US 2837831 A
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June 10, 1958 w, c, GATES I 2,837,831
' APPARATUS FOR VACUUM DRYING Filed March 15, 1955 V 4 Sheei-Sheet 2 I j/pek /a'fi- W/fizar 6. 62756, v jj,% MW Z June 10, 1958 w, c, GATES v 2,837,831
APPARATUS FOR VACUUM DRYING Filed March 15, 1955 fiqets-she g 3 5'0 55? /0- 559 ,g 2-1 June 10, 1958 v w. c. GATES 2,837,831
APPARATUS FOR VACUUM DRYING Filed March 15, 1955 4 Sheets-Sheet 4 UnitedStates Patent APPARATUS FOR VACUUM DRYING Wilbur C. Gates, Flossmoor, lll., assignor, by direct and mesne assignments, of one-half to Chicago Bridge & Iron: company, Chicago, 1th., a corporation of Illinois, and one-half to Baerguard, Inc.,- Chicago, 111., a corporation of Illinois Application March 15, 1955, Serial No. 494,504
teatime or. 34-92 This invention relates to apparatus for'treating a flow able, liquid-absorbing solid material and more particularly to treating such material by moving itthrough a zone at a predetermined, controlled pressure condition.
The apparatus of this invention is particularly useful, for example, in the drying'of a cereal such as wheat, rice, oats, and the like, particularly after such cereal has been vacuum puffed, in the drying of tobacco and in the drying of flour, powder, and the like.
As a result of the new apparatus of this invention, the following advantages are achieved when drying material: (.1) matting or fusing of the moistened solids is greatly reduced; (2) scorching of the material is prevented; and (3) the rate of drying is increased as a result of tumbling of the material. If the tumbling is too violent or extreme,- undesirable breakage of the product will occur. The apparatus and method of the present invention avoid such breakage.
Another advantage of the apparatus of this invention is that substantially uniform, desired temper or liquid content of the treated product is achieved. Careful heat profiling, i. e., regulation of the temperature of the regions through which the material passes, further aids in achieving the desired degree of substantially uniform temper.
.All of these advantages are achieved by apparatus which can be operated continually without time-consuming shut downs for charging the machine with the material to be treated, removing the treated material, or any other similar step.
When the apparatus of this invention is employed for drying material, it is preferred that the controlled pressure be a vacuum. Under such condition, the following additional advantages are achieved:' (1) becaus the vacuum condition increases the rate of evaporation, the temperature need not be r'aisedto a high figure; and (2) the quantity of material that can be dried during a given period of time by equipment of a particular size is greatly increased; and, as a corollary, vacuum drying equipment with a particular output rate occupies very much less space than would equipment required for drying at a comparable temperature under, for example, atmospheric conditions.
Following is a detailed-description of an embodiment of the apparatus of this invention which is directed to employment of the apparatus as a drier, and preferably as a vacuum drier. It is to be understood that the apparatus and method of this invention can also be employed to increase the liquid content of the material by a controlled, predetermined amount, whereby the temper of the treated material is substantially uniform.
The apparatus of this invention is illustrated in a preferred embodiment in the accompanying drawings and the method of this invention will be described by reference to the drawings, in which:
Figure 1 is a side elevational view of the apparatus of this invention;
Figures 2A, 2B and 2C are enlarged longitudinal sectional views of the input portion, middle portion and discharge portion, respectively, of the apparatus of Figure 1;
Figure 3 is a sectional view taken through the same apparatus along line 3-3 of Figure 2A;
Figure 4 is a sectional view taken substantially along line 4 4 of Figure 2A;
Figure 5 is a sectional view taken substantially along line 5-5 of Figure 2A; and
Figure 6 is a sectional view taken along line 6 6 of Figure 2C.
Material treating chamber in the embodiment of the apparatus of this invention shown in Figure 1, material treating chamber 19, as here shown, is a drier and slopes downwardly slightly from input port 11 to discharge port 12. A line 13 leads from a pressure control source, as for example a vacuum pump (not shown), to the chamber 16. When a vacuum pump is employed, it is preferred that it be capable of main taining a vacuum condition within the chamber 10 of as low as 0.1 inch of mercury absolute or lower.
The material to be dried, such as puffed rice, is introduced through input port it at the input end of the chamber 10 from a feed line 14, which is connected to the input port ii. In the event that a vacuum condition is maintained in the chamber to and the other end of the feed line 14 connects with a vacuum chamber of a vacuum pufiin-g gun not shown in the drawings, introduction of the material will not impair the vacuum condition within chamber 10. However, if the other end of the feed line 14 is at atmospheric pressure, suitable lock means should be provided at the input port Zil to avoid any substantial impairment of the vacuum condition within the chamber 10. I
Lock out chamber 15 is provided at discharge port 1 2 to permit removal of the dried material without any substantial change in the pressure condition within the chamber 10. The details of this lock out chamber 15 are explained in more detail below.
Various other parts of the apparatus, such as the means for achieving heat profiling within the rotatable outer drum 2t and inner drum 28, as shownin dotted lines in Figure 1, will be described in detail below.
Rotatable drums Rot-atable outer drum 26 is best seen in Figures 2A, 2B and 2C which collectively show this drum in longitirdinal section rotatably mounted within chamber 10 As seen in Figure 3, outer cylindiically-shaped drum 20 is mounted within chamber 16 on four pairs of revolvable Wheels 21, two pairs being positioned near one end of the outer drum 20 and the other two pairs, near the other end, as shown in Figures 2A and 2C. One wheel of each pair is located slightly to one side of the bottom of the outer drum is.
Outer dnnn 2b is rotated on these wheel mountings by means-or" a motor 23, mounted on the top of chamber 10. The drive axle of the motor passes through hermetic rotary seals 24. Gear 2% drives chain 26, which in turn drives gear 2? attached to the rotatable outer drum 2%).
Cylindrically sliaped inner drum 28 is rotatably mounted in spaced relation to and within the rotatable outer drum 20 by studs 29 which are fixedly attached to the inner drum Z8 and the outer drum 2% at either end. As shown in Figure 3 inner drum 28 carries a group of tumbling vanes 30 (described in more detail below) some ofwhich cooperate with studs 29 to aid in fixedly connecting the two drums.
The material to be dried passes through the annular space 31 between the two drums.
The slope of chamber 10 is determined by the de-' sired slope of rotatable outer drum 20. This depends,
in turn, on the amount and type of material to be fed through the chamber 10, rate of feed, the temperature in the chamber 10, and the rate of rotation of the drums. When vacuum puffed rice is to be dried under a maintained vacuum condition in' the chamber of about 0.1 inch of mercury absolute, it is preferred that the angle of downward slope for the outer drum 20 be in the range of between one and four degrees.
Input end 32 of outer drum 20 is here shown as As previously stated, the material to be dried is in troduced into the input port 11 from feed line 14. From there it drops into an input chute 34, through which it is fed directly into input end 32 of the rotatable drum.
As shown in Figs. 2A and 4, feed wheel 35 is provided. This wheel is fixedly attached to inner drum 28 at its input end. Blades 36 of this feed wheel are here shown as fan-shaped and assist in feeding material to be dried into annular space 31 at a uniform rate.
Tumbling vanes Both outer drum 20 and inner drum 28 are equipped with tumbling vanes. Outer tumbling vanes 50 are mounted on the interior surface of outer drum 20. It is preferred that the outer tumbling vanes 50 be scoopshaped in cross section as shown in Figs. 3 and 5. As drum 20 rotates, outer tumbling vanes 50 pick up material lying on the bottom of the outer drum and carry it up into the upper portion of the annular space 31 enclosed by the inner and outer drums 28 and 20 respectively. The outer tumbling vanes in the embodiment shown run parallel to the longitudinal axis of outer drum 20. However, they may be helical in arrangement if desired, or have any other suitable position so long as each vane runs lengthwise of outer drum 20.
Inner tumbling vanes 30 are mounted on the outer surface of inner drum 28. Like vanes 50, they run lengthwise of the drum on which they are mounted. In the embodiment shown, vanes 30 are T-shaped in cross section, as best seen in Figure 3. They may, however, have a straight cross section or be of any other suitable shape, so long as they are spaced from vanes 50.
Tumbling action Referring to Figure 3, the fiowable material carried up from the bottom of rotating outer drum 20 by outer tumbling vanes 50 will begin to spill out of these scoopshaped vanes at some point in the side portion of annular space 31. As any particular vane moves into the upper portion of the space enclosed by the two drums, it will spill out more and more of the material it holds. By the time an outer tumbling vane reaches the top, and starts down on the other side, all of the particles of material will have tumbled from the vane.
As the material tumbles out of vanes 50, any portion of the material that tends to form clumps by matting or fusing of the moist solid material will tend to be separated upon falling onto the inner drum 28. This will speed up the drying process by permitting more rapid evaporation from the smaller particles of the material than would be possible from larger clumps.
As best seen in Figure 5, outer, scoop-shaped tumbling vanes 50 extend into the input end 32 of outer drum 20, a part of the drum into which the inner tumbling 4 vanes 30 do not extend. Employment of these outer tumbling vanes 50 at the input end 32 of outer drum 20 results in more extreme tumbling of the material at the input end of the drier. Since the largest clumps of particles are more likely to form in this region because of the higher degree of moisture in the material at that stage and since the degree of moisture of the material is greatest, a great degree of tumbling in this region is preferred. These vanes, together with the frustum-shape of the input end 32, also aid in achieving uniform feeding of the material into annular space 31. As shown in Figures 2C and 6, tumbling vanes 50 also extend into the output end of rotatable outer drum 20. Instead of being scoop-shaped, it is preferred that these vanes be in the form of relatively low ridges 52 protruding from the inner surface of the outer drum 20. As a result, a mild tumbling action is achieved at this end of the drum and assists in causing the dried material to empty at a uniform rate into a surge hopper 53. This surge hopper is located immediately below the bottom of the output end of the outer drum 20.
Limitation of maximum free fall of particles It the tumbling produced by revolving vanes 50 and 30 is too extreme, undesirable breakage of the material being dried might result. To avoid this, it is preferred that tumbling vanes 50 be relatively closely spaced, as shown in Figure 3. Thus, even if not otherwise defiected, particles of material falling from vanes as high as position 50a or even position 50b in Figure 3 will have a fairly limited free fall before landing upon the next lower vane.
However, particles carried by vanes 50 into the extreme upper portion of the space enclosed by drum 20 would, unless otherwise deflected, have a free fall of substantially the full diameter of drum 20. The arrangement of inner drum 28 and inner tumbling vanes 2d mounted thereon helps to avoid this by limiting the maximum free fall to which the material is subjected.
Any materials falling from outer tumbling vanes 50 after they have traveled beyond about position 50]) will be caught by inner tumbling vanes 30 which have rotated into position 30a or beyond. Rotating inner drum 28 and inner tumbling vanes 30 carry this material around to the opposite side of annular space 31 and there permit it to drop to the bottom of the drum.
Cross bars 51 of each inner tumbling vane 30 helps to confine material which falls onto that vane as it rises on the ascending side. Further, it is seen that the opposite end of cross bar 51 operates on the descending side to restrain the material from sliding freely off tumbling vane 30 to drop to the bottom of the drum. Thus, tumbling produced by a drier carrying T-shaped inner tumbling vanes 30 is somewhat less active than if these vanes were simply straight members.
It is important to note that the distance between the inner surface of the outer drum and the outer surface of inner drum 28 may be varied, depending upon the type of material to be dried.
Outer tumbling vanes 50 and inner tumbling vanes 30 preferably are attached to their respective drums as by a continuous weld. This provides maximum heat transfer to the material to be dried. For the same reason, it is preferred to construct the tumbling vanes in solid form and of a metal having high heat conductance.
Heating elements Referring to Figures 2A, 2B, and 2C, metal steam coils 54, are fixedly mounted within the chamber 10 and surround the rotatable outer drum 20, being spaced therefrom. As here shown, these coils are arranged in separate banks surrounding different portions of outer drum 29. Each bank is fed by a different one of lines 55a, 55b, 55c, 55d, and 55e, which, in turn, is connected to a steam input feed line 16 through valves 18. Steam from a source not shown flows through the steam input line 16, valves 18, into each bank of coils 54, and is then exhausted to the atmosphere through line 17, which is connected to the terminal of each of the bank of coils 54. Condensate formed in the coils 54 is removed through line 17, which vents to the atmosphere or a vacuum depending on the temperature conditions and pressure in the coils. v
As a result, the amount of heat delivered to each bank and thus the temperature of each portion of the outer drum 20 surrounded by a bank of coils 54, may be separately controlled andprofile heating of the drier achieved. In order to achieve maximum drying rate, it is preferred to supply heat to inner drum 28. In the embodiment shown in Fig. 2C, inner drum 28 is divided into two compartments by a wall 28a. Each compartment is heated by means of input steam lines 56a and 56b, leading from a source of steam (not shown) through the end wall of the chamber 10, through a rotatable seal 58 (shown diagrammatically in Figure 2C) located at the closed end of the inner drum 28, and into the interior of inner drum 28. Steam line 56b passes through a hole in the wall 28a and terminates in the front. compartment. Steam, flowing through input lines 56a and 56b empties into the two compartments of inner drum 2S and provides a separate source'of heat to each compartment as Well as to the inner vanes 30.
Spent steam and condensate formed in the interior I of the inner drum 28 flows from the inner drum through an exhaust line 57, which leads from the closed end of each compartment of inner drum 28 through the rotatable seal 58 through the wall of the chamber and to atmosphere or a vacuum depending onthe temperature conditions and pressure in the compartments.
Within the limits imposed by the physical charactris tics of the apparatus, the temperature of predetermined portions of the annular space 31 may be controlled by regulation of the amount of steam introduced into each bank of heating coils 54 and into the interior of each. compartment of the inner drum Z8.
Heated gas colmt'erflow Figure 20 shows another feature of the apparatus of this invention which may be used to greatly-increase the rate of drying. This feature is the introduction into chamber ltlof a heated and/or dried gas flowing in the opposite direction from the flow of the material in the' Output l ck As previously explained, the dried material flows from the output end 33 of outer drum 26 into the surge hopper 53. This hopper passes through discharge port 12 of'c'hamber It). The material accumulates here until it is passed through lockout chamber 15 for removal from the drier.
Bottom wall 63 of the surge hopper 53 is here shown as frustum-shaped; This forms an approach space through which-the material" must flow to reach the entrance-to lock out chamber 15.
A metal shield member 64,. here shown as comicallyshaped, is so adapted that its circular edge fits snugly against walls 63. When so fittedQ-th'is shield stops the flow of material towards entrance port 65 of lock out chamber 15. The fit between shield 64 and wall 63 need -69, here shown as conical-shaped. A seal ring 70 is located about the circular entrance to lock out chamber 15. Conical-shaped cover 69 is so adapted that, when in an inverted position and pressed into the entrance to lock out chamber 15, the outer surface of the cover 69 forms a hermetically tight seal with seal ring 70. In order to open and close the entrance port 65, cover 69 is mounted on a rod 71 which terminates at a piston 72. This piston is actuated by a powered cylinder 73, and moves the cover up and down. The cover and sealing ring form a hermetic seal when the cover is in the up position. I
Discharge opening 74 of lock out chamber 15 is provided with a movable cover 76 bearing against a seal ring about the opening when in closed position. Cover 76 can be opened and closed by means of movement of rod 77a connecting the cover 76 with piston 77, which, in turn, is actuated by a powered cylinder 78.
The same pressure condition as exists in the chamber 10 may be produced in lock out chamber 15 by means of a pressure control device (not shown) connected to the chamber by a line 79 leading from the lock out chamber 15 through T -joint 80 and valve 81 tothe pressure cont'rol device. The branch of T-joint 8t) opposite valve 81 is connected through valve 82 to the atmosphere.
.Dis'charge of dried material In operation, the desired amount of dried material is permitted to accumulate in surge hopper 53. During this period,lock out chamber 15 is connected'to the pressure control source (not shown) so that the pressure within the lock out chamber is approximately the same order of magnitude as the pressure within chamber 10. Covers 69 and 76 are, of course, kept closed during this operation.
When the material is to be passed into the lock out chamber 15, cover 69 is opened, i. e., as here shown, moved downwardly, and shield member 64 is raised from its closed positionof contact with approach wall 63. The dried material may then pass freely into the lock out chamber 15.
When the desired amount of material has accumulated in lock out chamber 15, shield member 64 is first returned to its closed position, cutting off the flow of the material through entrance port 65. Cover 69 is closed after shield member 64 is moved into its closed position. By so doing, no solid material can become entrapped between cover 69 and seal ring 70 when the cover is moved into its closed position.
When cover 69 is in closed position, valve 81 is then closed, shutting ed the pressure control source and valve 82 is opened to the atmosphere. This brings lock out chamber 15 to atmospheric pressure. Cover 76 is then opened to permit the dried material to flow out. When lock out chamber 15 is empty, the cycle may be repeated.
' Heat profiling As explained above, different amounts of steam may be introduced through feed pipes 55a, 55b, 55c, 55d, and
552. The amount of steam introduced determines the 7 major heat transfer from steam coils 54 is effected through radiation of heat upon the wall of outer drum 20.
At the input end of outer drum 20, where the degree of moisture is the highest, it is preferred that the temperature be maintained at a higher level than in subsequent portions within annular space 31. As the material to be dried moves through annular space 31 towards the output end of the chamber 10, it becomes progres of cereals, and particularly vacuum pufied cereals, it is preferred to maintain a vacuum condition in the chamber 10.
In turn, the carefully controlled evaporation rate permits control, to within quite narrow limits, of substantially uniform temper or moisture content of the dried material discharged from the apparatus.
Additional accuracy of heat profiling is achievedby controlling the amount of steam delivered to each compartment of the inner drum 28 through steam pipes 56a and 56b.
In the drying of tobacco, as well as cereals, it is often desirable to toast the substantially uniformly tempered fiowable material. This is readily achieved by so controlling the amount of steam in at least the last bank of coils 54, such as that fed by line 55c, and the amount of steam in pipe 56a leading into the end compartment of the inner drum 28, that the temperature of the end wall portions of outer drum and inner drum 28 are high enough to toast the material to the desired degree. By virtue of the profile heating, the controlled pressure condition in the chamber 10 and the tumbling action, substantially uniform toasting is achieved.
Continuous operation The apparatus of this invention has been used to dry pufied cereals, such as rice, wheat, etc., with excellent results. It may also be used very satisfactorily to dry tobacco in both shredded and leaf form as well as powder and flour.
It is seen that all such materials may be dried in an uninterrupted continuous operation in which the moist, solid, fiowable material is continuously introduced at one end of the apparatus and is periodically discharged through discharge port 12 at the other.
The above detailed description of this invention is given for clearness of understanding only. No unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.
1. An apparatus for treating flowable, liquid-absorbing solid material, which comprises: an elongated hermetically sealed material treating chamber, means for.
controlling the pressure in the chamber, an input port at one end of the chamber and an output port at the other end of the chamber, an outer drum and an inner drum arranged concentrically to each other'and longitudinally aligned in the chamber, the outer drum having a receiving end and a discharge end, the inner drum being fixedly attached to the outer drum to form a drum unit, means for concentrically rotating the drum unit,
the inner side of the outer drum and the outer side of the inner drum having means for tumbling material in the drum unit, means for feeding material from the input port to the receiving end of the outer drum, means for progressively conveying the material from the receiving end of the outer drum, between the outer and inner drums, and out the discharge end of the outer drum, means communicating with the discharge end and output port, and heating means provided in the chamber between the inner chamber wall and the outside of the outer drum, said heating means having means for heating portions of the outer drum to different predetermined temperatures.
2. The apparatus of claim 1 in which the inner drum is closed at both ends and has heating means inside.
3. The apparatus of claim 1 in which the inner drum is shorter than the outer drum and is positioned intermediate the ends of the outer drum, the inner drum being closed at both ends.
4. The apparatus of claim 1 in which the receiving end of the outer drum is frustum shaped.
5. The apparatus of claim 1 in which the inner drum is shorter than the outer drum, one end of the inner drum being positioned inside the outer drum and spatially positioned from the receiving end of the outer drum, and a feed wheel in the outer drum positioned about at the said end of the inner drum, said feed wheel being fixed to rotate simultaneously with the drum unit.
6. The apparatus of claim 1 in which the output port has means communicating with a lock out chamber, said means containing at least two valves, one of said valves being capable of stopping passage of flowable solid material without forming a hermetic seal, the second of said valves being placed in said communicating means subsequent to the first valve and having means for creating a hermetic seal.
7. An apparatus for treating flowable, liquid-absorbing solid material, which comprises: an elongated hermetically sealed material treating chamber, means for controlling the pressure in the chamber, an input port at one end of the chamber and an output port at the other end of the chamber, an outer drum and an inner drum arranged concentrically to each other and longitudinally aligned in the chamber, the outer drum having a receiving end and a discharge end, the inner drum being fixedly attached to the outer drum to form a drum unit, said inner drum being shorter than the outer drum, one end of the inner drum being positioned inside the outer drum and spatially positioned from the receiving end of the outer drum, means for concentrically rotating the drum unit, the inner side of the outer drum and the outer side ofthe inner drum having means for tumbling material in the drum unit, feed wheel in the outer drum positioned about at the said end of the inner drum, said feed wheel being fixed to rotate simultaneously with the drum unit, means for feeding material from the input port to the receiving end of the outer drum, means for progressively conveying the material from the receiving end of the outer drum, between the outer and inner drums, and out the discharge end of the outer drum, and means communicating with the discharge end and output port.
References Cited in the file of this patent UNITED STATES PATENTS 907,925 Watters Dec. 29, 1908 1,196,376 Meyer Aug. 29, 1916 1,566,778 Statham Dec. 22, 1925 1,681,690 Vernay Aug. 21, 1928 2,073,553 Dienst Mar. 9, 1937 2,207,987 Kent et al. July 16, 1940 2,602,498 Overton July 8, 1952 FOREIGN PATENTS 44,284 Norway Aug. 1, 1927