Enabling Clean Ammonia: Practical Lessons from a Full Plant Conversion

Low-carbon ammonia is an attractive driver for decarbonization of many product chains. Here are some practical insights from a legacy plant that was updated for cleaner ammonia production

Ammonia production is under growing scrutiny as decarbonization becomes a global imperative. However, most operating plants were designed initially around steam methane reforming (SMR) powered by fossil fuels (known as “gray” ammonia), with limited provisions for cleaner alternatives. To stay competitive and compliant, producers are increasingly turning to targeted retrofits, system integration and process optimization to enable the use of lower-carbon “blue” or “green” hydrogen, thus lowering the overall carbon footprint of ammonia production. Blue hydrogen refers to SMR production with carbon-capture and storage (CCS) and green hydrogen refers to hydrogen produced via water electrolysis powered by renewable energy. Core units — such as ammonia synthesis loops, compression trains and heat-recovery systems — can be modified to handle blue or green hydrogen without significant disruption. This article presents actionable insights for clean-ammonia production from a full-conversion project in Europe, highlighting phased, cost-conscious approaches that reduce emissions while leveraging existing infrastructure.

 

From gray to clean ammonia

At a legacy ammonia plant in Europe, numerous potential process improvements were evaluated to fully convert the plant for cleaner production.

A comprehensive redesign of an existing ammonia synthesis loop was undertaken to enable operation exclusively using clean hydrogen, sourced primarily from the European Hydrogen Backbone (EHB) pipeline and supplemented by over-the-fence (OTF) hydrogen from urban solid waste (USW) gasification. The study evaluated major retrofits, including the installation of a new purification system to remove trace impurities and the complete phase-out of conventional reforming and CO₂-capture systems. Key regulatory and infrastructure drivers for this full-scale transition are discussed in more detail later in the article.

Drivers for full-scale conversion.Europe’s clean ammonia transition is driven by tightening carbon policy and expanding hydrogen infrastructure. The inclusion of hydrogen under the E.U. Emissions Trading System (ETS) — with carbon prices at €80–€90/ton CO₂ — and the upcoming Carbon Border Adjustment Mechanism (CBAM) are raising the cost of unabated production and imports.

While initiatives such as REPowerEU and the EHB are advancing the deployment of electrolyzers for green hydrogen production and pipeline connectivity, high gas prices and funding delays have slowed progress. Still, a phased conversion strategy — anchored in robust conceptual and process design — can minimize facility modifications and reduce capital intensity. For producers, this approach provides a pragmatic path to lowering carbon exposure, aligns with regulatory trends and enables access to emerging low-carbon markets.

 

Existing ammonia plant

The facility under study is a legacy ammonia plant constructed in the 1980s, currently operating at approximately 1,765 short tons per day (s.t./d) using natural gas as the primary feedstock. The plant follows a conventional process flow scheme, as illustrated in Figures 1a and 1b.

The existing steam system is also traditional in design. The syngas compressor turbine is driven by high-pressure (HP) steam, supplied from a header operating at approximately 1,800 psi. Meanwhile, the process air compressor turbine and the ammonia refrigeration compressor turbine are both connected to a medium-pressure (MP) steam header, operating at around 600 psi.

This baseline configuration served as the foundation for evaluating the technical and economic feasibility of a complete conversion to clean ammonia production using low-carbon hydrogen feedstocks.

 

Feedstock sourcing

The clean ammonia facility will utilize two distinct hydrogen feed sources:

1. OTF hydrogen produced via USW gasification, available from an adjacent third-party supplier
2. Pipeline-supplied hydrogen delivered through the European Hydrogen Backbone (EHB) network, expected to come online in alignment with the pipeline’s phased commissioning schedule

The USW-derived hydrogen will be available in limited quantities, sufficient to support approximately 35–40% of the plant’s total ammonia production capacity. The EHB pipeline will meet the remaining hydrogen requirement as infrastructure becomes operational.

Nitrogen feed will be supplied OTF via a dedicated pipeline from a nearby air separation unit (ASU), ensuring consistent purity and pressure for integration into the synthesis loop.

 

Feedstock quality

The hydrogen supplied via pipeline originates from diversified production sources and contains trace levels of several contaminants that must be addressed before synthesis. Key impurities identified in the feed include the following:

• Chlorides
• Inorganic sulfur
• CO
• CO₂
• Oxygen
• Formic acid
• Formaldehyde

These impurities pose a risk to both catalyst performance and to the integrity of downstream equipment. In particular, sulfur compounds and CO are known catalyst poisons, while chlorides can contribute to corrosion and fouling. Effective purification strategies are crucial for reducing these contaminants to levels compatible with the specifications of ammonia synthesis catalysts and for ensuring long-term plant reliability.

 

Key challenges and mitigation

The impurities in the hydrogen are poisonous to the synthesis catalyst and must be removed to well below the acceptable limits. The following challenges were posed for the design of the new hydrogen purification system.

A viable and cost-effective method for removing formic acid and formaldehyde was not available. Additionally, leading catalyst vendors lacked prior experience with these compounds, and the industry’s understanding of their behavior within the ammonia production process remains limited. A layer of special adsorbent was suggested to be added to the existing dryers to partially mitigate traces of formic acid and formaldehyde

Limited degree of hydrogen feed preheating (<500°F) due to the unavailability of HP steam. This means that the conventional catalysts used in ammonia-plant feed purification cannot be used to remove the impurities. Alternative lower-temperature catalysts were reviewed and carefully configured, incorporating numerous feedback points from different catalyst suppliers.

To minimize the cost, the existing desulfurization and methanation vessels were intended to be reused. A limited availability of feed hydrogen for an extended period also posed a challenge for the proper selection of the syngas compressor configuration.

Considering the low turndown requirements for the syngas compressor over an extended period and the cost of additional power consumption in the recycle mode of operation, the cost-benefit analysis suggested using two new 50% compressors. Furthermore, it was also determined that the amount of MP superheated-steam production within the synthesis loop will permit the operation of one 50% syngas compressor on the steam driver. This combination also provides added flexibility in the operation, with improved reliability.

In addition to hydrogen contamination and purification requirements, some additional challenges facing the project are listed below:

• Hydrogen availability
• Compressor configurations
• Synthesis loop re-rating and re- configuration
• Steam system needs
• Economic justification

 

Re-rating and re-configuration

The transition of the ammonia synthesis loop from conventional methane-based syngas — typically containing substantial levels of inert components, such as argon and methane — to a stoichiometric blend of high-purity hydrogen and nitrogen introduces a suite of complex process and engineering challenges. The virtual elimination of inert materials has a significant impact on both the catalyst bed’s thermodynamic equilibrium and kinetics, as well as the overall hydraulic assessment of the synthesis loop. Change in the circulation rate impacts heat-exchanger duties, system pressure drops and the turndown capability of syngas compressors.

Elevated reactant partial pressures in the feed stream shift the equilibrium conversion, enhancing ammonia yield per pass. However, this gain also requires recalibration of the reactor temperature profile and rerating to mitigate risks, such as catalyst sintering or localized hotspots. A thorough evaluation of equilibrium and kinetics performance, hydraulics of the synthesis loop and the mechanical integrity of existing equipment — originally engineered for higher inert dilution and different gas compositions — is essential.

The engineering team undertook a comprehensive re-rating of the entire synthesis loop across all projected operating scenarios, including a detailed kinetics assessment of the converter beds. This resulted in the optimization of critical operating parameters, including inert concentration, pressure, circulation rate, bed-temperature profiles, pressure-drop behavior, heat-exchanger loads and compressor performance (for both syngas and ammonia services). Catalyst-bed profiles were further validated through collaboration with all major catalyst suppliers to ensure the desired temperature profiles and ammonia production rates were achievable.

Key variables, including inert levels, circulation rate, ammonia conversion and operating and pressure drop characteristics, were mapped across both normal and turndown (T/D) modes for clean ammonia production and benchmarked against baseline gray ammonia operations, as shown in Figures 2a–2d.

In addition to process refinements, the configuration was adapted to accommodate superheated steam generation for the compressor drivers. This involved replacing the existing high-pressure boiler-feedwater exchanger with a new medium-pressure steam generator coupled with a superheater.

 

New configuration

In the revamped configuration, the majority of the front-end equipment from the legacy ammonia plant has been decommissioned. However, several components, including the existing desulfurizers, methanation vessels and selected heat exchangers, were successfully repurposed within the new feed-purification unit designed for blended hydrogen and nitrogen streams. Major modifications to the synthesis loop, illustrated in Figure 3, include the following:

• Reconfiguration of the syngas compression system with two new 50% capacity compressors — one steam-driven (ST) and the other motor-driven (M) — for operational flexibility and improved turndown performance
• Installation of a medium-pressure steam generator and superheater, replacing the high-pressure boiler feedwater (HP BFW) exchanger within the synthesis loop. The steam superheater package shown in Figure 3 includes an integrated BFW preheater, a steam generator and a steam superheater
• Addition of a new feed preheater in the purification section, utilizing steam to optimize feed temperature before synthesis

Steam system. The redesigned steam system is thermally balanced to minimize external steam import. MP superheated steam is generated within the synthesis loop and used to drive one of the new syngas compressors. The ammonia-refrigeration compressor turbine is also powered by MP steam, ensuring efficient energy utilization across the cycle. A minimal amount of steam is imported for a heat-integrated feed purification section.

Specific energy consumption. The specific energy consumption for clean ammonia production is estimated to be approximately 16% lower than that of the existing plant (on a higher-heating-value basis). This figure accounts for the energy content of the hydrogen feed, power required for nitrogen production, steam import/export credits and auxiliary power consumption (for instance, from pumps).

Carbon emissions. Scope 1 carbon emissions for the clean ammonia configuration are projected to be less than 0.2% of those from the existing plant. For reference, the current facility emits approximately 1.8 metric tons of CO₂ per metric ton of ammonia produced. This dramatic reduction underscores the decarbonization potential of complete hydrogen substitution and process electrification.

 

Economic justification

The economic rationale for complete conversion to clean ammonia production is reinforced by a convergence of regulatory, financial and infrastructure developments across Europe. Stringent environmental policies, notably the tightening of the E.U. Emissions Trading System (ETS) and the phased implementation of the CBAM, are driving up the cost of carbon-intensive production. With carbon prices exceeding €80–90 per metric ton of CO₂ and free allowances set to diminish, legacy ammonia plants face mounting compliance costs.

Simultaneously, the expansion of hydrogen infrastructure, including the European Hydrogen Backbone (EHB), is improving access to low-carbon hydrogen at scale. These developments, combined with funding mechanisms, such as the E.U. Innovation Fund and national-level incentives, significantly enhance the financial viability of clean ammonia projects.

In this context, the studied facility’s transition to clean hydrogen feedstock — sourced from both over-the-fence gasification and the EHB pipeline — offers a compelling long-term business case. The project has already advanced into the detailed engineering phase, supported by favorable policy alignment, infrastructure readiness and a clear pathway to mitigate carbon risk and achieve market differentiation.

 

Key takeaways

For ammonia plants looking toward strategic decarboniztion projects, the lessons learned by this project can provide some guidance and key insights:

• Full conversion is increasingly viable and economically justified, particularly in Europe, where rising carbon prices, tighter ETS/CBAM regulations and expanded hydrogen infrastructure (for instance, the European Hydrogen Backbone) are reshaping the cost-benefit equation
• Blue hydrogen offers a practical near-term bridge, enabling producers to decarbonize with lower technical risk and shorter implementation timelines. In contrast, green-hydrogen adoption remains contingent on supportive policy and market conditions
• For the complete conversion from gray ammonia to clean ammonia, a careful and comprehensive assessment of the synthesis loop, particularly the converter, must be conducted to determine new optimum operating parameters for different scenarios, ensuring compliance with the maximum permissible temperature limits of the catalyst and materials, and minimizing purge
• Systematic upgrades to core units — including the synthesis loop, compression train and steam network — are essential to maintain reliability and performance under low-carbon hydrogen operations 

Green hydrogen cases

Additional context for clean ammonia can be gained by examining efforts to implement production strategies using green hydrogen produced via electrolysis using renewable power. The below cases outline some work in this area.

Case 1 – Green hydrogen and oxygen integration to debottleneck a new U.S. facility. At a newly built U.S. ammonia plant equipped with cryogenic purification technology, an engineering team investigated the injection of green hydrogen and moderate oxygen enrichment to alleviate specific bottlenecks. These included overloaded arch burners, elevated tube metal temperatures in the steam methane reformer (SMR) and limitations in the cryogenic purifier. The integration strategy aimed to reduce carbon intensity, improve reliability and achieve a modest increase in ammonia production.

This U.S.-based ammonia plant, operating at approximately 2,800 s.t./d ( around 115% of nameplate capacity), features a modern configuration that includes a cryogenic purifier for removing inert gases and excess nitrogen from the syngas stream. During the initial evaluation, engineers identified several systems operating beyond their design limits — most notably the cryogenic purifier and the arch burners. Overfiring of the arch burners posed a reliability risk to the radiant tubes. At the same time, the overloaded cryogenic purifier resulted in increased purge gas losses to the fuel system, thereby reducing overall energy efficiency.

As part of a broader decarbonization initiative, the facility proposed installing a 20 MW electrolyzer to integrate green hydrogen into the process. The primary objective was to reduce carbon emissions and leverage federal incentives to establish a viable economic case. Given the limitations of the arch burners and cryogenic purifier, experts recommended a combined strategy: injecting green hydrogen downstream of the purifier, along with moderate oxygen enrichment.

Key findings from the study:

• Arch burner firing could be reduced by ~9%, bringing operation well within design limits.
• Radiant tube outlet temperatures decreased by ~34°F, with even greater reductions in tube metal temperatures, enhancing reliability and extending tube life.
• Cryogenic purifier loading was reduced, resulting in lower inert gas content in the make-up gas and a corresponding decrease in purge rate.
• Post-combustion CO₂ emissions were reduced by ~9%. Additional CO₂ emissions from the auxiliary boiler (used to offset a minor MP steam shortfall) were fully accounted for in the net emissions balance.
• Feed and fuel consumption decreased by ~0.3 MMBtu/s.t. compared to the base case.
• Oxygen injection was deemed feasible without a dedicated compressor based on commercial precedent. However, if a separate compressor were required, the economic viability of oxygen enrichment would be compromised.

Current status:  The electrolyzer project is currently on hold due to uncertainty surrounding the long-term availability of the Inflation Reduction Act (IRA) incentives.

Case 2 – Partial green hydrogen and cxygen Integration in a legacy U.S. plant. A legacy ammonia facility explored the integration of green hydrogen and moderate oxygen enrichment using a 20-MW electrolyzer system. While the oxygen enrichment pathway was ultimately deemed uneconomical due to the requirement for a dedicated compressor, the plant successfully implemented green hydrogen injection. As an early adopter, the facility capitalized on available federal incentives, achieving a viable business case despite high capital expenditure.

This legacy U.S.-based ammonia facility, operating at 1,800 stpd, evaluated the partial integration of green hydrogen and oxygen from a 20 MW Electrolyzer system to reduce carbon intensity and modestly increase production. The study, conducted by Kinetics Process Improvements, Inc. (KPI), shared similar objectives with Case 2, though without the added benefits of cryogenic purification.

Project Drivers:

• Initiate decarbonization through partial integration of green hydrogen.
• Gain operational experience with green ammonia production technologies.
• Leverage federal and state incentives under the Inflation Reduction Act (IRA) to establish a viable business case.

The plant investigated injecting green hydrogen downstream of the methanator, along with moderate oxygen enrichment. However, the requirement for a dedicated oxygen compressor significantly increased capital and operating costs, rendering the oxygen enrichment pathway economically unfeasible.

Despite shelving the oxygen integration, the facility successfully implemented green hydrogen integration using the 20 MW electrolyzer system. As an early mover, the plant was well-positioned to capitalize on federal and state-level incentives, enabling a commercially viable transition. The project also yielded valuable operational insights into the handling and integration of green hydrogen within a legacy ammonia framework.

Case 3 — Green hydrogen integration to expand capacity in a small U.S. plant. A smaller U.S.-based ammonia plant evaluated the injection of green hydrogen to increase production by approximately 20% while reducing carbon intensity. The plant had already installed a new converter rated at 120% capacity, but was constrained by limited syngas supply from the front end. Key drivers included the high cost of trucked-in ammonia (~20% of total output) and the availability of competitively priced green hydrogen. Multiple nitrogen sourcing options were assessed, with over-the-fence supply emerging as the most cost-effective solution.

This U.S.-based ammonia facility, currently operating at 550 s.t./d features a high-pressure synthesis loop (>4,000 psi) and reciprocating compressors. The plant recently installed a new, high-efficiency converter rated for approximately 120% of its nameplate capacity. However, the front-end reforming section remains unmodified. To capitalize on the converter’s latent capacity, the plant pursued a third-party offtake agreement for green hydrogen, aiming to expand production without major front-end upgrades.

Project drivers:

• Replace ~100 stpd of trucked-in ammonia with on-site production to reduce logistics costs.
• Leverage Inflation Reduction Act (IRA) incentives to lower carbon intensity and improve project economics.
• Utilize existing downstream capacity to minimize capital investment and operational disruption.

Engineers conducted a detailed evaluation of green hydrogen integration strategies to support an additional 100 s.t./d of ammonia production. The study also assessed nitrogen supply options, including front-end upgrades and on-site generation via PSA and cryogenic systems.

Key findings:

• Over-the-fence (OTF) nitrogen supply emerged as the most cost-effective solution, offering the lowest capital expenditure, minimal production loss, and the shortest turnaround time.
• The integration strategy avoids overloading the existing reformer and compression systems, enabling a streamlined capacity increase.

Current status: While technically viable and economically attractive under current policy frameworks, the project is under review due to uncertainty surrounding the long-term availability of IRA incentives. Alternate pathways are being explored to maintain project momentum. ♦ Edited by Mary Page Bailey

Acknowledgement

All figures provided by author

Author

VK Arora is the founder of Kinetic Process Improvements (KPI) Inc. (16000 Park Ten Place, Suite 903, Houston, TX, 77084; Phone: 281-717-4462; Email: vka@kpieng.com; Website: www.kpieng.com), and has led the company for over 20 years. He brings a track record of impactful leadership and practical, cost-effective process solutions in the petrochemical and clean energy sectors. An IIT Delhi alumnus and licensed engineer, he has spearheaded major projects in propane dehydrogenation, acrylic acid and esters, clean and green ammonia and carbon capture, compression and storage (CCS). His earlier roles at Lummus Technology, KBR, SABIC and Technip demonstrate a career rooted in strategic execution and technical excellence.