HEATING STOCK IN A HEATING CHAMBER

Abstract: A method for heating stock comprises feeding stock 9 to be heated into a heating chamber 1, causing heating gas to enter the heating chamber 1 to heat the stock 9 and leave the heating chamber 1 after heating the stock 9 and then removing the stock 9 from the heating chamber 1 on completion of heating, the heating gas being allowed to enter the heating chamber 1 by way of a plenum chamber 2,3 which communicates with the heating chamber 1. The heating gas may be supplied by a regenerative burner 4,5 as fuel combustion products. Where there are two such burners 4,5 one may be firing while the other is flueing.

Description: This invention relates to apparatus for heating stock and also to a method for heating stock in the apparatus. The apparatus for heating stock is of a type (hereinafter called the type referred to) comprising an elongate heating enclosure for receiving stock for heating with heating gas, said enclosure having a floor and a roof over the floor and two spaced opposite sides extending between said floor and roof, an elongate first plenum chamber disposed outside the heating enclosure and extending adjacent to a said side, an elongate second plenum chamber disposed outside the heating enclosure and extending adjacent to the other said side, means to provide said plenum chambers with said heating gas, and passages opening into the heating enclosure to allow heating gas from the plenum chambers to enter said heating enclosure. DE-C-3339585 discloses apparatus of the type referred to in which a third plenum chamber is coextensive with the first plenum chamber which is innermost in relation to the third plenum chamber and is separated therefrom by a vertical wall having a plurality of connecting ports through its lower part connecting the outer third plenum chamber with the inner first plenum chamber. A fourth plenum chamber is co-extensive with the second plenum chamber which is innermost in relation to the fourth plenum chamber and is separated therefrom by a vertical wall having a plurality of connecting ports through its lower part connecting the outer fourth plenum chamber with the second plenum chamber. Each opposite side of the heating enclosure has two sets of openings therethrough, each set being constituted by a plurality of openings opening into the adjacent inner first or second plenum chamber and arranged along the length of that plenum chamber; one set of openings being disposed adjacent to a roof of the corresponding first or second plenum chamber and the other set being disposed adjacent to a floor of the corresponding first or second plenum chamber. Horizontal distribution tubes of rectangular cross-section extend from each of the two opposite sides of the heating enclosure towards the opposite side and each distribution tube terminates in a dead-end just before it reaches the middle of the heating enclosure. Each aforesaid opening opens into the other end of a respective one of the said distribution tubes. The distribution tubes are divided into two groups, an upper group and a lower group. The roof of the heating enclosure comprises the distribution tubes of the upper group. The floor of the heating enclosure comprises the distribution tubes of the lower group. Each third or fourth plenum chamber has a respective outer side wall in which a plurality of fuel gas burners are disposed so that the hot products of combustion or heating gas generated simultaneously in each outer third and fourth plenum chamber passes through the connecting ports into the adjacent first or second plenum chamber and from the first and second plenum chambers into the distribution tubes. Each distribution tube in the upper group has a plurality of outlet nozzles in the bottom wall of the tube, and each distribution tube in the lower group has a plurality of outlet nozzles in the upper wall of the tube. Thus heating gas enters the heating enclosure through nozzles directed downwards from the roof and upwards from the floor of the heating enclosure. The plenum chambers and the groups of distribution tubes are disposed over about 38% of the total length of the heating enclosure starting at the work discharge end of the heating enclosure. Beyond that 38% length of the heating enclosure is the remainder of the heating enclosure extending up to the work receiving end. The roof over this remainder is mainly raised and is provided with a plurality of gas burners firing directly into the heating enclosure. Waste gas emerging from the heating enclosure is passed through a recuperative heat exchanger where the waste gas gives up heat to combustion air supplied along first and second supply lines each comprising a respective blower and a regulating valve. The first supply line feeds heated combustion air though the openings in the roof of the third plenum chamber whilst the second supply line simultaneously feeds heated combustion air through the openings in the roof of the fourth plenum chamber. From DE-C-3339585 it will be understood that there are at least two gas burners heating the heating enclosure where the roof is raised and at least two burners heating each of the third and fourth plenum chambers making a total of at least six burners to heat the heating enclosure. It would be an advantage, and also simplify the burner control system, if the number of burners needed to heat the enclosure could be reduced. Also since the front 62% of the length of the heating enclosure is heated by a markedly different system to that heating the rear 38% there is a problem in attaining a uniform distribution of heating gas throughout the heating enclosure. Also it would be an advantage if heat from the waste gas could be more efficiently transferred to the combustion air supplied to the plenum chambers. With a view to improving the chance of obtaining the aforementioned advantages and improving the chance of attaining a more uniform distribution of heating gas through the heating enclosure there is provided according to the invention apparatus for heating stock comprising an elongate heating enclosure for receiving stock for heating with heating gas, said enclosure having a floor and a roof over said floor and two spaced opposite sides extending between said floor and roof, an elongate first plenum chamber disposed outside the heating enclosure and extending adjacent to a said side, an elongate second plenum chamber disposed outside the heating enclosure and extending adjacent to the other said side, means to provide said plenum chambers with said heating gas, and openings opening into the heating enclosure to allow heating gas from the plenum chambers to enter said heating enclosure, wherein said first and second plenum chambers each extend along the length of the heating enclosure, a plurality of first ports communication the first plenum chamber with said heating enclosure into which the first ports open through a said side wall and each first port being disposed at a different position from the others so that the first ports are arrayed along the length of the heating enclosure, a plurality of second ports communicating the second plenum chamber with said heating enclosure into which the second ports open through the other said side wall and each second port being disposed at a different position from the others so that the second ports are arrayed along the length of the heating enclosure, each of said first and second plenum chambers having an opening at at least one end thereof, a first regenerative type burner communicating with the opening at said end of the first plenum chamber, a second regenerative type burner communicating with the opening at said end of the second plenum chamber, each burner being adapted to operate in a firing mode and in a flueing mode such that in the firing mode the burner supplies heating gas to its plenum chamber for subsequent distribution to the heating enclosure for heating the stock and in the flueing mode the burner receiving from its plenum chamber waste gas discharged from the heating enclosure, the arrangement being that, in use, when one burner is operating in the firing mode the other burner is operating in the flueing mode. An embodiment of the invention will now be particularly described with reference to the drawings in which:- Figure 1 is a side elevation partly in section of an apparatus for heating stock, and Figure 2 is a view along the lines II-II of Figure 1. Referring to the drawings, the apparatus comprises a heating chamber 1, two plenum chambers 2,3, each communicating with the heating chamber 1 and a pair of regenerative type burners 4,5, one burner communicating with a matching plenum chamber. The heating chamber 1 comprises an elongate generally rectangular or circular cross section furnace which is designed to reheat metal stock such as large section round or square billets. The chamber 1 forms an elongate enclosure to receive the stock to be heated such as a long billet (e.g. an aluminium log) or a multiplicity of billets (such as those used in forging or extrusion). The enclosure 6 is closed at either end by doors 7 and 8 which are raisable vertically to permit entry and discharge of a billet (such as that shown by reference 9). The billet 9 enters via door 7 and leaves via door 8. The floor 10 of the enclosure 6 is provided with a means of stock conveying such as driven rolls 11 along which the billet 9 can be moved into and out of the enclosure 6. Along opposite sides of the heating chamber and of the same length, are the plenum chambers 2,3, each of which forms a generally cylindrical bore 14 extending parallel to the adjoining side of the furnace and each of which communicate with the heating chamber 1 by way of several longitudinally spaced ports 15 along the length of the heating chamber 1. The plenum chamber 2 is displaced slightly vertically below the plenum chamber 3 and the plenum chambers 2,3, and the heating chamber 1 are refractory lined 16 and contained in an outermost casing 17. Each plenum chambers 2,3 is either closed at one end (not shown) and is provided at the other end with a regenerative type burner 4,5 each of which is arranged adjacent opposite ends of the heating chamber 1 or provided with regenerative type burners on both ends. The regenerative burners 4,5 are of conventional construction and comprise a fuel-fired burner 18 and associated regenerator chamber 19. In a firing mode each regenerative burner supplies its plenum chamber with heating gas in the form of fuel combustion products. In a flueing mode each burner receives waste gas from its plenum chamber for subsequent discharge. The regenerator chamber 19 communicates with the burner part 18 by way of a duct 20. During firing the regenerator chamber 19 supplies the burner part 18 with preheated air by way of the duct 20 for combustion with fuel, e.g. natural gas supplied to the burner part 18 by a fuel pipe 21. The air for preheating in the regenerator 19 is supplied to the regenerator 19 by a pipe 22. During flueing waste gas entering the burner part 18 is discharged to the regenerator chamber 19 by way of the duct 20 and is discharged from the regenerator 19 way of the pipe 22. In use, the stock heating can either be "batch" or "continuous" depending upon the process requirements. In the "batch" mode, which would be used for heating single long metal billets, one burner would fire into its plenum chamber for the complete heating cycle of the one billet within the heating chamber. The other plenum chamber would act as a manifold for receiving the waste combustion products from the heating chamber with the other burner operating in a flueing mode. On completion of the heating cycle the firing burner could be shut down whilst the heated billet was removed from the heating chamber which would be recharged with cold stock. On restart the burner which had previously been flueing would now fire while that burner which had previously been firing would now serve as a flue. This cycle would be repeated. In "continuous" mode which could be used for heating short billets where the heating chamber would contain a large number of individual billets, each burner firing period could be of predetermined duration, possibly to coincide with the discharge interval of the stock, or alternatively, the firing period could be controlled by the temperature of the waste gases leaving the regenerator of the burner which is flueing. The provision of the plenum chambers along the sides of the heating chamber enables the heating gas to be distributed to the heating chamber in a far more uniform manner than would be the case if as conventional the burners were to be firing directly into the heating chamber. Furthermore, the provision of plenum chambers enables the number of burners per particular heating chamber to be reduced together with the number and complexity of controls.

Claims: Apparatus for heating stock comprising an elongate heating enclosure (6) for receiving stock (9) for heating with heating gas, said enclosure having a floor (10) and a roof over said floor and two spaced opposite sides extending between said floor and roof, an elongate first plenum chamber (2) disposed outside the heating enclosure and extending adjacent to a said side, an elongate second plenum chamber (3) disposed outside the heating enclosure and extending adjacent to the other said side, means (4,5) to provide said plenum chambers with said heating gas, and openings (15) opening into the heating enclosure (6) to allow heating gas from the plenum chambers (2,3) to enter said heating enclosure, wherein said first and second plenum chambers (2,3) each extend along the length of the heating enclosure (6), a plurality of first ports (15) communicating the first plenum chamber (2) with said heating enclosure (6) into which the first ports open through a said side wall and each first port being disposed at a different position from the others so that the first ports are arrayed along the length of the heating enclosure (16), a plurality of second ports (15) communicating the second plenum chamber (3) with said heating enclosure (6) into which the second ports (15) open through the other said side wall and each second port (15) being disposed at a different position from the others so that the second ports (15) are arrayed along the length of the heating enclosure (6), each of said first and second plenum chambers (2,3) having an opening at at least one end thereof, a first regenerative type burner (4) communicating with the opening at said end of the first plenum chamber (2), a second regenerative type burner (5) communicating with the opening at said end of the second plenum chamber (3), each burner (4,5) being adapted to operate in a firing mode and in a flueing mode such that in the firing mode the burner (4 or 5) supplies heating gas to its plenum chamber (2 or 3) for subsequent distribution (15) to the heating enclosure (6) for heating the stock (9) and in the flueing mode the burner (4 or 5) receiving from its plenum chamber (2 or 3) waste gas discharged (15) from the heating enclosure (6), the arrangement being that, in use, when one burner (4 or 5) is operating in the firing mode the other burner (5 or 4) is operating in the flueing mode. Apparatus for heating stock as claimed in Claim 2, wherein each burner (4 or 5) fires heating gas into its plenum chamber (2 or 3) or receives waste gas therefrom in a direction parallel to the adjacent said side of the heating enclosure (6). Apparatus for heating stock as claimed in Claim 1 or Claim 2, wherein the first ports (15) open into the heating enclosure (6) at positions adjacent to the roof and the second ports (15) open into the heating enclosure at positions adjacent to the floor (10). A method of heating stock in apparatus as claimed in any one of Claims 1 to 3, wherein stock (9) to be heated is fed into the heating enclosure (6), heating gas is caused to enter the heating enclosure (6) from one of the burner arrangements (4 or 5) to heat the stock and leaves the heating enclosure (6) after heating the stock (9) and passes through the other burner arrangement (5 or 4), and the stock (9) is removed from the heating enclosure (6) on completion of heating.

Inventors: WADDINGTON, JOHN DORIAN
Applicants: BRITISH GAS PLC
Application year: 1987
Main classification: C21D9
IPC codes: B21J17, C21D1, F27B17, C21D9