Air quality control projects


Our Power the Future (PTF) projects invested in advanced power generation, renewable energy resources and improvements at existing power plants. The investments have allowed us to further reduce sulfur dioxide (SO2), nitrogen oxide (NOx) and particulate emissions, which began their steady reduction in the 1980s. Our implementation of new technologies at our generation facilities help us meet new state and federal air quality requirements while maintaining cost-effective reliability for our system.

Pleasant Prairie Power Plant

As part of our commitment to upgrade environmental performance, a new state-of-the-art Air Quality Control System (AQCS) was added to the Pleasant Prairie Power Plant. A selective catalytic reduction system was put in place to reduce NOx emissions, and a flue gas desulfurization system was constructed to reduce SO2.
Read more about the Pleasant Prairie project (PDF 437k)

Oak Creek Power Plant

A new AQCS was completed at Oak Creek Power Plant in 2012, which cut SO2 emissions by 80 to 90 percent and NOx emissions by 60 to 70 percent.
Read more about the Oak Creek project

How we produce electricity while reducing emissions

The process of generating electricity occurs in several steps. First, coal is burned in a large boiler to make high-pressure, high-temperature steam. A turbine converts the thermal energy in the steam to mechanical energy. The spinning turbine then drives the generator to produce electricity.

Specialized equipment is used at different points throughout the generation process to remove emissions from the units. The first step in reducing emissions occurs by utilizing a low NOx burner to burn the coal. This equipment regulates the rate of combustion of the coal by controlling the amount of air available at different elevations within the boiler to complete the combustion. This results in lower NOx emissions.

After exiting the boiler, the flue gas goes through an electrostatic precipitator (ESP). In the ESP, a series of positively charged collection plates, remove negatively charged particulate matter from the flue gas. The ESP captures more than ­­99 percent of the particulate matter in the flue gas.

Next, the wet flue gas desulfurization (FGD) system, also known as the wet FGD or “scrubber,” is used to control SO2 and hydrogen chloride, as well as other water-soluble emissions. As the flue gas passes through the scrubber, it is mixed with limestone slurry. The limestone reacts with the flue gas and absorbs the sulfur dioxide in the flue gas, forming calcium sulfite. Air (oxygen) is blown into the absorber tank causing a chemical reaction which converts the calcium sulfite into calcium sulfate or synthetic gypsum. The gypsum slurry is then dewatered and can be used as a valuable product to make wallboard for construction projects.

To reduce NOx emissions even further, a selective catalytic reduction system (SCR) is employed. 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.