Modelling the Fate of Sulphur During Pulverized Coal Combustion under Conventional and Oxy-fuel Conditions

Focus of the present study is on the fate of sulphur during coal combustion and modelling of the corresponding SOx formation mechanisms. The sulphur chemistry during coal combustion in general is briefly described and potential effects of the oxy-fuel conditions are explained. Details about the developed sulphur chemistry model which covers both heterogeneous and homogeneous reaction pathways are given. The model describes the sulphur transformation in a sequence of stages: the release of coal-bound sulphur, gas phase reactions of sulphuric species, and self-retention of sulphur oxides by coal ash. The model is evaluated against experimental data from IFK's semi-industrial scale furnace (500 kWth) firing lignite at conventional and oxy-fuel combustion conditions. Four reference cases are considered, i.e. air and oxy-fuel mode in both non-staged and staged operation. Based on the results from the basic combustion simulation with AIOLOS, the sulphur chemistry model has been applied in a subsequent post-processing step. The sulphur related results show that the general trends regarding the species concentrations may be predicted correctly. The specific characteristics and the effect of oxy-fuel conditions and oxidant staging are captured correspondingly within the simulation results. Yet, certain deficiencies concerning the quantitative prediction could be identified which necessitate further investigations.