Houston Chronicle: When natural gas prices soared in recent years, long-range planners for American utilities increasingly turned to coal-fired plants as the most economic way to address rising consumer demand for electricity. Because the U.S. has extensive deposits of coal, it was also touted as one way to help achieve domestic energy independence from foreign sources. As a result, dozens of new coal plants are on drawing boards around the country. Unfortunately, the cheap coal they are premised on may …