US2746170A - Rotary dryer - Google Patents

Description

May 22, 1956 J. P. wlLsoN ET AL 2,746,170

ROTARY DRYER 3 Sheets-Sheet l Filed Dec. 22, 1953 May 22 1956 J, P. WILSON ET AL 2,746,170

ROTARY DRYER 3 Sheets-Sheet 2 Filed Dec. 22. 1953 May 22, 1956 J. P. wlLsoN ETAL 2,746,170

ROTARY DRYER Filed DeC. 22, 1953 5 Sheets-Sheet 3 United States Patent O ROTARY DRYER Jack P. Wilson, Penn Wynne, Pa., and William R. Marshall, Jr., Madison, Wis., assignors to Proctor and Schwartz, Inc., Philadelphia, Pa., a corporation of Penn- Sylvania Application December 22, 1953, Serial No. 399,667

11 Claims. (Ci. 3'4-109) The present invention relates to new and useful improvements in dryers for powdered material and the like and more particularly to new and useful improvements in rotary dryers of this type wherein the material to be dried is carried entirely around the periphery of the drying drum, and the drying medium passes radially of the drum through the material.

Prior to the present invention, rotary dryers have usually consisted of a cylindrical drum or shell mounted at a slight incline to the horizontal on rolls which rotate the drum about its longitudinal axis. The material to be dried is fed into one end of the drum and discharged from the other end thereof while the movement of the material through the drum is caused by the rotation of the drum. Lifting llights of various designs may be attached longitudinally to the inner surface of the drum to increase the capacity of the dryer and to agitate or cascade the material to increase the rate of drying of the material. in these prior dryers the drying process is accomplished by passing heated gases longitudinally of the drum either parallel with or counter to the direction of flow of the Wet material in the drum. The heat for drying the material is transferred from the gases to the material principally by convection, although there are some rotary dryers in which as much as 30 percent of the heat needed for drying may be transferred from the drying gases to the shell and thence to the wet solid material by conduction from the shell to the material.

Rotary dryers of this type are limited essentially to two air iiow arrangements, namely parallel and counter ow or a combination of parallel and counter flow. They are also limited to a drying condition in which a fixed relationship is maintained in the dryer between the temperature of the drying gases and the material being dried, a relationship determined by the drying characteristics of the material, and the inlet temperature and velocity of the drying gases. rihis limitation present in conventional rotary dryers makes them inflexible in meeting any variations in operating conditions once a dryer has been installed, or in designing for any variations in temperature conditions which may be required in a dryer.

A further limitation of rotary dryers of this type is their low holdup capacity, the holdup capacity being defined as the percentage of the dryer volume occupied by the material being dried. The usual type rotary dryer is generally restricted to operating with a holdup of less than 6 percent while the usual range is approximately 4 percent. Since the holdup capacity is a direct measure of the retention time and drying capacity, a low holdup capacity naturally implies that a relatively large drying chamber will be required for a given drying problem.

Another disadvantage of the presently existing rotary dryers is that there is a non-uniform distribution of the material to be dried at any given section in the drying drum thereby giving rise to an uneven drying of the material and an uneven air distribution. In addition, the material in the prior rotary dryers is not uniformly positioned circumferentially of the drying drum and the 2,746,170 Patented May 22, 1956 major portion of the weight of the material is carried by the sidev of the drum which is moving upwardly. This exerts a torque on the drum opposing the direction of rotation of the drum thereby requiring greater horsepower to rotate the drum and lift the material from the bottom of the drum upwardly alongl one side thereof to cascade the material through the stream of drying medium.

According to the present invention a series of spaced inner and outer flights are positioned circumferentially of the drying drum and the material to be dried` is deposited in these flights and carried entirely around: the periphery of the drying drum duringV rotation thereof. The material being dried cascades back and forth between the inner and outer flightsv while the drying gases are directed radially inward of the drying drum through the cascading material thereby drying the material much quicker than is possible in the standard type rotary dryer. In addition Various heating zones may bev provided along the length of the dryer with this type of radiall ow of the drying gases to permit variation in the temperature of the drying gases passing through the rotating drying drum.

With the foregoing in mind, the principal object of the present invention is to provide a novel rotary dryer in which the rotary drying drum has a greater holdup capacity than the conventional! type of drying drums of similar dimensions thereby permitting a smaller dryer to be used for drying a given amount of material.

Another object of the present invention is to provide a novel rotary dryer in which material to be dried is cascaded back and forth between inner and outer troughs during rotation of the drying drum and the drying medium passes radially inward of the drying drum through the cascading material to dry the material more rapidly. This also provides' less attrition of the product due to the short distance of free fall of the cascading material.

Another object of the present invention is to provide a novel rotary dryer having a seriesY of heating zones therein which may be maintained at different temperatures to provide a closer control of the temperature of the material being dried while maintaining the material near the maximum allowable temperature.

Another object of the present invention is to provide a 'spill-free rotary drying drum wherein any material falling out of the troughs will be blown into a central longitudinal passage of the drum and drop back into one of the troughs.

A further object of the present invention is to provide a novel rotary dryer in which the temperatures in the different drying zones may be readily changed thereby providing a greater liexibility in operating conditions of the dryer.

A still further object of the present invention is to provide a novel rotary dryer having the features and characteristics `set forth which may be manufactured easily and cheaply and is entirely eicient and effective in operation and use.

These and other objects of the present invention and the various features and details of the operation and construction thereof are hereinafter more fully set forth and described with reference to the accompanying drawings, in which:

Fig. l is a side elevational view partially in section of a dryer made in accordance with the present invention;

Fig. 2 is a fragmentary side elevational view partially in section of the feed end of the drying drum of the present invention;

Fig. 3 is a side elevational View partially in section of the discharge end of the drying drum;

Fig. 4 is an enlarged transverse sectional View of the 3 Y drying drum taken on line 4 4, Fig. l, illustrating the construction ofthe drying drum.

Fig. 5 is a sectional view taken on line 5 5, Fig. l, illustrating 'the feed end of the drying drum;

Fig. Y6 is a sectional view taken on line 6 6, Fig. l, illustrating the discharge end of the drying drum and the means for collecting the material discharged from the drum;

Fig. 7 is a perspective view of a singleright member of the drying drum; and

Fig. 8 is a fragmentary transverse sectional view of one modified flight arrangement which may be used in the drying drumof the present invention.

Referring ymore specifically to the drawings, reference numeral 10 designates generally a dryer housing'containing a rotary drying drum 11 made in accordance with the present invention. VThe drum 11 is mounted in fthe housing 10 with its longitudinal axis inclined at a slight angle to the horizontal,V and the material to be dried is deposited into the upper or feed end of the drum and carried circumferentially of the drum as the drum'rotates while at the same time it is caused to move longitudinally of the drum toward the lower or discharge end thereof. A drying medium, preferable heated air, passes radially of the drum through the material being dried and is withdrawn from the housing llongitudinally of the drying drum Vso that the drying medium will pass through the material being carried circumferentially of the drum.

In accordance with the present invention the rotary drying drum 11 comprises a series of `similar flight members 12 having offset outer and inner trough portions 13 and 14, respectively, for example, as illustrated in Figs. 4 and 7. The outer trough portion 13 of each ight member 12 has an opening along one edge thereof facing radially inward of the drying drum 11 while the inner trough portion 14 has an opening along one face thereof facing outwardly of the drying drum. The flight members 12 are equally spaced circumferentially of the drying drum with the opening ofthe outer trough of one liight member overlapping the opening of the inner trough of the adjacent ight member. These flight members are spaced apart circumferentially of the drum to provide a series of radially extending air passages 15 between the side edges of adjacent outer trough portions terminating at the openings to the inner trough portions while a second series of radially extending air passages 16 are provided between the side edges of adjacent inner trough portions terminating at the openings to lthe outer trough portions.

According to the present invention the flight members 12 are supported solely by their extreme opposite end portions rto permit the drying medium to pass radially of the drying drum through the air passages 15 and 16. To this end a pair of relativelyshort cylindrical sleeve members 17 and 18 are positioned at the feed and discharge ends, respectively, of the drying drum and the outer peripheral edge of the outer trough portion of each ight member 12 is secured to the sleeves in any suitable manner. In addition, an end plate 19 having a small centeropeningv20 therein is positioned over the feed end of the drying drum and closes the open ends of the inner and outer troughs of the flight members 12.

As illustrated in Figs. l, 2 and 3, each of the sleeves 17 and 18 has a metallic ring or tire 21 and 22, respectively, thereon which rotatably mount the drying drum 11 on two pairs of support rolls 23 and 24. Since the drying drum is mounted at a slight incline to the horizontal a guide roll 25 engages the side edge of the tire 22 adjacent the discharge end of the drying drum to prevent relative longitudinal movement of the drying drum. `Rotary movement is imparted to the drying drum by means of a pinion 26 meshing with a ring gear 27 formed integrally with the tire 21 and driven, for example, by means of an electric motor 27 through a variable speed reducer 28. The support and guide rolls anddrive 'mechanism for the drying drum 11 are mounted onV a concrete base or pedestal 30 interiorly of the dryer housing 10 so that the drum is rotated in a fixed relative position in the housing 10. However, means may be provided to vary the inclination of the drum and thus vary the time of passage of the material through the drum. This may be accomplished, for example, by providing screw jacks or some other means (not shown) between the upper surface of the pedestal 30 andthe supports for rthe drum thereby permitting one or both pairs of support rolls 23 and 24 to be adjusted vertically in the housing. t

The material to be dried is fed at the desired rate through the central opening 20 in the end plate 19 at the feed end of the drying drum 11. This may be accomplished for example by means of a rotating feed screw 31 which transfers material from a feed hopper 32 to the drying drum 11. The speed of rotation of the feed screw may be varied 1to control the rate of feed of the material into the drum. The feed screw 31 terminates centrally of the feed end of the drying drum and deposits the material in the outer trough portion 13 of the lowermost flight member 12. At the same time, the drying drum 11 is continuously rotated so that each of the iiight members 12 receive an equal amount of material to be dried. By this construction, the material is not concentrated in one particular segment of the drying drum but is carried circumferentially of the drum thereby increasing the holdup capacity of the drum to several times the capacity of conventional drying drums, increasing the amount of material which contacts the walls of the drum to dry the material quicker and decreasing the power required to rotate the drum.

During rotation of the drying drum the material remains in the outer trough portion 13 of the flights 12 until the outer trough portion 13 has reached a point higher than its registering innerrtrough portion 14 at which time the material is transferred, or cascades, from the outer trough portion to the inner trough portion. The material then remains in the inner trough portion during rotation of the drying drum until the inner trough portion reaches a position higher than the outer trough portion and the material is again transferred or cascaded from the inner trough portion to the `outer trough portion.

This transfer of material back and forth between the inner and outer troughs is continued during each revolution of the drying drum while the material is transferred longitudinally of the drum toward the discharge end.

An important feature of the present invention is the passage of a heated drying medium radially of the drying drum through the cascading material in order to dry the material more rapidly. The drying medium is drawn into the housing through a series of vheating units 33 spaced longitudinally or" the drying drum and passes radially inward of the drying drum through the passages 15 about the outer periphery of the drying drum. The heated drying medium then circulates though the inner trough portion 14 of the flights 12, passes to the outer 'trough portion 13 of the adjacent iiight 12 and then is drawn radially inward to the center of the drying drum through the passages 16. A discharge duct 34 for the drying medium extends inwardly centrally of the discharge end of the drying drum to remove the drying medium longitudinally thereof. The drying medium is then drawn through a dust separator 35 by means of a blower 36 and a portion of the drying medium may then be reheated and returned to the dryer housing 10 where it again passes radially through the drying drum. The material collected in the separator 35 may be removed from the lower end thereof in the conventional manner.

As shown in Fig. 4, the heated dryingv medium passes through the material to be dried while it is cascading back and forth between the inner and outer trough portion of the flights 12 and also contacts the material while the material is in either the inner or outer trough. ln addition, the dryingmedium alsoheats each of the ilight members and this heat in turn is transferred to the material to be dried by conduction to assist in the drying operation. Thus this combination of passing the drying medium through the cascading material, contacting the material with the drying medium when it is not cascading, and heating the ight members which carry the material to be dried, dries the material in a relatively short period of time.

Another important feature of the present invention is the provision of means for obtaining different heat zones in the drying chamber so that a greater amount of heat may be provided to the wet material at the feed end of the drying drum and a lesser amount of heat may be provided to the drier material at the discharge end of the drying drum thereby permitting the material to be maintained near the maximum allowable temperature without any danger of overheating the material. Also, the rotary drum of the present invention may be used to cool material with very little attrition of the product and various cooling zones may be provided as desired, or a lesser amount of heat may be provided adjacent the feed end of the dryer and a greater amount at the discharge end. To accomplish this, a series of battles 38 are provided in the drying chamber closely surrounding the drying drum il and extending perpendicular to the longitudinal axis of the drying drum. These bales 33 divide the drying chamber into a series of zones and a separate heating unit 33 is provided at the entrance of each zone.

li desired, a greater number of heating elements may be provided in the heating unit for the zone adjacent the feed end of the drying drum while successively fewer heating elements may be positioned in the heating units in subsequent zones through the drying chamber, for example, as shown in Fig. l, or the temperature of the heating elements in the various Zones may be controlled separately to provide ditierent degrees of heat in the diiierent zones. In addition, a barde or damper 39 may be provided adjacent the entrance to each heating unit 33 to control the dow of the drying medium through the various zones in the drying chamber. By this construction the drying medium contacting the material at the feed end of the drying drum may be at a different temperature than the drying medium. in the adjacent zone and the temperature will decrease or increase correspondingly in each succeeding zone.

The rate oi feed of material to the drying drum, the angle of inclination of the drum and the speed of rotation of the drying drum is controlled to assure attaining the desired degree of dryness in the material as it reaches the discharge end of the drying drum. With reference to Fig. 3, as the material reaches the discharge end of the drying drum il it drops out or" the open ends of the ights i2 into a stationary collector ring or hood 41 where the material is collected and discharged from the dryer housing, for example, by being deposited on a conveyor 42 or by passing the material through a metering gate (not shown). The material thus removed from the dryer housing is then transferred to further material handling apparatus where the treatment of the material is completed.

A modified ight arrangement is illustrated in Fig. 8 of the drawings wherein two separate flight members 43 and 4d are provided instead of a single unitary iight member 12. in the illustrated embodiment of the present invention these flight members have a generally trapezoidal cross sectional shape and are spaced apart circumferentially of the drying drum. The inner open end of the outer flight member 43 is in registry with the air passage between the opposite inner ight members and the outer open end of the inner iight member is in registry with the air passage between the outer ight members. However, these ight members can have any desired shape and all that is necessary is that they be arranged in such a manner that the material is trans- 6 ferred back and forth between the flight members during rotation of the drying drum.

From the foregoing it will be observed that the present invention provides a novel rotary dryer in which the rotary drying drum has a greater holdup capacity than conventional drying drums of similar dimensions thereby permitting a smaller dryer to be used for a given amount of material with a lesser amount of power necessary to rotate the drum. In addition, it is apparent that the present invention provides a novel rotary dryer in which a series of separate temperature zones may be provided and wherein the material will be dried in a relatively short period of time with a minimum amount of attrition of the material.

While particular embodiments of the present invention have been illustrated and described herein, it is not intended to limit the invention to such a disclosure and changes and modifications may be incorporated and embodied therein within the scope of the following claims.

We claim:

l. A drying drum for powdered material and the like comprising a series of ilights spaced circumferentially of the drum, rst wall portions on each of said ilights dening an outer section opening inwardly of the drum, second wall portions on each of said tiights defining an inner section oiset from said outer section and opening outwardly of the drum, the opening of the outer section of each of said flights partially registering with the opening of the inner section of the adjacent Hight, means detining a rst passage of less width than the entrance of the inner section between adjacent ights extending from the exterior of the drum and terminating at substantially the mid-point of the entrance to the inner section of one of said adjacent tlights, and means deiining a second passage of less width than the entrance of the outer section between said adjacent flights extending from the interior of the drum and terminating at substantially the midpoint of the entrance to the outer section of the other of said adjacent ights.

2. A drying drum for powdered material and the like comprising a series of ights spaced circumferentially of the drum, iirst wall portions on each of said ights deiining an outer section opening inwardly of the drum, second wall portions on each of said flights defining an inner section offset from said outer section and opening outwardly of the drum, the opening of the outer section of each of said iiights partially registering with the opening of the inner section of the adjacent ight, a first passage of less width than the entrance of the inner section betweenl opposite first wall portions of adjacent flights extending from the exterior of the drum and terminating at substantially the midpoint of the entrance to the inner section of one of said adjacent flights, and a second passage of less width than the entrance of the outer section between opposite second wall portions of said adjacent ights extending from the interior of the drum and terminating at substantially the midpoint of the entrance to the outer section of the other of said adjacent ilights.

3. A drying drum for powdered material and the like comprising a series of ights spaced circumferentially of the drum, rst wall portions on each of said tlights defining an outer section opening radially inward of the drum, second wall portions on each of said ights dening an inner section otiset from said outer section and opening radially outward of the drum, the opening of the outer section of each of said ights partially registering with the opening of the inner section of the adjacent ight, a first passage of less width than the entrance of the inner section extending between opposite first wall portions of adjacent flights extending from the exterior of the drum and terminating at substantially the midpoint of the entrance to the inner section of one of said adjacent ights, a second passage of less Width than the entrance of the outer section extending between opposite second wall portions of said adjacent flights extending from the wall portions on each of said flights defining an outerV section extending longitudinally of the drum and opening inwardly thereof, second wall portions on each of said flights defining an inner section circumferentially offset from said outer section extending longitudinally of the drum and opening outwardly thereof, the opening of the outer section of each of said flights partially registering with the opening of the inner section of the adjacent flight, a first passage of less width than the entrance of the inner section extending between opposite rst wall portions of adjacent iiights extending from the exterior of thedrurn and longitudinally of the drum and terminating at substantially the midpoint of the Ventrance to the Vinner section of one of said adjacent ights, and a second passage of less width than the entrance of the outer section extending between opposite second wall portions of said adjacent flights extending from the interior of the drum and longitudinally of the drum and terminating at substantially the Vmidpoint of the entrance to the outer section of the other of said adjacent flights.

5. A drying drum for powdered material and the like comprising a series of similar iiights disposed in closely spaced relation 'circumferentially of the drum and extending parallel to the axis thereof for substantially the full Vlength of the drum, first wall portions on each of said flights defining an outer section extending longitudinally of the drum and opening radially inward thereof, second wall portions on each of said flights defining an 'inner section circumferentially offset from said outer section extending longitudinally of the drum and opening radially outward thereof, the opening of the outer section of each of said flights partially registering with the opening ofthe inner section of the adjacent ight, a first passage of less width than the entrance of the inner section extending radially between opposite first wall portions of adjacent ilights extending from the exterior of the drum and longitudinally of the drum and terminating at substantially the midpoint of the entrance to the inner section of one of said adjacent flights, a second passage of less width than the entrance of the outer section extending radially betweenropposite second wall portions of said adjacent ights extending from the interior of the drum and longitudinally of the drum and terminating at substantially the midpoint of the entrance to the outer section of the other of said adjacent ilights, and means at opposite ends of said drum secured to said ights to maintain ythe same in their spaced positions circumferentially of one end thereof, a plurality of flights circumferentially ofl the drum, said ilights having sections operable to receive the material deposited into the drum and carry the material crcumferentially of the drum during rotation thereof, means defining a series of passages between said flights each terminating substantially at the mid-point of a section entrance through which therdrying medium may pass and contact the material to be dried, and blower means to force the drying medium Vradially inward of said drum through each of said passages into contact with the material carried by the flights to dry the material. Y

7. In a rotary dryer for drying powdered material and the like by contacting the material with a drying medium, a housing, a drying drum rotatably mounted within said housing, drive means to rotate said drum, feed means to deposit the material to be dried into said drum at one end thereof, a plurality of flights spaced circumferentially of the drum, said ights operable to receive the material deposited into the drum and carry the material circumferentially of the drum during rotation thereof, means defining a series of passages between said ights through which the drying medium may pass and Contact the material to be dried, a plurality of bafes positioned interiorly of said housing about said drum substantially perpendicular to the longitudinal axis thereof dividing said housing into a series of zones, a heating unit for each zone,

Vand blower means to` force the drying medium through said heating units into said zones and radially inward of said drum through each of said passages in said drum l into contact with the material carried by the ights to dry the material.

8. ln a rotary dryer for drying powdered material and entially of the drum during rotation thereof, means deiining a series of radial passages between said flights extending longitudinally of the drum through which the drying medium may pass and contact the material to be dried, blower means to force the drying medium inwardly through the radial passages in said drum into contact with the material carried by the ights to dry the material, and Y means to withdraw the drying medium from said drum along the longitudinal axis thereof.

9. In a rotary dryer lfor drying powdered material and the like by contacting the material with a drying medium, a housing, a drying drum rotatably mounted within said housing disposed with its longitudinal axis at an incline to the horizontal, drive means to rotate said drum, feed means to deposit the material to be dried into said drum at one end thereof, a plurality of similar flights disposed in closely spaced relation circumferentially of the drum and extending substantially longitudinally of the axis thereof, said ights operable to receive the material deposited into the drum and carry the material circumferentially of the drum during rotation thereof, means de- Viining a series of radial passages between said ights extending longitudinally of the drum through which the drying medium may pass and contact the material to be dried, a plurality of baies positioned interiorly of said housing about said drum substantially perpendicular to the longitudinal axis thereof dividing said housing into a series of zones, a heating unit for each zone, blower means to force the drying medium through said heating units into said zones and inwardly through the radial passages in said drum into contact with the material carried by the flights to dry the material, and collection means operable to collect the dried material discharged from said drum and remove the same from the housing.

l0. In a rotary dryer for drying powdered material and the like by contacting the material with a drying medium, a housing, a drying drum rotatably mounted Within said housing disposed with its longitudinal axis at an incline to the horizontal, drive means to rotate said drum, feed means to deposit the material to be dried into said drum at one end thereofa plurality of similar material carrying sections to receive the material deposited in the drum, said sections disposed in closely spaced relation circumferentially of the drum extending substantially longitudif nally of the axis thereof and opening radially inward of the drum, a second plurality of material carrying sections opening radially outward of the drum substantially parallel to said rst sections and disposed circumferentially of the drum inwardly of said first sections, each of said sec` ond sections positioned with its opening disposed radially inward of the space between adjacent outer sections and operable upon rotation of the drum to receive the material from said first sections and redeposit the material into said rst sections, a plurality of baffles positioned interiorly of said housing about said drum substantially perpendicular to the longitudinal axis thereof dividing said housing into a series of zones, a heating unit for each zone, blower means to force the drying medium inwardly through said heating units into said zones and through the spaces between said sections into contact with the material carried by the sections to dry the material, means to withdraw the drying medium from said drum along the longitudinal axis thereof, and collection means operable to collect the dried material discharged from said drum and remove the same from the housing.

1l. In a rotary dryer for drying powdered material and the like by contacting the material with a drying medium, a housing, a drying drum rotatably mounted within said housing disposed with its longitudinal axis at an incline to the horizontal, a plurality of similar material carrying sections disposed in closely spaced relation circumferentially of the drum extending substantially longitudinally of the axis thereof and opening radially inward of the drum, means at one end of said drum to deposit the material to be dried in said sections, means to rotate said drum to carry the material circumferentially of the drum,

10 a second plurality of material carrying sections opening radially outward of the drum and disposed substantially parallel to said first sections spaced circumferentially of the drum inwardly of said rst sections, each of said second sections positioned with its opening oiset circumferentially with respect to the openings of said first sections and operable to receive material from said first sections during rotation of the drum and redeposit the material back into said rst sections, a plurality of baes positioned interiorly of said housing about said drum substantially perpendicular to the longitudinal axis thereof dividing said housing into a series of zones, a heating unit for each zone, blower means to force the drying medium through said heating units into said zones and through the spaces between said sections into contact with the material carried by the sections to dry the material, means to withdraw the drying medium from said drum along the longitudinal axis thereof, and collection means operable to collect the dried material discharged from said drum and remove the same from the housing.

References Cited in the tile of this patent UNITED STATES PATENTS 658,957 Mey Oct. 2, 1900 1,301,112 Douglas Apr. 22, 1919 1,345,260 Schwartz June 29, 1920 1,472,741 Ayres Oct. 30, 1923 FOREIGN PATENTS 657,815 France May 28, 1929

Images