coal is first fed into the oven chamber through a plurality of first filling units of a charging truck into first filling openings until the bases of the resultant cone - shaped charges are approximately in contact . thereafter , coal is fed through a plurality of second filling units of the charging truck into a plurality of second filling openings positioned between adjacent first filling openings . the above operations are repeated until the oven chamber is filled . the coarser coal is thus distributed in a plurality of diagonal layers in the oven chamber . filling gas is removed from the oven chamber during feeding through filling openings and filling units of the charging which are not being employed for feeding .