PURPOSE: To increase a removal rate of particulates in an effluent gas stream generated in combusting coal by containing a specific volume of a sodium compound solution with low rank coal.

CONSTITUTION: Treatment of coal before combustion is carried out using a spray by contacting a solution, preferably 1 to 70 wt.% concentration, of a sodium compound such as sodium hydroxide with low rank coal such as lignitic bituminous coal, lignite, mud coal at a ratio of sufficient amount of sodium to provide a fly ash having about 1.5 to 3.0 wt.% of Na2O in combustion.