Supercritical Carbon Dioxide Power Cycle Research Articles

Optimization Research on Improving Energy Efficiency of Staged Coal Gasification Coupled Supercritical Carbon Dioxide Power Cycle System

Optimization Research on Improving Energy Efficiency of Staged Coal Gasification Coupled Supercritical Carbon Dioxide Power Cycle System

Performance analyses and optimization of a regenerative supercritical carbon dioxide power cycle with intercooler and reheater

Performance analyses and optimization of a regenerative supercritical carbon dioxide power cycle with intercooler and reheater

Comparative study on the thermodynamic and economic performance of novel absorption power cycles driven by the waste heat from a supercritical CO2 cycle

In this study, the investigation on the performance improvement of the recompression supercritical carbon dioxide (sCO2) power cycle by integrating with two novel absorption power cycles (APC) are carried out. Comparative study, parametric analysis, single-objective and multi-objective optimizations on the thermodynamic and economic performance are conducted quantitatively for two proposed sCO2/APC systems and an original sCO2/APC system. Comparative study results indicate that the proposed APC3 subsystem can generate the highest mass flow rate of working fluid with the highest reheated temperature across the turbine, contributing to the highest net power output. Besides, the working fluid produced by the proposed APC2 subsystem is nearly the same as that of the original APC1 subsystem, but the net power output of APC2 subsystem is still slightly higher than that of APC1 subsystem due to the reheated working fluid with more potential to generate power of APC2 subsystem. In addition, the optimization results reveal that all APC subsystems studied here are able to improve the stand-alone sCO2 system performance in thermodynamics and economics, and two proposed sCO2/APC systems can further improve the overall performance of the original sCO2/APC system. In detail, the improvement of 0.31% and 2.35% for the exergy efficiency and 0.21% and 2.43% for the total product unit cost can be achieved by the sCO2/APC2 system and sCO2/APC3 system, respectively, compared with the sCO2/APC1 system.

Comparative investigation on the supercritical carbon dioxide power cycle for waste heat recovery of gas turbine

In this paper, a comparative investigation on the supercritical carbon dioxide power cycle for waste heat recovery of gas turbine is carried out. Four categories and six cycles are chosen to represent typical layout of supercritical carbon dioxide power cycle based on thorough literature reviews. The selected cycles are optimized and analyzed based on the results of single- and multi-objective optimization from the perspective of system efficiency, economic cost and configuration complexity. According to the exergy destruction analysis, several guidelines about the heat exchangers are proposed to enhance the thermal efficiency of gas turbine waste heat recovery system, including the avoiding of preheating, the utilization of partial heating layout, the employment of segmentation method and modified logarithmic mean temperature difference, the increase in the number of gas heater. The results indicate that turbine dominates the investment cost of power cycle. In conclusion, dual heated cascade cycle-II should be employed to pursue the maximized system efficiency. Otherwise, partial heating cycle is recommended due to its balanced overall performance.

Numerical Investigation of High Pressure CO2-Diluted Combustion Using a Flamelet-based Approach

ABSTRACT Direct-fired oxy-fuel combustion as a heat source is utilized in supercritical carbon dioxide (sCO2) power cycles, such as the Allam cycle, which has shown promise in delivering higher efficiencies while achieving the complete capture of combustion products in future generation carbon-neutral power plants. The design of dedicated burners for such cycles is key in determining their overall efficiency and viability. We present a series of numerical simulations on a prototype burner, currently in development, operating in an essentially non-premixed regime with a high pressure gaseous fuel, burning in the presence of a hot oxidant flow containing a mixture of recycled CO2 and pure oxygen. Simulations rely on a turbulent combustion model based on a simplified approach for diluted steady laminar flamelets. We investigate the effect of the degree of dilution as well as pressure on the flame structure, revealing a concurrent change in stoichiometric mixture fraction and quenching scalar dissipation. We also assess the effect of injector recess and of swirl in the oxidizer stream.

Experimental study of accidental release behavior of high-pressurized CO2 vessel

The accidental release is one of the main risks of carbon capture and storage (CCS) and supercritical carbon dioxide (S-CO2) power cycle system. The release of mass CO2 will present severe risks to pipeline, vessel and surrounding population. The study of CO2 release characteristics is helpful to understand the crack propagation and the diffusion behavior outside the crack. In this paper, to investigate release characteristics in vessel and diffusion phenomenon outside rupture, high pressure CO2 release experiments from pressurized vessel were carried out for different initial states (liquid and gaseous phase), temperature (20.0℃ to 50.0℃) and rupture sizes (1.0 mm, 2.0 mm, 3.0 mm). The transient pressure, mass flow rate, wall temperature, external jet structure and phase transition were studied following vessel release. The results show that different initial states will undergo different decompression process. As initial state is in liquid phase, fluid temperature is lower and circumferential wall temperature shows large gradient. Effects of initial temperature and nozzle sizes under different initial states on CO2 release characteristics were obtained. The experimental results show lower temperature will not damage material in experiment and results are of great significance for early leakage detection and model development.

Thermodynamic and exergoeconomic analysis of a novel CO2 based combined cooling, heating and power system

In this paper, a novel combined cooling, heating and power (CCHP) system consisting of a supercritical carbon dioxide (sCO2) power cycle, a transcritical carbon dioxide (tCO2) power cycle with a carbon dioxide based refrigeration cycle, and a direct heating (DH) system is proposed. In the novel system, the waste heat from sCO2 power cycle is recovered by the tCO2 power cycle to generate additional power and drive the CO2 based refrigeration cycle to provide cooling for users, and the DH system further recovers the waste heat from the sCO2/tCO2 power cycle and the refrigeration compressor outflow to feed heat for users. Mathematical models are developed to conduct the thermodynamic and exergoeconomic analysis of the proposed CCHP system, and parametric studies on the effects of different key parameters on the system performance are carried out. Besides that, the optimization and comparative researches are performed to find out and compare the maximum system exergy efficiency and minimum total product unit cost for the proposed CCHP system and the stand-alone sCO2 system. The results indicate that for different users’ demands, the proposed CCHP system can obtain the best improvement by 12.01% for the system exergy efficiency and 5.14% for the total product unit cost, and the worst improvement by 10.83% for the system exergy efficiency and 4.12% for the total product unit cost, compared with the stand-alone sCO2 power cycle. These results confirm the obvious superiority in thermodynamic and economic performance of the proposed CCHP system under different users’ demands.

Mean-Line Design of a Supercritical CO2 Micro Axial Turbine

Supercritical carbon dioxide (sCO2) power cycles are promising candidates for concentrated-solar power and waste-heat recovery applications, having advantages of compact turbomachinery and high cycle efficiencies at heat-source temperature in the range of 400 to 800 ∘C. However, for distributed-scale systems (0.1–1.0 MW) the choice of turbomachinery type is unclear. Radial turbines are known to be an effective machine for micro-scale applications. Alternatively, feasible single-stage axial turbine designs could be achieved allowing for better heat transfer control and improved bearing life. Thus, the aim of this study is to investigate the design of a single-stage 100 kW sCO2 axial turbine through the identification of optimal turbine design parameters from both mechanical and aerodynamic performance perspectives. For this purpose, a preliminary design tool has been developed and refined by accounting for passage losses using loss models that are widely used for the design of turbomachinery operating with fluids such as air or steam. The designs were assessed for a turbine that runs at inlet conditions of 923 K, 170 bar, expansion ratio of 3 and shaft speeds of 150k, 200k and 250k RPM respectively. It was found that feasible single-stage designs could be achieved if the turbine is designed with a high loading coefficient and low flow coefficient. Moreover, a turbine with the lowest degree of reaction, over a specified range from 0 to 0.5, was found to achieve the highest efficiency and highest inlet rotor angles.

Potential of Supercritical Carbon Dioxide Power Cycles to Reduce the Levelised Cost of Electricity of Contemporary Concentrated Solar Power Plants

This paper provides an assessment of the expected Levelised Cost of Electricity enabled by Concentrated Solar Power plants based on Supercritical Carbon Dioxide (sCO 2 ) technology. A global approach is presented, relying on previous results by the authors in order to ascertain whether these innovative power cycles have the potential to achieve the very low costs of electricity reported in the literature. From a previous thermodynamic analysis of sCO 2 cycles, three layouts are shortlisted and their installation costs are compared prior to assessing the corresponding cost of electricity. Amongst them, the Transcritical layout is then discarded due to the virtually impossible implementation in locations with high ambient temperature. The remaining layouts, Allam and Partial Cooling are then modelled and their Levelised Cost of Electricity is calculated for a number of cases and two different locations in North America. Each case is characterised by a different dispatch control scheme and set of financial assumptions. A Concentrated Solar Power plant based on steam turbine technology is also added to the assessment for the sake of comparison. The analysis yields electricity costs varying in the range from 8 to over 11 ¢/kWh, which is near but definitely not below the 6 ¢/kWh target set forth by different administrations. Nevertheless, in spite of the results, a review of the conservative assumptions adopted in the analysis suggests that attaining costs substantially lower than this is very likely. In other words, the results presented in this paper can be taken as an upper limit of the economic performance attainable by Supercritical Carbon Dioxide in Concentrated Solar Power applications.

Thermodynamic analysis on the combination of supercritical carbon dioxide power cycle and transcritical carbon dioxide refrigeration cycle for the waste heat recovery of shipboard

With excellent physical properties, carbon dioxide has been widely employed as a working fluid in efficient energy conversion technologies, which are represented by supercritical carbon dioxide Brayton cycle and transcritical carbon dioxide refrigeration cycle. In this contribution, with the aim to recover the waste heat of shipboard, a combined system coupling carbon dioxide Brayton cycle and refrigeration cycle is proposed to simultaneously produce power and cooling. In order to alleviate the temperature mismatch in recuperator and effectively utilize the discharged heat of refrigeration cycle, low temperature recuperator and gas cooler are shared by power and cooling cycles. For this novel waste heat recovery system, thermodynamic and economic models are developed to conduct energy, exergy and economic analysis. Thereafter, key cycle parameters including gas cooler pressure, evaporation temperature and turbine inlet temperature are investigated to reveal the effects on the system performances. The obtained results indicate that the energy and exergy efficiencies of the proposed system are respectively 42.42% and 39.05% under design conditions. The corresponding average energy cost is 9.28 $/GJ. At lower evaporation temperature and higher gas cooler pressure, the advantages of low temperature recuperator can be fully utilized and more work is produced. However, lower cooling capacity is obtained. Furthermore, the turbine inlet temperature has no effects on refrigeration cycle, and the net work decreases with the increase of inlet temperature. These results will be beneficial to improve the design and performance of combined power and cooling system for future shipboard applications.

Effect of printed circuit heat exchanger’s different designs on the performance of supercritical carbon dioxide Brayton cycle

Several fin configurations have been proposed in the literature to address the poor hydraulic performance associated with the PCHEs. However, the effect of the heat exchangers with proposed channel geometries on the performance of supercritical carbon dioxide(sCO2) power cycle is missing. In this context, the current study deals with the effects of different designs of the PCHEs varied by proposed channel configurations, heat exchanger’s effectiveness and design value of inlet Reynolds number on the performance of sCO2 power cycle. Moreover, a multi-object optimization study to find the best bargain between cycle’s efficiency and heat exchanger’s size is carried out using five different fin configurations (straight, zigzag, C-shaped, S-shaped, and airfoil fin channel configuration), heat exchanger’s effectiveness and inlet Reynolds number as a design variable. Results shows that enhancement in the hydraulic characteristics for a channel geometry that comes at the cost of thermal performance may not benefit the system’s efficiency. Optimization results suggest that C-shaped channel and zigzag channel geometries correspond to the cycle’s maximum efficiency and heat exchanger’s minimum size respectively. Optimization results further highlight that the comparison of channel geometries should be performed while in the setting of complete power generation cycle to account for all the variables involved.

Design and optimization of waste heat recovery system for supercritical carbon dioxide coal-fired power plant to enhance the dust collection efficiency

The supercritical carbon dioxide (SCO2) power cycle is a potential power cycle for coal-fired power plants. In the SCO2 power systems provided in previous studies, the boiler exhaust temperature is about 120 °C. To enhance the power plant efficiency and the dust collection efficiency of electrostatic precipitator, SCO2 power systems should be advanced to cool the boiler exhaust fluegas to nearly 95 °C. Therefore, systems of waste heat recovery from low-temperature fluegas are proposed and optimized in this study. Thermodynamic and optimization models are developed. The double reheat recompression SCO2 cycle is optimized as benchmark system. The benchmark system is improved to decrease the exergy loss and boiler exhaust, decrease the irreversibility of air preheater, and recover waste heat of the SCO2 cycle to preheat air to the air preheater. When the main compressor intercooling or bypass fluegas ahead the air preheater is adopted, the temperature of boiler exhaust fluegas can be decreased to around 95 °C which can ensure a high dust collection efficiency of electrostatic precipitator. The power plant efficiency is also increased as a result. However, if only low-temperature economizer is integrated, then the power plant efficiency is enhanced slightly by 0.09%-pts. If the low temperature economizer is integrated with other system improvements, the power plant efficiency can be enhanced by 0.89%-pts. Exergy analysis is also performed to reveal the mechanisms of efficiency enhancement.

Measurements of Density and Sound Speed in Mixtures Relevant to Supercritical CO2 Cycles

Abstract The objective of this research is to validate properties of mixtures relevant to supercritical carbon dioxide (sCO2) power cycles. Direct-fired sCO2 cycles are a promising technology for the future power generation systems. The working fluid of sCO2 cycles will be near and above critical point of CO2. One of the challenges is that the simulation of mixtures should consider real gas behavior. Expected operating conditions of Allam cycles reach up to 300 bar and 1000 °C. Characterizing the mixtures at the extreme conditions is an important issue in current researches and industrial applications. Thermophysical properties of mixtures may be beyond the valid range of the widely used database such as NIST REFPROP. Experimental data of mixture properties in the literature are limited which is necessary to develop high-fidelity design tools for sCO2 power cycles. We measured the density and sound speed of several multi-component mixtures. A temperature-controlled high-pressure test cell was used for the density measurements. Sound speed was measured by resonant frequency detection using an external speaker and a piezoelectric pressure sensor. Mixtures studied in this work include carbon dioxide, methane, oxygen, and water vapor. Properties of pure CO2 were measured to show the validity of our technique. Compositions were selected to be close to frozen mixtures at the inlet, mid-progress, and exhaust conditions of a model sCO2 combustor in the previous numerical simulation work. Corresponding reaction progress variables (RPV) were RPV = 0, 0.5, and 1. Temperature and pressure conditions of experiments are 310–450 K and 0–150 bar. In our study, density and sound speed from the NIST REFPROP database agree with experimental measurements within the range of our measurement uncertainties.

Energy minimization of carbon capture and storage by means of a novel process configuration

Carbon capture and storage is considered a key technology for decarbonizing the heat and power industries and achieving net zero emission targets. However, the significant energy requirements of the process as currently utilized hinders its widespread implementation. This work presents a novel process configuration by which the energy expenditures of carbon capture and storage can be minimized. This configuration is intended to enhance heat integration during the capture process through an innovative combination of three stripper modifications, namely lean vapor compression, a rich solvent split with vapor heat recovery and reboiler condensate heat recovery using a stripper inter-heater in a single flow-sheet. For carbon dioxide compression, a novel pressurization strategy involving carbon dioxide multi-stage compressors, a heat pump system and a supercritical carbon dioxide power cycle was designed and evaluated. The heat pump was used for carbon dioxide liquefaction while the supercritical carbon dioxide power cycle was employed to recover the intercooling heat. Through a comprehensive parametric investigation of the proposed configuration, the optimum value of the key operating parameters i.e., the split fraction, flash pressure, stripper inter-heater location, stripper inter-heater solvent flowrate, carbon dioxide liquefaction pressure and supercritical carbon dioxide cycle turbine pressure ratio were estimated. The performance of the proposed design at the optimized condition was quantified in terms of the reboiler heat duty, the carbon dioxide pressurization power and the equivalent work and compared to a baseline case post-combustion carbon capture and storage process. The proposed case reduced the reboiler heat duty from 3.36 GJ/TonneCO2 to 2.65 GJ/TonneCO2 and the electric power required for carbon dioxide compression from 16,691 kW to 14,708 kW. The results demonstrate that the new design can significantly reduce the reboiler duty, compression power and equivalent work by 21.1%, 11.88%, and 15.8%, respectively.

Performance improvement of supercritical carbon dioxide power cycles through its integration with bottoming heat recovery cycles and advanced heat exchanger design: A review

In this article, the performance improvement of supercritical carbon dioxide (sCO2) Brayton cycles through heat recovery and advanced heat exchanger (HX) design is reviewed. The configuration of sCO2 cycles and the bottleneck of the design of an efficient sCO2 cycle is first evaluated. It was found that heat rejected in the precooler is a large waste that could potentially enhance the overall sCO2 system performance. Then integration of the absorption cycle, organic Rankine cycle, and thermal desalination plant to the sCO2 cycle to recover the waste thermal energy is reviewed and discussed. Results showed that these bottoming heat recovery cycles could substantially improve the overall sCO2 system efficiency. The combined system of sCO2/absorption chiller, sCO2/ORC increases the cycle efficiency to about 78% and 79%, respectively. Also, a combined system of sCO2/desalination produces about 200 000 m3/day with a cost of less than $1.0/m3. Based on the review, the evaluation criteria are proposed for decision‐makers. Another bottleneck of the design of the sCO2 system is the HXs (recuperators) used in the sCO2 cycle which are relatively large and negatively affect the cycle compactness and performance. Therefore, various types of recuperators proposed and designed for sCO2 cycles are reviewed and evaluated. This review highlights the need for further research to enhance heat recovery, reduce the cost of bottoming cycles, and improve the design of HXs.

Experimental study on heat transfer of supercritical CO2 flowing in a mini tube under heating conditions

Supercritical carbon dioxide (S-CO2) power cycles hold great potential applications in various energy utilization systems, in which the heat transfer of S-CO2 is one of the most important issues. However, due to the complex thermophysical properties, it is still insufficient to predict heat transfer coefficient of S-CO2, especially under the heating conditions with high ratios of heat flux to mass flux (q/G). In this study, the heat transfer of S-CO2 is experimentally investigated in a mini tube (d = 2 mm) in the range of p = 7.6–8.4 MPa, q = 100–200 kW/m2 and G = 400–700 kg/m2 s, in which the ratio of q/G is within 250–500 J/kg. The parameter influences on heat transfer coefficient of S-CO2 are analyzed. It is found that the heat transfer coefficient decreases with increasing heat flux and decreasing mass flux, but is little affected by pressure. Under high q/G conditions, buoyancy effect is significant and heat transfer is deteriorated in the whole test section. Available heat transfer correlations for S-CO2 are compared with the experimental data; however, the prediction errors of these correlations are relatively high, especially in pseudo-critical regions. As a result, a new heat transfer correlation is developed for S-CO2 under high q/G conditions, in which buoyancy effect and variations in thermophysical properties are both taken into account.

Impact of Fluid Substitution on the Performance of an Axial Compressor Blade Cascade Working with Supercritical Carbon Dioxide

Abstract Recent research on turbomachinery design and analysis for supercritical carbon dioxide (sCO2) power cycles has relied on computational fluid dynamics. This has produced a large number of works whose approach is mostly case-specific, rather than of general application to sCO2 turbomachinery design. As opposed to such approach, this work explores the aerodynamic performance of compressor blade cascades operating on air and supercritical CO2 with the main objective to evaluate the usual aerodynamic parameters of the cascade for variable boundary conditions and geometries, enabling “full” or “partial” similarity. The results present both the global performance of the cascades and certain features of the local flow (trailing edge and wake). The discussion also highlights the mechanical limitations of the analysis (forces exerted on the blades), which is the main restriction for applying similarity laws to extrapolate the experience gained through decades of work on air turbomachinery to the new working fluid. This approach is a step toward the understanding and appropriate formulation of a multi-objective optimization problem for the design of such turbomachinery components where sCO2 is used as the operating fluid. With this objective, the paper aims to identify and analyze what would be expected if a common description of such computational design problems similar to those where air is the working fluid were used.

A Supercritical CO2 Waste Heat Recovery System Design for a Diesel Generator for Nuclear Power Plant Application

After the Fukushima accident, the importance of an emergency power supply for a nuclear power plant has been emphasized more. In order to maximize the performance of the existing emergency power source in operating nuclear power plants, adding a waste heat recovery system for the emergency power source is suggested for the first time in this study. In order to explore the possibility of the idea, a comparison of six supercritical carbon dioxide (S-CO2) power cycle layouts recovering waste heat from a 7.2 MW alternate alternating current diesel generator (AAC DG) is first presented. The diesel engine can supply two heat sources to the waste heat recovery system: one from exhaust gas and the other from scavenged air. Moreover, a sensitivity study of the cycles for different design parameters is performed, and the thermodynamic performances of the various cycles were evaluated. The main components, including turbomachinery and heat exchangers, are designed with in-house codes which have been validated with experiment data. Based on the designed cycle and components, the bottoming S-CO2 cycle performance under part load operating condition of AAC DG is analyzed by using a quasi-steady state cycle analysis method. It was found that a partial heating cycle has relatively higher net produced work while enjoying the benefit of a simple layout and smaller number of components. This study also revealed that further waste heat can be recovered by adjusting the flow split merging point of the partial heating cycle.

500℃ 대응 kW급 초임계 이산화탄소 발전 시스템 시험 장치 예비운전 특성 연구

초임계 이산화탄소 발전 사이클이란 증기 사이클과 마찬가지로 터보제너레이터를 구동하여 전기를 생산하지만 작동 유체로 증기가 아닌 이산화탄소를 사용하는 발전 사이클을 의미한다. 특히 사이클 전 공정에 걸쳐 초임계 이산화탄소가 상대적으로 높은 밀도로 존재하기 때문에 작은 크기의 터보기기나 열교환기를 사용 가능한 장점이 있다. 또한, 압축일이 적어 사이클의 효율이 높고, 저압부의 온도가 상온 이상이므로 물이 부족한 지역에서 건식냉각을 활용할 수 있는 장점도 있다. 본 논문에서는 500℃ 대응 kW급 초임계 이산화탄소 발전 시스템 시험 장치의 설계와 예비시험에 대하여 논의하고 있으며, 예비시험 결과로부터 초임계 이산화탄소 발전의 운전 절차를 정립하고, 그 특징을 살펴보았다.

Carbonate molten salt solar thermal pilot facility: Plant design, commissioning and operation up to 700 °C

Concentrated solar power (CSP) is not currently cost competitive with conventional power generation or other solar energy technologies, but it is attractive because it integrates commercially viable large-scale thermal energy storage (TES). To improve performance and reduce costs, supercritical carbon dioxide (s-CO2) power cycles have been proposed to increase the thermal-to-electric conversion to values above 50%. However, to achieve this target, the solar energy collected by the receiver and stored in the TES must be delivered to the power turbine at a temperature at or above 700 °C, while current advanced plants only provide thermal energy at 565 °C. For the first time, a high temperature (700 °C) molten salt experimental pilot plant for CSP was designed, built, and tested by Abengoa using carbonate salts as the heat transfer fluid. We demonstrate the feasibility of large-scale, industrially relevant operation between 400 and 700 °C, thus providing a solution to integrate higher efficiency s-CO2 power cycles. We address the key points in material compatibility, component design, instrumentation and system integration. Operational aspects such as preheating and filling procedures, start-up, maximum temperature reached, and the main challenges faced are described in detail. The heat losses in the loop and components are analyzed. We show that with appropriate electrical heat tracing elements, operation with carbonates is feasible and that the main subsystems that must be redesigned are the high temperature tanks and pumps. Lessons learned from the plant operation are summarized here to guide the design of future commercial scale high temperature molten salt plants.