The floating era has opened with Shells announcement of the worlds first FLNG development
Owners of stranded gas resources welcome the news that the world's first floating liquefied natural gas (FLNG) plant will soon be under construction. In association with key contractors Technip and Samsung Heavy Industries Shell has announced the go-ahead for a huge facility – the largest structure afloat anywhere - to be moored 200km off the coast of West Australia. This leading-edge project is designed to exploit the resources of the recently logged Prelude and nearby fields.
From discovery to first commercial offtake could be taking place within just 10 years if commissioning takes place as planned in 2017.
The sound rationale of an LNG plant that swings and moves up and down with the tide has been acknowledged for decades; the issue has been overcoming the multiple new technical problems it brings with it. Around the world there are known to be dozens of large offshore fields or clusters that have simply been too remote to exploit because of the absence of pipe-ashore infrastructure. Both sub-Saharan sea-boards contain several examples, and the search for more will undoubtedly be stepped up now that one version of the necessary development technology is being detail-engineered. West Africa's southwest corner, from Dakar to Monrovia, is a case in point.
25 year output
Side benefits are that on-land environmental and processing costs will be almost entirely avoided. The design concept is that when the gasfield is exhausted the whole facility is simply unhooked and moved elsewhere. Prelude is thought to be large enough to support nameplate output for 25 years; after this the whole facility could be rehabilitated with new refrigerant compressors and drivers and put to work elsewhere for as long again.
As with so many other ship-based process and transport technologies today's LNG industry owes a lot to the nitrogen 'fixers' who are responsible for anhydrous ammonia production and trade, another hazardous frozen gas. In the 1970s a US company pioneered the concept of barge mounting of small-scale naphtha-based facilities; construction under controlled conditions abroad then towing to the required locations in Eastern Africa. But the concept didn't catch on.
Shell's current engineering and design concept for Prelude development is simply colossal. When fully up and running the as-yet unnamed 'facility' (they don't call it a ship) will displace something like 600,000 tons – that's roughly the equivalent of half a dozen of the world's largest aircraft carriers.
Non-fixed construction projects
Samsung's yard on Geoje Island in South Korea is one of very few around the world which can handle a non-fixed construction project of this size.
Incorporating below-deck storage capacity for 426,000m3 of separated products (more than half as LNG itself) the Prelude facility will produce at least 3.6 mtpa of deep-frozen gas plus 1.3 mtpa condensate and 0.4 mtpa LPG. Unsurprisingly not much technical detail has been released but we assume it will incorporate Shell's own proven mixed-refrigerant liquefaction technology. But of course there are other well developed LNG processes in circulation, including different cascade procedures developed by Statoil/Linde and Phillips. Other developers are working on specially adapted technologies suitable for ultra-compact floating plants. The final Prelude scheme is said to be one-quarter the size of a single train with similar designed output on land.
All LNG plants are engineered to use circulated materials that match as closely as possible the cooling and heating curves of the process gas and refrigerants, allowing the most efficient thermodynamic process that minimises power consumption in terms of units of LNG produced.
In this case as much use as possible will be made of the cooling effect provided by the use of very deep sea water; circa 250m in the case of the Prelude project.
Common problems
All FLNG designers face a series of common and very complex problems. Fortunately the technology involved in building floating regasification plants is already well developed; 10 or so such quick-build terminals being already in operation or nearing completion around the world. Many of the solutions developed for resolving these issues, such as 'slosh-free' and ultra-securely insulated gas containment vessels and materials, can be applied to the much more complex and capital-intensive liquefaction process itself, several elements of which, such as product separation, refrigerant(s) circulation and heat exchanging, are acutely susceptible to the various and variable movements of any facility that is designed to float - and survive cyclone conditions too.
First there's the problem of destabilising product movement, solved by special baffles and keeping tanks as full as possible. Then there's reducing the whole plant's 'footprint', resolved by Shell by installing the process plant right on top of the storage tanks, and thereby leaving a useful flat deck area.
And not to be overlooked is the thorny issue of ensuring ship-to-ship offloading in complete safety, solved in this case by installing two mighty 6700hp thrusters at one end (plus another in reserve) to keep the two vessels in alignment.
The whole facility will be moored to the seabed by four separate lines, kept stable in the worst conditions imaginable by a towering 105m turret system.
Coming on top of the continuing boom in LNG production – world exports increased by nearly 23 per cent by volume last year and non-piped supplies now account for a 30 per cent of international gas business – the beginning of the ship-mounted era (our term) could transform the very bullish post-Fukushima gas market. This is already being heavily influenced by developments here in Africa, in Algeria and Nigeria in particular. Almost at the same time as the Prelude announcement the IEA described the coming period as a 'Golden age of gas?' (note the question mark) in which supplies could become really tight quite shortly.
If replicated widely this development could reverse that situation - not welcome news in the two countries cited but very much so elsewhere in SSA, such as in Angola, Namibia and maybe even Tanzania too.
Development
However to suggest that the Australian scheme is a prelude to successful development of stranded resources here would be a step much too far. The security implications of all this are massive, and neither West nor most of East Africa yet possess the onshore technical facilities required to maintain such a huge and high-tech structure. Weather and sea conditions, including those all-important 1/100 year events, have to be studied closely and predicated too. Capable of energising the whole of Hong Kong and more alone Prelude seems to be a project far too large for most possible sub-Saharan locations; some experts say floating liquefaction needs to be on a massive scale in order to provide the necessary stability of the facility or whatever this mammoth ends up being called.
Says the company's general manager for LNG Neil Gilmour: “This is a groundbreaking technology developed by Shell. It has the potential to change the way we produce natural gas.”
Nevertheless Shell's breakthrough in consortium with its partners is a massive technological achievement, and when the new Gas Exporting Countries Forum holds its first-ever Summit meeting in Qatar on 13 November (from SSA only Nigeria and Equatorial Guinea are signed up) the whole development and its implications are certain to be covered.
Ends
