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Thursday, July 7, 2011

REGASIFICATION TERMINAL TECHNOLOGY

 

The Freeport LNG terminal is a world-class regasification facility with a peak send-out capacity of more than 2.0 Bcf per day. The site is located approximately six miles from open water off a ship channel which is maintained at a depth of 45 feet, sufficient for all existing LNG carriers.


Major components of the Freeport LNG terminal include the following:

   
  Marine Terminal and LNG Transfer Lines
 

The facility includes a marine terminal consisting of a maneuvering area and one protected marine berth for unloading LNG tankers. The dock is designed to handle vessels with capacity between 88,000 and 267,000 cubic meters.


The marine facilities have been designed to provide safe berthing for the receipt and mooring of LNG ships and to ensure safe transfer of LNG cargoes.

Design of the facilities is in accordance with applicable codes and standards, including Oil Companies International Marine Forum, Society of International Gas Tanker and Terminal Operators, American Petroleum Institute, and American Society of Civil Engineers.

   
  LNG Storage
 

The facility features two LNG storage tanks, each with a capacity to hold 160,000 cubic meters (42.3 million gallons) of liquefied natural gas, maintaining its contents at a temperature of minus 260 degrees Fahrenheit. The tanks were built to withstand the vagaries of coastal storms, and can withstand a category five hurricane with wind gusts above 180 miles per hour. Each full-containment tank has a primary inner wall of 9% nickel steel and a secondary outer wall and roof of pre-stressed concrete that extends to the outside container. Around the outer perimeter where it encounters the weight of the tank walls, the foundation is five feet thick. A heating system was embedded in the foundation of each tank to guard against freezing the soil underneath and to preserve structural integrity of the foundations. There is a series of three submerged in-tank LNG send-out pumps that are used to move the LNG to the vaporization unit.

   
  Unique LNG Regasification System
 

Freeport LNG utilizes a closed-loop recirculation system with an air tower (named the "VE Tower" in honor of Volker Eyermann (1939-2005), Freeport LNG's Vice President of Engineering), enabling the terminal to take advantage of the high ambient temperature and high humidity conditions in the Texas Gulf Coast region. Historically, air towers have been used to reduce the heat of an industrial process system by exchanging the higher temperature of the process cooling system with the lower ambient temperature. However, the Freeport LNG air tower serves a heating function, providing vaporization heat during normal conditions. As a result of the use of the closed- loop system, for approximately nine months of the year, the air tower provides all of the heat required to regasify LNG. For the remainder of the year, the gas-fired indirect heaters act as a supplemental heat source for the vaporizers with the air tower providing varying amounts of the heat depending on local weather conditions.

   
 

Freeport LNG's VE Air Tower

   
  Natural Gas Send-out Pipeline
 

Natural gas makes its way to customers from the Quintana terminal through a 9.6-mile pipeline built to a metering station near Stratton Ridge, Texas. At Stratton Ridge, the Freeport LNG pipeline connects to the Dow, and ConocoPhillips and Kinder Morgan pipeline systems that have multiple outlets for natural gas to flow to customers throughout the state of Texas and beyond.

The pipeline to Stratton Ridge is unique in several respects. It was the first 42-inch gas pipeline built in the state of Texas. The huge pipe has a wall nearly one inch thick and is rated to operating pressures up to 1440 pounds per square inch. This 42-inch line is capable of accommodating natural gas flows of up to a total of four billion cubic feet of gas a day. Four horizontal directional drills were required along the pipeline's path to Stratton Ridge. The wetlands horizontal drill set a world record for pulling 42-inch pipe: 5100 feet, or nearly one mile.

While the pipe is in service, its performance and integrity is regularly monitored. A pipeline inspection device, or "pig," is inserted at a launch site along the pipeline and moves inside the pipeline to either clean the pipe or, in the case of a "smart" pig, to measure wall thickness and look for signs of corrosion. External corrosion of the pipe is managed with cathodic protection systems that induce an electric current near the pipe to impede the chemical process that generates corrosion.

   
  Boil-off Gas Reliquefaction
 

When the LNG terminal is sending out gas for its customers, boil-off gas (BOG) from the LNG storage tanks is part of the gas delivered to the customers and does not affect FLNG's inventory. However, during periods of low terminal utilization, Freeport LNG's inventory continues to boil off and must be compressed and sent to sales, thus gradually depleting the LNG volumes in the storage tanks.

   
 
Freeport LNG decided to install equipment to capture the boil-off gas, convert it back into liquid form and retain it within the terminal's LNG processing and storage system to maintain cryogenic conditions.
   
 

In August 2009, the boil-off gas reliquefaction unit was commissioned. It consists of a heat exchanger (cold box), one expander-compressor, two compression lube oil filters and three compressor units (powered by natural gas-fired engines, approximately 1,380 horsepower each).

   
 
  Freeport LNG's BOG reliquefaction process
   
 

The unit has a reliquefaction capacity of between 4.5 and 5.0 MMcf of boil-off gas a day, which represents between 200 and 220 cubic meters of liquid gas going back to the storage tanks.

The reliquefaction equipment allows Freeport LNG to avoid purchasing additional LNG to maintain a minimum inventory level and keep the facility cold and makes it possible for the terminal customers to keep LNG inventory in the tanks for extended periods and then reexport the LNG to markets that offer higher prices than the U.-S.- gas market. The BOG liquefaction plant also acts as a back-up to the existing BOG send-out pipeline compression.

                                    Boil-off gas reliquefaction train
   
 
 
Compressors
Cold box

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