Supercritical Power Research Articles

Energy and Exergy Analysis of a Coal-Fired Supercritical Power Plant

Yenilenebilir enerji kaynaklarıyla elektrik üretimi üzerine araştırmalar hızlı bir şekilde ilerlese de fosil yakıtlarla elektrik üretiminin hem dünyada hem Türkiye’de uzun bir süre daha sürmesi beklenmektedir. Hem çevrede oluşturduğu zararlı etkiler hem de tükenme riskinin yüksek olması, fosil yakıtların termik santrallerde verimli bir şekilde tüketilmesini zorunluluk haline getirmiştir. Fosil yakıtın bir türü olan kömür, elektrik üretmek amacıyla termik santrallerde yaygın olarak kullanılmaktadır. Kömür yakıtlı termik santrallerde kullanılan kazan, süper kritik bir kazan seçildiğinde santral verimi artırılabilir. Bu çalışmada Zonguldak ilinde bulunan Eren Enerji’ye ait kömür yakıtlı süper kritik termik santralin termodinamik performansı, enerji ve ekserji analiz metotlarıyla incelenmiştir. Santralde bulunan her bir elemana ait enerji kayıpları ve tersinmezlikler hesaplanmıştır. Enerji analizi, kömürün kimyasal enerjisinin %48.5’inin kondenserde soğutma suyuna aktarıldığını; ekserji analizi ise kömürün kimyasal ekserjisinin %49.2’sinin kazanda yok edildiğini göstermiştir. Santralin enerji verimi %33.65, ekserji verimi ise %31.42 olarak hesaplanmıştır.

Optimization and techno-economic comparison of regenerators and recuperators in sCO[formula omitted] recompression Brayton cycles for concentrating solar power applications

Supercritical CO2 power cycles might be capable of providing the cost reductions and efficiency improvements necessary to reach concentrating solar power (CSP) cost targets, but require large, highly effective recuperators. Fixed-bed regenerators are a periodic heat exchanger that could be an effective yet low-cost alternative to these recuperators. This study presents a techno-economic comparison of regenerators and recuperators for a 100 MWe supercritical CO2 power cycle for CSP applications. We quantify the levelized cost of energy (LCOE) for the power plant with both types of heat exchangers, and explore sensitivity of LCOE to parameters such as CSP-specific capital costs, power cycle component capital costs, and regenerator valve replacements costs. Results indicate that the incumbent printed circuit heat exchangers achieve the lowest LCOE, unless the upper extreme of PCHE capital cost and lower extremes of regenerator and valve capital and O&M costs are realized. Sensitivity analysis also illustrates that the primary heat exchanger cost is the most influential of power cycle components, and that CSP component capital cost is more influential than power cycle capital costs. This illustrates the importance of reducing the cost of heliostats, receivers, and thermal energy storage for achieving CSP LCOE targets.

Multiple processes modeling and identification for a cleaner supercritical power plant via Grey Wolf Optimizer

Validated mathematical modeling of clean coal power generation technologies is an essential subject of research that has a realized importance in the scientific communities working on the energy production and environment protection. This study presents a complete multiple processes modeling and simulation of a practical cleaner coal supercritical power plant (SCPP). The model covers a wider range of operation than ever published models before, which focus either on startup or on once-through operation. The model in this paper rather embeds the whole journey from recirculation mode during startup process up to the maximum produced power, then to emergency shut-down process in the same model. It has been found that slight adaptations in the once-through model parameters are sufficient to switch from one mode of process to another, which is useful in retaining simplified structure of the model. The fixed parameters of the model have been optimized by modern meta-heuristic technique of Grey Wolf Optimizer (GWO) and compared with Genetic Algorithms (GA). It has been proved that GWO has a sort of superiority over the GA for parameter identification of the SCPP model.

Design optimization of an additively manufactured prototype recuperator for supercritical CO2 power cycles

Supercritical CO2 (sCO2) power cycles are being developed due to their potential for high efficiency and reduced capital cost. It is necessary that these recuperators operate at high pressures and temperatures, up to 30 MPa and 900 K, with effectiveness values > 95% and pressure drops <1% to achieve high cycle efficiencies. Moreover, it is also necessary to have reasonable cost recuperators to control the capital costs of the sCO2 power cycles. In this study, a Plate Pin-Fin (PPF) heat exchanger has been proposed as an sCO2 recuperator. This preliminary recuperator design leverages capabilities enabled by additive manufacturing. Although the PPF design has characteristics similar to those of a plate heat exchanger, small diameter and relatively long fins are used to increase surface area, enhance heat transfer, and provide structural support for the partition plates that separate the fluid streams. Existing correlations for heat transfer and pressure drop were adapted for the PPF heat exchanger. These correlations were implemented in a 1D analytical model and used for the optimization of a 5-kWth high temperature recuperator for an indirect sCO2 cycle by varying the design parameters to minimize the quantity of material required. A 3D conjugate heat transfer numerical simulations were conducted to validate the heat transfer and pressure loss correlations. A steepest descent method was used to minimize heat exchanger mass for a 5-kW prototype recuperator subject to a maximum specified pressure drop. The design analysis indicated that an optimum PPF recuperator would be attained for the minimum allowable pin transverse spacing, minimum pin width, minimum pin height and near maximum cell aspect ratio. At a low material requirement of 0.216 kg/kW and a pressure drop, which is almost five times lower than the allowable pressure drop design target, the optimized PPF heat exchanger has the high potential to be an alternative to a printed circuit heat exchanger, which is a conservative design basis for the current state-of-the-art sCO2 recuperators.

Femtosecond multiple filamentation of an optical vortex in the mid-IR wavelength range in fused silica and fluorides

The results of experimental and theoretical study of the self-action of femtosecond optical vortices in the region of anomalous group velocity dispersion in fused silica and fluorides are presented. Multiple filamentation of an axially asymmetric annular beam with a phase dislocation of topological charge m = 1 at a wavelength of 1800 nm in a LiF crystal is investigated. It is found that for the experimentally recorded intensity profile of a vortex beam with two maxima on the diameter, the critical self-focusing power is approximately two times larger than the critical power of a unimodal Gaussian beam. In pulses with supercritical power in the vicinity of the intensity maxima, two coupled filaments, separated by a phase dislocation, are formed on the annular profile of the optical vortex, which prevents energy exchange during their formation. The length of vortex-beam plasma channels in a single pulse is found to be about 300 μm at a diameter of about 2 μm, which is close to the characteristics of plasma channels in a Gaussian beam.

A numerical investigation of methane ignition in supercritical CO2

The supercritical CO2 power cycle (sCO2) is a relatively new technology, which promises to reduce CO2 emissions with potentially higher efficiencies. However, due to challenging conditions posed by supercritical pressures, the ignition phenomena in sCO2 combustion are relatively less understood and studied. The primary objective of the current study is to elucidate ignition processes using homogeneous ignition calculations (HMI) and two-dimensional direct numerical simulations (DNS). To accurately model the supercritical conditions, the employed formulation includes the cubic Peng–Robinson equation of state, mass, and heat flux vectors derived from nonequilibrium thermodynamics and compressible form of governing equations. For selection of a suitable chemical mechanism, HMI calculations are employed to investigate the performance of existing skeletal mechanisms against shock-tube experimental data. The chemical characteristics of ignition are further studied using path flux and sensitivity analysis, with CH3O2 chemistry exhibiting the largest effect on accelerating the ignition process. Different chemical pathways of fuel breakdown are also discussed to aid in interpretation of subsequent DNS case. In the DNS case, autoignition of a two-dimensional mixing layer perturbed with pseudoturbulence is simulated. The ignition is found to be delayed compared to the HMI case, with the ignition kernels forming in a spotty manner. The two phenomena are primarily attributed to variation of scalar dissipation within the mixing layer. The ignition kernels expand and evolve into a tribrachial edge flame propagating along the stoichiometric isosurface. Further investigation on the structure of edge flame revealed an asymmetrical structure, with CH4 molecules being entirely consumed in the triple point region of the flame along the stoichiometric isosurface, and more stable fuels like CO burning in the non-premixed branch of the edge flame. The edge flame propagation speeds are also calculated, with variations found to be correlated with scalar dissipation and upstream progress variable of the reacting mixture.

Microstructural Evolution for Super304H Austenite Steel used in China Plants

Super304H (18Cr-9Ni-3Cu-Nb-N) austenite steel has high creep strength and has been used as the material of tubes in 600℃ class supercritical power plants in China. Many Super304H materials have run for more than 100,000 hours. Long-time service feature of these austenitic stainless steels has not been understood. An understanding of the long-term microstructural evolution under actually used conditions is a key for the improvement of these heat resistant steels. In this article, creep behavior of Super304H used in China plants was analyzed, microstructural evolution of Super304H materials after different service conditions were studied involving in optical microscope, TEM and SAXS. The results show, M23C6, Cu-rich particles, and σ phase were found to precipitate. A quantitative assessment of microstructure evolution was given during long-term creep.

Various Technology options of 'Application' of CCS on large coal-fired unit – A Rationale

Even though India has made great strides in expanding installed capacity from 1713.0 Megawatt in 1950 to be over 3,79.130 MW in March 2021, renewable energies provide 24.50% with a maximum capacity of over 91,154.0 MW. These contributions do have a high social and environmental effect on the people in rural and remote areas and our commitments to fighting climate change. Alternative energy sources for mega energy production, including such photovoltaic mega power under mission mode, solar thermal and solar panels, green energy techniques, CCTs, i.e., supercritical power plants, Incorporated Gasifying Combined Cycle (IGCC), and fluidization bed combustion (FBC), are important to the achievement of India's Green Power Mission. CCS (Carbon Capture and Sequestration) is a cutting-edge green power technique.

Additive manufacturing and testing of a ceramic heat exchanger for high-temperature and high-pressure applications for concentrating solar power

Heat exchangers with excellent corrosion and oxidation resistances are essential for the next-generation concentrating solar power (CSP) plants using a molten salt heat transfer fluid and a supercritical CO2 Brayton power cycle that can operate at temperatures >700 °C for higher efficiencies. Techniques were developed for additively manufacturing ceramic materials for applications involving high temperature, high pressure, and high corrosion resistance as needed for the CSP application. Based on a previous ceramic heat exchanger design with its cross-section geometry of the flow channels optimized for heat transfer and mechanical strength, lab-scale prototype heat exchangers, with integrated headers and incorporated flow channel dimensional compensations, were fabricated by using the binder jetting process. The printed prototype heat exchangers were successfully densified through the processes of liquid polymer infiltration and pyrolysis. In addition, thermophysical properties of the densified silicon carbide parts were measured to provide necessary design information. Experimental heat transfer testing of the lab-scale prototype heat exchanger was conducted, and the experimental data agreed reasonably well with the simulated results. This agreement provides validation of the simulation models for their applicability to the development of a full-scale ceramic heat exchanger.

Characterization of Microstructure and Mechanical Properties of Cr-Mo Grade P22/P91 Steel Dissimilar Welds for Supercritical Power Plant Application

Characterization of Microstructure and Mechanical Properties of Cr-Mo Grade P22/P91 Steel Dissimilar Welds for Supercritical Power Plant Application

Modeling Sand Particulate Flows Through Angled Apertures and Surfaces in Concentrated Solar-Thermal Power Receivers

Abstract Concentrated solar-thermal power towers are increasingly migrating toward sand-based particle receiver designs to improve thermal efficiency and reach temperatures above 1000 °C for air Brayton power cycles and supercritical CO2 power cycles. However, utilizing sand affords complexities in modeling particle flow characteristics due to variable geometric shape, size, and composition. Thus, the objective of this study is to model the particle flow characteristics of sand through variable angled chevron shapes and receiver hoppers to help formulate robust modeling for flow dynamics. Treating the chevrons as an array of apertures, a novel method of calculating sand particle mass flowrate across angled apertures and surfaces is developed. Employing high-speed photography and particle imaging velocimetry techniques, our results incorporate the impact of effective angles upon velocity, residence time, and breakage profiles of falling sand particles. This study determines that a Beverloo equation incorporating effective angles for velocity and aperture size effectively predicts mass flowrate through chevrons, which can serve as a reference for future particulate flow modeling in this field. Furthermore, increasing hopper and chevron tip angles resulted in a more significant decrease in particle diameter and curtain opacity after sand flow trials.

Thermodynamic assessment of combined supercritical CO2 cycle power systems with organic Rankine cycle or Kalina cycle

The supercritical carbon dioxide (S-CO2) Brayton cycle is considered to be one of the most promising cycles for the fourth-generation nuclear power system. In this paper, the S-CO2 Brayton combined cycles composed of organic Rankine cycle (ORC) and Kalina cycle as the bottom cycle are proposed to improve the cycle performance. A new system performance parameter η/Qv,max is introduced for the first time to evaluate the economy and compactness balance of the combined cycle. Parametric study based on different working fluids for bottom cycle is conducted, comparison study between the S-CO2 Brayton combined cycles and traditional S-CO2 Brayton reheating cycle are made. The comparison results show that R32 and Ammonia based S-CO2/ORC combined cycle obtain the best performance, with thermal efficiency enhanced by 2.015% and 2.036%, respectively. The S-CO2/Kalina combined cycle obtains an improvement by 1.79% with ammonia-water concentration at 0.85, which is slightly lower than S-CO2/ORC combined cycle. Superheating the organic working fluids can improve the exergy efficiency of the evaporator and increase ηorc/Qv,max, but the efficiency of the cycle is not necessarily improved. The temperature slip contributes in reducing the temperature difference in the evaporator, and this helps the S-CO2/Kalina combined cycle to better match the temperature changing characteristics of the heat source compared with ORC, and the slope of the CO2 heat transfer line near the critical point of CO2 is the key factor that limits the improvement of S-CO2/Kalina combined cycle efficiency.

Failure analysis of SS 304 HCu reheater tube of a supercritical power plant

The conducive atmosphere for corrosion and simultaneous presence of stress in the material often results in the phenomenon of stress corrosion cracking (SCC). SCC has been reported in both sensitized and un-sensitized austenitic stainless steels widely used in industry. The present investigation is centred around a reheater tube made of stainless-steel SS 304 HCu, which failed in a newly constructed power plant when subjected to hydro test. Optical and electron microscopy was used in the analysis in the vicinity of the attachment weld on the reheater tubes. Even though microstructural investigation showed no sign of sensitization, the presence of chloride (Cl), identified through SEM-EDS scan, and localized strain, identified through EBSD scans near the failed region, confirmed stress corrosion cracking in the material. The results obtained during the investigation have clearly brought out the cause of stress corrosion cracking in reheater tube. Further, it was observed that the weld bead size played an important role in inducing residual stress in the material and the bead size was modified to address the localized stresses at the weld; this helped in solving the problem.

Combined direct oxy‐combustion and concentrated solar supercritical carbon dioxide power system—Thermo, exergoeconomic, and quadruple optimization analyses

For the global future energy systems, concentrated solar power (CSP) and direct CO2 capture systems are of the most important key technologies, however, each of these systems has shortcomings. This study addresses the solar intermittency and power control complexity of the CSP systems and the substantial energy penalty of the direct oxy-combustion (DOC) supercritical carbon dioxide (sCO2) power systems by integrating both systems. Herein, innovative power cycle configurations that integrate the CSP tower system with DOC sCO2 power cycle are introduced. The configurations include two basic cycles for comparison and validation purposes and three integrated cycles. The basic configurations are: an intercooled sCO2 power cycle driven by DOC system (S1), and a stand-alone basic CSP tower system (S2). The integrated configurations are: CSP/DOC system where the CSP works as a preheater (S3); CSP/DOC system where the CSP works as a reheater (S4); and CSP/DOC system where each system heats part of the working fluid to drive its high-pressure turbine (S5). The hybrid configurations reduce the fuel and the parasitic power consumptions of the basic DOC systems (S1) and reduce the capital cost associated with the conventional CSP systems (S2) by eliminating the need for thermal storage. Over practical ranges of operational parameters, comprehensive thermoeconomic, exergoeconomic, and optimization analyses for the proposed configurations are performed. Compared to the conventional CSP system, the LCOE of the hybrid system is lower by 50%. Among the hybrid configurations, the energetic and exergetic performances of S4 are the best with the lowest LCOE. According to the optimization analysis, S4 has a thermal efficiency of 55.29% at LCOEs of 7.705¢/kWh. S3, S5, S2, and S1 have thermal efficiencies of 52.90%, 48.72%, 45.56%, and 40.54% at LCOE of 7.970, 8.138, 7.864, and 6.351¢/kWh, respectively.

Issues and solutions for integrity of pressure vessels and piping subjected to long-term creep exposure in supercritical thermal plants

ABSTRACT ASME BPVC Section VIII Division 2 (‘ASME VIII(2)’) and ASME B31.1 are being used not only for low-temperature design but also for high-temperature design in the creep range in supercritical thermal power plants. However, creep effects in ASME VIII(2) and B31.1 are taken into account implicitly, and there could be significant technical issues in terms of conservatism in the case of long-term operation in the creep range because their design evaluation results do not change across plant operation time. The conservatisms of ASME VIII(2) and B31.1 have been quantified based on comparisons with nuclear-grade design rules of ASME BPVC Section III Division 5 and RCC-MRx which take creep hold time into account explicitly. It was shown that ASME VIII(2) and B31.1 results could be non-conservative if operation time exceeds a certain time limit, which raises concerns around non-conservatism in the case of long-term operation within the creep range.

Comment on Rogalev et al. Structural and Parametric Optimization of S-CO2 Thermal Power Plants with a Pulverized Coal-Fired Boiler Operating in Russia. Energies 2021, 14, 7136

The reconstruction of ageing thermal power plants with the possibility of their increased efficiency, prolonged service and decreased environmental impact is an intensely debated and researched topic nowadays. Among various concepts, the replacement of the steam cycle by a supercritical CO2 cycle is proposed with the prospect of reaching higher efficiencies at the same working fluid inlet parameters as the ultra-supercritical steam cycles. A paper published previously by Rogalev et al. (2021) analyzed the variants of supercritical coal power plant reconstruction to a supercritical CO2 cycle and ranked them according to the cycle efficiency. This contribution comments on the scope and applied method in that paper aiming to provide additional input relevant to the decision-making process on thermal power plant reconstruction to such a cycle.

Numerical analysis of environment-friendly solar aided coal-fired supercritical thermal power plant cycle integrated with dual heat exchangers

The hybrid solar-coal supercritical steam thermal system has been developed in current research work. The proposed system uses a double-tank heat storage system to increase the stability of the solar tower system, and two heat exchangers to transfer heat from molten salt in the solar tower system to steam in a supercritical coal-fired thermal system. TRNSYS software has been used as a platform to build a model of the solar coal-fired hybrid supercritical steam thermal system. Local weather data is imported to simulate the characteristic year’s operation of a hybrid system under design and off-design working conditions. The variation of heat transferred from solar system to supercritical steam thermal system, power generated from supercritical steam thermal system, solar-electrical generation capacity, efficiency and proportion of solar power generation are compared and analyzed. The results show that after the system is integrated, the tower solar steam production mechanism will increase the output power of supercritical steam thermal system and reduce thermal efficiency of the integrated system. When boiler steam flow rate is kept at less than reference flow rate after joining with solar steam flow rate, total steam flow rate exceeds the reference flow rate, while solar steam flow rate increases.

Performance Evaluation of Supercritical Carbon Dioxide Recompression Cycle for High Temperature Electric Thermal Energy Storage

As interests in low carbon power generation are growing, the share of renewable energy power generation is increasing. Naturally, research on energy storage system is being conducted worldwide as a system to solve the intermittency problem of renewable energy. When renewable energy increases significantly, it is important to secure sufficient operating reserve with energy storage capability. In this paper, the performance of electric thermal energy system using 10MWe supercritical carbon dioxide recompression cycle is analyzed to investigate the feasibility of the proposed concept. Among many performance indicators, this paper mainly focused on the required thermal power for the system to stay in the stand-by mode, and the dynamic behavior of the proposed system during fast power ramp-up so that the potential of the system for providing ancillary services can be revealed. To investigate these issues, an on-design analysis is first conducted to determine the performance of the proposed system followed by component design to evaluate off-design performances and transient responses of the system. From the quasi-steady state analysis, break-even conditions are found for various inventory levels. In the transient analysis for power increasing operation from 0% to 100%, fluctuations in physical parameters are observed due to the sudden change in properties near pseudocritical pressure conditions. However, this issue can be mitigated with an appropriate inventory control system as shown in this paper. Thus, the proposed system shows promising transient performances for fast power ramp-up operation. This means that the electric thermal energy storage system with a dedicated supercritical carbon dioxide power cycle can be utilized as an operating reserve. The conclusions of this study are not only limited for the electric energy storage system application but also has an implication to the concentrating solar power or the advanced nuclear power plant application of the supercritical carbon dioxide recompression cycle.

Ratcheting fatigue of modified 9Cr-1Mo steel and Inconel alloy 617 at ambient temperature: Effect of uniform plastic strain

Modified 9Cr-1Mo steel and Inconel alloy 617 (IN-617) are two important structural materials, used for piping/ tubing components in nuclear and advanced supercritical power plants. Such components undergo ratcheting fatigue, due to the mean stress, arising from fluctuations in temperature and internal pressure. This investigation presents dominant role of uniform plastic strain on ratcheting fatigue resistance comparing ratcheting fatigue life of these two materials under identical normalized mean stress and stress amplitude, at ambient temperature. Accumulated plastic strain in IN-617 was considerably higher than that of modified 9Cr-1Mo steel, although ratcheting fatigue life of IN-617 was much higher than that of modified steel. Higher uniform strain in IN-617 was found to be cause of observed behavior. Thus, uniform tensile strain of material can be considered as an important parameter for selection of materials to be used as tubular products in power plants, experiencing ratcheting fatigue.

Effect of Ta addition on solidification microstructure and element segregation of IN617B nickel-base superalloy

IN617B nickel-base superalloy is considered as a good candidate material in 700 °C advanced ultra- supercritical coal-fired power plants. The effect of Ta addition on solidification microstructure and element segregation of IN617B alloy was investigated by OM, SEM, TEM, EDS, EPMA and thermodynamic calculation. The results showed that the solidification microstructure exhibited a dendritic segregation pattern with many primary carbides distributed in interdendritic regions, such as network M6C, lath M23C6 and granular Ti(C,N). The addition of Ta promoted the precipitation of Ta-rich MC significantly inhibiting the precipitation of M6C and M23C6, and reduced the segregation degree of Al, Mo and Ti alloying elements. The addition of Ta decreased the melting temperature of MC carbide, but did not impact the solidification path, that was, L→ γ matrix → MC or Ti(C,N) → M6C → M23C6, where MC and Ti(C,N) tended to form symbiotic microstructure with M6C. This study will provide theoretical basis and data support for the alloy optimization and casting structure control of IN617B nickel-based superalloy.