Polyacrylonitrile solution bubble content on-line monitoring system

Abstract

The invention discloses an on-line monitoring system for the bubble content of a polyacrylonitrile solution, and belongs to the technical field of carbon fiber production equipment. Comprising a defoaming tower, one side of the top of the defoaming tower is connected to a defoaming tower condenser, the output end of the bottom of the defoaming tower is connected to a polymer removal tank, and a polyacrylonitrile solution inlet pipeline is arranged on one side of the top of the defoaming tower. A primary filter, a secondary filter and a defoaming tower feeding pump are sequentially arranged on the liquid inlet pipeline from a feeding part to a defoaming tower connecting part; the diameter, the distribution density, the content and the movement speed of bubbles in the spinning solution can be detected in real time. During detection, the size, the distribution density and the movement speed of the bubbles can be calculated only according to a frequency spectrum intensity graph of signal light, and real-time display of the size, the content and the movement speed of the bubbles can be realized by utilizing an inversion algorithm program preset in a computer.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon fiber production equipment, and in particular relates to an online monitoring system for the bubble content of a polyacrylonitrile solution. Background Art

[0002] Carbon fiber is widely used in aerospace, wind power generation, sports goods and other fields due to its excellent properties such as high strength, high temperature resistance and corrosion resistance. Polyacrylonitrile-based carbon fiber is a fiber made of acrylonitrile as the main raw material through core process sections such as polymerization, spinning, pre-oxidation and carbonization. In the polymerization stage, azobisisobutyronitrile (AIBN) is used as an initiator for free radical polymerization, and its decomposition will release nitrogen.

[0003] Since the viscosity of the polymer increases immediately after the temperature drops, it is difficult for bubbles to overflow from the polymer. In addition, during the transportation of the spinning solution, the liquid flows too fast, which will also cause bubbles. If the spinning solution contains bubbles, it will affect the drafting process and thus reduce the performance of the carbon fiber product, and even cause hairy and broken fibers. During the on-site production process, the polymer solution will be degassed and manually observed through a sight glass to see if there are bubbles, but microbubbles are difficult to identify with the naked eye, so it is necessary to be able to detect and observe the bubbles inside the equipment. Summary of the invention

[0004] The present invention mainly solves the technical problems existing in the above-mentioned prior art and provides an online monitoring system for the bubble content of polyacrylonitrile solution.

[0005] The above technical problems of the present invention are mainly solved by the following technical solutions: an online monitoring system for the bubble content of a polyacrylonitrile solution, comprising a debubbling tower, one side of the top of the debubbling tower is connected to a debubbling tower condenser, and the output end of the bottom of the debubbling tower is connected to a depolymerization tank, characterized in that: a liquid inlet pipeline of the polyacrylonitrile solution is arranged on one side of the top of the debubbling tower, and the liquid inlet pipeline is sequentially provided with a primary filter, a secondary filter and a debubbling tower feed pump from the feed point to the debubbling tower connection point, a detection pipeline is connected to one side of the debubbling tower, a bubble detection device is arranged on the output end of the detection pipeline, a calibrated tube is connected to the detection pipeline, a circulating liquid inlet pump is connected to the output end of the bubble detection device, the output end of the circulating liquid inlet pump extends to the top of the debubbling tower, and a group of branch pipes are arranged at the output end of the circulating liquid inlet pump, and the branch pipes extend to the output end pipeline of the debubbling tower.

[0006] Preferably, a sub-pipeline is provided at the liquid inlet pipeline, the output end of the sub-pipeline is connected to the output end pipeline of the degassing tower feed pump, and the primary filter and the secondary filter are also provided on the sub-pipeline.

[0007] Preferably, a plurality of pneumatic shut-off valves are provided on the two branch pipes of the circulating liquid inlet pump.

[0008] Preferably, the bubble detection device comprises a shell, a detection pool is arranged in the middle of the shell, an inlet is arranged at the top of the detection pool, an outlet is arranged at the bottom of the detection pool, the inlet and outlet of the monitoring pool are connected to the detection pipeline of the debubbling tower, a laser is plugged into one side of the shell, a first beam expanding lens and a second beam expanding lens are respectively arranged on one side of the detection pool, the beam expanding lens is arranged on the side close to the laser, and a Fourier spectrum transform lens and an imaging lens are respectively arranged on the other side of the detection pool, the Fourier spectrum transform lens is located on one side of the detection pool, and the imaging lens is located on the side of the shell.

[0009] Preferably, support frames are respectively arranged at the top and bottom of the inner wall of the shell, a fixing groove is opened on the support frame, the Fourier spectrum transform lens is installed on the support frame through the fixing groove, sliders are arranged at the top and bottom of the first beam expander lens and the second beam expander lens, the first beam expander lens and the second beam expander lens are installed on the support frame through sliders, and adjustment knobs are arranged on the tops of the first beam expander lens, the second beam expander lens and the Fourier spectrum transform lens, and the adjustment knobs extend through the shell to the outside of the shell.

[0010] Preferably, an image sensor is connected to the outside of the housing, the image sensor and the imaging lens are connected to each other, one end of the image sensor is connected to an image acquisition card, and one end of the image acquisition card is connected to a computer via telecommunication.

[0011] Preferably, the detection cell is made of transparent material, is resistant to acid, alkali and organic solvents, has a light transmittance greater than 90%, is preferably 2 to 4 mm thick and is polished to Ra ≤ 0.01 μm.

[0012] The present invention has the beneficial effects:

[0013] 1. The present invention provides a laser beam through a laser, and cooperates with a first beam expansion lens and a second beam expansion lens to diffuse the beam until it is irradiated into a detection pool. The detection pool is made of fused quartz, which is resistant to acid, alkali and organic solvents, and has a light transmittance of more than 90%. In order to ensure the maximum light transmittance on the basis of the mechanical strength of the detection pool, the thickness is preferably 2 to 4 mm, polished to Ra ≤ 0.01 μm, and surface scattering interference is avoided. Mie scattering describes the scattering process that occurs when light waves encounter particles whose size is close to or greater than the wavelength of light. Since the bubble diameter is equivalent to the wavelength of the incident light, the detection of light signals based on Mie scattering (Mie Scattering) is the most accurate measurement. The imaging lens, image sensor and image acquisition card are used to convert the light signal into an electrical signal and transmit it to the computer for data reading, so as to better judge the internal bubble content in the liquid.

[0014] 2. The present invention can detect the diameter, distribution density, content and movement speed of the spinning solution bubbles in real time. When detecting, the size, distribution density and movement speed of the bubbles can be calculated based on the spectrum intensity diagram of the signal light. The inversion algorithm program preset in the computer can realize the real-time display of the bubble size, content and movement speed.

[0015] 3. The laser, lens, image sensor, image acquisition card and other components of the present invention are easy to purchase or prepare, and the market for lasers with high output beam quality and high sensitivity image sensors is mature and cost-effective, and the entire measurement system is stable and reliable. The process level of other components in the system is very mature, convenient and feasible, suitable for preparing carbon fiber materials by spinning method, and can be widely used for bubble monitoring in other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a detection process of the present invention;

[0017] Figure 2 It is a structural schematic diagram of a bubble detection device of the present invention;

[0018] Figure 3 It is a schematic diagram of the working principle of a bubble content detection device of the present invention.

[0019] In the figure: 1. primary filter; 2. secondary filter; 3. degassing tower feed pump; 4. bubble detection device; 41. shell; 42. laser; 43. first beam expanding lens; 44. first beam expanding lens; 45. fixing groove; 46. adjustment button; 47. support frame; 48. detection pool; 481. inlet; 482. outlet; 49. Fourier spectrum transform lens; 410. imaging lens; 411. image sensor; 412. image acquisition card; 413. computer; 5. circulating liquid feed pump; 6. pneumatic shut-off valve; 7. degassing tower. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0021] Embodiment: An online monitoring system for the bubble content of polyacrylonitrile solution, such as Figure 1-Figure 3As shown, it includes a degassing tower 7, one side of the top of the degassing tower 7 is connected to the degassing tower condenser, the output end of the bottom of the degassing tower 7 is connected to the depolymerization tank, one side of the top of the degassing tower 7 is provided with an inlet pipeline of the polyacrylonitrile solution, the inlet pipeline is provided with a primary filter 1, a secondary filter 2 and a degassing tower feed pump 3 in sequence from the feed point to the connection point of the degassing tower 7, one side of the degassing tower 7 is connected with a detection pipeline, a bubble detection device 4 is provided on the output end of the detection pipeline, a calibrated tube 71 is connected to the detection pipeline, wherein the calibrated tube 71 is made of fused quartz material and has a diameter range of 1 to 3 cm, a circulating liquid inlet pump 5 is connected to the output end of the circulating liquid inlet pump 5, the output end of the circulating liquid inlet pump 5 extends to the top of the degassing tower 7, a group of branch pipes are provided at the output end of the circulating liquid inlet pump 5, and the branch pipes extend to the output end pipeline of the degassing tower 7, and the pipelines in the system are all steam jacketed pipelines, and the temperature in the pipe is maintained at 65 to 75° C. to prevent the polyacrylonitrile solution from solidifying.

[0022] A group of pipelines is arranged at the liquid inlet pipeline, and the output end of the branch pipeline is connected to the output end pipeline of the degassing tower feed pump 3. The primary filter 1 and the secondary filter 2 are also arranged on the branch pipeline. The polyacrylonitrile solution feed is first filtered through the primary filter 1 (50μm~100μm) and the secondary filter 2 (5μm~50μm) to remove solid particles in the solution to prevent affecting spinning and bubble detection. The pipeline where the filter is located is provided with a bypass to facilitate maintenance and replacement without affecting normal production.

[0023] A plurality of pneumatic shut-off valves 6 are provided on the two branch pipes of the circulating liquid inlet pump 5. The plurality of pneumatic shut-off valves 6 are provided to facilitate subsequent maintenance operations.

[0024] The bubble detection device 4 includes a shell 41, a detection pool 48 is arranged in the middle of the shell 41, an inlet 481 is arranged on the top of the detection pool 48, and an outlet 482 is arranged on the bottom of the detection pool 48. The inlet 481 and the outlet 482 of the monitoring pool are connected to the detection pipeline of the debubbling tower 7. A laser 42 is plugged into one side of the shell 41. The light source is the laser 42. The laser 42 includes three core components: a gain medium, a pump source, and an optical resonant cavity. The pump source produces a population inversion in the gain medium. The choice of the gain medium determines the efficiency and characteristics of the laser emission, while the resonant cavity selectively reflects incoherent photons back to the gain medium, and replicates these reflected photons through stimulated radiation to generate a large number of coherent photons. The type of laser 42 is a tunable laser 42, which can emit light of different wavelengths, and its wavelength can be adjusted continuously or discretely within a certain range, thereby improving the measurement accuracy of bubbles within each diameter range. The output optical power of the laser 42 is adjustable, and the output power of the laser 42 can be appropriately adjusted according to the beam expansion multiple and the length of the detection cell 48;

[0025] A first beam expander lens 44 and a second beam expander lens 43 are respectively arranged on one side of the detection pool 48. The first beam expander lens 44 and the second beam expander lens 43 are composed of two convex lenses, which can enlarge the diameter of the laser beam and reduce the divergence angle of the beam. The beam expansion multiple of the beam expander lens can be changed according to the size of the detected raw liquid detection pool 48 and the adjustable support frame 47, which is helpful to control the distribution of the laser in space. The first beam expander lens 44 is arranged on the side close to the laser 42. A Fourier spectrum transform lens 49 and an imaging lens 410 are respectively arranged on the other side of the detection pool 48. The Fourier spectrum transform lens 49 is located on one side of the detection pool 48, and the imaging lens 410 is located on the side of the shell 41. Support frames 47 are respectively arranged on the top and bottom of the inner wall of the shell 41. A fixing groove 45 is opened on the support frame 47. The Fourier spectrum transform lens 49 is installed on the support frame 47 through the fixing groove 45. The top and bottom of the first beam expander lens 44 and the second beam expander lens 43 are both provided with sliding The first beam expanding lens 44 and the second beam expanding lens 43 are mounted on the supporting frame 47 through a slider. The tops of the first beam expanding lens 44, the second beam expanding lens 43 and the Fourier spectrum transform lens 49 are all provided with adjusting buttons 46. The adjusting buttons 46 extend through the shell 41 to the outside of the shell 41. The outside of the shell 41 is connected with an image sensor 411. The image sensor 411 and the imaging lens 410 are interconnected. One end of the image sensor 411 is connected with an image acquisition card 412. One end of the image acquisition card 412 is connected with a computer 413. The detection pool 48 is made of transparent material, and is resistant to acid, alkali and organic solvents, has a light transmittance of more than 90%, a thickness of preferably 2 to 4 mm and is polished to Ra≤0.01μm.

[0026] The principle of the present invention is as follows: first, polyacrylonitrile solution enters the degassing tower 7 through the nozzle at the top of the tower. Under vacuum, the bubbles inside the polyacrylonitrile solution will gradually escape from the inside and float to the surface of the solution due to the pressure difference. After the bubbles burst, they go to the condenser of the degassing tower 7. The original solution after degassing for a period of time enters the bubble content detection device, and the residual bubble content is monitored at a frequency of 1h / time. The output light of the laser 42 enters the detection pool 48 containing the inlet 481 and the outlet 482 after passing through the first beam expansion lens 44 and the second beam expansion lens 43. The adjustment button 46 changes the beam expansion multiple of the beam expansion lens by changing the distance between the first beam expansion lens 44 and the second beam expansion lens 43, which helps to control the distribution of the laser in space. After the light beam is scattered by the bubble group in the spinning solution, its output light is subjected to spectrum conversion through the Fourier spectrum conversion lens 49, and the spectrum diagram obtained by the conversion is imaged to the image sensor 411 through the imaging lens 410, and is displayed on the computer 413 after being collected by the image acquisition card 412. The laser 42 is a tunable laser 42, which can output light signals of different wavelengths to achieve accurate measurement of bubbles of different sizes. The power of its output light can be adjusted to cope with different actual working conditions. The light beam is scattered by the bubbles in the spinning solution. Since the bubble diameter is equivalent to the wavelength of the incident light, the light signal mainly composed of Mie scattered light is detected, and the measurement is most accurate. The Mie scattered light is spectrally transformed by the Fourier spectrum transform lens 49 and imaged by the imaging lens 410 on the image sensor 411 and collected by the image acquisition card 412 and processed by the computer 413. The scattered light intensity of the bubble group in different angle ranges is obtained by measurement, and then the relationship between the scattered light intensity of the bubble curtain and the bubble diameter and density is established. Then, through a mathematical inversion algorithm, the diameter and density distribution of the bubble are inferred from the measured scattered light intensity. When the bubble density ρ≤10 5 pcs / m 3 And when the average diameter D≤10μm, the carbon fiber spinning requirement is met. The computer 413 is also equipped with analysis and display software, which can analyze, process and display the data collected by the image acquisition card 412 in real time, so as to realize the real-time display of the bubble size, content and movement speed in the spinning solution, thereby realizing real-time and dynamic monitoring of the spinning solution in fiber preparation. Subsequently, the tested raw liquid is transported to the pump outlet 482 through a centrifugal pump. At this time, the two-branch pneumatic shut-off valve 6 performs an operation according to the result of the bubble content detection device.

[0027] The corresponding formula for the last test data is:

[0028] 1. Formula 1 is the adjustment principle formula of the bubble content device, which represents the parameters I0, d1, d2, d 傅 , M1, M2, M 傅The relationship between β and S is the Mie scattered light signal. In addition to the field of carbon fiber production, the adjustment range of different parameters can be set to be applied to other fields that need to detect bubble content during the production process. The image acquisition card obtains the Mie scattered light signal intensity;

[0029] 2. The computer calculates the bubble content ρ based on formula 2, the system constant K' and D (average bubble diameter) observed through the graduated tube. The system constant K' is obtained by inverse deduction, and k' is inverted from a standard bubble sample of ρ (such as a NIST traceable microsphere suspension) and the scattered light intensity.

[0030] Experimental calibration method

[0031] Step 1: Calibrate using standard samples

[0032] Select a standard solution with known bubble density ρ and average particle size D (for example: ρ 标 =1×10 5 pcs / m3,D 标 =50μm).

[0033] Measure the actual signal strength S 标 (Example: S 标 =1200mW).

[0034] Step 2: Calculate k′

[0035]

[0036] According to the transformation of formula 2:

[0037]

[0038] k′ is usually 10 -12 ~10 -10 mW·m 3 μm -6 .

[0039] Formula 1 (Relationship between Mie scattered light signal intensity and system parameters)

[0040]

[0041] Parameters and parameter ranges

[0042] S: meter scattered light signal (unit: W / m 2 );

[0043] I0: laser emission intensity (unit: W);

[0044] d1: distance from the first beam expander lens to the laser (range 10-35 mm);

[0045] d2: distance from the second beam expander lens to the laser (range 45-75 mm);

[0046] d 傅 : The distance from the Fourier transform lens to the laser (range 150-200 mm);

[0047] M1, M2: beam expansion multiples of the first and second beam expansion lenses (range 2 to 10);

[0048] M 傅 : The equivalent magnification of the Fourier lens (range 1 to 5);

[0049] β: Light path attenuation coefficient (unit: mm -1 , measured by light intensity attenuation of a bubble-free solution); Formula 2 (Relationship between Mie scattered light signal intensity and average bubble diameter and bubble density)

[0050] S=k′·ρ·D 6

[0051] S: meter scattered light signal intensity (unit: W / m 2 );

[0052] ρ: Bubble density (unit: cells / m 3 );

[0053] D: average bubble diameter (unit: m);

[0054] K': system constant (standard bubble sample of ρ, inversion calibration of scattered light intensity k');

[0055] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention should be considered to belong to the protection scope of the present invention.

Claims

1. An online monitoring system for the bubble content of a polyacrylonitrile solution, comprising a degassing tower (7), wherein the gas output end of the degassing tower (7) is connected to a degassing tower condenser, and the output end at the bottom of the degassing tower (7) is connected to a depolymerization tank, characterized in that: A liquid inlet pipeline for the polyacrylonitrile solution is arranged on one side of the top of the degassing tower (7), and a primary filter (1), a secondary filter (2) and a degassing tower feed pump (3) are arranged in sequence on the liquid inlet pipeline from the feed point to the connection point of the degassing tower (7). A detection pipeline is connected to one side of the degassing tower (7), and a bubble detection device (4) is arranged on the output end of the detection pipeline. A graduated tube (71) is connected to the detection pipeline. A circulating liquid inlet pump (5) is connected to the output end of the bubble detection device (4), and the output end of the circulating liquid inlet pump (5) extends to the top of the degassing tower (7). A group of branch pipes are arranged on the output end of the circulating liquid inlet pump (5), and the branch pipes extend to the output end pipeline of the degassing tower (7).

2. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 1, characterized in that: A sub-pipeline is arranged at the liquid inlet pipeline, the output end of the sub-pipeline is connected to the output end pipeline of the degassing tower feed pump (3), and the primary filter (1) and the secondary filter (2) are also arranged on the sub-pipeline.

3. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 1, characterized in that: A plurality of pneumatic shut-off valves (6) are provided on the two branch pipelines of the circulating liquid inlet pump (5).

4. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 1, characterized in that: The bubble detection device (4) comprises a shell (41), a detection pool (48) is arranged in the middle of the shell (41), an inlet (481) is arranged at the top of the detection pool (48), and an outlet (482) is arranged at the bottom of the detection pool (48), the inlet (481) and the outlet (482) of the detection pool are connected to the detection pipeline of the debubbling tower (7), a laser (42) is plugged into one side of the shell (41), a first beam expanding lens (43) and a second beam expanding lens (44) are arranged on one side of the detection pool (48), the first beam expanding lens (43) is arranged on the side close to the laser (42), and a Fourier spectrum transform lens (49) and an imaging lens (410) are arranged on the other side of the detection pool (48), the Fourier spectrum transform lens (49) is located on one side of the detection pool (48), and the imaging lens (410) is located on the side of the shell (41).

5. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 4, characterized in that: Support frames (47) are respectively arranged at the top and bottom of the inner wall of the shell (41), and a fixing groove (45) is opened on the support frame (47). The Fourier spectrum transform lens (49) is installed on the support frame (47) through the fixing groove (45). Slide blocks are arranged at the top and bottom of the first beam expander lens (43) and the second beam expander lens (44). The first beam expander lens (43) and the second beam expander lens (44) are installed on the support frame (47) through the slider. The tops of the first beam expander lens (43), the second beam expander lens (44) and the Fourier spectrum transform lens (49) are all provided with adjustment buttons (46), and the adjustment buttons (46) penetrate the shell (41) and extend to the outside of the shell (41).

6. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 4, characterized in that: The outside of the housing (41) is connected to an image sensor (411), the image sensor (411) and the imaging lens (410) are connected to each other, one end of the image sensor (411) is connected to an image acquisition card (412), and one end of the image acquisition card (412) is connected to a computer (413) via telecommunications.

7. The online monitoring system for bubble content in polyacrylonitrile solution according to claim 4, characterized in that: The detection pool (48) is made of transparent material, is resistant to acid, alkali and organic solvents, has a light transmittance greater than 90%, is preferably 2 to 4 mm thick and is polished to Ra≤0.01 μm.

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