Abstract: A screw-conveyor or auger feed and associated leveling system for underfeed stoker troughs receiving particulate, cominuted, or chunk material, such as "green" coal, by way of example, this for assuring a uniformly rising level of material relative to the trough. The stoker structure herein includes combustion beds which are air perforate and kept this way through periodically rising members such as tuyeres which shear or break up clinker-formation on such beds. A pneumatically-operated system may preferably be used to actuate such movable tuyeres relative to such combustion beds. Combustion air flows through the combustion beds upwardly but not over the trough; hot gasses rising rapidly from the combustion beds confine volatiles gently rising vertically from the cone within the trough for complete combustion, essentially eliminating smoke-production thereat.