In their efforts to create a more sustainable Sweden, electricity provider E.ON and the High Temperature Corrosion Centre HTC collaborate to improve the way renewable fuels are used in combined heat and power plants. They investigate how different structural materials are affected by the fireside environment, with the aim of increasing boiler efficiency and service life.
“Just over 30 years ago, Swedish combined heat and power plants operated on 80 per cent fossil fuels, but these days biofuels account for 90 per cent of the fuel mix instead, which unfortunately entails a number of challenges. Our goal is to transition completely to renewable fuels, and to achieve this HTC’s research is needed.”
– Anna Jonasson, process engineer at E.ON Heat.
Transitioning to biofuel
Back in the early 90s, the Swedish government decided to introduce a carbon dioxide charge on nonrenewable fuels. In 1995, following Sweden’s entry into the EU, a carbon dioxide tax was introduced. It was no longer advantageous for Sweden’s energy providers to burn oil or coal, and the transition to biofuel and renewable energy sources picked up speed.
“But the new fuels created problems. Illadapted materials in the furnaces, together with an aggressive flue gas environment, meant that boilers began to leak and break down prematurely. Boilers that had previously run without problems broke down after just a few years,” says Anna Jonasson.
The solution was to form HTC together with material suppliers, other electricity providers, state-owned Nutek and Chalmers.
“We needed to know more about corrosion mechanisms that affect boilers in order to adopt the right countermeasures. We can do this either by using more corrosion-resistant materials or attempting to make the flue gas environment less corrosive e.g. by using various fuel additives.”
Industry-related research with social relevance
In principle, combined heat and power plants can be run on any kind of fuel, fossil or renewable.
“Because combined heat and power plants generate both electricity and heat, they’re extremely efficient – more than 90 per cent of the energy can be extracted from the fuel”, says Jesper Liske, Associate Professor at the Division of Energy and Materials at Chalmers University of Technology.
HTC is researching the effect of combustion on boilers to achieve a greater understanding of the corrosion processes and discover which construction materials are most durable or most economically favourable. The tests are conducted partly in HTC’s lab at Chalmers in Gothenburg, where it is possible to analyse every minor change in the material, and partly at E.ON’s installations.
“We’re advancing on a pretty broad front with academic research on one flank and industry-related, applied methods on the other. The combination is important; it not only means science at the highest level but also has great social relevance.”
Increased life-span and temperature
HTC’s research has led to more and more corrosion-resistant materials in boilers, and this has increased both their service life and the temperatures the boilers can withstand.
“Our collaboration provides direct gains such as better and cheaper material use, while our suppliers have also made use of the knowledge and are currently developing better materials. HTC’s research provides benefits at several collaborative levels”, says Anna Jonasson.
The knowledge has also helped boiler furnaces remain in operation longer and with less downtime than before.
“Every stop means lost time and every start-up requires start fuel, which has an environmental impact per se.”
“At E.ON, we want to take responsibility and contribute to a more sustainable society.”
– Anna Jonasson, process engineer at E.ON Heat.
Sweden’s tomorrow is today’s responsibility
Today, combined heat and power plants account for around 9 per cent of the country’s electricity generation. However, electricity generated from biofuels needs to be more economically competitive compared to fossil fuels; the effects of corrosion on materials are still a limiting factor today. It is simply not possible to fire boilers as efficiently as with coal.
“Our primary task is to gain insights into the problems that arise. If we can increase boiler service life and efficiency with biobased combustion, we can also reduce carbon dioxide emissions. It’s an important step if Sweden is to reach its green objectives”, says Jesper Liske.
E.ON is investing in sustainability. The goal for 2025 is for the operation to include solely renewable and recycled fuels and to move away from fossil fuels entirely.
“At E.ON, we want to take responsibility and contribute to a more sustainable society. If we are to achieve our goals, research is essential; we need new solutions to achieve increased operating time, efficiency, service life and process reliability using biofuels”, says Anna Jonasson.