in the direction of the arrows 26 the ascending and rounded shape of the intermediate ceiling at the edges 27 improves the air flow in the circulation channel while preventing breakaway edges which lead to the formation of air turbulence a type of ventilation grid is formed by the approximate grid shaped stock structure of the blanks 25 arranged on the outermost right and left edges of the main tunnel 24 so that the circulated air can flow uniformly through the blanks firing elements may be arranged as far as the bottom blank in the firing zone so they are arranged in the longitudinal channels between the blanks of individual bogies trains running in opposite directions from one another fig3 shows the cross section according to fig2 this is shown in a view that is cutaway at the right and left it can be seen that neighboring circulation channels 22 are separated from one another by side walls 28 in the present exemplary embodiment a fan is provided for each circulating channel 22 which is the length of one furnace bogie when considered in the longitudinal direction fig4 shows the left end of the furnace section according to fig1 in a loading situation and with a loading and unloading device 31 the loading and unloading of the furnace section are performed by transfer stage 32 which has eight tracks and can move crosswise in direction c in the situation indicated with dotted.