Bibliometric Analysis on Supercritical CO2 Power Cycles for Concentrating Solar Power Applications

In recent years, supercritical CO₂ power cycles have received a large amount of interest due to their exceptional theoretical conversion efficiency above 50%, which is leading a revolution in power cycle research. Furthermore, this high efficiency can be achieved at a moderate temperature level, thus suiting concentrating solar power (CSP) applications, which are seen as a core business within supercritical technologies. In this context, numerous studies have been published, creating the need for a thorough analysis to identify research areas of interest and the main researchers in the field. In this work, a bibliometric analysis of supercritical CO₂ for CSP applications was undertaken considering all indexed publications within the Web of Science between 1990 and 2020. The main researchers and areas of interest were identified through network mapping and text mining techniques, thus providing the reader with an unbiased overview of sCO₂ research activities. The results of the review were compared with the most recent research projects and programs on sCO₂ for CSP applications. It was found that popular research areas in this topic are related to optimization and thermodynamics analysis, which reflects the significance of power cycle configuration and working conditions. Growing interest in medium temperature applications and the design of sCO₂ heat exchangers was also identified through density visualization maps and confirmed by a review of research projects.     

A high efficiency NH3/H2O absorption power cycle

A work producing cycle has been developed showing a thermodynamic efficiency considerably higher than that of the Rankine cycle. The new cycle employs a mixture of H₂O and NH₃ as the working fluid and uses an absorption process similar to that of absorption refrigerators. Its advantage over existing power cycles working with the same mixture (i.e. the Kalina cycle) is simplicity as far as devices, construction, operation and maintenance are concerned. For the detailed calculation of the proposed cycle a method has been developed, which employs analytical functions describing the thermodynamic properties of the NH₃/H₂O mixture. The proposed cycle has been compared with Rankine cycles working at the same temperature levels. For fixed upper (i.e. superheating) and lower (i.e. condensation) temperatures, the new cycle shows an efficiency 20% higher than that of the Rankine cycle if the boiling temperature is high, while for low boiling temperatures the superiority of the proposed cycle is much more pronounced. A parametric study has also been conducted for the new cycle, wwhich showed, inter alia, that the optimum difference between the mass fractions of the rich and weak solution is about 0.1 kg NH₃/kg mixture.     

Structural and Parametric Optimization of S–CO2 Nuclear Power Plants

The transition to the use of supercritical carbon dioxide as a working fluid for power generation units will significantly reduce the equipment′s overall dimensions while increasing fuel efficiency and environmental safety. Structural and parametric optimization of S–CO₂ nuclear power plants was carried out to ensure the maximum efficiency of electricity production. Based on the results of mathematical modeling, it was found that the transition to a carbon dioxide working fluid for the nuclear power plant with the BREST–OD–300 reactor leads to an increase of efficiency from 39.8 to 43.1%. Nuclear power plant transition from the Rankine water cycle to the carbon dioxide Brayton cycle with recompression is reasonable at a working fluid temperature above 455 °C due to the carbon dioxide cycle′s more effective regeneration system.     

Performances of Transcritical Power Cycles with CO2-Based Mixtures for the Waste Heat Recovery of ICE

In the waste heat recovery of the internal combustion engine (ICE), the transcritical CO₂ power cycle still faces the high operation pressure and difficulty in condensation. To overcome these challenges, CO₂ is mixed with organic fluids to form zeotropic mixtures. Thus, in this work, five organic fluids, namely R290, R600a, R600, R601a, and R601, are mixed with CO₂. Mixture performance in the waste heat recovery of ICE is evaluated, based on two transcritical power cycles, namely the recuperative cycle and split cycle. The results show that the split cycle always has better performance than the recuperative cycle. Under design conditions, CO₂/R290(0.3/0.7) has the best performance in the split cycle. The corresponding net work and cycle efficiency are respectively 21.05 kW and 20.44%. Furthermore, effects of key parameters such as turbine inlet temperature, turbine inlet pressure, and split ratio on the cycle performance are studied. With the increase of turbine inlet temperature, the net works of the recuperative cycle and split cycle firstly increase and then decrease. There exist peak values of net work in both cycles. Meanwhile, the net work of the split cycle firstly increases and then decreases with the increase of the split ratio. Thereafter, with the target of maximizing net work, these key parameters are optimized at different mass fractions of CO₂. The optimization results show that CO₂/R600 obtains the highest net work of 27.43 kW at the CO₂ mass fraction 0.9 in the split cycle.     

A freon-ammonia comparison applied in a mixed power cycle

The thermal efficiency of a cycle consisting of a combination of a Rankine power cycle and an absorption cycle has been examined with respect to upper cycle temperature and the solution used.Freon 22-DME. TEG and ammonia-NaSCN have been selected for comparison. An improvement of the Rankine cycle is expected. This improvement is higher for substances having a high latent heat. Although there is a strong dependence on the substance used in Rankine cycles, no considerable effect seems to exist in the combined cycle.     

Absorption heat-pump regeneration in a rankine steam cycle

This paper presents a system of regenerative heating incorporating an absorption heat pump in a Rankine steam cycle which can improve cycle efficiency. A simulation has been performed to estimate the Rankine cycle efficiency in the proposed Absorption Heat Pump Regeneration (AHPRG) heating system using the working pair R21³-DMETEG. The results show that the cycle efficiency can be improved considerably without reducing the work output by the incorporation of AHPRG for low-temperature heating of steam condensate. Further, the temperature of the heat-pump evaporator which absorbs the heat rejected at the steam condenser plays a predominant role in the cycle efficiency.     

Derived thermodynamic design data for rankine power cycle systems operating on R142b

Theoretical Rankine power cycle efficiencies ν_R and the (PR) have been presented for Rankine power cycles operating on R142b. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 25–125°C in 5°C increments. A composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO − T_CO) illustrates the feasible operating range for R142b power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of the Rankine power cycle systems operating on R142b.     

Derived thermodynamic design data for rankine power cycle systems operating on R502

Theoretical Rankine power cycle efficiencies ν_R and the pressure (PR) have been presented for Rankine power cycles operating on R502. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 35–80°C in 5°C increments. A composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO - T_CO illustrates the feasible operating range for R502 power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of Rankine power cycle systems operating on R502.     

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.     

An evaluation of a rankine cycle driven heat pump

This paper discusses a configuration of a Rankine cycle engine-driven heat pump, and includes a theoretical investigation of its performance characteristics. The system employs a Rankine power cycle, using R-113 as the working fluid, coupled to a vapour compression cycle heat pump using R-22. A novel feature of the concept is the use of hydraulically connected rolling diaphragm piston-cylinder devices as motor, compressor and pump.Heating and cooling COPs of 2.01 and 1.06 respectively are predicted, making the system potentially attractive where both heating and cooling are required.     

燃气-蒸汽联合循环余热回收系统性能研究

燃气发电是我国城市供电的主要形式之一,针对LNG接收站一体的电厂发电模式进行研究,提出一种新型燃气-蒸汽联合循环热电联供系统,利用超临界CO2布雷顿循环结合有机朗肯循环(ORC)辅助发电,将LNG作为冷源,对烟气余热进行三级利用.通过构建热力学和经济模型,以Aspen Plus软件模拟值为基础,结果表明:在消耗燃料1....     

Gas turbine waste heat recovery distillation system

This article presents a method for improving the gas turbine's performance through an efficient utilization of the waste heat in a distillation system with a special arrangement. This consists of two trains of VTE/MEB connected to increase the fresh water produced. Exhaust gases from the gas turbine are used in a multi-temperature level heat recovery system with five feed heaters, and gases are released to ambient at 130°C. Distillation top train has nine effects and evaporation range from 130 to 82°C while the bottom train has six effects with evaporation range from 76 to 46°C and is supplied with the steam leaves the last effect in the top train.Thermal analysis using a 32.67 MW gas turbine showed that the present arrangement can produce 3.2 million gallons per day (mgd) of fresh water with more than 4 g/kWh at a performance ratio (PR) of 8.8. This is 34% more than that produced in an existing gas-turbine distillation combination and 14% more than that expected from a reverse osmosis plant driven by a bottoming Rankine power cycle.     

Derived thermodynamic design data for rankine power cycle systems operating on R22

Theoretical Rankine power cycle efficiencies ν_R and the pressure (PR) have been presented for rankine power cycles operating on R22. These values are listed in tabular form for temperature drops of 5–75°C and for boiler temperatures 40–85°C in 5°C increments. Composite graph showing the relationship between ν_R, T_BO, (PR) and temperature drop (T_BO - T_CO) illustrates the feasible operating range for R22 power cycle systems. The derived thermodynamic data can be used for the rapid preliminary design of the Rankine power cycle systems operating on R22.     

The effect of the operating parameters of heat recovery steam generators on combined cycle/sea-water desalination plant performance

Combined gas/steam turbine cycle plants have been proposed for cogeneration of electricity and process steam. Examples are combined-cycle power plants coupled with sea-water desalination, district heating plants, chemical industries, etc. In combined heat and power plants, the gas turbine exhaust heat is utilized through the use of heat recovery steam generators (HRSG's). As a result, these waste heat generators (boilers), whether fired or unfired, control the performance of the combined plant lower side (bottoming cycle). Moreover, any changes made in the HRSG operating parameters (i.e. the pinch point, approach temperature, first and second stage pressures, and mass ratios) can greatly affect the HRSG performance and will eventually affect the overall combined plant performance. This paper presents a method to predict the performance of the heat recovery steam generators (HRSG)/steam bottoming cycle combined with sea-water desalination plant at various steam and exhaust gas conditions.     

Design of Closed-Cycle MHD Generator with Nonequilibrium Ionization and System

A closed-cycle MHD generator topping a steam bottoming plant is analyzed. The combined power plant involves three working fluids in three loops. The MHD loop is investigated more thoroughly since it is the least conventional of the three. Equations are developed to determine the geometric and thermodynamic variables throughout the MHD channel for inlet conditions of mass flow, temperature, pressure, and velocity. Limiting design parameters are output power, channel length, channel aspect ratio, Hall parameter, and interaction parameter. The basic closed-cycle MHD loop working fluid can consist of either argon or helium seeded with cesium. Both non-equilibrium ionization produced by the elevation of the electron temperature from joule heating of the plasma and thermal ionization are considered. Equations used to calculate the electrical conductivity and the elevation of electron temperatures are derived. These equations are coupled with the one-dimentional differential equations applicable to an MHD generator. The chief interest is in determining those MHD channel conditions which result in the most thermodynamically efficient MHD-steam plantcombination. Thus an overall heat balance forthe system is required. Equations are developed to calculate the gas properties at the various stations of the closed loop and to determine the overall efficiency of the cycle. A rather flexible computer program written in Fortran is used to solve the MHD generator equations and to make the overall heat balance. Some typical results presented demonstrate the feasibility and adaptability of the analysis for optimizing the thermal efficiency and the sensitivity of thermal efficiency to various parameters.     

Output power analyses for the thermodynamic cycles of thermal power plants

Thermal power plant is one of the important thermodynamic devices, which is very common in all kinds of power generation systems. In this paper, we use a new concept, entransy loss, as well as exergy destruction, to analyze the single reheating Rankine cycle unit and the single stage steam extraction regenerative Rankine cycle unit in power plants. This is the first time that the concept of entransy loss is applied to the analysis of the power plant Rankine cycles with reheating and steam extraction regeneration. In order to obtain the maximum output power, the operating conditions under variant vapor mass flow rates are optimized numerically, as well as the combustion temperatures and the off-design flow rates of the flue gas. The relationship between the output power and the exergy destruction rate and that between the output power and the entransy loss rate are discussed. It is found that both the minimum exergy destruction rate and the maximum entransy loss rate lead to the maximum output power when the combustion temperature and heat capacity flow rate of the flue gas are prescribed. Unlike the minimum exergy destruction rate, the maximum entransy loss rate is related to the maximum output power when the highest temperature and heat capacity flow rate of the flue gas are not prescribed.     

Operation of CANDU power reactor in thorium self-sufficient fuel cycle

This paper presents the results of calculations for CANDU reactor operation in thorium fuel cycle. Calculations are performed to estimate the feasibility of operation of heavy-water thermal neutron power reactor in self-sufficient thorium cycle. Parameters of active core and scheme of fuel reloading were considered to be the same as for standard operation in uranium cycle. Two modes of operations are discussed in the paper: mode of preliminary accumulation of ²³³U and mode of operation in self-sufficient cycle. For the mode of accumulation of ²³³U it was assumed for calculations that plutonium can be used as additional fissile material to provide neutrons for ²³³U production. Plutonium was placed in fuel channels, while ²³²Th was located in target channels. Maximum content of ²³³U in target channels was estimated to be ∼13 kg/t of ThO₂. This was achieved by irradiation for six years. The start of the reactor operation in the self-sufficient mode requires ²³³U content to be not less than 12 kg/t. For the mode of operation in self-sufficient cycle, it was assumed that all channels were loaded with identical fuel assemblies containing ThO₂ and certain amount of ²³³U. It is shown that nonuniform distribution of ²³³U in fuel assembly is preferable.      

混合工质中低温热力循环特性研究

本文从热力学第二定律角度出发,对氨水混合工质中低温动力循环进行了分析。通过与简单蒸汽循环的比较,揭示了混合工质热力循环的特性及本质,指出工质蒸发换热过程的匹配及冷凝过程是混合工质循环高效的关键。为了改善冷凝过程,可采用分馏冷凝系统取代传统的冷凝方式。同时,本文还探讨了一些基本规律,明确了余热回收过程中中低温段换热匹配的重要性     

Electrochemical behaviour of sputtered c-V2O5 and LiCoO2 thin films for solid state lithium microbatteries

Here are reported for the first time electrochemical data on all-solid-state lithium microbatteries using crystalline sputtered V₂O₅ thin films as cathode materials and LiPON as solid electrolyte. The stable specific capacity of 30 µAh/cm² found with a 2.4 µm thick film competes very well with the best values obtained for solid state microbatteries using amorphous films. With the challenge of decreasing the temperature of heat treatment for sputtered LiCoO₂ thin films, we show that a temperature of 500 °C combined with an optimized bias sputtering (-50 V) allows to get highly crystalline deposits, to minimize the presence of Co₃O₄ and to suppress any trace of the cubic phase. At the same time the theoretical specific capacity is reached in the 4.2 V-3 V range and a good cycling behaviour is achieved with a high capacity of 50 µAh/cm²/µm after 140 cycles at 10 µA.cm².     

Ignition delay times of methane and hydrogen highly diluted in carbon dioxide at high pressures up to 300 atm

The need for more efficient power cycles has attracted interest in super-critical CO₂ (sCO₂) cycles. However, the effects of high CO₂ dilution on auto-ignition at extremely high pressures has not been studied in depth. As part of the effort to understand oxy-fuel combustion with massive CO₂ dilution, we have measured shock tube ignition delay times (IDT) for methane/O₂/CO₂ mixtures and hydrogen/O₂/CO₂ mixtures using sidewall pressure and OH* emission near 306?nm. Ignition delay time was measured in two different facilities behind reflected shock waves over a range of temperatures, 1045–1578?K, in different pressures and mixture regimes, i.e., CH₄/O₂/CO₂ mixtures at 27–286 atm and H₂/O₂/CO₂ mixtures at 37–311 atm. The measured data were compared with the predictions of two recent kinetics models. Fair agreement was found between model and experiment over most of the operating conditions studied. For those conditions where kinetic models fail, the current ignition delay time measurements provide useful target data for development and validation of the mechanisms.