Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – By extrusion spraying or gravity fall through orifice
Patent
1991-06-17
1993-08-24
Theisen, Mary Lynn
Plastic and nonmetallic article shaping or treating: processes
Formation of solid particulate material directly from molten...
By extrusion spraying or gravity fall through orifice
264 63, 264 05, B29B 910
Patent
active
052386112
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for producing granulated particles from a powder which is insoluble in water, the dimensions of the formed granulated particles being substantially larger than those of the powder grains.
BACKGROUND OF THE INVENTION
Agglomeration is a fundamental process of the chemical industry.
A distinction is made in the art between a mechanical compactation, a thermal agglomeration such as for example sintering, and a chemical aggregation according to the methods described by Browning in Chem. Eng. 71(25), 1987, page 147 or by the document DE-37 16 286 A1.
The aim of these processes is often to obtain granulated particles which can be manipulated more easily than finely dispersed powders. In practice, this may concern fertilizers, which, in granulated form, are easier to distribute on the ground than powders, raw materials for the glass or ceramic manufacture, ashes from combustion or powders and muds collected by an air filter.
A particular application concerns the immobilization of radioactive or toxic and noxious waste in a cement matrix in spherical shape. Thus, these products can be transported pneumatically or wrapped and stored without a risk of proliferation.
The conventional methods for a mechanical compactation have the drawback that there remains always a small quantity of finely dispersed powder. Furthermore, and this applies to all known methods of thermal agglomeration and chemical aggregation, they do not supply particles of a given spherical diameter, but particles of varying shapes and dimensions. Finally, it is desirable to dispose of other methods in order to enlargen the variety of powders which can thus be processed.
The invention thus aims at presenting a process of producing granulated particles, the shape of which is similar to that of a sphere and the dimensions of which are hardly dispersed and can further be influenced by acting on certain parameters of the process. Moreover, the process according to the invention must be able to be utilized with a greater variety of basic powders than the known processes.
SUMMARY OF THE INVENTION
These objects are attained according to the invention by the fact that the powder is mixed with an aqueous solution of a cellulose chosen among methyl cellulose, hydroxypropyl methyl cellulose etheric hydroxybutyl methyl cellulose, and that then droplets of this mixture are made to fall into an aqueous solution of at least one salt or metallic hydroxide which does not react with said particles.
As to characteristics of certain preferred examples of operation of the process according to the invention, reference is made to the detailed description of the preferred embodiment which follows.
BRIEF DESCRIPTION OF THE DRAWING
The invention will now be described more in detail with reference to the unique FIGURE which shows a laboratory scale device for the application of said process.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The process substantially comprises the following steps:
The powder to be agglomerated is mixed with an aqueous solution of a carbohydrate based compound chosen among methyl cellulose, hydroxypropyl methyl cellulose and hydroxybutyl methyl cellulose. The methyl cellulose has the following chemical structure: ##STR1##
The quantity and the concentration of this compound in water are such that a stable, homogenous and sufficiently fluid suspension is obtained so that droplets can be formed. This concentration lies for example at 3,5%.
It has to be noted that the molecule of methyl cellulose is non-ionic (contrary to that of carboxy methyl cellulose used in the process according to DE-37 16 286 A1). Thus, it can not be precipitated in the form of an insoluble salt in polyvalent metallic ions.
This suspension is made to fall through holes or calibrated tubes of a diameter from some tenths of millimeter to some millimeters into an aqueous bath of at least one salt or metallic hydroxide not reacting with the particles in question. The concentration of this solution is such that the compou
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Brambilla Giovanni
Zamorani Edmondo
Euratom
Theisen Mary Lynn
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