Polymer cycle concentration apparatus and method and heat exchanger therefor

Abstract

The application discloses a polymer circulating concentration device and method and a heat exchanger thereof, relates to the field of polymer post-treatment, and comprises a shell, upper and lower heads fixed at two ends of the shell, a closed space formed between the upper head, the shell and the lower head, and a heat medium jacket or a heat coil provided on the outer wall of the upper head and the lower head; an upper tube plate and a lower tube plate fixed in the closed space, the upper tube plate and the lower tube plate used for separating the closed space into a first chamber, a second chamber and a third chamber from top to bottom; a plurality of heat exchange pipes vertically arranged in the second chamber and used for connecting the first chamber and the third chamber; a discharge port formed in the middle of the upper head, a feeding port arranged in the middle of the lower head, a shell-side heat medium outlet and a shell-side heat medium inlet arranged at the position corresponding to the second chamber of the shell; a first flow guide arranged in the first chamber; and a second flow guide arranged in the third chamber. The application can eliminate the head dead zone, reduce the temperature drop of the head and improve the devolatilization driving force.

Description

Technical Field

[0001] This invention relates to the field of polymer post-processing technology, and in particular to a polymer recycling concentration apparatus and method and its heat exchanger. Background Technology

[0002] In the production of polymers such as polyolefin elastomers (POE) and cyclic olefin copolymers (COC), the polymer solution (polymer solution) obtained after the polymerization reaction typically contains 80% to 90% volatile components such as solvent and unreacted monomers. Taking POE as an example, its solution polymerization process uses n-hexane as a solvent, and the polymer mass fraction in the polymer solution after polymerization is generally 8% to 20%. Taking COC as an example, its metallocene catalytic addition polymerization process uses toluene or cyclohexane as a solvent, and the polymer concentration in the polymer solution after polymerization is typically 5% to 15%.

[0003] To obtain polymers that meet product specifications, a concentration process is needed to remove most of the solvent and volatiles from the polymer solution. Industrially, static devolatilization combined with a screw devolatilization extruder is generally used to remove most of the volatiles. The core equipment for static devolatilization is the heat exchanger and the devolatilizer. Conventional shell-and-tube heat exchangers present three key problems when used for polymer concentration: (1) Dead zone in the end cap leads to product deterioration: In traditional planar tube sheet heat exchangers, the transition area between the end cap and the tube sheet forms a flow dead zone due to the abrupt change in the flow channel cross section; high-viscosity polymer liquid remains in this area for a long time, and the residence time can be 5 to 10 times the average residence time of the tube pass. Under high temperature conditions, thermal degradation and cross-linking side reactions occur, producing color spots and gels; for optical grade COC products, trace amounts of degradation products significantly affect the transmittance and haze index; for POE products, degradation leads to a wider molecular weight distribution and a decrease in mechanical properties; (2) The head temperature drop exacerbates the dead zone problem: The head area of ​​traditional heat exchangers is not heated, and the temperature is usually 10~30°C lower than that of the tube side. When high viscosity polymer liquid flows through this area, the viscosity increases by more than an order of magnitude, the fluidity deteriorates sharply, and even the polymer liquid solidifies and blocks, forcing the shutdown for cleaning. (3) Insufficient driving force for de-devouring and lengthy process: In traditional equipment, polymer liquid is pressurized by pump and enters heat exchanger, and then enters de-devourer for flash de-devouring through pressure reducing valve. There is no material circulation return, and the amount of de-devouring in one step is limited. POE production usually requires three-stage dynamic de-devouring, which requires large equipment investment and pressure reducing valve is easy to be damaged. Summary of the Invention

[0004] To address the technical problems existing in the background art, the present invention proposes a polymer circulation concentration device and method and its heat exchanger.

[0005] In a first aspect, the present invention provides a heat exchanger for a polymer circulation concentration device, comprising: a shell, an upper end cap and a lower end cap respectively fixed at the upper and lower ends of the shell, a sealed space being formed between the upper end cap, the shell and the lower end cap, and a heat tracing medium jacket or heat tracing coil being provided on the outer wall of the upper end cap and the lower end cap. An upper tube sheet and a lower tube sheet are fixed in the sealed space from top to bottom. The upper tube sheet and the lower tube sheet divide the sealed space into a first chamber, a second chamber and a third chamber arranged from top to bottom. The second chamber is vertically equipped with multiple heat exchange tubes for connecting the first chamber and the third chamber; The upper head has a discharge port in the middle, the lower head has a feed port in the middle, the shell side heat medium outlet is located at the top of the shell and the second chamber, and the shell side heat medium inlet is located at the bottom of the shell and the second chamber. The first chamber is equipped with a first guide element for collecting the polymer liquid flowing out of each heat exchange tube and accelerating its spraying from the outlet. The first guide element is a Venturi structure, which includes a tapered section, a throat and a diffusing section connected in sequence along the material flow direction. The large end of the tapered section faces the upper tube sheet and is used to collect the polymer liquid flowing out of each heat exchange tube. The large end of the diffusing section is connected to the outlet. The third chamber is equipped with a second flow guide for evenly distributing the polymer liquid entering the lower head to each heat exchange tube; the second flow guide has a horn structure, with the larger opening of the horn structure facing the lower tube sheet and the smaller opening of the horn structure facing the feed port of the lower head.

[0006] Preferably, both the upper tube sheet and the lower tube sheet are arc-shaped tube sheets, and each arc-shaped tube sheet is concave towards the corresponding upper or lower end cap.

[0007] Preferably, the radius of curvature of the arc-shaped tube sheet is 0.6 to 1.8 times the inner diameter of the shell.

[0008] Preferably, the throat sidewall is provided with an inert gas inlet for introducing inert gas.

[0009] Preferably, the inert gas inlet is a radial or tangential interface.

[0010] In a second aspect, the present invention also provides a polymer circulation concentration device, comprising: a polymer circulation tank, a circulation pump, a static mixer, an expansion pipe, a delivery pump, and a heat exchanger of the polymer circulation concentration device as described in any one of the first aspects. The bottom outlet of the polymer circulation tank is connected to the inlet of the circulation pump and the inlet of the transfer pump, respectively; the top of the polymer circulation tank is provided with a gas phase outlet for connecting to the solvent recovery system. The middle section of the polymer circulation tank is connected to the large-diameter section of the expansion pipe, the small-diameter section of the expansion pipe is connected to the outlet of the heat exchanger, the inlet of the heat exchanger is connected to the outlet of the static mixer, the first inlet of the static mixer is connected to the outlet of the circulation pump, and the second inlet of the static mixer is used to introduce the polymer solution to be concentrated.

[0011] Thirdly, the present invention also proposes a polymer recycling concentration method, employing the polymer recycling concentration apparatus described in any one of the second aspects, comprising: The polymer solution to be concentrated and the circulating polymer solution are respectively sent to a static mixer. After being mixed evenly in the static mixer, the polymer solution enters the heat exchanger. After being guided by the second flow guide, the polymer adhesive is distributed into each heat exchange tube and exchanges heat with the shell-side heat medium in the heat exchanger; wherein, the temperature of the polymer adhesive after the heat exchange is heated is below the boiling point of the solvent in the polymer adhesive. After being heated by heat exchange, the polymer liquid is collected by the first guide element and sprayed into the expansion pipe through the outlet. Due to the sudden pressure drop, flash evaporation and volatilization occur. The polymer solution after flash devolatilization is returned to the polymer circulation tank through the expansion pipe, and the gas phase generated by flash devolatilization is discharged to the solvent recovery system through the expansion pipe and the gas phase outlet of the polymer circulation tank. Real-time monitoring of polymer solution concentration in the polymer circulation tank; When the polymer solution concentration does not reach the target concentration, all polymer solutions are returned to the second inlet of the static mixer by the circulation pump as circulating material, and then mixed with the polymer solution to be concentrated to continue concentration. When the polymer solution concentration reaches the target concentration, a portion of the polymer solution is pressurized and output to the subsequent deep devolatilization equipment by the delivery pump, while the other portion is sent back to the second inlet of the static mixer as circulating material by the circulation pump, where it is mixed with the polymer solution to be concentrated and then further concentrated.

[0012] Preferably, the temperature of the shell-side heat medium is 160~250°C; the temperature of the heat tracing medium flowing in the heat tracing medium jacket or heat tracing coil is 150~220°C; the operating pressure inside the heat exchanger is 0.3~1.0MPaG, and the pressure inside the polymer circulation tank is 0.02~0.08MPaG.

[0013] In this invention, the proposed polymer circulation concentration device and method, along with its heat exchanger, utilizes the synergistic cooperation of a first and second flow guide to ensure a uniform residence time distribution of the polymer solution in the end cap region. This avoids thermal degradation and cross-linking caused by prolonged residence and eliminates dead zones in the end cap. Furthermore, the first flow guide can collect the polymer solution flowing from each heat exchange tube and accelerate its ejection from the outlet, shortening the flow residence time. This allows operation at higher temperatures without internal boiling, enabling the use of higher-temperature heat transfer media and increasing the heat transfer temperature difference. Additionally, by installing heat tracing medium jackets or heat tracing coils on the outer walls of both the upper and lower end caps, the temperature of the upper and lower end caps is maintained close to the tube-side temperature, preventing a sharp increase in viscosity or even solidification of the high-viscosity polymer solution due to temperature drop. This invention simultaneously eliminates dead zones in the end caps, reduces end cap temperature drop, and improves devolatilization driving force, resulting in a narrower molecular weight distribution and superior optical properties in the concentrated polymer, making it suitable for the production of optical-grade COC and high-performance POE products. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the heat exchanger in a polymer circulation concentration device according to one embodiment of the present invention.

[0015] Figure 2 This is a schematic diagram of the polymer recycling and concentration device in one embodiment of the present invention.

[0016] Explanation of reference numerals in the attached figures: 1-Polymer circulation tank, 2-Circulation pump, 3-Heat exchanger, 4-Expansion tube, 5-Static mixer, 6-Transfer pump, 311-Upper head, 3111-Upper head heating medium inlet, 3112-Upper head heating medium outlet, 3113-Discharge port, 3114-Inert gas injection port, 312-First guide element, 313-Upper flange, 314-Upper tube sheet, 315-Heat exchange tube, 316-Baffle plate, 317-Shell, 318-Lower tube sheet, 319-Lower flange, 320-Second guide element, 321-Lower head, 3171-Shell side heating medium inlet, 3172-Shell side heating medium outlet, 3211-Lower head heating medium inlet, 3212-Lower head heating medium outlet, 3213-Feed inlet. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] Firstly, referring to Figure 1 The present invention proposes a heat exchanger for a polymer circulation concentration device, comprising: a shell 317, an upper tube sheet 314, a lower tube sheet 318, an upper end cap 311, a lower end cap 321, and a plurality of heat exchange tubes 315. The upper end cap 311 and the lower end cap 321 are fixedly connected to both ends of the shell 317, forming a sealed space between the upper end cap 311, the shell 317 and the lower end cap 321; the upper tube sheet 314 and the lower tube sheet 318 are fixed in the chamber from top to bottom, and divide the sealed space into a first chamber, a second chamber and a third chamber arranged from top to bottom. Multiple heat exchange tubes 315 are vertically arranged in the second chamber, and both ends of each heat exchange tube 315 are fixedly connected to the upper tube sheet 314 and the lower tube sheet 318 respectively. The upper tube sheet 314 is provided with a first through hole for connecting the heat exchange tube 315 and the first chamber at the corresponding position of each heat exchange tube 315, and the lower tube sheet 318 is provided with a second through hole for connecting the heat exchange tube 315 and the third chamber at the corresponding position of each heat exchange tube 315. The upper end cap 311 has a discharge port 3113 in the middle, the lower end cap 321 has a feed port 3213 in the middle, the shell side heat medium outlet 3172 is provided at the top of the shell 317 and the second chamber, and the shell side heat medium inlet 3171 is provided at the bottom of the shell 317 and the second chamber.

[0019] In some embodiments, the upper tube sheet 314 and the lower tube sheet 318 are both arc-shaped tube sheets, and each arc-shaped tube sheet is concave to the corresponding upper end cap 311 or lower end cap 321.

[0020] The curved tube sheet design creates a smooth, continuous flow path between the end cap cavity and the tube sheet, fundamentally eliminating the sharp corners and dead angles between the traditional flat tube sheet and the end cap wall. Guided by the curved surface, the polymer adhesive flows smoothly into each heat exchange tube 315 without any stagnation.

[0021] In a further embodiment, the radius of curvature of the arc-shaped tube sheet is 0.6 to 1.8 times the inner diameter of the shell 317.

[0022] In some embodiments, the second chamber is provided with a plurality of baffles 316, which divide the second chamber into an S-shaped flow channel for connecting the shell-side heat medium outlet 3172 and the shell-side heat medium inlet 3171.

[0023] In some embodiments, a first guide member 312 is also included. The first guide member 312 is disposed in the first chamber and is used to collect the polymer liquid flowing out of each heat exchange tube 315 and accelerate its ejection from the outlet 3113.

[0024] In some further embodiments, the first guide element 312 is a venturi structure.

[0025] The Venturi structure includes a converging section, a throat, and a diverging section connected sequentially along the material flow direction. The large end of the converging section faces the upper tube sheet 314 and is used to collect the polymer liquid flowing out of each heat exchange tube 315. The large end of the diverging section is connected to the outlet 3113. The Venturi structure simultaneously serves the dual functions of guiding and collecting flow and pressurizing injection.

[0026] According to Bernoulli's equation and the continuity equation, the flow velocity of the polymer solution increases as it flows through the converging section. The throttling effect of the Venturi structure on the outlet 3113 increases the overall operating pressure within the heat exchanger shell 317 by 0.2~0.8 MPa. According to the Clausius-Clapeyron equation, the increased pressure within the shell 317 correspondingly raises the boiling point of the solvent in the polymer solution, allowing the use of a higher-temperature heat transfer medium without vaporizing the solvent within the heat exchange tube 315. This increases the heat transfer temperature difference, thereby improving the temperature rise and evaporation rate per cycle.

[0027] In practice, the throat diameter of the Venturi structure is calculated based on the pressure drop requirement, material volumetric flow rate, and material viscosity, using Bernoulli's equation and the continuity equation.

[0028] In a further embodiment, an inert gas inlet 3114 is provided on the throat sidewall, which is used to introduce inert gases such as nitrogen and argon.

[0029] It should be understood that, according to Dalton's law of partial pressures, inert gases can reduce the partial pressure of volatiles in the gas phase and increase the driving force for mass transfer in the liquid phase. With this configuration, the introduced inert gas is sheared and dispersed into microbubbles by the high-speed flowing polymer liquid at the throat, thereby increasing the gas-liquid contact area and enhancing the devolatilization effect.

[0030] In a further embodiment, the inert gas inlet 3114 is a radial or tangential interface, so that the introduced inert gas is sheared and dispersed into microbubbles by the high-speed flowing polymer liquid at the throat.

[0031] In some embodiments, a second flow guide 320 is also included. The second flow guide 320 is disposed in a third chamber between the lower tube sheet 318 and the lower end cap 321. The second flow guide 320 is used to uniformly distribute the polymer adhesive entering the lower end cap 321 to each heat exchange tube 315.

[0032] In some further embodiments, the second guide member 320 is a horn structure, with the larger opening of the horn structure facing the lower tube sheet 318 and the smaller opening of the horn structure facing the feed inlet 3213 of the lower end cap 321.

[0033] With this configuration, the second flow guide 320 of the horn structure can evenly distribute the polymer liquid entering the lower head 321 to the inlet of each heat exchange tube 315, avoiding the formation of dead zones due to excessively low local flow rates.

[0034] In some further embodiments, the cone angle of the second guide 320 is 60° to 100°.

[0035] In some embodiments, the outer walls of the upper end cap 311 and the lower end cap 321 are provided with heat tracing medium jackets or heat tracing coils, and independent heat tracing medium flows in the heat tracing medium jackets or heat tracing coils.

[0036] This configuration maintains the head temperature at 150~220°C through independent heat tracing medium circulation, keeping the temperature difference between the upper head 311 and the lower head 321 and the polymer solution in the heat exchange tube 315 within 20°C. This effectively reduces the temperature drop of the polymer solution in the head area, preventing the high-viscosity solution from increasing in viscosity or even solidifying due to temperature drop, thus avoiding the risk of solidification and blockage.

[0037] In some embodiments, the upper end cap 311 is fixedly connected to the top end of the housing 317 via the upper flange 313, and the lower end cap 321 is fixedly connected to the bottom end of the housing 317 via the lower flange 319.

[0038] Compared with the prior art, the present invention has the following beneficial effects: (1) By using the upper tube sheet 314 and lower tube sheet 318 with an arc-shaped tube sheet structure, the first flow guide 312 with a venturi structure, and the second flow guide 320 with a horn structure, the flow channel in the head area is smoothly transitioned, the residence time of the adhesive is evenly distributed, and thermal degradation and cross-linking caused by long-term residence are avoided, thus eliminating the dead zone of the head. Moreover, the venturi structure can pressurize and increase the operating pressure inside the shell 317, shorten the flow residence time, and can operate at higher temperatures without boiling inside the tube, thereby allowing the use of higher temperature heat medium and increasing the heat transfer temperature difference. The pressure drop and the inert gas partial pressure effect work together to enhance devolatilization, effectively improving the devolatilization efficiency. Furthermore, after eliminating the dead zone and excessive thermal degradation, the polymer molecular weight distribution is narrower, the optical performance is better, and it is suitable for the production of optical grade COC and high-performance POE products. (2) By providing heat tracing medium jackets or heat tracing coils on the outer walls of the upper head 311 and the lower head 321, the temperature of the head area in the upper head 311 and the lower head 321 is maintained close to the tube temperature, preventing the high viscosity adhesive from increasing in viscosity or even solidifying due to temperature drop.

[0039] It is important to understand that there is a coupled relationship between the dead zone of the heat exchanger head, the temperature drop of the head, and the insufficient driving force for devolatilization—the temperature drop leads to an increase in viscosity, the increased viscosity exacerbates the dead zone, and the degradation of the adhesive in the dead zone further increases the burden on volatile matter removal. This invention, through the synergistic arrangement of an arc-shaped tube sheet, a Venturi structure, a horn structure, and a heat tracing medium jacket or heat tracing coil, can simultaneously eliminate the dead zone of the head, reduce the temperature drop of the head, and improve the driving force for devolatilization.

[0040] Secondly, such as Figure 2 As shown, the present invention also proposes a polymer circulation concentration device, comprising: a polymer circulation tank 1, a circulation pump 2, a static mixer 5, an expansion pipe 4, a delivery pump 6, and a heat exchanger 3 of the polymer circulation concentration device as described in any one of the first aspects. The bottom outlet of polymer circulation tank 1 is connected to the inlet of circulation pump 2 and the inlet of transfer pump 6, respectively; the top of polymer circulation tank 1 is provided with a gas phase outlet for connecting to the solvent recovery system. The middle part of the polymer circulation tank 1 is connected to the large diameter section of the expansion pipe 4, the small diameter section of the expansion pipe 4 is connected to the outlet 3113 of the heat exchanger 3, the inlet 3213 of the heat exchanger 3 is connected to the outlet of the static mixer 5, the first inlet of the static mixer 5 is connected to the outlet of the circulation pump 2, and the second inlet of the static mixer 5 is used to introduce the polymer solution to be concentrated.

[0041] Thirdly, the present invention also proposes a polymer recycling concentration method, employing a polymer recycling concentration apparatus as described in any one of the second aspects, comprising: The polymer solution to be concentrated and the circulating polymer solution are respectively sent to the static mixer 5; The polymer slurry, after being uniformly mixed by the static mixer 5, enters the heat exchanger 3; After being guided by the second guide element 320, the polymer liquid is distributed into each heat exchange tube 315 and exchanges heat with the shell-side heat medium in the heat exchanger 3; wherein, the temperature of the polymer liquid after the heat exchange is heated is below the boiling point of the solvent in the polymer liquid. After being heated by heat exchange, the polymer liquid is collected by the first guide element 312 and sprayed into the expansion pipe 4 through the discharge port 3113, where flash evaporation and volatilization are triggered by a sudden drop in pressure. The devolatilized polymer solution returns to the polymer circulation tank 1 via the expansion pipe 4; The polymer solution after flash devolatilization is returned to the polymer circulation tank 1 through the expansion pipe 4, and the gas phase generated by flash devolatilization is discharged to the solvent recovery system through the expansion pipe 4 and the gas phase outlet of the polymer circulation tank 1. Real-time monitoring of polymer solution concentration in polymer circulation tank 1; When the polymer solution concentration does not reach the target concentration, all polymer solutions are returned to the static mixer 5 by the circulation pump 2 as circulating material, and then mixed with the polymer solution to be concentrated to continue the concentration process. When the polymer solution concentration reaches the target concentration, a portion of the polymer solution is pressurized and output by the delivery pump 6 to the subsequent deep devolatilization equipment, while the other portion is sent back to the static mixer 5 as circulating material by the circulation pump 2, where it is mixed with the polymer solution to be concentrated and then further concentrated.

[0042] In some embodiments, the temperature variation range of the shell-side heat medium during the heat exchange process is 160~250°C; the temperature variation range of the heat tracing medium flowing in the heat tracing medium jacket or heat tracing coil is 150~220°C, so that the temperature difference between the end cap region of the upper end cap 311 and the lower end cap 321 and the polymer adhesive temperature in the tube side of the heat exchange tube 315 is controlled within 20°C.

[0043] In some embodiments, it also includes: Nitrogen gas is introduced through an inert gas inlet, with a flow rate of 2% to 10% (by volume) of the polymer liquid flow rate.

[0044] During the circulation process, the operating pressure inside heat exchanger 3 is 0.3~1.0 MPaG, and the pressure inside polymer circulation tank 1 is 0.02~0.08 MPaG. When the polymer solution enters the expansion tube 4 through the Venturi structure, the pressure drops from 0.3~1.0 MPaG to 0.02~0.08 MPaG.

[0045] The present invention will now be described in conjunction with specific embodiments and accompanying drawings.

[0046] Example 1 This embodiment proposes a polymer circulation concentration device for concentrating polyolefin elastomer (POE) polymer solutions, comprising a polymer circulation tank 1 (effective volume 500L, with jacketed vacuum insulation), a circulation pump 2 (gear pump, flow rate 600L / h, head 0.6MPa), a static mixer 5 (SK type static mixer), a heat exchanger 3, an expansion pipe 4, and a transfer pump 6 (gear pump, flow rate 50L / h, head 0.8MPa).

[0047] In this embodiment, the heat exchanger 3 is a vertical shell-and-tube heat exchanger, including: a shell 317, an upper tube sheet 314, a lower tube sheet 318, an upper end cap 311, a lower end cap 321, and multiple heat exchange tubes 315.

[0048] The shell 317 has an inner diameter of 300 mm. The upper tube sheet 314 and lower tube sheet 318 are fixed to both ends of the shell 317, with an arc radius of curvature 1.2 times the inner diameter of the shell. There are 55 heat exchange tubes 315, with a total heat exchange area of ​​approximately 5.4 m². Each heat exchange tube 315 has a spiral insert to enhance the turbulence and heat transfer effect of the polymer solution.

[0049] The upper head 311 is a standard elliptical head, and its first guide element 312 is a Venturi structure, including a tapered section (cone angle 20°), a throat, and a diffusing section (cone angle 8°). An inert gas injection inlet 3114 is provided on the side wall of the throat. The second guide element 320 in the lower head 321 is a horn structure, with the larger opening of the horn structure facing the heat exchange tube 315.

[0050] Both the upper head 311 and the lower head 321 are equipped with heat-conducting oil jacket structures for heat tracing. The upper head 311's heat tracing medium inlet 3111 and outlet 3112 are located on both sides of the upper head 311, while the lower head 321's heat tracing medium inlet 3211 and outlet 3212 are located on both sides of the lower head 321. The shell-side heat medium inlet 3171 is located at the lower part of the shell 317, and the shell-side heat medium outlet 3172 is located at the upper part of the shell 317. The shell 317 contains arc-shaped baffles 316 spaced 200mm apart.

[0051] Materials and Process: POE polymer solution is produced by solution polymerization of ethylene and 1-octene, using n-hexane as the solvent. The initial polymer solids content is 15.0 wt%, and the target solids content is 80.0 wt%. Fresh POE polymer solution is fed into static mixer 5 at a rate of 40 L / h, where it is mixed with the circulating polymer solution (560 L / h) before entering heat exchanger 3 at a mixing flow rate of 600 L / h. The shell-side heat transfer oil temperature is 180°C, the internal operating pressure of heat exchanger 3 is 0.5 MPaG, and the vacuum degree of polymer circulation tank 1 is 0.05 MPaG.

[0052] Hexane has a boiling point of approximately 135°C at 0.5 MPaG and approximately 81°C at 0.05 MPaG. The polymer solution is heated from 45°C to 120°C in heat exchange tube 315; after being sprayed out through the Venturi structure to the expansion tube 4, the pressure drops to 0.05 MPaG, and the volatiles flash evaporate. Inert gas is injected into inlet 3114 with nitrogen at a volume flow rate of 5% to assist in the devastation. After flash evaporation, the temperature of the polymer solution drops to approximately 105°C.

[0053] After approximately 14 cycles, the solid content reaches over 80wt%. Pump 6 delivers the concentrated polymer solution to the subsequent screw devouring extruder. The product has a POE melt index of 3.5g / 10min, meeting the photovoltaic film grade requirements.

[0054] Example 2 This embodiment proposes a polymer circulation concentration device for concentrating cyclic olefin copolymer (COC) polymer solutions. The device structure is basically the same as that in Embodiment 1, except that: the radius of curvature of the arc-shaped tube sheet is 1.0 times the inner diameter of the shell 317; the cone angle of the horn structure of the second guide 320 is 80°; the heat exchanger 3 has 37 heat exchange tubes 315 with an inner diameter of 200mm in the shell 317, and a total heat exchange area of ​​about 2.3m².

[0055] Materials and Process: Norbornene and ethylene COC polymer solution, toluene as solvent, initial polymer solution solid content 10.0 wt%, viscosity at 80°C approximately 20 mPa·s, target solid content 50.0 wt%. Fresh COC polymer solution 30 L / h is fed into static mixer 5 to mix with circulating polymer solution (350 L / h), flow rate approximately 380 L / h. Shell-side heat transfer oil 240°C, heat tracing 200°C, heat exchanger 3 pressure 1.0 MPaG, polymer circulation tank 1 pressure 0.06 MPa.

[0056] Toluene has a boiling point of approximately 223°C at 1.0 MPaG and approximately 128°C at 0.06 MPaG. The polymer solution does not vaporize when heated from 55°C to 180°C; after passing through the Venturi structure and entering the expansion tube 4, it flashes at 0.06 MPaG. Inert gas is injected into inlet 3114, where 8% nitrogen by volume is introduced, and the temperature drops to approximately 160°C.

[0057] After approximately 18 cycles, the solid content reaches over 50 wt%. The product's COC transmittance is 91%, meeting optical grade specifications.

[0058] Example 3 This embodiment proposes a polymer circulation concentration device for concentrating polyolefin elastomer (POE) polymer solutions. The device is the same as in Embodiment 1, except that inert gas is not used and the heat transfer oil jacket structure is replaced with an electric heating belt.

[0059] Materials: Initial polymer solution solid content 12.0 wt%, target solid content 70.0 wt%. Process: Shell-side heat transfer oil 160°C, heating tracing 150°C, heat exchanger 3 pressure 0.4 MPaG, polymer circulation tank 1 vacuum degree 0.06 MPaG. Hexane has a boiling point of approximately 126°C at 0.4 MPaG. The polymer solution is heated from 40°C to 110°C, then injected into the expansion tube 4 via a Venturi mechanism and flashed at 0.06 MPaG, with the temperature dropping to approximately 95°C.

[0060] After approximately 17 cycles, the solid content reaches 70 wt%. Without the assistance of inert gas, the curved tube sheet and flow guide can still effectively eliminate dead zones, and the gel content of the product is reduced by about 65% compared with the traditional planar tube sheet process, with melt index fluctuation <±5%.

[0061] Comparative Example 1 A conventional planar tube sheet heat exchanger of the same specifications (without flow guides, Venturi, or heat tracing) was used, and the other conditions were the same as in Example 1. Without Venturi pressurization, the internal pressure of the planar tube sheet heat exchanger was only 0.15 MPa. To prevent vaporization, the shell-side heat transfer oil was kept at only 110°C, reducing the heat transfer temperature difference by approximately 40°C.

[0062] Actual measurements showed that the standard deviation of the residence time distribution of the end cap was 3.2 times that of Example 1; the end cap temperature was about 42°C lower than that of the tube side, and the viscosity increased by about 8 times; 24 cycles were required to achieve the same solid content; the melt index of the product fluctuated by ±10%, and the molecular weight distribution became wider.

[0063] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A heat exchanger for a polymer circulation concentration device, characterized in that, Includes: a shell, with an upper end cap and a lower end cap fixed at the upper and lower ends of the shell respectively, forming a sealed space between the upper end cap, the shell and the lower end cap, and the outer walls of the upper end cap and the lower end cap are provided with heat tracing medium jackets or heat tracing coils; An upper tube sheet and a lower tube sheet are fixed inside the sealed space, which divide the sealed space into a first chamber, a second chamber and a third chamber from top to bottom; multiple heat exchange tubes are vertically arranged in the second chamber to connect the first chamber and the third chamber; The upper head has a discharge port in the middle, the lower head has a feed port in the middle, the shell side heat medium outlet is located at the top of the shell and the second chamber, and the shell side heat medium inlet is located at the bottom of the shell and the second chamber. The first chamber is equipped with a first guide element for collecting the polymer liquid flowing out of each heat exchange tube and accelerating its spraying from the outlet. The first guide element is a Venturi structure, which includes a tapered section, a throat and a diffusing section connected in sequence along the material flow direction. The large end of the tapered section faces the upper tube sheet and is used to collect the polymer liquid flowing out of each heat exchange tube. The large end of the diffusing section is connected to the outlet. The third chamber is equipped with a second flow guide for evenly distributing the polymer liquid entering the lower head to each heat exchange tube; the second flow guide is a horn structure, with the larger opening of the horn structure facing the lower tube sheet and the smaller opening of the horn structure facing the feed inlet.

2. The heat exchanger of the polymer circulation concentration device according to claim 1, characterized in that, Both the upper and lower tube sheets are curved tube sheets, and each curved tube sheet is concave towards the corresponding upper or lower end cap.

3. The heat exchanger of the polymer circulation concentration device according to claim 2, characterized in that, The radius of curvature of the arc-shaped tube sheet is 0.6 to 1.8 times the inner diameter of the shell.

4. The heat exchanger of the polymer circulation concentration device according to claim 1, characterized in that, An inert gas inlet is provided on the side wall of the throat, which is used to introduce inert gas.

5. The heat exchanger of the polymer circulation concentration device according to claim 4, characterized in that, The inert gas inlet can be radial or tangential.

6. A polymer recycling and concentration device, comprising: Polymer circulation tank, circulation pump, static mixer, expansion pipe, transfer pump, and heat exchanger of the polymer circulation concentration device as described in any one of claims 1-5; The bottom outlet of the polymer circulation tank is connected to the inlet of the circulation pump and the inlet of the transfer pump, respectively, and the top of the polymer circulation tank is provided with a gas phase outlet for connecting to the solvent recovery system. The middle section of the polymer circulation tank is connected to the large-diameter section of the expansion pipe, the small-diameter section of the expansion pipe is connected to the outlet of the heat exchanger, the inlet of the heat exchanger is connected to the outlet of the static mixer, the first inlet of the static mixer is connected to the outlet of the circulation pump, and the second inlet of the static mixer is used to introduce the polymer solution to be concentrated.

7. A polymer recycling concentration method, using the polymer recycling concentration apparatus of claim 6, characterized in that, include: The polymer solution to be concentrated and the circulating polymer solution are respectively sent to a static mixer. After being mixed evenly in the static mixer, the polymer solution enters the heat exchanger. After being guided by the second flow guide, the polymer adhesive is distributed into each heat exchange tube and exchanges heat with the shell-side heat medium in the heat exchanger; wherein, the temperature of the polymer adhesive after the heat exchange is heated is below the boiling point of the solvent in the polymer adhesive. After being heated by heat exchange, the polymer liquid is collected by the first guide element and sprayed into the expansion pipe through the outlet. Due to the sudden drop in pressure, flash evaporation and volatilization occur. The polymer solution after flash devolatilization is returned to the polymer circulation tank through the expansion pipe, and the gas phase generated by flash devolatilization is discharged to the solvent recovery system through the expansion pipe and the gas phase outlet of the polymer circulation tank. Real-time monitoring of polymer solution concentration in the polymer circulation tank; When the polymer solution concentration does not reach the target concentration, all polymer solutions are returned to the static mixer as circulating material by the circulating pump, and then mixed with the polymer solution to be concentrated to continue the concentration process. When the polymer solution concentration reaches the target concentration, a portion of the polymer solution is pressurized and output to the subsequent deep devolatilization equipment by the delivery pump, while the other portion is sent back to the static mixer as circulating material by the circulation pump to be mixed with the polymer solution to be concentrated and then further concentrated.

8. The polymer recycling concentration method according to claim 6, characterized in that, The shell-side heat transfer medium temperature is 160~250°C; the temperature of the heat transfer medium flowing in the heat transfer medium jacket or heat transfer coil is 150~220°C; the operating pressure inside the heat exchanger is 0.3~1.0MPaG, and the pressure inside the polymer circulation tank is 0.02~0.08MPaG.

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