Chemistry: physical processes – Physical processes – Crystallization
Patent
1992-12-17
1994-03-22
Straub, Gary P.
Chemistry: physical processes
Physical processes
Crystallization
23303, 422252, B01D 900, C01D 130
Patent
active
052960005
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for crystallising an inorganic substance, using a bed of crystals, which is traversed by a solution supersaturated in the substance to be crystallised.
The "OSLO" crystalliser is an apparatus well known for crystallising inorganic substances (British Chemical Engineering, August 1971, Volume 16, No. 8, pages 681 to 685; The Chemical Engineer, July/August 1974, pages 443 to 445; British Patent GB-A-418,349). This known apparatus comprises a vertical cylindrical cell and a vertical tube which is disposed axially in the cell and ends in the immediate vicinity of the bottom of the latter; an annular vertical chamber is thus defined between the axial tube and the cylindrical wall of the cell. In the operation of this known apparatus, a bed of crystals in the annular chamber is used, through which a solution supersaturated in the substance which it is desired to crystallise is caused to flow (for example an aqueous supersaturated solution of sodium chloride). This solution is introduced into the apparatus via the axial tube, in such a way that it radially penetrates the annular chamber, close to the bottom thereof, and subjects the crystals of the bed to a common rotation, comprising an ascending translation along the wall of the cell and a descending translation along the axial tube.
In this known apparatus, the purpose is to produce regular crystalline grains of spherical shape, whose mean diameter should be controllable by an appropriate choice of the dimensions of the apparatus and of the operating conditions. In practice, however, this known apparatus is rather unsuitable for obtaining large spherical grains, particularly due to the fact of attrition generated within the bed of crystals and of the common rotation, to which these are subjected.
In the document EP-A-0,352,847 (SOLVAY & Cie), a process and equipment are described which eliminate the said drawbacks. In this process and this equipment, a fluidised-bed reactor is used and the solution supersaturated in the substance to be crystallised is caused to circulate upwards across a distributor in such a way that, above the latter, the fluidised bed of crystals is generated; the mother liquor from the crystallisation is collected above the bed and recycled to a point upstream of the bed, after it has been supersaturated to reconstitute the original supersaturated solution.
The invention perfects the process and equipment of document EP-A-0,352,847 by providing a means which reduces the risk of parasitic crystal formation below the fluidised bed.
Starting from this situation, the invention relates to a process for crystallising an inorganic substance in a fluidised bed of crystals, which is generated by subjecting a solution supersaturated in the substance to be crystallised to an ascending circulation across a distributor, located below the bed, of a fluidised-bed reactor, the mother liquor from the crystallisation being collected at the bed exit and being supersaturated to reconstitute the said supersaturated solution; according to the invention, a fraction of the supersaturated solution is taken off upstream of the distributor and recycled to a point downstream of the distributor, before the mother liquor is collected.
In the process according to the invention, the crystals of the bed serve as seeds for the crystallisation of the inorganic material by desupersaturation of the supersaturated solution. They are generally small regular crystals of the inorganic substance which it is intended to crystallise.
The level of supersaturation of the supersaturated solution depends on various parameters, in particular the nature of the inorganic material, on its temperature and on the possible presence of solid or dissolved impurities. In practice, everything else being equal, it is advantageous to establish a maximum supersaturation level, which must always be limited in order to avoid accidental crystallisations on the walls of the crystallisation equipment upstream of the crystal bed, and a
REFERENCES:
patent: 1860741 (1932-05-01), Jeremiasson
patent: 2042661 (1936-06-01), Jeremiassen
patent: 2219776 (1940-10-01), Henderson
patent: 3556733 (1971-01-01), Hedrick
patent: 3873275 (1975-03-01), Bennett
patent: 4174382 (1979-11-01), Menche
patent: 4797981 (1989-01-01), Ninane et al.
patent: 5124265 (1952-06-01), Randolph
patent: 5154909 (1992-10-01), Ninane et al.
British Chemical Engineering, Aug., 1971, vol. 16, No. 8, "Two Case Histories in the Design of Crystallisers", J. F. Witte et al., pp. 681-685.
The Chemical Engineer, Jul./Aug., 1974, "Types of Crystallisers", A. W. Bamforth, pp. 443-445.
Ind. Eng. Chem. Fundam., 1980, vol. 19, No. 1, "Fluid Mechanical Description of Fluidized Beds, Experimental Investigation of Convective Instabilities in Bounded Beds", G. P. Agarwal et al., pp. 59-66.
Chemical Engineers' Handbook, 4th Edition, 1963 "Fluidized Bed Systems", pp. 20-43 through 20-46.
precis de genie chimique, J. Givaudon et al., 1960 Chapter VI "Fluidisation", pp. 353-371.
Darmont Jacques
Detry Leopold
Solvay ( Societe Anonyme)
Straub Gary P.
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