Industrial-scale ammonia cracking technology addresses global energy transport challenges

The energy transition requires infrastructure to move low-carbon energy across continents, yet hydrogen remains difficult to transport at scale. Ammonia has emerged as the preferred carrier, with established infrastructure and proven safety records spanning decades. Converting that ammonia back to hydrogen at import destinations now depends on cracking technology that can operate efficiently at industrial scale – that technology is available today, writes Topsoe’s Joachim Harteg Jacobsen.

The reference advantage in a nascent market

The ammonia cracking market is experiencing renewed attention after years of limited activity, driven by the need to decarbonise hard-to-abate sectors through imported low-carbon or green energy. While several technology providers have announced plans to enter this space, the distinction between conceptual designs and proven industrial operation becomes critical when projects approach final investment decisions.

Topsoe holds the only large-scale ammonia cracking references currently in operation. The company's first major installation began operating in 1978, with the world's largest ammonia cracker – two parallel lines each processing 2,400 metric tonnes per day – commissioned in 1993 at the PIAP heavy water production plant in Argentina. Four reference plants continue running today, with some accumulating more than 300,000 hours of operation. This operational history provides validated data on catalyst performance, material behaviour under process conditions and long-term equipment reliability that newer entrants cannot replicate through modelling alone.

Material corrosion and catalyst insights from decades of operation

The extended operation of these reference plants revealed critical insights into failure mechanisms that would not emerge from shorter test campaigns. High-temperature ammonia environments create extreme corrosion conditions through nitridation, where nitrogen atoms penetrate metal crystal structures and alter material properties. Process streams with high ammonia concentrations at cracking temperatures are particularly aggressive.

Topsoe's database now contains nitridation data across different materials, process conditions and timeframes, drawn from both ammonia crackers and ammonia synthesis plants. This knowledge directly informs equipment design decisions, material specifications and maintenance schedules. The ability to predict material behaviour over multi-decade lifetimes reduces project risk and prevents costly equipment failures that could compromise hydrogen supply reliability.

The H2Retake™ process design and efficiency optimisation

The H2Retake™ technology builds on this operational experience while incorporating improvements from Topsoe's portfolio of more than 300 industrial steam methane reformer installations. The process centres on a side-fired, radiant-wall bayonet cracker – a design that offers superior temperature profile control along reactor tubes compared with alternative furnace configurations. Operators can inspect temperature distributions during operation and maintain consistency across all tubes, enabling better process optimisation and extended reactor tube and catalyst life.

The bayonet reactor design includes integrated feed-effluent heat exchange, which decouples the maximum cracking temperature from the reactor exit temperature. This arrangement achieves several objectives simultaneously: it reduces uncracked ammonia slip to below 1%, eliminates the need for downstream waste heat boilers and steam production, and enables the process to reach energy efficiencies above 96%. The reactor exit temperature remains safely below the maximum cracking temperature, reducing stress on downstream equipment and avoiding material selection challenges that would increase costs.

Waste heat recovery and the adiabatic pre-cracker

Energy efficiency in ammonia cracking depends largely on how effectively the process captures waste heat from the fired cracker. The H2Retake™ design routes flue gas through a waste heat section where it preheats incoming ammonia gas and drives the endothermic cracking reaction in an adiabatic pre-cracking reactor. This approach converts waste heat into additional hydrogen product rather than allowing it to leave the plant as a loss.

The ammonia cracking reaction requires approximately 46 kilojoules per mole of ammonia, while evaporating liquid ammonia from its standard storage condition at -33°C demands another 23 kilojoules per mole. These energy inputs are not losses but reflect the higher energy content of gaseous hydrogen compared with liquid ammonia per kilogram of hydrogen. The H2Retake™ design accounts for these thermodynamic requirements while minimising actual energy losses to less than 4% of total input.

Separation, recovery and purification systems

The process incorporates ammonia separation and recovery sections that recycle unconverted ammonia back to the feed stream. This design choice improves overall efficiency, reduces NOx levels entering the selective catalytic reduction unit, lowers ammonia concentrations at the purification section inlet and decreases sensitivity to variations in main cracker performance. The recovery system creates operational flexibility that proves valuable when adjusting production rates or managing feedstock quality variations.

Hydrogen purification uses pressure swing adsorption technology, which can be configured to deliver purity levels up to 99.999% depending on end-use requirements. The PSA tail gas, containing nitrogen and some hydrogen, combines with flash gas from the separation section to provide part of the fuel for the fired cracker. This internal fuel recycling ensures that hydrogen not captured in the product stream still contributes useful energy to the process rather than representing a loss.

Fuel flexibility and design variants

The standard H2Retake™ layout uses cracked gas to supplement PSA off-gas as fuel, eliminating direct CO₂ emissions. In this configuration, the incoming ammonia provides all necessary process energy, resulting in a hydrogen efficiency greater than 78%. This approach suits projects where the imported ammonia should supply complete energy requirements without relying on local fuel sources.

Alternative configurations can use external fuel such as natural gas or renewable gas to increase the hydrogen yield from ammonia. Depending on PSA configuration, this approach can achieve 96% hydrogen recovery from the ammonia feed while maintaining the 96% energy efficiency. Dual-fuel capability allows plants to switch between natural gas and cracked gas depending on economics or emissions regulations, providing commercial flexibility over the plant lifetime.

Capacity range and operational flexibility

The H2Retake™ design accommodates ammonia feed capacities from 100 to 3,100 metric tonnes per day in a single line. Without external fuel, this translates to approximately 430 metric tonnes per day of hydrogen; with external fuel, capacity reaches about 525 metric tonnes per day. The standard layout achieves 30% turndown with a 30-100% dynamic range and 1% per minute ramp rate, though solutions exist for lower turndown and faster ramping when project requirements demand it.

The process accepts either ambient pressure liquid ammonia at -33°C or ambient temperature pressurised liquid ammonia as feedstock. Product hydrogen exits at approximately 30 bar gauge without compression; projects requiring higher delivery pressure can add a booster compressor. This flexibility allows the technology to adapt to site-specific conditions and integration requirements with downstream users.

Catalyst development and industrial validation

H2Retake™ employs three nickel-based Topsoe catalysts optimised for different process positions. DNK-20 Retake handles the pre-cracking reactor, maintaining high activity as temperature drops through the adiabatic reactor due to the endothermic reaction. Its shape suits the pre-cracking application, and it offers high resistance to poisons, protecting downstream catalysts in the fired cracker.

DNK-30 and DNK-40 Retake are optimised for the top and bottom sections of the tubular fired cracker respectively. Both feature low pressure drop, high cracking activity and the catalytic, thermal and mechanical stability required for their positions. These catalysts draw on Topsoe's extensive experience with nickel-based reforming catalysts, and all three have been validated at industrial scale through installation and successful performance in two operating Topsoe ammonia cracking reference plants.

The efficiency calculation and round-trip considerations

Discussions of ammonia cracking efficiency sometimes conflate energy losses with the thermodynamic requirement to increase hydrogen's energy content from the liquid ammonia phase to pressurised gaseous hydrogen. From gaseous ammonia, the theoretical maximum hydrogen efficiency would be approximately 87% if all ammonia converted to hydrogen product with zero losses. Starting from liquid ammonia – the standard storage and transport condition – this theoretical maximum drops to about 81% when calculated using the lower heating value of the actual liquid ammonia feed stream.

The H2Retake™ process achieves hydrogen efficiency greater than 78% without external fuel, placing it close to the theoretical limit and confirming that actual energy losses remain below 4%. The difference between 81% theoretical maximum and 78% achieved efficiency represents genuine losses; the 19% consumed to lift hydrogen to higher energy content is not a loss but a thermodynamic necessity inherent to the ammonia-hydrogen system.

Comparative efficiency across hydrogen supply routes

When evaluating ammonia cracking efficiency, the relevant comparison includes alternative routes to delivered hydrogen. Locally produced blue hydrogen or green hydrogen from solid oxide electrolysis without storage or long-distance transport represents the most energy-efficient option, avoiding the conversion steps entirely. This route makes sense when local renewable energy is available at low cost, or when natural gas and CO₂ sequestration infrastructure exist nearby.

The ammonia cracking route shows moderately lower efficiency but enables storage and long-distance transport from remote, low-cost energy sources. Remote green ammonia production based on high-temperature solid oxide electrolysis, followed by shipping and cracking back to hydrogen, can approach the energy efficiency of locally produced green hydrogen from conventional electrolysis. This capability opens global energy trading and allows importing regions like northern Europe to access renewable resources from other continents.

What is the technology readiness and commercial availability of ammonia cracking?

The H2Retake™ technology operates at high technology readiness level due to its foundation in proven industrial ammonia cracking installations and incorporation of validated improvements from hundreds of reformer projects. The side-fired radiant-wall cracker design, bayonet reactor configuration, adiabatic pre-cracking and ammonia recovery systems all draw on industrial experience spanning decades. This reduces the technical risk profile compared with technologies that rely primarily on pilot testing or computational modelling.

Several ammonia cracking projects are advancing through planning phases in the European Union, South Korea and Japan as import infrastructure develops. These projects will connect to hydrogen pipelines serving industrial areas, creating the distribution network needed to support multiple end users. The ammonia production, shipping and import terminal infrastructure is already under construction in several regions, establishing the upstream and midstream elements of the value chain that ammonia cracking will complete.