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Renewable Energy from the OceanA Guide to OTEC$
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William H. Avery and Chih Wu

Print publication date: 1994

Print ISBN-13: 9780195071993

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195071993.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 27 November 2021

Open-Cycle OTEC

Open-Cycle OTEC

(p.210) 5 Open-Cycle OTEC
Renewable Energy from the Ocean

William H. Avery

Chih Wu

Oxford University Press

The historical development leading to the proposal by Claude to generate power by producing steam in flash evaporation of warm seawater has been discussed in Chapter 2. In this chapter, the thermodynamic fundamentals of the open-cycle concepts are discussed, leading to a detailed review of state of the art and commercial prospects of the process. There are several variations on the standard OTEC open-cycle (OC) system. The three major variations are “hybrid cycle” (Bartone, 1978), “mist lift cycle” (Ridgway, 1977), and “foam lift cycle” (Beck, 1975; Zener et al., 1975). These are advanced concepts that offer certain attractive features and are being investigated. The three cycles will be discussed in Sections 5.3, 5.4, and 5.5, respectively. The standard OTEC open cycle is discussed in the following. The modest but nearly steady temperature difference that exists between the warm surface water and the much colder water at great depth in some tropical regions of the world has attracted the attention of many thermodynamicists from the time that these temperature differences were first observed. From the thermodynamicist’s view, any significant temperature difference can be used to produce power. The open or Claude cycle is the forerunner of various OTEC cycles. The open cycle refers to the use of seawater as the working fluid. A schematic diagram of the system, which comprises a flash evaporator, vapor expansion turbine and generator, steam condenser, noncondensables-removing equipment, and deaerator, is shown in Fig. 5-1 (Chen, 1979). The cycle is a basic Rankine cycle for converting thermal energy of the warm surface water into electrical energy. In the cycle, the warm seawater is deaerated and then passed into a flash evaporation chamber, where a fraction of the seawater is converted into low-pressure steam. The steam is passed through a turbine, which extracts energy from it, and then exits into a condenser. This cycle derives the name “open” from the fact that the condensate is not returned to the evaporator as in the “closed” cycle. Instead, the condensate can be used as desalinated water if a surface condenser is used, or the condensate is mixed with the cooling water and the mixture is discharged back into the ocean.

Keywords:   Beck cycle, energy delivery, falling jet condensers, land-based plants, market potential, pumps, seawater ducting, turbine design, warm-water pipes

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