Combustion of pure carbon in the presence of H₂O and CO₂ using single and double film models

Abstract

In integrated gasification combined cycles systems, it is of interest to estimate the burn or gasification rate ( _ m), particle surface/wall temperature (T w ), and flame temperature (T f ), and also control of the T w and T f with free stream CO 2 and the H 2 O level, which promote endothermic reactions. In the past, char combustion in the air was modelled using either a conventional single film model (SFM), or a conventional double film model (DFM). In this study, modified SFM and DFM models, including both heterogeneous reactions of CO 2 and H 2 O with C, and gas phase oxidation of both CO and H 2 , were developed. The SFM and DFM were switched to SFM-DR (single film model with double reactions) and DFM-DR (double film model with double reactions). The SFM-DR assumes that the gas phase is frozen, with the final products being CO and H 2 , and the transfer numbervH 2 O;IV ; DFM-DR includes gas phase oxidation of both CO and H 2 with O 2 , with the final products being CO 2 and H 2 O and the same modified transfer number B under infinitely fast chemistry. Finally, six different char combustion cases with or without H 2 O and CO 2 in the free stream were simulated to obtain the flame profile for modified SFM-DR and DFM-DR. It was found that reasonable flame profiles of char combustion were obtained for both SFD-DR and DFM-DR. Moreover, the O 2 -rich combustion could promote the endothermic Boudouard and steam-carbon reactions. Finally, the burning rate (kg/m 2 Á s) decreased with the increase of particle diameter for both SFM-DR and DFM-DR.