Oak Creek Power Plant expansion

The Oak Creek Power Plant expansion includes two 615-megawatt (MW), coal-fired generating units with an extensive emission-control system. The Oak Creek facility is one of the cleanest and most efficient plants of its type in the United States.

Unit 1 began commercial operation on Feb. 2, 2010, and Unit 2 began commercial operation on Jan. 12, 2011.


The Oak Creek site has a long history of coal-fired power generation. Plans for the original Oak Creek Power Plant began in the late 1940s when energy demand was beginning to outpace the company’s generating capabilities.

In 1950, the company announced plans for a new 500-MW coal-fired power plant to be located in Oak Creek. When the first Oak Creek 120-MW unit was fired on Sept. 30, 1953, it was the largest power unit in Wisconsin. The second unit came on line the following year, and the additional two units that made up what would become known as the north plant, were added in 1956 and 1957.

With demand continuing to grow, plans were announced for an additional four units just south of the new units. The units at the south plant added an additional 1,150 MW upon completion in 1967. A 20-MW combustion turbine was added in 1969, bringing Oak Creek Power Plant’s total energy production to more than 1,600 MW.

In the late 1980s, units 1-4 (the north plant) were retired. Today, the south plant units at Oak Creek remain an integral part of our generation and are being equipped with an advanced emission-control system that will be operational by 2013.

In September 2000, Wisconsin Energy announced its Power the Future plan to meet growing energy demand. The plan included building two 545-MW natural-gas-fired units at the existing Port Washington Power Plant site, three 615-MW coal-fired units at the Oak Creek Power Plant site, improving existing generation and distribution facilities, and increasing renewable energy resources.

On Nov. 10, 2003, the Public Service Commission of Wisconsin issued a final decision authorizing a Certificate of Public Convenience and Necessity for the construction of two new supercritical pulverized coal units at Oak Creek. The third unit, using a technology called integrated gasification combined cycle, was denied because the technology was relatively uncertain at the time and the economics unfavorable for baseload generating purposes.

After almost two years of legal proceedings with project opponents, construction of the state’s largest private building project began on June 29, 2005.

Environmental impact

By 2013, Oak Creek Power Plant emissions, including new and existing units, will be reduced from 2000 levels by approximately 60 percent. The new units employ an advanced combustion technology that increases efficiency by operating at higher pressures and temperatures, resulting in fewer emissions.

The air quality control system on the new units captures more than 85 percent of nitrogen oxides (NOx), 99 percent of particulate matter, 97 percent of sulfur dioxide (SO2) and more than 90 percent of mercury.

Electricity production, emissions reduction

The electricity generating process occurs in several steps. First, coal is burned in a large boiler to make high-pressure, high-temperature steam. The steam turns a series of fan-like wheels connected to a turbine shaft. The spinning turbine then drives the generator to produce electricity.

Specialized equipment is used at different points during the generation process to remove emissions from the new units. The first step in reducing emissions occurs by using a low-NOx burner to burn the coal. This equipment regulates the amount of air needed to effectively burn the coal at a lower temperature, resulting in greater fuel efficiency and lower NOx emissions.

To further reduce NOx emissions, a selective catalytic reduction system (SCR) is used. Within this system, an ammonia solution is injected into the flue gas stream. The NOx in the flue gas reacts with the injected ammonia in the presence of a catalyst, producing nitrogen and water vapor.

The SCR’s efficiency of approximately 70 percent, combined with the low-NOx burners in the boiler, results in 85 percent NOx removal.

After the SCR, the flue gas goes through a baghouse. In the baghouse, more than 17,000 filter bags, each 25 feet long and 6 inches in diameter, capture fly ash and other small particulates. The baghouse captures more than 99 percent of the particulate matter.

Next, the wet flue gas desulphurization (FGD) system, also known as the scrubber, is used to control SO2 and hydrogen chloride, as well as other water-soluble emissions, including mercury. Passing through the scrubber, the flue gas is mixed with a limestone slurry. The limestone slurry reacts with the flue gas and absorbs the SO2 in the flue gas, forming calcium sulfite. Oxygen is blown into the absorber tank causing a chemical reaction that converts the calcium sulfite into calcium sulfate, also known as synthetic gypsum. The gypsum slurry is then dewatered and used as a valuable byproduct to make wallboard for construction projects and in agriculture to maintain chemical balances between soil, water and plants. The scrubber captures more than 97 percent of the SO2 in the flue gas.

The last piece of air quality control equipment on the new units is the wet electrostatic precipitator (WESP). The WESP removes sulfuric acid mist, aerosols and fine particulates from the flue gas. The WESP consists of a series of electrically charged collecting plates located in the casings of the WESP that capture the emissions. The plates are continuously washed with spray water to remove the collected material. This material is routed to the wet FGD system and is not a waste product. The WESP captures more than 94 percent of the sulfuric acid mist, aerosols and fine particulate matter from the flue gas.

Although there is no specific piece of equipment to remove mercury, the combination of bituminous coal, SCR, baghouse and wet FGD system results in a mercury removal efficiency of more than 90 percent.

Flyash and bottom ash are products of the coal combustion process for making electricity. At the Oak Creek expansion project, the flyash captured in the baghouse is used in various construction activities, including a replacement for Portland cement in concrete and a sludge stabilization additive at sewage treatment projects. Bottom ash is removed through the bottom of the boiler using a hydraulic removal system, and is used primarily as base material in road construction projects.

Air monitoring

To ensure the site is in compliance with all ambient air regulations, two air-monitoring stations are installed near the site. The first station monitors dust and fine particulate, and the second monitors SO2 and NOx. The data and reports are provided to the communities of Oak Creek and Caledonia and to the Wisconsin Department of Natural Resources.

Each generating unit also is equipped with monitors to ensure continuous examination of emissions during operation.

Oak Creek Expansion Units 1 and 2 fact sheet
View the DNR Chapter 30 permit for the Oak Creek project
(Permit conditions begin on page 20)