FI20245297A1 - Granular material handling equipment - Google Patents

Abstract

Apparatus (1) for treating granular material comprises a furnace unit (10) and a cooling unit (20), wherein the furnace unit (10) comprises a cylindrical rotatable heated furnace (11) in which the material to be treated is subjected to a thermomechanical treatment, and the cooling unit (20) comprises a cylindrical rotatable drum (21) for cooling the material treated in the furnace unit (10). The furnace unit (10) comprises at least two independently controllable heaters outside the furnace (11) in the axial direction of the furnace (11) for forming at least two separately heated heating zones in the furnace (11) in its axial direction.

Description

Equipment for handling granular material

Background of the invention

The invention relates to equipment for processing granular material.

FI publication 128118 B discloses an apparatus for cleaning used foundry sand. The apparatus comprises a rotatable heated drum, which forms a furnace in which the used foundry sand is subjected to a thermomechanical treatment. Furnaces such as those disclosed in FI publication are typically heated from the inside of the furnace at one end of the furnace by a gas or liquid gas burner. However, a problem with furnaces such as those mentioned is the control of the temperature profile of the material inside the furnace.

Brief description of the invention

The aim of the invention is to provide a new type of apparatus and its use for processing granular material.

The solution according to the invention is characterized by what is stated in the independent claims.

The apparatus comprises a furnace unit and a cooling unit, wherein the furnace unit comprises a cylindrical rotatable heated furnace in which the material to be treated is subjected to a thermomechanical treatment, and the cooling unit comprises a cylindrical rotatable drum for cooling the material treated in the furnace unit. The furnace unit further comprises at least two independently controllable heaters outside the furnace in the axial direction of the furnace for forming at least two separately heated heating zones in the furnace in its axial direction.

The advantage of the solution is that the material processed in the oven

S 25 time-controlled temperature profile, because the material being processed in the oven is heated

N indirectly by heating the furnace shell, and since the desired heating effect can be applied to the furnace shell with the heater corresponding to each heating zone in the corresponding section of the furnace shell. = Since the material being processed in the furnace must typically be at a certain minimum temperature in order for the desired reactions to occur in terms of the final result of the processing, the solution according to the 2 presented can in particular ensure an essentially uniform temperature profile of the material being processed in the drum throughout the entire heated area of the furnace.

N in such a way that the temperature of the material does not drop too low in terms of the aforementioned reactions, but also does not rise unnecessarily high in terms of efficient energy use.

The cooling unit following the furnace unit cools the granular material processed in the furnace unit to a temperature at which it can be immediately reused. For example, in foundries, the equipment according to the solution enables the immediate use of cleaned foundry sand in the manufacture of new molds. In this case, the manufacture of molds and the treatment of used foundry sand can be formed into a continuous process without intermediate storage of cleaned foundry sand, which also minimizes the amount of sand required in the cycle.

Certain embodiments of the invention are set forth in the dependent claims.

Brief description of the patterns

The invention will now be described in more detail in connection with some embodiments, with reference to the accompanying drawings, in which Figure 1 schematically shows a side view of an apparatus for processing granular material, Figure 2 schematically shows a side view and partly in cross-section of an oven unit, Figure 3 schematically shows a side view and partly in cross-section of an oven unit according to Figure 2, Figure 4 schematically shows a side view and partly in cross-section of an oven used in an oven unit, Figure 5 schematically shows a side view and partly in cross-section of another oven unit, and Figure 6 schematically shows a side view of another apparatus for processing granular material.

In the figures, certain embodiments of the invention are shown for clarity.

N for simplification. Similar parts are marked with the same numbers in the figures.

With numbers. 3

Detailed description of the invention

T Figure 1 shows schematically, from a side view, an apparatus 1 - 30 for processing granular material. Said granular material may be, for example, waste sand. Said waste sand may be, for example, foundry sand comprising a clay or resin-based binder. Said granular material may also be

N some other heat-treatable granular material, such as, for example, calcinable granular material.

The device 1 is specifically intended for cleaning granular material from impurities by applying a thermal-mechanical treatment to the granular material. The purpose of the treatment is to remove various impurities from the granular material so that the granular material can be reused either for its previous intended use before cleaning, or for some other intended use. When cleaning used foundry sand, the aim is to remove the binder remaining on the surface of the sand grains. After this, the sand can be reused either as foundry sand or for some other intended use.

The apparatus 1 according to Figure 1 comprises a furnace unit 10 and a cooling unit 20. The furnace unit 10 comprises a cylindrical rotatable heated furnace 11 for thermomechanically treating the material fed into the furnace 11 to remove impurities in the material. The furnace unit 10 further comprises a rotation motor 12 for rotating the furnace 11 around its longitudinal axis.

The cooling unit 20 comprises a cylindrical rotatable drum 21 for cooling the material processed in the furnace unit 10. The cooling unit 20 further comprises a rotation motor 22 for rotating the drum 21 about its longitudinal axis.

Figure 2 shows schematically a furnace unit 10 seen from the side and partially in cross-section in the axial direction of the furnace 11. Figure 3 shows schematically a furnace unit 10 seen from the end and in cross-section according to Figure 2. Figure 4 shows schematically a furnace 11 used in the furnace unit 10 seen from the side and in cross-section in the axial direction of the furnace 11.

With reference to Figures 1, 3 and 4, the general operating principle of the apparatus 1 shown in Figure 1 is as follows. The material to be processed is fed into the furnace unit

N 10 into the furnace 11 at the first end 11a of the furnace 11, as shown schematically in Figure 1 by the arrow indicated by the reference sign Fin10. The material fed into the furnace 11 flows through the furnace 11, and the material processed in the furnace 11 is removed from the furnace 11 at the second end 11b of the furnace 11, as shown schematically in Figure 1 by the reference sign

E Douro with the arrow indicated. The material processed in the furnace unit 10 is fed to the cooling

N to be placed in the drum 21 of the cooling unit 20 at the first end of the drum 21

N 21a, as shown schematically in Figure 1 with the reference number Finzo,

N. The material cooled in the drum 21 is removed from the drum 21 by the drum 21 operating

N 35 at the end 21b, as shown schematically in Figure 1 by the arrow indicated by the reference symbol Dourzo.

The cylindrical shell of the furnace 11, typically made of iron, partly defines at least one heated chamber in the axial direction of the furnace 11. According to one embodiment, the entire internal volume of the furnace 11 forms one continuous unconfined heated chamber extending from the first end 11a of the furnace 11 to the second end 11b of the furnace 11. According to another embodiment, the internal volume of the furnace 11 is divided into two or more chambers partially separated from each other in the axial direction of the furnace 11, whereby all said chambers or only some of said chambers may be heated chambers.

In each chamber of the furnace 11 heated to a high temperature, the material to be treated is subjected to a thermal effect, as a result of which the material to be treated is heated and the combustible material therein is burned away from the material to be treated. The temperature to which the material to be treated is heated depends on both the properties of the material to be treated and the properties of the material to be removed from the material to be treated. In the case of foundry sands, the temperature to which the material to be treated is typically about 750-950 degrees.

As the furnace 11 rotates, the material to be processed on the bottom of the furnace 11 rises with the furnace 11 along the inner surface of the furnace 11 until it falls back to the bottom of the furnace 11. As the material to be processed rises with the furnace 11 and falls back to the bottom of the furnace 11, the grains of the material to be processed rub and/or strike each other and/or the inner surface of the furnace 11. This subjects the material to be processed to mechanical treatment, which enhances the detachment of the material to be removed from the surface of the grains of the material to be processed from the material to be processed. In addition, said mechanical treatment causes mixing in the material to be processed, which evens out any temperature differences in the material on the bottom of the furnace 11.

The mechanical treatment applied to the material to be treated can be enhanced in the furnace 11 by one or more lifters 13 arranged on the inner surface of the furnace 11 shell. Figures 3 and 4 show schematically one such

T 30 lifter 13. Lifter 13 is from the direction of the first end 11a of the furnace 11 to the second end 11a of the furnace 11.

E extending towards the end 11b and from the inner circumference of the furnace 11 shell towards the central part of the furnace 11

N-oriented cantilever. Due to the effect of the lifter 13, a larger portion of the processed mass

N pieces of material can be lifted upwards with the oven 11 at a time as the oven 11 rotates, and

N is also higher than before. This increases the efficiency of the material being processed.

N 35 mixing effect and mechanical handling on the material, because a larger portion of the material can move with the furnace 11 and fall from a higher position back to the bottom of the furnace 11.

The hot material processed in the furnace unit 10 is cooled in the drum 21 of the cooling unit 20. The cooling can be carried out, for example, by a cooled or uncooled air flow at ambient temperature arranged from the second end 21b of the drum 21 to the first end 21a of the drum 21. In addition to this or alternatively, the shell of the drum 21 can be cooled from the outside. The above-mentioned lifters can also be used in the drum 21 to enhance the cooling effect on the material in the drum 21 by keeping the material in the drum 21 in motion and thus more evenly exposed to the cooling effect.

The granulated material treated with the cooling unit following the furnace unit can be cooled to a temperature at which it can be immediately reused. For example, in foundries, the equipment according to the solution enables the immediate use of cleaned foundry sand in the manufacture of new molds. In this case, the manufacture of molds and the treatment of used foundry sand can be formed into a continuous process without intermediate storage of cleaned foundry sand, which also minimizes the amount of sand needed in the cycle.

In order to heat the oven, the oven unit comprises at least two independently controllable heaters outside the oven in the axial direction of the oven to form at least two separately heated heating zones in the oven in its axial direction. In other words, the oven unit comprises at least a first heater and a second heater outside the oven in the axial direction of the oven, which are independently controllable to form a separately heated first heating zone and a second heating zone in the axial direction of the oven.

N Figures 2 and 3 show an embodiment of such a furnace unit 10. The furnace unit 10 according to Figures 2 and 3 comprises heaters 30 arranged on the outside of the furnace 11 at a distance of 30 from the outer surface of the shell of the furnace 11 in the radial direction of the furnace 11. Said heaters 30 are adapted to heat

The furnace 11 jacket and the material to be processed in the furnace 11 via said jacket

N materials. In the embodiment shown in Figure 2, there are 30 heaters in the furnace 11.

In the N cial direction, four pieces, but the 30 numbers of the mentioned heaters

The number of N may vary. Thus, said heaters 30 may be arranged in the axial direction of the furnace 11.

There may be two or more in the N 35 direction. In the embodiment shown in Figure 2, heaters 30 are arranged substantially along the entire length of the furnace 11, but there may also be sections in the furnace 11 where there is no heater.

The heaters 30 are independently controllable, i.e. separately from each other, whereby the said heaters 30 form a number of separately heated heating zones in the oven 11 in its axial direction corresponding to the number of heaters 30. Insulation 14 can be arranged around the oven 11 and the heaters 30, as appropriate, which both prevents heat from escaping from the oven unit 10 and protects the surroundings of the oven unit 11 from hot temperatures.

By using the said separately controlled heaters, heating zones are provided in the furnace 11 shell that are heated separately in the axial direction of the furnace 11, so that the desired heating effect can be applied to the furnace 11 shell in the section of the furnace 11 shell corresponding to each heating zone by the heater corresponding to the heating zone. The solution provides for the controlled formation of a temperature profile in the material being processed in the furnace 11. Since the material being processed in the furnace 11 must typically be at a certain minimum temperature in order for the desired reactions to occur in terms of the final result of the processing, by using the said separately controlled heaters, a substantially uniform temperature profile of the material being processed in the furnace 11 can be ensured in particular over the entire heated section of the furnace 11. In this case, each heater 30 produces such a heating effect for the heating zone corresponding to the heater 30 that the temperature of the material being processed in the furnace 11 would be essentially the same in each heating zone. Compared to a furnace heated by a gas or liquid gas burner at the end of the furnace, there is also the advantage that excessive heating of the material in the vicinity of the flame, which may be caused by the burner flame, can be avoided. In addition, some heaters corresponding to the heating zones can also be switched off completely if the material being processed in the furnace 11 is

In order to achieve the N-setting effect, it is not necessary to heat the oven with a heating zone corresponding to each heater. = In the embodiment shown in Figures 2 and 3, the heaters 30 are arranged around the oven 11, extending substantially around the entire outer circumference of the oven 11.

E This creates the effect of heating the oven 11 throughout its heating range.

N me 30 in its circumferential portion evenly so that the oven 11

S The jacket does not cool down when rotating from some of the circumferential sides of the furnace 11 jacket.

N shares.

N 35 According to one embodiment, the heater 30 is an electrically operated heater. The heater 30 comprises a support structure 31 and at least one heating effect producing element 32 arranged in connection with the support structure 31. In the exemplary embodiment shown in Figure 3, the heater 30 has twelve heating effect producing elements 32. The heater 30 further comprises a control unit 33 for controlling the supply of electricity to said at least one heating effect producing element 32 in order to heat the oven 11 by the action of said at least one heating effect producing element 32. The control unit 33 may be located outside the insulation 14, as shown schematically in Figure 2, or protected in the insulation 14. However, the control of the heaters 30 may also be implemented by a single control unit common to all heaters 30, which is configured to control each heater 30 separately.

The oven unit 10 may also comprise a temperature sensor 34 associated with each heater 30, which is connected, for example, to the control unit 33 of the heater 30 in question. The temperature sensor 34 may be arranged in the oven unit 10 in a section corresponding to the heater 30, either inside the oven 11 or between the oven 11 and the heater 30. The feedback produced by the temperature sensor 34 allows the heater 30 to achieve an accurate heating effect in the heating zone corresponding to the heater 30.

According to one embodiment, the element 32 producing the heating effect is an electric resistance and the control unit 33 is configured to control the electrical power supplied to the electric resistance in order to heat the oven 11 by the effect of the radiant heating produced by the electric resistance.

According to one embodiment, the element 32 producing the heating effect is a coil and the control unit 33 is configured to control the alternating current supplied to the coil in order to heat the furnace 11 by means of an induction current produced by the coil in the furnace 11 shell. < Figure 5 shows schematically a top view and a cross-sectional view of

Another oven unit 10. The oven unit 10 according to Figure 5 differs from the oven unit 10 according to Figure 3 in that in the oven unit 10 according to Figure 5, the heater 30 comprises four heater units 30a, 30b, 30c and 30d that are separable from each other in the circumferential direction of the oven 11, which together form the oven unit 10.

A heating element extending substantially around the entire outer circumference of the oven 11 is provided around the

N timen 30. Each heater unit 30a, 30b, 30c and 30d has an associated support

N structure 31a, 31b, 31c and 31d and at least one element producing a heating effect

N ment 32. In the embodiment shown in Figure 5, each heater unit has

In the N 35 housing 30a, 30b, 30c and 30d there are three elements 32 producing a heating effect.

In the embodiment according to Figure 5, the heater units 30a, 30b, 30c and 30d, which can be separated from each other, thus form a single heater 30 extending around the entire outer circumference of the oven 11. Each heater unit 30a, 30b, 30c and 30d can be controlled by a common control unit 33 intended for the heater 30 in question. Since the heater 30 is divided into parts corresponding to the heater units 30a, 30b, 30c and 30d, and if the insulation 14 is also divided into parts corresponding to the heater units 30a, 30b, 30c and 30d as schematically shown in Figure 5, the heater 30 can be dismantled in parts from around the oven 11, for example for maintenance operations.

Furthermore, in the embodiment according to Figure 5, in which the insulation 14 is divided into parts 14a, 14b, 14c, 14d corresponding to the heater units 30a, 30b, 30c and 30d as schematically shown in Figure 5, the portion 14a, 14b, 14c, 14d of the insulation 14 corresponding to each heater unit 30a, 30b, 30c and 30d can form the necessary support structure for the elements 32 producing the heating effect. The elements 32 producing the heating effect can then therefore be integrated as part of the insulation 14 and the support structures 31a, 31b, 31c, 31d can be dispensed with or the support structures 31a, 31b, 31c, 31d and the corresponding portions of the insulation 14 can be 14a, 14b, 14c, 14d together form an integrated support and insulation granule.

In the embodiment according to Figure 5, the heater 30 comprises four heater units 30a, 30b, 30c and 30d that can be separated from each other in the circumferential direction of the oven 11, so that they together form a heater 30 that extends around the oven 11 substantially around the entire outer circumference of the oven 11. In contrast to the embodiment according to Figure 5, the heater 30 may also comprise two, three or more than four heater units that can be separated from each other in the circumferential direction of the oven 11, so that they together form a heater 30 that extends around the oven 11 substantially around the entire outer circumference of the oven 11. The insulation 14 can be divided

N heater units to the corresponding sections. a According to one embodiment, the furnace unit comprises means for feeding oxygen-enriched = moistened air into the interior of the furnace. When the furnace shell is heated from the outside of the furnace, the material being fed into the interior of the furnace is

The amount of air may not be sufficient for complete combustion of the combustible material.

N In this embodiment, oxygen-enriched air is supplied to the inside of the furnace.

N in order to ensure the necessary conditions for complete combustion of the material burning in the furnace

The amount of oxygen in N is the amount of oxygen. In oxygen-enriched air, the amount of oxygen can be, for example,

N 35 about 21-80%.

According to one embodiment, the means for supplying oxygen-enriched air to the interior of the furnace comprises means for supplying oxygen-enriched air to the heating zone corresponding to at least one heater. In this embodiment, the oxygen-enriched air supplied to the heating zone corresponding to at least one heater ensures that the heating zone in question has sufficient oxygen to cause the combustion of the material burning in the heating zone in question to the extent that is possible, taking into account the forward flow of the material being processed in the furnace. Since the material fed into the furnace usually also enters the furnace with some air, this amount of air may be sufficient to maintain combustion in one or more heating zones closer to the first end of the furnace, but not necessarily sufficient to maintain combustion in one or more heating zones closer to the second end of the furnace. Therefore, supplying oxygen-enriched air to at least some of the heating zones of the furnace may be necessary to ensure complete combustion of the combustible material, but may not necessarily be necessary for all heating zones of the furnace.

Figure 4 schematically shows an embodiment of the furnace 11 in which oxygen-enriched air can be fed into the furnace 11. In the embodiment shown in Figure 4, reference number 40 indicates a source of oxygen-enriched air, which may be, for example, a container used for storing oxygen-enriched air or an apparatus used for generating oxygen-enriched air. Furthermore, in Figure 4, reference number 41 indicates a supply channel for feeding oxygen-enriched air from an oxygen-enriched air source 40 to the inside of the furnace 11. Nozzles 42 or other means suitable for a similar purpose are arranged in the supply channel 40 on the inside of the furnace 11, through which oxygen-enriched air fed along the supply channel 41 can be dosed to a portion corresponding to each nozzle 42.

N delle in the heated section of the furnace 11. Sensors a 43 can also be provided in the furnace 11 for measuring the residual oxygen content. The measured residual oxygen content can be used to adjust the amount of oxygen-enriched air supplied to the furnace 11.

T 30 In the embodiment according to Figure 4, the nozzles 42 are shown in the schematic diagram.

E-shaped, one piece of each heater 30 of Figure 2 corresponding to the heating zone

N per person. The necessary nozzles or other similar devices suitable for the purpose

However, the number of heating devices can be more than one heating zone.

N per person. If sufficient oxygen is available in any part of the furnace 11

N 35 to achieve combustion of the combustible material in that section to the extent that is possible taking into account the flow of the material to be processed in that section forward in the furnace, then the nozzles 42 can also be omitted from that section of the furnace 11.

According to one embodiment, the furnace of the furnace unit comprises means inside the furnace for influencing the flow of the material to be processed in the furnace.

In this embodiment, means are arranged inside the furnace 11, by the effect of which, as the furnace 11 rotates, the flow of the material being processed in the furnace from the direction of the first end 11a of the furnace 11 towards the second end of the furnace 11 is either enhanced or slowed down.

According to one embodiment, the furnace of the furnace unit comprises at least one baffle plate directed from the inner circumference of the furnace towards the central part of the furnace. Referring to this embodiment, Figure 4 also schematically shows an embodiment of the furnace 11, in which the furnace 11 comprises projections directed from the inner circumference of the shell of the furnace 11 towards the central part of the furnace 11. Said projections form baffle plates 44, which can be used to slow down the flow of the material to be processed in the furnace 11 so that the furnace 11 is kept at a sufficiently high filling level of the material to be processed. A sufficiently high filling level of the furnace 11 enhances the friction of the grains of the material to be processed against each other. A sufficiently high filling level of the furnace 11 also increases the amount of combustion energy available in the furnace 11, since the amount of combustible material to be removed in the furnace 11 increases. In addition, a sufficiently high filling level of the oven 11 stabilizes the cleaning process so that short-term small changes in the heating power produced by the heater, for example, do not immediately affect the temperature of the material bed formed by the material to be processed in the oven 11.

In the embodiment according to Figure 4, the baffle plates 44 are ring elements directed substantially perpendicularly from the inner circumference of the furnace shell 11 towards the central part of the furnace 11. However, the shape, position and dimensions of the baffle plates can be chosen in many different ways depending on their desired effect.

According to one embodiment, at least one baffle plate is arranged between the heating zones formed by heaters arranged side by side in the axial direction of the furnace. In the embodiment according to Figure 4, the furnace 11 comprises a total of three baffle plates 44, which in the embodiment according to Figure 4

E is arranged to be located in the heating zones corresponding to the heaters 30 of Figure 2.

N between the two. The structures that form the commonly mentioned dam plates can be read as

N in quantity fits one or more optional sections of the oven 11 in the oven

According to N, at which section or sections of the furnace the flow of the material to be processed is

We want to influence the temperature in the oven at N 35.

Figure 6 shows a schematic side view of another apparatus 1 for processing granular material. As described above, the apparatus 1 comprises a furnace unit 10 and a cooling unit 20. In addition, the apparatus 1 comprises a support structure 50 on which the furnace unit 10 and the cooling unit 20 are supported such that the cooling unit 20 is directly below the furnace unit 10.

The support structure 50 comprises a base 51. The base 51 may comprise, for example, handling openings or housings 52 adapted to receive the lifting fork of a forklift for moving the apparatus 1.

The support structure 50 further comprises a first horizontal support 53, on which the oven unit 10 is arranged to be supported. The support structure 50 further comprises essentially at both ends of the first horizontal support 53 or near its ends first vertical supports 54, by means of which the first horizontal support 53 is arranged to be supported by the base 51. Said first vertical supports 54 may be arranged at one or both ends of the first horizontal support 53 to be adjustable in height so that the position of the first horizontal support 53 can be adjusted in the axial direction of the oven 11 of the oven unit 10 in order to adjust the angle of inclination of the oven 11.

The support structure 50 further comprises a second horizontal support 55, on the support of which the cooling unit 20 is arranged. The second horizontal support 55 is arranged directly below the first horizontal support 53 such that the cooling unit 20 is directly below the oven unit 10. The support structure 50 further comprises essentially at both ends of the second horizontal support 55 or near its ends second vertical supports 56, by means of which the second horizontal support 55 is arranged to support the base 51. Said second vertical supports 56 may be arranged at one or both ends of the second horizontal support 55 to be adjustable in height so that the position of the second horizontal support 55 can be adjusted to the cooling unit.

N in the axial direction of the drum 21 of the cylinder 20 to adjust the tilt angle of the drum 21. = The production capacity of the material to be processed by the equipment 1, typically determined per hour — 30 —, or in other words, the material to be processed

E dark time, can be adjusted in many different ways. The mentioned ways are to install the equipment 1

N adjustment of the feed rate of the material to be fed, the oven unit 10, the oven 11 and/or

S temperature control of the cooling unit 20 drum 21, oven 11 and/or drum 21

N rotation speed adjustment, and/or adjustment of the tilt angle of the oven 11 and/or the drum 21.

N 35 Furthermore, the residence time of the material being processed in the furnace 11 and/or the drum 21 can be adjusted by selecting the dimensions and/or position of the lifters 13 and/or the dam plates.

The apparatus 1 as described above can be implemented in several different sizes according to the capacity required to process the material. The inner diameter of the furnace 11 can be, for example, 0.2-2 meters. The length of the furnace 11 can be, for example, 1.5-15 meters. The processing capacity of the furnace 11 can be, for example, 60-10,000 kilograms per hour. In addition to a fixed installation, the said apparatus 1 can be arranged, depending on its total weight and dimensions, for example, on a platform that can be moved by a forklift or on a platform equipped with wheels, which allows the apparatus to be easily moved.

It is obvious to a person skilled in the art that as technology develops, the basic idea of the invention can be implemented in many different ways. The invention and its embodiments are therefore not limited to the examples described above, but may vary within the scope of the claims. <t

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Claims (15)

Patent claims 1. Apparatus for treating granular material, the apparatus comprising a furnace unit and a cooling unit, wherein the furnace unit comprises a cylindrical rotatable heated furnace in which the material to be treated is subjected to thermomechanical treatment, and the cooling unit comprises a cylindrical rotatable drum for cooling the material treated in the furnace unit, and wherein the furnace unit comprises at least two independently controllable heaters outside the furnace in the axial direction of the furnace for forming at least two separately heated heating zones in the furnace in its axial direction. 2. Apparatus according to claim 1, characterized in that the heater is arranged around the outer circumference of the oven at a distance from the outer circumference of the oven. 3. Apparatus according to claim 1 or 2, characterized in that the heater is an electrically operated heater comprising at least one heating effect producing element and a control unit for controlling the supply of electricity to said at least one heating effect producing element for heating the oven by the effect of said at least one heating effect producing element. 4. Apparatus according to claim 3, characterized in that the heater comprises at least two heater units separable from each other in the circumferential direction of the oven and that each heater unit comprises at least one element producing a heating effect. 5. Apparatus according to claim 3 or 4, characterized in that the element producing the heating effect is an electric resistance and that the control unit S is configured to control the electrical power supplied to the electric resistance in order to heat the oven by the effect of the radiant heating produced by the electric resistance. = 6. Apparatus according to claim 3 or 4, characterized in that the element producing the heating effect is a coil and that the control unit is configured to control the alternating current supplied to the coil in order to heat the furnace by the effect of the induction current produced by the coil in the drum shell of the furnace. O 7. Apparatus according to any one of the preceding claims, characterized in that the oven unit comprises means for supplying oxygen-enriched air to the interior of the oven. 8. Apparatus according to claim 7, characterized in that the means for supplying oxygen-enriched air to the interior of the furnace comprise means for supplying oxygen-enriched air to a heating zone corresponding to at least one heater. 9. Apparatus according to any one of the preceding claims, characterized in that the oven of the oven unit comprises means inside the oven for influencing the flow of the material to be processed in the oven. 10. Apparatus according to claim 9, characterized in that the oven of the oven unit comprises at least one baffle plate directed from the inner circumference of the oven towards the central part of the oven. 11. Apparatus according to claim 10, characterized in that said at least one baffle plate is arranged between heating zones formed by adjacent heaters in the axial direction of the furnace. 12. Apparatus according to any one of the preceding claims, characterized in that the apparatus comprises a support structure on which the oven unit and the cooling unit are supported, and that the cooling unit is supported on the support structure directly below the oven unit. Use of an apparatus according to any one of claims 1 to 12 for processing granular material. Use according to claim 13 for cleaning waste sand. 15. Use according to claim 13 or 14 for cleaning used foundry sand. <t N O N O I 0 I a a N O N LO + N O N