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Niko Niemelä: Clean and efficient bioenergy with advanced simulation models

Tampere University
LocationHervannan kampus, Festia, Pieni Sali 1 (Korkeakoulunkatu 8, Tampere)
22.4.2022 9.00–13.00
LanguageEnglish
Entrance feeFree of charge
Väittelijän kuva
Bioenergy is the most significant renewable energy form in Finland. It plays an important role in climate change mitigation scenarios and green transition plans, also on a global scale. Biomass is needed in the peak load plants for balancing the variable wind and solar power in the grid, in the district heating plants, and in the high temperature industrial processes that are difficult to electrify. In his Doctoral Dissertation, M.Sc. Niko Niemelä developed advanced simulation models that can be used for designing clean and efficient bioenergy systems.

There is a lot of discussion going on about wind and solar power. That is a good thing, because their significance increases very rapidly. However, our energy production system is extremely complicated, and there is no single solution that could solve all the challenges related to green transition.

“Bioenergy is one part of the solution, being in the key position as a stabilizing factor when industry, transport, consumers, and energy production get more strongly integrated as one large energy system,” Niko Niemelä says.

District heat and peak power are needed in addition to wind. Combustion plants, that use biomass resources sustainably, have an important role in this.

“Pulverized fuel technology, that I studied in my thesis, is a good option for fast-response energy system, because the plants can be started up very quickly when electricity or heat is needed,” Niemelä continues.

Simulations can help to reduce emissions and ash-related problems

Biomass, such as wood, is needed also in many other applications than energy: for example, in manufacturing higher value products, in construction industry to replace concrete, and for replacing plastics. Biomass that ends up in energy production will increasingly be side streams from e.g. industry, agriculture and forestry.  Wood bark and straw are examples of these side streams.

"The side streams have often a high ash content, which is a challenge for combustion plants. The ash causes many technological problems, because it adheres on the furnace walls and corrodes the metal materials. The biomass fuels produce high nitrogen oxide emissions and a lot of fine particulate emissions like sulfates and soot. Minimizing the gaseous and particulate emissions is an essential goal in the design of combustion plants," Niemelä says.

Niko Niemelä considers the new modeling approaches the most significant achievement of his thesis, because they can be used for emission reduction and for widening the material selection for biomass heat and power generation. The models are used in computer simulations to describe the biomass particle combustion process, ash and fine particle behavior, gaseous emission and soot formation, and heat transfer in the furnaces.

“The simulations are extremely complicated because they model the interactions between turbulent flow and chemical reactions. As such, it was really fascinating to see how well the simulations and experiments agreed for a pilot reactor of Technical University of Munich, and for a district heating plant of Helen Ltd.,” Niemelä summarizes.

Computational fluid dynamics is useful in many disciplines

Niko Niemelä follows closely space and climate sciences. Computational fluid dynamics, that he uses in his work, is actively used in those fields as well.

“I was happily surprised when Syukuro Manabe won the latest Nobel prize in physics for his research in climate simulations. The same fluid dynamics laws apply everywhere, in the flame of a combustion plant, in the Earth’s atmosphere, and even in the scale of galaxies. This is extremely fascinating! I try to use examples from different fields in my own teaching in the courses related to numerical modeling,” Niemelä ends.

The doctoral dissertation of M.Sc. Niko Niemelä in the field of energy engineering titled Experimental and Modeling Studies of Pulverized Biomass Combustion will be publicly examined in the Faculty of Engineering and Natural Sciences at Tampere University at 12:00 on Friday 22.4.2022 in auditorium Pieni Sali 1 in Festia building, Korkeakoulunkatu 8, Tampere. The Opponents will be Professor Markus Broström from Umeå University and Assistant Professor Ville Vuorinen from Aalto University. The Custos will be Professor Jukka Konttinen from the Faculty of Engineering and Natural Sciences, Tampere University.

The dissertation is available online at: https://urn.fi/URN:ISBN:978-952-03-2348-6