WO1993011398A1

WO1993011398A1 - Furnace systems and charger mechanisms for furnaces

Info

Publication number: WO1993011398A1
Application number: PCT/GB1992/002258
Authority: WO
Inventors: Adrianus Jacobus Hengelmolen; Peter Marshall; David Charles Williams
Original assignee: Copermill Limited
Priority date: 1991-12-05
Filing date: 1992-12-04
Publication date: 1993-06-10
Also published as: AU3089992A; GB9125917D0

Abstract

A charger system for a furnace comprising a loading mechanism for loading scrap material into the furnace, the loading mechanism co-operating with the furnace to provide a substantially airtight arrangement whereby on opening of the furnace door to allow the scrap material to be loaded into the furnace the fumes normally emitted by the furnace are contained by the co-operation of the loading mechanism and the furnace to thereby prevent atmospheric pollution. In the same system, means may be provided for pre-heating the scrap material and for weighing the scrap prior to insertion into the furnace to provide more accurate control of the furnace operation.

Description

FURNACE SYSTEMS AND CHARGER MECHANISMS FOR FURNACES

This invention relates to furnace systems and charger mechanisms and methods for furnaces and has particular, but not exclusive reference to such mechanisms for closed well furnaces (CWF) and dry well furnaces (DWF) used in scrap metal recovery systems.

CWF's and DWF's are widely used in the scrap metal recovery field and as a result of countries becoming increasingly conscious of air pollution, such furnaces are being subjected to more and more stringent controls. One of the main problems with handling scrap metal, from the environmental standpoint, arises from the fact that scrap metal is contaminated in the sense of being painted or otherwise coated, and/or greasy/oily, and/or has synthetics material attached, for example. Each of these contaminants gives rise to fumes, often noxious, when the scrap metal is subjected to a high temperature. Thus, many CWF's and DWF's have relatively sophisticated equipment for handling, and rendering harmless, the fumes which are evolved when the scrap metal is heated in the furnace. However, there is still a problem with fumes escaping from the furnace when it is opened to receive a new charge of scrap metal, and with fumes being evolved even before a new charge actually enters the furnace due to the high temperature to which it is subjected as it approaches the open furnace. This problem of egress of fumes is aggravated by the concomitant ingress of air which can seriously impair the efficiency of the furnace, many of which operate in an oxygen-free atmosphere.

It is an object of the present invention to minimise, if not obviate, the problem of the egress of fumes and the ingress of air when a furnace is opened for loading therein a new charge of material.

According to a first aspect of the present invention there is provided a furnace system comprising a furnace comprising a loading aperture through which charges of new scrap metal can be loaded into the furnace, a door for the loading aperture, and a shroud around at least part of the door and dimensioned so as to house the door therewithin when the latter is opened, the system further comprising a charger mechanism co-operable with at least the shroud to form a substantially airtight compartment around the loading aperture.

According to a second aspect of the present invention there is provided a method of charging a furnace comprising the steps of :- a) providing a shroud around at least part of a loading aperture of a furnace, the shroud being dimensioned so as to contain therewithin a door for the aperture when the latter is opened; b) loading a charger mechanism with a charge of material, the charger mechanism being co-operable with at least the shroud to form a substantially airtight compartment around the loading aperture; c) opening the furnace door when said airtight compartment has been formed_? d) discharging from the charger mechanism the charge of material into the furnace, e) extracting from the airtight compartment any fumes escaping from the furnace, and f) closing the furnace door

Preferably, the method comprises the further step of purging the compartment, and hence the charger mechanism, with a gas, conveniently air, after the furnace door has been closed and prior to disengaging the charger mechanism from the shroud.

The method may also comprise the further step of pre¬ heating a charge of material within the charger mechanism prior to the charge being loaded into the furnace.

According to a third aspect of the present invention there is provided a charger mechanism for a furnace comprising a bucket pivotally mounted on a base frame and being pivotally movable between position in which it can be loaded with material to form a next charge for the furnace, and a position in which the charge of material can be discharged into the furnace.

Preferably, the bucket is mounted on a wheeled carriage adapted to run on rails so that precise alignment is always achieved between the charger mechanism and a loading aperture of the furnace. The bucket may be pivoted to a position such that it faces generally to one side of the charger mechanism for loading, and then pivoted to a discharge position in which it faces another side of the charger mechanism. These two sides may be opposed or adjacent, depending on whether the carriage is movable directly towards and away from the loading aperture of the furnace, or whether it is movable at right angles to that direction. A bucket in accordance with this third aspect of the present invention is particularly useful in connection with the first aspect of the invention and in that connection, although not exclusively so, the bucket may comprise a container open at one end and having mounted therein at or towards the opposite end a discharge mechanism generally of U-shaped configuration in each of the opposed limbs of which is mounted an extensible mechanism by which the discharge mechanism can be moved from said opposite end towards said open end in order to discharge from the bucket a charge of material previously loaded therein. With such an arrangement, the bucket can be self-contained in as much as the discharge or pusher mechanism is contained wholly within the bucket, as opposed to being provided externally of the bucket and connected to the pusher through the wall of the bucket as in known arrangements. The problem with providing a discharge mechanism mounted totally within a loader bucket is that of providing a sufficiently long stroke for the operating mechanism in order to be able to fully discharge a charge of material loaded therein. It will be appreciated that it is desirable to make a loader bucket as large as possible in order to maximise the size of charge and also to be able always to fully discharge a charge of material so that no material remains in the bucket because it is important for overall furnace control to know how much material is loaded into the furnace compared with the product of the furnace. These conflicting requirements are fully met by the use of a U- shaped discharge mechanism because the limbs of the "U" can be dimensioned so as to be able to achieve the required stroke of the mechanism and yet take up the minimum space within the bucket.

In a further embodiment the bucket is mounted onto a turntable arrangement enabling the bucket to be loaded from either the side or opposite end to the furnace door and to be rotated to enable the seal arrangement to mate with the seal on the furnace door when the charge is to be loaded into the furnace. According to a fourth aspect of the present invention there is provided a charger mechanism for a furnace comprising a loader bucket open at one end and having mounted therein at or towards the opposite end a discharge mechanism which is generally U-shaped, in each of the opposed limbs of the mechanism there being provided an extensible member by which the discharge mechanism is moved from the said opposite end of the bucket to the open end of the bucket in order to discharge therefrom a charge of material previously loaded into the bucket. Preferably, the extensible mechanisms are double- acting and may be in the form of double-acting hydraulic actuators. According to a fifth aspect of the present invention there is provided a charger mechanism for a furnace comprising a charger bucket mounted on a base frame via load cells. With this aspect of the invention, the weight of material loaded into the charger bucket is readily ascertained and fed to an overall control system of the furnace so that a measure of the productivity of the furnace can be obtained. The base frame is preferably mounted within a main frame structure by bearing members comprising load cells to thereby weigh the content of the bucket.

Preferably there are four load cells providing a four point loading for the base frame. According to a sixth aspect of the present invention there is provided a charger mechanism for a furnace comprising a charger bucket mounted on a base frame via adjustable means operable to adjust the height of the bucket. This aspect of the invention is particularly advantageous in being able to provide a standard charger mechanism which can be adjusted on site to suit a particular furnace or furnaces for which it is required, the sill height varying according to the design of furnace. It may be that if more than one furnace is provided on a given site, they are all of the same design, whereby the height of the charger bucket can be set and does not thereafter need to be changed. However, if the furnaces on a given site are of different types, then the height of the charger bucket may have to be adjusted according to the sill height of the furnace it is serving at a given instan . In a preferred embodiment the adjustable means comprises, hydraulic cylinder means. More preferably it comprises first and second hydraulic adjustment means.

A scrap metal recovery system embodying the present invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:-

Figures 1 to 5 illustrate a sequence of operation of a charger mechanism for a furnace, the charger mechanism being shown in relation to the loading door of the furnace, both items being shown in cross-section;

Figure 6 is a side view of the charger mechanism of Figures 1 to 5;

Figure 7 is a view from the left (rear view) of the charger mechanism of Figure 6; Figure 8 is a detail, to a larger scale of a component of the charger mechanism.

Figure 9 shows diagrammatically a front elevation view of the furnace illustrating the hood and seal arrangements;

Figure 10 shows a schematic diagrammatic view of the exterior of the charging mechanism of an embodiment of the present invention.

Figure 11 shows in greater detail a portion of the sealing mechanism; Figure 12 shows in greater detail one possible arrangement of the load cell arrangement of the present invention;

Figure 13 shows diagrammatically a side elevation of the furnace and charger mechanism according to the present invention in a first position; and

Figure 14 shows the arrangement of Figure 12 in a second position.

Referring first to Figures 1 to 5, the furnace 100, which may be a CWF or a DWF is only partially shown in cross sectional side elevation by way of a loading door 1 which in Figures 1 to 3 is shown in the closed position relative to a loading aperture 2 for the furnace. The door

1 is slidable relative to the front wall of the furnace which is inclined slightly rearwardly, the loading aperture

2 being surrounded by a heat-proof seal 3 with which the door 1 co-operates in the closed position. The bottom of the loading aperture 2 is defined by a sill 4 which is at a predetermined height from the ground and slopes inwardly of the furnace.

The door 1 is partly surrounded by a shroud 5, the shroud extending over the top of the door 1 and is dimensioned such that when the door is open, it moves upwardly within the shroud 5 but is still contained within the shroud.

A charger mechanism generally indicated at 6 is provided for loading the furnace with material, for example, scrap metal. The charger mechanism 6 is self- contained and comprises a generally rectangular base frame in the form of a carriage or chassis 7 mounted on wheels 8 which runs on rails 9 extending in a direction directly towards and away from the door 1 of the furnace. Thus, the charger mechanism 6 is always aligned with the door, and hence loading aperture 2. Each of the front pair of wheels is driven by a motor 10, the two wheels being driven in synchronism.

The charger mechanism 6 further comprises an inner frame 70 which is mounted inside the main frame 7 and is also generally rectangular a first pair of legs 11 and a second pair of legs 12, one end of each of these legs mounted on the inner frame 70 via a load cell 13. The first pair of legs 11 is mounted at the forward end of the charger mechanism 6 and extend rearwardly and upwardly, and the second pair of legs 12 is mounted at the rear end of the inner frame 70 and extend forwardly and upwardly, one leg from each pair being interconnected and defining an inverted "V" when seen in side view (Figures 4 and 5). At the apices of the legs 11,12 there is provided a mounting plate 14 (Figures 4 and 5) and between these mounting plates is pivotally mounted a loader bucket 15, the pivot point being indicated at 16 in Figures 1 to 5.

The loader bucket 15 is rectangular in plan view and side view except that the bottom 17 is shaped so as to accommodate pivotal movement of the bucket, and the open top of the bucket slopes downwardly from front to rear as seen in Figure 3 of the drawings. The loader bucket 15 is itself self-contained and has mounted therein at or towards the bottom 17 a discharge mechanism or pusher 19. The pusher 19 is generally U-shaped with the opposed limbs 21 thereof each housing a double-acting hydraulic actuator 22. The bottom of the pusher 19 is fitted with rollers 23 to assist in the movement and guidance of the pusher mechanism relative to the interior of the loader bucket 15. The upper edges of the opposed limbs 21 of the pusher mechanism 19 are fitted with sidewall extensions 24. A pair of double-acting hydraulic actuators 25 are connected between the rear edges of the loader bucket 15 and the inner frame 70 and are operable to effect the required tilting or pivotal movement of the loader bucket 15. Extending from each of the first pair of legs 11 is a frame member 26, these members being interconnected by a further frame member 27 and forming part of an upper framework 20 for the charger mechanism 6, this framework being completed by further frame members 28,29,31,32. This upper framework 20 is covered by sheetings 30, with which the floor of the carriage make the charger mechanism 6 totally enclosed save for a loader opening 33 which is closable by a door 38, which is pivotally mounted about the same pivot axis 16 as the loader bucket 15, and the front end of the mechanism which is normally open. The rear of the charger mechanism is arcuate, as is the door 38 so that the latter slides between its open and closed position on being pivoted about the axis 16, sliding movement being powered by an hydraulic actuator 39 (Figure 6), one at each side, acting between an extension 41 of one of three radial arms 42 mounting the door on its pivot shaft and a bracket 43 attached to the adjacent frame member 36. When in the closed position, the door 38 seals the loader opening 33. The front end of the charger mechanism 6 is, as already mentioned, open but is provided with a heat-proof seal 39 therearound, the front end being generally L-shaped as seen in side view.

In operation, the empty loader bucket 15 is pivoted rearwardly using the actuators 25 so that it assumes the position illustrated in Figure 1 of the drawings. Next, the door 38 is opened so as to allow access to the loader bucket 15 through the loader opening 37, whereby scrap metal 45 can be loaded using a forklift truck 46 or other apparatus, as shown in Figure 2 of the drawings. Before or after the bucket 15 has been loaded with the required amount of scrap metal, the carriage is moved along the rails 9 towards the furnace door 1 by actuating the motors 10 on the front wheels 8 of the carriage. This movement is continued until the seal 44 engages the sealing member 50 around the furnace door 1 as also seen in Figures 2 to 5 of the drawings. The charger mechanism 6 is held firmly in this position by hydraulic latches 47 (Figure 8) in order to ensure the integrity of the seal during the furnace loading operation and to avoid the need to counterbalance the charger mechanism during the loading of the furnace. It will be appreciated that when the charger mechanism is in the position illustrated in Figures 2 to 5 of the drawings, there is provided a closed compartment around the furnace loading aperture 2 which compartment is substantially airtight. With the charger mechanism 6 in this position, and prior to the furnace door 1 being opened, the charge of scrap metal in the loader bucket 15 can be subjected to pre-treatment by way of feeding hot gases into the sealed compartment via the furnace door shroud 5 or the casing of the charger mechanism, these gases being applied through an appropriate inlet and extracted through an outlet, the exhaust gases containing fumes as a result of gasification of paint, synthetic plastics, etc due to the heating thereof during this pre- treatment process. The exhaust fumes are taken to a fume purification system forming part of the furnace. It will be appreciated that once a charge 45 of scrap metal has been loaded into the bucket 15, whether before or after the carriage 7 is moved into sealing engagement with the furnace, the charger mechanism door 38 is closed using the actuator 39. When any pre-treatment of the scrap metal charge 45 has been completed, the furnace door 1 is opened and the loader bucket 15 pivoted to a generally horizontal position in which the side of the bucket which now forms the floor thereof overlaps the sill 4 of the furnace as illustrated in Figure 4 of the drawings. The charge of scrap metal 41 is now subjected to the intense heat of the furnace but if pre-treatment of the charge has taken place, then the gasification resulting from the exposure to this high temperature is less severe than would otherwise be the case and which can cause overloading of the fume purification system.

Finally the charge 41 of scrap metal has to be discharged from the loader bucket 15 into the furnace and to this end, the pusher 19 is moved from the closed end of the bucket towards the open end by actuation of the actuators 22, the upper edges of the limbs 21 of the pusher being substantially flush with the now lower outer edge of the bucket, whereby, in conjunction with the overlap between the bucket and sill, complete discharge of the charge 45 is accomplished, the extended sidewalls 24 ensuring that no part of the charge can fall from the furnace and be lost. This positive discharge of the total charge 45 into the furnace also prevents any of the scrap metal lodging in the loading aperture 2 and thus possibly causing damage to the door seal 3 when the door 1 is closed. This discharge of the load 45 is illustrated in Figure 5 of the drawings and when completed, the loader bucket is pivoted back to the generally vertical position, the furnace door 1 closed and then, if necessary, the charger mechanism 6 moved away from the furnace door to be loaded with a further load of scrap metal and the sequence of Figures 1 to 5 repeated. The bucket could, of course, be re-charged whilst the charger mechanism is in the position of Figures 4 and 5. However, prior to the breaking of the seal between the furnace and the charger mechanism 6, once the furnace door 1 has been closed, the compartment formed by the charger mechanism with the furnace may be purged with air or other gases to ensure that any fumes remaining therein are extracted prior to the charger mechanism again becoming open to the atmosphere and thus polluting the same with any fumes which remain.

The. ability to withdraw the charger mechanism 6 from the furnace enables a skimming operation to be carried out as and when necessary.

It will be seen that there is provided by the present invention an improved charging mechanism for a furnace which effectively eliminates the problem of fumes escaping to the atmosphere when the furnace door is opened for loading the next charge of material. When a pivotal loader bucket is employed, this can be arranged for charging from the rear or from the side of the charger, relative to the furnace, so as to accommodate any space limitations at a given site. Furthermore, the use of load cells 13 interposed between the loader bucket and its base frame allows instant and accurate information to be passed to the furnace control or monitoring system about the weight of a given charge.

With reference now to Figure 9, the seal 44' is shown to surround the door 1 area, overlapping the hood 5. An extraction system 51 for the hood 5 is shown diagrammatically which may in a particular embodiment allow forced extraction of gases from the hood 5. The door 1 rolls in known manner on rollers 1 ' in grooved tracking 1". With reference to Figure 10, the charger 60 is shown to be externally completely cladded. A skirt 60 may be used to provide a seal to the floor surface. The skirt 60 may be made in sections and may be of a strong rubber material such as used for conveyor belting. With reference to Figure 11, the door seal 44' may comprise, stainless steel or similar material sealing members on both the furnace and charger. The stainless steel or similar material seals provide a good seal which is strong enough to resist minor knocks. The bottom seal 440,441 may comprise two members 440 which provides the sealing and 441 which provides a backing member. The seal may be of simple design but must be heat resistant.

With reference to Figure 12, the load cell 13 may comprise a cylindrical load bearing member 130 situated to allow inner frame 70 to pivot on outer frame 7. The load cell measures in known manner the load between the two frames and the four load cells enable the total weight of the inner frame 70 to be measured thus enabling by subtraction operations the weight of any charge inserted into the charger.

With reference to Figure 13, the charger may comprise a rotary arrangement mounted on a large central pivot 600. The charge may be loaded into the charger in the position shown in Figure 13 or in an intermediate side on position and then the charger may be rotated to the position shown in Figure 14 to be mated to the furnace.

Sealing arrangements for the furnace including the cladding for the charger may be as previously described. The charger bucket need not, in this arrangement be pivoted but can be mounted to be driven forward by a hydraulic ram 602 on a trolley 604 mounted on wheels 606,608. With reference now to Figure 15, the charger may be provided • with means for preheating the charge, in particular to burn off any combustible materials present on the scrap.

The means may comprise a valve 640 connected to an existing blower system 641. A further valve 642 may be used to control the flow of hot flue gas from furnace 100 into the charger 6 when it is sealed.

The flue gas when valve 642 is closed and valve 640 is open passes via coupling 650 into charger 6 and then via coupler 651, valve 643, and blower 644 back into the furnace 100. Valve 645 is closed to enable this to occur. With valves 645 and 642 open a normal furnace recycling operation for the hot gas takes place.

By a further suitable valve means 646 and pipe means 647 connected for example to the exhaust fume outlet from a fume purification plant oxygen deficient fumes can be injected into charger 6 just prior to the furnace door being opened. This will decrease the oxygen in the charger and thus when the furnace door opens there is much less likelihood of an explosive burning of any combustible material still present on the scrap.

The exhaust on the hood can be used after the furnace door commences to open to ensure that hot gases are drawn away from the skirt or other sealing arrangement by creating a small negative pressure thus relieving pressure on the sealing system.

Claims

1. A furnace system comprising a furnace comprising a loading aperture through which charges of new scrap metal can be loaded into the furnace, a door for the loading aperture, and a shroud around at least part of the door and dimensioned so as to house the door therewithin when the latter is opened, the system further comprising a charger mechanism co-operable with at least the shroud to form a substantially airtight compartment around the loading aperture.

2. A method of charging a furnace comprising the steps of:- a) providing a shroud around at least part of a loading aperture of a furnace, the shroud being dimensioned so as to contain therewithin a door for the aperture when the latter is opened; b) loading a charger mechanism with a charge of material, the charger mechanism being co-operable with at least the shroud to form a substantially airtight compartment around the loading aperture; c) opening the furnace door when said airtight compartment has been formed; d) discharging from the charger mechanism the charge of material into the furnace, e) extracting from the airtight compartment any fumes escaping from the furnace, and f) closing the furnace door.

3. A method of charging a furnace as claimed in claim 2 in which the method comprises the further step of purging the compartment, and hence the charger mechanism, with a gas, conveniently air, after the furnace door has been closed and prior to disengaging the charger mechanism from the shroud.

4. A method of charging a furnace as claimed in claim 2 or claim 3 in which the method also comprises the further step of pre-heating a charge of material within the charger mechanism prior to the charge being loaded into the furnace.

5. A charger mechanism for a furnace as claimed in claim 1 comprising a bucket pivotally mounted on a base frame and being pivotally movable between position in which it can be loaded with material to form a next charge for the furnace, and a position in which the charge of material can be discharged into the furnace.

6. A charger mechanism as claimed in claim 5 in which the bucket is mounted on a wheeled carriage adapted to run on rails so that precise alignment is always achieved between the charger mechanism and a loading aperture of the furnace.

7. A charger mechanism as claimed in claim 6 in which the bucket is pivoted to a position such that it faces generally to one side of the charger mechanism for loading, and then pivoted to a discharge position in which it faces another side of the charger mechanism.

8. A charger mechanism as claimed in claim 7 in which the two sides are opposed or adjacent, depending on whether the carriage is movable directly towards and away from the loading aperture of the furnace, or whether it is movable at right angles to that direction.

9. A bucket for use in the charger mechanism of claim 5, the bucket comprising a container open at one end and having mounted therein at or towards the opposite end a discharge mechanism generally of U-shaped configuration in each of the opposed limbs of which is mounted an extensible mechanism by which the discharge mechanism can be moved from said opposite end towards said open end in order to discharge from the bucket a charge of material previously loaded therein.

10. A bucket as claimed in claim 9 in which the bucket is mounted onto a turntable arrangement enabling the bucket to be loaded from either the side or opposite end to the furnace door and to be rotated to enable the seal arrangement to mate with the seal on the furnace door when the charge is to be loaded into the furnace.

11. A charger mechanism for a furnace as claimed in claim 1 the charger mechanism comprising a loader bucket open at one end and having mounted therein at or towards the opposite end a discharge mechanism which is generally U- shaped, in each of the opposed limbs of the mechanism there is provided an extensible member by which the discharge mechanism is moved from the said opposite end of the bucket to the open end of the bucket in order to discharge therefrom a charge of material previously loaded into the bucket.

12. A charger mechanism as claimed in claim 11 in which the extensible mechanisms are double-acting and may be in the form of double-acting hydraulic actuators.

13. A charger mechanism for a furnace as claimed in claim 1 comprising a charger bucket mounted on a base frame via load cells.

14. A charger mechanism as claimed in claim 13 in which the base frame is mounted within a main frame structure by bearing members comprising load cells to thereby weigh the content of the bucket.

15. A charger mechanism as claimed in claim 14 in which there are four load cells providing a four point loading for the base frame.

16. A charger mechanism for a furnace as claimed in claim 1 comprising a charger bucket mounted on a base frame via adjustable means operable to adjust the height of the bucket.

17. A charger mechanism as claimed in claim 16 in which the adjustable means comprises hydraulic cylinder means.

18. A charger mechanism as claimed in claim 17 in which the adjustable means comprises first and second hydraulic adjustment means.