GB2216640A

GB2216640A - Scrap melting furnace

Info

Publication number: GB2216640A
Application number: GB8905287A
Authority: GB
Inventors: Roy Hall
Original assignee: CONEBRIGHT Ltd
Current assignee: CONEBRIGHT Ltd
Priority date: 1988-03-08
Filing date: 1989-03-08
Publication date: 1989-10-11
Anticipated expiration: 2009-03-08
Also published as: GB8805484D0; GB8905287D0; GB2216640B

Abstract

A generally tubular furnace (1) for the separation and recovery of two or more metals of different melting points comprises means (13) for collecting in molten form a lower-melting point component and means for rotating the furnace about a generally horizontal longitudinal axis, whereby a solid higher melting point component remaining after firing may be tipped out of the furnace through a discharge aperture (24) in a circumferential wall of the furnace. <IMAGE>

Description

"Improvements in or relating to furnaces" This invention concerns improvements in or relating to furnaces and more particularly relates to furnaces suitable for the separation and recovery of two or more metals of different melting point from mixed scrap, e.g. for recovering non-ferrous components from admixture with steel or iron.

It is known to carry out such separation in a reverberatory furnace of the sloping hearth type. The mixed scrap is placed on a hearth, which slopes towards the back of the furnace. The nonferrous components, generally aluminium or copper, melt and run down the hearth to a holding tank at the rear of the furnace while the iron or steel remains unmelted on the hearth. The problem comes when the ferrous scrap has to be removed from the furnace. The only practicable way of doing this is by hand raking "up-hill" through a half-open or fully open door. During this operation, the furnace man is subjected to the full heat of the brickwork and red-hot steel. The job is therefore very hot, exhausting and dangerous.Further handraking is usually necessary about half way through the firing, to distribute the charge on the heated brickwork and to assist in separation of the molten non-ferrous component from the scrap iron or steel.

This operation is particularly necessary with dense "fragmatised" scrap produced by modern hydraulic breaking equipment.

Attempts to charge and discharge the furnace mechanically using a pallet and forklift truck have proved only partially successful. Even if the pallet is made of alloy steel, it has a life of only a few weeks and has to be frequently replaced, thus negating the economic advantage of mechanising the operation.

It has also been proposed to process mixed scrap in a rotating stainless steel drum which is externally heated and has an internal Archimedean screw. The molten aluminium or other non-ferrous metal is removed through apertures in the drum, while the ferrous scrap is discharged in solid f-orm after passing right through the drum under the influence of Archimedean screw. This apparatus is extremely costly, both in terms of capital cost and in fuel consumed. Typically it uses about twice the amount of fuel of the sloping hearth apparatus per ton of scrap processed. Moreover if there is any magnesium in the scrap, this has a tendency to burn a hole in the stainless steel drum, necessitating shut-down of the apparatus and a costly repair.There is thus a continuing need for a furnace which will enable scrap of the kind described to be efficiently and economically processed without the need for hand labour to remove the unmelted residue.

In one aspect, the invention provides a furnace for the separation and recovery of two or more metals of different melting points, said furnace being of generally tubular form and comprising means for collecting in molten form a lower-melting point component and means for rotating said furnace about a generally horizontal longitudinal axis, whereby a solid higher-melting point component remaining at the end of the firing may be tipped out of said furnace through a discharge aperture in a circumferential wall thereof.

The furnace is preferably of substantially circular cross-section internally, although an elliptical cross-section or other configuration with internally rounded corners is also feasible.

The discharge aperture preferably communicates with the interior of said furnace by a short throat, one wall of this throat forming a tangent to the internal wall of the furnace.

The furnace may be charged through the discharge aperture or, more preferably, a charging hatch may be provided in one of the end faces thereof.

The discharge aperture may be provided with a door such as a hinged or pivoted door, or alternatively a refractory lined collar may be provided over a part of the furnace to cover the aperture when it is in this region.

An inwardly-extending perforated bridge wall may be provided to permit the passage of molten metal into a holding or discharge means while preventing movement of solid scrap along the longitudinal axis of said furnace. The molten metal holding means may be provided with a discharge spout or flume through which the aluminium, copper or the like may be run into ingot moulds or a holding furnace.

It is convenient to fuel the furnace by an oil or gas burner mounted in one end-wall. The combustion gases may be discharged through a flue in the opposite end-wall, or more preferably may exit through a flue placed adjacent to the burner, in a non-rotating portion of an end-wall. Alternatively a flue may be associated with the discharge aperture in which case a hood may be provided over the furnace to collect gases when the furnace is rotated to lie at any angle, or a flue may be associated with said perforated wall. The said means for collecting the lower melting point metal may also be in the said non-rotating portion, hence permitting the composition of the molten metal to be monitored and controlled during operation of the furnace.

The said non-rotating portion provides a safe location for a thermocouple, avoiding accidental damage by the moving charge, and also facilitates connection of the flue to an after-burner or fume abatement means.

The longitudinal axis of the furnace may be inclined at a small angle to the horizontal, e.g. up to 100, to encourage separation of the molten lower-melting point component from the solid scrap. Alternatively the rotational axis of the furnace may be horizontal and the refractory lining may be tapered to provide a sloping hearth In one embodiment the inclination of the furnace to the horizontal may be varied.

Viewed from a different aspect the invention provides a method of separating and recovering two or more components having different melting points comprising the steps of: loading the components into a furnace, heating the components within the furnace to a predetermined temperature, removing a molten component having a lower melting point from the furnace, and rotating the furnace to remove under gravity a solid component having a higher melting point.

The method may include a step of axially separating within the furnace a component having a lower melting point and a component having a higher melting point, by inclining an interior wall of the furnace at a slight angle to the horizontal and providing a perforated wall extending inwardly generally perpendicular to an axis of the furnace, to allow axial passage of a molten component under gravity away from one end of the furnace while retaining a solid component at that end.

Four embodiments of my invention will now be described by way of example only with reference to the accompanying drawings wherein: Fig. 1 is a vertical cross-section through the longitudinal axis of a first, preferred embodiment of the invention; Fig. 2 is a plan view of the apparatus of Fig. 1; Fig. 3 is an end elevational view of said first embodiment illustrating the burner/flue end of the furnace; Fig. 4 is an axial cross-section through said first embodiment taken through the discharge aperture; Fig. 5 is a vertical cross-section through the longitudinal axis of a second embodiment of the invention; Fig. 6 is a plan view of said second embodiment; Fig. 7 is an end elevational view of said second embodiment; Fig 8 is another similar cross-section taken through the discharge aperture thereof;; Fig. 9 is a vertical cross-section through the longitudinal axis of a third embodiment of the invention; Fig. 10 is a partially sectioned side view of a fourth embodiment; Fig. 11 is a plan view of the fourth embodiment; Fig. 12 is an end elevational view of the fourth embodiment; and Fig. 13 is an axial cross-section through the discharge aperture of the fourth embodiment.

Referring now to Fig. 1, the furnace comprises a cylindrical housing (1) having a refractory lining (6) of high alumina firebrick forming the hearth of the furnace; adjacent the end-wall (2) the lining is of decreased thickness to provide a molten metal holding well (13). These are all coaxial.

At its other end, the housing tapers to a reduced diameter and supports a hinged door (4) for charging and emergency raking, faced internally with refractory brick. A discharge aperture (24) in the circumferential wall of the furnace is closed by hinged doors (3) (shown open in Fig. 4).

As seen in Fig. 4, the discharge aperture (24) communicates with the interior of the furnace by a short throat (25) constituted by the wall thickness of the refractory lining, one wall (26) of this throat forming a tangent to the internal wall of the furnace, thus ensuring that no impedance is presented to the discharge of solid scrap after the firing.

A refractory bridge will (5) subtends approximately half of the internal circumference of the furnace.

The height of the wall is approximately one quarter of the internal diameter of the furnace, and slots (12) are cut through it. The purpose of the bridge wall is to strain off the molten aluminium or other low-melting point metal, retaining the higher-melting point scrap metal (generally iron or steel) on the hearth (6). A wall having different dimensions, for example subtending more than half of the internal circumference of the furnace, could be used.

The furnace is supported by two steel discs (7) of equal diameter, each having a steel tyre welded thereto (not shown). The discs (7) each rest on two rollers (8), one of which is driven by a motor (9) through a coupling (11). The motor comprises a reversible, variable speed gearbox (not shown). Depending on the weight of the furnace, it may be necessary to drive a roller at either end, in which case the motor (9) may be centrally mounted. The rollers supporting the charging end of the furnace are mounted higher than those supporting the burner end. The axis of the furnace is therefore at an angle of a few degrees to the horizontal, enabling the molten metal to run down through the slots (12) to the molten metal holding well (13).

A pouring spout or flume (21) runs from the holding well through the wall of the furnace, enabling discharge of the molten metal into a suitable receptacle, for example a ladle, holding furnace or ingot mould.

The central portion (10) of the end-wall (2) of the furnace remains stationery as the furnace rotates. This fixed portion (10) provides a convenient mounting for the burner (15) for gas or oil, flue (14) and thermocouple (16) as shown in Fig. 2.

An after-burner (22) and damper (23) may also be placed in the flue for control of combustion and smoke. As the flue is at the same end of the furnace as the burner, efficient use of the heat of combustion is ensured, as the gases must circulate through the entire body of the furnace.

The method of operation of the furnace is as follows. The furnace is initially loaded through either of the doors (3) or (4). The position of the furnace is shown in Fig. 1 with the doors (3) at the top. Alternatively, it may be more convenient to load the furnace with the doors (3) in a vertical plane, i.e. with the furnace turned 900 from the vertical. The doors are secured, the burner is ignited and the furnace starts to rotate at a very slow rate. If necessary, to facilitate melting and separation of the metal, the furnace may be rocked in alternate directions. The rotation greatly improves thermal efficiency, by continually bringing the charge into contact with the hot lining.

As the lower-melting point metal melts, it drains through the slots (12) in the bridge wall (5) and into the holding well (13). When the melting process is complete, the holding well (13) may be drained via flume (21) after the furnace has turned through 900 in a clockwise direction (as shown by the arrow in Figs. 3 and 4). The scrap ferrous metal is retained in the hearth by the bridge wall (5). As the furnace is rotated to the inverted position, the scrap falls into the throat (25). At this point, the doors (3) can be opened, as shown in Fig. 4, allowing the solid steel/iron scrap to fall into a skip or the like placed under the furnace. After further rotation and closure of the doors (3) the furnace can be recharged.In fact, it is feasible to rotate the furnace continously, the charge being inserted at a suitable point in the cycle through the door (4), the molten non-ferrous metal being discharged subsequently through flume (21) and the scrap ferrous component being discharged through doors (3) when the furnace is inverted. Thus the significant heat loss inevitable in a batch process can be avoided.

Another embodiment of my invention is shown in Figs. 5 to 8, wherein corresponding portions are denoted by the same references numerals used in Figs. 1 to 4. In this embodiment, the furnace may be top loaded or side loaded through a single removable door (3) which swivels about shaft (29) and is apertured at (27) to provide a flue. A door (4) in the end-wall remote from the burner may be provided to permit inspection and manual removal of any jams. This embodiment is of simplified design and, while sacrificing some efficiency and operational convenience, is particularly economical to manufature.

A further embodiment of my invention is shown in fig. 9. Again, corresponding portions are denoted by the same reference numerals as those used in Figs. 1 to 4. In this embodiment the holding well (13) is in the non-rotating portion of the furnace. This allows the furnace to operate until the holding well is full. The bridge wall (5) is substantially annular, and is higher than in the previous embodiments. This helps retain the heat in the rotating portion of the furnace. The advantage of this embodiment is that the molten metal may be monitored and the ingots produced to a specified standard. The furnace is top loaded, the burner (15) being mounted in the end wall of the rotating portion of the furnace. An extra burner (27) and means for tapping off some molten metal (28) may be provided in the holding well.

A fourth embodiment of the invention is shown in Figs. 10 to 13 with coresponding parts again denoted by the same reference numeral. The embodiment i-s similar to the third embodiment in that the furnace comprises a rotating portion and a nonrotating portion, the rotating portion only being shown. The furnace may be side loaded in the rotating portion through discharge aperture (24) or through end door (4). A hemi-cylindrical refractory lined collar (30) extends circumferentially around an upper part of the furnace to cover discharge aperture (24) when the furnace is rotated so that this aperture lies above the longitudinal axis of the furnace. A generally annular flue gap (31) is provided between the collar (30) and the outer wall of the furnace.If desired the area of the flue associated ith the discharge aperture may be increased by rotating the furnace so that the collar (30) leaves the discharge aperture partially uncovered.

The aperture (24) is fully opened for discharge by inverting the furnace.

The rotating part of this furnace is mounted through discs (7) and rollers (8) on a frame (32).

The frame is pivotally attached adjacent end wall (33) to a base at (34). The inclination of this part of the furnace to the horizontal may be varied by means of jacks (35) which may be used to adjust the height of the end of the rotating portion remote from end wall (33). The collar (30) is mounted on a self supporting frame so that the flue gap (31) may be varied by adjusting the height of the furnace.

A hemi-cylindrical hood (36) extends circumferentially around an upper part of the furnace to collect flue gases and feed them into an extractor and afterburner (37). The shape of the hood (36) allows it to collect gases whatever the angle of rotation of the furnace. The extractor and afterburner (37) is mounted on the same static frame (38) as the refractory lined collar (30), whereas the hood (36) is mounted on frame (32) so that it tilts with the rotating portion of the furnace.

In this embodiment the bridge wall between the hearth (6) and the molten metal holding well (not shown) is provided by the end wall (33) of the rotating portion of the furnace. This wall (33) extends across the full cross-section of this end of the furnace and is provided with a number of holes (39) which are shown spaced round the lower part of furnace in Fig. 12 at a radius slightly less than the internal radius of the rotating portion of the furnace at that end. In use when the furnace is inclined to the horizontal molten metal passes through these holes (39) from the hearth (6) into the molten metal holding well.

The holes (39) additionally act as an auxilliary flue through which hot gases emerge from the furnace, and under some circumstances they may act as the main or the only flue. Hot gases passing through holes (39) maintain the holes at a sufficiently high temperature to avoid solidification of a molten component passing through the holes from the rotating portion of the furnace to the molten metal holding well.

It is to be clearly understood that there are no particular features of the foregoing specification which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore form the basis of claims filed in connection with the application or any application claiming priority thereform and may be included in, added to, omitted from or deleted from any-of such claims if and when amended during the prosecution of this application in the filing or prosection of any divisional application based thereon. Furthermore the manner in which any of such features of the specification of any such claims are described or defined may be amended, broadened or otherwise modified in any manner which falls within the knowledge of a person skilled in the relevant art, for example so as to encompass, either implicitly or explicitly, equivalents or generalisations thereof.

Claims

1. A furnace for the separation and recovery of two or more metals of different melting points, said furnace being of generally tubular form and comprising means for collecting in molten form a lower-melting point component and means for rotating said furnace about a generally horizontal longitudinal axis, whereby a solid higher-melting point component remaining at the end of the firing may be tipped out of said furnace through a discharge aperture in a circumferential wall thereof.

2. A furnace as claimed in claim 1 wherein the internal cross-section of the furnace is substantially circular.

3. A furnace as claimed in any preceding claim wherein said discharge aperture communicates with the interior of the furnace by a short throat, one wall of the throat forming a tangent to the internal wall of the furnace.

4. A furnace as claimed in any preceding claim wherein a charging hatch is provided in one of the end faces thereof.

5. A furnace as claimed in any preceding claim wherein an inwardly extending perforated bridge wall is provided to permit passage of a molten component into a holding or discharge means while preventing movement of a solid component along longitudinal axis of the furnace.

i. A furnace as claimed in claim 5 wherein said olding means is provided with a discharge spout r flume through which a molten component may be ischarged.

7. A furnace as claimed in claim 5 or 6 wherein said holding means is provided in a part of the furnace which is not adapted to rotate.

8. A furnace as claimed in any preceding claim wherein a burner and a flue are mounted in a nonrotating part of an end wall of the furnace.

9. A furnace as claimed in any preceding claim having a flue associated with the discharge aperture.

10. A furnace as claimed in any preceding claim wherein hemi-tubular cover is provided over an upper part of the furnace to collect gases emerging therefrom through a flue associated with the discharge aperture, independently of the angular rotation of the furnace.

11. A furnace as claimed in any of claims 5 to 10 wherein openings in the perforated wall act as a flue for hot gases emerging from the furnace.

12. A furnace as claimed in any preceding claim wherein the refractory lining of the furnace is tapered to provide a sloping hearth.

13. A furnace as claimed in any preceding claim wherein a longitudinal axis of the furnace is inclined at a small angle to the horizontal to encourage separation of a molten component from a solid component.

14. A furnace as claimed in claim 13 wherein means are provided for varying the angle at which a longitudinal axis of the furnace is inclined to the horizontal.

15. A furnace as claimed in claim 14 wherein the furnace is mounted on a frame which may be pivoted about one end by means of jacks to vary the angle of inclination to the horizontal.

16. A furnace as claimed in claim 14 or 15 wherein a hemi-tubular collar is provided over an upper part of the furnace to cover the discharge aperture in that region, there being a flue gap between the collar and an outer wall of the furnace, the collar being mounted independently of the furnace such that the flue gap may be varied by adjusting the inclination of the furnace to the horizontal.

17. A furnace as claimed in any of claims 14 to 16 wherein said hemi-tubular cover is mounted so as to tilt with said furnace.

18. A furnace substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.

19. A furnace substantially as hereinbefore described with reference to Figures 5 to 8 of the accompanying drawings.

20. A furnace substantially as hereinbefore described with reference to Figure 9 of the accompanying drawings.

21. A furnace substantially as hereinbefore described with reference to Figures 10 to 12 of the accompanying drawings.

22. A method of separating and recovering two or more components having different melting points comprising the steps of: loading the components into a furnace, heating the components within the furnace to a predetermined temperature, removing a molten component having a lower melting point from the furnace, and rotating the furnace to remove under gravity a solid component having a higher melting point.

23. A method as claimed in claim 22 including a-step of axially separating within the furnace a component having a lower melting point and a component having a higher melting point, by inclining an interior wall of the furnace at a slight angle to the horizontal and providing a perforated wall extending inwardly generally perpendicular to an axis of the furnace, to allow axial passage of a molten component under gravity away from one end of the furnace while retaining a solid component at that end.

24. A method as claimed in either of claims 22 or 23 wherein a molten component is removed by rotating the furnace so that the molten component is discharged under gravity through a spout or flume, the furnace being further rotated to discharge a solid component.

25. A method as claimed in any of claims 22 to 24 wherein said furnace is rocked about a longitudinal axis to encourage separation of components.

26. A method as claimed in any of claims 22 to 25 wherein said furnace is continuously rotated.

27. A method of separating and recovering two components having different melting points substantially as hereinbefore described with reference to the accompanying drawings.