Patent GB-572106-A (GB)
Title: Direct-fired unit air heaters
IPC: F24H3/06
Filed: 1943-08-12
Abstract: 572,106. Air-heating furnaces. DRAVO CORPORATION. Aug. 12, 1943, No. 13068. Convention date, July 29, 1942. [Class 64 (i)] In an air heater comprising an elongated combustion chamber with a source of flame at one end, an outlet for gases at the other, and means for causing air to be heated to stream over its outer surface, a hollow baffle is provided between the source of flame and the outlet, the space in the baffle being open through the walls of the heating chamber. In the form shown in Figs. I and II, the combustion chamber, of which the side walls 1 and, if desired, the end walls 2 are corrugated, is surrounded by an outer casing the walls 4, 5 of which are spaced from those of the combustion chamber. Air is drawn through the space between the two casings by fans 7, and passes to outlets 8. The hollow baffle 26 extends across the full width of the combustion chamber. Its bottom is shaped so as to be higher at the centre of the chamber than at the sides, and is protected by a refractory covering 48. The interior of the baffle is divided by a partition 27 and a series of partitions perpendicular to it into a number of channels leading from inlets in the sides 1 to outlets in the roof of the combustion chamber. Louvres are associated with the inlets to deflect air into the baffle. In a modified form of baffle, air is supplied to it from below the combustion chamber through two vertical pipes. The combustion gases escape from the combustion chamber through pipes 23 leading to a chamber 24 from which the gases are drawn by a fan 25 which may be on the same shaft as the fans 7. The pipes 23 may contain twisted strips. Solid, liquid or gaseous fuel may be used. In the form shown, solid fuel with air from a fan 21 is fed by a stoker through a pipe 19 to a firebox 16 with refractory walls, which may be anchored to the side walls 1 by hooks 37 welded to them and embedded in the refractory material. An air passageway 33 in the rear refractory wall leads from the air space at one side to that at the other. Louvres are provided at each end of this passage. The walls of the combustion chamber are provided with fins 15, 40 of L-shape in horizontal section, the lower ends of the fins being being bent outwardly as at 45 to deflect the rising air towards the walls of the combustion chamber. These fins 15, 40 and an asbestos screen 44 protect the outer walls 4, 5 from radiant heat. Horizontal or vertical pipes for the passage of air may be provided in the space between the baffle and the back of the combustion chamber. In other forms, there is a plurality of hollow baffles like 26 with spaces beneath them for the passage of hot gases, alternating with similar hollow baffles with spaces above them instead of below, so that the hot gases have to take a tortuous path. In those forms, the pipes 23 are dispensed with, and the outlet for the hot gases is at the rear of the apparatus. The air to be heated may be drawn in by the fans at the top of the apparatus, and pass downwardly around the combustion chamber to outlets at the bottom. In that case baffles may be provided between the inner and outer casings to divert air into the hollow baffles within the combustion chamber. In another form, Fig. XXII, the baffles are hollow walls which entirely close the chamber except for openings 55, 56 at the bottom. Alternate baffles have a single central opening 55 and a pair of side openings 56, and further baffles 57 extend between the hollow baffles. Inclined deflectors on vertical partitions in each hollow baffle deflect the downflowing air into contact with the walls of the hollow baffle. The outer casing may be of sheet metal, asbestos board, or other non-metallic material. Specification 554,401 is referred to.