GB822939A - Improvements in and relating to granular fertilizers based on urea - Google Patents

Abstract

A process for the production of urea based granular fertilizers having a nitrogen content in the range 30% to 46% by weight comprises charging a granulating device with substantially dry material comprising urea and a filler selected from calcined calcium sulphate and kieselguhr, mixtures of these or mixtures of at least one of these with ground limestone and, while continuing the granulation, simultaneously introducing into the granulator a concentrated aqueous solution of urea, and drying the granules produced at a temperature not exceeding 100 DEG C. The expression "calcined calcium sulphate" includes calcium sulphate hemihydrate soluble anhydrite and any intermediate hydrated calcium sulphate but not insoluble anhydrite. Various granulators may be used, e.g. drum granulators and ribbon mixers but preferably paddle mixers or granulators; it is also desirable to provide the granulator with heating means e.g. a steam jacket. The dry material in the initial mixture may comprise crushed over-size and fines drained from a previous operation. Suitable fillers for granular products of the invention having a nitrogen content of 40 to 46% are calcined calcium sulphate or kieselguhr or mixtures of these and for those with nitrogen contents of from 30 to 40% a filler comprising a major proportion of limestone. The moisture content of the granules during drying is reduced to 1% or less, and the drying is preferably carried out in a countercurrent stream of hot gasses. Specifications 624,642 and 717,195 are referred to.