Cryostar, a world leading supplier of cryogenic equipment for natural gas and other applications, has successfully tested and commissioned two of its latest 6-stage fuel gas compressors (model CM6-200) on the 180,000 m3 SK Audace, the world’s first low-pressure gas-injection LNG carrier.
In total, Cryostar reports having received 28 orders for the CM6-200, all for installation on vessels with WinGD’s XDF dual-fuel 2-stroke marine engines. The company says that of the 28, two are operational on a navigating vessel, 14 are in the process of being installed with the balance awaiting installation. Before each unit is shipped, shop-testing, including operation with cold gas, is performed in the Cryostar factory during FAT (factory acceptance testing).
The 293m × 48m LNG vessel was delivered last month by Samsung Heavy Industries (SHI) to South Korean shipowner SK Shipping and Japanese trading conglomerate Marubeni Corporation. The vessel is equipped with WinGD X62DF main engines and Wartsila 34DF gensets. The compressors were designed to be able to ably manage the different fuel gas requirements for each engine type.
SK Resolute, sister ship to Audace, is scheduled to be delivered in January 2018.
Versatile Operation
According to Cryostar’s press release, “Although the configuration of machinery and systems represented something of a prototype for XDF, the gas trial was passed successfully with some minor tuning of control loops, allowing the system to operate as planned for all engine loads up to the required 4 ton/hour. All alarm and safety functions performed as planned and load adjustments as well as full engine trip was successfully handled over a period of 11 days.”
The CM6-200 compressors managed the wider than usual tank pressure range and very high methane content in the boiloff without issues. Full gas pressure was achieved as per specifications and higher inlet temperatures were also well handled. The CM6 is able to handle outlet pressure from 17 bara at -120°C to 12.6 bara at +45°C.
Design
Comparison of CM 300 (darker blue), CM2 (pink), CM4 (light blue) and CM6 (gray) CNG Compressors (Source: Cryostar)
These ground-breaking machines follow in the footsteps of the highly successful 4-stage compressors fitted to a large proportion of the DFDE and TFDE vessel fleet. CM6 advances the CM4 design by the integration of an additional high-speed shaft which enables operating speeds of over 45,000 rpm.
The integrally geared machines boast 6 compression stages in a triangular arrangement on both faces of the gearbox. Oil-free operation is assured, especially important when coupled with a reliquefaction plant. The skid mounted unit incorporates the lubrication, sealing and flow-control elements of the system, to make installation as simple as possible. Water inter- and after- coolers assist by reducing the power consumption while increasing the operation range. The current model line-up covers both X52DF and X62DF engine designs.
High speed shaft vibration and bearing temperature values remained below the acceptable thresholds for all operating cases demonstrating the robust behaviour of this centrifugal compressor. Seal gas consumption was in line with expectations set during the design stage.
Cryostar Synonymous with Dual-Fuel Engine Evolution
Cryostar was involved in pioneering the first DF vessels equipped with the 2-stage compressors (CM2). The next phase has seen owners fit more than 50 vessels with CM4 technology. The introduction of the CM6 in 2016 is a response to the growing demand by ship owners for larger vessels to run predominantly on LNG. The company has been selected by all LNG-carrier shipyards to fulfil the requirements of gas supply.
Source: Cryostar (an NGV Global Corporate Member)
