Coal breaker remaining. The sorting by size is particularly important for anthracite coal. In order to burn efficiently, air must flow evenly around anthracite. Subsequently, most anthracite coal is sold in uniform sizes. In the 1910s, there were six commercial sizes of coal (with the smallest size having three subsets): Coal pieces smaller than in size were considered "culm," and unable to be separated from the impurities (and thus useless). The grade of coal ranged from a low of 5 percent impurities for steam or broken coal to a high of 15 percent for pea-size coal and its subsets. Coal breakers were
Coal power in the United States and put pressure on older plants. In 2007, 59 proposed coal plants were cancelled, abandoned, or placed on hold by sponsors as a result of financing obstacles, regulatory decisions, judicial rulings, and new global warming legislation. The Stop Coal campaign has called for a moratorium on the construction of any new coal plants and for the phase out of all existing plants, citing concern for global warming. Others have called for a carbon tax and a requirement of carbon sequestration for all coal power plants. The creation in January 2009 of a Presidential task force (to look at ways to