System for purifying and compressing air to prepare standard gas

Abstract

The system comprises an oil-free air compressor (4), a refrigerator (7), a heat exchanger (8), a water removal molecular sieve (10), an activated carbon unit (13), a deep water removal unit (22), a gas cylinder assembly (24), target component pure gas sources (26 and 27), a standard gas cylinder (33) and a weighing device (34), the oilless air compressor and the refrigerating machine are respectively communicated with the heat exchanger; the dewatering molecular sieve is communicated with the heat exchanger through a first switching valve (9) and is communicated with the activated carbon unit through second switching valves (11 and 12); the activated carbon unit is communicated with the deep water removal unit through third switching valves (14 and 15); the deep water removal unit is communicated with the gas cylinder assembly through a fourth switching valve (23); the gas cylinder assembly is communicated with the standard gas cylinder through a first diaphragm stop valve (30), and a target component pure gas source is communicated with the standard gas cylinder through second diaphragm stop valves (28, 29); and the weighing device is used for weighing the standard gas cylinder.

Description

Technical Field

[0001] The invention belongs to the technical field of atmospheric standard substance analysis, and in particular relates to a system for purifying and compressing air to prepare standard gas. Background Art

[0002] Atmospheric environmental monitoring is usually affected by background gas composition. Clean atmosphere includes constant gas components such as nitrogen (78%), oxygen (20.8%), argon (0.19%), water vapor (1.0%), etc., as well as trace components such as about 400 μmol / mol carbon dioxide, 1.8 μmol / mol methane, 0.4 μmol / mol nitrous oxide, 0.5 μmol / mol hydrogen, 1.14 μmol / mol krypton and 0.086 μmol / mol xenon. The atmosphere affected by natural or human activities also contains nearly 300 species, with concentrations ranging from 10 -12 mol / mol-10 -6 Volatile organic components of mol / mol, these substances jointly participate in the earth's atmospheric chemical cycle, and the trend of their trace concentration changes has important research value for the assessment of climate change and the impact of human activities.

[0003] Various types of gas analyzers are used to monitor the above-mentioned atmospheric substances, usually including three categories: spectroscopy, chromatography and mass spectrometry. These instruments perform precise analysis and testing of target components and are usually interfered with by other substances in the atmospheric chemical components. For example, a slight change of 0.1% in the nitrogen, oxygen and argon content will interfere with the spectrometer's analysis of carbon dioxide, methane and nitrous oxide concentrations, causing the accuracy of the measurement data to deviate from the target; and volatile organic compounds with similar chemical properties will interfere with each other. The principles of the influence of these interference effects on measurements are not yet clear, and are collectively referred to as matrix effects. Traditional standard gas calibration usually uses a mixture of the target substance and nitrogen or nitrogen and oxygen, ignoring the interference of other components in the atmosphere. However, due to the complexity of the atmospheric matrix, it is difficult to completely simulate the real atmospheric matrix through artificial synthesis or pure gas mixing.

[0004] In addition, the existing technology obtains standard gas of specific concentration mainly by mixing pure substances one by one. Although it can simulate the concentration of specific target substances, it is often inefficient to add target gas components one by one for the background components of complex atmosphere. In addition, since the industrially purified raw materials used in the mixed preparation are affected by the isotope fractionation effect during the purification process, a large number of isotope ratios have a large deviation from the real atmosphere, which interferes with the analysis of the isotope ratio in the real sample, thereby causing the accurate value of the standard gas to be offset. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a pressing system, which uses a method of directly pressing the real air matrix atmosphere as the preparation raw material of the standard gas, and changes the concentration of the required standard gas by removing or adding specific target substances. This method is particularly suitable for preparing standard gas with real air as the matrix, and can solve the problem that traditional standard gases are difficult to simulate and prepare real atmosphere.

[0006] According to one aspect of the present invention, a system for purifying and compressing air to prepare standard gas is provided, characterized in that it comprises an oil-free air compressor (4), a refrigerator (7), a heat exchanger (8), a dehydration molecular sieve (10), an activated carbon unit (13), a deep dehydration unit (22), a gas cylinder assembly (24), a target component pure gas source (26, 27), a standard gas cylinder (33) and a weighing device (34);

[0007] The oil-free air compressor (4) and the refrigerator (7) are respectively connected to the heat exchanger (8) to cool the air compressed by the oil-free air compressor (4);

[0008] One end of the dehydration molecular sieve (10) is connected to the heat exchanger (8) via a first switching valve (9), and the other end is connected to one end of the activated carbon unit (13) via a second switching valve (11, 12);

[0009] The other end of the activated carbon unit (13) is connected to one end of the deep water removal unit (22) via a third switching valve (14, 15);

[0010] The other end of the deep water removal unit (22) is connected to the gas cylinder assembly (24) via a fourth switching valve (23);

[0011] The gas cylinder assembly (24) is connected to the calibration gas cylinder (33) via a first diaphragm stop valve (30), and the target component pure gas source (26, 27) is connected to the calibration gas cylinder (33) via a second diaphragm stop valve (28, 29); the weighing device (34) is used to weigh the calibration gas cylinder (33).

[0012] According to an embodiment of the present invention, the system for purifying and compressing air to prepare standard gas also includes a particulate filter (1), which is arranged at the front end of the oil-free air compressor (4) and is used to filter particulate matter in the air entering the oil-free air compressor (4).

[0013] According to an embodiment of the present invention, the system for purifying and compressing air to prepare standard gas also includes a carbon monoxide removal unit (16) and a carbon dioxide removal unit (19); one end of the carbon monoxide removal unit (16) is connected to the third switching valve (14, 15), and the other end is connected to one end of the carbon dioxide removal unit (19) through the fifth switching valve (17, 18); the other end of the carbon dioxide removal unit (19) is connected to the deep water removal unit (22) through the sixth switching valve (20, 21).

[0014] According to an embodiment of the present invention, a bypass is formed between the first switching valve (9) and the second switching valve (11, 12); a bypass is formed between the second switching valve (11, 12) and the third switching valve (14, 15); and a bypass is formed between the third switching valve (14, 15) and the fourth switching valve (23).

[0015] According to an embodiment of the present invention, a bypass is formed between the third switching valve (14, 15) and the fifth switching valve (17, 18), a bypass is formed between the fifth switching valve (17, 18) and the sixth switching valve (20, 21), and a bypass is formed between the sixth switching valve (20, 21) and the fourth switching valve (23).

[0016] According to an embodiment of the present invention, the water removal molecular sieve (10) is molecular sieve 3A, and the deep water removal unit (22) contains magnesium perchlorate.

[0017] According to an embodiment of the present invention, the carbon monoxide removal unit (16) comprises molecular sieve Sofnocat and the carbon dioxide removal unit (19) comprises caustic soda asbestos.

[0018] According to an embodiment of the present invention, a back pressure valve (25) is further provided before the first diaphragm stop valve (30) on the connection between the gas cylinder assembly (24) and the calibration gas cylinder (33).

[0019] According to an embodiment of the present invention, a high-pressure needle valve (31) is further provided at the front end of the calibration gas bottle (33).

[0020] The present invention adopts the compressed air method to prepare the environmental concentration standard gas. The standard gas containing nitrogen, oxygen, argon, carbon dioxide, methane, nitrous oxide and other components in real air can be directly prepared by compressing the environmental air with a high-pressure pump. The target component can be selectively removed or retained. The compressed gas is directly converted into the standard gas by the analytical instrument, which greatly saves the preparation time and improves the preparation efficiency. Since the raw material of the standard gas comes directly from the real air, the isotope ratio of each component can be kept consistent with the target to be measured, avoiding the systematic error caused thereby. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Schematic diagram of the system structure for preparing standard gas by purifying and compressing air according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. The shown contents are used to fully illustrate the contents of the present invention, but are not used to limit the present invention.

[0023] Figure 1 A schematic diagram of the structure of a system for preparing standard gas from purified and compressed air according to an embodiment of the present invention. Figure 1 The system for purifying and compressing air to prepare standard gas in the implementation scheme may include a particulate filter (1), an oil-free air compressor (4), a refrigerator (7), a heat exchanger (8), a dehydration molecular sieve (10), an activated carbon unit (13), a carbon monoxide removal unit (16), a carbon dioxide removal unit (19), a deep dehydration unit (22), a gas cylinder assembly (24), a target component pure gas source (26, 27), a standard gas cylinder (33) and a weighing device (34), which are described in detail below in conjunction with the accompanying drawings.

[0024] The particle filter (1) is arranged at the front end of the whole system, and is connected to the oil-free air compressor (4) through the pipeline (2), and is used to filter the particles in the air. For example, the particle filter can be a 0.2 μm glass fiber HEPA filter membrane or a stainless steel sintered mesh filter. After being filtered by the particle filter (1), the air enters the oil-free air compressor (4).

[0025] The oil-free air compressor (4) does not use lubricating oil during operation, thereby avoiding the introduction of oil components into the compressed air. The oil-free air compressor (4) can compress the collected atmosphere into high-pressure gas. The specific pressure of the high-pressure gas can be achieved by selecting an oil-free air compressor (4) with appropriate power parameters as needed. During this process, moisture in the air may condense, and the electric drain valve (3) can be used to automatically drain part of the condensed moisture at a fixed time. In addition, a safety valve (5) can also be installed on the oil-free air compressor (4).

[0026] The high-pressure gas in the oil-free air compressor (4) passes through the heat exchanger (8) and the refrigerator (7) to exchange heat to further reduce the gas temperature. The further condensed water is discharged from the cooling water outlet (6), and the non-condensable gas components enter the next unit of the system.

[0027] As shown in the figure, one end of the dehydration molecular sieve (10) is connected to the heat exchanger (8) through the first switching valve (9), and the other end is connected to one end of the activated carbon unit (13) through the second switching valve (11, 12). Non-condensable gas components can enter the dehydration molecular sieve (10) through the first switching valve (9) to further remove water in depth. For example, the dehydration molecular sieve (10) can be molecular sieve 3A, or other appropriate molecular sieve materials can be selected. The water vapor content in the air has a great interference to almost all spectral and mass spectrometry instruments. Therefore, deep removal of water can reduce the corresponding interference in the subsequent detection process and improve the accuracy of the detection.

[0028] One end of the dehydration molecular sieve (10) is connected to the activated carbon unit (13) via the second switching valve (11, 12). After the air flows through the dehydration molecular sieve (10), it can enter the activated carbon unit (13) via the second switching valve (11, 12). The activated carbon unit (13) is filled with activated carbon. The filled activated carbon can be columnar activated carbon particles with a diameter specification of 5-8 mm and a total pore volume of ≥0.8 cm 3 / g, can be used to remove volatile components such as benzene, toluene, formaldehyde, heptane, octane, ethylbenzene, trimethylbenzene, etc. in the air.

[0029] One end of the activated carbon unit (13) is connected to the carbon monoxide removal unit (16) through the third switching valve (14, 15). After the air flows through the activated carbon unit (13), it can enter the carbon monoxide removal unit (16) through the third switching valve (14, 15). The carbon monoxide removal unit (16) is used to remove part or all of the carbon monoxide components in the air. For example, molecular sieve Sofnocat can be used to remove carbon monoxide. Of course, other suitable materials can also be selected to remove carbon monoxide.

[0030] One end of the carbon monoxide removal unit (16) is connected to the carbon dioxide removal unit (19) through the fifth switching valve (17, 18). After the air flows through the carbon monoxide removal unit (16), it can enter the carbon dioxide removal unit (19) through the fifth switching valve (17, 18). The carbon dioxide removal unit (19) is used to remove part or all of the carbon dioxide in the air. For example, caustic soda asbestos can be used to remove carbon dioxide. Of course, other suitable materials can also be used.

[0031] One end of the carbon dioxide removal unit (19) is connected to the deep water removal unit (22) through the sixth switching valve (20, 21). After the air flows through the carbon dioxide removal unit (19), it can enter the deep water removal unit (22) through the sixth switching valve (20, 21). The deep water removal unit (22) is used to further remove moisture from the air. For example, magnesium perchlorate can be used to remove moisture. Afterwards, the air is pressed into the gas cylinder assembly (24) through the fourth switching valve (23). When the pressure in the gas cylinder assembly (24) reaches the required range, the oil-free air compressor can be turned off and the pressing is stopped.

[0032] With reference to the accompanying drawings, in the embodiment of the present invention, the first switching valve (9) and the second switching valve (11, 12) can be connected to form a bypass; the second switching valve (11, 12) and the third switching valve (14, 15) can be connected to form a bypass; the third switching valve (14, 15) and the fifth switching valve (17, 18) can be connected to form a bypass; the fifth switching valve (17, 18) and the sixth switching valve (20, 21) can be connected to form a bypass; the sixth switching valve (20, 21) and the fourth switching valve (23) can be connected to form a bypass. The air flow path can be adjusted by switching the switch direction of each switching valve. For example, when it is not necessary to remove carbon monoxide, the third switching valve (14, 15) can be connected to the fifth switching valve (17, 18) to close the flow path to the carbon monoxide removal unit (16), and the fifth switching valve (17, 18) can be switched to be connected to the third switching valve (14, 15) to close the cutout communicating with the carbon monoxide removal unit (16), so that a bypass is formed between the third switching valve (14, 15) and the fifth switching valve (17, 18), and air does not flow through the carbon monoxide removal unit (16). That is, the embodiment of the present invention can selectively retain the required components / remove some components by combined operation of each switching valve.

[0033] Afterwards, the gas cylinder assembly (24) can be used as a gas source to prepare standard gas.

[0034] More specifically, the gas cylinder assembly (24) is connected to the calibration gas cylinder (33) through a back pressure valve (25) and a first diaphragm stop valve (30). A high pressure needle valve (31) can also be provided at the front end of a gas pipeline (32) connected to the calibration gas cylinder (33). The high pressure air of the gas cylinder assembly (24) is injected into the calibration gas cylinder (33) through the pipeline, and is weighed by a weighing device (34) such as an electronic balance, and then the target gas in the calibration gas cylinder (33) is determined by an analytical instrument, thereby obtaining a standard gas with real air as the raw material. Since the raw material of the standard gas comes directly from real air, the isotopic ratio of its various components can be kept consistent with the target to be measured; in addition, real air contains a variety of gas components such as nitrogen, oxygen, argon, carbon dioxide, methane, nitrous oxide, etc., so it is equivalent to preparing standard gases of these components at the same time, which greatly improves the preparation efficiency of the standard gas.

[0035] For components whose concentration in the atmosphere is higher than the expected value (configured target value), the corresponding purification unit (removal unit) in the system can be turned on to remove a portion of the target component. For example, when the target component is 200 ppm of carbon dioxide, since the concentration of carbon dioxide in the atmosphere is higher than 200 ppm, the carbon dioxide removal unit (19) is turned on to charge a certain amount of carbon dioxide (or CO 2 concentration) to achieve a reduction in overall carbon dioxide concentration.

[0036] For the target component whose concentration in the atmosphere is lower than the expected concentration, the corresponding purification unit can be closed, and the target substance concentration is adjusted to the required range by adding the corresponding high-purity target gas. As shown in the figure, the system of the embodiment can also include a target component pure gas source (26, 27), and the target component pure gas source (26, 27) is connected to the standard gas bottle (33) via the second diaphragm stop valve (28, 29). For example, when the target component is 800ppm of carbon dioxide, since the carbon dioxide concentration in the atmosphere is lower than 800ppm, the carbon dioxide removal unit (19) is closed, and pure carbon dioxide is used as the target component pure gas source (26, 27), and quantitative pure carbon dioxide is injected into the standard gas bottle (33) to achieve the target concentration of carbon dioxide standard gas.

[0037] This system can compress the collected atmosphere into high-pressure gas through an oil-free air compressor, and selectively remove or retain the required components through a series of purification steps, and store them in high-pressure gas cylinders. For components in the atmosphere whose concentration is higher than the expected value, the purification unit is turned on to remove a part of them; for components in the atmosphere whose concentration is lower than the expected concentration, the purification unit can be closed through a bypass, and the concentration of the target substance can be adjusted to the required range by adding high-purity gas.

[0038] Example

[0039] Take the suppression of a certain city's ambient air standard gas as an example: select a summer night, under stable meteorological conditions, use this system to suppress standard gas, select a 50L aluminum alloy gas cylinder for the suppression gas cylinder, prepare a pressure of 11Mpa, and the target component is a greenhouse gas component. During operation, turn on the refrigerator 7, the dehydration molecular sieve 10 (molecular sieve 3A) and the deep dehydration unit 22 (magnesium perchlorate) for dehydration, turn off the carbon monoxide removal unit 16 (molecular sieve Sofnocat) and the carbon dioxide removal unit (caustic soda asbestos), retain the carbon monoxide and carbon dioxide components in the air, and after about 11 minutes, the 50L gas cylinder reaches the target pressure, and the gas cylinder and pump group are turned off. After the gas cylinder is laid flat and left to stand for 12 hours, the target components are measured using the prepared standard gas. The measurement method of each component is shown in Table 1 below.

[0040] Table 1: Measurement methods of each component

[0041]

[0042] The results are shown in Table 2 below:

[0043] Table 2: Greenhouse gas components and concentrations in suppressed urban air

[0044]

[0045]

[0046] The results show that the system of the present invention simultaneously obtains standard gases of multiple greenhouse gases using real air as raw materials, avoiding the deficiency of the traditional gas distribution method that does not consider the matrix effect. In addition, if the standard gas of the above 25 components is prepared by artificial synthesis, at least 25 components of raw materials need to be prepared, and the high-concentration primary gas is diluted step by step, and at least about 60 gas cylinders are consumed as a transition to the intermediate high concentration until the final mixed standard gas is prepared. However, by adopting the pressing method of the present invention, only the air raw material needs to be collected, pressed into the gas cylinder, and then calibrated and set, which can greatly reduce the preparation time and improve the preparation efficiency of the complex component standard gas.

[0047] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the embodiments herein, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A system for purifying and compressing air to prepare standard gas, characterized in that: It comprises an oil-free air compressor (4), a refrigerator (7), a heat exchanger (8), a dehydration molecular sieve (10), an activated carbon unit (13), a deep dehydration unit (22), a gas cylinder assembly (24), a target component pure gas source (26, 27), a standard gas cylinder (33) and a weighing device (34); The oil-free air compressor (4) and the refrigerator (7) are respectively connected to the heat exchanger (8) to cool the air compressed by the oil-free air compressor (4); One end of the dehydration molecular sieve (10) is connected to the heat exchanger (8) via a first switching valve (9), and the other end is connected to one end of the activated carbon unit (13) via a second switching valve (11, 12); The other end of the activated carbon unit (13) is connected to one end of the deep water removal unit (22) via a third switching valve (14, 15); The other end of the deep water removal unit (22) is connected to the gas cylinder assembly (24) via a fourth switching valve (23); The gas cylinder assembly (24) is connected to the calibration gas cylinder (33) via a first diaphragm stop valve (30), and the target component pure gas source (26, 27) is connected to the calibration gas cylinder (33) via a second diaphragm stop valve (28, 29); the weighing device (34) is used to weigh the calibration gas cylinder (33).

2. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: It also includes a particle filter (1) which is arranged at the front end of the oil-free air compressor (4) and is used to filter particles in the air entering the oil-free air compressor (4).

3. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: It also includes a carbon monoxide removal unit (16) and a carbon dioxide removal unit (19); one end of the carbon monoxide removal unit (16) is connected to the third switching valve (14, 15), and the other end is connected to one end of the carbon dioxide removal unit (19) through a fifth switching valve (17, 18); the other end of the carbon dioxide removal unit (19) is connected to the deep water removal unit (22) through a sixth switching valve (20, 21).

4. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: A bypass is formed between the first switching valve (9) and the second switching valve (11, 12); a bypass is formed between the second switching valve (11, 12) and the third switching valve (14, 15); and a bypass is formed between the third switching valve (14, 15) and the fourth switching valve (23).

5. The system for preparing standard gas by purifying and compressing air as claimed in claim 3, characterized in that: A bypass is formed between the third switching valve (14, 15) and the fifth switching valve (17, 18), a bypass is formed between the fifth switching valve (17, 18) and the sixth switching valve (20, 21), and a bypass is formed between the sixth switching valve (20, 21) and the fourth switching valve (23).

6. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: The dehydration molecular sieve (10) is molecular sieve 3A, and the deep dehydration unit (22) contains magnesium perchlorate.

7. The system for preparing standard gas by purifying and compressing air as claimed in claim 3, characterized in that: The carbon monoxide removal unit (16) contains molecular sieve Sofnocat and the carbon dioxide removal unit (19) contains caustic soda asbestos.

8. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: A back pressure valve (25) is also provided on the connection between the gas cylinder assembly (24) and the calibration gas cylinder (33) before the first diaphragm stop valve (30).

9. The system for preparing standard gas by purifying and compressing air as claimed in claim 1, characterized in that: A high-pressure needle valve (31) is also provided at the front end of the calibration gas bottle (33).

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