Methane and aerosol synchronous measurement gas chamber, system and working method

Abstract

The invention discloses a methane and aerosol synchronous measurement gas chamber, a system and a working method, and belongs to the field of coal mine underground methane and aerosol detection. The methane and aerosol synchronous measurement gas chamber comprises a horizontally-arranged gas chamber of a cylindrical structure, optical lenses are installed on circular openings in the two ends of the gas chamber respectively, a bladeless fan is arranged on an air inlet of the gas chamber, a diffusion-shaped external flow guide cover is arranged on an air outlet, and a flow velocity sensor is arranged on the inner side of the external flow guide cover. A pressure sensor is arranged on the inner side of the air chamber, and nozzles for spraying high-pressure air to the optical lens are arranged on the two sides of the bladeless fan respectively; a function generator, a laser controller, a laser and a collimating lens are sequentially arranged on one side of the methane and aerosol concentration synchronous measurement gas chamber, a focusing lens, a detector, a data acquisition card and a computer are sequentially arranged on the other side of the methane and aerosol concentration synchronous measurement gas chamber, the structure is simple, the device can be used for a long time in a scene with the dust content reaching the standard, and the measurement precision and reliability can be effectively guaranteed.

Description

Technical Field

[0001] The invention relates to the field of methane and aerosol detection in coal mines, and in particular to a methane and aerosol synchronous measurement chamber, system and working method. Background Art

[0002] Gas explosion and coal dust explosion are serious disasters in coal mines. They are highly destructive and sudden, often causing a large number of casualties and property losses. The main component of gas is methane. Aerosols are tiny solid or liquid particles suspended in the air, which have an important impact on atmospheric optics, climate and air quality. They also affect the health of people working on the front line in mines for a long time.

[0003] In recent years, the tunable diode laser absorption spectroscopy (TDLAS) technology has been continuously improved. It has the advantages of convenience, high efficiency, high selectivity, fast response time, and strong adaptability to complex environments. It is an important gas analysis method that can obtain characteristic parameters by tracking the infrared absorption spectrum of molecules.

[0004] When methane passes through an infrared beam, it absorbs light of a specific wavelength. The intensity of the absorbed light is measured to calculate the concentration of methane. Based on the physical and chemical properties of dust, the optical properties of dust mainly refer to the degree of scattering and absorption of light by dust. The degree of attenuation of the intensity of light passing through a dusty airflow (aerosol) is related to the shape and transparency of the dust. The effect of dust on light can be used for quantitative measurement. With the technical support of TDLAS, the optical properties of methane gas absorption of laser light and aerosol extinction of laser light are used to achieve the simultaneous concentration measurement of methane gas and aerosol in the same gas chamber and the same device. Summary of the invention

[0005] In view of the shortcomings of the above-mentioned technologies, a methane and aerosol synchronous measurement chamber, system and working method are provided, which have simple structure, good use effect, high detection accuracy, can work for a long time in a high dust environment, and are not affected by dust.

[0006] To achieve the above technical objectives, the present invention discloses a methane and aerosol concentration synchronous measurement chamber, comprising a horizontally arranged cylindrical structure chamber, optical lenses a and optical lenses b are respectively installed on the circular openings at both ends of the chamber, optical lenses a and optical lenses b are both concave reflectors with the reflection surface facing the air chamber, wherein optical lens a is provided with a small hole b, optical lens b is provided with a small hole a, small holes a7 and small holes b8 are conical openings, and the aperture inside the air chamber is small; small hole a7 is located directly above the center of optical lens b6, laser enters the chamber from small hole a7, and is emitted from small hole b8 after multiple reflections, and small hole b8 is located at an oblique angle to small hole a7;

[0007] Two openings of different sizes are respectively provided at radially symmetrical positions in the middle of the cylindrical wall of the air chamber, wherein the larger opening is the air inlet, on which a bladeless fan is provided, and the smaller opening is the air outlet, on which a diffusion-shaped external air guide cover is provided, a flow velocity sensor is provided on the inner side of the external air guide cover, a pressure sensor is provided on the inner side of the air chamber, an air inlet is provided on the side of the bladeless fan, the air inlet is connected to a ventilation pipe for clean air, the bladeless fan is a square-circular structure, a square-circular bladeless fan air outlet is provided on the side of the bladeless fan, the wind flow blown out of the bladeless fan air outlet flows closely along the curved surface of the inner wall of the bladeless fan air outlet, blows the fresh air flow evenly into the air chamber, and guides the mixed gas of methane gas and dust in the environment, and smoothly delivers the mixed gas into the air chamber; nozzles b for spraying high-pressure gas toward optical lens a and nozzle a for spraying clean air toward optical lens b are respectively provided on both sides of the bladeless fan, the high-pressure gases sprayed from nozzles a and nozzles b generate cyclones in the inner areas of optical lens a and optical lens b respectively, thereby preventing dust accumulation.

[0008] Furthermore, small hole a and small hole b are conical structures, and the aperture inside the air chamber is small; small hole a is located directly above the center of optical lens b, and the laser enters the air chamber from small hole a, and is emitted from small hole b after multiple reflections. Small hole b is located directly below the center of optical lens a, and small hole b is located at a diagonal position of small hole a; during detection, the laser emits a detection laser into the air chamber through a collimating lens toward small hole b, and the size of small hole a and small hole b is determined according to the spot diameter. After entering the air chamber, the detection laser is reflected back and forth between optical lens a and optical lens b and then emitted from small hole a, and the detection laser passes through the center of small hole a and small hole b.

[0009] Furthermore, the outlet of nozzle a is set at 30° to the horizontal plane and is in contact with the inner side of the optical lens b, and the outlet of nozzle b is set at 30° to the horizontal plane and is close to the inner side of the optical lens a.

[0010] Furthermore, under the action of the air inlet of the air chamber, the mixed gas of methane gas and dust in the mine environment is continuously pushed into the air chamber. The size of the air inlet matches the size of the bladeless fan. The air outlet of the air chamber connecting to the external air guide cover is smaller than the air inlet to ensure smooth entry of airflow and reduce pressure drop, preventing the airflow from generating vortices in the air chamber, which helps to maintain a stable airflow in the air chamber and improve overall efficiency.

[0011] A measurement system for a methane and aerosol concentration synchronous measurement chamber comprises a methane and aerosol concentration synchronous measurement chamber, a laser emitting device is arranged on the optical lens a side of the methane and aerosol concentration synchronous measurement chamber, and a laser receiving and analyzing device is arranged on the optical lens b side of the methane and aerosol concentration synchronous measurement chamber; the laser emitting device comprises a function generator, a laser controller, a laser and a collimating lens connected in sequence; the laser receiving and analyzing device comprises a focusing lens, a detector, a data acquisition card and a computer connected in sequence, and the computer is used to analyze the received laser signal to obtain the detected methane concentration information.

[0012] A method for operating a chamber for synchronously measuring methane and aerosol concentrations, comprising the following steps:

[0013] The methane and aerosol concentration synchronous measurement chamber is placed in the underground environment to be tested. At this time, a bladeless fan blows fresh air into the chamber through the air inlet, and at the same time, a mixed gas of methane and dust to be tested is filled into the chamber from the surrounding environment; compressed gas is sprayed into the chamber using nozzles a and b so that the dust in the chamber cannot adhere to the optical lenses a and b;

[0014] By introducing fresh air into the air chamber, the mixing of the mixed gas to be measured is promoted in the air chamber, and the amount of fresh air entering the air chamber through the air inlet, nozzle a and nozzle b is controlled to avoid excessive dilution of the concentration of the mixed gas to be measured. At the same time, the air pressure in the air chamber is ensured to be greater than the external environment to prevent external gas from entering the air chamber through small holes a and small holes b.

[0015] A laser transmitter is used to send a laser beam with a frequency of v into the gas chamber from a small hole a. The laser light is attenuated in intensity due to the extinction effect caused by the medium formed by the mixed gas to be measured, and an effective signal is obtained after repeated refraction between the optical lens b and the optical lens a, thereby obtaining an accurate concentration value of methane in the mixed gas to be measured. Finally, the laser light is emitted from the small hole b and is finally captured by the laser receiving and analyzing device. The corresponding detection information is obtained by analyzing the laser signal, and the methane concentration and dust information of the mixed gas in the gas chamber can be obtained by computer analysis.

[0016] Furthermore, when the concentration, temperature and pressure of the mixed gas of methane gas and dust are uniformly distributed, the change of laser intensity is expressed by the Beer-Lambert law:

[0017] I0=I·exp(-τL)·exp(-PX abs S(T)φ v L) (1)

[0018] Among them, I0 is the incident laser intensity, I is the outgoing laser intensity, τ is the dust turbidity, P is the total pressure of methane gas, and X absis the concentration of methane gas, S(T) is the spectral line intensity, φ v is a linear function, L is the optical path length;

[0019] For the light intensity change caused by dust particles extinction only, it can be considered that it is the same at each frequency. t To represent the intensity of the emitted laser after being extincted by dust only, then:

[0020] I t =I·exp(-τL) (2)

[0021] According to Mie scattering definition, dust turbidity τ is expressed as

[0022]

[0023] Where D is the dust diameter, N(D) is the dust number density, a is the particle light-facing area, ρ is the dust density, ω is the dust mass concentration, and k ext is the particle extinction coefficient, which can be calculated by formula (4):

[0024]

[0025] In the formula, a n ,b n is the Mie scattering coefficient; x is a dimensionless constant of the dust particle size, and its value is πD / λ, where λ is the wavelength of the incident laser.

[0026] Further, when the laser intensity I is only affected by dust extinction, t After that, the influence of methane absorption effect on laser intensity can be obtained:

[0027] I0=I t exp(-PX abs S(T)φ v L) (5)

[0028] The spectral absorption of methane gas molecules is expressed as:

[0029] a v =-ln(I0 / I t ) v =PX abs S(T)φ v L (6)

[0030] Since the linear function φ v is the normalization function, that is Therefore, the integral absorption A of the entire absorption spectrum can be obtained by using equation (6) in the entire frequency range:

[0031]

[0032] The methane gas concentration can be obtained by formula (7);

[0033] The dust-fitted spectral signal related to dust scattering represents the product of the dust turbidity φ and the absorption optical path length L:

[0034]

[0035] Combining equations (3) and (4), when the dust diameter D, dust density ρ and dust extinction coefficient k are known ext , the mass concentration ω of dust can be obtained.

[0036] Furthermore, the middle of the top of the air chamber (2) is taken as point 1, and the middle of the upper part of the external air guide cover (3) is taken as point 2. The formula (9) based on the Bernoulli equation is as follows:

[0037]

[0038] Where P1 is the pressure at point 1 in the air chamber, in Pa; P2 is the pressure at point 2 on the guide plate; ρ is the gas density, in kg / m 3 ; v1 represents the velocity of methane gas at point 1 in the gas chamber, in m / s; v2 represents the gas velocity at point 2 of the guide plate, in m / s; g represents the acceleration due to gravity, in m / s 2 ; h1 represents the height at point 1 in the air chamber, in m; h2 represents the height at point 2 of the guide plate, in m;

[0039] Assume that the mixed gas in the air chamber is: inviscid, has no volume force, flows steadily, flows along streamlines, and is incompressible; the height difference is very small, and the effect on the pressure difference can usually be ignored. The Bernoulli equation formula is as follows:

[0040]

[0041] It can be seen that the relationship between the pressure P2 in the air chamber and the flow rate v2 of the external air guide cover is as follows (12), which ensures that the mixed gas of methane gas and dust passes through the air chamber in the best state, and the concentration of methane gas and dust is obtained:

[0042]

[0043] Furthermore, in order to obtain the flow rate of the bladeless fan and the nozzle, an ultrasonic flow meter is added to the pipe connected to the bladeless fan and the pipe connected to the nozzle;

[0044] Let C mix It is the concentration of the mixed gas of methane gas and dust diluted by fresh air in the air chamber, in mg / m 3 ; C1 is the concentration of fresh air flow, unit: mg / m 3; C2 is the actual concentration of the mixed gas, in mg / m 3 ; Q1 is the fresh air flow through the bladeless fan and nozzle, which can be directly read by the ultrasonic flow meter, unit L / min; Q2 is the flow rate of the bladeless fan and the mixed gas in the air chamber, unit L / min; Q mix Q is the flow rate of the mixed gas, in L / min; in Q is the total flow rate of the mixed gas and fresh air in the air chamber at point 1, in L / min; out A is the flow rate at point 2 of the guide cover, in L / min; in is the cross-sectional area at point 1, in m 2 ; A out is the cross-sectional area at point 2, in m 2 ;

[0045] At this time, the flow rate of the bladeless fan (1) and the mixed gas in the air chamber is equal to the sum of the fresh air flow introduced by the bladeless fan and the nozzle and the mixed gas flow sucked from the environment:

[0046] Q2=Q1+Q mix (13)

[0047] The flow rate discharged from the air chamber through the outlet is equal to the total flow rate in the air chamber:

[0048] Q out =Q2 (14)

[0049] Inlet Q of air chamber in and the shroud outlet flow rate Q out There are different cross-sectional areas:

[0050] Q in =v1·A in (15)

[0051] Q out =v2·A out (16)

[0052] Substituting the velocity v1 of methane gas at point 1 in the gas chamber and the gas velocity v2 at point 2 of the guide plate into the above formula, we can get

[0053]

[0054] The flow velocity at point 1 is:

[0055]

[0056] Where Q in =Q2-Q1, substituting into the expression of v1 is:

[0057]

[0058] Q2=v2·A out (20)

[0059] Substituting the above formula, we can get the equation:

[0060]

[0061] According to the law of conservation of mass of mixed gases, the formula for dilution of mixed gases by fresh air is as follows:

[0062]

[0063] The fresh air flow does not contain mixed gas components, C1 = 0, and the formula is simplified to:

[0064]

[0065] Reintroduction The formula is further simplified, and the actual concentration of the mixed gas C2 in the environment is:

[0066] C2=C mix (1+R) (24)

[0067] The above formula can be used to remove the influence of fresh air mixed into the gas chamber on the measurement, and accurately obtain the actual concentration of methane gas in the environment.

[0068] Beneficial effect: The detection air chamber disclosed in the present invention has a large air inlet and a small air outlet, and its structure has significant advantages: when the mixed gas enters the air chamber from the air inlet, the air flow diffusion can ensure that the mixed gas is evenly distributed and fills the air chamber, avoiding the formation of strong vortices inside the air chamber, thereby providing a stable flow environment, and the design of inconsistent inlet and outlet sizes further enhances the uniformity of the mixed gas, ensuring that the sampled mixed gas is representative, thereby improving accuracy. At the same time, due to the small air outlet, according to the continuity equation, the air flow speed at the air outlet is accelerated, effectively reducing the gas retention time, and updating the mixed gas in the air chamber. This not only improves the gas flow efficiency, avoids measurement delays or uneven sampling caused by retention, but also maintains a positive pressure difference at the outlet, effectively preventing the external airflow from flowing back into the air chamber from the small hole of the laser channel, and improving the reliability of the air chamber measurement. In addition, the design of a small air outlet forms a micro-positive pressure environment inside the air chamber, which helps to stabilize the airflow and ensure the continuous inflow of fresh gas and mixed gas introduced by the bladeless fan, thereby providing ideal conditions for the long-term stable operation of the air chamber. This structural optimization significantly improves the performance and applicability of the air chamber in complex environments.

[0069] The present invention uses a bladeless fan to introduce the gas in the environment into the air chamber. Compared with a fan with blades, it has a long service life and will not accumulate dust, effectively solving the impact of dust on bearings and electrodes. In addition, the air chamber disclosed in the present invention is combined with a bladeless fan and a nozzle. The bladeless fan provides power for methane gas and dust, making the measurement more accurate. The fresh airflow blown out by the nozzle can clean the optical lens and reduce interference factors. This design makes the airflow inside the air chamber more stable, thereby improving the accuracy of the measurement of the concentration of the mixed gas of methane gas and dust, and improving the overall detection efficiency and reliability.

[0070] The present invention provides a method for eliminating the influence of introducing fresh air into an air chamber on the detection accuracy of methane in a mixed gas, which can ensure that the air chamber can continuously detect the methane content in the environment in real time under a dusty environment while ensuring the accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 This is a schematic diagram of the working process of the methane and aerosol synchronous measurement system in an embodiment of the present invention;

[0072] Figure 2 Schematic diagram of the structure of a gas chamber for synchronously measuring methane and aerosol in an embodiment of the present invention;

[0073] Figure 3 A schematic diagram of the structure of a bladeless fan in an embodiment of the present invention;

[0074] Figure 4 A schematic diagram of the working principle of a bladeless fan in an embodiment of the present invention;

[0075] Figure 5 is a schematic half-section diagram of a bladeless fan in an embodiment of the present invention;

[0076] Figure 6 Schematic cross-sectional view of a chamber for synchronously measuring methane and aerosol in an embodiment of the present invention;

[0077] Figure 7 It is a front view structural schematic diagram of a gas chamber for synchronously measuring methane and aerosol in an embodiment of the present invention;

[0078] Figure 8 This is a schematic diagram of fresh air ejected from a nozzle forming a cyclone on an optical lens in an embodiment of the present invention;

[0079] Fig. 9 Schematic diagram of the detection principle in the air chamber in an embodiment of the present invention.

[0080] Figure markings: bladeless fan-1, air chamber-2, external air guide cover-3, air inlet-4, optical lens a-5, optical lens b-6, small hole a-7, small hole b-8, nozzle-9, nozzle-10, pressure sensor-11, flow rate sensor-12, bladeless fan air outlet-13. DETAILED DESCRIPTION

[0081] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0082] When TDLAS is used to measure the flow field of methane gas and dust, methane gas absorbs laser light, and dust also absorbs and scatters laser light. At this time, the signal received by the detector carries the relevant information of methane gas and dust at the same time. If the absorption signal caused by gas molecule absorption and the extinction signal caused by dust extinction are separated, the simultaneous detection of methane and dust can be achieved. The air inlet 4 of the air chamber 2 of the present invention is larger than the air outlet 13 of the air chamber 2.

[0083] When a laser beam with a frequency of v passes through a medium where methane gas and dust coexist, the incident laser intensity is attenuated due to the extinction effect of the mixed gas medium. When the concentration, temperature and pressure of the medium are uniformly distributed, the change in laser intensity can be expressed by the Beer-Lambert law:

[0084]

[0085] Among them, I0 is the incident laser intensity, I is the outgoing laser intensity, τ is the dust turbidity, P is the total pressure of methane gas, and X abs is the concentration of methane gas, S(T) is the spectral line intensity, φ v is a linear function, and L is the optical path length.

[0086] For the light intensity change caused by dust extinction only, it can be considered that it is the same at each frequency. t To represent the intensity of the emitted laser after being extincted by dust only, then:

[0087] I t =I·exp(-τL) (2)

[0088] According to the Mie definition of Mie scattering, dust turbidity τ can be expressed as

[0089]

[0090] Where D is the dust diameter, N(D) is the dust number density, a is the particle light-facing area, ρ is the dust density, ω is the dust mass concentration, and k ext is the particle extinction coefficient, which can be calculated by formula (4):

[0091]

[0092] In the formula, a n ,b n is the Mie scattering coefficient, x is the dimensionless constant of the dust particle size, and its value is πD / λ, where λ is the wavelength of the incident laser. t Finally, the effect of methane absorption on laser intensity can be obtained by subtracting the data offset by pure dust from the detection data of dust and methane gas:

[0093]

[0094] The spectral absorption of methane gas molecules can be expressed as:

[0095] a v =-ln(I0 / I t ) v =PX abs S(T)φ v L (6)

[0096] Since the linear function φ v is the normalization function, that is Therefore, in the whole frequency range, the integral absorption A of the whole absorption spectrum can be obtained by applying equation (6):

[0097]

[0098] The methane gas concentration can be obtained by equation (7); the signal 2 related to dust scattering represents the product of the dust turbidity τ and the absorption optical path length L:

[0099]

[0100] According to the detection principle of this application, combined with equations (3) and (4), when the dust diameter D, dust density ρ and dust extinction coefficient k are known ext , the mass concentration ω of dust can be obtained.

[0101] When measuring the gas to be measured, two air flows enter the air chamber, one is fresh air blown out from the bladeless fan connected to the ventilation duct, and the other is the gas to be measured mixed with methane gas and dust in the environment. The introduction of fresh air can promote the mixing of the gas to be measured in the air chamber and ensure that the sensor obtains a representative gas sample. The amount of fresh air intake is controlled to avoid excessive dilution of the concentration of the gas to be measured. When measuring the mixed gas of methane gas and dust, it is necessary to monitor the air pressure in the air chamber and the flow rate of the gas out of the air chamber to keep the air chamber stable. For systems that use optical methods to measure gas concentration, stable airflow and pressure conditions in the air chamber can ensure the stability of the optical path and prevent the measurement signal from being disturbed. If the pressure in the air chamber is not balanced with the external environmental pressure (for example, slightly higher than the ambient pressure), external air can be prevented from entering the air chamber to prevent the dilution and contamination of the gas to be measured by external air, ensuring that the measured gas is pure. Monitoring pressure and flow rate can reduce the impact of external environmental changes on experimental results, especially when accurately measuring concentration, changes in air pressure may cause uneven diffusion and mixing of gases, thereby affecting the measurement results.

[0102] The middle of the top of the air chamber is taken as point 1, and the middle of the upper part of the external deflector is taken as point 2. The Bernoulli equation (9) is as follows:

[0103]

[0104] Where P1 is the pressure at point 1 in the air chamber, Pa; P2 is the pressure at point 2 on the guide plate; ρ is the gas density, kg / m 3 ; v1 represents the velocity of methane gas at point 1 in the gas chamber, m / s; v2 represents the gas velocity at point 2 of the guide plate, m / s; g represents the acceleration of gravity, m / s 2 ; h1 represents the height at point 1 in the air chamber, m; h2 represents the height at point 2 of the guide plate, m.

[0105] Assume that the gas in the air chamber is: inviscid, has no volume force, flows steadily, flows along streamlines, and is incompressible. The height difference is very small and its effect on the pressure difference can usually be ignored. The Bernoulli equation is as follows:

[0106]

[0107] It can be seen that the relationship between the pressure in the air chamber and the flow rate of the external air guide cover 3 is as follows (12), which ensures that the mixed gas of methane gas and dust passes through the air chamber in the best state and obtains accurate concentrations of methane gas and dust.

[0108]

[0109] Air chamber design

[0110] The air inlet 4 at the bottom of the bladeless fan 1 is connected to the ventilation pipe of the fresh air in the coal mine, and is surrounded by the annular inner lip of the fan head of the bladeless fan 1, and is blown into the air chamber 2 at a certain speed according to the square shape of the bladeless fan design. The fresh air blown out by the bladeless fan 1 serves as the driving force for the mixed gas of methane gas and dust to enter the designed air chamber 2, but the amount of air introduced must be carefully controlled to prevent excessive dilution and affect the concentration of the mixed gas. The square round shape designed by the bladeless fan 1 plays a role in guiding methane and dust into the air chamber, reducing the vortex and chaos of the airflow; with the bladeless design, the fresh air is accelerated and evenly pushed out through the internal annular structure, effectively improving the efficiency of the air flow, and has low noise, avoiding the exposure of the blades of traditional fans, and strong safety. The amount of air introduced can be controlled by adjusting the running speed of the fan.

[0111] Nozzle 9 and nozzle 10 are connected to the ventilation pipe containing fresh air in the coal mine. The nozzle angle is adjusted to 30°. The fresh air is blown at a certain wind speed to control the air volume to prevent the concentration of methane gas and dust from being diluted. The fresh air is blown in the circular shape of the optical lens, gradually approaching the center of the lens, blowing to the laser entrance port on the optical lens, and flowing out from it. This design avoids dust contamination of the optical lens when measuring the concentration of methane gas and dust, and does not affect the absorption and extinction of methane and dust on the laser, nor does it affect the emission of the laser.

[0112] Specific implementation methods

[0113] A method for operating a chamber for synchronously measuring methane and aerosol concentrations, comprising the following steps:

[0114] Step 1:

[0115] First, close the inlet 1 of the bladeless fan and the outlet of the external air guide cover 3 to prevent methane and dust from entering the environment. Connect the ventilation pipe and the air inlet 4, nozzle a9 and nozzle b10 of the bladeless fan, and introduce fresh air flow. The air flow is divided into two parts. One part is introduced into the bladeless fan 1 as a power to drive the mixed gas composed of methane gas and dust in the environment into the air chamber 2 according to a certain flow direction; the other part of fresh air is introduced into the air chamber 2 together to form an air flow along the air chamber wall and slowly approach the center of the optical lens on the optical lens a5 and the optical lens b6 as a purge optical lens, and then flow out from the small holes a7 and the small holes b8 on the optical lens, so as to prevent external dust from contaminating the mirror surface when detecting methane gas and dust. The laser transmitter is turned on, and a diode laser transmitter with a central wavelength of 1653.7nm is used as the excitation light source.

[0116] Step 2:

[0117] Close the bladeless fan inlet 1 in the device, leaving only the external air guide cover outlet 3, connect the ventilation pipe and the bladeless fan inlet 4, nozzle 9 and nozzle 10, and introduce fresh air flow. Detect the laser intensity in the air chamber 2 with only air. The collimated laser passes through the small hole a7 on the two optical lenses a5 and the optical lens b6 to form multiple reflections. Finally, the emitted laser passes through the small hole b8 and is received by the detector, as shown in FIG. Fig. 9 As shown, before the introduction of methane and dust, the first emission signal is taken as the initial light intensity I.

[0118] Step 3:

[0119] The entrance of the bladeless fan is opened to allow the methane gas and dust in the environment to enter the air chamber. Pay attention to the changes in the pressure sensor 11 and the flow rate sensor 12. The pressure in the air chamber 2 is set slightly higher than the air pressure in the mine (mine air pressure + 50 ~ 300Pa), forming a slight positive pressure to maintain the stability of the pressure in the air chamber 2 and the flow rate out of the air chamber, and avoid eddy currents or dead zones when the gas is mixed to affect the measurement results. Methane gas is flammable, and keeping it within a reasonable pressure range can reduce the risk of accidents. After a period of time, the received signal is stable, and the detector signal is transmitted to the computer to analyze the received extinction signal of the methane gas and dust mixed gas and the signal related to dust.

[0120] Step 4:

[0121] The relevant spectral signal is obtained after being processed by the wavelet denoising filtering algorithm compiled based on Labview. In order to effectively remove noise and improve the sensitivity and stability of the system, the wavelet denoising filtering algorithm is introduced in the data processing to reduce the noise of the signal.

[0122] Step 5:

[0123] According to formula (1), the extinction signal containing both methane and dust can be obtained from I0 and I, which is set as signal 1. Then the peak of the signal absorption is covered, and the remaining signal is fitted to obtain the spectral signal related to dust, which is set as signal 2. The absorption spectral signal related to methane gas is obtained by subtracting the dust-fitted spectral signal 2 from the extinction signal 1 containing both methane and dust, and the remaining signal is set as signal 3.

[0124] In order to obtain the flow rate of the bladeless fan and the nozzle, ultrasonic flow meters are added to the pipes connected to the bladeless fan and the nozzle;

[0125] Let C mix The concentration of the mixed gas of methane gas and dust diluted by fresh air in the gas chamber 2, in mg / m 3 ; C1 is the concentration of fresh air flow, unit: mg / m 3; C2 is the actual concentration of the mixed gas, in mg / m 3 ; Q1 is the fresh air flow through the bladeless fan and nozzle, which can be directly read by the ultrasonic flowmeter, unit I / min; Q2 is the flow rate of the bladeless fan and the mixed gas in the air chamber, unit L / min; Q mix Q is the flow rate of the mixed gas, in L / min; in Q is the total flow rate of the mixed gas and fresh air in the air chamber at point 1, in L / min; out A is the flow rate at point 2 of the guide cover, in L / min; in is the cross-sectional area at point 1, in m 2 ; A out is the cross-sectional area at point 2, in m 2 ;

[0126] At this time, the flow rate of the bladeless fan 1 and the mixed gas in the air chamber 2 is equal to the sum of the fresh air flow introduced by the bladeless fan 1 and the nozzle and the mixed gas flow inhaled from the environment:

[0127] Q2=Q1+Q mix (13)

[0128] The flow rate discharged from chamber 2 through the outlet is equal to the total flow rate in chamber (2):

[0129] Q out =Q2 (14)

[0130] Inlet Q of air chamber 2 in and the shroud outlet flow rate Q out There are different cross-sectional areas:

[0131] Q in =v1·A in (15)

[0132] Q out =v2·A out (16)

[0133] Substituting the velocity v1 of methane gas at point 1 in the gas chamber and the gas velocity v2 at point 2 of the guide plate into the above formula, we can get

[0134]

[0135] The flow velocity at point 1 is:

[0136]

[0137] Where Q in =Q2-Q1, substituting into the expression of v1 is:

[0138]

[0139] Q2=v2·A out (20)

[0140] Substituting the above formula, we can get the equation:

[0141]

[0142] According to the law of conservation of mass of mixed gases, the formula for dilution of mixed gases by fresh air is as follows:

[0143]

[0144] The fresh air flow does not contain mixed gas components, C1 = 0, and the formula is simplified to:

[0145]

[0146] Reintroduction The formula is further simplified, and the actual concentration of the mixed gas C2 in the environment is:

[0147] C2=C mix (1+R) (24)

[0148] The above formula can be used to remove the influence of fresh air mixed into the air chamber 2 on the measurement, and accurately obtain the actual concentration of methane gas in the environment.

Claims

1. A chamber for synchronously measuring methane and aerosol concentrations, characterized in that: It comprises a horizontally arranged cylindrical air chamber (2), wherein an optical lens a (5) and an optical lens b (6) are respectively mounted on circular openings at both ends of the air chamber (2), wherein both the optical lens a (5) and the optical lens b (6) are concave reflectors with the reflective surface facing the inside of the air chamber (2), wherein the optical lens a (5) is provided with a small hole b (8), and the optical lens b (6) is provided with a small hole a (7); Two openings of different sizes are respectively arranged at radially symmetrical positions in the middle of the cylindrical wall of the air chamber (2), wherein the larger opening is an air inlet, on which a bladeless fan (1) is arranged, and the smaller opening is an air outlet, on which an external air guide cover (3) of a diffusion shape is arranged, a flow velocity sensor (12) is arranged on the inner side of the external air guide cover (3), a pressure sensor (11) is arranged on the inner side of the air chamber (2), an air inlet (4) is arranged on the side of the bladeless fan (1), the air inlet (4) is connected to a ventilation pipe for clean air, the bladeless fan (1) is of a square-circular structure, a bladeless fan air outlet (13) of a square-circular structure is arranged on the side of the bladeless fan (1), and the bladeless fan outlet (13) of the bladeless fan is arranged on the side of the bladeless fan (1). The wind flow blown out of the air outlet (13) flows closely along the curved surface of the inner wall of the air outlet (13) of the bladeless fan, blows the fresh air flow evenly into the air chamber (2), and guides the mixed gas of methane gas and dust in the environment, so that the mixed gas is smoothly sent into the air chamber (2); a nozzle b (10) for spraying high-pressure gas toward the optical lens a (5) and a nozzle a (9) for spraying clean air toward the optical lens b (6) are respectively provided on both sides of the bladeless fan (1); the high-pressure gas sprayed by the nozzle a (9) and the nozzle b (10) respectively generates cyclones in the inner areas of the optical lens a (5) and the optical lens b (6), thereby preventing dust accumulation.

2. The methane and aerosol concentration synchronous measurement chamber according to claim 1, characterized in that: The small hole a (7) and the small hole b (8) are of conical structure, and the aperture inside the air chamber is small; the small hole a (7) is located just above the center of the optical lens b (6); the laser enters the air chamber (2) from the small hole a (7), and is emitted from the small hole b (8) after multiple reflections; the small hole b (8) is located just below the center of the optical lens a (5), and the small hole b (8) is located at a diagonal position of the small hole a (7); during detection, the laser emits a detection laser into the air chamber (2) through the collimating lens toward the small hole b (8); the size of the small hole a (7) and the small hole b (8) is determined according to the spot diameter; after entering the air chamber (2), the detection laser is reflected back and forth between the optical lens a (5) and the optical lens b (6) and then emitted from the small hole a (7); the detection laser passes through the center of the small hole a (7) and the small hole b (8).

3. The methane and aerosol concentration synchronous measurement chamber according to claim 1, characterized in that: The outlet of nozzle a (9) is set at 30° to the horizontal plane and is in contact with the inner side of the optical lens b (6), and the outlet of nozzle b (10) is set at 30° to the horizontal plane and is close to the inner side of the optical lens a (5).

4. The methane and aerosol concentration synchronous measurement chamber according to claim 1, characterized in that: Under the action of the air inlet of the air chamber (2), the mixed gas of methane gas and dust in the mine environment is continuously pushed into the air chamber (2). The size of the air inlet matches the size of the bladeless fan (1). The air outlet of the air chamber (2) connected to the external air guide cover (3) is smaller than the air inlet, so as to ensure smooth entry of the air flow and reduce the pressure drop, prevent the air flow from generating vortex in the air chamber (2), help maintain a stable air flow in the air chamber, and improve the overall efficiency.

5. A measurement system using the chamber for synchronously measuring methane and aerosol concentrations according to claim 1, characterized in that: The invention comprises a chamber for synchronously measuring the concentration of methane and aerosols, wherein a laser emitting device is arranged on the side of an optical lens a (5) of the chamber for synchronously measuring the concentration of methane and aerosols, and a laser receiving and analyzing device is arranged on the side of an optical lens b (6) of the chamber for synchronously measuring the concentration of methane and aerosols; the laser emitting device comprises a function generator, a laser controller, a laser and a collimating lens connected in sequence; the laser receiving and analyzing device comprises a focusing lens, a detector, a data acquisition card and a computer connected in sequence, and the computer is used to analyze the received laser signal to obtain the detected methane concentration information.

6. A method for using the chamber for synchronously measuring methane and aerosol concentrations according to claim 1, characterized in that: Here are the steps: The methane and aerosol concentration synchronous measurement chamber is placed in the underground environment to be tested, and at this time, the bladeless fan (1) blows fresh air into the chamber (2) through the air inlet (4), and at the same time, the methane and dust mixed gas to be tested is filled into the chamber (2) from the surrounding environment; the compressed gas is sprayed into the chamber (2) by the nozzle a (9) and the nozzle b (10) so that the dust in the chamber (2) cannot adhere to the optical lens a (5) and the optical lens b (6); By introducing fresh air into the air chamber (2), mixing of the mixed gas to be measured in the air chamber (2) is promoted, and the amount of fresh air entering the air chamber (2) through the air inlet (4), the nozzle a (9) and the nozzle b (10) is controlled to avoid excessive dilution of the concentration of the mixed gas to be measured, while ensuring that the air pressure in the air chamber (2) is greater than the external environment, thereby preventing external gas from entering the air chamber (2) through the small hole a (5) and the small hole b (6); A laser transmitter is used to send a laser beam with a frequency of v into the gas chamber (2) from the small hole a (5). The laser light is attenuated in intensity due to the extinction effect caused by the medium formed by the mixed gas to be measured, and is repeatedly refracted between the optical lens b (6) and the optical lens a (5) to obtain an effective signal, thereby obtaining an accurate concentration value of methane in the mixed gas to be measured. Finally, the laser light is emitted from the small hole b (6) and is finally captured by a laser receiving and analyzing device. The corresponding detection information is obtained by analyzing the laser signal, and the methane concentration and dust information of the mixed gas in the gas chamber (2) can be obtained by computer analysis.

7. The working method according to claim 6, characterized in that: When the concentration, temperature and pressure of the mixed gas of methane gas and dust are uniformly distributed, the change of laser intensity is expressed by the Beer-Lambert law: I0=I·exp(-τL)·exp(-PX abs S(T)φ v L) (1) Where I0 is the incident laser intensity, I is the outgoing laser intensity, τ is the dust turbidity, P is the total pressure of methane gas, and X abs is the concentration of methane gas, S(T) is the spectral line intensity, φ v is a linear function, L is the optical path length; For the light intensity change caused by dust particles extinction only, it can be considered that it is the same at each frequency. t To represent the intensity of the emitted laser after being extincted by dust only, then: I t =I·exp(-τL) (2) According to Mie scattering definition, dust turbidity τ is expressed as Where D is the dust diameter, N(D) is the dust number density, a is the particle light-facing area, ρ is the dust density, ω is the dust mass concentration, and k ext is the particle extinction coefficient, which can be calculated by formula (4): In the formula, a n ,b n is the Mie scattering coefficient; x is a dimensionless constant of the dust particle size, and its value is πD / λ, where λ is the wavelength of the incident laser.

8. The detection method according to claim 7, characterized in that: After obtaining the laser intensity I which is only affected by the dust extinction t After that, the influence of methane absorption effect on laser intensity can be obtained: I0=I t ·exp(-PX abs S(T)φ v L) (5) The spectral absorption of methane gas molecules is expressed as: the v =-ln(I0 / I t ) v =PX abs S(T)φ v L (6) Since the linear function φ v is the normalization function, that is Therefore, the integral absorption A of the entire absorption spectrum can be obtained by using equation (6) in the entire frequency range: The methane gas concentration can be obtained by formula (7); The dust-fitted spectral signal related to dust scattering represents the product of the dust turbidity τ and the absorption optical path length L: Combining equations (3) and (4), when the dust diameter D, dust density ρ and dust extinction coefficient k are known ext , the mass concentration ω of dust can be obtained.

9. The detection method according to claim 8, characterized in that: The middle of the top of the air chamber (2) is taken as point 1, and the middle of the upper part of the external air guide cover (3) is taken as point 2. The equation (9) based on the Bernoulli equation is as follows: Where P1 is the pressure at point 1 in the air chamber, in Pa; P2 is the pressure at point 2 on the guide plate; ρ is the gas density, in kg / m 3 ; v1 represents the velocity of methane gas at point 1 in the gas chamber, in m / s; v2 represents the gas velocity at point 2 of the guide plate, in m / s; g represents the acceleration due to gravity, in m / s 2 ; h1 represents the height at point 1 in the air chamber, in m; h2 represents the height at point 2 of the guide plate, in m; Assume that the mixed gas in the air chamber (2) is: inviscid, has no volume force, flows steadily, flows along streamlines, and is incompressible; the height difference is very small and its effect on the pressure difference can usually be ignored. The Bernoulli equation is expressed as follows: It can be seen that the relationship between the pressure P2 in the air chamber (2) and the flow rate v2 of the external guide cover (3) is as follows (12), which ensures that the mixed gas of methane gas and dust passes through the air chamber in the best state, and obtains the concentration of methane gas and dust:

10. The detection method according to claim 9, characterized in that: In order to obtain the flow rate of the bladeless fan and the nozzle, ultrasonic flow meters are added to the pipes connected to the bladeless fan and the nozzle; Let C mix The concentration of the mixed gas of methane gas and dust after being diluted by fresh air in the air chamber (2), in mg / m 3 ; C1 is the concentration of fresh air flow, unit: mg / m 3 ; C2 is the actual concentration of the mixed gas, in mg / m 3 ; Q1 is the fresh air flow through the bladeless fan and nozzle, which can be directly read by the ultrasonic flow meter, unit L / min; Q2 is the flow rate of the bladeless fan and the mixed gas in the air chamber, unit L / min; Q mix Q is the flow rate of the mixed gas, in L / min; in Q is the total flow rate of the mixed gas and fresh air in the air chamber at point 1, in L / min; out A is the flow rate at point 2 of the guide cover, in L / min; in is the cross-sectional area at point 1, in m 2 ; A out is the cross-sectional area at point 2, in m 2 ; At this time, the flow rate of the bladeless fan (1) and the mixed gas in the air chamber (2) is equal to the sum of the fresh air flow introduced by the bladeless fan (1) and the nozzle and the mixed gas flow sucked from the environment: Q2=Q1+Q mix (13) The flow rate discharged from the air chamber (2) through the outlet is equal to the total flow rate in the air chamber (2): Q out =Q2 (14) Inlet Q of air chamber (2) in and the shroud outlet flow rate Q out There are different cross-sectional areas: Q in =v1·A in (15) <h2 style=";text-align:left;direction:ltr">Q<h2 style=";text-align:left;direction:ltr"> out <h2 style=";text-align:left;direction:ltr"> <v2·A<h2 style=";text-align:left;direction:ltr"> out <h2 style=";text-align:left;direction:ltr"> (16) Substituting the velocity v1 of methane gas at point 1 in the gas chamber and the gas velocity v2 at point 2 of the guide plate into the above formula, we can get The flow velocity at point 1 is: Where Q in =Q2-Q1, substituting into the expression of v1 is: <h2 style=";text-align:left;direction:ltr">Q2=v2·A<h2 style=";text-align:left;direction:ltr"> out <h2 style=";text-align:left;direction:ltr"> (20) Substituting the above formula, we can get the equation: According to the law of conservation of mass of mixed gases, the formula for dilution of mixed gases by fresh air is as follows: The fresh air flow does not contain mixed gas components, C1 = 0, and the formula is simplified to: Reintroduction The formula is further simplified, and the actual concentration of the mixed gas C2 in the environment is: C2=C mix (1+R) (24) The above formula can be used to eliminate the influence of fresh air mixed into the gas chamber (2) on the measurement, and accurately obtain the actual concentration of methane gas in the environment.

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