Renewable electricity, particularly from sources like wind, solar, and other renewable resources, is rapidly becoming a cornerstone of the global effort to decarbonize various industries. One of its most promising applications for industrial needs is the production of green hydrogen through water electrolysis – a clean and versatile fuel with vast potential to power hard-to-abate sectors such as metals, mining, and the production of sustainable marine and aviation fuels. This transition is being actively supported by various government incentives across different regions and shifting consumer demands.
However, green hydrogen’s transformative potential extends beyond heavy industries and transportation. In agriculture, hydrogen – currently sourced from fossil fuels processing – plays a crucial role in the production of ammonia, the foundation for nitrogen-based fertilizers. Given that the nitrogen fertilizer industry accounts for a significant portion of global greenhouse gas (GHG) emissions, decarbonizing fertilizer production is critical. By adopting sustainable technologies, a renewable electricity-powered, integrated green fertilizer complex can revolutionize the sector, transforming how the global demand for food supply is met. Stamicarbon, the nitrogen technology licensor of MAIRE S.p.A., is at the forefront of enabling this value chain, driving greener farming practices for a sustainable future.
Green hydrogen to green ammonia
Green hydrogen, sourced from renewable electricity via electrolysis, is a clean fuel but presents challenges in terms of storage and transportation due to its low energy density and explosive nature. A widely considered alternative in the industry is green ammonia, which is produced by combining green hydrogen with nitrogen from the air. The key benefit of ammonia is that it is easier to store and transport, with a higher energy density compared to hydrogen. For instance, ammonia can be stored at −33°C or under moderate pressure, making it more cost-effective for long-term storage than hydrogen, which requires extremely high pressures or cryogenic temperatures.
The global infrastructure for ammonia storage, shipping, and application has been extensively developed over the past century, making ammonia a widely accepted and practical solution for large-scale deployment.
The ammonia production process, known as the Haber-Bosch process, was invented in 1913 and is a well-established technology. With certain modifications, this process can be adapted to produce green ammonia, effectively managing the fluctuating supply of renewable electricity. Given the current state of the industry – particularly the limited supply of electrolyzers and the limited availability and the higher costs associated with renewable electricity – small-scale green ammonia plants are emerging as optimal solutions.
In contrast to traditional fossil-fuel-powered ammonia production, the economy of scale plays a less significant role for green ammonia. Therefore, modular and scalable production offers a promising pathway for early adopters to meet their decarbonization goals.
Green ammonia process
Stamicarbon’s technology stands out by enabling ammonia production from renewable energy with minimal environmental impact. NX STAMI Green Ammonia™ technology has been designed to create the most effective layout for small to medium-sized plants relying on green feedstock, with capacities ranging between 50–500 MTPD.
This technology employs a high-pressure ammonia synthesis loop operating at around 300 bar, enhancing conversion efficiency while reducing the need for expensive refrigeration systems. The process flow, as shown in Figure 1, starts with the make-up gas – a mixture of hydrogen and nitrogen – generated from the upstream electrolyzer and nitrogen generation unit. This gas is then compressed in the electricity-driven multi-service reciprocating compressor to a pressure of over 300 bar. The recycle stream containing the unconverted gas is also recompressed to the same pressure.
The ammonia converter used in the NX STAMI Green Ammonia™ process is a single-bed axial-flow converter with a tubular design where the feed is pre-heated using the exothermal reaction on the catalyst side to a temperature necessary for ammonia synthesis. The start-up heater is integrated into the ammonia converter. Due to the high pressure, the reactor and catalyst volume can also be reduced.
The high pressure of the synthesis loop allows for single-stage ammonia condensation using cooling water. This eliminates the need for a refrigerating compressor, thus minimizing equipment count, leading to about 25–30% CAPEX savings. Over 70% of ammonia is recovered in separator 1, and part of the uncondensed ammonia is condensed in separator 2.
Ammonia can be produced at a pressurized condition (i.e., 16–18 bar) and ambient temperature to be stored in bullets, or at ambient pressure and −33 °C to be stored in atmospheric ammonia storage, or at any intermediate pressure level as required.
Sustainable fertilizer production
Green ammonia can be used directly in the production of urea, significantly reducing the carbon footprint associated with nitrogen-based fertilizers. However, there is an alternative pathway that may be more beneficial for specific regions or applications. Ammonium nitrate and nitric acid, key components of nitrate-based fertilizers, can offer even greater potential for reducing GHG emissions, making them a feasible and attractive option for sustainable agriculture in areas with the right conditions.
Nearly all the industrially produced nitric acid is manufactured by the high-temperature catalytic oxidation of ammonia (the Ostwald process) in two main steps:
- The oxidation of ammonia (NH₃) to form nitric oxide (NO), which is further oxidized to nitrogen dioxide (NO₂)
- The absorption of the nitrogen dioxide (NO₂) in water (H₂O) to form nitric acid (HNO₃)
Stamicarbon offers its NX STAMI Nitrates™ portfolio, which includes its proven mono- or dual-pressure designs. In the mono-pressure process (see Figure 3), the oxidation and absorption sections operate at the same pressure level. Different pressure levels are used for the oxidation and absorption sections in the dual-pressure process (see Figure 4). The oxidation section is operated at pressures between 4 and 6 bar, while the absorption section operates between 8 and 12 bar, combining the advantages of medium-pressure combustion with the efficiency of high-pressure absorption.
The main characteristic of both processes is a specific heat exchanger network downstream of ammonia oxidation. This configuration has several advantages. On the one hand, the heat exchange network has specific process conditions selected to prevent corrosion and ensure that no expensive materials are required for equipment manufacturing.
One of the key advantages of Stamicarbon’s nitric acid technology is its high energy efficiency: the process is designed to minimize heat losses and maximize heat recovery from the process streams. This decreases steam consumption and, hence, operational costs.
Stamicarbon’s technology is also designed with environmental concerns in mind. The technology incorporates measures to minimize emissions of greenhouse gases and other pollutants. The use of proprietary tertiary abatement technology allows for the elimination of nitrogen oxides and nitrous oxide, which can be reduced to almost zero, resulting in the disposal of an environmentally safe tail gas.
Integration of technologies in a green fertilizer complex
A green fertilizer complex, as shown in Figure 5, can integrate multiple units, including a green ammonia production plant, a nitric acid plant, a urea solution plant, and an ammonium nitrate solution plant. One key advantage of integration is the reduction of CAPEX and OPEX.
For example, the oxygen stream from the water electrolysis section can be incorporated into the nitric acid plant, as illustrated in Figure 6, reducing the need for conventional air-supplied oxygen
To maintain safety, the ammonia-oxygen mixture must remain below the explosive limit, requiring additional nitrogen, which can be sourced from recirculating tail gas. This approach provides several benefits:
- Reduction of NOx and N₂O emissions by up to 40% through tail gas recirculation
- Reduction of catalyst usage by up to 40%, along with a decrease in costs related to compressors and expanders
- More positive power balance since compressor power is reduced, with steam production rising by over 30%
Leveraging knowledge and decades of experience, Stamicarbon can offer an integrated, competitive solution, streamlining processes to reduce emissions, cut costs, and maximize operational efficiency.
The Meadowlark project
A prime example of integration of Stamicarbon’s technologies in action is the Meadowlark project in Gothenburg, Nebraska, USA. This state-of-the-art facility will be the first to incorporate Stamicarbon’s technologies in urea, nitric acid, and ammonium nitrate production.
Powered entirely by renewable energy, this plant will produce 450 MTPD of green ammonia. Down the line, the nitric acid plant, with a nameplate capacity of 330 MTPD, will be integrated with a urea section, neutralization section, and UAN mixing section. The nitric acid plant will operate at a constant pressure of 8 bar, combining the absorption and bleaching operations in a single piece of equipment. Due to the absence of a steam turbine, all high-pressure steam is exported and used in other sections of the fertilizer complex.
The facility is projected to produce impressive outputs: 365,000 tons of urea ammonium nitrate (UAN) and 146,000 tons of ammonium thiosulphate (ATS) per annum. In addition, the plant will produce 20 million gallons of diesel exhaust fluid (DEF) annually, targeting the developed heavy-truck transportation infrastructure in the region.
This project represents a fully integrated green fertilizer plant that will supply fertilizers to local farmers while utilizing waste CO₂.
Another example of the integration of Stamicarbon’s technologies is the FertigHy project in France. Stamicarbon, alongside NextChem Tech (MAIRE), has been awarded a feasibility study and pre-FEED contract for FertigHy’s first low-carbon fertilizer plant. Expected to begin construction in 2027, the plant will produce 500,000 tons of low-carbon nitrogen-based fertilizers annually, using hydrogen from renewable and low-carbon electricity. Stamicarbon’s NX STAMI Green Ammonia™ and NX STAMI Nitric Acid™ technologies will enable environmentally friendly ammonia production and highly efficient nitric acid processing with minimal greenhouse gas emissions.
Conclusion
The NX STAMI Green Ammonia™ process, with its modular design perfectly suited for small- to medium-scale, decentralized facilities, is a pioneering technology for green ammonia production. Based on proven natural gas-based technology, this process offers full flexibility in managing the intermittent nature of renewable energy, making it adaptable to various energy supply conditions. When combined with the NX STAMI Nitrates™ portfolio, green ammonia technology becomes a critical component in building sustainable fertilizer value chains.
By integrating renewable energy and green hydrogen with green ammonia and nitrates production, the global fertilizer industry can significantly reduce its greenhouse gas footprint and transform agricultural practices.
