The basic idea behind this MOOC, is to present recent data on fuel characterization, slagging, fouling, corrosion, and trace element transformations, in a course that can be readily provided for students and industry people. This ensures understanding and application of the research, and provides the students and industry with a forum for discussion of the very latest research results, as well as feedback from industry to the research group at DTU, on important new research subjects in the field. The specific aim of the MOOC, is that students will be able to; Explain basic physical and chemical differences between solid fuels like coal, biomass, waste etc., be able to characterize solid fuels, and to interpret fuel analyses of them Interpret and utilize data from advanced fuel and ash analyses (SEM, DTA/TGA, chemical fractionation, ash melting temperatures) Describe chemically and physically, how critical ash-forming elements are released to the gas phase, the mechanisms for formation of aerosols and fly ash particles, and explain how ash is transported from bulk gas to heat transfer surfaces Quantify the processes of deposit build-up, sintering and shedding Explain the fundamentals of high-temperature corrosion in thermal fuel conversion systems Can calculate viscosities as a function of temperature and composition, temperature profiles in a deposit, rates of deposit build-up and sintering, as well as porosity changes vs. time.