CN118688338A - A direct measurement device and analysis method for methane and non-methane total hydrocarbons in ambient air - Google Patents

Abstract

The invention provides a direct measurement device and an analysis method for methane and non-methane total hydrocarbons in the environment air, wherein the measurement device comprises a ten-way valve, a six-way valve, a non-methane total hydrocarbon enrichment trap, a first quantitative ring, a first EPC and an empty column which are connected with the ten-way valve, a second quantitative ring, a second EPC and a sampling pump which are connected with the six-way valve, an outlet of the empty column is connected with an FID detector, and a PQ column is arranged between the ten-way valve and the six-way valve. The non-methane total hydrocarbon enrichment trap comprises refrigeration equipment, a cold trap cavity, an enrichment pipe, heating equipment and a thermocouple; the refrigerating equipment is connected with the cold trap cavity, the enrichment pipe is arranged in the cold trap cavity, the heating equipment is directly connected with the enrichment pipe, and the thermocouple is arranged at the joint of the cold trap cavity and the refrigerating equipment. The device can realize direct enrichment and direct analysis of non-methane total hydrocarbons in the ambient air sample, avoids the adsorption of methane possibly caused by the adoption of the adsorbent, and has high detection accuracy.

Description

A direct measurement device and analysis method for methane and non-methane total hydrocarbons in ambient air

Technical Field

The invention belongs to the field of online monitoring of ambient air, and in particular relates to a direct measurement device and analysis method for methane and non-methane total hydrocarbons in ambient air.

Background Art

Nonmethane Hydrocarbons (NMHC) usually refers to all volatile hydrocarbons and their derivatives (mainly C2 to C8) except methane. HJ 38 and HJ 1012 stipulate that nonmethane hydrocarbons are the sum of other gaseous organic compounds after methane is deducted from total hydrocarbons under the measurement conditions specified in the standard (unless otherwise specified, the result is calculated in carbon). In environmental monitoring practice, it can be found that nonmethane hydrocarbons, in addition to hydrocarbons, also include hydrocarbon derivatives such as alcohols, aldehydes, acids, esters, ketones, and volatile organic substances above C8. Nonmethane hydrocarbons have greater photochemical activity and are precursors to the formation of photochemical smog.

At present, there are two methods for measuring methane and non-methane total hydrocarbons: one is to refer to "Gas Chromatography for Determination of Total Hydrocarbons, Methane and Non-methane Total Hydrocarbons in Waste Gas from Stationary Pollution Sources" (HJ 38-2017) and "Direct Injection-Gas Chromatography for Determination of Total Hydrocarbons, Methane and Non-methane Total Hydrocarbons in Ambient Air" (HJ 604-2017). The method used is the difference method, that is, two chromatographic columns are used to determine the content of total hydrocarbons and methane (in terms of carbon), and the difference between the two is the content of non-methane total hydrocarbons; the other is to refer to the "Technical Regulations for Continuous Automatic Monitoring of Non-methane Total Hydrocarbons in Ambient Air (Trial)", and the method used is the direct method, that is, by separating the methane from the total hydrocarbons through chromatographic column separation, valve switching, backflushing and other means, so that the non-methane total hydrocarbons have a separate peak and directly measure their concentration. After a large number of experiments and studies, it has been shown that the direct method is more suitable for the field of continuous online monitoring of non-methane total hydrocarbons in ambient air.

There are two main methods for directly measuring methane and non-methane hydrocarbons in ambient air on the market. One is the chromatographic column backflush mode, which separates methane and non-methane hydrocarbons through a chromatographic column, then backflushes the non-methane hydrocarbons to calculate the non-methane hydrocarbon content. This method has special requirements for chromatographic column selection. Methane must be separated from other hydrocarbons, and other hydrocarbons cannot be retained too strongly on the chromatographic column. The more components there are and the higher the carbon content of the components, the more severe the peak tailing will be, affecting quantification. In addition, since non-methane hydrocarbons are not enriched, when their content When the concentration is low, it is easy to fail to detect. The other is the adsorbent cold trap enrichment mode, that is, a large amount of ambient air is collected through the cold trap, and non-methane total hydrocarbons are adsorbed under the action of the adsorbent, and then the non-methane total hydrocarbons are released by heating and analysis, and the non-methane total hydrocarbon content is calculated. This method has high requirements on the adsorbent. The higher the component content, the lower the adsorption efficiency, the higher the carbon content of the component, the more difficult the analysis, the longer the use time, the easier the adsorbent is to denature. In addition, when the air humidity is high, large volume injection under low temperature conditions is prone to ice blockage of the adsorbent.

Summary of the invention

In view of the problems existing in the prior art, the present invention provides a non-methane total hydrocarbon enrichment trap, which can not only remove moisture from ambient air, but also enrich only the non-methane total hydrocarbon components in the ambient air and directly discharge the methane components in the ambient air. At the same time, the non-methane total hydrocarbons are enriched by deep cooling, thereby improving the enrichment efficiency of the non-methane total hydrocarbons; and based on the non-methane total hydrocarbon enrichment trap, a direct measurement device and analysis method for methane and non-methane total hydrocarbons in ambient air are provided.

The technical solution adopted by the present invention to solve the problems existing in the prior art is as follows:

A direct measurement device for methane and non-methane total hydrocarbons in ambient air comprises a ten-way valve and a six-way valve, a non-methane total hydrocarbon enrichment trap connected to the ten-way valve, a first quantitative loop, a first EPC (electronic pressure controller) and an empty column (empty chromatographic column), a second quantitative loop, a second EPC (electronic pressure controller) and a sampling pump connected to the six-way valve, the outlet of the empty column is connected to the FID detector (hydrogen flame ionization detector), and a PQ column (PQ chromatographic column) is further arranged between the ten-way valve and the six-way valve; the methane determination process in ambient air comprises: after the sample gas is extracted by the sampling pump and collected in the second quantitative loop, the methane in the sample gas is separated by the PQ column, and the methane content is detected by the FID detector; the non-methane total hydrocarbon determination process in ambient air comprises: after the sample gas is extracted by the sampling pump and collected in the first quantitative loop, the sample gas is low-temperature enriched in the non-methane total hydrocarbon enrichment trap, and then the non-methane total hydrocarbons are heated and resolved to enter the FID detector to detect the non-methane total hydrocarbon content in the ambient air sample.

The non-methane total hydrocarbon enrichment trap comprises a refrigeration device, a cold trap cavity, an enrichment tube, a heating device, and a thermocouple; the refrigeration device is connected to the cold trap cavity to provide a low-temperature environment for the cold trap cavity, the enrichment tube is placed in the cold trap cavity, the heating device is directly connected to the enrichment tube to quickly heat the enrichment tube, and the thermocouple is placed at the connection between the cold trap cavity and the refrigeration device to measure the temperature inside the cold trap cavity.

The enrichment tube comprises three sections of tubes, which are connected in series in sequence. The first section of the tube is an empty tube, located at position a in the cold trap chamber, and is used to remove moisture from the ambient air. The second section of the tube is an empty tube, located at position b in the cold trap chamber, and is used to enrich high-carbon components in non-methane total _hydrocarbons . The third section of the tube is an _AL2O3 coated tube, located at position c in the cold trap chamber, and is used to enrich low-carbon components in non-methane total hydrocarbons. Position a in the cold trap chamber is farthest from the refrigeration equipment, position b is the second, and position c is the closest. The temperatures of the three sections of the tube are: third section < second section < first section.

The refrigeration equipment is a Stirling refrigerator, and the lowest refrigeration temperature can reach -210°C. The heating equipment is a low-voltage high-current transformer, and the maximum heating power can reach 300w. The thermocouple is a K-type thermocouple, and the temperature measurement range is -300°C to 1000°C. The refrigeration equipment and the cold trap cavity, and the cold trap cavity and the enrichment tube are treated with a thermally conductive insulating coating.

The ten-way valve includes ten interfaces, namely: a ten-way valve sample gas inlet 10j, a first quantitative loop inlet 10a, a first quantitative loop outlet 10h, a ten-way valve sample gas outlet 10i, a first EPC inlet 10g, a non-methane enrichment trap inlet 10b, a non-methane enrichment trap outlet 10f, a PQ column outlet 10d, an empty column inlet 10c, and an exhaust port 10e.

The ten-way valve is a two-position ten-way valve, that is, it has two connected working states, namely position A and position B. When the ten-way valve is in position A, the first quantitative loop inlet 10a is connected to the ten-way valve sample gas inlet 10j, the non-methane enrichment trap inlet 10b is connected to the empty column inlet 10c, the PQ column outlet 10d is connected to the exhaust port 10e, the non-methane enrichment trap outlet 10f is connected to the first EPC inlet 10g, and the first quantitative loop outlet 10h is connected to the ten-way valve sample gas outlet 10i; when the ten-way valve is in position B, the first quantitative loop inlet 10a is connected to the non-methane enrichment trap inlet 10b, the empty column inlet 10c is connected to the PQ column outlet 10d, the exhaust port 10e is connected to the non-methane enrichment trap outlet 10f, the first EPC inlet 10g is connected to the first quantitative loop outlet 10h, and the ten-way valve sample gas outlet 10i is connected to the ten-way valve sample gas inlet 10j.

The six-way valve includes six interfaces: six-way valve sample gas inlet 6b, second quantitative loop inlet 6c, second quantitative loop outlet 6f, sampling pump inlet 6a, second EPC inlet 6e, and PQ column inlet 6d; wherein the ten-way valve sample gas outlet 10i is connected to the six-way valve sample gas inlet 6b.

The six-way valve is a two-position six-way valve, that is, it has two connecting working states, namely position A and position B. When the six-way valve is in position A: the sampling pump inlet 6a is connected to the second quantitative loop outlet 6f, the second EPC inlet 6e is connected to the PQ column inlet 6d, and the second quantitative loop inlet 6c is connected to the six-way valve sample gas inlet 6b. When the six-way valve is in position B: the sampling pump inlet 6a is connected to the six-way valve sample gas inlet 6b, the second quantitative loop inlet 6c is connected to the PQ column inlet 6d, and the second EPC inlet 6e is connected to the second quantitative loop outlet 6f.

The present invention also provides an analysis method of a direct measurement device for methane and non-methane total hydrocarbons in ambient air, comprising the following steps:

Step 1, sampling, the ten-way valve and the six-way valve are switched to position A, and the sample gas is drawn into the first quantitative ring and the second quantitative ring by the sampling pump;

Specifically, during the sampling stage: the sample gas (i.e., the ambient air to be tested) is connected to the sampling pump in sequence through the sample gas inlet 10j, the first quantitative ring inlet 10a, the first quantitative ring, the first quantitative ring outlet 10h, the ten-way valve sample gas outlet 10i, the six-way valve sample gas inlet 6b, the second quantitative ring inlet 6c, the second quantitative ring outlet 6f, and the sampling pump inlet 6a.

Step 2, methane analysis and non-methane total hydrocarbon enrichment, the ten-way valve and the six-way valve are switched to position B, one carrier gas (the carrier gas is high-purity helium with a purity of 99.999%) is used to carry the first quantitative loop sample into the non-methane total hydrocarbon enrichment trap for enrichment through the first EPC, and the enrichment temperature is -185°C to -165°C, and the other carrier gas is used to carry the second quantitative loop sample into the PQ column through the second EPC to separate methane, and the methane content is detected by the FID detector;

Specifically, during the methane analysis and non-methane total hydrocarbon enrichment stage: one carrier gas passes through the first EPC, the first EPC inlet 10g, the first quantitative loop outlet 10h, the first quantitative loop, the first quantitative loop inlet 10a, the non-methane enrichment trap inlet 10b, the non-methane total hydrocarbon enrichment trap, the non-methane enrichment trap outlet 10f, and the exhaust port 10e in sequence; the other carrier gas passes through the second EPC, the second EPC inlet 6e, the second quantitative loop outlet 6f, the second quantitative loop, the second quantitative loop inlet 6c, the PQ column inlet 6d, the PQ column, the PQ column outlet 10d, the empty column inlet 10c, the empty column, and reaches the FID detector in sequence.

Step 3, non-methane total hydrocarbon analysis and PQ column purging, the ten-way valve and the six-way valve are switched to position A, the non-methane total hydrocarbon enrichment trap is quickly heated to 120°C, one carrier gas passes through the first EPC to bring the heated and analyzed non-methane total hydrocarbon sample into the FID detector for detection to obtain the content of non-methane total hydrocarbons, and the other carrier gas passes through the second EPC to back-blow the PQ column residual components after separating methane, and is discharged through the exhaust port of the ten-way valve.

Specifically, during the non-methane total hydrocarbon analysis and PQ column purge stage, one carrier gas passes through the first EPC, the first EPC inlet 10g, the non-methane enrichment trap outlet 10f, the non-methane enrichment trap, the non-methane enrichment trap inlet 10b, the empty column inlet 10c, the empty column, and reaches the FID detector; the other carrier gas passes through the second EPC, the second EPC inlet 6e, the PQ column inlet 6d, the PQ column, the PQ column outlet 10d, and the exhaust port 10e for exhaust.

The present invention has the following advantages:

1. The present invention has found through multiple optimization experimental settings that when the temperature of the non-methane total hydrocarbon enrichment trap is -185°C to -165°C, methane can completely penetrate the non-methane total hydrocarbon enrichment trap, and non-methane total hydrocarbons can be 100% captured by the non-methane total hydrocarbon enrichment trap; therefore, the device of the present invention can achieve direct enrichment and direct analysis of non-methane total hydrocarbons, avoiding the adsorption of methane that may be caused by the adsorbent, and has high accuracy.

2. The non-methane total hydrocarbon enrichment trap of the present invention is composed of three sections of serially connected pipes. The three sections of pipes are sequentially connected in series. The first section of the pipe is an empty pipe located at position a in the cold trap cavity and is used to remove moisture from the ambient air. The second section of the pipe is an empty pipe located at position b in the cold trap cavity and is used to enrich the high-carbon components in the non-methane total hydrocarbons. The third section of the pipe is _{an AL2O3} coated pipe. The c position in the cold trap cavity is used to enrich the low-carbon components in the non-methane total hydrocarbons; wherein the a position in the cold trap cavity is farthest from the refrigeration equipment, the b position is the second, and the c position is the closest. When the thermocouple monitors that the temperature of the non-methane total hydrocarbon enrichment trap is -185°C to -165°C, the temperatures of the three positions are: c position (-185°C to -165°C) < b position (-140°C to -120°C) < a position (-50°C to -30°C); through this structural design, the present invention cleverly solves the shortcomings of ice blockage, low adsorption efficiency, easy penetration of low-carbon components, and easy residue of high-carbon components caused by adsorbent adsorption in the prior art, and has the advantages of high enrichment efficiency, high sensitivity, strong anti-interference ability, and low maintenance cost.

BRIEF DESCRIPTION OF THE DRAWINGS

1 is a schematic diagram of the structure of a device for directly measuring methane and non-methane total hydrocarbons in ambient air in a specific embodiment of the present invention;

FIG2 is a schematic diagram of the structure of a non-methane total hydrocarbon enrichment trap in a specific embodiment of the present invention;

3 is a gas flow chart A of a method for direct analysis of methane and non-methane total hydrocarbons in ambient air according to an embodiment of the present invention;

4 is a gas flow chart B of a method for direct analysis of methane and non-methane total hydrocarbons in ambient air according to an embodiment of the present invention;

5 is a gas flow chart C of a method for direct analysis of methane and non-methane total hydrocarbons in ambient air according to an embodiment of the present invention;

In Figure 2, 1-refrigeration equipment, 2-cold trap chamber, 3-enrichment tube A, 4-enrichment tube B, 5-enrichment tube C, 6-thermocouple, 7-heating equipment.

DETAILED DESCRIPTION

The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

As shown in Figure 1, a direct measurement device for methane and non-methane total hydrocarbons in ambient air includes a ten-way valve and a six-way valve, as well as a non-methane total hydrocarbon enrichment trap connected to the ten-way valve, a first quantitative ring, a first EPC (electronic pressure controller) and an empty column (empty chromatographic column), a second quantitative ring connected to the six-way valve, a second EPC (electronic pressure controller) and a sampling pump, the outlet of the empty column is connected to the FID detector, and a PQ column (PQ chromatographic column) is also provided between the ten-way valve and the six-way valve. Among them, both quantitative rings are quantitative rings produced by Vici Company of the United States, the volume of the first quantitative ring is 5ml, and the volume of the second quantitative ring is 2ml; the EPC and FID detectors are respectively EPC model 301-10051 and FID model FID-M401 produced by Shanghai Fuhe Automation Instrument Co., Ltd.; the sampling pump is a sampling pump model N86 produced by KNF Company of Germany.

The ten-way valve includes: a ten-way valve sample gas inlet 10j, a first quantitative loop inlet 10a, a first quantitative loop outlet 10h, a ten-way valve sample gas outlet 10i, a first EPC inlet 10g, a non-methane total hydrocarbon enrichment trap inlet 10b, a non-methane total hydrocarbon enrichment trap outlet 10f, a PQ column outlet 10d, an empty column inlet 10c, and an exhaust port 10e;

The six-way valve includes: a six-way valve sample gas inlet 6b, a second quantitative loop inlet 6c, a second quantitative loop outlet 6f, a sampling pump inlet 6a, a second EPC inlet 6e, and a PQ column inlet 6d; wherein the ten-way valve sample gas outlet 10i is connected to the six-way valve sample gas inlet 6b, and the empty column outlet is connected to the FID detector.

The ten-way valve is a two-position ten-way valve, that is, it has two connected working states, namely position A and position B. When the ten-way valve is in position A: the first quantitative loop inlet 10a is connected to the ten-way valve sample gas inlet 10j, the non-methane enrichment trap inlet 10b is connected to the empty column inlet 10c, the PQ column outlet 10d is connected to the exhaust port 10e, the non-methane enrichment trap outlet 10f is connected to the first EPC inlet 10g, and the first quantitative loop outlet 10h is connected to the ten-way valve sample gas outlet 10i. When the ten-way valve is in position B: the first quantitative loop inlet 10a is connected to the non-methane enrichment trap inlet 10b, the empty column inlet 10c is connected to the PQ column outlet 10d, the exhaust port 10e is connected to the non-methane enrichment trap outlet 10f, the first EPC inlet 10g is connected to the first quantitative loop outlet 10h, and the ten-way valve sample gas outlet 10i is connected to the ten-way valve sample gas inlet 10j.

The six-way valve is a two-position six-way valve, that is, it has two connecting working states, namely position A and position B. When the six-way valve is in position A: the sampling pump inlet 6a is connected to the second quantitative loop outlet 6f, the second EPC inlet 6e is connected to the PQ column inlet 6d, and the second quantitative loop inlet 6c is connected to the six-way valve sample gas inlet 6b. When the six-way valve is in position B: the sampling pump inlet 6a is connected to the six-way valve sample gas inlet 6b, the second quantitative loop inlet 6c is connected to the PQ column inlet 6d, and the second EPC inlet 6e is connected to the second quantitative loop outlet 6f.

As shown in FIG2 , the total non-methane hydrocarbon enrichment trap includes a refrigeration device 1, a cold trap cavity 2, an enrichment tube A3, an enrichment tube B4, an enrichment tube C5, a heating device 7, and a thermocouple 6; the refrigeration device 1 is connected to the cold trap cavity 2 to provide a low-temperature environment for the cold trap cavity 2, the enrichment tubes A3, B4, and C5 are placed in the cold trap cavity 2, the heating device 7 is directly connected to the enrichment tubes to quickly heat the enrichment tubes, and the thermocouple 6 is placed at the connection between the cold trap cavity 2 and the refrigeration device 1 to measure the temperature inside the cold trap cavity.

The enrichment tube includes three sections of tubes, namely, enrichment tube A3, enrichment tube B4, and enrichment tube C5. The three sections of tubes are connected in series in sequence. Enrichment tube A3 is an empty tube, located at position a in the cold trap cavity, and is used to remove moisture from the ambient air. Enrichment tube B4 is an empty tube, located at position b in the cold trap cavity, and is used to enrich high-carbon components in non-methane total hydrocarbons. _Enrichment tube C5 is an _AL2O3 coated tube, located at position c in the cold trap cavity, and is used to enrich low-carbon components in non-methane total hydrocarbons. Among them, position a in the cold trap cavity is farthest from the refrigeration equipment 1, position b is the second, and position c is the closest.

The refrigeration equipment 1 is a Stirling refrigerator, and the lowest refrigeration temperature can reach -210°C. The heating equipment 7 is a low-voltage high-current transformer, and the maximum heating power can reach 300w. The thermocouple 6 is a K-type thermocouple, and the temperature measurement range is -300°C to 1000°C. The refrigeration equipment 1 and the cold trap chamber 2, and the cold trap chamber 2 and the enrichment tube are treated with a thermal conductive insulating coating.

An analysis method based on a direct measurement device for methane and non-methane total hydrocarbons in ambient air comprises the following steps:

Step 1: Sampling. The ten-way valve and the six-way valve are switched to position A. The sample gas is drawn into the first quantitative loop and the second quantitative loop by the sampling pump.

Specifically, during the sampling stage, as shown in Figure 3: the sample gas is connected to the sampling pump through the sample gas inlet 10j, the first quantitative ring inlet 10a, the first quantitative ring, the first quantitative ring outlet 10h, the ten-way valve sample gas outlet 10i, the six-way valve sample gas inlet 6b, the second quantitative ring inlet 6c, the second quantitative ring outlet 6f, and the sampling pump inlet 6a.

Step 2: Methane analysis and non-methane total hydrocarbon enrichment. The ten-way valve and the six-way valve are switched to position B. One carrier gas passes through the first EPC to bring the first quantitative loop sample into the non-methane total hydrocarbon enrichment trap for enrichment. The enrichment temperature is -185°C. Another carrier gas passes through the second EPC to bring the second quantitative loop sample into the PQ column to separate methane. The methane content is detected by the FID detector.

Specifically, during the methane analysis and non-methane total hydrocarbon enrichment stage, as shown in Figure 4: one carrier gas passes through the first EPC, the first EPC inlet 10g, the first quantitative loop outlet 10h, the first quantitative loop, the first quantitative loop inlet 10a, the non-methane enrichment trap inlet 10b, the non-methane total hydrocarbon enrichment trap, the non-methane enrichment trap outlet 10f, and the exhaust port 10e in sequence; the other carrier gas passes through the second EPC, the second EPC inlet 6e, the second quantitative loop outlet 6f, the second quantitative loop, the second quantitative loop inlet 6c, the PQ column inlet 6d, the PQ column, the PQ column outlet 10d, the empty column inlet 10c, the empty column, and reaches the FID detector in sequence.

Step 3: Analysis of non-methane total hydrocarbons and purging of the PQ column. The ten-way valve and the six-way valve are switched to position A. The non-methane total hydrocarbon enrichment trap is quickly heated to 120°C. One carrier gas passes through the first EPC to bring the heated and resolved non-methane total hydrocarbon sample into the FID detector for detection to obtain the content of non-methane total hydrocarbons. The other carrier gas passes through the second EPC to back-blow the PQ column residual components after separating methane and discharge them through the exhaust port of the ten-way valve.

Specifically, during the non-methane total hydrocarbon analysis and PQ column purge stage, as shown in Figure 5: one carrier gas passes through the first EPC, the first EPC inlet 10g, the non-methane enrichment trap outlet 10f, the non-methane enrichment trap, the non-methane enrichment trap inlet 10b, the empty column inlet 10c, the empty column, and reaches the FID detector; the other carrier gas passes through the second EPC, the second EPC inlet 6e, the PQ column inlet 6d, the PQ column, the PQ column outlet 10d, and the exhaust port 10e for exhaust.

The protection scope of the present invention is not limited to the above-mentioned embodiments. Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the scope and spirit of the present invention. If these changes and modifications fall within the scope of the claims of the present invention and their equivalents, the intention of the present invention also includes these changes and modifications.

Claims (10)

1. A direct measurement device for methane and non-methane total hydrocarbons in ambient air, characterized in that it comprises a ten-way valve and a six-way valve, and a non-methane total hydrocarbon enrichment trap, a first quantitative loop, a first EPC and an empty column connected to the ten-way valve, a second quantitative loop, a second EPC and a sampling pump connected to the six-way valve, the outlet of the empty column is connected to the FID detector, and a PQ column is further provided between the ten-way valve and the six-way valve; The non-methane total hydrocarbon enrichment trap comprises a refrigeration device, a cold trap cavity, an enrichment tube, a heating device, and a thermocouple; the refrigeration device is connected to the cold trap cavity to provide a low-temperature environment for the cold trap cavity, the enrichment tube is placed in the cold trap cavity, the heating device is directly connected to the enrichment tube to quickly heat the enrichment tube, and the thermocouple is placed at the connection between the cold trap cavity and the refrigeration device to measure the temperature inside the cold trap cavity. 2. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as described in claim 1, characterized in that: the enrichment tube includes three sections of tubes, the three sections of tubes are connected in series in sequence, the first section of the tube is an empty tube, located at position a in the cold trap cavity, and is used to remove moisture from the ambient air, the second section of the tube is an empty tube, located at position b in the cold trap cavity, and is used to enrich high-carbon components in non-methane total hydrocarbons, and the third section of the tube is _{an AL2O3} coated tube, located at position c in the cold trap cavity, and is used to enrich low-carbon components in non-methane total hydrocarbons; wherein position a in the cold trap cavity is farthest from the refrigeration equipment, position b is second, and position c is closest, and the temperatures of the three sections of the tube are: third section < second section < first section. 3. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as described in claim 1, characterized in that: the refrigeration equipment is a Stirling refrigerator, the heating equipment is a low-voltage high-current transformer, the thermocouple is a K-type thermocouple, and the temperature measurement range is -300°C to 1000°C; a thermal conductive insulating coating is used between the refrigeration equipment and the cold trap cavity, and between the cold trap cavity and the enrichment tube. 4. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as described in claim 1, characterized in that: the ten-way valve includes ten interfaces, namely: a ten-way valve sample gas inlet (10j), a first quantitative loop inlet (10a), a first quantitative loop outlet (10h), a ten-way valve sample gas outlet (10i), a first EPC inlet (10g), a non-methane enrichment trap inlet (10b), a non-methane enrichment trap outlet (10f), a PQ column outlet (10d), an empty column inlet (10c), and an exhaust port (10e). 5. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as claimed in claim 4, characterized in that: the ten-way valve is a two-position ten-way valve, that is, it has two connected working states, namely position A and position B. When the ten-way valve is in position A: the first quantitative loop inlet (10a) is connected to the ten-way valve sample gas inlet (10j), the non-methane enrichment trap inlet (10b) is connected to the empty column inlet (10c), the PQ column outlet (10d) is connected to the emptying port (10e), and the non-methane enrichment trap outlet (10f) is connected to the first EPC inlet (10g), the first quantitative loop outlet (10h) is connected to the ten-way valve sample gas outlet (10i); when the ten-way valve is in position B: the first quantitative loop inlet (10a) is connected to the non-methane enrichment trap inlet (10b), the empty column inlet (10c) is connected to the PQ column outlet (10d), the exhaust port (10e) is connected to the non-methane enrichment trap outlet (10f), the first EPC inlet (10g) is connected to the first quantitative loop outlet (10h), and the ten-way valve sample gas outlet (10i) is connected to the ten-way valve sample gas inlet (10j). 6. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as described in claim 1, characterized in that: the six-way valve includes six interfaces: a six-way valve sample gas inlet (6b), a second quantitative loop inlet (6c), a second quantitative loop outlet (6f), a sampling pump inlet (6a), a second EPC inlet (6e), and a PQ column inlet (6d); wherein the ten-way valve sample gas outlet (10i) is connected to the six-way valve sample gas inlet (6b). 7. A direct measurement device for methane and non-methane total hydrocarbons in ambient air as claimed in claim 6, characterized in that: the six-way valve is a two-position six-way valve, that is, it has two connected working states, namely position A and position B. When the six-way valve is in position A: the sampling pump inlet (6a) is connected to the second quantitative loop outlet (6f), the second EPC inlet (6e) is connected to the PQ column inlet (6d), and the second quantitative loop inlet (6c) is connected to the six-way valve sample gas inlet (6b); when the six-way valve is in position B: the sampling pump inlet (6a) is connected to the six-way valve sample gas inlet (6b), the second quantitative loop inlet (6c) is connected to the PQ column inlet (6d), and the second EPC inlet (6e) is connected to the second quantitative loop outlet (6f). 8. The analysis method of the direct measurement device for methane and non-methane total hydrocarbons in ambient air according to any one of claims 1 to 7, characterized in that it comprises the following steps: Step 1, sampling: switch the ten-way valve and the six-way valve to position A, and draw the sample gas into the first quantitative loop and the second quantitative loop through the sampling pump; Step 2, methane analysis and non-methane total hydrocarbon enrichment: the ten-way valve and the six-way valve are switched to position B, one carrier gas passes through the first EPC to bring the first quantitative loop sample into the non-methane total hydrocarbon enrichment trap for enrichment, the enrichment temperature is -185°C to -165°C, and the other carrier gas passes through the second EPC to bring the second quantitative loop sample into the PQ column to separate methane, and the methane content is detected by the FID detector; Step 3, non-methane total hydrocarbon analysis and PQ column purging, the ten-way valve and the six-way valve are switched to position A, the non-methane total hydrocarbon enrichment trap is quickly heated to 120°C, one carrier gas passes through the first EPC to bring the heated and analyzed non-methane total hydrocarbon sample into the FID detector for detection to obtain the content of non-methane total hydrocarbons, and the other carrier gas passes through the second EPC to back-blow the PQ column residual components after separating methane, and is discharged through the exhaust port of the ten-way valve. 9. An analysis method for a direct measurement device for methane and non-methane total hydrocarbons in ambient air as claimed in claim 8, characterized in that the method specifically comprises the following steps: in the sampling stage: the sample gas is connected to the sampling pump in sequence through the sample gas inlet (10j), the first quantitative loop inlet (10a), the first quantitative loop, the first quantitative loop outlet (10h), the ten-way valve sample gas outlet (10i), the six-way valve sample gas inlet (6b), the second quantitative loop inlet (6c), the second quantitative loop outlet (6f), and the sampling pump inlet (6a); During the methane analysis and non-methane total hydrocarbon enrichment stage: one carrier gas passes through the first EPC, the first EPC inlet (10g), the first quantitative loop outlet (10h), the first quantitative loop, the first quantitative loop inlet (10a), the non-methane enrichment trap inlet (10b), the non-methane total hydrocarbon enrichment trap, the non-methane enrichment trap outlet (10f), and the exhaust port (10e) in sequence; the other carrier gas passes through the second EPC, the second EPC inlet (6e), the second quantitative loop outlet (6f), the second quantitative loop, the second quantitative loop inlet (6c), the PQ column inlet (6d), the PQ column, the PQ column outlet (10d), the empty column inlet (10c), the empty column, and reaches the FID detector in sequence; During the non-methane total hydrocarbon analysis and PQ column purging stage, one carrier gas passes through the first EPC, the first EPC inlet (10g), the non-methane enrichment trap outlet (10f), the non-methane enrichment trap, the non-methane enrichment trap inlet (10b), the empty column inlet (10c), the empty column, and reaches the FID detector; the other carrier gas passes through the second EPC, the second EPC inlet (6e), the PQ column inlet (6d), the PQ column, the PQ column outlet (10d), and the exhaust port (10e) for exhaust. 10. An analysis method for a direct measurement device for methane and non-methane total hydrocarbons in ambient air as claimed in claim 8, characterized in that: the carrier gas is high-purity helium with a purity of 99.999%, and the sample gas is the ambient air to be measured.