CN105910965A - Humidity adjusting device and method of aerosol collection sample feeding gas flow and measurement instrument - Google Patents

Abstract

A humidity regulating device for aerosol collection and sample air flow, comprising: a drying unit (3), which includes at least two drying tubes, each drying tube includes: an inner tube for passing the sample air flow, one-way through The steam film covers the outer wall of the inner tube to allow the water vapor in the sample gas flow to pass through. The outer tube is located outside the inner tube and the one-way gas-permeable membrane, and forms a space with the inner tube. The space is filled with Desiccant; a control system (4), used for controlling the flow of the sample gas flow into at least one other drying tube when the desiccant in a certain drying tube is deactivated. By setting up a water vapor permeable membrane, the device uses the principle of water vapor pressure difference to remove excess water vapor, thereby avoiding the loss of volatile substances in the particles caused by heating, and ensuring the accuracy and reliability of the subsequent physical, chemical and optical properties of the particles. .

Description

Humidity adjustment device and method for aerosol collection and sampling airflow, and measuring instrument

technical field

The present invention relates to a measurement method and device, and further relates to a humidity adjustment device for aerosol collection and sampling airflow, an adjustment method using the humidity adjustment device, and an atmospheric particle measuring instrument including the humidity adjustment device.

Background technique

Atmospheric particulate matter refers to solid or liquid particulate matter uniformly dispersed in the air. According to its particle size, it can be divided into total suspended particulate matter (TSP) and inhalable particulate matter (PM ₁₀ ). Among them, the inhalable particulate matter can be subdivided into fine particulate matter (PM _2.5 ) and coarse particles. Atmospheric particles directly affect the Earth's atmospheric radiation balance by scattering and absorbing radiation, and indirectly affect the Earth's atmospheric radiation balance by affecting the optical properties of clouds and the cloud's lifetime. Epidemiological and toxicological studies have shown that the incidence of diseases of the respiratory system and cardiovascular system, the number of hospitalizations, and the mortality rate of the population are all related to changes in the concentration of particulate matter in the atmosphere. In addition, atmospheric particulate matter is also the main reason for the frequent occurrence of haze pollution events in the central and eastern parts of my country. In general, haze refers to the pollutants (gas and particulate matter such as CO, SO ₂ , NO _x , NH ₃ , VOCs (volatile organic compounds), PM) emitted by various sources pass through the A series of physical and chemical processes that form fine particles and interact with water vapor to cause atmospheric extinction. The essence of haze is that the concentration of PM _2.5 in the atmosphere exceeds the standard. The scattering of radiation by aerosols is one of the important optical properties of aerosols. It is the main part of the radiative forcing of aerosols in the tropospheric atmosphere and the main reason for reducing the visibility of the ambient atmosphere. Aerosol optical properties are determined by the mass concentration, chemical composition, particle size, shape and mixing state of the aerosol. Therefore, in order to deeply study the internal relationship between aerosol and haze pollution, online, continuous and accurate monitoring of the above physical and chemical properties of aerosol is required. However, the above properties of aerosol are all related to the humidity of the atmosphere. Air humidity has a great influence on the scattering coefficient of aerosols. As the humidity increases, the hydrophilic chemical components (such as sulfates, nitrates, and some organic substances) in aerosols (especially fine particles) will absorb moisture. grow up, thereby increasing the scattering ability of particles.

The above-mentioned effects of humidity on the optical properties of aerosols show that before observing the physical and chemical properties of aerosols, such as mass concentration and chemical composition, and their optical properties, such as scattering coefficients, it is necessary to reduce the air humidity of the air inlet pipe of the online instrument to Obtain the above properties for dry aerosol particles. At present, the methods for air drying of the intake pipe on the market are mainly divided into three categories. The first type is to heat the intake pipe at a constant temperature, such as the vast majority of particle mass concentration monitors (such as the RP series instruments based on the oscillating balance method and the β-ray method of Thermoelectric Environmental Instruments of the United States) and particle scattering coefficient monitors ( For example, the three-band turbidimeter of TSI Company of the United States) adopts this method; the second type uses a drying tube filled with a desiccant, such as a particle chemical composition monitor (such as a time-of-flight mass spectrometer of Aerodyne Company of the United States) and a particle number concentration particle. Spectrometers (such as the scanning electric mobility particle size spectrometer of TSI Company of the United States) all adopt this method; the third method uses a one-way permeable membrane (such as Nafion membrane) to make the moisture in the intake pipe diffuse from the inside of the pipe to the outside of the pipe. Thereby reducing the humidity of the intake pipe, such as the filter membrane dynamic measurement system (FDMS) applied to the RP series instruments by Thermoelectric Environmental Instruments of the United States. Figure 1 shows the workflow of the filter dynamic measurement system. The solid line arrows show the flow direction of the sample gas, while the dotted line arrows show the flow direction of the dry air. The dry air and the sample gas flow in the opposite direction in the drying tube. Through the exchange of Nafion membrane in the drying tube, the dry air will Moisture is carried away, thereby reducing the relative humidity in the sample gas.

In addition, domestic researchers have also devoted themselves to the dehumidification research of particle sample collection. Zeng Limin and Liu Qiaoling of Peking University set up a condensing tube outside the sampling gas transmission tube, using water as a condensing agent, and at 5-15°C, part of the water vapor in the gas condenses on the tube wall and then slides down and drains out. Yan Peng from the Academy of Meteorological Sciences of the China Meteorological Administration used the method of water vapor addition combined with heating control to adjust the humidity of the sample gas flow. Based on the selective permeation characteristics of the water vapor permeation tube, the humidity of the sample gas flow in the permeation tube was controlled by adjusting the water temperature.

However, the dehumidification method of sample collection in the prior art has the following defects:

(1) The constant temperature heating process only increases the temperature, correspondingly reduces the relative humidity of the air, but does not remove the excess moisture of the sample gas. At the same time, part of the semi-volatile substances (such as semi-volatile organic compounds and nitrates, etc.) are volatilized and lost due to the increase of temperature, and the measurement of particulate matter containing high concentrations of these components is even more inaccurate;

(2) Although the drying tube method can effectively remove the moisture in the sample gas, when the air humidity is high, the desiccant will quickly deactivate after absorbing excess moisture, and the desiccant in the drying tube needs to be replaced frequently to maintain dehumidification Efficiency, not only requires a lot of manpower and material resources, but also affects the online observation of the instrument;

(3) The one-way osmotic membrane method is the method with the highest efficiency in removing moisture from the sample gas among the three types of methods. However, in case of polluted weather, high-concentration atmospheric particles are easy to adhere to the surface of the osmotic membrane, thereby reducing the dehumidification efficiency of the osmotic membrane and even causing its dehumidification. Inactivation;

(4) For the method of setting a condensation pipe outside the sampling gas transmission pipe, on the one hand, this method cannot deal with the excess water vapor in the air below 5°C, and the condensation and dehumidification effect is not ideal when the air temperature is 5-15°C. At the same time, due to the presence of condensed water droplets and water films on the air pipe wall in this method, these water droplets and water films will capture air particles, and the condensed and discharged water will take away these captured particles, resulting in low monitoring results. .

Contents of the invention

(1) Technical problems to be solved

In view of the defects in the above-mentioned prior art, in order to reduce the interference of air humidity on the physical, chemical and optical properties of atmospheric particles, the present invention provides a device and method for adjusting the humidity of aerosol collection and sampling airflow, and includes Atmospheric particulate matter measuring instrument of the regulating device.

(2) Technical solution

According to one aspect of the present invention, there is provided a humidity regulating device for aerosol collection and sampling airflow, comprising:

Drying unit, which includes at least two drying tubes, each drying tube includes: an inner tube for the passage of the sample gas flow, and a one-way vapor-permeable film covering the outer wall of the inner tube for the water vapor in the sample gas flow to pass through , the outer tube, located outside the inner tube and the one-way gas-permeable membrane, forms a space with the inner tube, and the space is filled with desiccant; the control system is used for when the desiccant in a certain drying tube is deactivated , controlling the flow of the sample gas flow into at least one other drying tube.

Preferably, the humidity adjustment device further includes an activation heater for heating the deactivated desiccant.

Preferably, the activation heater includes a silicone rubber heating plate, an insulation layer and an insulation tube, the silicone rubber heating plate is covered on the outer wall of the outer tube, and the silicone rubber heating plate is provided with an insulation layer and an insulation tube in sequence.

Preferably, the humidity adjustment device further includes a dry air generator and an air compression pump, which communicate with the space and are used to supply dry air to the space.

Preferably, the dry air generator and the air compression pump include a dry air generator and an air compression pump, the dry air generator is used to generate dry air, and the dry air is pumped into the space through the air compression pump.

Preferably, the control system is also used to monitor the temperature and humidity of the inlet and outlet of the drying tube, and judge whether the desiccant is deactivated according to the monitored humidity difference between the inlet and the outlet, and control the activation heater to heat the inactivated desiccant.

Preferably, the control system is also used to control the dry air generator and the air compressor pump to continue supplying dry air after the desiccant is deactivated, so as to accelerate the activation of the desiccant.

Preferably, the pore size of the one-way vapor-permeable membrane is 0.3-1.6 microns, and the outer wall aperture of the inner tube is larger than the pore size of the one-way vapor-permeable membrane, and it is further preferred that the one-way vapor-permeable membrane is a polytetrafluoroethylene membrane .

According to another aspect of the present invention, there is also provided an adjustment method for any one of the above described humidity adjustment devices, which is characterized in that it includes the steps:

S1: one of the drying tubes that feeds the sample gas flow into the drying unit;

S2: The water vapor in the sample gas flow enters the space between the inner tube and the outer tube through the one-way gas-permeable membrane covered on the inner tube, and is absorbed by the desiccant;

S3: After the desiccant in the drying tube absorbs water vapor to deactivate, the control system controls the sample gas flow to flow into other drying tubes.

According to another aspect of the present invention, there is also provided an instrument for measuring atmospheric particulate matter, which is characterized in that it includes any one of the above-mentioned humidity regulating devices for aerosol collection and sampling airflow.

(3) Beneficial effects

Through the above technical scheme, the beneficial effects of the present invention are:

(1) The present invention is simple in structure, easy to install, operate, and maintain, and can be directly connected to an on-line monitoring instrument for atmospheric particulate matter (placed behind the gas sampling cutting head), and is suitable for measuring instruments for physical, chemical and optical properties of particulate matter, such as the mass concentration of particulate matter On-line monitors, particle number concentration spectrometers, and particle optical instruments such as turbidimeters. The device of the present invention has a high degree of intelligence, and can monitor the humidity of the aerosol sampling airflow in real time, thereby ensuring the long-term, stable and efficient operation of the dehumidification and temperature regulation device;

(2) Compared with reducing the relative humidity only through the heating process without changing the actual content of water vapor in the sample gas, the present invention removes excessive water vapor by setting a water vapor permeable membrane and utilizing the principle of water vapor pressure difference, thereby avoiding the water vapor caused by heating. The loss of volatile substances in the particulate matter ensures the accuracy and reliability of the subsequent measurement results of the physical, chemical and optical properties of the particulate matter;

(3) Compared with the shortcoming that the desiccant in the drying tube is easy to deactivate, the present invention uses a polytetrafluoroethylene membrane and a desiccant in combination, and sets two sets of drying tubes for dehumidification and activation functions respectively;

(4) The present invention can automatically switch the working states of two sets of drying tubes according to changes in atmospheric humidity; and by adopting polytetrafluoroethylene film, its vapor permeability is strong (moisture permeability ≥ 10000g/m ² , 24h), but the price Much cheaper and easier to install than Nafion membranes;

(5) By setting the activation program and using dry air to purge, the air particles in the polluted weather can be prevented from attaching to the permeable membrane for a long time and cause its inactivation, so as to ensure the continuous operation of the particle monitoring instrument in a high-humidity environment.

Description of drawings

Fig. 1 is a schematic diagram of a membrane dynamic measurement system (FDMS) in the prior art.

Fig. 2 is a block diagram of the system composition of the aerosol collection and sampling airflow humidity automatic adjustment device according to a specific embodiment of the present invention.

Fig. 3 is a composition block diagram of a drying unit in a specific embodiment of the present invention.

Fig. 4 is a block diagram of a dry air generator, an air compression pump and an activation heater according to a specific embodiment of the present invention.

Fig. 5 is a block diagram of a control system of a specific embodiment of the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. In the specification, the same or similar reference numerals designate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the general inventive concept of the present invention, but should not be construed as a limitation of the present invention.

According to the general inventive concept of the present invention, a humidity regulating device for aerosol collection and sampling airflow is provided, including: a drying unit, which adopts a combined dehumidification method of a permeable membrane and a desiccant, and a control system for drying in a certain drying tube When the agent is deactivated, the inlet gas flow is controlled to flow into at least one other drying tube.

Preferably, the device may also include an activation heater for heating the deactivated desiccant in the activation drying tube.

Preferably, the device may also include a dry air generator and an air compressor pump for supplying dry air, providing a pressure difference for water vapor penetration, and accelerating the activation of the deactivated desiccant.

Each unit is described in detail below:

According to a specific embodiment of the present invention, a device for adjusting the humidity of airflow for aerosol collection and sampling is provided. The composition and structure diagram of the device is shown in FIG. 2 . Including dry air generator and air compressor pump 1, activation heater 2, drying unit 3 and control system 4.

Referring to Fig. 3, the drying unit 3 may include multiple sets of drying tubes, and this embodiment consists of two sets of drying tubes A and B. Each group of drying tubes can include: constant velocity variable diameter tube 5, inner tube 6, outer tube 7, desiccant (this embodiment specifically adopts silica gel 8) and one-way vapor-permeable film (for permeating water vapor and impervious to air particles) Material, this embodiment preferably adopts polytetrafluoroethylene film 9).

The outer tube 7 of the drying tube can be any material with good sealing performance. The embodiment adopts a plexiglass tube, and the upper and lower ends of the plexiglass tube are respectively provided with external threads; the top and bottom of the plexiglass tube are respectively provided with an upper seal cover and a lower seal Cover, the inner side of the upper sealing cover and the lower sealing cover are provided with internal threads; the top and bottom between the inner and outer pipes are fastened and sealed with plastic O-rings; the upper and lower sealing covers connect the inner and outer pipes and O-rings The type ring is sealed and fixed as a whole; one side of the plexiglass tube is provided with a sample gas inlet pipe and a dry gas outlet pipe above the bottom plastic seal ring, and a sample gas outlet pipe is arranged under the top plastic seal ring on the other side. Trachea and dry gas inlet pipe.

The inner tube 6 of the drying tube is a column material with a large opening ratio, and the preferred opening ratio is greater than that of the polytetrafluoroethylene film. 1.6 microns, preferably a polytetrafluoroethylene filter membrane 9 with a high vapor permeability pore size of 0.45 microns, and the diameter of the inner tube is 4 times the diameter of the sampling tube, thereby increasing the residence time of the sample gas in the dry inner tube. The inner pipe 6 is connected with the sampling inlet pipe and the sample gas outlet pipe through the constant velocity reducing pipe 5 .

When the sample air passes through the inner tube 6, due to the water vapor pressure difference inside and outside the inner tube 6, the water vapor in the sample air diffuses to the outer tube 7 through the polytetrafluoroethylene membrane and is filled in the dry space between the inner tube 6 and the outer tube 7. agent, in this embodiment, silica gel 8 is preferably adsorbed, and this process continues to achieve the purpose of reducing the air humidity of the sample. There are 2 groups of drying tubes mentioned above. When one group of drying tubes is deactivated, the gas path is switched to another group of drying tubes to work in turn.

As shown in FIG. 4 , the activation heater 2 includes a silicone rubber heating plate 10 , an insulating layer 11 and an insulating tube 12 (specifically, a plexiglass tube in this embodiment). The silicone rubber heating plate is covered on the outer wall of the drying tube outer tube 7, and the thermal insulation tube 12 with a diameter larger than the drying tube is sleeved on the drying tube outer tube 7, and an insulating layer 11 is set in the gap between the thermal insulation tube 12 and the drying tube outer tube 7, It is preferably a thermal insulation foam material, so as to keep the overall temperature of the drying tube at about 80°C when the heater is working. At this temperature, the water in the silica gel absorbing water slowly precipitates out, so as to achieve the purpose of activating the silica gel. The above-mentioned dry air generator is fixed on the outside of the drying unit in the box. It is a stainless steel hollow cylinder 14 covering the silicone rubber heating plate 10. The top of the stainless steel hollow cylinder 14 is connected to an air compressor pump 13 to input compressed air through a gas pipeline. The stainless steel hollow cylinder stays for a period of time (1 hour) to generate dry air at a temperature of around 80°C. The bottom of the above-mentioned stainless steel hollow cylinder 14 is connected with the dry air inlet pipe of the drying pipe through a gas pipeline. Assist in the activation and recovery of silica gel that has been saturated with moisture and has become discolored.

Referring to FIG. 5 , the control system 4 includes an industrial computer 15 , a thermocouple input module 16 , a relay output module 17 and a relay 18 . The control system is used to monitor the temperature and humidity at the inlet and outlet of the drying tube, judge whether the desiccant is deactivated according to the monitored humidity difference between the inlet and the outlet, and control the activation heater to heat the deactivated desiccant. Judging whether the desiccant is deactivated can be directly observed, or through instrument detection, such as detecting the humidity difference between the inlet and outlet of the drying tube, etc., to indirectly judge whether the desiccant can continue to be used; the control system is also used to control the desiccant after deactivation. The dry air generator and the air compression pump continue to feed dry air to accelerate the activation of the desiccant.

The relay output module ADAM4068 has 8 relay channels, which are respectively connected with 4 electric ball straight-through valves TA1-2 and TB1-2, 2 electromagnetic two-way stop valves FA and FB, one three-way solenoid valve F3 and one relay 18 . Four electric ball straight-through valves are respectively installed at the joints of the drying pipe and the constant velocity splitter. Two electromagnetic two-way valves FA and FB are installed at the outlet of the drying air at the top of the drying pipe, and one three-way valve F3 controls the drying air flow into the drying pipes A and B. The supply of heated dry air is controlled by the relay 18 in time-sharing of the dry air generator, and the switch of the air circuit is controlled by two electromagnetic two-way valves F4 and F5.

The adjustment method based on the above-mentioned drying system device may further comprise the steps:

The thermocouple input module ADAM4018 is connected with the temperature and humidity sensors 19 of the air inlet and outlet, and feeds back the temperature and humidity information to the industrial computer through the RS232 data serial port connection. Temperature and humidity data to adjust the working efficiency of the dry air generator. If the ambient humidity is too high, increase the heating temperature of the dry gas and the flow rate of the air compressed by the air compressor pump. The main control parameter of the dry gas heater is the current, which is collected by the industrial computer. The temperature at the outlet of the dry gas heater is used to control the current of the dry gas heater, and the dry gas is heated to an appropriate temperature (such as 80°C) to further reduce the relative humidity of the dry gas.

At the same time, the MCGS program compares the collected temperature and humidity data at the air outlet of the sample with the set humidity threshold (such as 40% relative humidity), determines the performance status of the drying tube, and feeds back the command action through the thermocouple input module Give the relay output module, and then control the switch closure of the solenoid valve, so that the work and activation function switching of the drying pipes A and B can be performed.

When the drying pipe A is in the observation state, TA1 and TA2 are opened, FA is closed, and the observation airflow passes through the drying pipe A and enters the measuring instrument. At the same time, TB1 and TB2 are in the closed state, the three-way valve is not energized, 1-3 is connected, FB is powered on, the drying tube B is in the recovery state of silica gel activation, the silicon rubber plate is powered, the drying tube B is heated, and the heating temperature control is adjusted. The voltage of the heating belt reaches a heating temperature of about 80°C, and is checked with a temperature measuring probe and a temperature display. At the same time, the dry air generated by the dry air generator blows through the B tube to accelerate the activation of the silica gel.

When the humidity at the air outlet of drying pipe A is greater than the set humidity threshold, TA1 and TA2 are closed, FA is turned on, F3 is powered on, drying pipe A is heated, and the dry air generated by the drying air generator blows through the inside of pipe A, drying Tube A is in the recovery state of silica gel activation, while drying tube B is in the working state.

In addition, the above definitions of each element and method are not limited to the various specific structures, shapes or methods mentioned in the embodiments, and those of ordinary skill in the art can easily modify or replace them, for example:

(1) The industrial computer in the control system can also be in the form of a single-chip microcomputer;

(2) The PTFE membrane used for water vapor exchange can be replaced by Nafion membrane;

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (10)

1. A humidity regulator for aerosol collection and sampling airflow, characterized in that it comprises: A drying unit (3), comprising at least two drying tubes, each drying tube comprising: Inner tube for the flow of the feed gas, A one-way vapor-permeable membrane covers the outer wall of the inner tube to allow the water vapor in the sample gas flow to pass through. The outer tube is located outside the inner tube and the one-way gas-permeable membrane and forms a space with the inner tube. The space Filled with desiccant; A control system (4), used for controlling the flow of the sample gas flow into at least one other drying tube when the desiccant in a certain drying tube is deactivated. 2 . The humidity regulating device for aerosol collection and sampling airflow according to claim 1 , further comprising an activation heater ( 2 ) for heating the deactivated desiccant. 3 . 3. aerosol according to claim 2 collects the humidity regulating device of sampling air flow, it is characterized in that, described activation heater (2) comprises silicon rubber heating plate, insulating layer and insulation pipe, and silicon rubber heating plate covers On the outer wall of the outer tube, the silicone rubber heating plate is provided with an insulating layer and an insulating tube in sequence. 4. The humidity regulating device for aerosol collection and sampling airflow according to claim 1, characterized in that it also includes a dry air generator and an air compression pump (1), which is communicated with the space for supplying air to the space Provide dry air. 5. the humidity regulating device of aerosol collection sample airflow according to claim 4, is characterized in that, described drying air generator and air compression pump (1) comprise drying air generator and air compression pump, described drying The air generator is used to generate dry air, which is pumped into the space by the air compressor. 6. The humidity regulating device for aerosol collection and sampling airflow according to claim 2, characterized in that, the control system is also used to monitor the temperature and humidity of the inlet and outlet of the drying tube, and according to the monitored inlet and outlet The humidity difference at the outlet determines whether the desiccant is deactivated, and controls the activation heater to heat the deactivated desiccant. 7. The humidity regulating device for aerosol collection and sampling air flow according to claim 4, wherein the control system is also used to control the dry air generator and the air compression pump to continue to pass through after the desiccant is deactivated. Into dry air to accelerate desiccant activation. 8. The humidity regulating device for aerosol collection and sampling airflow according to claim 1, characterized in that, the aperture of the one-way vapor-permeable membrane is 0.3-1.6 microns, and the aperture of the outer wall of the inner tube is larger than that of the one-way membrane. The pore size of the vapor-permeable membrane, preferably, the one-way vapor-permeable membrane is a polytetrafluoroethylene membrane. 9. A method for regulating humidity using any one of claims 1-8, characterized in that it comprises the steps of: S1: one of the drying tubes that feeds the sample gas flow into the drying unit; S2: The water vapor in the sample gas flow enters the space between the inner tube and the outer tube through the one-way gas-permeable membrane covered on the inner tube, and is absorbed by the desiccant; S3: After the desiccant in the drying tube absorbs water vapor to deactivate, the control system controls the sample gas flow to flow into other drying tubes. 10. An atmospheric particulate matter measuring instrument, characterized in that it comprises the humidity regulating device for aerosol collection and sampling airflow according to any one of claims 1-8.