The U.S. government yesterday expanded an ongoing legal battle against dirty, coal-burning power plants, adding 12 plants to a lawsuit it filed against utilities in November. The move comes just one day after the feds announced a landmark settlement under which a Florida utility will spend some $1 billion to clean up two dirty facilities. The suit charges that the utilities violated the Clean Air Act by making major modifications to old power plants without installing equipment required to control pollution. Coal-fired plants emit huge amounts of sulfur dioxide, nitrogen oxides, particulate matter, and greenhouse gases, pollutants that contribute to acid rain, smog, global warming, and serious health problems.