(738b) Optimal Design of Oxy-Fuel Combustion for Carbon Capture and Sequestration

Oxy-fuel combustion is a thermodynamically attractive concept that seeks to mitigate the penalties associated with CO2 capture from power plants. The main disadvantage is the need to separate oxygen from atmospheric air. This can be achieved using conventional cryogenic air separation or novel membranes. In either case, careful integration of the air separation, power generation and CO2 treatment is required to achieve high conversion efficiencies. Moreover, in order to obtain meaningful prediction of efficiencies detailed modeling of all processes involved is mandated, but this is often ignored in the literature. The talk describes modeling, design and optimization of various oxycombustion concepts.

In the first part of the talk, a semi-commercial pressurized oxy-coal combustion is considered. Multi-variable optimization is performed involving high-fidelity modeling of the power plant units. In particular, the model accounts for heat losses, flow leaks, pressure drops, irreversibilities, and several technological and economical considerations. Continuous and discrete variables are varied simultaneously to maximize thermal efficiency while satisfying techno-economic constraints. The optimization leads to significant efficiency improvement and more moderate operating conditions (lower pressure) compared to prior studies based on single-variable sensitivity analysis.

In the second part, integrated oxygen ion transport membranes (ITMs) are considered for oxygen separation for the oxycombustion of natural gas. Oxygen separation in an ITM system consists of many distinct physical processes, ranging from complex electrochemical and thermochemical reactions, to conventional heat and mass transfer. The dependence of ITM performance on power cycle operating conditions and system integration schemes must be captured in order to conduct meaningful process flow and optimization studies. An axially distributed, quasi two-dimensional model is presented based on fundamental conservation equations, semi-empirical oxygen transport equations obtained from the literature, and simplified fuel oxidation kinetic mechanisms. Several power cycles from the literature are considered, along with new proposals, including separation in a reactive environment. The detailed modeling demonstrates that several literature claims are overly optimistic since they neglect irreversibilities and operational constraints. Moreover, the model is used to examine the feasibility of novel concepts to overcome some of the challenges associated with the ITM. Finally, the merit of partial CO2 emission concepts is discussed.