11:10
Parallel Session: System Design, Optimization and Applications Ime
11:10
20 mins
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PERFORMANCE ANALYSYS OF HYBRID SOLAR OCEAN PLANTS WITH CLOSED ORC CYCLE
Paola Bombarda, Mario Gaia, Costante Invernizzi
Abstract: Among the renewable energy sources, Ocean Energy is encountering an increasing interest at present days. Several technologies can be applied in order to convert the ocean energy in electric power: in some areas power is produced by means of ad hoc developed turbines while in the equatorial and tropical belt the temperature difference between surface warm water and deep cold water allows the adoption of an OTEC system. Although the idea is very old (was first proposed in the late eighteen century) no commercial plant has been built. Nevertheless lot of studies are being conducted at present time and several prototypes are under construction. Some of the studies concern hybrid solar-ocean energy plants: in this case the ocean thermal gradient, which is usually comprised in the range 20-25 °C in the favourable belt, can be increased during day time.
The present study performs firstly a review of the state of the art for OTEC plants, and is then focused on a hybrid plant with closed ORC cycle, by investigating the obtainable performance with different suitable working fluids both during day and night operations.
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11:30
20 mins
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EVALUATION OF THE TECHNICAL FEASABILITY, ENERGY PERFORMANCE AND ECONOMICAL PROFITABILITY OF AN ORC-BASED MICRO-CHP SYSTEM INVOLVING A HERMETIC SCROLL EXPANDER
Jean-François Oudkerk, Sylvain Quoilin, Vincent Lemort
Abstract: The Organic Ranking Cycle (ORC) is often considered as a suitable technology for micro Combined Heat and Power (CHP): the ORC unit can indeed be associated with a boiler to produce heat (at the condenser of the cycle) and electricity (at the expander). The advantages of this technology are a high reliability and simple maintenance and a large fuel flexibility because of the external combustion.
For micro-CHP units (i.e a few kWe), scroll machines are often preferred to turbomachines as expansion device because of their low cost, simplicity, low rotating speed and their capacity to handle high pressure ratios. Moreover, scroll compressors do not require much adaption to work in expander mode.
This paper aims to evaluate the performance and profitability of an ORC-based micro-CHP system. It focuses more particularly on the use of a hermetic scroll compressor used as expander in the ORC.
The first part of the paper describes the design and the performance of a prototype of hermetic scroll expander (compressor adapted to work in expander mode), tested into a gas cycle test rig with R245fa as working fluid. A semi empirical model using a limited number of physical meaning parameters is then built and validated with the experimental results.
In the second part of the paper, this model is inserted into an ORC model and coupled with a boiler model. With this global model, three systems configuration are evaluated in term of electrical and thermal efficiencies and the best one is selected.
Once the best configuration is determined, the operation of the system is simulated on a full year in order to evaluate the seasonal performance of the ORC-based micro CHP system.
Using economical criteria such as net present value and levelized electricity cost, the profitability of the system is evaluated. Parametric studies are performed on the profitability varying several parameters like discount rate, price of fuel, subsidies…
Finally, adaptations of the hermetic scroll compressor are proposed to improve the efficiency of the system.
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11:50
20 mins
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OPTIMUM CONDITIONS OF A CARBON DIOXIDE TRANSCRITICAL POWER CYCLE FROM LOW TEMPERATURE HEAT SOURCE FOR POWER GENERATION
Fredy Velez, José J. Segovia, M. Carmen Martín, Gregorio Antolin, Cecilia Sanz, Farid Chejne
Abstract: Since that conventional steam power cycles cannot give a better performance to recover low-grade waste heat, and due to with this same purpose, other possible processes such as the Organic Rankine Cycles show the known pinching problem, the use of carbon dioxide in supercritical conditions solves both problems. The present paper aims to report the results obtained after analyzing energetic and exergetically the effect of the inlet turbine pressure on transcritical Rankine cycles using refrigerant carbon dioxide (CO2) as the working fluid, which achieves a variable temperature when heat is added to the working fluid, giving therefore a better fit with the heat source. The procedure for analyzing the behaviour of the proposed cycle has consisted in modifying the turbine input pressure, from 66 bar until the point in which the net work reaches approximately zero, while the inlet turbine temperature is maintained in a constant value of 150 ºC. As a result, the maximum value of the energy efficiency is 8.1% whereas the exergy efficiency has no maximum. On the other hand, while the operation pressure of the process rises, the exergy efficiency also increases.
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