A research into glycol freezing has shown that Alfa Laval's DuroShell can be used in more compact and cost-effective installations.
“The continued rise in the number of vessels sailing with LNG is one of the most significant trends in today’s marine industry,” says Jonny Hult, head of marine heat transfer equipment at Alfa Laval.
“With more and more ships relying on LNG as fuel, we are seeing greater demand for vaporiser technology that can dependably resist freezing and the fatigue caused by pressure and temperature. DuroShell is exceptional in this regard.”
DuroShell has been optimised for use as a vaporiser in fuel gas applications. With its 100% stainless steel design, it can reliably handle LNG entry temperatures that approach -170°C, or lower. Now, Alfa Laval has also performed an extensive laboratory freeze testing, gaining knowledge that will lead to lower capital and operational costs.
“Extreme low temperatures are not an issue for DuroShell, but a glycol mix with a freezing point of around -50°C has the potential to freeze when it meets plate surfaces as cold as -90°C,” Hult explains.
“Solving this problem with a higher glycol flow is a very expensive solution for our customers, so Alfa Laval has worked with SINTEF Energy Research to find the correlation of flows on both sides and thereby avoid freezing of fluid on the hot side.”
Hult concludes that this will let shipbuilders use a more compact plate-and-shell design with smaller pumps and pipes, which, in turn, will mean CAPEX and OPEX savings for the ship owner.
DuroShell’s ability to withstand the large temperature differences in fuel gas supply systems stems partly from its special CutWing plates, which feature the patented Alfa Laval RollerCoaster plate pattern. The RollerCoaster design provides high turbulence that improves heat transfer efficiency and thus significantly reduces the risk of freezing and fouling.
Another unique DuroShell feature is the PowerPack distribution tubes, which run all the way through the plate pack and secure an optimised flow distribution onto the heat transfer surface. This design further enhances the strength of the plate pack for added fatigue resistance in demanding LNG duties.
“From the laser-welded plate pack to RollerCoaster and PowerPack, DuroShell is loaded with features that help us secure far higher resistance to temperature and pressure fatigue than possible with conventional plate-and-shell designs,” adds Hult.
“Based on this and our knowledge about freezing behaviour, we can confidently state that DuroShell is the market’s best solution for LNG applications today.”
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