Sulfating of Alkali Chlorides in Waste-to-Energy

Examensarbete för masterexamen
Master Thesis
Innovative and sustainable chemical engineering (MPISC), MSc
Sundborg, Oskar
Tärnåsen, Albin
This thesis work involved the sulfation of alkali chlorides inWaste-to-Energy boilers. Sulfation, and thus removal, of these alkali chlorides is important since it can reduce high temperature corrosion and dioxin formation in the boiler. The objective was to investigate the impact that different properties such as temperature and composition have on the degree of sulfation, i.e. the fraction of alkali chlorides that have been sulfated. Two softwares were mainly used in this thesis work, namely Fluent and CHEMKIN. Fluent was used for a CFD-analysis to estimate the cooling rate and residence time of the flue gas in one of the investigated boilers and CHEMKIN was then used to simulate the course of sulfation in 1D. The results from the CFDanalysis proved to be insufficient due to the simplifications made. However, with the addition of a fictional flame the cooling rate could be estimated. The cooling rate could then be compared with a more realistic cooling rate and could thus be validated as a realistic representative. The residence time from the CFD-analysis was deemed to be realistic without any further actions. With the information gathered from the CFD-analysis, the kinetic simulations could be commenced in CHEMKIN. The results from these simulations show that it is possible to predict the degree of sulfation fairly well in both investigated boilers individually by adjusting parameters e.g. for mixing and carbon monoxide combustion. In other words, a general model that can predict the degree of sulfation for all boilers was not achieved but rather a framework that requires individually adjusted parameters for each investigated boiler. The model did however generally follow the same trends as the reference data which suggests that the kinetics are valid. With the aid of the model it was found that the presence of sulfur, radicals and slower cooling rates was favourable for the sulfation while chlorine and calcium suppresses it. Some phenomena could not be accounted for completely due to limitations of the model, such as mixing and variations over time. Additionally, the behavior of the gaseous sulfur is disputable. Some believe that sulfur dioxide is the most important sulfur specie in the sulfation process whilst others believe it to be sulfur trioxide. This makes the injection of sulfur problematic to implement into the model.
Energi , Hållbar utveckling , Energiteknik , Energy , Sustainable Development , Energy Engineering
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