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Urea process operating variables
Various parameters effect the conversion of ammonia and carbon dioxide to urea and water, including temperature, pressure, the mole ratio of ammonia to carbon dioxide, and the presence of water.
Corrosion difficulties increase with temperature, and a range of 180°-210°C is generally accepted as optimum for most processes.
The presence of small amounts of oxygen decreases corrosion; all processes use this method of minimising corrosion. To minimise the amount of oxygen used, among other benefits, new materials of construction (alloys) have been and are being developed to reduce the need for maintenance; one such material of construction is the duplex stainless steel Safurex.
Emissions from urea plants and operations have been reduced over time. Data and background information can be found in the IPPC reference document on BREF LVIC-AAF (2007).
Specific synthesis processes have been developed and constantly improved over time and are being offered by dedicated engineering companies (for example; Slack and Blouin, 1969; Kaasenbrood and Charmin, 1977; Visser, 2009).
Fertinform will not detail these modern-day processes but instead refers to UreaKnowHow for further specific and expert descriptions and advice.
There are several finishing processes that can be applied to urea. Urea can be prilled, granulated, flaked, pastillised, and crystallised of which prilling and granulation can be considered to be most important. Most new plants that plan to ship internationally utilise granulation because of its far superior handling and storage qualities, however, a dedicated market for prilled material remains.
Since prills are not as strong as granules in either crushing or impact strength, many new plants are using granulation processes for finishing.
Many prill producers add formaldehyde upstream of prilling in either the evaporators or to the melt, this improves the quality greatly and reduces dust emission and caking tendencies in bulk storage. Fluid bed granulation technology is the (only) technology that can offer single-train granulation units in sizes matching current (large) urea synthesis plant sizes.
European Commission. (2007). Integrated Pollution Prevention and Control, Reference Document on Best Available Techniques for the Manufacture of Large Volume Inorganic Chemicals – Ammonia, Acids and Fertilisers, August 2007 a revision and update of this document is ongoing (2021-2025).
Honti, G.D. 1976. “The Nitrogen Industry“, Volume 1, Akadémia Kiadó, Budapest, Hungary.
Kaasenbrood, P. J. C., and H. A. G. Charmin, (1977), The Urea Stripping Process, Stripping Technology, Phase Equilibria, and Thermodynamics, Proceedings of the International Fertiliser Society, 166.
Slack, A. V. and Blouin, G. M. 1969. “Urea Technology, A Critical Review,” Tennessee Valley Authority, Muscle Shoals, Alabama, U.S.A., TVA Circular Z-4, Proceedings of the Seminar on Fertilizer Technology, New Delhi, India, December 14.-16., 1969.
Tomlinson, T. E. (1970). Urea-Agronomic Implications, Proceedings of the International Fertiliser Society, 113.
Visser, J. (2009). Urea Technology – Past, Present and Future, Proceedings of the International Fertiliser Society, 648.
Watson, C. J. (2000). Urease Activity and Inhibition – Principles and Practice, Proceedings of the International Fertiliser Society, 454
Related IFS Proceedings
131, (1972), Some Fundamental Aspects of Urea Technology, S M Lemkowitz, M G R T de 166, (1977), Urea Stripping Process – Stripping Technology, Phase Equilibria and Thermodynamics, P J C Kaasenbrood, H A G Chermin, Cooker, P J van den Berg
167, (1977), An Integrated Process for Ammonia-Urea Manufacture, V Lagana, U Zardi
206, (1982), Materials of Construction for the Nitric Acid Process, K Nutall, A R Reid
257, (1987), Rationale for Mixed Ammonium Nitrate – Urea Fertilisers and Assessment of Granular Products, M K Garrett
582, (2006), IPPC: The BAT Reference Document (BREF) for the Manufacture of Ammonia, Acids and Fertilisers, B Serr
725, (2013), Urea-based NPK Granulation – Examination of Constraints and Potential Solutions, S R Doshi
770, (2015), World-Wide Trends in Urea Process Technologies, J M G Eijkenboom, M J Brouwer
805, (2019), The Carbon Footprint of Fertiliser Production: Regional Reference Values, A Hoxha, B Christensen
830, (2019), Principles and Applications of a Directory of Urea Safety Incidents, with Case Studies, M J Brouwer
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