Dsm N.v.

Hubertus J M Slangen

Tjay Tjien Tjioe

The invention relates to a process for drying melamine wet cake to produce a dry melamine powder showing improved bulk properties, the drying being effected with a contact dryer. In particular the invention relates to a process for drying melamine wet cake that contains predominantly melamine crystals that have crystallized from a melamine solution in a crystallizer, the drying being effected with a contact dryer. The invention also relates to the drying of a melamine wet cake whose percentage of fines having a diameter of <21 &mgr;m is less than 30 wt. %, the drying being effected with a contact dryer.

Process for drying melamine

Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt coming from the reactor to a vessel where the melamine melt is cooled with an evaporating cooling medium. The melamine melt comes from the melamine reactor at a temperature between the melting point of melamine and 450&deg; C. and is sprayed into a cooling vessel, via spraying means, having an ammonia environment with an increased ammonia pressure and cooled by means of an evaporating cooling medium to form melamine powder. The melamine melt is thereby converted into melamine powder having a temperature of 270&deg; C. or below after which the ammonia pressure is released and the melamine powder is cooled, at least for part of the cooling range, by the powder being set in motion mechanically and being cooled directly or indirectly and, if necessary, the melamine powder is cooled further.

Method for preparing melamine

Method for preparing melamine from urea via a high-pressure process in which solid melamine is obtained by transferring the melamine melt coming from the reactor to a vessel where the melamine melt is cooled with an evaporating cooling medium. The melamine melt comes from the melamine reactor at a temperature between the melting point of melamine and 450&deg; C. and is sprayed into a cooling vessel, via spraying means, and cooled by means of an evaporating cooling medium to form melamine powder. The cooling vessel has an ammonia environment with an increased ammonia pressure. The melamine melt is thereby converted into melamine powder having a temperature of between 200&deg; C. and the solidification point of melamine. The melamine powder is then cooled to a temperature below 200&deg; C. with the powder mechanically agitated and being cooled directly or indirectly, after which the ammonia pressure is released and, if necessary, the melamine powder is cooled further.

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Stein, Netherlands

Hubertus J M Slangen