They were using old cleaned coal. The on-site coal preparation plant reduced the sulfur and ash content in the coal to be burned by about half. Electostatic preciptators and scrubbers reduced the ash and sulfur dioxide content in the flue gas further. After I left, the scrubbers were enhanced to take out nitrous oxides. The cost of pretreating the coal and post treating the flue gases were the key reason why the coal plants were demolished and replaced with natural gas fired units. That and that the price of natural gas all but fell through the floor while the cost of coal kept increasing.
