| Gas turbine developments


Turning to a European milestone project, Ertan Yilmaz of Siemens Energy gave an overview of the world-first HYFLEXPOWER collaboration, a joint effort involving Engie, Centrax, and National Technical University of Athens, as well as Siemens Energy, which demonstrated power- to-H2


-to-power with 100% green hydrogen in an SGT-400 gas turbine employing DLE combustion. Interestingly, for all natural gas/hydrogen blends up to 100% H2 ppmvd@15% O2


, NOx .


A follow-up project, HycoFlex, aims to develop a retrofittable 100% H2


package for SGT-400


gas turbines that can be offered as a market ready product. There are also plans to scale the 100% H2DLE combustion technology platform developed as part of HYFLEXPOWER across Siemens Energy’s gas turbine portfolio. Elsewhere in Europe, DLR, SINTEF, Norwegian University of Science and Technology and Ansaldo Energia are jointly investigating the use of hydrogen in the sequential combustion system employed in Ansaldo’s GT36 turbine. The project, called FLEX4H2, aims to develop and validate a safe, efficient and highly fuel-flexible combustion system capable of operating with any hydrogen concentration up to 100% H2


, at H-Class


operating temperatures, while still meeting emission targets without any use of diluents. The rationale for the project is that gas turbines are seen as important for future grid stability but need to burn fuels with low CO2


footprint like hydrogen.


Constant Pressure Sequential Combustor (CPSC) technology, as employed in the GT36, is considered to offer unique opportunities due to the ability of the 2-stage combustion system to achieve increased operational and fuel flexibility. A presentation by Peter Griebel of DLR described results from a lab scale sequential combustor.


In the Netherlands, at its Moerdijk power plant, RWE, along with GE Vernova, has been looking at converting a 9FB gas fired turbine to hydrogen. This “lighthouse project” was the subject of a presentation by RWE’s Jappe Hoeben. Early stage development work on the Moerdijk plan, which envisages connection (by 2032 ish?) to Gasunie’s proposed Dutch hydrogen network, suggests that the Moerdijk high hydrogen conversion (to 80+ vol %) is “safe, flexible and emissions compliant” but “challenges are identified on the upstream side of the value chain.” The availability of hydrogen at pressure, along with the supporting network infrastructure for transportation and storage, is described as “uncertain” and the conclusion from work done so far on the Moerdijk project is that “the current policy and subsidy development trajectory may not be sufficient to support deep decarbonisation via the use of hydrogen by 2030.”


HVO and methanol


A somewhat more rapid decarbonisation option for gas turbines would appear to be converting to HVO (hydrotreated vegetable oil). This is something that Uniper has been been pursuing for several years, as recounted by Uniper’s Jon Runyon in his presentation. Building on extensive


testing, Uniper has now converted three OCGT sites in the Swedish disturbance reserve to commercial operation on HVO: Öresundsverket (2 x 63 MWe); Karlshamn (2 x 18.5 MWe); and Barsebäck (4 x 21 MWe). Conversion at a fourth Swedish disturbance reserve site (Halmstad, SGT5-2000E) is currently in progress. The table above, presented in the paper by


Runyon et al, shows, as the authors suggest, that “Uniper is not alone on the HVO journey.” Among the attractions of HVO is that there is already experience with it as a drop-in replacement for fossil diesel in the transport sector and it can achieve 80-90% gas turbine lifecycle CO2


reduction today (equivalent to


>90%vol hydrogen cofiring), according to Runyon et al.


Uniper experience shows that gas turbine performance is not hampered by using HVO, with “no immediate concerns that HVO will negatively impact on emissions compared with fossil gas, oil or diesel.” NOx


emissions can be


expected to be similar to fuel oil operation, while some emissions (eg, SO2


, CO, and dust) should be significantly less.


Methanol also shows promise as an alternative fuel for gas turbines, as indicated in a presentation from Siemens Energy/Industrial Turbine Co/Net Zero Technology Centre/Proman, presenter Siemens Energy’s Jacob Rivera. This focused on testing with aeroderivatives (SGT-A05, SGT-A20 and SGT-A35) equipped with modified injectors and combustors. The tests were carried out at RWG’s gas turbine test facility and the Centrax generating set test facility. Methanol’s compatibility with existing infrastructure, relative ease of transport and established handling and transport facilities, promise relatively short implementation lead times, Jacob Rivera et al suggest. Another major advantage is low NOx


emissions thanks


to methanol’s high heat of vapourisation and low adiabatic flame temperature (although the relatively low LHV requires more fuel flow to achieve a given power).


Overall, Rivera’s presentation concluded that methanol can be a low-lifecycle-CO2


alternative fuel that is “relatively well suited to use as a gas turbine liquid fuel.” Also, required modifications are relatively simple for Siemens Energy aeroderivatives.


The carbon capture route As well as alternative fuels, such as hydrogen, HVO and methanol, carbon capture offers another potential route for the decarbonisation of gas turbines and combined cycle power plants. A presentation from SINTEF, University of Florence and Baker Hughes looked at how hydrogen assisted exhaust gas recirculation might benefit the capture process, while authors from the University of Mons explored “the economic tipping point between H2


-based gas


turbines and CCS-enhanced gas turbines.” They believe there is a risk of both


technologies becoming trapped in the ‘innovation valley of death’ and conclude, among other things, that “only a strong reduction in H2 price can make H2


- based CCGT economic,”


echoing sentiments expressed elsewhere at the conference.


They also find that, as far as their analysis goes, CCS-enhanced combined cycle plants, just like hydrogen fuelled GTs, fail to achieve a positive ROI.


It will be interesting to see how CCUS integrated with gas turbines and CCGT, currently appearing to be attracting growing interest, fares in the next couple of years, particularly in comparison to hydrogen and alternative fuels. Looking ahead, IGTC 2027 will provide a very good opportunity to review progress.


www.modernpowersystems.com | November/December 2025 | 29 and low NOx was less than 25


Gas turbines operating on HVO, representing 1.7 GWe from 38 gas turbines. Source: Uniper


GT operator (status) Uniper (T)


Svensk Kraftreserv (T) Göteborg Energi (T) Uniper (T) Uniper (T) Uniper (C) Enel (T)


Stockholm Exergi (C) Enel (T)


Uniper (T) Svensk Kraftreserv (T)


Site ÖVT


Arendal Rya CHP Franken


Country GT OEM GT Type (Capacity, MWe)


Sweden Siemens Energy V93.0 (63) Sweden Rolls-Royce


Avon (15)


Taylor’s Lane UK ÖVT


Las Salinas Värtaverket Arona BVT


Stallbacka


KVT BVT


Sweden Siemens Energy SGT-800 (45) Germany Siemens Energy V93.1 (63) Rolls-Royce


Sweden Siemens Energy V93.0 (63) Spain


GE Vernova Pratt & Whitney FT8 (25)


Olympus (17.5) MS6001B (37.5)


Sweden Siemens Energy SGT-800 (62) Spain


Sweden Pratt & Whitney FT4 (21) Sweden Stal-Laval


Tennessee Valley Authority (T) Johnsonville US Uniper (C) Uniper (C)


GE Vernova Sweden Rolls-Royce


Notes: T= trial; C = commercial operation; OVT = Öresundsverket; KVT = Karlshamn; BVT = Barsebäck Uniper has a further HVO conversion underway, at Halmstad, Sweden


SSE Thermal has two planned HVO conversion projects: Tarbert, Ireland, AE94.3A (300 MWe), planned operation 2027; and Platin, Ireland, SGT-800 (57 MWe), planned operation 2028.


GT120 (70) 7EA (85)


Olympus (18.5) Sweden Pratt & Whitney FT4 (21)


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