Hydrogen fuel and renewable energy are becoming increasingly relevant in the gas turbine industry as the world shifts towards decarbonization. Hydrogen fuel, in particular, is seen as a promising alternative to traditional fossil fuels due to its clean-burning properties. As a result, many gas turbine manufacturers are exploring ways to modify existing engines to run on hydrogen or hydrogen mixtures. Additionally, the use of renewable energy sources such as wind and solar power to generate hydrogen fuel is gaining traction, providing a sustainable solution for the gas turbine industry. These developments are crucial in reducing carbon emissions and meeting climate goals, making hydrogen and renewable energy an essential focus for the future of the gas turbine industry.

In light of these developments, one of the key methods to achieve decarbonization is to use a mixed renewable gas (e.g., green hydrogen, biogas, syngas) or pure hydrogen (in the future) as a fuel for stationary gas turbine engines (GTE) that generate electricity.

The main advantage of this method is that companies need not design and manufacture fundamentally new engines for hydrogen combustion. Instead, modifying the existing GTE fleet is sufficient. Another benefit of introducing hydrogen gas turbine technology is the possibility of using idle or underutilized equipment, thereby providing a new lifecycle.

When modifying a gas turbine engine to operate on hydrogen, the combustion chamber unit requires significant changes in the first place. Leading companies in the production of gas turbine engines use different approaches to develop a modular low-emission combustion chamber capable of burning pure hydrogen and its mixtures. Some examples of state-of-the-art combustion chambers are shown in Figure 2.

For more information about existing modifications of combustion chambers that can run on both hydrogen-natural gas mixtures and pure hydrogen, please refer to [3].

However, besides fuel control and delivery system transformation (to handle the increased fuel flow rate of the plant compared to gas turbines operated on natural gas or diesel) [2], the modification of expensive GTE parts such as compressors and turbines may be needed.

Compared to natural gas, hydrogen combustion leads to a lower mass flow rate and a different composition of the product gases, with a higher water content that influences the molecular weight and the specific heat of the mixture. The most relevant effects on the operation of a gas turbine are a variation of the enthalpy drop in the expansion, a variation of the flow rate at the turbine inlet, which, in turn, affects the turbine/compressor matching, and a variation of the heat-transfer coefficient on the outer side of the turbine blades, affecting the cooling system performance [4]. Considering these effects, the following solutions can be used:

• Install variable geometry guide vanes (VGV); no significant modifications are required to the GTE, and the stall margin is guaranteed.
• Increase pressure ratio by installing one or more high-pressure compressor stages when variable geometry guide vanes remain fully open and compressor/turbine matching is reset by increasing the design pressure ratio.
• Redesign of the turbine geometry; the compressor is unchanged, and the turbine blade height is increased to ensure the required gas flow and the amount of cooling flow is adapted to operate at the same pressure ratio and turbine inlet temperature.
• Install variable geometry nozzle vanes; no major modifications are required to the GTE and the stall margin of the compressor is guaranteed (for uncooled turbines).

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To deal with these challenges, AxSTREAM gives you a hand to modify existing impeller machines (install VGVs, add compressor stages with their full design, redesign turbine, find the amount of required cooling flow, etc.), ensure turbine/compressor matching by ION, obtain new performances of the machines and so on. One such example of an AxSTREAM ION workflow for gas turbines is shown in Figure 3.

The red part of the above image includes the calculation algorithm convergence and initial guesses, as well as the assignment of restagger angles of IGV/VGVs considering flight conditions. The blue part of the image combines all turbomachinery flowpaths 1D/2D models and combustion chamber calculation methodology. Finally, the green part of the image contains the gas turbine units, which have their geometry modeled in AxSTREAM. This software is essential for creating accurate simulations of the gas turbine units, allowing for precise and detailed analysis of their performance and efficiency.

If you’re interested in exploring how AxSTREAM can help you with your next gas turbine design project, get in touch by emailing us at Info@Softinway.com.

References

1. https://www.ansaldoenergia.com/offering/equipment/turbomachinery/heavy-duty-gas-turbine/ae943a 
2. https://etn.global/wp-content/uploads/2020/02/ETN-Hydrogen-Gas-Turbines-report.pdf
3. https://blog.softinway.com/the-evolution-of-gas-turbines-from-the-first-designs-to-the-latest-environmentally-friendly-development-trends-part-2/
4. Chiesa P., Lozza G, Mazzocchi L., Using Hydrogen as Gas Turbine Fuel. Journal of Engineering for Gas Turbines and Power, 2005, vol 127, p. 73-80.

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• Source: https://blog.softinway.com/modifying-gas-turbines-to-burn-hydrogen-fuel/