CN115356184A - Thermal diffusion tube device and method for removing volatile substances in motor vehicle exhaust - Google Patents

Abstract

The invention relates to a thermal diffusion tube device and a method for removing volatile substances in tail gas of a motor vehicle, which can thermally dilute the tail gas and remove the volatile substances in the tail gas sampling process. The sample gas that gets into high temperature diluting device through the sampling pipe mixes with the sheath gas after heating in the high temperature diluting pipe, later through the pipe wall heating, reaches and predetermines the temperature and have better temperature distribution. And the sample gas after high-temperature dilution leaves the high-temperature dilution device and enters the volatile substance removing device. Volatile substances are evaporated at a set high temperature and are adsorbed by the active carbon in the adsorption device, so that the effect of removing the volatile substances is achieved. And finally, the tail gas from which the volatile substances are removed enters a dilution cooling device, and the dilution ratio of the cooling dilution part is adjusted according to the temperature of the inlet sample gas, so that the temperature of the diluted tail gas meets the temperature requirement of the rear-end particle number concentration measuring device.

Description

Thermal diffusion tube device and method for removing volatile substances in motor vehicle exhaust

technical field

The invention relates to the technical field of tail gas removal, in particular to a thermal diffusion tube device and method for removing volatile substances in motor vehicle tail gas.

Background technique

In recent years, with the rapid improvement of the country's economic level, the number of motor vehicles has increased year by year. The emission of motor vehicle exhaust has a great impact on air quality, and the ultrafine particles contained in the exhaust have a great impact on human health. Studies have shown that the smaller the particle size, the greater the harm to the human body. The accumulation of particulate matter will also reduce the visibility of the air and seriously interfere with the production and life of human society. Therefore, it is necessary to carry out accurate detection of the number concentration of ultrafine particulate matter in motor vehicle exhaust, so as to take effective measures to reduce the content of ultrafine particulate matter in the air. Since the ultrafine particulate matter emitted by motor vehicle exhaust contains volatile and semi-volatile substances, this has a great impact on the measurement of non-volatile particulate matter in the exhaust gas. Volatile and semi-volatile substances can be condensed and nucleated or attached to the On non-volatile particulate matter, in order to change the particle size distribution and number concentration measurement of non-volatile particulate matter. Therefore, when measuring the particle number concentration of motor vehicle exhaust, the volatile and semi-volatile substances in the exhaust should be removed first to reduce their influence on the measurement results.

At present, the devices used in the world to remove volatile substances from motor vehicle exhaust are mainly divided into three categories: the first category is the method of evaporating tubes combined with back-end dilution. The volatile substances removed by this method are extremely limited, and most of them still evaporate in the end. Reactive substances will attach or re-nucleate again, and it is difficult to miniaturize due to the large volume of the evaporation tube required; the second type is the heating tube combined with the adsorption tube, the removal efficiency of this method is better than that of the evaporation tube plus rear-end dilution method, but the total volume of related equipment for commercialization and laboratory use is about one meter at present, and no relevant miniaturization work has been carried out; the heat diffusion tube mentioned in the existing patent CN113504160A does not have a length of one meter for the heat diffusion tube The volume is optimized, and the structure of the heating tube is too complicated to meet the needs of portability. The design of adding a flow-by-flow fan to the heating tube mentioned in this patent is too complicated and unreliable. The high-temperature environment will affect the work of the flow-by-flow fan and the cooling speed of the heating tube will not be greatly improved. The valve when the two heating tubes are heated alternately also has a certain degree of influence on the airtightness of the device; the third type is the catalytic cracking method, which has the highest removal efficiency for volatile substances, but due to the complex structure and relatively small contact surface with the gas If there are too many, the non-volatile particulate matter to be measured will have a large loss, which will affect the subsequent measurement of the particle number concentration. In summary, the miniaturized heating tube and adsorption tube solution can not only ensure the portability of the equipment, but also meet the removal efficiency of volatile substances in motor vehicles. Based on the above advantages and disadvantages of the device and method for removing volatile substances from motor vehicle exhaust, the present invention proposes a thermal diffusion tube that can be thermally diluted, miniaturized, and can ensure volatile substance removal efficiency and low particle loss efficiency.

Contents of the invention

The object of the present invention is to provide a thermal diffusion tube device and a removal method for removing volatile substances in motor vehicle exhaust, which are used for the removal of volatile and semi-volatile substances in the measurement of the concentration of particulate matter in motor vehicle exhaust, aiming to eliminate the Volatile or semi-volatile substances in the exhaust gas, so as to measure the real particle number concentration of motor vehicle exhaust.

To achieve the above object, the technical implementation scheme of the present invention is:

A thermal diffusion pipe device for removing volatile substances in motor vehicle exhaust, comprising a high-temperature dilution device, an adsorption device connected by a flange behind the high-temperature dilution device, and a cooling dilution device connected after the adsorption device with the same structure as the high-temperature dilution device device;

The high temperature dilution device comprises a metal tube with a certain wall thickness, a circulating sheath gas channel located in the tube wall, a circulating sheath gas elbow with a certain length at the outlet end of the adsorption tube, a sheath gas outlet welded on the tube wall and The inlet, the sheath gas sample gas mixing outlet located in the tube wall, the metal shell embedded with the heating coil surrounding the outer wall of the metal tube, and the high temperature resistant sealing gaskets at both ends of the metal tube;

The adsorption device includes a stainless steel tube, a steel mesh coaxial with the stainless steel tube, activated carbon for adsorbing volatile substances filled between the stainless steel tube and the coaxial steel mesh, gaskets at both ends of the stainless steel tube for sealing, and inner threaded metal cover;

The cooling and dilution device includes a metal tube with a certain wall thickness, a circulating sheath gas channel located in the tube wall, a sheath gas outlet and inlet welded on the tube wall, and high temperature resistant sealing gaskets at both ends of the cylinder;

The heating device of the high-temperature dilution device wraps the metal tube to heat the sheath gas and the sample gas;

The wall of the cooling dilution tube forms a cooling circuit to dilute and cool the sample gas to meet the requirements of the back-end detection instrument;

The high-temperature dilution device adopts a circulating loop sheath gas channel, which can fully heat the sheath gas;

The heated high-temperature sheath gas is mixed with the sample gas. The diluent gas is mixed with a cylindrical baffle at the mixing place. After buffering, it is mixed with the sample gas to avoid turbulence caused by direct mixing and loss of particulate matter. The high-temperature sheath gas dilutes and initially heats the sample gas, and after mixing evenly, it conducts secondary heating in the sample gas channel;

The circulating sheath gas loop in the high-temperature dilution tube extends to the adsorption tube, so that the front end of the adsorption tube maintains a certain temperature, and ensures that the temperature of the aerosol drops from the heated dilution tube to the adsorption tube steadily;

The cylindrical parts of the heating dilution device and the cooling dilution device are made of stainless steel, and the gaskets used for end face sealing in the high temperature dilution device are made of graphite;

The inner wall of the cylindrical adsorption device adopts a steel mesh with a certain porosity, so that the gaseous volatile substances are adsorbed by the activated carbon through the steel mesh;

The outlet of the adsorption tube and the outlet of the cooling and dilution device adopt a metal ferrule tee, which is used to place a thermocouple or a PT100 temperature measuring device;

The present invention also relates to a method of the above-mentioned tail gas pretreatment device, the method comprising the following steps:

(1) Motor vehicle exhaust gas is collected into the high-temperature dilution device through the sampling pipe, and mixed with the heated high-temperature sheath gas in the high-temperature dilution device at the inlet;

(2) After mixing with the high-temperature sheath gas, the gas at the end of the sampling tube is split according to the set flow rate of the sheath gas and the sample gas, and the part that splits into the cylindrical adsorption device is the diluted sample gas;

(3) The diluted sample gas diverted into the sheath gas circuit at the end of the high-temperature dilution device passes through the cooling copper pipe, filter, water eliminator, filter, air pump, and filter, and then enters the sampling pipe again to mix with the sampling exhaust gas;

(4) The high-temperature dilution device and the adsorption device are connected and sealed by flanges. The sheath gas circuit of the high-temperature dilution tube extends to the adsorption material layer of the adsorption tube by bending copper tubes, so that the sample gas at the outlet of the high-temperature dilution tube is adsorbed Slowly lower the temperature in the tube to prevent the evaporated volatile or semi-volatile substances from condensing and re-nucleating or adsorbing on the surface of the particles;

(5) The diluted sample gas passes through the adsorption device. Due to high temperature heating, the volatile or semi-volatile substances evaporate into a gaseous state, diffuse to the tube wall of the adsorption device and are adsorbed by activated carbon;

(6) After the diluted sample gas passes through the adsorption device, the removal efficiency of volatile or semi-volatile substances reaches more than 99%, and then enters the cooling and dilution device to cool the diluted sample gas to the measurement temperature required by the back-end detection device.

In summary, the present invention provides an exhaust gas pre-treatment device capable of performing high-temperature in-situ dilution sampling of exhaust gas and removing volatile and semi-volatile substances in exhaust gas. The device and method can pretreat components of motor vehicle exhaust gas , so that the measurement results of the number concentration of motor vehicle exhaust particles are more accurate. The device adopts a high-temperature dilution module, which eliminates the thermal dilution part of the traditional volatile substance removal device. After high-temperature dilution, the sample gas is passed into the adsorption tube containing activated carbon to absorb the evaporated volatile and semi-volatile substances. Into the cooling dilution tube to adjust the gas temperature. The device satisfies the pre-conditioning function of the exhaust gas particle number concentration measurement of the motor vehicle exhaust, improves portability, and satisfies the real-time measurement of the motor vehicle exhaust.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Compared with most of the thermal diffusion tubes in previous papers or commercial production, the structure of the present invention is significantly reduced, and the mainstream 500mm desorption tube and 500mm adsorption tube are shortened to 140mm and 200mm respectively, so that it has better Portability;

(2) The mainstream thermal diffusion tube does not have the function of diluting the sample gas. This invention combines the dilution function with the removal of volatile substances and semi-volatile substances of the thermal diffusion tube, and innovatively uses high-temperature sheath gas to dilute the sample gas at high temperature heating;

(3) In the present invention, the high-temperature dilution device has a better temperature distribution, and can stably maintain a sufficient effective heating distance in a shorter residence time, so that volatile substances and semi-volatile substances can be fully evaporated;

(4) The sheath gas circulation loop of the high-temperature dilution device in the present invention is connected by a curved copper tube, and stretches into the adsorption tube to dissipate heat, so as to ensure the steady decline of the temperature at the junction of the heating tube and the adsorption tube, reduce the thermophoretic loss of particulate matter, and prevent Volatile or semi-volatile substances undergo heavy nuclei due to a sudden drop in temperature;

(5) A cooling device can be added to the sheath gas circuit of the high-temperature dilution device in the present invention. By cooling the cooling copper tube, the requirement for rapidly reducing the temperature of the high-temperature dilution device can be achieved, and the time resolution of the instrument can be improved.

Description of drawings

Fig. 1 is a schematic structural view of the device for removing volatile substances in the present invention.

in:

11. Particle sample gas inlet, 12. Front cover of high temperature dilution device, 13. Particle inlet sealing gasket, 14. Metal tube, 15. Sheath gas circuit extension tube, 16. Particle outlet, 17. Sheath gas inlet, 18. Sheath Gas outlet, 19. Sheath gas circuit, 111. Main air path of heating dilution tube, 21. Adsorption tube inlet, 22. Front cover of adsorption tube device, 23. Main body of adsorption tube, 24. Stainless steel mesh, 25. Back cover of adsorption tube device , 26. The outlet of the adsorption tube, 27. The main gas path of the adsorption tube, 31. The inlet of the cooling and diluting device, 32. The front cover of the cooling and diluting device, 33. The inlet sealing gasket, 34. The main body of the cooling and diluting device, 35. The outlet sealing gasket , 36, cooling and dilution device outlet, 37, cooling and dilution device sheath gas inlet, 38, cooling and dilution device sheath gas outlet, 39, cooling sheath gas circuit;

Detailed ways

A kind of thermal diffusion pipe device for removing volatile substances in motor vehicle exhaust as shown in Figure 1 comprises a high-temperature dilution device with a dilution function, an adsorption device (adsorption tube) connected at the outlet of the high-temperature dilution device with a flange and a hoop ) and a cooling dilution device with the same structure as the high-temperature dilution device connected behind the adsorption device; wherein the high-temperature dilution device is heated at a high temperature through a heating jacket. Except for volatile carbon particles, motor vehicle exhaust still contains a certain proportion of volatile and semi-volatile substances. These substances will attach to non-volatile particles or condense and nucleate themselves after the temperature of the exhaust gas is lowered, which greatly affects the engine. Accurate measurement of particle number concentration in motor vehicle exhaust. Therefore, the present invention adopts the method of high temperature dilution heating combined with activated carbon adsorption to adsorb and remove the volatile and semi-volatile substances in the tail gas.

The high temperature dilution device comprises a metal tube 14 with a certain wall thickness, a high temperature dilution device front cover 12, a circulating sheath gas circuit 19 located in the metal tube wall, a sheath gas inlet 17 located on the high temperature dilution device front cover 12, The sheath gas outlet 18 and the sample gas inlet 11, the metal jacket with a built-in heating coil surrounding the outside of the cylinder, the high temperature resistant sealing gasket 13 between the front cover 12 of the high temperature dilution device and the metal pipe 14;

The gas path is sealed between the front cover 12 of the high temperature dilution device and the metal pipe 14 through a high temperature resistant sealing gasket 13, and the material of the high temperature resistant sealing gasket 13 is graphite. After sealing, screw in two No. 3 screws from the side of the front cover 12 of the high-temperature dilution device to fix it.

The circulating sheath gas circuit 19 is an air path formed by punching holes in the wall thickness of the metal pipe 14. By drilling 4 through holes in the metal pipe wall, grooves are dug at both ends of the metal pipe to connect the through holes. Form the circulating sheath gas circuit 19 in a manner. The clean air enters the circulating sheath air circuit 19 through the sheath gas inlet 17, circulates in the four-way through-hole air circuit and is heated by the heated metal tube 14, and finally enters the high temperature through the sheath gas outlet 18 on the front cover 12 of the high temperature dilution device. In the main gas path 111 of the metal pipe 14 of the dilution device, and mix with the tail gas sample gas drawn in at the sample gas inlet 11;

The heating device of the high-temperature dilution device wraps the metal tube to heat the sheath gas and the sample gas;

The circulating sheath gas circuit 19 is adopted in the high-temperature dilution device, which can fully heat the sheath gas;

The sheath gas outlet 18 of the high-temperature dilution device is perpendicular to the sample gas inlet 11, so that the sample gas and the sheath gas are fully mixed, thereby achieving the purpose of high-temperature dilution and ensuring the uniformity of dilution;

In the high-temperature dilution device, the ratio of the sheath gas to the sample gas should be moderate, and the flow rate of the sample gas should be determined on the premise that the sheath gas can be mixed with the sample gas at a set temperature. Time is defined. Therefore, to determine the sample gas sheath gas flow rate, first determine the appropriate total flow rate, and then determine the ratio of the total flow rate of the sample gas and sheath gas mixture to the sample gas, that is, the dilution ratio. The dilution ratio is set at 5; the calculation is based on 1L/MIN total flow , when the dilution ratio is 5, the sample gas intake is 0.2L/MIN, and the sheath gas intake is 0.8L/MIN.

The high-temperature dilution device and the adsorption tube are connected by a sheath gas circulation loop 19 through a curved copper tube, which extends into the adsorption tube to dissipate heat, so as to ensure a steady drop in temperature at the junction between the heating tube and the adsorption tube, and reduce the thermophoretic loss of particulate matter , to prevent renucleation of volatile or semi-volatile substances due to a sudden drop in temperature;

The sheath gas flowing back to the high-temperature dilution device from the bent copper tube in the adsorption tube is heated again and mixed with the sample gas. The dilution gas is mixed with a cylindrical baffle at the mixing place, and mixed with the sample gas after buffering to avoid turbulence caused by direct mixing and loss of particulate matter. . The high-temperature sheath gas dilutes and initially heats the sample gas, and after mixing evenly, it conducts secondary heating in the sample gas channel;

The curved copper tube extending into the adsorption tube is connected with the circulating sheath gas circuit 19 in the high-temperature dilution tube by means of a metal ferrule, the outlet of the circulating sheath gas circuit is screwed into the metal ferrule, and the entrance of the curved copper tube is made of a metal ferrule. Ferrule seal connection. The outlet of the curved copper pipe is connected to another part of the passage in the circulating sheath gas circuit, and the connection method is the same as that of the entrance of the curved copper pipe.

The end of the metal tube 14 of the high-temperature dilution tube is connected to the flange, and the two parts are sealed with a graphite gasket, which is fixed by screwing two No. 3 screws on the side of the flange;

The left side of the main body 23 of the adsorption tube is connected to the flange, and a graphite gasket is used to seal the two parts, and two No. 3 screws are screwed into the side of the flange to fix it;

The flange connected to the end of the metal pipe 14 and the flange connected to the inlet side of the adsorption tube are sealed with a graphite gasket between the two flanges. Then clamp the two flanges with circular clamps and fix them.

The main gas path of the high-temperature dilution tube forms a passage with the flange and the adsorption tube. After the sheath gas and sample gas heated by the circulating gas path are mixed at the inlet of the high-temperature dilution tube, they are further heated through the main gas path of the high-temperature dilution tube and leave the high-temperature dilution tube. The tube enters the main gas path 27 of the adsorption tube.

The adsorption device includes a metal cylindrical shell 23, a steel mesh 24 coaxial with the metal cylindrical shell, activated carbon for adsorbing volatile substances filled between the metal cylindrical shell 23 and the coaxial steel mesh 24, and the metal cylindrical shell 23. Gaskets and internal threaded metal end caps for sealing;

The activated carbon in the adsorption tube is replaced by removing the end covers 22, 25 at both ends of the adsorption tube;

The coaxial steel mesh 24 in the adsorption tube ensures a relatively high opening ratio under the condition that the activated carbon does not leak, so as to increase the airflow diffusion adsorption area;

The inner wall of the adsorption device adopts a steel mesh 24 with a certain porosity, so that gaseous volatile substances are adsorbed by activated carbon through the steel mesh 24;

The two ends of the steel mesh 24 in the adsorption tube are fixed by metal ferrules at the inlets and outlets 21 and 26 of the adsorption tube;

The airflow heated by the high-temperature dilution tube enters the adsorption tube and the temperature gradually drops. Because there is a temperature drop gradient with the adsorption tube wall, there will be a thermophoretic force from the center of the adsorption tube to the adsorption tube wall. Under the action of motion force, the volatile particulate matter in the gaseous sample gas stream that has been heated at high temperature first diffuses into the activated carbon layer in the adsorption tube and is adsorbed. Part of the non-volatile particulate matter to be measured will also enter the activated carbon layer and be lost. The remaining non-volatile particulate matter to be measured gradually cools down and leaves the adsorption tube.

The cooling and dilution device comprises a metal tube 34 with a certain wall thickness, a cooling and dilution device front cover 32, a circulating sheath gas circuit 39 positioned in the tube wall, a sheath gas inlet 37 positioned on the cooling and dilution device front cover 32, and a sample The gas inlet 31, the high temperature resistant sealing gasket 33 between the front cover 32 of the cooling and dilution device and the metal pipe 34, the rear cover 40 of the cooling and dilution device, the sheath gas outlet 38 and the sample gas outlet 36 located on the rear cover 40 of the cooling and dilution device, The back cover 40 of the cooling and dilution device and the metal pipe 34 are sealed with a high temperature resistant sealing gasket 35;

The air path is sealed between the front cover 32 of the cooling and dilution device and the metal pipe 34 through a high temperature resistant sealing gasket 33, and the material of the high temperature resistant sealing gasket 33 is graphite. After sealing, two No. 3 screws are screwed in from the side of the front cover 32 of the high-temperature dilution device to fix it.

Two No. 3 screws are screwed into the side of the back cover 40 of the cooling and dilution device to fix the back cover of the cooling and dilution device, the high-temperature-resistant sealing gasket 35 and the metal pipe 34 together;

The circulating sheath air circuit 39 is an air path formed by punching holes in the wall thickness of the metal pipe 34. By drilling 4 through holes in the metal pipe wall, grooves are dug at both ends of the metal pipe to connect the through holes. Form the circulating sheath gas circuit 39 in a manner. Clean air enters the circulating sheath gas circuit 39 through the sheath gas inlet 37, circulates in the 4-way through-hole air circuit, and finally leaves the cooling and dilution device through the sheath gas outlet 38 on the back cover 40 of the cooling and dilution device;

The sheath gas outlet 38 of the cooling and dilution device is perpendicular to the sample gas inlet 31, so that the sample gas and the sheath gas are fully mixed, thereby achieving the purpose of cooling and dilution, and ensuring the uniformity of dilution;

In the cooling and dilution device, the sample gas is diluted by the sheath gas in the same manner as the flow rate of the sheath gas drawn in and the sheath gas discharged. For example, the sample gas entering the cooling and dilution device through the sample gas inlet 31 of the cooling and dilution device is 1L/MIN, and the sheath gas entering the cooling and dilution device through the sheath gas inlet 37 is 4L/MIN. Mixing, the final 4L/MIN mixed gas leaves the cooling and dilution device through the sheath gas outlet 38, and the 1L/MIN mixed gas leaves the cooling and dilution device through the sample gas outlet 36 of the cooling and dilution device and enters the back-end particle counting device for measurement. At this time, the dilution ratio is the flow rate of the sheath gas and the flow rate of the sample gas to the flow rate of the sample gas, and the dilution ratio is 5;

The metal pipes 14, 34 of the heating dilution device and the cooling dilution device are all made of stainless steel;

The gaskets 13, 33, and 35 used for high-temperature sealing of the end faces in the high-temperature dilution device are made of graphite;

The inlet 11 of the high-temperature dilution device, the outlet 26 of the adsorption tube, and the outlet 36 of the cooling dilution device adopt a metal ferrule tee for placing a thermocouple or a PT100 temperature measuring device;

The present invention also relates to a method of the above-mentioned tail gas pretreatment device, the method comprising the following steps:

(1) Motor vehicle exhaust gas is collected into the high-temperature dilution device through the sampling pipe, and mixed with the heated high-temperature sheath gas in the high-temperature dilution device at the inlet;

(2) The total flow after the motor vehicle exhaust gas is mixed with the high-temperature sheath gas continues to be heated in the main gas path 111 of the high-temperature dilution pipe, and the volatile substances and semi-volatile substances contained in the heated high-temperature total flow are volatilized at high temperature , and enter the adsorption tube with the total flow;

(3) After the total flow enters the adsorption tube, volatile substances and semi-volatile substances diffuse to the wall of the adsorption tube and are absorbed by the activated carbon filled in the adsorption tube. The removal efficiency of volatile or semi-volatile substances reaches more than 99%, and the remaining Non-volatile carbon particles leave the adsorption tube;

(4) The sheath gas circulation circuit of the high-temperature dilution device is connected by a bent copper tube, and extends into the adsorption tube for heat dissipation, so as to ensure a stable temperature drop at the connection between the heating tube and the adsorption tube;

(5) After the total flow leaves the adsorption tube, it is mixed with the sheath gas in the cooling and dilution device to cool and dilute the total flow, and cool the total flow to the measurement temperature required by the back-end detection device;

(6) Part of the total flow at the end of the cooling and dilution device leaves the cooling and dilution device through the sheath gas outlet 38 of the cooling and dilution device, and passes through the cooling coil, filter, water eliminator, filter, air pump, and after the filter, it passes through the inlet of the cooling and dilution device 37 Entering the cooling dilution unit to mix with the total flow at the outlet of the adsorption tube.

In summary, the present invention provides an exhaust gas pre-treatment device capable of performing high-temperature in-situ dilution sampling of exhaust gas and removing volatile and semi-volatile substances in exhaust gas. The device and method can pretreat components of motor vehicle exhaust gas , so that the measurement results of the number concentration of motor vehicle exhaust particles are more accurate. The device adopts a high-temperature dilution module, which eliminates the thermal dilution part of the traditional volatile substance removal device. After high-temperature dilution, the sample gas is passed into the adsorption tube containing activated carbon to absorb the evaporated volatile and semi-volatile substances. Into the cooling dilution tube to adjust the gas temperature. The device satisfies the pre-conditioning function of the exhaust gas particle number concentration measurement of the motor vehicle exhaust, improves portability, and satisfies the real-time measurement of the motor vehicle exhaust.

The above-mentioned embodiments are only descriptions of preferred implementations of the present invention, and are not intended to limit the scope of the present invention. All such modifications and improvements should fall within the scope of protection defined by the claims of the present invention.

Claims (10)

1. A thermal diffusion tube device for removing volatile substances in motor vehicle exhaust, comprising a high-temperature dilution device, an adsorption device and a cooling and dilution device, characterized in that: the adsorption device is connected to the high-temperature dilution device by a flange, and the cooling and dilution device is connected after the adsorption device; The high-temperature dilution device includes a metal pipe one, a circulating sheath gas passage located in the wall, and a circulating sheath gas elbow at the outlet end of the metal pipe one, and also includes a sheath gas outlet and an inlet welded on the pipe wall, and a sheath gas outlet located in the pipe wall. The sheath gas sample gas mixing outlet, the metal shell embedded with the heating coil surrounding the outer wall of the metal tube, and the high temperature resistant sealing gaskets at both ends of the metal tube; The adsorption device includes a stainless steel tube, a steel mesh coaxial with the stainless steel tube, activated carbon for adsorbing volatile substances filled between the stainless steel tube and the coaxial steel mesh, gaskets at both ends of the stainless steel tube for sealing, and inner threaded metal cover; The cooling and dilution device includes a metal tube two, a circulating sheath gas channel located in the tube wall, a sheath gas outlet and an inlet welded on the tube wall, and high-temperature resistant sealing gaskets at both ends of the metal tube two. 2. A kind of thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, characterized in that, the circulating sheath gas passage is the air gas formed by punching holes in the metal tube-tube wall. A circulating sheath gas circuit is formed by drilling four through holes in the metal pipe wall and digging grooves at both ends of the metal pipe to connect the through holes. 3. A thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, wherein the sheath gas outlet of the high-temperature dilution device is perpendicular to the sample gas inlet. 4. A kind of thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, characterized in that, after the sheath gas flowing back to the high-temperature dilution device from the curved copper tube in the adsorption tube is heated again, it is mixed with the sample gas Mixing, a cylindrical baffle is used for the sheath gas at the mixing place. 5. A kind of thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, characterized in that, the curved copper tube stretching into the adsorption tube and the circulating sheath gas circuit in the high-temperature dilution tube adopt metal The outlet of the circulating sheath gas circuit is screwed into the metal ferrule with an internal thread, and the entrance of the curved copper pipe is sealed with a metal ferrule. 6. A kind of thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, characterized in that, one end of the metal tube is connected with the flange, and sealed with a graphite gasket. Screw in two No. 3 screws on one side of the blue plate to fix it; The left side of the main body of the adsorption tube is connected to the second flange, and is sealed with a graphite gasket, and two No. 3 screws are screwed into the side of the second flange to fix it; The flange connected to one end of the metal pipe and the flange connected to the inlet side of the adsorption tube are sealed with a graphite gasket in the middle of the two flanges, and then the two flanges are clamped and fixed with a circular clamp. 7. A heat diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, wherein the metal tubes of the heating and dilution device and the cooling and dilution device are all made of stainless steel, and the high temperature dilution device Gaskets for face seals are made of graphite. 8. A heat diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, wherein the two ends of the steel mesh are fixed by the inlet and outlet ferrules of the adsorption tube. 9. A kind of thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to claim 1, characterized in that, the outlet of the adsorption tube and the outlet of the cooling and dilution device adopt a metal ferrule tee for placing thermocouples or PT100 temperature measuring device. 10. A method for removing volatile substances in motor vehicle exhaust, using the thermal diffusion tube device for removing volatile substances in motor vehicle exhaust according to any one of claims 1 to 9, characterized in that: the method comprises the following steps : (1) Motor vehicle exhaust gas is collected into the high-temperature dilution device through the sampling pipe, and mixed with the heated high-temperature sheath gas in the high-temperature dilution device at the inlet; (2) After mixing with the high-temperature sheath gas, the gas at the end of the sampling tube is split according to the set flow rate of the sheath gas and the sample gas, and the part that splits into the adsorption device is the diluted sample gas; (3) The diluted sample gas diverted into the sheath gas circuit at the end of the high-temperature dilution device passes through the cooling copper pipe, filter, water eliminator, filter, air pump, and filter, and then enters the sampling pipe again to mix with the sampling exhaust gas; (4) The high-temperature dilution device and the adsorption device are connected and sealed by flanges. The sheath gas circuit of the high-temperature dilution tube extends to the adsorption material layer of the adsorption tube by bending copper tubes, so that the sample gas at the outlet of the high-temperature dilution tube is adsorbed Slowly lower the temperature in the tube to prevent the evaporated volatile or semi-volatile substances from condensing here to re-nucleate or adsorb on the surface of the particles; (5) The diluted sample gas passes through the adsorption device. Due to high temperature heating, the volatile or semi-volatile substances evaporate into a gaseous state, diffuse to the tube wall of the adsorption device and are adsorbed by activated carbon; (6) After the diluted sample gas passes through the adsorption device, it enters the cooling and dilution device to cool the diluted sample gas to the measurement temperature required by the back-end detection device.

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