Clean Coal is not strictly or legally defined, but refers generally to a Low-sulfur coal. Generally, this refers to a coal or a blend of coals that meets sulfur dioxide emission standards for air quality without the need for flue gas desulfurization.
This will be coal which contains 1 percent or less sulfur by weight. By air quality standards, "low sulfur coal" contains 0.6 pounds or less sulfur per million Btu, which is equivalent to 1.2 pounds of sulfur dioxide per million Btu.
The term Compliance coal is often used alternately to describe clean coal. This classification refers to coal quality and use.
From “The Science and technology Dictionary”
What is “Clean coal Technology”?
This term describes any technology (including use of low sulfur coals) associated with reducing the emissions of sulfur dioxide, nitrogen oxides and other emissions like particulates from coal-based electricity generation.
In action, the U.S. EPA released data on five criteria pollutants (carbon monoxide, volatile organic compounds, sulfur dioxide, nitrogen oxide and particulates) which fell by over 77% per billion kilowatt-hours during the period 1970 to 2005.
How does the cost of coal as a heat energy source compare with other fossil fuels?
The U.S. Energy Information Administration released the following figures for 2008, the last year for which data is available.
The costs of various forms of fossil fuels per million British Thermal Units (BTU), is as follows:
Coal - $2.04/million BTU
Clearly, coal is the most cost effective form of heat energy in the fossil fuel sector.
What is coal worth in the ground?
The in-the-ground value of coal is somewhat subjective, since the value is partially linked to the cost of bringing it to the surface and preparing it for market. However, it remains a good and interesting question.
Liberty Coal Energy has approximately 125 million tons of coal in its two current projects.
Of course, the ultimate cost to produce a saleable product is several times the acquisition number, along with the capital cost to build a mine. Powder river coals are currently selling in the $12 to $15 per ton range, and have been stable or rising. Increased demand should tend to increase the price.