FR2659028A1 - PROCESS AND DEVICE FOR OBTAINING CRYSTALLIZATION PRODUCTS HAVING A DEFINED GRAIN SIZE FROM SURSATURED SOLUTIONS, IN PARTICULAR SALT SOLUTIONS. - Google Patents

Abstract

The invention describes a method and a device for obtaining crystallization products having a defined grain size, a determined current profile being established and maintained in the crystallization chamber.

Description

PROCESS AND DEVICE FOR OBTAINING PRODUCTS

  CRYSTALLIZATION HAVING GRAIN SIZE

  DEFINED, FROM SUPERSATURATED SOLUTIONS, IN PARTICULAR FROM

SALINE SOLUTIONS.

  The invention relates to a method and a device for obtaining crystallization products having a defined grain size, from

  supersaturated solutions, especially saline solutions.

  Part of the field of salt crystallization carried out universally at the industrial level, is constituted by crystallization from solutions in which a supersaturation has been created, the crystallization product being extracted by considerably reducing this supersaturation Supersaturations in such saline solutions can for example be obtained by vaporization of the solvent, or by cooling the solutions, or alternatively by both measures at the same time A drawback specific to all known methods and devices intended for obtaining crystallization products having a size of defined grain, from solutions, for example solutions of potassium salts, lies in the fact that by maintaining determined conditions, it is certainly preferable to form crystals of a determined grain size, but that 'however it is impossible to avoid the formation of considerable quantities very fine grains, grains

  downgraded lower or downgraded upper.

  The object of the invention therefore consists in providing a method and a device for the manufacture of crystallization products having a defined grain size, from supersaturated solutions, in particular saline solutions such as, for example, potassium salt solutions, by guaranteeing that, apart from these crystallization products of a determined grain size, not at all, or a very small proportion, of very fine grains appear

  grains downgraded lower or downgraded higher.

  This object is achieved by the process according to the invention, according to which a current (arrow X) directed against the force of gravity is produced in a container, and by which the crystals growing in the solution are kept in suspension until a certain size and weight are reached, and then evacuated downwards, after reaching this predetermined size and weight. Consequently, the crystallization product is kept in suspension, by the current, until that it has reached a size and in particular a weight which is greater than the force exerted by the current on the individual grain of crystallization When the grain has reached a determined weight, it falls downward, through the current, because gravity, and can be discharged there The current itself is produced by the circulation of the saline solution from the container; at the same time, it is also possible, if necessary, to add fresh solution to maintain the desired saturation level of the solution. In more detail, the method is characterized in that the current has a non-rectilinear speed profile in vertical section through the container, the speed of the current having, according to a particular characteristic of the invention, a minimum at the center of the profile speed This allows the individual grains of the crystallization product to fall towards the bottom, against the direction of the current, at a determined location in the container, namely precisely where the speed of the speed profile

presents a minimum.

  The device for implementing the method is characterized, in accordance with the invention, in that the container is composed of a truncated cone directed downwards and which comprises, at its lower end, a device for producing the current, which according to a characteristic of the invention is carried out

  in the form of an annular chamber.

  The fact of producing the device intended to produce the vertical current, in the form of an annular chamber, offers the possibility of producing, in the external zone of the annular chamber, a vertical partial current clearly much stronger than in the internal zone of this annular chamber This means that the crystallization products growing in the current fall down into the central zone of the annular chamber, against

  the direction of the current, to be extracted at the bottom.

  According to a preferred embodiment, the center of the annular chamber is constituted by a tube which extends as far as the lower zone of the truncated cone. This makes it possible to obtain the formation of a precisely defined speed profile. In particular thanks to the arrangement of this tube in the annular chamber, with the possibility of vertical sliding, we define, depending on the value of which the tube enters the annular chamber and in the lower part of the truncated cone, the grain size distribution of the product of crystallization, since it is thus possible to optimize the rate of inflow of the solution on the grains of the crystallization product, and thus the duration

  the state of grain suspension.

  The classification effect generated by the special configuration of the speed profile is further increased, especially in combination with the conical shape of the crystallization chamber. The finest particles are carried away by the solution and the largest particles accumulate. in the deepest area of the floating bed From there, it is possible to evacuate the desired grains, thanks to the

  possibility of current adjustment.

  To prevent the formation of deposit layers on the truncated cone, even in the case of very high supersaturations, a cone angle of 5 to 15 degrees is proposed, preferably 6 to 8 degrees. Furthermore, according to another characteristic of the invention, a cylindrical part is connected to the end of the truncated cone located upwards Furthermore the annular chamber is of cylindrical configuration and comprises at least one supply line; the ratio of the inside diameter to the outside diameter of the annular chamber is from 0.5 to 0.9, and preferably approximately

0.8.

  Another advantage lies in the fact that the residence times of the mother solutions in the crystallization chamber are exceptionally short with this

  process, and are less than 1000 or even 100 seconds.

  This eliminates possible agglomeration reactions and possible detergent inclusions, which also makes it possible to obtain greater purity of the crystallization product. The highest purity as well as obtaining homogeneous grain products.

  constitute the essential advantages of this invention.

  The single figure attached, with regard to

  which will be described below,

  shows an exemplary embodiment of the device for obtaining crystallization products having

a specific grain size.

  The device itself is constituted by a truncated cone generally designated by (1); at the end of the truncated cone located upwards, is connected without transition, a part of cylindrical shape (2) At its end situated downward, the truncated cone has an annular chamber designated as a whole by (3) The truncated cone designated by (1) here essentially constitutes the container in which the current is produced and where the crystallization bed is formed. The annular chamber designated by (3) consists of a cylindrical outer casing (4) and a tube (5) mounted with the possibility of vertical sliding, in this cylindrical casing On the cylindrical casing (4) there is a pipe supply (6) which is intended for supplying solutions, possibly also fresh solution, to establish a vertical current (arrow X) in the annular space designated by (7) The tube (5) also comprises a supply line (8) for the solution which may also be fresh solution, for example. In addition, the tube is open downwards to allow the grains to be discharged downwards

  of the crystallization product forming in suspension.

  For the formation of a well-defined velocity profile, particularly in the horizontal direction, it turned out that the ratio of the inside diameter to the outside diameter of the annular chamber should be between 0.5 and 0.9 and take preferably a value approximately equal to 0.8 The device itself still has various connections; thus, for example, a supply line can be provided for the product constituting the germs for the formation of

crystallization products.

  However, it is also possible to bring the product constituting the crystallization seeds into the container, with the fresh solution (pipes

6 and 8).

  At the upper end of the container, there is an evacuation pipe (9) for extracting the solution from the crystallization chamber. The solution extracted by the evacuation pipe (9) can be reintroduced into the container. through the annular chamber (3), this in particular by the supply lines (6) and (8), and serves to maintain the current If necessary, and to maintain the saturation rate of the solution, it is also possible to bring fresh solution through the chamber

annular (3).

Claims (7)

CLAIMS.   1 Process for obtaining crystallization products having a defined grain size, from supersaturated solutions, especially saline solutions, characterized in that a current (arrow X) directed against the product is produced of the force of gravity, and thanks to which the growing crystals in the solution, are kept in suspension until reaching a determined size and weight, then being evacuated downwards, after having reached this predetermined size and weight. 2 Method according to claim 1, characterized in that the current (arrow X) has, in vertical section through the container, a profile of speed not straight.   3 Method according to claim 2, characterized in that the current speed has a   minimum in the center of the speed profile.   4 Device for implementing the method according to claim 1, characterized in that the container comprises a truncated cone (1) directed downward and which has at its lower end, a   device intended to produce the current.   Device according to claim 4, characterized in that the device intended to produce the current is produced in the form of a chamber annular (3).   6 Device according to claim 5, characterized in that the center of the annular chamber (3) consists of a tube (5) which extends up to in the truncated cone (1).   7 Device according to claim 6, characterized in that the tube (5) is disposed in the annular chamber (3) with the possibility of vertical sliding. 8 Device according to claim 4, characterized in that the cone angle of the truncated cone   (1) is 5 to 15 degrees, preferably 6 to 8 degrees.   9 Device according to claim 4, characterized in that a cylindrical part (2) is connected to the end of the truncated cone located upwards. 10 Device according to claim 5, characterized in that the annular chamber (3) is of cylindrical shape and comprises at least one pipe supply (6).   11 Device according to claim 5, characterized in that the ratio of the inside diameter to the outside diameter of the annular chamber (3) is between 0.5 and 0.9, and is preferably approximately equal to 0.8.