Date of Graduation
Statler College of Engineering and Mineral Resources
Mechanical and Aerospace Engineering
Identified by the DoE among the novel and transformational technologies, staged-pressurized oxy-fuel combustion (SPOC) is a promising low-cost, low-emission, and highly efficient tool for carbon capture utilization and storage (CCUS), with pulverized coal burning under elevated pressures and low recycled flue gas. A lab-scale SPOC facility, under establishment at Washington University in St. Louis (WUSTL), causes the critical need to develop accurate and reliable computational models to assist the ongoing WUSTL experiments. This constitutes the driving motivation of the present work. Specifically, comprehensive three-dimensional Large-eddy simulations (LES) of the lab-scale SPOC reactor, with most of important characteristics of a multi-phase flow, are performed by means of the commercial computational fluid dynamics (CFD) package ANSYS Fluent. Various models for fluid-particle interaction, pulverized coal combustion, convective and radiative heat transfer, transport of species, and turbulence-chemistry interaction under pressurized oxy-firing conditions are scrutinized. The overall 100 kW of the thermal power generated by the SPOC reactor is divided between 90 kW resulting from oxy-coal combustion and 10 kW from a methane-aided pilot-flame, which serves as a stabilizer for oxy-coal combustion. The Eulerian-Lagrangian description of the phases is employed to model fluid-particle interaction, with a two-way coupling mechanism enabled. Turbulent burning is modeled with the species transport model, solving for the transport of eight species (volatiles, O2, H2O vapor, CO, N2, H2, CH4, and bulk CO2). The simulations account for such key phenomena as coal devolatilization and char combustion; gasification and oxidation with modified diffusion rates in a pressurized environment; and radiation heat transfer. In particular, user-defined functions (UDF) are implemented in the ANSYS Fluent to properly model the particle emissivity and the gas mixture absorption coefficients. The present research has resulted in the following three major conclusions.
First, it is demonstrated that the effect of particle-particle interaction on the injection of pulverized coal into the SPOC burner is negligible, while fluid-particle interaction is the dominant mechanism. Second, a successful strategy how to transition from the Reynolds-averaged Navier Stokes (RANS) simulations to an LES is developed and tested on various sub-grid scale (SGS) models. In particular, it is shown that the Classical Smagorinsky model is unable to model SPOC with purely coal burning. Instead, the Dynamic-Stress Smagorinsky-Lilly model is proposed to be used in the LES framework. Finally, turbulent dispersion of particles is analyzed, with a particular focus on the Stokes number. It is concluded that a poor dispersion and possible wall impactions occur for pulverized coal particles exceeding 500 μm, which may subsequently cause the slagging problems in the experimental facility.
Islas Montero, Alain, "Towards Large Eddy Simulation of a Staged, Pressurized Oxy-fuel Combustor" (2020). Graduate Theses, Dissertations, and Problem Reports. 7672.
Available for download on Saturday, July 31, 2021