直面“恶劣”海况 FLNG技术更迭 逆境求生（下）

Rigid fightback

Nevertheless, the leading exponent of the long-established approach to LNG offloading is not giving up easily.

FMC Technologies’ expertise is based around using an articulating system of rigid steel pipe arms and swivels. FMC has held on to win both Satu and Prelude using extended versions of its side-by-side systems that can still deal with the increased demands of those projects. Four of its 16-inch Olaf arms are mounted on Prelude to handle its LNG.

And even when faced with the need to go tandem, FMC has its act in shape. Over the last seven years, the company has evolved its Atol offering and regards this as now ready for deployment. Atol is an aerial array of free-hanging pipes and swivels that extends from a large gantry in a system able to reach out aft over a vessel separation distance of 100 metres or more.

Meanwhile, at the smaller end of the diameter scale, Dutch company Gutteling has for some years been notching up a satisfying record for providing flexible LNG hose for commercial service — albeit in fairly benign settings. In recent years, its hose has been used for operations such as inshore ship-to-ship transfers for the likes of Gasnor and Excelerate.

Configurations

An important factor in the tandem loading debate is the question of manifold position – bow versus midships. With the world’s present fleet of LNG carriers standardised on mid-ships manifolds to receive and discharge their cargoes, a move to the bow is an expensive prospect.

Yet if a tandem transfer system does not have to reach all the way along the carrier to midships then the journey is typically shortened by about 150 meters. This means reduced pressure losses and boil-off gas.

Nevertheless, much emphasis remains on continuing to use midships manifolds if possible. Novel efforts include proposals that use the HiLoad mooring unit to hold the carrier safely offset at a shorter hose distance.

However, “is a change to bow loading such a big deal?”, questions consultant Brian Songhurst. “For tandem systems you also need DP capability in your carrier, of course, and for coming projects you are likely to be ordering new anyway,” he says. Recently retired from his role as director of LNG at Thyssen E&P, Songhurst has been keeping his hand in with things like a contribution to the 2016 book LNG Markets In Transition, published by the Oxford Institute for Energy Studies on 6 September.

Project hopes

One way or another, the advanced LNG offloading groups are holding faith that their day will come. But hopes have been raised and dashed a number of times in recent years.
In late 2009, Petrobras held a design competition for a large proposed floating LNG platform of about 2.7 million tonnes per annum liquefaction capacity. That project is now on hold.

More recently the possibility of up to three huge liquefaction platforms, each in the same league as Prelude, at Woodside’s Browse basin fields has yielded to an onshore alternative. Indonesia’s Abadi has gone the same way.

Perhaps the most interesting prospect of all so far has been ExxonMobil’s currently deferred Scarborough project. Also of north-west Australia but with tougher design conditions than Prelude, the operator had aerial tandem offloading as its base case here right from the start, and is said to have put significant effort into technology qualification for such a system.

But for now, Satu and Prelude remain the most demanding FLNG projects under way.

Satu, also known as PFLNG-1, is on course to become the world’s first large-scale floating liquefaction platform to start up. After construction in South Korea by the Technip/Daewoo joint venture, this 1.2 million tpa vessel, 365 meters long, reached the Kanowit gas field off Malaysia on 30 May this year.

It is now commissioning, with start-up likely by the end of this year. And although the second Petronas FLNG project — for the Rotan field — at one time appeared under the shadow of cancellation, it is now continuing, but at a slowed pace. The hull has been completed at Samsung and looks likely to be on stream by 2020.

Meanwhile, Shell’s world-beating 490-metre long Prelude platform, designed to produce 3.6 million tpa of LNG, continues its majestic and extended path to completion at Samsung in South Korea. The operator has never given an on stream target date. Currently commentators predict 2018.

So it could be a while before tandem offloading becomes a reality for LNG. As Songhurst notes, even if offshore liquefaction does pick up pace, in the current era of low prices “few would consider going into rough water when there are probably easier pickings in calmer settings closer to shore”.

In its latest World FLNG market forecast to 2022, published in August, UK market analyst Douglas Westwood notes a flat picture for sanctioning of largescale capital intensive liquefaction units over the past 24 months. However, “despite near-term concerns, the long-term viability of FLNG technology is clear”, says author Mark Adeosun.