Pressure Gain Combustion Power Plant Analysis and Cycle Thermo-Economic Optimisation

The urgency of combating climate change has accelerated the push for next-generation power plant technologies. Gas turbines operating on the conventional Joule or Brayton cycle are widely used in electricity production due to their high power density, operational flexibility, fuel flexibility and lower emissions compared to other power plants. The gas turbine technology has matured a lot due to decades of advancements in combustion, turbomachinery, metallurgy and turbine blade cooling technologies. However, the potential for further major performance improvements in them has nearly plateaued and the main limitations are set by the fundamental thermodynamic cycle itself. Therefore, to achieve considerable efficiency and power improvements in modern gas turbines, it is essential to make radical changes in the gas turbine thermodynamic cycle itself. In this regard, Pressure Gain Combustion (PGC), which increases the pressure of the working fluid during the cycle heat addition process, has emerged as a very promising technology to significantly improve the performance of conventional gas turbines operating with isobaric combustion. The research work describes a comprehensive thermodynamic and techno-economic analysis of the gas turbine simple and combined cycle with innovative PGC at a wide range of operating conditions with practical cycle losses and novel steam integration strategies. This theoretical research was performed with the aim of developing a detailed understanding of real gas turbine cycles with PGC combustors in order to generate the best design guidelines for the development of more efficient, clean and sustainable power generation technologies for the future. Pressure gain combustion was represented by the zero-dimensional steady-state models of constant volume combustion (CVC) and rotating detonation combustion (RDC). All simulations were performed in two software tools, WTEMP (Web-based Thermo-Economic Modular Program) and WECoMP (Web-based Economic Cogeneration Modular Program), developed by the Thermochemical Power Group (TPG) at the University of Genova. Results of the on-design thermodynamic analysis showed that, compared to conventional Joule-based gas turbine simple cycle, the PGC gas turbines should be designed with a slightly lower cycle pressure ratio and high turbine inlet temperature (TIT). A higher TIT cycle was found to reduce the negative impact of practical losses in the PGC combustor. In the combined cycle configuration, the work advantage from PGC in the topping cycle was higher than the loss in bottoming cycle work from reduced gas turbine outlet temperature, which showed that PGC technology is beneficial in improving the overall performance of the combined cycles. Furthermore, exergy analysis of the PGC simple cycle showed that a combustor with pressure gain destroys less exergy than conventional constant pressure combustion in the cycle heat addition process, which is the largest source of exergy destruction in current gas turbines, which shows the exergy advantage of the PGC combustors. Moreover, the RDC combustor was found to be less beneficial than the CVC combustor at the cycle level due to its lower pressure gain. Integrating turbine blade cooling with the steam bottoming cycle through various strategies was found to significantly improve the efficiency and work output of the PGC combined cycles. Closed-loop steam cooling, in which both stator and rotor blades are steam cooled, offered the highest potential for performance improvement. The next best strategy was found to be Mixed loop steam cooling, in which the stator is steam cooled while the rotor is air cooled. It delivered slightly less performance but is easier to implement in practice. A novel, simple gas turbine layout with a mixer between the PGC combustor and turbine that decouples the combustor outlet temperature from the turbine and allows the combustor to provide maximum pressure gain through stoichiometric operation was found to further increase the benefit from pressure gain compared to the conventional gas turbine layout. This new layout also exploited the potential of steam cooling integration slightly more than the conventional layout. In terms of the techno-economic potential of a PGC combustor, a PGC simple cycle gas turbine with realistically expected pressure gain was found to significantly reduce the annual fuel consumption and carbon dioxide emission compared to conventional gas turbine power plants. Finally, a novel approach of cooling the gas turbine blades through the exhaust of a combined cycle was found to improve the carbon capture process in current combined cycles by reducing the exhaust flow rate and increasing the concentration of carbon dioxide in the exhaust, potentially enabling considerable technical and economic benefits in the carbon capture process of combined cycle power plants.