EP0483933A2 - Process and apparatus for refining bulk material - Google Patents

Abstract

The invention relates to a process and an apparatus for refining the particle surface(s) of contaminated bulk material, in particular for the (secondary) refining of sand, in particular thermally (pre-) regenerated sand, in particular used foundry sand, the bulk material which is to undergo refining or secondary refining is subjected to a gas under excess pressure (= a stream of compressed gas) and fluidised by this supply of (compressed) gas in such a way that refinement is carried out (exclusively by friction or rubbing of the surface of the particles without subjecting the particles to impact against fixed or movable walls), and to an apparatus which has a vessel provided with an inlet and an outlet for the bulk material and, for the formation of a fluidised layer, is provided with a gas-permeable inlet flow base, characterised by at least one nozzle arranged above the inlet flow base and connected to a source of compressed gas, the flow of compressed gas from the nozzle being directed into the interior of the fluidised layer. <IMAGE>

Description

The invention relates to a method for the (mechanical) cleaning of the grain surface (s) of contaminated bulk material, in particular for the (post) cleaning of, in particular, thermally (pre) regenerated sand, in particular foundry used sand.

The present invention further relates to a device for carrying out the aforementioned method with a container provided with a bulk material inlet and a bulk material outlet, which is provided with a gas-permeable inflow base for the formation of a fluidized bed, which is supplied with fluidizing gas from a fluidizing gas source.

As is well known in the relevant specialist world, this bulk material generally falls in a wide variety of technological processes using bulk material (such as and in particular sand) after the relevant process has been carried out. in a contaminated form and was therefore not only qualified as a waste product, but was also treated accordingly by dumping it in landfills or otherwise disposing of it (and thereby also preventing it from being partially reused).

This applies, for example, and in particular to old foundry sands which have always been present in large quantities and which have been treated as molding materials with inorganic and / or organic chemical binders and which are so contaminated after the casting process, in particular due to the previously added binders. that old foundry sand as such (ie without regeneration) cannot easily be reused. A regeneration and thus an (at least partial) recovery of contaminated bulk material requires in the aforementioned exemplary case that binder casings and other contaminants of the grains of sand essentially consisting of quartz are separated from them and separated out.

Such binder casings occur in the case of foundry (waste) sand in the case of inorganically bound molding sands, in particular because the bentonite generally added as molding material - depending on the heat applied during casting - on the surface of the sand grains by fireclaying (oolithization) essentially in the form of a shell fixed. Furthermore, shiny carbon and additives that form it continue to contaminate the molding sand used for casting (= old foundry sand).

As summarized in DE-OS 4 008 849, technologies for regenerating used foundry sands have already been proposed in DE-OS 31 03 030, 38 15 877, 30 19 069 and US Pat. No. 2,783,511. which, however, lead to satisfactory results neither from a technical nor from an economic point of view. DE-OS 4 008 849 itself proposes a method and a device for the regeneration of old foundry sands, which leads to very considerable technical and thus also economic improvements compared to the previous state of the art, but it has been shown that this technology too is still room for improvement, as follows:

• pH-Wert
• Oolithisierung
• Schlämmstoff
• Gesamt-C-Inhalt
• Glühverlust und
• Körnung < 90 µ

gekennzeichnet, wobei die (zulässigen) Grenzwerte dieser Parameter für jedes Formverfahren aufgrund entsprechender Erfahrungen definiert bzw. festgelegt sind. Werden diese Parameter-Grenzwerte überschritten, so ist eine Wiederverwendbarkeit von regeneriertem Gießerei-Altsand zwar grundsätzlich ebenfalls möglich, jedoch nur in entsprechenden sog. Formstoffkreisläufen.The quality of the regrind for (as far as possible) unrestricted reusability for various molding processes is determined, in particular, by the parameters

• PH value
• Oolithization
• Slurry
• Total C content
• Loss on ignition and
• Grain size <90 µ

characterized, the (permissible) limit values of these parameters for each molding process being defined or established based on corresponding experience. If these parameter limit values are exceeded, the reuse of regenerated foundry sand is in principle also possible, but only in the so-called molding material cycles.

It is therefore always necessary to check the specific task or, taking into account the specific task, to check which limit values for the specific application must be observed.

The regenerate from a thermal foundry sand processing process is basically or generally already of a relatively high quality, but still contains constituents of charred resins, additives and / or chamotte on the grain surface as well as undesirable (because disruptive) fines. To optimally set the desired or required quality of the regenerate, it would therefore be necessary or highly desirable to also at least partially or predominantly free the regenerate from these contaminants. The same applies evidently to other processing methods.

If one thinks of such a (post) cleaning of a mechanical (post) cleaning, it should be noted that it is known per se that the mechanical cleaning of bulk goods, which is always desirable and gentle on the grain, results in the cleaning effect essentially due to friction or abrasion effects is achieved when the individual bulk goods (in the aforementioned example, therefore, the grains of sand) move rubbing against each other relative to each other. Too high a relative speed of the bulk material grains to one another or to other cleaning elements is critical insofar as there is a reduction in the grain size, grain destruction and / or damage to the grain surfaces and in particular if the (subsequent) cleaning of the bulk material grains is too intensive considerable wear and tear of cleaning parts due to impact effects with corresponding (too high) pulse energy.

Several methods and devices are known with which mechanical removal of such contaminants is effected. Impact and friction effects on the grains of sand among themselves, as well as on fixed or moving ones Apparatus parts causes. Examples include impact and ball mills, vibration pots and scrubbing drums, as well as the particularly frequently used impact cleaning systems according to Jacob, Simpson and Webac. In order to keep grain damage and destruction as low as possible, attempts are generally made to keep the impact forces lower by means of suitable measures, for example inclination of the impact surfaces, and to make friction effects more effective.

Common to all these devices and the processes to be carried out with them is the considerable disadvantage of a relatively large grain destruction, which i.a. The higher the quality requirements of the regrind, the greater the reason, because if the quality requirements are relatively high, logically and accordingly consequently the impact speeds are set accordingly high or the number of passes through the cleaning apparatus is increased, but at the same time necessarily in addition to the relative good cleaning effect comes to a high degree of grain destruction.

The present invention is therefore based on the object of providing a method of the type described at the outset and a device which is suitable and specific for carrying it out, by means of which the contaminated grain surfaces of bulk material can be cleaned and cleaned gently (mechanically) and in a manner which is gentle on the grain.

As a solution to the procedural part of the above-mentioned object, it is provided according to the invention that the bulk material to be cleaned or subsequently cleaned is subjected to a gas flow which is under pressure and is put into a swirling state by this gas application, so that the cleaning takes place while avoiding impact or impact stresses the grains on fixed or movable walls are made solely by rubbing or abrasive (surface) stress on the grains, while the solution of the device Part of the above object in a generic device for carrying out the aforementioned method is characterized by at least one nozzle arranged above the inflow floor, the pressure gas flow of which is directed into the interior of the fluidized bed, in which the bulk material to be cleaned or cleaned is expediently and accordingly preferably located.

Accordingly, with the present invention, as a highly advantageous addition to the thermal treatment according to DE-OS 40 08 849 (sd in particular according to Example 2 and the technology described so far in this document), it is proposed according to the invention that the bulk material to be cleaned or re-cleaned into one To shift the fluidized bed state, as will be explained in detail below.

It is pointed out that the speed of sound of the gas in the nozzle with a pre-pressure in front of the nozzles of approx. 2.3 bar abs. is already reached (with a fluidized bed back pressure of approx. 1.15 bar abs.), and that the inflow velocity (= speed of sound) remains constant with increasing admission pressure, but the inflowing gas mass (and thus the impulse) increases (nevertheless) with increasing pressure.

It is particularly important here that, in contrast to the prior art methods described above, the dwell time within which these abrasive effects are effective can be extended practically as long as desired. It follows from this that the desired ideal type of mechanical sand regeneration is actually achieved by the method according to the invention, exclusively by rubbing off the adhering binder shells or other impurities.

In an embodiment of the invention, the nozzles can be arranged in height and / or laterally offset from one another, so that there can be no collision of sand streams accelerated by opposing air jets.

The method according to the invention also offers the possibility of letting the cleaning process run in the heat. As a result, organic components, e.g. from the remains of plastic binders, can be removed thermally. In this way it is also possible to burn out such organic compounds, which contaminate the dusts discharged from the fluidized bed with the exhaust gas, into harmless residues. With this variant, the method according to the invention thus offers the possibility of combining the thermal and mechanical operations of thorough sand regeneration in a single step.

This economically very positive possibility is supplemented by some even more significant advantages. It is particularly important to note that the fluidized bed follows its own laws that differ from those of pneumatic conveying. This results in a much more economical mode of operation, since only a relatively small amount of energy is required to fluidize a solid. Only a small amount of energy is sufficient for the air flow that flows in to generate the flow phenomena described above in the fluidized bed. In sum, this results in an energy expenditure for the inventive method which is only about 20% of the energy consumption required for conventional pneumatic methods. These economic advantages are supplemented by a high yield of high-quality sand regenerate with little loss of grain.

The greater benefit, however, lies in the lower destruction of good grain and the lower costs for transport, new sand and landfill. About 15% by weight less grain is destroyed. The average grain size in the proportion> 0.09 falls in the course of cleaning by approx. 10% with a cleaning time of 1 hour.

In terms of the method, it is preferably provided that the pressurized gas flow is directed at at least one loading point onto / into the bulk material to be cleaned, with the at least one pressurized gas loading point being most preferably arranged in the edge region of the bulk quantity to be cleaned in each case, but can obviously also be located in its interior.

In addition, it has proven to be expedient if at least one second pressurized gas pressurization point is arranged at least substantially opposite one another, so that this can result in - possibly at several points or several "polluter points" - that the bulk material to be cleaned lies in the area of (at least) two gas flows which are essentially opposite to each other and is therefore cleaned particularly intensively (afterwards), the friction or abrasive effects being an (exactly) dosed impact effect between the grains (but not on walls) or internals) is superimposed by the choice of the vortex state of the layer (more or less loosened) and the gas jet pulse (pre-pressure in front of the nozzle) only according to different penetration depths into the layer.

In an embodiment of the present invention, it has also proven to be particularly expedient if the pressurized gas at at least one pressurized gas application point is directed essentially tangentially to the outer surface of the bulk material quantity to be cleaned, as a result of which - in particular if this measure is implemented at two or more points - the bulk material to be cleaned can be set into a rotational movement which positively influences the desired effect, the friction effect being able to be increased on wear walls or wear internals suitable for this purpose.

It has not only proven to be extremely useful if the pressurization intensity of at least one (preferably all) pressurized gas pressurization points can be adjusted so that the pressurized gas pressurization can be optimally adapted to the respective technological task, but if pressurized gas compressed air is also used, which the in here Not only solves the task in question in the most expedient manner, but is also available or can be made available inexpensively.

In the device according to the invention, at least one second nozzle is therefore preferably arranged on at least one first nozzle on the opposite side of the fluidized bed or of the bulk material to be cleaned, the flow intensity of at least one (preferably all) nozzle (s) preferably being adjustable, i.e. can be controllable or regulatable.

As already explained above from the point of view of process technology, the device according to the invention can preferably have a plurality of nozzles which are preferably arranged in pairs essentially opposite one another, in such a way that the central axes of the nozzles form parallels, have an angle to one another or else lie on a common line.

Further preferred refinements of the present invention (be it in terms of method or device) are described in the subclaims.

Fig. 1

eine schematische Darstellung einer erfindungsgemäßen Vorrichtung in Seitenansicht; und

Fig. 2

eine schematische Darstellung in der Art eines Schaltschemas, welche insbesondere die Druckgasführung verdeutlichen soll.

The invention is explained below using an exemplary embodiment with reference to a drawing. It shows:

Fig. 1

a schematic representation of a device according to the invention in side view; and

Fig. 2

is a schematic representation in the manner of a circuit diagram, which is intended to clarify in particular the compressed gas flow.

1 of the drawing shows a device 1, designated as a whole for mechanical subsequent cleaning of thermally (pre-) regenerated foundry used sand 2, with a bulk material inlet (not shown in detail) and a container 3 provided with a bulk material outlet, which is essentially rectangular or is conical to its vertical axis of symmetry 4.

In order to form a fluidized bed in the area of the old foundry sand 2 to be regenerated, the container 3 is provided with a gas-permeable inflow base 5 which e.g. consists of a ball bed and from below via a line 6 from a compressed air source, not shown, in the direction of arrow 7 with fluidizing vortex air.

Above the inflow base 5, 8 nozzles 9 are arranged in the region of the fluidized bed, which are essentially opposite each other in pairs and are fed by a compressed gas source (not shown) in the direction of arrow 10 via a common throttle element 11, which is arranged in a compressed air supply line 12 and feeds a ring line 13 which is connected to the nozzles 9. The compressed air supply line 12 and thus the ring line 13 can be connected to a single throttle element 11, so that the exposure intensity of the foundry sand 2 to be cleaned can be adjusted uniformly at all nozzles 9; however, several of the compressed air supply line 12 'can also be shown in FIG. 2 (In the example according to FIG. 2 shown in plan view) branch off the compressed air supply line 12 ″, in each of which a throttle element 11 is arranged, so that the exposure intensity of the old foundry sand 2 to be cleaned can be adjusted accordingly differently in different zones of the fluidized bed. A corresponding possibility of adaptation can be seen not only - as in the exemplary embodiment according to FIG. 2 - in different zones of the fluidized bed, but it may also be possible to provide a different application intensity in one zone if each of the nozzles 9 has its own throttle element 11 immediately arranges, as is readily apparent to the person skilled in the art and should accordingly be clear.

It should be pointed out that the container 3 does not necessarily have to have a rectangular / conical cross section, but that it can also be circular, for example. A circular cross section of the container 3 (at least in the area of the fluidized bed 8) is particularly expedient if at least some of the nozzles 9 are arranged in such a way that the bulk material 2 to be regenerated (or the fluidized bed 8) rotates during operation For example, and in particular about the rotational symmetry axis 4 of the container 3, as this can often be particularly useful.

It should also be pointed out that, in an embodiment of the present invention, dividing walls extending into the container 3, starting in the calming space 3 ', can be arranged up to just above the inflow floor 5 of the fluidized bed 8, which divides the free container interior into at least two (or possibly also more) Subdivide sectors. The purpose of this is to avoid the back-mixing of already largely cleaned bulk goods with newly added material. This means that several fluidized beds are connected in series.

In the case of fluidized beds with a circular cross section, the subdivision can be made by concentric regions or by fluidized beds arranged one above the other.

Furthermore, it should be noted that the outflow diameter of the nozzles 9 in the aforementioned embodiment is 3.4 mm, but could also be both smaller and larger.

For the rest, it should be noted that the container 3 can be provided with a circumferential rubber lining 14 in the region of the fluidized bed 9, and that one or more heat exchangers (not shown) can be arranged in the upper region of the fluidized bed 8 above the nozzles of the container 3 which is reusable or reusable heat from the post-cleaning process, especially if the post-cleaning fluidized bed is connected downstream of a thermal fluidized bed.

From the section 3 'of the container 3, the gas introduced into the device 1 according to the arrows 7 or 10 through the lines 6 or 12 or 12' after exiting the fluidized bed 8 and thus out of the used sand 2 to be cleaned upwards and finally out of device 1 according to arrow 15.

Furthermore, reference is made to FIG. 2 that this can also represent a side view (and not a top view) of a preferred embodiment.

With the present invention, a method and a highly practical device for carrying it out have been created, by means of which bulk material to be cleaned, which ia was previously used technologically, is to be cleaned (mechanically) or re-cleaned in a highly expedient manner, with extreme (adjustable) grain protection with an incredibly effective cleaning efficiency, the subject of the present invention being in particular also for subsequent cleaning of foundries -Own sand has proven to be extremely useful, which had previously been subjected to thermal (but possibly also other) processing.

REFERENCE SIGN LIST (LIST OF REFERENCE NUMERALS)

1

contraption

2nd

Old foundry sand (pre-regenerated)

3rd

Container 3 'section (of 3)

4th

Axis of symmetry

5

Inflow floor (of 3)

6

management

7

arrow

8th

fluidized bed

9

Nozzles

1

0 arrow

11

Throttling device

12, 12 '

Compressed air supply line

13

Loop

14

Rubber lining

15

arrow

16

17th

18th

19th

20th

21

22

23

24th

25th

26

27th

28

29

30th

Claims (20)

Process for cleaning the grain surface (s) of contaminated bulk material, in particular for the (post) cleaning of, in particular, thermally (pre-) regenerated sand, in particular foundry sand, characterized in that the bulk material to be cleaned or subsequently cleaned has such a pressure standing gas (= a pressurized gas flow) and is put into a swirling state by this (pressurized) gas supply, so that the cleaning while avoiding impact or impact loads on the grains on fixed or movable walls is caused solely by rubbing or abrasive (surfaces -) The grains are stressed. A method according to claim 1, characterized in that the compressed gas flow is directed at at least one loading point onto / into the bulk material to be cleaned. Method according to Claim 2, characterized in that the at least one pressurized gas application point is arranged in the edge region of the bulk material quantity to be cleaned in each case. Method according to one or more of the preceding claims, characterized in that at least one first pressurized gas application point is opposite at least one second pressurized gas application point, the axes of which are at an angle, form parallels or are arranged on a common line. Method according to one or more of the preceding claims, characterized in that the pressurized gas is conducted at least at one pressurized gas application point substantially tangentially to the outer surfaces / outer region sections of the bulk material to be cleaned / the bulk material quantity to be cleaned. Method according to one or more of the preceding claims, characterized in that compressed air is used as the compressed gas. Method according to one or more of the preceding claims, characterized in that the intensity of the pressurized gas is adjustable. Device for cleaning the grain surface (s) of contaminated bulk material, in particular for the (post) cleaning of, in particular, thermally (pre) regenerated sand, in particular Old foundry sand, with a container provided with a bulk material inlet and a bulk material outlet, which, in order to form a fluidized bed, is provided with a gas-permeable inflow base, to which fluid gas is to be applied from a fluid gas source, for carrying out the method according to one or more of the preceding claims by means of at least one nozzle (9) arranged above the inflow base (5) and connected to a compressed gas source, the compressed gas flow of which is directed into the interior of the fluidized bed (8). Apparatus according to claim 8, characterized in that at least one second nozzle (9) is assigned to at least one first nozzle (9) on the opposite side of the fluidized bed (8) or of the bulk material (2) to be cleaned. Apparatus according to claim 8 or 9, characterized in that the flow intensity of at least one nozzle (9) is adjustable. Apparatus according to claim 9, characterized in that the flow intensity of all nozzles (9) is adjustable. Device according to one or more of claims 8 to 11, characterized in that a plurality of nozzles (9) are provided, each of which are arranged in pairs essentially opposite one another or whose center lines form parallels. Device according to one or more of claims 8 to 12, characterized in that the inflow base (8) or the like in a manner known per se from a ball bed consists. Device according to one or more of claims 8 to 13, characterized in that the container (3) has an essentially circular cross section at least in the region of the fluidized bed (8). Device according to one or more of claims 8 to 14, characterized in that at least some of the nozzles (9) are arranged in such a way that the bulk material (2) to be cleaned rotates during operation, in particular around the axis of rotation symmetry (4) of the container (3) is to be moved. Device according to one or more of claims 8 to 13 and possibly 15, characterized in that the container (3) has a rectangular cross section at least in the region of the fluidized bed (8). Device according to one or more of claims 8 to 16, characterized in that in the container (3) at least in the region of the fluidized bed (8) or the like partition walls. are arranged, which divide the free container interior into at least two sections. Device according to one or more of claims 8 to 17, characterized in that the diameter of the nozzles (9) is approximately 1 to 2 mm. Device according to one or more of claims 8 to 18, characterized in that the container (3) at least in the region of the fluidized bed (8) with a buffer material (14) such as e.g. Rubber lined. Device according to one or more of claims 8 to 19, characterized in that at least one heat exchanger is arranged above the cleaning area.

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