Franken power plant testing conversion to HVO and reporting initial successes

Uniper has a clear goal of completely decarbonizing the company by 2035. In order to make this plan a reality, the Uniper power plant at the Franken site in Nuremberg is also working to boost its green credentials. Power plant manager Stefan Ritter reports that it has been very successful in doing so. Stefan Ritter has been with the company for 32 years and knows the Franken power plant like the back of his hand. In order to make the site greener, Ritter and his team are relying on fuels such as hydrotreated vegetable oil – HVO for short. As a green fuel, it is intended to provide an environmentally friendly alternative to fossil fuels such as gas or petroleum. However, before the switch to HVO can be successfully made, the feasibility must first be thoroughly investigated.

Innovative fuel is like the fire department of the energy supply industry

The Franken power plant operates two units with a net output of 823 megawatts and were commissioned 1973 and 1976. They are operated using gas or light fuel oil. This pairing ensures reliable security of supply and, most recently, proved itself last winter. As a peaking power plant, the power plant runs only a few hours a year, with few startups. Ritter has a fitting comparison for this: "We're like the fire department. Everything has to work reliably when it really counts. That's why we are always on standby and ensure that there are no problems when we are needed." The system must then fill gaps in supply as quickly as possible in order to ensure security of supply. Although the plant is now comparatively old and is not as efficient as modern power plants, it is used optimally as an auxiliary or peaking power plant. To ensure that it remains future-proof, it is also important to push ahead with decarbonizing it and making it greener.

"We asked ourselves — what can be improved in a plant like ours?" says Stefan Ritter. A good alternative quickly became apparent in the case of liquid fuel, in other words fuel oil — this alternative is HVO. It has similar properties to diesel or light fuel oil, but is derived from green waste, thereby playing its part in helping Uniper meet its environmental goals.

Investigations with HVO produce good results

In 2022, the experts at the Franken power plant began testing the use of HVO. As part of this, an operational test of the gas turbine with the hydrotreated vegetable oil was successful. The team completely converted from oil to HVO in this process. "Last year, we tested the plant's large boiler for the first time and operated the auxiliary steam generator with HVO," the power plant manager explains. The auxiliary steam generator is responsible for building heating and uses auxiliary heat to ensure that the power plant can be put into operation. In addition, it serves as part of the city of Nuremberg's municipal heating. "In the course of the tests, we switched the entire fuel oil infrastructure to HVO and investigated various load cases — from low load to full load." The team assesses numerous parameters, such as emissions, consumption and also whether a modification is required. "For example, we are looking at whether the air-fuel ratio is appropriate," says Ritter.

The tests with the HVO biofuel are going well and show that no process engineering adaptations of the plant are required. The team at the Franken site works closely with Uniper's Making Net Zero Possible team during the investigations. Together, they closely investigate and evaluate potential risks or hazards that could arise from switching to HVO. Numerous colleagues from different departments and Uniper sites pool their knowledge in this process. Tests with HVO will continue this year at the Franken power plant. "Unit 1 has 20 burners. We will try to run two levels with HVO, which is eight burners in total," explains Stefan Ritter. In doing so, the team wants to further investigate how combustion in a large boiler behaves.

So far, tests with HVO have yielded very positive results, as the green liquid fuel offers good conditions — and not just in terms of technical parameters and compatibility with the plant. Ultimately, all emission limits were met during the test and, according to current findings, nitrogen oxides also appear to be lower than with fossil fuels. HVO is also a good alternative due to its long-term availability. However, there are still challenges from an economic point of view.

Challenges in converting to HVO

"HVO is currently about twice as expensive as fuel oil," Ritter reveals. "The market still has some growing to do — and it will. Nevertheless, HVO will probably never be as cheap as gas or oil." Ritter believes that politicians need to make clear guidelines here. "Higher carbon taxation consequently makes HVO projects more attractive, because it reduces the gap in price between green and fossil fuels."

Holistic measures make the Franken power plant greener

However, research into HVO is not the end of the Franken site's environmentally friendly efforts, as hydrogen could also offer an alternative. Ritter and his team are already talking to the local energy supplier, N-ERGIE Netz, to determine whether a hydrogen plant in the core network could be viable, which is also a matter of technical feasibility. "This is a parallel line of investigation," says Ritter. 

An important fossil of electricity production

Stefan Ritter explains the importance of conventional power generation and says: "Of course, the plant's a fossil, but an important one. It is used to compensate for the so-called 'dunkelflaute' and ensure reliable security of supply." The 'dunkelflaute' describes periods in which there is no wind, and the sun is not shining. This is exactly when auxiliary power plants such as the one at the Franken site spring into action. As a result, even aging power plants play a crucial role in securing the overall supply. This will continue to be the case in the future, something which is also demonstrated by the fact that we are training our own specialists at the Franken site for the first time. "The expertise that we need simply is not available in the job market. That is why we are now training specialists ourselves," states Stefan Ritter, explaining another investment in the future at the Franken power plant.