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[en] This work presents a second law analysis efficiency of cogeneration steam turbine unit with backpressure steam turbine. By using the input/product output method is calculated the exergy efficiency of steam turbine unit at four different operational modes. It is obtained the allocation of useful exergy in electricity and released heat to consumers and exergy losses. It is evaluated the impact of referent environment temperature and mass flow from controlled extraction on exergy efficiency.
[en] Highlights: • A solar-driven Kalina cycle is investigated by advanced exergoeconomic analysis. • The highest exergy efficiencies are related to the separator and turbine with the values. • Rotary machinery have more than 83% avoidable share of exergy destruction rate. - Abstract: A Kalina cycle driven by solar energy resource is evaluated by conventional exergy and exergoeconomic analysis methods. Because conventional exergy analyses isn’t able to give information about costs of the irreversibilities and investment, advanced exergy is investigated. Based on the conventional exergy analyses, the most exergy destruction occurs in a heater with a value of 94.44 kW. Also the highest exergy efficiencies are related to the separator and turbine with the values of 99.67% and 89.81%, respectively. Advanced exergy analyses demonstrates absorber (1.3 $/h) and one of the pumps (0.009 $/h) have the highest and lowest exergy destruction cost rate, respectively. Also the results show turbine (85.88%) and separator (1.105%) have the highest and lowest exergoeconomic factor, respectively. Finally, in order to determine optimum point of the inlet temperatures and pressure ratio of the pumps and turbine (rotary machines), a parametric study is applied at different stages.
[en] This paper studies the experimental and exergy analysis of solar still with the sand heat energy storage system. The cumulative yield from solar still with and without energy storage material is found to be 3.3 and 1.89 kg/m2, respectively for 8-h operation. Results show that the exergy efficiency of the system is higher with the least water depth of 0.02 m (mw = 20 kg). Competitive analysis of second law efficiency shows that the exergy efficiency improves the system by 30% than conventional single slope solar still without any heat storage. The maximum exergy efficiency with energy storage material is found as 13.2% and it is less than the conventional solar still without any material inside the basin.
[en] Highlights: • Hourly productivity improves by inserting the reticular porous layer in the basin. • The efficiency improves by inserting the reticular porous layer inside the basin. • The maximum exergy efficiency from the modified system is found as 7.33%. - Abstract: In this paper, an experimental study with the exergy analysis are performed to investigate the application of a reticular porous insert in a single slope solar still for performance improvement. Two single slope solar stills containing conventional and modified by inserting a reticular porous layer are fabricated and experimented together. Two stills have the same dimensions. The porous insert was made up by black sponge rubber. All tests were taken in Semnan with geographical coordinates of 35°33′N, 53°23′E, Iran. Hourly water and glass temperatures, productivity, and efficiency of two stills are measured and evaluated experimentally. Moreover, the exergy efficiencies of the solar stills are obtained and presented. Finally, a cost analysis is performed to investigate the modified still economically. It was concluded that the daily total water productions for one day of the experiment are 3263 and 3829 cc/m2 for the conventional and modified stills, respectively. Accordingly, the modified still produces about 17.35% more distilled water in comparison to the conventional one during one day. Finally, the costs per liter per square meter for the modified and conventional stills are 0.0095 and 0.0108 $/L/m2, respectively.
[en] Thermal energy recovery of pyrometallurgy slags is a worldwide problem that is widely concerned for decades. As chemical recovery method, molten slag cascade recovery method (MS-WHCR) is proposed in this work. As typical endothermic chemical reactions, pyrolysis, gasification, calcination and reforming reactions are applied in this method. Gasification–pyrolysis system, calcination–pyrolysis system, enhanced pyrolysis system (R-SEP) and fixed carbon gasification and sorption-enhanced pyrolysis system (CG–SEP) systems of MS-WHCR method are designed. Based on the first law of thermodynamics and second law of thermodynamics, enthalpy–exergy compass analysis method is applied to analyze the exergy efficiency, consumption of reactants and products of designed MS-WHCR method, compared with traditional water quenched (WQ) method and gravity bed waste heat recovery (GWHR) method. As calculation example, 1000kg copper slag is used in this paper. The results showed that the exergy efficiency and exergy loss of WQ method are 20.7% and −947 MJ respectively. By WQ method, energy quality of molten copper slag is discounted. Copper slag particles should be fast cooled during granulation process. Thus, lots of air is blown in to make enough heat transfer with copper slag particles, which generate some exergy loss. And exergy efficiency of GWHR method is 76.9%. Using chemical endothermic reactions, MS-WHCR method improves the exergy efficiency of molten slag waste heat recovery. There is a slight fluctuation of exergy efficiency by MS-WHCR method for four kinds of systems from 66.6 to 70.1%. Fixed carbon and combustible syngas are acquired by MS-WHCR. And enhanced pyrolysis process in proposed R-SEP and CG–SEP systems improves hydrogen contents in syngas.
[en] Highlights: • Advanced exergoeconomic analysis is done on a new helium extraction process. • Cost of exergy destruction and exergy destruction rate are calculated. • Three different strategies are suggested to improve performance of the components. - Abstract: An advanced method of exergoeconomic analysis was applied to a newly developed process configuration used for recovering helium from natural gas. In this process, a three stage propane refrigeration cycle is incorporated to provide a portion of the required refrigeration. Sensitivity analysis was also carried out for exergoeconomic factors and exergy destruction cost of the effective devices. In comparison with the existing processes, the proposed process has better performance in extracting the helium from the feed gas. Based on the results of conventional method, HE-105 and HE-104 heat exchangers have the highest extent of exergy destruction cost equal to 1889.68 $/hr and 1263.58 $/hr, respectively. The outcome of the advanced exergoeconomic analysis suggests that the exergy destruction cost (investment cost) of the compressors is avoidable while it is not true for the heat exchangers. Moreover, the exergy destruction costs induced from the remaining components are not considerable, thus the interactions among the process equipment is not strong.
[en] Highlights: • Single slope solar still coupled with N-identical PVT FPCs has been proposed. • EPBT of the proposed still is found to be 89.90% lower than that of N-PVT-CPC-SS. • An improvement of 27.5% in water production cost over N-PVT-CPC-SS is achieved. • LCCE of N-PVT-FPC-SS is 56.25% higher than that of N-PVT-CPC-SS. - Abstract: This paper communicates the improvement in performance of single slope solar still (SS) by including N identical partially covered photovoltaic thermal (PVT) collectors. Three models have been considered namely, SS included with N identical partially covered PVT flat plate collectors (N-PVT-FPC-SS); SS included with N identical partially covered PVT compound parabolic concentrator collectors (N-PVT-CPC-SS) and conventional SS (CSS). In this work, yearly production of potable water, energy, exergy, energy metrics, cost of distillate output and cogeneration efficiency have been computed for the proposed N-PVT-FPC-SS at 0.14 m water depth under optimized condition for New Delhi, India. Results obtained have been compared with results reported by researchers previously and it has been concluded that exergy based energy payback time is lower by 89.90% and 44.45%; energy production factor is higher by 46.67% and 31.11%; life cycle conversion efficiency is higher by 56.25% and 37.50% and production cost of potable water is lower by 27.05% and 3.20% for the proposed N-PVT-FPC-SS than N-PVT-CPC-SS and CSS respectively. The proposed system can produce potable water on commercial scale and at the same time, it can meet DC electrical power need.
[en] Highlights: • Comparative study of cascaded and novel integrated system is presented. • Novel integrated system operates at lower generator temperature of 60 °C than cascaded system. • Advanced exergy analysis results of novel integrated system are presented. • Component priorities for performance improvement of system are represented by Sanky diagram. • 35.2% of total irreversibility can be avoided by improving the efficiency parameters. - Abstract: In present work, a novel configuration of vapor compression-absorption integrated refrigeration system (VCAIRS) is analyzed. Unlike previous vapor compression-absorption cascaded refrigeration system (VCACRS), proposed configuration works at lower generator temperature of 60 °C. Thus, allowing the use of low grade waste heat for its operation. The performance of VCAIRS is also compared with the equivalent vapor compression refrigeration system (VCRS) and VCACRS for the same cooling capacity of 100 kW. The comparative study result shows that electrical energy requirement in VCAIRS is 21.4% more as compared to VCACRS but it is still 63% less as compared to the equivalent VCRS. Further, the second law efficiency of VCAIRS, VCACRS and VCRS are determined to be 27.9%, 32.7% and 18.8%, respectively. Thus, both the VCAIRS and VCACRS are energy and exergy efficient configurations; but, VCACRS results in more energy efficient cooling technology in the foreseeable future as it utilizes heat at lower generator temperature as compared to VCACRS. After the comparative performance study, the exergetic performance of VCAIRS is further explored based on the coefficient of structural bonds (CSB) and advanced exergy analysis methods. Highest CSB of 4.39 is obtained for high pressure solution heat exchanger but its overall contribution in total irreversibility rate is merely 0.2%; whereas, the highest contribution of 17.4% in total irreversibility rate is by compressor 1 but CSB value computed for it is merely 1.73. Further, advance exergy analysis results show that 35.2% of total irreversibility rate of VCAIRS can be avoided by improving the efficiency parameter of components of system.
[en] Highlights: • Exergy analysis of a process with supercritical water gasification of coal is conducted. • The exergy conversion mechanism of the process is obtained. • The exergy destruction and distribution of the process is analyzed. • A maximum exergy efficiency of 89.18% is obtained. - Abstract: Supercritical water gasification (SCWG) is a promising technology for clean and efficient coal utilization. The exergy analyses on the processes with integrated SCWG of coal and syngas separation are conducted for clear understanding about the exergy distributions in the processes. The energy level of the heat provided for the gasifier is upgraded to the energy level of the syngas, which is driven by the decrease of energy levels from the coal to the syngas. The minimum temperatures of the heat provided for the gasifier are obtained in different coal-water-slurry concentrations (CWSCs). The total exergy destruction firstly increases, and then decreases with increasing CWSC. The maximum total exergy destruction of the process is obtained when the CWSC is approximately 10%. The exergy efficiency of the process has a converse trend with the total exergy destruction. When the CWSC is in the range of 6% and 20%, the maximum exergy efficiency is 89.18%. The origins for the production of the exergy destruction are also studied.
[en] This paper highlights an investigation on the comparative analyses of exergetic performance with optimum volume concentration of hybrid nanofluids in a plate heat exchanger (PHE). Different types of hybrid nanofluids (Al2O3 + MWCNT/water, TiO2 + MWCNT/water, ZnO + MWCNT/water, and CeO2 + MWCNT/water) as coolant have been tested. Proportion of 0.75% of nanofluid has been found to be the optimum volume concentration. The requisite thermal and physical properties of the hybrid nanofluids were measured at 35 °C. Various exergetic performance parameters have been examined for comparing different hybrid nanofluids. The highest reduction in exergy loss of CeO2 + MWCNT/water hybrid nanofluid has been obtained at a concentration of about 24.75%. Entropy generation decreased with the increase in volume concentration. The results established that CeO2 + MWCNT/water hybrid nanofluid can be a promising coolant for exergetic performances in a PHE. (paper)