Characterization of a Flex-Fuel Oxy-Combustion System Through Experimental Investigation and Computational Modeling
Oxy-fuel combustion has the potential to offer high thermal efficiency and lower pollutants emission compared to other existing combustion technologies. More than 63% of the world’s electricity is produced by fossil fuel combustion which also is the major reason for greenhouse gas emissions. Oxy combustion offers a solution to it. Oxy combustion uses pure oxygen as an oxidizer instead of air which eliminates the NOx and SOx products from the exhaust. In oxy-combustion flue gas mainly consists of CO2 and water vapor. Furthermore, combustion in presence of pure oxygen results in higher flame temperature and hence promises higher thermal efficiency. Furthermore, the CO2 can be captured from the exhaust and recirculated back into the combustion chamber to reduce radiation loss. Due to its thermal and environmental potential oxy-fuel technology is currently undergoing a rapid development towards commercialization with many several industrial projects. This advanced power generation technology also has a wide range of engineering applications in the gas turbine, boiler, and aerospace industries. Commercializing this combustion concept faces impediments from several fronts due to the existing knowledge gap. Combustion in oxy-combustion environments results in a very high flame temperature laying in the 30000C range. Metal body exposed to high temperature during combustion deteriorates at an increasing rate causing the combustor chamber to be damaged. Furthermore, operating parameters for a continuous steady-state operation are needed to be optimized. Recent work done by the UTEP-Aerospace Center research groups proposes a vertical 5 MWth oxy-combustor with two burners and a CO2 injection port. The combustor has fuel flexibility (flex-fuel) and can operate with multiple fuel. The primary objective of this dissertation is to perform a qualitative analysis of this two-burner oxy-fuel combustion and present a high fidelity CFD model of the combustor for future scaling up. A commercial computational fluid dynamics tool, Simcenter Star CCM+ was used to model the system. The CFD model is designed to simulate a real-life combustion environment and can operate at different inlet conditions. In this study inlet conditions for the models are kept similar to the experimental ones to validate their fidelity. The expertise gained from this study is important to design combustors accurately and safely at a higher thermal rating and at elevated pressures. The combustor was operated at firing inputs ranging from 50 kWth to 110 kWth. and the experiments were run in two different CO2 settings. Combustions were conducted without any injected CO2 and contained only methane and pure oxygen as inputs. These test points were studied for highest thermal output. Later the similar tests were conducted by injecting various CO2 mass percentages to imitate different flue gas recirculation settings for the industrial scale power plants. Data points obtained from these experiments were used to find combustor operability for combustion in recirculated flue gas environment. The tests were run at a near 1 stoichiometry ratio and the injected CO2 mass percentage varied between 0-80%. It was determined that the tests can be conducted for at least 2 minutes without overheating the combustor. The digital counterpart of the model was used to predict several combustion properties which also was compared with the experimental data. The model was designed by combining several combustion physics sub models including a four-step robust chemistry models and surface to surface radiation model. Effect of dilution on radiative heat flux was measured from the experiments for different input conditions. Maximum radiation was found at the no dilution cases and at a higher dilution steady state heat flux was achieved suggesting the potential of industry scale use. For 110 kW peak radiative heat flux was found to be 56 kW/m2 at no dilution case which dropped down to a steady 12 kW/m2 at 80% dilution. The digital counterpart of the combustor was found to have high fidelity as many crucial thermo-fluidic properties predicted by it fall within a reasonable range of the tested data and hence it can be used for future oxy-fuel combustion research. The peak experimental heat fluxes for 68 and 46 kW-without dilution cases are 27 and 15 kW/m2 respectively and the CFD model predicted quite similar values for these two cases which are 14.6 and 11 kW/m2. The flame temperature predicted by the model for different cases also were validated with previous work. Deviation of the simulated combustion temperature from the analytical and literature values ranges between 3-13%. Based on the heat flux, combustion temperature, gas concentration and other property analysis with the experimental and simulated data it was concluded that the combustor could operate effectively in an industrial setting by setting the optimum input configuration.
Mechanical engineering|Energy|Computational physics
Khan, Mohieminul I, "Characterization of a Flex-Fuel Oxy-Combustion System Through Experimental Investigation and Computational Modeling" (2023). ETD Collection for University of Texas, El Paso. AAI29324674.