METHOD AND APPARATUS FOR COOLING A MATERIAL

Abstract: The present invention relates to a method of and apparatus for cooling a material, such as lime, treated in a rotary tubular kiln, in a cooler associated with the kiln. The cooler comprises at least one chamber, into the inlet of which hot material treated in the kiln drops from the kiln via a chute/chutes connecting the kiln and said chamber and forms a material bed in the lowermost portion of said chamber, and the material flows further countercurrently in relation to the cooling gas flow, discharging from the outlet end of the chamber. Material is circulated in the inlet end of the cooling chamber and material is returned thereto so that the material being circulated and the material being returned form at the position of the chute/chutes said layer, onto which the fresh hot material dropping from the kiln continuously forms a new bed and is mixed with the material being circulated and the material being returned.

Description: METHOD AND APPARATUS FOR COOLING A MATERIAL The present invention relates to a method of and apparatus for cooling a material, such as lime, which has been treated in a rotary tubular kiln, in a cooler associated with the kiln. The present invention concentrates on intensifying the cooling of a material treated in a rotary tubular kiln and discharged hot therefrom. A cooler used in rotary tubular kilns is a so-called sector cooler. It is a device located outside the shell of the tubular kiln and formed of two cylinders positioned one inside the other, rotating together with the kiln. It is supported to the kiln shell by attaching it thereto at its inlet end and by way of sliding joint at its discharge end. The object of the cooler is to cool hot material coming from the kiln, such as burnt lime generated from lime mud, and to pre-heat combustion air entering the kiln, respectively. The outer and inner shells of the cooler are joint together by means of elongated plates arranged in the radial direction, whereby the annular space formed between the shells may be divided into the desired number of cooling sectors. At its inlet end the cooler is secured by welding to the kiln shell via drop chutes. Through the drop chutes, hot material is led from the kiln to the inlet end of the cooler. The inlet end is provided with a conical part, receiving the material passing via the drop chutes. A radiation shield fixedly connected to a discharge hopper for cooled material surrounds the cooler. In sector coolers, the inlet end thereof is typically a conical and relatively elongated element. As the number of drop chutes (drop ducts) between the kiln shell and the cooler is typically 8 - 10, the feed of the material to be cooled to the conical part of the cooler is usually pulsating, whereby e.g. hot lime passes from the kiln directly, quickly and partially also unevenly to the sector part, especially if the feed cone is very sharp. Not all of the material streams entering the sectors are equal, which also contributes to the back flow of material. In addition to that, a local heat load may be generated on a relatively short length at the forepart of the sector portion, which heat load also burdens the constructions. Due to the above mentioned, especially if the material to be cooled is over- heated and has become tenacious, a further problem may have been the accumulation of the material to be cooled in places where the major temperature peaks prevail. This means that the foreparts of the sectors may be clogged, which in part prevents the flow of the lime and further contributes to e.g. the back flow. Further, the feed cone creates at the forepart of the cooler a large space unused with respect to combustion air and the material to be cooled, which decreases the efficient heat transfer area and length of the cooler and thus also the coefficient thereof. Mostly only in the lowermost portion of the cone there is a single continuous lime bed with a relatively small contact surface with the cooling air. The surface layer of the lime bed efficiently isolates the lime inside the bed from air and prevents the cooling of the lime. US publication A-4089641 describes a construction relating to satellite coolers of rotary tubular kilns, the purpose of which construction is to protect the inner wall of the cooler against the effect of hot material passing from the kiln. A deflector plate positioned inside the satellite cooler restricts the passage of the material so that material discharged from the kiln into the cooler during a previous revolution forms a protective layer, onto which the hot material discharging from the kiln impinges. According to said publication, this prevents rapid wear of the refractory lining when producing clinker in cement kilns. On the other hand, heat transfer from the protective layer to the environment, i.e. cooling of the material, takes place in principle during one revolution of the kiln only, until the satellite cooler together with the kiln again reaches its lowermost position. Heat transfer from the hot material discharging from the kiln to combustion air is not specifically intensified. An object of this invention is to enhance the cooling of hot material passing from the kiln in the coolers of rotary tubular kilns. Especially the object of this invention is to intensify heat transfer from hot material, such as lime, to the cooling airflow at the inlet end of the cooler as well as in the drop chutes between the kiln and the cooler. At the same time, an object of the invention is to reduce the heat load that the constructions of the cooler are subject to. In order to effect these objects, the present invention relates to a method of cooling a material, such as lime, treated in a rotary tubular kiln in a cooler associated with the kiln, which cooler comprises at least one chamber, to the inlet of which hot material treated in the kiln drops from the kiln via a chute/chutes connecting the kiln and said chamber and forms in the lowermost portion of said chamber a material bed, whereby material being at the location of the chute drops onto a material layer formed of material that has earlier dropped out of the chute, and the material further flows through the chamber countercurrently in relation to the cooling gas flow and is discharged from the outlet end of the chamber. A characteristic feature of the invention is that material is circulated at the inlet end of the cooling chamber and returned thereto so that at the location of the chute/chutes the material being circulated and the material being returned form a layer, onto which fresh hot material dropping from the kiln continuously forms a new bed and is mixed with the material being circulated and the material being returned. Further, the formed material bed is preferably continuously divided to parts that are made to fall through the cooling gas flow to form said material bed. The invention relates also to an apparatus for cooling a material treated in a tubular kiln, which apparatus comprises at least two cylindrical shells disposed one inside the other, surrounding the kiln and rotating together with the kiln around the longitudinal axis of the kiln, which shells are mounted at the discharge end of the kiln concentrically with the kiln, and between which shells an annular space is formed, said space communicating with the kiln via a chute/chutes connecting the kiln and said space; hot material treated in the kiln drops from the kiln via said chutes into the inlet end of said annular space forming a bed of material in the lowermost portion of said space. Characteristic features of the apparatuses are disclosed in the appended claims. In the present invention, material that is already somewhat cooled is circulated so that a protective layer is provided that acts as insulant between the hot material bed and the cooler at the inlet end of the cooler chamber or the annular space in an area whereto the hottest material, such as lime, coming from the kiln, drops. This reduces the heat loads that the cooling elements are subject to. According to the invention, intensifying the cooling is based on increasing the contact surface, i.e. the heat transfer surface between the cooling air and the material to be cooled. Fl-patent application 20000782 discloses a sector cooler, in which the conical construction of the inlet end thereof has been replaced with a cylinder, whereby the effect of the cooling air flow can cover a greater amount of material and the cooling is intensified. The present invention may preferably be applied in connection with this kind of cooler construction. When practicing the method according to the invention, the cooling is further intensified by an increase in the heat transfer surface between the material bed and the cooling combustion air, which increasing heat transfer surface is a result of the accretion of said material bed due to the circulation and returning of the material to be cooled, such as lime. The heat being transferred from the hot material during the cooling is most appropriately utilized to preheat the combustion air. As the volume of the feed cylinder is larger than that of the feed cone used in older coolers, it can accommodate a larger lime bed, in which circulating lime that is returned from the forepart of the cooling sectors and is already somewhat cooled is efficiently mixed with the hot lime coming from the kiln, due to the rotating motion of the kiln. As a result of the mixing, the lime being fed to the cooling sector portion is cooled so that sintering of the hot lime on the forepart walls of the sector portion is prevented. In the material bed the surface layer cools down first. If only one continuous bed of material, which is not mixed, is provided in the cooler, the material on the surface thereof acts after cooling as an insulant and efficiently prevents heat transfer from inside the bed to the ambient air. The cooling may be further intensified according to a preferred embodiment of the invention by means of increasing the contact surface between the hot material and the cooling air by dividing the material bed at the inlet end of the cooler to multiple sections. Thus, a greater part of the material to be cooled is taken into contact with the air. By decomposing at least part of the material bed into separate particles to the cooling gas flow at the ascending or descending side of the cooler, the cooling may be further intensified. According to one embodiment, it is further possible to return at least part of the material bed back into the kiln in the zone of the drop chutes, whereby they are further "flushed" by the combustion air flowing through the chute and being cooler than the material. This is effected by moving the material bed upwards by applicable means during the rotation of the kiln, whereby material drops back into the kiln through the drop chutes at the uppermost position and through the drop chutes facing downward further into the cooler. The present invention is disclosed in more detail with reference to the appended figures, of which Fig. 1 illustrates a preferred apparatus for effecting the method according to the invention. The Figure illustrates an elevation view of a tubular kiln cooler and a cross-section taken along line A - A; Fig. 2 illustrates another preferred apparatus for effecting the method according to the invention. The Figure illustrates an elevation view of a tubular kiln cooler and a cross-section taken along line A - A; Fig. 3 illustrates a third preferred apparatus for effecting the method according to the invention. The Figure illustrates the cooler in cross section seen from the end of the kiln; Fig. 4 illustrates a fourth preferred apparatus for effecting the method according to the invention. The Figure illustrates the cooler in cross section seen from the end of the kiln; Fig. 5 illustrates a fifth preferred apparatus for effecting the method according to the invention. The Figure illustrates an elevation view of a tubular kiln cooler and a cross section according to line A - A; and Fig. 6 illustrates a sixth preferred apparatus for effecting the method according to the invention. The Figure illustrates the cooler in cross section seen from the end of the kiln. Fig. 1 is a cross-sectional view of the cooling end of a rotary tubular kiln, via which cooling end the material treated in the kiln is discharged therefrom. The discharge end of a rotary tubular kiln 1 is supported in a way known per se by means of a support ring (not shown) to the supporting rolls as the kiln rotates around its longitudinal axis L. The material to be thermally treated, such as lime mud, is transferred as known per se through the kiln and heated and decomposed in the kiln by means of flue gases and heat radiation to burnt lime and carbon dioxide. The thermally treated material is discharged via the outlet 5 of the kiln, which outlet communicates with the cooler 2. The cooler 2 comprises two cylindrical shells 6 and 7 located one inside the other, which shells are mounted at the discharge end of the kiln 1 concentrically with the kiln, surround the kiln and rotate together with the kiln. An annular space 8 is formed between them. The inner cylindrical shell 6 is fastened at one end to the kiln via drop chutes (drop ducts) 3. Via the drop chutes the inlet opening 11 of the annular space 8 of the cooler communicates with the discharge opening 5 of the kiln for leading the hot material from the kiln into the cooler 2. Multiple drop chutes 3 are provided around the circumference of the kiln. The shells 6 and 7 are fastened together by means of longitudinal intermediate walls 16 that divide the annular space to cooling sectors. The annular space 8 is arranged to have at least two separate parts so that each cylindrical shell 6 and 7 comprises at least two cylinders fastened to each other and positioned in the direction of the longitudinal axis L of the kiln consecutively. The inner shell 6 comprises consecutive cylindrical parts, cylinders 6a and 6b, and the outer shell 7 comprises consecutive cylinders 7a and 7b. Due to the construction of the shells in two parts, the cooler may be divided in the longitudinal direction into two separate parts. The cooler part, through which the material to be treated flows first, is later referred to as "pre-cooler" 12 and the part, wherefrom the material exits the kiln and is passed to the process is later referred to as "secondary cooler" 13. The pre-cooler 12 comprising cylinders 6a and 7a is located at the inlet end of the cooler 2 and receives the hot material coming from the drop chutes, which material forms a bed 26 on the inner surface of the outer cylinder 7a. The inlet end of the cylinder 6a is supported to the kiln 1 via these drop chutes 3. The discharge end of the pre-cooler 12 is supported at the joint 20 of the pre- cooler and the secondary cooler by means of a light slide joint 22 known per se to the inlet end of the secondary cooler, which allows for the necessary radial and axial motion. The cylinders 6a and 7a extend at the joint 20 to a sufficient extent inside the annular space 13 formed by the cylinders 6b and 7b for forming a slide joint between the pre-cooler and the secondary cooler 13. The inlet end of the inner cylinder 6b of the secondary cooler is fastened by means of elements 24 and the discharge end by means of elements 25 to the shell of the kiln 1. At the inlet end of the pre-cooler 12 - surrounding the drop chutes 3 - there is no feed cone, but both the outer shell 7a and the inner shell 6a are cylindrical along the whole of their length, whereby a "feed cylinder" is provided at the drop chutes. In the zone of the feed cylinder there are no intermediate walls 16 connecting the shells 6 and 7. The transfer of the material to be cooled inside the cooler from the bed of material 26 is effected by feeding devices known per se, such as feed flights 19 which may be located on any wall of the cooler space. The transfer may be effected by separate members as well, said members being arranged inside the cooler space. On the outer circumference of the cooler 2 there is provided a feeding spiral 14 which introduces the material possibly passed through from the joint 20 of the pre-cooler and secondary cooler back to the process. The cooled material is discharged from the secondary cooler 13 through an opening 21 to a discharge hopper (not shown). Cooling air enters the coolers 2 through the outlet 21 and flows countercurrently with respect to the material and ultimately flows via the drop chutes 3 into the kiln 1 as combustion air. In the apparatus according to Fig. 1 , the circulation and returning of the material according to the invention is effected by means of troughs 4 of an appro- priate size, which are welded at the inlet end of the pre-cooler and which circulate and at the same time cool and also mix the desired amount of the material to be cooled with the hot lime stream coming from the kiln in the lowermost portion of the feed cylinder. In the solution according to Fig. 2, lightening openings 27 (Fig. 1) at the forepart of the intermediate walls 16 of the pre-cooler, on the outer circumference, are omitted and an appropriate laminar element 9 is fastened e.g. by welding at the forepart of the intermediate wall. The laminar element 9 has to be such that a plane surface 9a is formed at the end of the intermediate wall, which plane surface restricts the feed of material to be cooled between the cooling sectors, whereby material is returned into the feed cylinder, below the hot material coming from the kiln through the drop chute 3. In this way, a desired filling degree and more efficient internal circulation are effected in the feed cylinder of the pre-cooler. The height and number of feed elements (feed flat bars 9) located on the outer circumference of the feed cylinder of the pre-cooler and at the forepart of the sectors, as well as the inclination of the elements in relation to each other, are determined so that preferably an appropriate filling degree and internal circulation are effected in the feed cylinder of the pre-cooler. The reference numerals of Fig. 2 - 6 are the same as in Fig. 1 , where appropriate. In the solutions according to Figures 3 and 4, the ends of drop chutes 3 going into the pre-cooler are covered with a plate 10 (Fig. 3) or with plain bars 18 (Fig. 4). Thus, a pocket-like space 28 is formed at the end of each drop chute, which space prevents the material from dropping directly into the feed cylinder of the pre-cooler. In this way, the contacting heat surface between the material being treated and the cooling air is increased to some extent. Fig. 5 further illustrates an apparatus for effecting the invention. The drop chutes 3 in connection with the feed end of the pre-cooler 12 are extended inside the feed cylinder so that the extensions 22 of the chutes extend adequately to the lime bed 26. The chutes are extended in a single-side method so that the trailing side 23 (in the rotational direction of the kiln the latter side of the chute) of each chute 3 is shorter, whereby e.g. the flowing of the cooling air (shown by arrow in the Fig.) into the kiln is not prevented. So the leading side 22 of the drop chute (in the rotation direction of the kiln the anterior side) forms a feed plane (a feed flight), by means of which, if required, a circulation of desired volume for the material being cooled is effected at the feed end of the cooler and a feed of desired volume is effected in the sector part formed by the intermediate walls 16, from which sector part some of the material returns back into the feed cylinder. Additionally, part of the bed may be divided into separate particles into the cooling gas flow inside the cooler. This is effected so that when the kiln rotates, the side of the drop chute 3 that acts as the feed plane (extension 22) scoops along material to be cooled, and as the drop chutes travel upwards under the effect of the rotational motion of the kiln to a position more inclined than the angle of repose of the material, the material will flow downwards onto the outer shell of the feed cylinder, partly in form of separate particles being mixed with air. The leading edge of the drop chute has to extend into the feed cylinder to such a distance that the feed plane formed thereof can efficiently remove and lift the material bed. The extensions of the drop chutes serve also to prevent uncontrolled return of lime via the drop chutes into the kiln onto the burner pipe. The whole internal circulation of the material may be divided into several parts of bed in a controlled way also by means of a "regulation edge" on the trailing side of the drop chute 3. The regulation edge is part 29 on the trailing side 23 of the drop chute that extends into the annular space 8. By means of the regulation edge 29, part of the material circulation may be returned back to the cooling air flow in the drop chutes and at the same time back into the kiln, wherefrom it again drops back into the cooler. By means of the regulation edge 29, part of the material circulation may be divided into separate particles into the cooling gas flow also in the descending zone of the pre-cooler 12, wherein the drop chutes rotate downwards. In this way, the contacting heat surface between the material and the cooling air may be increased in a con- trolled way. Further, material, e.g. lime, that has been cooled during the circulation, forms a protective bed-type layer in the bottom part of the feed cylinder, which layer protects the constructions against hot material entering directly from the kiln. Fig. 6 illustrates a solution, in which the drop chutes also extend into the feed cylinder, but so that an appropriate distance is left between the end of the drop chute 3 and the outer shell 7 of the feed cylinder, which distance is es- sentially longer than in the apparatus of Fig. 5. Thus, the drop chutes do not extend to the material bed. Plate- or bucket-like lifting elements 30 are attached (e.g. by welding) radially in the longitudinal direction to the inner surface 7a of the feed cylinder, between the drop chutes 3, the shape and height of which elements 30 is adapted so that they move the material bed located in the bottom part of the feed cylinder upwards in the ascending part of the cooler in form of parts of material bed 26a, from which ascending part the parts partly drop down divid- ing into separate particles both into the cooling gas flow and partly also onto the drop chute located lower. In this way, a circulation of the material being cooled is effected in the zone of the feed cylinder, in principle similar to that of Fig. 5. The application of the invention is not restricted to a cooler construction described in the above, but the invention may as well be applied in connection with other cooling device constructions, in which the essential characteristic features of the invention may be effected.

Claims: Claims: 1. Method of cooling a material, such as lime, treated in a rotary tubular kiln, in a cooler associated with the kiln, said cooler comprising at least one chamber, in the inlet end of which chamber hot material treated in the kiln drops from the kiln via a chute/s connecting the kiln and said chamber and forms a material bed in the lowermost portion of said chamber, whereby the material drops at the chute onto a layer formed of material having dropped earlier, and the material flows further countercurrently in relation to the cooling gas flow through the chamber, discharging from the outlet end of the chamber, characterized in that material is circulated in the inlet end of the cooling chamber and material is returned thereto so that at the chute/chutes said layer is formed of the material being circulated and the material being returned, onto which layer fresh hot material dropping from the kiln continuously forms a new bed and is mixed with the material being circulated and the material being returned. 2. Method according to claim 1 , characterized in that the formed material bed is continuously divided into parts which are made to drop through the cooling gas flow to form said layer. 3. Method according to claim 1 or 2, characterized in that in the inlet end of the chamber, at least part of the formed material bed is divided into sepa- rate particles into the cooling gas flow. 4. Apparatus for cooling a material, such as lime, treated in a rotary tubular kiln (1 ), said apparatus comprising at least two cylindrical shells (6, 7) disposed one inside the other and surrounding the kiln and rotating together with the kiln around the longitudinal axis (L) of the kiln, said shells being mounted in the outlet end of the kiln concentrically with the kiln and between which shells an annular space (8) is formed communicating with the kiln via a chute/s (3) connecting the kiln and said space, via which chutes hot material treated in the kiln drops from the kiln forming into the inlet end of the annular space a material bed (26) in the lowermost portion of said space, characterized in that trough-like means (4) are arranged in the end wall of the inlet end of the annular space (8) for returning material that has been dropped from the kiln back below the hot material dropping from the kiln. 5. An apparatus for cooling a material treated in a rotary tubular kiln (1), such as lime, said apparatus comprising at least two cylindrical shells (6, 7) disposed one inside the other, surrounding the kiln and rotating together with the kiln around the longitudinal axis (L) of the kiln, said shells being mounted in the outlet end of the kiln concentrically with the kiln, between which shells an annular space (8) is formed communicating with the kiln via a chute/chute (3) connecting the kiln and said space, via which chutes hot material treated in the kiln drops from the kiln into the inlet end of the annular space forming a material bed (26) in the lowermost portion of said space, the parts of which cylindrical shells (6, 7) after the inlet end being connected to each other by means of radial longitudinal intermediate walls (16), between which walls the material being cooled flows, characterized in that planar elements (9) are at- tached to the first end of the longitudinal intermediate walls (16) in the flow direction of the material being cooled to restrict the flow of the material in between the intermediate walls and thus to return part of the flowing material back into the inlet end of the annular space below the hot material dropping from the kiln. 6. Apparatus according to claim 5, characterized in that the drop chute/chutes (3) have, in the rotational direction of the kiln, a leading side (22) and a trailing side (23), of which the leading side (22) is essentially longer than the trailing side (23) so that the leading side extends essentially to the material bed (26), whereby the leading side acts as a feed plane lifting and removing material from the material bed. 7. Apparatus according to claim 6, characterized in that the trailing side (23) of the drop chute/chutes extends inside the annular space (8) to such a distance (29) that it effects the material lifted by the leading side (22) to be returned into the lowermost portion of the annular space in multiple separate portions. 8. Apparatus according to claim 5, characterized in that plate- or bucketlike elements (30) are attached to the inner surface of the outer shell (7) of the annular space (8) for lifting part of the material bed in the rotational direction of the kiln to the ascending part of said shell. 9. Apparatus according to claim 8, characterized in that the drop chute/chutes (3) have in the rotational direction a leading side and a trailing side, of which the leading side is longer than the trailing side and that the trailing side extends inside the annular space (8) to such a distance (29) that it causes the material lifted by the plate- or bucket-like elements (30) is returned into the bottom part of the annular space in multiple separate portions.

Inventors: AHVENAINEN ARTO, AHVENAINEN, ARTO
Applicants: AHVENAINEN ARTO, ANDRITZ AHLSTROM OY, AHVENAINEN, ARTO, ANDRITZ-AHLSTROM OY
Application year: 2001
Main classification: F25B
IPC codes: C04B2, F27B7