This is where Dual Internally and Externally Structured Tube for Air Coolers (DIESTA) technology comes in. It started with a partnership between Total and the French Environment and Energy Management Agency (ADEME)5, initiated in 2008 via the ADEME-Total Energy Efficiency Program.
Sylvie Padilla, head of the companies and green technology department at ADEME, remembers the encounter between two players interested in energy efficiency. "At the time, Total was looking to get involved in this type of initiative and promote a type of open innovation for its customers and itself."
As part of this Energy Efficiency Program, a public-private partnership was formed to launch calls for energy-related projects in the industry. Out of a total of 163 projects submitted, 55 were shortlisted and 35 went on to the demonstrator stage. Eight are now "in the catalog" and at least four are in use at industrial sites.
DIESTA is one of the four. Co-developed with three international companies — Wieland, Kelvion and TechnipFMC — this technology is applied to finned tubes in air-cooled heat exchangers. Air coolers chill, condense and subcool the propane used as a coolant in liquefaction trains. Their finned tubes ensure the heat exchange between the fluid to be chilled or condensed (propane) and the cold source (the air fanned through the air cooler). DIESTA finned tubes were specifically designed with modifications to the interior surface of both the tube and the outside fins to optimize the air-cooling process. The new design improves the rate of heat exchange between the tube-side propane and fin-side air by around 15 percent.
As Thierry Schuhler, head of Total's cross-functional Energy Efficiency R&D Program, explains: "The aluminum alloy sleeve that covers DIESTA's exterior surface holds fins that are dimpled and grooved, rather than smooth as they would be on a standard tube. This allows for better air distribution and increased turbulence, two factors that help to improve the heat transfer coefficient."