Thermodynamic Cycle Research Articles

Energy, Exergy & Environmental Analysis of a Combined Cycle with Pre-combustion CO2 Capture and N2 Injected into the Compressor of the Gas Turbine

Power plants are a major source of CO2 emissions in the environment, which cause global warming; due to this issue, CO2 capture from hydrocarbon fuels is one of the key technology options to reduce greenhouse gases. Pre-combustion capture of CO2 in the combined gas and steam turbine cycle has been investigated in this paper. The first step in the pre-combustion method is to react the fuel with oxygen, which comes from the air separation unit and produces a mixture of hydrogen and carbon monoxide. The CO is converted to CO2 in a water-shift reactor, and a physical absorbent removes the CO2; a hydrogen-rich fuel is produced, which can be burnt in a gas turbine with minimal CO2 emissions. This paper presents a thermodynamic cycle analysis, where pre-combustion CO2 capture is applied in a combined cycle where the main goal is to reduce the CO2 emission into the atmosphere. The main parameters are varied to examine the influence on cycle performance. The cycle performance results for the combined cycle with CH4 as fuel are presented and compared to the combined cycle with precombustion CO2 capture, both with and without Nitrogen injection into the compressor. An exergy analysis is carried out to determine which case has more exergy destruction. The results indicate that at 45 oC the combined cycle efficiency is raised by around 3 % when the pre-combustion CO2 capture without Nitrogen injection into the compressor is used, and the power output has been increased by 29 %. The performance of combined cycle with CO2 capture can be further enhanced by the N2 acquired from the air separation process and injected into the compressor’s middle stage. The results demonstrate a good improvement in the performance; the power output increases by 48 % and efficiency by 4.2 %. However, exergy destruction is increased when the CO2 capture, both with and without N2 injection into the compressor is used. Nevertheless, pre-combustion capture requires large monetary investment for a new-build plant where also the CO2 emission is reduced by 100 %.

Subcritical and supercritical Rankine steam cycles, under elevated temperatures up to 900°C and absolute pressures up to 400 bara

The Rankine cycle is a conceptual arrangement of four processes as a closed vapor power thermodynamic cycle, where a working fluid (especially water as a liquid, as a vapor, and as a liquid-vapor mixture) can be used to convert heat into mechanical energy (shaft rotation). This cycle and its variants are widely used in electric power generation through utility-scale thermal power plants, such as coal-fired power plants and nuclear power plants. In the steam-based Rankine cycle, water should be pressurized and heated to be in the form of very hot high-pressure water vapor called “superheated steam,” before the useful process of expansion inside a steam turbine section occurs. If the absolute pressure and temperature of the superheated steam are both above the critical values for water (220.6 bara and 374.0°C), the cycle is classified as “supercritical.” Otherwise, the cycle is classified as “subcritical.” This study considers the impact of the temperature and pressure, independently, on the performance of a steam Rankine cycle. Starting from a representative condition for a subcritical cycle (600°C peak temperature and 50 bara peak absolute pressure), either the peak temperature or the peak absolute pressure of the cycle is increased with regular steps (up to 900°C, with a temperature step of 50°C, and up to 400 bara, with a pressure step of 50 bar). The variation of five scale-independent performance metrics is investigated in response to the elevated temperature and the elevated pressure. Thus, a total of 10 response curves are presented. When the temperature increased, all the five response variables were improved in a nearly linear profile. On the other hand, increasing the pressure did not give a monotonic linear improvement for each response variable. In particular, the cycle efficiency seemed to approach a limiting maximum value of 45% approximately, where further increases in the pressure cause diminishing improvements in the efficiency. When varying the peak pressure, an optimum minimum ratio of (water-mass-to-output-power) is found at 203 bara, although the cycle efficiency still increases beyond this value. In the present research work, the web-based tool for calculating steam properties by the British company Spirax Sarco Limited, and the software program mini-REFPROP by NIST (United States National Institute of Standards and Technology) were used for finding the necessary specific enthalpies (energy content) of water at different stages within the steam cycle. Both tools were found consistent with each other, as well as with the Python-based software package Cantera for simulating thermo-chemical-transport processes. The results showed that if the peak temperature reaches 900°C, a gain of about 5 percentage points (pp) in the thermal cycle efficiency becomes possible (compared to the case of having a base peak temperature of 600°C), as the predicted efficiency was found to increase from 38.60% (base case) to 43.67%. For the influence of the steam peak pressure, operating in the subcritical regime but close to the critical point appears to be a good choice given the gradual decline in efficiency gains at higher pressures. About 4.7 percentage point increase was found at the high subcritical peak pressure of 200 bara (compared to a base subcritical peak pressure of 50 bara). The results of this study also showed that the liquid water droplet mass fraction at the steam turbine exit diminishes from 11.00% at 600°C to only 1.48% at 900°C, which is favorable. This mass fraction grows from 11.00% at 50 bara to 27.89% at 400 bara, which is not acceptable. Every 100°C increase in the superheating temperature between 600°C and 900°C was found to cause aa increase in the cycle thermal efficiency by about 1.69 percentage points, and simultaneous a beneficial increase in the steam quality at the turbine exit by about 3.17 percentage points.

Enhancement in thermodynamic cycle condensation of a coal-fired power plant by integrating a PCM heat storage tank into the indirect dry cooling system

Enhancement in thermodynamic cycle condensation of a coal-fired power plant by integrating a PCM heat storage tank into the indirect dry cooling system

Thermodynamic evaluations of the acceptorless dehydrogenation and hydrogenation of pre-aromatic and aromatic N-heterocycles in acetonitrile.

N-heterocycles are important chemical hydrogen-storage materials, and the acceptorless dehydrogenation and hydrogenation of N-heterocycles as organic hydrogen carriers have been widely studied, with the main focus on the catalyst synthesis and design, investigation of the redox mechanisms, and extension of substrate scope. In this work, the Gibbs free energies of the dehydrogenation of pre-aromatic N-heterocycles (YH2) and the hydrogenation of aromatic N-heterocycles (Y), i.e., ΔGH2R(YH2) and ΔGH2A(Y), were derived by constructing thermodynamic cycles using Hess' law. The thermodynamic abilities for the acceptorless dehydrogenation and hydrogenation of 78 pre-aromatic N-heterocycles (YH2) and related 78 aromatic N-heterocycles (Y) were well evaluated and discussed in acetonitrile. Moreover, the applications of the two thermodynamic parameters in identifying pre-aromatic N-heterocycles possessing reversible dehydrogenation and hydrogenation properties and the selection of the pre-aromatic N-heterocyclic hydrogen reductants in catalytic hydrogenation were considered and are discussed in detail. Undoubtedly, this work focuses on two new thermodynamic parameters of pre-aromatic and aromatic N-heterocycles, namely ΔGH2R(YH2) and ΔGH2A(Y), which are important supplements to our previous work to offer precise insights into the chemical hydrogen storage and hydrogenation reactions of pre-aromatic and aromatic N-heterocycles.

Studies on the thermal cycle performance of solar thermal power generation under different heat sources

Solar thermal power generation is an important way to solve the future power demand, and some countries have entered the commercial application stage. According to the heat source temperatures provided by different solar thermal collector systems, different thermodynamic cycle modes of power generation systems were proposed so that the appropriate thermal cycle modes and working mediums at different heat source temperatures were obtained. The results show that, under a low-temperature heat source, in an organic Rankine cycle with R600 as the working medium, the cycle efficiency is 13.40% when the temperature of the turbine inlet is 100°C and the pressure is 1.5 MPa; the cycle thermal efficiency is 12.00% when the temperature of turbine inlet is 90°C. Under the conditions of medium temperature heat source, in the Rankine cycle with regenerative heat and R141b as a working medium, the efficiency is about 26.59% when the temperature of the turbine inlet is 220°C and the pressure is 3.0 MPa. Under the conditions of a high-temperature heat source, in the reheat extraction steam Rankine cycle, the theoretical cycle efficiency can reach 34.32% when the temperature of the turbine inlet is 380°C, the pressure is 8 MPa, and the condensation temperature is 41.5°C. The studies can provide a fundamental basis for the design of solar thermal power generation systems with different heat source conditions.

Performance comparison of transcritical cycle and organic Rankine cycle coupled with Chingshui geothermal reservoir

The Chingshui geothermal field stands out as the most significant geothermal field in Taiwan. Understanding the sustainability of geothermal energy is important for its long-term use. In the present study, a numerical model Chingshui reservoir based on geological conditions is developed by using a thermal-hydraulic-mechanical (THM) model in the COMSOL to evaluate the depth’s effect of the production well on the different binary cycles. The thermodynamic cycles of two configurations, namely the organic Rankine cycle (ORC) and transcritical Rankine cycle (TRC), are established by using MATLAB and coupled with the Chingshui reservoir through the COMSOL Livelink module. The study focuses on different well depths’ effects on the cycle performance. The results show the system efficiencies of the ORC and TRC under different well depths were 5.77% and 13.76%, and 9.64% and 16.31%, respectively.

Numerical investigation on the heat transfer of air/helium precooler for air-breathing pre-cooled engine

Installing a precooler behind the intake is an effective approach for hypersonic air-breathing pre-cooled engine to cool the hot incoming air. Synergetic air-breathing rocket engine is a revolutionary hypersonic air-breathing pre-cooled engine with complex thermodynamic cycle i.e. air cycle, helium cycle. Air/helium precooler is a key component and its configuration and operating condition have great effect on the performance characteristics of air-breathing pre-cooled engine. Thus, the minimum periodic flow and heat transfer model of the precooler are established. The effects of key parameters on the heat transfer performance of precooler are numerically studied. The results indicate that: when the tube row number increases from 7 to 15, the average heat transfer coefficient of air side decreases by 57%, the heat exchange rate increases by 19%, and effectiveness increases by 18.4%. The tube transverse pitch can enhance the heat transfer coefficient of air and helium side, while the heat exchange rate decreases by 33 % when the tube transverse pitch increases from 1.5 to 3.5. The helium inlet velocity can improve the heat transfer performance of precooler and reduce the flow resistance of air side.

Daily thermodynamic analysis of a solar dish-driven reheating organic Rankine cycle

Solar concentrating systems can play a critical role in the future for designing sustainable cities. The goal of this investigation is the energy analysis of a solar-driven power plant based on the solar dish collector, storage thermal tank and a reheating organic Rankine cycle. The present thermodynamic cycle is a more efficient choice compared to other similar designs due to the existence of a double expansion with an intermediate reheating. Also, the use of the solar dish collector enables efficient operation in medium and high temperatures. More specifically, this investigation is performed on dynamic conditions aiming to determine the unit?s performance on a usual summer day. The analysis is done with a dynamic model based on mathematical formulas which are inserted into Engineering Equation Solver. The simulation results proved that a collecting area of 500 m2 (50 modules) coupled with a storage tank of 5 m3 volume that feeds an Organic Rankine Cycle of 50 kWel nominal power leads to daily electricity production of 577 kWhel. The system efficiency is found to be 12.6%, the thermodynamic cycle efficiency 20.8% and the solar field thermal efficiency 60.8%. Therefore, it is obvious that the suggested unit leads to satisfying results, and it is a promising one for the design of sustainable renewably driven units in the future.

Radical ligand transfer: mechanism and reactivity governed by three-component thermodynamics

Energy of off-diagonal states, associated with the thermodynamic cycle characterizing the mechanism, affects the barrier for radical ligand transfer and determines, which scenario, R−/electron transfer or R+/electron transfer, is the operative one.

Organic Rankin and Brayton-Joule, a Comprehensive Library for Integrating Conventional and Renewable Energy Generation

The thermodynamic cycles for energy generation are the baseline for development in different types of energy generation, and they are the primary principle for the mix of fossil and renewable energy. In this paper, a detailed description of the organic Rankine and Brayton-Joule cycles has been presented as a comprehensive reference library for linking renewable energy and fossil energy, and an explanation of the governing and basic equations that formulate When developed to be flexible in the use of the research methodology used in this field. This paper provides a comprehensive reference library for linking renewable energy and fossil energy by presenting a detailed description of the organic Rankine and Brayton-Joule cycles. It includes an explanation of the governing equations and basic formulations, as well as a flexible research methodology for use in this field.

Air separation and N2 purification with Ba0.15Sr0.85FeO3-δ via a two-step thermochemical process

Thermochemical air separation to produce high-purity N2 was demonstrated in a vertical tube reactor via a two-step reduction–oxidation cycle with an A-site substituted perovskite Ba0.15Sr0.85FeO3–δ (BSF1585). BSF1585 particles were synthesized and characterized in terms of their chemical, morphological, and thermophysical properties. A thermodynamic cycle model and sensitivity analysis using computational heat and mass transfer models of the reactor were used to select the system operating parameters for a concentrating solar thermal-driven process. Thermal reduction up to 800 °C in air and temperature-swing air separation from 800 °C to minimum temperatures between 400 and 600 °C were performed in the reactor containing a 35 g packed bed of BSF1585. The reactor was characterized for dispersion, and air separation was characterized via mass spectrometry. Gas measurements indicated that the reactor produced N2 with O2 impurity concentrations as low as 0.02 % for > 30 min of operation. A parametric study of air flow rates suggested that differences in observed and thermodynamically predicted O2 impurities were due to imperfect gas transport in the bed. Temperature swing reduction/oxidation cycling experiments between 800 and 400 °C in air were conducted with no statistically significant degradation in N2 purity over 50 cycles.

Simulation model of 177 MWe coal-fired double power unit

Model-based studies are widely used in the analysis and optimization of complex energy conversion processes in large thermal power plants. The creation and validation of a model of a power unit utilizing Bulgarian lignite enables us to study in detail the redistribution of heat flows in that unit. Along with the ability to optimize the thermodynamic cycle of energy generation, this research method enables us to conduct many study tasks that cannot be realized by conducting expensive and complex industrial experiments. The current article presents the creation of thermodynamic simulation model of a 4th power unit firing lignite coal in Maritsa East 2 TPP. Validation of the numerical solution was performed with data from the "Operating Instructions for the boilers”, design heat balance calculations for steam turbine installation and performance test results onsite on two different loads.

Thermal conductivity measurements for n-nonane and n-undecane at elevated temperature and pressure

Hydrocarbons have wide applications in various industrial processes, and the knowledge of thermophysical properties is the foundation for their utilization. As an important thermophysical property, the thermal conductivity of fluids is vital in the evaluation of energy conversion quality, like heat transfer enhancement, thermodynamic cycle efficiency evaluation, etc. Therefore, obtaining accurate experimental data is of great importance for the utilization of hydrocarbons. Here, the thermal conductivities of liquid n-nonane and n-undecane were investigated using the transient hot-wire method (combined expanded uncertainty is 2.0 %) with a wide temperature and pressure range from 293.15 to 523.15 K and 0.1 to 15.0 MPa. For the convenience of engineering applications, a polynomial as a function of temperature and pressure was proposed to correlate the experimental data, the average absolute deviations between experimental data and fitted data are 0.29 % for n-nonane and 0.35 % for n-undecane, which indicates that the polynomial describes the experimental data well in the measured region. Meanwhile, the available literary data were collected and compared with our results, and good agreement was found between literary data and our results. This work is not only helpful for the industrial applications of hydrocarbons but also helps to understand the internal mechanism of the thermal conductivity of hydrocarbons.

Theoretical investigation of a novel distributed compression cycle for CO2 trans-critical system

Efficient cooling of the trans-critical CO2 vapor compression cycle to improve system performance is a crucial research topic. This paper proposes an innovative approach called distribution compression (DC) to achieve the same effect as subcooling in a trans-critical CO2 thermodynamic cycle. In the DC system, the trans-critical CO2 at the gas cooler outlet is no longer further cooled but subjected to a secondary pressure boost and releases heat in ordinary heat sink conditions as in the gas cooler. Thermodynamics calculated the change in performance of the DC system under different working conditions with different secondary boost ratios. The optimal secondary boost ratio related to evaporation and gas cooler outlet temperatures under optimal discharge pressure based on the baseline system was obtained. The results show that compared with the baseline system, the DC system can effectively improve the system performance, and the maximum refrigeration COP increase is between 8.2 % ∼ 10.76 %, and the maximum heating COP increase is between 5.37 % ∼ 6.34 %. The cooling or heating capacity increase can reach up to about 26 %. The ideal secondary boost ratio in a DC system is not highly demanding, and the increased input power for the second input power for the secondary boost will not exceed 20 % relative to the baseline system. Comparing the COP of the DC system over current systems that only use a single subcooling technology still shows advantages. The DC system provides a new idea to improve the performance of the trans-critical CO2 vapor compression cycle.

Magnetocaloric effect in the Laves phases RCo2 (R = Er, Ho, Dy, and Tb) in high magnetic fields

The heavy rare-earth-based Laves phases are well-studied intermetallic materials that stand out for their remarkably high magnetocaloric effects, particularly at cryogenic temperatures. In this study, we present the findings of our comprehensive investigation of cobalt Laves phases RCo2 with R standing for erbium, holmium, dysprosium, and terbium. This includes the determination of the magnetocaloric effect by indirect methods using calorimetric and magnetization data. Furthermore, for the first time in these materials, we directly measured the adiabatic temperature change at high magnetic fields up to 20 T. The largest ΔTad value of 17 K, we obtained for ErCo2. Because the order of the transition significantly impacts the efficiency of thermodynamic cycles, we have also focused on determining the transition order in these materials. This was done through the application of established methods and a recently proposed quantitative criterion including the value of the local exponent n. Further, we compare our results with other materials using a straightforward material-based figure of merit - the temperature-averaged entropy change (TEC). Our results demonstrate the great potential of these materials for applications such as for magnetic hydrogen liquefaction.

On the Description of Electrode Materials Based on the Quantification of Ionic and Electronic Work Functions

During decharging of a lithium ion battery (LIB) electrons are transferred from the cathode material to the outer circuit and lithium ions are transferred into the electrolyte. Here, the energy required to take electrons and lithium ions out of two prototypical cathode materials, LixFePO4 and LixMn2O4 is investigated as a function of the state of lithiation, x [1]. Ionic work functions are measured by thermionic emission, electronic work functions are measured either by thermionic emission or by photoelectron spectroscopy. The work functions measured vary significantly with x for LixFePO4 with moderate, low-dimensional ionic and electronic conductivities but rather little for cubic LixMn2O4 with ca. three orders of magnitude higher ionic and electronic conductivities [2]. The experimental data are supported and rationalized by static energy-landscape calculations and molecular dynamics simulations of the Lithium migration as a function of Lithium content and electric field strength [1]. This study provides new insight into the role of ionic contributions to the energy balance in LIBs. Current efforts are aimed at a complete energetic description of LIBs as previously discussed for LiCoO2 [3].[1] J. Schepp, J. Schuch, J.P. Hofmann, S. Adams, K.-M. Weitzel, to be published[2] M. Park, X. Zhang, M. Chung, G.B. Less, A.M. Sastry, A review of conduction phenomena in Li-ion batteries, Journal of Power Sources 195 (2010) 7904–7929.[3] S. Schuld, R. Hausbrand, M. Fingerle, W. Jaegermann, K.-M. Weitzel, Experimental Studies on Work Functions of Li+ Ions and Electrons in the Battery Electrode Material LiCoO2 A Thermodynamic Cycle Combining Ionic and Electronic Structure, Adv. Energy Mater. 8 (2018) 1703411.

Molecular Dynamics Simulation of an Iron(III) Binding Site on the Fc Domain of IgG1 Relevant for Visible Light-Induced Protein Fragmentation.

Molecular dynamics simulations were employed to investigate the interaction between Fe(III) and an iron-binding site composed of THR259, ASP252, and GLU261 on the Fc domain of an IgG1. The goal was to provide microscopic mechanistic information for the photochemical, iron-dependent site-specific oxidative fragmentation of IgG1 at THR259 reported in our previous paper. The distance between Fe(III) and residues of interest as well as the binding pocket size was examined for both protonated and deprotonated THR259. The Fe(III) binding free energy (ΔG) was estimated by using an umbrella sampling approach. The pKa shift of the THR259 hydroxyl group caused by the presence of nearby Fe(III) was estimated based on a thermodynamic cycle. The simulation results show that Fe(III) resides inside the proposed binding pocket and profoundly changes the pocket configuration. The ΔG values indicate that the pocket possesses a strong binding affinity for Fe(III). Furthermore, Fe(III) profoundly lowers the pKa value of the THR259 hydroxyl group by 5.4 pKa units.

Thermo-economic analysis of the impact of the interaction between two neighboring dry cooling towers on power generation of dual thermal power units and the energy-efficient operation strategy

Thermo-hydraulic behavior of the dry cooling tower and thermodynamic performance of the power unit was coupled by a well-developed computational framework. The interaction between two neighboring towers was detected through a numerical model under variable working conditions, and the impact of cooling performance variation of each tower on cycle efficiency of the corresponding unit was quantified by a thermo-economic model. Results showed that tower interaction mostly impacts heat rejections of radiators at the neighboring halves of both towers. A higher unit load ensures both towers better cooling performances subject to crosswind. The unfavorable wind-effect on cooling behavior of the upstream tower mitigates with increasing wind attack angle, while that on the downstream tower varies little initially and drops sharply as wind attack angle approaching 90°. For each unit, thermodynamic cycle efficiency is more sensitive to crosswind under a higher unit load. Cycle efficiency grows with unit load at low wind speeds, but generally increases and then decreases with unit load at medium–high wind speeds. Dual units should operate at the same load to maximize operational energy efficiency. Otherwise, the unit corresponding to the upstream tower should follow higher and lower load commands under small-medium and large wind attack angles, respectively.

Molecular modelling of energy storage performance on metal organic frameworks/ethane nanoparticles nanofluids mixtures and derivatives

Through the utilization of optimum working fluids, thermodynamic cycles may perform more effectively. In this study, we used molecular modeling approaches to conduct computational studies on nanofluids of ethane and its derivatives with metal organic frameworks (ZIF-8). DMol3 was used to investigate the structure and electrical behavior of nanomaterials prior to as well as following fluid adsorption. The adsorption behavior of the refrigerant gases ethane (R-170), fluroethane (R-161), and difluroethane (R-152a) on ZIF-8 was investigated using grand canonical Monte Carlo simulations at various temperatures. Additionally, R-170/ZIF-8, R-161/ZIF-8, and R-152a/ZIF-8 nanofluids' stability and thermal energy storage traits were assessed. The outcomes demonstrate a decrease in the order of R-170 > R-152a > R-161 in the adsorption of the fluids on ZIF-8. Additionally, adding ZIF-8 nanomaterial to R-170, R-161 and R-152a fluids improved their ability to store energy, but improvements at higher ZIF-8 concentrations revealed sensitive dependence on the pressure and temperature conditions, particularly the fluid under consideration's critical temperature. To validate the computational findings, they were contrasted with previously collected experimental data.

Performance Simulation of Thermodynamic Design for a New Turboshaft Engine

For a search and rescue (SAR) helicopter, the requirements of long-range and twin-engine are becoming increasingly important. In this paper, the overall performance of a new turboshaft engine for SAR helicopters is simulated. Firstly, the main performance parameters of competitor engines are collected and compared, and the thermodynamic cycle parameters of the new engine are proposed subsequently. Then, an engine model is created in Turbomatch and the overall performance of this model at the design point is calculated. Finally, the off-design performances at different conditions of output power, ambient temperature, altitudes and flight Mach numbers (Ma) are investigated. A strategy of variable stator vane (VSV) for the anti-surge control of the axial compressor is also introduced. The results of the performance simulation indicate that this engine is quite competitive with lower specific fuel consumption (SFC) and higher specific power (SP) compared to the current SAR helicopter engines.