Main Compressor Research Articles

High-performance aerodynamic design of supercritical CO2 centrifugal compressor for the Megawatt-class nuclear microreactor (MSC-GFR)

Design of the SCO2 centrifugal compressor is critical for the fuel economy and power output of the nuclear microreactors. In this study, we developed a high-performance aerodynamic design & analysis platform (XJHPCCD) for real-gas centrifugal compressors. Based on the single-zone method, the platform realizes efficient and fast solution to the direct and inverse problems of centrifugal stages in real gases. Using the XJHPCCD platform, we performed a principal component analysis on the performance prediction errors in different combinations of the multiply expressed loss mechanisms. On the results of composite analysis, an optimal loss model was proposed regarding the hundred-kW SCO2 compressor in Megawatt-class microreactors. By coupling the optimal loss model in performance prediction, the errors of pressure rises were reduced from 5–10% to 3% for the Sandia’s verified model, greatly promoting the reliability of aerodynamic analyses. To demonstrate the engineering values of the specifically optimized toolkit, we numerically conducted a design research on the main compressor of a 1 MWt SCO2-cooled fast breeder microreactor (MSC-GFR). Results showed the XJHPCCD platform (coupled with the optimal loss model) has well satisfied the technical demands with high-performance aerodynamic design and low prediction errors. Thereby, it is proved that we have successfully proposed a specifically optimized aerodynamic toolkit for the component design of Megawatt-class microreactors.

Off-design and control performance analysis of a novel supercritical carbon dioxide power cycle for waste heat recovery

A novel supercritical carbon dioxide power cycle (sCO2) for waste heat recovery (WHR) is developed. This novel cycle has high efficiency, and it could make a more complete utilization of the waste heat. Besides, the flexible and independent controls of recompression compressor and main compressor can be made to obtain the better off-design performance. The off-design and control performance of this system is quantitatively investigated in this paper. The results indicate that the optimal net power output increases as mass flow rate or temperature of flue gas increases, whereas it decreases with increasing ambient temperature. The first and second highest exergy destruction shares always belong to the cooler and LTWHE under various external conditions. The adjustment of two compressor outlet pressures should be a priority under various mass flow rates or temperatures of flue gas, while the adjustment of cycle minimum pressure should be given a high-priority rating in response to variation of ambient temperature. Moreover, the control performance of recompression compressor is more sensitive to the variation of flue gas mass flow rate, while the control performance of main compressor is more sensitive to the variation of flue gas temperature and ambient temperature.

Experimental study of the startup of a supercritical CO2 recompression power system

The supercritical CO2 Brayton cycle is a revolutionary power conversion technology. However, due to the lack of experimental research, the cycle's dynamic characteristics and control rules are still unclear. This study presents experimental research of a 300 kW supercritical CO2 recompression cycle power system based on two integrated high-speed turbo-alternator-compressor units, and characteristics of dynamic control, flow transition, and thermal inertia of the cycle are presented. The difficulty of generator startup increases with initial pressure, therefore a low-pressure startup strategy is proposed and verified. During startup, the closing time of turbine bypass value and control performance of the main compressor inlet temperature are found to have great influence on the stable operation of the cycle, and relevant control strategies are verified and discussed. The study also presents the existence, transformation mechanism, and flow characteristics of four flow modes during the startup of recompression cycle. These findings are of great help to judge the flow pattern of CO2 in the complex piping system and improve the transparency and safety level of system operation. Test results also show that despite the large thermal inertia, the load of recompression cycle can be quickly adjusted.

Off-design performance and control strategies of sCO2 recompression power systems considering compressor operating safety

The supercritical carbon dioxide (sCO2) power cycle is a promising power cycle in the field of thermal power generation. The system is often operated under off-design conditions, which would lead to the unsafe or unstable operation of the sCO2 power system. The performance of the sCO2 recompression cycle system under off-design working conditions by different control strategies is investigated in this paper. A one-dimensional design prediction model for centrifugal compressors is introduced to predict off-design system performance and the operating conditions and safety of centrifugal compressors under the 5 control strategies are simulated and compared. To show the difference between the control strategies, the thermal efficiency was compared, the highest thermal efficiency of the system is 11.2 % by the inventory control method, and the lowest thermal efficiency is 5.45 % by the turbine bypass control method. The compressor backflow control method makes the main compressor has a choking risk and the recompressor has a surging risk when the output power of the system is small. The speed variations of centrifugal compressors are 39.55 % (MC) and 34.71 % (RC) using the inventory control method. A hybrid control strategy (the compressor backflow and inventory control strategies) is proposed based on the performance maps of centrifugal compressors. The turbine efficiency is improved by 4.5 % and the system thermal efficiency is improved by 7.1 % by using the hybrid control strategy. The hybrid control strategy can solve the problem of dangerous working conditions of centrifugal compressors. The results of this study can guide the system control and operational safety of sCO2 recompression cycles.

Thermo-Economic Comparative Study and Multi-Objective Optimization of Supercritical CO2-Based Mixtures Brayton Cycle Combined With Absorption Refrigeration Cycle

Abstract In this paper, a novel system based on the combination of a supercritical recompression Brayton cycle (SRBC) and LiBr-H2O absorption refrigeration cycle (ARC) is proposed, in which ARC utilizes the waste heat of SRBC for cooling and further reduces the main compressor inlet temperature. The potential of using xenon and krypton as additives for the supercritical CO2 Brayton cycle is explored via comparative analysis. The results show that CO2/Krypton is more suitable to be the working fluid of the combined system because of its higher thermal efficiency and lower costs. The effects of the operating parameters and mass fraction of krypton on the thermo-economic performance of the combined system are discussed. Multi-objective optimization is applied to simultaneously optimize the thermal efficiency and total product unit cost of the system. Compared with the stand-alone cycle, the combined system can improve the cycle efficiency over a wide temperature range. The exergy efficiency of SRBC/ARC using CO2/Krypton (0.64/0.36) increased from 0.638 to 0.688, from 0.653 to 0.665, and from 0.586 to 0.646 at ambient temperature T0 = 10, 25, 35 °C, respectively, increasing by 7.84%, 1.84%, and 10.24% compared with that of SCO2RBC. The combined system will achieve its full potential when the critical temperature of the working fluid is close to the ambient temperature.

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%.

Multistage Smoothing Compressor for Multistep Pulse Compressors

Ultrahigh peak-power lasers are important scientific tools for frontier laser physics research, in which both the peak power improvement and operating safety are very important. Based on spatial-chirp-induced beam smoothing in both the near field and far field, a multistage-smoothing-based multistep pulse compressor (MS-MPC) is proposed here to further improve safety and operating convenience. In the MS-MPC, beam smoothing is not simply executed in the pre-compressor or main compressor but is separated into multiple stages. As a result, important and expensive optics are directly protected in every stage. The prism-pair-based pre-compressor induces a small spatial chirp, making it both easier to achieve than the previous multistep pulse compressor and sufficient to protect the first grating directly. Furthermore, the asymmetric four-grating compressor, which serves as the main compressor, induces a spatial chirp that further smooths the laser beam, protecting the last grating. In this way, a 10 s to 100 s petawatt laser pulse can be compressed with a single laser beam using the currently available optics. Additionally, an extra beam-smoothing stage can be added before the main amplifier to safeguard the largest amplification crystal from damage. The MS-MPC can be easily integrated into all existing PW laser facilities to improve their potential compressed pulse energy and operational safety.

Reliability analysis of the compressed air supplying system in underground mines

Despite the high cost and low efficiency, compressed air is mostly used in underground mining for ore extraction, hoisting, and mineral processing operations. Failures of compressed air systems not only threaten the health and safety of workers but also contribute to inefficient control of airflow and stopped all equipment that operates by compressed air. In such uncertain conditions, mine managers are faced with the big challenge to supply enough compressed air, and therefore, the reliability evaluation of these systems is essential. This paper aims to analyze the reliability of the compressed air system using the Markov modeling approach as a case study, Qaleh-Zari Copper Mine, Iran. To achieve this, the state space diagram was constructed considering all relevant states for all compressors in the main compressor house of the mine. The failure and repair rate of all main and reserve compressors were calculated for all possible transitions between states to obtain the probability of being of the system in each of the states. Moreover, the probability of failure at any time period was considered to study the reliability behavior. The results of this study show that there is 31.5% probability that the compressed air supplying system is in operating condition with two main and one standby compressors. The system probability that two main compressors are remain in the operation without failure for one months is 92.32%. Furthermore, the lifetime of the system is estimated 33 months when at least one main compressor is active.

Preliminary Design and Numerical Investigation of a Centrifugal Compressor for Supercritical Carbon Dioxide Operating in the Vicinity of Its Critical Thermodynamic State

Waste heat recovery is one of the main practices used to reduce the carbon footprint of the industrial sector regarding environmental concern. The supercritical carbon dioxide (s-CO2) cycle is one of the most attractive heat-to-power technologies; due to the abrupt variation in CO2 properties in the vicinity of its critical point, small compression work is required and finally a high cycle efficiency is achieved. In the literature, among the various proposed layouts, the recompression s-CO2 Brayton cycle is considered to be the most efficient one. The most critical component of such a cycle is definitely the main compressor, as the related usual design procedures have been developed in the past for ideal gas as a working fluid. This study presents a methodology for the preliminary design of a centrifugal compressor with a vaned diffuser, suitable for fulfilling the desired operating requirements of a particular supercritical CO2 recompression Brayton cycle. Furthermore, it demonstrates the numerical investigation of the three-dimensional (3D) flow phenomena occurring in it, focusing on the investigation of possible condensation. To this end, a one-dimensional flow model was developed to provide information regarding the geometry of the compressor and predict its prospective performance. Commercial computational fluid dynamics (CFD) software was then employed to examine the three-dimensional flow. The effect of accuracy in the evaluation of real gas properties approaching the critical point was examined, showing that a look-up table with more points around the critical point can reduce the numerical relative error by up to 0.3% for the value of specific heat capacity. In addition, the possibility of condensation occurrence was investigated at the impeller’s inlet, where the flow is accelerated. The supersaturation pressure ratio was defined and implemented in order to identify regions where static pressure is lower than saturation pressure, possibly leading to local two-phase flow.

Thermodynamic optimisation of a booster-ejector vapour compression refrigeration system using solar energy and R152a/Cu nano-refrigerant

Conventional vapour compression refrigeration systems require high electrical energy for low temperature applications. For the first time in the literature to reduce this required energy, comprehensive thermodynamic analysis and optimization of booster-assisted ejector expansion vapour compression refrigeration system with R152a/Cu nano-refrigerant are presented for low-temperature applications. Solar panels are used to cover the total compressor work, using the climate data of Izmir, Turkey. According to the thermodynamic optimization findings, the use of nanoparticles in the refrigeration system led to several improvements when compared to the R152a refrigeration system. These enhancements include a reduction of 6.52-11.71% in the main compressor discharge temperature, a decrease of 18.46-34.48% in the total exergy destruction rate, an increase of 3.08-4.04% in the entrainment ratio, a reduction of 0.089-3.25% in the ejector area ratio, a decrease of 8.34-14.27% in the panel area, and an increase of 8.09-14.05% in both the coefficient of performance and exergy efficiency. Another thing worth mentioning is that coefficient of performance and exergy efficiency improved by 2.06% and 1.96%, respectively, while total exergy destruction reduced by 4.83% compared to our previous study. The results obtained from the thermodynamic optimisation provide a useful reference for the design of an experimental system, as they provide evidence of model validity and can guide the implementation of the system.

Split‐flow layouts of supercritical CO2 Brayton cycle for coal‐fired power plant considering the flue gas residual heat utilization

AbstractThe utilization of residual energy of high‐temperature flue gas at the tail of coal‐fired boilers has attracted widespread attention in recent years. The thermal performances of the boiler and system in different split‐flow layouts still need to be analyzed and compared in detail. Thermodynamic models for four different splitting layouts of supercritical carbon dioxide (S‐CO2) Brayton cycles tailored for coal‐fired power plant are built and validated. By performing the process simulations, the effects of splitting ratios on the system thermal performance are comparatively analyzed when the secondary split point and the confluence point are set at different positions. The maximum system efficiency of the two‐split layout with a secondary splitting point at the inlet of the cold side of the high‐temperature recuperator (HTR) can be obtained within a range of secondary split ratio. The maximal and minimal boundaries are determined by the exhaust flue gas temperature and the heat capacity match in the recuperators, respectively. The mass flow rate of the cold stream in the low‐temperature recuperator (LTR) should be kept unchanged by constraining the sum of primary and secondary split ratios, the constant to prevent the cycle efficiency from decreasing dramatically, if the splitting layout with the split point at the outlet of the main compressor (MC) is used. The two‐splitting layout with a secondary splitting point at the inlet of the cold side of the HTR has the best performance by comparing the system efficiencies of different layouts. If there are any improved coupling approaches of the S‐CO2 Brayton cycle and boiler, this paper can provide the reference for the selections of the split ratios.

Thermo-economic analysis and multi-objective optimization of supercritical Brayton cycles with CO2-based mixtures

• A thermo-economic analysis of Brayton cycle with CO 2 -based mixtures is performed. • The Pareto fronts of 3 working fluids are obtained by multi-objective optimization. • SCO 2 -Xe cycle shows the best thermodynamic performance compared to others. • CO 2 -Kr shows the potential for development through thermo-economic analysis. The Supercritical carbon dioxide recompression Brayton cycle (SCO 2 RBC) is regarded as one of the most promising thermal power conversion systems and mixing other gases with CO 2 to change the critical point represents an effective strategy to improve the performance of the Brayton cycle. In this work, the feasibility of using xenon and krypton as additives to the SCO 2 RBC is investigated via thermodynamic analysis. The effects of the key parameters on the thermo-economic performance of recompression Brayton cycles using CO 2 , CO 2 /xenon (mass fraction 0.55/0.45) and CO 2 /krypton (mass fraction 0.755/0.245) as working fluids are discussed by means of parametric analysis. A non-dominated sorting genetic algorithm is employed to simultaneously optimize the cycle exergy efficiency and the levelized cost of energy. The total thermal conductance, the main compressor outlet pressure, pressure ratio and split ratio are selected as the decision variables. The optimum solutions with their corresponding decision variables are selected from the Pareto frontiers. The results show that the supercritical CO 2 /krypton cycle has the huge development potential. Specifically, the optimum exergy efficiencies of Brayton cycles using CO 2 , CO 2 /xenon and CO 2 /krypton as working fluids are 0.585, 0.646 and 0.664. The addition of xenon can improve cycle efficiency up to 12.08 % higher than SCO 2 RBC while the levelized cost of energy also increased by 10.04%. The cycle efficiency of the supercritical CO 2 /krypton cycle is 9.44% higher while the cost is 2.49% higher compared to the SCO 2 RBC. There are suitable decision variables to make the cost of the cycle using CO 2 / krypton lower than that using CO 2 while achieving the same exergy efficiency when the required exergy efficiency is in the range of 0.60-0.62. The exergy destruction distribution of Brayton cycle illustrates that high temperature recuperator is the highest exergy destruction component and using CO 2 -based binary mixtures can reduce the total exergy destruction effectively.

A 100-PW compressor based on single-pass single-grating pair

Abstract A multistep pulse compressor (MPC) based on a single-pass single-grating pair (SSGP) is proposed to simplify the entire multi-petawatt (PW) compressor. Only one grating pair with relatively long perpendicular distance is used to generate the same amount of spectral chirp compared with a four-grating main compressor. As SSGP compressor induces the largest spatial chirp, it can introduce the best beam-smoothing effect to the laser beam on the last grating. When considering the diffraction loss of only two gratings, the total compression efficiency of the SSGP compressor is even larger than that of a four-grating main compressor. Furthermore, the wavefront aberration induced by the SSGP compressor can be better compensated by using deformable mirrors; however, it is difficult or complicated to be well compensated in a four-grating compressor. Approximately 50–100 PW laser pulses can be obtained using this SSGP-based multistage-smoothing MPC with a single laser beam.

Energy, exergy and economic analyses of an optimal use of cryogenic liquid turbine expander in air separation units

Cryogenic liquid turbine expanders have emerged quite recently as a replacement for traditional Joule-Thomson valves in cryogenic processes for energy saving purpose. However, introducing a liquid turbine expander into the cryogenic air separation unit (ASU) can influence the operating points of ASU components, and the maximum benefits arising from the liquid turbine expander have not yet been reported. To fill such a gap, thermodynamic models are first established for ASU components, including the main air compressor, booster air compressor, cryogenic gas and liquid turbine expanders, main heat exchanger, cryogenic pump, and distillation column. To achieve the best possible use of the liquid turbine expander, an optimization method is developed by incorporating the thermodynamic models with the particle swarm optimization algorithm, in which the total minimization power consumption of ASU is the optimization goal while the flow rates and pressures of the high pressure air stream and the air stream drawn from the booster air compressor middle section together with the temperature of the medium pressure air stream exiting the main heat exchanger midway act as the optimization variables. Then, energy, exergy and economic analyses are conducted and the corresponding indexes are chosen to quantitatively evaluate the influence of the liquid turbine expander on the air separation process. For the case study, ASUs of 35000 Nm3/h oxygen production capacity with and without a cryogenic liquid turbine expander are optimized, respectively. The results show that the ASU total power saving through the use of liquid turbine expander is 4.2-fold its output shaft power; thus, the energy consumption of unit oxygen decreases by 2.12% and the overall exergy efficiency increases by 1%. In addition, the economic analysis shows that the period of return of the liquid turbine expander in the ASU is estimated to be 1.75 years.

Numerical performance of a water source transcritical CO2 heat pump with mechanical subcooling

In order to improve their efficiency, transcritical CO2 heat pumps need to resort to the use of a subcooling method. Among the different subcooling methods, dedicated mechanical subcooling (DMS) systems and internal heat exchangers (IHX) are currently the more promising technologies. This paper presents a numerical study of a transcritical water source CO2 heat pump during hot water generation using different subcooling methods. Ten different configurations, including both, IHX and DMS, separately and combined in different layouts, some of them not studied previously, are analyzed numerically under the same operating conditions in order to compare their performance. A description of the numerical model is presented: compressors are modeled using the performance curves provided by their manufacturers, expansion valves are modeled as isenthalpic, and heat exchangers are modeled by deriving correlations for the evaporation/condensation pressure and heat transfer rate obtained using a 1D cell-by-cell discretization method previously applied to all heat exchangers. Results are presented for different water heating conditions and show that in most configurations analyzed, the use of a DMS does not improve the performance of the system compared to the base system with IHX. There is only an improvement in the efficiency for two of the configurations analyzed, those in which the main CO2 cycle and the DMS cycle are coupled by the water flowing first through the evaporator of the auxiliary cycle and then through the gas cooler of the main cycle. Specifically, compared to the base cycle with IHX, the configuration that provides the best results (Conf. F* according to the nomenclature used in this work) gives average improvements of around 26% in efficiency and almost 160% in the heating capacity, while the optimum gas cooler pressure is reduced by an average of 12%. Even more, compared to the best performance system previously studied by other authors (indirect DMS without IHX, Conf. F in this work) this configuration improves the efficiency by almost 8.5%, with a decrease in the total capacity lower than 1% and similar gas cooler pressure. The results also show that the auxiliary compressor capacity and the way in which the water is distributed among the main and the auxiliary cycle have an important influence on the efficiency of the system, although that influence depends on the configuration studied. For the configuration that provides the best efficiency (Conf. F*), the optimum efficiency is obtained when the auxiliary compressor capacity is similar to the capacity of the main compressor (55% of the total heating capacity comes from the auxiliary cycle), and the water is mostly heated in the auxiliary cycle (85% of the water flow heated in the condenser of the auxiliary cycle, 15% heated in the gas cooler of the main cycle).

Thermodynamic analysis and performance evaluation of a novel energy storage-based supercritical CO2 power system with ejector driven by nuclear energy

The application of supercritical CO2 (S-CO2) in power generation systems shows huge advantages of compactness and high efficiency for nuclear energy utilization. However, it is difficult to achieve a quick response for reactor power regulation system in isolated power gird, and amounts of nuclear heat is wasted by bypass regulation to track the power load. In this paper, a novel energy storage-based supercritical CO2 power system with ejector is proposed to realize the rapid energy storage and energy release in system operation to guarantee high conversion efficiency of nuclear energy. Thermodynamic mathematical models are established to examine the performance of the proposed system. The parametric analysis and optimization are performed to acquire the optimum system performance. Furthermore, the performance evaluation in energy storage conditions and energy release conditions are presented to show the power regulation capacity of the proposed system. Results show that the appropriate split ratios of recompression supercritical CO2 power system for different main compressor outlet pressures are both about 0.3. The optimum thermal efficiency of the proposed system is 44.58% and the corresponding exergy efficiency is 66.94% under the given system conditions. In addition, 10% of mass flow rate storage for the S-CO2 results in a decrease in power load of 41.2%, and 10% of mass flow rate release for the S-CO2 can achieve an increase in power load of 45.59%. Furthermore, the maximum regulation capacity for the power load increases with the pressure of the high-pressure energy storage tank. Meanwhile, the energy release conditions with a low pressure of high-pressure energy storage tank and a high entrainment ratio of the ejector result in the decrease in net power output.

Dynamic response and emergency measures under failure conditions of sCO2 Brayton cycle

AbstractThe sCO2 Brayton cycle has gained interest because of its flexibility and ability to provide higher thermomechanical conversion efficiency. Studies on failure conditions and corresponding emergency measures are of great significance to ensure the safety of the system, while there are limited studies related to the sCO2 Brayton cycle because the test circuit has not been applied in practice at present. In this study, we have developed a dynamic model of the CO2 Brayton cycle, and carefully validated its components against experimental data. Preliminary safety assessment and dynamic response under loss of cooling water (LOCW), loss of heat source (LOHS), and pipeline leakage have been analyzed. Emergency strategies are proposed to maintain the safe operation under failure conditions. The primary objective of this study is to reveal the dynamic performance and emergency measures under failure conditions of the sCO2 Brayton cycle. The results demonstrate that the system net power decreases at rates close to 10%/s and less than 0.1%/s under LOCW and LOHS, respectively. The system responds more dramatically under LOCW compared with LOHS. The system needs emergency measures under LOCW, while it has sufficient time to realize a normal slow shutdown under LOHS. The leakage rate is at least five times higher in the high‐pressure pipeline compared with the low‐pressure pipeline for the same area of the leakage hole. Under pipeline leakage, the heat source should be cut‐off slowly, and the rotation speeds of the main compressor and recompressor should be reduced simultaneously to protect the system.

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.

Completely Recuperative Supercritical CO2 Recompression Brayton/Absorption Combined Power/Cooling Cycle: Performance Assessment and Optimization

Excessive heat losses and water consumption in cooling units are significant constraints restricting the application circumstances and performances for the SCO2 Brayton cycle, and the heat exchange capacity in the precooler (PRC) is typically 1.5 times that of power generation. Therefore, this research offers a high-integrated combined power/cooling system in which two waste heat exchangers (WHEs) and a rectifier (RET) are used instead of the PRC to achieve 100% exhaust heat recovery. Each component’s energy and exergy models are developed, and the operational characteristics, coupling relationships, and exergy destruction distribution are examined. Results indicate that, when compared to the Brayton cycle, the thermal and exergy efficiency is considerably increased, and the concentration difference and WHE1 pitch point difference have significant influences on system performance. Further exergoeconomic and optimization analysis reveals that the superior exergy case is mostly recommended for relevant thermal and exergy efficiency increasing rates of 13.7% and 9.17%, respectively, and the unit cost is 81.33% that of the base case. Turbine 1 (TUR1) and main compressor (MCP) are the first and second highest cost rates, respectively, and RET and generator (GEN) account for roughly 34% exergy destruction rate and 20% exergy destruction cost rate, respectively. In addition, reducing heat transfer differences in relevant equipment can further promote system performance.

Thermodynamic analysis of supercritical Brayton cycles using CO2-based binary mixtures for solar power tower system application

Supercritical CO2 Brayton cycle has the advantages of high thermoelectric conversion efficiency and compact structure. However, the high ambient temperature in the desert environment would reduce the cycle thermal efficiency. In this paper, three additive gases were mixed with CO2 to reduce the effect of ambient temperature on cycle efficiency. The thermodynamic analysis method based on the optimal split ratio was applied to evaluate the potential of CO2-based binary mixtures in the SPT systems application for the first time. Meanwhile, the impact of critical cycle parameters on system performance was analyzed and the internal connection of the phenomenon was investigated by discussing the exergy loss of each component under typical operating conditions. The results show that the optimal split ratio decreases with the increase of main compressor inlet temperature and turbine inlet pressure. The change of turbine inlet temperature has little effect on the optimal split ratio. CO2-propane has the potential for practical application because the pressure ratio has little effect on the optimal split ratio. Moreover, it is found that the thermal and exergy efficiencies of CO2-propane are increased by 2.34% and 1.51% compared with CO2 under typical operating conditions based on genetic algorithm optimization.