WO2025191212A1

WO2025191212A1 - Apparatus for processing granular material

Info

Publication number: WO2025191212A1
Application number: PCT/FI2025/050120
Authority: WO
Inventors: Jarkko Partinen; Toni WESIN; Jukka Nieminen
Original assignee: Resand Oy
Current assignee: Resand Oy
Priority date: 2024-03-13
Filing date: 2025-03-12
Publication date: 2025-09-18
Anticipated expiration: 2026-09-13
Also published as: FI20245297A1

Abstract

An apparatus (1) for processing granular material comprises a kiln unit (10) and a cooling unit (20), wherein the kiln unit (10) comprises a cylindrical rotatable heatable kiln (11) where thermomechanical treatment is applied to material being processed and the cooling unit (20) comprises a cylindrical rotatable drum (21) for cooling the material processed in the kiln unit (10). The kiln unit (10) comprises outside the kiln (11) in the axial direction of the kiln (11) at least two separately controllable heaters for forming at least two separately heatable heating zones to the kiln (11) in its axial direction.

Description

Apparatus for processing granular material

Background of the invention

The invention relates to an apparatus for processing granular material. Fl-publication 128118 B presents an apparatus for cleaning used foundry sand. The apparatus comprises a rotatable heatable drum, which forms a kiln, where thermomechanical treatment is applied to used foundry sand. It is characteristic of kilns similar to the one described in the Fl-publication that they are heated from inside the kiln from one end of the kiln by a gas or liquefied gas burner. However, a problem with the kilns of said kind is the control of the temperature profile of material inside the kiln.

Brief description of the invention

The object of the invention is to introduce a new kind of an apparatus and its use for processing granular material.

The solution according to the invention is characterised by what is disclosed in the independent claims.

The apparatus comprises a kiln unit and a cooling unit, wherein the kiln unit comprises a cylindrical rotatable heatable kiln where thermomechanical treatment is applied to material being processed and the cooling unit comprises a cylindrical rotatable drum for cooling the material processed in the kiln unit. The kiln unit further comprises outside the kiln in the axial direction of the kiln at least two separately controllable heaters for forming at least two separately heatable heating zones to the kiln in its axial direction.

The advantage of the solution is that the material processed in the kiln is provided with a controlled temperature profile because the material processed in the kiln is heated indirectly by heating the kiln jacket and because, on each section of the kiln jacket corresponding to each heating zone, it is possible to apply a preferred heating effect to the kiln jacket by the heater corresponding the heating zone in question. As the material processed in the kiln must typically be at a specific minimum temperature in order for preferred reactions to be carried out in terms of the end-result of the treatment, a solution similar to the presented one can particularly ensure the substantially even temperature profile of the material processed in the drum for the whole heatable section of the kiln such that the temperature of the material will not decrease too low in terms of said reactions or will not increase unnecessary high in terms of efficient energy use. The cooling unit following the kiln unit can cool down the granular material processed in the kiln unit to a temperature where it is immediately re-usable. For example in foundries, the apparatus according to the solution enables the immediate use of cleaned foundry sand in the manufacture of new moulds. In this case, the manufacture of moulds and the treatment of used foundry sand can be formed a continuous process without the intermediate storage of cleaned foundry sand, which also minimizes the amount of sand required in the cycle.

Some embodiments of the invention are presented in the dependent claims.

Brief description of the drawings

The invention will now be described in closer detail in connection with some embodiments and with reference to the accompanying drawings, wherein

Figure 1 schematically shows a side view of an apparatus for processing granular material,

Figure 2 schematically shows a side view of a kiln unit partly in crosssection,

Figure 3 schematically shows an end view of the kiln unit of Figure 2 in cross section.

Figure 4 schematically shows a side view of a kiln usable in the kiln unit partly in cross-section,

Figure 5 schematically shows a side view of another kiln unit in crosssection, and

Figure 6 schematically shows a side view of another apparatus for processing granular material.

For reasons of clarity, some embodiments of the invention are illustrated in the figures in a simplified form. Similar parts are indicated in the figures by the same reference numbers.

Detailed description of the invention

Figure 1 schematically shows a side view of an apparatus 1 for processing granular material. Said granular material can be e.g. waste sand. Said waste sand can be e.g. foundry sand which comprises clay- or resin-based binding agent. Said granular material can also be some other heat-treatable granular material, such as e.g. calcinatable granular material.

The apparatus 1 is particularly intended for cleaning granular material from impurities by a thermomechanical treatment applied to the granular material. The purpose of the treatment is to remove various impurities from the granular material such that the granular material is re-usable for an earlier intended use that was implemented before the cleaning or for some other intended use. When cleaning used foundry sand, the purpose is to remove binder agent remaining on the surface of sand grains from the sand. After this, the sand can be re-used either as foundry sand or for some other purpose.

The apparatus 1 of Figure 1 comprises a kiln unit 10 and a cooling unit 20. The kiln unit 10 comprises a cylindrical rotatable heatable kiln 11 for the thermomechanical treatment of material fed to the kiln 11 in order to remove impurities contained by the material. The kiln unit 10 further comprises a rotating motor 12 for rotating the kiln 11 around its longitudinal axis. The cooling unit 20 comprises a cylindrical rotatable drum 21 for cooling down the material processed in the kiln unit 10. The cooling unit 20 additionally comprises a rotating motor 22 for rotating the drum 21 around its longitudinal axis.

Figure 2 schematically shows a side view of a kiln unit 10 partially in cross section in the axial direction of a kiln 11. Figure 3 schematically shows an end view of the kiln unit 10 of Figure 2 in cross section. Figure 4 schematically shows a side view of a kiln 11 used in the kiln unit 10 in cross section in the axial direction of the kiln 11.

With reference to Figures 1, 3 and 4, the general operation principle of the apparatus 1 shown in Figure 1 is the following. Material to be processed is fed to the kiln 11 of the kiln unit 10 at a first end Ila of the kiln 11 like schematically shown by an arrow designated with reference sign FINio in Figure 1. The material fed to the kiln 11 flows through the kiln 11, and the material processed in the kiln 11 is removed from the kiln 11 at a second end 11b of the kiln 11 like schematically shown by an arrow designated with reference sign DOUTIO in Figure 1. The material processed in the kiln unit 10 is fed to be cooled in a drum 21 of the cooling unit 20 at a first end 21a of the drum 21 like schematically shown by an arrow designated with reference sign F1N20 in Figure 1. The material cooled down in the drum 21 is removed from the drum 21 at a second end 21b of the drum 21 like schematically shown by an arrow designated with reference sign DOUT2O in Figure 1.

For its part, the cylindrical jacket of the kiln 11 typically manufactured of iron limits at least one heatable chamber to the kiln 11 in its axial direction. According to an embodiment, the whole internal volume of the kiln 11 forms one uniform unlimited heatable chamber from the firstend Ila ofthe kiln 11 to the second end 11b of the kiln 11. According to another embodiment, the internal volume of the kiln 11 is divided in the axial direction of the kiln 11 into two or more chambers partially separated from each other, whereby all said chambers or only part of said chambers can be heatable chambers.

In each chamber of the kiln 11 heated to a high temperature, a thermal effect is applied to the material being processed, as a result of which, the material being processed is heated and its burnable components burn out of the material being processed. The temperature to which the material being processed is heated depends on both the characteristics of the material being processed and the characteristics of components being removed from the material being processed. In case of foundry sands, the temperature to which the material being processed is heated is typically about 750-950 degrees.

When the kiln 11 rotates, the material being processed at the bottom of the kiln 11 rises along with the kiln 11 upwards on the inner surface of the jacket of the kiln 11 until it drops back to the bottom of the kiln 11. When the material being processed rises along the kiln 11 and drops back to the bottom of the kiln 11, grains in the material being processed are rubbed and/or hit against each other and/or against the inner surface of the jacket of the kiln 11. This applies a mechanical treatment to the material being processed which intensifies the removal of component on the surface of the grains of the material being processed from the material being processed. Additionally, said mechanical treatment brings about mixing in the material being processed, which balances possible temperature difference in the material at the bottom of the kiln 11.

The mechanical treatment applied to the material being processed can be intensified in the kiln 11 by means of one or more lifters 13 arranged on the inner surface of the jacket of the kiln 11. Figures 3 and 4 schematically show such a lifter 13. The lifter 13 is a projection extending from the direction of the first end Ila of the kiln 11 towards the second end 11b of the kiln 11 and directed from the inner circle of the jacket of the kiln 11 towards the middle of the kiln 11. From the effect of the lifter 13, a larger share of the material being processed can at a time rise upwards and, at the same time, higher than previously along the kiln 11 when the kiln 11 rotates. This intensifies the mixing effect applied to the material being processed and the mechanical treatment because a larger share of the material can move along the kiln 11 and drop from higher back to the bottom of the kiln 11.

Hot material processed in the kiln unit 10 is cooled down in the drum 21 of the cooling unit 20. The cooling can be implemented by e.g. an airflow that is cooled or uncooled, being in ambient temperature, arranged from the direction of the second end 21b of the drum 21 in the direction of the first end 21a of the drum 21. In addition to this or alternatively, the jacket of the drum 21 can be cooled from the outside. It is also possible to use for the drum 21 the above-mentioned lifters to intensify the cooling effect applied to the material in the drum 21 by keeping the material in the drum 21 moving and thus more evenly disposed to the cooling effect.

The cooling unit following the kiln unit can cool down the granular material processed in the cooling unit to a temperature where it is immediately reusable. For example in foundries, the apparatus according to the solution enables the immediate use of cleaned foundry sand in the manufacture of new moulds. In this case, the manufacture of moulds and the processing of used foundry sand can be formed a continuous process without the intermediate storage of cleaned foundry sand, which also minimizes the amount of sand required in the cycle.

For heating the kiln, the kiln unit comprises outside the kiln in the axial direction of the kiln at least two separately controllable heaters for forming at least two separately heatable heating zones to the kiln in its axial direction. In other words, the kiln unit comprises outside the kiln in the axial direction of the kiln at least a first heater and a second heater which are independently controllable for forming separately heatable first heating zone and second heating zone to the kiln in its axial direction.

Figures 2 and 3 show an embodiment of a kiln unit 10 of said kind. The kiln unit 10 of Figures 2 and 3 comprises outside the kiln 11 heaters 30 arranged at a distance from the outer surface of the jacket of the kiln 11 in the direction of the radius of the kiln 11. Said heaters 30 are configured to heat the jacket of the kiln 11 and, by means of said jacket, the material being processed in the kiln 11. The embodiment of Figure 2 includes four of the heaters 30 in the axial direction of the kiln 11 but the number of said heaters 30 can vary. Therefore, there can be two or more of said heaters 30 in the axial direction of the kiln 11. In the embodiment of Figure 2, there are heaters 30 arranged substantially for the whole length of the kiln 11 but the kiln 11 can also include sections where there is no heater.

The heaters 30 are controllable independently i.e. separately from each other, whereby said heaters 30 form to the kiln 11 in its axial direction a number of separately heatable heating zones that equals to the number of the heaters 30. Around the kiln 11 and the heaters 30, it is possible to arrange as appropriate an insulation 14 which both prevents the heat from escaping the kiln unit 10 and protects the environment of the kiln unit 11 from high temperatures. By using said separately controllable heaters, the jacket of the kiln 11 is provided in the axial direction of the kiln 11 with separately heatable heating zones such that at each section of the jacket of the kiln 11 corresponding to each heating zone a preferred heating effect can be applied to the jacket of the kiln 11 by the heater corresponding to the heating zone. This solution achieves the controlled forming of a temperature profile in the material being processed in the kiln 11. Because the material being processed in the kiln 11 must typically be in a specific minimum temperature to implement reactions preferred from the viewpoint of the end-result of the treatment, the use of said separately controllable heaters can particularly ensure the essentially even temperature profile of the material being processed in the kiln 11 for the whole heatable section of the kiln 11. In this case, each heater 30 produces such a heating effect to the heating zone corresponding to the heater 30 that the temperature of the material being processed in the kiln 11 on each heating zone would be essentially the same. An advantage of this compared with a kiln heated from the end of the kiln by a gas or liquid gas burner is also that the excessive heating of the material possible caused by the burner flame is avoided near the flame. Furthermore, it is also possible to turn off the heaters corresponding to some of the heating zones if it is not necessary to heat the kiln on the heating zones corresponding to each heater to provide the treating effect of the material being processed in the kiln 11.

In the embodiment of Figures 2 and 3, the heaters 30 are arranged around the kiln 11 substantially extending around the whole outer circle of the kiln 11. This provides such an effect that the kiln 11 is heated on its section parallel to the circle related to the heater 30 evenly such that the jacket of the kiln 11 does not cool down from some sections parallel to the circle of the jacket of the kiln 11 when rotating.

According to an embodiment, the heater 30 is an electric heater. The heater 30 comprises a support structure 31 and at least one element 32 producing a heating effect arranged into connection with the support structure 31. In the embodiment of Figure 3, the heater 30 includes twelve elements 32 producing a heating effect. The heater 30 further comprises a control unit 33 to control the supply of electricity to said at least one element 32 producing a heating effect for heating the kiln 11 from the effect of said atleast one element 32 producing a heating effect. The control unit 33 can be located outside the isolation 14, like schematically shown in Figure 2, or protected in the isolation 14. However, the control of the heaters 30 can also be implemented with one control unit common to all of the heaters 30 which is configured to control each heater 30 separately.

The kiln unit 10 can also comprise a temperature sensor 34 related to each heater 30 which is connected e.g. to the control unit 33 of the heater 30 in question. The temperature sensor 34 can be arranged in the kiln unit 10 to a section corresponding to the heater 30 either inside the kiln 11 or between the kiln 11 and the heater 30. By means of feedback produced by the temperature sensor 34, it is possible to realize an accurate heating effect with the heater 30 in the heating zone corresponding to the heater 30.

According to an embodiment, the element 32 producing the heating effect is a resistor and the control unit 33 is configured to control the electric power supplied to the resistor for heating the kiln 11 from the effect of radiant heating produced by the resistor.

According to an 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 for heating the kiln 11 by means of induction current produced by the coil to the jacket of the kiln 11.

Figure 5 is a schematic end view of a second kiln unit 10 in cross-section. The kiln unit 10 of Figure 5 differs from the kiln unit 10 of Figure 3 such that, in the kiln unit 10 of Figure 5, the heater 30 comprises parallel with the circle of the kiln 11 four heater units 30a, 30b, 30c and 30d separable from each other which together form a heater 30 around the kiln 11 extending around the whole outer circle of the kiln 11. Each heater unit 30a, 30b, 30c and 30d include a support structure 31a, 31b, 31c and 31d and at least one element 32 producing a heating effect related to it. In the embodiment of Figure 5, each heater unit 30a, 30b, 30c and 30d includes three elements 32 producing a heating effect.

In the embodiment of Figure 5, the heater units 30a, 30b, 30c and 30d, which are separable from each other, thus form one heater 30 extending around the whole outer circle of the kiln 11. Each heater unit 30a, 30b, 30c and 30d can be controlled by the common control unit 33 intended for the heater 30 in question. Because 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, in accordance what is schematically shown in Figure 5, into parts corresponding to the heater units 30a, 30b, 30c and 30d, the heater 30 can be disassembled in parts from around the kiln 11 e.g. for maintenance. Furthermore in the embodiment of Figure 5, where the insulation 14 is divided, in accordance what is schematically shown in Figure 5, into parts 14a, 14b, 14c, 14d corresponding to the heater units 30a, 30b, 30c and 30d, the section 14a, 14b, 14c, 14d of the insulation 14 corresponding to each heater unit 30a, 30b, 30c and 30d can form a required support structure for elements 32 producing a heating effect. The elements 32 producing the heating effect can then be integrated as a part of the insulation 14, and it is possible to abandon the support structures 31a, 31b, 31c, 3 Id, or the support structures 31a, 31b, 31c, 3 Id and the sections 14a, 14b, 14c, 14d of the insulation 14 correspondingto the support structures together form an integrated support and insulation structure.

In the embodiment of Figure 5, the heater 30 comprises parallel with the circle of the kiln 11 four heater units 30a, 30b, 30c and 30d separable from each other which together form a heater 30 around the kiln 11 extending around the whole outer circle of the kiln 11. Different from the embodiment of Figure 5, the heater 30 can also comprise parallel with the circle of the kiln 11 two, three or more than four heater units separable from each other such that they together form a heater 30 around the kiln 11 extending around the whole outer circle of the kiln 11. The insulation 14 can be divided into sections corresponding to the heater units.

According to an embodiment, the kiln unit comprises means for feeding oxygen-rich air inside the kiln. When the jacket of the kiln is heated from outside the kiln, the amount of air ending up inside the kiln along with the material being fed is not necessarily enough for the complete burning of the burnable component. In this embodiment, oxygen-rich air is thus fed inside the kiln in order to ensure the amount of oxygen required for the complete burning of the component in the kiln. In oxygen-rich air, the share of oxygen can be e.g. about 21-80%.

According to an embodiment, the means for feeding oxygen-rich air inside the kiln comprises means for feeding oxygen-rich air to a heating zone corresponding to at least one heater. In this embodiment, the oxygen-rich air fed to a heating zone corresponding to at least one heater ensures that the heating zone in question has sufficiently oxygen to provide the burning of burnable component in the heating zone in question so much so what is possible when considering the flow of the material being processed forward in the kiln. Because an amount of air usually ends up in the kiln along with the material being fed to the kiln, this amount of air might be sufficient to maintain burning on one or more heating zones closer to the first end of the kiln but not necessarily sufficient to maintain burning on one or more heating zones closer to the second end of the kiln. Due to this, the feeding of oxygen-rich air to at least some of the heating zones in the kiln might be necessary for ensuring the complete combustion of burnable component but not necessarily required for all heating zones in the kiln.

Figure 4 schematically shows such an embodiment of the kiln 11 wherein oxygen-rich air can be fed to the kiln 11. In the embodiment of Figure 4, reference number 40 designates a source of oxygen-rich air which can be e.g. a container used for storage of oxygen-rich air or an apparatus used for generating oxy- gen-rich air. Furthermore, reference number 41 in Figure 4 shows a feed channel for feeding oxygen-rich air from the source 40 of oxygen-rich air inside the kiln 11. The feed channel 40 is provided in the internal section of the kiln 11 with nozzles 42 or other means suitable for equivalent purpose via which the oxygen-rich air fed along the feed channel 41 can be dosed to a section corresponding to each nozzle 42 in the heated section of the kiln 11. It is also possible to arrange sensors 43 for measuring the residual oxygen content in the kiln 11. The measured residual oxygen content can be used for adjusting the amount of oxygen-rich air fed to the kiln 11.

In the embodiment of Figure 4, the nozzles 42 are schematically presented one piece for each heating zone corresponding to the heater 30 of Figure 2. However, the number of required nozzles or other means suitable for the equivalent purpose can be more than one per heating zone. If some section of the kiln 11 has sufficiently available oxygen to provide the burning of the burnable component in the section in question in such an amount that it is possible when considering the flow of the material being processed forward in the kiln, the nozzles 42 can also be omitted from the section of the kiln 11 in question.

According to an embodiment, the kiln of the kiln unit comprises means inside the kiln for affecting the flow of the material being processed in the kiln. In this embodiment, there are means arranged inside the kiln 11, by the effect of which means, when the kiln 11 rotates, the flow of the material being processed from the direction of the first end Ila of the kiln 11 towards the second end of the kiln 11 is either accelerated or decelerated.

According to an embodiment, the kiln of the kiln unit comprises at least one dam plate directed from the inner circle of the kiln towards the middle of the kiln. With reference to this embodiment, Figure 4 also schematically shows such an embodiment of the kiln 11, wherein the kiln 11 comprises projections directed from the inner circle of the jacket of the kiln 11 towards the middle of the kiln 11. Said projections form dam plates 44 which can decelerate the flow of the material being processed in the kiln 11 such that a sufficiently high degree of fullness of the material being processed is maintained in the kiln 11. The sufficiently high degree of fullness of the kiln 11 intensifies the rubbing of the grains of the material being processed against each other. The sufficiently high degree of fullness of the kiln 11 also increases the amount of burning energy usable in the kiln 11 because the amount of removable burning component in the kiln 11 increases. Additionally, the sufficiently high degree of fullness of the kiln 11 stabilizes the cleaning process such that small short-term changes e.g. in the heating efficiency of the heater will not immediately affect the temperature of the material layer formed by the material being processed in the kiln 11.

In the embodiment of Figure 4, the dam plates 44 are annular elements directed from the inner circle of the jacket of the kiln 11 substantially towards the middle of the kiln 11. The shape, position and dimensions of the dam plates can still be chosen in many different ways depending on their preferred effect.

According to an embodiment, at least one dam plate is arranged in the axial direction of the kiln between the heating zones formed by the heaters arranged side by side. In the embodiment of Figure 4, the kiln 11 comprises the total of three dam plates 44 which in the embodiment of Figure 4 are arranged to be located between the heating zones corresponding to the heaters 30 of Figure 2. Commonly, it is possible to arrange one or more structures forming said dam plates in the kiln for optional sections of the kiln 11 based on which section or sections of the kiln the flow of the material being processed is wished to affect.

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

The support structure 50 comprises a base 51. The base 51 can comprise e.g. handling openings or boxes 52 which are configured to receive the lifting fork of a fork truck to move the apparatus 1.

The support structure 50 further comprises a first horizontal support 53 supported by which the kiln unit 10 is arranged. Additionally, the support structure 50 comprises substantially at both ends of the first horizontal support 53 or close to its ends first vertical supports 54 via which the first horizontal support 53 is arranged to be supported by the base 51. Said first vertical supports 54 can be arranged at one end or both ends of the first horizontal support 53 adjustable of their height such that the position of the first horizontal support 53 can be adjusted in the axial direction of the kiln 11 of the kiln unit 10 for adjusting the tilt angle of the kiln 11.

The support structure 50 further comprises a second horizontal support 55 to 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 kiln unit 10. Additionally, the support structure 50 comprises substantially at both ends of the second horizontal support 55 or close to its ends second vertical supports 56 via which the second horizontal support 55 is arranged to be supported by the base 51. Said second vertical supports 56 can be arranged at one end or both ends of the second horizontal support 55 adjustable by their height such that the position of the second horizontal support 55 can be adjusted in the axial direction of the drum 21 of the cooling unit 20 for adjusting the tilt angle of the drum 21.

The production capacity of the material being processed by the apparatus 1, typically determined hour-specifically, or in other words, the turn-around time of the material being processed can be adjusted by many different ways. Said ways are the adjustment of the feeding speed of the material being processed to the apparatus 1, the adjustment of the temperature of the kiln 11 of the kiln unit 10 and/or the drum 21 of the cooling unit 20, the adjustment of the rotation speed of the kiln 11 and/or the drum 21, and/or the adjustment of the tilt angle of the kiln 11 and/or the drum 21. Additionally, the dwell time of the material being processed in the kiln 11 and/or the drum 21 can be adjusted by the selection of the dimensions and/or position of the lifters 13 and/or dam plates.

An apparatus 1 of the above description can be implemented in many different size categories based on the capacity required for processing the material. The inner diameter of the kiln 11 can be e.g. 0.2-2 metres. The length of the kiln 11 can be e.g. 1.5-15 metres. The processing capacity of the kiln 11 can be e.g. 60- 10,000 kilograms per hour. In addition to a fixed installation, said apparatus 1 can be, depending on its total weight and dimensions, arranged e.g. on a base movable by a fork truck or a base provided with wheels, which enables the easy movability of the apparatus.

Those skilled in the art will find it obvious that, as technology advances, the basic idea of the invention may be implemented in many different ways. The invention and its embodiments are thus not restricted to the examples described above but may vary within the scope of the claims.

Claims

1. An apparatus (1) for processing granular material, which apparatus

(I) comprises a kiln unit (10) and a cooling unit (20), wherein the kiln unit (10) comprises a cylindrical rotatable heatable kiln (11) where thermomechanical treatment is applied to material being processed and the cooling unit (20) comprises a cylindrical rotatable drum (21) for cooling the material processed in the kiln unit

(10), and wherein the kiln unit (10) comprises outside the kiln (11) in the axial direction of the kiln (11) at least two independently controllable heaters (30) for forming at least two separately heatable heating zones to the kiln (11) in its axial direction, characterized in that the heater (30) is arranged around the outer circle of the kiln

(II) at a distance from the outer circle of the kiln (11).

2. An apparatus according to claim 1, characterized in that the heater (30) is an electric heater which comprises at least one element (32) producing a heating effect and a control unit (33) to control the supply of electricity to said at least one element (32) producing a heating effect for heating the kiln (11) from the effect of said at least one element (32) producing a heating effect.

3. An apparatus according to claim 2, characterized in that the heater (30) comprises parallel to the circle of the kiln (11) at least two heater units (30a, 30b, 30c, 30d) separable from each other and that each heater unit (30a, 30b, 30c, 30d) comprises at least one element (32) producing a heating effect.

4. An apparatus according to claim 2 or 3, characterized in that the element (32) producing the heating effect is a resistor and the control unit (33) is configured to control the electric power supplied to the resistor for heating the kiln

(11) from the effect of radiant heating produced by the resistor.

5. An apparatus according to claim 2 or 3, characterized in that the element (32) producing the heating effect is a coil and that the control unit (33) is configured to control the alternating current fed to the coil for heating the kiln (11) from the effect of induction current produced by the coil to the jacket of the drum of the kiln (11).

6. An apparatus according to any one of the preceding claims, characterized in that the kiln unit (10) comprises means for feeding oxygen-rich air inside the kiln (11).

7. An apparatus according to claim 6, characterized in that the means for feeding oxygen-rich air inside the kiln (11) comprise means (40, 41, 42) for feeding oxygen-rich air to a heating zone corresponding to at least one heater (30).

8. An apparatus according to any one of the preceding claims, characterized in that the kiln (11) of the kiln unit (10) comprises means inside the kiln (11) for affecting the flow of material being processed in the kiln (11).

9. An apparatus according to claim 8, characterized in that the kiln (11) of the kiln unit (10) comprises at least one dam plate (44) directed from the inner circle of the kiln (11) towards the middle of the kiln (11).

10. An apparatus according to claim 9, characterized in that said at least one dam plate (44) is arranged in the axial direction of the kiln (11) between heating zones formed by heaters (30) side by side.

11. An apparatus according to any one of the preceding claims, characterized in that the apparatus (1) comprises a support structure (50), to which the kiln unit (10) and the cooling unit (20) are supported, and that the cooling unit (20) is supported to the support structure (50) directly below the kiln unit (10).

12. Use of an apparatus (1) according to any one of claims 1-11 for processing granular material.

13. Use according to claim 12 for cleaning waste sand.

14. Use of claim 12 or 13 for cleaning used foundry sand.