The main control features of fertiliser granulation plants are described using as an example an orthodox process for the manufacture of high analysis compound fertilisers from solid and liquid feeds. A mathematical model is outlined and used for a discussion of the stability and dynamic characteristics of the granulation loop and can be used to recommend guide-lines for control procedure. Granulation theory, which considers the relationship between solution phase and size enlargement in the granulator, is shown to be useful for practical control actions. The best use of conventional instrumentation is outlined and a computer-controlled plant is described in terms of the theoretical treatment. It is shown how automatic feed-back control over granulation is obtained by evaluating conditions in the granulator and monitoring performance with specially developed instruments for on-line determination of composition and granule size.
Advances in the theoretical treatment of granulation, drying, crushing and process control are also applicable to the newer granulation processes which are evolving. The main design and operational requirements of robust, reliable on-line instruments are now established and possible future directions of development are outlined.
J A Bland, J L Hawksley and W J Perkins, Imperial Chemical Industries Ltd (ICI), Billingham, UK.
44 pages, 11 figures, 3 tables, 19 refs.