Experimental and numerical studies of thermal radiation in gas, coal and co-fired pilot test facilities

Licentiatavhandling, 2017

Throughout the industrialized era, fossil fuels have been used extensively in combustion processes to generate heat and electricity. However, the combustion of such fuels creates emissions of greenhouse gases, mainly carbon dioxide, and other hazardous products. As these gases are released to the atmosphere, they contribute to global warming, which is a global issue of concern. It is therefore of great importance to study combustion processes and explore new ways to reduce their environmental impacts. One way of reducing emissions of greenhouse gases is to replace the energy source: from fossil to renewable. To attain a better understanding of the combustion process experimental and modeling work is needed. Such work can be undertaken to increase the efficiency and demonstrate the possible effects of fuel substitution. The first half of this thesis focuses on the rotary kiln process, which is used in iron ore pellet production, and studies the associated rotating furnace and the radiative heat transfer process. The experimental work was performed during a measurement campaign in a down-scaled version of the furnace, and the results are compared and modeled using a discrete transfer model for different fuels. The focus is on comparing a reference coal with co-firing cases that employ a combination of 70% reference coal and 30% biomass for two different types of biomass. The results reveal the possibility of using co-firing in a full-scale rotary kiln, which is not expected to have any significant impact on the radiative heat transfer within the process. Measurements from a similar but earlier campaign were used together with a radiative model, using the discrete ordinates method to study the process in three dimensions. While still under development, this model predicts trends when the operational conditions of the rotary kiln process are changed. The second half of this thesis work focuses on soot formation in different propane flames. The combustion conditions were varied while the process stoichiometry was maintained, and soot formation was analyzed using two different measurement techniques. In the first campaign, the soot volume fraction was measured by gas extraction using a scanning mobility particle sizer (SMPS), together with a photo-acoustic soot spectrometer (PASS-3), to study the radiative properties of the soot particles. In the second campaign, the soot volume fraction was measured using laser-induced incandescence (LII) together with an extinction laser. In both campaigns, the radiative intensity was measured, and the different flames were modeled using a discrete transfer model of the radiative heat transfer. The differences between the modeled and measured radiative intensities were found to be small in both campaigns.