The Memphis Light, Gas and Water Division's (MLGW) gas system had been experiencing steady growth, requiring a need for additional peaking service. Instead of purchasing capacity and being obligated to pay the high cost associated with pipeline transportation, MLGW decided to build their own LNG peak shaving facility in Memphis, Tennessee. The peak shaving facility includes a liquefaction system, an LNG storage tank, a sendout system, plant emergency electrical power generators for vaporization and related utility support systems.
The 5.5 million standard cubic feet per day (MMSCFD) liquefaction system, used to fill the storage tank, is CB&I's proprietary Mixed Refrigerant Liquefier (MRL) system. The MRL system, which uses relatively simple equipment, provides high efficiency through compressor interstage cooling and water evaporative refrigerant condensers.
One billion standard cubic feet (BSCF) of LNG storage is provided by a steel, double-wall, flat-bottom tank with a suspended deck. The insulation on the suspended deck and in the annular space between the steel walls is expanded perlite powder. The load-bearing bottom insulation is foamglass blocks. The outer tank is carbon steel, the inner tank containing the cryogenic liquid is 9% nickel steel, and the suspended deck is aluminum.
The sendout system delivers up to 150 MMSCFD of vaporized gas at 450 to 850 pounds per square inch gauge (PSIG) and 60oF to the pipeline. Each of the two LNG pumps starts with a variable frequency drive (VFD) to reduce starting inrush current and then switches over to across-the-line power for vaporization operation.
A truck load/unload station provides for a transfer of the LNG. The integrated distributed control system includes programmable logic controllers connected to a remote site via a plant data highway. The plant is controlled through a graphic interface presented on screens that we developed and can be remotely operated and monitored via closed-circuit television from the MLGW Arlington LNG facility about 35 miles away.