1,721,046 research outputs found
Minimizing Entropy Generation To Optimize the Heat Transfer Surface of a Heat Recovery Boiler in a Combined Cycle Power Plant
No full textThe design of finned tube bundles involves numerous geometric parameters affecting the heat transfer coefficient and the pressure drops which should be accounted for in the boiler design in order to reduce entropy generation and ultimately capital costs. In this work, the geometric dimensions that maximize the boiler's exergetic efficiency (tube diameter, fin height, fin thickness, number of fins per meter, transversal and longitudinal pitch) are examined. The exergetic efficiency resulting from the finite temperature difference in the heat transfer and the pressure drops on the gas and the water/steam sides - a measure of the entropy generated - is determined as a function of the geometric parameters, with correlations from the literature applied in calculating the heat transfer coefficients and the pressure drops
Comparison of the solid oxide fuel cell system for micro CHP using natural gas with a system using a mixture of natural gas and hydrogen
No full textSolid oxide fuel cell systems for combined heat and power production (SOFC μCHP) fueled by natural gas are attractive because of their high electrical and total efficiency even at small scale. The development of a hydrogen economy will increase the availability of distributed hydrogen as a pure gas. Alternatively, hydrogen may be blended with natural gas in the grid. This study investigates the performance of SOFC μCHP systems, while using a fuel varying from pure hydrogen to pure methane via mixtures of hydrogen and methane called Hythane. Flowsheet models of external as well as internal reforming fuel cell systems were developed in Cycle-Tempo simulation software. Results show that both the external as well as the internal reforming system can operated on all fuel gas compositions varying from pure hydrogen to pure methane, thus allowing for a transition towards a hydrogen economy via the mixing of hydrogen into the natural gas grid. Although the natural gas based systems have a higher electrical efficiency, the introduction of hydrogen into the gas leads to a higher total efficiency of the combined heat and power system. The addition of hydrogen into the fuel minimizes the problems of thermal stress and thermal shock associated with the use of methane in internal reforming fuel cell systems. The internal reforming system showed a higher performance compared to the external reforming system for all Hythane gas mixtures in terms of not only electrical efficiency but also in terms of thermal and total efficiency.Economics of Technology and Innovatio
Un sistema integrato con gas naturale, fluido geotermico e rifiuti solidi urbani per la produzione di energia elettrica
No full textSustainable water-energy innovations for higher comfort of living in remote and rural areas from developing countries: From seawater to hydrogen through reversible Solid Oxide Cells
No full textAccess to affordable renewable energy and clean water are among the most prominent challenges humankind faces to ensure a non-discriminatory comfort of living. Innovation in system engineering meets with new energy carriers, enabling synergistic effects defined as “sector-coupling”. For instance, hydrogen and Reversible Solid Oxide Cells (rSOCs) are innovative technologies that yield multiple valuable effects. This paper evaluates the impact of such technology in novel PV-hybrid storage mini-grids with close access to seawater, achieving simultaneous renewable energy storage and seawater desalination thereby. The novel mini-grid operation is simulated in archetypal rural communities from developing countries (Sub-Saharan Africa) for 365 days of operation. The study encompasses three development scenarios in agreement with sustainability policies in force. The analysis of results allows finding the fittest mini-grid asset to achieve techno-economic optimization. A trade-off solution is identified with a critical reading of results in a future perspective: the Levelized Cost Of Electricity (LCOE) for a system with at least 70% renewables penetration is in the range of 0.29–0.43 €/kWh, while the rSOC runs with the only energy storage task. Moreover, the availability of seawater pushes LCOE below 0.20 €/kWh since it is also possible to benefit from the desalination function. This result aligns with the most economic mini-grid asset that can be implemented while embedding a significant energy performance increase
A single flash integrated gas turbine-geothermal power plant with non-condensable gas combustion
No full textIn this work the possibility of improving the performance of the 20 MW standard geothermal power plant of ENEL (Italian Electric Power Company) has been studied. The conventional geothermal cycle was modified by adding a gas turbine, an organic Rankine cycle (ORC), and a flash separator. Exhaust heat from the gas turbine is recovered in a geothermal steam superheater and by the ORC. The results of a thermodynamic analysis have been applied to a test case based on the Mt. Amiata geothermal field, where geothermal fluid has a water mass fraction ranging from 30 to 50% by wt. and about 8% by wt. of the steam fraction is non condensable gases (NCG). The non condensable gases are a mixture of CO 2 (about 95% by weight), H 2S, H 2, Hg, NH 3 and CH 4. Legislation on the emission of some of these substances into the atmosphere means that geothermal power plants are now equipped with gas clean-up devices but these increase the plant capital costs and reduce performance. Some of the components contained in the NCG, however, such as H 2S, H 2 and CH 4, have an acceptable lower heating value (LHV) and can be considered a source of energy. Hence, they could be burned to reduce their environmental impact while recovering energy that would otherwise be lost. In the power plant presented in this paper, NCG are mixed with inlet air in the gas turbine and burnt in the combustion chamber, thus helping to increase hybrid cycle performance.
In this work the possibility of improving the performance of the 20 MW standard geothermal power plant of ENEL (Italian Electric Power Company) has been studied. The conventional geothermal cycle was modified by adding a gas turbine, an organic Rankine cycle (ORC), and a flash separator. Exhaust heat from the gas turbine is recovered in a geothermal steam superheater and by the ORC. The results of a thermodynamic analysis have been applied to a test case based on the Mt. Amiata geothermal field, where geothermal fluid has a water mass fraction ranging from 30 to 50% by wt. and about 8% by wt. of the steam fraction is non condensable gases (NCG). The non condensable gases are a mixture of CO 2 (about 95% by weight), H 2S, H 2, Hg, NH 3 and CH 4. Legislation on the emission of some of these substances into the atmosphere means that geothermal power plants are now equipped with gas clean-up devices but these increase the plant capital costs and reduce performance. Some of the components contained in the NCG, however, such as H 2S, H 2 and CH 4, have an acceptable lower heating value (LHV) and can be considered a source of energy. Hence, they could be burned to reduce their environmental impact while recovering energy that would otherwise be lost. In the power plant presented in this paper, NCG are mixed with inlet air in the gas turbine and burnt in the combustion chamber, thus helping to increase hybrid cycle performance
Tecniche di Intelligenza Artificiale Applicate alla Regolazione della Velocità di una Galleria del Vento
No full text
Study of Possible Optimisation Criteria for Geothermal Power Plants
No full textThe possibility of exploiting low temperature liquid-dominated geothermal sources can considerably increase the use of this kind of renewable energy. Improvements in the performance of geothermal cycles are possible by using closed Rankine and Kalina cycles, whose working fluid may be a pure substance or a two-component mixture. In this paper three configurations of the Rankine cycle are examined and compared to conventional single and dual flash steam power plants. The Kalina cycle system no. 12 has also been studied. Results showed that there is a potential for optimisation of the performance, by modifying the main parameters, such as turbine inlet pressure and type of flui
Study of the Steam Turbine Trip in a 20 MW Geothermal Plant
No full textIn vapour-dominated geothermal sources a large amount of non-condensable gas is mixed with the steam and requires extraction from the condenser, generally by means of a compressor. A plant has been studied in which this compressor is directly coupled, via gearboxes, to the steam turbine shaft. When a 'trip' occurs (and this may often happen when considerable load variations cause a small plant to get out of synchronism), very high torque readings have been measured at the turbine-compressor coupling. This paper presents a computer simulation which has been developed for the system to explore ways of reducing these high torque
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