Centralia Power Plant New CCGT Unit, WA, USA

TransAlta has expanded its Centralia Big Hanaford power plant site with a 248MW combined-cycle gas turbine (CCGT) unit. The site has two coal-fired units, and operates as a merchant power plant. Acquired in 2000, Centralia is TransAlta's only coal-fired power plant in the United States. It generates enough electricity each year to supply a city about the size of Seattle. Net generation has been 10,478,711MWh.

TransAlta has also invested in emission control technology to cut sulfur dioxide emissions by 90%, as well as nitrogen oxide emissions. The Centralia power plant is equipped with scrubbers, gas turbines, a steam turbine and a heat recovery steam generator (HRSG). As well as the power generation units, Centralia also has a coal mine which can fuel the coal-powered power units.

CENTRALIA PLANT

Centralia power plant and coal mine are based in Lewis County, Washington, 5 miles north of Centralia. The mine is already subject to some revegetation and covers more than 14,000 acres of typical low-elevation woodland. Reclamation at the site includes reforestation that is establishing the pre-mining forestry land use. It was bought by TransAlta in May 2000 for $554 million and the deal was subject to a number of conditions relating to the future management. The mine was priced at $101 million and the power plant cost $453 million. The new plant is located on the site of TransAlta's 1,340MW coal-fired power.

Construction of the gas-fired power plant commenced in April 2001, and it began operation in August 2002.

The construction of a new power plant in the area is welcome as the region's generators are only just able to meet winter-time demand. Conscious of California's energy difficulties, the state authorities are eager to boost power production.

GENERATING UNITS

The existing coal-fired plant consists of two generating units with a total capacity of 1,340MW. The units were built in the early 1970s.

The new gas fired plant added 248MW of electricity to the Pacific Northwest energy market and is on the same site as TransAlta's coal-fired power plant. The cost of the new gas-fired unit was $215 million.

COAL FIRED UNITS

Each of the coal-fired units at Centralia is more than 200ft high. Powered coal is fed through 64 nozzles to feed them. The temperature can be as high as 3,000°C. This generates the pressurized steam to drive two massive steam turbines (over 100ft long, and weighing 600t each).

The units use two P&H 4100XPB coal shovels to transport the coal to the generators. These employ Optima Plus dipper and load 270t/245m haulers supplied by P&H Mining Equipment.

The Centralia plant's coal-fired units use 70% local coal, mainly supplied by the nearby coal mine.

ENVIRONMENTAL IMPROVEMENTS AND EMISSION REDUCTION

When TransAlta bought the plant, it agreed to uphold the recommendations of a collaborative decision-making process among key stakeholders in the area. In keeping with those recommendations, TransAlta installed $200 million US scrubbers on the plant, making it among the cleanest coal-fired power plants in North America. The scrubbing technology was supplied by ABB Environmental Systems.

CONTRACTORS FOR THE POWER PLANT

TransAlta is a joint venture. The partners are: PacifiCorp (47.5%), Avista Energy, Seattle City Light, Tacoma Power, Snohomish PUD, Puget Sound Energy and Grays Harbor County PUD.

Stone & Webster, in a consortium with ABB Environmental Systems, was awarded the engineering, procurement and construction contract from PacifiCorp to design and build a flue gas desulfurisation system for the Centralia power plant.