US3263340A - Multiple run drier improvements - Google Patents

Description

8 Sheets-Sheet 1 Filed Nov 15, 1965 IN VENTOR HORACE L. SMITH, JR.

M M M ATTORNEYS 2, 1966 H. SMITH, JR

MULTIPLE RUN DRIER IMPROVEMENTS 2 Sheets-Sheet 2 Filed Nov 13, 1963 INVENTOR HORACE. L. SMITH, JR.

BY JM,%M ATTORNEYS United States Patent 3,263,340 MULTHPLE RUN DRIER IMPROVEMENTS iorace L. Smith, In, Richmond, Va., assignor to Hupp Corporation, Cleveland, ()hio, a corporation of Virginia Fiied Nov. 13, 1963, Ser. No. 323,519 4 Claims. (Cl. 3460) This is a continuation-in-part of application Serial No. 237,586, filed November 14, 1962, now United States Patent No. 3,228,114.

This invention relates to the heat treatment of web and sheet materials, and more particularly to drying con tinuous paper web and pulp sheet. Description of this invention will therefore be made in connection with pulp paper drying, it being understood however, that it may have general application to the drying, or heat treating, of web or continuous sheet materials.

In the manufacture of paper pulp sheet and paper most drying is presently carried out today by passing newly formed paper web over large steam heated drum driers. The disadvantages of these drying systems are numerous, but foremost is the expense involved. A large paper machine, using 60 inch diameter driers with a trim width of 200 inches, may employ as many as 100 or more of such driers each presently costing $15,000 to 25,000.00 installed in the machine. Paper shrinks as it dries. This necessitates driving the drums in sections with a very complicated control arrangement to compensate for dimensional changes in length as the sheet dries, by gradually changing the rotation speed of the driers progressively throughout the length of the machine. Even with the most sophisticated controls, tension accumulates in the sheet causing frequent breaks resulting in immediate loss of material and time until all of the break is cleared out and the machine started in normal production again. One reason for these frequent breaks is that the distance the sheet moves between two adjacent driers known as the draw, is very short thus affording no margin or slack to enable the sheet to flex.

Another serious disadvantage of the present conventional steam heated rotary driers is the difficulty of removing the condensate from these driers at higher operating speeds. A 60 inch drier rotating at a surface speed of 2000 feet per minute develops 14 g; therefore, one pound of condensate exerts a radial force of 14 lbs. and acts as a centrifuge causing the condensate to form a diflicult to remove hollow cylinder of water inside the drier. The condensate thermal conductivity being only of carbon steel, causes a very high temperature gradient from the condensing temperature of the steam to the drier outer shell temperature. Paper manufacturers are today leaning toward faster machines, capable of producing paper at speeds in the order of 3000 feet per minute. Since centrifugal force varies as the square of the speed, increased operating speeds exaggerate the condensate problem. The present invention is capable of operating at such speeds, or higher, without the frequent sheet breaks and other disadvantages of the slower prior drum drier systems. Briefly, this is accomplished by providing a drier system characterized by long horizontal runs with the sheet supported directly by separated idler rolls without supporting conveyor belts and heating by radiating panels which permit higher operating temperatures with substantially increased speed and production capabilities and with improved paper quality. My improved arrangement provides much more flexibility for the give and take of the sheet, greatly reduces initial machine and setting up costs, frequency of breaks and down time, and operating and maintenance costs. To obtain the full benefits of the high speed horizontal runs, the supporting rolls are preferably displaced vertically relative to each other to prosive support rollers may therefore be increased.

3,263,340 Patented August 2, 1966 vide compensating paper chordal arch runs that minimize high speed sheet flutter.

In many applications of the present invention the support rolls are spaced quite close together in the region where the wet sheet first enters the multiple run drier section. As the web passes through this section it dries and becomes stronger; and the distance between succes- In drying lightweight paper and other products having little tensile strength at high speeds, it may be necessary, in order to provide sufficient support, to space at least the initial support rolls so close together that the operation of the drier will be adversely affected to an appreciable extent.

If they are too closely spaced, the support rolls create two problems. First, in the present invention, radiant heaters are preferably located beneath the horizontally moving web to increase heat input to the web. Too closely spaced support rolls block significant amounts of the radiant energy emanating from these radiators and directed toward the web, materially decreasing the drier efficiency. Second, the presence of too closely spaced support rolls may tend to increase the rate at which breaks occur in the web.

In another aspect, the present invention relates to novel, improved driers of the multiple run type which are especially useful for high speed drying of products having little tensile strength. Generally, the driers provided for drying such products are similar to and embody the novel features of the driers discussed above. In these driers, however, a supporting felt is employed on at least the initial runs of the drier to support the wet Web, permitting the support rolls to be spaced much further apart than would otherwise be possible.

The felts most commonly employed heretofore in paper drying apparatus are, as the term felt implies, belts of felted material and are opaque to infrared radiation. Ordinary felts are therefore unsuitable for use in the present invention in which radiant heaters are located beneath the moving web. In addition, conventional felts hinder the escape of evolved moisture and other volatile substances from adjacent the lower side of the web, seriously retarding the drying process.

It has also been proposed heretofore that the supporting felt be made from wire mesh. Wire mesh felts are also unsuitable for use in the present invention. They have the advantage over conventional felts that a substantial portion of the radiant energy emanating from radiators beneath the web can pass through the mesh openings to the web so that wire mesh felts are significantly less opaque to infrared radiation than conventional felts. Also, evolved volatiles can pass through the mesh openings, eliminating the retarding influence of conventional felts which tend to prevent this moisture from escaping. However, in the present invention, the supporting felts are constantly flexed as they pass over the support rolls and the end and other direction changing rolls. Wire mesh belts deteriorate so rapidly under this constant flexing that they are economically impractical.

In the present invention the above-discussed disadvantages of the prior felts are eliminated by making the felts from an open mesh synthetic material which is, preferably, at least partially transparent to infrared radiation having wave lengths of 3.5 to 5 microns (i.e., infrared radiation emitted from radiators at temperatures ranging from 600 F. to a little over 1000 F). Several advantages fiow from the utilization of the novel felts described above. Support rolls can be spaced much further apart, so that the amount of radiant energy emanating from radiators beneath the web and blocked by the support rolls becomes negligible.

In contrast to the results that would be obtained if conventional felts were employed in the novel driers of the present invention, all or substantially all of the radiant energy generated by radiators beneath the web being dried can be delivered to the web. At the same time, evolved volatiles can readily pass from adjacent the web through the openings in the mesh. The preferred open synthetic felt is also a material improvement over a wire mesh felt since it is effected to only a negligible extent by flexing. In addition, they are substantially more transparent to infrared radiation than wire mesh felts since the strands of wire in the latter are opaque to energy in the infrared portion of the electromagnetic spectrum and the radiant energy can, therefore, only pass through the openings in the mesh. The strands of the synthetic open mesh felts employed in the present invention, in contrast, are relatively or even completely transparent to infrared radiation so that energy emanating from radiators beneath the web can pass through the strands to the Web as well as the mesh openings. This is an advantage of significant importance, as the mesh openings may constitute a maximum of 50% of the area of a felt.

From the foregoing, it will be apparent that it is a primary object of this invention to provide improved high speed relatively low cost pulp and paper drying methods and apparatus for producing improved quality paper and like products.

It is another object of the present invention to provide novel improved multiple run driers for drying products having low tensile strengths at high speeds.

Another specific object of the present invention resides in the provision of multiple run driers equipped with an improved product supporting medium for increasing the efliciency of the drying process.

Still further objects and advantages of the present invention will become apparent to those skilled in this art from the appended claims and following description of the preferred mode of carrying out this invention taken in connection with the accompanying drawings wherein:

FIGURE 1 is a diagrammatic elevation of an embodiment of the present invention which is particularly useful for drying products which, when wet, have low tensile strengths; and

FIGURE 2 is a fragment of FIGURE 1, to an enlarged scale.

Referring now to FIGURES 1 and 2, the novel multiple run paper drying apparatus 300 illustrated in these figures is especially useful for drying products having low tensile strength when wet and therefore requiring substantial support. Drying apparatus 300 includes a plurality of support rolls 302 arranged in seven superimposed, spaced apart levels indicated generally by reference characters 304a-g, providing seven generally horizontal runs. As shown in FIGURE 1, rolls 302 are substantially equidistantly spaced along each run; and adjacent rolls along each run are vertically displaced to form a slight chordal arch in the product being dried to eliminate high speed flutter of the drying web.

Also incorporated in drying apparatus 300 are a plurality of rotatably mounted, direction changing rolls 306. Direction changing rolls 306 are located at the ends of drying apparatus 300 between each pair of adjacent runs 304 with the rolls between successive runs alternated at the left-hand and right-hand end of the dryer. For example, direction changing roll 306a is located at the right-hand end of drying apparatus 300 between levels 304g and 304 and direction changing roll 3015b is located at the left-hand end of the drying apparatus between levels 304-f and 304a.

The novel drying apparatus 300 illustrated in FIG- URES 1 and 2 employs one or more endless belts, hereinafter termed felts to support the wet product until it has dried to a state in which it has sufficient tensile strength to be supported solely on rolls 302. In the illustrated embodiment of the present invention, two felts are employed to support the drying product as it passes through runs 304g and 304]. The length of the runs are in the order of up to feet or longer. For many products, two such felts will be sumcient since, by the time the product has traveled through the second run 304,, it will have sufficient tensile strength that felts will be unnecessary for its support through succeeding runs. For other products, it may be only necessary to employ one felt on the first or initial run. If a very weak product is being dried, it may be necessary to employ felts on more than two or even all runs.

The felt 308 employed to support the drying product as it passes through the initial horizontal run 304g is trained over the support rolls 302 forming run 304g. At the right-hand end of drying apparatus 300, the felt is trained around direction changing roll 306a. From direction changing roll 306a, felt 308 is trained around, successively, idler rolls 310 and 312. From idler 312, felt 3-08 passes over idler rolls 314 located below the felt supporting rolls 302 to the left-hand end of drying apparatus 300 where it passes around an idler roll 316.

The felt 318 employed to support the drying product as it passes through horizontal run 30 5f is supported in much the same manner as felt 308. Starting with the right-hand end of drying apparatus 300, felt 318 moves over the support rolls 302 delineating run 304 to the left-hand end of the apparatus where it passes around direction changing roll 30612 and then, successively, idler rolls 320 and 322. From idler roll 322, the lower run of felt 318 is trained over rolls 324 (arranged in the manner of the rolls 314 discussed above) which guide its movement as it moves toward the right-hand end of the machine. At the right-hand end of the machine, felt 318 is trained over an idler roll 326.

To move the product through drying apparatus 300 and to impart movement to felts 308 and 318, direction changing rolls 306 may be driven in the manner discussed in the parent application.

Felts 308 and 318 are preferably woven from synthetic materials which are at least partially transparent to infrared radiation having wave lengths from 3.5 to 5.0 microns and are preferably of an open mesh construction. In the preferred embodiment, a weave is employed which will produce from 30 to 50% open area in the mesh. Suitable felts, having varying degrees of transparency for radiation of the wave length described above and mesh openings in the range of percentages described above are available from the Formex Company, a division of Huyck Corporation, and from the Appleton Wire Company. Any one of a number of weaves supplied by these and other companies may be employed although it is deemed prefer-able to use a material having as high a degree of transparency to infrared radiation as is compatible with the strength and other physical requirements of a particular installation and to employ a mesh having as much open area as possible to facilitate the escape of evolved moisture and other volatiles from adjacent the drying product and to facilitate circulation of a scouring gas into contact with the product. One such material which may be employed in the practice of the present invention is the Formex Companys Design #41. Formex Design #41 is basically a polyester open weave mesh of approximately 40% free opening. The free openings are of course completely transparent to radiant energy of the wave lengths described above; and the filaments are partially transparent to radiant energy with wave lengths in this range. Polyester in film form is marketed under the name Mylar and 111 filament form under the name Dacron.

To increase the normal force between the product being dried and the direction changing driving rolls 30 endless felts 328 are employed. AS is best ShOWn FIGURE 2, each felt 328 engages the moving product over substantially the same arcuate extent as that over which the direction changing roll 306 is contacted by the moving product. As felt 328 moves out of engagement with moving product passing over the associated direction changing roll 306, the felt 328 moves successively over rolls 330, 332, and 334, the latter roll guiding felt 328 back into contact with the moving product on the direction changing roll. The felt increases the normal force (and therefore the frictional force) between the product and the direction changing roll, decreasing slippage between the direction changing rolls and the moving product. In addition, for the reasons pointed out in the parent application, felts 328 prevent the drying product from pulling away from the direction changing rolls due to centrifugal force when the apparatus is operated at high speeds. For example, the drying product may be moving at a linear speed of up to 2000 or more feet per minute.

To evolve moisture and other volatiles from the product being dried, panel type radiant heaters 336 and 338 are employed. Radiators 336 are disposed parallel to and above the path of the moving product in each of the runs 304a-g. Radiators 338 are similarly employed, in each run, beneath the path of the product. The radiators 336 and 338 of this embodiment are preferably of the type discussed in detail in the parent application.

To scour the surfaces of the drying web in order to remove evolved moisture and other volatiles from adjacent these surfaces, high velocity streams of air moving parallel to the direction of travel of the drying product are preferably employed. As shown in FIGURE 2, drying units, each including two plenums 340 and 342 spaced lengthwise of the web and extending transversely thereacross are employed above and below the web on each of the first five runs 304g-304c. As shown in FIG- URE 1, air units are employed at the left-hand and righthand end portions of drying apparatus 300 on each of these five runs. On the first or initial run 304g, additional units are employed in the center of apparatus 300 so that the surface of the drying product is scoured by high velocity gas substantially throughout run 304g.

The high velocity scouring gas is preferably air and may be supplied in the manner described in the parent application. The heated drying air may be delivered, for example, to plenum 340. From plenum 340' the drying air passes through a nozzle 344 spanning the Width of the product web. The air emerging from nozzle 344 is travelling in a direction generally parallel to the movement of the web, as shown by the arrows 346 in FIG- URE 2. The drying air, together with its burdens of evolved moisture and other volatiles, flows from adjacent the drying product into plenum 342. The air circulator exhausts the spent air from plenum 342, discharging it to the ambient atmosphere or recirculating portions of it to increase the humidity of the air delivered to plenum 340.

It is not necessary that the air flow in the same direction as the web is moving. Indeed, for some applications, countercurrent flow of the air may be preferable. In this case the air is delivered through plenum 342 and exhausted from plenum 340 in the manner described above.

The product to be dried in drying apparatus 300 may be formed in any desired manner such as by Fourdrinier or British Inverform equipment or by cylinder type forming equipment or in any other desired manner. The Wet product 348 thus formed, depending upon its characteristics, may be first passed through a preliminary dryer as described in the parent application or may be conveyed directly to drying apparatus 300. As it reaches drying apparatus 300, web 348 is delivered onto the felt 308 moving over roller 316. Felt 308 supports web 348 as it moves through run 304g where it is dried by radiators 336 and 338 which evolve moisture and/ or other solvents from web 348; and by the high velocity air moving parallel to the direction of movement which carry the evolved moisture and/or other volatiles from adjacent the surface of web 348, preventing the formation of a stagnant layer of volatiles adjacent the web surfaces and thereby insuring maximum drying efliciency. At the right-hand end of drying apparatus 300, the now partially dried web 348 passes around direction changing roll 306a onto felt 318 which is moving from right to left and which supports web 348 as it moves back to ward the left-hand end of drying apparatus 300 in run 304 Typically, by the time web 348 has passed through the second run 304 it will have sufficient tensile strength to be supported by support rolls 302 without use of a felt. However, as indicated above, if deemed necessary, felts may also be employed in conjunction with each of the succeeding runs 340e-a.

In any event, after reaching the left-hand end of drying apparatus 300 in run 3041, web 348 passes around direction changing roll 306b and then moves alternately toward the right and toward the left through succeeding runs until, finally, it reaches the right-hand end of drying apparatus 300 in run 304a and is taken out of the drying machine around direction changing roll 3060 for further treatment.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics therefor. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. In multiple run drying apparatus for continuous, moving webs of paper and like products, comprising:

(a) support rolls arranged in superimposed, spaced apart, substantially horizontal rows to form a multiplicity of web drying runs;

(b) a product supporting felt trained over the support rolls in at least the initial one of said runs; and

(c) radiant heating means for each of said runs; the

improvements wherein (d) the radiant heating means comprises radiators both above and below the path of the web through each of said runs for simultaneously heating both sides of said web;

(e) said felts being made substantially entirely of an open mesh synthetic material.

2. The multiple run drying apparatus as defined in claim 1, wherein the mesh openings of said felt constitute about 30%50% of the area of said felt.

3. The multiple run drying apparatus as defined in claim 1, wherein said material is at least partially transparent to radiant energy having a wave length in the range of 3.5 to 5.0 microns.

4. The multiple run drying apparatus as defined in clalm 1, together with means for forcing: air parallel to the direction of movement of the web being dried and against the upper and lower surfaces thereof to scour from adjacent the surface of said web volatiles evolved therefrom by said radiant heating means.

References Cited by the Examiner UNITED STATES PATENTS 1,432,729 10/1922 Pinder 34-60 2,454,370 11/1948 Beaubien 34-60 X 3,084,448 5/196'3 Dungler 34-155 FREDERICK L. MATTESON, JR., Primary Examiner.

JOHN J. CAMBY, Assistant Examiner.

Claims (1)

1. IN MULTIPLE RUN DRYING APPARATUS FOR CONTINUOUS, MOVING WEBS OF PAPER AND LIKE PRODUCTS, COMPRISING: (A) SUPPORT ROLLS ARRANGED IN SUPERIMPOSED, SPACED APART, SUBSTANTIALLY HORIZONTAL ROWS TO FORM A MULTIPLICITY OF WEB DRYING RUNS; (B) A PRODUCT SUPPORTING FELT TRAINED OVER THE SUPPORT ROLLS IN AT LEAST THE INITIAL ONE OF SAID RUNS; AND (C) RADIANT HEATING MEANS FOR EACH OF SAID RUNS; THE IMPROVEMENTS WHEREIN (D) THE RADIANT HEATING MEANS COMPRISES RADIATORS BOTH ABOVE AND BELOW THE PATH OF THE WEB THROUGH EACH OF SAID RUNS FOR SIMULTANEOUSLY HEATING BOTH SIDES OF SAID WEB; (E) SAID FELTS BEING MADE SUBSTANTIALLY ENTIRELY OF AN OPEN MESH SYNTHETIC MATERIAL.

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