with fuel-supporting surfaces having fuel advancing elements that are movable, but remain essentially in the same place, e.g. with rollers or reciprocating grate bars

Full Title

Combustion apparatus with driven means for agitating the burning fuel; Combustion apparatus with driven means for advancing the burning fuel through the combustion chamber > with movable, e.g. vibratable, fuel-supporting surfaces; with fuel-supporting surfaces that have movable parts > with fuel supporting surfaces that are specially adapted for advancing fuel through the combustion zone > with fuel-supporting surfaces having fuel advancing elements that are movable, but remain essentially in the same place, e.g. with rollers or reciprocating grate bars