St. Clair Power Plant

The Saint Clair Power Plant is a major coal- and oil-fired power plant owned by Detroit Edison, a subsidiary of DTE Energy. It is located at 42°45′52″N 82°28′21″W in St. Clair County, Michigan, on the west bank of St. Clair River. The plant is next to the newer Belle River Power Plant in East China, Michigan. The first four units of St. Clair were built in 1953–1954 Since then, three more generating units have been added to the plant. St. Clair was the world's largest power plant after the 1969 addition of unit 7 . The St. Clair Power Plant generates 1982 megawatts in total. It is Detroit Edison's second largest power producer. The power plant has a large impact on the local economy, employing about 400 workers.

Units

A total of seven coal-fired boilers were ultimately built at St. Clair, although only six remain operational.

Units 1-4

Units 1-4 are 163 MW Babcock & Wilcox boilers tied to GE and Allis-Chalmers steam turbines. These are the four original units at St. Clair. Generating units 1-4 are St. Clair's base load units, usually running at full capacity. The flue gases from those units exit through south stack, which was erected in the late 1970s when new electrostatic precipitators were added to these units. When the plant was first built, there were four relatively short stacks, one for each unit.

Unit 5

Unit 5 is St. Clair's only decommissioned unit. Its cyclone boiler produced 300 MW, and was taken out of service in 1979 do to a mechanical problem with the boiler.

Unit 6

Units 6 is a tangentially fired Combustion Engineering boiler tied to a Westinghouse turbine. Commissioned in 1961, this unit produces 321 MW.

Unit 7

Unit 7 is also a tangentially fired Combustion Engineering boiler tied to a Westinghouse steam turbine. It was commissioned in 1969. Unit 7 is rated at 451 MW, originally built to produce over 500 MW. This unit is St. Clair's largest generating unit, but has a small electrostatic precipitator, causing opacity problems with the when burning western coal.

Other Units

An oil-fueled gas turbine Unit 11, rated at 18.5 MWe, was added in 1968. Two smaller oil-fueled internal-combustion generators, totaling 5.4 MWe, were added as units 12A and 12B in 1970.

History

St. Clair Power Plant came online in August 1953, and was the largest in the DTE Energy network. This was what St. Clair looked like in in the mid 1950's [1]. At that time, its capacity was 652 MW. Later, units 5, 6 and 7 were added to meet growing demands for power in Metro Detroit, with St. Clair producing 1571 MW. After the completion of unit 7 in 1969, St. Clair Power Plant was the world's largest. In the middle to late 1970s, the plant was converted to burn Western subbituminous coal. The conversion resulted in lower unit power ratings and necessitated the installation of larger electrostatic precipitators on Units 1–4 and Unit 6. This also included building a new stack for units 1-4. In addition, low NOx burners and overfire air ports have been installed on all of St. Clair's generating units.

Coal sources

Coal blend used

St. Clair burns a blend of low-sulfur Western coal (from the Decker (Powder River Basin) and Spring Creek mines in Montana) and high-sulfur Pittsburgh-seam Eastern coal. Blending is done in the coal yard with variable speed feeders. Although the nominal blend is 85% Western and 15% Eastern coal, the exact blend depends on a number of factors including demand requirements, coal prices, stockpile inventory, and unit availability. In the summer months, for example, the blend trends toward 70/30 on Units 6 and 7 to gain additional generating capacity by firing more Eastern coal with its higher heating value. The higher sulfur content of the Eastern coal also helps prevent opacity excursions with the electrostatic precipitator on Unit 7.

Transportation and stockpiling

The Western coal is delivered to Superior, Wisconsin, by unit train and then barged to St. Clair on 60,000-ton ships. Because the ships typically cannot operate on the Great Lakes from late December until late March, the plant must stockpile between 2.1 and 2.4 million tons for the winter season. Eastern coal is delivered by rail. Because of decline in production, the plant's seasonal stockpiling of Eastern coal declined from 140,000 tons to 20,000–30,000 tons in 2004.

Operational data

St. Clair is a base load power plant , dispatched after DTE Energy's Fermi 2 nuclear unit and the neighboring Belle River coal-fired power plant. Between 1999 and 2003, St. Clair's capacity factor averaged 57%, plant heat rate averaged 10,449 Btu/kWh, and the equivalent forced outage rate averaged 18%.

Connections to power grid

The plant is connected to the power grid via numerous 345,000 and 120,000 volt transmission lines. The St. Clair has one 345 kV line (St. Clair-Lambton #1 and one 230 kV line (St. Clair-Lambton #2) that interconnect with Hydro One across the St. Clair River in Ontario, Canada.

Environmental impact

Sulphur dioxide

With its oldest unit dating back to the 1950s, the plant was ranked 74^th on the United States list of dirtiest power plants in terms of sulphur dioxide emissions per megawatt-hour of electrical energy produced in 2006. Sulphur emissions could be lowered by using FGD's, better known as SO₂ "scrubbers", like those of Lambton Generating Station across the St. Clair River. Currently, these scrubbers are being installed at DTE's Monroe Power Plant, and may eventually be added at the St. Clair site as well.

Waste Water

All of the waste heat generated by the plant (about twice its electrical output) is released into the St. Clair River. This water is used in large condensers to cool the used steam back to its liquid form. Water used in the condensers is treated, filtered, and replaced back into the river. Other water used on site for cleaning boilers and to drive the turbines is treated in settling ponds where ash and particulate are suspended from the water. The water is purified and pumped back to the river. The particulate is taken to the St. Clair/Belle River ash landfill a few miles north. As a policy for the plant, all water is replaced in the river cleaner than when it was removed.

References

Aerial views of DTE Energy, St. Clair Power Plant http://www.aerialpics.com/B/stclair.html