Modelling the fate of sulphur during pulverized coal combustion under conventional and oxy-fuel conditions

摘要

Focus of the present study is on the fate of sulphur during coal combustion and modelling of the corresponding SO_x 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 kW_(th)) 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.