Doctoral dissertation

Dissertation: Lasers reveal the secrets of high-temperature chemistry – aid for sustainable power production

Jan Viljanen
Efficient use of renewable fuels for power production requires new information and advanced techniques. Laser-based methods developed in Jan Viljanen’s doctoral Thesis enable online monitoring of fast chemical reactions and the reaction conditions in otherwise inaccessible environments.

Environmental concern is forcing power and heat industry, which is a major source of greenhouse gases, to change its production methods and feedstocks. To reduce the emissions, thermal power production has to move from fossil fuels to renewable biomass feedstocks, such as industrial, agricultural, and communal waste. Challenging fuels set new requirements for combustion process control and monitoring. Hence, new techniques are needed for online monitoring of chemical reactions and conditions in combustion environments.

The new monitoring methods developed in Jan Viljanen’s Thesis open new possibilities for studying chemical reaction kinetics and elemental composition especially in flue gases released during biomass combustion. Laser-based measurement methods enable online analysis of high-temperature chemistry even in challenging conditions.

 “Photons are great! They measure things with speed of light and do not complain if they are sent to a thousand degrees hot furnace,” tells Jan Viljanen, who returns Tampere just in time for the doctoral defence from a measurement campaign in the United States.

Online monitoring of the reaction conditions and the chemical concentrations aid power plant providers and operators to optimize the biomass reactor process and help make power production with biomass feedstocks sustainable. In his Thesis, Jan analyzed the reaction kinetics of potassium in flue gas released during biomass combustion. Potassium is significant problem in biomass combustion as it causes, for example, high corrosion rates on steel surfaces.

“On the other hand, when the elemental reaction kinetics are well known, they can be utilized to monitor the reaction conditions, such as temperature and reacting compound concentrations,” explains Viljanen.

Sensitivity to online elemental monitoring

Continuously measured information of elements released from single fuel particles during the combustion process is an important parameter for process simulations and optimization. Originally, Jan developed, in collaboration with the University of Adelaide, a new microwave assisted laser-induced breakdown spectroscopy (MW-LIBS) method for mineral monitoring but noticed soon its feasibility also for combustion studies.

“Microwave assistance increased LIBS technique’s sensitivity a 100-fold and, on the other hand, improved also its feasibility for measurement of high concentrations. This kind of concentration dynamics are typical for elemental release during single particle biomass combustion, hence, we decided to apply the technique for this,” tells Viljanen.

MW-LIBS, that bases on laser-induced plasma emission, has been demonstrated for elemental monitoring in gaseous, solid, and liquid samples since its development. Thus, the technique has vast application potential in different fields of industry and science.

MSc (Tech) Jan Viljanen’s doctoral dissertation in the field of photonics entitled “Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion” will be publicly examined at the Faculty of Engineering and Natural Sciences of Tampere University (TAU) in auditorium S3 of Sähkötalo building (address: Korkeakoulunkatu 3, Tampere, Finland) at 12 noon on Friday, 29 March 2019. The opponent will be Dr. Zhongshan Li (Lund University, Sweden). Professor Juha Toivonen from the Physics Unit at Tampere University will act as Chairman.

Jan Viljanen comes from Lahti and currently works in the Applied Optics group at Tampere University.

The dissertation is available online at http://urn.fi/URN:ISBN:978-952-03-1022-6