Process and apparatus for treating a starting product

Abstract

A process for treating a starting product consisting of preferably 5-30% polymer and 70-95% solvent is characterized by the following steps: - at a process temperature specific to the respective polymer, the starting product is directed into a delivery unit, which generally takes the form of a pump. - the starting product passes a one-way valve (9), - the starting product is heated and also pressurized in a plate heat exchanger (2), - the heated and pressurized starting product is introduced into a mixing kneader (5) as a flash discharge, under the control of a pressure-maintaining valve (8), and processed as an intermediate product and - is transported away as product through an output (7).

Description

[0001] Method and device for treating a starting product

[0002] Technical area

[0003] The invention relates to a method for treating a starting product according to the preamble of claim 1 and a device according to the preamble of claim 6.

[0004] State of the art

[0005] Such processes are already known and in use in a wide variety of forms and embodiments. For example, EP 2 328 937 B discloses that, in order to process a starting product, a pre-concentration or concentration takes place between a stirred tank and an extruder, which is characterized by a so-called flash evaporation. Flash evaporation is a thermal separation process involving a sudden drop in pressure when the product enters a container, so that part of the solvent in the product passes directly into the gas phase due to a thermal flash. Flash refers to sudden flash evaporation. This process has the advantage of a high evaporation capacity due to the flash, resulting in large vapor flows. However, it is also associated with cooling of the product, which contains less solvent after flash evaporation and is therefore more concentrated.Cooling is a direct consequence of the gas equation or the energy removal caused by the flash. Cooling, in turn, reduces the product's flowability. Flashpots typically have sloped walls to allow the product to flow gravimetrically toward the flashpot's outlet opening. However, if the flowability is too low, the flashpot will no longer empty, resulting in a flowability limit. A larger flash would cool the product so much that the flowability limit would be exceeded, preventing the flashpot from emptying and quickly clogging. Thus, the product's flowability limit represents a limitation of the evaporation capacity of conventional flashpots, as described in EP 2 328 903 B1.

[0006] After the flash pot, a complex and energy-intensive reheating process must take place in a tubular heat exchanger. This poses the risk of fowling, where deposits form on the surfaces of the heat tubes before the feedstock is fed to the extruder for residual degassing. This, in turn, leads to increased labor input because the deposits must be removed from the tubes of the tubular heat exchanger, requiring the entire system to be shut down, which in turn increases costs. Furthermore, tubular heat exchangers, due to their design, are not suitable for applying the desired pressure to the feedstock to enable the so-called explosive flash discharge to occur inside the mixer-kneader. Object of the invention

[0007] The object of the invention is to improve the mixing kneaders according to the prior art in such a way that a method and a device are provided in which the processing of a starting product to a final product is achieved as cheaply as possible, whereby the method and the device manage the processing of a product more efficiently, smaller, more cost-effectively and at the same time also more reliably.

[0008] Solution to the task

[0009] The features of claim 1 and the features of claim 6 lead to the solution of the problem.

[0010] Advantageous embodiments are described in the subclaims.

[0011] A process according to the invention for treating a starting product, which preferably consists of 5-30% polymer and 70-95% solvent, is characterized by the following steps: the starting product is fed into a conveying unit, which is usually a pump, at a process temperature specific to the respective polymer. The starting product passes through a one-way valve, unidirectionally, to prevent a pressure drop as a result of backflow into the pump under any operating condition. The starting product is preferably heated in a spiral plate heat exchanger to, for example, 180°C and the pressure is additionally increased. The maximum temperature depends on the type of polymer, the solvent, and the maximum permissible pressure in this part of the system.The mixed, heated and pressurized starting product is introduced into a mixing kneader as a flash discharge controlled by a pressure control valve and processed as an intermediate product, and transported away as a product through a discharge.

[0012] The starting material can be, for example, rubber, thermoplastic elastomers, or thermoplastics. The composition of the starting product typically consists of 5-30% polymer and 70-95% solvent, but depending on the starting product, the component content can also fall outside this range and reach values ​​of 50% or slightly higher.

[0013] The starting product is fed to a feed pump, usually from an intermediate tank, ideally with an agitator to prevent demixing.

[0014] The feed product passes through a one-way valve after leaving the feed pump. This is intended to prevent a pressure drop in the feed product above the pump, for example, when the pump is in operation.

[0015] In a subsequent step, the starting product is guided / conducted / pressed, or transported in some other way, through a spiral plate heat exchanger, where it is heated to the maximum process temperature and additionally pressure-increased. Spiral plate heat exchangers can also be heat plate exchangers. This depends on the size of the overall system and / or the total pressure resulting from the temperature increase.

[0016] The use of spiral plate heat exchangers in the pre-mixing stage has not been considered in the prior art, even though it is more cost-effective and, due to its design, allows for greater pressure to be built up in the feedstock. The plate heat exchangers previously used in the prior art served only as an intermediate step before the feedstock could be subjected to pre-concentration or concentration in a so-called flash pot.

[0017] In the flash pot, a portion of the solvent was evaporated in a first step at elevated temperatures. This, in turn, presented the problem of a sludge forming in the funnel-shaped outlet of the flash pot, which had to be kept fluid at all times. To ensure fluidity, the degree of concentration had to be limited depending on the resulting viscosity of the polymer solution. A gear pump then pumped the starting product, concentrated according to the state of the art, to a tubular heat exchanger for reheating.

[0018] In the prior art, tubular heat exchangers were considered the only option for reheating due to the pressure loss resulting from the higher viscosity of the concentrated starting product. The disadvantage of tubular heat exchangers was that increasing the pressure of the concentrated starting product was very complex. However, increasing the pressure was and is necessary to achieve effective flash discharge in the downstream mixer-kneader. The disadvantage of a less effective flash discharge was compensated in the prior art by the complex and expensive installation of the flash pot upstream.

[0019] The use of the spiral plate heat exchanger now makes it possible to feed the mixer kneader with a feed product at high temperature and high pressure, achieving a particularly effective flash discharge in the mixer kneader. This eliminates the costs of the flash pot and the tubular heat exchanger, as well as the associated increased maintenance work and costs. By omitting the flash pot and the tubular heat exchanger and adjusting the capacity of the spiral plate heat exchanger, it is possible to feed the feed product to the mixer kneader at high pressure and high temperature, ensuring a particularly effective, fast, and safe flash discharge.

[0020] The plate heat exchanger plays an important role here, since the starting product is heated highly efficiently due to the geometric conditions of the exchanger and the resulting short residence time of the starting product in the heat exchanger at high temperature means that the risk of polymer damage can be eliminated.

[0021] Another advantage of the heated and pressurized feedstock is that the pressure-maintaining valve can be operated with fewer problems and failures. The pressure-maintaining valve, also known as an equilibar, is designed as a pressure-controlled capillary. Two membranes sealed to each other by pressure are spaced apart when the side pressure is greater than the preset pressure between the two membranes. The advantage of the pressurized feedstock in the spiral plate heat exchanger always ensures sufficient side pressure to open the two membranes of the pressure-maintaining valve without the risk of an uncontrolled pressure drop. Consequently, the user can pulse the pressurized feedstock as desired to ensure controlled opening and closing of the two membranes.With state-of-the-art tubular heat exchangers, this could only be achieved with great effort and additional steps and was not always process-reliable.

[0022] A further advantage of the described process is that, due to the high temperature and high pressure levels of the starting product, an effective flash discharge can occur in the mixing kneader. After the flash discharge, in which a high percentage of the solvent is explosively released in the mixing kneader, an intermediate product is created, which is immediately cooled by flash evaporation upon entering the mixing kneader. The intermediate product, whose polymer temperature is now non-critical, can also be effectively processed further in the mixing kneader before being transported away as a product through a discharge outlet. This has the advantage that the mixing kneader can be used more optimally due to its design. High temperatures and pressures, which lead to a correspondingly effective flash discharge, are not a problem for a mixing kneader. In the prior art, the mixing kneader was therefore not able to optimally exploit its advantages.

[0023] In a preferred embodiment, the flash discharge is introduced into the mixing kneader after the vapor dome in one process direction. The mixing kneader also contains clearance elements that transport the intermediate product away from the vapor dome, thus ensuring reliable vapor removal. Furthermore, processing elements are arranged in the mixing kneader to convert the intermediate product into the final product. The product is fed to the discharge by means of discharge elements in the mixing kneader.

[0024] The clearance elements, the processing elements, and the discharge elements are arranged on a shaft in the mixer-kneader. From a rear plate of the mixer-kneader to the discharge, the clearance elements are arranged first on the shaft, followed by the processing elements, and finally the discharge elements.

[0025] A device according to the invention serves to treat a starting product consisting preferably of 5-30% polymer and 70-95% solvent, or in exceptional cases as mentioned above, up to more than 50% polymer. The polymers mentioned above for the process also apply to this device. Furthermore, the plate heat exchanger is arranged between the conveying unit and the mixing kneader. This wording is intended to clarify that no tubular heat exchanger, flash pot, or other concentration device is interposed.

[0026] The starting product concentration is constant between the conveying unit and the mixing kneader. "Consistent concentration" means that the composition of the starting product remains essentially constant on its way from the conveying unit to the mixing kneader. This excludes minor fluctuations that may arise, for example, from existing safety devices such as valves or the like.

[0027] The unidirectional valve described above is located between the pumping unit and the plate heat exchanger. The above statements also apply to the device.

[0028] A pressure relief valve is located between the plate heat exchanger and the mixer-kneader. The above statements also apply to the device.

[0029] The flash inlet is arranged between a vapor dome and the discharge of the mixer-kneader. The statements above also apply to the device. By arranging the flash inlet between the vapor dome and the discharge, the design of the mixer-kneader can be advantageously utilized. Between the flash inlet and the outlet, there is no element, such as the vapor dome, that weakens the structure of the mixer-kneader. The vapor dome is arranged towards the rear plate of the mixer-kneader. The discharge is arranged opposite on a front plate of the mixer-kneader. This creates a gun-barrel shape for the mixer-kneader, which ensures additional safety and process stability, especially during flash discharges. In addition, the use of a plate heat exchanger or spiral plate heat exchanger is claimed for the device according to the invention described above.

[0030] In the exemplary embodiment according to the invention, the flash introduction can occur via one or more points in the mixing kneader. A flash introduction is defined by the fact that a starting product subjected to excess pressure and excess temperature immediately relaxes upon entering a process chamber or working chamber of the mixing kneader, subsequently releasing a portion of the solvent contained in a solution. The excess pressure and excess temperature refer to the pressure and temperature of the starting product before entering the mixing kneader, compared to the pressure and temperature in the process chamber of the mixing kneader. Simultaneously with the relaxation of the pressure, the starting product also cools. This results in an explosive expansion of the starting product, which allows the solvent to escape particularly easily. This results in atomization of the polymer.In the prior art, these polymer atomizations are drawn into the vapor dome with the solvent and settle on the dome wall. This can even lead to blockage of the vapor dome. The polymer that has settled on the dome wall is also subject to continuous thermal stress, resulting in thermal damage. If such thermally damaged particles fall back into the regular product in the mixer-kneader, this leads to undesirable contamination of the product, which in turn can reduce product quality. This is prevented by the vapor dome arrangement described here, so that the mixer-kneader can operate trouble-free for longer with this vapor dome arrangement.

[0031] The flash inlet is operatively connected to the pressure-maintaining valve. The arrangement of the pressure-maintaining valve directly upstream of the flash inlet allows the feedstock to be introduced into the mixer-kneader in batches, allowing for explosive expansion, and then the next batch of feedstock to be introduced into the mixer-kneader for explosive expansion. The batches can, of course, also overlap.

[0032] Regardless of the pressure and temperature in the mixer, the starting product exhibits relative overpressure and elevated temperature. This can lead to a flash, generating foam that is prevented from rising into the vapor dome by the release elements.

[0033] The vapor dome is located in a section of the rear plate or, in exceptional cases, flush with the rear plate. The primary goal here is to keep the area below the vapor dome in the mixer housing as clear as possible. By arranging the vapor dome flush with the rear plate, the area to be kept clear is kept as small as possible. In the design in which the vapor dome is positioned offset from the rear plate toward the front plate, cost savings can be achieved during production, allowing both variants to implement the inventive concept equally.

[0034] The closer the vapor dome is positioned to the back plate, the smaller the area that needs to be kept clear in the mixer kneader. The smaller the area that needs to be kept clear, the better the mixer kneader can be used. While arranging the vapor dome flush with the back plate optimally reduces the area that needs to be kept clear, this is offset by higher manufacturing costs. Therefore, a specialist must determine whether and how far the vapor dome should be from the back plate.

[0035] Naturally, the mixing kneader according to the invention is longer in its axial extent than mixing kneaders without a vapor dome on the side facing away from the first flash inlet in the product flow direction. The section between the vapor dome and the first flash inlet contains little or no product and is thus used for vapor removal but not for vapor-generating product processing. However, this cost disadvantage can be reduced in the mixing kneader according to the invention by designing the vapor dome shorter in its axial extent than in its radial extent, rather than circular. This minimizes the section between the back plate and the first flash inlet in the mixing kneader. This minimizes the size difference compared to a mixing kneader for similar processes but without the inventive design. The number of flash inlets can vary.

[0036] "Product" always refers to the polymer-containing portion of the product stream, which, as intended, is enriched with increasing amounts of polymer while the solvent content is reduced. Therefore, the product must be defined such that a specific ratio of polymer to solvent is achieved. The solvent content can also be zero.

[0037] In one embodiment, the vapor dome and the flash inlet are arranged longitudinally adjacent to each other in a north pole region of the mixing kneader. The north pole region is assumed to be the region of the mixing kneader that opposes the direction of gravitational force in the upper region. A south pole region would therefore be the region of the mixing kneader arranged in the direction of gravitational force.

[0038] In a further embodiment, the vapor dome is arranged in the north pole region of the mixing kneader and the flash inlet is arranged in an equatorial region of the mixing kneader.

[0039] The equatorial region here means approximately the region whose center is located centrally on the surface of the mixer-kneader, running from the north pole region to the south pole region. Half of the path from the center to the north pole region and from the south pole region to the north pole region is covered by the equatorial region. In this embodiment, the shaft is arranged such that the starting product introduced by the flash feed is transported away. For this purpose, the clearance elements arranged on the shaft, as already described above, are used.

[0040] The vapor dome can be designed with heating. This allows for better utilization of the mixing kneader and prevents unwanted condensation of the vapors in the vapor dome. Preferably, the temperature can be set independently of the temperature in the mixing kneader, in a housing shell, or in the mixing kneader shaft. This allows a specifically selected temperature in one wall of the vapor dome to ensure condensation such that the resulting condensate flow (also called reflux) flows along the walls of the vapor dome downwards into the intermediate product in the mixing kneader, cleaning it of fine particles that have settled there.

[0041] The vapor dome section of the work chamber may include a temperature sensor. This can be used to measure the product temperature.

[0042] Character description

[0043] Further advantages, features and details of the invention will become apparent from the following description of preferred embodiments and from the drawings, which show:

[0044] Figure 1 shows a device Vs according to the prior art;

[0045] Figure 2 shows a device V according to the invention e .

[0046] Example

[0047] Figure 1 describes a prior art device Vs. This device Vs serves to process a starting product between a container 18 and a mixer-kneader 5. Preconcentration or concentration takes place. This preconcentration is initially achieved by heating in a plate heat exchanger 15. The starting product is then fed to a preconcentrator or flash pot 3. There, a portion of the starting product, particularly the solvent, evaporates, resulting in a drop in the temperature of the starting product.

[0048] This temperature drop is then compensated for in a tubular heat exchanger 4. The reheated starting product is then fed to the mixing kneader 5 via a metering valve.

[0049] The resulting increase in the viscosity of the starting product is characteristic of the state of the art. In addition, the flowability of the starting product during concentration in a funnel-shaped outlet 16 of the flash pot 3 must be taken into account. A sump forms in the funnel-shaped outlet 16. This sump must always remain flowable to prevent the outlet 16 from becoming blocked. The evaporation and cooling that take place in the flash pot 3 counteract the flowability. If this does not happen, parts of the sump can settle in the outlet 16 in the form of deposits, which then require costly cleaning. The flash pot must also be provided with a sufficiently large volume, as there is a risk of foam formation during the flash process. If the foam does not have sufficient volume, there is a risk that the flash process cannot be maintained.This risk of foam formation is additionally counteracted in the prior art by adding cost-increasing additives. A gear pump (not shown in detail) is connected to the outlet 16, which feeds the concentrated starting product to a complex and energy-intensive reheating process in a tubular heat exchanger 4.

[0050] The tubular heat exchanger 4, in turn, involves the so-called fowling risk, whereby a deposit repeatedly forms on the heat tubes before the concentrated starting product is fed to the mixing kneader 5. This, in turn, leads to increased labor input because the deposit must be removed from the tubes of the tubular heat exchanger 4, which requires the entire system to be shut down, which in turn leads to increased costs.

[0051] Figure 2 shows a device V according to the invention e. The conveyor unit 1 is shown, to which a one-way valve 9 is connected. A plate heat exchanger 2 and a pressure-maintaining valve 8 are connected to the one-way valve 9, before the mixing kneader 5 is arranged.

[0052] The mixing kneader 5 has a rear plate 14 and a front plate 17, between which a shaft 13 is arranged. Clearance elements 10, processing elements 11, and discharge elements 12 are arranged on the shaft 13 in the direction of production. The direction of production means the direction from the rear plate 14 to the front plate 17. A flash inlet (not shown in detail) is arranged between a vapor dome 6 and a discharge 7 on the front plate 17 of the mixing kneader 5. "Between the vapor dome 6 and the discharge 7" means that the flash inlet can be arranged over the entire surface of the mixing kneader 5, as long as the clearance elements 10 can maintain their function of keeping a vapor functional area of ​​the vapor dome 6 clear. In this context, it should also be noted that the same applies to the function of the discharge elements 12.In fact, the flash entry must be regularly provided in the area of ​​the processing elements 11 so that the processing elements 11 can process the intermediate product into a product.

[0053] Referring to Figure 2, the functioning of the device according to the invention is explained as follows:

[0054] First, the starting product is mixed in the conveying unit 1 at a maximum temperature of 120°C. The mixed starting product passes through the one-way valve 9 and is heated to 180°C in the spiral plate heat exchanger 2, where it is additionally pressurized. The mixed, heated, and pressurized starting product is introduced into the mixing kneader 5 as a flash discharge, controlled by the pressure-maintaining valve 8, processed as an intermediate product, and finally transported away as a product through the discharge 7.

[0055] The flash discharge is introduced into the mixing kneader 5 between a vapor dome 6 and the discharge 7. After the flash discharge, the vapors are drawn towards the vapor dome 6, and the intermediate product is transported away from the vapor dome 6 or the vapor function area by the clearance elements 10. A controlled spatial separation of vapor and intermediate product takes place after the flash discharge. The processing elements 11 in the mixing kneader 5, which are arranged between the clearance elements 10 and the discharge elements 12, convert the intermediate product into the product. The discharge elements 12, in turn, feed the product to the discharge 7, so that further flash discharges can occur in the area of ​​the processing elements 11.

[0056] List of reference symbols

Claims

Patent claims 1 .Process for treating a starting product, which preferably consists of 5 - 30% polymer and 70 - 95% solvent, is characterized by the following steps: - the starting product is fed into a conveying unit, which is usually a pump, at a process temperature specific to the respective polymer; - the starting product passes through a one-way valve (9), - the mixed starting product is heated in a plate heat exchanger and additionally pressure increased. - the mixed, heated and pressurised starting product is introduced into a mixing kneader (5) as a flash discharge controlled by a pressure control valve (8) and processed as an intermediate product, and - as product transported away through a discharge (7).

2. Method according to claim 1, characterized in that the flash discharge is introduced into the mixing kneader (5) between a vapor dome (6) and the discharge (7).

3. Method according to claim 1 or 2, characterized in that in the mixing kneader (5) clearance elements (10) transport the intermediate product away from a vapor discharge area.

4. Method according to one of the preceding claims, characterized in that in the mixing kneader (5) processing elements (11) convert the intermediate product into the product.

5. Method according to one of the preceding claims, characterized in that in the mixing kneader (5) discharge elements (12) feed the product to the discharge (7).

6. Device for treating a starting product consisting of preferably 5 - 30% polymer and 70 - 95% solvent, characterized in that a plate heat exchanger (2) is arranged between a conveying unit (1) and a mixing kneader (5), the starting product having the same concentration between the conveying unit (1) and the mixing kneader (5).

7. Device according to claim 6, characterized in that a one-way valve (9) is arranged between the conveying unit (1) and the spiral plate heat exchanger (2).

8. Device according to claim 6 or 7, characterized in that a pressure holding valve (8) is arranged between the spiral plate heat exchanger (2) and the mixing kneader (5).

9. Device according to one of the preceding claims, characterized in that a flash inlet is arranged between a vapor dome (6) and a discharge (7) of the mixing kneader (5).

10. Device according to one of the preceding claims, characterized in that the mixing kneader (5) has clearance elements (10), processing elements (11) and discharge elements (12) on a shaft (13).

11. Device according to claim 10, characterized in that from a back plate (14) of the mixing kneader (5) to the discharge (7) first the clearance elements (10), then the processing elements (11) and subsequently the discharge elements (12) are arranged on the shaft (13).

12. Use of a plate heat exchanger (2) for a device according to claims 6 to 11.

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