Sustainable ammonia production

Ammonia is vital to global food security through nitrogen fertilizers and supports a wide range of downstream chemical value chains. Beyond its established role in agriculture, ammonia is increasingly seen as an enabler of the energy transition, serving as a hydrogen carrier and potential fuel. It can support hard-to-electrify sectors, including maritime transport, heavy industry, and power generation.

To make ammonia a key element in the energy transition, the industry does not need to create an entirely new supply chain; it can build on a century-old platform and scale it for new low-carbon applications.

At the same time, nitrogen fertilizers remain a strong conventional demand driver. Ammonia production is expected to rise substantially by mid-century, driven mainly by population and economic growth. The key question is not whether ammonia volumes will grow, but how quickly demand from emerging energy applications will materialise and how the industry can support that growth.

Decarbonisation challenge

Traditional ammonia production combines nitrogen from air with hydrogen that is typically derived from fossil fuels (commonly natural gas via steam methane reforming), followed by synthesis in the Haber-Bosch loop. This conventional route delivers highly reliable, world-scale production, but comes with significant CO2 emissions as byproducts of hydrogen generation and process energy use.

To tackle this challenge, blue ammonia at scale through carbon capture and storage (CCS) integration and green ammonia from renewable electricity are gaining industrial traction. Large-capacity facilities are increasingly being designed around high-capture configurations where CO2 is dehydrated, compressed, and sent for utilisation or permanent storage. In parallel, green ammonia projects are advancing, with renewable resources, grid conditions, and policy frameworks supporting competitive electrolytic hydrogen. Here, hydrogen is produced by water electrolysis powered by wind, solar, hydro, or geothermal energy, combined with nitrogen from air separation, and synthesised in the Haber-Bosch loop, producing ammonia with a substantially lower greenhouse-gas footprint.

In this landscape, technology is the practical bridge between ambition and bankable projects. Decarbonisation at industrial scale is not only a question of selecting a “route,” but of executing it efficiently and reliably: optimising heat integration and synthesis loop performance, minimising energy losses across compression and refrigeration, and designing plants for stable operation. Technology must address challenges like variable renewable power on the green pathway or CO2 capture and handling on the blue pathway. Integration becomes even more powerful when ammonia is viewed as part of a fertilizer value chain, where steam balance, CO2 utilisation (for downstream products such as urea), and energy efficiency can be optimised as one system rather than isolated units.

World-scale blue ammonia

To meet the rising demand for low-cost, high-efficiency ammonia production on world scale, Nextchem (MAIRE Group) offers the NX STAMI™ Ammonia medium-pressure design via its nitrogen technology licensor Stamicarbon. This is an optimised Haber-Bosch process, adjusted for capacities from 50 up to 3,500 tonnes/day. It is ideally suited for large ammonia plants using natural gas or other feedstocks. It can be efficiently paired with front-end solutions like steam methane reforming (SMR) or autothermal reforming (ATR) and carbon capture solutions. With over 45 industrial references from small to large scales, the medium-pressure design is a proven, cost-effective solution for reliability and scale.

In Nextchem’s medium-pressure design (Fig. 1), ammonia synthesis is carried out in a multi-bed radial-flow reactor configuration that minimises pressure drop. This design maximises the per-pass conversion of hydrogen and nitrogen with the smallest possible catalyst volume. The converter’s first catalyst bed has superior temperature control, enabling more efficient operation and extending catalyst life by avoiding hot spots. The result is a highly efficient loop that ensures more ammonia yield while consuming less energy. By tailoring key operating parameters (pressure, flow rates, recycle ratios) to a client’s needs, the design can be modified for optimal performance in different scenarios.

A conventional large-scale ammonia plant using this design can be made significantly more sustainable by integrating carbon capture into the front-end. Nextchem can also provide an advanced ATR technology that is particularly advantageous for “blue ammonia” projects. ATR yields a high-pressure syngas stream with a high concentration of CO2, which makes downstream carbon capture far more efficient. ATR-based ammonia production can enable carbon capture rates higher than 98% achieved with 40% less solvent circulation compared to a conventional amine-based solvent technology. Nextchem’s ATR operates at a high pressure (60+ barg), reducing the compression duty needed in the ammonia synthesis loop compared to conventional reforming at lower pressures and reducing the reactor size compared to conventional ATR. This translates to lower capital cost profile and lower operating costs. Moreover, the ATR route uses robust, well-proven equipment and a simplified process scheme that improves overall energy efficiency rates. When coupled with CCUS, an ATR-based ammonia plant can deliver world-scale output with a significantly smaller carbon footprint – delivering “big blue” ammonia at competitive economics.

Scalable green ammonia

Meeting the demand for smaller capacities, Nextchem’s NX STAMI™ Ammonia high-pressure design (Fig. 2) is a green ammonia technology for plants ranging from 50 up to 500 t/d. This process is engineered to maximise efficiency and simplicity in plants powered by renewable energy. It features a high-pressure synthesis loop (operating at over 300 bar) that drives the ammonia formation reaction to a high conversion per pass. By elevating the loop pressure, the need for extensive recycle compression and refrigeration is greatly reduced – an important advantage in smaller plants where simplicity and energy efficiency compensate for the lack of economy of scale. High pressure in the loop allows ammonia to condense with cooling water in a single stage, eliminating the need for a costly refrigeration compressor. This significantly lowers equipment count and contributes to an estimated 25–30% reduction in capital expenditures for the synthesis section alone.

The high-pressure design is characterised by a single-bed axial-flow ammonia converter with a compact tubular reactor design. Inside the converter, heat exchanger tubes are submerged within the catalyst bed to carefully control the temperature. Precise temperature control prevents hot-spot formation and catalyst sintering, prolonging catalyst life and maintaining performance. An integrated start-up heater is also included within the converter, allowing the reactor to heat up smoothly during plant start-up. Thanks to the high operating pressure, the converter and other equipment can be made more compact, and the overall footprint of the plant remains very small – a key benefit for decentralised or modular green ammonia installations.

The entire synthesis loop (both fresh make-up gas and recycle gas) is handled by a single, electrically driven reciprocating compressor, which supplies all services. This not only minimises the number of compressors required but also improves reliability and cuts maintenance costs. Nextchem’s high-pressure green ammonia design is ideal for distributed, smaller-scale projects that can be scaled up as renewable infrastructure grows.

NX STAMI™ Ammonia high-pressure technology has four operating references, giving the strongest reference list in the sub-500 t/d. By leveraging this proven technology, early movers in the green ammonia space are achieving their decarbonisation goals while positioning themselves for future expansion as electrolyser and renewable capacity grow.

Achieving operational efficiency through integration

Significant synergies can be gained by integrating green ammonia plants with downstream units. For example, green ammonia can feed directly into a urea plant to produce low-carbon urea fertilizer, cutting the overall carbon footprint per ton of product. Alternatively, ammonia can be converted to nitric acid and ammonium nitrate, which in some cases offers even greater greenhouse gas reduction potential for fertilizer production. In an integrated low-carbon fertilizer complex, shared streams, like the oxygen from water electrolysis, can boost efficiency. These integrations save energy, reduce emissions, and achieve savings in capital and operating costs by leveraging shared resources.

Conclusion

While medium-pressure and high-pressure ammonia technologies are typically associated with different capacity ranges, they are not feedstock-dependent. Medium-pressure technology can be effectively paired with electrolyser-based hydrogen, while high-pressure designs can provide a competitive solution for fossil-based and blue ammonia production, particularly when combined with front-end technologies such as NX CPO or e-SMR. By connecting these ammonia production technologies with downstream processes such as urea and nitrates at early stages, Nextchem can design fully integrated, future-proof fertilizer complexes.