1.Pre-combustion is get rid of impurities, such as dust from coal, rubble and debris, inorganic compounds, such as Pyritic. Sulfur to reduce the amount of ash and sulfur. The cleaning method such as
1.1 Physical Cleaning is the separation of substances that don't need, such as dust, debris, rubble and Pyritic Sulfur from flesh coal.
1.2 Chemical Cleaning is the use of chemical leaching properties minerals and organic sulfur. Which cannot be removed by the cleaning method physical chemical methods such as Molten Caustic Leaching