US3094397A - Rotary dryer - Google Patents

Description

E. B. LOPKER ROTARY DRYER Filed Sept. 28. 1960 FIG. 2

FIG. 3

INVENmR. EDWIN B. LOPKER a 4 gm l June 18, 1963 FIG. 4

Patented June 18, 1963 3,094,397 ROTARY DRYER Edwin B. Lopker, Joliet, lll., assignor to Olin Mathieson Chemical Corporation, East Alton, Dl., a corporation of Virginia Filed Sept. 28, 1960, Ser. No. 59,937 Claims. (Cl. 134-128) This invention relates to rotary dryers, calciners, and dryer-calciners and particularly to such dryers having internal recirculation means.

Rotary dryers are used extensively in the drying and treating of a variety of granular materials on a large scale. Such dryers usually consist of a revolving cylinder slightly inclined from the horizontal. The material being treated or dried is fed continuously into the upper end of the dryer and discharged at the lower end. These dryers which are driven by any suitable means can be heated to appropriate temperatures by passing hot air or gas over the material, by inserting burners or coils within the dryer, or by other conventional heating means. Shelves or flights have been attached to the internal wall of the cylinder so as to cascade the granular material within the heating zone.

It is frequently desirable to provide means for the recirculation of at least a portion of the product being treated with such equipment. This permits conditioning of the feed material as well as a means for controlling the conditions existing within the equipment. Such recirculation is often accomplished by various types of conveyers external to `the rotary dryer or calciner unit. These external conveyers are quite satisfactory when the volume of material to be recirculated is relatively small. However, when the amount of material that must be recirculated becomes substantial in proportion to the amount oi material being processed, the cost of external conveying equipment becomes excessive. Thus, in such instances, some attempt has been made to utilize the rotary dryer as its own recirculator. These prior art methods of internal recirculation include the utilization of reverse ilighting, darn rings, and the like in the rotary unit. One other method that has met with only a modicum of success is the provision of an inner tubular shell smaller in diameter than the shell of the rotary unit and the positioning of a reverse helical ilighting in the annular space between the two shells. Such an arrangement is quite effective and has very high capacity but is subject to one very serious drawback that renders it commercially impractical. This inherent disadvantage of all previous double shelled rotary dryers stems from the divergent degree of thermal expansion of the various components. When in operation the temperatures encountered throughout the length and radial axis of the dryer cannot be maintained constant. Thus, thermal expansion, both longitudinally and radially materially induces strains and distortions in the apparatus. Furthermore, the inner shell must be maintained in axial shell. While some units of this type have been attempted, the original installation is exceedingly expensive `and the subsequent maintenance practically prohibitive.

Therefore, it is an object of the present invention to provide a new and novel double shell dryer which overcomes the disadvantages of the prior art. A more specilc object is to provide a rotary dryer having internal recirculation means which overcomes the problem of thermal expansion. A further object of this invention is to provide such apparatus having inherent llexibility of operation.

These and other objects are accomplished in accordance with this invention generally speaking by providing a double walled rotary dryer in which the inner shell is formed of a plurality of individual segments or portions. These portions are in the form of curved rectangles, a number of which cooperate to form the inner shell. One

surface of each portion is provided with segmented lflighting for recirculation of the material being treated. The ilighting is also segmented and upon assembly provides movement of material longitudinally by means of at least one `helical path with the inner and also within the annular space, thus providing a recirculation path lbetween the inner and outer shells. The llighting and the portions making up the inner shell are generally of unitary construction and can be joined by welding, brazing or the like. Alternately the llighting can be bolted or otherwise secured to the separate portions of the inner shell. When assembling the dryer of this invention, each completed segment is then fastened to the inner side of the external rotary unit by bolting, welding, or other conventional means. The portions making up the inner shell do not completely abut one another so as to form a perfectly leak-proof continuous construction. Such a leak-tight inner tube is not essential and in fact would be undesirable since it would tend to prevent the segments from accommodating their own thermal expansion.

This invention provides extreme flexibility of operation in that recirculation and mixing can be controlled within any desired limits. By extending the inner tube and the helical ilighting through all or a portion of the rotary unit, the mixing and recirculation can be confined to one or more sections of the unit or can be distributed uniformly throughout its length. Thus, the inner tube can extend throughout the length of the outer tube or, alternately, intermittent portions of the outer tube can be provided with an inner tube and the attached circulating helices. The recirculation ratio can be controlled by the number and shape of the flights and also by blocking entry to one or more of the flights. Also, this ratio can be modified by providing holes in the inner shell to serve as exits and entries to limit the path of travel within the helical ilights. The internal nights are generally positioned radially to the surface of the inner shell and form a uniform spiral or helix thereabout. However, it will be readily appreciated that these internal llights can assume any desired configuration.

Also any conventional apparatus can be employed in connection with the interior surface of the inner shell. Thus, this inner surface can be smooth, pocketed for cascading, or can be provided with Scrapers, chains, and similar prior art devices to facilitate mixing.

The invention and the manner in which it accomplishes its objects will be more readily understood by reference to the drawing in which:

FIGURE l is a longitudinal oblique sectional view of a rotary dryer made in yaccordance with the present invention;

FIGURE 2 is .a cross-sectional view of the unit illustrated in FIGURE l;

FIGURE 3 is a fragmentary sectional view illustrating the construction of the dryer; and

FIGURE 4 is a perspective view illustrating another modiication of .the invention.

As shown in FIGURE 1, the rotary dryer is provided with a substantially cylindrical outer shell 1 and a concentric inner shel-l indicated generally at 2. These shells are separated from one another and maintained in spaced relationship by one or more helical flights 3. The inner shell 2 is made up of a number of separate portions 4, which are arranged in side-by-side and end-to-end relationship so as to provide a substantially continuous tubular structure. The helical llighting 3 and portions 4 of the inner tube are preferably of unitary construction obtained by brazing or the like, but these members can be joined together in any suitable manner. The outer extremity of the tlighting can be secured to the interior surface of the outer shell by bolts, screws, or by other suitable means. This is particularly well shown in FIGURE 3 in which ights 3 `are secured tothe outer shell 1 by bolts 5 passing through extensions 6 at the base of the liighting. As shown in `the drawing, the length of the helical Path taken by the material being treated can be altered by the provision of one or more holes 11 passing through inner plate 2.

The embodiment set forth in FIGURE 4 of the drawing illustrates a modification of the invention in which the portions 4 of the inner shell are pro-vided with both internal and external liighting. The external iiighting 7 is adapted for connection to the outer shell 1 by means of holes 8 in basal extensions 9 of the flighting. Likewise, the internal surface of portions 4 of the inner shell are provided with reverse circulating fiights 10. It will be readily appreciated that iiights 10 can be modified by making them parallel to the longitudinal axis of the unit or by providing them with curved surfaces, so as to emphasize the `cascading effect obtained thereby. Likewise, these internal flights can be continuous or intermittent and uniform or variable,

In operation the unit is rotated upon its longitudinal axis and heated by any conventional means. The outer shell is then partially lilled with the material being treated and a portion thereof travels in a helical path, defined by ights 3, between the inner and outer shells, while the remainder thereof passes through the inner shell. The ratios of the material being recirculated is readily controlled by blocking one or more of the spaces between the flights or by providing entries such as 11 between the inner and outer shells. When `additional manipulation of the material is desired the internal surface of the inner shell 2 can be modified by providing it with internal flights 10 as illustrated in FIGURE 4 of the drawing.

While one complete embodiment has been disclosed in detail and modifications therein suggested, it is to be understood that the example given is for purposes of illustration only and not by way of limitation. It is recognized ythat those skilled in the art will make appropriate adjustment of the variables in the apparatus in order to adapt it to the peculiarities of Aany given operation, and consequently it is to be distinctly understood that the invention is not limited to the example given except as indicated in the appended claims.

What is claimed is:

l. A rotary dryer comprising two concentric substantially cylindrical shells separated by segmented helical llighting, the inner shell being segmented longitudinally and radially and being attached to the iiighting.

2. A rotary dryer comprising an outer substantially cylindrical shell and a concentric inner shell, the shells being separated by an annular space, a helical iiighting within the space, the liighting being divided into a plurality of segments and the inner shell being formed of a plurality of individual portions attached to the fiighting.

3. A rotary dryer comprising an outer substantially cylindrical shell and a concentric inner shell, the shells being separated by an annular space, a helical ighting in the space, the flighting being divided into a plurality of segments, the inner shell being formed of a plurality of individual portions with each portion of the inner shell attached to adjacent segments of `the flighting.

4. A rotary dryer comprising an outer substantially cylindrical shell and a concentric inner shell, the inner and outer shells being separated by a substantially `annular space, at least one helical flighting in the space, the1iight ing being formed of a plurality of segments, the inner shell being shorter than the outer shell and formed o-f a plurality of individual portions with each portion of the inner shell `attached to adjacent segments of the ighting.

5. A rotary dryer having a substantially cylindrical outer shell and means for internal recirculation, said means comprising a segmented helical flighting internally secured to the outer shell, and plate-like members secured to the iiighting, the members cooperating to form an inner shell concentric with the outer shell, :said shells being separated by an annular space.

References Cited in the file of this patent UNITED STATES PATENTS 1,551,196 Hiller Aug. 25, 1925 1,867,148 Harrington July 12, 1932 2,126,029 Parker Aug. 9, 1938

Claims (1)

1. 5. A ROTARY DRYER HAVING A SUBSTANTIALLY CYLINDRICAL OUTER SHELL AND MEANS FOR INTERNAL RECIRCULATION, SAID MEANS COMPRISING A SEGMENTED HELICAL FLIGHTING INTERNALLY SECURED TO THE OUTER SHELL, AND PLATE-LIKE MEMBERS SECURED TO THE FLIGHTING, THE MEMBERS COOPERATING TO FORM AN INNER SHELL CONCENTRIC WITH THE OUTER SHELL, SAID SHELLS BEING SEPARATED BY AN ANNULAR SPACE.

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