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This study presents a thermodynamic analysis of the bottoming cycle in a triple-pressure reheat combined-cycle power plant to evaluate the effects of various design parameters on the cycle performance. The important design parameters include the three inlet pressures and temperatures in the steam turbines, condenser pressure, and pinch point temperature of the heat recovery steam generator. These parameters significantly affect the power output of each steam turbine, which, in turn, influences the overall power output of the combined-cycle power plant. The analysis showed the effect of each parameter on the bottoming-cycle power output and thermal efficiency. Off-design conditions can significantly affect cycle performance, which can be used to understand the behavior of the combined cycle plant. A better understanding of the cycle can help achieve better bottoming-cycle designs that produce higher power outputs and efficiencies. [ABSTRACT FROM AUTHOR]

Fast and efficient mixing of high-speed shear flow formed by fuel and oxidizer is of great importance for the improvement of rocket-based combined cycle engine performance. Nevertheless, the existence of compressibility effects of high-speed flow significantly inhibits the growth process of a mixing layer. Moreover, a finite-length combustor of the engine calls for more effective enhanced-mixing strategies to complete mixing in a shorter streamwise distance. To this end, in present paper, the strategy called dual plate cavity (DPC) is proposed to promote mixing. Three cases including the benchmark, front-DPC and back-DPC cases are selected to perform the comparative study. By means of high-order direct numerical simulations, the structure evolution characteristics and turbulence intensity distributions are researched. The index of velocity thickness is utilized to assess the mixing layer growth. The results indicate that with the introduction of DPC, the mixing process is dramatically promoted. The penetration behavior of newly found T-shaped structures into the upper main stream can engulf more fluid into the mixing region. Specifically, in the back-DPC case, the coexistence of both large-scale and small-scale structures in the far flow field can improve the turbulence intensity. The spatial correlation analysis results show that with the influence of DPC, the structure sizes are much larger than that of the benchmark case in the same streamwise position. Meanwhile, the contour line equal to 0.5 possesses property of distortion for the back-DPC case. The drastic pulsation of a mixing layer edge can obviously promote the mixing process. Through exploration of the enhanced-mixing mechanisms, this work indicates that the proposed DPC strategy is a good candidate for efficient mixing, and in the future, more detailed work including three-dimensional simulations concerning the strategy optimization is suggested to be performed. [ABSTRACT FROM AUTHOR]

The ongoing transition to energy systems with high shares of variable renewables motivates the development of novel thermal power cycles that operate economically at low capacity factors to accommodate wind and solar intermittency. This study presents two recuperated power cycles with low capital costs for this market segment: (1) the near-isothermal hydrogen turbine (NIHT) concept, capable of achieving combined cycle efficiencies without a bottoming cycle through fuel combustion in the expansion path, and (2) the intercooled recuperated water-injected (IRWI) power cycle that employs conventional combustion technology at an efficiency cost of only 4% points. The economic assessment carried out in this work reveals that the proposed cycles increasingly outperform combined cycle benchmarks with and without CO2 capture as the plant capacity factor reduces below 50%. When the cost of fuel storage and delivery by pipelines is included in the evaluation, however, plants fired by hydrogen lose competitiveness relative to natural gas-fired plants due to the high fuel delivery costs caused by the low volumetric energy density of hydrogen. This important but uncertain cost component could erode the business case for future hydrogen-fired power plants, in which case the IRWI concept powered by natural gas emerges as a promising solution. [ABSTRACT FROM AUTHOR]

The Mach 6-capable turbine based combined cycle engine is a potential first-stage propulsion for TSTO mission. In order to improve thrust-to-weight ratio, an innovative tandem combined ramjet engine-FABRE (Fan Augmented Air-Breathing Ramjet Engine) is designed utilizing a versatile multi-mode combustor working at both high-speed ramjet mode and low-speed turbocharged mode. Employing the strut as mixer and flame holder in multi-mode combustor presents theoretical advantages. Nonetheless, a thorough investigation into its practical feasibility and combustion characteristics is essential. This paper experimentally verifies the feasibility of strut approach in multi-mode combustor at various speeds and evaluates the effects of different strut schemes on flow field structure, thermodynamic characteristics, and combustion performance via simulation. The experimental results affirm that employing the strut scheme as a combustion organization method enables the multi-mode combustor to operate effectively under diverse inflow conditions at both high and low speeds. Simulation results further validate that these strut solutions consistently demonstrate superior combustion performance. Additionally, the influences of the strut geometry on heat release and high-temperature area are highly consistent with its effects on combustion efficiency. At low speed, wider struts lead to increased combustion efficiency, while at high speed, they initially rise before declining with further widening. Regardless of speed, increasing strut slant angle consistently reduces efficiency. At low speed, widening the strut lowers the total pressure recovery coefficient, peaking at 45° with varying strut slant angle. Conversely, at high speed, changes in strut width minimally impact, while increasing strut slant angle reduces the coefficient. These conclusions provide valuable insights for the optimization of combustion organization in the design of combined ramjet engine with a wide range of operating conditions. • An innovative Mach 6-capable combined ramjet engine is designed to enhance the thrust-to-weight ratio for TSTO. • Experimentally validating the strut scheme for combustion organization in multi-mode combustor. • Combustion characteristics are numerically investigated using different strut schemes. [ABSTRACT FROM AUTHOR]

The Supercritical Carbon Dioxide Brayton Cycle (sCO2-BC) is a highly efficient and eco-friendly alternative for marine propulsion. The adoption of sCO2-BC aligns with the industry's focus on sustainability and can help meet emission regulations. In this context, the current study introduces a cascade system that harnesses the exhaust gases from a marine Gas Turbine Propulsion System to serve as a heat source for a bottoming Supercritical Carbon Dioxide Brayton Cycle (sCO2-BC), which facilitates an onboard heat recovery system. The investigation primarily focuses on the recompression cycle layouts of the sCO2-BC. To assess the performance of the bottoming cycle layouts and the overall cascade system, various parameters of the recompression sCO2-BC are analyzed. These parameters include the mass flow rate of CO2 in the bottoming cycle and the effectiveness of both the low-temperature recuperator (LTR) and the high-temperature recuperator (HTR). For conducting the cycle simulations, two codes are built and integrated; this first code models the thermodynamic cycle, while the second code models the recuperators. The research shows that incorporating the sCO2 Brayton Cycle as a bottoming cycle has the potential to greatly improve the efficiency of the entire system, increasing it from 54% to 59%. Therefore, it provides a useful framework for advancing energy-efficient gas turbine systems and future research. [ABSTRACT FROM AUTHOR]

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Day after day, stricter environmental regulations and rising operating costs and fuel prices are forcing the shipping industry to find more effective ways of designing and operating energy-efficient ships. One of the ways to produce electricity efficiently is to create a waste heat-driven liquid metal–water binary vapor power plant. The liquid metal Rankine cycle systems could be considered topping cycles. Liquid metal binary cycles share characteristics like those of the steam Rankine power plants. They have the potential for high conversion efficiency, they will likely produce lower-cost power in plants of large capacity rather than small, and they will operate more efficiently at design capacity rather than at partial load. As a result, liquid metal topping cycles may find application primarily as base-load plants onboard ships. In this study, a waste heat-driven liquid metal–water binary vapor power plant onboard a ship is designed and thermodynamically analyzed. The waste heat onboard the vessel is the exhaust gas of the LM2500 marine gas turbine. Mercury and Cesium are selected as liquid metals in the topping cycle, while water is used in the bottoming cycle in binary power plants. Engineering Equation Solver (EES) software (V11.898) is used to perform analyses. For the turbine inlet temperature of 550 °C, while the total net work output of the binary cycle system is calculated to be 104.84 kJ/kg liquid metal and 1740.29 kJ/kg liquid metal for mercury and cesium, respectively, the efficiency of the binary cycle system is calculated to be 31.9% and 26.3% for mercury and cesium as liquid metal, respectively. This study shows that the binary cycle has a thermal efficiency of 26.32% and 31.91% for cesium and mercury, respectively, depending on liquid metal condensing pressure, and a binary cycle thermal efficiency of 25.9% and 30.9% for cesium and mercury, respectively, depending on liquid metal turbine inlet temperature, and these are possible with marine engine waste heat-driven liquid metal–water binary vapor cycles. [ABSTRACT FROM AUTHOR]

In order to reduce greenhouse gas emissions associated with power generation, the replacement of fossil fuels with renewables must be accompanied by the availability of dispatchable sources needed to balance electricity demand and production. Combined cycle (CC) power plants adopting post-combustion capture (PCC) can serve this purpose, ensuring near-zero CO2 emissions at the stack, as well as high efficiency and load flexibility. In particular, the chemical absorption process is the most established approach for industrial-scale applications, although widespread implementation is lacking. In this study, different natural gas combined cycle (NGCC) configurations were modeled to estimate the burden of retrofitting the capture process to existing power plants on thermodynamic performance. Simulations under steady-state conditions covered the widest possible load range, depending on the gas turbine (GT) model. Attention was paid to the net power loss and net efficiency penalty attributable to PCC. The former can be mitigated by lowering the GT air–fuel ratio to increase the CO2 concentration (XCO2) in the exhaust, thus decreasing the regeneration energy. The latter is reduced when the topping cycle is more efficient than the bottoming cycle for a given GT load. This is likely to be the case in the less-complex heat recovery units. [ABSTRACT FROM AUTHOR]

To attain a net zero-carbon emissions energy system, the grid needs dispatchable and flexible power production capable of responding to wind and solar energy variability. Hydrogen-fired gas turbines could play a role in meeting this requirement in the electricity grid; however, research and development are needed to assess the impact of the fuel change on these systems. This study aims to determine the effect of fuel switching on the cycle performance of a typical aero-derivative gas turbine, ranging from 25-35MW when combined with various steam-based bottoming cycles using Aspen Plus thermodynamic simulations. The gas turbine cycle's efficiency and net output power increased by about 2.26% and 5.24%, respectively, when fueled with hydrogen for the constant TIT control strategy compared with the base case. The other two control strategies—constant TOT and heat input—are also positive. The performance of the combined heat and power configurations, expressed by the fuel charged to power, is better for almost all the hydrogen-fired cases compared with the methane case. This implies that using hydrogen as fuel in the gas turbine and duct-firing requires less fuel to produce heat and electricity. Although hydrogen integration into the overall system may pose challenges with auxiliary equipment, storage, supply, and combustion, hydrogen as fuel shows promise in improving the performance of gas turbine combined heat and power units. • Hydrogen for GTs will be an enabler of low-carbon and flexible power production. • Switching to hydrogen enhances power and heat production in all operating strategies. • The GT performance improves with the hydrogen fraction for all operating strategies. • Hydrogen firing increases the operational flexibility of GT-based CHP configurations. [ABSTRACT FROM AUTHOR]

Power plant engineers today are primarily focused on maximizing the extraction of fuel energy. This objective involves improving the efficiencies of different thermodynamic elements and the overall cycle in terms of both first and second laws of thermodynamics. To achieve this, engineers are employing various techniques aimed at increasing these efficiencies. In the present work, one such technique being utilized is the substitution of water/steam with a different working fluid. By changing the working fluid, engineers aim to optimize the thermodynamic performance of the power plant. In this study, the analysis focuses on the utilization of an ammonia-water mixture combined with Trans critical carbon dioxide in a heat recovery vapor generator. The results of this research reveal that the highest work output and second law efficiency achieved are 1192 kJ/sec and 81.68% respectively. These optimal values are obtained when the topping cycle pressure is set to 50 bar, and the turbine inlet temperatures are 500°C and 300°C for the ammonia-water mixture and Trans critical carbon dioxide respectively. Furthermore, the maximum first law efficiency of 43.57% is observed when the topping cycle pressure is set to 50 bar, the bottoming cycle pressure is set to 160 bar, and the turbine inlet temperature is 300°C. The analysis also reveals that the heat source is responsible for the majority of energy destruction, with a maximum of 1970 kJ/sec of available energy being destroyed at a temperature of 500°C. To achieve the highest values of thermodynamic performance parameters, it is recommended to maintain low pressure in the absorber and condenser. Additionally, the analysis indicates that the cost of electricity generation reaches its peak when the condenser pressure is set at 70 bar, amounting to 0.050 USD/kWh. [ABSTRACT FROM AUTHOR]

We examined how working-fluid properties impact the organic Rankine cycle (ORC) and bottoming cycle in a cogeneration system, and compared the sizes of turbines according to different working fluids. Working fluids R123, R245fa, and R245ca were selected based on factors such as the T-s diagram slope, environmental impact, and safety. The latent heat for vaporization significantly impacted ORC and bottoming-cycle performance. R123 produced the lowest bottoming cycle output of 38.49 MW and an ORC output of 1.95 MW. R245ca required a bigger turbine size, leading to the largest volume flow rate of 20 m3/s at the ORC turbine outlet. The bottoming-cycle output was 38.68 MW and the ORC generated 2.61 MW, which were the highest. R245fa showed promise in terms of compact turbine size due to its smallest volume flow of 14.96 m3/s at the ORC turbine outlet, even though the overall output was 250 kW lower than that of R245ca. [ABSTRACT FROM AUTHOR]

Combination of different power cycle scenarios is of prime importance in achieving maximum energy utilization from solar‐driven multigeneration systems. To fulfill such objective, the present article proposes a novel energy distribution system, leveraging a combination of direct‐fed organic Rankine cycle (ORC) and a bottom‐cycled arrangement of Kalina cycle system (KCS) and double‐effect absorption refrigeration cycle (DEARC) within a parabolic trough solar collector powered trigeneration system. The study explores three different ORC configurations: simple ORC; ORC equipped with internal heat exchanger (ORC‐IHE) and regenerative ORC (RORC). It is shown that although higher efficiencies are achievable from a larger portion of PTSC energy absorbed by the ORC, the ORC energy absorption is limited by ORC evaporator temperature differences, and there is unused energy that can be recovered by the KCS, based on the proposed energy system. The results indicate that the addition of bottoming KCS leads to a considerable increase in the exergy efficiency of ORC, ORC‐IHE and RORC‐based systems by 11.7%, 30.7% and 32.6%, respectively. The impact of different ORC configurations, key ORC parameters and various organic working fluids on the energetic/exergetic efficiencies is also examined to find the optimal configuration. In terms of overall energetic/exergetic efficiencies, the highest performance belongs to ORC (78.4%/30.4%) while the lowest energetic and exergetic efficiencies belong to ORC‐IHE and RORC, respectively (56.3% and 25.65%). On the basis of a comparative study with the available literature, these values are higher than what is already reported for similar solar‐driven multigeneration systems. Appropriate thermal match and lower exergy destruction in the KCS, and bottoming cycle arrangement of the DEARC are the main reasons for such enhanced performance. This research not only contributes valuable insights into efficient solar‐driven systems but also sets a new benchmark for performance metrics in the existing literature. [ABSTRACT FROM AUTHOR]

Inlet unstart prediction and warning are strictly crucial to the operation of hypersonic engines, especially for combined cycle engines where implementation across a wide speed range poses significant challenges. This paper proposes a realization method that involves constructing the conditions of critical backpressure ratios for the inlet unstart and unstart warning states within a wide speed range and establishing the backpressure prediction models for each engine mode. The detection of the unstart and unstart warning states is achieved by predicting the backpressure ratio at the exit of the isolator and comparing it to the critical backpressure ratios. To achieve this, numerical simulations for a three-dimensional inward-turning multiducted hypersonic combined inlet at various Mach numbers and backpressure ratios are carried out to obtain the dataset of surface pressure. A 10-fold cross-validation support vector machine (10-CV SVM) is used to solve the unstart boundary of surface pressure, and an unstart margin is set to determine the unstart warning boundary. A back propagation (BP) neural network is constructed to estimate the critical backpressure ratios at each working point within a wide speed range. The data information of surface pressure on the boundaries is used as the input for the predictions. The overall average regression correlation coefficient approaches 0.99 on the test dataset at each working point. The backpressure prediction models are established by the one-dimensional convolutional neural network (1D-CNN). Only 2 to 4 measurement points of surface pressure are considered for cross-validation evaluation, and the mean absolute percentage error is between 4% and 8% with the average prediction time not exceeding 2 ms. Finally, the proposed method and prediction models are validated by wind tunnel experimental data. [ABSTRACT FROM AUTHOR]

Solar power tower technology has strong potential among the other concentration solar power techniques for large power generation. Therefore, it is necessary to make a new and efficient power conversion system for utilizing the solar power tower system. In present research, a novel combined cycle is proposed to generate power for the application of the solar power tower. The pre‐compression configuration of the Brayton cycle is used as a topping cycle in which helium is taken as the working fluid. The transcritical CO2 cycle is used as bottoming cycle for using the waste heat. The proposed system is investigated based on exergy, energy, and exergoenvironmental point of view using computational technique engineering equation solver. Also, the parametric analysis is carried out to check the impact of the different variables on the system performance. It is concluded that the overall plant's optimized thermal and exergy efficiencies are obtained as 31.59% and 33.12%, respectively, at 800 °C optimum temperature of combined cycle and 850 W m−2 of direct normal irradiation and 2.278 of compressor pressure ratio. However, exergetic stability factor and exergoenvironmental impact index are observed as 0.5952 and 0.6801 respectively. The present proposed system performs better than the previous studies with fewer components. [ABSTRACT FROM AUTHOR]

A significant part of energy of fuel supplied is lost in internal combustion engines in the form of atmospheric discharge of engine exhaust gases which are considered as a big source of engine inefficiency and formation of pollutant emissions. To address this issue, a bottoming cycle combining the transcritical CO2 (T-CO2) refrigeration cycle and the supercritical CO2 (sCO2) power cycle is employed, aiming to produce cooling for food preservation by utilizing the exhaust heat of homogeneous charge compression ignition (HCCI) engine powering the refrigerated truck. The operative variables and their effect on thermal and exergetic efficiency of HCCI engine and the combined system are investigated. At the base case operative conditions, the thermal and exergy efficiencies of natural gas fueled HCCI engine are improved significantly from 48.69% to 61.28% and from 41.14% to 42.79%, respectively, after employing the sCO2 powered T-CO2 refrigeration cycle. Promotion of equivalence ratio from 0.3 to 0.9 enhances the thermal and exergy efficiencies of HCCI engine from 47.44% to 49.54% and from 40.14% to 42.12%, respectively. Increasing of engine speed from 1400 r.p.m to 2200 r.p.m provides marginal improvement in HCCI engine efficiencies but the efficiencies of combined cycle are significantly improved from 57.67% to 65.18% and from 40.64% to 45.06%, respectively. Finally, exergy analysis applied to determine the sources of non-idealities within the system revealed that out 361 kW (100%) fuel exergy supplied to the system, HCCI engine destroys 93.31 kW (25.85%), catalytic convertor destroys15.49 kW (4.29%), and the in-cylinder heat transfer losses and system exhaust losses are found as 35.72 kW (9.91%) and 16.61 kW (4.61%), respectively. [ABSTRACT FROM AUTHOR]

• A Cascade 2-stage condensation ORC is integrated with LNG vaporizing at 6 bar. • Simultaneous optimization in 3 levels is implemented using Genetic algorithm. • Novel variable definition method accelerates accurate result achievements. • Structure, working fluids, and variables optimized considering vital constraints. • A structure is proposed based on the exergy analysis result. One of the most efficient methods of exergy recovery during the regasification process is integrating the LNG stream with an Organic Rankine Cycle (ORC) to generate electricity. This study employs a cascade structure of ORC consisting of two double-stage condensations operating at 6 bar regasification pressure. To obtain an optimal ORC system integrated with an LNG, three optimization levels for a specific heat source are addressed, including process variables, working fluids, and structure. Ten process variables and two working fluid variables for the top and bottom cycle among 13 candidates of refrigerants were optimized to provide the maximum power output. The results determined that refrigerants of R41 and R1150 have the best performance in the optimized process conditions for the top and bottom cycles, respectively. For the regasification of 36 tonnes per hour of an LNG stream, the produced net power and the exergy efficiency are achieved by 2116.76 kW and 0.29, respectively. The exergy analysis revealed that employing the double-stage condenser ORC is not a good choice. Accordingly, a cascade-parallel structure is proposed for further studies. [ABSTRACT FROM AUTHOR]

Current study examined the effect of solar power tower (SPT) design parameters (solar emittance, concentration ratio and heat transfer fluid velocity, solar irradiation) on SPT-integrated combined cascade sCO2 (CSCO2) cycle and organic Rankine cycle (ORC) using ultra-low global warming potential (GWP) hydro fluoro olefins (HFO) fluids. Exergy efficiency, thermal efficiency and net output power were considered as performance parameters. A computational technique was used for the analysis. It was investigated that thermal and exergy efficiencies of the standalone (SPT+ CSCO2) cycle improved by 2.36% and 2.41%, respectively, by the incorporation of the ORC as bottoming cycle. Highest exergy efficiency, thermal efficiency and net output power were increased with solar irradiation, concentration ratio, heat transfer fluid velocity while decreased with solar emittance. Highest performance were found with R1224yd(E) while lowest with R1234yf among other considered low GWP fluids at current input conditions. [ABSTRACT FROM AUTHOR]

The energy and exergy evaluation of simple gas turbine (SGT), gas turbine with air bottoming cycle (GT-ABC), and partial oxidation gas turbine (POGT) are studied. The governing equations for each cycle are solved using energy equation Solver (EES) software. The characteristics performance for selected cycles are discussed and verified with that obtained for available practical cycles (SGT, GT-ABC, POGT). The present results show a good agreement with the practical one. The effects of significant operational parameters, turbine inlet temperature (TIT), compression ratio (CR), and compressor inlet temperature (CIT), on the specific fuel consumption, energy and exergy efficiencies are discussed. According to the findings, a reduction in CIT and a rise in TIT and CR led to enhance energy and exergy efficiency for each configuration with different ranges. Results revealed that the GT-ABC and POGT cycles are more efficient than those of SGT at the same operational parameters. The energy and exergy efficiencies are 38.4%, 36.2% for SGT, 40%, 37.8 % for GT-ABC, and 41.6%, 39.3% for POGT. The POGT cycle has a better energy and exergy performance at a lower pressure ratio than the SGT and GT-ABC. [ABSTRACT FROM AUTHOR]

This paper reports the Maisotsenko's cycle‐based waste heat recovery system with enhanced humidification to exploit the maximum waste heat recovery potential of the gas turbine. This research uses an integrated methodology coupling thermodynamic balances with heat transfer model of air saturator. The performance of the system is deduced which are assisted with sensitivity analysis indicating the optimal mass flow rate ratio (0.7–0.8) and pressure ratio (4.5–5.0) between the topping and bottoming cycles, and the air saturator split (extraction) ratio (0.5). The net‐work output, energy, and exergy efficiencies of the system are found to be ≈58.39 MW, ≈55.85%, and ≈52.79%, respectively. The maximum exergy destruction ratios are found as 68.2% for the combustion chamber, 16.0% for the topping turbine, 5.7% for topping compressor, 4.9% air saturator. The integration of Maisotsenko's cycle‐based waste heat recovery system with a comprehensive thermodynamic model, as demonstrated in this research, offers valuable insights into enhancing the efficiency, cost‐effectiveness, and environmental impact of gas turbines. By presenting fundamental equations related to thermodynamic balances, this work serves as an invaluable educational resource, equipping future researchers and students with the knowledge and skills needed to advance the study of thermodynamics and sustainable energy solutions. [ABSTRACT FROM AUTHOR]

The amount of resources devoted to saltwater desalination is substantial and will only rise as the scarcity of water escalates globally. Desalination techniques for seawater, particularly thermal desalination techniques, require a lot of energy and utilize conventional energy sources. The goal of this article is to examine the integration of thermal desalination techniques with carbon capture and sequestration (CCS) power generation. This study utilizes an oxy-combustion-based zero-emission power plant and investigates the performance of a humidification-dehumidification (HDH) cycle integrated with the main cycle. The system constitutes two main cycles, namely (i) oxy-combustion power generation cycle (OPGC) and (ii) humidification-dehumidification (HDH) cycle. The performance of several bottoming cycles coupled with a closed-air-open-water water-heated (CAOW-WH) HDH system is studied to evaluate the thermodynamic feasibility of the system. The effect of top and bottom temperatures of the HDH system and mass flow rates are optimized for gain output ratio (GOR) and recovery rate (RR). A sensitivity analysis of the integrated system was also conducted, and the effect of oxy-combustion operating parameters on the net cycle efficiency was examined. This analysis offers crucial design considerations for such integrated systems to generate power with zero emissions and produces sweet water without additional energy costs. [ABSTRACT FROM AUTHOR]

In this study, the performance of the organic Rankine cycle combined with the partial cooling supercritical CO2 cycle as the bottoming cycle for recovering the low grade heat powered by a solar power tower was evaluated. Ecofriendly fluids were taken into consideration. To simulate the model under consideration, a computer programme was created in engineering equation solver software. The impacts of solar radiation, concentration ratio, solar incidence angle, CO2 turbine inlet temperature, heat exchanger effectiveness and main compressor inlet temperature were investigated. Based on working fluid R1224yd(Z), it was determined that the combined cycle's thermal efficiency, exergy efficiency, and power output improved from 35.16% to 55.43%, 37.73% to 59.42%, and 188 kW to 298.5 kW, respectively, as solar irradiation raised from 0.4 kW/m2 to 0.95 kW/m2. Lower the solar incidence angle and higher the concentration ratio can enhance the combined system's performance. Amongst the working fluids that were taken into account, R1224yd(Z) was suggested as having superior performance. [ABSTRACT FROM AUTHOR]

The use of combined cycle power plants though had led the pathway to maximize the fuel energy utilization but the part-load operation of these plants is of concern. In this work, an exergoeconomic comparison of 11 different reheat combined cycle arrangements hasbeen carried out under their part-load operations for varying bottoming cycle parametersnamely steambleedfraction, deaerator pressure, separator temperature, absorber pressure, and condenser pressure. The results depict that the absorber has the highest exergy destruction with second law efficiency of 23.55% at thepart load of 25% for the combined cycle power plant having high pressure drum with steam as working fluid and low pressure drum with ammonia-water as working fluid. The comparison also shows the highest cost of electricity production as 0.1243USD/kWh for the combined cycle power plant having ammonia-water as working fluid in bottoming cycle and operating at part load of 25%. While the minimum price of electricity produced is 0.05USD/kWh at 25% part load for CCPP having double pressure HRVG's at condenser pressure of 0.09 bar. [ABSTRACT FROM AUTHOR]

Optimal thermo-economic integration of renewable energy sources with multi-generation energy systems is a prime research topic today. The present study proposes a multi-criteria evaluation method of such integration, based on combined heating and power (CHP), and combined cooling and power (CCP) scenarios, for three different solar intensities. Three novel solar-driven tri-generation systems are selected. They include different organic Rankine cycle (ORC) architectures and a Kalina cycle system (KCS) and a double-effect absorption refrigeration cycle as bottoming cycles. Evaluation of the tri-generation systems, both with and without the KCS system, indicates a performance improvement of up to 23% in various thermoeconomic characteristics when the KCS system is present. Selection of the suitable tri-generation system for each condition and optimization of the working fluid are carried out based on a multi-attribute decision-making method. P-xylene is found as the optimal organic working fluid for ORC and ORC (ORC integrated with internal heat exchanger) based systems, and benzene for the regenerative ORC-based system in both CHP and CCP scenarios. Multi-criteria analysis shows that ORC-based system outperforms other systems with net outranking flow of 0.44 (0.39) for CHP (CCP) application. The optimal configuration gives 95.6 M$ and 1.99 years for net present value and dynamic payback period, and 83.03% and 34.55% for energy and exergy efficiencies, respectively. [ABSTRACT FROM AUTHOR]

In today's scenario, ensuring sustainability of energy system particularly in the field of power generation is a major concern, and in this regard, exergy analysis is widely accepted tool. For this purpose, first, a comprehensive performance is carried out between two gas turbine plants, i.e., GT2 (case I) and GT1 (case II) using various exergy performance parameters. Further, a comprehensive performance evaluation is carried out between three cases; GT2 (case I), GT1 (case II) and CCPP (case III) using different sustainability indicators such as exergy efficiency, waste exergy ratio, exergy destruction factor and recoverable exergy ratio. Results demonstrate that exergetic sustainability index of combined cycle power plant (CCPP) is 0.45 when compared with GT2 (0.29) and GT1 (0.28). The increased sustainability index is because of the incorporation of a bottoming cycle, which ultimately decreases waste exergy ratio and leads to an increase in exergy efficiency and sustainability index of CCPP. [ABSTRACT FROM AUTHOR]

Gas turbine power plants have important roles in the global power generation market. This paper, for the first time, thermodynamically examines the impact of steam injection for a combined cycle, including a gas turbine cycle with a two-stage turbine and carbon dioxide recompression. The combined cycle is compared with the simple case without steam injection. Steam injection's impact was observed on important parameters such as energy efficiency, exergy efficiency, and output power. It is revealed that the steam injection reduced exergy destruction in components compared to the simple case. The efficiencies for both cases were obtained. The energy and exergy efficiencies, respectively, were found to be 30.4% and 29.4% for the simple case, and 35.3% and 34.1% for the case with steam injection. Also, incorporating steam injection reduced the emissions of carbon dioxide. [ABSTRACT FROM AUTHOR]

Marine transportation facilitates the transportation of fuels and goods over long distances cost-effectively, but their environmental impact has increased due to the utilization of fossil fuels. This paper presents a new marine engine design comprising a steam Rankine cycle, gas Brayton cycle, and solid oxide fuel cell to replace a two-stroke internal combustion engine. Hydrogen, methane, dimethyl ether, ethanol, and methanol are selected as eco-friendly fuels. This hybrid combined engine is attached to a multi-effect desalination unit to take the advantage of waste energy from the exhaust gases. The engine is thermodynamically analyzed using the Aspen Plus software to assess its performance energetically and exergetically. It is found that the engine's total power is increased by 40% to an average of 15,546 kW with average thermal and exergetic efficiencies of 61% and 43%, respectively. The maximum power reaches 16,780 kW with maximum carbon emission reductions of 53% and a minimum specific fuel consumption of 337 g kWh−1 which is a reduction of 17%. In addition, the waste energy is used to deliver 20.3 kg s−1 freshwater by desalinating seawater. The proposed engine system has better performance and less environmental impact, which makes it a better choice than traditional engines. [ABSTRACT FROM AUTHOR]

In this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (C E E P) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNO x in C E E P. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency. • Impact of combustion chamber wall heat loss on the engine's performance and multiobjective optimization is investigated. • A heat flux of 10 MW/m2 decreases overall efficiency by 1.1% and increases emission based performance by 2 kJ/gNO x. • Increasing hydrogen flow rate and decreasing air flow rate and cruise speed improve the engine's performance. • Optimum cruise altitude and core nozzle outlet area are 23 km and 4.94 m2. • Optimized design has 20.35% lower NO x emissions than the base design. [ABSTRACT FROM AUTHOR]

The present work deals with the deployment of an air bottoming cycle as a technology for thermal energy valorization. This solution is integrated within the preheater tower on an Algerian cement plant. A combined MATLAB-Coolprop optimization tool has been developed to carry out a thermo-economic calculation allowing to design and optimize the air bottoming cycle and also check its economic returns. The developed code employs the genetic algorithm through a multi-objective function aiming to maximize the cycle's net power output as a priority objective, then minimize the heat exchanger's area of exchange, and also maximize the cycle's net present value. through the implemented models on it, the code gives the ability to confirm the applicability of this technology through the Algerian market which is characterized by one of the cheapest prices of electricity in the world that doesn't exceed 0.040 $ kWh-1. The obtained results highlight that the implementation of such technology for energy valorization purposes from the preheater tower of the selected cement plant can be a profitable and attractive solution, particularly in scenarios of water scarcity. Since the implementation of this technology presented a power capacity of 1.2 MW covering then around 7.8% of the electricity demand of the investigated cement plant. The economic analysis of the proposed ABC cycle pointed out a net present value of 6.59 M$, and a payback time less than 3.6 years, besides a Levelized cost of energy less than 0.017 $ kWh-1 which is a comparable value to the subsidized prices of electricity in the Algerian market. [ABSTRACT FROM AUTHOR]

The integrated solar combined cycle (ISCC) system is a proven solution for grid-connected power generation from solar energy. How to further improve the ISCC system efficiency and propose a more efficient system solution has become a research focus. A novel gas turbine combined cycle (GTCC) benchmark system is proposed by replacing the conventional steam Rankine bottom cycle with a supercritical CO2 Brayton cycle, whose output power and efficiency are increased by 9.07 MW and 1.3%, respectively, compared to those of the conventional GTCC system. Furthermore, the novel ISCC systems are established with the parabolic trough solar collector (PTC) and the solar tower (ST) collector coupled to the novel GTCC system. Thermal performance analysis, exergy performance analysis, and the sensitivity analysis of the ISCC systems have been performed, and the results show that the system efficiencies of both ISCC systems are lower than that of the GTCC system, at 57.1% and 57.5%, respectively, but the power generation of the ISCC system with PTC is greater than that of the benchmark system, while that of the ISCC system with ST is less than that of the benchmark system. The photoelectric efficiency of the ISCC system with PTC is 27.6%, which is 2.1% greater than that of ISCC system with ST. In the ISCC system with PTC, the components with the highest exergy destruction and the lowest exergy efficiency are the combustion chamber, and PTC, respectively. ST is the component with the highest exergy destruction and the lowest exergy efficiency in the ISCC system with ST. With the increase in direct normal irradiance (DNI), the total output power, solar energy output power, and photoelectric efficiency of the ISCC system with PTC increase, while the system efficiency decreases; the solar energy output power and photoelectric efficiency of the ISCC system with ST increase, while the total output power and system efficiency decrease. The photoelectric efficiency of the ISCC system with PTC is greater when the DNI is greater than 600 W/m2; conversely, the photoelectric efficiency of the ISCC system with ST is greater. After sensitivity analysis, the optimal intercooler pressure for the ISCC system is 11.3 MPa. [ABSTRACT FROM AUTHOR]

With the development of combined cycle engines, it is urgent to estimate more quickly and accurately the flow capture capacity and starting performance of variable geometry inlets over a wide Mach number range. Based on the flow field and parameter fitting, two prediction methods for the curved axisymmetric inlet with lip translation scheme have been proposed. The method based on the flow field of the reference inlet is more efficient than the parameters-based prediction method, as it can accurately predict the lip translation distance and the corresponding flow coefficient over the entire working range of the inlet without additional numerical calculations. Moreover, the starting Mach number is accurately predicted by the fitting method based on the throat Mach number of the reference inlet, with a relative error of only 0.95% compared to the numerical simulation. The flow coefficient-based method is simple and accurate for predicting lip translation distances with a known starting Mach number, with a relative error of only 1.65% compared to numerical simulations. The prediction approaches can overcome the drawbacks of the standard iterative algorithms and significantly enhance computational accuracy and efficiency. [ABSTRACT FROM AUTHOR]

The vessel's waste heat has the characteristics of a large temperature gradient, huge recoverable volumes, and various properties. TEG-ORC combined cycle is a promising method for multiple vessels waste heat cascade utilization. Keeping the evaporation pressure at 0.7Mpa, R245fa of low toxicity and environmental friendly is employed for the research under the conditions of different bottom cycle ratios(₣) and superheating. The interaction between essential parameters and system performance is explored. As the ₣ gets larger, the system net power output (Wnet), the system thermal efficiency (ηs) and the waste heat utilization of main engine flue gas (fg) gradually increase, the power-production cost (Cg) of the system gradually decreases. When the degree of superheat increases from 3.36K to 9.23K, the output power of the expander increases synchronously. The results show that superheating improves the combined cycle Wnet and fg while reducing theCg. The stability and safety of the ORC unit are further enhanced by expanding the ₣. When the ₣ is 0.885 and superheat is 11.28 K, Wnet is 965.18 W, ηs is 8.74%, and the Cg of the system is 0.5363 $ k Wh−1, and the rate of fg is 85.07%. [ABSTRACT FROM AUTHOR]

This paper presents the energy and exergy analysis of the gas turbine combined cycle during part-load operation under the exhaust gas recirculation - inlet/variable guide vane control (EGR-IGVC) strategy. The exergy destruction across each component and the energy and exergy efficiency of the topping, bottoming, and combined cycle are determined. Results show that EGR-IGVC and IGVC both effectively enhance the part-load efficiency of the combined cycle compared to fuel flow control (FFC) because higher turbine exhaust temperature allows more exergy to enter the bottoming cycle and increases bottoming cycle power output. However, EGR-IGVC decreases the bottoming cycle energy and exergy efficiency compared with IGVC. Even so, EGR-IGVC increases the topping cycle energy and exergy efficiency and can obtain a higher bottoming cycle power output. The combined cycle efficiency is enhanced by 0.97–1.21 percentage points over IGVC at 40 %–90 % loads. Exergy analysis has important guiding significance for further improving the part-load performance of the combined cycle. [ABSTRACT FROM AUTHOR]

A marine combined compression-ejector refrigeration machine that comprises conventional refrigeration and air-conditioning system using single-stage refrigeration machine and an ejector refrigeration machine is proposed and studied. The ejector refrigeration machine is driven by the waste heat from the single-stage refrigeration machine and acts as the bottom cycle of the single-stage refrigeration machine. A system analysis shows that the COP of a compression-ejector refrigeration machine is significantly higher than a one-stage refrigeration system. Improvement in COP can be as high as 19.3% for evaporating temperature of the single-stage refrigeration machine Tc at -40°C. Influence of flowing part of ejector profile, operating parameters, scheme and cycle of the marine combined compression-ejector refrigeration machine on its performance characteristics is shown. Rational methods to increase efficiency of marine combined compression-ejector refrigeration machine, operating with environmentally friendly lowboiling refrigerant R245fa, are offered and investigated. The present study shows that the combined compression-ejector refrigeration machine using the ejector refrigeration machine as the bottom cycle of the one-stage refrigeration machine is viable. The opportunities of implementing solar panels, raised challenges for older reefer vessels (20-40years) force to analyse situation. While opportunities exist for efficiency improvement and environmental alignment, challenges in retrofitting older vessels, especially those nearing the end of their operational life, make economic viability a critical consideration. The analysis of the possible solar panel application estimates a cost range of 398,269.20 to 426,717.00 euros, emphasizing the need for careful evaluation. The conclusion advocates against implementing solar panels on the researched vessel, highlighting the lack of justification in both economic and operational efficiency aspects. [ABSTRACT FROM AUTHOR]

Integrated solar combined cycle (ISCC) systems play a pivotal role in the utilization of non-fossil energy; however, the efficient application of solar energy has emerged as a primary issue in the study of ISCC systems. Therefore, it is extremely urgent to propose the best optimization scheme for ISCC under different operating conditions. In this paper, according to the idea of temperature matching and cascade utilization, the optimization of the ISCC system is carried out with the genetic algorithm for the whole working conditions, and the optimization schemes with the highest photoelectric efficiency and system efficiency under different working conditions are derived. In comparison with two optimization schemes with different objective functions, the conclusion can be drawn that: At 100% gas turbine load—30% DNI and 100% gas turbine load—100% DNI working conditions, respectively, the maximum system efficiency of 56.32% and the maximum solar photoelectric efficiency of 35.5% are attained. With the decreasing of gas turbine load, the solar energy integration position will gradually change from the topping cycle to the bottom cycle; with the gas turbine load variation from 100% to 75%, the optimal photoelectric efficiency model prefers two-stage integration, and up to 141.3 MW of solar energy could be integrated, which is greater than the maximum value of 127.1 MW for the optimal system efficiency model. Regarding the heat collection choice of bottom cycle, the optimal photoelectric efficiency model prefers the high-pressure boiler (HPB), while the optimal system efficiency model prefers the high-pressure superheater (HPS). The comparison between the optimal solution and the actual cases confirms the correctness of the optimization results and provides guidance for the subsequent ISCC study. [ABSTRACT FROM AUTHOR]

Fuel cells are a promising power source in the electric propulsion systems for zero-emission vessels. The electric efficiency of fuel cells can be increased to 55% practically, but significant amounts of remaining energy from the electrochemical reaction are wasted as heat. This article proposes a hybrid propulsion system for ships that utilizes both the electric energy and thermal energy generated by fuel cells. The electric power capacity of fuel cells and the steam generation capacity of recovered heat from fuel cell systems are calculated, and then the propulsion power of the hybrid system is simulated by MATLAB Simulink. The overall energy efficiency of the proposed ship propulsion system is compared with that of conventional systems by comparing fuel consumption rate. Simulation results indicate that the proposed hybrid propulsion system can increase energy efficiency by 22.5% by additional utilization of the recovered heat from fuel cells. [Display omitted] • A new hybrid ship propulsion system with a fuel cell is proposed. • The thermal energy of the fuel cell is utilized by a bottoming cycle. • An electric motor and a steam turbine drive the propeller shaft. • The efficiency of the proposed system is 22.5% higher than the conventional system. • The proposed system can reduce fuel consumption by up to 17.5%. [ABSTRACT FROM AUTHOR]

Assessing the economic viability of new high-speed systems concepts since the early design phases is crucial for the success of future hypersonic vehicles including cruisers, reusable access-to-space and re-entry systems. Besides literature reports few parametric cost models for high-speed vehicles, all of them makes exclusively use of mass as parameter and none of the models moves beyond the vehicle level. This paper describes a new parametric cost estimation model which moves beyond the state-of-the-art methodologies (1) by integrating vehicle design and operational parameters (in addition to the mass) as cost drivers for the prediction of the vehicle life-cycle cost, (2) by introducing prediction margins accounting for the uncertainties on the data-driven correlations, (3) by providing a first estimate of the costs of every on-board subsystem, including combined cycle engines and multi-functional subsystems, (4) by increasing the granularity of the analysis up to technology level, thus providing a valuable support to Technology Roadmaping activities. The parametric cost estimation model has been refined and exploited in the context of the Horizon 2020 STRATOFLY project, where the technological, operational, environmental, and economic viability of a Mach 8 waverider concept have been investigated. • Innovative RDTE&PROD cost estimation methodology for civil high-speed vehicle. • New parametric equations using vehicle design and operational parameters as drivers. • Costs predictions at subsystems level including complex multi-functional subsystems. • Cost estimation as valuable support to technology roadmapping activities. • Technology Readiness Level as new cost driver for the RDTE cost of vehicles. [ABSTRACT FROM AUTHOR]

The single-expansion ramp nozzle (SERN) has a compact structure and adaptability under off-design conditions, which is one of the nozzle configurations that the combined cycle engine gives priority to. Flow separation is likely to occur when the nozzle operates at low-pressure ratios. Subsonic regions, such as separation bubbles, recirculation zone, and boundary layer, also exist in the overexpanded flow field. At this point, the varying external flow field can affect the flow field inside the nozzle, which may lead to the transition of the flow separation pattern. The majority of relevant studies are conducted in a static environment because of experimental conditions limitations. This paper numerically simulates the transitions of separation patterns during the acceleration and deceleration processes of a short flap SERN. The separation transitions mechanism is analyzed, as well as the performance impact of the transitions. Current results show that the separation pattern transition happens during both the acceleration and deceleration processes, and free shock separation is a relatively stable state. The separation pattern transition occurs as a function of the external flow field, recirculation zone, boundary layer, and separation shock wave coupling. Compared with previous studies on the long flap SERN, the coupling mechanisms of the internal and external flow fields of the two nozzles were found to be different. The shock wave structure of the short flap SERN's flow field is stable during the transition processes, and the nozzle performance does not exhibit a step change. The hysteresis of the short flap SERN is also weaker. [ABSTRACT FROM AUTHOR]

Waste heat recovery technology has gained popularity due to its ability to save energy for both financial and environmental reasons. In this article, a new technology, thermal power generation (TEG)‐organic Rankine cycle (ORC) combined cycle system, is proposed to recycle cascaded waste heat of ships. The bottom cycle ratios are an important parameter affecting the combined cycle system, but its effect under more working conditions is unknown. Therefore, keeping the evaporator pressure at 0.7 MPa, the environmental‐friendly R245fa working fluid is employed to implement an experimental study on the variation law of the main performance parameters such as the system power output (Wnet), the system thermal efficiency (ηs), power‐production cost (Cg), and waste heat utilization of main engine flue gas (fg) under different TEG/ORC bottom cycle ratios (BCR). At the same time, the TEG‐ORC combined cycle system's performance of the R22 and R245fa is compared. With the increase of the BCR, the Wnet, ηs, and fg increase, but the Cg of the system decreases. When the BCR is 0.885, the Wnet, ηs, Cg, and the rate of fg is 688.4 W, 9.09%, 0.5194 $/kWh, and 85.07%, respectively. This study provides a reference for the clarification and further optimization of the TEG‐ORC combined cycle mechanism. [ABSTRACT FROM AUTHOR]

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In this study, a boil-off gas reliquefaction system that is a part of liquid ethylene gas (LEG) carriers is evaluated. The reliquefaction system is formed by two thermally interconnected two-stage refrigeration cycles. The working fluid of the bottoming cycle is ethylene; the working fluid of the topping cycle is propylene. The research is based on determining the irreversibilities in the reliquefaction system cycles using the entropy-cycle method of thermodynamic analysis. The impact of the process performance in the main components on the reliquefaction system energy efficiency has been evaluated by the entropy-cycle method. The greatest thermodynamic irreversibility is observed in the two-stage compression process of the bottoming cycle (9%), total throttling irreversibility in the reliquefaction system (8.5%), and vapor superheating at the suction into the low stage of the two-stage compressor of the bottoming cycle (8%). The results of the study showed that it is necessary to improve the design of expansion devices using the replacement of throttle devices with ejectors when designing cascade ethylene reliquefaction plants. In addition, when operating such systems much attention should be paid to the condition of the insulation of cargo pipelines and the parameters of the cooling system of the cargo compressor. [ABSTRACT FROM AUTHOR]

As the bottom cycle of gas turbine waste heat utilization, the S-CO2 cycle can enhance the power output capacity of the system. Based on the energy analysis of the recompression cycle and the partial cooling cycle for gas turbine waste heat utilization, the two cycles are improved from the matching of heat exchange flow of regenerator and heater in this paper. Under the same parameters, compared with the cycle before improvement, increase in heat source utilization rate and net power output of improved cycles is 45.69% and 39.31%, 43.54 MW and 35.43 MW, and the power consumption cost is decreased by 0.6106 $/kWh and 0.6289 $/kWh. However, as part of heat recovery inside the system is replaced by the heat of the heat source, the thermal efficiency is decreased by 10.43% and 8.7%, respectively. Variable parameter study is conducted on the two improved cycles to analyze the cycle characteristics from the perspective of energy, exergy, and economy (3E). The results showed that the improved recompression cycle has a high thermal power conversion capacity, higher system thermal efficiency and exergy efficiency and lower power generation cost, while the improved partial cooling cycle has higher waste heat utilization potential. However, the area of heat exchangers in both cycles tends to increase, which is not conducive to the compactness of the system. [ABSTRACT FROM AUTHOR]

The gas turbine combined cycle (GTCC) system has the advantages of high power density, high efficiency, and fast start-stop control, which will occupy an important position in the next-generation power system. In this paper, two groups of reheat cycle gas turbines with different thermal parameters are compared and the reheat and recuperative cycle is constructed by adding a recuperator to the recommended reheat cycle. Two typical sCO2 cycles are selected to construct a combined cycle system with simple cycle, reheat cycle, reheat, and recuperative cycle, respectively. In the range of gas turbine pressure ratio of 32–56, the parameters of GTCC with turbine inlet temperature of 1750°C are optimized based on the system calculation method of total physical properties, and the thermodynamic performance of the GTCC system was evaluated. The research shows that the reheat cycle with a TRIT (inlet temperature of the turbine after reheat) of 1250°C has higher efficiency and lower specific net work than the reheat cycle with a TRIT of 1750°C, and the relatively low exhaust temperature is more suitable for the sCO2 bottoming cycle. In addition, compared with the simple cycle, the optimal topping cycle thermal efficiency of the reheat and regenerative cycle is only reduced by 0.1%, but the exhaust temperature is higher. Under the same sCO2 cycle form, the combined cycle efficiency is improved by 1.5–2.0%. The thermal efficiency of the reheat and regenerative cycle gas turbine combined cycle (RCRHCC) studied in this paper can reach up to 67.53%, which has the potential to become the next generation of GTCC units. [ABSTRACT FROM AUTHOR]

This study aims to improve existing fossil gas turbine power plants by waste heat recovery. These power plants function with an air simple cycle (ASC) and are implemented where water resources are limited. Modeling and simulation of ASC and two advanced energy conversion systems are performed. They are the gas turbine–air bottoming cycle (GT-ABC) and gas turbine–supercritical carbon dioxide bottoming cycle (GT-sc-CO2BC). The main intent is to assess the benefits of employing sc-CO2 as a working fluid in a closed Brayton bottoming cycle compared to air, based on the energetic and exergetic performance and economic and environmental impact. Analyses of ASC, GT-ABC, and GT-sc-CO2BC are performed for various topping gas turbine powers: large (plant 1); medium (plant 2); and low (plant 3). The results of the energetic and exergetic analyses indicate that there is a significant improvement in the output power (ranging from 22% to 25%); and energy and exergy efficiencies of GT-ABC and GT-sc-CO2BC (up to 8% and 11%, respectively) compared to that of ASC. To provide better insight into the behavior of these technologies and achieve their better integration, we investigate the influence of varying the bottoming compressor pressure ratio, the ambient temperature, and the gas flow rate in the bottoming cycle. The results of the environmental and economic analyses show that the amount of CO2 emissions in GT-sc-CO2BC is reduced by 10% more than in GT ABC. The results also show that GT-ABC improves the NPV between 17.69% and 30% but GT-sc-CO2BC improves it even more, between 25.79% and 33.30%. [ABSTRACT FROM AUTHOR]

A performance assessment of advanced sCO2 Brayton cycles integrated with a concentrated solar power and waste heat recovery systems was conducted. Five advanced sCO2 Brayton cycles are examined for the bottoming cycle: dual heater, dual expansion, cascade, partial recuperation, and Kimzey cycles. This study reveals that the dual heater and dual expansion cycles have the best performance among the advanced sCO2 Brayton cycles considered. The findings reveal that the highest cycle efficiency is for the dual heater and dual expansion cycles (29.18%) followed by the Kimzey cycle (27.73%), then the cascade cycle (26.29%). Consequently, the least cycle efficiency is for the partial recuperation cycle (25%). Furthermore, the highest net power takes place in the dual heater and dual expansion cycles. Finally, the findings demonstrate that increasing the pressure ratio of advanced sCO2 Brayton cycles, within the range considered, results in a reduction of the cycle efficiency. [ABSTRACT FROM AUTHOR]

The design and part load performance simulation of a natural gas combined cycle power plant (CCPP) is of great importance and is affected by various load regulation strategies during operation. In this work, a new regulation strategy with inlet air cooling (IAC) system integration is proposed for CCPP load regulation and performance assessment. The regulation strategy uses an IAC system and gas turbine inlet temperature (TIT/T4) named as IAC-T4, which is little different from the concept of inlet air heating (IAH) regulation. The analysis is performed using a simulation program and compared with inlet guide vane (IGV-T4) regulation to predict the behaviour of CCPP during part load operation. The result shows that the IAC-T4 regulation strategy reasonably enhance the part load performance. The efficiency increment is in the range of 0.25–1.02% with variation of load from 80 to 100%. The drop-in fuel consumption rate varies 0.53–2.02% for load reduction from 80 to 50%. The variation of topping cycle exergy efficiency for both the regulation strategies is between 7.9 and 8.2% under full load and part load. Whereas for both the control strategy the bottoming cycle efficiency variation was found to be 36.11–37.15% with a steam temperature limit of 564 °C. Moreover, it is observed that the topping cycle exerts a substantial impact in the CCPP performance for the IAC-T4 regulation strategy compared with IGV-T4 regulation strategy. The heat recovery steam generator (HRSG) exergy efficiency variation for both the strategy is relatively small, as the heat exergy of GT exhaust recovered effectively for all load cases. In conclusion, this study attempts a new approach for CCPP load regulation and part load thermal performance enhancement using IAC system integration. [ABSTRACT FROM AUTHOR]

In the contemporary context, significant importance is attributed to micro and small-scale Organic Rankine Cycle (ORC) units that are specifically designed for decentralized electricity generation. An essential component within each ORC system is the expander, available in both volumetric and turboexpander configurations. In the existing biogas plant with an Internal Combustion Engine (ICE), the ORC, functioning as a bottoming cycle (BORC) on ICE waste heat, is installed. The BORC utilizes the heat from exhaust gases and the cooling water of the ICE. The paper investigates the effects of various working fluids on both the thermodynamic efficiency of the BORC and the isentropic efficiency of the turboexpander, thus influencing the design parameters of the turboexpander (e.g., number of stages, stator and rotor blade heights, etc.). The BORC, employing the working fluid R141b, has exhibited superior thermodynamic performance, demonstrating a commendable 63.5 kW in net power with a thermodynamic efficiency of 13 %, and ultimately increased the power of the ICE (537 kW) by approx. 12 %. Regarding the turbine component, the turbine operating with the R141b working fluid demonstrated the highest power output and isentropic efficiency, achieving values of 64.14 kW and 67.4 %, respectively. A design was developed for the same turbine, with aerodynamically perfect profiles specially designed for the stator and rotor blades. • In recent decades there has been a significant increase in interest in the use of waste heat (WH). • For the use of WH from internal combustion engine (ICE) the organic Rankine cycle (ORC) comes to the fore. • An important component of every ORC is the expander. • The working fluid influences both on efficiency of ORC and turbine design. • ORC increased the power of the ICE (537 kW) by approx. 12 % (63.54 kW). [ABSTRACT FROM AUTHOR]

This study presents a dynamic simulation analysis of the bottoming cycle in a 400 MW combined cycle power plant (CCPP) featuring a heat recovery steam generator (HRSG) and triple-pressure reheat steam cycle. Traditional simulation tools have limitations in controlling specific design parameters, such as the heat transfer coefficient and equipment geometry, which affect the accuracy of transient response simulations. Therefore, a MATLAB-based simulation program was developed to more precisely model the transient behavior of the CCPP, including the pressure, flow rate, and temperature variations across the heat exchangers and the steam turbine power outputs under partial load conditions. This study focuses on the effect of proportional-derivative (PD) control on the stability of HRSG drum water levels. Transient conditions were simulated by reducing the load, which resulted in significant changes in the steam cycle parameters. The results demonstrate that the PD controller effectively stabilizes the drum water levels during load changes, which prevents issues, such as overheating or turbine blade damage, caused by excessive water levels. Moreover, the findings reveal that the choice of PD controller parameters directly influences water level fluctuations and recovery time, with higher gains improving stability. In addition, the simulation results confirm that even at a partial load, the steam turbine inlet temperature stabilizes, and the steam cycle operates efficiently, producing approximately 93.4% of the net power generated under full-load conditions. Hence, this study highlights the importance of accurate simulations and effective control mechanisms to ensure the safe and reliable operation of large CCPPs under transient conditions. [ABSTRACT FROM AUTHOR]