Analysis of gas turbine systems for sustainable energy conversion

Sammanfattning: Increased energy demands and fear of global warming due tothe emission of greenhouse gases call for development of newefficient power generation systems with low or no carbondioxide(CO2) emissions. In this thesis, two different gasturbine power generation systems, which are designed with theseissues in mind, are theoretically investigated and analyzed.Inthe first gas turbine system, the fuel is combusted using ametal oxide as an oxidant instead of oxygen in the air. Thisprocess is known as Chemical Looping Combustion (CLC). CLC isclaimed to decrease combustion exergy destruction and increasethe power generation efficiency. Another advantage is thepossibility to separate CO2without a costly and energy demanding gasseparation process. The system analysis presented includescomputer-based simulations of CLC gas turbine systems withdifferent metal oxides as oxygen carriers and different fuels.An exergy analysis comparing the exergy destruction of the gasturbine system with CLC and conventional combustion is alsopresented. The results show that it is theoretically possibleto increase the power generation efficiency of a simple gasturbine system by introducing CLC. A combined gas/steam turbinecycle system with CLC is, however, estimated to reach a similarefficiency as the conventional combined cycle system. If thebenefit of easy and energy-efficient CO2separation is accounted for, a CLC combined cyclesystem has a potential to be favorable compared to a combinedcycle system with CO2separation.In the second investigation, a solid, CO2-neutral biomass fuel is used in a small-scaleexternally fired gas turbine system for cogeneration of powerand district heating. Both open and closed gas turbines withdifferent working fluids are simulated and analyzed regardingthermodynamic performance, equipment size, and economics. Theresults show that it is possible to reach high power generationefficiency and total (power-and-heat) efficiency with thesuggested system. The economic analysis reveals that the costof electricity from theEFGT plant is competitive with the moreconventional alternatives for biomass based cogeneration in thesame size range (<10 MWe).Keywords:power generation, Chemical Looping Combustion,CO2separation, oxygen carrier, biomass fuel, closedcycle gas turbine, externally fired gas turbine