US3248798A

US3248798A - Process and apparatus for continuous drying of continuous web materials

Info

Publication number: US3248798A
Application number: US214757A
Authority: US
Inventors: Bernard W Burgess
Original assignee: Pulp Paper Res Inst
Current assignee: Pulp and Paper Research Institute of Canada
Priority date: 1962-08-03
Filing date: 1962-08-03
Publication date: 1966-05-03
Anticipated expiration: 1983-05-03
Also published as: GB994951A; SE302719B

Description

May 3, 1966 B. w. BURGESS 3,248,798

PROCESS AND APPARATUS FOR CONTINUOUS DRYING OF CONTINUOUS WEB MATERIALS Filed Aug. 5, 1962 4 Sheets-Sheet 1 5 42 I 00 J T 0W on\ m 1 0mm O 0 1 1/ lo;

FIG.

May 3, 1966 B. w. BURGESS 3,248,793

PROCESS AND APPARATUS FOR CONTINUOUS DRYING 0F CONTINUOUS WEB MATERIALS Filed Aug. 5, 1962 4 Sheets-Sheet 2 FIG. 3

law 8277 l/Mgwffess M /%W%M Wm May 3, 1966 B. w. BURGESS 3,248,798

PROCESS AND APPARATUS FOR CONTINUOUS DRYING 0F CONTINUOUS WEB MATERIALS Filed Aug. 5, 1962 4 Sheets-Sheet 5 @Hvmrd W gum e $7 1% fi- 277%V%ld124,

May 3, 1966 B. w. BURGESS 3,248,798

PROCESS AND APPARATUS FOR CONTINUOUS DRYING OF CONTINUOUS WEB MATERIALS 4 Sheets-Sheet 4 Filed Aug. 5, 1962 III- fielv7ard 45 m,

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United States Patent Cfifice Patented May 3, 1966 3,248,798 PROCESS AND APPARATUS FOR CONTINUOUS DRYING F CONTINUOUS WEB MATERIALS Bernard W. Burgess, Senneville, Quebec, Canada, assignor to Pulp & Paper Research Institute of Canada, Montreal, Quebec, Canada Filed Aug. 3, 1962, Ser. No. 214,757 16 Claims. (Cl. 349) This invention relates to a continuous process and apparatus for the drying of continuous web materials. More particularly it is directed to a process and apparatus for the drying of webs of paper and paperboard.

According to the method most commonly followed up to the present time for'drying paper and paperboard, the wet web is passed around a series of internally-heated cylinders (known as dryers) with the web in contact with a segment of each dryer and usually held against it by a dryer felt that is under tension. One of the chief disadvantages of this method is the multiplicity of dryers required to accomplish the drying operation to a satisfactory degree and this necessitates costly capital equipment, at great deal of space, and continuing maintenance. A further disadvantage is that this method requires the use of large quantities of heated scavenger air to promote the removal of the evaporated moisture. It is not uncommon to use between 20 and 70 tons of such air per ton of product dried and this involves an expenditureof energy to heat the scavenger air and to move it through the dryers. Furthermore it is essential that as much heat as possible be recovered from this air by the installation of expensive hoods and heat recovery equipment. Even the use of such large quantities of heated air does not satisfactorily remove the evaporated moisture from the pockets defined by the moving web, the dryers and the dryer felts. High humidity conditions exist in these pockets, thus impeding the drying process as well as causing uneven drying. Another difliculty with this conventional method is the problem of establishing a sufliciently high heat transfer rate between the dryers and the sheet because of the poor heat conduction from said dryers to the web resulting from the generation and accumulation of steam between the web and the dryer surface, this accumulation tending to lift the web ofl? the dryers. These difliculties not only adversely influence the drying capacity of dryers and thereby necessitate a multiplicity of dryers, but also give rise to uneven drying of the web.

Another method sometimes used for drying paper is the Minton Dryer in which the web passes over a series of internally-heated cylinders that are placed inside a vacuum chamber. This has the advantage that the moisture evaporated from the web is removed continuously by the vacuum system. The method has the disadvantage that it does not ensure intimate contact of the web with the drying cylinder and therefore does not provide satisfactory heat transfer. In addition, the Minton Dryer has a number of operating difficulties, the chief of which stems from the necessity of breaking the vacuum seal when a break in the web being dried occurs.

In another method for drying web materials, the webis passed through a heated fluidized bed. This method has the advantage that it utilizes the characteristic high heat transfer rates of a fluidized bed. However, it is unsatisfactory for drying relatively weak webs because such webs are subject to breakdowns which result in stoppage of the drying operation and if, in order to overcome this web breakage problem, screens or other supporting means are used, heat transfer in interfered with. Furthermore, if the web is not transported through the bed in contact with a supporting medium, it is not subjected to any restraint as is necessary in many cases to avoid undesirable dimensional changes.

While the present invention is not to be limited to any particular theory, it is believed that in the drying of materials, two major processes take place, namely: transfer of heat to the substance being dried (i.e. heat transfer) and transport of the evaporated vapours away from the substance (i.e. mass transfer). The temperature difference between the heating medium and the material being dried provides the driving force for the heat transfer process. The vapour pressure gradient between the evaporating surface and the ambient atmosphere provides the driving force for the mass transfer process. It is preferable to provide a high temperature difference combined with a high vapour pressure difference so as to obtain high rates of drying. Also, it is preferable to reduce the thickness of the boundary layers between the material and the heating medium and between the material and the ambient atmosphere in order to increase the rates of heat and mass transfer and there-fore the rate of drying.

By one aspect of this invention there is now provided an apparatus for the continuous drying of a continuous wet web, said apparatus comprising: a chamber; a heated fluidized bed adapted to be present within said chamber; and pervious means associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed; said pervious means including an inner surface communicating with an outer surface, means for subjecting at least a portion of said inner surface to sub-atmospheric pressure and thus subjecting the connected outer surface which communicates with said portion of saidinner surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct contact with the entire said connected outer surface, at least a part of said portion of said web being submerged in said fluidized bed. In operation, then, consecutive portions of the web are dried by substantially simultaneous contact, on one side of the web, by the sub-atmospheric pressure, and, on the other side, by the heat of the heated fluidized bed. In more specific terms, by this aspect of the present invention, there may be provided an apparatus for the continuous drying of a continuously moving wet web, said apparatus comprising a chamber; a heated fluidized bed within said chamber; and a pervious surface, for example a moving surface, such as a loop of a moving endless belt on two or more rotatable hollow rollers, or a single, rotatable hollow roller, or a stationary surface, such as a hemicylindrical hollow tube, all, or a portion of, which is submerged in the bed is subjected to the sub-atmospheric pressure, said pervious means including an inner surface communicating with an outer surface, means for subjecting at least a portion of said inner surface to sub-atmospheric pressure and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct contact with the entire said connected outer surface, at least a part of said portion of said web being submerged in said fluidized bed. The web being dried is thus transported through a portion of the fluidized bed while it is supported on at least a portion of the pervious surface and, while it is so transported, is exposed on one side directly to the heated fluidized bed and, substantially simultaneously on the other side is subjected to a sub-atmospheric pressure acting through the pervious surface throughout a portion or all of the period during which the web is submerged in the fluidized bed. By another aspect of this invention, there is provided a continuous process for drying a continuous web, said process comprising: continuously conveying said web so as to support said web while it passes through said bed and to expose one side thereof directly to a heated fluidized bed and so as to expose the other side of said web to a sub-atmospheric pressure acting through at least a portion of a supporting pervious surface, the web being supported on the sub-atmospheric pressure side by at least a portion of said pervious surface, the said sub-atmospheric pressure being maintained within the said hollow pervious member by having the portion of the pervious surface which is under sub-atmospheric pressure completely covered by said web, such pervious surface being a moving surface, such as a loop of a moving endless belt on two or more rotatable hollow rolls, or a rotatable hollow roller, whereby the web is in non-sliding friction contact therewith.

By yet another aspect of this invention, a fixed, nonmoving pervious surface that is entirely or partially submerged in the heated fluidized bed, such as a hollow hemi cylindrical tube whose rounded segment is wholly or par-' tially within the heated fluidized bed, is substituted for the moving pervious surface described above, the continuous web being dried being passed through a portion of the fluidized bed such that said web passes in sliding frictional contact over at least a portion of the supporting pervious surface and there being subjected on the one side in contact with the pervious surface to sub-atmospheric pressures acting through at least a portion of a supporting pervious surface, the said sub-atmospheric pressure being maintained within the said hollow pervious member by having the portion of the pervious surface which is under sub-atmospheric pressure completely covered by said web, at least a part of that portion of said web being substantially simultaneously subjected on the other side to direct contact with the fluidized bed. This aspect of the invention would normally be restricted to relatively strong webs and to sub-atmospheric pressures that are close to atmospheric pressures.

By another aspect of this invention, there is provided a process for drying a web, said process comprising: continuously feeding said web through a portion of a heated fluidized bed in such a manner as to support said web while it passes through said bed and to subject one side of said web to sub-atmospheric pressures during at least a portion of the time during which it is submerged in.

the bed, at least a portion of the other side of the web immediately opposite thereto being at substantially the same time in direct contact with said heated fluidized bed.

One advantage of the present invention is that the web is subjected to the conditions of high heat transfer characteristic of fluidized beds while at the same time is sub jected to conditions of high mass transfer through the simultaneous application to the heated web of the subatmospheric pressures. Because of the suppression of the boiling point of the liquid to be evaporated resulting from the use of sub-atmospheric pressures, a still higher temperature difference is obtained between the fluidized bed andthe web than when atmospheric pressures are used. This tends to increase the rate of heat transfer to the web still further.

It is a further advantage of this invention that the thicknesses of the boundary layers are substantially reduced and thereby the resistance to heat transfer to, and mass transfer from, the web of such boundary layers is decreased. This boundary layer reduction is accomplished by the turbulent action of the fluidized bed on one side of the web being dried and the action of the sub-atmospheric pressure on the other side of the web. This reduction in boundary layer thickness is promoted also for pervious webs by the passage of drying vapours from the fluidized bed (i.e. the fluidizing gas) through the sheet under the influence of the sub-atmospheric pressure. This passage of vapours has a further advantage in that it aids evaporation by helping to carry the heat into and the evaporated moisture out of, the interstices of the web.

It is a further advantage of this invention that the use of large quantities of heated scavenger air characteristic of conventional cylinder drying machines is avoided and thereby the installation of costly dryer ventilating systems and the expenditure of energy necessary to move and heat the scavenger air are also avoided.

An additional advantage of the present invention is the fact that the web may be firmly supported while it is being dried. This results, not only in the avoidance of undesirable dimensional changes, but also in the minimizing of breakage of any relatively weak material.

When superheated steam is used as the fluidizing gas and when the material to be evaporated is water, the vapour drawn through the foraminous surface by the subatmospheric pressure is primarily water vapour, virtually uncontaminated by air. It is therefore another feature of this invention that the latent heat of the evaporated moisture and the latent heat of the fluidizing gas that is drawn through the web and the foraminous surface may be recovered to a large extent.

The use of high fluidized bed temperatures does not decrease the contact between the heating medium and the web and thereby decrease heat transfer (as is the case with the conventional cylinder dryers and the Minton Dryer when high dryer temperatures are used), but rather increases the heat transfer rate from the fluidized bed to the web. The temperature at which the fluidized bed may be operated is limited only by the characteristics of the material being dried and/ or of the vapour being evaporated and/or of the fluidized particles and may be up to 500 F. or higher. Another feature of this invention therefore is that temperatures in excess of those commonly used for drying web materials on conventional cylinder dryers or'Minton Dryers may be used to advantage to the limit that such elevated temperatures are not injurious to the web, to the fluidized particles or to the vapour being evaporated.

Another feature of this invention is that dryer felts are not required to ensure intimate contact between the drying medium and the web, thus saving the cost of the felts.

Another advantage of this invention is that means are provided for more uniform drying of the web than is possible with conventional cylinder dryers. This is possible because the fluidized bed is a highly mobile heat source with a high thermal conductivity and with, when fluidized particles with high heat capacity are used, a high heat capacity. Furthermore, the absence of pockets containing air of high humidity as found in conventional cylinder dryingmachines facilitates uniform drying In most cases it would be desirable to cover the fluidized bed chamber so that a substantial portion of the fluidizing gas not drawn through the web may be recovered, passed through heaters if necessary, and then re-introduced into the bottom of the chamber as a portion of the heated fluidizing gas, or may be used for other purposes. When the fluidized bed is so covered the web can be passed into and out of the bed through narrow slits or through the nips of pairs of rollers or through other suitable means.

The material being fluidized may be any particles capable of being fluidized which is non-reactive with the web being dried and with the fluidizing gas. If the web is porous the particles should be of a size greater than the pore size of the web being dried. Practically speaking, the particles may be of a size of about 400 to 1000p. Examples of suitable particles include sand, glass beads, silica gel and the like. Also, magnetic or magnetizable particles, such as iron particles or steel shot may be used. Such particles are advantageously used if it is found that the fluidized particles adhere to the wet web. If such be the case, they may be removed by conventional means, as by an electromagnet.

The hot gas used to fluidize the bed must be clean, but otherwise may be any suitable gas which is stable at the temperatures used and which is non-reactive with the material being fluidized, the liquid being evaporated and the web being dried. Examples of such gases include hot air, hot flue gases and superheated steam.

The web being dried may be any wet web, for example, paper, paperboard, textiles, fiberglass, regenerated cellulose film, etc. In addition, it is not essential for the web to be wet with water; webs wet with other liquids, e.g., organic solvents may also be dried by the present invention.

In drawings which illustrate embodiments of the present invention:

FIG. 1 is a diagrammatic vertical cross-sectional view of an apparatus according to this invention,

FIG. 2 is a partial view of a modification of the apparatus shown in FIG. 1,

. FIG. 3 is a diagrammatic vertical cross-sectional view of another apparatus according to this invention,

FIG. 4 is a partial diagrammatic cross-sectional View of yet another apparatus according to this invention,

FIG. 5 is a perspective view of a portion of the apparatus shown in FIG. 4,

FIG. 6 is a vertical cross-section of a portion of the apparatus shown in FIG. 4, and

FIG. 7 is a diagrammatic partial view of yet another apparatus according to the present invention.

Turning to FIG. 1, the apparatus 10 comprises a generally rectangularparallelepiped 11, divided into an upper compartment 12 and a lower plenum chamber 13 by a plate 14 provided with a plurality of perforations 15. However, plate 14 may be foraminous rather than perforated. The compartment 12 is adapted to be heated, as shown, by internal heat exchanger tubes 16 and by external heat exchanger tubes 17. However, either the internal or the external heat exchanger tubes, or in fact any other suitable means known to those skilled in the art, may be used for the heating. The upper compartment 12 is adapted to contain fluidiza'ble particles 13 which are fluidized by the passage of fluidizing gas from plenum chamber 13 through perforation in plate 14. The gases emerging from the bed are returned by blower 23 and lines 19, which are jacketed by heat exchangers 20, to the inlet conduit 25 which is heated by heat exchangers 22. Make-up heated fluidizing gas enters through inlet conduit 25, mixes with recirculating fluidizing gas and is passed to the plenum chamber 13, through outlet 26. A cover 27 assists in the recirculation of the fiuidizing gases.

Within the upper compartment 12 is a roller 28 rotatable counterclockwise provided with apertures 29, the size and number and distribution of the apertures being selected according to principles known to those skilled in this art. While the roller is shown as having a perforated shell, it may also have a forminous shell. The perforated roller is designed so that the perforations do not extend completely to the outside edges thereof, i.e., it is provided with a pair of unperforated rings, whose purpose and function will be explained hereinafter. The roller 28 is rotatably mounted on hollow shaft 30. Shaft 30 is connected to a source of sub-atmospheric pressure (not shown) so that the interior of hollow roller 28 is maintained under such sub-atmospheric pressure by means of apertures 31 in shaft 30. However, a segment 32 of the interior of roller 28 is maintained at atmospheric pressure for it is separated from the remainder of the interior by means of fork 33. Pressure seals 34 extend from the ends of the fork 33 to the walls of the roller 28 and along the segment of the circular end walls of the cylindrical roller 28 contained by fork 33.

The apparatus also includes a primary guide roller 35 rotatable clockwise on shaft 36, secondary guide roller 37 rotatable clockwise on shaft 38 and tertiary guide roller 39 rotatable counterclockwise on shaft 40. A sealing strip and doctor 41 extends from cover 27 in association with primary guide roller 35, while a sealing strip and doctor 42 extends from cover 27 in association with secondary guide roller 37. Roller 37 is a hollow perforated roller' provided with an interior portion 37a subjected to subatmospheric pressure by means of a perforated central drum 37b connected to a source of sub-atmospheric pressure. A seal 37c assures that the sub-atmospheric pressure extends only to that part of roller 37 which contacts the web 46. A doctor with trough 43 is provided in association with tertiary guide roller 39 for the purpose of carrying away liquid and other material doctored off roller 39. In addition a nozzle 44 is provided to keep the dead space 45 under sufficient positive pressure so as to exclude any fluidizable particles 18 or other foreign matter. It is connected to a source of positive pressure and to a support (not shown).

In order to illustrate the means for placing the process into operation reference is made to FIG. 1. A narrow strip or tail of the continuous web, not shown, is fed around the primary guide roller 35 and then the rotating foraminous roll 28 and then around the secondary guide roller 37 by guide or back-tender ropes according to the method in common use for threading the web through a conventional paper drying machine. Once the tail has been fed around the roll 28 and secondary guide roller 37, the width of the tail is increased until it equals the full width of the web 46. The full width of the web 46 is less than the width of the roller 28 but greater than the width of the perforated areaof roller 28. Thus, the side edges of the web 46 rest on the unperforated edge rings of the roller 28, thus helping to maintain the interior of the roller under sub-atmospheric pressure. The sub-atmospheric pressure would normally be applied to the inside of the foraminous roll 28 at this time, but could be applied earlier if, for example, there was a tendency for the web to drop away from the roll. It is important that the height of the quiescent fluidiz'able particles 18 be below the bottom of the roller 28, to enable the web 46 to be placed around the roller 28. The fluidizing gas is then passed through plate 14 and through preferably preheated quiescent particles 18 in the upper compartment 12 so as to create fluidized bed conditions. Other methods, such as would be obvious to a person experienced in the handling of web materials, may be used equally as well.

FIG. 2 shows a modification of the apparatus of FIG. 1 when the material being fluidized is of a magnetizable type, such as steel shot. In such case, a magnetic roller 47 rotatable in a clockwise direction on shaft 48 is mounted near foraminous roll 28. A doctor 49 is used in conjunction with roller 47. In operation, if any of the steel shot which is the material in the fluidized bed adheres to the web 46, such steel shot is attracted to the roller 47 and is doctored off by doctor 49 and returned to the fluidized bed.

FIG. 3 shows another embodiment of the apparatus according to the present invention. The vessel 10 together with its heating means and fiuidizing gas recirculation means are the same in the embodiment as in the embodiment of FIGS. 1 and 2 and so the same reference numerals have been used. However, the means for bringing the wet web into contact with the fluidized bed is different.

Such means comprise an upper roller 50, lower roller 51 and box 52 divided into two vertical boxes 52a and 52b. Upper roller 50 is shown as a solid roller rotatable in a counterclockwise direction on a shaft 53 and lower roller 51 is shown as a solid roller rotatable in a counterclockwise direction on a shaft 54. Passing around rollers 50 and 51 is a continuous belt 61 which is either perforated o-r foraminous. Box 52 is composed of two sides 55, each of which is provided with a plurality of perforations 56, a solid top section 57, and a solid bottom section 58 and solid ends (not shown). Within box 52 is a tube 59 connected to a source of sub-atmospheric pressure (not shown) and provided with a plurality of apertures 60 leading to the interior of box 52. In this way the interior of box 52 is maintained under sub-atmospheric pressure.

In this embodiment, there is provided primary guide roller 35, rotatable in a clockwise direction on shaft 36, and secondary guide roller 37 rotatable in a clockwise direction on shaft 38. The web being dried is referred to as 46. In operation, the web 46 passes around one side of primary guide roller 35, and is nipped at its point of contact with belt 61 on upper roller 50 and passes downwardly in contact with the belt 6-1 which is touching one side 55 of box 52, where the web is subjected to the influence of. the sub-atmospheric pressure acting from within box 52. Then the web is guided by belt 61 around lower roller 51 and then upwardly in contact with belt 61 which is touching the other side 55, where the web is again subjected to the influence of sub-atmospheric pressure. Then the web is led by belt 61 to the upper roller 51. Then the web is nipped by secondary guide roller 37 and is then led away. If desired, although not shown, roll 37 may be a hollow foraminous roll provided with an internal structure to maintaina portion of its interior under sub-atmospheric pressure. The web 46 would then be subjected to sub-atmospheric pressure at the nip where it is nipped between the roll 37 and the belt 61 and for a short distance thereafter. This would aid in transferring the web 46 from the belt 61 to the roll 37.

In this way the web being dried is subjected to the influence of a heated fluidized bed on one side of the web while it is simultaneously subjected to the influence of sub-atmospheric pressure on the other side of the web.

Under some conditions, it may be desirable to subject the web to different degrees of sub-atmospheric pressure during its travel on belt 61. This may be accomplished by subjecting chamber 52a to a different sub-atmospheric pressure than chamber 52!).

FIGS. 4, and 6 also show a variation in the manner of contacting the moving web with the fluidized bed. The actual configuration of the fluidized bed is not shown in FIGS. 4, 5 and 6 but generally it would conform to that shown in FIGS. 1 and 3.

The basic difference in the embodiment of FIGS. 4, 5 and 6 is the fact that a belt 70, which may be either perforated or foraminous, is interposed between a portion of the source of sub-atmospheric pressure and the web being dried.

The embodiment in FIGS. 4, 5 and 6 shows a box 62 with a conduit 63 leading to a source of sub-atmospheric pressure (not shown). Running around box 62 by means of first drive roller 64 rotatable counterclockwise on drive shaft 65, second drive roller '66 rotatable counterclockwise on drive shaft 67 and third drive roller 68 rotatable counterclockwise on drive shaft 69, is belt 70. The web 46 being dried is adapted to be led in contact with the heated fluidized bed 18 and with the sub-atmospheric pressure within box 62 through the intermediary of the belt 70.

FIGS. 5 and 6 show the structure of the box 62. Thus, the box consists of side Walls 71, top 72 and four belt supporting rollers 73, each rotatable counterclockwise 'on shafts 7 4. As shown in FIG. 6, side walls 71 are provided with conduits 75. Through these conduits, a gas under pressure is passed so that fluidized particles from the bed 18 will tend not to enter between box 62. and track 70, and to keep particles away from the inner side of the belt 70 in its travel between box 62 and roller 65.

As shown in FIG. 5, only one of the four belt supporting rollers 73 is seen, for the sake of clarity. In addition, the belt 76 is provided with an impervious sealing edge 76 at each side edge thereof, to seal the ends of box 62 so as to retain the sub-atmospheric pressure therein.

In operation, the same basic principles apply as in the use of the embodiment of FIGS. 1-3.

FIG. 7 shows a portion of a modified vessel according to another embodiment of this invention. Only the means for bringing the wet Web into contact with the fluidized bed are shown, the other parts of the apparatus being the same as shown for the embodiment in FIG. 1.

chamber '77 adapted to be brought to sub-atmospheric pressure and provided with a semi-cylindrical bottom 78 and a solid flat top 80. The bottom 78 may be either perforated, in which case it is provided with a plurality of apertures 79, or it may be foraminous. Within the chamber 77 is a tube 81 connected to a source of subatmospheric pressure (not shown). Connection between the source of sub-atmospheric pressure and the interior of chamber 77 is by means of apertures 82 in tube 31.

In operation, the wet web 46 is passed in-sliding contact with, and supported by, the semi-cylindrical surface 78. Because such surface is either perforated or foraminous, the web is subjected, on one side, to the influence of the sub-atmospheric pressure acting from within chamber '77 and simultaneously on the other side is subjected to the influence of the heated fluidized bed 18.

It will be observed that the process of this invention and the apparatus specially adapted to carry out such process have been described with reference to a single perforated supporting means and a single fluidized bed, other variations may be made without departing from the scope of this invention. Thus, the continuous wet web may be passed in supported contact with a series of consecutive foraminous supporting means in a single fluidized bed. Alternatively, the continuous wet web may be passed consecutively through a series of units, each containing but one foraminous supporting means. In addition, the wet web may be passed consecutively through a series of units,

each provided with a series of consecutive foraminous supporting means.

I claim:

ll. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed adapted to be set up within said chamber, and pervious means associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed; said pervious means including an inner surface communicating with an outer surface, and means for subjecting at least a portion of said inner surface to sub-atmospheric pressure thus drawing gases through said 'web to said inner surface through the communication between said outer surface and said inner surface and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed and maintained in contact with said pervious means. i

2. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed within said chamber, and a rotatable hollow foraminous roller associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed; said roller including an inner surface communicating with an out-er surface, and means for subjecting at least a portion of said inner surface to sub-atmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a portion of the length of the Web being adapted to be conveyed through said heated fluidized bed in direct non-sliding contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed and maintained in contact with said foraminous roller.

3. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed of magnetizable material within said chamher, a rotatable, hollow, foraminous roller associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed, and means operable to attract said magnetizable material, said means being situated adjacent said roller; said roller including an inner surface communicating with an outer surface, and means for subjecting at least a portion of said inner surface to sub-atmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct nonsliding contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed; and whereby any magnetizable, fiuidizable material which has adhered to said wet web may be attracted to said means, and then may be returned to said fluidized bed and maintained in contact with said foraminous roller.

4. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed within said chamber, and movable foraminous means associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed; said foraminous means including a pair of rollers, a foraminous belt running around said rollers and a chamber situated between said rollers and surrounded by said foraminous belt, said chamber including at least a pair of mutually opposed walls, each wall being provided with an inner surface communicating with an outer surface, and means for subjecting at least a portion of said inner surface to sub-atmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface, and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure, and simultaneously subjecting the portion of said belt running around the said connected outer surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct non-sliding contact with the entire said portion of said belt running around the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed and maintained in contact with said movable foraminous means,

5. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed within said chamber, and movable foraminous means associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed, said foraminous means comprising at least one roller, a zone subjected to sub-atmospheric pressure, and a pervious belt adapted to run in supported contact with said roller and to pass said zone, said belt including an inner surface communicating with an outer surface, so that on passage of said belt adjacent said zone at least a portion of said inner surface is subjected to subatmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface and thus the connected outer surface which communicates with said portion of said inner surface is also subjected to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct non-sliding contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged' in said fluidized bed and maintained in contact with said movable foraminous means.

6. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: a chamber, a heated fluidized bed within said chamber, and fixed foraminous means associated with said bed for supporting said web while a portion of said web is in contact with said heated fluidized bed; said foraminous means comprising a semicylindrical hollow chamber, at least a portion of the curved wall .of said chamber including an inner surface communicating with an outer surface, and means for subjecting at least a portion of said inner surface to subatmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface and. thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a portion of the length of the web being adapted to be conveyed through said heated fluidized bed in direct sliding frictional contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed and maintained in contact with said fixed foraminous means.

7. Apparatus for the continuous drying of continuous wet webs, said apparatus comprising: an enclosed cham her, a heated fluidized bed within said chamber; a primary guide roller, rotatable clockwise, associated with said chamber; a hollow foraminous cylinder rotatable counterclockwise associated with said chamber for supporting said web while a portion of said web is in contact with said heated fluidized bed; said cylinder including an inner surface communicating with an outer surface, and means for subjecting at least a portion of said inner surface to sub-atmospheric pressure thus drawing gases through said web to said inner surface through the communication between said outer surface and said inner surface and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; a secondary guide roller rotatable clockwise, associated with said chamber; and a tertiary guide roller rotatable counterclockwise, associated with said chamber; said web being adapted to be conveyed through said heated fluidized bed by first being nipped between said tertiary guide roller and said primary guide roller, then being nipped between said primary guide roller and said cylinder, then being nipped between said cylinder and said secondary guide roller and finally being nipped between said secondary guide roller and said tertiary guide roller, said web thus being in direct non-sliding contact with the entire said connected outer surface, at least a part of said portion of said web being maintained submerged in said fluidized bed and maintained in contact with said hollow foraminous cylinder.

8. The apparatus of claim 7 wherein there is also included a magnetic roller adjacent said cylinder and said secondary roller, adapted to attract any magnetizable fiuidizable material adhering to said web as said web passes through a bed of said magnetizable fiuidizable material;

9. The apparatus of claim 7 wherein said secondary guide roller is also provided with an inner surface communicating with an outer surface; and means for subjecting at least a portion of said inner surface to subatmospheric pressure and thus subjecting the connected outer surface which communicates with said portion of said inner surface to the same said sub-atmospheric pressure; whereby said web is urged away from said cylinder and attracted to said secondary roller adjacent the nip between said cylinder and said secondary guide roller.

10. A continuous process for drying a continuous web, said process comprising: continuously feeding said web through a portion of a heated fluidized bed supporting said web while it passes through said bed and continuously subjecting one side of said web to sub-atmospheric pressures during at least a portion of the time during which it is submerged in the bed.

11. A continuous process for drying a continuous web, said process comprising: continuously conveying said web through a portion of a heated fluidized bed supporting said web while it passes through said bed, continuously exposing one side thereof directly to said heated fluidized bed and continuously subjecting the other side of said web to a sub-atmospheric pressure acting through at least a portion of a supporting pervious surface so that the web is supported on the sub-atmospheric pressure side by at least a portion of said pervious surface, maintaining said sub-atmospheric pressure within the said pervious surface by having the portion of the pervious surface which is under sub-atmospheric pressure completely covered by said web, and maintaining at least a portion of the other side of the Web immediately opposite thereto at substan tially the same time in direct contact with said heated fluidized bed.

12. A continuous process for drying a continuous web, said process comprising: continuously conveying said web so as to support said web while it passes through said bed and to expose one side thereof directly to a heated fluidized bed and continuously subjecting the other side of saidweb to a sub-atmospheric pressure, acting through at least a portion of a moving supporting foraminous surface, the Web being supported on the sub-atmospheric pressure side by at least a portion of said forarninc-us surface, maintaining said sub-atmospheric pressure within the said foraminous surface by having the portion of the foraminous surface which is under sub-atmospheric pressure completely covered by said web, at least a portion of the other side ofthe web immediately opposite thereto being at substantially the same time in direct con tact with said heated fluidized bed whereby the web is conveyed through said heated fluidized bed in direct nonsliding contact with a portion of the outer surface of said foraminous surface,

13. A continuous process for drying a continuous web, said process comprising: continuously conveying said web through a portion of a heated fluidized bed so as to support said web while it passes through said bed and to expose one side thereof directly to said heated fluidized bed and continuously subjecting the other side of said web to a sub-atmospheric pressure, acting through at least a portion of a fixed supporting forarninous surface, the web being supported on the sub-atmospheric pressure side by at least a portion of said foraminous surface, maintaining the said sub-atmospheric pressure within the said foraminous surface by having the portion of the forarninous surface which is under sub-atmospheric pressure completely covered by said web, at least a portion of the other side of the web immediately opposite thereto being at substantially the same time in direct contact with said heated fluidized bed whereby the web is conveyed through said heated fluidized bed in direct sliding contact with a portion of the outer surface of said foraminous surface.

14. The process of claim 12 wherein the fluidized bed comprises magnetizable particles.

15. The process of claim 12 wherein the fluidized bed is fluidized by the passage therethrough of superheated steam.

16. The process of claim 12 wherein the wet web is a paper sheet.

References Cited by the Examiner UNITED STATES PATENTS 2,785,478 3/1957 Audas.

2,879,607 3/1959 Fleissner 341 14 2,896,336 7/1959 Shoumatoif 34-86 2,938,276 5/1960 Doleman 34-95 2,981,631 4/1961 Nagel.

FOREIGN PATENTS 338,547 11/1930 Great Britain.

817,992 8/1959 Great Britain.

885,226 12/1961 Great Britain.

JOHN J. CAMBY, Acting Primary Examiner.

Claims

10. A CONTINUOUS PROCESS FOR DRYING A CONTINUOUS WEB, SAID PROCESS COMPRISING: CONTINUOUSLY FEEDING SAID WEB THROUGH A PORTION OF A HEATED FLUIDIZED BED SUPPORTING SAID WEB WHILE IT PASSES THROUGH SAID BED AND CONTINUOUSLY SUBJECTING ONE SIDE OF SAID WEB TO SUB-ATOMSPHERIC PRESSURES DURING AT LEAST A PORTION OF THE TIME DURING WHICH IT IS SUBMERGED IN THE BED.