Pulverized fuel furnace of the vertical axis cyclone type

Claim 1

A PULVERIZED FUEL FURNACE HAVING A VERTICAL CYCLONE TYPE COMBUSTION CHAMBER INCLUDING A TOP GAS OUTLET DUCT AXIALLY IMMERSED IN SAID CYCLONE TYPE CHAMBER WITH THE WALLS OF SAID DUCT BEING SPACED FROM THE WALLS OF SAID CHAMBER AND COMPRISING INTERNALLY COOLED TUBES IN SIDEBY-SIDE RELATION; MEANS FOR TANGENTIALLY DISCHARGING FUEL AND AIR INTO THE SPACE BETWEEN SAID DUCT AND THE WALL OF SAID COMBUSTION CHAMBER FOR BURNING SAID FUEL IN SAID CHAMBER AND FOR PRODUCING A ROTATING STREAM OF COMBUSTION GASES; THE WALL OF SAID GAS OUTLET DUCT HAVING A LOWER EDGE DEFINING AN AXIAL OPENING FOR RECEIVING SAID ROTATING STREAM OF GASES; SAID DUCT WALL COMPRISING A WAVE-LIKE SURFACE PROVIDED ON THE INSIDE THEREOF WITH ALTERNATE RIDGES AND VALLEYS GENERALLY EXTENDING IN AN AXIAL DIRECTION AND UNIFORMLY DISTRIBUTED OVER THE PERIPHERY OF SAID DUCT WALL; MEANS FORMING IN THE BOTTOM OF SAID VALLEYS RESTRICTED OPENINGS SURROUNDED BY DUCT WALL PORTIONS; SAID OPENINGS EXTENDING THROUGH SAID WALL, BEING LONGITUDINALLY ELONGATED AND OF SUCH SIZE AS TO PERMIT ONLY A MINOR FLOW OF GASES THERETHROUGH.