Columbia 630MW Energy Center, Calhoun County, USA

Calpine Corporation's Columbia Energy Center is now producing 630MW in Gaston, South Carolina, USA. The cogeneration facility provides 500MW to the local utility grid for both inside and outside the state – to load serving utilities, municipalities and cooperatives. It supplies the rest, along with a reliable source of steam, to the adjacent Voridian plant. That has allowed Voridian, a division of Eastman Chemical Company, to shut down three coal-fired boilers at its Columbia site.

The $365m Columbia Energy Center created more than 200 new jobs during construction and now employs 25 people full time. The facility is located on a 20-acre site in Calhoun County, and came online in May 2004. In June 2008, the plant was given an Energy Star CHP Award, recognising the project's pollution reduction and energy efficiency qualities.

General Electric gas-fired turbines

Powered by two General Electric 7FA natural gas-fired combustion turbines and a Toshiba steam turbine, the Columbia Energy Center is a CHP system.

The turbines feed two Nooter / Eriksen heat recovery steam generators, which provide steam for a steam turbine. Recovered heat from the turbines' exhaust produces up to one million pounds of steam an hour that is used by the adjacent Voridian plant for the manufacture of thermoplastic polymer resins.

The 171.7MW 7FA turbines have an 18-stage axial compressor and a three-stage turbine, and feature reduced nitrogen oxide and carbon monoxide emissions. A cold-end drive and axial exhaust help reach net efficiencies over 58% in combined cycle operation. The turbines have a heat rate of nearly 9,900kJ/kWh, a pressure ratio of 16.0:1, and a mass flow of 445kg/sec. Turbine speed is 3,600rpm, and exhaust temperature is 601°C.

GE's DLN 2.6 (dry low NOx) combustor produces less than 9ppm NOx and CO to reduce the need for exhaust cleanup systems. The DLN-2.6 combustor added a sixth burner to the previous design, with the centre nozzle fuelled separately from the outer nozzles. It also eliminated the need for a diffusion mode.

54% operating efficiency

With an operating efficiency of around 54%, the CHP needs about 31% less fuel than typical onsite thermal generation and purchased electricity. Based on this comparison, the CHP system reduces CO2 emissions by an estimated 142,000t a year. The Columbia Energy Center is about 10% more efficient than other generators in the state, making the energy an attractive commodity for utilities.

Throughout the construction process, the plant also had a large impact on Calhoun County. That included $41m in salaries for 650 employees, $90m spent in construction materials with around 60 to 70% purchased from local vendors, $10m to 90 subcontractors, $6m in miscellaneous services like surveying, permitting and housing, and $1.5m in gravel for groundwork.

US's largest independent power producer

The construction of the plant was coordinated and managed by Calpine using a general contractor. Calpine managed all aspects of the project, including engineering and design, construction, fuel supply, operations and power marketing.

Calpine is the largest independent power producer in the US with 92 facilities and more than 26,000MW in operation. The company generates power at plants it owns or leases in 21 states in the United States, three provinces in Canada, Mexico and in the United Kingdom. Calpine is also the world's largest producer of renewable geothermal energy, and owns or controls approximately one trillion cubic feet equivalent of proved natural gas reserves in the United States and Canada.

Within South Carolina, Calpine has more than 1,400MW in operation. In addition to Columbia, the company has the 830MW Broad River Energy Center peaking facility in Gaffney. Combined, the two energy plants put out 1,400MW, representing a roughly $700m investment.