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Investigation of combustion of lignite and torrefied biomass in a thermogravimetric analyzer (TGA) and in a circulating fluidized bed (CFB) under oxy-fuel combustion conditions

Barzegar, Ramin
In this study, the combustion of Turkish lignites (Orhaneli and Soma), torrefied woodchip, and their blends was studied under oxygen-enriched and oxy-fuel combustion conditions in a thermogravimetric analyzer. The iso-conversional kinetic methods were used to estimate the Arrhenius parameters and the uncertainty assessments associated with the kinetic calculations were considered. The co-combustion experiments showed a synergetic effect between the biomass samples and Orhaneli lignite. Based on the obtained results, Orhaneli lignite and the biomass torrefied at 300°C-30 min torrefaction conditions were selected for further analysis in a laboratory scale Circulating Fluidized Bed Combustor (CFBC). The CFBC experiments were conducted under oxygen-enriched and oxy-fuel combustion conditions and included the addition of calcium-based sorbents (Çan limestone and Eskişehir dolomite) for in-situ adsorption of sulfur dioxide emission. The conducted CFBC experiments showed that the sulfur dioxide removal was more effective with the addition of Çan limestone with the particle size of 1-2 mm and Ca/S ratio of 2. Also, increasing the oxygen concentration was an effective solution in sulfur retention. Furthermore, the combustion process in the CFBC was numerically simulated and the results were compared with the experiments. The simulation results showed a good agreement with the experimental data in estimation of the combustor temperature and carbon-based efficiency.