Design and Operability of a Pressurized Oxy-Combustion System

Fossil fuel powers more than two-thirds of the world’s electricity, a significant share of which is derived from coal power plants. Despite coal being an abundant and energy-rich fuel, the major halt to its progress is greenhouse gas emissions. Greenhouse gases are detrimental to the environment. The search for clean fossil fuel leads to the oxy-combustion process. Oxy-fuel combustion produces sequestrable carbon dioxide as exhaust. Pressurization makes carbon capture more accessible and more energy-efficient. Pressurized oxy-combustion cycles can achieve theoretically high thermal efficiencies along with a 90% carbon capture rate. Additionally, the high energy density allows smaller turbomachinery and save capital cost. Thus, the primary objective of this dissertation is to present the design and operability of a pressurized oxy-combustor system. The initial part of the dissertation investigates different thermodynamic cycles and presents a model that can be adapted for existing power plants. The thermodynamic model will be used in the later part to design the proposed combustor. The two cycles analyzed are ENEL and TIPS. Both of the processes are high pressure oxy-combustion cycles. This study focuses on qualitative analyses of the cycles using a commercially available software called Aspen Plus®. A detailed benchmark study has been performed to validate the modeling process. ENEL and TIPS cycles are designed in the software, adopting the same principles. Recirculation ratio and pressures are varied to find the efficiency range of the cycles. Power calculations are done to find overall and net efficiency for a fixed recirculation ratio. The efficiencies of the cycles are compared to select an optimum cycle. A recirculation ratio of 50% is selected for implementation. The comparison shows that ENEL is marginally efficient over TIPS, at the cost of a pressure difference of about 70bars. Technology Readiness Level analysis is performed to present the availability of the specialized equipment for the cycles. From the TRL analysis, it is seen that the cost and availability of high pressure equipment surmount the edge of TIPS over ENEL. Thus, ENEL is chosen as the better cycle for investigating a scaled experiment considering efficiency and viability. The later part of the dissertation focuses on developing the combustor\u27s design for a pressurized oxy-combustion cycle. The proposed combustor is a powerhead-mounted design aimed to produce 1MW of thermal output. The design presented is modular and versatile. The design has been developed to withstand high pressure and temperature. It has three main flanged sections: powerhead, combustor body and exhaust. Each section is designed to meet different criteria of the pressurized oxy-combustion system derived from the cycle analysis. The powerhead mounting enables to skid-mount the system and gain a mobile system. The flanged design allows the addition of secondary bodies to investigate different flame lengths and thermal loads. Thus, it adds the usability of the design as a remote power production unit. The body is equipped with sensors for thermal mapping. Optical windows on the body are used to investigate flame characteristics such as flame holding, flame lengths, etc. A refractory layer protects the combustor body from fouling and oxidation from the high oxygen flow and increased thermal stress. The exhaust is designed to collect wastes from the system while separating exhaust gases for emission analyses. The different aspects of the design of a down-fired pressurized swirl combustor are presented in this dissertation