Abstract
In the tropics and subtropics, the heat absorbed by the ocean presents a massive opportunity to power subsea assets, expand to marginal fields, and energize islands and coastal communities. Similar to geothermal or waste heat extraction, Ocean Thermal Energy Conversion (OTEC), provides baseload power from an Organic Rankine Cycle system utilizing the surface warm ocean water and cold deep ocean water. To reach the deep ocean water, large-diameter intake is a critical enabler.
Floating, Production, Storage and Offloading (FPSO) vessels have been used for many years to recover oil from remote reservoirs, or where the water depth makes a fixed leg platform impractical. To increase the efficiency of the utility and process systems on board these vessels, particularly in equatorial waters, they often have seawater intake risers (SWIR) installed enabling them to obtain colder and cleaner seawater from below sea level.
As the world energy demand increases, and the desire for cleaner fuels strengthens, a number of major oil and gas companies are developing Floating Liquefied Natural Gas (FLNG) vessels to harvest natural gas ‘stranded’ in reservoirs that have previously been considered too uneconomic to develop due to their geographical location in terms of water depth or distance from shore which makes the construction of an export pipeline and/or a receiving terminal prohibitively expensive.
An FLNG vessel liquefies the harvested natural gas using the onboard processing facilities and then stores the liquefied natural gas (LNG) in tanks until such time that it can be offloaded and transported onshore via a sea going vessel. Liquefication is achieved by cooling the natural gas to approximately -162°C, which due to cost, complexity and efficiency of the process, requires large volumes of seawater and for which it is beneficial to reach and import water of as low temperature as practical from below sea level using SWIR’s.