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Title: Study of closed-cycle gas turbine for application to small modular reactors (SMRs) and coal-fired power generation through modelling and simulation
Author: Olumayegun, Olumide
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Closed-cycle GT has the potential for improved efficiency of electricity generation, compact and simple design, and reduced CO2 emissions and therefore could complement conventional power conversion systems (PCSs). However, power generation from closed-cycle GT needs to be demonstrated to establish the integrity, operation and performance of the plant before commercial deployment can be realised. This thesis provides an understanding, through modelling and simulation, of the thermodynamic performance and component design parameters, and the dynamic behaviours, operation and control of closed-cycle GTs for the purpose of assessing their feasibility for near-term demonstration. A systematic, full-scope study was performed for nitrogen closed-cycle GT coupled to small modular sodium-cooled fast reactor (SM-SFR) and supercritical carbon dioxide (s-CO2) closed-cycle GT coupled to small modular pressurised water reactor (SM-PWR). The study included selection between alternative plant designs, steady state performance analysis, preliminary design of components, dynamic model development and simulation of plant transients, and design of control systems. Additionally, performance evaluation was performed for s-CO2 closed-cycle GT for application to coal-fired power generation integrated with solvent based PCC. Intercooled closed-cycle GT using nitrogen as working fluid and with a single shaft configuration has been one common PCS option for possible near-term demonstration of SFR. In this work, a new nitrogen cycle configuration was proposed to further simplify the design of the turbomachinery and reduce turbomachinery size without compromising the cycle efficiency. Mathematical models in Matlab were developed for steady state thermodynamic analysis of the cycles and for preliminary design of the heat exchangers, turbines and compressors. The study indicated that the new configuration has the potential to simplify the design of turbomachinery, reduce the size of turbomachinery and provide opportunity for improving the efficiency of the turbomachinery. Dynamic model of the new nitrogen cycle power plant was developed in Matlab/Simulink. Control schemes, which enables the plant to satisfy the operational requirements under load-following and loss-of-load conditions, were implemented. Inventory control is unable to keep the generator speed within the specified ±30 rpm of the synchronous speed during normal load-following operation. However, bypass valve control is able to maintain the generator speed within ±17 rpm of the synchronous speed. Maximum generator shaft overspeed is below 105% during sudden loss-of-load condition, which is below the 120% maximum limit. Hence, stable and controllable operation of the nitrogen GT power plant is possible. Matlab models were developed for thermodynamic performance analysis and preliminary design of components for s-CO2 closed-cycle GTs coupled to SM-PWR. Recompression s-CO2 layout is the most common configuration for s-CO2 cycle power plant. However, the performance assessment of the recompression s-CO2 cycle for application to PWR shows that temperature of the turbine exhaust is too low to allow any meaningful recuperation in the high temperature recuperator. Hence, a new layout is suggested. The efficiency of the new layout is comparable to that of the recompression cycle and higher than that of the simple recuperated cycle layout. Investigation of the impact of heat exchanger design on plant performance showed that the recompression cycles have higher pressure losses than the simple recuperated cycle. Therefore, if the heat exchanger design and pressure loss is considered in performance evaluation, the recompression cycles might not be that superior to the simple cycle. However, parametric analysis indicated that the new layout is the most promising for application to PWR. Dynamic modelling, simulation and control system design was also carried out for the new s-CO2 layout coupled to SM-PWR. Inventory/pressure control is not considered to avoid issues associated with the rapid variation of CO2 properties around the critical point. To effectively control the plant, flow split control and throttle valve were added to the normal control systems (bypass valve, control rod, coolant pump and cooling water control). The change in shaft speed during load-following operation is about ±27 rpm while shaft overspeed during loss-of-load is about 107% of the synchronous speed. These are all within the allowable shaft speed limit. Aspen Plus simulation was performed to evaluate the thermodynamic performance of cascaded s-CO2 cycles coupled to coal-fired furnace and integrated with 90% post-combustion CO2 capture. Three bottoming s-CO2 cycles were investigated: simple recuperated cycle, partial heating cycle and the newly proposed s-CO2 cycle. Results for a 290 bar and 593 0C power cycle without CO2 capture showed that the configuration with the new cycle as bottoming cycle has the highest plant net efficiency of 42.96% (HHV), followed by the simple recuperated, 42.46% and the partial heating, 42.44%. Integration of CO2 capture reduced the efficiencies of the new cycle, the simple recuperated and the partial heating configurations to 31.76%, 31.22% and 31.13% respectively. Without CO2 capture, the efficiencies of the coal-fired supercritical CO2 cycle plants were about 3.34-3.86% point higher than the reference steam cycle plant and about 0.68-1.31% point higher with CO2 capture. The findings so far underscored the promising potential of cascaded s-CO2 power cycles for coal-fired power plant application.
Supervisor: Wang, Meihong Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available