A method of removing impurities from heavy fuel includes providing a first stationary adsorption column. The method further includes packing adsorbent particles that have a particle size distribution wherein at least about 50% of the particles have a diameter greater than about 18 microns in the first column. The method further includes diluting heavy fuel with a solvent to form a solvent-fuel mixture, and supplying the solvent-fuel mixture through the first column to facilitate removing impurities from the mixture.