Advanced Power Cycles Research Articles

Performance Comparison of Advanced Transcritical Power Cycles with High-Temperature Working Fluids for the Engine Waste Heat Recovery

To efficiently recover the waste heat of mobile engine, two advanced transcritical power cycles, namely split cycle and dual pressure cycle, are employed, based on the recuperative cycle. Performances of the two cycles are analyzed and compared through the development of thermodynamic models. Under given gas conditions, seven high-temperature working fluids, namely propane, butane, isobutane, pentane, isopentane, neopentane, and cyclopentane, are selected for the two cycles. At the design system parameters, the highest work 48.71 kW, is obtained by the split cycle with butane. For most of fluids, the split cycle has a higher work than the dual pressure cycle. Furthermore, with the increase of turbine inlet pressure, net work of the split cycle goes up firstly and then decreases, while the work of dual pressure cycle increases slowly. For the split cycle, there exists a split ratio to get the maximum network. However, for the dual pressure cycle, the larger the evaporation temperature, the higher the net work. On this basis, system parameters are optimized by genetic algorithm to maximize net work. The results indicate that the highest work 49.96 kW of split cycle is obtained by pentane. For the considered fluids, except cyclopentane, split cycle always has a higher work than dual pressure cycle. Due to the higher net work and fewer system components, split cycle is recommended for the engine waste heat recovery.

Coupling chemical looping combustion of solid fuels with advanced steam cycles for CO2 capture: A process modelling study

Chemical looping combustion is a cost-competitive solution for producing low carbon electricity. In this paper, we investigate by means of a process modelling study, the coupling of chemical looping combustion of solid fuels with advanced steam-based power cycles, viz. supercritical, ultra-supercritical and advanced ultra-supercritical Rankine cycles. The energy and exergy efficiencies of the various chemical looping combustion power plant configurations are compared against the reference plants without carbon capture. Our models incorporate practical considerations for reactor design. With an upper operating temperature limit of 950 °C, the maximum efficiencies achievable by integrated gasification combined cycle chemical looping combustion (IGCC–CLC) and in situ gasification chemical looping combustion power plants (iG-CLC) are 41.3% and 41.5%, respectively. Overall, iG-CLC emerges as the most efficient CLC configuration. Comparing to an integrated gasification combined cycle without carbon capture, the energy efficiency penalties for capturing CO2 from iG-CLC coupled with subcritical, supercritical, ultra-supercritical or advanced ultra-supercritical steam cycles are 5.1%, 5.0%, 5.2% or 13.0%, respectively. The biomass-fired chemical looping combustion power plants also show low energy efficiency penalties (<2.5%) compared to the reference biomass power plants without CO2 capture. Our modelling results suggest that chemical looping combustion will remain an attractive carbon capture technology for solid fuel power plants, in a future when supercritical steam turbines become the norm.

Waste heat management of direct carbon fuel cell with advanced supercritical carbon dioxide power cycle – A thermodynamic-electrochemical modeling approach

This study evaluates the performance of a hybrid supercritical carbon dioxide (SCO2) power cycle, which uses the waste heat of a direct carbon fuel cell (DCFC). Three different configurations including a standalone DCFC, an integrated system consisting of a DCFC coupled with a simple SCO2, and another hybrid system consisting of a DCFC and a partial cooling SCO2 are examined and characterized. In the proposed systems, the effects of the electric current density, operating temperature, anode dimensions, and the pinch point temperature difference in the SCO2 evaporator are then discussed. Considering the optimum operational region of the supercritical cycle, the partial cooling SCO2 was found to be a very promising power cycle for coupling with DCFC. Integrating a supercritical CO2 cycle with DCFC can compensate for the loss of efficiency and power density caused by decrease in fuel cell temperature. There is even an operating window in which the performance of the introduced integrated systems is practically independent of the fuel cell temperature. Results show that at the current density of 1000 A/m2, the rate of change in power density and efficiency of the standalone DCFC system is 0.47 W/m2 and 0.058% per unit of fuel cell temperature, respectively. For the integrated DCFC and partial cooling SCO2 system, however, those rates reduce to 0.13 W/m2 and 0.02% per unit of temperature.

Efficiency limits of high-temperature transparent packed-bed solar receivers

Gas-phase solar receivers represent one of the best near-term solutions for providing temperatures in excess of 1000 K. However, as the desired outlet temperature increases, heat losses also inexorably increase. To mitigate this trade-off, this research systematically analyses a semi-transparent packed-bed solar receiver which can enable absorption to occur within the receiver's volume rather than on the surface (where thermal emission losses occur). As such, this study aims to find the limits-and the key limiting factors-for the overall performance of this new class of the receiver. This was done by exploring a wide range of geometrical (e.g., ~0.01 to ~ 1.45 spheres per cm3 or D/dp ranging from 3 to 15) and operational parameters. This parametric study was conducted by coupling a comprehensive heat transfer model with ray tracing and a surface-to-surface radiation model. For a 1000 K outlet temperature, an effective maximum receiver efficiency of just over 70% was achieved with 18 rows of transparent spheres (i.e., D/dp = 9 or ~ 0.3 spheres per cm3). This analysis also revealed a critical dimensionless parameter, Ω, which must be kept near a value of 1 to maximise the effective efficiency. This proposed dimensionless parameter was derived from the ratio of conduction to convective heat transfer multiplied by the ratio of absorbed solar power to input pumping power. Overall, this study's results indicate that semi-transparent packed beds represent a promising near-term design for cost-effective, high-temperature solar receivers, which can be used in advanced power cycles.

Multiple wall temperature peaks during forced convective heat transfer of supercritical carbon dioxide in tubes

Heat transfer deterioration (HTD) is defined as having one or multiple wall temperature peaks along the flow length for supercritical heat transfer. The single-peak phenomenon has been widely reported in the literature, but the multi-peak phenomenon is seldomly studied and not well understood. Here, the convective heat transfer of supercritical carbon dioxide in vertical tubes is investigated, with pressure, mass flux, and heat flux in the ranges of 7.5~23 MPa, 400~1500 kg/m2s, and 25~450 kW/m2, respectively, and inner tube diameter covering 8, 10, and 12 mm. Sudden changes are observed between normal heat transfer (NHT) without wall temperature peak and HTD by crossing a global critical supercritical boiling number (SBO) based on the pseudo-boiling theory. For HTD, we show that inner diameter and pressure have significant influences on whether the multi-peak phenomenon occurs: it takes place for inner diameter of 12 mm only and under pressure of ~8 and ~12.5 MPa. It is found that friction factors for multi-peak cases are obviously larger than those for single-peak or NHT cases, which is successfully explained by the orifice contraction effect due to the strong “vapor” expansion at the tube cross-section corresponding to the sharp wall temperature peak. The multi-peak phenomenon is shown to be governed by the competition between the local evaporation momentum force and inertia force along the flow length. Our work enhances the understanding of supercritical heat transfer and verifies the validity of pseudo-boiling assumption, and can also benefit engineering applications in advanced power cycles.

Supercritical CO2 cycle for coal-fired power plant based on calcium looping combustion

Calcium looping combustion (CaLC), which comprises an indirectly-heated calciner, is characterised with lower energy intensity and economic penalties compared to that of mature CO2 capture technologies. As CaLC is a standalone power boiler, integration of advanced power cycles can lead to further improvement in net efficiency and reduction in the cost of electricity. Therefore, this study aimed to propose routes for the integration of the supercritical CO2 cycle (sCO2) with CaLC and to evaluate their benefits with respect to the conventional steam cycle. Such processes were modelled in Aspen Plus™. Moreover, the effect of the operating conditions on the techno-economic performance of the considered cases was evaluated. This study has shown that implementation of the optimised recompression sCO2 cycle with a clean gas cooler resulted in the net efficiency and break-even price of electricity of 37.3%HHV and 75.13 €/MWh, respectively. These are 0.7%HHV points lower and 26% higher, respectively, than that of the conventional coal-fired power plant without CO2 capture. Such performance, however, is superior to retrofits of coal-fired power plants with mature CO2 capture technologies as well as CaLC with a conventional steam cycle, proving the benefits of linking CaLC with advanced power cycles.

Modeling and simulation of an integrated regenerative transcritical cycle with a small modular reactor

In recent years, small modular reactors (SMR) have gained substantial development advancement and world-wide acceptance. While various advanced power cycles (e.g. supercritical CO2 Brayton cycle) have been proposed for Gen IV reactors, the steam cycle remains the only cycle for light water reactors. In this work, a unique regenerative transcritical power cycle using small molecule organic fluids (methanol and ethanol) was modeled with the reactor coolant loop of a small modular light-water reactor. In addition to modeling the thermodynamic cycle and associated transport processes for prominent components, the solution algorithms of the combined cycle model using MATLAB/REFPROP are illustrated in this article. The simulation results show that, by leveraging the superior thermophysical properties around the critical points of the working fluids, the transcritical methanol/ethanol cycles have shown similar performance as the steam cycle in terms of thermal efficiency and power output. With further system optimization, the regenerative transcritical cycle is expected to offer increased power output from the small modular light-water reactor as an alternative energy conversion system.

High pressure ignition delay times of H2/CO mixture in carbon dioxide and argon diluent

Ignition Delay Time (IDT) plays a significant role in combustion process of advanced power cycles such as direct-fired supercritical carbon dioxide (sCO2) cycle. In this cycle, fuel and oxidizer are heavily diluted with carbon dioxide (CO2) and autoignite at a combustor inlet pressure range of 10–30 MPa and a temperature range of 900–1500 K. A fuel candidate for sCO2 power cycle applications is syngas (H2/CO mixture); however, its ignition properties at these conditions are not studied. Moreover, the existing chemical kinetics models have not been evaluated for H2/CO mixtures applications relevant to elevated pressure conditions and under large dilution levels of CO2. Therefore, two tasks are performed in this study. First, IDTs of a H2/CO=95:5 mixture at stoichiometric and rich (Φ=2) conditions are measured in a high-pressure shock tube under 95.5% CO2 dilution level and at 10 MPa and 20 MPa for a temperature range of 1161–1365 K. For the experimental conditions considered in this work, Aramco 2.0, FFCM-1, HP-Mech and USC Mech II kinetic models are capable of capturing IDT data. Second, similar experiments are conducted by replacing the CO2 dilute gas with Argon (Ar) to understand the chemical effect of CO2 on IDT globally. Sensitivity analysis results reveal that for both diluents, reaction H + O2(+M)=HO2(+M) is the most important reaction in controlling ignition. Further, a rate of production analysis shows that CO2 has a competing effect on OH radical production. On one hand, CO2 accelerates the consumption of H radicals through H + O2+CO2→HO2+CO2 therefore hindering HO2+HOH+OH reaction for OH production. On the other hand, CO2 is shown to enhance OH production through H2O2+M=OH+OH+M. These kinetic effects from CO2 cancel out, therefore CO2 does not significantly alter the IDT globally when compared to the Ar bath case. This is confirmed by both experimental results and simulation.

Advanced power cycles for coal-fired power plants based on calcium looping combustion: A techno-economic feasibility assessment

Carbon capture and storage is crucial to decarbonising the power sector, as no other technology can significantly reduce emissions from fossil fuel power generation systems. Yet, the mature CO2 capture technologies result in net efficiency penalties of at least 7% points. Emerging technologies, such as calcium looping combustion, can reduce the net efficiency penalty to 2.4% points. Further reductions can be achieved by replacing the conventional steam cycle with advanced power cycles. This study aimed to assess the techno-economic feasibility of the coal-fired power plant based on calcium looping combustion with different advanced Brayton cycles. These included single power cycles, such as recompression supercritical CO2, simple supercritical CO2 cycle, and xenon cycle, as well as combined power cycles based on helium, nitrogen and recompression supercritical CO2 cycles. The net efficiency and break-even electricity price, which was estimated using the net present value method, were used as the key techno-economic performance indicators. A parametric study was also conducted to assess the impact of the key thermodynamic parameters. This study showed that the case based on a single recompression supercritical CO2 cycle had the best overall techno-economic performance, while the recompression supercritical CO2 combined cycle case had the best techno-economic performance among combined cycle cases. The former was characterised with a net efficiency of 38.9%, which is higher than that of the reference coal-fired power plant without CO2 capture (38.0%). Such performance was achieved at a break-even electricity price of 71.2 €/MWel,neth, corresponding to a cost of CO2 avoided of 16.3 €/tCO2.

A novel high-temperature (>700 °C), volumetric receiver with a packed bed of transparent and absorbing spheres

The concentrated solar power industry requires high-temperature receivers to push towards advanced power cycles. However, as the outlet temperature of a receiver increases, radiation losses (which are ∝T4) become dominant. In addition, at high temperatures, not many liquid working fluids are suitable. To address these issues, this research proposes an innovative, robust design of a gas-phase cavity receiver which utilises semi-transparent spheres as a volumetric absorption medium. The motivation behind this design is to break the long-standing outlet temperature versus efficiency trade-off by maximising the “volumetric effect” (i.e. obtaining a higher outlet fluid temperature than the receiver’s surface temperature). A range of designs were compared (i.e. packed beds of semi-transparent and high-transparency quartz spheres against an opaque bed of ceramic spheres). This study is important because it determines how the volumetric effect modifies the overall receiver efficiency via a holistic metric (proposed herein) which accounts for the optical, thermal, and pumping power efficiencies. Through a detailed ray-tracing analysis and a comprehensive thermal circuit model, this study reveals that a semi-transparent quartz packed bed receiver can have an overall receiver efficiency of around 80% at outlet temperatures above 700 °C. Most significantly, the best proposed design achieved a high value for the elusive volumetric effect (e.g. a maximum index value of 1.45). Based upon these results, the authors can conclude that these packed bed designs represent a promising new pathway towards reliable and cost-effective high-temperature and high-efficiency receivers which can be implemented into advanced, high-temperature power cycles.

The general supercritical heat transfer correlation for vertical up-flow tubes: K number correlation

The objective of this paper is to present a general supercritical heat transfer (SHT) correlation for advanced power cycles. In textbooks, supercritical fluid is considered to have single-phase structure. However, various SHT correlations incorporating buoyancy/acceleration effects fail to predict heat transfer coefficients. Here, pseud-boiling assumption is introduced to deal with SHT. Supercritical fluid is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. Similarity analysis between subcritical boiling and SHT creates a new dimensionless parameter, the K number, representing evaporation induced momentum force relative to inertia force to govern the growth of wall attached vapor-like fluid layer thickness, which is key to dominate SHT. Thus, SHT is correlated in a simple form as Nu=CRebn1Prb,aven2Kn3, where Nu, Reb, Prb,ave are Nusselt number, Reynolds number and Prandtl number, respectively. Totally, 5560 data points, including our newly obtained 2028 data points for S-CO2 with pressures up to 21 MPa, and other 3532 data points cited from 18 articles for carbon dioxide, water and R134a, are used to determine the coefficients C and n1−n3, yielding the expression ofNu=0.0012Reb0.9484Prb,ave0.718K−0.0313. The negative exponent −0.0313 for the K number explains the improved heat transfer by increasing pressures. By comparing with experiment database, the general correlation has better prediction accuracy than the widely cited correlations in the literature. The correlation is also compared with R22 data. Even though such data are not involved in the development of the SHT correlation, the correlation excellently matched the experimental data. This work paves a new road to understand SHT. The correlation ensures heat exchangers operating at supercritical pressures to be designed more accurately and safely.

Integrated optical-thermal-mechanical model for investigations into high temperature sodium receiver operation

An integrated optical-thermal-mechanical model is used to simulate the interaction between a heliostat field and sodium-cooled receiver through diurnal CSP plant operation. The cumulative heat flux on the receiver is controlled using a heliostat aiming strategy. A semi-empirical heat transfer model returns the receiver thermal profile based on the incident heat flux map, with aiming strategy solutions regulated by allowable flux density (AFD) data. A number of tube materials and inlet-outlet temperature combinations are investigated, with receiver thermal power output indicating suitable constructions for the delivery of elevated temperatures required for advanced power cycles. The selection of tube material is critical in maximising the heat absorption capabilities. The excellent creep-fatigue strength of Inconel 617 and Haynes 230 at high temperature yields a potential improvement in daily power output of up to 18% over more conventional heat exchanger materials. For these more traditional alloys, the aiming strategy requires a greater spillage allowance in order to generate a heat flux profile that satisfies lower mechanical reliability limits. The Ni-based superalloys alloys permit operation to temperatures far beyond conventional limits (>700°C), however the net power output is curtailed by greater heat losses at the receiver and an increased spillage requirement due to diminishing AFD levels.

Comparative study on humidified gas turbine cycles with different air saturator designs

The urge for more energy-efficient power plant systems to relieve the energy crisis triggers the design for more advanced power cycles. The humidified gas turbine cycle is considered one of the potential choices, and the air saturator performance is critical to the energy merit of such kind of system. To understand more, the performances of humidified gas turbine cycles with two types of air saturator designs were compared in this study. Type 1 air saturator was a hybrid design which combined an indirect evaporative cooler with a Maisotsenko cycle while Type 2 was a conventional indirect evaporative cooler. Detailed heat and mass transfer analysis was taken into account in the air saturator modelling. Through system simulations, it was found that all the humidified gas turbine cycle systems offered higher system efficiencies than a simple gas turbine system with recuperator. Besides, parametric studies were conducted which highlighted the effects of system inlet air temperature, turbine inlet temperature, water injection rate, and part-load ratio on the performances of the different humidified gas turbine cycle designs. The employment of Type 1 air saturator offered 9.34% and 23.55% enhancement in the system efficiencies as compared to those using Type 2 air saturator under the design and 50% part-load ratio conditions respectively. This reinforced the benefit of applying Maisotsenko cycle to the air saturator design of humidified gas turbine cycle for the enhancement of system efficiency.

Performance analysis on novel thermodynamic cycle under the guidance of 3D construction method

The efficiency improvement of organic Rankine cycle, which is an efficient way to recover the waste heat of internal combustion engines, is an eternal topic. The 3D construction method of thermodynamic cycle provides a possible way to construct efficient thermodynamic cycles based on zeotropic working fluid, whose core is to improve the thermodynamic performance by using different working fluids in different thermodynamic processes. Based on the 3D construction method of thermodynamic cycle, a composition adjustment organic Rankine cycle was proposed in this paper to recover the waste heat of internal combustion engines. The optimum working fluid used in trunk and branch processes were selected according to the requirements of different thermodynamic processes. The effects of key parameters were analyzed, and the optimized operation conditions and optimal performance were obtained. The results shown that the composition adjustment organic Rankine cycle performs best when using R123/toluene (0.9/0.1) in trunk process and R123/toluene (0.96/0.04), R123/toluene (0.66/0.34) in low-pressure and high-pressure branch processes, respectively. Under the optimal condition, the net output power, thermal efficiency and exergy efficiency are 50.07 kW, 10.96% and 45.79%, respectively. The irreversible losses in evaporator I and evaporator II account for 35.01% and 30.54% of the total irreversible losses in composition adjustment organic Rankine cycle respectively. This work provided an advanced power cycle for the waste heat recovery of internal combustion engines. What’s more, composition adjustment organic Rankine cycle proves the feasibility of the 3D construction method and opens up a novel way to construct efficient thermodynamic cycles.

Investigation on humidified gas turbine cycles with Maisotsenko-cycle-based air saturator

The urge for more energy-efficient power plant systems triggered the design for more advanced power cycle designs. The current simple cycle gas turbine shows its advantage on cost but does not fully exploit the energy available in the flue gas. In this paper, two more efficient humidified gas turbine cycles were investigated. Type 1 was a hybrid design which combined an indirect evaporative cooler with a Maisotsenko cycle and Type 2 a conventional indirect evaporative cooler as air saturator. The simulation results indicated how the operating conditions such as pressure ratio and air flow changed with the designs. Both humidified gas turbine cycle systems offered better system efficiencies than a conventional gas turbine system with recuperator and the application of Maisotsenko cycle based air saturator could further improve the gas turbine cycle efficiency. Parametric studies were also conducted which highlighted the effects of water injection rate and part-load ratio on the comparative performances of the different humidified gas turbine cycle designs.

Thermo-economic analysis of high-temperature sensible thermal storage with different ternary eutectic alkali and alkaline earth metal chlorides

Molten salt mixtures with alkali and alkaline earth metal chlorides were developed for high-temperature sensible thermal energy storage in support of concurrent efforts to develop high-temperature advanced power cycles for concentrating solar power applications. Four ternary chloride mixtures with different cation combinations (Na, K, Li, Mg) were designed using the FactSage® software, and for three of these, the eutectic point was experimentally validated by differential scanning calorimetry. Specific heat capacity measurements were conducted following the ASTM E1269 standard, and were measured between 1.18 J/g/K and 1.31 J/g/K. The mass loss of the molten chloride salts was studied under three different gas blankets of nitrogen, argon and air by thermogravimetric analysis. All the selected salt mixtures were stable up to 700 °C, although weight loss due to vaporisation becomes significant around this temperature due to the high vapour pressure of the chloride salt mixtures. However, it is expected that operation at a temperature up to around 750 °C will be feasible in a closed system with an inert environment. Additionally, removal of chemically-bonded water and salt purification may need to be considered for extending the operating temperature. In terms of economic performance, although the inclusion of LiCl in the ternary eutectic mixtures is advantageous for reducing melting point and increasing specific heat capacity, at current costs, these benefits are unlikely to be justified unless LiCl cost reduces by a factor of three. The NaCl-KCl-MgCl2 mixture has the lowest cost per unit energy stored, at 4.5 USD/kWh.

Exergoeconomic investigation of flue gas driven ejector absorption power system integrated with PEM electrolyser for hydrogen generation

This study aims to investigate the thermodynamic and economic aspects of a low temperature flue gas driven advanced absorption power cycle (AAPC) integrated to PEM electrolyser (PEME) for hydrogen and oxygen production. Flue gases from a small-scale coal fired power plant are utilized to energize the generator of the AAPC system. Produced power drives the PEME for primarily hydrogen generation, and oxygen as a byproduct. Use of ejector enhances the power production in the turbine favoring plant performance. The present integrated system produces daily amounts of ∼1.15 kg H2 and ∼4.59 kg O2 at 140 °C maximum cycle temperature with a capacity factor of 85%, 30 years of plant life and 5% annual interest rate. Cost of electricity and hydrogen are found to be 0.049 $/kWh and 2.43 $/kg, with overall energy and exergy efficiencies of 5.9% and 17.8%, respectively. The highest cost contributors are the APC turbine and the PEM electrolyser where these two accounts for almost 94% of total plant cost. Total cost of the plant is found to be ∼$61200. Cost of produced hydrogen shows promising results compared to those of electrolysis-based hydrogen production systems.

Performance of molten sodium vs. molten salts in a packed bed thermal energy storage

Concentrating solar power plants are currently working with Solar Salt and conventional Rankine steam power cycles with upper temperatures of 565 °C. To achieve higher efficiencies, advanced power cycles are currently investigated (500–700 °C). As heat transfer fluids, both molten sodium and three types of molten salt are considered in this study. For power tower plants, the heat transfer fluid is typically also the storage medium. This is the case for state-of-the-art commercial plants using molten salt, and past and present pilot plants using sodium. However, this work shows for both cases that a packed bed arrangement, where the heat transfer fluid is replaced by a filler material, may be a technically feasible and economically viable alternative. Furthermore, for sodium there are additional safety concerns related to having a large sodium inventory, which the packed bed arrangement can help alleviate. In this study, a 40 MWhth storage system with quartzite as filler material is numerically investigated with a one-dimensional model. The results are evaluated in terms of discharge efficiency, pumping power, storage cost and thermocline degradation during standby to assess the potential of this storage solution for future scientific investigations. The packed bed system with sodium shows slightly higher discharge efficiencies (96.8%) than with molten salt (95.2–95.7%) and also lower required pumping power. However, the thermocline region expands faster during standby due to the high thermal conductivity of sodium. The influence of porosity, tank diameter-to-height ratio and filler particle diameter is analysed in a parametric study. Highest discharge efficiencies are achieved for both sodium and molten salts with small tank diameter-to-height ratios and small filler particles. For sodium, low porosities are preferable, while for molten salts, high porosities lead to better discharge efficiencies.

Improved design of supercritical CO2 Brayton cycle for coal-fired power plant

As an advanced power cycle, supercritical CO2 (sCO2) Brayton cycle has been considered as a promising alternative of conventional steam Rankine cycle for coal-fired power plants. The sCO2 power cycle must be improved to deal with coal-fired system integration constraints since coal-fired boiler is significantly different from nuclear and CSP heaters. The inlet temperature of the working fluid entering coal-fired boiler in sCO2 cycle is much higher than that in steam cycle, as it can be preheated more sufficiently in recuperators. Hence, the exhaust heat of coal-fired boiler flue gas cannot be fully utilized itself. It is of great importance to study on how to make good use of the exhaust heat of flue gas. An in-house code of sCO2 Brayton cycle tailored for coal-fired power plant was developed at first. Then, three improved cycle layouts for better utilization of the exhaust heat of flue gas were proposed, which were assessed in depth based on comprehensive analyses of both sCO2 boiler and cycle layout. The improved cycle with a second split flow to the boiler was proved to be the most effective one. With parameters of 31MPa/600 °C/620 °C, the maximum net efficiency was improved from a based value of 45.96% to an optimized value of 50.71%. It was also higher than that of a state-of-the-art ultra-supercritical steam power plant with same paremeters (about 46%–47%). Finally, the effects of the second split flow ratio on net efficiency were analyzed, and the equations to calculate the optimal range of second split flow ratio was derived.

Validation of Lifetime Prediction of IGBT Modules Based on Linear Damage Accumulation by Means of Superimposed Power Cycling Tests

In this paper, the lifetime prediction of power device modules based on the linear damage accumulation is studied in conjunction with simple mission profiles of converters. Superimposed power cycling conditions, which are called simple mission profiles in this paper, are made based on a lifetime model in respect to junction temperature swing duration. This model has been built based on 39 power cycling test results of 600-V 30-A three-phase-molded IGBT modules. Six tests are performed under three superimposed power cycling conditions using an advanced power cycling test setup. The experimental results validate the lifetime prediction of the IGBT modules based on the linear damage accumulation by comparing the test results with the predicted lifetime from the lifetime model. Furthermore, the test results show the importance of the junction temperature swing duration effect for the lifetime prediction of IGBT modules under power converter applications.