Public defence, Mechanical Engineering, M.Sc. Matthias Re

Title of the thesis: Oxy-fuel combustion retrofits for flexible low-carbon power and heat generation: Integration of electrolysis to waste-to-energy and CCGT plants

Thesis defender: Matthias Re 
Opponent: Prof. Cataldo de Blasio, Åbo Akademi, Finland 
Custos: Prof. Mika Järvinen, Aalto University School of Engineering

Finland aims to become carbon neutral by 2035. Reaching this goal requires advances across multiple sectors, including new ways to reduce emissions from heat and power generation while maintaining energy security. Renewable electricity production is expanding rapidly, and green hydrogen production is expected to grow alongside them. However, renewable electricity production depends on weather conditions, while heat and electricity must remain continuously available, especially during cold periods in countries such as Finland. Existing thermal power plants therefore still play an important role in balancing the energy system and securing district heating supply. Green hydrogen is produced using electrolysis, a process that splits water into hydrogen and oxygen. While the hydrogen has an important role in future low-carbon industries, the large amounts of oxygen produced as a by-product are often overlooked. 

This doctoral thesis investigates how existing waste-to-energy combined heat and power plants and natural gas combined-cycle power plants can be retrofitted to oxy-fuel combustion systems integrated with electrolysis. Oxy-fuel combustion is a carbon capture technology in which fuel is burned using pure oxygen instead of air. This creates a potential synergy between hydrogen production and low-carbon heat and power generation. 

The research evaluated both technical performance and economic feasibility under future low-carbon energy system conditions. The results show that the retrofitted systems can capture nearly all carbon dioxide emissions from the studied plants while continuing to provide district heating and flexible electricity generation. In addition, integrating electrolysis enables simultaneous hydrogen production and increases heat recovery within the system. The captured carbon dioxide streams reached purities of approximately 98–99%. 

The thesis also demonstrates that integrating carbon capture with hydrogen production fundamentally changes the operational role of thermal power plants. Rather than functioning only as conventional electricity producers, the retrofitted plants can operate as flexible energy systems that support renewable integration, district heating supply, and long-term emission reductions. 
Key words: oxy-fuel combustion, electrolysis, hydrogen, AspenPlus, combined heat and power, combined cycle gas turbine, waste-heat recovery, break-even price, profit, renewable energy grid integration

Thesis available for public display 7 days prior to the defence at Aalto University's public display page. 

Contact information: matthias.re@aalto.fi