Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Performance Analysis of OTEC Plants With Multilevel Organic Rankine Cycle and Solar Hybridization

[+] Author and Article Information
Paola Bombarda

Dipartimento di Energia,
Politecnico di Milano,
Via Lambruschini 4,
20156 Milano, Italy
e-mail: paola.bombarda@polimi.it

Costante Invernizzi

Dipartimento di Ingegneria Meccanica
e Industriale,
Università degli Studi di Brescia,
Via Branze 38,
25123 Brescia, Italy

Mario Gaia

Turboden srl,
Via Cernaia 10,
25124 Brescia, Italy

Theoretical potential is derived from natural and climatic (physical) parameters (e.g., total solar irradiation on a continent's surface). The theoretical potential can be quantified with reasonable accuracy, but the information is of limited practical relevance. It represents the upper limit of what can be produced from an energy resource based on physical principles and current scientific knowledge. It does not take into account energy losses during the conversion process necessary to make use of the resource nor any kind of barriers.

No explicit reference to costs, barriers, or policies is made.

The same happens for the condensation process, occurring at different temperatures, i.e., at different pressure levels.

Heat exchanger pressure drop is evaluated during heat exchanger sizing procedure, in the next paragraph.

Contributed by the International Gas Turbine Institute of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received March 3, 2012; final manuscript received September 11, 2012; published online March 18, 2013. Assoc. Editor: Piero Colonna.

J. Eng. Gas Turbines Power 135(4), 042302 (Mar 18, 2013) (8 pages) Paper No: GTP-12-1070; doi: 10.1115/1.4007729 History: Received March 03, 2012; Revised September 11, 2012

Among the renewable energy sources, ocean energy is encountering an increasing interest. Several technologies can be applied in order to convert the ocean energy into electric power: among these, ocean thermal energy conversion (OTEC) is an interesting technology in the equatorial and tropical belt, where the temperature difference between surface warm water and deep cold water allows one to implement a power cycle. Although the idea is very old (it was first proposed in the late nineteenth century), no commercial plant has ever been built. Nevertheless, a large number of studies are being conducted at the present time, and several prototypes are under construction. A few 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 favorable belt, can be increased during daytime, thanks to the solar contribution. This paper addresses topics that are crucial in order to make OTEC viable, and some technical solutions are suggested and evaluated. The closed cycle option is selected and implemented by means of an organic Rankine cycle (ORC) power plant, featuring multiple ORC modules in series on the warm water flow; with a three-level cycle, the performance is approximately 30% better if compared to the single-level cycle. In addition, the hybrid solar-OTEC plant is considered in order to investigate the obtainable performance during both day and night operation; this option could provide efficiency benefit, allowing one to almost triplicate the energy produced during daytime for the same prescribed water flow.

Copyright © 2013 by ASME
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Grahic Jump Location
Fig. 2

Optimization process

Grahic Jump Location
Fig. 3

Multiple ORC plant: three-level scheme

Grahic Jump Location
Fig. 4

Hybrid solar OTEC plant



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