Due to the water-cooled side expansion developed by KBS-Feuerungstechnik and protected by a US patent (for the structure), a redirection of the primary air from the lower area of the grate frame, with the existing ash funnels, via the side support boxes into the combustion chamber is prevented to over 90%.

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The side boxes are pressed against the right and left sides of the grate track with a predefined pretensioning force by means of existing pretensioning elements; this measure prevents an excessive gap in the side area of the furnace grate.