Siemens Energy and others are teaming up with Wien Energie for a wide-ranging demonstration of green hydrogen co-firing of SGT5-4000F gas turbine at the Donaustadt CHP power station in support of goals to decarbonize power and heat generation.
Wien Energie, with partners Siemens Energy, German energy company RheinEnergie, and the Austrian energy company Verbund Thermal Power, are currently executing test operations of its Donaustadt CHP plant with a blend of green hydrogen and natural gas.
During the demonstration project the plant’s SGT5-4000F gas turbine is being operated with a blend of 15%(v) hydrogen. The target is to double the hydrogen concentration to 30%(v) in a second test at a later date.
The pioneering project at Donaustadt enables the Wien Energie team to:
- Take a first step toward decarbonizing the power and heat sector.
- Test DLE combustor optimized for hydrogen/natural gas blends.
- Join others in EU and elsewhere to demonstrate vital future energy solutions.
Wien Energie’s Donaustadt 1-on-1 combined cycle power station is a major source of electricity and heat for Vienna, and one of the world’s most advanced combined heating and power plants (CHP). Operating since 2001, it has a capacity of up to 250MWth (CHP winter operation) for district heating and up to about 390MWe for electricity (summer operation).
Typical performance parameters for Donaustadt CHP during winter and summer operation (Fuel: Natural Gas)
| Performance parameters |
Winter |
Summer |
| Net electrical capacity |
~360MWe |
~390MWe |
| District heating capacity |
~250MWth |
0 |
| Net electrical efficiency |
51.0% |
58.2% |
| CHP Fuel efficiency |
~87% |
Wien Energie runs approximately 1,300 kilometers of district heating pipes and a considerable part of the system is fed by Donaustadt. In 2021 the Donaustadt plant generated electricity for around 850,000 households and heat for over 150,000. Yet, despite these already impressive statistics – including an energy utilization rate approaching 87% – the plant’s operators are looking to the future and how the CHP industry may tackle the challenges of the energy transition.
Green goals and challenges
Many governments have declared their commitment to achieving net-zero (CO2 emissions) power generation by mid-century. For its part, Vienna, as well as all of Austria, has set its target date at 2040.
Increasing the share of renewables will be paramount to achieving this goal. However, generating energy mainly through solar and wind poses new challenges, as it could also mean losing traditional baseload and dispatchable power capabilities as well as grid stability services.
Stored green hydrogen may offer a solution. If produced from surplus (otherwise curtailed) renewable electricity during the summer and placed in storage, it could be used via H2 co-firing to reduce natural gas use during the winter period. Doing so would also partly compensate for the gap in power supply due to lower renewable energy and higher heat demand during the winter.
Low-carbon fuels to fill gap
Firing the plant on clean fuels will meet increased consumer demand for energy while supplying decarbonized heat and power at times when wind and solar energy systems are less available (i.e., meet the so-called “residual load”). CHP plants such as Donaustadt are indispensable for district heating today and will continue to play an important role in coming years as demand for centralized sources for heat grows. To achieve net-zero goals, heat generation will need to be decarbonized along with power generation. The hydrogen co-firing test run at Donaustadt demonstrated a way forward.
The SGT5 4000F reliable workhorse
The Donaustadt demonstration project had its roots in 2020, when Wien Energie and Siemens Energy started discussions. The two companies have a long-standing relationship, based on several power plant projects as well as maintenance contracts for Wien Energie’s Siemens Energy gas turbines. The 20+ year-old SGT5-4000F installed at Donaustadt became an early candidate for the hydrogen project and agreement to move forward was soon reached.
Since introduction of the 4000F-series gas turbine frame in 1997, it remains a reliable workhorse for many power stations. Currently, 115 SGT5-4000F units with an installed capacity of more than 31 gigawatts are in operation within the EU alone, and many more are operating around the world.
The SGT5-4000F gas turbine design was optimized for high power and efficiency, and ease of maintenance, all aimed at lowering power generation costs. It boasts a 15-stage axial flow compressor, a durable annular combustion system, and a fully air-cooled 4-stage turbine. Thanks to its steam raising capability, the SGT5-4000F is well suited for combined cycle and cogeneration (CHP) applications, including process steam and district heating.
Getting ready for H2 co-firing
With plans set to conduct the hydrogen co-firing demonstration at Donaustadt in 2023, a maintenance outage scheduled for 2021 was delayed to 2022 to implement the Hydrogen and Efficiency Package (HEP) upgrade for improved performance, and to make the core engine H2-ready as well.
Both upgrades required a combustion system modification (burner and combustion chamber) so combining them into one outage resulted in cost and scheduling synergies. Additionally, the gas turbine peripherals were partially prepared for the H2 co-firing during the same outage. The remaining scope of site modifications were implemented in early summer 2023.
2-stage test program
During 2021 and 2022, the project group developed a conceptual plan for a two-stage H2 co-firing test program at Donaustadt. The tests successfully reached admixing up to 15%(v) green hydrogen with natural gas during several test days, and further evaluations are still ongoing.
Calculations show the clear potential in terms of reduction of CO2 emissions. Even admixing only 15%(v) of green hydrogen for Donaustadt could save around 33,000 metric tons of CO2 per year, if the required amount of green hydrogen was available. At 30%(v) admixing, the reduction in CO2 emissions would be about double. (Note: about 1200 kg/hr of green hydrogen is needed for a 15%(v) hydrogen blend to operate the Donaustadt SGT5-4000F at full load. For 30%(v) blend about 2,500 kg/hr is required.)
The tests were based on a typical power plant operating profile with load ramps, start-up, shut-down, base load as well as with varying hydrogen content in the fuel gas. As a result of these tests, the project team gained insight into optimally configuring and operating hydrogen-burning gas turbines, and monitored the effects of blending hydrogen with natural gas on the gas turbine itself.
Mastering hydrogen
In its standard configuration, the SGT5-4000F is certified to burn up to 1%(v) hydrogen, while the natural gas network in Austria usually contains just around one-tenth that amount. With higher percentages, it can be expected that flame characteristics and combustion acoustics will be affected, and NOx emissions tend to increase.
For example, hydrogen mixtures can be expected cause the flame to move upstream, towards the burners inside the combustion chamber. With such changes in flame position, the burner material temperatures could increase and need to be monitored accordingly.
Basically, the various challenges of burning mixtures with higher hydrogen content in premixed DLE combustion systems relate directly to the considerably higher reactivity of hydrogen compared to natural gas (i.e., mostly methane). This means that it was expected to exhibit increased flame speed, lower auto-ignition delay, and increased flame temperature vs. natural gas – all of which could affect the operation of the fuel-air premixing tubes and injection nozzles. The change in flame position is just one of these challenges.
Preparing turbine and power plant
To prepare for the program, an SGT5-4000F burner of the type used at Donaustadt was tested at Siemens Energy’s Clean Energy Center (CEC) in Ludwigsfelde, Germany.
This dedicated state-of-the-art high-pressure test facility can test combustion and turbine flows up to 100MWth. Multiple test cells allow testing of a variety of combustor sizes and configurations and provide the ability to simulate a wide range of realistic operating conditions with precise fuel mixtures.
Testing was performed with increasing H2 content and at different pressure levels, with all relevant key parameters, such as output, efficiency, emissions, and flame stability being monitored, measured, and analyzed. In the end, the optimal burner configuration for Donaustadt was confirmed, helping to stabilize the combustion process while minimizing NOx emission levels.
Installing a new burner at Donaustadt was not the only preparatory step taken. Instrumentation and controls were modified, including sensors for the combustion system and the fuel gas supply system.
Additionally, an H2 supply and mixing system had to be developed and installed. The overall plant components affected by the blending of H2 were checked for their capability of up to 15%(v) H2 and modified where necessary. This included consideration of material suitability, fire and explosion protection, and general safety precautions.
Outlook for higher H2 content
With significantly higher H2 content fuel blends being considered for the future (including up to 100% H2), impacts on the overall plant must be better understood. Areas which could be affected by change in fuel and combustion characteristics include the fuel system, the water/steam cycle, catalyst, and more, which have to be checked and potentially modified accordingly.
Possible additional changes to the gas turbine might include better temperature protection through different thermal barrier coating and better cooling of the combustion system and the turbine area. Selection of materials to better withstand hydrogen embrittlement might also be required in the future.
Donaustadt an important start
Given the goal of significantly reducing CO2 emissions from power and heat generation, the Donaustadt tests were a significant milestone despite testing only 15-30%(v) hydrogen. (Note: 15% and 30% H2 admixed to natural gas results in about 5%(wt) and 11%(wt) reduction in CO2 production, respectively.)
Demonstrating that a modified modern gas-turbine based CHP plant can handle admixing 15%(v) green hydrogen during a test under real load conditions could play an important and necessary starting point in the step-by-step process of decarbonizing the power and heat sector.
Following the initial test program, which runs with truck-delivered green hydrogen, a continuous operation of pre-mixed fuel gas (via the gas grid) of 5%(v) H2 is expected to be initiated.
The second test with 30%(v) H2 will be another incremental step on the way toward 100% H2 and is expected within the coming years. However, the real challenge in meeting the goal of net-zero in the coming decades is not the gas turbine or CHP plant technologies. Rather, it lies in the commitment by government authorities and industry to scale-up production and supply of the huge amounts of green hydrogen required to meet the goal.
Challenges ahead for green hydrogen
While gas turbines can run on other “clean” fuels, such as biomass or hydrotreated vegetable oil, green hydrogen has by far the greatest potential for scale-up. First and foremost, production needs to greatly increase from todays (near-zero) levels, while conversely, production costs must significantly decrease over time.
But progress in developing the required infrastructure for storing and distributing hydrogen at large scale is still in its early beginnings. A cohesive national, regional, European, and perhaps a global hydrogen strategy will be needed to realize the potential of green hydrogen.
CHP as part of a net-zero economy
Vienna plans to become climate-neutral by 2040, and as shown in a 2021 study, district heating is an important building block in its decarbonization strategy.
Demand for heating in Vienna is expected to grow by as much as 56% over the next 20 years. Most of this heat is expected to be generated by geothermal energy and large heat pumps. Still, the share supplied by CHP plants – while decreasing overall – will continue to play an important part in clean heat generation.
In 2040, according to the Vienna net-zero plan, 3.9TWh (3,900GWh) of green gases are expected to be used in CHPs. Thus, these power plants will continue to help securing energy supply as well as decarbonize power and heat generation. What’s more, the switch to green fuel will enable continued use of the existing power plant and district heating infrastructure.
Collaboration with industry partners
The test run at Donaustadt power plant represents one of many steps needed in our quest for climate-neutral energy generation, as heavy-duty turbines will be an essential element of that future. Donaustadt also demonstrated another important factor needed to reach net zero emissions: close collaboration will be required with industry partners.
Even if Donaustadt never runs on 100% green hydrogen, that’s not to detract from its importance. This project represents a step forward on the bridge to a decarbonized energy future.
About the authors: Michael Kotschan, is Hydrogen Expert at Wien Energie and Thomas Johnke is Product Manager, H2 DeCarb Upgrades, at Siemens Energy
