초록 ▼

◦우리나라의 연간 전력 소비량은 세계적으로 상위권에 속해 있으며, 전력을 생산하는 방법으로는 화력발전의 비중이 높아 CO₂의 배출량도 세계 10위임. 이에 정부는 온실가스 감축을 위해 신재생에너지 기술 확보 및 실용화에 주안을 두고 있으며, 에너지 공급의 탈 화석화를 실현하기 위한 국가에너지기본계획을 수립하고 추진 중임. 신재생에너지의 하나인 해양심층수 열에너지의 자원화 기술은 저탄소․녹색성장을 위한 해양자원의 다각적 이용을 위한 핵심기술로서 자원 확보와 환경 개선을 위해 국내외에서 새롭게 주목을 받고 있음

◦우리나라의 연간 전력 소비량은 세계적으로 상위권에 속해 있으며, 전력을 생산하는 방법으로는 화력발전의 비중이 높아 CO₂의 배출량도 세계 10위임. 이에 정부는 온실가스 감축을 위해 신재생에너지 기술 확보 및 실용화에 주안을 두고 있으며, 에너지 공급의 탈 화석화를 실현하기 위한 국가에너지기본계획을 수립하고 추진 중임. 신재생에너지의 하나인 해양심층수 열에너지의 자원화 기술은 저탄소․녹색성장을 위한 해양자원의 다각적 이용을 위한 핵심기술로서 자원 확보와 환경 개선을 위해 국내외에서 새롭게 주목을 받고 있음
◦해양심층수 에너지의 해양온도차 발전과 냉난방 이용을 대상으로 연구개발의 경제적 타당성을 평가하였으며, 해양온도차 발전에 대한 경제성 분석은 시범개발 실증사업으로 고려하고 있는 1MW급 온도차발전 플랜트에서 해양심층수 및 발전소 온배수를 이용하여 전기를 생산할 경우를 대상으로 하였음. 경제성 분석결과는 현재의 국내 전기료 수준으로는 경제성이 미흡한 것으로 분석되었으나 연구개발을 통해 상용화 규모로 개발하여 전기 생산 뿐 아니라 식수 및 탄소배출권 등을 고려하면 경제성은 양호해 질 수 있을 것으로 판단됨
◦해양심층수의 냉난방 이용은 1,000RT급을 대상으로 경제성을 분석하였음. 해수 냉난방 이용의 경제성은 양호한 편이며, 탄소배출권을 고려하면 충분한 경제성을 확보할 수 있을 것으로 추정되었음. 최근, 석유 가격이 지속적으로 상승하여 전기료 상승 부담이 커지고 있고, 탄소배출권 거래가격도 2013년부터는 지속적인 상승이 예상되어 경제성은 더욱 좋아질 것임. 이를 해양온도차 발전, 담수화, 물질추출, 농수산 이용 등과 연계하여 다단계 이용하면 경제적 파급효과가 커질 수 있을 것으로 판단되어, 조기 실용화 및 보급 확산을 위한 연구개발이 필요한 것으로 판단됨
◦해양온도차 발전기술을 확보하고 미래 상용화 대열에 참여하여 신재생 에너지 자급율을 향상시키고, 해외자원 개발에 활용하기 위한 연구개발 추진전략 및 단계별 연구내용을 체계화하였음. 해양온도차 발전을 위한 일부 핵심기술 및 요소장치들은 국내에서 성숙도가 높은 부분도 있으므로 요소기술 및 장치들을 적용 개선및 자체 개발로 분류하고, 효율을 높이거나 비용을 저렴화하는 연구개발에 집중할 필요가 있음. 이를 위해, 산학연간 협동 및 선진기관과 협력하여 핵심기술을 습득하거나 보완하는 전략이 필요함. 주요 연구대상은 내식성 열교환기의 대형화, 고효율 자연냉매 사이클 개발, 터빈 발전기 설계 및 제작, 고효율 자연냉매를 이용한 사이클 개발 등으로 발전효율을 높이고, 취수관(라이저) 개발을 통한 안정적 열원 확보와 해양구조물의 최적 배치를 통해 안정성과 경제성을 높이는 방향으로 연구개발을 추진하여야 함
◦해수 냉난방 이용기술의 추진전략 및 단계별 연구내용은 해양온도차 발전에 비하여 국내 관련기술의 수준이 높은 편이며, 국내에서 소규모 설비를 생산하거나 도입 적용한 사례도 있기 때문에 기술 격차가 크지 않아 조기 실용화를 가능할 것으로 판단됨. 따라서 주요 연구대상을 취수관 및 취수시스템 개발, 해수열 교환기및 열펌프 효율 향상에 두고, 자원조사 및 환경개선 뿐 아니라 복합이용 및 최적관리 등을 통해 녹색성장을실현하는 종합기술로 체계화하여 나가야 함. 이를 통해, 조기 실용화 및 효율 개선을 병행하여 녹색도시를 위한 기반조성에 활용하고 보급 확산할 수 있도록 연구개발을 추진하여야 함

Abstract ▼

1. Object and need of deep seawater thermal energy
○ The industrialization due to the tremendous use of a fossil fuel and rapid development of science and technology has been improved the quality of human life nowadays, but the air pollution emitted by the consumption of fossil fuel causes big pr

1. Object and need of deep seawater thermal energy
○ The industrialization due to the tremendous use of a fossil fuel and rapid development of science and technology has been improved the quality of human life nowadays, but the air pollution emitted by the consumption of fossil fuel causes big problem such as the global warming, climate change etc
○ Framework Convention on Climate Change(FCCC) for dealing with the global warming was signed in 1994, and the Kyoto Protocol which includes practical norm for FCCC officially took effect in 2005
○ Korea was exempted from on the watch list of countries which need to keep the first duty pledge. But Korea already has become one of the developed nations as a OECD member country and is ranking the world's tenth place in the field of greenhouse gas emission. Moreover, the energy consumption will be increased to promote economic development hereafter
○ Also, the steam power generation plant to produce electricity accounts for the biggest part in case of our country and the annual power consumption is part of the top-ranking all over the world. Meanwhile, CO₂ emission is the tenth in the world with the high ratio of electricity production by the steam power generation plant
○ Technology which the thermal energy of deep seawater converts to the alternative resource to reduce the CO₂ emission is important field for low carbon and green growth, both abroad and here at home. The research and development on OTEC and SWAC are included in the essential field for green technology and industry.
○ The thermal energy potentials of deep seawater in our country is a huge amount, the thermal energy potentials for seawater thermal energy conversion exist as the energy of temperature difference, from 1.5×10¹¹ to 3.5×10¹¹ GWh/year per latitude 1^o × longitude 1^o. (The seawater thermal energy potentials for SWAC were investigated over an average of 130 Tcal/month in Korea)
2. Concept for the use of deep seawater thermal energy
○ The heating and cooling energy as seawater as the thermal source is supplied for the use of sea water air conditioning (SWAC) is supplied
○ There are two methods of SWAC system. One is by direct transfer or transfer through other medium, the other is by using heat pump
○ The necessary equipment for SWAC consists of a heat exchanger, a heat pump, a water intake facility, a monitoring and a control panel
○ The ocean thermal energy conversion (OTEC) is a system designed to transform the thermal energy by temperature difference between deep seawater and warm seawater into electricity. The method for OTEC is using turbine and thermal transfer, and OTEC is mostly operated by turbine method
○ There are 5 methods for power generation such as a closed cycle, an open cycle, a hybrid cycle, a moisture cycle and a foam cycle
3. Industrial trends and technology status for the use of deep seawater thermal energy
○ The first experiment of ocean thermal energy conversion was performed by S. Claude in 1926. Some of trials were sporadically attempted to prove OTEC until 1960's, but failed to utilize due to mass supply of oil
○ The research resumed after the first oil crisis in 1973 and field experiments were performed by US and Japan until the mid-1980. US established the schedule to build 100 floating OTEC plants with the capacity of 100MW and commercialize with 40~400MW capacity. But, it couldn't realize because the oil was stabilized with low price
○ The oil price went up in 2008 and was estimated to rise over $300 in the near future. The research and development for OTEC plant is being resumed to commercialize all of the world
○ Also, the commercialization for SWAC system using deep seawater and surface or middle layer seawater is in process due to the increase of oil price and the reduction of CO₂ emission in and outside the country
○ The deep seawater wasn't used for alternative energy in the country, but the basic research for core technology was performed to 20kW closed cycle OTEC lant with R-22 by In-ha University in 1999 and the basic research for the development of OTEC plant structure was carried out by Korea Ocean Research & Development Institute in 2001
○ Also, the basic experiment as a part of project, multipurpose development of deep seawater of the East Sea, which is one of the national research project, was performed for the use of deep seawater thermal energy to SWAC, now the study on SWAC for practical commercialization is now on process by use of surface or mid-layered seawater
4. Analysis and direction for research and development
○ The first documented reference to the use of seawater temperature difference to produce electricity is found in D'Arsonval's paper published in 1881. He referred to the importance of using seawater temperature difference instead of fossil fuel which causes the global warming
○ The research and development budget over 500 billion won was invested since Claude attempted to prove the power generation by seawater temperature difference in 1930.
○ After 1st oil crisis in 1970's, the research resumed until the mid-1980 and the experiments of small scaled floating plants were performed by US and Japan. The oil price went up in 2008 and was estimated to rise over $300 in the near future. The commercialization for OTEC was resumed in and outside the country
○ Also, the first research for the use of deep seawater was attempted to apply SWAC for its own building by NELHA in Hawaii. Recently, NELHA is pumping up around 150,000m3/day of deep seawater using HDPE pipeline with 1.2m diameter, and undertaking the fundamental research to apply SWAC to Kona Airport using a part of their deep seawater
○ The research for OTEC was only limited to the basic study for 20kW closed cycle OTEC equipment and ocean structure in Korea
○ Also, deep seawater was only applied to the part of building, DOWARC (Deep Ocean Water Application Research Center), for cooling. A SWAC experiment was performed for Marine Tourism & Leisure Sports Center in Sam-cheok campus, Kang-won National University, and another case study was performed for cooling and heating in the dormitory, Maritime University
5. Economic evaluation for the use of deep seawater thermal energy
○ A 1MW-scale OTEC plant can be considered as two types: a gross power 1MW OTEC plant and a net power 1MW OTEC plant. In this report, we aimed to develop a net power 1MW plant with an assumption that the generation is an open-cycle type, which is getting popular recently for the reason of economic effectiveness
○ Also, considering that OTEC is a high public-benefit project in the respect of renewable energy development, the R&D cost was excluded in the calculation. The economic evaluation only considered the installation and operation costs after the technology development
○ On the other hand, the byproducts from the 'net power 1MW Open cycle OTEC system,' such as the carbon emission credit earning and portable (pure) water, were included in the economic evaluation
○ The estimated unit cost of OTEC　power generation was compared with the unit costs from other types of renewable energy. As a result, the OTEC unit cost is similar to that of biofuel and lower (higer in economic efficiency) than solar power. If the 1MW plant is operated throughout one year, it reduces the emission of 4,236tons of carbon dioxide
○ In the economic evaluation of SWAC system, a hybrid system was assumed to apply, that is, the system utilizes deep seawater for cooling in summer, and surface water for heating in winter. The SWAC system is consisted of the heat exchanger, water intake pump and pipe, heat pump, and other auxiliaries
○ Analysis of the electric power usage for cooling
- Assumption: 40% of the annual electric power consumption is used for cooling
․9,660,000kW × 40% = 3,864,000kW
- Calculation: The unit cost for electricity was calculated by dividing the actual power consumption by the total payment for electricity for the one-year period (March 2008-March 2009). The actual value(85 Won/kw) was applied
․3,864,000kW × 73.8% × 85Won/kW = 198,803,000Won
○ Analysis of the gas usage for heating
- Assumption: 80% of the annual gas consumption is used for heating. The assumption is drawn from the actual value analysis
․1,220,000kg × 80% = 976,000kg
- Calculation: The unit cost for gas was calculated by dividing the actual consumption by the total payment for gas for the one-year period (March 2008-March 2009). The actual value(1,078 Won/kg) was applied
․976,000kg × 63.2% × 1,078Won/kg = 664,945,000 Won
○ Initial cost of 1,000 RT SWAC system is estimated as about 4.1 billion won. It includes intaking and heat pump systems using 20,000㎥/day of seawater
○ Annual operation cost for 1,000 RT SWAC is estimated as 450 million won. It onsists of 300 million won of operations and 150 million won of repair and replacement
○ As a result of the economic analysis of SWAC system, it is economically viable on the condition of the current level of costs and for the facilities of the level of 1,000RT(pilot project level)
○ The SWAC system is currently viable. In the future, the economic viability is expected to be higher with the anticipation that the cost of fossil fuel (e.g., petroleum) will continually increase, leading to a rise in the electricity rates, and that the carbon emission credit trading cost will also continually increase after 2013 when the second commitment period of green house gas emission reduction is commenced
○ Similar to the OTEC system, the SWAC system requires high initial cost. Therefore, continuous R&D efforts for the system and the intake facilities are expected to further raise the economic viabilities
○ The SWAC system with deep seawater thermal energy will also increase the carbon emission credits
- Carbon emission reduction by saving electricity: approx. 1,692 tons
- Carbon emission reduction by saving gas: approx. 1,268 tons
○ In total, it is expected that approximately 2,960 tons of carbon emission credits will be earned. It helps the economic efficiency of the system. (The credit trading cost is assumed to be around 20 USD/ton)
- 2,960ton/year × 20$ × 1,100won/$ = 65,120,000won
6. Goal and strategy for research and development
○ The ultimate goal is commercialization of the OTEC and SWAC systems, leading to enhance the energy self-sufficiency and platform technologies for oversea entry
○ Many OTEC technologies and core equipments has been advanced with domestic capacities. These core technologies and equipments need to be categorized for further improvement for adaptation and development of high technology. For the integration and operation optimization, a strategy is required to form a cooperation mechanism with institutions with advanced technologies, and to promptly learn core technologies
○ Areas that need improvement include the scale-up of heat exchanger with corrosion resistance, raising the turbine power generator efficiency, and the optimization of the arrangement of offshore structures and raising their stability and viability
○ Core research items include analysis, design and installation technologies of cheaper intake pipes(or risers) and cheaper heat exchangers etc
○ Compared to OTEC, the small scale SWAC system has been developed and applied domestically and the technology gap is comparably not significant. The SWAC system needs to be proceeded with a goal of early commercialization
○ Necessary technologies used in SWAC include resource surveys and environmental assessment, intake pipe and system, seawater heat exchanger and heat pump, and multiple use and management optimization of deep seawater. It is required to introduce, apply, and improve these technologies while there needs to be a focus on lowering costs of seawater intake-discharge pipes and heat exchangers, scale-up and raising efficiency of heat pumps, and raising benefits due to multiple use