The history
Studies into offshore LNG (Liquified Natural Gas) production have been conducted since the early 1970s, but it was only in the mid 1990s that significant research backed by experimental development began.
In 1997, Mobil developed a FLNG (Floating Liquified Natural Gas) production concept based on a large, square structure with a moon-pool, commonly known as “The Doughnut”. In 1999, a major study was commissioned as a joint project by Chevron Corporation and several other oil and gas companies. This was closely followed by the so-called ‘Azure’ research project, conducted by the European Union and several oil and gas companies.
Shell’s Prelude
A number of major gas and oil companies are still researching and considering FLNG developments, with several initiatives planned for the future. However, the world’s first development of FLNG will be Shell’s ‘Prelude’ FLNG project, 200 kilometres offshore Western Australia. Floating above an offshore natural gas field, the FLNG facility will theoretically produce, liquify, store and transfer LNG (and potentially LPG and condensate) at sea before carriers ship it directly to markets.
Moving LNG production to an offshore setting presents a demanding set of challenges. In terms of the design and construction of the FLNG facility, every element of a conventional LNG facility needs to fit into an area roughly one quarter the size, whilst maintaining the utmost levels of safety and giving increased flexibility to LNG production.
Once a facility is in operation, wave motion will present another major challenge. LNG containment systems need to be capable of withstanding the damage that can occur when the sea’s wave and current motions cause sloshing in the partly filled tanks. Product transfers also need to deal with the effects of winds, waves and currents in the open seas.
The Prelude FLNG facility will produce at least 5.3 million tonnes per annum of LNG, condensate and LPG and will chill the gas produced to -162oC, shrinking its volume by 600 times so it can be shipped to customers in other parts of the world. (PIC 1) It will measure 488 metres long (higher than the Petronas Towers in Kuala Lumpar and the same height as Taipei 101 in Taipei!) and will displace around 600,000 tonnes of water, making it the largest offshore facility in the world.
The facility will be constructed in a nearby shipyard, one of a few in the world that is big enough to handle a facility of this size. It will then be towed to its location in Western Australia where it will be moored and hooked up to the undersea infrastructure and the whole production system commissioned. It will remain permanently moored here for around 25 years before needing to dock for inspection and overhaul.
The project will create around 350 permanent jobs, provide taxes and revenues to Australia, create opportunities for local businesses and result in Shell spending billions in capital and operating expenditure.
Developing the gas at this location will reduce the impact on sensitive coastal habitats as the facility avoids the need for shoreline pipe crossings, dredging and jetty works.
Measurement Challenges
Being offshore does however bring extra challenges in terms of safety and equipment specification. In the event of a potentially hazardous gas leak, crew need the maximum amount of time to react and thus gas detectors need to be fast response. However false alarms can result in facility shut down or even evacuation, so detectors must also be highly dependable even when faced with saltwater spray and the high levels of vibration or solar exposure typical of a marine installation.
Crowcon already has a strong track record in offering a number of solutions for FPSO’s (Floating Production Storage and Offloading). Working with oil rather than gas but otherwise sharing many things in common, applications such as inerting, product storage and confined space entry checks exist in both types of vessel.
A number of Crowcon’s portable products are used by workers on FPSO’s as they are easy-to-use, are a one-button operation and have pre-set alarm levels. Similarly Crowcon’s fixed detectors and sampling systems are easily managed and integrated into existing control systems.
It is essential that products sold for use on a vessel comply with the standards relevant to the country where the ship is registered. Many of Crowcon’s gas detectors are approved to the European Marine Equipment Directive which means they can be installed on vessels in Europe or other countries that recognise the MED Directive.
