DEVICE FOR PRODUCING EXPANDED GRANULATED MATERIAL.

Abstract

A device for producing expanded granulated material (2) from mineral material (1) in the form of sand grains with an expanding agent, comprising a kiln (3) with a kiln draft (4), having an upper end (5) and a lower end (6), wherein a conveying section (7) extends between the two ends and passes through a number of heating zones (8) arranged separately from each other in the conveying direction (12), wherein at least one feeding means (10, 11) is provided for loading at least the unexpanded material into the kiln draft at one of the two ends in the direction of the other of the two ends.The invention provides at least one steering element (13), which is disposed at least partially in the furnace draft, wherein the steering element forms a separation, gap or space (15) with an internal wall (14) of the furnace draft, at least in the region of one of the two ends, wherein the at least one feeding means is designed to load the material into the gap or space.

Description

DEVICE FOR PRODUCING EXPANDED GRANULATED MATERIAL Field of Invention The present invention relates to a device for producing an expanded granulated material from mineral material in the form of sand grains with an expanding agent, for example, for producing an expanded granulated material of perlite or obsidian sand with water bound as an expanding agent. The device comprises a kiln with a substantially vertically positioned kiln draft having an upper end and a lower end, wherein a conveying section extends between the two ends and passes through a plurality of heating zones arranged separately from each other in a conveying direction. Each heating zone comprises at least one independently controllable heating element for heating the particular material to a critical temperature and expanding the sand grains. Furthermore, at least one feeding means is provided.which is adapted to feed at least the unexpanded material to one of the two ends of the kiln shaft into the kiln shaft in the direction of the other of the two ends of the kiln shaft, to expand the material in the last half, preferably in the last third, of the conveying section, as seen in the conveying direction, wherein at least one steering element is provided, which is arranged at least in sections in the kiln shaft, wherein the steering element forms a gap, separation or space with an internal wall of the kiln shaft, at least in the region of one of the two ends of the kiln shaft, wherein the at least one feeding means is adapted to feed the unexpanded material into the gap. WO 2013 / 053635 A1 discloses a method and device for expanding mineral material in the form of sand grains, particularly closed-cell sand, containing an expanding agent such as bound water. In this process, the material is fed from the top into a kiln having a substantially vertical kiln shaft. By gravity, the material is conveyed through the kiln shaft from its upper end to its lower end, along a conveying section in the direction of conveying. The conveying section passes through several heating zones arranged separately in the direction of conveying and equipped with independently controllable heating elements to heat the material to a critical temperature and expand the sand grains. The expanded granulated material is discharged at the lower end.Due to the buoyancy forces that occur in the furnace draft, caused, among other things, by the draft chimney effect and which have different effects due to the varying densities before and after expansion, this type of expansion is suitable for raw sands with grain sizes typically greater than or equal to 75 microns, particularly greater than or equal to 100 microns. For finer grains, the buoyancy forces become too great for a reliable expansion result. Furthermore, with fine grain sizes, there is a greater risk of agglomeration on the inner wall of the furnace draft because particles that are too light or have too low a density remain suspended in the heating region for too long.In this case, the particles continue to absorb energy after expansion and soften again without an isenthalpic shape change that would cause cooling, which in turn significantly increases the risk of agglomeration on the inner wall of the kiln draft. This danger increases as the grain band narrows, since, figuratively speaking, there are no longer enough coarser, and at the same time heavier, particles to pull the finer particles against the buoyancy forces. To expand raw sands with finer grain sizes, WO 2016 / 191788 Al and WO 2018 / 191763 Al describe feeding or injecting the material, along with a quantity of air, from the bottom up into the kiln draft and conveying it through the draft. It has been recognized that when feeding very fine grains in combination with blowing, different flows must be synchronized to subsequently obtain a uniform flow profile through the kiln draft and avoid turbulence, as this favors agglomeration on the draft wall. Such agglomeration, in turn, causes successive overgrowth of the draft and, consequently, obstruction of heat radiation, which in turn leads to poorer expansion results. WO 2021 / 060157 A1 describes a vertically positioned kiln for firing lime, particularly limestone and dolomite. The kiln has an outer and an inner tube between which the material to be burned moves (due to gravity), with the material being fed into the kiln from above by means of a feeding device. EP 0007977 A1 describes a method, also known as an annular draft furnace, for burning lumpy combustion material, such as limestone, dolomite, magnesite, or the like, wherein the annular shaft and the inner shaft are alternately charged with fresh air and combustion gases and are connected to the exhaust gas discharge, respectively. The annular space and the inner shaft are formed by a shaft insert in the furnace draft. Object of the Invention ctoc in / zznz / E / Y Therefore, the object of the present invention is to provide a device for the production of an expanded granulated material that overcomes the disadvantages mentioned above. In particular, the device is designed to allow the expansion of unprocessed sands with fine particle sizes, preferably with particle sizes less than or equal to 120 microns, and more specifically with particle sizes in the range of 50 to 100 microns and a narrow grain band, preferably with an expanded product that is as uniform as possible. Brief Description of the Invention To solve the aforementioned problem, the invention provides a device for producing an expanded granulated material of mineral material in the form of sand grains with an expanding agent, for example, for producing an expanded granulated material of perlite or obsidian sand with water bound as an expanding agent. The device comprises a kiln with a substantially vertically arranged kiln draft having an upper end and a lower end, wherein a conveying section extends between the two ends and passes through a plurality of heating zones arranged separately from each other in the conveying direction, wherein each of the heating zones has at least one independently controllable heating element to heat the material to at least a critical temperature and expand the sand grains.wherein at least one feeding means is provided, which is adapted to feed at least the unexpanded material to one of the two ends of the kiln shaft in the direction of the other of the two ends of the kiln shaft, to expand the material, as seen in the conveying direction, in the last half, preferably the last third, of the conveying section, wherein at least one steering element is provided, which is arranged at least in sections in the kiln shaft, wherein the steering element forms a separation, gap or space with an internal wall of the kiln shaft, at least in the region of one of the two ends of the kiln shaft, wherein the at least one feeding means is adapted to feed the unexpanded material into the gap or space,that freestanding fastening means are provided for at least one steering element so that at least one steering element can be removed from the furnace draft and reinserted as necessary. The conveying direction is parallel to the vertical or plumb line and can be from top to bottom or vice versa. This means that at least one element of direction can be provided whether the material is fed from above or from below. In the case of top feeding, the material to be expanded is conveyed at least partially along the conveying section by gravity. When fed from below, the material to be expanded is normally fed into the kiln draft along with a quantity of air and conveyed through the kiln draft. Heating elements can be used to define heating zones, since each of the different heating zones must have at least one heating element and these heating elements must be independently controllable. For the sake of completeness, it is noted that, as seen in the transport direction, the last half is the second half or the last third is the third third. In principle, a single steering element can be provided. This element may consist of several parts, where several smaller steering elements can be combined to form a larger steering element or integrated into it. However, several separate steering elements can also be provided. At least one steering element is manufactured from one or more materials capable of withstanding the temperatures found in the furnace draft. These materials can be, for example, metals, particularly stainless steels or nickel-based alloys, or carbon fiber or ceramics, in particular CfrQC I 017707 Ε / ΥΙΛΙ advanced ceramics. It should be noted that the steering element does not have to be entirely within the furnace flue; it can also protrude from the flue in sections without impairing its function, as described in more detail below. For example, a portion of the steering element can be provided at the upper and / or lower ends of the furnace flue to protrude for securing purposes. However, of course, it can also be provided that at least one steering element is arranged entirely within the furnace draft and is only secured within it. The inner wall defines the furnace shaft. The steering element is separated from the inner wall of the furnace shaft, such that a space is formed at least in the region of one of the two ends of the furnace shaft, that is, in the region of the end of the furnace shaft intended for feeding the material to be expanded, where the space is preferably an annular space. In this case, annular space should be understood in particular as circumferential, without this implying any restriction to a circular shape. Since the gap or space is now formed—at least in section—by the arrangement of the steering element in the kiln shaft, and the unexpanded material is fed via this gap or space, the feed material is thus kept away from the radial center of the kiln shaft, at least in the region of the beginning of the conveying section. In this case and in what follows, "radial" should be understood independently of the specific cross-sectional shape of the kiln shaft. This means that regardless of whether the cross-section of the kiln shaft normal to the conveying section or the conveying direction is circular or not—for example, whether the cross-section is elliptical, rectangular, or square—its center is referred to as the radial center or radial midpoint. Consequently, a radial direction points away from the radial center. In particular, if the feed is from the top, an upward flow of heated air / gases (stack flow) caused by the stack effect typically occurs in the radial center region of the kiln draft, preventing material transport by gravity. However, the air / stack flow cannot strike or influence the material in the cavity. Furthermore, since it is a hollow and not simply an opening (especially an annular one), the material is directed towards and into the furnace draft. Such a direction can be extended over the entire transport section, particularly if the direction element extends over the entire transport section. Typically, the length of the transport section can be in the range of 3 to 20 m, preferably 5 to 15 m, and particularly preferably 6 to 10 m. If the steering element, and therefore the gap, extends over only part of the conveying section, for example, just a few meters, the material is guided to the gap from one side over that portion of the conveying section. However, in this case, a certain steering effect is still generally noticeable at least beyond the end of the steering element, due to the forced uniformity of movement, particularly the direction of movement, of the individual material particles into the gap. Consequently, in the case of top feeding, the material can be prevented from coming into contact with the airflow described earlier at the radial center, even a short distance after exiting the gap. However, the flow conditions and therefore the residence time of the particles, as well as the heat transfer to the particles in the furnace draft, can also be specifically influenced by at least one steering element when fed from below. Due to the relatively narrow space or gap and the resulting increase in flow velocities (turbulent flow for Reynolds number Re > 10L4 (104) ), the flows that form in the gap region, particularly flows from the gap or annular space, favor heat transfer to the carrier gas and, therefore, also to the particles. Due to mixing in turbulent flows, heat transfer is greater than in laminar flow (the heat transfer coefficient α increases). This means that the steering element favors the expansion of very fine and narrow feed fractions of the material, which in particular can have diameters less than or equal to 120 microns, preferably less than or equal to 100 microns. Another effect of the steering element is that all the material, or feed material, at least at the beginning of the conveying section, moves very close together along the inner wall and therefore relatively close to the heating elements. This results in uniform heating of all the material grains in terms of both time and location, which in turn leads to uniform expansion results. This applies to both top and bottom feeds. Furthermore, the steering element causes the feed material to be irradiated both by the actively heated external side of the furnace or furnace draft and by the steering element itself, because the steering element reflects or absorbs some of the radiant energy and then re-emits it. This means that the steering element can act as a passive heat source. The degree of reflection or emission can depend on the design of the steering element, particularly the material of the steering element, such that the steering element forms a passive heat source that can be adjusted to a certain degree. The direction element thus has multiple positive effects on the expansion result, which can reinforce each other. It has been recognized that each of the different feed fractions of the material to be expanded may require a different optimum length of the steering element, which can typically range from one to several meters. Accordingly, in a preferred embodiment of the device according to the invention, at least one steering element, as seen in the conveying direction, extends at most to the end of the first half, preferably at most to the end of the first third, and most preferably at most to the end of the first quarter, of the conveying section. Accordingly, the steering element can originate from one of the two ends of the furnace shaft, or in the region of one of the two ends of the furnace shaft, or from the outer edge of one of the two ends of the furnace shaft. The aforementioned limitation of the maximum extension of the steering element, as seen in the transport direction, can be provided in particular in modes with feeding of the material to be expanded from above. Alternatively, or additionally, a minimum length of the steering element can be provided to achieve optimal expansion results depending on the feed fraction. This minimum length can be provided particularly for methods where the material to be expanded is fed from below. Accordingly, in a preferred embodiment of the device according to the invention, it is provided that the at least one steering element extends over at least a quarter of the transport section, preferably over at least a third of the transport section, and particularly preferably over the entire transport section. In a preferred embodiment of the device according to the invention, the cavity or space, as seen along the transport direction, is provided to extend completely circumferentially, at least in sections, around a radial center of the furnace draft. Consequently, the material to be expanded can be introduced into the furnace draft without any problem and, if necessary, also in very large quantities simultaneously from all sides, in particular distributed uniformly over the entire cross-section of the annular cavity or space, which allows for very high expansion or production rates. If the steering element is secured exclusively outside the furnace shaft, the gap or space can also be designed completely circumferentially with respect to the radial center of the furnace shaft along the entire length of the steering element in the conveying direction, thus maximizing the use of space within the furnace shaft. On the other hand, if securing elements are required for the steering element within the furnace shaft, the gap or space can still be designed in sections along the conveying direction—that is, in the section or sections where no securing elements are present—completely around the radial center of the furnace shaft. Preferably, when the gap or space around the radial center of the furnace draft extends around, that is, through an angular interval of 360°, the directional element is radially airtight, particularly gas-tight. Accordingly, this applies regardless of whether the cross-section of the furnace draft is circular or not. Consequently, the path of the gap does not have to be circular, but can also be elliptical, rectangular, or square, for example. It should be noted at this point that, in general, the radial center of the furnace draft and the radial center of the baffle plate can coincide. A radial center for the baffle plate can be assumed even if the baffle plate does not completely surround this radial center. Optionally, the baffle plate can be mentally extended so that it surrounds the radial center in a full 360°. In a preferred embodiment of the device according to the invention, the gap or clearance is provided to have a variable width in the transport direction by at least 50%, preferably at least 65%, and most preferably at least 80%, wherein the width of the gap is preferably at most 10 cm. The width of the gap corresponds to a distance between the inner wall of the furnace flue and the steering element or a surface of the steering element facing the inner wall. Preferably, the gap width can be measured radially or perpendicular to the steering element and / or the inner wall. Specifically, the gap width for a point on the baffle plate surface facing the inner wall can be determined as the shortest distance between this point and the inner wall of the furnace draft. ctroc i η / ζζηζ / Ε / γίΛΐ By varying the gap width in the transport direction—that is, by extending the steering element in the transport direction in the region where the gap forms—the residence time of the sand grains along the transport section can be specifically influenced or adjusted. In particular, increasing the gap width in a certain region of the transport section can result in a longer residence time than in regions with a smaller gap width, and vice versa. However, it is also conceivable in principle to have modalities in which the width of the gap hardly varies in the direction of transport or is essentially constant. In any case, the shape of the steering element can be adapted accordingly to the shape of the cross-section of the furnace flue. The specified variation range can typically be related to an average value of the gap width in the transport direction or to a minimum or maximum gap width, the latter in particular in the case of the possible maximum gap width mentioned. Based on the above, a relative dimensioning of the opening is generally sensible; that is, without specifying exact values ​​in centimeters. In some cases, however, dimensioning based on absolute values ​​can be useful. ctroc i η / ζζηζ / Ε / γίΛΐ constant . In a preferred embodiment of the device according to the invention, it is provided that, at least along a portion of the conveying section, the furnace flue has, transversely, particularly perpendicular to the conveying direction, a cross-section that is at least sectionally round, preferably substantially circular or substantially elliptical, which is bounded by the inner wall. While the circular cross-section is the most stable with respect to distortion stresses, in the case of the ellipse, the ratio of circumference to cross-sectional area is significantly better, in that more of the circumferential area (of the inner wall) is available for energy radiation. The cross-section of the furnace draft should be clearly understood without the optionally provided steering element. It should be understood that "substantially" means that certain deviations from mathematically perfect circles or ellipses are, of course, possible and, as a rule, even unavoidable, if only for manufacturing reasons. Optionally, slight deviations from the mathematically perfect circle or ellipse shape may also be intentionally provided for. Preferably, the furnace draft that constitutes a cavity has the cross-sectional shape along the entire transport section. In sections, the cross-sectional shape may deviate from the aforementioned round / circular / elliptical shape, for example, where such sections or subsections are connected by straight sections or subsections. It is understood that the cross-sectional shape may also be perfectly round / circular / elliptical along at least a portion of the conveying section. Transitions from one cross-sectional shape to another are preferably designed so that there is no flow turbulence forming in the furnace draft. Alternatively or additionally, the cross-section may have corners. Accordingly, in a preferred embodiment of the device according to the invention, it is provided that, at least along a portion of the conveying section, the furnace draft has, transversely, and particularly perpendicularly to the conveying direction, a cross-sectional shape that is at least partially angular, preferably substantially rectangular or substantially square, and is delimited by the inner wall. The relatively large circumference of the cross-section, in relation to the cross-sectional region, may be advantageous, since this can create space for heating elements with a correspondingly large area and more area can be made available for energy transfer to the material to be expanded, than would be the case with a purely round or even circular cross-section. The cross-section of the furnace draft must again be clearly understood without the optionally provided steering element. Essentially, it must be understood that certain deviations from mathematically perfect rectangles or squares are, of course, possible and, as a rule, even unavoidable, if only for manufacturing reasons. Optionally, slight deviations from the mathematically perfect rectangular or square shape can also be deliberately included; in particular, rounded corners are possible in practice. Preferably, the furnace draft that constitutes a cavity has the cross-sectional shape along most of the transport section, preferably along the entire transport section. In sections, the cross-sectional shape may deviate from the angular / rectangular / square shape, for example, in that such sections or partial sections are connected by round or partial sections. It is understood that the cross-sectional shape may also be completely angular / rectangular / square along at least a portion of the transport section. Transitions from one cross-sectional shape to another are preferably designed so that no flow turbulence forms in the furnace draft. In a preferred embodiment of the device according to the invention, the inner wall is formed by at least one boundary element, preferably made of high-temperature resistant steel, and at least one steering element is made of the same material as the boundary element. This choice of material ensures that the same performance requirements are met for both the boundary and steering elements. Furthermore, this same material choice also results in the same coefficients of thermal expansion, thus preventing distortion due to different thermal expansion and ensuring a uniform shape of the cavity or space. Preferably, the oven is constructed of one or more materials, particularly thermal insulating materials, when viewed radially behind the limiting element. High-temperature steel is a well-known type of stainless steel. On the one hand, the limiting element allows for a structurally simple way in which the material fed into the furnace draft cannot come into contact with the heating elements, which, as seen radially, are arranged behind the limiting element. On the other hand, the presence of at least one limiting element makes it very easy to create a desired cross-sectional shape for the furnace draft and, optionally, adapt it to different applications. Choosing the right material for the boundary element allows it to be used across all temperature ranges relevant to the application without compromising its functionality. When expanding perlite or obsidian, metallic materials are particularly relevant. However, it would also be conceivable—especially for other minerals requiring higher calcination temperatures—to manufacture the boundary element from a suitable material other than metal, such as carbon fiber or high-performance ceramics. As mentioned several times, it is possible to provide methods in which the material to be expanded is introduced from below into the kiln flue. Accordingly, in a preferred embodiment of the device according to the invention, at least one feeding means is arranged to draw the unexpanded material, along with a quantity of air, from the lower end of the kiln flue towards the upper end, such that the air forms an upward-flowing airflow by which the material is conveyed from below along the conveying section to be expanded in the upper (or second) half, preferably the upper (or third) of the conveying section. It would be conceivable, for example, to draw in a volume of air by means of a vacuum source or a fan through an (intake) nozzle connected upstream of the kiln draft and to feed the material, for example, by means of a duct, into the airflow entering the nozzle. This means that the at least one feeding means may comprise, for example, such a nozzle, as well as means known per se for generating or drawing in the volume of air, for example, a vacuum source and / or an (air) fan, wherein the vacuum source or fan is / are connected downstream of the kiln draft—also as the duct or hopper. In this case, the material can be fed in a measured or metered manner. In a particularly preferred embodiment of the device according to the invention, it is provided that the at least one feeding means comprises at least one suction or aspiration nozzle connected upstream of the furnace draft and preferably a diffuser connected downstream of the suction or aspiration nozzle. In particular, the diffuser can be designed to disperse the material in the air volume before the expansion process and to reduce the relatively high flow velocities at the inlet nozzle. As already mentioned several times, it is possible to provide methods in which the material to be expanded is fed from above into the furnace shaft. Accordingly, in a preferred embodiment of the device according to the invention, at least one feeding means is adapted to feed the unexpanded material into the furnace shaft at the upper end of the furnace shaft, in the direction of the lower end of the furnace shaft, such that the material is conveyed from top to bottom along the conveying section, at least by gravity, to be expanded in the lower half, preferably the lower third, of the conveying section. Accordingly, the at least one feeding means may comprise, for example, a conduit or hopper for feeding the material to be expanded. The at least one feeding means may further preferably comprise at least one valve, particularly controllable, for the material to allow particularly precise dosing of the material. In addition to gravity, other means of feeding or transport can be provided, such as process air or gas flowing from top to bottom or blown or sucked into the furnace draft. For the sake of completeness, it should be mentioned that, because the expansion process is known to be isenthalpic and accompanied by a temperature rise, this rise can be specifically detected or located, regardless of whether the material to be expanded is fed into the kiln from the top or the bottom. In particular, this can be used to determine the appropriate temperature treatment of the expanded sand grains after the actual expansion process, in order to influence their surface properties. For example, further heating above the critical temperature can be prevented to avoid surface cracking. Alternatively, such a further temperature increase can be deliberately initiated if it intentionally results in, or even causes, surface cracking of the sand grains. As mentioned, in the device according to the invention, releasable fastening means are provided for at least one steering element, in order to be able to remove the at least one steering element from the oven and reinsert it as necessary. This means that the steering element is removable or reinsertable. This makes the device much more versatile, since, on the one hand, the steering element can be completely removed without difficulty if feed fractions with very coarse grain sizes are to be expanded, particularly those with diameters of several hundred microns or more. On the other hand, of course, different steering elements that are optimally suited to the respective feed fraction can also be installed, removed, or converted as needed without any problems. Typically, the removal or installation of the respective steering element is carried out at a relatively low temperature, particularly at room temperature, possibly waiting for the device to cool down first after a production process. For the sake of order, it should be noted that, as usual, "releasable" should be understood as being releaseable in a non-destructive manner, which implies reuse. Suitable fastening means are well known. In particular, a wide range of different threaded connections and / or known positive locking connections, such as hook and eye combinations, locking bolts, or bayonet locks, or any combination of such connections, can be used as fastening means. CfrQC I 017707 Ε / ΥΙΛΙ appropriate . As explained above, the steering element can be manufactured from a wide variety of materials. In a preferred embodiment of the device according to the invention, at least one steering element is made of metal, particularly high-temperature resistant steel. This ensures that the steering element can be used in all temperature ranges relevant during the expansion of materials such as pearlite or obsidian, without affecting its function or causing damage. Furthermore, the choice of the aforementioned material for the steering element results in particularly good reflection or emission of the heat or thermal radiation generated by the heating elements.This means that the steering element is optimally adapted as a passive heat source, as explained in more detail above, saving energy and costs. In a preferred embodiment of the device according to the invention, a clearance is provided between the at least one steering element and a radial center of the furnace shaft, at least along the entire length of the at least one steering element in the furnace shaft, preferably along the entire length of the at least one steering element, parallel to the transport direction. In this context, it is not excluded that the steering element may be formed outside the furnace shaft, such that a section of the steering element is located in the region of the longitudinal axis of the furnace shaft, which within the furnace shaft typically extends congruently with the radial center of the furnace shaft. On one hand, the free space allows air / gases, particularly the aforementioned chimney flue, to escape from the kiln draft in the radial center region. On the other hand, the free space can be used to introduce forced air into the kiln draft from the outside, which can be used to influence the flow conditions in the kiln draft and, therefore, the residence time of the raw sand or, after expansion, the expansion material in the kiln draft. Brief Description of the Drawings The invention will now be explained in more detail by means of embodiment examples. The drawings are illustrative and intended to depict the idea of ​​the invention, but in no way restrict it or even reproduce it conclusively. The drawings show the following: Figure 1 shows a schematic cross-sectional view of one embodiment of a device according to the invention for the production of expanded granulated material, wherein the feeding or transport of the granulated material to be expanded is carried out from top to bottom in a kiln shaft. Figure 2 shows a schematic cross-sectional view of another embodiment of the device according to the invention, wherein the granulated material to be expanded is introduced or transported to the furnace shaft from the bottom up. Detailed Description of Preferred Options Figure 1 shows a device according to the invention for producing expanded granulated material 2 from mineral material in the form of sand grains with an expanding agent. In the embodiment shown, the material is perlite sand 1 in which water (referred to as crystallization water) is bound and acts as the expanding agent. The device comprises a kiln 3 having a substantially vertical kiln shaft 4 having an upper end 5 and a lower end 6. A conveying section 7 extends between the two ends 5, 6, indicated in Figure 1 by a dashed line (in Figure 2 by a dashed line), wherein the dashed line in Figure 1 (the dashed line in Figure 2) also marks a radial center 16 of the kiln shaft 4.The transport section 7 leads through a plurality of heating zones 8 arranged separately from each other in the transport direction 12 (indicated by horizontal dotted lines in Figure 1), wherein each of the heating zones 8 has at least one heating element 9 that can be independently controlled from each other to heat the perlite sand 1, in particular, to a critical temperature and to expand the perlite sand grains 1. In the mode examples shown, the heating elements 9 are electrically operated and can be controlled by a regulation and control unit (not shown). The device further comprises feeding means which, in the embodiment of Figure 1, include a valve 10 for regulating the feed of the perlite sand 1 also as process air 21 and are adapted to feed the unexpanded perlite sand 1 (together with process air 21) at the upper end 5 of the furnace shaft 4 in the direction of the lower end 6 of the furnace shaft 4 to the furnace shaft 4 to expand the perlite sand 1, as seen in the transport direction 12, in the last half, preferably the last third, of the transport section 7. This means that in the embodiment of Figure 1, the perlite sand 1 is conveyed mainly by gravity from top to bottom along the transport section 7, with the process air 21, which may have been blown or drawn in with the perlite sand 1, supporting the falling motion of the perlite sand 1. This heats the process air 21 flowing downwards through the furnace draft 4. In principle, this can lead to an increase in the flow velocity in the furnace draft 4, which can shorten the residence time of all the perlite sand particles 1 in the furnace draft 4. To avoid this and to compensate for the increase in the flow velocity of the first process air, or to maintain the flow velocity approximately constant, the furnace draft 4 in the example modality of Figure 1 is designed to be wider at the bottom than at the top. This means that the cross-section of the furnace draft 4 normal to the conveying direction 12 increases from the upper end 5 to the lower end 6. However, it should be emphasized that even if the perlite sand 1 is fed into the upper end 5 of the furnace draft 4, furnace drafts 4 with a constant or approximately constant cross-section are of course also possible. The cross-section of furnace shaft 4 is delimited by an internal wall 14 of furnace shaft 4, which in the modality examples shown is formed by at least one delimiting element of high-temperature resistant steel. The furnace flue 4 or furnace 3 is thermally insulated from the outside by means of thermal insulation 24. Temperature sensors 23 are arranged in vertically separate positions 22, with at least one temperature sensor 23 located in each heating zone 8. In the exemplary mode shown in Figure 1, the temperature of the perlite sand 1 is determined via the temperature prevailing in the respective heating zone 8.Heating elements 9 and temperature sensors 23 are connected to the regulation and control unit (not shown), which determines the position or region 25 in the furnace draft 4 where the expansion of the perlite sand grains 1 takes place, based on temperature data. In this position or region 25, a significant temperature reduction, a temperature drop of, for example, more than 100°C, occurs in the expanded perlite sand 1. This temperature drop results from the isenthalpic expansion process of the perlite sand 1, where the expansion occurs due to a softening of the surface of the perlite sand grains 1 followed by an expansion process due to the water vapor or water vapor pressure that forms within the perlite sand grains 1.For example, perlite sand 1 may have approximately 780°C immediately before its expansion and only approximately 590°C immediately after the isenthalpic expansion process; that is, a temperature drop of 190°C occurs in this example, and depending on the material, the temperature drop is typically at least 20°C, preferably at least 100°C. By means of the regulation and control unit (not shown), those heating elements 9 which, as seen in the transport direction 12, are located after the temperature drop position or region 25 can be specifically or automatically regulated so that the desired energy input can take place. It should be noted that the aforementioned temperature drop does not necessarily manifest itself as a temperature decrease in this automatic regulation, but optionally as an interval in which more energy is required to maintain the temperature, so that the use of temperature sensors 23 to detect the temperature drop can also be dispensed with. In particular, these heating elements 9 can be regulated in such a way that there is no additional or repeated increase in the temperature of the expanded perlite sand or granulated material 2 or that it is ensured that the expanded granulated material 2 is of closed cell configuration. In the example mode of figure 1, the expanded granulated material 2 is discharged at the lower end 6 and fed via a water-cooled duct 20 to an air entrainment / suction flow 26 that operates with cold air 27. The cold air 27 or cold air 28 with expanded perlite sand 2 c^qc i η / ζζηζ / E / γίΛΐ is drawn in, for example, by means of a vacuum pump or a fan (not shown). The device according to the invention has at least one steering element 13, which is arranged at least in sections in the furnace shaft 4, wherein the steering element 13 forms a gap or space 15 with the inner wall 14 of the furnace shaft 4 at least in the region of one of the two ends 5, 6 of the furnace shaft 4, wherein the at least one feeding means is configured to feed the unexpanded perlite sand 1 into the gap or space 15. In the example configuration of Figure 1, the steering element 13 is correspondingly arranged in the upper end region 5. The valve 10 and the process air 21 are arranged such that the perlite sand 1 is fed into the shaft 15 in the upper end region 5. This means that the perlite sand 1 enters the furnace shaft 4 when it enters the shaft 15. It should be emphasized that in the example modality of figure 1, the perlite sand 1 is introduced through the upper end 5 over the entire gap 15, but in figure 1, for reasons of clarity, only the perlite sand 1 is shown, which is introduced into the gap or space 15 on the left side of the image. The steering element 13 protects the perlite sand 1 from an upward flow of heated air / gases (chimney flux) that forms in the radial center region 16 of the furnace draft 4. This prevents the very fine granulated material with diameters less than 100 microns, particularly less than 75 microns, from being obstructed by the chimney flux and from expanding as desired. This is due in particular to the fact that, without a steering element 13, the perlite sand particles 1, after cooling due to the isenthalpic expansion process, are reheated. This causes the perlite sand particles 1 to soften again, but they can no longer cool enthalpically by changing their shape, thus creating a greater risk of agglomeration on the inner wall 14. Such chimney flow can easily escape upwards from the furnace draft 4 through a free space 19. This free space 19 is arranged or formed, along the entire length of the steering element 13 parallel to the transport direction 12, between the steering element 13 and the radial center 16 of the furnace draft 4. Furthermore, the steering element 13 guides the perlite sand 1 specifically near the inner wall 14, resulting in uniform heating of all the perlite sand grains 1 in terms of time and location, which in turn produces a uniform expansion result c^qc i η / ζζηζ / E / γίΛΐ. In the example mode of figure 1, the steering element 13 extends in the furnace draft 4 from the upper end 5 to approximately the end of the first third of the conveying section 7. However, the uniformity of movement, in particular the direction of movement of the perlite sand grains 1 to the gap 15 effected by the steering element 13 also acts a little beyond the end of the steering element 13. In the modality examples shown, the steering element 13 is made of high-temperature resistant steel and appropriately reflects the heat radiation caused by the heating elements 9. This means that the steering element 13 also acts as a passive heater for the perlite sand 1 located between the inner wall 14 and the steering element 13. In the example shown in Figure 1, the steering element 13 is fully disposed in and secured to the furnace shaft 4. Detachable fastening means (not shown) are provided for securing the steering element 13, allowing it to be removed from the furnace shaft 4 and reinserted as needed. Apart from the regions along the conveying direction 12 where fastening means are provided, the opening 15 extends completely around the radial center 16 of the furnace shaft 4. c^qc i η / ζζηζ / Ε / γίΛΐ As can be seen from the cross-sectional view in Figure 1, the shape of the steering element 13 is adapted to the cross-section of the furnace draft 4, in that the steering element 13 extends essentially parallel to the inner wall 14. Consequently, the gap or space 15 has a gap width 17 which, in the illustrated example, varies only slightly along the entire length of the steering element 13 in the conveying direction 12 and is preferably approximately constant. However, it should be noted that variants of the design are also possible in which the gap width 17 varies by at least 50% in the conveying direction 12 to selectively adjust the residence time of the perlite sand grains 1 in different regions along the conveying section 7. Furthermore, in the example mode of Figure 1, the width of the gap 17 hardly varies in the circumferential direction 18 and is preferably approximately constant. This applies to all positions or regions along the conveying section 7 over which the direction element 13 extends, particularly in the perlite sand feed region 1, i.e., in the upper end region 5 in the example mode of Figure 1. It should be noted, however, that mode variants are also possible in which the width of the gap 17 varies significantly in the circumferential direction 18, although it is generally clearly less than in the conveying direction 12, for example, by at most 5%. The most obvious difference between the variant shown in Figure 2 and that shown in Figure 1 is the feeding of the perlite sand 1 to be expanded (not shown separately in Figure 2 for clarity) from below into the kiln shaft 4, with the conveying direction 12 facing upwards from below. Consequently, at least one conveying element 3 is arranged in the kiln shaft 4 at least in the region of the lower end 6 of the kiln shaft 4 and forms the void 15 therein together with the inner wall 14.In this case, the at least one feeding means comprises a suction nozzle 11 connected upstream of the furnace draft 4 and a fan 34 and is configured to draw the unexpanded perlite sand 1 together with a quantity of air at the lower end 6 of the furnace draft 4 in the direction of the upper end 5 of the furnace draft 4 to the furnace draft 4, such that the perlite sand 1 is fed into the cavity 15. The quantity of air thus forms an upward-flowing airflow, by means of which the perlite sand 1 is conveyed upward along the conveying section 7 to expand in the upper half, preferably the upper third, of the conveying section 7. In the example mode of Figure 2, the feeding means c^qc i η / ζζηζ / E / γίΛΐ further comprise a diffuser 30 downstream of the suction nozzle 11, which is attached to the lower end 6 of the furnace draft 4. The diffuser 30 can help to disperse the perlite sand 1 in the air volume prior to the expansion process, in order to obtain or maintain a uniform distribution of the perlite sand 1 in the airflow. The suction nozzle 11 is supplied with perlite sand 1 via a vibrating channel 35, with the perlite sand 1 being fed to the vibrating channel 35 in metered quantities from a supply container 29 via a metering screw 33. Air is also drawn in through the suction nozzle 11 (by means of the fan 34), forming a suction airflow 31. The airflow or suction airflow 31 can be adjusted by the appropriate selection or design of the suction nozzle 11 and / or by selecting an appropriate suction speed (by means of the fan 34). The latter can, in principle, also be automated by means of the regulating and control unit (not shown). In the modality example in Figure 2, the steering element 13 extends over approximately one or the first quarter of the conveying section 7, and yet it can also extend considerably further, in particular over the entire conveying section 7 in the furnace shaft 4. The latter is indicated in Figure 2 by the dashed lines yc^qc i η / ζζηζ / E / γίΛΐ. The steering element 13 is also basically adapted to the cross-sectional shape of the furnace shaft 4 in the example mode of Figure 2. As in the example mode of Figure 1, the width of the gap 17 in the example mode of Figure 2 hardly varies in the circumferential direction 18 and is preferably essentially constant. This applies to all positions or regions along the conveying section 7 over which the steering element 13 extends, particularly in the perlite sand feed region 1, that is, in the case of the example mode of Figure 2, in the lower end region 6. However, it should also be noted in this case that variants of the mode are also possible, in which the width of the gap 17 varies significantly in the circumferential direction 18, although generally much less than in the conveying direction 12, for example, by a maximum of 5%. Although Figure 2 does not show a variation of the gap width 17 in the transport direction 12, along the transport section 7 or in the transport direction 12, the gap width 17 can also vary much more than in the circumferential direction 18 in the exemplary mode, as shown in Figure 2, for example by at least 50%, to specifically adjust the residence time of the perlite sand grains 1 in different regions along the c^qc i η / ζζηζ / E / γίΛΐ transport section 7. However, in both variants of modality shown, the width of gap 17 is at most 10 cm. In the example configuration shown in Figure 2, the steering element 13 is fixed to the diffuser 30, preferably in a removable manner. Consequently, as seen along the transport direction 12, there is an extension of the gap 15 completely around the radial center 16. In the exemplary configuration shown in Figure 2, an absolute temperature measurement is performed (however, the temperature sensors are not shown for clarity). Additionally, the energy consumption of the heating elements 9, or how this energy consumption changes along the transport section 7, is determined. Immediately after the expansion process and the associated temperature drop, the temperature difference between the expanded granulated material 2 (not shown separately in Figure 2 for clarity) and the heating elements 9 is significantly greater than the difference between the perlite sand 1 and the heating elements 9 immediately before the expansion process. Consequently, the heat flow also increases, provided the measured temperature remains constant.This means that the observed change in heat flow or energy consumption of the heating elements 9 from one heating zone 8 to the next ctroc i η / ζζηζ / E / γίΛΐ is an increase, whereas, due to the successive heating of the perlite sand 1 before the expansion process, the change in energy consumption along the transport section 7 is a decrease. For regulation purposes, in particular for regulation along the remaining transport section 7 after the temperature drop, the heating elements 9 are connected to the regulation and control unit (not shown) in such a way that, for example, an increase in the material temperature along the remaining transport section 7 or above the critical temperature can be specifically prevented or enabled. The discharge of the expanded granulated material 2 from the kiln shaft 4 takes place (along with the heated air) via a collection section 32 adjacent to the upper end 5 of the kiln shaft 4. By means of an air intake / suction flow 26, which operates with cold air 27, the expanded granulated material 2 continues to be conveyed. The cold air 27 or cold air 28 containing expanded perlite sand 2 is drawn in, as previously mentioned, for example, by a vacuum pump or fan (not shown). List of Reference Signs Perlite sand Expanded granulated material ctroc i η / ζζηζ / Ε / γίΛΐ Oven Oven draft Upper end of the oven flue Lower end of the oven flue Transport section Warming zone Heating element Valve Suction nozzle Transportation Department Steering element Inner wall of the oven flue Gap, separation or space Radial center of the furnace draft Width of the gap or space Circumferential direction water-cooled duct free space Process air Position for temperature measurement Temperature sensor Thermal insulation Position or interval of the temperature drop Air entrainment / suction flow Cold air dragging air Cool, fresh air with expanded perlite sand or expanded granular material Supply container Diffuser Suction airflow 32 Collection section dosing screw Fan Vibratory conduit

Claims

1. A device for producing an expanded granular material from mineral material in the form of sand grains with an expanding agent, for example, for producing an expanded granular material from perlite sand or obsidian sand with bound water as the expanding agent, the device comprising a kiln with a substantially vertically positioned kiln draft having an upper end and a lower end, wherein a conveying section extends between the two ends and passes through a plurality of heating zones arranged separately from each other in a conveying direction, wherein each of the heating zones comprises at least one heating element, which can be independently controlled to heat the material to at least a critical temperature and expand the sand grains, wherein further at least one feeding means is provided,which is adapted to feed at least the unexpanded material to one of the two ends of the furnace shaft in the direction of the other of the two ends of the furnace shaft, to expand the material, as seen in the transport direction, in the last half of the transport section, wherein at least one steering element is provided, which is arranged at least in sections in the furnace shaft, wherein the steering element CfrQC I 017707 E / YILI forms a gap or space with an internal wall of the furnace shaft, at least in the region of one of the two ends of the furnace shaft, wherein the at least one feeding means is adapted to feed the unexpanded material into the gap or space, characterized in that releasable clamping means are provided for the at least one steering element to be able to remove the at least one steering element from the furnace shaft and reinsert it as necessary.

2. The device according to claim 1, characterized in that the at least one steering element, as seen in the transport direction, extends at most to the end of the first half of the transport section.

3. The device according to any of claims 1 to 2, characterized in that the at least one steering element extends over at least a quarter of the transport section.

4. The device according to any of claims 1 to 2, characterized in that the gap or space, as seen along the transport direction, extends at least in sections around a radial center of the furnace draft around its entire circumference.

5. The device according to any of claims 1 to 2, characterized in that the gap or space ctroc i η / ζζηζ / E / γίΛΐ 47 has a gap width that varies in the transport direction by at least 50%.

6. The device according to any of claims 1 to 2, characterized in that the gap or space has a gap width that varies in the circumferential direction around a radial center of the furnace draft by a maximum of 35%.

7. The device according to any of claims 1 to 2, characterized in that at least along a portion of the transport section, the furnace draft has transversely to the transport direction a sectionally round cross-section that is limited by the inner wall.

8. The device according to any of claims 1 to 2, characterized in that at least along a portion of the transport section, the furnace flue has, transverse to the transport direction, a cross-section that is at least sectionally angular and is delimited by the inner wall.

9. The device according to any of claims 1 to 2, characterized in that the inner wall is formed by at least one delimiting element and in that the at least one steering element is made of the same material as the at least one delimiting element.

10. The device according to any of claims 1 to 92, characterized in that the at least one feeding means is adapted to draw the unexpanded material into the kiln flue together with a quantity of air at the lower end of the kiln flue in the direction of the upper end of the kiln flue, such that the quantity of air forms an airflow flowing from bottom to top, by means of which the material is conveyed from bottom to top along the conveying section, to expand in the upper half of the conveying section.

11. The device according to claim 10, characterized in that the at least one feeding means comprises at least one suction or aspiration nozzle connected upstream of the furnace draft.

12. The device according to any of claims 1 to 2, characterized in that the at least one feeding means is adapted to feed the unexpanded material at the upper end of the furnace shaft in the direction from the lower end of the furnace shaft to the furnace shaft, such that the material is transported from top to bottom along the transport section at least by gravity, to expand in the lower half of the transport section.

13. The device according to any of claims 1 to 2, characterized in that at least one steering element is made of metal.

14. The device according to any of claims 1 to 2, characterized in that a free space is disposed between the at least one steering element and a radial center of the furnace draft, at least along the entire length of the at least one steering element in the furnace draft.

15. The device according to claim 5, characterized in that the width of the opening is at most 10 cm.

16. The device according to claim 6, characterized in that the width of the opening is at most 10 cm.

17. The device according to claim 9, characterized in that at least one delimiting element is made of high-temperature resistant steel.

18. The device according to claim 11, characterized in that the at least one feeding means comprises a diffuser connected downstream of the suction or aspiration nozzle.

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