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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The simultaneous use of gas turbine reheating and recuperation is favorable for improving the efficiency of the gas turbine combined cycle (GTCC). However, less power output is obtained from the combined cycle with both reheating and recuperation than with only reheating. Three cases of coolant cooling were analyzed to compensate for the power deficit and improve the efficiency: coolant inter-cooling, coolant pre-cooling, and conventional inter-cooling. The cycle with gas turbine reheating, recuperation, and coolant inter-cooling (RCRHCC-CIC) was predicted to be the most efficient among the three cases and showed higher efficiency than the conventional simple-cycle GTCC. In addition, scenarios of both the cycle improvement and required enhancements of the design parameters of components were investigated to achieve 67% cycle efficiency. RCRHCC-CIC achieved 67% efficiency with less enhancement of the component parameters in comparison to the simple-cycle GTCC, including 2% points less compressor efficiency and a more than 10% smaller flow path diameter. In conclusion, RCRHCC-CIC could be a possible option to reach the next level of GTCC efficiency goals.

This study used computational fluid dynamics (CFD) to predict the operating characteristics and performance of a ten-stage high-pressure turbine (HPT) of an ultra-supercritical (USC) steam turbine. Focus was centered on validating the use of CFD for such steam turbines, particularly for predicting global performance and operation. To accomplish this, we compared the predicted performance under the design conditions with reference design data, and we also compared the simulated off-design operation characteristics with those predicted by a semi-theoretical method. After confirming the feasibility of the CFD calculation, we investigated the impacts of the rotor tip clearance and flow addition inside the turbine through an overload valve (OLV). The mass flow versus pressure ratio flow characteristics predicted by the CFD were very close to those from the semi-theoretical method. The tip clearance calculation showed that stage efficiency decreases more in a higher reaction stage than in a lower reaction stage, which is consistent with available literature data. Increasing the OLV flow increases the flow and pressure ratio of rear stages but decreases those of front stages, leading to net power boosting but with a small efficiency loss.

In gas turbine combined heat and power systems, steam injection is a good way to cope with seasonal variations in electricity and heat demands. However, even though thermal energy demand decreases considerably in cooling seasons, the surplus exhaust heat cannot be fully utilized for steam injection in conventional operation because of a reduction in compressor surge margin. This study suggests a modified operation to increase power output without damaging the minimum allowable surge margin. This can be realized by extracting some of the compressor discharge air and supplying it to the turbine exhaust side. This paper shows that the modified operation allows for more steam to be injected in comparison to conventional steam-injected operation while maintaining the same compressor surge margin. The modified operation provides another merit of modulating the heat-to-power-generation ratio by controlling both the amount of air bypass and the steam injection rate. In particular, pure power generating operation, where generated steam is fully injected such that no heat output is available, is possible without decreasing the surge margin below a desired minimum value. The impact of the air bypass is demonstrated for a sample ambient temperature condition and the trend with ambient temperature variation is also illustrated.

This study simulated a triple combined cycle which combines a gas turbine combined cycle (GTCC) and a solid oxide fuel cell (SOFC) system, and the expected performance is presented. The impact of post-combustion carbon capture was also evaluated. Commercially available F-class and J-class gas turbines were considered, which represent the present technology standard and an emerging technology. A state-of-the-art post-combustion carbon capture technology was used. The analysis showed that the efficiency of the triple combined cycle is a weak function of the gas turbine class. The efficiency of the F-class-based system without carbon capture is slightly over 70%, and that of the J-class-based system is slightly lower. The efficiency penalty due to carbon capture is around 5 percentage points in the triple combined cycle. The power share of the gas and steam turbines increases with increasing turbine inlet temperature, reaching more than half in the J-class-based system. The degree of increase required for the turbine annulus area to operate the gas turbine safely without compressor surge problems was estimated. The relative efficiency reduction due to an increase in carbon capture rate is lower in the triple combined cycle compared to the GTCC.

This study investigated the economics of co-firing biogas and natural gas within a small gas turbine combined heat and power (CHP) plant. The thermodynamic performance of the CHP plant was calculated with varying gas mixing ratios, forming the basis for the economic analysis. A cost balance equation was used to calculate the costs of electricity and heat. The methodology was validated, and parametric analyses were used to investigate the influence of gas mixing ratio and heat sales ratio on the costs of electricity and heat. The cost of electricity generation from the CHP plant was compared to that of a central combined cycle power plant, and an economical gas mixing ratio range were suggested for various heat sales ratios. It was revealed that the effect of the heat sales ratio on the cost of electricity becomes greater as the proportion of natural gas is increased. It was also demonstrated that the economic return from the installation of CHP systems is substantially affected by the gas mixing ratio and heat sales ratio. Sensitivity analysis showed that influence of economic factors on the CHP plant is greater when a higher proportion of natural gas is used.

We evaluated the economic feasibility of small CHP (combined heat and power) and CC (combined cycle) systems using a 5 MW-class gas turbine fueled with biogas. The significance of this study is that we used practical hourly and seasonal variations of the CHP and CC performance based on detailed performance analysis. Using the investment and running costs of the entire facilities and the prices of electricity and heat, economic indices such as the annual gross margin, the net present value of the cash flow and the payback period were estimated. Two kinds of heat demand patterns were compared in the CHP system. Major findings are as follows. A strong dependence of the project economics on heat sales was observed. Both of the CHP cases showed an economic benefit over both the CC system and the gas turbine-only system. Another important finding is that the CHP system would be more beneficial than the CC system in terms of the total net present value after twenty years as long as the annual heat demand is over thirty percent of the annual electricity supply. The effect of increasing prices and costs was also simulated, and improvements in project economics were estimated.

The integration between a gas turbine and an air separation unit (ASU) is important in IGCC plants. The portion of ASU air extracted from the gas turbine and the degree of nitrogen supply from the ASU to the gas turbine side are important operating parameters. Their effect on the gas turbine performance and operability should be considered in a wide ambient temperature range. In this study, appropriate nitrogen dilution rate and turbine inlet temperature that satisfy the two limitations of turbine blade temperature and maximum allowable power output were predicted. The air integration was set at zero. The simulation showed that the power output increases and turbine blade temperature decreases as the nitrogen dilution increases. The maximum allowable power output can be obtained under medium and low ambient temperature ranges. Under a high ambient temperature range, the achievable power is less than the maximum power.

Overheating of turbine blades is one of the major concerns in using low calorific value fuels in gas turbines. In this work, we examined the deviation of operating conditions of a gas turbine fired with a low calorific value gas fuel, with a focus on the turbine blade temperatures. Several measures to suppress blade overheating were compared in terms of the power output and efficiency of the gas turbine combined cycle plant. Blade overheating can be prevented by decreasing the firing temperature without the need for hardware modifications, but the accompanying power reduction is considerable. As a remedy to this large reduction in power, modulation of the coolant supply to each blade row was simulated, and a much lower power penalty was observed. Moreover, pre-cooling of the coolant enhances the power output further by reducing the coolant supply. Pre-cooling recovers 80% of the available maximum augmentation of the combined cycle by simply switching the fuel from natural gas to low calorific value gas. Pre-cooling also provides higher overall combined cycle efficiency compared to under-firing.

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.

In an IGCC (integrated gasification combined cycle) plant, the operating environment of the gas turbine (GT) deviates from the design conditions due to its integration with both the gasifier and the air separation unit (ASU). In particular, a trial to design the entire system with low GT–ASU integration would cause a decrease in the compressor surge margin and the turbine blade overheating. In this study, modification of the turbine and compressor to avoid a decrease in the surge margin and overheating was simulated, and the result was compared with the case without modification. The entire IGCC plant was modeled and the full off-design operation of the gas turbine was simulated. Under-firing and a decrease in dilution nitrogen can mitigate the two problems without component modification but inevitably cause a considerable performance penalty in the low integration degree regime. Both turbine modification (annulus area increase) and compressor modification (increase in the surge pressure ratio) enabled a continuous increase in power and efficiency with decreasing integration degree. In the very low integration degree regime, the power benefits of the two modifications were similar and considerable. A sensible power boost can be achieved if the turbine coolant modulation can be adopted instead of under-firing in modification strategies.

This study simulated the operation of a steam injected gas turbine combined heat and power (CHP) system. A full off-design analysis was carried out to examine the change in the turbine blade temperature caused by steam injection. The prediction of turbine blade temperature was performed for the operating modes suggested in the previous study where the limitation of compressor surge margin reduction was analyzed in the steam injected gas turbine. It was found that both the fully injected and partially injected operations suggested in the previous study would cause the blade temperature to exceed that of the pure CHP operation and the under-firing operation would provide too low blade temperature. An optimal operation was proposed where both the turbine inlet temperature and the injection amount were modulated to keep both the reference turbine blade temperature and the minimum compressor surge margin. The modulation was intended to maintain a stable compressor operation and turbine life. It was shown that the optimal operation would provide a larger power output than the under-firing operation and a higher efficiency than the original partially injected operation.

The gas turbine combined cycle is the most mature and efficient power generation system. While enhancing design performance continuously, a parallel effort to make up for the shortcomings of the gas turbine should be pursued. The most critical drawback is the large power loss in hot season when electricity demand is usually the highest. Therefore, it is important to implement an effective power boosting measure in gas turbine based power plants, especially in areas where the annual average temperature is much higher than the standard design ambient temperature. The simplest method in general is to reduce the gas turbine inlet air temperature by any means. Several schemes are commercially available, such as mechanical chilling, evaporative cooling, inlet fogging and absorption chilling. All of them have merits and demerits, either thermodynamically and economically. In this study, we focused our interest on the absorption chilling method. Theoretically, absorption chilling provides as much cooling effect (air temperature reduction) as the mechanical chilling, while electric power consumption is negligibly small. A distinct feature of an absorption chiller in contrast to a mechanical chiller is that thermal energy (heat) is needed to drive the chilling system. In this research, we propose an innovative idea of making the independent heat supply unnecessary. The new method provides simultaneous cooling of the turbine coolant and the inlet air using an absorption chiller. The inlet cooling and coolant precooling boost the gas turbine power synergistically. We predicted the system performance using cycle simulation and compared it with that of the conventional mechanical cooling 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.

Effects of coolant pre-cooling and fuel pre-heating on the performance of a combined cycle using a F-class gas turbine were investigated. Coolant pre-cooling results in an increase of power output but a decrease in efficiency. Performance variation due to the fuel pre-heating depends on the location of the heat source for the pre-heating in the bottoming cycle (heat recovery steam generator). It was demonstrated that a careful selection of the heat source location would enhance efficiency with a minimal power penalty. The effect of combining the coolant pre-cooling and fuel pre-heating was also investigated. It was found that a favorable combination would yield power augmentation, while efficiency remains close to the reference value. † 1. 서 론 가스터빈은 복합발전의 주 기기로써 발전 분야에서 중요한 역할을 하고 있다. 가스터빈은 단독 운전 시 30% 중, 후반의 효율을 내고 증기터빈과 연계된 복합발전 시스템을 구성할 때에는 50% 중반 이상의 효율을 낼 수 있다. 최근에 출시된 최고성능 가스터빈들(예를 들어 H Class)의 경우 복합사이클에서 60% 이상의 효율을 목표로 하고 있다. (1) 하지만 현재까지 설치되어 있는 발전설비의 규모나 사용처에 따라 사용되는 가스터빈의 출력범위가 상이하고 복합발전의 효율도 차이를 보인다. 이에 따라 가스터빈의 효율 및 출력을 향상시키기 위한 많은 시도가 이루어지고 있다. 최근 많은 연구가 이루어지고 있는 가스터빈 입구냉각의 경우를 보면, Najjar 등

We investigated the influence of firing biogas on the performance and operating characteristics of gas turbines. Combined heat and power systems based on two different gas turbines (simple and recuperative cycle engines) in a similar power class were simulated. A full off-design analysis was performed to predict the variations in operations due to firing biogas instead of natural gas. A wide range of biogas compositions differing in CH4 content was simulated. Without consideration of operating restrictions on the compressor and turbine, using biogas was predicted to augment the power output in both engines. Power output increased as CH4 content decreased. The main reason is the increase in turbine power due to increased fuel flow. Gas turbine efficiency increased with decreasing CH4 content in the simple cycle engine, but decreased in the recuperative cycle engine. Net efficiency including the fuel compression power consumption decreased with decreasing CH4 content even in the simple cycle engine. The heat recovery also increased by firing biogas. However, the increased turbine flow was accompanied by a surge margin reduction of the compressor and overheating of the turbine blade. These two problems were more severe in simple cycle gas turbines and as the ambient temperature increased. The turbine blade temperature and the compressor surge margin could be recovered to the reference values by either under-firing or compressor air bleeding, which are effective for blade temperature control and surge margin control, respectively. However, satisfaction of both restrictions by a single modulation caused excessive power and efficiency losses. An optimal combination between under-firing and air bleeding would minimize the performance penalty.

Solid oxide fuel cell/gas turbine hybrid systems that use three gas turbines having different power outputs were devised and their performance was compared. The power shares of the gas turbine and fuel cell and the net system efficiency were compared among the three systems, and their variations with the design fuel cell temperature were investigated. The system efficiency was predicted to be insensitive to the fuel cell temperature in the sub-MW system, but it increased with increasing fuel cell temperature in both the multi-MW and hundred-MW systems. The influence of air bypass around the fuel cell on the system performance was also investigated.

Cooling of hot sections, especially the turbine nozzle and rotor blades, has a significant impact on gas turbine performance. In this study, the influence of precooling of the cooling air on the performance of gas turbines and their combined cycle plants was investigated. A state-of-the-art F-class gas turbine was selected, and its design performance was deliberately simulated using detailed component models including turbine blade cooling. Off-design analysis was used to simulate changes in the operating conditions and performance of the gas turbines due to precooling of the cooling air. Thermodynamic and aerodynamic models were used to simulate the performance of the cooled nozzle and rotor blade. In the combined cycle plant, the heat rejected from the cooling air was recovered at the bottoming steam cycle to optimize the overall plant performance. With a 200K decrease of all cooling air stream, an almost 1.78% power upgrade due to increase in main gas flow and a 0.70 percent point efficiency decrease due to the fuel flow increase to maintain design turbine inlet temperature were predicted.

This study simulated the effect of steam injection on the performance and operation of a gas turbine combined heat and power (CHP) system. A commercial simple cycle gas turbine was analyzed. A full off-design analysis was carried out to investigate the variations in not only engine performance but also the operating characteristics of the compressor caused by steam injection. Variation in engine performance and operation characteristics according to various operation modes were examined. First, the impact of full steam injection was investigated. Then, operations aiming to guarantee a minimum compressor surge margin, such as under-firing and partial steam injection, were investigated. The former and latter were turned out to be relatively superior to each other in terms of power and efficiency, respectively. †† 1. 서 론 일반적으로 수백MW의 전력을 생산할 수 있는 대형 가스터빈에 비하여 수MW의 소형 가스터빈은 주로 자가발전을 포함한 분산 발전에 사용된다. 특히, 전력 공급이 원활하지 못한 지역이나 발전 요금이 고가인 피크부하 시간대에는 기존에 공급되는 전력 외에 소형 가스터빈으로 전력을 생산하여서 전력 수급을 용이하게 할 수도 있다. 또한 최근 가스터빈 열병합 발전을 이용한 Community Energy System(CES)이 각광을 받고 있는데, 역시 소형 가스터빈의 좋은 응용 분야이다

In this study, system layouts for integrated gasification solid oxide fuel cell/gas turbine (IG-SOFC/GT) systems were proposed and their performance was comparatively evaluated. A baseline IGCC was simulated, and the calculation models were validated. Based on the IGCC system, two IG-SOFC/GT system layouts with different SOFC thermal management methods were established, and their performance was analyzed. The IG-SOFC/GT systems were found to produce much higher power and better efficiency than the IGCC. With regard to SOFC thermal management, the exit gas recirculation scheme showed better performance than the cathode heat exchange scheme. The impact of CO2 capture was investigated in both the IGCC and IG-SOFC/GT systems, and the penalties in power output and efficiency due to pre-combustion CO2 capture were found to be milder in the IG-SOFC/GT systems than in the IGCC. An IG-SOFC/GT system adopting oxy-combustion-based CO2 capture was proposed, and its thermal efficiency was predicted to be sensibly higher than the system with pre-combustion CO2 capture. Its net power output was predicted to be less than that of the system with pre-combustion technology, but was still much larger than that of the IGCC with pre-combustion CO2 capture.

We investigated the effects of firing syngas in a gas turbine designed for natural gas. Four different syngases were evaluated as fuels for a gas turbine in the integrated gasification combined cycle (IGCC). A full off-design analysis of the gas turbine was performed. Without any restrictions on gas turbine operation, as the heating value of the syngas decreases, a greater net system power output and efficiency is possible due to the increased turbine mass flow. However, the gas turbine is more vulnerable to compressor surge and the blade metal becomes more overheated. These two problems can be mitigated by reductions in two parameters: the firing temperature and the nitrogen flow to the combustor. With the restrictions on surge margin and metal temperature, the net system performance decreases compared to the cases without restrictions, especially in the surge margin control range. The net power outputs of all syngas cases converge to a similar level as the degree of integration approaches zero. The difference in net power output between unrestricted and restricted operation increases as the fuel heating value decreases. The optimal integration degree, which shows the greatest net system power output and efficiency, increases with decreasing syngas heating value.

An integrated power generation system combining solid oxide fuel cell (SOFC) and oxy-fuel combustion technology is proposed. The system is revised from a pressurized SOFC-gas turbine hybrid system to capture CO2 almost completely while maintaining high efficiency. The system consists of SOFC, gas turbine, oxy-combustion bottoming cycle, and CO2 capture and compression process. An ion transport membrane (ITM) is used to separate oxygen from the cathode exit air. The fuel cell operates at an elevated pressure to facilitate the use of the ITM, which requires high pressure and temperature. The remaining fuel at the SOFC anode exit is completely burned with oxygen at the oxy-combustor. Almost all of the CO2 generated during the reforming process of the SOFC and at the oxy-fuel combustor is extracted from the condenser of the oxy-combustion cycle. The oxygen-depleted high pressure air from the SOFC cathode expands at the gas turbine. Therefore, the expander of the oxy-combustion cycle and the gas turbine provides additional power output. The two major design variables (steam expander inlet temperature and condenser pressure) of the oxy-fuel combustion system are determined through parametric analysis. There exists an optimal condenser pressure (below atmospheric pressure) in terms of global energy efficiency considering both the system power output and CO2 compression power consumption. It was shown that the integrated system can be designed to have almost equivalent system efficiency as the simple SOFC-gas turbine hybrid system. With the voltage of 0.752 V at the SOFC operating at 900 °C and 8 bar, system efficiency over 69.2% is predicted. Efficiency penalty due to the CO2 capture and compression up to 150 bar is around 6.1%.

This study analyzes the performance of hybrid power systems combining a solid oxide fuel cell (SOFC) and a gas turbine (GT). Research focus is given to the influence of the size-dependent gas turbine performance on hybrid system performance. Three hybrid systems adopting different gas turbines (kW, sub-MW, multi-MW classes) are designed. As the gas turbine power increases (i.e. as the gas turbine performance enhances), the gas turbine power portion increases and the hybrid system efficiency increases. The hybrid system shows efficiency improvement over the SOFC only system even in the case where the gas turbine net power is nearly zero. The increase of gas turbine pressure ratio contributes to the net hybrid system power output in all of the three cases, while system efficiency is almost independent on the pressure ratio.

MW-class gas turbines are suitable for distributed generation systems such as community energy systems(CES). Recently, biogas is acknowledged as an alternative energy source, and its use in gas turbines is expected to increase. Steam injection is an effective way to improve performance of gas turbines. This study intended to examine the influence of injecting steam and using biogas as the fuel on the operation and performance a gas turbine combined heat and power (CHP) system. A commercial gas turbine of 6 MW class was used for this study. The primary concern of this study is a comparative analysis of system performance in a wide biogas composition range. In addition, the effect of steam temperature and injected steam rate on gas turbine and CHP performance was investigated.

As the need for clean coal technology grows, research and development efforts for integrated gasification combined cycle (IGCC) plants have increased worldwide. An IGCC plant couples a gas turbine with a gasification block. Various technical issues exist in designing the entire system. Among these issues, the matching between the gas turbine and the air separation unit is especially important. In particular, the operating condition of a gas turbine in an IGCC plant may be very different from that of its original design. In this study, we analyzed the impact of the use of syngas on operating conditions of the gas turbine in an IGCC plant. We evaluated the performance of a gas turbine under operating limitations in terms of compressor surge and turbine metal temperature. Although a lower degree of integration may theoretically allow higher gas turbine power output and efficiency, it causes a reduction in compressor surge margin and overheating of the turbine metal. The turbine overheating problem may be solved using several methods, such as a reduction in the firing temperature or an increase in the turbine cooling air. The latter yields a much smaller performance penalty. To achieve an acceptable margin for the compressor surge, either further reduction in the firing temperature or further increase in the coolant is required. Ventilation of some of the nitrogen generated by the air separation unit, i.e., a reduction of the nitrogen supply to the combustor, is another option. Coolant modulation yields the lowest performance penalty. Reduction of the nitrogen supply provides much greater system power output than control of the firing temperature. For nitrogen flow and firing temperature controls, there are optimal levels of integration degrees in terms of net system power output and efficiency.

초록:본연구에서는물을재순환하는이상적인순산소발전시스템의작동조검변화에따른성능해석을수행하였다. 순산소발전시스템에서의터빈은작동유체의연소기출구온도에따라증기터빈또는가스터빈을사용할수있다. 본연구의순산소사이클에서는터빈입구온도를가스터빈수준으로가정하였으며, 터빈출구의과열도증대를위해재열시스템을채택하였다. 또한터빈출력증대를위해터빈출구압력을진공상태로가정하였으며, 이에따라가스터빈출구에서추가의팽창과정이요구된다. 터빈입구온도, 압력비, 응축기압력과같은중요작동조건의변화에따른시스템성능이해석되었으며, 시스템구성변화에따른효율변화도검토하였다. 결론에서는성능을최적화시키면서고순도의이산화탄소회수가가능한순산소발전시스템의최적작동조건을제안하였다.Abstract: In this study, an ideal water-recirculated oxy-fuel power generation system is proposed. The resultsof parametric studies of the performance characteristics of the system are discussed. For a given choice ofthe turbine inlet temperature, the turbine, which produces power, can be either a gas or a steam turbine. Formaximum efficiency, the turbine inlet temperature is selected as the level of state-of-the-art gas turbines andthe reheat cycle may be adopted not only to enhance the turbine power but also to maintain dryness of thewater with a turbine exhaust temperature that is as high as possible. To obtain a low condensationtemperature for a high purity of CO

An IGCC (integrated gasification combined cycle) plant consists of a power block and a gasifier block, and a smooth integration of these two parts is important. This work has analyzed the influences of the major design options on the performance of an IGCC plant. These options include the method of integrating a gas turbine with an air separation unit and the degree of nitrogen supply from the ASU to the gas turbine combustor. Research focus was given to the effect of each option on the gas turbine operating condition along with plant performance. Initially, an analysis adopting an existing gas turbine without any modifications of its components was performed to examine the influence of two design options on the operability of the gas turbine and performance of the entire IGCC plant. It is shown that a high integration degree, where much of the air required at the air separation unit is supplied by the gas turbine compressor, can be a better option considering both the system performance and operation limitation of the gas turbine. The nitrogen supply enhances system performance, but a high supply ratio can only be acceptable in high integration degree designs. Secondly, the modifications of gas turbine components to resume the operating surge margin, such as increasing the maximum compressor pressure ratio by adding a couple of stages and increasing turbine swallowing capacity, were simulated and their effects on system performance were examined. Modification can be a good option when a low integration degree is to be adopted, as it provides a considerable power increase.

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.

Integrated gasification combined cycle (IGCC) is an environment friendly method of using coal. Several commercial IGCC plants have been built worldwide during the past decade, and a domestic development project has also been launched recently. Operation and performance characteristics of a gas turbine in the IGCC plant deviates from those of original gas turbines due to several factors such as increased amount of fuel supply and integration with other components. In this study, performance of a gas turbine in the IGCC plant is analyzed considering its integration with the air separation unit (ASU). Influence of the degree of integration (split of air supplies to ASU from the auxiliary compressor and the gas turbine compressor) on the system performance is investigated. In addition, effect of modulating nitrogen return flow from the gasifier to the gas turbine on the operating characteristics of the gas turbine is examined. † 인하대학교 기계공학부 E-mail : kts@inha.ac.kr TEL : (032)876-7308 FAX : (032)876-7308 * 인하대학교 대학원 ** 서울대학교 기계항공공학부 *** 한국전력연구원