Fuel-flexible gas turbine combustion technology for clean and efficient ammonia firing

Expected Outcome

The use of hydrogen in gas turbines holds significant promise as an enabler for a low-carbon economy and may serve as a pivotal tool in achieving the objectives of the European Green Deal. Nevertheless, the challenges associated with hydrogen storage and distribution remain major obstacles for its widespread adoption. Ammonia emerges as a complementary enabler of the hydrogen economy, functioning as a carbon-free energy carrier with properties well-suited for long-term storage and long-distance transport. Compared to hydrogen, liquefied ammonia storage is significantly less expensive and complex, and it exhibits a much narrower explosive range, enhancing its safety profile. Furthermore, a single mole of ammonia contains more hydrogen atoms than a mole of pure molecular hydrogen and it is entirely carbon-free if it is produced from renewable hydrogen. These characteristics make ammonia not only a practical medium for hydrogen transport but also a viable fuel option for direct use in gas turbines, supporting efforts to decarbonise the existing power generation infrastructure.

However, the direct use of ammonia as gas-turbine fuel presents several significant challenges. Firstly, its narrow flammability limits, low reactivity, and slow burning rate introduce serious issues with flame stabilisation. Recent research suggests that partially decomposing ammonia into a mixture of ammonia, hydrogen, and nitrogen - achieved by utilising waste heat from the gas turbine - can help overcome these combustion challenges while also enhancing cycle performance. Secondly, a more challenging issue arises from the fuel-bound nitrogen in the ammonia molecule. Under the fuel-lean conditions typical of modern, clean and efficient natural gas-fired gas turbines, this nitrogen is readily oxidised in the presence of excess oxygen, leading to unacceptable emissions of nitrogen oxides (NOx), which are strictly regulated atmospheric pollutants, as well as nitrous oxide (N2O), a potent greenhouse gas. Lastly, eventual emissions of unburned NH3 and of HCN (from methane co-firing) - both very toxic compounds at low concentrations - pose serious health risks. All these issues necessitate careful optimisation of the combustion system to ensure both efficiency, safety and environmental compliance.

Consequently, a paradigm shift that re-assesses state-of-the-art Dry-Low Emission (DLE) combustion technologies is required to improve fuel flexibility and enable clean and efficient combustion of ammonia in modern gas turbines.

The term “NH3-based fuel” introduced here and used below indicates a fuel consisting of pure ammonia or of partially decomposed ammonia. The case of complete ammonia decomposition to a binary mixture of hydrogen and nitrogen as well as the removal of nitrogen are considered out of scope.

Project results are expected to contribute to all the following expected outcomes:

• Fundamental understanding and detailed characterisation of the combustion physics of NH3-based fuels at gas turbine-relevant operating conditions, i.e., high reactants temperature and pressure, including the potential occurrence of blending with backup fuels;
• Provide the basis for a reliable and fuel-flexible combustion system and verify its ability to cleanly and efficiently operate with NH3-based fuels, or hydrogen , at gas turbine-relevant operating conditions, i.e., high reactants temperature and pressure.;
• Enable breakthrough multi-fuel combustion system technology and facilitate a full-scale gas turbine demonstrator by 2035 to enhance European leadership in decarbonisation technologies for gas turbines;
• Pave the way for utilisation of ammonia as carbon-free energy vector in power generation by means of substantiated technological feasibility, safety and risk assessment, including the environmental, social and economic benefit/risk balance.

Project results are expected to contribute to the following objectives and Key Performance Indicators (KPI) of the Clean Hydrogen Joint Undertaking (JU) Strategic Research and Innovation Agenda (SRIA):

• Development of new gas turbine combustion system characterised by increased fuel flexibility to allow clean and efficient operation with pure ammonia or ammonia blended with hydrogen.

The proposal is expected to address following KPIs:

• (KPI 1): Dual-fuel operation & firing capability across the complete range from 100% NH3-based fuels to 100% backup fuels
• (KPI 2): NOx emissions for NH3-based fuels: <300 mg/MJ[1]
• (KPI 3): Maximum efficiency reduction[2] in operation with NH3-based fuels: <2% points
• (KPI 4): N2O, NH3 & HCN emissions for NH3-based fuels: <10 ppm (@15% O2)

Scope

Standard gas turbine combustion technologies developed and optimised for ultra-low NOx emissions of lean premixed natural gas mixtures are not able to burn ammonia or ammonia-hydrogen blends within existing normative emission limits. Therefore, a paradigm shift is required to develop novel fuel-flexible combustion technologies that enable clean and efficient ammonia operation of gas turbines, as well as backup fuels as fallback solution. In this context, the development of novel combustion systems for clean and efficient utilisation of NH3-based fuels in gas turbines should investigate, understand and solve challenges related to: 1) poor flame stability due to low ammonia reactivity; 2) significant NOx and N2O emissions due to oxidation of fuel-bound nitrogen; 3) lethal levels of toxic compounds in the exhaust gas, as unburnt NH3 (ammonia slip) and HCN .

The proposed project is expected to address the following areas of research and innovation to achieve the expected outcomes for NH3-based fuels.

• Improved chemical reactions kinetics for the oxidation of NH3-based fuels, including validation against available measurements of fundamental flame properties (flame speeds, ignition delay times, extinction strain rates), its pyrolysis and relevant emissions (NOx, N2O, NH3, HCN);
• Fundamental combustion properties of NH3-based fuels at high reactants temperature and pressure (minimum 10 bar);
• Static flame stabilisation (flashback and blow-out characterisation and control) of premixed and non-premixed flames of NH3-based fuels at high reactants temperature and pressure (minimum 10 bar);
• Dynamic flame stabilisation (characterisation and control of thermo-acoustic instabilities) of premixed and non-premixed flames of NH3-based fuels at high reactants temperature and pressure (minimum 10 bar);
• Design of novel injection schemes and staging strategies to enable clean (low emissions) and efficient (no unburnt fuel) combustion of NH3-based fuels;
• Demonstration of combustion concepts for NH3-based fuels and validation of combustion models in dedicated atmospheric and high-pressure combustion tests with full-scale engine combustor hardware (TRL 5);
• Advanced combustion models and combustor concepts enabling clean and efficient gas turbine operation with NH3-based fuels;
• Technological feasibility, safety and risk assessment for utilisation of NH3-based fuels in power generation, including the environmental, social and economic benefit/risk balance (e.g. evaluation of cost reduction and efficiency improvements vs consequences in case of accident).

The topic provides an excellent opportunity to enhance the maturity level of combustion of NH3-based fuels for power generating systems, enabling their widespread deployment and utilisation in the future energy system. In this regard non-proprietary fundamental experimental and numerical data should be made available after project completion to facilitate the development of future combustors.

Proposals should build upon and complement projects funded by the Clean Hydrogen JU such as Flex4H2[3], HyPowerGT, InsigH2t[4], ACHIEVE[5], ACCEPT[6].

International cooperation with entities with suitable expertise, interest, or facilities, from Countries which are neither EU Member States nor Horizon Europe Associated countries, is encouraged, in particular with the Japan’s[7] national research and development agency, NEDO[8] (see section 2.2.6.7 International Cooperation).

For additional elements applicable to all topics please refer to section 2.2.3.2.

Activities are expected to achieve TRL 5 by the end of the project - see General Annex B.

The JU estimates that an EU contribution of maximum EUR 5.00 million would allow these outcomes to be addressed appropriately.

Technology Readiness Level - Technology readiness level expected from completed projects

Activities are expected to achieve TRL 5 by the end of the project - see General Annex B.

[1] <30 mg/MJ with use of SCR or operation with backup fuel

[2] with respect to NG operation

[3] https://cordis.europa.eu/project/id/101101427

[4] https://cordis.europa.eu/project/id/101192349

[5] https://cordis.europa.eu/project/id/101137955

[6] https://cordis.europa.eu/project/id/101192557

[7] A Cooperation Agreement was signed in 2024 between the Clean Hydrogen JU and NEDO, which had the purpose of accelerating the deployment of hydrogen through exploring synergies between these two organsations https://www.clean-hydrogen.europa.eu/media/news/clean-hydrogen-partnership-signs-cooperation-agreement-japans-nedo-2024-06-03_en

[8] New Energy and Industrial Technology Development Organization of Japan.