Author ORCID Identifier
Semester
Summer
Date of Graduation
2025
Document Type
Dissertation
Degree Type
PhD
College
Statler College of Engineering and Mineral Resources
Department
Mechanical and Aerospace Engineering
Committee Chair
V'yacheslav Akkerman
Committee Member
Richard Axelbaum
Committee Member
Wade Huebsch
Committee Member
Hailin Li
Committee Member
Victor Mucino
Abstract
Pressurized oxy-combustion (POC) is emerging as a promising and transformative technology for carbon capture, utilization, and storage, offering advantages of low cost, low emissions, and high efficiency. POC operates by burning pulverized coal at elevated pressures in a recycled flue gas environment, typically rich in O₂ and CO₂. This study presents a comprehensive numerical investigation into the fundamental behaviors of lab-scale POC reactors, using both two-dimensional (2D) Reynolds-Averaged Navier-Stokes (RANS) simulations and three-dimensional (3D) Large-Eddy Simulations (LES) with the commercial computational fluidized dynamics (CFD) software package ANSYS Fluent.
The primary focus of this work is to understand flame stabilization and system dynamics pressurized conditions. The study evaluates various burner and combustor configurations operating at half-load (50 kW) and full-load (100 kW) capacities. The 2D RANS simulations are used to analyze recirculation zones and the mechanisms behind flame stabilization. Key parameters examined include the bluff-body blockage ratio, bluff-body geometry (comparing disk-shaped and tulip-shaped designs), and oxidizer mass flow rate. For the disk-shaped burner, results reveal that an optimal blockage ratio enhances flame stability, and the flame anchoring position varies as the blockage ratio changes. In contrast, the tulip-shaped burner generates a significantly different recirculation structure, producing a larger hot zone in the near-burner region, which may contribute to improved flame stability.
LES is employed to capture POC system dynamics and flow structures. This allows for detailed observation of the flame-flow interplay. Notably, larger temperature fluctuations are observed in the upstream region compared to downstream. Particle behavior is also investigated using LES, revealing the distribution and motion of coal particles in the POC system. Particle dynamic analyses show that particle size plays a significant role in determining flame stability, heat transfer, and trajectory within the pressurized combustor. Stokes numbers based on turbulent fluctuations, extracted from LES results, indicate that particles smaller than 100 µm closely follow the gas flow, while larger particles deviate more significantly. Moreover, particle trajectories are sensitive to particle release location and particle size.
Another important aspect of the study involves examining how boundary conditions influence particle concentration at the burner inlet. Under high-pressure conditions, the volumetric concentration of coal particles often approaches—or exceeds—the limitations of CFD solvers such as ANSYS Fluent. This necessitates a re-evaluation of particle–fluid–wall interactions. To address this, the effects of particle release method, injection location, and particle size are systematically analyzed. In simulations of a 15-bar, 100 kWₜₕ combustor, modeled using the RANS approach, an unusual velocity profile is observed near the inlet wall of the fuel flow—characterized by a velocity “blip”—which deviates from classical fully developed tube flow. This observation motivates further investigation into the role of particle loading in this region. It is found that adjusting the particle injection location helps align the gas-phase velocity with that of the single-phase flow.
Given the distinct thermophysical conditions in POC systems compared to conventional atmospheric coal combustion, existing CFD radiation models require re-examination. The gray-gas assumption for gas–particle mixtures is evaluated for both RANS and LES approaches. A large-particle radiation model is used to estimate the emissivity and absorptivity of the gas–particle mixture under elevated pressures and high CO₂/H₂O concentrations—conditions that significantly influence radiative heat transfer. This study performs a detailed thermal radiation analysis, incorporating both the statistical narrow-band model and large-particle model. Results show that, at a furnace temperature of 1500 K and with minimal particle loss, thermal radiation is dominated by the particulate cloud. Under these conditions, the gas–particle mixture behaves effectively as a graybody. For example, with a gas mixture containing 40% H₂O and 60% CO₂ by volume, an increase in pressure to 15 bar and a radiation path length of 100 cm yields a spectral radiation profile that closely resembles that of a blackbody at the same temperature. Furthermore, the emissivity of the particulate cloud is found to increase with particle concentration and decrease with particle diameter (when mass is held constant). Notably, emissivity in oxy-combustion conditions exceeds that observed in conventional air-fired combustion. These findings support the validity of the gray-gas assumption for POC systems and provide crucial insights for the design and simulation of next-generation pressurized combustors.
Recommended Citation
Li, Lei, "NUMERICAL INVESTIGATION OF PRESSURIZED OXY-COMBUSTION" (2025). Graduate Theses, Dissertations, and Problem Reports. 12973.
https://researchrepository.wvu.edu/etd/12973