DE19520675C2 - Method and device for crystallization - Google Patents

Description

The invention relates to a method and an apparatus for crystallizing Substances by cooling a liquid medium containing the substance according to the generic part of the first and fifth claims.

Crystallization processes of substances are in different designs men known and serve, for example, fractions of different sub separate stamping components and / or cleaning substances perform. An application can be particularly in the field of food technology, where a typical task is to mix mixtures of Separate ingredients from different fats. The fats show different melting points, so that after a melt and an closing cooling defined within predetermined temperature intervals Crystallize product components.

An apparatus and a method for separating such fusible organi shear mixtures are described for example in DE-A 41 32 892. A One particular task here is fractionation of palm oil.

DE-A 25 24 545 has disclosed a freeze finishing process, in which a container is used which contains a liquid melting material from pure and contains impure materials, the pure materials being in crystalline form are divorced. The melt is essentially in a liquid state in the Container held, with a rotatable cooling shaft immersed in the melt becomes. On the cooling shaft, heterogeneous material in crystalline form is mixed in the we deposited substantial radial grain growth with respect to the cooling shaft, the Crystals contain essentially pure material and at least the grain boundaries  are partly formed by the impure materials. The heterogeneous material is separated from the cooling shaft while maintaining the crystalline form.

DE-B 12 85 983 shows a cooling crystallizer that is upright standing container and a tube inside, through which coolant flows system, which is formed by a multi-U-shaped tube, which with the upper part protruding from the solution to be cooled an elastically held on the container frame is firmly connected is connected to a device generating vibrations.

Palm oil is an inexpensive and versatile raw material for production from food, detergent products and technical lubricants to towards fuel replacement. Each use requires special product properties, which could be generated by different procedural treatments sen.

Here, the fractionation of palm oil has developed particularly well. At the Frak tioning are controlled by controlled temperature control Palm oils or palm oil fractions in a stirred crystallizer at temperatures below crystallized half of the melting point, then in a membrane filter press filtered off and pressed at up to 25 bar.

It is extremely important for the filtration and the subsequent pressing process tig that the crystals as large as possible and against a pressure load when pressing are sufficiently resistant. Large crystals have a specifically small size surface, form larger capillaries and thus promote the purity of the Products after the solid-liquid separation.

The crystal growth and the final size of the crystals is due to the careful temperature reduction and that for the heat exchange process essential stirring affected.  

The crystallization of palm oils or of palm oil fractions is carried out in stirred crystallizers in different, successive stages using hot water, cooling water and / or cold water or cooling sole performed. It is important to ensure that adequate heat exchange between the cooling medium and the product especially with small temperature differences below the crystallization point tes takes place. Large temperature differences and / or insufficient heat Exchange rate or flow to the cooling surfaces leads to the occupancy of the heat exchange surfaces with crystals and to significantly extend the crystallization times. In the worst case, the process has to be stopped and started again be.

To avoid covering the heat exchange surfaces and a good warmth to achieve an exchange between the heating or cooling medium and the product Product stirred during crystallization. The agitators are arranged centrally net and equipped with variable speed drives.

The centrally installed agitators, such as paddles, blades or bars, rotate around the common axis of the drive shaft.

The peripheral speed of the stirring elements is at the outer diameter largest and lowest on the shaft. This leads to uneven shear and destruction of crystals already formed in the outer zones of the stirrer works. If there is insufficient flow to the heat exchange surfaces, the An sticking crystals on the cooling surfaces.

Especially towards the end of the crystallization process and with high solids divide the agitator speed must be reduced to the higher toughness the suspension to minimize shear through the agitator and the crystals to protect. In terms of process technology, this is precisely during the crystallization phase disadvantageous because the temperature of the suspension drops only slightly is necessary, but the very significant, released heat of crystallization is removed must be led. In addition, there is sufficient heat flow to ensure metal surfaces to avoid a fixed occupation with crystals.  

Because of the spatial distance of the stirrer from the cooling surfaces, the on the radius of the agitator bar different flow conditions and in Process flow different product parameters have stirred crystallizers Significant procedural disadvantages, which are evident in the crystallizers from Bele Make the heat exchange surfaces noticeable and / or the product quality ten from the subsequent filtration press process in the membrane filter press adversely affected by crystals that are too small.

For the proper growth of the crystals without covering the cooling surfaces with crystals it is necessary that with the smallest possible temperature differences and / or large heat transfer numbers between product and cooling medium gear is being processed. This makes the flow of large amounts of coolant through the Heat exchanger and defined flow conditions on the heat exchange surfaces necessary.

The heat exchange surfaces of the stirred crystallizers exist because of the physical favorable heat transfer ratio for cross-flow ring bodies in the Usually from coils connected in parallel. The number of coils is limited due to the limited space in the crystallizer. To accommodate the required heating surface and to reduce the pressure loss during flow Men of the cooling medium through the pipes become coils with comparatively large nominal values used. For technical reasons, pipes are included larger wall thicknesses required. This leads to severe and, especially when used of stainless steels, expensive constructions.

In addition, pipes with large diameters have the same inflow otherwise speeds a lower heat transfer than pipes with smaller Diameter. This leads to specifically larger heat exchange surfaces based on the apparatus volume for crystallizers with large nominal diameters. The warmth Exchange surfaces of the known stirred crystallizers are on the outside of the apparatus Diameter arranged vertically or as several spirals lying on top of each other built-in. Both construction principles lead to a spatially concentrated  Arrangement of the heat exchange surfaces in the apparatus to provide enough space for a rotie to provide stirring agitator.

In addition, constructions are known in which the heat exchange surface Chen are placed in one another as double jacket pipes. Between the resulting The cooling surfaces move a paddle or scratch that is centered on one mounted shaft is attached. Because of the different movement diameters water comes to different stirring speeds with the above be written disadvantages. In addition, comparatively flat walls have one significantly less favorable heat transfer coefficient than z. B. pipes.

The most suitable crystals for filtration and subsequent pressing can be generated in so-called resting trays without stirring. Here the product is filled in trays with a very low filling level, which are conditioned by air-conditioning te channels are led. Because of the insufficient heat transfer the crystallization times are very long.

The investment in such a crystallization facility is only worthwhile for the production of very pure and high quality products. Crystals produced in this way can be pressed with pressures of more than 50 bar.

Because of the properties of the previously known methods described above and devices are taking into account economic constraints So far not all requirements for a high efficiency in the through management of the crystallization and any subsequent pressing to meet gears.

The object of the present invention is therefore to introduce a method of ge named type to improve such that by equalizing the heat transfer current and gentler substance treatment an improved crystal growth is achieved with reduced energy consumption.  

Another object of the present invention is to introduce a device to construct the type mentioned so that an improved crystal growth under is supported.

According to the method, this object is achieved by the characterizing part of claim 1 specified features solved.

This object is illustrated by the in the characterizing part of claim 5 given characteristics solved.

Advantageous developments of the method according to the invention and the inventions Device according to the invention are to be found in the associated subclaims to take.  

The proposed procedure is no longer the crystallizing substance from an agitator mixed and directed past stationary cooling surfaces, but it becomes the cooling element within the crystallizing substance moves. The medium is moving this makes it much slower and it is between the  individual cooling elements and the medium evenly distributed relative motion produces a sufficient To ensure heat dissipation. This will Shear stresses of the growing crystals clearly reduced and larger crystals can be produced.

By dividing the cooling element into several tubular heat transfer elements will each of the Heat transfer elements a certain spatial Assigned area of the medium to be crystallized and the heat is dissipated from this area. By a Coordination of the spatial extension of the Heat transfer elements as well as the size of the continuous closed circulation routes can ensure this be worn that in the entire area of the to be cooled Medium heat dissipation is guaranteed.

By moving the heat transfer elements with same speed is for an even Crystal growth catered for. Implementation of the centric Rotational movement of the drive shaft in a plurality with respect to the drive shaft of eccentric movements of the Heat transfer elements leads to a simple one device-technical implementation, which no additional and Discharge of the cooling and heating medium via a rotating one Shaft needed.

Due to the combination of features according to the invention, a Variety of benefits can be achieved. In particular there is a uniform movement of the Heat exchange surfaces to optimize the heat transfer between the medium and the cooling element and for Minimization of the shear stress on the suspension during the crystallization process. Furthermore become impermissibly high shear stresses  Centrally suspended agitators avoided. There is one Reduction of the apparatus weight by avoiding the separate agitators. To minimize currents within the crystallizer can be used Heat exchange surfaces can be evenly distributed.

By dividing the cooling element into a plurality of heat transfer elements it is possible to use many pipes small diameter with thin wall thicknesses to connect in parallel and thereby improve the Heat transfer with reduced pressure loss of the Coolant and a reduction in To achieve construction weight. The heating or Cooling system is used during the crystallization process successively with hot water, cooling water and cold water acted upon. When switching from hot to cooling water or from cooling to cold water is inevitable Mixing and energy loss.

A heating or cooling system with pipes of small nominal width has significantly less heat transfer volume. Overall will this reduces mixing and saves energy.

The realization of for all heat transfer elements constant movement speed also has the Advantage that the heat transfer improves and Shear stresses on the crystals can be reduced because a minimization of the movement speeds when Crystallization process can take place. It will be the with agitators relatively high speeds of movement on the outer circumference and the insufficiently small Movement speeds avoided in the central area. This eliminates both the shear stress on outer scope as well as the occupancy of the  Heat exchange surfaces in the central area through a insufficient flow.

Uniform heat dissipation while ensuring a simple mechanical structure is supported that tubes are used as heat transfer elements, those with a substantially parallel orientation are provided to each other and that the tubes with their Longitudinal axes in the direction of a longitudinal axis of the Crystallizer can be arranged.

The same speed of movement Heat transfer elements can be done in a simple manner be realized that each heat transfer element on a circular path is moved.

To ensure a spatially distributed heat dissipation within the crystallizer it is proposed that the Centers of the circular orbits of the individual Heat transfer elements offset to one Shaft center line of a moving the cooling elements Drive shaft are arranged.

A further equalization of the procedures can can be achieved in that two cooling elements such that are moved relative to the shaft centerline by a superposition of the individual movements of the unbalance individual cooling elements can be compensated.

This allows the use of inexpensive components achieved that the cooling element from pipes is trained.

To enable a supply of a variety of Pipes with coolant, it is appropriate that each  two pipes in the area of their one bottom of the Crystals facing ends by redirection are interconnected and that the pipes are in the area its extension facing away from the diversion with a Distributor for coolant on the one hand and a collector for coolant, on the other hand, are connected.

To absorb the weight of the cooling element and to simultaneously enable movements of the Cooling element is proposed that the cooling element is suspended.

A simple mechanical realization of the Movement specification for the cooling element can thereby done that the motion transformer as a Crankshaft is formed, in which a coupling with the Cooling elements via crank pin.

A smooth run through balancing will be particularly in that the crystallizer supports two or more Has heat exchange elements, their associated Crank pin in the direction of rotation of the drive shaft so are arranged offset to each other that the mass forces balanced in rotation.

To provide easy coolant circulation it is proposed that the cooling elements have flexible Inlets and outlets with a coolant supply are connected.

Uniform crystallization is carried out supported by the fact that in an interior of the Crystallizer essentially with the tubes are evenly spaced from each other.  

A cylindrical contour for the cooling elements Ensuring both a balance and one uniform coverage of the interior of the Crystallizer is supported in that the Distributors and collectors essentially as circular laid pipes are formed.

To transmit the movements of the movement transformer on the individual tubes of the cooling elements suggested that both the distributor and the Collectors on radial struts with the motion transformer are connected.

A further increase in efficiency at Cooling can take place in that instead of Smooth tubes, tubes with shafts or fins for Surface enlargement can be used.

Exemplary embodiments of the invention are shown in the drawing shown schematically. Show it:

Fig. 1 shows a cross section through a crystallizer with internal cooling member and the outer cooling element,

Fig. 2 is a partial view of another cross-section through the device of FIG. 1 illustrating supply terminals of the cooling elements,

Fig. 3 is a horizontal section through the device of FIG. 3 in a plane above the cooling elements and

Fig. 4 is a plan view of the apparatus of FIG. 2.

In Fig. 1, a crystallizer ( 1 ) is shown, which is essentially cylindrical and has a wall ( 2 ) and a testicle ( 3 ). A sealable passage ( 4 ) can be arranged in the region of the base ( 3 ). In the embodiment in Fig. 1, two cooling elements ( 6 , 7 ) are arranged in an interior ( 5 ) of the crystallizer ( 1 ). Each of the cooling elements ( 6 , 7 ) consists of a plurality of heat transfer elements ( 8 ), each consisting of two tubes ( 9 , 10 ) running essentially parallel to one another and one of the tubes ( 9 , 10 ) in the area of their base ( 3 ) facing diversion connecting diversion ( 11 ) are formed. In the area of their ends facing away from the diversion ( 11 ), the pipes ( 9 , 10 ) are connected to a distributor ( 12 ) on the one hand and a collector ( 13 ) on the other.

In particular, it is contemplated to provide a plurality of distributors ( 12 ) and collectors ( 13 ) which are each designed as circular pipes and are connected to feeders ( 16 ) and discharge lines ( 17 ) via branches ( 14 , 15 ). In particular, it is also contemplated to form the feeds ( 16 ) and derivatives ( 17 ) from flexible elements, for example hoses. The cooling elements ( 6 , 7 ) are movably connected to cross struts ( 19 ) via suspensions ( 18 ), which extend above the cooling elements ( 6 , 7 ) and can be connected to the walls ( 2 ). However, it is also possible to provide other static fastenings for the cross struts ( 19 ).

To adjust the height, the suspensions ( 18 ) can be formed from threaded rods ( 20 ) which are inserted into sleeves ( 21 ) with ends facing one another. By turning the sleeves ( 21 ) accordingly, the height of the cooling elements ( 6 , 7 ) is adjusted relative to the cross struts ( 19 ) with a suitable pairing of right-hand and right-hand threads.

The tubes ( 9 , 10 ) are braced against one another by spacer elements ( 22 ). Ribs can also be used to improve heat transfer. The distributors ( 12 ) and collectors ( 13 ) are connected via radial struts ( 23 ) to a movement transformer ( 24 ) which converts a rotational movement of a drive shaft ( 25 ) into movements of the cooling elements ( 6 , 7 ). In the embodiment in Fig. 1, the drive shaft ( 25 ) is guided in a sleeve ( 26 ) which is stiffened relative to the cross struts ( 19 ) by diagonal struts ( 27 ).

The movement transformer ( 24 ) is designed as a crankshaft, in which the respective crank pins ( 28 ) have pin center lines ( 29 ) which are offset from a shaft center line ( 30 ) of the drive shaft ( 25 ). A rotational movement of the drive shaft ( 25 ) is hereby converted into rotational movements of the individual tubes ( 9 , 10 ), each of the tubes ( 9 , 10 ) being moved in a circular path relative to its own reference axis and the distance of the respective tube center line from the respective reference axis corresponds to the distance of the journal center line ( 29 ) from the shaft center line ( 30 ). All tubes ( 9 , 10 ) are hereby moved around their respective reference lines at a constant speed.

To improve the stability, stiffening plates ( 31 ) are arranged in the region of the transition from the suspensions ( 18 ) to the distributors ( 12 ) and the collectors ( 13 ). In the embodiment in FIG. 1, the cooling elements ( 6 , 7 ) form cylindrical bodies, the contours of which are spanned by a large number of tubes ( 9 , 10 ). The cooling element ( 6 ) is contoured as an outer hollow cylinder within which the inner cooling element ( 7 ) is guided. In particular, when using two cooling elements ( 6 , 7 ) taking into account the cooling liquid according to FIG. 1, it is intended to offset the crank pins ( 28 ) in the direction of rotation by 180 degrees and the masses of the cooling elements ( 6 , 7 ) taking into account the To dimension the cooling liquid so that it is balanced relative to the shaft center line ( 30 ). This supports a low-vibration, quiet run.

The pipe cross sections for the distributors ( 12 ) and the collectors ( 13 ) are dimensioned such that, when combined with the pipe cross sections of the pipes ( 9 , 10 ) provided for heat exchange, uniform pressure losses occur and, as a result, corresponding amounts of hot or Cooling water can be supplied to the individual heat exchangers.

The drive shaft ( 25 ) is used to connect the motion transformer ( 24 ) to a drive motor, not shown. In particular, it is contemplated to insert the drive shaft essentially vertically into the interior ( 5 ) from above and to arrange the tubes ( 9 , 10 ) also essentially vertically. The distributors ( 12 ) and collectors ( 13 ), however, extend essentially in the horizontal direction. In order to facilitate the connection installation, it is particularly intended to arrange the distributors ( 12 ) and the collectors ( 13 ) at different heights. An expedient embodiment consists in providing each of the cooling elements ( 6 , 7 ) with three suspensions ( 18 ). The bearing of the crank pins ( 28 ) in the area of the motion transformer ( 24 ) can be designed as a plain bearing or as a roller bearing.

Each cooling element ( 6 , 7 ) can be formed from two heat exchange registers arranged opposite one another, which are provided with tubes ( 9 , 10 ) which are arranged uniformly over the cross section of the apparatus. As a result, the complete cross-sectional area of the crystallizer ( 1 ) is covered by the circular pendulum movements of the tubes ( 9 , 10 ). When realizing inner and outer cooling elements ( 6 , 7 ) which are balanced in terms of their structural weight, it is also taken into account that, in addition to the material of the tubes ( 9 , 10 ), the mass of the cooling water is also included in the structural weight. The choice of different pipe cross sections can compensate for the influence of the coolant on the building weight.

From the representation in Fig. 2 it can be seen that two distributors ( 12 ) and two collectors ( 13 ) are provided for the outer cooling element ( 6 ), each of which is designed as a concentrically arranged tube circles. For connecting the distributor ( 12 ) and the collector ( 13 ) branches ( 14 ) are used, which are fork-shaped. Three distributors ( 12 ) and three collectors ( 13 ) are installed for the inner cooling element ( 7 ). Here the branches ( 15 ) consist of three-finger forked elements.

Fig. 3 shows a horizontal sectional view of the circular structure of the distributor ( 12 ) and the collector ( 13 ). It can also be seen that with respect to a center point of the circle spanned by the wall ( 2 ), the center points of the cooling elements ( 6 , 7 ) are offset opposite one another. It can also be clearly seen in this horizontal sectional view that the dimensions of the cooling elements ( 6 , 7 ) are selected such that the entire interior space ( 5 ) is covered by the moving cooling elements ( 6 , 7 ) during the movements carried out.

The top view shown in FIG. 4 illustrates the star-shaped arrangement of six cross struts ( 9 , 10 ). Two cross struts ( 9 , 10 ) are connected to each other by a tangential strut ( 32 ). In the area of the tangential struts ( 32 ) there are articulation points ( 33 ) for the suspensions ( 18 ) of the inner cooling element ( 7 ) and in the area of three transverse struts ( 19 ) are articulation points ( 34 ) for the suspensions ( 18 ) of the outer cooling element ( 6 ) arranged. The articulation points ( 33 ) and the articulation points ( 34 ) are each offset from one another by 120 degrees in the circumferential direction. The articulation points ( 34 ) are offset relative to the articulation points ( 33 ) by about 20 to 30 degrees, preferably 22.5 degrees, in the circumferential direction.

Claims (16)

1. A method for crystallizing substances by cooling a liquid medium containing the substance in a crystallizer, in particular for crystallizing organic fats from a melt, in which the medium rests substantially relative to a wall of the crystallizer, at least one inside the crystallizer in a plurality of tubular heat transfer elements divided cooling element for cooling the liquid medium is arranged relative to the medium and in which a relative movement between the medium and the cooling element is generated, characterized in that the heat transfer elements on circularly closed Umlaufwe conditions substantially at the same speed relative be moved to the medium. 2. The method according to claim 1, characterized in that tubes ( 9 , 10 ) are used as heat transfer elements, which are provided with a substantially parallel orientation to each other and that the tubes ( 9 , 10 ) with their longitudinal axes in the direction of a longitudinal axis of Crystallizer ( 1 ) are arranged. 3. The method according to any one of claims 1 or 2, characterized in that centers of the circular paths of the individual heat transfer elements ver sets to a shaft center line ( 30 ) of the cooling elements ( 6 , 7 ) moving drive shaft ( 25 ) are arranged. 4. The method according to any one of claims 1 to 3, characterized in that two cooling elements ( 6 , 7 ) are moved relative to the shaft center line ( 30 ) in such a way that imbalances of the individual cooling elements ( 6 , 7 ) are compensated by superimposing the individual movements . 5. Apparatus for crystallizing substances by cooling a liquid medium contained in the substance, which is essentially designed as a crystallizer, which has a wall delimiting the medium and at least one cooling element movable relative to the wall of the crystallizer for heat removal from the medium, characterized in that the cooling element ( 6 , 7 ) is connected via a coupling to a drive shaft ( 25 ) and in that the coupling acts as a motion transformer ( 24 ) for converting a central rotation of the drive shaft ( 25 ) into a relative to the drive shaft ( 25 ) eccentric movement of the cooling element ( 6 , 7 ) on a closed circular path is formed. 6. The device according to claim 5, characterized in that the cooling element ( 6 , 7 ) from tubes ( 9 , 10 ) is formed. 7. Apparatus according to claim 5 or 6, characterized in that two tubes ( 9 , 10 ) in the region of a bottom ( 3 ) of the crystallizer ( 1 ) facing th ends are connected to one another by a bypass ( 11 ) and that the tubes ( 9 , 10 ) are connected in the area of their extension facing away from the diversion ( 11 ) to a distributor ( 12 ) for coolant on the one hand and a collector ( 13 ) for coolant on the other. 8. Device according to one of claims 5 to 7, characterized in that the cooling element ( 6 , 7 ) is suspended in an oscillating manner. 9. Device according to one of claims 5 to 8, characterized in that the movement transformer ( 24 ) is designed as a crankshaft, in which a coupling with the cooling elements ( 6 , 7 ) via crank pin ( 28 ). 10. Device according to one of claims 5 to 9, characterized in that the crystallizer ( 1 , 2 ) cooling elements ( 6 , 7 ), the associated drive shaft ( 25 ) are arranged offset by approximately 180 degrees to each other. 11. Device according to one of claims 5 to 10, characterized in that the cooling elements ( 6 , 7 ) via flexible feeds ( 16 ) and derivatives ( 17 ) are connected to a coolant supply. 12. Device according to one of claims 5 to 11, characterized in that in an interior ( 5 ) of the crystallizer ( 1 ), the tubes ( 9 , 10 ) are distributed substantially at equal distances from one another. 13. Device according to one of claims 5 to 12, characterized in that the masses of the cooling elements ( 6 , 7 ) and the masses of the cooling liquid stored in the cooling elements ( 6 , 7 ) are arranged balanced relative to the shaft center line ( 30 ). 14. Device according to one of claims 5 to 13, characterized in that the distributor ( 12 ) and the collector ( 13 ) are designed essentially as circular pipes. 15. The device according to one of claims 5 to 14, characterized in that both the distributor ( 12 ) and the collector ( 13 ) via radial struts ( 23 ) with the movement transformer ( 24 ) are connected. 16. The device according to one of claims 5 to 15, characterized in that ribs are arranged at least in the region of some of the tubes ( 9 , 10 ).