Granulation of fertilisers is one of the most frequently used techniques for the particulation of melts or solutions. Typically, the size distribution of particulates is between 2 and 4 mm, with prilled fertilisers (prills) mostly having a size between 1 and 3 mm. Larger particles are preferred for centrifugal spreaders, as the mechanical spreading distance has increased throughout the decennia. In aerial applications much larger granules are preferred. The term ‘granular’ implies a controlled size range and is derived from the Latin ‘granus’, suggesting a size close to cereal grains.
Within the overall granulation process, various specific operations can be identified:
- Granulation
- Drying
- Screening
- Crushing
- Recycle loop
- Cooling
- Coating
The granulation process has been greatly affected by improved control of the recycled material. The right selection of crushers, screening devices and stable feeds provides the basis for controlling the granulation loop. Since about 2005, the application of advanced process control (APC) systems has further optimised the granulation loop and led to significant capacity increases without changing (increasing) the hardware of an existing plant.
Agglomeration and accretion are the main fundamentals in granulation. Knowledge of the details of granule formation can help the industry to further control production through process automation. Although a number of approaches have been made including so-called fuzzy control methods, mathematical models and advanced process control, the breakthrough to achieve a fully automated NPK production is still somewhat elusive. Granulation has remained an art, rather than a science.
The granulation section of FerTechInform covers the basics of granulation, utilising content from the IFDC Fertilizer Manual – the two main methods of granulation, physical and chemical parameters for producing agglomerated NPKs, and processes for manufacturing compound fertilisers. This is supplemented by more focused information from, in particular, IFS Proceedings 783, which covers a brief history of granulation, the terminology of granulation, and the various types of granulation equipment.
Links to related IFS Proceedings
7, (1949), Slurry Dispersion Methods for the Granulation of Superphosphate Fertilisers, T Procter.
216, (1983), Granulation of Ammonium Phosphates – Recent Experiences , K J Barnett, D M Ivell, S F Smith
450, (2000), Self-Sustaining Decomposition of NPK Fertilisers Containing Ammonium Nitrate, H Kiiski.
556 (2005) Centrifugal Fertiliser Spreaders: A New Method for their Evaluation and Testing, E Piron, D Miclet
734 (2013) Method of Calculating Effects of Uneven Spreading of Fertiliser Nitrogen, I R Richards, R D Hobson
816 (2017), The improvement of centrifugal fertiliser spreaders for precision application control, M Nørremark, M Nielsen, K Persson
Links to external resources
Barut, R.F. and Kotlarevsky, I. (1978). ‘The Use of MAP in Large Capacity Granulation Plants,’ ISMA Technical Conference, Orlando, Florida, USA, 23-27 October.
Ivel, D. and Blackwell, M. (2000). ‘Startup of One of the World’s Largest DAP Plants – WMC Fertilisers,’ International Fertiliser Association, Conference, New Orleans, Louisiana, October.
Maartensdijk, A.S. (1976). ‘Direct Production of Granulated Superphosphates and PK-Compounds,’ ISMA Technical Conference, The Hague, The Netherlands, September 13- 16.
Olivares del Valle, J., Lopez Nino, J.L. and Castillas Revilla, J. (1980). ‘Practical Aspects of Operation of a Granulation Plant for NPK Fertilisers of 1000 TM/Day,’ IFA Technical Conference, Vienna, Austria, 11-13 November.
Podilchuck, I., Charlton, W.T. and Pask, M.D. (1975). Modern Approach to the Design of Granular Fertiliser Plants, Fisons Ltd., Fertiliser Division.
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