COUPLING OF A RADIATION MODEL WITH SYSTEM MODEL OF BUBBLING FLUIDIZED BED COMBUSTORS

Date

2023-12-25

Author

Yaşar, Mehmet Soner

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Currently, none of the steady-state and transient bubbling fluidized bed combustor models couples the solution of the radiative transfer equation with the solution of conservation equations of other transport processes although thermal radiation is of considerable importance in such systems, as such an objective requires both accurate and computationally efficient methods for not only the solution of radiative transfer but also the estimation of radiative properties of particle-laden combustion gases. Therefore, in this study, 1-D steady-state and transient comprehensive system models for combustion of lignite and co-combustion of lignite and cotton residue with limestone addition is coupled with a 3-D radiation model based on the method of line solution of discrete ordinates method utilizing spectral radiative properties of combustion gases, particles, and walls. Furthermore, a 2-D computational fluid dynamics model for the combustion of lignite only is developed using the commercial software ANSYS Fluent and coupled with both accurate and computationally efficient methods for the estimation of radiative properties of particle-laden combustion gases. Predictive accuracies of all models are validated against measurements obtained from METU 0.3 MWt atmospheric bubbling fluidized bed (ABFBC) combustion test rig firing lignite or co-firing lignite with cotton residue and limestone addition. The outcome of this study provides comprehensive, accurate, and computationally efficient tools for simulation of steady-state and transient bubbling fluidized bed combustors and reveals the significant impact of radiative heat transfer in modeling of industrial boilers. Moreover, this study revealed the importance of the combustion gases, soot particles, fine and coarse fly ash particles and proper treatment of their radiative properties for the radiative heat transfer predictions under the conditions of bubbling fluidized bed combustors firing lignite or co-firing lignite with biomass and limestone addition. Finally, the predictions of the coupled steady state and transient bubbling fluidized bed combustor models indicate that using a sophisticated radiation model provides more accurate temperature predictions for the freeboard of METU 0.3 MWt ABFBC test rig compared to the bubbling fluidized bed combustor models without coupling.

Subject Keywords

Radiative Heat Transfer, Non-Gray Gas Radiation, Mathematical Modeling, Bubbling Fluidized Bed Combustors, Coal/Biomass Co-Combustion, CFD

URI

https://hdl.handle.net/11511/107760

Collections

Graduate School of Natural and Applied Sciences, Thesis