Ammonia in Fertiliser Manufacturing: Urea, Ammonium Nitrate and DAP Production Chain

Ammonia is the molecular bridge between atmospheric nitrogen and the food on your plate. Without ammonia-based fertilisers, global crop yields would collapse to a fraction of their current levels, and the world could not sustain its present population. Approximately 80 percent of all ammonia produced globally flows into the fertiliser industry, where it is either applied directly to soil or converted into the major nitrogen fertiliser products that reach farmers around the world. At Jaysons Chemical Industries, we supply high-purity anhydrous ammonia and liquor ammonia to fertiliser manufacturers and agricultural customers across India and internationally. This article explores the complete ammonia in fertiliser manufacturing value chain, from the Haber-Bosch synthesis plant to the urea granule, the ammonium nitrate prill, and the DAP granule that ultimately delivers nitrogen to the soil. Explore our resources on ammonia in agriculture and anhydrous ammonia uses in agriculture for the full agronomic context.

1. The Ammonia-Fertiliser Connection

Nitrogen is the most growth-limiting nutrient in most agricultural soils. While nitrogen makes up approximately 78 percent of the atmosphere, it exists as diatomic nitrogen gas (N2), which plants cannot directly absorb. Biological nitrogen fixation by soil bacteria provides some plant-available nitrogen, but not enough to support the intensive crop yields required by modern agriculture.

The Haber-Bosch process, developed in the early twentieth century, made it possible to convert atmospheric nitrogen to ammonia on an industrial scale. Ammonia (NH3) contains nitrogen in a form that can be directly utilised by plants as a soil amendment, or converted to a range of solid and liquid nitrogen fertilisers that are stable, concentrated, and suited to global trade. The world produces approximately 185 million tonnes of ammonia annually, of which around 150 million tonnes is used for fertiliser applications.

2. Ammonia Production: The Haber-Bosch Process

All fertiliser-grade ammonia begins with the Haber-Bosch synthesis process, in which atmospheric nitrogen (N2) and hydrogen (H2) are reacted at high temperature and pressure over an iron catalyst to produce ammonia. The reaction is: N2 + 3H2 yields 2NH3 (with a standard enthalpy change of -92 kJ/mol, making it an exothermic reaction).

Industrial ammonia plants operate at pressures of 150 to 300 bar and temperatures of 400 to 500 degrees Celsius, achieving single-pass conversions of 15 to 25 percent with unreacted gases recycled to improve overall conversion to 95 percent or higher. The hydrogen feedstock is produced primarily by steam methane reforming (SMR) of natural gas, making natural gas both the energy source and the hydrogen source for conventional ammonia production. Green ammonia plants use electrolytic hydrogen from renewable electricity, as described in our article on green ammonia production science.

3. Urea Production from Ammonia

Urea (CO(NH2)2) is the world’s most widely traded nitrogen fertiliser, accounting for approximately 50 percent of global nitrogen fertiliser consumption. With a nitrogen content of 46.3 percent by weight, it is the most nitrogen-dense solid fertiliser and is economical to transport and store.

The Urea Synthesis Reaction

Urea is produced by reacting ammonia with carbon dioxide in two sequential steps. First, ammonia and CO2 combine to form ammonium carbamate: 2NH3 + CO2 yields NH2COONH4. This reaction is fast and essentially complete. Second, ammonium carbamate dehydrates at elevated temperature to form urea and water: NH2COONH4 yields CO(NH2)2 + H2O. The second reaction is slower and does not reach completion at typical reactor conditions, requiring separation and recycling of unconverted carbamate.

Urea Plant Operations

Industrial urea plants operate at temperatures of 160 to 200 degrees Celsius and pressures of 140 to 200 bar. The urea melt leaving the reactor typically contains 70 to 80 percent urea, which is concentrated to 99.7 percent by multi-stage evaporation under vacuum. The molten urea is then converted to solid product by prilling (spraying through a prilling tower to form spherical droplets that solidify as they fall) or granulation (coating growing granule seeds with urea melt in a rotating drum or fluidised bed). For every tonne of urea produced, approximately 567 kg of ammonia and 733 kg of CO2 are consumed.

4. Ammonium Nitrate Production Chain

Ammonium nitrate (AN) provides two forms of nitrogen — ammonium nitrogen and nitrate nitrogen — that are taken up by plants through different mechanisms, offering agronomic flexibility. It contains 33 to 35 percent nitrogen and is used both as a direct fertiliser and as a component of compound fertiliser formulations such as calcium ammonium nitrate (CAN) and ammonium nitrate phosphate (ANP).

Step 1: Nitric Acid Production

The ammonium nitrate production chain begins with the Ostwald process for nitric acid synthesis. In the Ostwald process, ammonia is catalytically oxidised over platinum-rhodium gauze catalysts at 850 to 950 degrees Celsius to produce nitric oxide (NO): 4NH3 + 5O2 yields 4NO + 6H2O. The NO is further oxidised to nitrogen dioxide (NO2) and absorbed in water to produce nitric acid (HNO3): 3NO2 + H2O yields 2HNO3 + NO. This means that ammonia is the feedstock for both sides of the ammonium nitrate synthesis reaction.

Step 2: Neutralisation

Gaseous ammonia is neutralised with dilute nitric acid (50 to 65 percent concentration) in a neutralisation reactor, producing an ammonium nitrate solution and releasing considerable heat: NH3 + HNO3 yields NH4NO3. The neutralisation heat is used to concentrate the solution by evaporation. The process typically produces a 70 to 95 percent ammonium nitrate solution.

Step 3: Solidification

The concentrated ammonium nitrate solution is further concentrated to melt purity (99.7 percent) and then prilled or granulated as per the urea process. Ammonium nitrate products are coated with anti-caking agents and conditioned to maintain granule integrity during storage. Given ammonium nitrate’s oxidising properties and potential for detonation at high temperatures or under confinement, its storage and transport are subject to strict regulatory controls distinct from those applicable to urea.

5. DAP Fertiliser Production Chain

Di-ammonium phosphate, universally known as DAP, is the world’s most widely used phosphate fertiliser, with a standard analysis of 18-46-0 (18 percent nitrogen, 46 percent P2O5). Its dual nutrient content makes it particularly valuable for cereal crops that require both nitrogen and phosphorus at planting.

Phosphoric Acid Production

DAP production begins with phosphoric acid, produced by digesting phosphate rock (primarily fluorapatite) with sulphuric acid in the wet process: Ca10(PO4)6F2 + 10H2SO4 yields 6H3PO4 + 10CaSO4 + 2HF. The resulting phosphoric acid solution (28 to 32 percent P2O5) is purified and concentrated for use in DAP synthesis.

Ammonia-Phosphoric Acid Reaction

DAP is produced in two stages. In the first stage, ammonia is reacted with phosphoric acid in a pre-neutralisation reactor at a mole ratio of approximately 1.4 ammonia to 1 phosphoric acid, producing a MAP-rich slurry. In the second stage, additional ammonia is added to bring the ratio to 2:1, producing the DAP product slurry: 2NH3 + H3PO4 yields (NH4)2HPO4. The slurry is then granulated, dried, and screened to produce the finished DAP granule.

6. Other Ammonia-Based Fertilisers

Beyond urea, ammonium nitrate, and DAP, ammonia is the nitrogen source for a wide range of additional fertiliser products serving specific soil conditions and crop requirements.

Ammonium Sulphate

Ammonium sulphate (21-0-0-24S) is produced by reacting ammonia with sulphuric acid. It is valued for supplying both nitrogen and sulphur, making it particularly effective on sulphur-deficient soils. It is a byproduct of caprolactam (nylon intermediate) production and coke-oven operations, as well as a direct synthesis product for markets requiring its acidifying soil effect.

Mono-Ammonium Phosphate (MAP)

MAP (11-52-0) is produced using the same phosphoric acid neutralisation process as DAP but at a lower ammonia-to-acid ratio of 1:1. It provides a highly concentrated phosphate nutrient with a moderate nitrogen contribution and is widely used as a starter fertiliser and in compound fertiliser blends.

Calcium Ammonium Nitrate (CAN)

CAN is produced by blending ammonium nitrate with calcium carbonate or dolomite. It contains 26 to 27 percent nitrogen and is a preferred nitrogen fertiliser in Europe due to its lower explosive risk compared to pure ammonium nitrate and its neutral-to-basic soil pH effect.

7. Direct Application of Anhydrous Ammonia

Anhydrous ammonia with a nitrogen content of 82 percent by weight is the most nitrogen-concentrated fertiliser in existence. In North America and parts of Europe, it is injected directly into the soil at depths of 15 to 20 cm as a pre-plant or side-dress nitrogen application for cereal crops including corn, wheat, and sorghum. The injected ammonia dissolves in soil moisture and is converted to ammonium, which is retained by soil particles and subsequently nitrified to nitrate for plant uptake.

Direct application of anhydrous ammonia requires specialised nurse tanks, high-pressure applicator equipment, and significant safety infrastructure including SCBA on every operator unit. The economics are favourable due to the high nitrogen concentration and lower cost per unit of nitrogen compared to solid fertilisers, but the safety requirements and infrastructure investment limit its adoption primarily to large-scale commercial farming operations. Our page on anhydrous ammonia uses in agriculture explores these applications in detail.

8. Fertiliser Comparison Table

9. Safety and Storage in Fertiliser Manufacturing

The production chain for ammonia-based fertilisers involves multiple hazardous chemical streams requiring robust safety management systems. Ammonia itself, at the head of the process chain, is the most acute inhalation hazard. Nitric acid in the ammonium nitrate chain is a strong oxidising acid. Solid ammonium nitrate presents unique storage and fire risks due to its oxidising properties and susceptibility to detonation under specific conditions.

Ammonia Storage at Fertiliser Plants

Large-scale fertiliser manufacturing facilities typically store ammonia in refrigerated atmospheric tanks (at -33 degrees Celsius) or pressurised tanks at ambient temperature, often in quantities of thousands of tonnes. These quantities place the facilities firmly within OSHA PSM and EPA RMP coverage, requiring comprehensive process safety management programmes. Gas detection, emergency response planning, and regular safety audits are non-negotiable requirements. Our resources on safe ammonia handling and storage and ammonia gas leak detection are directly applicable to fertiliser plant operations.

10. Ammonia and Fertiliser Manufacturing in India

India is the world’s second-largest producer and consumer of fertilisers, with agricultural demand supported by a combination of domestic production capacity and significant imports. The Indian government provides substantial fertiliser subsidies that make nitrogen fertilisers, particularly urea, accessible to smallholder farmers, driving demand that in turn supports the ammonia supply chain.

Key Takeaways

• Approximately 80 percent of globally produced ammonia is consumed by the fertiliser industry, feeding roughly half the world’s population.
• Urea production consumes approximately 567 kg of ammonia per tonne of product and delivers 46.3 percent nitrogen by weight.
• Ammonium nitrate production uses ammonia both directly (neutralisation) and indirectly (via nitric acid production through the Ostwald process).
• DAP production combines ammonia and phosphoric acid in a 2:1 molar ratio, delivering 18 percent nitrogen and 46 percent P2O5 per granule.
• Anhydrous ammonia is the most nitrogen-dense fertiliser (82 percent N) and can be applied directly via soil injection for cereal crops.
• Fertiliser manufacturing facilities using ammonia above PSM threshold quantities require comprehensive process safety management programmes.
• India’s fertiliser industry depends on both domestic Haber-Bosch production and imported ammonia and finished products to meet agricultural demand.

Frequently Asked Questions