Green ammonia: Haldor Topsoe’s solid oxide electrolyzer

Haldor Topsoe has greatly improved the near-term prospects for green ammonia by announcing a demonstration of its next-generation ammonia synthesis plant. This new technology uses a solid oxide electrolysis cell to make synthesis gas (hydrogen and nitrogen), which feeds Haldor Topsoe’s existing technology: the Haber-Bosch plant. The product is ammonia, made from air, water, and renewable electricity.

The “SOC4NH3” project was recently awarded funds from the Danish Energy Agency, allowing Haldor Topsoe to demonstrate the system with its academic partners, and to deliver a feasibility study for a small industrial-scale green ammonia pilot plant, which it hopes to build by 2025. There are two dimensions to this technology that make it so important: its credibility and its efficiency.

First, the technology owner: Haldor Topsoe is a highly respected technology development company, and it commands a global market-leading position in the ammonia industry (it has built 60 ammonia plants since 2000 and currently services 248 ammonia catalyst charges around the world). Haldor Topsoe’s status makes it credible when it claims, as it does in recent presentations, that its new technology could be commercially available by 2030.

Second, the technology: Haldor Topsoe’s solid oxide electrolysis cell (SOEC) ammonia plant represents an optimized integration of electrolyzer and Haber-Bosch (HB) units. It has the potential to reduce both capex and opex, relative to other electrolyzer technologies but also relative to conventional ammonia plants using natural gas. The system has been designed to reduce capex by eliminating the need for an air separation unit (ASU). This is nice for the prospects of large-scale green ammonia but, combined with the scalability of electrolyzers, it significantly improves the economics of small-scale ammonia production (at small scales, the ASU becomes very expensive). For opex, which is dominated by energy costs in any ammonia technology, the SOEC-HB is estimated to produce green ammonia with a specific energy consumption of about 7.2 MWh per ton, which is 26 GJ per ton. In other words, its green ammonia plant could be more energy efficient than today’s best state-of-the-art natural gas-fed ammonia plant, which consumes around 28 GJ per ton.

SOC4NH3 project funding
SOC4NH3 is one of 46 projects that were awarded grants at the end of 2018 totaling DKK 234 million (USD $36 million) by the Danish Energy Agency, through its Energy Technology Development and Demonstration Program (EUDP). The EUDP funding is intended to help local companies to commercialize sustainable technologies, which can then be exported.

“[EUDP] contributes to knowledge about the green projects of the future, and it especially contributes to increasing export of energy technology solutions. For each unit of allocated state subsidy, we increase export[s] two fold …

We need to research and develop new solutions that can contribute to tackling the major issue of climate change the world is facing. If we are to be a front runner, it is important to always focus on the newest technologies, and these grants contribute to that end.”
Danish Minister of Energy, Utilities and Climate, Lars Christian Lilleholt, quoted in Funding for robots and climate-friendly ammonia to accelerate green energy, Energy Watch, 12/20/2018

SOC4NH3 has a total budget of DKK 26.8 million (about USD $4 million), of which the EUDP is contributing DKK 15.9 million. The project began in January 2019 and runs through April 2022.

The SOEC will be demonstrated alongside another new Haldor Topsoe technology: a solid oxide fuel cell (SOFC) that generates combined heat and power using ammonia as a fuel. In full, there are four elements to the SOC4NH3 project:

  1. Demonstration of green ammonia production from renewable energy, air, and water, using a 50 kW solid oxide electrolysis cell (SOEC), at the University of Aarhus in Foulum.
  2. Demonstration of combined heat and power generation from ammonia fuel, using a 1.5 kW single stack solid oxide fuel cell (SOFC), at DTU (Danmarks Tekniske Universitet) Department of Energy Conversion and Storage.
  3. Techno-economic and socio-economic studies on the production of green ammonia and use of ammonia as an energy vector in a decarbonized economy.
  4. Engineering design and site-specific feasibility study for an industrial-scale (1-2 metric ton per day) green ammonia pilot plant, using Haldor Topsoe’s all-electric SOEC ammonia technology.

A new research project, SOC4NH3 (Solid Oxide Cell based production and use of ammonia) with a number of strong partners will over the next years develop and demonstrate the technology and thereby bring it a big step closer a commercial breakthrough.

“We expect that ammonia can be used for transportation and efficient storage of energy. The greatest advantage of ammonia is that it has a high energy density which makes it an effective fuel and energy storage option – and it can thereby solve some of the most important challenges of creating a sustainable energy system of the future,” says project leader, Senior Principal Scientist John Bøgild Hansen, Haldor Topsoe A/S.
Haldor Topsoe announcement, Ammonia can become the CO2-free fuel of the future, 02/21/2019

Haldor Topsoe’s commercial partners for the techno-economic and socio-economic studies, contributing perspectives from across the entire energy value chain, include Energinet, the Danish electricity and natural gas distributor; Vestas, a global market leader in wind turbine manufacturing; Equinor, Norway’s national oil company; and Ørsted Wind Power (“We’ve built more offshore wind farms than any other developer in the world and we’ve only just begun“).

Haldor Topsoe’s SOEC energy efficiency
Perhaps the most important aspect of Haldor Topsoe’s SOEC-HB technology, beyond the fact that it can be carbon-free, is its promise of higher energy efficiency.

In conventional plants today, ammonia is made by combining hydrogen, produced from coal or natural gas or another fossil fuel, with nitrogen, produced by an air separation unit (ASU). Fossil hydrocarbons aren’t the only viable source of hydrogen but, in most places, they are the cheapest. I’ve previously written about how today’s natural gas-fed Haber-Bosch plant is almost perfectly energy efficient, due to decades of incremental innovation co-optimizing the steam methane reformation (SMR) units, which produce hydrogen from natural gas, and the HB units.

Since the start of the 20th Century, however, ammonia plants around the world have used electrolyzers to produce hydrogen from water, making industrial quantities of carbon-free “green” ammonia. Due to economics, only a couple of these plants still operate today. This technology always uses alkaline electrolysis cells (AEC) to produce the hydrogen that is fed to the HB unit. AEC is a mature technology but, unlike SMR, it did not evolve alongside HB; it has not been integrated and co-optimized over decades into the design and engineering of an ammonia plant.

The latest AEC ammonia technology will be demonstrated in a pilot plant in South Australia, with an estimated energy consumption of 10 MWh per ton of ammonia. That is roughly equivalent to 36 GJ per ton, which is the ammonia industry’s current average net energy efficiency (according to the IFA Benchmark). This is respectable performance but less energy efficient than today’s best available (fossil) technology (roughly 28 GJ per ton for a state-of-the-art, world-scale SMR-HB plant).

Click to enlarge. John Bøgild Hansen, NH3 Fuel Conference presentation, Solid Oxide Cell Enabled Ammonia Synthesis and Ammonia Based Power Production, November 2017
Haldor Topsoe’s new SOEC-HB, on the other hand, is estimated to produce ammonia with an energy consumption of about 7.2 MWh per ton. This is roughly 26 GJ and is better than today’s best available technology.

Of this 7.2 MWh per ton, 94% of the energy is consumed by the SOEC in the production of synthesis gas (hydrogen and nitrogen) and only 6% is used by the HB unit for ammonia synthesis.

Haldor Topsoe’s SOEC cost efficiency
Exactly like AEC-HB, an SOEC could be used to produce hydrogen, alongside an ASU to produce nitrogen, in order to feed the HB unit. This green ammonia plant would represent a conventional use of an electrolyzer, but it would be an unintegrated, unoptimized technology. Compared to the AEC, the SOEC exhibits a fundamentally different chemistry, with perhaps greater potential for optimization with the HB unit. Haldor Topsoe has focused on this potential.

Click to enlarge. Process flow diagram to show solid oxide electrolysis cell and air separation unit feeding Haber-Bosch unit. Source: Haldor Topsoe.
Click to enlarge. Process flow diagram to show solid oxide electrolysis cell producing both hydrogen and nitrogen to feed Haber-Bosch unit. Source: Haldor Topsoe.
The AEC splits water by transporting hydroxide ions (OH) across a membrane, whereas the SOEC transfers oxide ions (O2-) across its membrane. It is the oxygen separating aspect of this chemistry that allows Haldor Topsoe to make a major cost-saving change in its design of a green ammonia plant: the elimination of the ASU. In Haldor Topsoe’s integrated technology, the SOEC produces both the hydrogen and the nitrogen required by the HB unit.

The nitrogen is produced from the air input simply by burning some of the hydrogen that was made by the electrolyzer, which removes oxygen from the air and generates steam. This means that the electrolyzer must produce more hydrogen than the HB unit alone requires, implying a hit to the system’s energy efficiency. However, another aspect of the SOEC that differentiates it from the AEC is its ability to consume power in the form of either electricity or heat. Therefore, the steam generated by burning hydrogen can be almost completely recycled within the system, providing both water input and heat energy to the electrolyzer, and thus allowing the system to operate at a lower voltage. In this way, the high energy efficiency of the SOEC can be almost completely maintained while eliminating the ASU from the system.

This energetic trade-off – swapping heat for electricity – has an economic impact: the capital savings achieved by eliminating the ASU from the system are earned by investing in an expanded SOEC stack area. The techno-economic study coming out of the SOC4NH3 project will aim to identify the project specifications and market conditions to optimize this trade-off.


  1. Dale Goynes says:

    Topsoe is on the right track. Electrochemistry has a strong future.

    A better comparison is to look at the economics once the cost of electricity to drive electrolysis is factored in. Yes, overall energy consumption may be slightly reduced from fossil-based technologies, but the form and resulting cost of that energy must be considered. Solid oxide electrolysis is promising for syngas and hydrogen production, but requires too much energy input in the specific form of electricity to be economical at this point in time.

    Although CAPEX is reduced, economics are impacted negatively overall by driving up the OPEX through cost of electrical power consumption. Much more research is needed to reduce energy input and address long-term reliability issues. This is likely a factor influencing their far-away targeted 2030 entry to market.

    Dale Goynes, PE

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