Nitrogen+Syngas 367 Sept-Oct 2020
30 September 2020
Ammonium nitrate – still growing
AMMONIUM NITRATE
Ammonium nitrate – still growing
In spite of continuing safety concerns due to the Beirut explosion, and the rise of the use of urea as a nitrogen fertilizer, ammonium nitrate demand continues to increase in several key markets.
Ammonium nitrate’s first major commercial use was as a component of blasting agents, and it remains the basis of most commercial explosives on the market, in particular as the mixture ammonium nitrate/fuel oil (ANFO). However, after WWII, it became popular as a fertilizer as well. The growing popularity of urea, which contains 42% nitrogen by weight compared to AN’s average of 33-34%,has meant that, especially in the developing fertilizer markets of India, China and South America, urea has become preferred as a more efficient way of transporting nitrogen, and AN’s share of the nitrogen fertilizer market has steadily dropped. Restrictions imposed following a series of accidents have also led some countries to ban the use of straight AN as a fertilizer. Nevertheless, its versatility and its rapid uptake by plants continues to ensure that it is preferred by farmers in some markets.
Manufacture
Ammonium nitrate is produced by the acid base neutralisation reaction of nitric acid with ammonia. As nitric acid is also made from ammonia oxidation, AN plants are typically co-located with ammonia and nitric acid production. The ammonium nitrate is formed as a solution in water. For production of solid AN it is then typically concentrated in an evapourator or concentrator to a solution strength of 95-99% AN at high temperature (ca 150°C). This AN ‘melt’ is then passed to a prill tower or granulator to produce the solid AN prills.
Prill density can be varied by using different concentrations of ammonium nitrate melt. Low density prills, at a density of around 1.29, are formed from 95-97.5% AN melt, while high density prills, at a density of around 1.65, are formed from a 99.5-99.8% melt. Low density prills are more porous than high density prills and so absorb e.g. oil more easily. For this reason low density prills are used for making blasting agents – this is known as ‘technical’ or ‘industrial’ grade AN (TAN/IGAN). The high density prills are used as fertilizers (fertilizer grade AN or FGAN), with a typical nitrogen nutrient content of 33-34%. Because of the similarity in IGAN and FGAN production, both from an ammonium nitrate liquor, the IGAN industry originally evolved largely as an ‘adjunct’ to the production of FGAN. However, because of regulatory hurdles in storage and transport of AN, plants tend to be relatively close to areas of end user demand, and as fertilizer and mining areas are often not the same, there has been a gradual polarisation of the industry into dedicated facilities producing one or the other.
The melt can also be mixed with other chemicals to produce other end products. One popular method is to mix the melt 75-25% with calcium carbonate (limestone) to produce calcium ammonium nitrate (CAN). Dolomite (calcium magnesium carbonate) can be substituted for calcium carbonate to produce magnesium ammonium carbonate (MAN).
Finally, the non-concentrated ammonium nitrate solution direct from the reactor can instead be mixed with a solution of urea to produce a solution called urea ammonium nitrate (UAN). UAN is typically available in three different concentrations: 28%, 30% and 32% nitrogen. The most popular form – 32% nitrogen – is a mixture of 45% ammonium nitrate, 35% urea and 20% water. Ammonia and nitric acid are used to adjust solution pH to close to 7.
Since ammonium nitrate is hygroscopic and therefore readily attracts moisture from air, in its solid form it is usually coated with an anti-caking compound, and is stored in air-conditioned warehouses or sealed bags. However, its high solubility does make it ideally suited for using solutions for fertigation or foliar sprays.
Agronomic benefits
Ammonium nitrate is popular as a fertilizer because its nitrogen is present in a form more readily available to the plant than urea, which must be oxidised to nitrate in the soil. The nitrate in AN moves readily with soil water to the roots, where it is immediately available for plant uptake, while the ammonium ion is taken up by roots or gradually converted to nitrate by soil microorganisms. Its rapid uptake means that it is less susceptible to volatilisation than urea, and if applied correctly leads to less leaching into ground water. It also makes it suited to areas with shorter growing seasons, such as in many northern latitudes in Canada, Europe and Russia. Ammonium nitrate generates 90% fewer ammonia emissions per unit of nitrogen than urea, which is a factor in many countries which are trying to reduce ammonia emissions, especially in Europe.
One of the interesting developments in recent years has been a significant switch in China from the use of straight urea as a fertilizer to an increasing reliance on NPK blends as a way of increasing the efficiency of nutrient use in the country, especially now that the government has tried to cap overall use of nutrients to try and tackle environmental issues. This means that there is increasing need for AN and CAN as part of NPK blends. Although Chinese AN consumption is down from its peak year of 2014, it has nevertheless increased by 50% in the past decade.
Production
Total production of ammonium nitrate in terms of million tonnes N was about 21.1 million t/a in 2019. This figure has risen steadily if patchily this century, as Figure 1 shows, at an average annual growth rate of 4.4%. Of this total, about 34% was represented by straight AN fertilizer, 29% by technical/industrial grade ammonium nitrate, intended for commercial explosive use, 19% by calcium and magnesium ammonium nitrate (CAN/MAN – but mainly the former) and 17% by urea ammonium nitrate solutions (UAN). A small proportion is also used in the direct manufacture of ammonium sulphate nitrate and other derivatives. CAN and straight AN fertilizer is also often blended into various NPK fertilizers.
Table 1 breaks down production and consumption by region. However, note that the ‘AN’ figure in the first column also includes ammonium nitrate which is then used to make UAN, and that about half of the nitrogen content of the UAN figure comes from its urea component.
Demand
Demand for AN is concentrated in three main regions: Western Europe, North America, and Eastern Europe/Russia, which collectively account for two thirds of all consumption. However, each is quite different in terms of how that AN is used. In Western Europe, restrictions on the sale of straight AN fertilizer in countries such as Turkey, Germany, Ireland and parts of the UK due to its potential for misuse has led to substitution with calcium ammonium nitrate (CAN). Western Europe is the only significant market for CAN, responsible for three quarters of all demand.
In the US, conversely, a preference for fertilizer solutions but a corresponding tightening of regulations on the storage, transport and use of ammonia for direct application, on grounds of safety and security, has led to a rapid increase in demand for UAN solutions, and the North American market is heavily skewed towards UAN, with straight AN mostly used as a mining explosive.
Consumption in Eastern Europe and Russia has been rising rapidly. Russian consumption of AN has more than tripled since 2000. CAN and UAN are not major features of this market. The rise in domestic consumption in Russia has helped alleviate one issue that had bedevilled the global AN market – allegations of so-called ‘dumping’, or sale of product at below cost price in order to increase market share. Both the US and European
Union maintained anti-dumping tariffs on sales of Russian AN from most producers for many years following the breakup of the Soviet Union in the early 1990s, alleging that natural gas feedstock prices were being subsidised. The gradual spread of freer gas market pricing globally and the pickup in domestic demand in Russia has eased many of these concerns and in 2016 the US removed its tariffs and the EU reduced its tariffs in 2018. The situation is still not completely resolved however – in 2019 the EU imposed duties on UAN imports from Russia, although it also imposed duties on UAN from Trinidad and the US.
Looking to the future, UAN use continues to increase in the US, and AN compounds in NPKs and other fertilizers are likely to see continuing growth in Asia. On the explosives side, the main use for commercial explosives is in the mining and quarrying industries, and for large volumes of IGAN use is mainly confined to the coal, gold, iron ore and copper mining industries, which between them account for more than 70% of all IGAN consumption. Of these, coal is the largest share. Coal consumption is slowly falling from a 2013 peak, as Europe moves away from coal for environmental reasons and the US for economic ones. China, the largest consumer, is also trying to move its economy away from coal dependence and consumption has plateaued there. However, mining for copper and iron ore continues to increase, albeit at a slower rate than during the commodities boom of the first two decades of the century, driven by China’s rapid industrialisation.
Covid has had a major impact on mining around the world. Orica, the world’s largest supplier of IGAN, says that it currently anticipates a 10-15% drop in IGAN demand in 2020 as a result of Covid restrictions. However, the longer term growth prospects for the sector remain positive, at around 1.5% year on year, and Orica brought a new IGAN plant on-stream in Australia earlier this year.
Safety and security
The August 4th explosion in Beirut, believed to have been caused by 2,750 tonnes of AN being improperly stored at a warehouse in the port district, has once again reopened the question of ammonium nitrate’s suitability as a fertilizer. Incidents around the world, both accidents and deliberate misuse have led to progressive tightening of regulations over the past few decades, usually on a national basis. Afghanistan, China, Colombia, the Philippines have all banned the sale of AN as a fertilizer because of security concerns, and most recently in Turkey, straight AN was banned as a fertilizer following a series of terrorist incidents in 2016. Brazil, the major user in South America, moved to a licensing system on AN purchase for importers and traders last year, which applies to all forms of AN. Russia maintains limits on warehousing and how long AN can be stored, and following the devastating explosion in Tianjin in China in 2015, many Chinese ports and railway authorities have introduced additional restrictions on import and storage of AN-based compounds. India banned import of bulk, loose AN following the same incident, though it can still be imported in bagged form. In Europe, sale of any AN-based compound with a nitrogen content of more than 16% is prohibited to anyone not on an approved list of buyers.
All of these regulations place additional cost burdens on supply of AN, and the worry for the industry after any major incident is that there will be pressure on regulators to introduce tighter measures on the storage and transport of AN which progressively leads to the industry dying the ‘death of 1,000 cuts’ as each new regulation, perhaps not significant in itself, leads to increased costs which make it less competitive, or place such a burden on wholesalers and distributors that they can no longer be bothered to deal in it. So far the uniqueness of the situation in Beirut appears to have mitigated somewhat against that, but it has placed AN uncomfortably back in the spotlight again. It is certainly possible that there will be further substitution into forms perceived as less dangerous such as CAN, UAN or NPK blends over the coming years. However, the general utility of AN as a fertilizer as described in the ‘agronomic benefits’ section above, has so far managed to avoid any more general ban in spite of these concerns. Indeed, back in 1999 this magazine carried an article by a respected industry consultant predicting the eventual demise of AN as a fertilizer for precisely the reasons detailed above, yet here we are, 20 years later, and the market has instead grown.
