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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.

As the proportion of power generation using renewable energy increases, it is important to improve the operational flexibility of gas turbines (GTs) for the stability of power grids. Increasing the ramp-rate of GTs is a general solution. However, a higher ramp-rate increases the turbine inlet temperature (TIT), its rate of change, and the fluctuation of the frequency of produced electricity, which are negative side effects. This study proposes a method to optimize the set-point schedule for a PID controller to improve the ramp-rate while decreasing the negative impacts. The set-point schedule was optimized for a 170-MW class GT using a genetic algorithm to minimize the difference between the value of the process variable and the set-point value of the conventional control. The advanced control reduced the fluctuation of the rotation speed by 20% at the reference ramp-rates (12 MW/min and 15 MW/min). The maximum TIT decreased by 6.3 °C, and its maximum rate of change decreased from 0.7 °C/s to 0.4 °C/s. The advantage of the advanced control becomes more marked as the ramp-rate increases. Even at a much higher ramp-rate (50 MW/min), the advanced control decreased the rotation speed fluctuation by 40% in comparison to the conventional control at the reference ramp-rate.

A new type of stepped seal with a ribbed casing is proposed to efficiently reduce the leakage at the tips of turbine blades. The leakage characteristics of two different types of labyrinth seals (conventional seal vs. ribbed seal) were compared and analyzed through computational fluid dynamics (CFD) in a wide operating range of pressure ratios and clearances. The analysis showed that the ribbed seal has superior leakage performance to the conventional seal at all clearance sizes. With the same clearance size (S/H = 1.0), the flow function of the ribbed seal was approximately 21.5–42.6% less than that of the conventional seal. Also, different trends of variation in the flow function according to the increase of the clearance were found between the conventional and ribbed seals. The leakage flow inside the labyrinth seal was analyzed to explain the cause of this difference in tendency, and it was confirmed that the added ribs cause collision between the leakage flow and the tooth wall, even with the increase of the clearance. Also, the ribbed seal enables operation at a larger clearance with the same leakage performance when comparing the absolute leakage flow rate of the two seals. In addition, a parametric study on the influence of the rib height and rib inclination angle revealed that the flow function generally decreases as both parameters increase.

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.

Manufacturers are trying to increase ramp rates to improve the operational flexibility of gas turbines. However, higher ramp rates lead to rapid variation in the combustion gas temperature and shorten the life of the turbine. To increase the rate without reducing the life, this study considers the use of a compressed air energy storage (CAES). Injecting pressurized air that is stored in CAES into the combustor of a gas turbine increases the power output of the gas turbine without increasing fuel supply. Therefore, the ramp rate of the turbine can be increased while suppressing the temperature change of the combustion gas. The injection schedule was optimized through a dynamic simulation to increase the ramp rate. A genetic algorithm was used in the optimization of the schedule. The optimized schedule turned out to be a simple form consisting of a linear increase and decrease in the injection flow rate. Furthermore, despite the increased ramp rate, the fluctuation of turbine inlet temperature could be maintained under a safe level due to the optimized compressed air injection.

Gas turbines are likely to face critical situations such as compressor surge and stall in the sub-idle operation region. Thus, it is important to predict the operation characteristics of gas turbines accurately by using simulations in the sub-idle region. However, sufficient information about the component performance maps in the sub-idle region is generally not available, and extrapolation methods are usually used to generate data. However, extrapolation methods tend to generate physically invalid data points in very low-speed regimes, which sometimes cause critical numerical problems in simulations of engine performance. This study proposes a new method to generate performance data in the sub-idle region of turbine performance maps through interpolation. A zero point is introduced where the pressure ratio is one and the mass flow rate is zero. Performance data were generated between the existing performance curve and the zero point using the interpolation. To validate the proposed method, it was applied to publicly available turbine performance maps. It was confirmed that the proposed method improves the numerical matching between the compressor and turbine maps and thus expands the predictable operating regime by as much as 23.3% compared to a conventional extrapolation method.

An integrated gasification combined cycle (IGCC) power plant uses fuel made by coal gasification for gas turbines. The oxygen required for the gasification reaction is supplied using a cryogenic air separation unit (ASU), and a large amount of nitrogen is generated. In the conventional IGCC, nitrogen generated in the ASU is injected into the combustor to generate more power. However, since the temperature of the injected nitrogen is lower than that of the air supplied to the combustor, injecting nitrogen requires more fuel to maintain a constant outlet temperature (i.e., turbine inlet temperature (TIT)). We propose a novel system configuration to improve the performance of the IGCC and analyzed its effects. We used nitrogen generated in the ASU as a turbine blade coolant instead of compressed air. Since the nitrogen temperature was lower than the temperature of compressed air, the turbine blades can be protected with a lower flow rate of coolant. As a result, both the power and efficiency are increased. We also investigated possibilities for further performance improvement by changing design parameters and determined the design point that maximizes the efficiency.

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.

Distributed power generation is gaining attention as a solution for the transmission loss and site selection in centralized power generation. Polymer-electrolyte membrane fuel cells (PEMFCs) are suitable as a distributed power source for residential areas because of their high efficiency and low environmental impact. This study proposes a combined power generation system for recovering waste heat from both the cell stack and the reformer of a PEMFC by applying an organic Rankine cycle (ORC). The best working fluid with the highest ORC power output (i.e., the highest combined system efficiency) was identified through a parametric study of different working fluids. An economic analysis was also performed for different working fluids, waste heat sources, and types of system operation. The results show that the installation cost of the ORC can be recovered within the fuel cell's lifetime in all design cases. Greater cumulative profit can be generated by maintaining the same power output as the stand-alone PEMFC system for greater efficiency than when increasing the power output to sell surplus power. The results demonstrate that the optimal heat recovery from the PEMFC system is both thermodynamically and economically beneficial.

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.

A critical issue concerning the gas turbine is that its power decreases considerably with increasing ambient temperature. Recently, it was proposed to maximize the power output of gas turbines in hot seasons through the simultaneous cooling of inlet air and hot parts cooling air, using an absorption chiller. This study serves to expand this concept and applies simultaneous cooling to combined cycle power plants using an H-class engine, the latest gas turbine model. Two methods for coolant pre-cooling were comparatively investigated and the best option was selected. The proposed dual cooling was compared with other conventional cooling schemes and their combinations. These include simple inlet air cooling using a mechanical chiller or an absorption chiller, and the combination of each of these schemes with independent cooling of the coolant by ambient air. The maximum degrees of coolant pre-cooling and inlet air cooling using the largest capacity commercial absorption chiller were predicted to be 45 K and 11 K, respectively, and the power boost of the combined cycle plant was estimated to be 8.2%, which was larger than that obtained with any other scheme. An economic analysis confirmed the feasibility of the dual cooling scheme.

The turbine inlet temperature (TIT) has a significant effect on the performance of gas turbines, and enhanced cooling methods are being applied to the latest gas turbines to increase this temperature. The coolant pre-cooling (CPC) is also used to improve the cooling performance. In this study, coolant inter-cooling (CIC) is proposed to reduce the coolant temperature and improve the gas turbine performance further. The air required for turbine cooling is extracted from the middle of the compressor, cooled, and pressurized by a separate compressor. This decreases both the coolant temperature and the power needed to compress it. The effect of CIC on the performance of a combined cycle power plant was analyzed in comparison with the conventional CPC method using an H-class gas turbine. A heat recovery system was considered to collect the heat wasted in the coolant cooling process and generates additional steam in the bottoming cycle. Various locations of the water source for the heat recovery were compared, and the optimal ones were selected. The proposed method enables higher power output and efficiency in a combined cycle power plant than the CPC method.

This study evaluated the leakage characteristics of a stepped labyrinth seal. Experiments and computational fluid dynamics (CFD) analysis were conducted for a wide range of pressure ratios and clearance sizes, and the effect of the clearance on the leakage characteristics was analyzed by determining the performance of the seal using a dimensionless parameter. It was observed from the analysis that the performance parameter of the seal decreases as the clearance size increases, but it tends to increase when the clearance size exceeds a certain value. In other words, it was revealed that there exists a specific clearance size (Smin) which minimizes the performance parameter of the seal. To identify the cause of this tendency change, a flow analysis was conducted using CFD. It was confirmed that the leakage characteristics of the stepped seal are affected by the size of the cavity, which is the space between the teeth. Therefore, a parametric study was conducted on the design parameters related to the cavity size (tooth height and pitch). The results show that the performance parameter decreases as the tooth height and pitch decreases. Moreover, Smin increases as the tooth height increases and the pitch decreases.

Extending the operating range and improving the partial load efficiency of the gas turbine combined cycle (GTCC) is becoming increasingly important. This paper proposes a novel method to achieve the two goals simultaneously. To fulfill the research objective, the combination of exhaust heat recuperation and inlet bleed heating (IBH) was adopted and evaluated. A cycle simulation was conducted to confirm whether the research goal could be achieved. A recuperator was installed between the compressor and combustor of the gas turbine, and the degree of heat recuperation was modulated during partial load operation to enhance the cycle efficiency compared to the conventional GTCC plant. In contrast to the conventional GTCC plant, the recuperation ratio was modulated before control of the variable inlet guide vane (VIGV) began. This means that the recuperation control covers the high partial load regime. The gas turbine power remained almost constant in this regime because the inlet flow rate and turbine inlet temperature were kept constant. In contrast, the power of the bottoming cycle decreased with increasing recuperation ratio due to the decrease in exhaust gas energy. After the recuperation ratio reached a limit, the load control was the same, as in conventional plants: VIGV control followed by fuel only control. The purpose of using IBH was to reduce CO emissions in the low load regime. Some of the compressor discharge air was recirculated to the compressor inlet, and the combustion temperature was maintained at a high level. The simulation showed that both IBH and recuperation are effective in extending the operating range. The predicted reduction in the turndown ratio was approximately 10%p. The partial load efficiency improvement by the recuperation was sensible. The efficiency remained higher than the full load efficiency over a wide partial load range. The efficiency of the recuperated GTCC was 4.1%p higher at 50% power than that of the conventional GTCC.

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.

The major cause of the performance degradation of industrial gas turbines is compressor fouling due to airborne contaminants. Performance diagnostics is required to evaluate degradation precisely. In general, the measured performance in the fully opened inlet guide vane (IGV) condition is regarded as full-load performance and used for diagnostics. A new diagnostic method is proposed in this study. A scheme to determine whether the measured performance is at full-load operation is suggested. If operation is not at full-load, a virtual gas turbine state corresponding to the measured data is modeled using adaptive modeling. Then, the virtual full-load performance and the corrected performance are predicted using a reference firing temperature. This calculation methodology is applied to almost two-years of data of a 150 MW class gas turbine. The analysis revealed that the maximum reduction of power output and efficiency are 14.8 MW and 0.8 percentage points compared with the rated performance. In addition, it was shown that if the measured performance is used directly, the maximum deviation in the predicted power degradation was as much as 4.9 MW (2.8%) compared with the rated performance. This paper demonstrates the necessity of a model-based analysis for enhancing the accuracy of performance diagnostics.

Micro gas turbines are manufactured to have a compact structure and small volume, which makes them more vulnerable to internal leakages compared to heavy-duty gas turbines. Accordingly, precise diagnosis of the performance degradation in a micro gas turbine is important. This study investigates the characteristics of degradation. Performance maps were used for the compressor and turbine, and a multi-segment counter-flow heat exchanger model was used for the recuperator. The component models were refined using actual operation data, resulting in precise simulation of the reference operation without leakage. A performance analysis was carried out, and the results were analyzed for three types of leakage with the following paths: from the compressor outlet to the recuperator’s cold-side outlet, from the compressor outlet to the combustor outlet, and from the combustor inlet to the turbine outlet. The third path produced the largest reduction in engine efficiency. The degradations were also compared with those related to compressor fouling and turbine erosion, which are the most common causes of degradation in a gas turbine. Even when qualitatively similar performance changes were observed, the root cause could be determined by analyzing differences in performance parameters such as the fuel flow.

Optimization of the sizing and operation strategy of a complex energy system requires a large computational burden because of the non-linear nature of the mathematical problem. Accordingly, using a conventional numerical method with only a physics-based model for complete optimization is impractical. To resolve this problem, this paper adopted an optimization method of using an artificial intelligence scheme that combines an artificial neural network (ANN) and a genetic algorithm (GA). Especially, the ANN was constructed based on results from a physics-based model to obtain a large amount of accurate simulation data in a short time frame. A distributed generation (DG) system based on a gas turbine (GT) and renewable energy (RE) was simulated to demonstrate the usefulness of the optimization method. In consideration of the capacity and partial load performance of the GT, the optimization of the sizing and operation strategy of the DG system was performed for three system design scenarios. The optimization criteria were cost-effectiveness and eco-friendliness. The method reduced the calculation time by more than three orders of magnitude while maintaining the same accuracy as the physics-based model. The approach and methodology are expected to be applicable to accurate and fast optimization of various sophisticated energy systems.

Because of the increasing challenges raised by climate change, power generation from renewable energy sources is steadily increasing to reduce greenhouse gas emissions, especially CO2. However, this has escalated concerns about the instability of the power grid and surplus power generated because of the intermittent power output of renewable energy. To resolve these issues, this study investigates two technical options that integrate a power-to-gas (PtG) process using surplus wind power and the gas turbine combined cycle (GTCC). In the first option, hydrogen produced using a power-to-hydrogen (PtH) process is directly used as fuel for the GTCC. In the second, hydrogen from the PtH process is converted into synthetic natural gas by capturing carbon dioxide from the GTCC exhaust, which is used as fuel for the GTCC. An annual operational analysis of a 420-MW-class GTCC was conducted, which shows that the CO2 emissions of the GTCC-PtH and GTCC-PtM plants could be reduced by 95.5% and 89.7%, respectively, in comparison to a conventional GTCC plant. An economic analysis was performed to evaluate the economic feasibility of the two plants using the projected cost data for the year 2030, which showed that the GTCC-PtH would be a more viable option.

Performance and economic feasibility analysis was conducted on compressed air energy storage (CAES), where steam injection was applied. The pressure and temperature of the stored air change according to the operation of the CAES, having a great influence on the performance of the system. Considering this, the off-design analysis model was applied to each component. Dimensionless performance maps were applied to each compressor and turbine. A conventional CAES (C-CAES) was modeled based on commercialized CAESs, and a steam-injected CAES (SI-CAES) was then devised by adding a heat recovery steam generator. The system was assumed to store compressed air during the off-peak time and generate power during the peak time. The electricity generation of SI-CAES was predicted to be 7% greater than that of C-CAES but the efficiency decreased by approximately 0.8%. The estimated payback period was less than 6.5 years. If the heat recovery is added to the compression process, the efficiency increases. It was predicted that the heat recovery would result in a longer payback period but the maximum would be less than 10 years. Overall, steam injection is an effective method for augmenting the power generation of CAES for peak load management.

This study proposes a system layout that provides a very high efficiency of around 75% while achieving an extremely high carbon capture rate approaching 100%. The system is a quadruple power generation system combined with an oxy-combustion carbon capture which allows for a very small efficiency penalty. The quadruple system produces power from a solid oxide fuel cell, molten carbonate fuel cell, gas turbine, and organic Rankine cycle. Through a comparison among post-combustion, pre-combustion, and oxy-combustion carbon capture techniques, the oxy-combustion capture system was selected as a candidate for the zero-carbon emission system because it turned out to exhibit the highest efficiency. A parametric analysis revealed that only five of eight design parameters affect the carbon capture rate. The results of the parametric analysis were used for an artificial intelligence method combining an artificial neural network and a genetic algorithm to maximize both the carbon capture rate and system efficiency. As a result, the efficiency penalty was minimized while achieving zero carbon emission. The net efficiency of the resulting carbon-free oxy-combustion system was predicted to be 75.4%, which is only 2.7% points lower than that of a reference oxy-combustion system without carbon capture.

A recuperator was applied to the semi-closed oxy-fuel combustion combined cycle (SCOC-CC) to reduce its very high optimal design pressure ratio to a feasible level. The recuperator was installed in different locations in the heat recovery system: (1) before the entire heat recovery steam generator (HRSG) of the bottoming steam cycle and (2) before the HP evaporator of the HRSG. Component design parameters from state-of-the-art gas turbines (F and H classes) were used. A thermodynamic cooling model was used to estimate the reasonable amount of turbine coolant needed to maintain the turbine blade temperature of each stage at a feasible level. The turbine stage efficiency was corrected while considering the effect of turbine blade loading. The optimal pressure ratio ranges in terms of net system efficiency were found, and the influence of the recuperator effectiveness on the cycle performance was investigated. The optimal pressure ratio of the recuperated SCOC-CC was about 40–50, which was considerably lower than that of the simple SCOC-CC. The net efficiency of the recuperated SCOC-CC increased by as much as 0.6 and 1.3 percentage points in the F- and H-class gas turbines cases, respectively. The benefits of the recuperated cycle were discussed.

In this study, two heat recovery systems, a Rankine cycle (ORC) and a trans-critical CO2 cycle (tCO2), were applied to a micro gas turbine(MGT) and their performance was compared. The off-design performance of the two bottoming cycles with the load variation of the MGT was also analyzed. The performance curve, the effectiveness-NTU method, and the Stodola’s equation were used to model the off-design operations of all bottoming cycle components, such as a pump, a turbine and heat exchangers. According to the calculations, the power output of the ORC was higher than that of the tCO2 cycle when the MGT operated at a full load. On the other hand, because the power output variation with the MGT load change is larger in the ORC, the power output of tCO2 becomes larger when MGT operates at a part load below 75%. Therefore, the tCO2 is suitable for a heat recovery system utilizing MGT exhaust gas in places where the MGT needs to operate at low loads during many of its operating hours. On the other hand, the ORC is more suitable in applications where the MGT can operate at near full load conditions.

The use of brush seals in turbomachinery has increased steadily in recent years because they reduce leakage and improve operating stability. This study evaluates the performance enhancement of a 500 MW-class steam turbine plant that results from replacing conventional seals with brush add-up seals for the inter-stage packing seal locations. Leakage flow rates of all seal locations in high- and intermediate-pressure turbines were estimated, and the brush add-up seal was found to reduce leakage by 50–68%. The entire power plant was simulated using a stage-by-stage turbine model and stage efficiency correction. With the advanced seals in all inter-stage locations of the high- and intermediate-pressure turbines, 0.44% and 0.33% increases in power output and efficiency were predicted. A larger performance benefit was observed with the installation in the high-pressure turbine. An economic analysis shows that the seal replacement is quite cost-effective. The predicted net present value was quite large compared to the initial cost, and the estimated payback period was less than a year. The replacement in all the high-pressure turbine stages and in the front stages of the intermediate-pressure turbine stages has the highest business value.

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.

A precise prediction of the power generation capacity of each power plant in an electric grid is important for managing the grid stably by preventing mismatch between the electric demand and power production. This prediction also helps power plant owners maintain their facilities because it allows effective performance monitoring. This paper proposes a unique analysis tool for predicting the near-term power generation capacity of cogeneration combined cycle power plants using correction curves and real operating data. The plant operation was simulated using the well-simulated design performance and an off-design calculation model consisting of performance correction curves and thermodynamic modeling. Real operation data of several seven-day periods were simulated using the developed tool. The data of the first five days was used as a tool set up leading to a calculation of the power correction factor. The obtained power correction factor reflected the performance degradation quite well. The data of the last two days was used for tool validation. The discrepancy between the predicted and measured power outputs were less than 2%. The proposed method can be used for both performance monitoring and a prediction of the power generation capacity of gas turbine-based power plants.

There has been increasing demand for cogeneration power plants, which provides high energy utilization. Research on upgrading power plant performance is also being actively pursued. The organic Rankine cycle (ORC) can operate with mid- and low-temperature heat sources and is suitable for enhancing performance of existing power plants. In this study, an off-design analysis model for the ORC was developed, which is driven by waste heat or residual heat from a combined cycle cogeneration plant. The applied heat sources are the exhaust gas from the heat recovery steam generator (Case 1) and waste heat from a heat storage unit (Case 2). Optimal design points of the ORC were selected based on the design heat source condition of each case. Then, the available ORC power output for each case was predicted using actual long-term plant operation data and a validated off-design analysis model. The ORC capacity of Case 2 was almost two times larger than that of Case 1. The predicted average electricity generation of both cases was less than the design output. The results of this paper reveal the importance of both the prediction of electricity generation using actual plant operation data and the need for optimal ORC system sizing.

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.

Gas turbines are most widely used for power generation and operate under various conditions and loads. Gas turbine control is important to cope with various situations, and the turbine inlet temperature (TIT) is the most important parameter because it is directly related to the power output and life cycle of the turbine. Thus, precise prediction and control of the TIT are important in terms of the stable operation and life cycle management of gas turbines. This paper proposes a new method to predict non-measured parameters such as the air flow and TIT using Kalman filter techniques. The Kalman filter is widely used for estimating the instantaneous state of a system and can estimate non-measured parameters. The Kalman filter algorithm was implemented in a gas turbine analysis program using MATLAB. The reliability of the new method was verified through various case studies using virtual data and real operating data. The results were compared with those of a model-based gas turbine diagnostics program. The computing time of the Kalman filter and model-based diagnostics program were also compared to confirm the capability of the new method. The results indicate that the new method is more suitable for diagnostics and monitoring applications than the model-based analysis program. Finally, two case studies were performed to confirm the feasibility of the new method using two virtual datasets. The results confirm that the Kalman filter can predict the non-measured parameters precisely.

Carbon capture and storage (CCS) processes have been studied to reduce carbon dioxide in power generation, especially in coal plants because they have been highlighted as the main source of carbon dioxide emission. In this study, the impact of oxygen supply method on the performance of the integrated gasification fuel cell (IGFC) with carbon capture was compared. The target system is based on a solid oxide fuel cell and uses the syngas produced by coal gasification as a fuel. In the reference IGFC, the oxygen required for gasification and oxy-combustion is separated through an air separation unit (ASU). On the other hand, in the system proposed in this study, oxygen is separated through an ion transport membrane (ITM). The temperature and pressure conditions, as well as the purity of the oxygen separated from the ITM, were assumed to be the same as those of the oxygen separated from the ASU, and the composition of the syngas was kept constant. The proposed system indicated a 4.0% increase in output and a 1.6%p increase in efficiency compared to that of the reference IGFC. In addition, performance was analyzed according to the operating condition of the ITM, and the change in performance within its possible operating range was found to be less than 0.3%, which was insignificant.

The demand for clean energy continues to increase as the human society becomes more aware of environmental challenges such as global warming. Various power systems based on high-temperature fuel cells have been proposed, especially hybrid systems combining a fuel cell with a gas turbine, and research on carbon capture and storage technology to prevent the emission of greenhouse gases is already underway. This study suggests a new method to innovatively enhance the efficiency of a molten carbonate fuel cell/micro gas turbine hybrid system including carbon capture. The key technology adopted to improve the net cycle efficiency is off-gas recirculation. The hybrid system incorporating oxy-combustion capture was devised, and its performance was compared with that of a post-combustion system based on a hybrid system. A molten carbonate fuel cell system based on a commercial unit was modeled. Externally supplied water for reforming was not needed as a result of the presence of the water vapor in the recirculated anode off-gas. The analyses confirmed that the thermal efficiencies of all the systems (MCFC stand-alone, hybrid, hybrid with oxy-combustion capture, hybrid with post-combustion capture) were significantly improved by introducing the off-gas recirculation. In particular, the largest efficiency improvement was observed for the oxy-combustion hybrid system. Its efficiency is over 57% and is even higher than that of the post-combustion hybrid system.

There is increasing interest in zero-carbon-emission power to prevent global warming. This study investigated an effective way to minimize the efficiency penalty and achieve near-zero carbon emission in a small-scale triple combined cycle. The power block of the cycle includes a solid oxide fuel cell, micro gas turbine, and organic Rankine cycle. The three oxy-combustion capture systems are a semi-closed cycle, a cycle using an ion transport membrane, and a cycle where the membrane is replaced with an air separation unit. A parametric analysis was performed to determine an optimal pressure ratio for each cycle. The performance characteristics of the three cycles and a cycle with conventional post-combustion capture were compared. It was found out that the cycle using an air separation unit is more efficient than the other two cycles and captures highly pure carbon dioxide. The efficiency penalty due to carbon capture is only 4.4%, resulting in 58% net efficiency. The most significant finding is that using the cryogenic air separation unit is more favorable than using the ion transport membrane to separate oxygen in a small triple combined cycle operating at low pressure, in contrast to one with high pressure.

An in-house program that is capable of simulating the transient operations of micro gas turbines was developed. This paper describes the program setup and simulation of a commercial engine. Physics-based governing equations and characteristic models were applied to each component of the engine. The program was modularized fully using object-oriented programing for high maintainability and extensibility. To achieve both a short computing time and high accuracy, the recuperator was divided into multiple one-dimensional segments and its governing equation was linearized. To simulate a real commercial engine, scaled compressor and turbine performance maps, and the characteristic equations of the recuperator were adopted. The maps and the characteristic parameters of the recuperator were fine-tuned using the real operation data of the engine for better simulation accuracy. The thermal inertia of the recuperator, which plays a critical role in the transient behavior of the engine, was estimated using real shut-down data. The load following operation of the engine was simulated and close agreement with the test data was confirmed. The program is expected to be used for a range of purposes, such as supplementing the development test, designing robust control logic, and diagnosing the engine performance.

We investigated several viable options for combining a gas turbine and a solid oxide fuel cell to achieve very high power generation efficiency. The backbone of the combination is the solid oxide fuel cell/gas turbine dual combined cycle and the solid oxide fuel cell/gas and steam turbine triple combined cycle. The object of analysis is central power plants on the order of hundreds of MW. The gas turbine parameters were taken from an F-class commercial engine, and state-of-the-art parameters of the SOFC were used. In each of the two cycles, the use of a recuperative heat exchanger was considered as a design option. The performance of the combined cycles using the commercial gas turbine was estimated in the first part of the study, and optimal design performance was predicted in the second part assuming a completely revised gas turbine design. Overall, the triple combined cycle was expected to provide better efficiency than the dual combined cycle. Its optimal efficiency was predicted to be over 75%, which is about three percentage points higher than that of the dual combined cycle. The optimal efficiencies of the recuperated and non-recuperated systems were almost the same, which provides flexibility in selecting a system configuration.