US3497191A - Heat transfer means for rotary kilns - Google Patents

Description

Feb. 24, 1970 I R. D. GANTZ 3,

HEAT TRANSFER MEANS FOR ROTARY KILNS Filed March 11 1968 .2 sheets-sheet 1 i n T. k v

4/ FIG. 1 Il {iii "'20 Z 3 in: "q" 76 I I I I F 24 :1 I F Lj Feb. 24, 1970 R. D. GANTZ 3,497,191

HEAT TRANSFER MEANS FOR ROTARY'KILNS Filed March 11 1968 2 Sheets-Sheet 2 States Patent 3,497,191 HEAT TRANSFER MEANS FOR ROTARY KILNS Ray D. Gantz, 2292 Dorset Road, Columbus, Ohio 43221 Filed Mar. 11, 1968, Ser. No. 712,234 Int. Cl. F27b 7/20; F26b 25/08 US. Cl. 263-33 8 Claims ABSTRACT OF THE DISCLOSURE Heat transfer elements consisting of a plurality of interconnected segments. The elements made up by the segments are suspended from the wall of a rotary kiln for contact with material, such as a slurry, as it moves through the kiln whereby a heat transfer relationship is achieved between the elements and the material. The individual segments are formed from a pair of spaced apart base members with spacer means extending between the base members. The spacer means are formed of a plurality of lengths of materials, for example the helices of a coil spring or individual rods, whereby the combined length of the spacer means greatly exceeds the distance between the base members. This provides maximum surface area for the heat transfer function while also providing a segment design which is otherwise ideally suited for contact with the slurries.

This invention relates to improvements in heat transfer elements of the type employed in rotary kilns. Rotary kilns are usually employed for the handling of materials such as slurries, sludges or dry compounds wherein the materials are moved progressively through the kilns. The kilns are referred to as rotary pyro-processing kilns, and heat transfer elements are usually employed in pre-heating sections of such kilns.

Rotary kilns of the type referred to are employed in the production of Portland cement, in the activating of lime sludge, for lime filtration, in pulp and paper operations, in other chemical operations, and in various pyroprocessing plants. Materials of the type characteristic of such processing are introduced into the kilns in the form of a wet slurry or sludge with a moisture content between 30 and 50 percent. In some cases, the kilns also handle dry compounds having little or no moisture content.

The kilns are usually mounted on foundation piers with a downward slope between inch and inch per foot length. The kilns may extend for over 500 feet and for an inside diameter between 14 and 16 feet. The materials fed into the kilns move slowly along the length, and the kiln is continuously rotated during this time. The heating means for the kiln are usually located at the extreme lower end, and temperatures in this area may be Well in excess of 2000". The hot gases move toward the entry end of the kiln and become progressively cooler.

It is desirable to provide a pre-heating zone adjacent the entry end. Heat transfer elements are situated in this pre-heating zone. The elements may be suspended from a point to 20 feet downhill from the entry end, and then extend for from 40 to 150 feet. Typically the preheating zone extends approximately the total length of a kiln. The heat transfer elements comprise a plurality of interconnected segments which hang downwardly when suspended from the top of the kiln and which form a pile when they are moved to the bottom of the kiln if the kiln rotates. The elements are connected all around the inside wall whereby suspended elements as well as a pile of elements at the bottom of the kiln will always be provided in the pre-heating zone.

3,497,19 l Patented Feb. 24, 1 970 The elements may be hung in curtain-festoon or garland fashions. The festoon or garland arrangement is employed where it is desirable to influence the material passing through the pre-heating zone. These arrangements may accelerate the movement of the material by acting in the manner of a screw conveyor or they may be arranged to slow down the movement of the material. It will be understood that conventional techniques for suspending of the elements are contemplated.

In the maintenance of rotary kilns of the type described, there are numerous instances where repair of the lengths of heat transfer elements must be undertaken. These elements are subject to relatively severe conditions because of heat, abrasion, and corrosion. It is, therefore, desirable to provide heat transfer elements which can be economically produced and maintained. In addition, the design of the elements must be such that efiicient heat transfer can be accomplished.

Applicants copending application Ser. No. 643,509, now Patent No. 3,442,497, issued May 6, 1969 describes certain heat transfer elements which provide certain advantages in operations of the type described. The heat transfer elements of the instant invention distinguish from these previously disclosed elements, and the heat transfer elements of this invention are particularly characterized by extremely efficient heat transfer capabilities. Furthermore, the elements of this invention provide definite advantages from the standpoint of initial assembly operations and from the standpoint of handling ease.

It is, therefore a general object of this invention to provide improved heat transfer elements for use in rotary kilns.

It is a more specific object of this invention to provide heat transfer elements which are extremely efficient from the standpoint of heat transfer capabilities and which provide other features lending economy and efficiency to the operation of rotary kilns.

These and other objects of this invention will appear hereinafter, and for purposes of illustration, but not of limitation, specific embodiments of the invention are shown in the accompanying drawings in which:

FIGURE 1 is an elevational view, partly cut away, of a segment designed for use in heat transfer elements of the type contemplated by this invention;

FIGURES 2 and 3 comprise detail views of base members suitable for use at the opposite ends of the segments;

FIGURE 4 is an elevational view of a modified form of a segment for use in heat transfer elements of the type contemplated by the invention;

FIGURE 5 is a plan view taken about the line 5-5 of FIGURE 4;

FIGURE 6 is a sectional view taken about the line 6-6 of FIGURE 4; and

FIGURE 7 is a schematic illustration of a rotary kiln employing heat transfer elements.

The heat transfer elements of this invention generally comprise a plurality of segments with each segment mcluding a pair of spaced-apart base members. Spacer means extend between the base members, and link means are associated with each base member to permit securing of the segments together to form the desired elongated heat transfer element.

The spacer means for the heat transfer elements comprise a plurality of lengths of material with the combined lengths of the spacer means greatly exceeding the distance between the base members. This provides a large surface area for heat transfer. In addition, the design permits use of materials which are relatively thick whereby a high degree of heat retention can be achieved. The combination of the high heat transfer capabilities and the high retention capabilities greatly add to the efliciency of the heat transfer elements made up of segments of the type described herein.

The heat transfer elements formed of the segments referred to are disposed in rotary kilns, for example, of the type handling slurries utilized in the manufacture of Portland cement or lime sludges. In such kilns, the materials are moved progressively from the feed end of the kiln into contact with heat transfer elements located in a pre-heating section.

The heat transfer elements formed of the segments referred to are preferably attached all around the interior surface of the kiln. In any particular position of the kiln, at least a portion of each transfer element in the top half of the kiln will hang downwardly. At the same time, the heat transfer elements in the bottom half of the kiln will form a pile. As the kiln rotates, the position of each heat transfer element constantly changes; however, there will always be a portion hanging from the top of the kiln, and another portion forming a pile at the bottom of the kiln. The slurry or other material which is delivered into the kiln, will come into contact with the heat transfer elements in the'pre-heating zone. These elements will, therefore, operate to transfer heat, which has been absorbed by the elements when hanging in the exiting hot gas stream, to the slurry or other type work load. After pre-heating, the slurry or other material will be moved to the calcining and burning zones.

The accompanying drawings illustrate segments of heat transfer elements of the type contemplated by this invention. The segment shown in FIGURE 1 includes base members 12 and 14. The base member 12 includes a pair of links 16 which define a central opening 18. The op posed base member 14 defines a single link 20 defining a central opening 22.

A bolt 24 extends within the aligned openings 18 and 22 for connecting adjacent links together. The bolts 24 are attached by means of the nut 26. Where nuts and bolts are used as illustrated in FIGURE 1 or in the other figures, peening or welding of the bolt ends is preferred to avoid loosening.

The base members 12 and 14 are held in spaced-apart relationship by means of a central rod 28. The rod 28 defines threaded ends 30 which are received in threaded central openings defined by the base members 12 and 14.

The base members each define a cup section 32. A coil spring 34 extends around the rod 28 with the helices 36 at the ends of the coil spring being received Within these cup portions.

It will be noted that the coil spring 34, rod 28, and base members with associated links are formed of relatively thick material. This material, which may be steel, will retain heat more readily than thinner sections of material. Furthermore, by providing greater thickness in the material, an increase in surface area of the material can be achieved. This provides greater heat transfer capabilities. When a slurry or other material comes into contact with the segment, there will be a large surface area available whereby direct contact with a large proportion of the slurry material can be achieved. Since a high degree of heat retention is provided in the segments, the available heat will be correspondingly increased. Thus, there will be no great heat loss from the segments during inactive portions of their operating cycle, for example, when the elements which include the segments are suspended from the top of the kiln with all segments being out of contact with the slurry but in contact with gas streams moving within the kiln.

In the assembly of the segments 10, the rod 28 can be attached to one base member and the spring 34 then placed around the rod. The other base member can then be screwed into place whereby assembly is achieved in only a few very simple steps. Compression of the spring is preferred during this assembly operation to insure that the spring will be tightly held in the assembly.

The spring should be designed so that the lengths of the spring formed by the helices will have a combined length greatly in excess of the spacing between the base members. The spacing between the adjacent helices should be relatively small since maximum surface area is best achieved by providing a maximum number of turns per inch between the base members. It should be noted, however, that it is important to keep the spacing large enough so that the material within the kiln will shift within the spring for contact with the interior surface of the spring, the opposed surfaces of the cup portions 32, and the exterior surface of the rod 28. This feature is very important since maximum heat transfer contact is achieved with this arrangement. Thus, it is an important feature of the invention to provide segment designs which are characterized by a high mass for heat retention while at the same time utilizing virtually all surfaces as heat transfer areas.

It will be apparent that the link arrangements provide the necessary flexibility in elements made up of segments of the type illustrated. Thus, the segments are free to swivel relative to each other. This flexibility is available whether the segments are hung in curtain or garland fashion.

FIGURES 4, 5 and 6 illustrate a modified construction 40. This construction includes base members 42 and 44. The base member 42 is provided with a pair of links 46 defining central openings 48. The base member 44 is provided with a link 50 defining central opening 52. A bolt arrangement may be employed for securing the links of adjacent segments together to form a completed heat transfer element.

Spacer means in the form of rods 54 extend between the base members. In the embodiment shown, the spacer means are provided with threaded ends, and nuts 56 secure the spacer means relative to thebase members. A central rod 58 defining threaded ends 60 extends between the base members and holds the base members together. It will be appreciated that the openings in the base members which receive the rods 54 could be threaded where by the need for nuts 56 would be eliminated.

As best shown in FIGURES 5 and 6, the rods 54 extend around the periphery of the base members. The central rod 58 is positioned within the confines of the peripheral rods, and it will be appreciated that additional interior rods could be provided for increasing the mass and surface area of the segments.

As previously indicated, the segments can be hung in garland or catenary fashion, that is, Where both ends are attached to the walls of the kiln. With this arrangement, a swivel or swivels should be included at some point be tween the ends of the lengths to insure that the garlands will assume a natural position.

FIGURE 7 illustrates the manner in which the segments are located in a rotary kiln 70. The lengths 72 of segments alternately hang vertically when suspended from the top and then rest in a pile as the kiln rotates.

The advantages of the instant invention are achieved by providing a plurality of lengths of material in posi tion between opposed base members with the combined lengths significantly exceeding the spacing between the base members. Other means for securing a maximum number of lengths for thereby increasing the mass and ex posed surface area will be apparent. For example, trans verse extending rods could be secured to a central rod thereby providing a finned arrangement. The constructions illustrated are, however, preferred since their design provides maximum economy, and efiiciency from the standpoint of initial manufacture of the parts and from the standpoint of assembly. Stainless steel and cast alloy steel are preferred materials for the manufacture of the structures since these materials are more durable when exposed to the kiln atmospheres.

Threaded connections have been illustrated since welds are to be avoided except possibly in areas which do not involve points of high stress. Thus, the high temperatures in the kilns may weaken the welds to a substantial degree. The threaded connections also greatly facilitate repair op erations since segments, or parts thereof, can be easily replaced with this arrangement.

The segments illustrated also provide distinct advantages over segments which are relatively short. With such segments, the heat transfer elements are characterized by a large number of joints per lineal foot. It has been found that the greater the number of joints, the greater the tendency toward dusting in a kiln. Dusting occurs as a result of the mechanical action of the heat transfer elements on the slurry, and the creation of large amounts of dust results in clogging of areas of the furnace when the dust is picked up by exhaust gases. The individual segments of this invention may be quite long, for example two or three feet, whereby the number of joints in a heat transfer element will be substantially reduced. This reduces the tendency toward creation of dust and, therefore, provides distinct improvements in the kiln operation.

It will be understood that various changes and modifications may be made in the above described construction which provide the characteristics of this invention without departing from the spirit thereof.

That which is claimed is:

1. In a rotary kiln wherein a slurry is moved progressively through the kiln and is acted upon by a plurality of heat transfer elements attached at spaced intervals around the inside wall of the kiln, said elements consisting of a plurality of interconnected segments, said ele ments alternately hanging downwardly when located at the top of the kiln while being disposed in a pile at the bottom of the kiln as the kiln rotates, the improvement wherein each of said segments comprises a pair of spacedapart base members, spacer means extending between said base members, and link means associated with each of said base members for securing said segments together, said link means extending outwardly from one side of each base member and said spacer means being positioned on the opposite sides of said base members, each of said spacer means being formed of a plurality of lengths of material, the total length of said spacer means being substantially greater than the distance between said base members, and wherein the individual lengths of said spacer means are disposed in closely spaced relationship with respect to each other, substantially all surface area portions of said spacer means, said base members, and said link means being exposed to act as heat transfer surfaces.

2. A construction in accordance with claim 1 wherein said spacer means include a helically shaped element, said lengths comprising the individual helices of said element.

3. A construction in accordance with claim 2 wherein said base members are cup-shaped, the helices at the opposite ends of said element being received within the cup portions defined by said base members.

4. A construction in accordance with claim 3 wherein one base member for a segment includes two spacedapart link portions defining aligned openings, the other base member comprising a single link portion defining a central opening and adapted to fit between the two link portions on a base member of an adjacent segment, and bolt means extending through all of the openings defined by the link portions of interconnected base members for releasably holding the segments together.

5. A construction in accordance with claim 4 including at least one rod extending between said base members within the confines of said helically shaped element, said rod being secured to the center portions of opposed base members for securing the base members and helically shaped element together.

6. A construction in accordance with claim 1 wherein said lengths comprise a plurality of rods with the opposite ends of each rod being connected to opposed peripheral portions of the base members of a particular segment.

7. A construction in accordance with claim 6 including at least one additional rod extending between said base members within the confines of the peripherally located rods.

8. A construction in accordance with claim 7 wherein one base member for a segment includes two spaced-apart link portions defining aligned openings, the other base member comprising a single link portion defining a central opening and adapted to fit between the two link portions on a base member of an adjacent segment, and bolt means extending through all of the openings defined by the link portions of interconnected base members for releasably holding the segments together.

References Cited UNITED STATES PATENTS 3,135,504 6/1964 Chisler.

JOHN J. CAMBY, Primary Examiner US. Cl. X.R. 34-l42

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