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In the gas turbine, gaps inevitably exist between the stationary and rotating parts. To improve the performance of gas turbines, tip leakage flow through the gaps must be minimized. The labyrinth seal increases the flow resistance by placing a number of teeth to minimize leakage flow. The labyrinth seal is still adopted in many fields because of its relatively high thermal resistance, simple structure, and wide pressure range. In this paper, the effects of geometric parameters (straight and stepped with solid land, tip clearance, number of teeth, and tooth front angle) on leakage flow were experimentally studied and the seal performance was described using the flow function. Also, flow visualization within the labyrinth seal was conducted using the Schlieren method. The dimensionless tip clearance (C/a) was adjusted from 0.8 to 3.3 (where a is tooth tip width) and the pressure ratio was adjusted from 1.1 to 3.0. The tooth front angle of the stepped seal was 90° and 60°. Results show that the flow function increased as the pressure ratio increased, however it tended to remain constant if the pressure ratio was higher than 2.0. At the same test condition, the flow function of the stepped labyrinth seal was smaller than that of the straight seal for all tested pressure ratios. Also, the seal performance was better for larger number of teeth, smaller tip clearance, and smaller tooth front angle cases. Based on the measured results, a new correlation for the labyrinth seals was suggested.

This study analyzes the performance of an integrated power generation system that combines a gas turbine combined cycle (GTCC) with a methanation process. The methanation process uses hydrogen provided by a power-to-gas (PtG) process and carbon dioxide captured from the exhaust gas of the GTCC. The research aim was to maximize the GTCC performance through an effective integration between the GTCC and methanation. Two methods were proposed to utilize the steam generated from the methanation process. One was to supply it to the steam turbine bottoming cycle of the GTCC, and the other was to inject it into the GT combustor. Also investigated was the injection of oxygen generated in the PtG process into the gas turbine combustor. The largest improvements in the power and efficiency were predicted to be 19.3 % and 4.9 % through the combination of the steam supply to the bottoming cycle and the oxygen injection to the combustor.

Phosphoric acid fuel cells (PAFCs) are appropriate for applications that require high-quality power because of their high reliability. We propose a system that combines an 11 MW PAFC and an organic Rankine cycle (ORC). The ORC recovers waste heat from the PAFC and produces power. The performance and economics of the system were simulated with changes in the working parameters of the PAFC and ORC to find economically optimal design conditions. The optimal working conditions with the best economic performance were found between the operating conditions with the maximum power and the maximum efficiency. The best design conditions were predicted for various ORC working fluids: the power was between 14.63 and 15.51 MW, and the efficiency was between 40.35 and 42.75 %. The maximum improvements of the power and efficiency over the stand-alone PAFC system were 41.77 % and 47.18 %, and the estimated payback period was around 5.50 years.

This study investigates the possibility of achieving 65 % efficiency in a gas turbine combined cycle. Several options to realize it were compared. A sensitivity analysis was performed for the latest H-class gas turbine in a simple cycle to quickly and easily predict the performance variation due to changes in each design parameter. When each design parameter was improved by the same percentage, the combined cycle efficiency was maximized by the improvement in turbine efficiency. The degree of increase in the combined cycle power was the largest when improving the turbine inlet temperature (TIT). To realize the turbine industry’s goal of 65 % efficiency in the combined cycle, the efficiency of the compressor and the turbine should be improved by 2 %, the TIT should be increased by 100 °C, and the pressure ratio should be increased from 23 to 32 in comparison to current H-class gas turbines. The possibility of improving the cycle performance was also investigated through modifications of the gas turbine cycle, such as reheating, inter-cooling, and recuperation. When reheating and recuperation were adopted simultaneously, a cycle efficiency of 65 % was possible with an increase of 1 % in both the compressor and turbine efficiencies, which is a moderate and practical improvement.

This study presents a performance prediction of triple combined cycles that use a solid oxide fuel cell (SOFC) and a gas turbine combined cycle (GTCC) with carbon capture technologies. Post- and oxy-combustion capture technologies were comparatively analyzed. The component design parameters of a commercial F-class gas turbine and SOFC were used. Minimizing the turbine inlet temperature (i.e., no extra fuel supplied to the combustor) resulted in higher net cycle efficiency. With post-combustion capture, the net cycle efficiency reached approximately 70 % when no fuel was supplied to the combustor, but the maximum CO2 capture rate was limited to 80 %. When a dual combined cycle was adopted, the CO2 capture rate increased to 91 %, while the net efficiency was approximately 69 %. With oxy-combustion capture, the optimum pressure ratio was higher than in the normal triple combined cycle, and the net cycle efficiency was lower than that of the post-combustion cycle. However, there was a critical advantage of a larger power output with nearly complete carbon capture. The impact of the location of the oxygen supply was examined in the oxy-combustion cycle with extra fuel supplied to the combustor, and supplying all the fuel to the SOFC improved the cycle performance.

Carbon capture and storage (CCS) technology has been studied actively in recent years to address global warming. This paper aimed to make a consistent comparison of different capture technologies applied to the natural gas-fired combined cycle (NGCC). Multiple power plant systems based on a standard NGCC using three different carbon capture technologies (post-combustion, pre-combustion, and oxycombustion) were proposed, and their net performance was compared. The optimal pressure ratio of the oxy-combustion technology system was obtained. The variations in the net cycle performance of the three systems were compared using the specific CO2 capture. The net power of the post-combustion capture scheme is lower than that of all other systems, but it has the highest efficiency. However, its biggest disadvantage is a much lower CO2 capture rate than the oxy-combustion capture which exhibits nearly 100 % capture rate. The conclusion is that the oxy-combustion capture would provide both the highest net efficiency and power output if a high capture rate of over 92 % was required.

The performance of gas turbine degrades as the operating hours accumulate, and compressor fouling is the dominant factor. Compressor fouling can increase the turbine inlet temperature (i.e., over-firing). The diagnosis of over-firing is important because it affects the performance and lifetime of the turbine. This paper proposes new performance diagnosis logic for gas turbines that considers over-firing. The aim is to eliminate the effects of over-firing due to the compressor fouling. The key feature is analyzing the performance degradation based on modification in the turbine inlet temperature. An in-house code was developed to realize the logic. First, the code was verified through a comparison with a commercial software package, GateCycle 6.1.2, using real operating data of an industrial gas turbine during almost two years. Then, virtual operation data under compressor fouling were generated and used for the validation of the logic. The conventional diagnostic logic could predict the degradation in usual operation but could not evaluate the actual performance degradation correctly in a power control operation where power generation should comply with the power demand. However, the new logic evaluated the exact performance degradation for the entire period analyzed. The results confirm the importance of considering over-firing for exact performance diagnosis.

Energy storage is becoming increasingly important for addressing the imbalance between power demand and supply. This study analyzes the performance of a dual system that combines compressed air energy storage (CAES) with a natural gas combined cycle (NGCC). The first was thermal integration, where the exhaust air from the CAES outlet is supplied to the bottoming steam cycle of the NGCC. The second was flow integration where some air from the CAES high-pressure expander outlet is injected to the gas turbine combustor of the NGCC. The reference design conditions were an inlet temperature of 900 °C for the low-pressure expander (LPE) of the CAES and a turbine inlet temperature of 1500 °C for the NGCC. Simple thermal integration could not improve the performance compared to independent operation, but the flow integration improved the power. An 8 % increase in power is expected at 20 % injection. When both the thermal and flow integrations were used simultaneously, the power increment decreased slightly, but the efficiency improved. An increase in the temperature of the LPE improves the CAES performance but reduces the synergistic effect from the integration with the NGCC.

Combined cycles using Solid oxide fuel cells (SOFCs) are expected to provide very high efficiency. The SOFCs are combined with a Gas turbine (GT) or a Gas turbine combined cycle (GTCC). The major SOFC design parameters greatly impact the combined cycle efficiency because the SOFC still produces a majority of the electricity in the combined cycles. In this paper, the influence of the SOFC’s fuel utilization on the efficiency of the combined cycles is carried out using parametric analysis. It is demonstrated and validated that an optimal fuel utilization exists. Four types of SOFC/GT and SOFC/GTCC combined cycles are analyzed. Each combined cycle is found to have an optimal fuel utilization, which is always lower than that of the SOFC-alone system. The main reason is that the turbine inlet temperature rises and thus GT or GTCC power increases with decreasing fuel utilization because of the increased remaining fuel after the cell stack. The value decreases as the power share of the turbomachinery part increases. The peak efficiencies of the SOFC/GT and SOFC/GTCC were predicted to be over 72 % and 76 %. The optimal fuel utilization corresponding to peak efficiency was 0.8 for the SOFC-alone system, 0.7 for the SOFC/GT system, and 0.6 for the SOFC/GTCC system.

In a steam turbine, leakage occurs at the gap between the rotor shafts and diaphragms and is injected into the main stream at the inlet of the rotor blade. Although this hub leakage flow is small, it affects the main flow, especially in the rotor passage. This study uses computational fluid dynamics to investigate the influence of hub leakage flow re-entry on the aerodynamic performance of turbine stages of a 10-stage high-pressure steam turbine operating at USC conditions. Each stage was individually investigated in regard to the influence of stage reaction on the efficiency drop. The flow field of the turbine without the leakage flow was analyzed first, and then the variations in flow phenomena and stage efficiency were investigated with increasing leakage flow ratio. Our analysis shows that the efficiency drop depends strongly on the stage reaction. The first stage designed with 21 % reaction showed an efficiency drop of approximately 1 % for 1 % increase in leakage flow, which is almost twice that of the last three stages with an average stage reaction of 48 %.

In this study, a program for analyzing the transient behaviors of heavy-duty gas turbines was developed. Focus was given to simulating a practical load-following operation. A distinct feature of our work is that all of the gas turbine components are modularized to enhance the expandability of the program. We used object-oriented programing for this purpose. Mass and energy balances and performance maps for the compressor and turbine were used for the modeling, and a multivariable numerical solving technique was used to enhance the numerical stability. The fundamental thermodynamic modeling of the program was validated by comparison of the transient response of a simulated gas turbine with that of a commercial program. PID control was adopted for simultaneous control of the rotational shaft speed and turbine exhaust temperature by the modulations of the fuel flow and the opening of the compressor inlet guide vane at the same time. The influence of the magnitude of load change and ramp rate was investigated. Stable control of the gas turbine was possible, even for a very rapid change of load.

We predicted the available maximum power output of Integrated gasification combined cycle (IGCC) plants under the operating limitations of a gas turbine. The power block of the IGCC using an F-class gas turbine was modeled, and its interactions of mass and energy with other components such as a gasifier and an air separation unit were considered. Variation in the gas turbine power output with nitrogen dilution was simulated, and the operating conditions under which the power should be limited below an allowable maximum were determined. The maximum net power output of the IGCC plant under the restrictions of syngas turbine power (232 MW) and blade temperature were estimated in a wide range in terms of ambient temperature and integration degree, and the optimal integration degree for each ambient temperature is suggested. At relatively high temperatures over 19°C, zero integration degree (air for the air separation unit is supplied solely from the ambient) provides the highest net power output and efficiency. As ambient temperature decreases, a higher integration degree provides higher net power. The optimal net IGCC power output varies from 260 MW to 347 MW (33%) in the ambient temperature range of 40°C to -10°C, while the optimal net efficiency varies by about one percentage point.

We investigated key design features of the integrated gasification solid oxide fuel cell/gas turbine (IG-SOFC/GT) system including carbon dioxide capture. Two different types of system configurations that depend on the carbon dioxide capture scheme (pre- and oxycombustion captures) were examined. Research focus was given to the effect of the gas turbine specification on the performance of the entire system. IG-SOFC/GT systems using two different gas turbines were analyzed, and their performances were compared. A parametric analysis was carried out to further understand the performance comparison. We found that the net system efficiency was not very sensitive to the turbine inlet temperature and the pressure ratio. As a result, similar net efficiencies were observed between the systems using two gas turbines with quite different specifications. In addition, a revision of the system layout was investigated and it was found that the power capacity of the system could be increased and the system efficiency could also be slightly enhanced by supplying nitrogen separated from the air separation unit to the fuel cell rather than to the gas turbine combustor.

The influence of steam injection and hot gas bypass on the performance and operation of a combined heat and power (CHP) system using a recuperative cycle gas turbine was investigated. A full off-design analysis was used to investigate not only the change in performance but also the variation in engine operation caused by steam injection. The performance improvement capability and operating limitations of full steam injection was examined. Selected operations (partial steam injection and underfiring) that secure minimum compressor surge margin were comparatively analyzed. Partial steam injection was found to be a better option than underfiring in all thermodynamic aspects. Under ISO condition, power and efficiency improvements in the partial injection targeted at a 10% surge margin are 27% and 7.4%, respectively. This study also investigated the increase in steam generation brought by the bypass of turbine exhaust gas around the recuperator. This bypass provided high operational flexibility by varying the capacity of thermal energy supply in both the pure CHP operation and the steam-injected operation. In particular, in the steam-injected operation, the capacity of thermal energy supply can be largely increased by the said bypass, while producing a greater power output than the pure CHP system.

This paper presents models for simulating the operation of a polymer electrolyte membrane fuel cell (PEMFC) system and the results of the dynamic simulations. The entire system included a PEMFC stack and balance-of-plant components such as an air supply blower, a membrane humidifier, a fuel supply unit, and a heat management unit. Mathematical modeling for the computation of power generation and heat transfer of the PEMFC stack, the heat and mass transfer of the humidifier, and the energy transfer of the cooling system was set up. Theoretical and experiential data such as the voltage-current density relationship of the cell stack and the performance maps of blowers and pumps, together with semi-theoretical heat and mass transfer equations, were used to represent the characteristics of all the components. The effect of the thermal inertia of solid parts was considered in the fuel cell stack, the membrane humidifier, and the radiator. System dynamic behaviors under various operating conditions due to changes in stack current and ambient temperature were predicted. The sudden abnormal operations of the cooling water circulation pump and the radiator fan were also simulated as an example of component malfunctions.

Polymer electrolyte membrane fuel cells (PEMFCs) have many good characteristics for small power sources such as low operating temperature and high power density. In this study, the effects of thermal management on the performance of PEMFC systems using natural gas fuel, and the effects of integrating PEMFC systems with turbomachines, were investigated. Firstly, performance of various system configurations differing in the thermal management of reforming and stack cooling processes was comparatively analyzed. Then, various integrated system combinations with turbomachines (compressors and turbines) were analyzed. We performed a parametric analysis of the influence of turbine inlet temperature and compressor pressure ratio on system performance, and a 10% difference in efficiency among four simple PEMFC systems was predicted. Pressurization of the PEMFC with adequate thermal management may improve system efficiency, while efficiency enhancement from corresponding simple PEMFC systems was hard to achieve in the ambient pressure integrated systems.

Balance-of-plant components, especially the air supply system, have a critical impact on the operating condition, performance, and reliability of polymer electrolyte fuel cells (PEMFCs). Thus, we investigated the performance and operating characteristics of a coupled system integrating a PEMFC and an air supply unit. The performance characteristics of the fuel cell stack were modeled using a semi-experimental correlation, and the operating characteristics of a shell-and-tube type membrane humidifier was modeled using heat and mass transfer principles. The models of both components were validated. A turbo-blower determined the condition of the air supplied to the humidifier and its characteristics were modeled using a performance map. A program was developed to simulate the operation of a PEMFC system consisting of the fuel cell stack and the air supply unit, and its operating characteristics at various conditions were investigated. In particular, the effects of operating conditions (ambient temperature and load) on the performance of both the humidifier and the fuel cell stack were examined, and the variations of critical operating parameters were analyzed.

With increasing concerns on global warming, reduction of CO2 emission has become a hot issue and studies of CO2 capture and storage (CCS) technology in power plant applications are in progress. Oxy-fuel combustion is one of the several available technologies that intend to capture CO2. Since the combustion gas consists mainly of CO2 and H2O in oxy-fuel combustion systems, it is easy to separate CO2 from the flue gas using a simple mechanical method instead of complex chemical processes. There have been suggested a couple of power cycles using different recirculation fluids for combustion dilution purpose. This study aimed to investigate the influence of CO2 capture on the performance of two promising oxy-fuel combustion power cycles adopting H2O and CO2 as the recirculation fluid. Optimal integration between the carbon capture process and the power cycle was examined and the influences of carbon capture on the entire system performance were compared for the two cycles.

This study analyzed the influence of configuration and clearance on the leakage behavior of labyrinth seals. Both computational fluid dynamics (CFD) and an analytical tool were used to predict the leakage flow of two different (straight and stepped) seal configurations with various clearances. The predicted results were compared with experimental data. The CFD gives a better agreement with the experimental result than the analytical model on average. In the straight seal, the dependence of the discharge coefficient on the clearance is considerable, while it is much smaller in the stepped seal. The CFD captures the entire behavior sufficiently well, but the analytical model overpredicts the clearance dependence in the stepped seal. The CFD also predicts well the influence of the flow direction on the leakage flow. The advantage of the stepped seal over the straight seal becomes more evident as the clearance gets larger. As the clearance becomes sufficiently small, the advantage of the stepped seal reduces.

This study analyzed the influence of steam injection on the performance of hybrid systems combining a solid oxide fuel cell and a gas turbine. Two different configurations (pressurized system and ambient pressure system) were examined and the effects of injecting steam, generated by recovering heat from the exhaust gas, on system performances were compared. Performance variations according to the design of different turbine inlet temperatures were examined. Two representative gas turbine pressure ratios were used. Without steam injection, the pressurized system generally exhibits higher system efficiency than the ambient pressure system. The steam injection augments gas turbine power, thus increasing the power capacity of the hybrid system. The power boost effect due to the steam injection is generally greater in the relatively higher pressure ratio design in both the pressurized and ambient pressure systems. The effect of the steam injection on system efficiency varies depending on system configurations and design conditions. The pressurized system hardly takes advantage of the steam injection in terms of system efficiency. On the other hand, the steam injection contributes to the efficiency improvement of the ambient pressure system in some design conditions. In particular, a higher pressure ratio provides a better chance of efficiency increase due to the steam injection.

In this work, component characteristics of a reheat cycle gas turbine in a commercial combined cycle power plant were evaluated. An inverse performance analysis, in which component characteristic parameters were estimated based on measured performance data, was carried out. The measured parameters were the power, the fuel flow rates of two combustors, and the temperatures and pressures at various locations such as the compressor discharge, exits of both the high-and low-pressure turbines. The estimated parameters from the analysis include the compressor and turbine efficiencies and the inlet air flow rate. The analysis was performed for a wide operation range in terms of the ambient temperature and load, providing a database for the variations of the characteristic parameters with changes in the operating condition. In addition, a sensitivity analysis was performed to examine the influence of the uncertainties of the measured parameters on the estimated parameters. The analysis program can be further developed into a performance diagnosis tool and the obtained component characteristic data can be used as reference database.

This paper presents analysis results for the hybrid power system combining a solid oxide fuel cell and a gas turbine. Two system layouts, with the major difference being the operating pressure of the fuel cell, were considered and their thermodynamic design performances were compared. Critical temperature parameters affecting the design performances of the hybrid systems were considered as constraints for the system design. In addition to energy analysis, exergy analysis has been adopted to examine the performance differences depending on system layouts and design conditions. Under a relaxed temperature constraint on the cell, the ambient pressure system exhibits relatively larger power capacity but requires both higher cell temperature and temperature rise at the cell for a given gas turbine design condition. The pressurized system utilizes the high temperature gas from the fuel cell more effectively than the ambient pressure system, and thus exhibits better efficiency. Under a restricted temperature constraint on the cell, the efficiency advantage of the pressurized system becomes manifested.

This study aims to analyze engine performance and component characteristics of a micro gas turbine based on detailed measurement of various parameters. A test facility to measure performance of a micro gas turbine was set up and performance parameters such as turbine exit temperature, exhaust gas temperature, engine inlet temperature, compressor discharge pressure and temperature, and fuel and air flow rates were measured. The net gas turbine performance (power and efficiency based on the gas turbine shaft end) was isolated and analyzed. With the aid of measurement based simulation, component characteristic parameters such as turbine inlet temperature, compressor efficiency, turbine efficiency and recuperator effectiveness were estimated. Behaviors of the estimated characteristic parameters with operating condition change were examined and sensitivities of estimated parameters to the measured parameters were analyzed.

This study analyzes the design and part load performance of a power generation system combining a micro gas turbine (MGT) and an organic Rankine cycle (ORC). Design performances of cycles adopting several different organic fluids are analyzed and compared with performance of the steam based cycle. All of the organic fluids recover greater MGT exhaust heat than the steam cycle (much lower stack temperature), but their bottoming cycle efficiencies are lower. R123 provides higher combined cycle efficiency than steam does. The efficiencies of the combined cycle with organic fluids are maximized when the turbine exhaust heat of the MGT is fully recovered at the MGT recuperator, whereas the efficiency of the combined cycle with steam shows an almost reverse trend. Since organic fluids have much higher density than steam, they allow more compact systems. The efficiency of the combined cycle, based on a MGT with 30 percent efficiency, can reach almost 40 percent. Also, the part load operation of the combined system is analyzed. Two representative power control methods are considered and their performances are compared. The variable speed control of the MGT exhibits far better combined cycle part load efficiency than the fuel only control despite slightly lower bottoming cycle performance.

Deteriorated performance data of a micro gas turbine were generated and the artificial neural network was applied to predict the deteriorated component characteristics. A program to simulate operation of a micro gas turbine was set up and deterioration of each component (compressor, turbine and recuperator) was modeled by changes in the component characteristic parameters such as compressor and turbine efficiency, their flow capacities and recuperator effectiveness and pressure drop. Single and double faults (degradation of single and two parameters) were simulated. The neural network was trained with a majority of the generated deterioration data. Then, the remaining data were used to check the predictability of the neural network. Given measurable performance parameters as inputs to the neural network, characteristic parameters of each component were predicted and compared with original data. The neural network produced sufficiently accurate prediction. Using a smaller number of input parameters decreased prediction accuracy. However, an acceptable accuracy was observed even without information on several input parameters.