MADISON, Wis. (AP) – The owners of one of Wisconsin’s largest coal-fired power plants want to spend $150 million on more pollution control equipment. Alliant Energy, Madison Gas and Electric and Wisconsin Public Service Corp. filed a proposal with state regulators Wednesday to add a selective catalytic reduction system to one of the two units at the Columbia Energy Center near Portage. The project is needed to comply with terms of a settlement Alliant subsidiary Wisconsin Power and Light reached with the U.S. Environmental Protection Agency and the Sierra Club. It’s designed to reduce the unit’s nitrogen oxide emissions by 50 percent. It would be completed in 2018. Work is expected to be completed this fall on a $625 million system to reduce sulfur dioxide and mercury emissions from both units at the plant.