In 1912, West Virginia began storing liquefied natural gas (LNG) commercially and, 47 years later, in 1959, the Methane Pioneer carried the first cargo of LNG via sea from Louisiana to the United Kingdom. Today, there are 96 LNG storage facilities throughout the United States. As popularity of this energy source increases (demand is expected to grow from 1% to 3% by 2008), so does the demand for storage facilities.
Three full-containment LNG storage tanks are being constructed simultaneously in Cameron, La., representing the first new LNG receipt terminals in North America in more than 20 years. These tanks—each 254 feet in diameter with 134-foot-high walls—will store the LNG received via tanker before entering the U.S. energy market in gaseous form. The $750 million project by owner Sempra Energy will have the capacity to regasify up to 1½ billion cubic feet of natural gas per day.
The wall cross section batters from 3 feet at its base to 2½ feet at one-third of the final wall height, then runs vertically to the top with a constant thickness. Four buttresses, each about 5½ feet thick and almost 15 feet long, have been integrated into the ring wall to act as vertical bracing elements.
Baker Concrete Construction, Monroe, Ohio, worked with engineers from formwork and scaffolding manufacturer PERI to develop a climbing formwork solution—VARIO GT 24 girder wall formwork supported by
CB climbing brackets. Compared with conventional circular formwork, anchor points can be kept to a minimum using this system because formwork ties can be spaced further apart. With a permissible fresh concrete pressure of 940 psf, only two DW 20 tie points are required with a concrete lift height of 15.3 feet. Numerous steel embeds and pipes in the walls had to be taken into consideration when determining the tie positions of the pre-assembled formwork panels, each approximately 10½ feet wide and 16 feet high. Panels are connected by friction-locked connections between the steel walers using articulated couplings.
Different sized wood blocks were used between the formwork girders and steel walers to create the correct radius for the tanks. Without these shims, says Darrell Crowson, project manager at Baker, the actual form panels are straight. “This design is advantageous, as it will allow us to use the same straight panels for tanks of varying radiuses by using differently shaped blocks,” he says.
Each tank was started one month apart with the mat foundations and the walls scheduled at 36 weeks per tank. Each tank has its own form-work, reinforcing, and PT crew, with one placing crew oscillating between the three tanks. The mat foundation, walls, and preparation for the roof was completed in 44 weeks. One lift consisting of 25,600 square feet of formwork and 1250 cubic yards of concrete is cycled every 13 working days, with one day between tank pours, says Crowson.
Crews are using four different boom pumps, ranging from 42 to 61 meters, to place the concrete in one complete circle at a time, which takes approximately eight hours. A high-slump mix was used that maintained a low water-cement ratio with a high-range water reducer. Microsilica also was added to the mix to make a denser concrete to improve corrosion resistance.
“The surface has not required rubbing or patching,” says Crowson. “It also meets tolerances for roundness and plumbness required to allow the roof to be airlifted on the inside of the tank.”
The climbing scaffold system can be moved in only one crane lift from cycle to cycle. In each case, two panels connect together with a CB platform to form an individual climbing unit, which then are moved separately in
successive order around the tanks to maintain a continuous working platform. For each tank, 80 climbing units are in use, with 78 internal panels and 78 external panels on 40 platforms. The roller bearings on the climbing scaffolding's carriages enable the formwork elements to be retracted 2½ feet for stripping and cleaning. That allows Baker crews to climb the circular containers in two-week cycles.
The tanks will be fully operational in 2008. One additional tank will be built afterward to increase production capacity in the years ahead.
Life of LNG
Natural gas is converted to liquefied natural gas (LNG) by cooling it to -260° F. That process reduces its volume by a factor of more than 600—the equivalent of compressing a beach ball to the size of a ping pong ball—allowing natural gas to efficiently be transported by sea. Upon reaching the United States, the gas is stored as a liquid until it is warmed back into its gaseous form and transported under pressure through pipelines for use in homes or factories. Source: Center for Liquefied Natural Gas