To build a storage structure bigger than London’s Royal Albert Hall on an isolated stretch of coastline in Western India is ambitious enough…
To construct three of them in record-breaking time, each capable of holding over 35 million gallons of liquid gas at minus 165 degrees C, in a climate, fluctuating between arid heat and torrential monsoon rainfall, is testing to say the least.
But, based on the huge logistical challenges so far overcome by the Kvaerner project team creating India’s first LNG terminal midway between Mumbai and Goa, their goal seems more and more achievable as each day passes.
Kvaerner has brought together its worldwide expertise in civils and processing for this US280million (£175 m) project to design and build a Liquefied Natural Gas supply facility for a major power station expansion scheme on behalf of Dabhol Power Corporation.
Under the lump-sum turnkey contract awarded by Enron International in December 1998, Kvaerner has to supply, construct and equip a facility to transfer LNG form from ships to the storage tanks, then convert it back into gas for export to the power plant and the local grid.
Targeted for final handover in March 2002 and with first deliveries of LNG due late next year, the new terminal is part of a US$500 million scheme to provide Dabhol Power Station with a second 1440MW plant, a jetty and an export gas pipeline.
It marks the first fully integrated partnership between Kvaerner Construction and Kvaerner E&C. The two business areas are joining forces to provide the LNG industry with a fully integrated global service.
Kvaerner Construction’s Roy Isden is the project director and has recently been appointed general manager of Kvaerner’s LNG business stream. Working alongside him is Paul Emson, Kvaerner E&C project manager for processing.
Roy Isden commented: “The Dabhol project, which introduces natural gas to the west coast of India, combines our broad technical and managerial abilities together with our long experience of the Indian construction market.”
With an annual throughput of five million tonnes, the terminal will export LNG at two levels – a low-pressure feed for both power plants (the first one currently runs on Naphtha) and at high-pressure into the regional gas distribution network.
Kvaerner’s task involves:
Fitting out an offloading jetty with mechanised LNG unloading arms;
Installing insulated pipelines running two kilometres from the jetty head to a storage and processing area;
Building three giant concrete and steel circular tanks each of 160,000 cubic metres capacity, with regasification process and pumping facilities.
It is the towering scale of these tanks that dominates the site, built at three levels into a hillside in a narrow, rocky valley surrounded by 120-metre high cliffs. Kvaerner is building the first three out of six planned LNG tanks that are believed to be the world’s biggest, or at least serious contenders for the heavyweight title.
The design is based on proven technology from Whessoe LGA. The outer concrete shells of two tanks are complete while work on the third is progressing steadily.
To speed construction both the pre-stressed outer walls of the tanks and the dome-shaped roofs, are being built simultaneously. The roofs are being assembled from 600 steel plates inside the tank shells. To complete the external works, these massive covers, weighing 770 tonnes are gradually floated 40 metres up to the top by pumping air into the sealed void beneath them, and then locked and welded into position, like the lid of a can. The roof on the first tank has already been floated in position in a seven hour operation using two 900 CFM fans. The other two are due to follow and the tanks should have their external structures completed by July.
The internal workings will follow, including a metre-wide layer of expanded perlite insulation sandwiched between the outer wall and an inner steel casing. A suspended deck under the roof of each tank will contain a metre-thick blanket of fibreglass insulation. A layer of foam glass is installed between the inner tank and the base, with tank base heating to prevent the surrounding earth from freezing.
Concrete for the pre-stressed outer wall is cast in curved shuttering which climbs up the wall as work progresses. Ten shuttering lifts will reach the top of the 40-metre structure. The curved dome roof adds a further 15 metres - and structural steelwork for inspection access to the top pushes the overall height to close on 60 metres.
These gargantuan storage drums have a capacity far bigger than the Royal Albert Hall, whose volume is just under 100,000 cubic metres. At just over 47 metres, the top of the world-famous London landmark is some eight metres below the rooftop of the Dabhol tanks. And, at a little less than 66 metres long and just over 56 metres wide, the ovoid concert hall would fit inside each one.
“They’re certainly large enough to hold a major concert party,” remarked Roy Isden. “The scale is very impressive and from the inside they look even bigger.”
Although this is Kvaerner’s first joint venture into LNG tanks, Roy Isden and Paul Emson describe the design and construction timetable as being “very tight given the location” for building storage structures of this type, let alone this stature.
At Dabhol, the schedule for completing a tank, fully closed off and insulated, is targeted to be accomplished within 30 months, against an industry norm of between 33 and 36 months. “If we meet programme - and I think we should - it will be the fastest construction time anywhere for this kind of structure,” said Roy Isden.
Squeezed into a narrow valley and deluged by monsoons from June to September, the site layout raised particular design challenges, with up to 25 cubic metres of rainfall per second discharging through gradients of 10 degrees and sections of interconnecting piperacks needing to climb inclines of up to 24 degrees.
To fit the complex into the slender valley, 550,000 cubic meters of rock-blasting and 450,000 cubic meters of earthworks have been carried out since work began at the beginning of 1999. Although founded on mostly basalt rock, large amounts of concrete had to be pumped into subterranean voids and faults, but now all main site access roads and elevations, plus bulk earth works have been completed.
The desolate nature of this estuarine fishing region on the south-western side of Maharashtra state is such that just about every single item needed to serve this project and its workforce – apart from local aggregate - has to be imported.
The nearest sizeable town may be only 40 kilometres distant - but it is at least two hours away by car, due to the rugged and poor state of the roads. Further up the Konkan coastline is the port and resort of Ratnagiri, a four-hour journey each way. Mumbai, formerly Bombay, is around 260 kilometres north – and a bumpy seven-hour ride.
Consequently, Kvaerner’s main mode of transport for personnel is by helicopter, taking them three times a week between the site landing pad and Mumbai in 70 minutes.
“The construction and process engineering is straightforward - it is the logistics that is the key to the job. It all comes back to that,” says Roy Isden.
The remoteness of the location has led to the maxim among site staff: “If you don’t take it with you, you won’t find it there.” A fair-sized ‘town’ has grown up adjacent to the site to accommodate Kvaerner’s 2,000-strong workforce plus the various other teams who are expanding Dabhol power station. Together with power workers and those building the second power station and terminal jetty, it amounts to a population of some 7,000 staff and labourers.
The terminal construction programme has been planned to skirt round the monsoon seasons. The project is running in two phases: enabling works and tank construction will be finishing with the onset of the summer monsoons this year. On site fabrication of the first shipment of stainless steel pipe, due before the onset of the monsoon, will mark the switch to ME&I.
Because it is shallow the construction jetty, which serves the project presents its own problems. It is accessible only to specialised low-draught self-unloading vessels and offloading is impossible during the monsoons. The first of these specially chartered vessels will be carrying the 8,000 freight tonnes of stainless steel pipe which is being manufactured and coated in factories all over Europe. The pipe will be transported to Venice, Italy, for consolidation before onward transportation to Dahbol.
In procurement terms, Dabhol, with its limited transport links, has been a global challenge, combining the technologies of four continents to achieve co-ordinated and timely support to meet a tight programme.
Around 80 per cent of materials and equipment is shipped from Europe, the USA and Japan, using a UK-based marine agent. This includes highly-specialised LNG plant such as pumps, pipe supports, bellows, vaporisers, and Boil-Off-Gas condensers, which have to be transferred to shallow craft for the final leg.
The construction jetty is also the main entry point for bulk materials like cement and steel, while some onshore procurements are ferried to Mumbai and brought down by road. Steel plates for the inner tanks and structural steel is being formed at a fabrication yard in Dubai before being shipped by barge to Dahbol.
So far, the project’s nerve-centre has been London, where the procurement and engineering has originated. Kvaerner designers have created a virtual model using 3D software, so they can clearly observe how the numerous services and disciplines interface, enabling them to forward clash-free designs to site.
Now the main focus is shifting to Dabhol itself, with growing emphasis on process installation. Some 15 kilometres of cryogenic insulated stainless steel pipework is involved, which has to be cut and prepared in a big fabrication yard set up on site.
Integrated working with suppliers is especially important when everything connected to the LNG pipe runs must be designed to be cryogenically insulated, including cold supports fixed into the ground.
“It’s difficult to get right, because qualities of sturdiness and good insulation don’t go easily together,” said Paul Emson. “Supports have to be a complex combination of steel and resin-based insulation barriers that have sufficient strength and rigidity.”
Working on a programme that still has two years to completion, it would be tempting to be relaxed at this stage about pre-commissioning, yet this could well produce the project’s greatest challenge.
Each storage tank must be hydro-tested, requiring at least 100,000 cubic metres of water. Capturing sufficient fresh supplies to test such huge water-tight structures could present a difficulty. Ironically, despite the annual deluge of rainwater, there is nowhere locally that at present holds such large reserves.
“The original plan was to draw off from the station firefighting system, but this is not now possible,” explained Roy Isden. “At this moment, we have no way to draw off and store this amount of water … it’s simply one more logistical problem we have to solve.”
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