Reaction Kinetics of Sulphur and Nitrogen Chemistry in Pressurized Flue Gases: A Comparison of Modelling and Experimental Results

Examensarbete för masterexamen
Master Thesis
Jansson, Erik
Oxy-fuel combustion enables fossil fuel combustion without greenhouse gas emissions, by the including capture and subsequent storage of the CO2 formed. In order to make this possible the CO2 must be compressed and liquefied. In the compression section of the oxy-fuel process, a variety of compounds are present, such as water vapour, nitrogen oxides (NOx) and sulphuric oxides (SOx). The chemistry of NOx and SOx under pressurised conditions in gas-liquid systems is still under discussion and there is no consensus about which mechanisms that are of importance. This is important to find out in order to design an appropriate technical solution for the control of NOx and SOx in the outlet streams. The aim of this thesis work is to evaluate the NOx and SOx chemistry under pressurized gas-liquid conditions by comparing the major previous works in the area. Experimental work at Imperial College [1-4] and at Henri Poincaré University [5] are compared to a recently developed model by Pettersson [6, 7]. The comparison is made by developing a new model using the reaction mechanism in Pettersson’s model for simulation of the reactors in the experiments. The results show that the rate-determining step for acid formation from NOx is the oxidation of NO to NO2, which has been shown in earlier studies [6, 7]. In the liquid phase (in absence of SOx) NO2 forms nitrous and nitric acid. Nitrous acid slowly dissociates to nitric acid and NO. SO2 forms mainly sulphurous acid when absorbed into the liquid phase. In presence of both NOx and SOx at low pH, the nitrous and sulphurous acid react and form N2O, which diffuses into the gas phase where it is stable. At pH-values above 4, the N2O formation is unimportant and instead hydroxylamine disulfonic acid (HADS) is formed. There are indications in the experiments at Imperial College [3], but not in the model, showing that NOx might be able to catalyze formation of sulphuric acid from SO2. However, the experimental results points in different directions and it is not possible to confirm that this is an important mechanism; additional experimental work is thus required to confirm this mechanism.
Energi , Hållbar utveckling , Kemiteknik , Energy , Sustainable Development , Chemical Engineering
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