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
1997-09-05
1999-10-12
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 5, B29B 910
Patent
active
059650710
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process for preparing granular urea from liquid drops or sprayed drops of a urea solution. In the present invention, urea liquid is a general term for molten urea and an aqueous urea solution.
DESCRIPTION OF THE RELATED ART
Various processes for preparing granular urea are known. In general, a prilling tower method and a fluidized, spouted bed method are employed.
In the prilling tower method, an aqueous urea solution containing moisture of 0.1 to 0.3% by weight is caused to fall from the top of a prilling tower in the form of liquid droplets, and falling liquid drops are cooled and solidified by contacting them with an ascending air current coming from the bottom of the prilling tower, whereby urea particles called prill are produced.
Urea grains obtained by this method are relatively small (0.5 to 2.5 mm) and have a low mechanical strength.
The fluidized, spouted bed method is used to produce a grain which is larger than the grain produced by the prilling tower method and has a high mechanical strength and is specifically disclosed in U.S. Pat. No. 4,219,589 and JP-B-4-63729.
For example, a method is disclosed in JP-B-463729, in which a urea solution is fed in the form of fine liquid drops into a fluidized bed in which a spouted bed comprising urea seed grains is scattered, to adhere the urea solution on the urea seed particles, followed by drying and solidifying, whereby large-sized urea grains are produced.
As disclosed in U.S. Pat. No. 3,067,177, U.S. Pat. No. 3,112,343 and JP-B-50-34536, it is well known that in these processes for preparing granular urea by the fluidized, spouted bed method, an additive is added to a urea solution for the purposes of improving the mechanical strength and coagulation resistance of a large-sized urea grain product and enhance the granulating efficiency, that is, losing a part of the urea solution in the form of very fine dusts without it being used for forming the grains in granulating. This additive is an aqueous formaldehyde solution or a urea/formaldehyde reaction product (it is commercially available under a trade name of, for example, Formurea 80).
In the process for preparing prill urea by the prilling tower method, it is substantially impossible to remove moisture. The mechanical strength and coagulation resistance of the resulting urea grains can be improved by adding 0.3 to 0.6% by weight of formaldehyde. However, the use of an aqueous formaldehyde solution as a formaldehyde source results in the addition of a lot of water to the urea because the content of formaldehyde in the aqueous formaldehyde solution is usually 30 to 37% by weight and a large quantity of water is contained therein. This increases the moisture contained in the resulting urea grains and in turn deteriorates the quality of the urea grains. Accordingly, an aqueous formaldehyde solution can not be used for the prilling tower method in which the moisture in the process steps can not be removed.
On the other hand, a process for preparing large-sized urea grains by the fluidized, spouted bed method has the capability of evaporating the moisture to some extent in the granulating facility thereof. However, in the case where moisture exceeding the evaporation capability of the granulating facility is present, for example, in the case where a more diluted aqueous formaldehyde solution than that expected in designing can not help from being used, the water content of the urea and formaldehyde mixture has to be reduced down to a given level or lower before introducing it into the granulating facility.
As described above, an aqueous formaldehyde solution usually contains 30 to 37% by weight of formaldehyde and therefore contains a lot of water. The use of this aqueous formaldehyde solution concentrated simply to 37% by weight or more results in deteriorating the stability of the aqueous formaldehyde solution and depositing a polymer of formaldehyde, which in turn makes it difficult to feed formaldehyde in a prescribed amount.
Meanwhile, in
REFERENCES:
patent: 3059280 (1962-10-01), Laehder
patent: 3067177 (1962-12-01), Greco et al.
patent: 3112343 (1963-11-01), Allgeuer et al.
patent: 3130225 (1964-04-01), Friend
patent: 3686373 (1972-08-01), Griesheimer et al.
patent: 4219589 (1980-08-01), Niks et al.
patent: 4390483 (1983-06-01), Willems et al.
Fujii Hidetsugu
Morikawa Haruyuki
Theisen Mary Lynn
Toyo Engineering Corporation
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