Brayton Cycle Power Research Articles

Study on the dynamic characteristics of a concentrated solar power plant with the supercritical CO2 Brayton cycle coupled with different thermal energy storage methods

The paper aims to study the impact of Thermal Energy Storage (TES) technology on the dynamic characteristics of Concentrated Solar Power (CSP). An integrated dynamic model of a CSP plant is firstly established, which combines the concentrating system, the TES system, and S–CO2 Brayton power cycle system. Three TES alternatives are considered: two-tank molten salt TES (TT-TES), packed-bed TES with solid fillers (PBS-TES), packed-bed TES with phase change materials (PBP-TES). Using this integrated dynamic model, the thermal performance and economic feasibility of different TES technologies applied to CSP are compared and analyzed. The results indicate that utilization of packed-bed TES primarily impacts the optical efficiency of the heliostat field and the thermal efficiency of the power cycle, while having minimal effect on the receiver's thermal efficiency. Furthermore, during the vernal equinox, the daily average system efficiencies of CSP configurations integrating TT-TES, PBS-TES, PBP-TES technologies are 26.0 %, 25.5 %, and 24.5 %, respectively. Meanwhile, the use of packed-bed TES systems significantly reduces the material cost of the TES. In comparison to the TT-TES, the PBP-TES and the PBS-TES can reduce cost by 21.2 % and 42.3 %, respectively, and decrease TES volume by 83.0 % and 63.8 %, respectively.

Design and development of a stable supercritical CO2 centrifugal compressor

Introducing supercritical carbon dioxide (s-CO2) as a working fluid can enhance the power generation of Brayton cycles. However, various challenges are involved in designing, and developing a stable s-CO2 centrifugal compressor on a reasonably sized s-CO2 Brayton cycle. This article presents a 1-D design and development procedure for s-CO2 centrifugal compressors suitable for Brayton power cycles. The 1-D compressor design approach employs the Widom region, AMC, and internal and external loss models to optimize the compressor design. The 1-D design code is validated with CFD simulation and experimental data from Sandia. Further, a new stable compressor for a 10 MWe s-CO2 Brayton cycle is designed, proposed, and discussed in this paper. Based on the 1-D design code and the CFD results, the newly designed compressor exhibits an improved operational range. Additionally, a loss analysis of the designed s-CO2 compressor revealed that internal losses accounted for 75.8% of the total enthalpy loss. The compressor's internal flow behavior at choke is investigated by utilizing a novel analogy between the impeller at choke and a converging–diverging nozzle. The CFD results showed that condensation is inevitable in an s-CO2 centrifugal compressor operation; however, condensation does not significantly affect compressor performance near the design point.

Performance comparison of three supercritical CO2 solar thermal power systems with compressed fluid and molten salt energy storage

In recent years, the supercritical carbon dioxide (sCO2) Brayton cycle power generation system has gradually attracted the attention of academics as a solar thermal power generation technology. To achieve the stable and effective use of solar energy, three sCO2 solar power generation systems were studied in this paper. These systems included a molten salt thermal storage system, a compressed CO2 energy storage system, and a combined molten salt thermal storage and compressed CO2 energy storage system. The thermodynamic analysis model of the sCO2 power generation system is constructed, and a mathematical model of the solar power tower system is produced. The operating conditions, thermal efficiency, exergy efficiency, and economics of these three systems on typical days are investigated and compared. The results indicate that the power generation system coupled with compressed CO2 storage has higher thermal and exergy efficiencies than the other two systems with the same daily heliostat field. The thermal efficiencies can be as high as 6.56% and 5.91% respectively, and the exergy efficiencies as high as 5.76% and 6.22% respectively. The system coupled with compressed CO2 energy storage is more cost-effective and has a shorter payback period than the system coupled with molten salt thermal storage system and the system with both forms of energy storage.

Search for the Optimal Design of a Supercritical-CO2 Brayton Power Cycle from a Superstructure-Based Approach Implemented in a Commercial Simulation Software

Improving the efficiency and flexibility of fossil-fired power plants remains a current and challenging issue. In that regard, supercritical CO2 Brayton cycles offer promising potential. This paper aims to apply a process synthesis approach to the design of a closed Brayton cycle using supercritical CO2 as a working fluid with a coal furnace as a heat source. The general methodology presented here for designing closed power cycles includes the construction of a superstructure containing all relevant possible cycle layouts, the formulation of the cycle-synthesis problem as a mathematical optimization problem, and its solution using an appropriate algorithm. This study was conducted with the help of a process simulation commercial software (PROSIM) and using the Mixed-Integer Distributed Ant Colony Optimization (MIDACO) as a commercial optimization algorithm. This work highlights the limits of a purely technical optimization approach that would ignore the economical layer. The optimal structure obtained regarding Levelized Cost Of Electricity (LCOE) minimization is a configuration with one reheat of the supercritical CO2 in the boiler, two recuperators, and one recompression loop around the low-temperature recuperator; it is associated with a cycle efficiency of 49.35 % and a 10% reduction in the LCOE in comparison to the optimal case found through energy optimization under typical design heuristics constraints.

Effects of inlet working condition and heat load on supercritical CO2 compressor performance

The supercritical carbon dioxide (sCO2) Brayton power cycle is more effective than the conventional power cycle and is more widely applicable to heat sources. The inlet working conditions of the compressor have a higher influence on their operating performance because the thermophysical properties of the CO2 vary dramatically close to the critical point. The flow in the sCO2 compressor is simulated and the compressor performance is analyzed. The results show that the sCO2 centrifugal compressor operates outside of its intended parameters due to the change in inlet temperature. The sCO2 compressor requires more power as the inlet temperature increases. The compressor power is 582 kW when the inlet temperature is at 304 K. But the power is doubled when the inlet temperature increases to 314 K, and the change in the isentropic efficiency is within 5%. The increase in the inlet temperature significantly reduces the risk of condensation in centrifugal compressors. When the heat load of the sCO2 power system changes, the inlet pressure to the turbine can be kept constant by regulating the rotational speed of compressors. With the increase in rotational speed, the incidence loss and condensation risk increase.

Thermodynamics analysis of the supercritical CO2 binary mixtures for Brayton power cycles

Supercritical CO2 Brayton-based cycles are a promising technology for concentrated solar power plants. Their high efficiency can be improved by using CO2 mixtures as working fluid instead of pure CO2. This work studies 3 cycle topologies: simple recompression (RCC), recompression with main compressor intercooling (RCMCI) and partial cooling recompression (PCRC), across a range of regenerator conductance (UA), compressor and turbine inlet temperatures. Each topology is simulated with different working fluids: CO2, CO2–NH3, CO2–SO2, CO2–COS and CO2–H2S. The influence of the working fluid, operating conditions and cycle irreversibility on the overall efficiency has been analyzed in depth, finding two interesting, opposing trends. The mixtures with higher critical pressure improve the heat absorption and rejection temperatures of the cycles, but also increase irreversibility. The combination of topology and mixture that achieves the best compromise between both trends will have the higher efficiency. In general, using RCMCI instead of PCRC or RCC can improve efficiency by up to 4% depending on the working fluid and operating conditions. Using a mixture instead of pure CO2 by up to near 3%.

The study of energy filtering management process for microgrid based on the dynamic response model of vanadium redox flow battery

For the efficient application of vanadium redox flow battery (VRB) in microgrid containing the clean renewable energy and advanced coal-fired power system such as the supercritical carbon dioxide (S-CO2) Brayton cycle power plant, a feasible energy filtering optimization process is proposed in this paper. A coupled dynamic response model of VRB and an optimized load distribution algorithm are covered in the process. First, the Ustack-Ibattery-SOC curves are fitted based on the coupled calculation model of VRB. The equivalent resistance of the simplified equivalent circuit model is further calculated. The dynamic response model is refined for the fast calculation of real-time efficiencies. Second, a basic operation scheme and an optimized operation scheme based on the moving average filtering method are selected as the load distribution algorithms. An energy filtering optimization management process that includes a configuration optimization design part and a load distribution part is further constructed. Finally, a case application is carried out to verify the feasibility of the proposed energy management process. The relevant results are presented as follows. First, the combination of the experimental data and the fitted curves can be used to calculate the equivalent resistance of the dynamic response model. The maximum Ustack of 86.14 V is obtained at the SOC of 0.99 and Ibattery of 10A when charging. Second, when applying the optimized operation scheme, the time average efficiency of VRB is operating at an efficient level of 82.75%. The change frequency of load command for each equipment and its dynamic response characteristic can be well matched. Finally, compared to the case where the basic operation scheme is selected in the experimental system, the time average efficiency of VRB is increased from 69.50% to 82.13%., the time average efficiency of S-CO2 power plant is increased from 39.79% to 40.02%. The application of energy filtering optimization management process for the actual microgrid is feasible. The study can provide the operation scheme and case application for VRB energy storage system in the actual microgrid.

Design and optimal thermal efficiency contrastive analysis on closed Brayton cycle systems with different fluids of fluoride-salt-cooled high-temperature advanced reactor

To match the advantages of Fluoride-Salt-cooled high-Temperature Advanced Reactor, the closed Brayton cycle system was considered as the energy conversion system, and the thermodynamic analysis, conjugate gradient optimization, and exergy analysis were performed. The pinch point constraint method based on simultaneous equations was proposed to improve the calculation efficiency and ensure the unity of comparison standards, and the exergy analysis was used to quantify and optimize the exergy losses for the equipment. The thermodynamic characteristics of the power cycle systems with various fluids were analyzed, including far-critical fluids: air, nitrogen, helium, and argon, and near-critical fluids: carbon dioxide, sulfur hexafluoride, propane, and xenon. The results of the thermodynamic analysis show that for near-critical fluids, the efficiency of the SF6 cycle is the highest reaching 46.6% without considering the chemical reactions, while for far-critical fluids: air and N2, the thermal efficiencies are 45.6% and 45.5% respectively. The thermal efficiency of the far-critical fluid cycle is more sensitive to turbine efficiency, meaning enough thermal efficiency can be achieved without too high adiabatic efficiency of the compressor and isentropic efficiency of the turbine. However, far-critical fluid cycles do not have this characteristic. The results of the exergy analysis show the CO2 cycle has the highest potential to improve thermal efficiency, which has the highest improvement from 43.48% to 49.31% with the recompression process. The method and conclusion of this paper can provide references for the design and optimization of the Brayton power cycle system.

Optimum combination of diesel and concentrating solar in remote area power generation using supercritical CO2 turbines

Electrification of remote communities is a great challenge worldwide. Their reliance on economically and environmentally unfavourable diesel generators makes these communities attractive target markets for renewables. Concentrating solar thermal (CST) plants operating on supercritical CO2 (s-CO2) Brayton power cycles have been proposed for their high efficiency, compactness, compatibility with natural air-cooling, and capability of being built at a small size without significant efficiency penalties. Thermal energy storage (TES) technology can mitigate intermittency problems. This study aims to identify the optimal configuration of hybrid CST and diesel generation (DG) for different types of remote locations based on annual simulations involving key system design features including solar multiple, TES size, and CST size. One novelty in this study is the inclusion of actual weather information and load demand profiles for selected potential locations. Another is that a realistic economic model for s-CO2 power blocks for small to medium sizes, based on accurate cost data, is presented. More importantly, a realistic representation of the s-CO2 turbine, which includes isentropic efficiencies varying at off-design conditions, is used. This facilitates a study into the effects that the inclusion of realistic off-design turbine information has on the thermodynamic and techno-economic performances of the system. This is done by comparing the simulation results with results obtained using a conventional method that uses a constant turbine efficiency. This paper presents the optimal system configurations offering the lowest levelised cost of energy (LCOE) obtained using three-variable exhaustive search optimisation. The results show that the system is an economically favourable option and provides substantial environmental benefits.

Structural stress analysis of hybrid heat exchangers in the S-CO2 power cycle for marine waste heat recovery

Due to its high thermodynamic efficiency and small equipment size, the S-CO2 Brayton power cycle is a leading candidate for ship waste heat utilization. The hybrid heat exchanger formed by diffusion bonding of fins and etched plates can be used for heat exchange between the high temperature flue gas and the high pressure S-CO2. However, the law of structural strength is not clear for the hybrid heat exchanger. It is critical to carry out structural stress analysis. In this study, to assess the structural strength of the hybrid heat exchanger, the FEM was used and compared with a currently used method from ASME codes. The results show that the thermal stress caused by the temperature gradient is independent of the absolute temperature value. The change in the supercritical carbon pressure in the etched channel affects the mechanical stress more than the exhaust gas in the fin channel. Under design conditions, thermal stress and mechanical stress are equally important to the total stress of the hybrid heat exchanger. Moreover, the total stress is not a simple numerical superposition of thermal stress and mechanical stress but instead indicates a complex effect. From the FEM results, the etched channel exit that withstands a higher pressure load is the weakest point in the hybrid heat exchanger core. The FEM is a more comprehensive means for structural assessment than the ASME codes. This research can provide guidance for structural stress analysis of hybrid heat exchangers

Investigation of the polygeneration system integrated with gas engine-driven heat pump system and CO2 Brayton cycle for waste heat recovery

A gas engine-driven heat pump system could provide cooling and heating, and fully recover the waste heat. The temperature of the waste heat recovered from the gas engine cylinder jacket and exhaust gas was more than 90℃ and 350℃, respectively. The supercritical CO2 Brayton power cycle is considered a promising primary mover of the combined cooling, heating, and power system to potentially provide higher efficiency. Therefore, a polygeneration system composed of gas engine-driven heat pump system and CO2 Brayton cycle was proposed for cooling, heating, and electricity. Experiments of gas engine-driven heat pump system were conducted and the performances were also investigated in the cooling mode. Meanwhile, the thermodynamic performances of the CO2 Brayton cycle were analyzed. The results indicated that the cooling capacity and waste heat increased with the increase of gas engine speed and decreased with the decrease of evaporator water inlet temperature, the primary energy ratio was 1.032, 0.963, and 0.893 at the gas engine speeds of 1260 r/min, 1510 r/min, and 1820 r/min, respectively, and the increasing range was over 43.5 %. In addition, the maximum net power output of CO2 Brayton cycle was 0.97, 1.68, and 2.14 kW, and the gas engine fuel economy was 12.05, 12.35, and 12.10 kg/kWh at the gas engine speeds 1260 r/min, 1510 r/min, and 1820 r/min, respectively. The decreasing range of gas engine fuel with CO2 Brayton cycle system was 8.6 %, 12.3 %, and 12.5 %, respectively.

Study of the heat transfer deterioration of supercritical CO2 in vertical pipes using a hybrid RANS/LES method

Heat transfer deterioration (HTD) is one of the core factors affecting the efficiency of the supercritical carbon dioxide (S–CO2) Brayton cycle. When HTD occurs in a heat exchanger, the local wall temperature increases sharply, which may lead to pinch points in the heat exchanger of the circulation system and excessive thermal resistance, resulting in safety problems during the operation of Brayton cycle power generation systems. In studies concerning the HTD of S–CO2, most simulations currently use Reynolds-averaged equations (RANS) to predict and analyze the S–CO2 flowing upward in vertical tube transfer deterioration problems. In this paper, a hybrid RANS/LES method is used for simulations. The RANS model is used to describe the HTD in the near-wall region, and the LES model is used to calculate the flow details in the bulk region and accurately describe the flow regime and vortex structure of a compressible fluid with variable properties. Firstly, the growth and evolution process of HTD is analyzed from the transient-state, and then the corresponding relationship between HTD temperature and velocity field is expounded from the steady-state. Finally, combined with the buoyancy effect, acceleration effect and relaminarization caused by the change of S–CO2 physical properties, the mechanism of the occurrence and recovery of HTD flowing in vertical tubes and the second peak of wall temperature is expounded.

Effect of stress on corrosion behavior of martensitic and austenitic steels in supercritical carbon dioxide at 550 °C and 20 MPa

Corrosion of alloys in supercritical carbon dioxide (S-CO2) Brayton cycle power generation systems is a critical issue. In this study, we investigated the corrosion behaviors of martensitic AISI 616 and austenitic AISI 304 exposed to S-CO2 at 550 °C and 20 MPa. The effect of stress loading on the corrosion behavior was studied. A 9-μm-thick double-layer oxide with an outer layer of Fe3O4 and an inner layer of (Fe, Cr)-rich oxide was formed on the surface of the AISI 616. When stress was applied, the oxide layer thickness increased significantly to 15 µm. Stress loading thus promoted carbon deposition, accelerated the oxidation rate, and increased oxide thickness. AISI 304 generated a monolayer of (Fe, Cr)-rich oxide that was much thinner than that of AISI 616 owing to its high Cr content. In addition, the effect of stress on the corrosion of AISI 304 was weaker than that of AISI 616.

Boosting the Efficiency of Future Fusion Power Plants Combining Energy and Heat Production

A selection of Rankine and Brayton power cycles for fusion and fission nuclear power plants (NPPs) has been modeled in a framework that integrates the engineering equation solver (EES) and the PROCESS systems code. The combined production of heat and electricity has been studied, and efficiency improvements have been obtained for all cycles. The primary energy savings (PES) indicator has been evaluated for the different layouts. The economic viability, which considers the production and distribution costs of the layouts, is discussed. The combined production decreases costs and greenhouse gas emissions and appears profitable for Rankine and supercritical CO2 cycles. Potential pricing of the externalities of emissions and an increase in fossil fuel prices would improve the competitiveness of all presented layouts.

Efficiency-Focused Maintenance Model to Recover the Performance of a Gas Turbine with Inlet Air Cooling and Affected by Fouling

Efficiency-Centered Maintenance (ECM) models are vital in the industry since they increase the overall efficiency of the system and the availability of assets, considerably reducing polluting emissions and operating costs. Because of this, it has been tried to quantify the potential of ECM models in improving power generation systems. This paper presents an ECM model to recover the performance of a gas turbine that has suffered performance degradation due to exposure to fouling and variations in the compressor inlet air temperature. A strategy has been designed and implemented in order to define and schedule activities that, economically and energetically justified, have restored the performance of a simple Brayton cycle power generation facility. The net power output and the Heat Rate have been the performance indicators selected for monitoring the energetic condition of the gas turbine. Similarly, the availability and the mean time between interventions have been maintenance indicators. The results indicate that net power and availability have increased by 5%, the Heat Rate has decreased by 2%, and the mean time between interventions has increased by 5.7 times. The power degradation rate has been reduced from 9% to 1%, ending with an annual degradation of 7.4%. With the results obtained, it has been confirmed that the ECM applied to power cycles increases the system's operational efficiency, reducing costs and polluting emissions.

Optimal design of dual-stage combined cycles to recover LNG cold energy and low-temperature waste thermal energy for sustainable power generation

To overcome the shortcomings of the low net power output of a single power generation cycle for LNG cold energy recovery, investigating dual-stage combined cycles with different cycle configurations under the same heat and cold source conditions is mandatory. Hence, this study proposes 12 dual-stage combined power generation cycles to utilize LNG cold energy and low-temperature (below 200 °C ) waste thermal energy. The developed method adopts an organic Rankine cycle and Brayton cycle as the bottoming cycle and the organic Rankine cycle, Brayton cycle, and supercritical carbon dioxide power cycle as the topping cycle with parallel and serial configurations. The optimization results show that the thermodynamic and economic performance are compared quantitatively. The optimally combined cycle is a dual-stage serial organic Rankine cycle with the highest specific net power output of 202.15 kJ/kg and lowest levelized cost of electricity of 0.11 $/kWh. Regarding the parallel configuration, it can enhance thermal and exergy efficiency via its internal heat integration. Moreover, the evaporation and condensation pressure of the bottoming cycle has a more significant influence on the optimally combined cycle than the topping cycle. Overall, this study paves the way to design economics-efficient dual-stage combined cycles for sustainable power generation by utilizing LNG cold energy and low-temperature waste thermal energy.

Binder jet additive manufacturing of ceramic heat exchangers for concentrating solar power applications with thermal energy storage in molten chlorides

Triply periodic minimal surface (TPMS) geometries can only be fabricated by additive manufacturing methods and are of interest for heat exchangers. Ceramic TPMS heat exchangers can operate at higher temperatures and pressures with superior performance and increased operating efficiencies compared to metal heat exchangers. The properties of ultra-high temperature ceramic (UHTC) materials are also favorable for heat exchangers and potentially suited to concentrated solar power (CSP) systems, such as those based on a molten chloride salt thermal energy storage (TES) medium used to heat CO 2 in a closed-loop Brayton power cycle. We intended to demonstrate binder jet additive manufacturing feasibility of a UHTC-TPMS structure by printing and sintering a null candidate. We aimed to achieve parts with a relative density ≥ 92 % of theoretical and to provide a TPMS part demonstration. The target density indicates the transition from intermediate to final stage sintering, a requirement to inhibit gas permeability and for sintering complex near net shapes to full density with sinter-HIP technology. The goal of the TPMS part demonstration was to determine if printing and sintering parameters developed from test coupons apply to the complex geometries that will eventually be used in a heat exchanger design. Our objective was to print cubic TPMS parts with a 9 cm 3 volume and sinter it without distorting and cracking. We were able to sinter ZrB 2 -MoSi 2 composite parts based on the Schwarz-D TPMS and achieve isotropic shrinkage up to 60 % by volume, resulting in densities ranging from 92 % to 96 % of theoretical. • Advanced heat exchanger design based on a triply periodic minimal surface (TPMS). • Ultra-high temperature ceramic (UHTC) materials of construction. • Binder jet additive manufacturing and sintering of ZrB2-MoSi2 Schwarz-D cells. • Utilization of conventional powder feedstocks. • Achieving isotropic shrinkage and densities of 92–98 % of theoretical.

Critical components in supercritical CO2 Brayton cycle power blocks for solar power systems: Degradation mechanisms and failure consequences

This review presents an overview of the critical components in supercritical CO2 Brayton cycle power block systems along with their degradation mechanisms and possible consequences in Concentrated Solar Power (CSP) systems. Requirements for high strength, efficiency, and environmental compatibility are also discussed. sCO2 turbines are advantageous because of their small size and significantly reduced number of turbomachinery components. These components are exposed to a sCO2 environment with high pressures, temperatures, and thermal cycling that can result in premature failure due to fatigue, creep, corrosion, stress corrosion cracking, erosion, and carburization. Nickel and stainless steel candidate alloys have been proposed for sCO2 service and at these operational conditions their failures are discussed. The consequences of loss of containment for typical system designs are also explored with specific reference to potential exothermic reactions with other heat transfer media such as sodium.

Design and Optimization of the Inlet Header Structure in Microchannel Heat Exchanger Based on Flow Distribution Uniformity

The flow distribution in a printed circuit heat exchanger (PCHE) is of great theoretical and practical significance in the Brayton cycle power generation system. For the straight barrel inlet header PCHE, when S-CO2 flows in the PCHE, the structural types and working parameters of the inlet header and diversion zone may lead to differences in the flow distribution in each channel of the PCHE. This flow distribution difference affects the thermal hydraulic characteristics of the PCHE. A numerical simulation method was applied to explore the flow uniformity of the PCHE and the overall performance and analyze the influence of the type of straight barrel inlet header PCHE. Within each layer, the flow showed an uneven flow distribution, and the optimized inlet header was the tapered type. The results showed that when the taper angle varies from 6° to 9°, the flow distribution in each layer is relatively uniform. The comprehensive heat transfer performance of the straight-channel PCHE can be improved by 17.3–19.7%. Finally, the response surface and a genetic algorithm were combined to optimize the inlet header. The heat transfer performance of the optimized PCHE was improved by 19.7%.

Off-design optimization for solar power plant coupling with a recompression supercritical CO2 Brayton cycle and a turbine-driven main compressor

• Regression learner is utilized to predict the cooling tower performance. • Off-design optimization is performed for solar power tower with a turbine-driven compressor. • The proposed off-design control scheme improves yearly power output by 1.02%. • The high ambient temperature causes a loss of 0.66% of the yearly power output. The recompression supercritical carbon dioxide Brayton cycle is one of the most promising candidate power blocks for the solar power tower plant. As an important component, the main compressor can be driven by an electric motor or a turbine. The layout with the turbine-driven main compressor has the advantages of low cost, high efficiency, and safety during loss-of-load conditions. For such a system, the main compressor and the turbines are connected with the synchronous generator and assumed to be operated with a constant shaft speed, which has a big challenge for the operation under off-design conditions with various ambient temperatures, and the corresponding optimal operation parameters and control schemes are lacking. Especially in the condition of low ambient temperature, the traditional control scheme, which usually maintains the main compressor inlet temperature at the design-point value, obviously underestimates the efficiency of the solar power tower system. In the present study, an integrated model of solar power tower coupling with the Brayton power cycle is developed, and the particle swarm optimization algorithm is utilized to search for the optimal operation parameters and control schemes under off-design conditions with various ambient temperatures. Finally, annual performance analyses are conducted to investigate the actual effects of the proposed control schemes. The results indicate that: in the case with low ambient temperature, the proposed control scheme improves the power cycle efficiency by 0.78%; the total power output of 390 MW·h (accounting for 1.02% of the yearly power output) can be saved. In the case with high ambient temperature, the power cycle efficiency experiences an inevitable decrease, which causes the total wasted power output of 253 MW·h (accounting for 0.66% of the yearly power output); the losses caused by high ambient temperature are restrained in a small range by the proposed control schemes.