US3363328A - Rotary drying drum - Google Patents

Description

Jan. 16, 1968 lc s ET AL ROTARY DRYING DRUM 3 Sheets Sheet 1 Filed Nov. 26', 1965 3%. 7 pm ALI Jan. 16, 1968 w, A, l s ET AL 3,363,328

ROTARY DRYING DRUM Filed Nov. 26, 1965 5 heets-Sheet 2 Jan. 16, 1968 w. A. DICKENS ET AL 3,363,328

ROTARY DRY ING DRUM Filed Nov. 26, 1965 3 Sheets-Sheet 5 United States Patent 3,363,328 ROTARY DRYING DRUM William A. Dickens and Sung Ho Hong, Neenah, Wis, a

signors to Kimberly-Clark Corporation, Neenah, Wis, a corporation of Delaware Filed Nov. 26, 1965, Ser. No. 509,916 3 Claims. (Cl. 34-124) ABSTRACT OF THE DISCLGSURE A rotary drum for drying sheet material adapted to have a condensible heating fluid supplied to it and having a series of longitudinally extending grooves in its internal surface and a pair of circumferential grooves in communication with and at the ends of the longitudinal grooves and having condensate removal pipes extending outwardly into said circumferential grooves for removing condensate from inside the drum.

The invention relates to rotatable drum constructions and more particularly to heated drier drums for drying paper webs and the like.

Paper is conventionally dried by means of hollow drums heated with condensing steam and having the paper webs passing over the drums. The steam is supplied to the interior of such a drum at steam pressures up to 125 pounds per square inch which corresponds to a temperature of 353 F., and a 12-foot diameter drier drum of this type supplied with this steam pressure is suflicient for drying paper tissue at speeds of the order of 3,000 feet per minute.

Obviously, relatively high strength drum constructions are needed in order to withstand such steam pressures; and, if the steam temperature is raised, for example to 450 F., in an attempt to provide higher drying speeds, the required steam pressure would be greater, such as about 400 pounds per square inch for the 450 F. temperature, and these higher pressures necessitate still heavier drier drums with still thicker shells. The thicker shells would have the effect of increasingly impeding the heat transfer to the sheet on the shells, and the heavier drums would have higher initial costs. Therefore, the increases, if any, in drying speed would be relatively small, and the extra cost of such heavy drums could not be expected to justify the small increases in drying speed obtainable.

It is an object of the present invention to provide an improved drier drum and a system for supplying heating fluid to the drum by means of which the relatively thin drums may be heated to higher temperatures than those obtainable using steam in the conventional manner; and, more particularly, it is an object to utilize fluid materials in such systems which have higher boiling points than that of water so as to accomplish this result.

More particularly, it is an object of the invention to provide an improved drier drum of this type having a series of inwardly extending ribs on its inner periphery which will allow a direct contact between portions of the inner drum surface and the vapor of the heating fluid applied to the drum but which will yet allow the condensed heating fluid to collect on the inner surface of the drum and to be drawn out of the drier drum. It is contemplated that the ribs shall preferably extend longitudinally of the drier drum, so that siphons or collecting pipes may be provided at the ends of the drum to collect the condensed heating fluid flowing between the ribs. The drum is rotatable and the siphons or condensate collecting tubes may be either rotatable or stationary; however, the latter is preferred since the relative rotation between the siphons and the drum may be utilized to provide a pumping effect to the condensed heating fluid, propelling fit into and through the siphons for removal from the rum.

The invention consists of the novel constructions, arrangements and devices to be hereinafter described and claimed for carrying out the above stated objects, and such other objects, as will be apparent from the following description of a preferred form of the invention, illustrated with reference to the accompanying drawings, wherein:

FIG. 1 is a fragmentary, longitudinal, sectional view of a drier drum incorporating the principles of the invention;

FIG. 2 is a diagrammatic illustration of a source of supply of heated fluid for the drier drum;

FIG. 3 is a sectional view taken on line 33 of FIG. 1;

FIG. 4 is a sectional view taken on line 44 of FIG. 1;

FIG. 5 is a fragmentary view similar to FIG. 3 but on a further enlarged scale and of a small portion of the outer shell of the drier drum;

FIG. 6 is a longitudinal, sectional view of a portion of the outer shell of the drier drum; and

FIG. 7 is a view similar to FIG. 1 and showing a modified drier drum.

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

The drier drum and fluid supply system to the drum illustrated in the above mentioned figures are preferably used with a fluid material which has a substantially higher boiling point than that of water and which is relatively inert so as to eliminate corrosion problems with respect to the drum. A material for example, that is satisfactory, is a low melting point mixture of diphenyl and diphenyloxide. This material is a colorless, non-corrosive liquid and one form (commercially known as Dowtherm E) has a condensing temperature of about 445 F. at 33.4 pounds per square inch (gauge pressure) and a latent heat of 107 B.t.u.s per pound. Another form of this material (known commercially as Dowtherm A) has a condensing temperature of about 450 F. at -7.7 pounds per square inch and a latent heat of 129 B.t.u.s per pound. Used in the same drier drum heating system to obtain the same drying eflect Dowtherm E could be operated at 30 to 40 pounds per square inch within the drum while Dowtherm A would be operated at 7 pounds per square inch. Both of these operating pressures could be compared to the conventional operating pressure for steam of pounds per square inch. Also, for purposes of comparison, steam at this pressure has a condensing temperature of 353 F. and a latent heat of 868 B.t.u.s per pound. Dowtherm A and Dowtherm E used under the above mentioned operating pressures of 30 to 40 pounds per square inch for Dowtherm E and 7 pounds per square inch for Dowtherm A would provide a heat flux through a certain drier drum of 25,500 B.t.u.s per hour per square foot, while the steam at 125 pounds per square inch in the same system would provide only 17,000 B.t.u.s per hour per square foot due to the lower temperatures of operation of the steam.

Referring now to the drawings and in particular to FIGS. 1, 3, 4, 5 and 6, the illustrated drier drum may be seen to comprise an outer cylindrical shell 10 and end walls or heads 11 and 12. The end walls '11 and 12 are respectively provided with longitudinally extending tubular end portions 13 and 14 by means of which the drum is rotatably mounted in bearings 15 and 16, the bearings being suitably mounted on pedestals or other standards (not shown). The shell 10 and the heads 11 and 12 are suitably fixed together as by conventional studs or screws (not shown).

A fixed hollow axle or shaft 17 extends through the drum and through the end portions '13 and 14 of the heads 11 and 12. Pressure seals 18 and 19 are provided on the shaft 17 and within the head portions 13 and 14 for sealing the internal cavity 20 of the drum with re spect to the shaft 17. Tubes 21 and 22 of insulating material are also provided within the head portions 13 and 14 so as to insulate, to some extent, the seals 18 and 19 with respect to high temperature fluid within the drum.

A plurality of vapor outlet tubes or nozzles 23 are fixed in the tubular shaft 17 and are directed into the cavity 20 for discharging vapor from the shaft 17 into the cavity 20. A vapor inlet port 24 is provided in the shaft 17 for supplying heated vapor to the shaft and thereby to the cavity 20 through the tubes 23.

The shell on its internal peripheral surface is formed with a series of ribs 25 which are integral with the shell 10 and which are separated by grooves 26. The ribs 25 and grooves 26 extend longitudinally of the drier drum and shell 10 and terminate slightly short of attachment end flanges 10a and 10b of the shell 10, leaving internal peripheral grooves 27 and 28 between the flanges 10a and 10b and the internal ribs 25.

A plurality of siphon pipes 29 are fixed with respect to and are carried by the stationary tubular shaft -17, and the outer ends of these pipes 29 extend into the grooves 27 and 28. As may be seen from FIG. 4, the pipes 29 are bent at right angles on their ends to have terminal portions 29a which lie approximately parallel with the adjacent internal surface of the shell 10. The shell 10 rotates in the direction indicated by the arow 30, and the terminal portions 29a of the pipes 29 extend in the opposite direction from the direction of rotation of the shell.

A condensate collecting and discharge tube 31 extends through the center of the hollow shaft 17, and each of the pipes 29 is connected to the tube 31. A support 32 is preferably provided for each of the siphon pipes 29, and the supports 32 are fixed with respect to the hollow shaft 17 and with respect to the siphon pipes. The heads 11 and 12 are preferably provided with radially extending fins 33 and 34 adjacent the pipes 29 and supports 32, as shown.

The source of heated fluid for the drier drum may comprise various heating systems; however, for illustrative purposes, the system shown in FIG. 2 is suggested. The FIG. 2 system comprises a boiler 35 for heating liquid which may utilize natural gas from a source 36. The boiler is connected to the port 24 for the central shaft 17 by means of a conduit 37. The tube 31 within the stationary hollow shaft '17. of the drier drum is connected by means of a conduit 38 with a separating and receiving tank 39, and the tank 39 is connected by means of a conduit 40 with the boiler 35. A pump 41 is disposed in the conduit 40. A compressor 42 is provided in a conduit 43 connecting the upper end of the tank 39 with the conduit 37, and the upper end of the tank 39 is also connected by means of a conduit 44, which has a pump 45 therein, with a storage tank 46 for the heating liquid.

In operation, the heating fluid, which may be one of the Dowtherm mixtures above mentioned, is heated in the boiler 35 and passes as a vapor from the boiler through the conduit 37 to the central shaft 17 of the drier drum. The vapor is discharged through nozzles 23 from the shaft 17 into the cavity 20 of the drier drum, and the vapor heats the shell 10 of the drum and condenses in the drum. The condensate, along with some of the vapor, enters into the siphon pipes 29 and passes through them to the central tube 31 of the drum and passes through the conduit 38 to the separating and receiving tank 39. The compressor 42 removes the vapor from the tank 39, which exists above a body 47 of the fluid in the bottom of the tank 39, and returns it into the conduit 37. The body of liquid 47 is maintained at a predetermined height within the tank 39 by automatic controlling means (not shown) which operates the pump 45 to pump fluid from the storage tank 46 into the tank 39 as needed, and the pump 41 pumps the heating fluid in liquid form from the hot- 4 tom of the tank 39 through the conduit 40 to the boiler 35, as needed, to maintain the desired supply of heated vapor to the drier drum.

The paper sheet 48 (see FIG. 1) that is dried by the shell 10 is substantially coextensive with the ribs 25 within the drum, and the drum is rotated to pass the sheet over it and dry the sheet. The heated vapor that is discharged from the nozzles 23 into the cavity 20 of the drum heats the shell 10, and this heat is efiective on the web 48 for drying the web as the web passes over the shell 10 during rotation of the drier drum. The vapor as it cools in heating the shell 1% condenses to a large extent releasing its heat of condensation, and the condensate passes longitudinally of the drum within the grooves 26 toward the peripheral grooves 27 and 28 at the ends of the ribs 25. As will be observed from FIG. 4, the ends 29a of the pipes 29 extend into directions opposite to the direction of rotation of the drum indicated by the arrow 30; and, since the condensate moves with the shell -10 and the pipes 29 are stationary, the pipe ends 29a tend to scoop the condensate into them. Some of the vapor also passes into the pipes 29 and due to its pressure forces the condensate into the pipes 29, and this combination of condensate and vapor passes from the pipes 29 into the central tube 31 for passage through the remainder of the system as above described.

It will be understood that the pressures of the heating fluid within the system may vary; however, as an example, the pressure within the boiler 35 may be 50 pounds per square inch; the pressure within the cavity 20 of the drier drum may be 30 pounds per square inch; and the pressure of the vapor within the tank 39 above the body of liquid 47 may be 10 pounds per square inch.

Utilizing the high boiling point heat transfer liquids above mentioned to provide a high shell heating effect, it will be apparent, advantageously, that the vaporized liquid need be at or only slightly above atmospheric pressure in lieu of the high pressures that are necessary using steam for a high heating effect; and, as a result, the drum construction can be relatively light, since it does not need to withstand high pressures. Therefore, the tension stays commonly used in steam heated drier drums for papermaking, such as the stays 52 of the drum shown and described in Malmstrom et al. Patent No. 3,099,543, issued July 30, 1963, need not be used while yet the drier drum may be made with a relatively thin shell 10 providing relatively ready, unimpededheat transfer. Thus, utilizing the relatively light drier drum, using Dowtherm E, for example, operating pressures within the drum of only 30 to 40 pounds per square inch provide a much greater heating effect and paper drying effect than does steam at an operating pressure of pounds per square inch used with a relatively heavy drier drum of the type shown in the above mentioned Malmstrom et al. patent. Utilizing the Dowtherm, the system is capable of providing about a 50 percent increase in the heat flux per square foot through the drier shell as compared with steam, and this heat flux increase provides a substantial increase in the possible speed of drying for a paper web, such as a speed increase of 600 to 1,000 feet per minute for a 7 /2 pounds per 2,880 square foot paper sheet dried on a 12-foot diameter drier, for example. 7

It is contemplated that the illustrated drier and supply system shall be capable of effective paper drying operation at high speeds, such as above 5,000 feet per minute. At some high speeds of this general magnitude, the condensate flow within the drier drum becomes laminar in nature, and the liquid heating medium in the form of condensate within the drier drum is an insulator. Therefore, the system for effectively and expeditiously removing condensate without allowing it to build up in the drum has been provided, the system comprising the longitudinally extending grooves 26 allowing condensate to flow longitudinally of the drum to the peripheral grooves 27 and 28 in which the siphon pipes 29 are effective for removing the condensate. As an important feature, the

system allows the inner surfaces of the ribs 25 to be in direct contact with the heating fluid in its vapor form as supplied through the nozzles 23, since condensate is mainly in the grooves 26 in the portion of the shell located beneath the sheet 48; and there thus exists a very effective heat transfer from the vapor to the shell 10.

The arrangement of the ribs 25 and the grooves 26 extending longitudinally of the drier drum, used with high boiling point liquid such as Dowtherm, not only provides higher heat fluxes through the shell 10, due to the higher temperatures with which the Dowtherm may be used as compared with those of steam and due to the relative thinness of the shell 10 attributable to the reduced pressures of operation, but the rib and groove construction also provides a much improved temperature uniformity in the shell. The heat transfer behavior of the condensate in the grooves 26 is quite uniform inasmuch as the flow of condensate in the grooves is practically laminar and its thickness and thickness gradient from the center of each groove 26 to the ends of the grooves are very small at the high speeds of operation contemplated for the drier drum. The high centrifugal force on the condensate within the shell 10 can be expected to maintain the condensate thickness in the grooves 26 at not substantially more than 0.1 inch in the middle of the shell 10 and to maintain less than 0.04 inch difference in condensate thickness in the grooves 26 from the middle of the shell 10 to the ends of the ribs 25, due to the low viscosity of the Dow therm liquid at the temperatures at which used. Temperature uniformity is also promoted inasmuch as the flow of condensate through the grooves 26 is undisturbed by the siphoning action of the siphon pipes 29, except at the end of the grooves 26, which are outside the area or width of the sheet that is being dried.

Although the shell 10 may be formed of any suitable material, such as copper-nickel alloy described in the patent to John F. Klement, No. 2,937,965, it is contemplated that preferably the shell 10, as Well as the heads 11 and 12, shall be made of cast iron of the conventional compositions now used for drier drums for paper machines, since very satisfactory creping by creping blades for manufacturing creped tissue may be obtained off of such cast iron shells. Although the dimensions of the ribs 25 and grooves 26 are not considered critical; as an example, the ribs 25 may have heights of 2 inches, and the ribs and the grooves may have widths (peripherally of the shell 10) of about 1% inch. The thickness of the shell 10 may, for example, be about 1% inch, measured between the bottoms of the grooves 26 and the outer surface of the shell 10. Due to the fact that lower pressures of operation are possible using fluids of the type herein contemplated, cross stays for strengthening the drier are not needed; and, therefore, it is possible to use the stationary siphon pipes 29 cooperating with the ro tatable shell 10 and acting as a kind of centripetal pump for removing the condensate within the shell 19. Utilizing a heating fluid of this type having a lower heat of vaporization, the condensate formation Will be considerably greater than utilizing steam, and hence it is important that an eflicient condensate removal system be provided, such as one of this type having a pumping action. Since there is this pumping action, a minimum amount of the vapor of the heating fluid need be utilized for removing the condensate out of the drier drum.

Although, as has been above explained, the invention is preferably used with relatively thin, unstayed drier drums, nevertheless, the invention may also be used with a stayed head drier of the type illustrated in the above mentioned Malmstrom et al. patent, if desired. The drum illustrated in FIG. 7 is of the stayed type and comprises a central hollow shaft 49 having end journals 50 for rotatably supporting the drier in suitable bearings (not shown). The shaft 49 is provided with a plurality of outwardly directed, heating fluid discharge openings 51 in it. The heating medium may be supplied to a port 52 at one end of the shaft 49, and a condensate withdrawal tube 53 may be disposed within and fixed with respect to the shaft 49 and may extend out of the shaft 49 at its other end.

The drum comprises a relatively thin cylindrical outer shell 54 rigidly secured at its ends to relatively flat ringshaped heads 55 and 56 which are fixed with respect to the hollow shaft Q9, so that the shell 54, heads 55 and 56 and the the shaft 49 all rotate together. The heads 55 and 56 are provided with short, integral cylindrical sections 57 and 58, and a plurality of circumferentially spaced stays 59 connect the cylindrical sections 57 and 58.

The internal surface of the shell 54 is provided with ribs 25a. The ribs 25a extend longitudinally of the drum and terminate short of the ends of the shell 54 so as to provide circumferential grooves 27a and 28a adjacent the ends of the shell. Siphon pipes 60 extend from the tube 53, outwardly through the shaft 49, and into the grooves 27a and 28a. A plurality of the pipes 60 are provided for each of the circumferential grooves 27a and 28a, and these pipes are circumferentially spaced within the drum and extend between the stays 59.

Heating fluid in the form of vapor is supplied to the port 52 for the purpose of heating the drum, and it flows through the openings 51 into the internal cavity 61 within the drum. The heating fluid condenses within the cavity 61 and heats the outer shell 54 particularly by direct contact of the heating fluid vapor with the ribs 25a in the same manner as the heating fluid is effective for heating the shell 10 in the first embodiment. Condensed heating fluid flows between the ribs 25:: longitudinally of the drum to each of the circumferential grooves 27a and 28a in which it collects. Due to the pressure of the heating fluid within the cavity 61, which is higher than the pressure maintained in the tube 53, some heating fluid in vapor form flows into the pipes 60 and at the same time draws condensed heating fluid into these pipes out of the circumferential grooves 27a and 23a, and the condensed heating fluid flows from the pipes 60 into the tube 53 for return to the system for heating the fluid.

We wish it to be understood that the invention is not to be limited to the specific constructions and arrangements shown and described, except only insofar as the claims may be so limited, as it will be understood to those skilled in the art that changes may be made without departing from the principles of the invention. In particular, it will be understood that although we have described the ribs 25 and 25a as being longitudinal with respect to the drier drums and shells l0 and 54, the ribs can instead be formed slightly helically within the shells, such that the grooves between the ribs are not substantially increased in length and are thus substantially longitudinal; and we consider that the ribs 25 and 25a should be helically inclined no more than for an angle of 25 with respect to the longitudinal center of the drum for them to be considered substantially longitudinal. Also, it will be understood that, although we have described the drum for use in connection with the drying of paper, the drum also can be used for drying any other sheet material.

What is claimed is:

1. Drying mechanism for sheet material comprising a hollow shell closed on its ends and rotatably mounted, said shell being provided with alternate ribs and grooves on its inner surface which extend longitudinally of the shell, said grooves being of substantially uniform. depth for their complete length, said ribs being discontinuous adjacent the ends of the shell so as to provide circumferential grooves disposed on both ends of said shell in communication with said longitudinal grooves, means for supplying a condensible heating fluid into said shell, and means for withdrawing condensate from the shell and in cluding a pipe extending into each of said circumferential grooves whereby condensate may flow through each of said longitudinal grooves from the center of each 7 groove to its opposite ends and into said circumferential grooves and may flow from the latter through said pipes.

2. Drying mechanism according to claim 1, said condensate withdrawing means including a stationary tube than that of water and conduit means for connecting said source with said hollow shell.

References Cited extending longitudinally through said shell and said pipes 5 UNITED STATES PATENTS being connected with said tube and being stationary, each 971,176 9/ 1910 Dexter 34-119 of said pipes on its end Within one of said circumferential gultchins 34-125 u ton 34 -124 grooves hav ng a portion extending opposite to the direc- 2,413,567 12/1946 H mb stel 3 124 ion of rotation of said shell so that the pipes act to scoop 10 3 099 543 7/1963 Malmstrom et 31 34-124 condensate from the circumferential grooves into the pipes 3:217:426 11/1965 Barnscheidt et X as the condensate travels along with said shell. 3,224,110 12/1965 Kroon 34 124 3. Drying mechanism according to claim 1, said heating fluid supplying means including a source of a heated 1 fluid of a type having a substantially higher boiling point 5 FREDERICK L. MATTESON, IR., Primary Examiner.

A. D. HERRMANN, Assistant Examiner.

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