US2555450A - High-frequency dehydrating method and apparatus - Google Patents

Description

June 5, 1951 LEE 2,555,450

HIGH-FREQUENCY DEHYDRATING METHOD AND APPARATUS Filed Nov. 29, 1943 .EZ'G.1 1 1713.13 as Z9 21 62 +rovcuu/n am Pufm 62 e5 4i ist- '10 47 FIG. 5 i 17 4 45 sofi aye - 1o .3 28 FIG. 2 55251 11 as 28 46 18 86 59 40 1O g 74 0 r J 8 v"" Z0 fisw r {1443 a 72 21 'INVENTOR zz ROYAL LEE 2425 5534: 65535 .37 )fue ATTORNEY Patented June 5, 1951 HIGH-FREQUENCY DEHYDRATING METHOD AND APPARATUS Royal Lee, Milwaukee, Wis., assignor to Lee Foundation for Nutritional Research, Milwaukee, Wis., a corporation of Wisconsin Application November 29, 1943, Serial No. 512,219

Claims.

The present invention relates to the treatment of material by the use of high-frequency electrical energy, and more particularly to the dehydration of moist material, such as animal and vegetable matter.

An object of the invention is to provide an improved method and apparatus for expeditiously dehydrating moist material by high-frequency inductional heating.

Another object is to provide a dehydrating method and apparatus wherein a high-frequency field acts locally on the material and is relatively shiftable with respect to the material to effect progressive drying of the material.

Still another object is to provide automatic control of the relative displacement of the highfrequency field and the material as the drying progresses.

A further object is to provide a dehydrating apparatus which will facilitate application of the high-frequency field to the material while it is confined in a closed chamber.

A still further object is to provide a low pressure dehydrating apparatus which will facilitate removal of the moisture from the drying zone and permit drying at temperatures sufiiciently low to avoid injury to the material.

The invention further consists in the several features hereinafter described and claimed.

In the accompanying drawing, illustrating certain embodiments of the invention for carrying out the method of the invention,

Fig. 1 is an elevation, partly in section, of a dehydrating apparatus arranged in accordance with the invention, parts of electrical circuits thereof being shown schematically, and different positions of a movable high-frequency heating coil being shown in full and broken lines;

Fig. 2 is a top view of the apparatus, a drying chamber thereof being shown in transverse section;

Fig. 3 is a fragmentary sectional elevation of a modified form of dehydrating apparatus;

Fig. 4 is a sectional view taken generally along the line 4-4 of Fig.3, and

Fig. 5 is an elevation of another modified form of dehydrating apparatus.

Referring to Figs. 1 and 2 of the drawing, Ill designates an upright tubular insulating casing, such as of high-grade glass or ceramic material. The tubular casing I0 is of elongated shape and has a bell-mouthed lower end I I which is suitably sealed onto a cup-shaped condenser shell or housing I2 of metal or insulating material,

the condenser housing having an inturned top I flange I3 and having wheeled supporting legs I4 adapted to rest on a supporting surface I5, such as a floor or table top. The upper end of the tubular casing I 0 is closed by a detachable domed cover It preferably formed of insulating material, the cover having a suitable sealing engagement with the casing ID. The tubular casing II! is thus closed at both ends and forms therein a vacuum chamber which is evacuated through a valved pipe attached to the cover, or through a similar pipe i8 attached to the condenser housing, or through both of these pipes. A coiled pipe I9 is mounted in the condenser housing to receive a cooling medium such as brine, and a drain fitting is attached to the lower part of the condenser housing. The brine is at a temperature which is preferably below the freezing point of water.

The tubular casing I0 is adapted to receive therein a batch of moist material 2| to be dried, such as various animal glands, from which hormones, vitamins, extracts and other values are to be recovered. Preferably, these glands are cut as little as possible so as to minimize mingling of the various fluids contained therein. The material is placed in an elongated porous bag 22 which is inserted in a supporting sleeve 23 of suitable insulating material, such as a hardened plastic. The sleeve 23 loosely fits in the outer casing I0 and rests at its lower end on the inturned top flange I3 of the condenser housing I2. The inner side of the sleeve has spaced longitudinal ribs 24 forming vapor channels 25 opening at their upper and lower ends. The bag 22 beam at its sides on the inner edges of the ribs and at its bottom on a perforated insulating plate 26 which rests on shoulders 21 formed on widened lower portions of the ribs, so as to space the bottom of the bag well above the condenser housing |2, especially when the latter housing is formed of metal. In some instances a perforated vertical tube 28 of insulating material is mounted centrally within the bag to form a vapor passage.

The material 2| in the vacuum chamber is dried by high-frequency inductional heat. The induction element is here shown to be a coil 29 which coaxiallysurrounds the tubular insulating casing I0 and is supplied by high-frequency current from a suitable generator, such as an electron tube oscillator 30 of conventional type. The coil is preferably considerabl shorter than the bag 22 and is translatable axially of the casing I0 for progressively heating and drying the material 2|. The active travel of the coil is preferably downward although in some instances it may be upward.

A hollow base member 3| is adapted to rest on the supporting surface l5 adjacent to the condenser housing and houses therein the oscillator 3E] and a power supply unit 32 for the oscillator. Spaced vertical posts 33 are rigidly mounted on the base member and support a pulley 3s between their upper ends. A block or carriage S5 of insulating material is slidably mounted on the posts and forms a mounting for the coils .29, the latter being confined by an insulating cleat 36. In some instances the coil 29 may be hollow and attached to flexible insulating conduits 31 to receive a cooling medium. The slidable coil mounting carriage 35 is supported by a cord or cable 38 passing over the pulley 34 and around a winding drum 39 driven by a reversible electric motor 40, as through a worm gearing connection 4|. In the specific construction shown, the coil mounting carriage will descend by gravity. The motor is operated in one direction to control the descent of the carriage, and is operated in the other direction to raise the carriage. The coil 29 is connected or couple-d to the oscillator in any suitable manner as by'a coaxial cable 42 having sufficient flexibility to permit the desired travel of the coil. In some instances, means may be provided for laterally positioning the material holding unit with respect to the oscillator unit, so as to aline the coil 29 with respect to the tubular casing NJ. The positioning means is here shown to comprise guide projections 43 carried on the base member 3| and laterally engageable with the condenser housing l2.

The reversible coil-shifting motor 46, in addition to having a conventional manual control, not shown, is also under automatic control, as hereinafter described, to regulate the travel of the coil 29 during the drying operation and to stop the motor at the end of the drying operation. For this purpose, use is made of the fact that certain electrical characteristics of the oscillator will vary with the load. For example, the plate current and grid current of the oscillator will increase with the load. In the present instance the plate lead 44 of the oscillator has in series therewith the coils of a feed relay 4?; and a limit relay 45. The feed relay 45 has contacts il which close when the load drops a predetermined amount, say to 75% of normal load, and the limit relay 416 has contacts ea which open when the load drops to a greater extent, say of nor-- mal load. The motor is connected to supply conductors 49 in one of which the relay contacts 41 and 48 are connected in series. If desired, the limit relay 4?: may also have a second set of contacts 53 which operate with the contacts 48, and which are connected in series with conductors 51 forming a part of any suitable control circuit for the oscillator or its power supply unit. The contacts 50 may control the oscillator in various ways, as by reducing or stopping oscillation, or by deenergizing the power supply unit, either partially or completely, thus rendering the oscillator ineffective. As is well understood in the electron tube art, it is sometimes desirable to keep an oscillator tube cathode heated even though the demand for high-frequency current may temporarily cease.

In setting up the apparatus for use, the high frequency heating coil 29 is raised to its uppermost position in which it is above the level of the top of the tubular insulating casing Hi, this being effected by suitably energizing the motor to. The

porous bag 22 is placed in the internally ribbed insulating sleeve 23 and is loaded with the material 2| to be dried, the sleeve being either inside or outside the casing It during the loading operation. After the bag is loaded and in place in the casing l6, the cover It is mounted on the casing. Air is then exhausted from the casing and cooling fluid is passed through the coiled condenser pipe is. The loaded casing unit and the oscillator unit are then moved relatively along the sup porting surface l5 to bring the elevated coil 29 into alignment with the casing, whereupon the coil is lowered to the full line starting position of Fig. 1, adjacent to the upper end of the bag. The oscillator 30 is then started in operation, causing inductional heating of the moist material in the upper end portion of the bag and locally drying the material. The water vapor from the material passes along the channels 25 and the central perforated tube 28, and substantially all the vapor is condensed on the cooling pipe IS, only a very small part passing out through the exhaust pipes. As the material in the upper end of the bag dries, the load on the oscillator decreases and the feed relay contacts 4? close, thus energizing the motor 4!! and causing the high-frequency coil 29 to descend a short distance toward the moist portion of the material. The load on the oscillator thereupon increases, reopening the feed relay contacts 41 and stopping the motor. The high-frequency coil 29 thus gradually and intermittently descends to its lowermost position, indicated by broken lines in Fig. 1, and the material in the bag is progressively dried without danger of overheating or scorching. If necessary, water may be occasionally drained from the cold condenser housing. When the coil reaches its lowermost position, the load on the oscillator decreases to such a value as to cause actuation of the limit relay 45, thus opening the motor circuit and also partially or completely deenergizing the oscillator. One pass of the coil 29 along the casing in is ordinarily sufficient to dry the material, but, if desired, the coil may be given a second traverse, the relays 45 and 46 being suitably reset or readjusted. After the drying operation is completed, the vacuum in the casing I0 is broken and the cover [6 is removed. The coil 29 is then raised to its uppermost position, permitting the casing unit to be moved aside and the bag of dried material to be removed from the casing. In the meantime, the high-frequency coil may be applied to another casing unit while the first casing unit is being unloaded and reloaded.

The condenser housing I2 is in relatively free and open communication with the casing H1, thus insuring eflicient condensation of the evolved water vapor. Since substantially all the vapor is condensed in the housing [2, a low pressure can be maintained in the drying chamber with the use of relatively small evacuating pipes and pump equipment. Because of the vacuum in the drying chamber, the drying temperature is relatively low, thus avoiding deterioration of the organic material. Preferably, the temperature of the material does not exceed 125 F. The progres sive heating of the material by the high-frequency coil permits effective heating without requiring excessively large amounts of high-frequency power, and also permits the use of a lowinductance coil.

The high-frequency power is preferably generated in the range of frequencies corresponding to l to 30 meters wave length, although these are not to be regarded as limiting values. The energy is applied either at a single frequency or in a band of frequencies, and in some instances the frequency may be varied during the treatment of the material, as where it is desired to destroy various molds or other micro-organisms having different lethal frequencies. The variation in frequency may be effected at any time during the treatment by adjusting tuning capacity or inductance of the oscillator circuit. The frequencies used will depend on the nature of the material and th micro-organisms present. For example, a frequency corresponding to about 12% meters has been found to destroy the spores which form green mold in thorn-apple juice, and a frequency corresponding to about 16 meters has been found to destroy the spores which form yel' low mold in this juice.

The casing I0 is preferably arranged in a vertical position, as shown, but in some cases it may be placed in a horizontal or inclined position.

The dried material is treated in various ways, as by pulverizing it and subjecting it to various selective solvents to recover the desired values. The pulverized material may also be used as such or incorporated into other materials.

In the modified form of apparatus shown in Figs. 3 and 4, the material 2| to be dried is placed in a stack of removable trays 62 which are suitably separated and centered, as by notched and shouldered cross bars 63 of insulatin material extending diametrically within the insulating casing H], the stacked trays being supported by a ribbed ring 64, and being spaced from the inner walls of the casing H] to form vapor passages. The apparatus of Figs. 3 and 4 is otherwise similar in construction and operation to that of Fig. 1.

In the modified form of apparatus shown in Fig. 5, the housed oscillator is secured to and movable with the coil mounting carriage 35, thus permitting short leads to the movable heating coil 29. This arrangement also facilitates th use of the higher oscillator frequencies. The carriage-guiding posts 33 are secured to a base member H which is here shown to have supporting wheels 12. A limit switch 86 is carried on the base H and is operated by the coil-mounting car riage 35 when th latter reaches the lower end of its travel. The limit switch 86 takes the place of the limit relay 46 of Fig. 1 and performs the same switching functions to control the motor and oscillator. The apparatus of Fig. 5 is otherwise similar to that of Fig. 1.

While it is preferred to move the heating coil with respect to the casing unit during the operation of the apparatus, it will be obvious that the casing unit may be moved with respect to the coil. Instead of operating the feed motor 60 intermittently, it will be apparent that the motor may operate continuously at a suitably adjusted speed under the control of the feed relay.

When a liquid organic material is to be dried, it is mixed with previously dried material to form a paste which is solid enough so that it will not foam when the boilin point of the contained water is reached. In the case of a liquid containing a relatively large amount of water, such as fruit juice and sugar cane juice, it is desirable to effect a preliminary concentration of the liquid, as by freezing and centrifuging, preferably in a non-oxidizing atmosphere. The resulting concentrated liquid or syrup is then used to form the paste. The liquid and dried material forming the paste are ordinarily of the same nature, but in some instances they may be of different nature; for example, a fruit juice concentrate may form 6 a paste with raw sugar produced by drying cane uice.

The moist mass of material is placed in the vacuum chamber, as by means of trays, and is subjected to a high-frequency field while under a vacuum, in the manner above described. Because of the low pressure in the vacuum chamber, the boiling point of the water in the pasty mass is lowered sufficiently to avoid damage to the organic nutritive material, and the water is rapidly evaporated from the mass by the inductional heat produced in the mass. The heating effect of the high-frequency field ceases as soon as the water is substantially eliminated, thus avoiding overheating of the material.

While it is preferred to control the coil-shifting motor 40 by running it intermittently, it is also possible to run the motor continuously at a controlled variable speed. By way of example, the feed relay 45 may reduce the motor current instead of stopping the current flow.

What I claim as new and desire to secure by Letters Patent is:

1. Apparatus for dehydrating organic material comprising a tubular insulating vacuum casing adapted to receive therein a batch of the material, high-frequency heating means including a coil surrounding the casing for locally heating the material, and means for relatively shifting said coil in an axial direction along said casing for progressively heating the material.

2. Apparatus for treating organic material,

comprising an upright tubular insulating vacuum casing adapted to receive therein a batch of the material, means for maintaining a vacuum in said casing, high-frequency means including a coil surrounding the casing and relatively movable in an axial direction along the casing, and impelling means for effecting relative axial movement of said coil along said casing to treat portions of said material in succession.

3. Apparatus for dehydrating organic material, comprising a tubular insulating vacuum casing adapted to receive the material, means for maintaining a vacuum in said casing, ribs of insulation extending longitudinally in said casing at the sides thereof and forming longitudinal vapor passages, a material container of insulation in said casing supported by said ribs, and highfrequency heating means including a field element adjacent to said casing for heating the material.

4. Apparatus for dehydrating organic material, comprising a tubular insulating vacuum casing, means for maintaining a vacuum in said casing, a stack of insulating trays in said casing for receiving the material, insulating cross bars between said tray for spacing said trays from each other and from the inner sides of said casing, and high-frequency means exterior to said casing for heating the material.

5. Apparatus for dehydrating organic material, comprising an upright tubular casing adapted to receive the material and forming a vacuum chamber, a condenser at the lower end of the casing for condensing water vapor evolved from the material, said condenser supporting said casing, a closure at the upper end of said casing to permit access to the interior of the casing, high-frequency means including a field element intermediate said ends for heating the material in the casing, and actuating means for moving said field element vertically along said casing.

ROYAL LEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number umbe Number 8 Name Date Tival Oct. 30, 1934 Smith g Mar. 5, 1935 Hart 1- May 11, 1937 Smith July 19, 1938 Gentele Oct. 11, 1938 Christensen Dec. 17, 1940 Nicholas Dec. 31, 1940 Stephen Feb. 11, 1941 Toulmin Dec. 23, 1941 Some June 30, 1942 Reichel et a1 Nov. 17, 1942 Ross 1 June 1, 1943 Bierwirth Aug. 3, 1943 Burkhart Feb. 29, 1944 Vang Mar. 21, 1944 Christie Oct. 10, 1944 Hoyler July 9, 1946 FOREIGN PATENTS Country Date Germany Sept. 18, 1933

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