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Research Papers

Design Optimization of Shore-Based Low Temperature Thermal Desalination System Utilizing the Ocean Thermal Energy

[+] Author and Article Information
Sami Mutair

Institute of Ocean Energy,
Saga University,
1-Honjo-machi, Saga City,
Saga Prefecture 840-8502, Japan
e-mail: samymutair@hotmail.com

Yasuyuki Ikegami

Institute of Ocean Energy,
Saga University,
1-Honjo-machi, Saga City,
Saga Prefecture 840-8502, Japan
e-mail: ikegami@ioes.saga-u.ac.jp

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received January 27, 2014; final manuscript received April 18, 2014; published online May 13, 2014. Editor: Gilles Flamant.

J. Sol. Energy Eng 136(4), 041005 (May 13, 2014) (8 pages) Paper No: SOL-14-1030; doi: 10.1115/1.4027575 History: Received January 27, 2014; Revised April 18, 2014

A model for calculation and optimization of seawater desalination process is presented. In this process, temperature difference between the upper and the lower strata of the ocean is utilized in producing fresh water, by evaporating the warm surface seawater at a reduced pressure and then condensing the generated steam by using the colder seawater drawn from the depth of the ocean to produce distilled water. In order to make the optimization process realistic, the developed model takes into consideration the characteristics of the proposed location such as temperature and density variation with depth, seabed topography, and subsequently the actual lengths of the cold and the warm seawater intake pipes. This article gives details of the process and investigates on the influence of various parameters on its economics. As electricity is the sole source of energy used, the objective function was taken as the specific energy, i.e., the amount of electrical energy required for producing a unit mass of distilled water. Results indicate that distilled water can be produced at a value as low as 5.5 kWh per ton, which makes the process competitive with most of the existing desalination technologies.

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References

Gleick, P. H., 2002, “Dirty Water: Estimated Deaths from Water-Related Diseases 2000–2020,” Pacific Institute for Studies in Development, Environment, and Security. Available at: http://www.pacinst.org/wp-content/uploads/sites/21/2013/02/water_related_deaths_report3.pdf
World Health Organization (WHO), 2000, “Global Water Supply and Sanitation Assessment 2000 Report.” Available at: http://www.who.int/water_sanitation_health/monitoring/jmp2000.pdf
Lisa, H., President of (IDA) in November 2009 Talk, “The Current State of Desalination,” International Desalination Association
Vega, L. A., 2002, “Ocean Thermal Energy Conversion Primer,” Mar. Technol. Soc. J., 36(4), pp. 25–35. [CrossRef]
Ikegami, Y., Urata, K., Bando, A., Wajima, T., Ohto, K., Nakaoka, T., Tabuchi, K., and Kamano, T., 2005, “Oceanic Observation and Investigation for Utilization of Ocean Energy in the Fiji,” Proceedings of the 15th International Offshore and Polar Engineering Conference, Seoul, Korea.
Mutair, S., and Ikegami, Y., 2010, “Experimental Investigation on the Characteristics of Flash Evaporation From Superheated Water Jets for Desalination,” Desalination, 251, pp. 103–111. [CrossRef]
Mutair, S., and Ikegami, Y., 2009, “Experimental Study on Flash Evaporation From Superheated Water Jets: Influencing Factors and Formulation of Correlation,” Int. J. Heat Mass Transfer, 52(23–24), pp. 5643–5651. [CrossRef]
Stoughton, R. W., and Lietzke, M. H., 1967, “Thermodynamic Properties of Sea Salt Solutions,” J. Chem. Eng. Data, 12(1), pp. 101–104. [CrossRef]
Bharathan, D., Parsons, B. K., and Althof, J. A., 1988, “Direct-Contact Condensers for Open-Cycle OTEC Applications,” National Renewable Energy Laboratory Report ERI/TP-252-3108 for DOE Contract No. DE-AC02-83CH10093.
Taborek, J., 1988, Process Heat Exchangers, Hemisphere, Washington, D. C.

Figures

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Fig. 1

Typical temperature variation profile in tropical oceans

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Fig. 2

Schematic of LTTD process with DCC

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Fig. 3

Variation of seawater depth with horizontal distance from shoreline near the proposed location

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Fig. 4

Variation of the specific energy consumption with saturation temperature at the evaporator

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Fig. 5

Variation of the specific heat transfer area with saturation temperature at the evaporator

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Fig. 6

Variation of the optimum specific energy and the corresponding specific heat transfer area with cold seawater inlet temperature

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Fig. 7

Variation of the cold seawater pipe length, intake depth, and the equivalent hydrostatic head with cold seawater temperature

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Fig. 8

Variation of the optimum specific energy and the corresponding specific heat transfer area with liquid flow velocities at the plate heat exchanger

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Fig. 9

Representation of forces balance in the cold seawater line

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