Patent Application
20110067257
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.
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.
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.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
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
Flow of condensate 30 through the condensate disposal system 12 is illustrated in
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
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
Of course, inclination of the outer wall 50 may incline in two directions. As shown, the outer wall may have a first inclined section 50A and an oppositely inclined section 50B. Also, the outer wall 50 may have a neutral zone 50C which extends along a perceptible if minimal distance along a direction parallel to the axis of rotation 22. This limited neutral zone 50C is not great enough to disrupt flow of condensate 30 due to centrifugal forces towards the pickup opening 54.
It will be appreciated that
The two condensate disposal systems 112A, 112B 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 112A, 112B, the Yankee dryer 110 may be generally similar in structure and function as the Yankee dryer 10 of
A Yankee dryer may have three condensate disposal systems such as the condensate disposal systems 112A, 112B, 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 112A, 112B 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 112A, 112B.
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
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
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.
