Heat processing apparatus

Abstract: Apparatus for heat processing scrap materials, particularly for de-contaminating aluminium can scrap, as shown in the single drawing, has a rotary kiln (10) defining a furnace chamber (12) along which the material is fed; with hot gas circulation means including a duct (32) leading through the chamber from the input end to an enclosure (24) at the output end from which the gases pass back in contra-flow to the material through the furnace chamber itself to return to the input end, the remaining parts of the gas circulation means, typically including an after burner (42) through which the exhausted gases are recirculated, being at the input end of the furnace to provide a compact unitary and readily adaptable construction in which heat losses are minimised.

Description: This invention relates to apparatus for heat processing metal scrap materials in the recovery of their useful constituents and removal as by vapourization or burning of contaminants such as lacquer or paint coatings. The invention is particularly but not exclusively applicable to the recycling of metal containers typically aluminium or aluminium alloy beverage cans. An apparatus as defined in the preamble of claim 1 is disclosed in GB-A-2 229 801. Thus, it is known to provide said apparatus incorporating a heated furnace kiln through which the scrap material is passed, with circulation of hot gases through the kiln in a closed circuit for said vapourization or burning of contaminants. GB-A-0151518 describes a rotary drying drum having a furnace connected to the end for infeed of hot gases which pass down a duct along the centre of the drum to return to the same end along the space between the duct and the drum outer wall. Material is fed through said one end into said space to be acted on by the hot gases but there is no fixed structure or provision for material outflow at the other end to enable continuous treatment of a through flow of material. Also the outgoing gases are exhausted to atmosphere by a suction fan without recirculation or any provision for removing contaminants. The object of the present invention is to provide heat processing apparatus for the above purpose, incorporating a rotary kiln, which is economical to manufacture and install, compact, adaptable in design, and effective and efficient in operation. According to the invention there is provided apparatus for heat processing metal scrap material as defined by Claim 1 of the appended claims. An embodiment of the invention is now more particularly described with reference to the accompanying drawing being a diagrammatic longitudinal sectional elevation of apparatus for heat processing aluminium alloy beverage can scrap for removal from the shredded scrap material of lacquer coating and other contaminants prior to recovery and remelting of the metal content for recycling. The apparatus comprises a rotary kiln 10 defining an enclosed furnace chamber 12. The axis of the kiln is inclined so that it slopes downwardly from its material input end 14 to its material output end 16 i.e. from left to right as viewed in the drawing, the extremities of the rotating kiln being provided with airtight seals 18,20 connecting it with respective non-rotating upper and lower enclosure formations 22,24 at said respective ends in conventional manner. The scrap material is fed into the chamber from a hopper or the like (not shown) through a delivery chute 26 opening into inlet end 14 to pass along a feed path through the rotating kiln, exiting from a discharge chute 28 at the output end 16 to drop onto a conveyor 30. Gas circulation means of the apparatus comprises an inlet duct 32 extending co-axially of chamber 12 through the rotating kiln 10 to open into said chamber within closure formation 24 i.e. at the material output end of the chamber. Duct 32 is conveniently mounted for rotation with kiln 10, its upper end opening through the end wall of the closure formation 22 at the material input end of the chamber by way of a further airtight seal 34. Heated gases at controlled temperature are fed into duct 32 from an ante-chamber 36 defined by fixed structure of the gas circulation means all of which is at or immediately adjacent to said material input end 14. It is preferred that the gas flow within chamber 12 is operated at negative pressure, i.e. less than ambient atmospheric pressure in the manner described in our said co-pending application GB-A-2229801 to avoid any escape of contaminated gases e.g. if there should be any leakage past the various seals. Said negative pressure is induced by a centrifugal fan 38 in an outlet flue 40 opening from the top of closure formation 22 at the material input end 14 of chamber 12. Thus the circulation of hot gases through chamber 12 is firstly along duct 32 not in direct contact with the material flow but supplying indirect heat by radiation from the exterior of duct 32, then by flow in direct contact with the material from end 16 up to end 14 i.e. in the opposite direction to the travel of the material through kiln 10 to be exhausted from said chamber through flue 40 under the action of fan 38. Flue 40 opens into the upper end of a vertical after burner chamber 42 disposed alongside ante-chamber 36 and containing a gas fuelled or other burner head 44, the temperature in chamber 42 being such that the lacquer and other contaminant content of the exhaust gases is further broken down at a higher temperature than that in the kiln chamber 12. The gases exiting from the bottom of chamber 42 pass into the ante-chamber 36, a proportion thereof being recirculated through the kiln chamber 12 as described above and a proportion being led off from ante-chamber 36 through a branch duct 46 for after-treatment and eventual disposal. Provision (not shown) may be made for cooling the gases fed into furnace chamber 12. Delivery chute 26 is preferably arranged so that the material passing therethrough is preheated, e.g. in part by radiant heat from the upper end of inlet duct 32, for drying the material and raising its temperature before it enters the chamber 12, again providing increased efficiency of operation and minimising heat loss. It will be seen that substantially the whole of the gas circulation means other than the parts actually contained within chamber 12 are located at or immediately adjacent to the material input end 14 thereof. Thus external duct work is reduced to a minimum so saving cost and labour in manufacture and installation and also enhancing operative efficiency by reducing heat loss. The compact construction also saves space and facilitates control and monitoring of operation. Control means (not shown) are provided for monitoring and regulating the operating temperatures in chamber 12 and elsewhere, regulating the flow rate of the gases etc as described in our said application GB-A-2229801. Moreover standard gas circulation means or components thereof and related and ancillary equipment can be employed without any substantial modification to serve a range of sizes of rotary kiln, in particular the axial length of kiln 10 and the associated inlet duct 32 can readily be varied by merely altering the spacing between the external parts of the gas circulation means and the stationary enclosure formation 24 at the material output end 16 remote from the circulation means, no rearrangement or reconstruction of external ducting or the like being necessary. Apart from the features referred to above the manner of operation and its automatic control and monitoring will be effected substantially as described in our said co-pending application GB-A-2229801 to which reference is made for further detail.

Claims: Apparatus for heat processing metal scrap material contaminated with coating substances to purify and recover the metal content and to degrade or destroy the contaminants with minimum atmospheric pollution, said apparatus comprising: a kiln structure defining an enclosed furnace chamber (12) having a feed path extending therethrough from a material input end (14) to a material output end (16) of the chamber: and gas circulation means (36,38) for providing a flow of heated gases into and through the chamber to act directly on the material in said feed path in use to purge the contaminants therefrom, said kiln structure including; a rotating kiln (10) defining the major part of said chamber and feed path, a first non-rotative enclosure formation (22) through which a material inlet (26) opens into the input end of the chamber, which formation is connected through an air tight seal (18) to the input end of said kiln, and from which opens an outlet flue through which the gases exit from the chamber, and a second non-rotating enclosure formation (24) from which a material discharge outlet (28) opens from the output end of the chamber, which formation is connected through an airtight seal (20) to the output end of said kiln ; a recirculation connection (40) externally of the kiln structure and at or adjacent said first enclosure formation thereof for operative recirculation of at least part of the gases exhausted from the furnace through said flue to an inlet duct (32), said recirculation connection including flow inducing means (38) acting to exhaust said gases from the input end of the furnace chamber whereby the gas flow pressure within the chamber is less than that of the ambient atmosphere in use, and an after burner (42,44) for high temperature disposal or breaking down of the contaminant content of the gases so exhausted in use. said gas circulation means including said inlet duct (32), characterised in that the inlet duct (32) extends through said first formation (22) and coaxially through the kiln to open into the chamber in said second enclosure formation (24) and adjacent the output end, whereby the whole of said flow of gases returns through the furnace chamber from the latter end to the input end in direct contact with the material travelling in the opposite direction along said feed path in use. Apparatus as in Claim 1 characterised in that the rotating kiln (10) is centred on an inclined axis to facilitate the feed of material therethrough with the first formation (22) at the upper end and the second formation (24) at the lower end. Apparatus as in Claim 2 characterised in that the inlet duct (32) rotates in common with the kiln. Apparatus as in Claim 1 characterised in that the circulation means includes control means for regulating the operating temperature of said gases. Apparatus as in Claim 1 characterised in that the circulation means includes cooling means acting on the gases fed to the inlet duct (32) in use to reduce their temperature to a predetermined level. Apparatus as in Claim 1 characterised in that said material inlet (26) leading to said input end of the chamber (12) is a chute disposed so as to be subjected to heat from the gas circulation means whereby the material is operatively preheated for entry to the chamber.

Inventors: PERRY OPHNEIL HENRY, RILEY GEOFFREY, PERRY, OPHNEIL HENRY, RILEY, GEOFFREY
Applicants: STEIN ATKINSON STRODY LTD, STEIN ATKINSON STORDY LIMITED
Application year: 1992
Main classification: C22B21
IPC codes: B03B9, C22B1, C22B21, F27D13