This column is based on “Ammonium Nitrate Porous Prills Production Process – Cost Analysis,” a report published by Intratec Solutions. It can be found at: www.intratec.us/analysis/ammonium-nitrate-production-cost.
Ammonium nitrate (NH4NO3) is one of the most commercially important ammonium compounds, both in terms of production volume and usage. Its importance comes from the fact that the salt incorporates nitrogen, and makes it readily available in both forms used by plants and crops: nitrate ion and ammonia. While fertilizers are the main use of ammonium nitrate, it is also used in other industries, such as mining, military and civil engineering.
NH4 NO3 is mainly commercialized in the following forms: aqueous solution, prills (pellets) and granules. The main grades are related to the content of nitrogen, usually ranging from 20 to 34.5 wt.% in solid forms.
The process examined here (Figure 1) is a typical vacuum-neutralization process, which consists of two major sections: neutralization and finishing.
Neutralization. Initially, liquid ammonia is evaporated, superheated and sent to a neutralization reactor, along with a nitric acid solution and circulating ammonium nitrate solution. The ammonia reacts with nitric acid to produce ammonium nitrate. The reaction occurs under a slightly pressurized atmosphere, in order to prevent the ammonium nitrate solution from boiling and to minimize ammonia losses.
The ammonium nitrate solution, heated by the highly exothermic neutralization reaction, overflows to a flash vessel under vacuum, in which water is partially evaporated. The vapor obtained is used to heat neutralization feed streams, while the concentrated ammonium nitrate is split: a portion is circulated to the neutralizer, while the rest is fed to a second neutralizer with additional ammonia. The product from the second neutralizer is routed to a thermosyphon evaporation system, in which the solution is steam heated under vacuum. The ammonium nitrate melt obtained is directed to a prilling step downstream.
Finishing. The ammonium nitrate melt is initially mixed with a solution of dry magnesium oxide (MgO) to improve its storage properties. Subsequently, the ammonium nitrate melt is mixed with a prilling additive and sprayed at the top of a prilling tower. The ammonium nitrate prills are dried in rotating drums, then screened, cooled and coated with an anticaking agent. Off-specification material is recycled to the process. Finally, the ammonium nitrate prills are packed in bags and stored. Also, waste air from the prilling and drying steps is scrubbed before being discharged to the atmosphere.
The commercial production of ammonium nitrate prills is mainly based on the neutralization reaction of ammonia and nitric acid. Ammonium nitrate production can be integrated with a nitric acid plant. In this case, ammonia is the only raw material. The diagram in Figure 2 presents the major production pathways for ammonium nitrate.
The total operating cost (raw materials, utilities, fixed costs and depreciation costs) estimated to produce ammonium nitrate was about $400 per ton of ammonium nitrate in the fourth quarter of 2015. The analysis was based on a plant constructed in the U.S. with the capacity to produce 400,000 metric tons per year of the compound.
Edited by Scott Jenkins
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