Carbon-free power generation – from idea to solution

The BIGH2 project develops gas turbines that can use carbon-free fuels that eliminate CO₂ emissions. The aim of the project is to develop solutions that enable gas turbines to perform as well with carbon-free fuels as with today’s fossil fuels.

Gas power plants have higher efficiency and significantly lower CO₂ emissions than coal-fired power plants, but emissions from gas power plants must nevertheless be reduced to meet climate targets.

“A fundamental idea for BIGH2 has therefore been to facilitate the transition to low carbon fuels”, says project manager Andrea Gruber at SINTEF.

Carbon fuel

Hydrogen is a promising alternative to fossil fuels because combustion of hydrogen gives water vapor (H₂O) instead of CO₂ as a product in the exhaust gas, but there are also challenges with the use of hydrogen as a fuel:

Hydrogen has low density, so it must be transported under high pressure, or in liquid form at very low temperature.

Higher safety risk because the hydrogen is very explosive (wide flammability range and low ignition temperature).

Combustion of hydrogen results in high flame temperatures that can result in emissions of nitrogen oxides (NO_x) that exceed statutory emission limits. NO_x is a local pollution that can cause people respiratory problems and cause acid rain.

Controlling combustion is more challenging for hydrogen than for hydrocarbons, and combined with high flame temperatures, it increases the risk of emergency shutdowns and damage to the turbines.

The challenges of hydrogen led the project to choose to study the use of ammonia (NH₃) as fuel.  Ammonia is produced in large quantities all over the world, including as a raw material for the production of fertilizers, so there is already a well-developed infrastructure for transporting ammonia.

Phase 3 of the BIGH2 project studied the combustion of hydrogen and ammonia in models of combustion chambers of an industrial gas turbine from Siemens.  The combustion chamber is the part of a gas turbine where the flame stands.

Ammonia has inferior combustion properties compared to fossil fuels, and must be mixed with more reactive substances to achieve a stable flame.  Splitting a share of ammonia fuel into hydrogen and nitrogen results in improved combustion properties of the fuel mixture.   Since this splitting is an energy-intensive process, the project has focused on identifying the energy-optimal mixing ratio of ammonia, hydrogen and nitrogen.

“In our process, we use the waste heat from the gas turbine to split ammonia to increase the reactivity of the fuel and at the same time we achieve an increase in the efficiency of the plant.  This solution may reduce the costs of different CCS chains”, says Andrea Gruber.

Reduced NO_x emissions

One challenge is that the combustion of ammonia-enriched fuels, if not done correctly, can also result in significant emissions of NO_X and potent greenhouse gases such as nitrous oxide (N₂O). By organizing the combustion at different stages of the combustion chamber, the project has managed to reduce the formation of NO_X and N₂O to an acceptable level.

Andrea Gruber and his research team worked long office hours before experimental work was carried out in the laboratory.  Many small-scale combustion experiments were carried out in SINTEF’s pressurized combustion rig at Gløshaugen to test the flame stability of the various fuel mixtures, and to measure the emissions of NO_x.  Measurement data from the experiments were then used in numerical simulation software to model flames of various compositions of ammonia, hydrogen and nitrogen.  Data was exchanged with partners at NTNU in Trondheim and with Sandia National Laboratories in the USA.

“The most important result from the project is that we have now seen that it is possible to use ammonia as an energy carrier – no major obstacles have been found.  BIGH2 has shown us how this can be done. We didn’t have that knowledge when the project started,” says Andrea Gruber.

Broad collaboration

SINTEF worked with NTNU, Siemens and Equinor as partners in the project, while Sandia  National Laboratories (USA) and the University of California, San Diego were involved as external partners.

Future plans

“Future work will focus on the development and demonstration of a modified DLE (dry low emission) burner and combustion chamber.  We now know that this can be done but we must find the optimal way to implement the solution in a gas turbine.  The main goal is to achieve fuel flexibility, i.e. to create a gas turbine that can seamlessly transition between natural gas firing and the application of an optimized ammonia-based fuel, in a realistic burner design,” says Andrea Gruber.

Scientific publications

• Chemical kinetics of hydrogen/ammonia flames:
  • https://doi.org/10.1002/er.4891
• Spatial patter of NO_x formation in hydrogen/ammonia flames:
  • https://doi.org/10.1016/j.combustflame.2021.111520
• Blow-out limits of hydrogen/ammonia vs methane turbulent flames:
  • https://doi.org/10.1016/j.proci.2020.07.011
• Pressure scaling of flame propagation in hydrogen-enriched flames:
  • https://doi.org/10.1016/j.combustflame.2021.111740
• Experimental demonstration of rich-lean staging of hydrogen/ammonia combustion in a gas turbine burner:
  • https://doi.org/10.1115/GT2021-60057