Cool gas

Hackberry, La., plant to supply LNG to new niche

By Karla Wall

Sempra LNG, a division of Sempra Energy, will complete work on its Cameron Liquefied Natural Gas receiving terminal and storage facility in Hackberry, La., during the third quarter of 2008.

The facility will offload two LNG tankers per day and have the capability of processing 1.5 billion cu. ft. of LNG daily. Tankers will range in size from 850-1,050 ft. in length and carry 1.6 to 4.3 cu. ft. of LNG each.

Primary contractors Aker Kvaerner of Norway and Tokyo-based Ishikawajima-Harima Heavy Industries began work on the project in August 2005.

Alan Zachary, Cameron LNG construction manager, said at peak the project will employ up to 800 workers. Once operational, the terminal will have 50 to 60 full-time permanent employees on staff.

The Cameron LNG terminal is one of several being constructed in the southwest Louisiana area. Sempra chose to take over the site when Dynergy Inc. abandoned its Hackberry LNG project and felt it was an ideal site because of the natural gas pipeline already in existence in the area and because of its location in sparsely populated area, Zachary said.

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The 275-acre terminal, located on the Calcasieu River, will consist of three storage tanks, each with a capacity of 1.5 million cu. ft. LNG is natural gas that has been cooled to minus 260 degrees Fahrenheit for shipment and storage. Cooled to its liquid state, LNG takes up to 600 times less volume than in its gaseous form. Ten submerged compression vaporizing units will be located on the site to heat the natural gas back to its gaseous state for transport in pipelines.

An administration building will also be located on the site.

Site preparation included the removal of approximately 400,000 cu. yds. of unusable dredge material from an existing dredge soil disposal cell, Zachary said. The site was built up with approximately 350,000 cu. yds. of clay and gravel.

A marine basin and turnaround area is being dredged to a depth of 45 ft. using hydraulic pontoon dredging equipment. Zachary said most of the dredge material has been used to build up the site.

LNG will be offloaded from the tankers using one of three unloading arms located in two unloading jetties in the marine basin.

"There will be one unloading arm at each jetty," Zachary said. "They'll be equipped with safety valves."

The unloading arms will be cooled just prior to receiving LNG from the ship by vapors produced by the LNG stored on the ship, said Ron Hand, project engineer with Sempra.

"The ship sends cold vapors produced by the LNG through the arm prior to pumping," Hand said.

The LNG is piped through stainless steel pipe to one of the three storage tanks, each 230 ft. in diameter and 160 ft. in height. Each tank is constructed on 18- by 18-in. precast concrete pilings, ranging in length from 90 to 110 ft. The tanks are 6 ft. above ground. A 3-in. slab of 6,000-psi concrete is topped by an insulating layer of 2,000-psi concrete and further insulated by a 2-in.-thick layer of 9 percent nickel, Zachary said.

The walls of the tanks are 6 ft. thick and consist of a 3-ft. outer layer of 6,000 psi concrete and a 3-ft. inner wall of foam glass. Slab and walls are post-tensioned using more than 5 million ft. of 5/8-in. diameter steel cable, Hand said.

Concrete foundations for the tanks has been poured in four pours of 1,600 cubic yards each, Zachary said. Pours are performed from midnight through 4 a.m., taking advantage of the cooler nighttime temperatures to keep the concrete at adequate temperatures. Approximately 40,000 cu. yds. of concrete will be used for the tanks, Zachary said.

LNG is pumped to one of the vaporizer units by a pump situated at the bottom of each tank through 24-in.-diameter stainless steel pipe, Hand said. The units are each situated in a concrete basin, roughly 15 ft. wide, 40 ft. long and 10 ft. deep. The basins will be filled with water.

A 120-btu burner will be situated at one end of the basin and each unit will contain two small pipes -- a process tube that carries the LNG and a larger sparger pipe that carries the exhaust off the burner, heating the water in the unit to about 75 degrees. The LNG carried through the process tube is thus heated to a gaseous state as it passes through the water. Vaporized natural gas is used as fuel for the process, Hand said.

From the vaporizer units, the gas is sent through 36-in. pipe to a meter station and then through the 35-mi., 36-in.-diameter Cameron Interstate Pipeline, owned by Sempra, to connect to major interstate and intrastate pipelines for transport to central and eastern U.S. destinations.

More than 120,000 ft. of pipe is being used for the project, ranging in size from 12 in. for circulation and cooling to 36 in. for send-out from the vaporizer. To accommodate the cold LNG, all piping from the unloading arms to the vaporizer are stainless steel and insulated with cellular glass.

From the vaporizer, all piping is carbon steel. Piping will be routed through pipe racks at an elevation of 9 ft., which is the 100-year flood level for the area, Zachary said. Pipe racks are constructed of 6,000-psi concrete and supported by 6,000-psi concrete pilings.

In the future the facility will be expanded to add one storage tank and increase the terminal's output to a total of 2.65 billion cu. ft. per day.

The expansion will take up nearly 15 acres of the 275-acre site.