LNG is natural gas that has been cooled to about minus 260 degrees Fahrenheit for storage as a liquid. LNG is more compact than its gaseous equivalent with a volumetric difference of approximately 600 to 1. This difference in volume allows AGL Resources to store a large quantity of natural gas in a relatively compact storage space.
Most LNG storage facilities in the United States were constructed solely for use by local utilities. Storage facilities in utilities' service areas often hold LNG for an extended period of time to meet peak demand. LNG accounts for only a small portion of working gas in storage, but it often represents a significant part of a company's supply portfolio for peak days.
LNG facilities are often constructed with a higher degree of "deliverability" (the amount of gas the facility can send out under peak conditions relative to inventory) than traditional underground storage facilities such as depleted reservoirs, aquifers and salt caverns.
AGL Resources' LNG facilities
LNG plays an important role in AGL Resources' strategy to meet the growing demand for safe, reliable natural gas in the states served by its utilities. AGL Resources owns and operates five LNG peak-shaving facilities, which supply gas when customer demand is highest.
The largest, the Riverdale LNG plant located in Riverdale, Ga., has storage capacity of 31 million gallons or 2.56 billion cubic feet (Bcf) of natural gas in its two storage tanks. Located south of Atlanta, the plant is supplied by two interstate pipelines. It is connected to Atlanta Gas Light's beltline pipeline system for distribution of gas to the Atlanta market. The plant is able to deliver 400,000 Dth/day of gas during peak send-out.
The Cherokee LNG plant, located north of Atlanta in Ball Ground, Ga., has a single storage tank with a capacity of 24.4 million gallons or 2 Bcf equivalent of natural gas. The 934-acre site was designed to accommodate a second tank of equal capacity if warranted. This plant receives supply from three pipelines and can deliver an equivalent of 625,000 Dth/day of peak send-out to Atlanta Gas Light's Atlanta market.
AGL Resources also owns and operates an LNG plant in Macon, Ga. This plant's single tank storage capacity is 18 million gallons or the equivalent of 1.5 Bcf, although the plant is capable of delivering up to 140,000 Dth/day. The Atlanta Gas Light distribution system has been constructed in a way to allow this plant's send-out to be sent into the Atlanta area of the system if demand requires it.
In Tennessee, AGL Resources subsidiary Chattanooga Gas receives peak day supplies from its Chattanooga plant, which holds the equivalent of 1.2 Bcf. This facility is supplied by two pipelines and can currently deliver up to approximately 62,000 Mcf/day to the Chattanooga Gas market, a load limited amount.
AGL Resources also owns an approximately 60,000 gallon-per-day liquefied natural gas facility located in Trussville, Alabama. The Trussville facility is AGL Resources' first LNG facility dedicated solely to the merchant market.
In Virginia, AGL Resources subsidiary Virginia Natural Gas has access to the Columbia Gas Transmission Company's Chesapeake LNG facility. This plant is located at the end of the Columbia Gas pipeline on the south side of the Virginia Natural Gas service territory. Access to this facility provides Virginia Natural Gas with a send-out capability of up to 52,090 Dth/day and a storage capacity of 778,500 Dth.
The estimated total capacity of LNG storage facilities in the lower 48 states as of mid-2001 (excluding marine facility storage) was 86 billion cubic feet (Bcf). AGL Resources' storage capacity accounts for more than 8 Bcf or more than 9 percent of that total. The 7.3 Bcf of AGL Resources-operated storage also comprises 33 percent of the existing LNG storage in the Southeast.
In addition, AGL Resources owns two portable vaporization units that can be transported to any location in the AGL Resources system. When coupled with tractor-trailer LNG tankers, these units can supplement an AGL Resources utility's pipeline system. This service is critical to avoid loss of service to customers in times of peak demand.
Propane-air storage is also a common choice for utilities to meet their short-term peak demand energy needs. However, unlike LNG, propane is not pipeline-quality gas. It must be blended or mixed into a flowing gas stream.
One advantage of propane-air plants is their ability to be refilled via supplies that are trucked in, eliminating the need for a directly connected pipeline. In times of critical need and without other cost-effective options, propane-air plants can be a valuable supply option.
AGL Resources owns and operates three propane-air plants. Two are located in the southern part of the Virginia Natural Gas system. The first propane plant is capable of supplying up to 40,032 Dth/day, with a storage capacity of 247,171 Dth. The second is capable of sending out up to 28,800 Dth/day, with a storage capacity of 288,000 Dth. The third propane air plant is located in the northern part of the Virginia Natural Gas system. It has a storage capacity of 213,019 Dth equivalent and send-out capability of up to 18,348 Dth/day.
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