This section on NPK compound fertilisers comprises these pages:
NPK fertilisers, often referred to as compound fertilisers, contain all three primary nutrients in one grade. A large number of variations are possible:
- All nutrients are present in each granule or prill, each particle shows the same formulation, all raw materials have been first dissolved to obtain a uniform slurry which is particulated, complex fertilisers;
- Solid raw materials can be mixed in a drum or reactor and the ingredients are particulated by steam and/or liquids (water, dilute fertiliser solutions); the particles are not uniform in their composition but each particle will likely contain some amount of each primary nutrient; a compound fertiliser.
- A multi-nutrient solid in which the components like ammonium nitrate, potassium salts and phosphate materials are simply mixed as solids, a compound fertiliser, a blend.
- NP(K) materials are obtained through the nitrophosphate process. Rock phosphate is processed with nitric acid and large amounts of a co-product, such as calcium nitrate or calcium ammonium nitrate, are co-produced. The resulting NP(K) formulations are complex fertilisers.
The production and marketing of compound fertilisers are unique compared with commodity-type fertilisers such as urea, ammonium phosphates, and potash. Unlike commodity-type fertilisers, compound fertilisers are usually manufactured (formulated) to meet local or regional crop requirements. Often, in addition to containing various ratios of the primary nutrients (N + P2O5 + K2O), they contain certain secondary and micronutrients specific to the crop needs in a particular agroclimatic region.
The total annual worldwide production of all fertiliser materials amounted to about 700 million tonnes in 2018, containing about 250 million tonnes of nutrients (N + P2O5 + K2O). Of this total, compound fertilizers, excluding physical mixtures (bulk blends), accounted for about 20%, or about 140 million tonnes of product annually. (Source: Fertilizers Europe)
Raw materials and processes
Raw materials and processes vary over a wide range and have been extensively described in literature. As described above, compound fertilisers can be produced either by blending or granulation. The· method used for granule formation has a pronounced impact on the design and operation of the granulation process equipment. Therefore, a good knowledge of the primary mechanisms of granule formation, growth, and consolidation is essential in determining the design features of the granulation process. There are four main types of granulation processes, all of which are described within this resource.:
Various licensing and technology companies supply proprietary and custom-based processes for compound fertilisers. Examples of literature describing various production processes for compound granulated fertilizers are Kargaeva and Kiiski.
The ultimate granulation plant is the plant that can make multiple formulations (N, P, K, S, micro-nutrients) of granular products including Diammoinium phosphate (DAP), Monoammoinium phosphate (MAP), NPK, NP(K)S, and Triple Superphosphate (TSP) and can also add micro-nutrients, see Dennis and Ettouimi, 2019. In the past a granulation plant made one product and shipped the product to a retailer that blended ingredients for the customer. Over the last few years there has been a trend for the fertiliser producer to combine the ingredients in the granulation process for the customer, rather than producing a blended product. A major driver of this trend has been the consistency in chemistry appearance and granule size that can be achieved by granulation. While blended products can achieve consistency, especially when handled in bags, unless care is taken the blend can eventually segregate into the original components, resulting in unequal distribution of the different chemical components on the field. If the ingredients are combined in the granule, they cannot segregate.
Dual pipe reactor technology (DPR): a granulation pipe reactor (GPR) and dryer reactor pipe (DRP) technology can be used to produce a range of finished compound fertilizers. A GPR and DPR can be combined. The use of a liquid ammonia sparger inside the GPR is also possible.
The production of ammonium sulphate with a GPR is possible; in this case there is a special design of the GPR to accommodate the much larger heat of reaction with sulphuric acid; at higher sulphuric acid amounts the material of construction of the pipe reactor is stainless steel in combination with a double lining using different linings.
The production of blended NPK products is covered in the FerTechInform section on Blending, which draws heavily on the EFBA Handbook of solid fertiliser blending.
The nitrophosphate process is described in Lüth, 1967, Nitzschmann and Reuvers, 1994, Reuvers and Wichmann, 1992, Reuvers, 1993, Reuvers. and Meyer, 1998, FEA, 2017, Reuvers, 2017, Jenssen, T.K. and Kongshaug, G. (2003) Diehl et al, 1986.
Dennis, C. and Ettouimi, S. (2019). The ultimate granulation plant, JESA Technologies, SYMPHOS 2019, 5th International Symposium on Innovation in the Phosphate Industry, pages 1 – 8.
EFBA. (2016). Handbook of solid fertiliser blending – Code of good practice for quality, European Fertilizer Blenders Association, Third Edition, edited by Jo Gilbertson and Estelle Vallin, 2016.
Ivell, D. (2019). NPK production routes, Worley, Fertilizer International, 492, September-October 2019, pages 1 – 5.
Ivell, D. (2022). Routes to Granular Products, International Fertiliser Society webinar, February 2022.
Kargaeva, N. (2016). Granulation technology with flexibility to produce a range of specialty fertilizers, , Proceedings International Fertiliser Society, 782.
Kiiski, H.T and Kells, A.G. (2016). Granulation of complex fertilizers, Proceedings International Fertiliser Society, 783.
Lüth, G. (1967). 40 years nitrophoska. Presentation before the Fertilizer Industry Round Table, 17th Annual Meeting, Washington, D. C., USA, 17.11.1967, pages 114–117.
Marcon, G. (2021). Complex fertilizers process – NPKs, , Casale, webinar, 10.06.2021.
Nitzschmann, R. E. and Reuvers, J. G. A. (1994). Nitrophosphate-based NPK fertiliser: Air pollution control. Pollution Control in Fertilizer Production, edited by C.A. Hodge and N.N. Popovici, Chapter 31, 419–431.
Reuvers, J. G. A. and Wichmann, W. (1992). Agronomical and technological advantages of modern nitrophosphates. Fertiliser Association of India, 1992 Seminar, New Delhi, India, 10–12.12.1992, paper SIII-2, pages 1-10.
Reuvers, J. G. A. (1993). Environmental aspects of the nitrophosphate concept. Presentation to the International Workshop on “Nitric Acid-Based Fertilizers and the Environment”, Brussels, Belgium, 14.–18.06.1993. Proceedings, No. 16, pages 153-161.
Reuvers, J. G. A. and Meyer, T. (1998). The BASF nitrophosphate process. Presentation to the 48th Annual Meeting of the Fertilizer Industry Round Table, Annapolis, Maryland, USA, 26–28.10.1998, pages 143–153.
Production of ammonia, nitric acid, urea and N-fertilizer, Umweltbundesamt (Federal Environment Agency), Vienna, Austria, 2017.
Links to related IFS Proceedings
34, (1955), Compound Fertiliser Formulation, R Stewart.
49, (1958), Gaseous Effluents from Granulation Plants, F J Harris.
56, (1959), Concentration (of fertilisers) – First Francis New Memorial Lecture, H U Cunningham.
61, (1960), Rotary Coolers and Driers – Some Related Aspects of Design, S J Porter, W G Masson.
91, (1966), NPK Fertiliser Production Using Superphosphoric Acid, G Bischofberger, R R Heck.
109, (1969), Prilling of Compound Fertilisers, F E Steenwinkel, J W Hoogendonk.
119, (1970), Control of Fertiliser Granulation Plants, J A Bland, J Hawksley, W Perkins.
141, (1974), Solids Handling and Metering in an NPK Prilling Plant, W J Kelly.
146, (1975), Off-Line Data Logging for NPK Plants, I K Watson.
237, (1985), Production of Chloride-Free NPK Fertiliser and Feedgrade Dicalcium Phosphate, K C Knudsen.
243, (1986), Nitrophosphates with Variable Water Solubility: Preparation and Properties, L Diehl, K F Kummer, H Oertel.
244, (1986), Adapting a Pipe Reactor to a Blunger for NPK Production, R J Milborne, D W Philip.
245, (1986), New Diammonium Phosphate Technology – Powdered or Granular DAP, L M Marzo, J L Lopez-Nino.
245, (1986), Dual Pipe Reactor Process for DAP, NP and NPK Production, P Chinal, Y Cotonea, C Debateux, J F Priat.
271, (1988), On-Line Data Logging for NPK Plants, I K Watson, D W Philip.
450, (2000), Self-Sustaining Decomposition of NPK Fertilisers Containing Ammonium Nitrate, H Kiiski.
451, (2000), Design of Rotary Driers and their Application in the Fertiliser Industry, I C Kemp, R J Milborne.
509, (2003), Energy Consumption and Greenhouse Gas Emissions in Fertiliser Production, t K Jenssen, G Kongshaug.
725, (2013), Urea-based NPK Granulation – Examination of Constraints and Potential Solutions, S R Doshi.
782, (2016), Granulation Technology with Flexibility to Produce a Range of Specialist Products, N Kargaeva.
783, (2016), Granulation of Complex Fertilisers, H Kiiski and A Kells.
805, (2019), The Carbon Footprint of Fertiliser Production: Regional Reference Values, A Hoxha, B Christensen.
856, (2021), Progress in Using Artificial Intelligence in Process Control to Reduce Energy Usage, S. Rademakers.
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