Lower capital costs, shorter on-stream time, reduced coastal environment impacts and flexibility – these are some of the advantages that led to the development of the floating storage and regasification unit (FSRU). Typically, these units are similar in appearance to large barges, and are moored semi-permanently offshore from the regasified liquefied natural gas (LNG) delivery sites and fed by standard LNG carriers (LNGC). A special subset of the FSRU concept are LNGCs that have full regasification capability and are able to transport LNG from a liquefaction plant to a delivery site and then regasify this LNG off-shore. These special vessels are known as LNG Shuttle and Regasification Vessels (SRVs). As a result of being subjected to the vertical and lateral movements of the vessel while under way, in addition to the movements when at its mooring location, the SRV experiences more severe exposure to motion. To put a regasification unit on board a floating, seagoing vessel, it was necessary to develop machinery, components and systems that would perform during and after exposure to the movement of the vessel and the swell of the ocean. The pumps on board the vessel experience different levels of acceleration during the various stages of SRV rotation, as shown in Table 1.
Liquefied Natural Gas Pumps for Shuttle And Regasification Vessels
Figure 1 shows the Nikkiso Cryo regasification ship pump set, which has been used on board the Excelerate Energy fleet of vessels since 2004. On the left of Figure 1 is the emergency/in-tank pump that, on an SRV vessel, is the primary feeder to the deck-mounted high-pressure send-out and line-packing pumps (shown on the Horizontal Assembly Stand© and the far right of Figure 1, respectively). The in-tank pumpsare located inside the emergency wells found on a traditional LNG carrier. Unlike the original emergency pumps that are part of a classic ship set, these primary pumps are permanently lowered in the column. The pumps feed the suction drum, and are rated for a flow of 620m3/h, with a differential head of 115m. The pump rated power is 200kW.The send-out pumps are located on the bow of the ship. They are mounted in their own suction vessel, which is integrated onto skids. These pumps feed the vaporisers at a flow of 205m3/h, with a differential head of 2,370m. The pump rated power is 1,100kW.
Line packing pumps are operated during the start-up of the re-gasification unit to pressurise the vaporisers and the downstream pipeline smoothly without any liquid hammer. These 200kW pumps deliver the same differential head as the send-out pumps (2,370m), but at a lower flow rate (20m3 per hour). The line packing pumps are vessels mounted on the bow of the ship along with the send-out pumps. In more recent projects, such as those involving the vessels Golar Winter and Neptune (Höegh LNG), larger send-out pumps have been developed, which have 15 stages and a pump rated power of 1,500kW.
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