US3808700A

US3808700A - Rotary drying drum

Info

Publication number: US3808700A
Application number: US00318009A
Authority: US
Inventors: J Kraus
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1972-12-26
Filing date: 1972-12-26
Publication date: 1974-05-07
Anticipated expiration: 1991-05-07
Also published as: DE2303334A1; DE2303334C3; CA1007850A; DE2303334B2

Abstract

Rotary drying drum for high-speed drying of thin webs such as paper or the like comprising a hollow cylinder mounted for rotation and adapted to receive a condensable fluid and discharge condensate. Improved heat transfer is obtained by spoiler bars positioned around the inner drum circumference generally parallel to the drum axis. The invention includes dividing these bars into segments and attaching each segment; a single fixture may be used for each segment and end contact with adjacent bar segments prevents the segments from rotational movement around the fixture point. As a result, performance is improved due to the ability of the bar segments to expand and flex with the drum''s surface without excessive stress on the attaching fixtures.

Description

United States Patent [191 Kraus ROTARY DRYING DRUM [75] Inventor: James J Kraus, Neenah, Wis.

[73] Assignee: Kimberly-Clark Corporation,

Neenah, Wis.

[22] Filed: Dec. 26, 1972 [21] Appl. No.: 318,009

FOREIGN P TENTS OR APPLICATIONS 1,138,144 12/1968 Great Britain 165/81 [111 3,808,700 4451 May 7,1974

Primary ExaminerJohn J. Camby Assistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-Daniel J. Hanlon, Jr.; Raymond J. Miller; William D. Herrick 7] ABSTRACT Rotary drying drum for high-speed drying of thin webs such as paper or the like comprising a hollow cylinder mounted for rotation and adapted to receive a condensable fluid and discharge condensate. Improved heat transfer is obtained by spoiler bars positioned around the inner drum circumference generally parallel to the drum axis. The invention includes dividing these bars into segments and attaching each segment; a single fixture may be used for each segment and end contactwith adjacent bar segments prevents the segments from rotational movement around the fixture point. As a result, performance is improved due to the ability of the bar segments to expand and flex with the drums surface without excessive stress on the attaching fixtures. v

4 Claims, 8 Drawing Figures 'PATENTEDHAY Y 1914 SHEET 2 OF 4 lWI. E] ii FIG.3

PATENTEDM 11914 FIG. 4

SHEET 3 OF 4 FIGS FIG.6

FIG.7

PATENTED M 7 I97 SHEET B [If 4 FIG. 8

BACKGROUND OF THE INVENTION The invention relates to dryer drums particularly adaptable for papermaking machines. The drying section of a papermaking machine generally includes a series of dryer drums, each of which has a cylindrical shell, spaced heads extending across the shell to close the open ends thereof, journals for rotatively mounting the shell, conduits for introducing a condensable fluid into the shell and conduits forwithdrawing condensate from the shell. The paper web travels from one of these dryer drums to the others in such a drying section. Particularly for lightweight paper webs, a single so-called Yankee dryer drum is utilized. A Yankee dryer drum also comprises a cylindrical shell and spaced heads and is generally of the same construction as the dryer drums previously mentioned; however, a Yankee dryer drum is ordinarily of substantially greater diameter, and onlyone of these drumsis generallyused in a'papermaking machine. However, with either type of drum, the smaller type or the large Yankee type,'there are certain operating limitations due to the collection of condensate in the drum.

The interior of such a dryer drum has a condensable fluid (usually steam) admitted to it so that the dryer shell is heated for drying paper web traveling over the shell. Condensate forms within the shell as the fluid gives off its heat tothe shell; and, at low speeds, the condensate pools within the bottom part of the drum. At higher peripheral speeds, such as above 1,000 feet per minute at which most of the drums arepresently run, the condensate rims within the dryer shell, tending to collect in a cylindrical layer about the complete internal periphery of the shell, Although the condensate layer is at the temperature of the fluid generally, heat transfer through the condensate layer is relatively slow since the body of condensate within the drum keeps the fluid away from direct action on the dryer shell. Thus, as these dryer drums are ordinarily operated, the layer of condensate within the dryer shell is kept at a minimum thickness for maximum heat transfer.

It has also been found that, in addition to the rimming effect of the condensate at higher dryer speeds, the

condensate also oscillates circularly about the internal surface of the drum. The cause of the oscillation is the force of gravity which alternately retards and accelerates' the condensate ring within the drum.

The periodical Das Papier," Vol. 14, No. 10a, of October, 1960 (pages 600 -609), in an article written by Barnscheidt and Schadler, gives a description of this oscillating movement of condensate in a steam heated cylinder or dryer drum, and the authors of this article describe therein the use of rails or bars within the drum for increasing condensate turbulence to increase heat flow through the condensate. These bars (also the subject of USP No. 3,217,426 to Barnscheidt and Staud) are spaced on approximately 10 inch centers. According to the article, the rails cause a surface wave associated with oscillation of the condensate within the dryer shell, and Branscheidt and Schadler apparently indicate in their patent that resonating conditions are undesirable and may be avoided by spacing the bars at unequal peripheral distances. The authors conclude atbars r m r o .9.3inshJi l1 w rabsstin their dryer.

In US. Pat. No. 3,724,094 assigned to the assignee' of the present invention, Appel and Hong describe an improved drying drum arrangement in which the bars are attached in a specific configuration to produce resonating conditions in the condensate. In this manner, a greater degree of turbulence is introduced in the condensate layer, and heat transfer even further increased.

However, the present invention is directed to a further improvement in the operation of such drying drums.'The bars are generally thinner than the dryer shell and, since they are first contacted by the hot steam, they tend to expand more rapidly than the shell. Additionally, in mostcases, the dryer drum is operated in a nip configuration with a pressure roll. This pressure roll causes radial deflection of the drum surface and contributes to loosening of the bars, particularly near the ends. In either event, the damage done if a bar becomes loose within a rotating drum can cause extended periods of downtime for replacement of the dislodged bar.

SUMMARY OF THE INVENTION Briefly, in accordance with the present invention, there is provided a rotary drying drum especially adapted for papermaking machines and having spoiler bars extending axially and attached to the internal drum periphery. In particular, the present invention is directed to an improved segmented bar structure which can be attached by a single attachment means per segment and provides for some degree of bar flexing with the dryer surface as well as thermal expansion of the segments. Rotational movement of the bar segments about the single attachment means is inhibited by contact with the ends of adjacent bar segments. The result is improved dryer operation for extended periods with a minimum amount of downtime and fewer incidences of bar dislodgement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section view of a Yankee dryer drum having aseries of condensate impeding bars fixed on the inner surface;

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1-

FIG. 7 is a top view of the embodiment shown in FIG.

FIG. 8 is a fragmentary side elevational view of a section of a papermaking machine incorporatingthe dryer drum illustrated in the preceding figures.

FIG. 3 is 'a sectional view taken on line 3-3 of FIG.

Like characters of reference designate like parts in the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 1, the dryer drum comprises a thin cylindrical outer shell and a pair of relatively flat ring-shaped heads 11 and 12. The heads 11 and 12 are rigidly secured to the ends of the shell 10 and are supported by a hollow central axle or shaft 13. An integral bolting flange .14 is provided at each end of the shell 10, and each flange mates with a similar peripheral flange 15 on the adjacent head. The rigid attachment of the shell to each head may be made by a plurality of bolts 16 inserted from the insideof the shell and drawn up by nuts on the outside of the head.

A short cylindrical section 17 has a machined bolting flange 18 provided at its inner end and is formed integrally with each of the heads 11 and 12, each section extending longitudinally of the shell 10 and at a radial location which is intermediate the inner and outer edges of the head. A plurality of heavy staying members 19 extend between the heads 11 and 12 longitudinally of the dryer, being fixed with respect to the flanges 18 by means of flanges 20 formed on the staying members 19 and bolts 21 extending through the

flanges

18 and 20. The staying members 19 control the bowing of the heads 11 and 12 to eliminate stress occurring in the shell 10 at or near its connections to the heads 11 and 12.

The heads 11 and 12 and shell 10 and the central shaft 13 are of cast construction. The shaft 13 is formed in two

halves

22 and 23, and the halves are provided with flanges 24 and 25, with bolts 26 extending through the flanges to fix the

halves

22 and 33 together. Two

separate compartments

27 and 28 are provided within the shaft 13 by means of a separator 29 within the half 22. An enlarged bolting flange 30 is provided near each end of the shaft 13, and each head 11 and 12 is provided with a flange 31 that mates with a flange 30, the

flanges

30 and 31 being fixed together by means of bolts 32. Journals 33 are provided on the ends of the shaft 13 for rotatably supporting the dryer in suitable bearings, and a shaft extension 34 is provided at one end of the shaft 13 for mounting a driving gear or sprocket or the like.

Bores

35 and 36, respectively, in communication with the

compartments

27 and 28, are provided in the shaft 13 at its ends.

Bores

35 and 36 may respectively be'utilized to provide steam or other condensable fluids under pressure into the compartment 27 and for withdrawing the condensate from the compartment 28.

A plurality of steam supply pipes 37 having rows of steam discharge openings 38 in them may be used for supplying steam under pressure to the interior of the dryer drum. The pipes 37 are connected to the compartment 27, and the pipes 37 extend axially with respect to the shaft 13 and may be appropriately fixed adjacent their ends to the shaft 13.

The dryer is provided with a condensate withdrawal system which comprises a pair of

manifolds

39 and 40 positioned oppositely from each other with respect to the shaft 13 and located adjacent the inner surface of the shell 10. The

manifolds

39 and 40 are supported at their ends from the bolting flanges 18 by means of supports 41 and are supported intermediate their ends from the staying members 19 by means of ties 42.

A plurality of equal length small diameter tubes.43 (FIG. 3) extend radially through each of the

manifolds

39 and 40. The tubes 43 have their outer ends 44 terminating closely adjacent the inner surface of the shell 10 and have their inner ends 45 terminating well within the associated manifold close to the longitudinal center of the manifold.

The manifold 40 has a pair of arcuately shaped branch pipes 46 and 47 (FIG. 2) connected with it, and the manifold 39 has a pair of

similar pipes

48 and 49 connected with it. The

pipes

46 and 48 are connected together by means of a Y-shaped fitting 50, and the central leg of the fitting 50 is connected'by means of a radially extending pipe 51 with the shaft 13 and particularly with the compartment 28 in the shaft. The

pipes

47 and 49 are connected similarly with the compartment 28 utilizing a Y-shaped fitting 52 connected to a radially extending pipe 53. The

branch pipes

46, 47, 48 and 49 are supported intermediate their ends by means of support brackets 54 extending between adjacent staying members 19 and tie rods 55 extending between the brackets 54 and the

pipes

46, 47, 48 and 49.

A plurality of bars, A, B, C, D, E, F, G, H, I, J, K, L,

etc., are longitudinally disposed within the shell 10 and are fixed to the internal shell surface. In accordance with the present invention, each of the bars, A, B, C, etc. is divided into segments and each segment fixed by means of a single attachment means 56 extending through the bar to the shell 10 as will be described in detail with reference to the later drawings. A manhole 57, closed by a removable cover 58, is provided in each of the heads 11 and 12 so that workmen may enter the dryer drum when it is stationary and unheated for the purpose of fixing the bars A, B, C, etc., within theshell l0.

The dryer drum may be mounted in a papermaking machine as illustrated diagrammatically in FIG. 8. The journals 33 of the shaft 13 may be mounted in bearings 59 which are secured to a supporting frame 60. The wet paper web to be dried is carried by a felt web 61 which travels around felt rolls 62. The paper web is forced against the surface of the dryer shell 10 by a pressure roll 63 which is rotatably mounted in brackets '64 attached to arms 65. The arms 65 are each pivoted at.66 to the frame 60, and the pressure roll 63 is forced against the surface of the dryer shell 10 by a hydraulic or pneumaticactuator 67 which bears against each arm I The dried paper web may be removed from the surface of the dryer shell by a creping doctor which includes a doctor blade 68 secured within a doctor blade holder 69. The blade 68 and holder 69 may be supported by conventional mechanism including shafts 70 carried by the supporting frame 60 and rotatably mounted within'guide blocks71. The blocks 71 in turn are slidably mounted within a slide assembly 72 attached to a pivot frame 73 carried by the frame 60. Through the slide arrangement provided by the guide block 71 and slide assembly 72, the vertical position of the doctor blade 68 can be varied as desired to obtain the best creping angle. The doctor blade holder 69 and the blade 68 are pivoted from a toggle mechanism 74 which is attached through a lever arm 75 to one of the shafts 70. A spring loading mechanism 76 is connected through the toggle mechanism 74 to provide a resilient contact for the doctor blade against the surface of the dryer shell 10.

In operation, a moist paper'web is directed onto the outer surface of the shell 10, being carried by the felt web 61; and the pressure roll 63, which exerts a substantial pressure on and has a pressure nip with the dryer drum, forces the paper web against the outer surface of the shell and causes the paper web to adhere onto the shell 10. A sprocket or other driving mechanism (not shown) on the extension 34 may be utilized for drivingly rotating the dryer drum. The web is dried as the drum rotates, and the web is creped off the outer surface of the drum by means of the creping blade 68. Alternatively, the paper web may be simply pulled off the surface of the dryer drum without the use of such a blade.

Steam under pressure is supplied to the compartment 27 through the bore 35, and the steam enters the internal compartment of the drum through the supply pipes 37 and the openings 38 in the pipes 37. The steam heats the dryer drum for drying the paper web; and, as the steam loses heat, it condenses into water. The water condensate remains on the internal surface of the shell 10 and rims or lies completely around the shell due to the action of centrifugal force. The condensate removal system including the

manifolds

39 and 40, the small diameter tubes 43 and the

condensate withdrawal pipes

46, 47, 48,49, 51 and 53 remove this condensate.

The tube ends 44 are located very close to the internal surface of the shell 10, and steam within the dryer drum rushes to these ends of the tubes, since the pressure within the tubes and in the connected

manifolds

39 and 40 is lower than the pressure of the steam within. the drum. The steam, in entering the ends 44 of the tubes 43, sweeps across the inner surface of the dryer drum and atomizes the condensate existing on the inner drum surface. Thus, a steam-water mixture passes radially inward through the bores of the tubes 43 into the

manifolds

39 and 40.

Some of the steam condenses as it passes through the tubes 43, but the pressure of the steam within the dryer drum is sufficient to move the water-steam mixture inward and some condensation takes place also within the

manifolds

39 and 40. The water condensate tends to collect on the outer walls of the

manifolds

39 and 40 and moves from these outer walls into the

pipes

46, 47, 48 and 49 and from these last mentioned pipes into the compartment 28 through the

fittings

50 and 52 and the

radially extending pipes

52 and 53.

The steam condensate withdrawal system is substantially that disclosed in Joseph B. Webb US. Pat. No. 3,359,647; and this patent may be referred to for more details of the withdrawal system. Of course, the invention is not limited to use in combination with any particular condensate removal system, and others such as scoops or dippers may be utilized as well.

Assuming that the dryer drum is rotating at relatively high speeds, such as 1,000 feet per minute peripheral speed or greater, the dryer condensate tends to rim the drum completely around the drum; and this rimming is accompanied by oscillation of the condensate circularly about the internal surface of the drum. This oscillation is apparently caused by the force of gravity, alternately retarding and accelerating the water ring within the drum. As the water ring oscillates in-the drum, it flows over the bars A, B, C, D, etc.; and these coefficient (BTUs per hour per square foot per degree Fahrenheit) from the steam through the dryer shell 10. The condensate layer thus rendered turbulent is reduced from a uniform thickness layer to one that is of very non-uniform thickness, allowing greater heat transfer; and, in addition, the turbulent flow of the condensate apparently scrubs off a water film from the interior surface of the dryer which action contributes to the increase in heat transfer. The height of the various bars, A, B, etc., is preferably maintained sufficiently small so that the condensate sloshes over the bars, not only for increasing the turbulence but also for allowing the condensate to flow to to the tubes 43 which are disposed in two opposite longitudinal rows on the internal surface of the drum.

The separation of the bars peripherally within the shell 10 is preferably determined in accordance with the aforementioned Appel/I-Iong patent. In this manner resonance of sloshing in the spaces between the bars A,

B, C, etc., occurs so that the condensate rises to a maxi-' mum height at the bars. Preferably a minimum average thickness of condensate is used in the drum, inasmuch as the condensate is a poor conductor of heat; and it is contemplated that the average condensate thickness shall be within the range of about 1 to 7 1/2 millimeters and preferably about one millimeter.

Turning now to FIGS. 4 and 5, one embodiment of the improved bars and attachment-of the present invention will be described. As shown therein, each bar A, B, C, etc., is composed of a plurality of segments a, b, 0, etc. These segments are each attached to outer shell 10 by a single fastener 56 placed near the center of the segment and which may be a screw, as illustrated. Additional fasteners may, of course, be used if desired. To maintain the segments in alignment, each end is in contact with the end of an adjacent segment. In this embodiment, each segment, excluding of course the end ones, has a tongue 77 on one end and a matching groove 78 in the opposite end. The tongue of one segment fits into the groove of the adjacent segment so that a substantially continuous bar is formed. This tongue and groove, segmented arrangement allows some flexing in the drum radial direction along with the drum surface so that undue stress is not placed on the fasteners. It is also preferred that some length clearance be provided for individual segment thermal expansion by making the groove slightly longer than the tongue. As illustrated, the end segments are preferably somewhat shorter than the others so that the attachment is placed closer to'the free ends of the bar.

The bars are generally thinner than the dryer shell and, since they are first contacted by the hot steam, they tend to expand more rapidly than the shell. By dividing the bars into segments and making the grooves slightly longer than the corresponding tongues, this increased expansion is easily accomodated by the present invention.

FIGS. 6 and 7 illustrate an alternative embodiment. In this case, instead of machining or otherwise forming a tongue and groove into the ends of the individual segments, the ends of adjacent segments are placed in slightly overlapping and abutting position as illustrated. Thus, while the segments are not in strict alignment, the individual segments are prevented from rotation about the axis of the fastener by contact with the ends of adjacent segments. Because of the necessity to install the segments in strictly parallel positions, this embodiment is somewhat less preferred.

While it is not critical to the present invention, it is preferred that the bar segment be in the range of from 7 to ll inches in length depending upon factors such as the overall width of the machine, and the diameter of the dryer cylinder. With respect to the height of the bars, A, B, C, etc., the analysis does not indicate any particular optimum height, but an approximate desirable range can be identified. When the bars are spaced such that sloshing occurs at or near resonant frequency for the waves in the spaces between the bars A, B, etc., then the fluid rises up first at one end of the space and then at the other end. The height of the mass of condensate when it sloshes against either side of each bar should be greater thanthe height of the bar so that some of the condensate spills over the bar into the next space, and this spillage causes the condensate to migrate around the internal surface of the shell toward the condensate withdrawal tubes 43, assuming that between 25 to 50% of the condensate originally in the space between adjacent bars A, B, etc., spills over a bar into the next space. For these purposes, it has been found that the bar height should be between 1.5 and 7.5 times the average'condensate depth in the dryer; and it is preferred that the bar height should be between 2 and 3 times the average condensate depth for rapid migration of condensate in the dryer, although substantial improvement in heat transfer can be expected for bar heights between 1.5 and 4 times the average condensate depth.

It will be understood that the average condensate depth can be regulated by moving the outer ends 44 of the tubes 43 toward and away from the internal surface of the shell 10; and preferably the tube ends 44 shall be located so close to the internal surface of the shell 10 that the average condensate depth is no greater than 3 millimeters, inasmuch as thicker condensate layers would cause an unduly great retardation of heat flow. Due to the possibility of hot spots near the ends 44 of the individual siphon tubes 43, it is preferred that the condensate depths used shall not be less than 1 millimeter.

Since the average condensate depth is preferably between 1 millimeter and 3 millimeters, the permissible bar heights mentioned above are between 1.5 millimeters and 22.5 millimeters, more preferably between 1.5 millimeters and 12 millimeters, and still more preferably between 2 millimeters and 9 millimeters. These heights correspond, respectively, to the range of 1.5 to 7.5, the range of 1.5 to 4 and the range of 2 to 3 times the average condensate depth mentioned above. For further description and illustration of the condensate behavior within the dryer drum, reference may be had to the aforementioned Appel/Hong patent.

The width of the bars A, B, etc. is quite immaterial insofar as the condensate motion within the dryer shell is concerned; however, if a bar is too wide, it will have an undesirable insulating effect with respect to the outer shells surface which may produce a wet streak inthe paper being dried. Each of the bars A, B, etc. should, therefore, be considerably narrower than the thickness of the dryer shell. The dryer shell may have a thickness of from 1 1/4 inches to 2 inches, for example, and the width of the bar may thus well be one half inch or less and should preferably be 3/8 inch 'to 1/2 fore not limited to any specific bar spacing but will have advantages in the devices described by Barnscheidt et al aswell.

Although the improved dryer drum of the present invention has been deribed in connection with a source of steam for heating the drum, it may also be used with other condensible heating fluids; for example, with Dowtherm E and Dowtherm'A which are particularly described in US. Pat. No. 3,363,328 for Rotary Drying Drum, issued Jan. 16, 1968, to Hong and Dickens. As is mentioned in said prior US. Pat. No. 3,363,328, particularly in col. 2, lines 27 to 59 of the patent, these fluids termed Dowtherm E and Dowtherm A have higher condensing temperatures than water and may thus supply more heat to a dryer drum.

Thus, it is apparent that there has been provided in accordance with the invention, an improved rotary drying drum that fully satisfies the objects, aims, and advantages set forth above. While the invention has been described in connection with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives,

modifications, and variations as fall within the spirit and broad scope of the appended claims.

I claim:

, 1. In a rotary drying drum having journals for mounting the drum, a connection for supplying a condensible fluid, a condensate removal connection for removing condensate out of the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum,

the improvement wherein said bars are comprised of segments which are attached to the inside surface of the drum and maintained in position by contact with the ends of adjacent segments, each of substantially all of said segments being attached by a single fixture.

2. The rotary drying drum of claim 1 wherein the contact between the ends of adjacent bar segments is maintained by providing a tongue on the end of onebar 4. The rotary drying drum of claim 1 wherein the contact with the ends of adjacent bar segments is provided by staggering adjacent segments and overlapping the segments so that the ends of adjacent bars contact each other.

l l l 4 222 3 UNITED STATES PATENT OFFICE 3 I CERTIFICATE OF CORRECTION ?atent No. 3I-808-r700 Dated May 7, 1974 Inventor(s) James J. Kraus It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

"'1 Column 1 line 37, delete the comma, Column 2, line 4, "Branscheidt" should, read Barnscheidt Column 3, line 35, "33" should read 23 Column 5, line .48-, "52" should read 51 Signed and sealed this 1st day of October 1974.

- (SEAL) Attest:

5 McCOYM'. GIBSON-JR. C.'MARSML DANN Attesting Officer Commissioner of Patents

Claims

1. In a rotary drying drum having journals for mounting the drum, a connection for supplying a condensible fluid, a condensate removal connection for removing condensate out of the drum, and a plurality of bars extending lengthwise of the drum and disposed on the inside surface of the drum for giving turbulence to the condensate in the drum, the improvement wherein said bars are comprised of segments which are attached to the inside surface of the drum and maintained in position by contact with the ends of adjacent segments, each of substantiaLly all of said segments being attached by a single fixture.

2. The rotary drying drum of claim 1 wherein the contact between the ends of adjacent bar segments is maintained by providing a tongue on the end of one bar segment which substantially matches a groove in the end of the adjacent bar segment.

3. The rotary drying drum of claim 2 wherein the groove is slightly longer than the corresponding tongue to provide for thermal expansion of the bar segments.

4. The rotary drying drum of claim 1 wherein the contact with the ends of adjacent bar segments is provided by staggering adjacent segments and overlapping the segments so that the ends of adjacent bars contact each other.