Patent Publication Number: US-2011067257-A1

Title: Yankee dryer having centrifugally assisted condensate collection

Description:
FIELD OF THE INVENTION 
     The present invention pertains to Yankee dryers and more particularly to a Yankee dryer having a system of condensate collection and disposal which utilizes centrifugal force from operation of the Yankee dryer. 
     BACKGROUND OF THE INVENTION 
     A Yankee dryer essentially comprises a large generally cylindrical drum which is internally heated by pressurized steam to dry a paper web on its outside shell surface. The thermal gradients through the pressure containing components, specifically the shell of the cylinder, cause condensate to form on the inside surface of this shell, which must be evacuated for efficient heat transfer in drying the paper web. As the Yankee dryers rotate at high speeds, this condensate is physically forced to the shell inside surface and typically removed using a condensate removal system. 
     Removal of condensate requires a differential motive pressure from the source to the evacuation point or points to force the condensate into the condensate removal system through a pickup device, usually designated for ribbed bore shells as straws. Once the condensate is in the straw, typical condensate removal systems rely substantially on this differential motive pressure to force the steam through the straws into a condensate header. Once in the header, the differential motive pressure must force the condensate through the condensate header to an additional evacuation point, typically named a riser pipe, which is then pulled or suctioned to the center of the drum for evacuation to the external environment of the Yankee dryer through one of the supporting ends of the drum. 
     Manufacturers of Yankee dryers have necessarily used the centrifugal forces due to rotation of the drum to pool or isolate the condensate to the bore of a plain bore shell, or to the grooves of a Yankee dryer having a ribbed bore. No specific condensate system has been configured to reduce the amount of differential motive steam required to remove the condensate using the centrifugal forces due to rotation by geometrically using the intrinsic mechanical advantage of these forces. 
     Since, for conventional condensate systems, the differential motive pressure is the only significant application of force to cause the condensate to flow efficiently through the condensate removal system, there exist a need to exploit these intrinsic forces to reduce energy consumption and thus enhance efficiency of the condensate removal system as a whole. 
     SUMMARY OF THE INVENTION 
     The present invention provides a way to exploit centrifugal forces to assist in evacuating condensate from rotating Yankee dryers. The collection apparatus is arranged to cause condensate to flow from a condition dispersed along the length of the cylindrical drum to a central collection point for example under the influence of centrifugal forces. This is accomplished by arranging collection conduits such as individual liquid pickup straws and a collection header into which the pickup straws discharge collected condensate each to have liquid pick up points that are at a lesser radial distance from the axis of rotation than the discharge ends. The collection header terminate may have a central location within the cylindrical drum near the outer surface thereof. A disposal riser conduit may take in collected condensate from the collection header at the central location. Liquids are thus collected from along the length of the drum and delivered with the assistance of centrifugal forces to the central location, where they may enter the disposal riser conduit. Pressure from steam used to dry the unfinished materials for example may provide the motive power to force the collected condensate within the disposal riser conduit towards the axis of rotation and ultimately to the exterior of the cylindrical drum. 
     The operative premise of the present invention is that centrifugal forces are exploited to deliver condensate laterally from along the length of the cylindrical drum to one or more collection points for disposal. There is no ineffectual effort to utilize centrifugal forces to force collected condensate towards the axis of rotation, which flow would be opposed rather than assisted by centrifugal forces. 
     The novel collection apparatus and associated pickup straws may be furnished as a modular unit for installing into new Yankee dryers and for retrofitting existing Yankee dryers. The modular units may be fabricated in one size or capacity, so that an appropriate number of modules may be installed into any given Yankee dryer. Thus a production run of one model or size or capacity of modules may serve all or almost all of the Yankee dryers in use or contemplated for use in the paper industry. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Similar reference characters denote corresponding features consistently throughout the attached drawings. 
         FIG. 1  is a diagrammatic perspective view of a Yankee dryer incorporating a condensate evacuation system according to at least one aspect of the invention, the Yankee dryer being partly broken away to reveal internal detail. 
         FIG. 2  is an end view of the interior of the Yankee dryer of  FIG. 1 . 
         FIG. 3  is a cross sectional view of the Yankee dryer of  FIG. 1 . 
         FIG. 4  is an end view of the interior of another Yankee dryer according to a further aspect of the invention. 
         FIG. 5  is a side detail view of the center of  FIG. 4 . 
         FIG. 6  is a block diagram summarizing steps of a method according to a sill further aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an improved Yankee dryer  10  having a centrifugally assisted condensate disposal system  12  incorporated thereinto. The Yankee dryer  10  comprises a cylindrical drum  14  comprising a circumferential wall  15 , a first end wall  16 , a second end wall  18 , and a mainstay  20  disposed to position the cylindrical drum  14  relative to an environmental support (not shown). An axis of rotation  22  extends along the length of the cylindrical drum  14  and is generally horizontal when the Yankee dryer  10  is mounted in the usual position for use in drying unfinished raw material for paper making. Because Yankee dryers are conventional, not all of the structural features of the improved Yankee dryer  10  will be shown. For example, mounting structure for mounting the Yankee dryer  10  suitably within its operating environment, a drive system for rotating the Yankee dryer  10  about the axis of rotation  22 , and a steam supply system for drying the unfinished raw material all are omitted for clarity of the view. 
     Conventional Yankee dryers have condensate disposal systems which include components which are similar to those of the improved Yankee dryer  10 , but which components are not arranged according to the inventive concept. For purposes of general review and understanding, the condensate disposal system  12  comprises one or more liquid collection units each comprising a collection header  24  and a plurality of pickup straws  26  which project laterally from the collection header  24 . The collection header  24  is a hollow conduit disposed in fluid communication with each pickup straw  26 . Each pickup straw  26  comprises a pickup opening  28  which opens to the interior of the cylindrical drum  14  to take in condensate  30  (see  FIG. 2 ) and a discharge opening  32  which opens to the interior of the collection header  24 . 
     Flow of condensate  30  through the condensate disposal system  12  is illustrated in  FIG. 2 . The collection header  24  is mounted very close to or as depicted, abutting the circumferential wall  15  of the cylindrical drum  14 . Each pickup straw  26  may project laterally from the collection header  24  such that an included angle  34  formed between the center line  36  of each pickup straw  26  and the center line  38  of a disposal riser pipe or disposal riser conduit  40  is an acute angle having a magnitude lying within a range of about eighty degrees to about ninety degrees. The disposal riser conduit  40  is disposed in fluid communication with the collection header  24  and is arranged to extend to the axis of rotation  22 , and along the axis of rotation  22  to the first end wall  16  and from the first end wall  16  to the exterior of the cylindrical drum  14 . This is shown in  FIG. 1 . Discharged condensate  30  may be disposed of or reused in any suitable way. 
     The pickup straws  26  are arranged such that their pickup openings  28  are still conventionally located in specific points of the condensate film or pools. The differential motive steam pressure is critically used to urge this condensate into the pickup openings  28  of the individual straws  26  located in the groove bottoms of the ribbed bore of the drum  14  of the Yankee dryer  10 . As employed herein, radial distances will be understood to refer to distances extending in directions radiating from the axis of rotation  22 . Alternatively stated, the pickup opening  28  of each one of the pickup straws  26  is located at a first radius or radial distance from the axis of rotation, and the discharge opening  32  of the pickup straw  26  is located at a second radius or radial distance from the axis of rotation  22 . The length of an individual straw  26  dictates the rate of velocity change required by the differential motive steam which must be overcome to move the condensate  30  from the pickup opening  28  to the discharge opening  32  along the length of the straw  26 . The shorter the length of the straw  26 , the higher the rate of velocity reduction must be to move the condensate  30  from the pickup opening  28  to the discharge opening  32 . Increasing the length of each pickup straw  26  reduces the amount of differential motive steam pressure required to move the condensate  30  from the pickup opening  28  to the discharge opening  32 . The flow of condensate  30  is indicated by arrows  44 . This causes the condensate  30  to flow to a more central point such as the intake openings  54  of the disposal riser conduit  40 . Hence, in one aspect of the invention, collection of condensate  30  is accomplished using less differential motive steam pressure than in existing conventional condensate removal systems (not shown). 
     The collection header  24  may be arranged so that it extends along its length in a direction essentially parallel to the axis of rotation  22 . The pickup straws  26  may extend essentially perpendicularly to the length of the collection header  24 . 
     Turning now to  FIG. 3 , the collection header  24  has opposed ends  46  and  48 . The outer wall  50  of the collection header  50 , which is that facing the circumferential wall  15 , inclines continuously along most of its length (where the length is parallel or relative to the axis of rotation  22 ) such that the radial distance from the axis of rotation  22  to the inner surface  52  of the outer wall  50  of the collection header  24  is greatest at the location of the pickup opening  54  of the disposal riser conduit  40  and is smallest at the opposed ends  46 ,  48  of the collection header  24 . 
     The pickup opening  54  of the disposal riser conduit  40  is disposed in fluid communication with the collection header  24 , so as to draw collected condensate  30  from the collection header for ultimate disposal to the exterior of the Yankee dryer  10 . 
     Alternatively stated, outer wall  50  of the collection header  24  and the circumferential wall  15  of the cylindrical drum  14  each have length which is oriented parallel to the length of the other. The outer wall  50  of the collection header  24  and the circumferential wall  15  of the cylindrical drum  14  form an included angle  56  therebetween (the included angle  56  is taken along the respective lengths of the collection header  24  and of the circumferential wall  15 ). The included angle is between 0.1 degree and about ten degrees. 
     This causes condensate  30  (see  FIG. 2 ) to flow towards the pickup opening  54  from locations distant therefrom under the influence of centrifugal forces arising from rotation of the cylindrical drum. 
     Of course, inclination of the outer wall  50  may incline in two directions. As shown, the outer wall may have a first inclined section  50 A and an oppositely inclined section  50 B. Also, the outer wall  50  may have a neutral zone  50 C which extends along a perceptible if minimal distance along a direction parallel to the axis of rotation  22 . This limited neutral zone  50 C is not great enough to disrupt flow of condensate  30  due to centrifugal forces towards the pickup opening  54 . 
     It will be appreciated that  FIGS. 1 ,  2 , and  3  are diagrammatic and not literal in nature. In practice, the condensate disposal system of a Yankee dryer such as the condensate disposal system  12  of the Yankee dryer  10  will comprise at least two condensate disposal systems  12 . This is illustrated in  FIG. 4  wherein a Yankee dryer  110  may have two condensate disposal systems  112 A,  112 B are shown. Each condensate disposal system  112 A or  112 B has a respective disposal riser conduit  140 A or  140 B. The disposal riser conduits  140 A,  140 B may join at the axis of rotation  122  to form a singular or common disposal conduit  142  as shown in  FIG. 5 . The common disposal pipe  142  may extend along the rotational axis  122  of the Yankee dryer  110  and extend to the exterior thereof. 
     The two condensate disposal systems  112 A,  112 B may be offset from one another by an angle  144  of one hundred eighty degrees with respect to the axis of rotation  122 . 
     In respects other than those of the plural condensate disposal systems  112 A,  112 B, the Yankee dryer  110  may be generally similar in structure and function as the Yankee dryer  10  of  FIG. 1 . 
     A Yankee dryer may have three condensate disposal systems such as the condensate disposal systems  112 A,  112 B, offset from one another by angles of one hundred twenty degrees. Angular offset or spacing about an axis of rotation such as the axis of rotation  122  may be equal to three hundred sixty degrees divided by the number of condensate disposal systems actually installed. This number may be two, three, four, five or even more as desired. 
     Condensate disposal systems such as the condensate disposal systems  112 A,  112 B may be arranged not only at the same point along the length or rotational axis of their associated Yankee dryer, but may be provided in plural tiers each comprising two or more angularly offset condensate disposal systems. Each tier may be regarded as two or more condensate disposal systems which is axially spaced apart from another tier or plurality of condensate disposal systems such as the condensate disposal systems  112 A,  112 B. 
     The apparatus of a novel condensate disposal system such as the condensate disposal system  12  which includes the collection header  24  and the pickup straws  26  may be provided as a single prefabricated module which is installable within an otherwise conventional Yankee dryer. The pickup straws  26  may be permanently fixed to the collection header  24  to become a module. Modules may include an opening for receiving a disposal riser conduit such as the disposal riser conduit  40  of  FIG. 1 , or may have a short pipe nipple extending from the collection header of the module, such as the collection header  24 , so that a disposal riser conduit may be readily joined to the module outside the collection header. 
     The module may comprise brackets, attachment tabs, spacers, adapters or other structure for attaching a module in place within a Yankee dryer and to enable a particular module to be compatible with Yankee dryers of different makes, models, dimensions, and configurations. 
     Use of condensate disposal systems in modular form enables for example Yankee dryers of different throughput rates to be accommodated by installation of different numbers of condensate disposal system modules. Identical modules may be installed in different numbers depending upon the condensate rejection rate of different Yankee dryers, thereby enabling diverse models of Yankee dryers to be served by one model or configuration of modules. For example, a Yankee dryer may be provided with two modules spaced one hundred eighty degrees apart with respect to the axis of rotation, with three modules spaced one hundred twenty degrees apart with respect to the axis of rotation, or with four modules spaced ninety degrees apart with respect to the axis of rotation. Modules may also be positioned in tiers. For example, a first tier located near a first end wall may include three modules, with a second tier located near a second end wall of the same Yankee dryer including an additional three modules. Total condensate disposal capacity may thus be provided in increments corresponding to the number of identical condensate removal modules installed in the Yankee dryer. Although Yankee dryers differ within limits as to capacity and throughput, they are fabricated within a limited range of dimensions. Therefore, only one model or design of a module may be required to serve Yankee dryers actually in production or use. 
     According to a further aspect then, the invention may be regarded as a method  60  of equipping different types or models of Yankee dryers. Steps of this method  60  are shown in  FIG. 6 . The method  60  may comprise a step  62  of fabricating condensate disposal system modules to only one design, wherein one design signifies that each condensate disposal module is essentially identical to others being fabricated; a step  64  of installing at least two of the identical condensate disposal system modules in a particular Yankee dryer; a step  66  of installing other ones of the identical condensate disposal system modules in a different Yankee dryer; and a step  68  of installing identical condensate disposal system modules in any one Yankee dryer in proportion to the condensate production rate of the one Yankee dryer. 
     The term central location, as applied to the point within a cylindrical drum such as the cylindrical drum  14  from which a discharge conduit such as the disposal riser conduit  40  collects condensate is not intended to imply a location that is centered within the cylindrical drum. Rather, the term is intended to connote a singular pickup point for condensed liquids dispersed widely outside that pickup point. 
     Description of the outer wall of a collection header such as the collection header  24  as continuously inclining does not necessarily imply that the slope of the outer wall is identical at all points along the length of the outer wall of the collection header. 
     While the invention has been presented in terms of a single collection point for collecting condensate, it would be possible to have a plurality of collection points and a plurality of discharge conduits for each one collection header or for several collection headers, such as the collection header  24 , if desired. For example, a Yankee dryer according to a further aspect of the invention (not shown) could have two condensate evacuation systems formed in essentially in mirror image configurations, each discharging to a different end of the cylindrical drum. Also, redundant collection systems having two different collection points could be arranged to discharge collected condensate to the same side of the cylindrical drum. 
     Where used, the term “at least one” explicitly contemplates two or more of the referenced item. 
     While the present has been described in connection with what is considered the most practical and preferred embodiments, it is to be understood that the present invention is not to be limited to the disclosed arrangements, but is intended to cover various arrangements which are included within the spirit and scope of the broadest possible interpretation of the appended claims so as to encompass all modifications and equivalent arrangements which are possible.