Chemistry: physical processes – Physical processes – Crystallization
Patent
1996-03-29
1998-03-10
Straub, Gary P.
Chemistry: physical processes
Physical processes
Crystallization
4222451, 422254, 585812, B01D 900, C07L 714
Patent
active
057256080
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention pertains to a process and an apparatus for material separation by crystallization from the melt, in which the melt is introduced into a gap between two opposing walls in motion which can both be cooled, remains as a crystallate adhering to at least one wall and is conveyed out of the gap and collected.
A process and an apparatus of that type is known from DE 40 41 670-C (corresponding to U.S. Pat. No. 5,445,108), in which two continuous belts are installed one above the other such that their sides facing one another run horizontal and parallel to one another. The lower belt is constructed somewhat longer than the upper and has an upstream section extending past the upper belt to receive the melt. The lower belt, which is a steel belt, is tempered such that the melt remains above its crystallization point. The upper belt, in contrast, likewise made of steel and cooled from the interior, is brought to a temperature at which a crystal layer can form upon it. Since the upper belt is brought into contact with the melt and runs in a direction opposite to the melt conveyed by the lower belt, the crystal layer clinging to the upper belt can be conveyed out of the gap and then mechanically removed in the vicinity of a return roll. In this known process only one conveyor wall is available for production of crystallate, the other assumes transport and temperature maintenance functions.
An advantage of such processes and installations is that a continuous crystallate formation is achieved compared to processes and apparatuses which function with, for example, vertically cooled or heated walls of parallel robes, in which a fluid mixture flows inside the robes as a trickling film downward from the top, while the cooling medium is located outside the tubes. Such processes and apparatuses can only be operated non-continuously.
However, an installation for material separation by continuous crystallization was made known (EP 0 488 953 A1) in which an inclined cooled continuous belt is used which is cooled on its upper side from the inside and is provided with charging locations for a fluid mixture or a melt over this upper side. In this set-up, as well, the crystal build-up proceeds on one wall surface only and the inclination of the belt is only then used to carry the mother liquor away downward at an angle.
Finally, a vertical channel formed by moving belts is known, as in FR-A 2 182 168, in which the fluid medium is filled upward. In this design, the channel is formed from the four inner sides of four continuous vertical belts and has a square cross section. The belts travel such that the sides facing the channel travel downward. At least two opposing belts are cooled or heated so that crystals form on them which are conveyed downward to a grinder and crashed. The residual fluid gravitates also to the area of the grinder. The recovery of the solid substances can thus be impaired.
In contrast, the objective of designing a process and apparatus of the type named above, but more effectively, is the basis of this invention.
SUMMARY OF THE INVENTION
To meet this objective, the process according to the invention is provided with both walls moving in the same direction and in essentially a vertical direction upward, and the melt is introduced into the gap countercurrent to the motion of the walls with the crystallate clinging to them. With this type of process, both walls moving upward can be utilized for formation of crystallate. The yield from installations according to this process can then be doubled. The gravitation is utilized in order to move the melt countercurrent to the walls. The process can be very easily implemented, then, if the melt is prepared for corresponding heating prior to feed to the gap.
An advantageous development of the process according to the invention arises when the walls are moved with differing velocities and/or a differing cooling is undertaken in the direction of motion. Through these measures, it is possible to produce crystallate at differing condi
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Fischer Oskar
Konig Axel
Ulrich Joachim
Santrade Ltd.
Straub Gary P.
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