US3056213A - Heated fluid drier for a papermaking machine - Google Patents

Description

Oct. 2, 1962 H. B. KELLOGG HEATED FLUID DRIER FOR A PAPERMAKING MACHINE 2 Sheets-Sheet 1 Filed July 31, 1958 HEATED FLUID DRIER FOR A PAPERNAKING MACHINE Filed July 31, 1958 Oct. 2, 1962 H. B. KELLOGG' 2 Sheets-Sheet 2 MT I I I I I I l I I I I LW l. I) m w a 8 m llllllllllll lime W w 3 s a f. a W H M C E 1 1 1 I 1 I l iM H A W 0 n 0 w 6 Q T/ME, 9 ($565.)

United States Patent 3,056,213 HEATED FLUID DRIER FOR A PAPERMAKING MACHINE Harry B. Kellogg, Appleton, Wis., assignor to Kimberly- Clark Corporation, Neenah, Wis., a corporation of Delaware Filed July 31, 1958, Ser. No. 752,219 8 Claims. (Cl. 3423) This invention relates to the continuous drying of thin sheets of material, particularly such as paper, by application to the surface of a heated, revolving drum. In a particular and preferred application, the invention comprises a method and apparatus for facilitating the removal of water from a wet paper sheet at the time of its application to a revolving, heated drying drum, thus lightening the drying load imposed upon the drum. In consequence, through the use of the invention the operational speed of the drying drum may be increased. Since the capacity for drying is commonly the limiting factor upon speed of operation of a papermaking machine as a whole, employment of the present invention permits an increased speed of operation of the papermaking machine.

Details of the objects and advantages of the invention will become apparent in the following explanation and description of the attached drawings, in which:

FIGURE 1 is a schematic side elevation of the drier section of a paper machine incorporating a preferred embodiment of the present invention,

FIGURE 2 is an enlargement of a part of FIGURE 1, and

FIGURES 3 and 4 are diagrams showing representative characteristics of the invention.

The present invention is particularly adapted to the drying of a sheet of paper or the like by the use of the well known Yankee drier. Referring to FIGURE 1, the drying section of a typical paper machine using a Yankee drier includes a rotatable cylindrical Yankee drier drum or shell 10, a pressure roll 11, and a tail roll 12. The wet web 13 of paper is carried from the web forming end of the machine to the drier section by a felt 14, the felt passing in contact around the tail and pressure rolls and then being led back toward the web forming end of the paper machine as at 15. At the nip 16 of pressure roll 11 and drier drum the web or sheet 13 is applied to the surface of revolving drum 10 to be dried during the duration of its contact therewith. The operation customarily is so performed that substantially complete dry ing of the sheet. occursduring this contact and the sheet 13 is then removed from the surface of drum 10 and wound up or otherwise handled in a conventional manner.

Pressure roll 11 ordinarily is mounted to exert considerable pressure upon felt 14 and web 13 at the nip between roll 11 and drum 10, so that a substantial portion of the water in the felt and the web literally is squeezed therefrom. While in some installations the water thus removed is allowed merely to drain away, in other conventional installations the cylindrical surface of roll 11. is perforated and a suction box is located within the roll, whereby water squeezed from web or sheet 13 and felt 14 is by the vacuum in the suction box removed from the nip and conventionally disposed of. i

In the usual paper machine installation, comprising the combination of a sheet forming and a sheet drying section, the speed of operation of the machine as a whole is limited by the speed at which the drying section of the machine is able to dry the web of paper which has been formed. Consequently, any method and means by which the drying speed can be increased will permit a corresponding increase in operational speed of the paper machine as a Whole. Since the drying of the sheet is simply a removal of the water therefrom, any method by which Patented Oct. 2, 1962 such removal may be effected will be satisfactory, whether it involves evaporation of the water from the sheet, mechanical separation or otherwise, so long as. there are not attendant adverse effects counterbalancing the increase in speed which may be attained.

This invention provides a method and means whereby the mechanical removal of water from sheet 13, through the use of pressure roll11 and suction box 20, may be accomplished to a remarkably increased degree, thus lightening the burden of moisture removal by evaporation which is imposed upon drier drum 10 and permitting a faster operation of the drier.

Felt 14, and to some degree sheet 13 itself are far from completely pervious to water transmission. Consequently, they provide a substantial resistance to the mechanical removal of water from sheet 13 (and incidentally from felt 14) which results from the pressing action at the nip 16 and also a resistance to the removal of such water by suction box 20.

Referring also to FIGURE 2, a puddle 21 of water tends to be formed as a result of the squeezing of the water from sheet 13 and felt 14 at nip 16. By virtue of the presence of suction box 20, however, the formation of such a puddle is either completely or substantially avoided, and rather the water is drawn from sheet 13 and felt 14 as shown by the arrows, the water being drawn through the suction holes 22 in the shell of suction pressure roll 11.

Upon reflection it will be understood that a reduction in the viscosity of the water at nip 16 as compared to that normally existing, will produce a reduction in the mechanical resistance to flow of the water squeezed out at the nip, which water is removed from the zone of nip 16 by suction box 20. Removal of the entire amount of water involved, including that from felt 14, will be enhanced by decreasing the mechanical resistance to removal of the total amount of water at the nip including that present in felt 14. However, since it is only sheet 13 which is to be dried by drier 10, substantially the entire useful result will have been achieved if improvement is obtained merely in connection with removal of water from web 13. Therefore, the total useful effect will have been substantially obtained by, for example, a reduction in the viscosity of the water in the sheet 13 only.

The reduction in the viscosity of the water can of course be accomplished by the addition of heat thereto to increase its temperature. Since as above indicated, there is a need for reduction in viscosity of the water only in sheet 13, and consequently there is essentially only a waste of energy if the water in felt 14 also is heated, it is desirable to raise the temperature of the water in sheet 13 by a means and method which substantially avoids temperature increases of the water in the felt.

Since the reduction in viscosity will be effective only if the condition exists at the time the water is being squeezed and removed from sheet 13 at nip 16, it is clear that any application of heat to reduce the viscosity of the water in sheet 13 must continue to be effective as of the time the sheet enters the nip. Further the heat must be applied in a manner such that there will be no attendant adverse effects, such as scorching and the like, upon the sheet, the felt or other adjacent materials.

Referring again to FIGURE 1,- a preferred form of the invention comprises the application against sheet 13 of a gas flame 25, the gas being fed from a series of nozzles shown diagrammatically at 26 and located. transversely across the sheet. Nozzles 26 may be supplied with gas in any suitable manner. It will be observed that the gas flame rides with sheet 13 substantially into nip 16 so that the source of heat for lowering the viscosity of the water in sheet 13 is effective substantially up to the point where the increased fluidity is of use, that is, at the nip.

In an actual operation, involving the drying of 7.6 lb.

(per ream of 2880 sq. ft.) basis Weight paper on a conventional Yankee drier 12 feet in diameter, a drying speed of 1250 feet per minute resulted in an unsatisfactorily wet sheet, having a moisture content of 17.5 percent. In this particular operation, pressure of the steam applied to heat drier was 28.5 p.s.i.g. and sheet 13 contacted the heated exterior surface of Yankee drum 10 through approximately 85 percent of the circumference of the drum. The sheet comprised 60 percent kraft pulp and 40 percent sulfite pulp, and was applied to the drier at a consistency of 37.5 percent.

A gas flame was then applied to the sheet under the above conditions, as disclosed in FIGURE 1, the flame at its earliest contact being applied 1.5 feet ahead of nip 16, and resulting from the feeding of 3.16 cubic feet per minute of natural gas per foot of width of web 13. Upon reaching equilibrium, the moisture content of the sheet upon leaving the drier had been reduced to 8.25 percent, a satisfactory figure. This would obviously permit a great increase in drying speed before the initial 17.5 percent moisture content in the final sheet would be reached.

The above results are in accord with those ascertained in accordance with standard theoretical calculations. In the drying of solids containing sufiicient moisture so that the exposed surface is thoroughly wet, there first occurs a period of drying at constant rate, continuing so long as the surface behaves as thoroughly wet, and thereafter a period of falling rate of evaporation. The moisture content at which the rate of drying changes from constant to falling rate is called the critical water content, T expressed as Weight of water per unit of bone dry (B.D.) stock. The evaporation will continue until the sheet reaches a moisture content in equilibrium with the air to which it is exposed, called the equilibrium moisture, E. The difference between the moisture, T, in the sheet and the equilibrium moisture is known as the free moisture or water, W.

FIGURE 3 graphically illustrates these periods of drying, the falling rate period being shown as linear, although in the drying of some materials this rate may be curvilinear. However, the rate curve eventually reaches zero at the point E at which the water content is in equilibrium with the air.

If in the falling rate period the rate of drying, dT/dfi, is linear, i.e., dt/d0=K(T-E), the total drying time for fixed drying conditions may readily be calculated. Integrating between the limits T=-T and 6:0 to T and 0 1, the time to dry from W to final free moisture is 1 T,,E 1 W. F 1n ln (1) Where W is the free Water and is equal to TE. This indicates that the time rate in the falling-rate period of drying is proportional to the reduction in free water. K is a drying constant of the particular drier, independent bf moisture content of the sheet.

Since the drying rate at the beginning of the falling rate period is the same as that in the constant rate period,

For the actual operation referred to above, without application of the gas flame, by measurement it was ascertained that T =1.668 and T=0.212 lb. H O/lb. B.D. fiber. It was assumed that T and E would have the reasonable values 0.41 and 0.01 lb. H O/Ib. B.D. fiber, respectively. The total drying time was 1250 =1.54see.

Substituting in Equation 4,

1 W -OAO 0.40

W =1.284 lbs. H O/lb. B.D. fiber, the total Water removed from the sheet by the drier per lb. B.D. fiber. And T =W +E=L294 lbs. H O/lb. B.D. fiber. It is clear that the difference between T with the pre-heating and T without pre-heating represents the additional water removed from sheet 13 by roll 11 and suction box 20 as a result of the increased fluidity of the water in sheet 13. This difference, 1.668 minus 1.294 (equals 0.374 lb. H O/lb. B.D. fiber) represents a remarkable decreased load imposed on the drier. Thus, by virtue of the use of the pre-heating means the consistency of the sheet applied to the drier must have been increased to approximately Thus, through use of the pre-heating means the sheet consistency has been increased from 37.5 percent to 43.6 percent. This considerable change further reveals the greatly reduced drying load on the drier, thus permitting a substantial increase in drying speed for a given set of conditions.

Now, calculating the time required, with the use of the gas flame, to dry a sheet of this consistency to the 17.5 percent moisture content originally resulting without the gas flame,

Thus, it is seen that by use of the gas flame as previously described, the drying time required to attain the stated degree of drying would be reduced to 75.7 percent of the time otherwise required, other conditions being equal. From this it is again clearly shown that pre-heating of the sheet permits a great increase in drying speed. (See Walker, McAd'ams and Gilliland, Principles of Chemical Engineering, 3rd ed., pp. 642-658.)

Referring again to FIGURE 3, in addition to the drying rate curve for the operation previously described without the pre-heating of sheet 13, there is shown the curve for the situation where the pre-heating is incorporated as previously described. It Will be observed that the only difference between the two curves, other conditions being equal, lies in the fact that with pre-heating the sheet was applied at T =1.294, while without pro-heating T =1.668.

FIGURE 4 shows representative characteristics for the above described drier with and without the pre-heating improvement, again based on the considerations previously described. The upper curve in FIGURE 4 is based upon the unconditioned sheet at 62.5 percent water content (1.668 lb. H O/lb. B.D. fiber), while the lower curve is based upon a sheet applied at 56.4 percent moisture (1.294 lb. H O/lb. B.D. fiber) as obtained with preheating of the sheet. As previously described, the drying occurs at a constant rate down to the critical point, 29.1 percent moisture (0.41 lb. H O/lb. B.D. fiber), and thereafter drying is at a decreasing rate, requiring a relatively longer time to achieve an equal amount of moisture evaporation. It will be observed that the typical curves of FIGURE 4 have been brought down to a finally-dried condition of 8.25 percent moisture. It is readily seen that the present invention provides substantially lesser drying times at both the critical and final points, 0 and (i respectively, than the corresponding times required without the use of the present invention, 0,, and 0, respectively.

From the above, it is apparent that use of the present invention provides a very significant and substantial improvement in the art of drying, in particular providing the greatly increased speeds of drying and/or a substantially greater degree of drying.

The sheet 13, instead of being heated by a gas flame from the nozzles shown diagrammatically at 26 may instead be heated just prior to the nip between the drier drum and the pressure roll 11 by a steam shower. In this case, steam is supplied to the series of diagrammatically illustrated nozzles 26 in lieu of the gas.

In order to best achieve the described advantages mentioned, the heat applied to sheet 13 preferably should be of relatively high intensity, with the heat transfer being primarily by convection and/or steam condensation, and the actual heating medium (basically hot gas if a gas flame is used) preferably is of relatively low specific heat. The heating method should not involve any substantial pressing of sheet 13 against felt 14, for if this occurs an increased part of the heating effect on the water in sheet 13 will be lost through transmission of the heat to the water in felt 14. For maximum benefit at greatest economy in required heat, the heat should have low penetration beyond sheet 13; thus a radiant heat source is not particularly desirable. It will be appreciated that a material such as felt 14 has some insulating quality, which quality is retained in proportion to the absence of conductivity between the felt and sheet 13.

An especially important desideratum is that the application of heat continue sutficiently toward the nip or point of application of the sheet to the drying surface to insure that the sheet to be dried (particularly the moisture in the sheet) will substantially retain its elevated temperature and consequent reduced moisture viscosity at the time of mechanical removal of water therefrom. It is in this way that the optimum benefit is obtained, with maximum removal of moisture through the mechanical means, resulting in least drying demand upon the drying surface, with the resulting advantage in increased drying capacity.

Having now described the invention and preferred means for accomplishing its objectives, it is to be understood that limitations on the scope of the invention are intended only as specifically set forth in the appended claims.

What is claimed is:

1. The method of drying a continuous wet web of sheet material comprising supporting said web upon an endless felt traveling over a pair of spaced rolls, passing said web and felt through a pressure nip of one of said rolls and a drier drum, heating said drier drum, separating said felt from said web at said nip, maintaining said web in drying contact with said drier drum to dry the web, and heating said web by applying a heated fluid to said web on the pass of said felt and web between said two rolls and adjacent to and immediately prior in the travel of the web to said pressure nip for raising the temperature and lowering the viscosity of the water in said web for increasing the drying effect of said drier drum.

2. The method of drying a continuous wet web of sheet material comprising supporting said web upon a traveling endless felt, passing said sheet and felt through a pressure nip of a pair of rolls, heating one of said rolls, separating said felt from said web at said nip, maintaining said web in drying contact with said one roll to dry the web, and applying a gas flame to said web adjacent to said pressure nip so that the gas flame travels into the nip for raising the temperature and lowering the viscosity of the water in said web as it reaches the nip for increasing the drying effect of said heated roll.

3. The method of drying a continuous wet web of sheet material comprising supporting said Web upon a traveling endless felt, passing said Web and felt through a pressure nip of a pair of rolls, heating one of said rolls, separating said felt from said Web at said nip, maintaining said web in drying contact with said one roll to dry the sheet, and applying a steam shower to said web adjacent to and immediately prior in the travel of the web to said pressure nip for raising the temperature and lowering the viscosity of the water in said web substantially at said nip for increasing the drying effect of said heated roll.

4. The method of drying a continuous wet paper web comprising supporting said web upon an endless felt, passing said web and felt through a pressure nip of a roll and a drier drum, said roll being provided with a vacuum device in it for drawing up moisture from the periphery of the roll, heating said drier drum, separating said felt from said paper at said nip, maintaining said paper in drying contact with said drier drum to dry the paper and applying a gas flame to said paper web in the direction of travel of the paper Web so that the gas flame extends into said nip for raising the temperature and lowering the viscosity of the water in said paper for increasing the effectiveness of the vacuum device in said roll and the drying effect of said drier drum.

5. Apparatus (for the drying of a continuous web of sheet material comprising a rotatable drier drum, means for heating said drum, an endless felt, means for mova-bly supporting said endless felt and including a pair of spaced rolls, one of said rolls being located adjacent said drum so as to pass said felt and web through a pressure nip of the roll and drum, and means for heating the portion of the web supported by the pass of felt between said two rolls and including means for applying a heated fluid to this portion of the web for raising the temperature and lowering the viscosity of the water in said Web just prior to said pressure nip for increasing the drying effect of said drum.

6. Apparatus for the drying of a paper web comprising a rotatable drier drum, means for heating said drum, an endless felt, means for movably supporting said felt and including a pair of spaced rolls, one of said rolls being located adjacent said drum so as to pass said web and felt through a pressure nip of the roll and drum, a water suction device located within said one roll, and means for imposing a gas flame against a portion of said web supported by the pass of felt between said two rolls for raising the temperature and lowering the viscosity of the water in the web just prior to said pressure nip for increasing the effectiveness of said suction device and the drying effect of said drum.

7. Apparatus for the drying of a paper web comprising a rotatable drier drum, means for heating said drum, an endless felt, means for movably supporting said felt and including a pair of spaced rolls, one of said rolls being located adjacent said drum so as to pass said Web and felt through a pressure nip of the roll and drum, a water suction device located within said one roll, and means for imposing a steam shower against a portion of said web supported by the pass of felt between said two rolls for raising the temperature and lowering the viscosity of the water in the web just prior to said pressure nip for increasing the effectiveness of said suction device and the drying effect of said drum.

8. Apparatus for the drying of a paper web comprising a rotatable drier drum, means for heating said dr-um, an endless felt, means for movably supporting said felt and including a pair of spaced rolls, one of said rolls being located adjacent said drum so as to pass said web and felt through a pressure nip of the roll and drum, a water suction device located within said one roll and arranged to draw moisture from said pressure nip between said roll and drum, and gas nozzles for imposing a gas flame against said web on the pass of the web between said two rolls and being directed toward said nip so as to direct the gas flame into the nip and raise the temperature and lower the viscosity of the water in said web from a point of [first application of the gas flame on the Web to said n-ip for increasing the water expressing efiect of said suction device and the drying effect of said drum.

Levi 3 July 4, 1916 Sass Nov. 30, 1920 8 Pinder Oct. 17, 1922 Danninger et al. Apr. 28, 1931 Tompkins July 26, 1932 MacArthur May 9, 1939 Wellmar June 28, 1955 Gillis Aug. 28, 1956 Hornbostel Mar. 12, 1957 Hombostel July 30, 1959 Freeman Aug. 30, 1960 FOREIGN PATENTS Switzerland Aug. 1, 1953 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nos 3,05%213 October 2 1962 Harry BO Kellogg It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4,, lines 41 to 43 after the equation insert lal secs.a

Signed and sealed this 28th day of May 1963:.

(SEAL) Attest:

ERNEST W. SWIDER Attesting Officer DAVID L. LADD Commissioner of Patents

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