Patent GB-287623-A (GB)
Title: Improvements in or relating to ovens of the direct flame continuous tunnel type
IPC: F27B9/30
Filed: 1926-12-22
Abstract: 287,623. Williamson, J. Dec. 22, 1926. Tunnel furnaces and kilns. -In a continuous tunnel oven of the direct flame type in which the gases from the firing zone are employed to preheat incoming goods indirectly, i.e. without actual contact with the goods, there is provided, in connection with side flues for taking off the gases from the firing zone, a system of dampers bv which the course of the flame through the goods can be varied in the longitudinal and transverse directions. The firing zone D, Fig. 2a, is heated by burners 1 supplied through damper-controlled passages 2, 4 with gas and air from main ducts 3, 5, the flames passing downwardly through the goods G and entering side offtake flues 11 through apertures 10. The flues 11 are provided with supplementary ports 14, 15, supplied with gas and air respectively from sources separate from those feeding the main burners 1, for reheating the gases before they pass into the continuations 11<a>, 11<b>, 11<c>, of the flues 11 which extend to the entrance end of the oven. The flues 11<c> are formed by cast iron pipes screened from the oven by partitions 19 the spaces between which and the oven walls are divided by vertical walls 20 into compartments, into the first x of which air is admitted at 22. The air passing upwardly through x enters the tunnel at 24, passes downwardly through the freshly charged goods and enters the second compartment at 25 to be again reheated by contact with the pipes 11<c>. After traversing in this manner the length of the preheating zone A, the air passes into a flue 27 through which it is drawn by a fan 13 into the chimney 12, this latter also receiving the waste gases from the flues 11<c> when the dampers 37, 38 are open. The flue 27 is extended over the section B of the oven and receives, through openings 28, vapours and moisture evolved by the goods. The flues 11<a>, which may also have supplementary burners, are adapted to be cut off from the flues 11 by dampers 33, 34, Fig. 2a, and to be placed in communicaton with the oven by dampers 35, 36. The oven may be fired from one or both sides by setting the gas and air dampers 6, 7 accordingly, and, by suitable manipulation of the dampers 33 - - 38, the flame may be caused to pass through the goods in a transverse, diagonal, or longitudinal direction; alternation of the flame from one side of the oven to the other can be effected by alternate actuation of the members comprising each pair of dampers. The burners 1 in the firing zone are separated by walls 40, Figs. 2a, 10, which are formed to provide for the flame upwardly expanding spaces which at the top are of a length equal to that of a truck 9. The air supplied to the burners 1 is heated in a sealed space below the trucks 9, being forced through this space and into the ducts 5 by nozzles 66, Figs. 3, 10, which project into bent conduits 67 from pipes 65 supplied with air or steam under pressure. The air supply to the supplementary burners in the flues 11 is taken from overhead flues 16 communicating with recuperators 42 arranged at the entrance to the cooling zone E and having valve-controlled inlets from the external atmosphere. Incorporated in the oven roof near the recuperators 42 is a water-heater 44 through which the kiln atmosphere continuously circulates, the water from this heater serving, if desired, as feed-water for a watertube boiler disposed at the entrance end of the oven and traversed by the waste gases on their way to the atmosphere. The cooling in the latter part of the zone E is effected partlv by direct contact with the goods of cold air admitted through openings 47 and escaping through apertures 48 to a roof flue 49, and partly by indirect transfer of heat by means of air circulating through the goods and over a flue system 18 similar to that in the preheating zone A. The tubes 18<b> of this system communicate with the atmosphere at 51, Fig. 1<b>, and the air heated therein passes either to the atmosphere through flue 49 and chimney 50 or to the recuperators 42. The latter may also receive air from the space below the trucks 9 through pipes 67<a>, Fig. 10, the pressure conduits 65 being extended into the cooling zone for this purpose. The hot air flues 16 are formed with outlets delivering into the oven space above the flues 11. When the goods being fired require salt-glazing, the salt is supplied immediately above the burners 1 through earthenware pipes 56<a>, Fig. 3, communicating with hoppers 58 and fitted with screw feeders 57. According to another construction the salt is fed by a rotary pocketed drum from hoppers to inclined shoots extending through the roof of the oven. Fig. 13 shows a modified form of oven in which the flames from the burners 1 enter below the flues 11, the gases passing upwardly through the goods and entering the side flues 11 at the tops thereof. In the construction shown in Fig. 15, which is suitable where the lateral space for the oven is limited, the flues 11 are of rectangular section and their outer walls are formed by the adjacent walls 70 of the oven, the supply passages 4<x> from the air ducts 5 extending upwardly through these flues. In this case the oven is formed with a double crown to provide a combustion chamber 75 from which the flames pass to the oven through openings 76 in the lower crown 73. A similarly constructed modification of the oven shown in Fig. 13 is also described. Solid fuel or oil may be used instead of gas.