Supercritical Power Research Articles

Data-driven structural synthesis of supercritical CO2 power cycles

With new materials, objectives or constraints, it becomes increasingly difficult to develop optimal processes using conventional heuristics-based or superstructure-based methods. Hence, data-driven alternatives have emerged recently, to increase creativity and accelerate the development of innovative technologies without requiring extensive industrial feedback. However, beyond these proof-of-concepts and the promise of automation they hold, a deeper understanding of the behaviour and use of these advanced algorithms by the process engineer is still needed. In this paper, we provide the first data-driven solution for designing supercritical CO2 power cycle for waste heat recovery, a challenging industrial use case with lack of consensus on the optimal layout from the field literature. We then examine the issue of artificial intelligence acceptance by the process engineer, and formulate a set of basic requirements to foster user acceptance - robustness, control, understanding of the results, small time-to-solution. The numerical experiments confirm the robustness of the method, able to produce optimal designs performing as well as a set of selected expert layouts, yet only from the specification of the unit operations (turbomachinery and heat exchangers). We provide tools to exploit the vast amount of generated data, with pattern mining techniques to extract heuristic rules, thereby explaining the decision-making process. As a result, this paper shows how the process engineer can interact with the data-driven design approaches, by refocusing on the areas of domain expertise, namely, definition and analysis of the physical problem.

Prediction of supercritical CO2 heat transfer behaviors by combining transfer learning and deep learning based on multi-fidelity data

The flow and heat transfer characteristics of supercritical CO2 are important for heat exchanger design and the safe operation of supercritical CO2 power cycles. However, it is difficult to predict the supercritical heat transfer behaviors due to the non-monotonic temperature distribution in the case of the heat transfer deterioration (HTD) phenomenon. For low-cost, fast and accurate prediction of the supercritical heat transfer behavior, this study proposed a transfer learning model based on multi-fidelity data to achieve fast prediction with acceptable accuracy over a wide range of working conditions. This method fully utilized the low fidelity data (empirical correlations) and the medium fidelity data (numerical results) to generate a large amount of data for pretraining, in which the Latin Hypercube Sampling (LHS) method combined with the HTD correlation was used for sampling. For fine-tuning, high fidelity data from experiments was employed. Compared to the deep learning model trained directly with high fidelity dataset, the transfer learning model demonstrated vastly improved predictive performance on both the test and validation datasets. Additionally, the coefficient of determination R2 was discussed to preventing from “physical overfitting”. Instead of excessively pursuing the high R2 (close to 1), the validity of the prediction should be concerned, especially when using the non-smooth experimental data as the dataset for model training. Moreover, the trained models and the relative files are available at Supplementary materials.

Activated Tungsten Inert Gas Weld Characteristics of P91 Joint for Advanced Ultra Supercritical Power Plant Applications

Activated Tungsten Inert Gas Weld Characteristics of P91 Joint for Advanced Ultra Supercritical Power Plant Applications

Flow loss mechanisms investigation on a novel corotating scroll expander for supercritical carbon dioxide power system

Flow loss mechanisms investigation on a novel corotating scroll expander for supercritical carbon dioxide power system

Innovative integrated solar combined cycle: Enhancing dispatchability with a partial recuperative gas turbine and supercritical CO2 bottoming cycle, coupled with an ORC

Concentrating solar power is crucial in the future energy mix due to its ability to integrate thermal energy storage, thus providing dispatchability. One way to address the current high costs of this technology is by using higher temperatures, which can, however, lead to issues with heat transfer fluids and storage. A promising integrated solar combined cycle is here proposed to solve that current major issue. A partially recuperated gas turbine is coupled to a solar tower system using a Brayton supercritical CO2 power cycle, which recovers heat at two temperature levels. An Organic Rankine Cycle is also used to exploit the low-temperature flue gases. The performance at the design point is assessed under different solar contributions. The modulation of the thermal duty in the gas turbine recuperator allows reaching a nearly constant power production in the plant (180 MWe): 56 % coming from the gas turbine, 39 % from the CO2 power cycle, and 5 % from the ORC. The global efficiency achieved is 57.2 %. Carbon dioxide emissions range from 236 g CO2/kWhe (86 g CH4/kWhe are consumed) with the maximum solar contribution to 346 g CO2/kWhe (126 g CH4/kWh are consumed) with no solar contribution.

Performance assessment of a solar aided dual-fuel supercritical steam power plant for power boosting under different operating loads

Fuel supply due to political conflict and decarbonization is the most challenging standup for the energy sector and electricity generation. Therefore, the present study introduces a thermodynamic analysis for a modeled supercritical solar aided power plant (SAPP) using two types of fuel at different operating loads, i.e., 50%, 75%, and 100%. The proposed SAPP is investigated in terms of energy, exergy, and steam flow rates to verify the advantages of using SAPP over conventional power plants. In the SAPP, the condensate water passes into the heat exchangers using a working fluid of Therminol VP-1. Additionally, the turbine extraction steam at 100% load is minimized, and it is eliminated at 50% and 75% loads. The results show that the recovered amount of feed water extraction increases the mechanical power for SAPP-based natural gas in comparison with the conventional supercritical steam power plant by 16, 21, and 9.7% at an operating load of 50%, 75%, and 100%, respectively. Consequently, SAPP-based natural gas maintains an increase in the overall energy efficiency compared with the CPP of 13.7, 17, and 1.9% at an operating load of 50%, 75%, and 100%, respectively. As well, the mechanical power of the SAPP-based oil fuel increases compared with CPP by 25.7, 27.6, and 17.4% at 50%, 75%, and 100% loads, respectively. Whereas, the overall energy efficiency enhances due to using the SAPP-based oil fuel compared with that of the CPP by 20.6, 21.9, and 7% at a load of 50%, 75%, and 100%, respectively.

Thermo-economic assessment and systematic comparison of combined supercritical CO2 and organic Rankine cycle (SCO2-ORC) systems for solar power tower plants

Solar power towers (SPTs) integrated with thermal energy storage are promising solutions for solar energy utilisation. Supercritical CO2 power cycles are acknowledged as an attractive option for dry-cooling SPT plants. However, abundant low-grade waste heat exists in the SCO2 gas cooler, which is directly dissipated to the ambient. In order to further improve the performance of SCO2-based SPT plants, organic Rankine cycle (ORC) systems can be introduced as a bottoming cycle subsystem. In this paper, an ORC subsystem is added to four different SCO2 cycle layouts, i.e., recuperated (RE), recompression (RC), intercooling (IC), and partial cooling (PC) cycles, to form combined cycle systems for SPT applications. A parametric study reveals that the thermal efficiency of the power block (i.e., the whole power cycle system), and the salt temperature difference across the receiver are the determining factors of the thermo-economic performance of SPT-SCO2-ORC plants. Design optimisation and annual performance evaluations are implemented using actual weather data in Delingha, China. Compared to the SPT plant with a standalone recuperated SCO2 cycle system, the annual electricity generation is increased by 19 % by integrating a bottoming ORC subsystem. The SPT-RC-ORC system produces the maximum electricity generation of 123 GW·h/year, while the SPT-RE-ORC system achieves the lowest levelised cost of electricity (LCOE) of 0.12 $/kW·h and the minimum payback time of 8.8 years. A wide range of solar irradiance conditions is further considered to generalise the performance evaluation of such combined cycle systems, with results showing that with the highest solar irradiance investigated (3700 sunshine hours, 1000 W/m2·h), the LCOE of the SPT-RE-ORC plant can be as low as 0.07 $/kW·h and the payback time is as short as 6 years. This study investigates optimal SCO2-ORC configurations for SPT applications based on annual performance evaluations, and presents preliminary assessments of the thermo-economic potential of ushc SPT-SCO2-ORC plants across a variety of solar resource conditions.

Performance evaluation of once-through steam generator of a 626 MW supercritical oil-fired steam power plant under a variable operating load

Unforeseeable growth in the global population needs growing technological advances in establishing power plants to overcome this critical issue by reducing greenhouse gases. In the present study, a thermodynamic analysis for a 626 MW supercritical oil-fired steam power plant under different operating loads of 50%, 75%, 100%, and 105% at a sliding-pressure operation is conducted. Based on the actual operation of the examined plant, the results show that the condenser has the highest energy loss. As well, at a 100% full load, 88.6% of the total exergy is destructed in the once-through steam generator, followed by the turbine, and then the condenser. Hence, a significant concern is introduced toward the steam generator since it has the largest exergy destruction percentage relative to other cycle components. The heat transfer sets inside a once-through steam generator are studied and analyzed. The exergy destruction in the combustion process represents 58.6% and 54% of the overall boiler exergy destruction at an operating load of 50% and 100%, respectively. In addition, the evaporator has higher exergy destruction in comparison with other heating surfaces in the furnace.

Thermodynamic performance analysis of solid oxide fuel cell - combined cooling, heating and power system with integrated supercritical CO2 power cycle - organic Rankine cycle and absorption refrigeration cycle

A novel cascade energy utilization system with Solid Oxide Fuel Cell (SOFC) as the prime mover is designed and analyzed. The upper loop contains SOFC and Gas Turbine (GT), and the bottom loop includes Supercritical CO2 (SCO2) power cycle - Organic Rankine Cycle (ORC) combined cycle, single - effect Absorption Refrigeration Cycle (ARC), and heating subsystem. Based on simulation data and mathematical models of the system, energy analysis, conventional and graphical exergy analysis, and sensitivity analysis are conducted. The simulation result demonstrates that the net power efficiency, overall energy efficiency, exergy efficiency and SOFC electrical generation efficiency are 59.62%, 77.61%, 59.08% and 43.18%, respectively. The exergy analysis reveals that the system exergy losses obtained from conventional exergy and graphical exergy analysis are 383.29 kW and 372.46 kW, respectively, a relative error of 2.91%. However, the SOFC subsystem has the greatest exergy destruction, reaching 65.77% (graphical exergy analysis) or 65.06% (conventional exergy analysis) of the total system exergy loss. The system with favorable energy efficiency provides a reference direction for the future research and optimization of Solid Oxide Fuel Cell (SOFC) - Combined Cooling, Heating and Power (CCHP) system.

Improvement design and performance assessment of two supercritical carbon dioxide power cycles for waste heat recovery

Waste heat recovery (WHR) from thermal engines and industrial processes is significantly beneficial to cutting fossil fuel consumptions and carbon dioxide emissions. Recompression supercritical carbon dioxide (sCO2) power cycles have many advantages of high efficiency, compact design and environmentally friendly property, and they are regarded as the competitive and promising energy conversion technology for WHR. However, a large space is still left for recompression sCO2 power cycle to improve its capability with regard to waste heat extraction and power output. The novelty of this work is the development of two novel sCO2 power cycles based on the recompression sCO2 cycle aimed at thoroughly and efficiently reusing the waste heat. Thermodynamic and exergoeconomic models are established to perform the quantitative parametric analyses, multi-objective optimizations, exergy and exergoeconomic analyses on the proposed systems. The results indicate that the second proposed system is preferred, since it can significantly improve the net power output by 43.81% and 12.32% while reducing the total product unit cost by 7.24% and 10.39%, compared with the traditional recompression sCO2 cycle and the improved sCO2 cycle, respectively. Although the first proposed system has a better performance in waste heat extraction and net power output, it requires a higher cost.

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

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

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.

Techno-economic assessment of a numbering-up approach for a 100 MWe third generation sodium-salt CSP system

This work presents the design and techno-economic analysis of a 100 MWe concentrated solar power (CSP) system using a supercritical CO2 power block with 700 °C input temperature. Aiming to leverage the relatively higher efficiency of small heliostat fields and potential multi-build discounts, a numbering-up approach is examined, developing four alternative configurations (1×100, 2×50, 3×33, and 4×25MW˙e), in which each module has its own dedicated tower, heliostat field, receiver, thermal storage and power block. A comprehensive techno-economic model is combined with detailed annual simulations to yield levelised cost of energy (LCOE) estimations and analyse the potential of system numbering-up for high-temperature next-generation CSP systems based on liquid heat transfer fluids (HTFs). The simulations are verified against the System Advisor Model with differences in the LCOE calculations within ±1.0%. Comparing the four systems shows that a 1×100MW˙e system leads to an LCOE of 54.88USD/MWh˙e, lower than for the numbered-up modules. However, the LCOE difference between configurations with one and two modules is moderate, with the 2×50MW˙e configuration showing an LCOE of 55.99USD/MWh˙e (+2%). Despite their higher annual conversion efficiencies, the 3×33MW˙e and 4×25MW˙e systems are more capital-intensive and escalate LCOE by 6.9 and 12.2%, respectively. With size-dependent power block efficiency, further LCOE escalation with numbered-up systems is observed, however, multi-build savings could potentially reverse this cost escalation and a 13.9–19.6% saving on the two-module system would allow them to break even.

Artificial intelligence driven smart operation of large industrial complexes supporting the net-zero goal: Coal power plants

The true potential of artificial intelligence (AI) is to contribute towards the performance enhancement and informed decision making for the operation of the large industrial complexes like coal power plants. In this paper, AI based modelling and optimization framework is developed and deployed for the smart and efficient operation of a 660 MW supercritical coal power plant. The industrial data under various power generation capacity of the plant is collected, visualized, processed and subsequently, utilized to train artificial neural network (ANN) model for predicting the power generation. The ANN model presents good predictability and generalization performance in external validation test with R2 = 0.99 and RMSE =2.69 MW. The partial derivative of the ANN model is taken with respect to the input variable to evaluate the variable’ sensitivity on the power generation. It is found that main steam flow rate is the most significant variable having percentage significance value of 75.3 %. Nonlinear programming (NLP) technique is applied to maximize the power generation. The NLP-simulated optimized values of the input variables are verified on the power generation operation. The plant-level performance indicators are improved under optimum operating mode of power generation: savings in fuel consumption (3 t/h), improvement in thermal efficiency (1.3 %) and reduction in emissions discharge (50.5 kt/y). It is also investigated that maximum power production capacity of the plant is reduced from 660 MW to 635 MW when the emissions discharge limit is changed from 510 t/h to 470 t/h. It is concluded that the improved plant-level performance indicators and informed decision making present the potential of AI based modelling and optimization analysis to reliably contribute to net-zero goal from the coal power plant.

Design and optimization of intermediate heat exchanger for lead-bismuth cooled fast reactor coupled with supercritical carbon dioxide Brayton cycle

Printed circuit heat exchanger has become a new choice for the intermediate heat exchanger of the lead/lead–bismuth cooled fast reactor coupled with supercritical carbon dioxide nuclear power system because of its large heat transfer area density, high power density and ability to work at high temperature and high pressure. In this study, the channel dimensions of the intermediate heat exchanger were optimized to improve its thermal–hydraulic performance. An in-house code for the thermal–hydraulic design of printed circuit heat exchanger with lead–bismuth and supercritical carbon dioxide as working fluid was built. The relationship between the cold side pressure drop of intermediate heat exchanger and cycle efficiency of the nuclear power system is revealed. The power density and pressure drop of the cold side are selected as two optimization objectives, and the multi-objective optimization process is conducted with the non-dominated sorting genetic algorithms II. The optimal design results of the intermediate heat exchanger are obtained with Pareto-front method. The Pareto-front shows that when the heat exchange density increases, the pressure loss of the cold side also increases, but more quickly than the former. Finally, considering the design limitations, the intermediate heat exchanger core design scheme is selected by the auxiliary function which considering both capital cost and operating cost.

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.

Advances in solar thermal power plants based on pressurised central receivers and supercritical power cycles

This work addresses the comparative thermo-economic study of different configurations of solar thermal power plants, based on supercritical power cycles and pressurised central receiver systems. For all the cases examined, two innovations are introduced in the solar subsystem, compared to other similar studies. Firstly, the heat transfer fluid in the receiver is either a pressurised gas or a supercritical fluid. Secondly, the receiver is composed of compact structures performing as absorber panels, arranged in a radial configuration. The investigation considers different supercritical CO2 recompression cycles of 50 MWe, including a novel proposal of a directly coupled cycle with heat input downstream of the turbine. Furthermore, the study evaluates different heat transfer fluids in the receiver, specifically CO2, N2, and He, concluding that the former is preferred due to its better thermal performance.The main results show that an increase in the receiver inlet pressure yields to a reduction in its size, favouring the thermal efficiency but penalising the optical efficiency of the solar field. Therefore, optimal working pressures may exist for each configuration, depending on the operating temperature. When comparing the optimal configurations, it is observed that the plant based on the intercooling cycle demonstrates the highest overall efficiency, reaching 32.05%. At last, an economic analysis is conducted to assess the viability of the identified optimal configurations. In this regard, the plant based on the partial-cooling cycle exhibits the lowest levelised cost of electricity at 0.15 $/kWh. This is primarily due to its lower investment cost. The innovative directly coupled cycle follows closely with a cost of 0.17 $/kWh, driven by its high electricity production resulting from its low self-consumption.

Pressure Profile and Stiffness Analysis of Supercritical CO2 Inside a Rotating Annulus Cooling Passage Using Computational Fluid Dynamics

Abstract The recent supercritical CO2 (sCO2) power turbine configuration development introduced a cooling zone parametric model to overcome the existing technical challenges. The parametric model is the annulus cooling passage with a supercritical CO2 coolant consisting of radial clearance, length, and shaft diameter are the geometrical parameters. This study aims to investigate the pressure profile and stiffness coefficient of the cooling passage using computational fluid dynamics and to explore the validity of the assumptions that exist in the simplified analysis. The effect of eccentricity ratio, shaft speed, and axial length are investigated. The result showed that, like the hydrodynamic bearing, the supercritical CO2 swirling in the annulus passage produces substantial mechanical support on the shaft. Hence, the cooling zone stiffness contribution should be included in the supercritical CO2 turbine shaft vibration analysis which is not presently taken into consideration.

Coupling chemical looping air separation with the Allam cycle – A thermodynamic analysis

The Allam cycle is a class of oxy-fuel combustion power cycles using supercritical CO2 (s-CO2) as the thermal fluid to achieve power generation with inherent capture of CO2. Compared to other conventional CO2 capture techniques, the Allam cycle stands out owing to its high fuel-to-electricity conversion efficiency (55–59%), the elimination of the Rankine cycle and reduced physical footprint. A key source of energy penalty of Allam cycle comes from the air separation unit (ASU), which supplies pure oxygen via an energy intensive cryogenic process. This paper presents a thermodynamic analysis of a novel supercritical CO2-based power generation scheme, in which a natural gas fuelled Allam cycle is integrated with a chemical looping air separation (CLAS) system, which supplies oxygen to the combustor. The modelling results show that the Allam-chemical looping air separation (Allam-CLAS) process can achieve 56.04% net electrical efficiency with a 100% CO2 capture rate, when a Co3O4-based oxygen carrier is used. This is 6% higher than the Allam cycle coupled to a cryogenic ASU. The exergetic efficiency of the Allam-CLAS system driven by the Co3O4-CoO redox cycle is 57.13%, also more favourable than a conventional Allam-ASU system (with reported exergetic efficiency of 53.4%). This newly proposed Allam-CLAS power cycle presents a highly efficient, and simple solution to generate zero-carbon electricity from natural gas.

Thermoeconomic Analysis of Concentrated Solar Power Plants Based on Supercritical Power Cycles

Solar thermal power plants are an alternative for the future energy context, allowing for a progressive decarbonisation of electricity production. One way to improve the performance of such plants is the use of supercritical CO2 power cycles. This article focuses on a solar thermal plant with a central solar receiver coupled to a partial cooling cycle, and it conducts a comparative study from both a thermal and economic perspective with the aim of optimising the configuration of the receiver. The design of the solar receiver is based on a radial configuration, with absorber panels converging on the tower axis; the absorber panels are compact structures through which a pressurised gas circulates. The different configurations analysed keep a constant thermal power provided by the receiver while varying the number of panels and their dimensions. The results demonstrate the existence of an optimal configuration that maximises the exergy efficiency of the solar subsystem, taking into account both the receiver exergy efficiency and the heliostat field optical efficiency. The evolution of electricity generation cost follows a similar trend to that of the exergy efficiency, exhibiting minimum values when this efficiency is at its maximum.