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Table 12 Comparison of the power output depending on steam usage rate. H. Jung, J. Hwang / Energy 75 (2014) 443e452 451 Fig. 8. Temperature variation of the discharge side of the primary condenser depending on the steam usage rate. We also found a decrease in the temperature of the waste water on the discharge side of the primary condenser if cold deep sea water is re-used at the inlet of the primary condenser. This reduction effect is shown in Fig. 8. In the summer, circulating water enters the condensing loop at 30 C and is discharged at 37.7 C. If the deep sea water on the discharge side of the secondary condenser is re-used in the PRC with a 30% steam reuse rate C-OTEC and we assume a constant condenser pressure, the temperature of the discharged circulating water of the primary condenser then decreases to 26.1 C. In case of direct injection, the temperature of discharged water becomes 21.2 C. Table 12 shows the output variations of the PRC and C-OTEC depending on steam usage rate by case (once-through, re-use of the secondary condenser circulating water and direct injection). The case of re-using the SRC discharged water is slightly better than direct injection because the load of the PRC condenser de- creases when SRC uses the steam as the heat source. However, the difference decreases by increase of steam usage rate. 4. Conclusions We proposed a C-OTEC which uses the latent heat of the steam in the condenser in a large power plant, differing from the concept of a conventional OTEC system. The prototype of C-OTEC will be built at the Yeongdong power plant in order to demonstrate the validity of the research. A sensitivity analysis of the reference design model and the design parameters for the conceptual model was performed. It is concluded that the proposed C-OTEC offers three types of benefits. It would not only generate additional electric output from the waste heat in the condenser but would also be beneficial for the PRC to increase its output. In addition, the C-OTEC does not require warm sea water pump, which is neces- sary for conventional OTEC and other C-OTEC. The increased output of the PRC is due to the increased efficiency with the operation of C-OTEC system. C-OTEC is more effective in older power plants which have difficulty in maintaining their rated output during the summer season. This study demonstrated that the proposed C-OTEC concept can contribute to coastal power plant by improving the condenser vacuum, reducing the pumping power and decreasing the temperature on the discharge side. This unit can also maintain or enhance the output levels. The feasibility of these systems could be improved with the optimized fabrication of main components such as turbines and heat exchangers, but the current disadvantage is expected to be mitigated when a prototype C-OTEC is constructed and operating experience accumulates in the future. KEPCO (Korea Electric Power Corporation) Research Institute is managing the research project of constructing the C- OTEC prototype, and it will be operational by the end of 2014. Design variables will be optimized through operation and testing within a year. Acknowledgment This work was supported by the New & Renewable Energy Core Technology Program through a grant from the Korea Institute of Energy Technology Evaluation and Planning (KETEP), via the Min- istry of Trade, Industry & Energy of the Republic of Korea (No. 2011T100100378). References [1] Daniel TH. A brief history of OTEC Research at NELHA. Natural Energy Labo- ratory of Hawaii; 1999. [2] Semmari Hamza, Stitou Driss, Mauran Sylvain. A novel Carnot-based cycle for ocean thermal energy conversion. Energy 2012;43:361e75. [3] Tchanche Bertrand F, Lambrinos Gr, Frangoudakis A, Papadakis G. Low-grade heat conversion into power using organic Rankine cycles e a review of various applications. Renew Sustain Energy Rev 2011;15:3963e79. [4] Straatman Paul JT, van Sark Wilfried GJHM. A new hybrid ocean thermal energy conversioneoffshore solar pond (OTECeOSP) design: a cost optimi- zation approach. Sol Energy 2008;82:520e7. [5] Vega LA. Economics of ocean thermal energy conversion (OTEC): an update. In: Offshore Technology Conference. Huston, Texas, USA; 2010. [6] Kim GW, Lee ME, Lee KS, Park JS, Jeong WM, Kang SK, Soh JG, Kim HN. An overview of ocean renewable energy resources in Korea. Renew Sustain En- ergy Rev 2012;16:2278e88. [7] Kim NJ, Jeon YH, Kim CB. Cycle simulation on OTEC system using the condenser effluent from nuclear power plant. J Korea Sol Energy Soc 2007;27(3):37. [8] Soto Rodrigo, Vergara Julio. Thermal power plant efficiency enhance- ment with ocean thermal energy conversion. Appl Therm Eng 2014;62: 105e12. [9] Kang YY, Park SS, Kim NJ. A study on regenerative OTEC system using the condenser effluent of Uljin Nuclear Power Plant. Korea J Air-Condit Refrig Eng 2012;24(7):591. [10] National Refrigerants, Inc. Material safety data sheet; 13/06/2014. Available from: www.refrigerants.com/msds.aspx. [11] Yeh RH, Su TZ, Yang MS. Maximum output of an OTEC power plant. Ocean Eng 2005;32:685e700. [12] Hung TC, Wang SK, Kuo CH, Pei BS, Tsai KF. A study of organic working fluids on system efficiency of an ORC using low-grade energy sources. Energy 2010;35:1403e11. [13] Odum Howard T. Emergy evaluation of an OTEC electrical power system. Energy 2000;25:389e93. [14] Zhang S, Wang H, Guo T. Performance comparison and parametric optimi- zation of subcritical organic Rankine cycle (ORC) and transcritical power cycle system for low-temperature geothermal power generation. Appl Energy 2011:2740e5. [15] Kuo CR, Hsu SW, Chang KH, Wang CC. Analysis of a 50 kW organic Rankine cycle system. Energy 2011;36:5877e85. [16] Wang D, Ling X, Peng H, Liu L, Tao LL. Efficiency and optimal performance evaluation of organic Rankine cycle for low grade waste heat power gener- ation. Energy 2013;50:343e52. [17] Stijepovic Mirko Z, Linke Patrick, Papadopoulos Athanasios I, Grujic Aleksandar S. On the role of working fluid properties in organic Rankine cycle performance. Appl Therm Eng 2012;36:406e13. [18] Ministry of Environment, National Institute of Environmental Research. Chemical management and regulations collection. Seoul, Korea; 2009. [19] Calm JM, Hourhan GCH. Refrigerant data summary. Eng Syst 2001;18:74e88. [20] American Elements. Dielectric constant of solutions; 13/06/2014. Available from: www.americanelements.com/dielectric-constant.html. [21] Parsons Robert. Fundamentals handbook (SI). ASHRAE; 2001. Extraction rate PRC Once (C-OTEC, through MWe) Re-use Direct injection 0% 10% 120.46 121.07 (0.746) e 124.54 (0.746) e 124.06 (0) 20% 121.57 (1.490) 127.09 (1.490) 126.40 (0) 30% 122.07 (2.228) 128.18 (2.228) 127.80 (0)PDF Image | Feasibility study of a combined Ocean Thermal Energy Conversion method in South Korea
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