UAN solution

The nitrogen solution, known by the acronym UAN (Urea Ammonium Nitrate), is a liquid nitrogenous fertiliser produced by blending concentrated solutions of urea and ammonium nitrate. Its nitrogen content typically ranges from 28% to 32%, though bespoke formulations incorporating additional nutrients may also be manufactured^[1]. This composition combines three nitrogen forms — ammoniacal, nitric and ureic — altering its agronomic behaviour relative to solid fertilisers.

Manufacture

The process relies on the continuous or batch mixing of urea and ammonium nitrate solutions, followed by cooling^[2]. In continuous mode, feedstocks are fed at steady rates into static mixers, with ongoing adjustment of flow, pH and specific gravity^[2]. Batch processing employs a vessel fitted with an agitator and load cells, with dissolution optionally assisted by recirculation and heat exchange^[2]. Final pH is adjusted through addition of nitric acid or gaseous ammonia, prior to incorporation of a corrosion inhibitor for safeguarding carbon steel tanks^[2][3].

Production may be integrated within a fertiliser complex: in the CO₂ stripping process with partial recycle, unconverted gases from the urea section are recovered into UAN solution, bypassing several finishing stages^[4]. Unit capacities range from 200 to 2,000 t/d, with most large facilities located at integrated sites producing urea and/or ammonium nitrate^[1].

For one tonne of 30% nitrogen solution, consumption amounts to 327.7 kg of urea (46% N) and 425.7 kg of ammonium nitrate (33-34% N), supplemented by 244.9 kg of water, 0.3 kg of ammonia and 1.4 kg of corrosion inhibitor^[3]. Energy consumption varies between 10 and 11 kWh/t, depending on feedstock physical state and ambient temperature^[3].

Geographical distribution and market

UAN usage is highly polarised: a predominantly North American fertiliser, whilst Europe favours nitrates and warm regions prefer urea^[5][6]. In the United States, UAN accounted for 26% of nitrogen application in 2022, behind direct application ammonia (27%) and ahead of nitrates (2%)^[6]. Conversely, its share is nil in Western and Central Europe (0% in 2022), Brazil (0%) and China (negligible)^[6]. In India, where urea dominates with 81% of nitrogen inputs, UAN does not feature^[6].

Urea, the fastest-growing nitrogen product, is better suited to hot climates^[5][6]. Nitrates, being less concentrated in nitrogen (27-34% N versus 46% for urea), tolerate long-haul transport poorly, encouraging regional consumption^[7][3]. UAN, being a liquid solution, requires dedicated storage and application infrastructure historically developed in North America.

Global production of ammonium nitrate solution (ANS), the UAN feedstock, is estimated at 40-45 Mt/year^[8]. IFA statistics incorporate the nitric share of UAN within ammonium nitrate figures: total nitrate production (AN/CAN including this UAN portion) reached 19.1 Mt N in 2023, comprising 15.6 Mt of AN and 3.5 Mt of CAN/MAN^[7]. Over 2013-2023, trend growth was flat^[7]. Russia ranks as the leading producer, followed by the United States and China^[7].

In Western Europe, UAN consumption stood at 3.72 Mt of solution in 1998/99, with 41% sourced from imports^[1]. This reliance on external supply, coupled with currently weak offtake, illustrates the product's decline on the continent.

Regulation

UAN solutions fall under European Regulation 2003/2003/EC concerning fertilisers^[8]. The urea-ammonium nitrate blend entails storage precautions related to safety: the risk of thermal decomposition of ammonium nitrate, albeit diluted, necessitates rigorous temperature management. The corrosion inhibitor constitutes a technical requirement for protecting carbon steel storage infrastructure^[3].