US2858942A - Centrifugal separator - Google Patents

Description

Nov. 4, 1958 Filed May 21. 1954 E. P. WENZELBERGER CENTRIFUGAL' SEPARATOR I 2 Sheets-Sheet 1 INVENTOR 1. W000 I? WWZEL BERGER BY M ATTORNEYS E. P. WENZELBERGER 2,858,942

Nov. 4, 1958 CENTRIFUGAL SEPARATOR 2 Sheets-Sheet 2 Filed May 21. D 1954 INVENTOR fLWOOD R WE/VZE'LfiERGER ATTORNEYS United States Patent CENTRIFUGAL SEPARATOR Elwood P. Wenzelberger, Dayton, Ohio, assignor, by mesne assignments, to Union Carbide Corporation, New York, N. Y., a corporation of New York Application May 21, 1954, Serial No. 431,359 2 Claims. (Cl. 210-374) This invention relates to centrifugal separators, and more particularly to centrifugal separators for continuously separating solid particles from liquids, especially slurries where the solid phase is greater in bulk than the liquid phase and the specific gravity of the latter phase is greater than the solid phase.

It is an object of the invention to provide a machine which is adapted to quickly and efliciently separate solid particles, such as ice crystals, from an aqueous icy slush and deliver the ice particles substantially free of the mother liquid.

Another object of the invention is to provide a centrifugal separator which is operable to separate or filter viscous materials containing a mixture of solids and liquid which is fed into the separator either as intermittent batches or fed continuously thereinto.

Another object of the invention is to provide an improved separator of the centrifugal type which is useful for separating viscous materials, for example ice, icy slush as produced in step-freeze dehydration processes, such as employed for dehydrating fruit and vegetable juices, whereby the ice particles may be separated from the liquid or juice portion and washed free of any juice adhering thereto and discharging ice particles therefrom while recovering the juice or mother liquor concentrate.

Another object of the invention is to provide an improved centrifuging separator adapted for use in the dehydration of foods, e. g., fruit and vegetable juices, by freezing, the centrifuge of the invention being adapted for substitution for the centrifuge as used in step-freeze apparatus and methods described in my U. S. Patents Nos. 2,559,204 and 2,559,205.

Another object of the invention is to provide a centrifuging machine which is adapted to be operated continuously on a slurry of ice particles and viscous syrup, e. g., citrus juices, and delivered thereto from one or more freezing tanks, and efiiciently separate the ice particles from the juice and deliver the same concurrently while discharging the partially or substantially completely dehydrated juice, the latter being in condition for packing and shipment, or may be re-circulated back to the freezing tanks for an additional freezing cycle to recover a juice concentrate of the desired degree Brix.

This and other objects and advantages will become apparent as the description proceeds, the invention being illustrated by a preferred embodiment in the drawings wherein:

Figure 1 illustrates a verticalsectional view taken longitudinally through a centrifugal separator constructed and operated in accordance with this invention;

Figure 2 is a view in cross-section taken substantially on the line 22 of Figure l, and looking in the direction of the arrows;

Figure 3 is a similar sectional view as Figure 2, and taken substantially on the line 3-3 of Figure 1, looking in the direction of the arrows, the hopper and associated parts being shown in dotted lines in the interest of clearness;

Figure 4 is a detailed sectional view on an enlarged scale, and taken on the line 4-4 of Figure 1, looking in the direction of the arrows;

clligure 5 is a view in perspective of the wire basket; an

Figure 6 is a fragmentary view of the basket of Figure 5 illustrating the construction of the end portion where the material enters the basket.

The invention will be described with particular reference to its use in separating ice crystals from juice concentrate or mother liquor as produced in step-freeze dehydration processes. The invention, however, may be utilized with advantage where it is desired to separate solid particles fiom liquid, especially viscous liquids, and wherein the specific gravity of the liquid is greater than the solid phase.

In the carrying out of step-freeze dehydration treatment, for example in the preparation of citrus concentrates by freezing out the water as ice crystals, the process is based on the theory that pure ice can be formed as crystals in flotation by controlling the freezing and agitating conditions so that there is a relatively small differential between the ice forming point of the solution and the refrigerating medium, this differential preferably being retained to between about 57 F By maintaining a small differential temperature between the freezing cycles, and stirring the material vigorously, it is possible to form fine ice crystals which are substantially uniform in size and to avoid formation of white ice which occludes solids. The formation of agglomerates of ice particles is also avoided so that a clean separation of the ice particles from the liquid is thereby achieved. In this manner, by employing a relatively small difierential temperature between the initial ice forming point of water of the solution and the temperature of the container as controlled by the refrigerating medium, the transformation of the water constituent to ice takes place within a short time interval. The ice forming point of the solution is approximately the temperature imposed upon the solution in the container, the temperature being held there until the ice formation ceases. The time interval for each cycle is determined by the rate of heat transferred to the refrigerant medium. It has been found that the heat transfer can be effected while maintaining small temperature differentials. For example, when freeze dehydrating orange juice, if a ratio of one square foot of refrigerating surface for each 1 to 1 /2 gallons of juice is maintained, the process produces the desired transformation of water to ice crystals and thus dehydrates the juice. When such ratios are held substantially constant, the freezing time period or cycle, for example 1220 minutes, for completion of ice formation remains substantially constant regardless of the quantity of liquid being processed.

In order to obtain fine ice crystals in a relatively pure form without occluded solids and/or juice, the temperature of the cooling liquid must be held practically constant, being maintained at a predetermined lower temperature, e. g., below the ice-forming temperature of the solution. To speed the ice crystal formation under these conditions, the system must possess high heat exchange capacity. This is brought about by first agitation of the solution which brings about a rapid change of the liquid interphase in contact with the freezing surfaces, and secondly, by maintaining a ratio of approximately one square foot of cooling surface for each 1 to 1 /2 gallons of solution being treated, and finally by maintaining the flow of refrigerant capable of removing a relatively large quantity of heat.

The step-freeze dehydration \process is thus based upon "a system of heat exchange in which a low differential is maintained between the ice forming temperature of the solutionand the temperature of-the solution.

It is also found that the stages of progressively lowering the temperature shall start initially above zero and that i the successive stages be -atrelatively small temperature reduction, such'asaforementioned,--betweenabout 57 F. and that the temperature -of. the liquid in the second stage for instance, should-be approximatelythe temperature of the refrigerant in the first stage, and so on throughthe stages. lt'will, of course, be understood that these differentials in temperature will 'varywith the liquidsand the solids being treated,;but the principle of the operation for-dehydration-by-step-freezing remains the same.

Accordingly, by avoiding extremes of temperature, and-- 4 withan outside temperature of 13 F.; the next tanktemperature is held at 13 F. with an outside temperature of 8 F.; and in the fourth tank a temperature of 8 F. is maintained with an outside temperature of 3 F.; while in the last tank a temperature of 3 F. is maintained with an .outside temperature of 2 F. In such a cycle of freeze-dehydration, thestep-by-step differentialtemperature of 5 F. is thus maintained. In this manner free, clear ice crystals are secured at each freezing stage which are easily maintained as a slurry .by the stirrer in each tank. This principle of a multiple series of step-freezing, starting the temperature in the initial tank just above the freezing point of the juice and progressively reducing it, makes possible that the water may be progressivelyfrozen out and removed to produce a final juice concentrate of the desired degree Brix, for example between 4388.

The present invention may be utilized to receive the liquid slurry of ice crystals and fruit juice as delivered from the freezing tanks of the several stages, and operated to continuously separate the ice crystalsfrom the juice concentrate. The centrifuge may be operated continuously inasmuch asthe icy slush delivered from the various tanks may be combined, or delivered separately to the centrifugefor removal of the-ice crystals. Thus, the centrifuge operates as a commonseparator for the ice crystals formed ,during the various stages of the stepfreeze operation.

Referringmore particularly to the: drawings and particularly to. Figure 1, there isprovided a centrifuge comprising an outer casing 10. and a rotatable, inner bowl 12, the walls of which are formed of a screen or suitably perforated. member 13. The centrifuging machine is suitably mounted on supports 14 and may; be secured to.

the floor for permanent mounting if desired.

A feeding hopper 16 is arranged to receive the slurry mass such as liquid juice and solid ice particles as delivered from one or more of the. freezing tanks of the step-freeze system as described. The icy slush is fed into the screw conveyor 17 which comprises a casing 18 and internal screw 19 having spiral threads 20 arranged for moving the material to the left, as seen in Figure 1 of the drawings, whenthe screw 19 is rotated clockwise as viewed from the right side. The feed screw 19 is suitably driven by a pulley 22, the same being operated through a variable speed drive mechanism, not shown, to provide a suitable feed rate of material to the bowl 13. Preferably the screw feed is rotated at approximately 150 R. P. M. but this may be varied depending upon the thickness oftheslurry and the-solids content. terial entering through the hopper is fed to the left, as shown by the arrows in Figure 1, and enters the bowl 13. The bowl 13 is of smaller diameter than the outer casing 10 so as to leave a chamber 24 for receiving juice or mother liquor which .fiowsthrough the perforated wall 25 and downwardly into the chamber 27 from whence it is discharged through the opening 28 and the conduit 29.

Operating in the bowl or basket 13 is a similar screw conveyor 30 which is. provided with screw thread members 32 for advancing the slushy mass from the entrance opening 34 therealong to the opposite end of the bowl 3. The bowl is suitably divided into two sections A and .8, section A being divided from section B by a radial web 36. Substantially all of the liquid or mother juice is thrown out or discharged from the perforated bowl 13 while the slurry mass is moved through section A of the bowl into section B.

The feed-screw 19 is suitably journalled for rotation in bearing members 38 and 39 which receive the central shaft 4t) of the screw to which the feed screw blades 20' are suitably keyed.

The bowl 13 is provided with guide rings 41 and 42 intermediate its ends, which are adapted to receive the internal guide flanges 43 and 44 respectively of the casing 10.- The end wall 46 of the bowl 13 is adapted to close the end of the basket, except for the central opening 47 through which the material is fed from the screw member 19. The opposite end of the bowl is left open,

as at 49, except for the spider frame member 51.

The bowl or basket 13 is suitably journalled asat 48,

at the entrance end and at the opposite end is suitably attached to the tubular shaft 50 which is journalled in the hub portion 52 of the casing 10. Suitable bearings 53 are provided for journalling the outer end of the tubular shaft 50. Keyed to this tubular shaft'50 is a drive pulley 55 which in turn is driven by a motor, preferably the same motor that drives the feed screw 19. The large diameter feed screw 30 is carried on the central tubular shaft 57, the same being journalled at the opposite end,

as at 58, and being driven by the drive pulley 60 keyed to the outer end of the tubular shaft 57.

Communicating with the tubular shaft 57 is a conduit 62 which in turn is connected to a source of water, such as tap water, the tubular shaft being provided with perforated openings 64 centrally of the compartment B of the centrifugal bowl 13, as shown in Figure 1. The tubularshaft 57 is suitably blocked off by webbing 66 so that water admitted through the conduit 62 cannot flow cent6rally through the tubular shaft beyond the perforation The discharge end of the perforated bowl 13 is provided with a discharge chamber 68, which forms an extension of the casing 10, as illustrated in Figure 1.' The discharge chamber 68 provides an annular chamber surrounding the end of the bowl 13 and receives the solid particles, for example ice crystals in the case of citrus juice concentrates, and thesame is discharged through the opening 70. Water for washing the ice crystals which is introduced through the conduit 62 and discharge opening 64 in the tubular shaft 57 drains downwardly in the compartment B and is collected in the chamber 72 at the bottom of the casing 10 and is discharged through the opening 73 and connecting conduit 74, as illustrated in Figure 1.

As shown in Figure 4, the central tubular shaft 57 is provided with a reduced diameter cylindrical portion which is journalled as at 82 in the coupling member 85. The stationary tube 62 is connected to the coupling 85 through the cap 87 which is suitably bolted to the coupling 85, as at 88. The inner end of the conduit 62 is provided with a flange 90 which is retained in the chamber 91 of the coupling 87and sealed against leakage by the packing Thema-- member 92. A similar packing 93 is provided in the coupling 85 for sealing the tubular member 80 against leakage when water is admitted through the conduit 62 to the perforated section 64 of the tubular shaft 57.

In operation the liquid-solid mixture, for example icy slush, as received from a step-freeze tank is introduced into the hopper as moved by the arrows 96 and is conveyed :along by the screw conveyor 19 into the centrifuging perforated bowl 13. This perforated bowl or basket is rotated at approximately 1400 R. P. M., whereas the screw member 30 is rotated at a higher R. P. M., e. g. 1475 'R. P. M. The drive pulleys 55 and 60 aforementioned, may be driven from the same motor which operates the drive pulley 22 of the feed screw 19. The feed screw 19 is operated at a speed sufficient to keep the material uniformly moving into the centrifuging bowl 13 without jamming or clogging the same. Generally operation of the speed screw at 150 R. P. M. provides proper operation of this feed screw.

The speeds of the basket or bowl 13, screw 30 and feed screw 19 may, of course, be changed to suit different materials being treated and the desired speed of separation. With the material being constantly fed into the rotating bowl, the liquid part of the slurry is substantially all thrown out by centrifuging action in section A of the centrifuging bowl. As the material is moved towards the other end of the bowl, the solid particles, or in the case of freeze dehydration, the ice particles are moved along into the end section B and are washed with water introduced through the conduit 62, the wash water being discharged through the conduit 74. This wash Water may be returned for further concentration or added to the liquid concentrate. Finally the solid particles or ice crystals are discharged through the open end of the bowl, as at 49, into the chamber 68 and thence through the opening 70 where they may be collected and used for seeding the juice which is to be re-cycled through the freeze dehydrating tanks, or discarded.

The centrifugal apparatus provides a centrifugal separator which may be operated to quickly and continuously separate solids from the viscous material. The material being acted upon is conveyed uniformly through the apparatus for the feed hopper into the rotating screen and thence through or along from one end of the screen to the other while the liquid is separated and the solid particles are conveyed along and finally washed before they are discharged from the spinning bowl.

The centrifugal bowl is fitted closely to the rotating screw which screw is of the desired pitch to convey the liquid and solids slowly from one end of the spinning bowl to the other. By driving the screw somewhat faster than the bowl, for example 50-150 R. P. M. faster, this creates a conveying action within the spinning bowl at a rate dependent upon the differential R. P. M. difference between the bowl and the screw, being also dependent upon the pitch of the screw 30.

At the same time the centrifuging forces cause the liquid portion to separate and pass through the screen wall 25 and thus separating the liquid portion from the solid portion as the same is conveyed along through the spinning bowl. For fine ice particles the mesh screen or perforations in the wall 25 may be on the order of 100- mesh or higher. The combined action of the rotating screw and spinning bowl is preferably timed so as to allow the material to progress from about three-quarters of the bowl length, after which all of the liquid should be out, before the water reaches the solid particles of ice which are to be washed.

The solids are continued to be conveyed along the longitudinal axis of the bowl under a water spray while the solids are being centrifuged and are thus thoroughly washed so that any solids or liquids such as the mother liquor, is subjected to both centrifuging force, as well as washing action and the same is thus removed, the washed solids or ice particles are then pushed out at the end of the bowl, as at the opening 49, and past the spider 51, and out through the discharge opening where they may be collected.

What is claimed is:

1. A centrifugal apparatus for separating ice crystals from refrigerated juice concentrates, said apparatus comprising an elongated casing, a rotatable bowl, having perforated walls arranged in said casing, said perforated bowl having inlet and outlet means connected thereto, said inlet means comprising an auger for feeding material into said bowl, said perforated bowl comprising screw means arranged therein having screw elements substantially the same diameter as the bowl, concentric means for simultaneously rotating said screw means and said perforated bowl at differential speeds, means comprising a hollow central shaft extending into said perforated bowl, said hollow shaft having perforations on the inner end thereof, means for discharging washing fiuid therethrough into said perforated bowl, said casing being divided into two sections by an annular ring secured to the inside of said casing, means for discharging liquid concentrates from said sections independently, and said outlet means arranged to discharge ice crystals from said bowl.

2. A centrifugal apparatus for separating ice crystals from refrigerated juice concentrates, said apparatus comprising an elongated casing, a rotatable bowl having perforated Walls arranged in said casing, said perforated bowl having inlet and outlet openings thereto, means comprising an anger for feeding material into the inlet of said bowl and screw means arranged at the opposite end of said bowl to discharge ice crystals therefrom, said perforated bowl enclosing said screw means therein having screw elements substantially the same diameter as the bowl, driving means for simultaneously rotating said screw means and said perforated bowl at differential speeds, means comprising a hollow central shaft mounted in said casing extending into said perforated bowl, said hollow shaft having perforations on the inner end thereof and comprising means to discharge Washing fluid into said perforated bowl, said casing being divided into'two sections by an internal annular ring secured thereto, independent liquid discharge means connected to said sections, means for collecting ice crystals at the discharge end of said perforated bowl.

References Cited in the file of this patent UNITED STATES PATENTS 239,222 Burgess Mar. 22, 1881 605,087 Dividsen June 7, 1898 962,052 Roberts June 21, 1910 1,804,108 Pardo et a1. May 5, 1931 2,559,204 Wenzelberger July 3, 1951 2,588,337 Sperti Mar. 11, 1952 2,657,555 Wenzelberger Nov. 3, 1953

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