3. Renewable energy resources from the ocean
3.1. Ocean thermal energy conversion (OTEC)
3.1.1. Background
OTEC produces electricity from the natural thermal gradient of the ocean, using the heat stored in warm surface water to create steam to drive a turbine, while pumping cold, deep water to the surface to recondense the steam. In closed-cycle OTEC (Fig. 1a), warm seawater heats a working fluid with a low boiling point, such as ammonia, and the ammonia vapor turns a turbine, which drives a generator. The vapor is then condensed by the cold water and cycled back through the system. In an open-cycle plant (Fig. 1b), warm seawater from the surface is pumped into a vacuum chamber where it is flash evaporated, and the resulting steam drives the turbine. Cold seawater is then brought to the surface and used to condense the steam into water, which is returned to the environment. Hybrid plants (Fig. 1c), combining benefits of the two systems, would use closed-cycle generation combined with a second-stage flash evaporator to desalinate water [1]. OTEC plants can either be built onshore or on offshore floating platforms. Floating platforms could be larger and do not require the use of valuable coastal land, but incur the added expense and impact of transporting energy to the shore. Energy can be transported via seafloor cable, a well-developed but costly technology that impacts the environment by disrupting seafloor communities, or stored in the form of chemical energy as hydrogen, ammonia or methanol. Plantships used to produce hydrogen, ammonia or methanol would “graze” the ocean slowly, store products for about a month, then transfer products to a tanker that would take the products to shore [6].
3. ทรัพยากรทดแทนพลังงานจากมหาสมุทร3.1 แปลงพลังงานความร้อนมหาสมุทร (OTEC)3.1.1. พื้นหลังOTEC produces electricity from the natural thermal gradient of the ocean, using the heat stored in warm surface water to create steam to drive a turbine, while pumping cold, deep water to the surface to recondense the steam. In closed-cycle OTEC (Fig. 1a), warm seawater heats a working fluid with a low boiling point, such as ammonia, and the ammonia vapor turns a turbine, which drives a generator. The vapor is then condensed by the cold water and cycled back through the system. In an open-cycle plant (Fig. 1b), warm seawater from the surface is pumped into a vacuum chamber where it is flash evaporated, and the resulting steam drives the turbine. Cold seawater is then brought to the surface and used to condense the steam into water, which is returned to the environment. Hybrid plants (Fig. 1c), combining benefits of the two systems, would use closed-cycle generation combined with a second-stage flash evaporator to desalinate water [1]. OTEC plants can either be built onshore or on offshore floating platforms. Floating platforms could be larger and do not require the use of valuable coastal land, but incur the added expense and impact of transporting energy to the shore. Energy can be transported via seafloor cable, a well-developed but costly technology that impacts the environment by disrupting seafloor communities, or stored in the form of chemical energy as hydrogen, ammonia or methanol. Plantships used to produce hydrogen, ammonia or methanol would “graze” the ocean slowly, store products for about a month, then transfer products to a tanker that would take the products to shore [6].
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