US2932091A - Heated shell drum dryers - Google Patents

Description

. tima-amr April l2, 1960 G. D. DAY 2,932,091

HEATED SHELL DRUM DRYERS Filed oct. s, 195e '10 2 3 sheets-sheen 1 Y 'III/III' A www ZZ N VEN TUR GEoRsE Damm DA Y e.. Patent gemf April 12, 1960 s. D. DAY

HEATED SHELL DRUM DRYERS 3 Sheets-Sheet 2 Filed Oct. 8, 1956 /VVENTR GEORGE DONALDDAY Y BY Qqt e Patent Agent April l2, 1960 G. D. DAY I 2,932,091

HEATED SHELL DRUM DRYERS Filed Oct. 8, 1956 3 Sheets-Sheet 3 i I I I nl e i I I I. n v .N EU l M l M I, f' l 'i 2- I P I I i "f f Q l l I I I I I I I x I |J` I 2 I 9a ,n Q6

NVENTUR Gea/we Damm DAY IBYRE' Patent Agen HEATED SHELL DRUM DRYERS George Donald Day, Ottawa, Ontario, Canada Application October 8, 1956, Serial No. 614,516 Aa claims. (ci. .t4-124) This invention relates to improvements in rotatable heated rolls, and in particular relates to a thin-shelled drum form of dryer adapted to Vbe heated internally for theI drying of a web of paper passing over the external surface of the drum as in Vthe drying `end of a papermaking machine. y

'The invention also extends to the 'construction of ya heated shell over whoseY surface uniformity of temperature is required for use in any application where jan extended surface is required to be maintained at a given temperature.

Conventional dryer rolls in paper-making machines have numerous disadvantages Aand defects. :Cylindrical `'driers according to present practice in the paper industry for the drying of moist webs of paper issuing from a `Fonrdrinier machine are massive structures; with heavy shells of cast iron or steel several inches thick. Steam at elevated pressure is admitted Ainto the hollow cylinder to heat the shell and the heat of condensing steam is `conducted through the metal to the surface of the r'oll where the web contacts it `to cause evaporation of 'water in the web. Condensate gathers in the shell and is removed by gathering means.' It is well known `that inv order to attain an exterior surface temperature on such a Working roll above the boiling point of water at atmospheric pressure, it is necessary to employ rather high vsteam' pressures corresponding to temperatures several tens of degrees above the desired surface temperature. This is due in Vpart to the effect of a film of condensate which gathers on the inner wall of the Vvcylinder land acts as a barrier to effective heat flow. In addition the condition of the metal surface on the inside of the'drier,

-which is usually rough and scaly, represents -a further barrier to heat dowV and is variable in its effect over different parts of the roll, so that the temperature of the surface may vary locally to the detriment Vof uniformity "of the finished web. v 'p l Hence although the drier may be operated with steam at a definite inlet pressure, for example "ten pounds per square inch gauge, the working ltemperature atthe surface of the roll cannot be directly ascertainedv by 'the operator supervising the operation `ofa grOupof-drier rolls. pressure is not a reliable indication inasmuch asv the"jcon The steam temperature correlatedto 'the zgauge version factor allowing for effects of lm, interior scale,

and roll thickness is variable. This is `a serious detriment to eicient operation, since'it is vv'ell known in the art "of paper-making that the output of dried web 'increases iwith Aincreased roll surface temperature, 'at the 'rate of approximately one and one-half percent higher output for each degree Fahrenheit rise in temperature. Therefore with a given inlet steam pressure available to a machine, the substitution fof improved drierrolls per- -m'its either that the total number of drier rolls in a ltrain may be considerably reduced, or Vthe rate of movement of the webover a given number of rollsV maybe considerably increased. u

Existing cast-iron shell dryers .are also' defective-in 2,932,091 teenies A1#- 1?, i??? that'the steam filling the pressure vessel ,gives up heat to the ends walls closing the vessel, which are usually massive, heat flow thereinto being relatively unimpe'ded by a film of condensate, with the result that due 'to the conduction of heat from such heated ends of the vessel the margins of the web receive extra heat and dry faster. This effect is noted generally for a distance of about two feet inwardly along the roll face from the end Walls of a large diameter dryer. Heretofore, in orderrto compensate for the relatively super-heated margins of the rolls, the web has been deliberately pre-squeezed non-uniformly over its width vas it issues from the wet end vof Athe machine, by crowning the presser rollsvso as to leave 4more water in the margins of the web, with the object of achieving a concurrent attainment of dryness in all parts of its width after the web has traversed theentire train rof dryers. The maintenance of rolls and heat inputffor this compensation involves Vconsiderable maintenance and delicate adjustment in order to achieve a uniform product of high quality. l Y

Al further objection to the prior art Vform of drier 'that by the construction of `a cast-iron thick shell vessel, the tensile forces across any longitudinal Vdiametral plane become very large at the higher pressures Qf'steam required to transfer heat at effective rates through the metal, with the consequence that there is hazard of bursting. It must be )noted that the stored energy in a roll of large diameter, which may be ten feet, `represents 'a very large destructive potential on rupture ofthe vessel. Accordingly the design has usually required eX- tremely liberal safety factors, resulting in ponderous `rolls and increased capital costs. p r

The present invention provides a construction fofa dryer which avoids the large mass inherent in the `design of a conventional thick-walled cast-iron pressure vessel Vforming the prior art drying rolls, by making'a cylindric roll or casing an element of a heat kexchanger comprising a series of steam ducts having parallel axes integral with the inner surface of the cylinder, the transverse Ydinner;- sions of a duct being a small fraction 'of the .diameter 'lof a roll. Such construction makes possible the userof much higher drying temperatures and steam pressures with a greatly reduced thickness of shell material. With the system according to the present invention the effective surface temperature f the cylinder or rollin contact lwith the web of paper is substantially `the same as that open at both ends, servingtas an elernentpofajheatex-V changer comprising a large plurality vof pipes, `tubes or ducts integrally formed with Vand .bonded to its inner surfaceV and aligned parallel with each other Yand with the cylinder axis, for conveying steam admitted common to all the said pipes or tubes by way of an annular header; a similar header spaced axially from `the steam header and also communicating with each tube or ducty serves to collect condensates; a series of axially spaced bracing structuresY orpframes secured as bulkheads within the cylinder provide rigidity and serve as support for an axle` within which steam is led to the -s'team header and condensate is conveyed from `the condensate header. .t

By the practice lof the present invention steam is J caused to flow with a relatively high velocity within the exchanger passages, and the temperature along the length of each tube or duct is maintained substantially uniform. In addition, due to the scrubbing action of the relatively high velocity steam, any condensate within the ducts or pipes is cleared away rapidly so that a lm of appreciable thickness does not tend to build up as a'barrier to ow of heat into the roll face. In fact, that part of each tube or duct lying radially inwardly of the cylinder improves the conduction of heat to the v roll surface by providing a llow path along the metal wall of the duct to the integral joint made with the roll. It is a primary object of the invention to provide a simple and economical construction of a dryer .roll comprising a single cylindric shell having a plurality of steam conveying tubes or ducts secured to the inner periphery thereof.

Another object of the invention is the provision of a dryer roll having eicient scavenging of condensate Afrom the inner surfaces of steam passages by the joint action of high velocity steam and by provision of a condensate header into which condensate is drained to prevent obstruction thereby.

Yet another object of the invention is the fabrication of a heat exchanger roll comprising a cylindric shell and an integrally bonded metal body having a plurality of parallel ducts formed therein separated by areas con- `tiguous with the shell and permanently joined therewith.

It is a further object of the invention to realize a drier roll having excellent rigidity and freedom from deflection under load by employing a cylindric shell and C a plurality of duct bodies spaced about the inner periphof radial frames or spiders spaced axially along the length of the roll and secured both to the inner periphery of the roll and to the cylinder axle.

Yet another object is the provision of a drier roll of high eciency 'and having greatly reduced mass without high sacrifice in rigidity and freedom of deflection, permitting reduction in the pass and strength of end shafts, bearings, and machine frames. Still another object of the invention is the realization of a drier wherein variation of driving load ldue to variable accumulations of condensate is avoided.l

A more complete understanding of the invention and of the best mode of carrying it into effect may be gained by a reading of the following specification wherein embodiments of the invention are described in conjunction with the accompanying gures of drawing:

Figure 1 is a side elevation view partly in section Aof a dryer constructed according to the invention;

Figure 2 is a section taken on the line 2-2 of Figure 1 showing the steam conveying passages joined to the shell;

Figure 3 is a section taken on the line 3 3 of Figure 1 showing the condensate collecting header and the axle passages;

Figure 4 is a section taken in a radial plane through an end of a spider element of Figure 2;

Fig. 5 is a view at right angles to the section of Figure 5 showing the end of the brace and itsjoint with the shell;

Figure 6 is a cross section similar to that shown in Figure 3 showing an alternative duct structure;

Figure 7 is a partial section of the ducts in Figure 6;

Figure 8 illustrates a construction and arrangement of steam and condensate headers for use with very wide webs; and,

Figure 9 describes a method of fabricating the heat exchanger. Referring'frst to Figure 1, a dryer roll according to the invention generally designated'at 10 comprises a pair ofV bearings 11 and 12 co-axially aligned -withthe axis of the roll, and a smooth cylindric roll body 13 coaxial with the axis of the shafts. A hollow thick-walled pipe 14 co-axial and co-extensive with the roll 13 serves as a duct for inlet steam, and is secured to pedestal flanges 21 at its ends. A condensate collecting pipe 15 is enclosed within one end of the tube 14 and is led out to a condenser system (not shown) by way of the hollow bearing 11. Similarly high pressure steam is led from a source (not shown) by way of a hollow shaft 11 into the tube 14, and is carried therealong to flow into the generally radially extending distributors 16 which are joined to the opposite end of the tube 14. The distributors terminate in a circular header tube 17 joined to the inner periphery of one end of the roll A large plurality of parallelly spaced tubes 22 lying about the inner periphery of the roll 13 terminate upon and communicate with the tube 17. l

The tubes 22 are bonded in good heat-conducting relation to the roll body 13, preferably by welded joints. As

Y shown in Figure 9, a system of ducts 22 may be realized by laminating, upon the interior surface of a roll or shell 13 previously formed as a cylinder, a continuous strip of lighter gauge sheet metal 30 which is formed with curved portions 31 bowed away from the roll face and intervening strips 32, the latter being integrally joined with the cylinder as by seam welding. Each duct is thereby formed separate and distinct from its neighbors whereby for a` given pressure of steam lling the duct the unit stresses in the outer shell 13 are very considerably less than the tensile stress which is developed across a longitudinal diametral plane passed through a large diameter hollow roll of the prior art. A significant advantage of the construction lies in the improved moment of linertia of the resulting shell body in a transverse l section due to the disposition of duct material lying 'radially inwardly of the shell, with a consequent stiening of the structure against deflection.

It is entirely feasible toform the heat exchanger by using a ductile material for the sheet 30, which is applied evenly over the inner surface and seam welded thereto at` intervals leaving intervening areas unbonded, after which thebowed portions 31 are produced by hydraulically expanding the unbonded metal in a manner well known in the art.

It also lies within the scope of the invention to form the ducts by laying up a plurality of separate. strips whose edges are aligned adjacently in parallel, and 50 depositing metal between the butted ends by welding to produce Huid-tight joints and to bond them to the roll. At their opposite ends the tubes are joined with a Y condensate header 19 generally similar in construction to the steam header but of a radius somewhat larger than that of; the roll 13, to the rim of which it is integrally joined. A number of syphons 18 extend generally radially within the header 19 towards the outermost radius thereof, and are connected at their inner ends with the pipe 15. A layer of insulation 33 may be attached to the inner wall of the array of ducts 22 for the purpose Iofpreventing heat loss to the dryer room.

A plurality of disc-like frames 23 are secured upon the tube'14 and have their outer edges bonded with the -shell 13. As best Seen by reference to Figure 5, a frame comprises a plurality of radial angularly spaced spokes 23 in the form of tubeswhose outer ends are slotted in adiametral plane to receive a metal plate 24 which is welded to the tube, the outer edge of which plate being attached between a pair of adjacent tubes 22 and welded thereto and to the shell 13. At the inner ends of a frame the tubes are similarly slotted in diametral planes i Y as best shown by Figure 2 and are welded to a relatively thin metal disk 25 secured on the shaft.

In the construction of a frame the outer plates 24 l.are rst'joned'withthe ends of spokes 23', and the n'ng lsecured,thereto. The spokes are 25 is placed uporr'rithegshaft hin'litsgproper position and uput intofnlace and are weldedto the ring and to th nerfaceofthe' .roll, ,preferably with plates 24 alignedaxilly upon theaarieas 3,2. A modilation of the arrangements .for inlet vof steam ,and remoyal of condensate the design of very long irolls for use with wide webs is shown in Figures, "The construction generally vis as described "hereinbefore, 'with the exception that the steam header 17 is positioned intermediate the ends of the roll, and a pair of condensate collecting headers 19, 19 are disposed at each end thereof. By this arrangement the quantity of condensate collected at either header is halved, and the scrubbing action in each duct is improved over that attained in an extremely long duct.

The operation of dryer rolls according to the present invention involves considerably less difiiculty in starting up and bringing Ythem to operating temperature since there is less mass of metal to be heated, andthe volume of air to be purged from the system by incoming steam is far less than that involved in starting up pressure vessel types of drier rolls.

An alternative construction of a `duct system aliixed to the inner periphery of a cylind-ric shell is described with reference to Figures 6 and 7, wherein a plurality of passages 22 are realized by attaching metal strips, folded longitudinally approximately to an angle of 90 degrees to form walls 26 and 27, to both the inner surface of the shell 13 and to the fold region of a strip already in position. In fabricating such structure, a strip is placed in adjacent position to a preceding duct and one edge welded to the inner roll face by a weld 28, while the other edge is welded to the fold line of the previously attached duct, along the joint29. In this manner a succession of ducts are laid up in progression about the inner periphery of the cylinder until the free edge of the first strip which was attached by its one end to the shell is joined with the fold line of the last strip, thereby completing a ring of ducts.

I claim:

l. A dryer roll `comprising an openaended internally braced `sheet metal shell supported on a hollow shaft and having a cylindric face, a plurality of fluid-guiding ducts having parallel axes and having wall portions thereof co-extensive with and joined at spaced intervals to the inner surface of said shell and having remaining wall portions radially spaced inwards of said shell for conveying fluid in heat exchange relation with the inner secured to the inner surface of said shell joined! to and communicating with each of said fluid guiding ducts and having at least one fluid inlet duct connecting therewith, a second fluid-collecting annular duct having an outer diameter greater than the shell diameter spaced from said first fluid distributing duct and secured to one end ofthe shell and connecting with each of said fluid guiding ducts, and at least one uid outlet duct extending radially into and terminating within said fluid gathering duct -radially outwardly of the shell.

2. A dryer roll as in claim l wherein said fluid inlet and said liuid outlet ducts extend coaxially within the shaft.

3. A dryer roll as in claim l having a plurality of axially spaced frames rigidly secured upon said hollow shaft, and wherein said shell is supported on the peripheries of said frames.

4; A rotatable dryer roll comprising a cylindric` shell internally braced and rigidly mounted on an axial hollow shaft by a series of axially spaced transverse frames, an inner wall of uted cylindric form bonded to the inner surface of said shell along the radially outwardly protruding ridges between the flutes to define with said shell a plurality of separate flow-guiding passages, a steam chamber of annular ring form bonded to the shell and to the inner wall in communicating relation with surface of said shell, a first annular uid distributing duct j said Vpassages, ha condensate l'-hiea'delenaeetl :axially from said-chamber connecting with the ends Vof Saduassases and having an internal diameter greaterfthantheiinternal diameter of said shell, at least one inlet duct connected with the ,steam chamber. .forlsupplying 'the :latter with steam, atleast `one .outletduet nconnected with the con- .densate header for removing condensate and steam therefrom, the termination lof an outlet ductwithinthefheader `-lyingradially outwardly `ofthe nnerradius of the shell.

5. A roll as in claim 4 wherein said inlet and said outlet lducts extend coaxially within the said shaft.

6. A dryer drum comprising an outer sheet metal cylindric shell and an inner sheet metal wall laminated thereto and bonded along areas extending parallel to the cylinder axis and spaced about the periphery of the shell, the unbonded portions Yof the wall being formed convexly inwardly to define a plurality of passages for guiding fluid therein in direct heat exchange relation with said shell, a hollow annular metal body joined to the inner surface of the shell and connected with all of said passages, a header spaced axially from the said body secured to an end of the laminate and connecting with the ends of said passages, a shaft coaxial of the shell and rigidly mounted in support relation therewith, and pipes for ingress of fluid to the ymetal body and for discharge of fluid from the header respectively joined thereto and to respective conduits in said shaft.

7. A drum. as in claim 6 wherein said shaft and shell are correlated and secured in fixed relation by a plurality of bracing frames disposed transversely of the cylinder axis and spaced along the shaft and secured to said shell and said shaft.

8. A dryer roll construction comprising a cylindric sheet metal shell internally braced and rigidly mounted on an axial hollow shaft by a series of axially spaced transverse frames, a plurality of sheet metal folded strips each having a longitudinal fold line to form a pair of walls whereof one wall is disposed in an axial plane passed radially through the cylinder with the free edge of said wall joined with the inner surface of the shell, and the other wall is disposed in a chordal plane parallel with the axis of the cylinder having its free edge joined to a like adjacent strip at the region of its fold line to form with said inner surface a series of separate ducts spaced about the inner periphery of the shell, a liuid chamber disposed on the inner surface of the roll joined to and communicating with each duct, a discharge header closing the open ends of said ducts and communicating with each and joined to an end of the shell, said header having a maximum internal diameter ygreater than the internal diameter of said shell, conduit means extending within said header having open ends terminating therein radially beyond the surface of the shell and joined to an axial passage within the shell, and liuid inlet conduit means joined with said chamber for supplying fluid thereto.

9. A rotatable drum dryer comprising a straight hollow shaft adapted to convey steam therethrough, an outer shell having a smooth cylindric outer surface, an inner shell mounted coaxially with said outer shell on said shaft,

vand dening together with said outer shell an annular space, a plurality of radial support members joined with said shaft and said inner shell, a plurality of partitions disposed between said shells and coextensive therewith, said partitions being regularly spaced about the periphery of the inner shell to define a corresponding number of parallel flow-guiding passages for conveying fluid therethrough in heat exchange relation with said outer shell, an annular steam chamber connecting with said passages, a `condensate header spaced axially from said chamber closing an end of said annular space and connecting with said passages, a discharge conduit disposed within the shaft, at least one inlet pipe connecting said shaft with said chamber for supplying steam to said passages, and at least one pipe connected with said con- References Cited inthe le of this patent I '5 A -2,905,661 f. L1

duit andterxninatng in said header having its end4 ldisposed radially outwardly of the outer shell for discharging iow frorn said header. Y l

UNITED STATES PATENTS snuck Au'gao, `1927 -Holthouse Apr. 24,1945

8 FOREIGN PATENTS Germany Auk. 31, 1900 vGermany June 28, 1905 Germany Mar. 19, 1906 Germany Feb. 28, 1908 Great Britain ,Jan. 17, 1929 Germany Aug. 13, 1931

Images