US1751552A - Method of and apparatus for drying wood pulp and the like - Google Patents

Description

March 25, 1930. R. D. KEHOE 1,751,552

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE,LIKE

Filed Feb. 15, 1928 3 Sheets-Sheet 1 R. D. KEHOE March 25, 1930.

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKE Filed Fe b. 15, 1928 3 Sheets-Sheet 2 Qwwzntoz RE K HOE March 25, 1930.

R. D. KEHOE METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKE Filed Feb. 15, 1928 3 Sheets-Sheet 3 Patented Mar. 25, 1930 UNITED STATES PATENT OFFICE RICHARD D. KEHOE, OF NEW YORK, N. Y.

METHOD OF AND APPARATUS FOR DRYING WOOD PULP AND THE LIKE Application filed February 15, 1928. Serial No. 254,576.

This'invention relates to a method of and apparatus for drying wood pulp, wood chi s, bark, cellulose fibers and pulp, grains, and t e I like, and particularly wood pulp. I The principal object of this invention is to provide a commercially practical, rapid and efiicient process of drying materials of the character referred to above to a predetermined degree of moisture content without injury .to the materials being treated.

Another object of this invention is to provide a process of rapidly drying materials of the character referred to above to a predetermined degree of moisture content wherein the extent of controlof the drying apparatus during the drying operation is reduced to a minimum.

A further object of this invention is to provide a process for rapidly removing substantially all of the moisture content from materials of the character above referred to without injury to such materials.

A further object of this invention is to provide a drying process capable of rapidly 25 drying materials being treated under standard conditions of control and thereafter conditioning such materials to secure a predetermined degree of moisture content therein.

A further object of this invention is to provide a process of drying substantially wet wood pulp wherein such pulp is subjected to a relatively high temperature to remove the bulb of moisture therein, thereafter subjected to progressively decreasing temperatures, after which the pulp is subjected to the action of currents of air at ordinary temperatures, and finally suitably conditioned to provide a predetermined mosture content therein.

A further object of this invention is to provide an apparatus particularly adapted for use in connection with the practice of my its weight and conse uently the freight charges incident to its s ipment. The shipment of the pulp in a wet condition also possesses other material disadvantages, namely, the wet pulp is greatly subject to discoloration, and when the ulp is shipped during the winter it becomes rozen and chippers must be used for breaking the pulp into small pieces to permit its mixture with water when it is ready to be used. 'The chippers thus employed reduce the quality of the pulp by breaking the fibres thereof. It is wholly desirable therefore to ship the pulp in a dry condition, but great difliculty has been experienced in drying the pulp Without injuring the fibres thereof. As is well known, the quality of high degree wood pulp is dependent upon the preservation of the length of the fibres, and when the pulp is dried under the influence of heat, the latter usually injures the fibres by charring them, and this is particularly true if it is attempted to dry the pulp in sheet form. It has been proposed to shred the pulp before drying it, but the usual types of shredders have been found to cause mechanical injury to the fibres, thus reducing the value of the pulp. In the manufacture of paper stock,'the first step in the process consists in mixing or chipping the pulp in order to permit it readily to be mixed with water, and it has been found that when dry pulp is provided the mixing devices may be operated with substantially half the power ordinarily required when wet pulp is' employed, and less injury is done to the fibres. 8 The present invention contemplates a method wherein wood pulp, as well as other materials, may be rapidly dried to any desired degree of moisture content without appreciable injury to the material being treated thereby avoiding the disadvantages above referred to.

In the accompanying drawings I have shown a preferred form of apparatus particularly adapted for use in the practice of my process. In this showing,

Figure 1 is a side elevation, parts being cut away,

Figure 2 is a plan view,

Figure 3 is a sectional view taken on line 3-3 of Figure 1, I

Figure 4 is a section taken on line 44 of Fi ure 2,

igure 5 is a detail longitudinal trans verse section, and,

' drier 11 of standard construction to which the material to be treated is delivered through the pipe 12 from the reservoir 13 wherein the material in finely' divided condition is disposed in a body of liquid 14. From the drum drier 11 the, material is conveyed by a belt conveyor or felt 15 to a pair of expressing rollers 16 of usual construction from which the material is carried in the form of a sheet 17 througha second pair of rollers 18 to a breaking-up device 19 which is of any suitable construction capable of dividing the sheet material into shredded or finely divided form Without material injury to the fibres thereof. The preliminary drying apparatus 10 is well known in the art and per se forms no part of the present invention.

The breaking-up device or shredder 19 is 4 preferably arranged over a bin or hopper 2O having arranged therein a conveyor 21 which is adapted to deliver thefinely divided material in the hopper 20 to a moving belt 22 which carries the material into a first stage drying chamber designated generally by the reference numeral 23. The chamber 23 is of box like construction and is divided longitudinally thereof by partitions 24 and 25 into three compartments 23, 23, and 23. Travcling conveyors 26 and 27 carried by suitable rollers 28 are arranged in compartment 23 below the conveyor 22. Each of the conveyors travels in a direction opposite to that of the adjacent conveyor, the conveyors being driven by any suitable means (not shown). The compartment 23 communicates with the central compartment 23 through a plurality of openings 29 adjacent the upper portion of the chamber 23 and a plurality of openings 30 adjacent the lower portion of the chamber 23. A plurality of heating coils 31 are arranged in the central compartment 23 as shown in detail in Figure 3, and a plurality of fans 32 driven in any suitable manner as by means of a motor 33 are arranged in the openings 29 and adapted to force air from the central compartment 23 into compartment 23, the heated air passing into the latter. compartment through the openings 29 and being returned to the heating compartment through the openings 30. An exhaust by forming a plurality 0 pipe 34 extends through the outer casing of the chamber 23 and communicates with the central compartment 23 to conduct off heated air exhausted therefrom by means of a fan 35 arranged in the pipe 34. The conveyor 27 extends through an opening 36 in the outlet end of the first stage drying chamber 23 into the second stage drying chamber designated generally by the reference numeral 37.

The drying chamber 37 comprises an elongated box-like casing divided longitudinally thereof by means of a partition 38 extending substantially vertically throughout 'a portion of the height of the chamber 37. At one side of the chamber 37, shafts 39 are arranged in opposite ends of the casing and each of,

the shafts carries a roller 40. An apron or endless conveyor 41, preferably formed of flexible wire mesh, passes aroundthe rollers 40. Any suitable means may be provided for driving the shafts 39, the speed of rotation being relatively slow for a purpose to be described. Above the conveyor 41 a plurality of transverse partitions 42 extend between the outer walls of the chamber 37. The transverse partitions 42 are secured to the top of the casing 37 in any suitable manner and the bottom edges of the partitions are spaced from the conveyor 41. It will be apparent that the transverse partitions divide the upper portion of the chamber 37 into a plurality of compartments. A plurality of heating coils 45 are arranged in each of these compartments and, as shown in detail in Figure 4, extend across the entire upper portion of the heating chamber 37. One outer wall of the chamber 37 is stepped-in as at 46, 47 and 48. A plurality of vertical partitions 49 extend from the top to the bottom of the elongated compartment between the central partition 38 and outer stepped-in wall therecompartments 52. As clearly shown, the compartments 52 progressively decrease in size toward the outlet end of the chamber 23 for a purpose hereinafter to be described.

In each of the compartments 52 are arran ed a plurality of heat interchangers 56 preferably of the corrugated plate type and these heat interchanges progressively decrease in size toward the outlet end of the I chamber 37. The heat interchangers seareber 74 from the charm the sump 61 is inclined toward the inlet end of the casin 37 for a purpose hereinafter to be describef. A lurality of pipes 62 provided with space nozzles 63 are arranged below the conveyor 41 and extend substantially throughout the length of the chamber 37. Elongated deflectors 64 are arranged below the pipe 62 and extend over the shoulders of the foundation as shown in Figure 4. The portion of the chamber 37 below the conveyor 41 is connected to each of the compartments 52 by means of a plurality of openin s 65 having staggered air deflectors or be es 66 arranged therein. Below the heat interchangers 56 are arranged a plurality of fans 67 carried by the lower ends of shafts 68 suitably journalled in supporting frames 69. The shafts 68 extend upwardly through the compartments 52 and are rotated in any suitable manner as for example, by means of motors 70 arranged on the top of the casing 37 The chamber 37 adjacent the forward end thereof is provided with a hot air exhaust pipe 71 having an exhaust fan 72 arranged therein. The chamber 37 is also provided adjacent the outlet end thereof with an air inlet pipe 73.

An atmospheric chamber designated generally by the reference numeral 74 is arranged adjacent the outlet end of the chamber 37 and is provided with an air inlet 75 and an exhaust stack 76 having an exhaust fan 77 arranged therein. A closure member 78, preferably a flexible curtain separates the chamber 37. An endless conveyor 79 is arranged in the lower portion of the chamber 74 and is adapted to receive material discharged from the conveyor 41. A pair of vertically arranged endless conveyor belts 80 are arranged adjacent the delivery end of the conveyor 79 and are ada ted to receive material therefrom and b rictional engagement carry such material upwardly and deliver it to an endless conveyor 81 extending into a conditioning chamber designated generally by the reference numeral 82.

The conditioning chamber 82 is substantially identical in structure with the first stage heating chamber 23 and is provided with endless conveyor belts 83 and 84 arranged below the conveyor 81. Each of such conveyors is designed to move in a direction opposite to that of the next adjacent conveyor belt. The chamber 83 is divided substantially centrally thereof into two compartments by means of a partition 85. In the one of these compartments is disposed a plurality of heating coils 86 extending substantially throughout the height of such compartment. Circulation of air through the conveyor compartment and the heating compartment of the chamber 83 is provided by means of fans 87. The lower conveyor belt extends through an opening in the outer end of the chamber 82 which opening. is closed by a suitable closure. member 88, preferably a. flexible curtain. The chamber 82 is provided with an air exhaust pipe 89 connected to a discharge ipe 90 having a valve or damper 91 therein and to a pipe 92 having a valve or damper 93 therein which pi e is connected to the air. inlet pipe 73 of t e chamber 37 I As heretofore stated while my process and apparatus may be employed in connection with various materials they are particularly adapted for use in connection with the drying of substantially wet wood pulp and it is in connection with such material that the preferred practice of my process and operation of the apparatus are hereinafter described.

The operation of the apparatus is as follows:

In the preferred practice of my process finely divided wood pulp is introduced into a body of water in the reservoir 13 and conducted therefrom through the pipe 12 into the drum drier 11 where in a known manner a substantial proportion of the water contained in the pulp is removed. The partially dried pulp is then carried on the felt 15 to the pressure rolls 16 where an additional amount of water is removed and the pulp is formed into a sheet 17 which is carried between the ressure rolls 18 to the breaking-up device 19.

y this preliminary drying treatment approximately from 40 to 50 per cent of the water in the pulp will be removed. The pulp in finely divided condition is dropped from the breaking-up device into the bin 20 and is carried by the conveyor 21 to the belt 22' which in turn conveys the material into the first stage drying chamber 23. The delivery end of the conveyor 22 is so arranged as to deposit the finely divided pulp upon the conveyor 26 which moves in an opposite direction therefrom. This conveyor then discharges the material upon the oppositely moving conveyor 27 which carries the material out of the chamber 23 to the chamber 37 and deposits it on the coveyor 41. Although wood pulp in dry condition is easily injured by the action of excessive heat, if a substantial amount of water is present in the pulp it may be heated to relatively high temperatures since the water content fprotects the pulp from the charring action 0 the heat. Hence, a temperature from 250 to 300 F., is preferably maintained in thevchamber 23 by means of the heating coils 31. Air withdrawn through the openings 30 into the chamber 23 wherein it is heated is forced by means of the fans 32 into the chamber 23 and circulated downwardly therethrough thereby heating the pulp to the desired degree whereby a substantial proportion of the remaining water content of the pulp is removed. It will be apparent that by arranging the conveyors in the chamber 23 as shown and described a relativelylong heating action may be secured in a relatively small chamber. Moreover, it will be apparent that the speed of movement of the conveyors may be regulated according to the percentage of water present in the pulp, the greater the amount of water the slower the speed of movement through the chamber 23.

The partially dried pulp delivered from the conveyor 27 to the conveyor 41 travels along the upper apron toward the outlet end of thechamber 37 The rolls 4O revolve rela tively slowly, thus causing the pulp to travel at a relatively slow linear speed through the casing 37. If desired, the shredded pulp may be periodically agitated or turned by anv suitable device (not shown) to present different sides of the pulp pieces to the action of the drying medium. While it is contemplated that any conventional turningJdeViceS necessary for the purpose may e used throughout the length of the conveyor 41, it is to be particularly noted that incident to the relative disposition and arrangement of the respective conveyors 22, 26, 27 and 41 that v the pulp in more or less shredded condition is i turned in falling from one conveyor to the next succeeding conveyor; that is to say, the material in being dellvered from one conveyor to the next in series will, in falling through the space from the pulp receiving surface of one conveyor to the pulp receiving surface of the next conveyor, be caused to turn or rearrange itself with respect to its position on the preceding conveyor, so that through this means the pulp is turned or rearran ed in order that a more effective heating 0 the pulp particles is possible than if such particles remained in one position throughout the transit through the drier. During the passage of the pulp through the chamber 37 from the inlet toward the outlet end thereof, a counter current of air will be created in the chamber by the fan 72 and discharge pipe or stack 71. 'The air delivered into the chamber 37 from the pipe .73 passes beneath the apron 41 and during its passagev through the chamber will be picked up by the first pair of fans 67 adj acent the outlet end of the chamber and forced upwardly through the heat interchangers 56 arranged thereabove. During the passage of air through the heat interchangers it will be preliminarily heated and after passing through the heat interchangers 56 will be heated to an additional extent by contact with the coilsarranged in the top of the chamber 37. The air will then be directed downwardly onto the shredded pulp on the apron 41. The next pair of fans 67 tends to pull the air downwardly through the mesh of the apron thus causing it to pass against and around the pulp thereon. The second pair of fans will repeat the operation of the first pair, the air pulled downwardly through .the

apron being forced into the second heating compartment wherein it is heated by the heat interchanger and the coiltherein. This action will be repeated throughout the length of the apparatus. When the air reaches the forward end of the apparatus it will be discharged through the stack 71.

As previously stated the pulp when in dry condition is easily injured by the action of excessive heat and accordingly air delivered to the chamber 37 from the pipe 73 is supplied at a temperature not substantially in excess of 120 F. However, as the air reaches portions of the pulp containing greater percentages of water it may be heated to higher temperatures as will be apparent. Accordingly each successive heating compartment from the outlet to the inlet end of the chamber 37 is adapted to progressively increase the temperature of the drying medium, the temperature being increased in proportion to the increase ofthe water content of the pulp. For this reason the heat interchangers 56 which are supplied with hot air from the chamber 23 by means of the pipe 34 progressively decrease in size from the inlet to the outlet end of the apparatus. The degree or increase of the temperature in each successive compartment of the chamber 37 is dependent upon the percentage of water in the pulp delivered at the inlet end of the apparatus. In the first compartment of the chamber 37 adjacent the chamber the temperature is maintained at approximately from 200 to 250 F. The next adjacent compartment is referably maintained at a temperature of rom 175 to 200 F. The next compartment is preferably mainta ned at a temperature of from 150 to 175 F. and the last compartment is maintained at from 120 to 150 F. It will be apparent that if the chamber 37 is made up of a greater or less number of compartments the range of temperature in each compartment will be modified accordingly.

Unless provision be made in the chamber 37 to avoid it, finely divided portions of the pulp, commonly known as dust or linters,

will be entrained in the currents of air and carried through the heating compartments and deposited on the heating coils whereby the finely divided pulp Will be charred. Hence, in the final product there will be a substantial proportion of charred pulp. In order to avoid this condition I provide sprays of water from the pipe 62 through the nozzles 63 in the portion of the chamber 37 below the conveyor 41. Any finely divided pulp passing downwardly from the conveyor 41 in the current of air is entrained in the spray of water and carried downwardly with the water into the sump 61. The sump is inclined toward the forward end of the chamber 47 and hence the water and the pulp in the sum will be directed toward the forward end of t e apparatus. From this point the water and the pulp may be disposed of as desired. If a substantial amountof finely divided pulp is present in the water it may be conducted from the sump 61 into the reservoir 13 by any suitable means (not shown), whereby such finely divided pulp may be recovered. The employment of sprays of water in the chamber 37 below the conveyor 41 has another and highly important advanta e. The water serves to cool the air after it as passed through the shredded pulp on the conveyor 41 whereby its capacity for-further drying is materially increased as will be apparent.

After the pul has passed through the chamber 37 it is elivered by the conveyor 41 into the atmospheric treating chamber 74 where atmospheric air, which may be dehumidified if desired, is introduced through the inlet 75 and circulated in the chamber and withdrawn by means of the fan 77 and the stack 76. The temperature in the chamber 74 is maintained at approximately from 50 to 80 F. Such treatment serves to lower the sensible heat of the pulp with the resulting removal of additional amounts of moisture from the pulp. After the pulp has passed across the lower ortion of a c amber 74 on the conveyor 7 9 it is'carried upwardly by means of the conveyors 80 and delivered to the conveyors 81 which carry the pulp into the conditioning chamber 82.

In the conditioning chamber 82 the pulp is carried downwardly by means of the conveyors 83 and 84 in a manner similar to that in the chamber 23. During the passage of the pulp through the conditioning chamber 82 air is circulated through the pulp by means of the fans 87 and the air heated to the desired degree by means of the coils 86. In the preferred practice of the process the temperature in the chamber 82 is maintained at approximately from 100 to 150 F. Moreover, the humidity in the conditioning chamber 82 is controlled by any suitable humidifying device (not shown) so that the pulp as finally discharged from the conditioning chamber 82 will have a predetermined degree of moisture content therein. After passing through the chamber 82 the pulp is discharged by the conveyor 84 through the outlet opening and is then ready for shipment.

In the event that temperatures approching the upper limit of the range of temperatures preferably employed in the chamber 82 is employed in the practice of the process the heated air discharged from the chamber through the pipe 89 is preferably conducted through the pipe 92 to the pi e 73 from which the air is introduced into t e outlet end of the heating chamber 37. If desired the heating the passage of pulp therethrough. In

the usual processes a difierence in external temperatures or humidity necessitates variation of control at numerous points throughout the apparatus in order to produce a standard product. In my device however the conditions throughout the apparatus, except in the conditioning chamber 82, may be kept constant regardless of external conditions of temperature and humidity. Since such external conditions affect the moisture content of the pulponly within a relatively small range such conditions may be compensated for in the conditioning chamber 82 in order to provide a standard product. Hence, a defi-' nite control of only one part of the apparatus is required.

Another important advantage of my apparatus is that the amount of fuel necessary to heat the drying medium is materially reduced by employing the heated air discharged from one set of chambers for heating the air in others of the chambers. While, broadly, this is merely the application of the principles of heat interchange, it will be apparent that these principles are applied in a novel manner in my apparatus.

As will be understood when the process and apparatus are employed in connection with the drying of materials other than wood pulp the conditions of temperature will be varied according to the nature and moisture content of material being treated.

While I have described in detail the preferred practice of my process and the preferred form of apparatus to be used it will be understood that the details of procedure the air is directed after passing through the pulp, to thereby initially raise the temperature of the air, and means for directing the exhaust from the rimary heating chamber through said heat interchangers for heating the latter.

2. A pulp drying ap aratus, including a primary heating cham er, heating means therein, a plurality of superimposed relatively reversed conveyors in said chamber, a secondary heating chamber, a plurality of independent heating zones in such secondary chamber, a plurality of heat interchangers in said secondary chamber, connections between said heat interchangers and the primary heating chamber, and a single pulp conveyor moving through all zones of the secondary heating chamber.

3. A pulp drying apparatus including a primary heatin chamber, air heating means therein, a plura ity of superimposed relatively reversed pulp conveyors in said chamber, .a secondar heating chamber including a series of in ependent heating zones, air heating means in each zone, means for utilizing the exhaust from the primary chamber for partly heating the air of each zone after passage of the air through the pulp, a single conveyor operative through all zones of the secondary chamber, means for forcing heated air through the pulp on the conveyor, and means operative below the conveyor for clearing the air of suspended pulp particles.

' 4. A pulp drylng apparatus including a primary heating chamber, air heating means therein, a pul conveyor therein, a secondary heating cham er, a single pulp conveyor operative therein, a plurality of successively decreased heating units in said secondary heating chamber, means for forcing heated air through the pulp on the conveyor at a plurality of spaced points in the travel of the pulp, and means for spraying the air below the conveyor with water.

5. A pulp drying apparatus including a primary heating chamber, a plurality of superimposed relatively reversed conveyors in said chamber, air heating means in said chamber, means for forcing the heated air through the pulp on said conveyors, a secondary heating chamber, a single conveyor operative therein, a plurality of heating means in said secondary chamber, each of said heating means being of progressively less heating effect in the direction of travel of the material, means for forcin air heated by the said heating means throug the pulp on the conveyor, an atmospheric chamber, a conveyor therein to receive the pulp from said single conveyor, and a conditioning chamber to regeive the pulp from the atmospheric cham- 6. A pulp drying apparatus including a heating-chamber, a pulp conveyor moving longitudinally of the chamber, means in the chamber for heating said air through the ulp on the conveyor, and a spray arranged elow the conveyor for clearingthe air of suspended pulp particles after the air has passed through the pulp.

7. A pulp drying apparatus including a base, a heating chamber supported'thereon, a pulp conveyor movable longitudinally of the chamber, heating means arranged in the secondary heating chamber having a plurality of heating zones therein, a single material -conveyor for carrying the material through all of said zones in succession, means for directing a current of air longitudinally of the secondary heating chamber in a direction opposite that of the travel of the material, air heating means in each zone including a preliminary'heating element and a final heating element, means for directing the exhaust of the primary heating chamber through the preliminary heating elements of all zones of the secondary heating chamber, and means for delivering air from said air current from beneath the material on the conveyor to a position above said'material, said means causing the air to be heated in succession by the preliminary heater and final heater.

9. A pulp drying apparatus including a primary heating chamber, air heating means therein, a pulp conveyor therein, a secondary heating chamber, a single pulp conveyor operative in said secondary heating chamber, and a plurality of air heating means arranged in distinctive heating zones in said secondary heating chamber, each of said air heating means including a heat interchanger heated by the exhaust from the primary chamber and an independent heating coil.

10. A pulp drying apparatus including a primary heating chamber, air heating means therein, a pulp conveyor therein, a secondary heating chamber, a single pulp conveyor operative in said secondary heating chamber, and a plurality of air heating means arranged in distinctive heating zones in said secondary heating chamber, each of said air heating means including a heat interchanger heated by the exhaust fromthe primary chamber and an independent heating coil, the heat interchangers and heating coils of each heating means being of decreasing heating effeet in the direction of travel of the material.

11. A pulp drying apparatus including a plurality of heating chambers, each provided with means for supplying heat at varying temperatures, a plurality of superimposed independent conveyors for carrying the pulp air, means for directing through said plurality of heating chambers, said conveyors being arranged to receive the pulp in succession one from the other, the pulp particles in delivery from one conveyor to the next succeeding conveyor being permitted a free falling movement, whereby the particles have a tendency to change their relative positions and relations on each succeeding conveyor, to permit a more effective heating of the respective particles, the final con- 1 veyor passing successively through heating chambers which are of gradually reduced temperatures toward the outlet end of the apparatus, means for subjecting the dried pulp to atmospheric treatment after passing through the last one of the heating chambers, and means at the outlet end of the apparatus for conditioning the particles of pulp passed through the heating chambers after the pulp has been subjected to atmospheric treatment.

In testimony whereof I aflix my signature.

RICHARD D. KEHOE.

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