to inject VOCs solution, allowing for precise control of the advance speed of the micro-injection needle 2. Furthermore, the capillary injection line 3 utilizes capillary micropores for liquid inlet, ensuring continuous and stable liquid inlet and effectively resolving issues of instability, pulsation, and intermittent liquid vaporization during the vaporization process, thus guaranteeing a stable VOCs solution source. The flow rate and pressure of the dilution gas from the dilution gas source 13 are controlled by a pressure reducing valve 9, a pressure regulating valve 8, a needle valve 10, and a mass flow meter 12, ensuring a stable dilution gas source. VOCs solution vaporization occurs within a quartz liner 51 filled with glass wool, resulting in uniform vaporization and ensuring a stable vaporization process. Therefore, this invention addresses the shortcomings of existing dynamic generator methods—uniform vaporization, unstable vaporization, and pulsation / intermittent liquid vaporization—from three aspects: liquid source, gas source, and vaporization process.

[0065] In addition, this utility model also discloses an evaluation method for a VOCs gas generating device with stable concentration. This method is used to evaluate the aforementioned VOCs gas generating device with stable concentration, and includes:

[0066] S1. Verification of gas concentration:

[0067] Obtain the standard gas. The standard gas is a VOCs gas of known concentration. The VOCs gas is prepared according to the concentration of the standard gas using a stable VOCs gas generator, and the test gas is collected.

[0068] The concentrations of the standard gas and the test gas were measured using a pre-concentration / gas chromatography-mass spectrometry (GC-MS) instrument, with each measurement repeated n times (n≥6). The average value of the measured values ​​was calculated, and the actual concentration of the gas generated by the stable VOCs gas generator was calculated using the following formula:

[0069]

[0070] In the formula: ρ A The actual concentration of the test gas is nmol·mol⁻¹. -1 . ρ S The nominal concentration of the standard gas is nmol·mol⁻¹. -1 . The average value of the test gas measurements is nmol·mol⁻¹. -1 . The average value of the concentration measurements of the standard gas is given in nmol·mol⁻¹. -1 .

[0071] Specifically, the accuracy of the concentration of the standard gas can be ensured by purchasing national primary or secondary gas standard materials with known concentrations. The prepared VOCs gas can be collected using gas sampling bags or SUMMA canisters.

[0072] S2. Stability test of VOCs gas generator with stable concentration:

[0073] After the VOCs gas generator with stable concentration has been operating stably, it is set to generate a specified concentration of VOCs gas. Data is collected every time interval t (t≥0.5h), for a total of n groups (n≥2). The collected VOCs gas is measured using a pre-concentration / gas chromatography-mass spectrometry (GC-MS) instrument. Each group is measured m times (m≥2), and the average of the m measurements is taken as the measured value for that group. The stability of the VOCs gas generator with stable concentration is calculated using the following formula:

[0074]

[0075] In the formula: S represents the stability of the gas generated by the VOCs gas generator with stable concentration, in percentage (%). The maximum value of gas concentration among groups, nmol·mol -1 ; The minimum value of gas concentration among groups, nmol·mol -1; The gas concentration is the average value among groups, nmol·mol⁻¹ -1 C is the range coefficient;

[0076] S3. Uncertainty assessment:

[0077] Based on the formula in step S1 and according to the uncertainty propagation law, the formula for calculating the combined standard uncertainty is obtained:

[0078] u r 2 =c1 2 u1 2 +c2 2 u2 2 +c3 2 u3 2 =u1 2 +u2 2 +u3 2 ;

[0079] This formula is based on JJF1059.1-2012 (Evaluation and Expression of Measurement Uncertainty), where u1 is the uncertainty of the standard gas; u2 is the uncertainty of the pre-concentration / gas chromatography-mass spectrometry instrument; u3 is the relative standard uncertainty introduced by the stable VOCs gas generator; and c1, c2, and c3 are sensitivity coefficients.

[0080] Wherein, u1 is calculated using the following formula:

[0081]

[0082] In the formula, U s denoted as , where is the expanded uncertainty of the standard gas; k is the coverage factor.

[0083] u2 is calculated using the following formula:

[0084]

[0085] In the formula, y si Let n be the value of the standard gas measured in the i-th time, and n mol·mol⁻¹ -1 ; The average of n measurements, nmol·mol -1 n represents the number of measurements; m represents the number of repeated measurements.

[0086] u3 is calculated using the following formula:

[0087]

[0088] In the formula, S represents the stability of the gas generated by the VOCs gas generator with stable concentration; m represents the number of repeated measurements.

[0089] u r The following formula is used to calculate:

[0090] U r =k×u r ;

[0091] In the formula, u r denoted as the combined standard uncertainty; k is the confidence factor.

[0092] In the evaluation method of the VOCs gas generator with stable concentration of this utility model, the accuracy of the gas concentration generated by the device is evaluated in step S1, the stability of the gas generated by the device is evaluated in step S2, and the uncertainty of the gas generated by the device is evaluated in step S3, thereby achieving a comprehensive evaluation of the performance of the VOCs gas generator with stable concentration.

[0093] It should be noted that steps S1 and S2 are independent of each other and do not interfere with each other. Therefore, the order in which steps S1 and S2 are performed can be interchanged.

[0094] The following evaluation, using a VOCs gas generator with stable concentrations producing toluene as an example, will assess the performance of such a generator:

[0095] First, perform step S1, purchasing 5 μmol·mol⁻¹ -1 Toluene gas standard reference material GBW(E)081675 (U = 2.6%, k = 2) in nitrogen was diluted using a dynamic dilution apparatus to a concentration of 5 μmol·mol⁻¹. -1 The gaseous standard was diluted to 10 nmol·mol⁻¹ -1 (The gas dynamic dilution device is compatible with accurate dilution from 20 to 1000 times). Toluene gas of the corresponding concentration is generated using the stable VOCs gas generator of this invention, and collected using a gas sampling bag / souma canister. The gaseous standard and the gas generated by the device are measured using a pre-concentration / gas chromatography-mass spectrometry (GC-MS) instrument, with each measurement repeated 6 times, and the average value is taken. and The results are shown in Tables 1 and 2.

[0096] Table 1. Repeatability test results of toluene gas standard material

[0097]

[0098] Table 2. Repeatability test results of toluene gas generated by the device.

[0099]

[0100] Next, calculate the actual concentration value ρ of the gas generated by the VOCs gas generator with stable concentration. A :

[0101]

[0102] The relative error between the verified value and the design value of the gas concentration generated by the stable VOCs gas generator was calculated using the following formula. The verification results of the pre-concentration / gas chromatography-mass spectrometry are shown in Table 3.

[0103]

[0104] In the formula: δ represents the relative error of the gas generated by the device; %; ρ A The verification value for the gas generated by the device is nmol·mol⁻¹. -1 ;ρ D The design concentration of the gas generated by the device is nmol·mol⁻¹. -1 .

[0105] Table 3. Verification results of gas concentration generated by the pre-concentration / gas chromatography-mass spectrometry instrument (nmol·mol⁻¹) -1

[0106]

[0107] Next, proceed to step S2. After the VOCs gas generator with stable concentration is operating stably, set its generation concentration to 10 nmol·mol⁻¹. -1 Toluene gas was collected every 1 hour using a gas sampling bag / souma canister, for a total of 6 groups. Each group was measured 3 times. Under the selected instrument operating conditions, the collected gas was measured using a pre-concentration / gas chromatography-mass spectrometry system. The average of the 3 measurements was taken as the measured value of the group. The stability of the VOCs gas generator with stable concentration was calculated according to the following formula. The results are shown in Table 4.

[0108]

[0109] In the formula: C is 1.69.

[0110] Table 4 Results of device stability test

[0111]

[0112] Finally, implement step S3:

[0113] First, calculate the relative standard uncertainty introduced by the diluted gaseous standard: The toluene gaseous standard used in the verification is diluted by a dynamic dilution apparatus, and the concentration of the standard gas is taken as the concentration. The relative standard uncertainty u1 introduced by the diluted gaseous standard is composed of the standard uncertainty component u introduced by the certified gaseous standard. rel (C s The standard uncertainty component u introduced by the gas dynamic dilution device rel (F) is composed of.

[0114] Calculate the diluted concentration using the following formula.

[0115]

[0116] In the formula: C si The concentration of the gaseous standard substance after dilution is nmol·mol⁻¹. -1 C s The concentration of the gaseous standard substance is nmol·mol⁻¹. -1 F1 is the flow rate of the gaseous standard substance in the dynamic gas dilution device, mL / min; F2 is the zero air flow rate in the dynamic gas dilution device, mL / min.

[0117] C s F1 and F2 are independent of each other, therefore the formula for the combined relative standard uncertainty can be obtained from the uncertainty propagation law as follows:

[0118]

[0119] In the formula: u c,rel (C si ) represents the relative standard uncertainty, %, of the concentration value of the gaseous standard substance after dilution; u rel (C s ) represents the relative standard uncertainty of the gaseous standard reference, in %; u rel (F1) represents the relative standard uncertainty, %, of the flow rate of the gaseous standard substance in the dynamic gas dilution device; rel (F2) represents the relative standard uncertainty of zero air flow in the dynamic gas dilution device, %.

[0120] Since the expanded relative uncertainty of the gaseous standard is 2.6%, and k = 2, the relative standard uncertainty is 1.3%. The relative standard uncertainty of the calibrated flow rate of the gas flow controller in the dynamic gas dilution device is 1%. Therefore, the combined standard relative uncertainty can be obtained as follows:

[0121] Next, calculate the relative standard uncertainty u2 introduced by repeated measurements of pre-concentration / gas chromatography-mass spectrometry, which is obtained by the following formula:

[0122]

[0123] In the formula: y si Let n be the value of the i-th determination of the gaseous standard substance, in nmol·mol⁻¹ -1 ; The average of n measurements, nmol·mol -1 n represents the number of measurements; m represents the number of repeated measurements.

[0124] The relative standard uncertainty introduced by repeated measurements in the pre-concentration / gas chromatography-mass spectrometry was calculated to be:

[0125] u2 = RSD = 0.36%.

[0126] Then, the relative standard uncertainty u introduced by the stability of the VOCs gas generator with stable concentration is calculated. 3， It is calculated by the following formula:

[0127]

[0128] In the formula: S represents the stability of the VOCs gas generator with stable concentration; m represents the number of repeated measurements.

[0129] The relative standard uncertainty introduced by the stability of a VOCs gas generator with stable concentration was calculated.

[0130] Finally, the relative expanded uncertainty U of the concentration generated by the stable VOCs gas generator was calculated. r It can be calculated using the following formula:

[0131] U r =k×u r ;

[0132] In the formula: u r denoted as the combined standard uncertainty; k is the confidence factor.

[0133] Each standard uncertainty component is independent and uncorrelated. The relative standard uncertainty and relative expanded uncertainty are synthesized (with coverage factor k = 2 and confidence level P = 95%), and the results are shown in Table 5.

[0134] Table 5 Uncertainty components and uncertainty assessment results

[0135]

[0136] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A VOCs gas generator with stable concentration, characterized in that: It includes a sample introduction assembly, a vaporization assembly, a gas source assembly, a mixer (7), and a pressure control assembly; among which, The injection assembly includes a precision injection pump (1), a micro-injection needle (2), and a capillary injection line (3); one end of the capillary injection line (3) is connected to the micro-injection needle (2), and the other end is connected to the vaporization assembly; the precision injection pump (1) is connected to the micro-injection needle (2) and is used to drive the micro-injection needle (2) to inject the VOCs solution contained in the micro-injection needle (2) into the injection line; The vaporization assembly includes a shell (5), a quartz liner (51), a heater (52), a quartz capillary column (53), and a vaporization channel (54); the vaporization channel (54) is disposed inside the shell (5); the quartz liner (51) is disposed inside the vaporization channel; the quartz capillary column (53) is located outside the shell (5); a diversion port (6) is provided on the side wall of the vaporization channel (54); the quartz liner (51) is connected to the capillary injection line (3), the quartz capillary column (53), and the diversion port (6) so that the VOCs solution is vaporized in the quartz liner (51) and flows to the quartz capillary column (53) and the diversion port (6) respectively; the quartz liner (51) is filled with glass wool. The gas source assembly includes a dilution gas source (13); the dilution gas source (13) is connected to the quartz liner (51); The mixer (7) has a first inlet, a second inlet, and a first outlet; the first inlet is connected to the dilution gas source (13); the second inlet is connected to the quartz capillary column (53); and the first outlet is used to discharge the gas inside the mixer (7). The pressure control assembly includes a pressure regulating valve (8) and a needle valve (10); the pressure regulating valve (8) is disposed between the dilution gas source (13) and the housing (5); the needle valve (10) is disposed downstream of the diversion port (6); the pressure regulating valve (8) is used to regulate the flow rate of the dilution gas released from the dilution gas source (13) into the quartz liner (51) and stabilize the pressure of the gas flowing into the quartz capillary column (53); the needle valve (10) is used to regulate the flow rate of the gas flowing out of the diversion port (6), thereby regulating the flow rate of the gas in the quartz liner (51) into the quartz capillary column (53).

2. The VOCs gas generator with stable concentration according to claim 1, characterized in that: The pressure control assembly also includes a back pressure valve (11). The back pressure valve (11) is connected to the mixer (7) to stabilize the gas pressure discharged from the mixer (7) and eliminate fluctuations in flow and pressure at the outlet of the mixer (7).

3. The VOCs gas generator with stable concentration according to claim 2, characterized in that: The gas source assembly also includes a pressure reducing valve (9). The pressure reducing valve (9) is connected to the dilution gas source (13) and is used to adjust the output pressure of the dilution gas source (13).

4. The VOCs gas generator with stable concentration according to claim 3, characterized in that: The pressure control assembly also includes a mass flow meter (12); The mass flow meter (12) is located between the dilution gas source (13) and the mixer (7) to control the flow rate of the dilution gas input from the dilution gas source (13) into the mixer (7).

5. The VOCs gas generator with stable concentration according to claim 1, characterized in that, The sample injection assembly also includes a contaminant liquid bottle (4) and a three-way inlet valve (41). The pollutant liquid bottle (4) is used to hold VOCs solution; the two inlets of the three-way inlet valve (41) are connected to the micro-injection needle (2) and the pollutant liquid bottle (4) respectively, and the outlet is connected to the capillary injection tube (3); The three-way inlet valve (41) is used to control the micro-injection needle (2) to connect with the capillary injection line (3) to inject the VOCs solution into the quartz liner (51), or to control the micro-injection needle (2) to connect with the contaminant bottle (4) so ​​that the micro-injection needle (2) can draw the VOCs solution from the contaminant bottle (4).

6. The VOCs gas generator with stable concentration according to claim 1, characterized in that, It also includes exhaust gas treatment components; The waste gas treatment component includes an adsorbent tube (14). The front end of the adsorbent tube (14) is connected to the outlet of the needle valve (10) and the first outlet for treating unused VOCs gas.

7. The VOCs gas generator with stable concentration according to claim 6, characterized in that, The exhaust gas treatment assembly also includes a VOCs sensor (15). The VOCs sensor (15) is located at the end of the adsorbent tube (14) and is used to monitor the VOCs content in the gas discharged from the end of the adsorbent tube (14).

8. The VOCs gas generator with stable concentration according to claim 1, characterized in that, In the VOCs gas generator with stable concentration, all components in contact with VOCs have undergone silanization treatment.

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