The engines on BP’s six new Partnership-class vessels set new parameters in low-emission, low-cost propulsion for LNG carriers, writes Selwyn Parker
BP’s Partnership-class represents a big technological step forward for LNG tankers. At a capacity of 173,400 m3 - 12% more than the oil giant’s earlier class of Gem ships such as the British Ruby - they will be the largest and most advanced LNG vessels BP Shipping has ever launched, boasting a design speed of 20 knots.
Each ship is powered by two MAN Energy Solutions’ tri-fuel, two-stroke ME-GI engines, the first Tier 3 gas-burning engines of their kind, according to BP.
Compared with the Gem-class vessels, these new carriers are 25% more efficient, largely thanks to the propulsion system’s ability to tap boil-off gas (BoG) for fuel.
As BP Shipping site construction manager Sandy Farquhar explained, most of the existing fleet uses BoG to power either the steam turbine or dual-fuel, diesel-electric engines. The Partnership carriers however are equipped with a five-stage compressor designed by Korean shipbuilders DSME. This technology raises the pressure of the gas from just above atmospheric level to 300 bar. The gas is then piped to the engines for fuel, or to the reliquefaction system.
“The gas vapour becomes a useable, lower-carbon commodity to replace fuel oil,” explained Mr Farquhar.
It also cuts costs. BP estimates that the capacity to reliquefy unused BoG and pump it back to the cargo tanks will save an estimated 35,000 m3 of LNG over the lifetime of the Partnership-class ships.
“It is all about transporting cargos at significantly lower unit costs than it was a few years ago because of mounting competition”
Lower unit costs
For LNG tankers, as is the case elsewhere, an engine’s economy is becoming ever-more important for operators: “It is all about transporting cargos at significantly lower unit costs than it was a few years ago because of mounting competition,” said BP supply and trading chief operating officer for LNG Jonty Shepard.
“Profit margins are dropping off as the big trading houses start to get involved in LNG for the first time,” he added.
The six Partnership vessels will ply the world’s oceans, transporting gas to and from India, China, America and Australia – all well established markets – as well as the newer markets of Pakistan, Jordan, Egypt and Bangladesh, where demand for LNG-sourced energy is rising rapidly.
Meantime MAN is continuing to develop its gas-powered two-stroke propulsion systems, such as the ME-GIE (the E standing for ethane). Two of German shipmanager Hartmann Reederei’s vessels, Gaschem Beluga and Gaschem Orca, have been notching up operational hours with these prototype engines since they were launched last year. In May, the ships had collectively accumulated 10,000 hours transporting ethane from America to European refiners.
“Overall, the propulsion system performs an even better fuel consumption than predicted,” confirmed Hartmann Reederei fleet manager Capt Ulrich Adami. “We are recording higher sea-passage speeds during heavy weather in the Atlantic. I believe the [vessels] are among the fastest across the Atlantic.”
Highly versatile because they can run on LPG and methane as well as ethane, or a combination of the three, the ME-GIE engines live up to their billing. According to Hartmann Reederei, ethane has been the sole fuel for around 98% of the Atlantic passages.
Still not satisfied, MAN’s engineers are working to reduce the ME-GIE’s consumption of pilot oil to an almost negligible 1%.