Patent Publication Number: US-3878028-A

Title: Method and apparatus for distributing feed stock to dryer drum

Description:
United States Patent [191 Balch Apr. 15, 1975 METHOD AND APPARATUS FOR DISTRIBUTING FEED STOCK TO DRYER DRUM [75] Inventor: John T. Balch, Birmingham, Ala.  
  [73] Assignee: Envirotech Corporation, Menlo Park, Calif.  
 [22] Filed: Aug. 20, 1973 [21] App]. No.: 389,459  
 [52] U.S. Cl 159/4 SR; 159/48; 159/10; 159/12 [51] Int. Cl ..B01d 1/16;B01d 1/22; F26b 3/12 8 Field of Search 159/4 SR, 7, 8, 9, 10, 159/11, 12, 49  
 [56] References Cited UNITED STATES PATENTS 1,317,777 10/1919 Collis 159/11 R 1,597,809 8/1926 Lavett 159/5 1,667,291 4/1928 Lavett 159/11 R UX 1,727,843 9/1929 Tilley 159/11 R 1,732,819 10/1929 Pehrson 159/4 SR UX 1,803,792 5/1931 Christensen..... 11,837,702 12/1931 Canfield 159/4 SR UX FOREIGN PATENTS OR APPLICATIONS 27,718 11/1905 United Kingdom 159/11 R 562,212 11/1923 France 159/12 646,668 6/1936 Germany.. 928,965 12/1947 France 159/11 R Primary Examiner-Jack Sofer Attorney, Agent, or Firm-Harold L. Stowell [57] ABSTRACT A feed stock to be dried is evenly distributed over the cylindrical surface of a rotating dryer drum by providing a trough of the feed stock below and coextensive with the axial length of the drum and releasing pressurized gas at a plurality of longitudinally spaced points below the surface of a pool of feed stock maintained in the trough.  
 4 Claims, 8 Drawing Figures FEED STOCK RETURN PAN FEED STOCK D13 RB UTlNG TROUGH FEED STOCK INLET RETURN PAN OUTLET DRAIN TEEAPRISIQTS DRYER DRUM CAKE REMOVAL MEANS 32 90 FEED STOCK RETURN H6 PAN FEED STOCK DISTRIB&#39; 62 5O UTING TROUGH W5 36 22 64 I I Y Y J FEED/STOCK \SEZKIRN PAN OUTLET INLET FIG. 1  
 DRYER DRUM FEED STOCK DISTRIBUTING TROUGH 32 t oMPREssEn GAS INLET i FEED STOCK 62 RETURN PAN RETURN PAN l l DRAIN METHOD AND APPARATUS FOR DISTRIBUTING FEED STOCK TO DRYER DRUM THE PRESENT INVENTION The present invention is directed to methods for uniformly depositing on a rotating drum or drums of single or twin heated drum dryers, or vacuum drum dryers and the like a predetermined layer of feed slurry and to apparatus for carrying out such methods.  
 THE STATE OF THE ART In operation of atmospheric, vacuum or pressurized drum type dryers, it is essential that the feed stock be evenly distributed over the cylindrical surface of the drum at a coverage rate that can be adjusted to accommodate for variations in feed stock physical properties that occur from one dryer application to the next. Any variation in the rate or uniformity of the feed application to the dryer drum surface may result in a reduction in production capacity and often results in undesirable variations in dry product character.  
  Many different materials can, and are, processed on atmospheric and vacuum drum type dryers. Each material is described by its own set of physical properties and these properties can vary substantially from one material to the next.  
  The most common method of applying the feed material to the dryer drum surface is to introduce it into the valley formed by two identical drums located side by side in the same horizontal plane, with drum rotation downward through the pinch point. Suitable seals at each end of the drums prevent feed loss at the ends of the reservoir and the clearance between the cylindrical surface of the drums is adjusted to minimize or prevent leakage at this point. The liquid feed level in such reservoirs is normally set at the highest practical level for that feed material, the limits relating to the degree of turbulance caused by boiling, and other considerations common to the art.  
  In such dryer operation, the fresh stock enters the top of the feed reservoir in a continuous flow by one of several well known methods. This material is retained in the reservoir for a period of time during which boiling and liquid evaporation occurs resulting in a concentration of solids at the pinch point of the two rolls. The concentrated feed material which often is of a pasty, putty-like consistency is extruded through the pinch point and bonds to the hot drum surfaces to thereby provide a coating on each of the two drums.  
  In many such operations, the feed stock is so fluid that it easily flows through the closest practical nip openings, and it is necessary to grind the dryer drums to extremely close tolerances to reduce the leakage rate to within limits that can be tolerated. Arts to overcome the leakage problem have included using, for example:  
  a. bottom splash feed with reversed direction of drum rotation;  
 b. spray feed; and  
 c. dip feed with single and double drum equipment.  
  Besides the leakage problems referred to above, many feed materials, on concentration, will form rocklike lumps which separate the two drums causing a loss of all or a part of the material contained in the reservoir substantially reducing the concentration of material remaining in the reservoir and also reducing the time-rate of evaporation on the dryer. Arts to overcome the drum separating problem have included using, for example:  
  a. bottom splash feed with reversed direction of drum rotation;  
 b. spray feed;  
  c. dip feed with single and double drum equipment; and  
 (1. single or multiple auxiliary roll feed.  
  With all known arts, the drum drying of many low viscosity feed materials and materials that form rock-like lumps on concentration is not economical or is otherwise not feasible or desirable.  
 OBJECTS OF THE PRESENT INVENTION An object of the present invention is to remedy the difficulties referred to above and in particular, an object of the present invention is to provide a method of feed material application to the drum in a single or multiple drum dryer that is not affected by the formation of hard, rock-like substance on concentration.  
  Another object of the invention is to provide a feed system that does not require close tolerance drum finishes to insure uniform application of feed material to the drum without product loss.  
  Still another object of the invention is to provide a new and simple method of and apparatus for increasing the thickness and uniformity of feed applications to dryer drums and thereby improve dryer capacity or performance and/or reduce equipment cost.  
  Still another object of the present invention is to provide a method of and apparatus for uniform application of substantially any chemical solution, slurry or mixture to drum drying apparatus.  
 GENERAL DESCRIPTION OF THE INVENTION The present invention may be generally described as relating primarily to methods and apparatus by which a thin layer of a fluid substance can be evenly applied to a rotating surface and, more particularly, to novel and highly effective methods of and apparatus for delivering to the outside cylindrical surface of an atmospheric or vacuum drum dryer a uniform coating of the chemical solution, slurry or mixture that is to be dried, and which may be generally defined as comprising the steps:  
  a. maintaining a pool of feed stock below and coextensive with the axial length of a drum to be coated;  
 b. rotating the drum while c. releasing pressurized gas at a plurality of longitudinally spaced points below the surface of the pool in a direction generally normal to the drum surface; which method steps may be carried out in apparatus consisting essentially of:  
  a. a dryer drum mounted for rotation on a generally horizontal axis;  
  b. an elongated trough having a length at least coextensive to the axial length of the rotating drum;  
  c. means mounting the trough below the cylindrical surface of the drum;  
  d. means for maintaining a pool of feed stock in said trough; and  
  e. means for releasing pressurized gas at a plurality of longitudinally spaced points below the surface of the pool and in a direction generally normal to the drum surface.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a fragmentary vertical sectional view on line 11 of FIG. 2 of a single heated drum dryer having associated therewith the improved feed stock distributing means of the present invention:  
  FIG. 2 is a fragmentary longitudinal sectional view on line 2-2 of FIG. 1; I h  
  FIG. 3 is a top plan view of the slurry or feed stock return pan;  
  FIG. 4 is an enlarged fragmentary partial sectional view of the structure shown in FIG. 3 including an illustration of the distribution trough for the assembly; 7  
  FIG. 5 is a fragmentary perspective view of a pressurized gas header for the assembly;  
  FIG. 6 is a fragmentary top plan view of the feed trough shown in FIGS. 1, 2 and 4;  
  FIG. 7 is a section substantially on line 77 of FIG. 6 including the support means and the supported header for directing pressurized gas to the feed stock to be distributed; and  
  FIG. 8 is a diagrammatic illustration of another form of the present invention employing a pair of dryer drums and a pair of feed troughs.  
  Referring to the drawing and in particular to FIGS. 1 and 2 thereof, 10 generally designates an improved rotary drum type dryer assembly. The assembly includes a dryer drum 12 having a cylindrical drying surface 14 and ends or heads 16 and 18. Each of the heads 16 and 18 is provided with an axial sub-shaft 19, the outer ends of which are journalled in bearings such as bearing 20 each of which is mounted on a support member 22 so that the drum is mounted for rotation about a horizontal axis defined by the subshafts 19. Drive means for rotating the drum in the direction of the directional arrow A, FIG. 1, are provided at one end of the assembly, not shown, which drive means may be of conventional construction and provided with means whereby the speed of rotation may be readily controlled.  
  Above the cylindrical surface of the dryer drum is mounted an exhaust hood 24 and condensate drip pan 26. The hood is connected via outlet pipe 28 with a suitable source of ventilation whereby exhaust gases, fumes and the like evolving from the feed stock during the drying operation may be removed from the environment of the dryer. Since the form or the nature of the dryer drum per se is not critical to the present invention, the illustrated dryer drum is representative of the atmospheric or vacuum gas type heated dryers well known in the art. The cylindrical surface 14 of the dryer drum may be heated by directing steam to the interior of the drum or the drum and the feed stock to be dried may be subjected to heat from banks of radiant or infrared type external or internal heaters.  
  Mounted below the cylindrical surface ofthe drum is the apparatus for uniformly feeding a feed stock to the external surface ofthe drum which assembly is generally designated 30. The assembly 30 includes a feed trough 32 at least coextensive with the longitudinal axis of the drum 12; dispensing means 34 for the feed stock maintained in the trough 32 and feed stock return pan 36 which as shown in the drawings has a length slightly greater than the length of the drum 12.  
  The assembly may also include auxiliary dryer equipment such as&#39;dried ,cakeremoval means 40 consisting of a doctor blade 42 which is urged toward and away from the cylindrical surfaceof the drum by ram means 44 adapted to rock the doctor knife carrying bracket 46 about pivotal axis 48.  
  Referring now to FIGS. 3 and 4, the slurry or feed stock return pan 36 includes leading longitudinal edge member 50 which lies relatively close to the cylindrical surface of the drum as at 52, a bottom plate 54 and a trailing edge deflector plate 56. The bottom of the return pan 54 has mounted therein at least one flush outlet drain pipe 58 which may be connected to the vat or tank containing the feed stock to be dried, etc. The return pan also includes a pair of end walls 60 which assist in retaining the feed stock which is directed toward the external surface of the rotating drum within the confines of the machine.  
  The pan 36 is mounted to a plurality of L shaped support members 62 which in turn are carried by major longitudinal support members 64 and 66.  
  Referring now to FIGS. 1, 2, 4, 5 and 7, mounted within the feed stock return pan 36 is a feed stock distributing trough 32. The trough 32 is of generally U- shape and includes a bottom 72, forward and rearward side walls 74 and 76 and end walls 78. The pan or trough 32 is mounted within the return pan 36 by bracket means generally designated 80 to maintain the.  
 bottom 54 of the pan and the bottom 72 of the trough in spaced relationship. Along each of the top edge plates 82 and 84 of the trough 32 are secured a plurality of spaced upstanding threaded studs 86.  
  The studs 86 adjustably support brackets 88 which in turn carry the pressure gas header generally designated 90 and more clearly shown in FIG. 5 of the drawing. The brackets 88, of generally U configuration, have arms 92 bored to be slidably received on the studs 86 and a pair of lock nuts 94 anchor the brackets to their respective studs at the desired height. Each of the brackets 88 has its base portion 96 bored to receive the legs of a U-clamp 98 which U-clamps secure the header 90 thereto. In an assembly wherein the longitudinal length of the dryer drum is about 12 feet, 8 brackets such as bracket 88 have provided satisfactory results.  
  Referring again to FIG. 5, the header 90 is provided with a milled flat 100 on its upper cylindrical surface and in the zone of the milled flat a plurality of outlet orifices 102 are provided. With a 12 foot drum, a header pipe 90 of about inch internal diameter having l/l6 inch diameter outlet orifices 102 on about 2 inch centers provides satisfactory operation when the header is attached at each end to a source of compressed air at about 10 pounds per square inch.  
  The trough 76 is fed with the slurry or feed stock ma terial to be dried through a pair of inlet nipples 104 and adjacent the outlet of the inlet nipples 104 a small baffle may be mounted as indicated at 106 to reduce channelling and turbulence within the trough. Further, the trough 32 is provided with a pair of overflow nipples or standpipes 108 which determine the maximum level of the liquid in the trough which level is maintained at least above the milled flat 100 on the gas header 90.  
  Further, the trough is provided with a number of small drain openings 110 in the bottom wall 72 which assist in circulation of the feed stock. The standpipes 108 and the drain openings 110 direct the feed stock into the feed stock return pan 36. The compressed gas connected to the header 90 is via conduit 112, FIG. 2, of the drawing, and slurry to be dried is fed to the inlet nipples 104 via valved conduits 114 and flexible conduits 116.  
  In operation of this form of the invention the dryer drum 12 is heated and rotated at, for example, 1 to rpm. A slurry to be dried is valved into the trough 32 and when the trough is filled to the level of the stand or overflow pipes 108 compressed air from an external source at about 10 pounds per square inch is directed to the gas header 90. The compressed gas issuing from the plurality of outlet orifices 102 entrains the slurry and directs it toward the lower cylindrical surface of the slowly rotating heated drum. With the plurality of outlet orifices, a very uniform coating is provided for the drum and once the coating has dried to the desired amount, actuation of the pressure fluid ram 44 urges the doctor blade 42 toward the cylindrical surface of the rotating drum and the dry material from the feed stock is removed from its external surface.  
  As hereinbefore set forth, the feed stock distributing system of the present invention is also applicable to twin rotating dryer drums. Referring now to FIG. 8 where similar mechanisms are provided with primed reference characters, 10&#39; generally designates a twin drum type slurry dryer and includes drums 12&#39; mounted for rotation on horizontal axes with the external surfaces of the drums in close proximity. Mounted below the pair of drums is a feed stock return pan 60 provided with one or more outlet drains generally designated 58. Mounted in association with the feed stock return pan 60&#39; are a pair of feed troughs 32 with each feed trough positioned directly below its associated dryer drum 12&#39;. Each of the feed troughs 32&#39; has mounted therein a pressure gas header 90&#39; provided with a plurality of gas outlet jets or ports similar to those illustrated in FIG. 5 of the drawing. Feed stock to be dried is directed to each of the troughs 32 via a conduit 120 having a pair of branch conduits 122 positioned to discharge the slurry directly into the respective troughs. A valve 124 may be provided in the line to control the rate of flow of the slurry to the troughs. Excess feed stock or slurry in the troughs 32&#39; discharge into the feed stock return pan 60&#39; via longitudinal edges 126 along the inner longitudinal edge of each of the troughs 32&#39;. Operation of this form of the invention is like the operation of the previous form in that discharge of the pressured gas via the headers 90&#39; causes the slurry contained in the troughs 32&#39; to be directed onto the lower surfaces of drums 12 as the drums rotate in the direction of the directional arrows.  
  From the foregoing description of embodiments of the present invention, it will be seen that the objects and advantages hereinbefore set forth and others are fully accomplished.  
 I claim:  
  1. A method of distributing a dryable feed stock to a rotating drum surface comprising a. maintaining a pool of feed stock in spaced relationship below and coextensive with the axial length of a drum to be coated;  
 b. rotating the drum while c. releasing pressurized gas at a plurality of longitudinally spaced points below the surface of the pool in a direction generally normal to the drum surface at a pressure effective to entrain a portion of the feed stock and direct it toward and into contact with the rotating drum surface.  
 2. A method of drying a feed stock comprising a. heating the external surface of a dryer drum mounted for rotation on a horizontal axis;  
 b. maintaining a pool of feed stock to be dried in spaced relationship below and coextensive with the axial length of the heated drum;  
 c. releasing pressurized gas at a plurality of longitudinally spaced points below the surface of the pool of feed stock with the release of the gases being in a direction generally normal to the drum surface at a pressure effective to entrain a portion of the feed stock and direct it toward and into contact with the rotating drum surface.  
 3. Apparatus for drying a dryable feed stock comprisa. a dryer drum mounted for rotation on a generally horizontal axis;  
 b. an elongated trough having a length at least coextensive to the axial length of the rotating drum;  
 c. means mounting the trough below the cylindrical surface of the drum;  
 d. means for maintaining a pool of feed stock in said trough in spaced relationship to the opposed surface of the drum; and  
 e. means for releasing pressurized gas at a plurality of longitudinally spaced points below the surface of the pool and in a direction generally normal to the drum surface at a pressure effective to entrain a portion of the feed stock and direct it toward and into contact with the rotating drum surface.  
  4. Apparatus as defined in claim 3 wherein the means for releasing pressurized gas at a plurality of longitudinally spaced points comprises a header mounted within said trough and substantially longitudinally coextensive therewith; and a plurality of outlet orifices in said header with the orifices directed generally towards the surface of said drum.