Rapid progress has marked the first year of construction work at the South Hook regasification terminal site near Milford Haven, where slipforming the concrete walls to form the fourth giant LNG storage tank was completed over Christmas.
South Hook LNG Terminal Company, owned by Qatar Petroleum and ExxonMobil, has leased the 500-acre site from Esso Petroleum, which still owns the former refinery location. Sitting in a"drowned river valley", the site gives sheltered deep-water access for some of the worlds largest seagoing vessels at any state of the tide.
Turnkey contractor Chicago Bridge&Iron (CB&I) was awarded an initial engineering, procurement and construction contract for the first phase of South Hook, believed to be worth up to $750 million, in November 2004.
This phase covered the refurbishment of a loading berth on the existing jetty and construction of three storage tanks and associated facilities.
A few months later CB&Is workscope was extended when it was awarded a $325 million EPC contract for the second phase of the terminal construction, including a second loading berth, two additional storage tanks and the expansion of the associated facilities.
The five LNG tanks, each big enough to fit Londons Albert Hall inside, will sit in a large hole from which some 2 million tonnes of soil was excavated during the initial site preparation work.
The spoil was used to landscape the site and screen the plant off from the nearest road.
CB&I arrived on site in February 2005, starting work on the first tank base in June. Construction of the concrete outer wall of the first tank started on 2 September with the first three tanks taking only two-and-a-half months to erect.
Each tank is fairly squat, measuring just 27.5 metres in height or 39 metres once the roof is included."The concrete construction work to build each tank, which is a 24 hour-a-day operation, has only taken about 14 days for each one,"says Don Rees, the site manager for South Hook.
The slipforming process for the outer wall, a construction method previously used to build North Sea platforms, involves continuously filling the mould of a tank with concrete to create a cast. This process is significantly faster than the usual method of gradually building such walls using scaffolding and shuttering.
Concrete construction of the last of the five tanks is expected to be completed by next month."However, although this is impressive it is probably only about 10% of the total work needed to complete the tank as you still have all the steelwork, insulation and a lot of pipework to go on,"adds Rees.
Each tank is being built with a 700 millimetre-thick tensioned outer concrete wall, about a metre of insulation and an inner nickel steel tank that holds the LNG. This double-containment method is designed to ensure that if the structural integrity of either the outer or inner tank is breached then the surviving wall will continue to hold the LNG.
The first of three roofs for the tanks comprising phase one of the project is due to start going into place during March. Using a novel lifting operation, the formwork for each roof will be'floatedto the roof level using air pressure from fans underneath.
This frame will then be welded into place and used as formwork for building the roof with concrete and reinforcing.
Refurbishment of the LNG jetty where the carriers will offload is under way with the original walkways, gantries, ladders and steelwork all being stripped away. Typically it is expected an LNG carrier will dock at South Hook every two to three days, taking around 18 hours to offload its cargo.
A fleet of 14 new carriers are to be used on the route between Ras Laffan in Qatar and South Hook--eight Q-Flex vessels each with a capacity of 200,000 cubic metres and six Q-Max ships each able to hold 265,000 cbm.
Each of the five tanks will hold around 155,000 cbm of LNG. The product will arrive at a temperature of minus 160 degrees Centigrade and will remain at that level in the storage tanks.
South Hook will process the LNG using submerged combustion vaporisers (SCVs) to turn it back into gas at an ambient temperature. This process was chosen over the open rack system, which would have required pumping thousands of gallons of seawater from the Haven with adverse environmental implications for the local ecology.
The SCV equipment will be built on an area next to the tanks where a nitrogen plant will also be constructed. South Hook will make its own nitrogen on site, adding it to the gas at the final stage once it has vaporised before it is metered and put into the National Transmission System.
The addition of nitrogen is required to trim the calorific value of the gas so it meets the so-called Wobbe Index standard for UK gas quality. The Department of Trade and Industry (DTI) had expressed concerns that some overseas gas would not burn properly on UK appliances.
Rees says the South Hook project, which is around 20% complete, is right on schedule for first phase completion in October 2007, with phase two doubling capacity around a year later. Some of the first cargoes will likely be used to commission the terminal as systems are tested and it builds up to maximum throughput.
Currently there are more than 800 workers on the giant construction site and this is expected to peak at 1200 in the last quarter of 2006 or early 2007. Once South Hook is up and running it will have a permanent staff of 65 employees, primarly a mix of process operators to control the plant around the clock.
Utility company National Grid Transco expects a decision soon from the DTI on an environmental impact assessment submitted last year to build a 120-kilometre pipeline to take the gas from the South Hook and Dragon LNG terminals to the village of Aberdulais, north of Swansea, where it will join the UKs existing high-pressure pipeline grid.
The spur pipe route has been fixed, although difficult negotiations for rights of way continue with some local landowners. With its DTI application expected to be approved, Transco plans to build the line during the summers of 2006 and 2007.
The utility has also outlined plans to reinforce the main existing pipeline, which runs from Felindre, near Swansea, to Tirley in Gloucestershire.
However, this has also met with some opposition, primarily from the Brecon Beacons National Park Authority, which is concerned over the environmental impact as it passes through 26 kilometres of the park.
Transco says it plans to use engineering techniques when laying the line that will minimise the effect on the environment."We have no reason to believe the South Hook project will be delayed or constrained by a lack of transmission capacity,"says an ExxonMobil spokesman.
© Upstream 2006
