28.4.2023
Doctoral Thesis on the Reduction of Nitrogen Oxides When Using Biomass Waste as Fuel
MSc Daniel Schmid’s doctoral thesis in Inorganic Chemistry will be put forth for public defence at the Faculty of Science and Engineering at Åbo Akademi University.
The thesis is entitled Laboratory Studies on Aqueous Absorption and High Temperature Chemistry of NOx and SOx in Thermal Conversion of Biomass Waste.
The Public defence of the doctoral thesis takes place on 5 May 2023 at 1.15 PM in auditorium Argentum, Aurum, Henrikinkatu 2, Turku. Professor Fredrik Normann, Chalmers University of Technology, Sweden will serve as opponent and Professor emeritus Mikko Hupa, Åbo Akademi University, as custos.
Summary
Biomass waste from the agriculture and forest industry can be thermally converted to recover energy and to produce ash that can be reused for various purposes. Biomass waste is in many cases a demanding fuel, partly due to high concentrations of nitrogen and alkali metals. In combustion, fuel-bound nitrogen is converted into nitrogen oxides (NOx), which are harmful to the environment and cause acid rain and smog. Alkali metals such as potassium and sodium cause corrosion in combustion plants, which has a negative impact on energy efficiency, reduces plant life and imposes high material requirements. The thesis experimentally investigated the formation of nitrogen oxides (NOx) from pretreated biomass waste in an electrically heated reactor under combustion and gasification conditions, absorption of NOx in a laboratory scrubber system with sulfur additives and sulfation of corrosive sodium salts in a so-called multi jet reactor at temperatures up to 1500 °C.
The thesis shows that pretreatment of biomass waste affects the reactions of the fuel nitrogen and thus the amount of NOx formed during combustion. Pretreatment of biomass is an important method i.a. to improve the fuel’s physical properties. Pretreated fuels in some cases had higher NOx emissions, which is partly explained by a change in the ash composition. The absorption experiments showed that aqueous solutions with sulfite and thiosulfate could effectively absorb NOx from fuel gas. Addition of thiosulfate reduced the reaction rate of sulfite oxidation and enabled an efficient absorption of NOx. The dissertation’s high-temperature experiments with a multi-jet reactor provided new information regarding the sulfation of sodium chloride and sodium hydroxide into less corrosive compounds. The sulfation reactions were investigated with a new kinetic model and with thermodynamic modeling. The results of the thesis contribute to being able to eliminate chemistry-related problems in the industrial thermal conversion of demanding fuels.
Daniel Schmid is born in 1995 in Heidenheim an der Brenz, Germany. He can be reached by email on daniel.schmid@abo.fi.
The doctoral thesis can be read online through the Doria publication archive.
Click here for a press photo of the doctoral student.