by Manoj Ravi, Yulong Ding and Josh Makepeace
In this discussion paper, we explore the potential of ‘green ammonia’ to not only decarbonise fertiliser production, but also pave way for environmentally cleaner energy system and facilitate our transition to a renewable energy-based global society.
Why do we need green ammonia?
Ammonia (NH3) – the major ingredient of agricultural fertilisers that helps feed nearly half the world’s population – is one of the most important chemicals for sustaining human life on the planet. However, its manufacture is responsible for around 2% of the global carbon dioxide (CO2) emissions, a greenhouse gas that is the primary driver of global climate change. Its carbon footprint per tonne is significantly higher than other high production volume chemicals. This is because the process currently relies on fossil fuel feedstocks. Therefore, a new ‘green ammonia’ production process with net-zero carbon emissions needs to be implemented.
Ammonia is manufactured by reacting nitrogen and hydrogen gas together. As the most abundant gas in the atmosphere, nitrogen can be easily separated from air. Conversely, hydrogen does not occur naturally in substantial amounts and needs to be extracted from other sources. In current ammonia production, hydrogen is extracted from fossil fuels, with carbon dioxide as a by-product. Consequently, ammonia production cannot be decarbonised simply by transitioning the electricity grid to low-carbon energy. If we are to minimise the carbon footprint of ammonia production, there must be a transition towards green ammonia whereby hydrogen is generated from the use of renewable electricity to split water. In this way, green ammonia is manufactured from a feedstock comprising air, water and renewable electricity, making it an environmentally clean and widely-accessible process.
Figure 1 – A comparison of existing ammonia production with the green ammonia production process.
What are the opportunities for green ammonia use beyond fertilisers?
While the decarbonisation of ammonia production for fertilisers is already critical to meeting net-zero emissions targets, green ammonia also has immense potential to serve as a next-generation zero-carbon fuel. In this way, it represents a highly-flexible way of storing renewable energy and a key complementary technology to direct electrification.
Ammonia is easily stored as a liquid using modest pressure or refrigeration; in this form, its energy density per unit volume is around 40% that of petrol. This makes it an attractive energy storage mechanism for long-duration energy storage or large amounts of energy, and a possible solution to the longstanding challenge of storing hydrogen cheaply.
Transportation: Ammonia can be used directly as a fuel – burnt in an internal combustion engine – or ‘cracked’ to release its stored hydrogen to power electric cars, buses and trains. This flexible end-use of ammonia has prompted serious consideration of its use in the transportation sector. The maritime industry, which currently relies almost exclusively on heavily polluting oil-based fuels is actively exploring the use of ammonia as a direct fuel. Critically, there is potential to retrofit existing two-stroke maritime engines for ammonia use, which provides a viable pathway to decarbonising long-lived shipping vessels. Furthermore, by circumventing the challenge of storing hydrogen in very-high-pressure tanks, ammonia may also provide a cost-effective refuelling infrastructure for hydrogen-powered vehicles.
Grid-balancing: The demand for electricity tends to fluctuate throughout a day, and across different seasons in a year. In the UK, for example, energy demand increases by around one third during the winter months. The electricity distribution grid must be able to respond to these varying demands. In a renewables-based grid, this is challenging because of the inherent intermittency of solar and wind power. Consequently, energy storage technologies are indispensable to the smooth functioning of power distribution networks, storing energy during times of excess, ready to use when demand outstrips supply. A chemical fuel like ammonia, with high energy density and straightforward storage requirements, is well placed as a long-duration energy store, complementing the rapid response which can be achieved with batteries and pumped hydro.
Renewable energy commodity: The cost of renewable electricity now largely depends on the quality of the wind/solar resource. However, connecting remote areas with outstanding renewable energy resources to markets looking for cheaper energy is a key challenge when it comes to take advantage of those cost variations. Unlike hydrogen, which is also actively explored as an energy store, ammonia does not need to be stored under very high pressures or very low temperatures, leading to lower transport costs. Furthermore, being an already widely manufactured industrial chemical, a robust global ammonia distribution infrastructure at the megatonne scale is already in place, which can be harnessed to unlock the enormous potential of this market. Because of this, ammonia has great potential to act as a global renewable energy commodity.
Figure 2 – Ammonia: key facts
Where are the applications of green ammonia being demonstrated?
The diverse applications of green ammonia, as outlined above, have evolved beyond the stage of conceptualisation, with several pilot-scale demonstrations now being reported:
- MAN Energy Solutions has released plans for a commercially-available two-stroke engine running on ammonia by 2024, and a retrofit package for existing vessels the following year.
- A consortium led by Siemens built the Green Ammonia Demonstrator, based at the Rutherford Appleton Laboratory in the UK, which is one of the first systems to demonstrate the viability of small-scale green ammonia production and the full cycle of power-ammonia-power.
- Yara, one of the world’s leading fertiliser companies, has partnered with ENGIE to test green hydrogen technology for ammonia manufacture in their facility in Western Australia. In the same region, the ‘Asian Renewable Energy Hub’ project, which began in 2014, continues to make rapid progress. The 26 GW renewable energy project will include an annual green ammonia production capacity of nearly 10 million tonnes, and would approximately double Australia’s installed renewable electricity capacity in a single project.
- In the Netherlands, Yara has teamed up withØrsted, a renowned offshore wind developer, with the aim of manufacturing 75000 tonnes of green ammonia per year. Companies like Haldor Topsoe and Maersk have also recently unveiled plans for green ammonia projects.
- Air Products has partnered with the Saudi Arabian Government to announce a 4 GW solar project at NEOM which will produce green ammonia.
By no means do the projects cited above constitute an exhaustive list of green ammonia projects worldwide, yet they illustrate the growing global interest in the technology, which has now started to reverberate in government policies too. The Japanese Ministry for Economy, Trade and Industry’s roadmap for fuel ammonia targets green ammonia imports of 3 Mt by 2030 to support co-firing in power plants and shipping fuels, increasing to 30 Mt by 2050. While the Indian Government is set to invite bids for green ammonia projects in 2021, the German Government is financing a feasibility study into ammonia-based hydrogen transport as part of its ambition to invest 9 billion euros in green hydrogen for industrial use. Likewise, the Canadian Government recently led the development of a hydrogen strategy for the country, which integrates aspects of green ammonia to achieve net-zero emissions by 2050.
What challenges need to be overcome?
Notwithstanding the appreciable technological progress and increasing governmental policy focus on green ammonia, there are a few key barriers that must be overcome for the technology to become a prominent strategy in the pursuit of decarbonisation. The first of these challenges is posed by the ‘scale’ on which green ammonia would need to be manufactured. The current annual global production of ‘brown’ ammonia is over 175 million metric tonnes. This capacity, which primarily caters for the production of fertilisers, might appear to be significant; however, in order to decarbonise maritime transportation alone, replacing the energy content from existing fuels would require almost all of the current global ammonia production volume. Therefore, green ammonia would need to be manufactured in substantially larger quantities, and this would possibly require the proliferation of small-scale production facilities that have good access to renewable electricity to complement the traditional, centralised, large-scale nature of ammonia manufacture.
Given the urgency to decarbonise, the deployment of green ammonia production would need to be achieved in a relatively short timeframe. Encouragingly, much of the necessary technology exists to be able to begin this transition. What is needed now is support for projects which combine these existing technologies to the green ammonia supply chain: demonstrating the viability of green ammonia production, direct ammonia fuel in combustion engines and gas turbines, and ammonia cracking units which can supply high-purity hydrogen for fuel cell vehicles. There will be immense downward pressure on the cost of the final energy delivered, particularly if green ammonia contributes to decarbonising heat and grid-balancing applications. Efforts to produce technologies which integrate different energy storage processes to improve overall efficiency should be prioritised. Public and private support for these projects, including through the use of subsidy schemes such as those which have so effectively promoted the deployment of wind and solar energy, will help drive down costs and meet the challenging pace of transition required. Similarly, implementing accredited standards for the carbon footprint of fertilisers and fuels derived from ammonia may help generate a consumer drive for sustainable ammonia products.
While ammonia’s potential contributions as a zero-carbon fuel are clear, its corrosive nature and the toxic impacts of its uncontrolled release into the environment must be considered in any expanded use. Efforts to minimise excess nitrogen release through the use of fertilisers remain a critical environmental stewardship focus. In contrast to use in agriculture, the uses of ammonia as a sustainable fuel would only be designed to release harmless nitrogen gas back into the environment. The existing safe practices for handling and transporting ammonia can be readily applied to these new contexts. Nevertheless, appropriate regulations from governments which enable the use of ammonia in energy applications, but also ensure safety and minimise any emissions of ammonia or nitrogen oxides must be developed.
Of course, research and development focused on improving the economic competitiveness of green ammonia will be critical. Scientists in academia and industry continue to work on these aspects. These include initiatives such as developing improved catalysts for ammonia production and cracking, entirely new paradigms for ammonia production directly from air and water, as well as better process integration. For example, there are potential synergies between different energy storage technologies, such as liquid air energy storage and green ammonia production, which may improve overall cost and efficiency.
There is also a clear argument for extensive public outreach for the concept of green ammonia. For instance, the substantial carbon footprint of agricultural produce that the general population consumes often gets overlooked. With regards to next-generation transportation, electric vehicles have become a topic of active discussion in the public domain, and so has green hydrogen as an alternative fuel. It is important that green ammonia now enters this conversation more prominently. Besides educating the general public about ammonia’s potential to be a transportation fuel, such a discussion will also allow addressing public perceptions of the risks associated with using ammonia.
Summary
Green ammonia has enormous potential in the grand global challenge of decarbonisation. The technology will continue to help us feed the world’s growing population but at much lower environmental impact. By virtue of being a hydrogen and energy store, ammonia can feature in wide-ranging applications, including being used as a transportation fuel and for grid balancing. Despite numerous demonstration projects being underway, there are several barriers that currently preclude the manufacture and use of green ammonia on a global scale. Overcoming these barriers will require government initiatives and public engagement to complement R&D efforts. Meeting the world’s increasing energy needs and reducing carbon emissions do not need to be mutually exclusive, and green ammonia shows that both these demands can be met. The versatility of green ammonia to be an alternate technology in many of the leading carbon-intensive sectors makes a stronger case for a greater dialogue among policy makers and the general public. The mission of achieving net-zero emissions by 2050 is highly challenging but one that is essential. And without green ammonia being deployed on a large scale, succeeding in this global mission will be all the more difficult.