EP0998999A1

EP0998999A1 - Casting sand reclamation apparatus

Info

Publication number: EP0998999A1
Application number: EP99308890A
Authority: EP
Inventors: Timothy George Henson; Graham Jones; Jacqueline Lewis
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-11-07
Filing date: 1999-11-08
Publication date: 2000-05-10
Also published as: GB9926202D0; GB9824461D0; GB2343397A

Abstract

A reactor vessel (1) suitable for use in the reclamation of foundry sand comprises a vessel (1) having an integral upper tubular portion (2) and a lower depending frustoconical portion (3). The reactor vessel is contained within an insulating frame (6) supported by legs (7) and provided with a lid (8). The vessel is provided with diametrically opposed sand inlet (16) and sand outlet ports (21) and at least one outlet port (26) for gaseous impurities. Means are provided to fluidise the sand within the reactor vessel (1) comprising a series of oxygen containing gas inlet nozzles (31). The vessel (1) is provided with an indirect heater to heat the sand to a predetermined temperature.

Description

The present invention relates to apparatus for use in the reclamation of used foundry sand.
Increased costs, disposal problems and environmental issues associated with the disposal of used foundry sand have made it more desirable to reuse the foundry sand. The sand from foundry processes is usually mixed with resins, binders, dust, metallic particles and the other impurities and must therefore be reclaimed from the sand/impurity mixture before it can be reused.
Methods and apparatus for reclamation of foundry sand are known in the art, however they often have associated maintenance problems and are not particularly efficient. For example it is known to heat the foundry sand to burn off the impurities by feeding combustible gases into a reactor vessel containing foundry sand and igniting the gas to give direct heating of the sand. This method of heating often causes hot spots to develop particularly around the gas inlet ports. At such hot spots the sand may form a glass like substance which can block the gas inlet ports leading to a decrease in the efficiency of the apparatus.
Sand reclamation apparatus generally require the sand bed to be fluidised, however, the shape of the reactor vessel and lack of adequate fluidising gas pressure, e.g. through blockage of gas inlet ports leads to poor fluidisation.
For maintenance purposes it is desirable to be able to empty the reactor vessel, however the design of many of the prior art reactors does not allow the sand to be readily moved therefrom.
It is known for weld cracks to occur in prior art reactor vessels tightly contained within a frame as a result of expansion on heating. Furthermore, prior art designs of foundry sand reactor vessels and frames do not always provide for easy removal of the reactor vessel from the frame for the replacement or cleaning thereof.
The object of the present invention is therefore to provide an apparatus for reclamation of used foundry sand which is efficient and easy to maintain and which addresses the problems associated with prior art designs.
According to a first aspect the present invention provides a reactor vessel adapted for use in the reclamation of foundry sand the vessel having an open end and a closed end, inlet and outlet ports for sand, at least one outlet port for gaseous impurities, means to fluidise the sand within the reactor vessel and means provided within the vessel to heat the sand to a predetermined temperature wherein the means to heat the sand to a predetermined temperature comprises an indirect heater.
The heater comprises a heating element situated inside the reactor vessel, preferably in the fluidised sand. The heater is preferably fired by a fan and a gas burner situated outside the reactor vessel. The heating element preferably comprises a hollow metal tube extending into the vessel having an inlet for hot gases from the burner and an outlet for exhaust gases, preferably an upwardly extending flue. Heat transfer to the sand may be improved by the provision of fins extending outwardly of the walls of the heating element.
The use of indirect rather than direct heating of the sand within the reactor vessel creates more uniform heating of the sand than is achieved with direct heating methods thereby reducing the creation of hot spots.
According to a second aspect the present invention provides a reactor vessel adapted for use in the reclamation of foundry sand having an open end and a closed end, inlet and outlet ports for sand, at least one outlet port for gaseous impurities, means provided within the vessel to heat the sand to a predetermined temperature, means to fluidise the sand within the reactor vessel and wherein the reactor vessel comprises an integral upper tubular portion and a lower depending frustoconical portion.
The walls of the frustoconical portion are preferably downwardly inclined at an angle of 30° to the horizontal. A closable outlet is preferably positioned at the lowest point of the frustoconical portion.
The circular cross section allows enhanced swirling of the sand within the vessel as the vessel does not have any corners in which sand can become lodged. Enhanced swirling increases the efficiency of the fluidisation and reclamation processes. When it is required to empty sand from the reactor the closable outlet in the lower portion is opened and the sand is allowed to drain out without the need for entering the reactor.
Sand entering the vessel may have passed through a sieve to remove large particles such as metallic particles.
The sand inlet port is preferably situated near to the open upper end of the reactor vessel and the sand may be fed through the inlet by means of a screw feed from a hopper. The inlet preferably exits into the vessel above a series of deflector plates. The deflector plates preferable extend outwardly from the upwardly extending exhaust flue. Preferably there are two opposing deflector plates each provided with one or more inwardly extending downwardly angled projections. Preferably the projections are staggered along the length of the deflector plates and extend inwardly beyond the central axis between the two deflector plates to provide a torturous passageway for the sand.
The sand passing between the deflector plates contacts the projections which serve to break up any agglomerates and also pre-heat the sand.
The sand outlet preferably comprises an outlet pipe of adjustable height and acts as a weir allowing the swirling, fluidised sand to flow over its edges and out of the vessel. The sand outlet passes through the wall of the reactor vessel and is preferably downwardly directed at an angle of 30° to the horizontal.
The sand inlet port and sand outlet port are preferably positioned diametrically opposite each other so that the sand travels round the vessel from inlet to outlet.
The means to create a fluidised bed preferably comprises a series of oxygen containing gas, e.g. air, inlet nozzles provided in the wall of the frustoconical lower portion of the reactor.
The nozzles may be at right angles to the wall of the frustoconical portion or alternatively they may be directed around the circumference of the frustoconical portion and inclined at an angle of 30° - 60° thereto to increase swirling of the sand around the reactor vessel and therefore improve fluidisation and heat transfer.
The nozzles preferably have individual gas supply lines. Valve means are preferably provided so that each nozzle can be opened or closed in isolation. The use of individual gas supply lines can improve gas flow through the nozzles into the reactor vessel and therefore increases swirling and fluidisation. Another advantage of the individual gas supplies is the improved ease of maintenance, each nozzle can be isolated in turn to locate any problems and in the event of a blockage the pressure to the blocked nozzle can be increased. Each nozzle can easily be inserted or removed, preferably by use of a plate which is locked in position on rotation by clamps.
Preferably the reactor vessel is loosely enclosed by an insulated frame to allow expansion of the vessel when heated, preferably provided with a lid to close the top of the reactor vessel.
An embodiment of the reactor vessel of the present invention will now be described with reference to the drawing, in which:
Figure 1 shows a cross sectional view of the reactor vessel of the present invention.
Figure 2 shows a cross sectional view of a nozzle of the present invention.
Figure 1 shows a reactor vessel 1 having an upper tubular section 2 and a lower integral frustoconical section 3. The angle (A) of decline of the wall of the frustoconical section 3 to the horizontal is 30°. The lowest point of section 3 is provided with an outlet 4 closed by a removable cover 5. The outlet 4 is provided with a flange 15 extending outwardly and transverse therefrom to which the cover 5 can be secured by means of bolts (not shown).
The reactor vessel 1 is supported by an insulated frame 6 having legs 7 and a lid 8 secured to said frame 6 by hinge 11 for easy opening and closing and the lid being provided with a lip 9 co-operating with a lip 10 provided on the frame 6, the lips 9, 10 having corresponding apertures for receipt of a securing bolt to hold the lid 8 closed during use. In an alternative embodiment the lid 8 may be secured to the frame 6 by means of two or more bolts passing through a number of sets of co-operating lips 9 and 10 (not shown).
The reactor vessel 1 is held in position within the frame 6 by an annular ring 40 positioned at the top of legs 7 and contacting lower portion 3. The vessel is provided with push fit locators 12a,b,c for connection of inlet and outlet tubes for sand and inlet for the heater to the vessel and which pass through the frame 6 and through the wall of the vessel 1 and which locators 12a,b,c are easily removed to allowed separation of the vessel 1 from the frame 6 for cleaning or repair.
The locators 12a,b,c each comprise a cylindrical hollow portion having a flange 15a,b,c extending outwardly from the circumference thereof at right angles to the cylindrical portion. The locators 12a,b,c pass through channels 13a,b,c provided through the insulated frame 6, and through apertures in the wall of the vessel 1 and flanges 15a,b,c are secured by bolts to flanges 14a,b,c extending from the circumference of channels 13a,b,c at right angles thereto. Sand may escape through the apertures in the walls of the vessel but will build up around the locators 12a,b,c to create a seal.
A sand inlet tube 16 having a flange 41 extending circumferentially and at right angles thereto joins the cylindrical portion of locator 12a and the flange 41 of inlet tube 16 is secured to flanges 14a and 15a by bolts. The sand inlet tube 16 exits into the upper portion 2 of the reactor vessel 1 near to the upper end thereof.
The sand is fed into the reactor vessel 1 along tube 16 by means of hopper 17 and a standard screw feed mechanism. The sand exits the inlet tube 16 inside the upper portion 2 of the reactor vessel 1 passes between vertical deflector plates 18 secured to the exhaust flue 26 and 18a secured to plate 18 at the end of the inlet tube 16. The vertical deflector plates 18 have projections 19 on their inner surface, each projection is angled downwards to the horizontal at about 45° and extends inwardly beyond the central axis between the two deflector plates.
A dust/impurities outlet tube 20 having a flange 42 extending circumferentially and at right angles thereto joins the cylindrical portion of locator 12c from the reactor vessel 1 to a dust bag house. The flange of impurities outlet tube 20 is secured to flanges 14c and 15c by bolts. The impurities outlet tube 20 is positioned near the upper end of the upper portion 2 of reactor vessel 1.
A sand outlet tube 21 is provided from the reactor vessel 1 and may lead to a cooling plant or a storage container. The outlet tube 21 passes through the wall of the upper portion 2 of the reactor vessel 1 at about one third the height of the upper portion 2 measured from the lower end thereof and through a channel 22 provided in the insulated frame 6. The outlet tube 21 and the channel 22 are angled downwardly at 30° to the horizontal. The height of the outlet tube 21 inside the vessel 1 is adjustable by pushing the tube 21 further into the reactor vessel 1 to increase the height or pulling it further out to decrease the height. The tube 21 is held in position by a flange clamp 23 co-operating with a flange extending circumferentially from channel 22 and angled so that the flanges are parallel to the frame 6.
The reactor vessel 1 is provided with a heater having a heating element 25 positioned at the bottom of the upper portion 2. Heat is provided by a gas burner 24 and a fan situated outside the reactor vessel 1 that project combustible gases through an open end of heating element 25. The heating element 25 comprises a hollow tube extending into the vessel and being arcuate in shape extending around substantially the whole circumference of the vessel and exiting into an exhaust flue 26. The flue 26 leads into a cowl 27 which passes through an aperture in the lid 8. The heating element 25 and flue 26 are provided with fins 28, 28a to increase heat transfer. The heating element 25 is supported by support 29 secured to the lower wall of portion 2 of reactor vessel 1. The open end of the heating element is received by the cylindrical portion of locator 12b from inside the reactor vessel 1 and the outlet 30 for the burner 24 and fan is also received in the cylindrical portion of the locator 12b and secured to flange 14b and 15b by means of a corresponding flange 36 on the burner 30 from outside the vessel 1. The flue is supported at the upper end of upper portion 2 by position locators 35.
Oxygen containing gas, e.g. air, inlet nozzles 31 are provided in the walls of the lower portion 3 of reactor vessel 1, the nozzles each have a gas supply line 32 fed by an air tank 33 supplied by a fan (not shown). The nozzles 31 are provided with valves to allow one or more of the nozzles 31 to be closed independently of the other nozzles 31. The nozzles are at right angles to the walls of the lower portion 3 of the reactor vessel 1. Alternatively the nozzles may be directed around the circumference of the frustoconical portion and inclined at 30-60°C thereto.
Temperature sensors are provided in portions 2 and 3 and a pressure sensor is provided in portion 2.
Figure 2 shows a gas inlet nozzle 31 which passes through and is secured to a plate 50. The nozzle 31 has a gas inlet end 31a and a gas outlet end 31b having a small outlet point 53. The gas inlet 31a and the gas outlet 31b are joined by a substantially J-shaped pipe so that the outlet end 31b is hooked and the outlet point 53 is directed towards but slightly spaced apart from the inner surface of the wall 52 of the lower portion 3. The design makes it difficult for sand to enter the outlet point 53 and cause a blockage.
The nozzle 31 is locked in position by means of the plate 50 being held in position against the outer surface of the wall 52 of the lower section 3 by two sets of clamps 51.
In use the nozzle is passed through an aperture 54 in the wall 52 of the lower portion 3 until the plate 50 contacts the outer surface of the wall 52 of the lower portion 3. The plate is then rotated through 90° so that the plate passes between the clamps 51 and the wall 52 of the lower portion. The clamps are then tightened.
In use of the sand reclamation apparatus sand from the foundry is fed into hopper 17 and down sand inlet tube 16 by means of the screw feed mechanism. The sand may already have passed through a sieve to remove large particles such as metallic particles although some will remain in the sand and will fall to the bottom of the vessel owing to their weight. The sand exiting the inlet tube 16 passes between deflector plates 18 contacting the projections 19 as it falls which breaks up any lumps of sand and pre-heats the sand owing to the proximity of the deflector plates to the flue.
When the process is begun the level of sand must cover the heating element 25 before the burner is turned on and heats the heating element to approximately 700°C. The used foundry sand fed into the vessel 1 is fluidised by feeding an oxygen containing gas such as air through the nozzles 31 via supply pipes 32 and air tank 33. The fluidisation of the sand gives uniform heating so that impurities around the sand are burnt off usually as oxide dusts which get carried upwards in the airflow to the area above the sand bed which is at a higher temperature than the sand bed, the dust is burnt further and then sucked through the impurities outlet tube 20 to the dust bag house.
Exhaust gases from the burner are vented to the atmosphere via flue 26. The flue is provided with a damper which adjusts the exhaust gas outlet rates and consequentially the running temperature of the apparatus.
The positioning of the sand inlet 16 and sand outlet 21 ports diametrically opposite to one another ensures that the sand entering the vessel 1 through inlet port 16 has to travel at least half way round the vessel 1 to get to the outlet port 21 which should allow sufficient time for the impurities to be burnt off.
The reactor vessel 1 can be removed from the frame 6 by removing the burner 24, the sand inlet pipe 16, the impurities outlet pipe 20 and the sand outlet pipe 21. If any sand is left inside the vessel it can be drained by unbolting the cover 5 of the outlet 4. The lid 8 can then be unbolted and raised after removal of cowl 27. The exhaust flue 26 and heating element 25 can be lifted out of the reactor vessel 1. The locating elements 12a,b,c can then be unbolted and removed and the reactor vessel can be lifted out of the frame 6. Re-insertion of the vessel 1 is the reverse of the procedure described above.

Claims

A reactor vessel (1) adapted for use in the reclamation of foundry sand the vessel (1) having an open end and a closed end, inlet (16) and outlet ports (21) for sand, at least one outlet port (26) for gaseous impurities, means to fluidise the sand within the reactor vessel (1) and means provided within the vessel to heat the sand to a predetermined temperature wherein the means to heat the sand to a predetermined temperature comprises an indirect heater.
A vessel according to Claim 1 which comprises an integral upper tubular portion (2) and a lower depending frustoconical portion (3).
A vessel (1) according to Claim 2 wherein the means to create a fluidised bed comprises a series of oxygen containing gas inlet nozzles (31) provided in the wall of the frustoconical lower portion (3) of the reactor (1).
A vessel (1) according to Claim 3 wherein the nozzles (31) are at right angles to the wall of the frustoconical portion (3).
A vessel (1) according to Claim 3 wherein the nozzles (31) are directed around the circumference of the frustoconical portion (3) and inclined at an angle of 30° - 60° thereto.
A vessel (1) according to any one of Claims 3-5 wherein the nozzles (31) have individual gas supply lines (32).
A vessel (1) according to Claim 6 wherein valve means are provided so that each nozzle (31) can be opened or closed in isolation.
A vessel according to any preceding claim wherein the heater includes a heating element (25) comprising a hollow metal tube extending into the vessel (1) having an inlet for hot gases from a burner located externally of the vessel and an outlet for exhaust gases (26).
A vessel (1) according to any preceding claim wherein the sand inlet port (16) exits into the vessel above a series of substantially vertical deflector plates (18 and 18a).
A vessel (1) according to Claim 9 wherein there are two opposing deflector plates (18 and 18a) each provided with one or more inwardly extending downwardly angled projections (19).
A vessel (1) according to Claim 10 wherein the projections (19) are staggered along the length of the deflector plates (18 and 18a) and extend inwardly beyond the central axis between two deflector plates to provide a torturous passageway for the sand.
A vessel (1) according to any preceding claim wherein the sand outlet (21) comprises an outlet pipe of adjustable height and acts as a weir allowing the swirling, fluidised sand to flow over its edges and out of the vessel (1).
A vessel (1) according to any preceding claim wherein the sand inlet port (16) and sand outlet port (21) are positioned diametrically opposite each other so that the sand travels round the vessel (1) from inlet (16) to outlet (21).
A vessel (1) according to any preceding claim which is loosely enclosed by an insulated frame (6) to allow expansion of the vessel (1) when heated.