The role of ammonia as a carbon-free fuel in decarbonisation of coal power generation

Image:© International Conference on Fuel Ammonia 2021
According to the Intergovernmental Panel on Climate Change, to limit global warming to below 2°C above pre-industrial levels with at least 66% probability, global net anthropogenic CO2 emissions need to decline by 25% by 2030 from 2010 level and reach net zero emissions (NZE) around 2070. If we wish to control global warming to ≤1.5°C, the world will need to cut CO2 emissions by 45% by 2030 and be NZE by around 2050.

Recently, many countries, including some of the world’s largest economies such as China, the European Union (EU), France, the United Kingdom, Japan, and South Korea have announced ambitious plans to reach net zero emissions by 2050 or 2060. President Biden also announced in April 2021 that the US would aim to achieve a 50-52% reduction in greenhouse gas emissions in 2030 from 2005 levels, and to reach NZE by no later than 2050. The German government raised its climate ambition to target NZE by 2045. To meet the climate objectives, the power sector, industry, transport and other sectors such buildings and agriculture must all decarbonise within the next few decades. This will need innovative solutions, technologies and policies.

The need to address climate change is driving a fundamental change in power systems globally. There has been a rapid expansion in the deployment of renewable energy sources such as solar, wind and biomass in recent years. Many developed countries such as the UK, Germany and other EU member states have deadlines for the closure of all coal-fired power plants. In the USA, 28% of coal power generation capacity totalling 88.7 GW was shuttered between 2011 and 2020, and 2.7 GW of coal power capacity is scheduled to retire in 2021. As part of its efforts towards decarbonisation, Japan plans to phase out inefficient coal power plants and reduce coal’s share in power generation from 31% in 2020 to 26% by 2030. However, despite the rapid developments in renewable power and the recent closure of a large number of coal power plants worldwide (especially those small, inefficient and polluting ones in China and India), coal remains the largest fuel source for power generation. Globally, coal’s share in electricity generation was 35.1% in 2020. Also, new coal power plants with nearly 130 GW capacity are under construction in 2021, and coal power plants with a total capacity of ~184 GW are planned to be built. In addition, countries such as China, India, Bangladesh and Vietnam have a young coal fleet, with an average age of less than 15 years and so they will probably be in service for many more years (coal power plants have a service life of 30-50 years). According to the International Energy Agency (IEA), around 1250 GW of coal power plants worldwide that were in operation or under construction in 2019 could not only still be in service by 2030, but could also still have a remaining lifetime of at least 20 years. Therefore, cutting CO2 emissions from these plants is vital in meeting environmental targets and achieving net zero emissions.

There are various technological routes to reduce CO2 emissions from coal power generation such as improving energy efficiency and carbon capture, utilisation and storage (CCUS). Cofiring of low-carbon fuels, traditionally biomass, in coal power plants has shown to reduce carbon emissions with relatively low investments. In recent years, the use of ammonia as a carbon-free fuel for power has received increasing attentions.

Combustion of ammonia produces mainly H2O and N2, two components that are benign to the environment. Replacing part or all of fossil fuel with ammonia in boilers or combustion turbines can lower CO2 emissions from fossil fuelled power plants proportionate to the amount of reduced fossil fuel use.

In recognising the potential of ammonia as hydrogen carrying energy vector, the Cross-ministerial Strategic Innovation Promotion Program (SIP) of Japan set up hydrogen and ammonia related technology roadmap, the Strategic Plan for Hydrogen Utilisation in 2017, and promoted research and development (R&D) of ammonia direct combustion/co-combustion and utilisation. A 22-member Green Ammonia Consortium led by Tokyo Gas was created in 2017, seeking to demonstrate hydrogen, ammonia and hydrides as building blocks of a hydrogen economy and to develop an ammonia value chain. At the end of 2020, Japan’s Ministry of Economy, Trade and Industry (METI) announced that it had chosen the fuel ammonia industry as one of the prioritised areas in its ‘Green growth strategy’ action plan. Japan is cooperating with energy-producing, renewable-rich countries such as Australia and Saudi Arabia to establish a stable, low-cost, and flexible fuel ammonia supply chain. With strong market signals from Japan, the Energy Council of Australian government published the National Hydrogen Strategy in 2019, and a new chapter of the ammonia fuel association was opened aiming to working closely with the hydrogen fuel community and increasing awareness of the use of ammonia for energy storage and power generation. In the USA, Advanced Research Projects Agency-Energy (ARPA-E) of Department of Energy (DOE) launched Renewable Energy to Fuels through Utilisation of Energy-Dense Liquids (REFUEL) Program to develop scalable technologies for conversion of renewable power-to-fuel-to-power. REFUEL projects were set up to support the development of energy sources such as ammonia that could be readily produced and easily transported. In 2016, ARPA-E announced $32.7 million of funding for 13 R&D projects of synthesis and use of ammonia under the REFUEL program. The UK has also shown strong interest and several studies on the production and use of ammonia as a fuel or for energy storage have been carried out by companies, universities and government agencies such as Siemens, Ecuity Consulting, Oxford University, Cardiff University and the UK’s Science & Technology Facilities Council (STFC). In the EU, the Netherlands leads in promoting the production and utilisation of ammonia. Funded by the Ministry of Economic Affairs, The Netherlands, and led by the Institute for Sustainable Process Technology (ISPT), a consortium comprising universities, energy, utility and industrial companies carried out the Power-to-Ammonia project to investigate the value chains and business cases to produce green ammonia suitable for various market applications, in particular, energy storage and power generation.

With an increasing global interest in the use of ammonia for power, the IEA has recently become a promoter of the production and use of ammonia as a CO2-free fuel of the future. In several recent studies, IEA recognises that, as an energy carrier, ammonia is much cheaper to transport and store and thus, the most economically competitive alternative to hydrogen for distribution.

Also, IEA has identified the technologies for producing green ammonia and for using it as a low-carbon fuel in various applications such as power generation and road transport, maritime shipping and aviation.

Under the various programs and R&D projects, progress in clean ammonia production and utilisation has been made. In particular, significant development in cofiring ammonia at coal power plants has been achieved in Japan. In 2017, the Japanese Chugoku Electric Power Corporation successfully demonstrated the cofiring of ammonia and coal, with a 1% share of ammonia (in terms of total heat input) at one of their 120 MW commercial coal power generating unit. Using ammonia as fuel raises concerns about an increase in NOx emissions, but the demonstration showed that NOx emissions from ammonia cofiring with coal could be controlled within the usual limits and any ammonia slip into exhaust gas could be avoided. Higher shares of ammonia in fuel mix might be feasible with minor adjustments to a coal power plant. In smaller furnaces with a capacity of 10 MWth, blending shares of 20% ammonia have been achieved without problems, and without any slippage of ammonia into exhaust gas. Currently, Japan’s JERA Company and IHI Corporation are working on a demonstration project of cofiring 20% (heat input) of ammonia at a large-scale commercial coal-fired power plant. A small scale test began at JERA’s Hekinan power plant unit 5 on 6 October 2021. The project will run for approximately 4 years and aims to achieving an ammonia cofiring rate of 20% at Hekinan power plant 1000 MW unit 4 by 2024. When fully developed and commercialised, the technologies can play a crucial role in decarbonise thermal power generation in Asian countries and beyond where coal power plants provide key flexibility and other system services. METI has recently proposed a new target to finalise development of a coal burner that can cofire ammonia at >50% rate and of a fully ammonia-fired gas turbine by 2030.

To raise awareness of ammonia as a direct fuel and promote investment and international cooperation in establishment and expansion of fuel ammonia supply chain and market, Japan’s METI hold the first International Conference on Fuel Ammonia on 6 October 2021. At the virtual conference, the IEA announced the release of a new report on ‘The role of low-carbon fuels in the clean energy transitions of the power sector’, and presented its analysis of the potential deployment of low-carbon ammonia in the power sector. Speakers from countries around the world including Australia, Indonesia, Japan, Chile, France, Norway, Saudi Arabia, and the USA, talked the initiatives taken by the energy and utility companies, industries, and the government in their country to develop ammonia supply chain and to promote R&D and deployment of fuel ammonia for power. Also at the conference, an inter-company co-operation agreement for development of ammonia-fuelled power generation was signed between Japan’s METI and IHI Corporation and Malaysia’s Tenaga Nasional Generation Sdn Bhd and PETRONAS Carigali Sdn Bhd.

The message is clear that ammonia as a carbon-free fuel could be used to decarbonise thermal power generation. Therefore, it can play an important role in the clean energy transitions of the power sector, especially in the emerging and developing economies that rely strongly on fossil fuelled power generation.