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Online Laser Diagnostics for High-Temperature Chemistry in Biomass Combustion

Research output: Book/ReportDoctoral thesisCollection of Articles


Original languageEnglish
PublisherTampere University
Number of pages106
ISBN (Electronic)978-952-03-1022-6
ISBN (Print)978-952-03-1021-9
Publication statusPublished - 29 Mar 2019
Publication typeG5 Doctoral dissertation (article)

Publication series

NameTampere University Dissertations
ISSN (Print)2489-9860
ISSN (Electronic)2490-0028


Increasing concern over environment and new energy policies are driving the thermal heat and power industry towards new CO2 neutral fuels, such as biomass, and novel combustion schemes. Therefore new operational control and monitoring concepts are required to provide information of the combustion processes. Alkali elements and compounds have been identified to be one of the greatest challenges associated with thermal conversion of biomass as they cause severe operational problems in power plant boilers. In this Thesis, a new method to monitor temperature and O2 concentration during thermal conversion of biomass is developed. Collinear Photofragmentation and Atomic Absorption Spectroscopy (CPFAAS) is utilized to measure potassium reaction kinetics in lean combustion conditions, which provides valuable information for high temperature reaction models and simulations. The new information on potassium reaction kinetics with O2 enables online monitoring of temperature and O2 concentration utilizing the CPFAAS signal.

Microwave-Assisted Laser-Induced Breakdown Spectroscopy (MW-LIBS) is demonstrated for the first time at ambient atmospheric conditions with impressive 93fold enhancement in limit of detection (LOD). MW-LIBS is further applied for online elemental monitoring during thermal conversion of biomass fuels as it improves detection of trace elements and reduces adverse self-absorption effects in high-concentration conditions. To enable the benefits of MW-LIBS, a novel burner for flame calibration is introduced. The burner allows calibration of LIBS for extended concentration range enabling quantitative elemental release monitoring during thermal conversion of different biomass fuels with varying elemental content. The elemental release behavior of biomass fuels is paramount for thermal conversion models and simulations that provide boiler operators and manufacturers crucial information on how to optimize the thermal processes and mitigate the alkali associated problems. Furthermore, as the novel MW-LIBS approach requires no or minimal sample preparation, it has great application potential for online elemental monitoring in different fields of science where low LOD or high sensitivity is required.

The novel CPFAAS and MW-LIBS approaches provide simple and versatile methods for online high-temperature chemistry monitoring from laboratory-scale systems up to full-scale power plant boilers. Laser diagnostics will play a significant role in optimization and in process control of future thermal power generation as it enables development of online sensor networks to monitor and forecast the plant behavior.

Field of science, Statistics Finland