1. Introduction
2. Calcium ammonium nitrate production – technology and industrial processes
3. Production technology for calcium ammonium nitrate – some special aspects

Introduction

Calcium ammonium nitrate nowadays typically contains ammonium nitrate (AN) at a concentration just below 80%, typical grades are CAN-26% N and CAN-27% N.

In the 1960s, the usual grade of calcium ammonium nitrate was around 21% N, corresponding to an ammonium nitrate concentration of about 60 %.

Calcium ammonium nitrate contains ammonium nitrate and limestone, dolomite, chalk, or precipitated calcium carbonate. These calcium and magnesium carbonates are alkaline in nature and are present in an amount of at least 20%. The presence of carbonates reduces significantly the hazardous properties of the mixtures compared to highly concentrated ammonium nitrate. For that reason, calcium ammonium nitrate is used predominantly in various countries, for example, in the Netherlands and in Germany.

The calcium and/or magnesium carbonates in CAN bring an additional agronomic value. These carbonates exert a neutralising effect, in the sense that they neutralise any free acid. Calcium ammonium nitrate is preferably used on acid soils because of this alkaline (liming) effect.

Existing regulatory limits for calcium ammonium nitrate in storage and transportation regulations in many countries allow up to 80% AN content and classify it as a non-hazardous product.

This concentration limit represents an accepted standard used around the world as the threshold for differentiating CAN from straight fertiliser grade ammonium nitrate and establishes it as a fertiliser that is safe and not susceptible to accidental explosion.

Calcium ammonium nitrate has been produced in millions of tons per year for many decades in many different parts of the world and is a leading N source in many markets.

Calcium ammonium nitrate production – technology and industrial processes

Calcium ammonium nitrate has been described in much detail in numerous publications during the past 20 years. The production of CAN is in many ways quite similar to the production of concentrated ammonium nitrate.

The reader is referred to a number of recent publications that describe the industrial processes in detail, see References and External Resources. Following the guidance and information given, further references on the properties, on safety and quality aspects, and on present-day industrial processes regarding calcium ammonium nitrate can be found.

The related sections of FerTechInform describing ammonium nitrate contain much information equally applicable to calcium ammonium nitrate. In the following sections, certain properties related to calcium ammonium nitrate are explicitly discussed.

A number of design and engineering companies offer particulation processes, such as prilling, granulation and fluidised bed processes.

Some of the older processes are described in the IFDC / UNIDO Fertilizer Manual, 1998.

Production technology for calcium ammonium nitrate – some special aspects

Stabilising salts for calcium ammonium nitrate

For calcium ammonium nitrate the addition of internal additives – stabilisers – is common. The amount of such internal additives is usually in the range 10 – 20 kg per tonne. Stabilising salts can be, for example, aluminium sulphate, potassium sulphate, iron sulphate, or ammonium sulphate, are described in the literature.

The presence of calcium carbonate in the product allows for the formation of small amounts of calcium nitrate – depending on the manufacturing process and the operating parameters such as the product acidity (pH). Low pH and possibly the recycling of scrubbing liquids may lead to the formation of more calcium nitrate. Calcium nitrate is very hygroscopic and, as such, can exert detrimental effects on the quality of calcium ammonium nitrate. To avoid this, internal additives are added, most of which tend to capture any calcium nitrate. These additives usually contain the sulphate ion and examples of such internal additives are ammonium sulphate, magnesium sulphate, aluminium sulphate, calcium sulphate and potassium sulphate, each by itself or in combination with other additives. The sulphate ion and the calcium ion combine to form the less soluble calcium sulphate dihydrate (gypsum), thereby also binding water.

Pan granulation plant

Dry recycled material is fed at a controlled rate to the inclined rotating pan granulator; in this granulator a hot melt, which is virtually moisture free, is sprayed onto the moving bed of solids and solidifies on the cool particles. Round granules are formed by agglomeration, and, as their size increases, they move upwards in the rotating pan, finally rolling over the rim. Cooled granules are conveyed to a screen. Oversize material from the screen is fed to a crusher and the crushed material, undersize granules, and dust from the cyclones, are recycled to the pan. In Europe, presently there appears to be only one CAN manufacturing plant in Greece using this process (European Commission, 2007).

Autothermal granulation

Under certain boundary conditions, the heat of crystallisation of ammonium nitrate is sufficient for the granulation and drying of calcium ammonium nitrate. No burner for supplying hot air is needed. The process can be especially viable if calcium carbonate originating from the nitrophosphate process and washed with diluted ammonium nitrate solution, is used. Under such conditions, the calcium carbonate need not to be dried and there also is no need for hot air from a burner for drying. At least one plant in Europe is applying this configuration (Wiesenberger, 2002; Federal Environment Agency, Austria, 2017).

The wet electrostatic precipitator for reduction of dust emissions

Wet electrostatic precipitators offer efficient emission control for, among others, sub-micron particulates. Whereas wet precipitators have shown advantages such as proven performance, compactness, robust design, automatic operation, and low operating costs in many other fields, their application for fertiliser off-gases is relatively new. A first wet precipitator was installed on a calcium ammonium nitrate plant in late 2017 and has proven its successful application for fertilisers (AWS Corporation, 2021).

References

AWS Corporation. (2021). Wet Electrostatic precipitator

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 ; pages 363 – 385.

IFDC / UNIDO. (1998). Fertilizer Manual, Development Center (IFDC), Kluwer Academic Publishers.

Wiesenberger, H. (2002). State-of-the-art for the production of fertilisers with regard to the IPPC-Directive, H. Federal Environment Agency, Austria, Monographien, Band 105, M-105, Vienna.

Umweltbundesamt (Federal Environment Agency). (2017). Production of ammonia, nitric acid, urea and N-fertilizer, Vienna, Austria.

Links to related IFS Proceedings

235, (1985), Fluid Bed Granulation of Ammonium Nitrate and Calcium Ammonium Nitrate, J P Bruynseels

438, (1999), Life Cycle Approach to Nutrient and Energy Efficiency in European Agriculture, J Küsters

508, (2003), Product Stewardship Applied to Fertilisers, H Kiiski, R J Milborne

580, (2006), Safety Testing of Ammonium Nitrate Products, R J A Kersten, E I V van den Hengel, A C van der Steen

582, (2006), IPPC: ‘The BAT Reference Document (BREF) for the Manufacture of Ammonia, Acids and Fertilisers’, B Serr

583, (2006), Phase Stabilisation of Ammonium Nitrate Fertilisers, H Kiiski

764, (2015), Ion-Exchange Treatment of Effluent from Ammonium Nitrate Plants for Nitrogen and Water Recovery, N Arion, G Mommaerts

767, (2015), Update on Fluidised Drum Granulation Technology and its Applicability for Different Fertilisers, S Valkov

788, (2016), Improvements in Nitrogen Addition to the Fertiliser Production Flowsheet, I Blazsek and M J Cousins

Links to external resources

Ammonium nitrate regulatory update, Nitrogen + Syngas, Nr. 313, September – October 2011, pages 30 – 32, and Editorial, page 4.

AWS Corporation. (2017). Zero emission philosophy – wet electrostatic precipitator dedusting for AN/CAN based fertilizer plant,

Fertilizers Europe. (2022). Guidance for the storage, handling and transportation of solid mineral fertilizers, second edition.

Helfensteyn, S. and Falkus, H. (2014). Optimization of a CAN granulation process with INCA advanced process control. Paper dated 03.01.2014.

Kamermann, P and Erben, A. (2006). The UHDE pugmill granulation, the process for safe and reliable production of CAN and other AN-based fertilizers, IFA Technical Symposium, Vilnius, Lithuania, 25. – 28.

Kersten, R.J.A., van den Hengel, E.I.V. and van der Steen, A.C. (2006) Safety testing of ammonium nitrate products, (TNO Defense, Security, and Safety), 2006, Proceedings International Fertiliser Society, 580, pages 01 – 12. This article has been summarized in Nitrogen & Methanol, No. 266.

Nitzschmann, R. E. and Reuvers, J. G. A. (1994). Ammonium nitrate and nitrochalk. Pollution Control in Fertilizer Production, edited by C.A. Hodge and N.N. Popovici, Chapter 9, 99–107.

Sjölin, C. (1971). The influence of moisture on the structure and quality of NH₄NO₃ – prills, J. Agr. Food Chem., Volume 19, No. 1, pages 83 – 95.