Flamelet tabulation methods for SO_x formation in pulverized solid fuel combustion

In this paper, four different flamelet tabulation methods are evaluated for predicting SO_x formation, including SO, SO₂ and SO₃, in pulverized coal flames with fuel-bound sulfur. The flamelet tabulation methods are evaluated in laminar counterflow flames under different operating conditions, and compared to the detailed chemistry solutions used for reference. The SO_x species mass fractions are obtained by either extracting them directly from the flamelet library or solving the corresponding transport equations using source terms from the flamelet library. The results show that different from the other major species, O₂ is sensitive to the local combustion mode, and large discrepancies are obtained if the local combustion mode is incorrectly represented. The predicted O₂ has a direct effect on H₂S oxidation. It is found that SO_x species mass fractions can be accurately predicted by all flamelet tabulation methods in most regions of the computational domain, although there are non-negligible discrepancies in relevant regions where the premixed combustion mode is dominant. The differences between the flamelet predictions and the detailed chemistry solutions are quantified by introducing a newly defined parameter, which is formulated based on the difference between the flamelet predictions and the detailed chemistry solutions. The suitability of the flamelet model in predicting the SO_x formation in pulverized coal flames with fuel-bound sulfur is justified through a chemical timescale analysis. The chemical timescale analysis is consistent with the findings for the flamelet predictions.