CENTRIFUGATION EQUIPMENT
APPLICATIONS Special equipment a n d materials a r e increasing t h e r a n g e of centrifugal separators. Emphasis is o n unusual applications by JULlAN C . SMITH, Cornell University, Ithaca, N . Y .
CENTRIFUGAL
SEPARATORS began finding applications in the process industries about 80 years ago. The earliest uses were in sugar manufacture and in separating cream from milk. These two applications still account for a substantial number of the new separators made each year, but the number of other applications has grown to a large and ever-increasing value. Available types, also, have proliferated from the original two to a wide diversity of machines. Common industrial centrifuges and their typical applications have been described by several authors (7, 2, 4, 5 ) . This article gives a brief review of these more-or-less “standard” applications, but is chiefly concerned with new or unusual uses which extend the range of application of centrifugal separators and demonstrate their capabilities and limitations. Excluded from this discussion are the uses of laboratory and analytical separators, including bottle centrifuges, laboratory models of industrial machines, and ultracentrifuges.
Available Industrial Machines and Typical Applications Industrial centrifuges may be classified in several ways, but almost all of them fall into one of two classes. I n one class are machines which separate by sedimentation and depend on the difference in density between phases. The other class contains filtration machines, in which liquid is forced through a filter medium by centrifugal action. A few machines perform both functions in a single unit. I n each class are machines which discharge solids intermittently and those in which solids discharge is continuous, Sedimentation Centrifuges. This class contains slow-speed, large-diameter separators with intermittent solids removal ; high-speed, high-force separators with occasional manual removal of accumulated solids ; high-speed separators with continuous or periodic discharge of a slurry or sludge; and mod-
erate-speed units with continuous sludge discharge. Included also are machines which classify solid particles according to density or particle size. INTERMITTENT SOLIDS REMOVAL. Slow-speed batch sedimentation centrifuges contain imperforate bowls 12 to 84 inches in diameter. I n appearance, they resemble top-suspended or horizontal-basket filtering centrifugals. Their operating cycle includes a feed period which may be several hours long, a period for compacting solids, a skimming period, and a period for unloading a t reduced bowl speed. Operation may be manual or fully automatic. Such machines are used for removing easily settled solids from large volumes of dilute slurries. A typical application is the recovery and concentration of acid-precipitated soybean protein curd. Feed is admitted a t the rate of 100 g.p.m. for about 20 minutes, followed by a 6-minute period for cake compaction, skimming, decelerating the bowl, and unloading the solids. I n another application, calcium sulfate is removed from acidified spent molasses obtained from sugar refining, after which clarified molasses is processed further to recover yeast. The top-suspended bowl is 48 inches in diameter by 24 inches deep, and handles 35 g.p.m. of molasses at 185’ F. A layer of calcium sulfate 4 to 5 inches thick builds u p in about 1 hour. High-speed sedimentation centrifuges with manual solids discharge include tubular and disk machines. Their uses include liquid-liquid separations, clarification of liquids by removal of small amounts of solids, concentration of emulsions, classification of fine solids, and the partial separation of gases of differing molecular weights. Industrial tubular machines are 4 to 6 inches in diameter, turn a t speeds u p to 15,000 r.p.m., and generate centrifugal forces as high as 16,000 times the force of gravity. They are simple in construction and easy to clean, and have the best operating characteristics of any
centrifuge on viscous liquids. Typical applications include purification of lubricating and fuel oils; harvesting of bacteria; clarification of nitrocellulose dope and molten chicle; dewaxing of petroleum residual stocks in hydrocarbon solution; recovery of finely divided metal particles such as silver from film scrap, platinum from spent catalyst, and germanium from forming and sawing operations. The bowl holds u p to 350 cubic inches of solids. Throughput normally ranges from 1 to 10 g.p.m. of liquid. A modified tubular centrifuge containing several concentric annular chambers connected in series is used for relatively simple clarification problems. Its chief application is in clarifying brewers’ wort at rates u p to about 30 g.p.m. The solid-wall disk centrifuge was first developed as a milk separator and still finds wide application in this service. I t is useful for concentrating other emulsions also-notably natural and synthetic rubber latexes. I t finds a wide variety of applications, overlapping to some extent the applications of tubular machines. Typical uses include the purification of lubricating and fuel oils, separation of wash water from fats in refining vegetable oils, fish oils and whale oil; separation of acid sludge from the acid treatment of petroleum stocks; separation of solvent extracts from antibiotic fermentation broths; and removal of water from jet fuel. Industrial separators range from 6 to 30 inches in inside diameter, with liquid throughputs as great as several hundred gallons per minute on easy separations. Some disk centrifuges include openings in the bowl wall which open periodically to discharge accumulated solids. These openings may be individually valved ports, “self actuated” by the accumulation of solids or externally actuated from an hydraulic circuit, or they may be peripheral slots perhaps 5 inches long by 3 / 8 inch high automatically uncovered a t intervals by VOL. 53, NO. 6
JUNE 1961
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f
HEAVY LIQUID
SOLIQS
P I
LIGHT
/rI
i Figure 1. fuge
Tubular high-speed centri-
Feed jets into the bowl through a nozzle at the bottom and separate into two liquid layers which discharge from the top o f the bowl. Solids accumulate in the bowl
hydraulic action. Self-actuating valve bowls are used in recovering wool grease from scouring liquors. Externally actuated valve b3wls find application when the flow rate required for satisfactory clarification is low and the density of the separated sludge is not much greater than that of the liquid. Such machines are used to remove excess pulp from pineapple and orange juices. Slot-discharge centrifuges, with their large openings, can handle a wide variety of relatively coarse solids. They have been used in clarifying fruit and vegetable juices, concentration of precipitated proteins, and the removal of leafy particles from carnauba wax.
COZITINUOL'SSLURRY DISCHARGE. Disk centrifuges with peripheral nozzles 0.030 to 0.1 inch in diameter discharge a concentrated slurry and may simultaneously separate one liquid phase from another. Recirculation of the slurry permits increasing its solids content to fairly high values and also permits displacement washing. Strainers are usually included on the feed and recycle systems to remove solid particles larger than half the diameter of the nozzles. Bowl diameters range from 4 to 30 inches, with throughputs of liquid up to several hundred gallons per minute. A typical separation might involve 100 g.p.m. of total feed. 20 g.p.m. discharged through the nozzles, a slurry recycle of 16 g.p.m. and a net underflow rate of 4 g.p.m. Uses include the concentration and washing of corn starch and gluten; clarification of wetprocess phosphoric acid ; purification of heavy fuel oils; recovery of citrus oils from peel wash liquid; concentration of yeast from fermenter broths. CONTINUOUSSLUDGE DISCHARGE. Solid-wall sedimentation machines are often provided ivith internal conveyors which move the settled solids along the bowl wall, out of the pond of liquid, and out through slots at one end of the bowl. Liquid escapes through overflow ports in the cover plate of the other end of the bowl. The bowls may have a horizontal or vertical axis of rotation, and may be conical, cylindrical, or part cylindrical and part conical. The conveyor rotates more slowly than the bowl, with a speed differential between l / 2 0 and 1 / ~ $ of ~ the bowl speed. Typical applications include liquid removal from poly(viny1 chloride) and polyolefins; classification of dispersed clay to remove particles larger than 3 to 4 microns in diameter; recovery of supported metal catalysts from organic reactions; re-
b BOWL
Figure 3. General view of nozzle-discharge centrifuge Feed enters at the top o f thermachine through o filter which re. moves oversize particles (coorfesy Sharples Carp.)
SLURRY
A
ISC CHARGE Figure 2.
Nozzle-discharge centrifuge
Solids discharge as a dilute slurry through peripheral nozzles in the bowl; clarified heavy and light liquids discharge separately as from a simple disk centrifuge
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INDUSTRIAL AND ENGINEERING CHEMISTRY
moval of solids from sewage and industrial wastes; dewatering of coarse crystals of KC1 and NaCl; and the dewatering of coal. Slow differential speeds are needed with easily disintegrated solids, as in separating uncooked meat tissue from melted animal fat. The moisture content of the discharged solids depends on the particle size and particlc-size range. Typical values are 3 to 5% (wet basis) for coarse crystals; 10 to 1570 for medium size crystals; 30 to 35y0 for oversize clay particles and metal oxide sludges; 20 to 5070 for organic polymers; and 60 to 6570 for proteinaceous solids. Filtering Centrifugals. Centrifugal filters are divided into those with intermittent manual discharge of the solids, those with intermittent but fully automatic solids discharge, and those with continuous solids discharge. LVithin each division are several types of somewhat different areas of application. MANUALSOLIDS DISCHARGE.For many years all centrifugal filters were unloaded manually, but with increasing labor costs and the development of more reliable contrcls the importance of manual-discharge machines is diminishing. They are still useful, however, whenever various batches of different characteristics must be filtered in the same machine or where the production rate is too low to justify automatic controls. In all of them is a filter medium, such as metal cloth, perforated metal plates, or fabrics of various materials, through which liquid passes and on which a cake 1 to 7 inches thick is
CE/APPLICATIONS
Figure 4.
Conical-bowl helical-conveyor
continuous sedimentation centrifuge
Slurry feed enters the stationary central p i p e and sprays out into the bowl forming a pond. The conveyor moves sedimented solids to the right, out of the pond, and discharges the sludge through slots at the small end o f the bowl. Clarified liauid ercaDes through ports in the plate covering the large end o f the bowl (courtesy Sharples Corp.)
deposited. The cake may be washed and spun dry, after which the basket is slowed down and the solids unloaded with a knife, or, with some materials, by hand. There are three main types: top-suspended, link-suspended, and solidcurb machines.
Top-suspended centrifugals are typ ically 30 to 48 inches in diameter. They have long been used in sugar refining, handling large tonnages on cycles as short as 2l/2 minutes per load, and have found application on a variety of other crystalline materials, both organic and inorganic. Typical basket loads are 100 to 400 pounds, and operating cycles-except with sugar-normally range between 6 and 20 minutes. In link-suspended machines, the bas-
ket and drive, and somctimes the casing, are suspended from three vertical posts in such a way that they are free to find their own center of rotation. With this construction any gyrations of an unbalanced basket take place within an enclosed space, so that these machines are easier to seal than are topsuspended units. Formerly they were used chiefly for drying textiles, and were loaded and unloaded through a door in the casing roof. With the development of bottom unloading through the basket floor they have been made adaptable to crystal filtration, and are used in many applications where top-suspended cenwifugals were formerly used. Link-suspended machines have basket diameters between 12 and 60 inches or more. In addition to clothes drying in laundries and dry-cleaning establishments their uses include the dewatering of washed fruits and vegetables, filtration and washing of fine crystalline solids from aqueous and organic liquids, and dewatering and washing of fibrous and granular solids such as polymers. Small-diameter underdriven heavyduty centrifugals are used for a variety of special purposes, such as deoiling of metal chips, impregnation and coating of small assemblies, and the removal of excess liquid from coated parts. The basket is normally loaded and unloaded by hand from the top. I n many machines the basket has a solid wall and is conical, with the large end a t the top. The liquid “filters” upward through the layer of solids and escapes over the top rim of the basket. AUTOMATIC SOLIDSDISCHARGE. Recent years have seen the development of
Figure 5. Continuous helical-conveyor sedimentation centrifuges (A) Conical bowl.
(6) Cylindrical bowl. In this machine, the conveyor diameter is reduced near the discharge end so that accumulated sediment forms its own “beach” upon which sludge is conveyed out o f the “pond” (courtesy Sharples Corp.)
Figure 6. Vertical cylindrical-conical helical-conveyor sedimentation centrifuge (courtesy Sharples Corp. ) VOL. 53, NO. 6
JUNE 1961
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- 'LOTOR
-
Figure 7. Top suspended basket centrifugal The perforated basket is lined with a support screen and a filter medium. Deposited cake is washed, spun dry, and unloaded b y the knife through the basket floor at reduced basket speed
SOLIDS. DISCHARGE
fully automatic top-suspended and linksuspended centrifugal filters, in which the basket is decelerated to perhaps 35 r.p.m. for unloading. In one make the direction of rotation is reversed during the unloading period. These automatic machines find application on the same materials as their manually operated counterparts, but only when the product is uniform enough, and the production rate is high enough to justify economically automatic operation. Most widely used on sugar, automatic machines are also filtering borax (on a 2-minute cycle), KC1 (on 3- to 5-minute cycles), 50-mesh nickel sulfate, and a variety of other materials including nitrocellulose. Linksuspended machines are favored when the cycle is longer than 5 minutes; topsuspended machines can be accelerated faster and are used when shorter cycles are possible and desirable. A recent development is a basket with a conical bottom which moves downward during the unloading period, permitting the
UNUSUAL APPLICATIONS Abrasive Solids. Abrasion and erosion are serious problems in centrifugal separation, and with high-speed separators it is desirable to remove abrasive solids from the feed. This may be done by passing the feed through metal screens, settling tanks, or liquid cyclones. In some centrifuges, however, abrasive materials are routinely handled. For example, solid-bowl scroll-conveyor centrifuges classify corundum for use as a lens grinding abrasive, with quantitative removal of all particles larger than 5 microns. Similar machines are operating on a sludge of fine iron oxide containing a substantial number of fairly coarse iron particles. A Russian automatic knife-discharge centrifugal (6) reconditions foundry sand containing clay and abrasive sand particles. An external spray removes insoluble residual sediment from the screen under a pressure of 80-140 pounds per square inch. The unloader knife lasts about 100 hours. Corrosive Materials. Centrifugal separators handle an enormous variety of highly corrosive materials at a variety of temperatures. High-speed centrifuges are made in steel, stainless steel, and Inconel; scroll-conveyor machines are usually made of steel or stainless steel; basket centrifuges are also made of monel and rubber-coated steel, with Hastelloy or titanium auxiliary parts. Nearly all metals of sufficient strength have been used at times in special machines. One problem in which corrosion was severe was the removal of iron sulfate monohydrate from 5070 H2S04 at 90" F. in a scroll-discharge solid-bowl machine. Type 31 6 stainless steel proved to be satisfactory for the bowl; the conveyor and other auxiliary parts required replacement with another material. Manufacturing a pharmaceutical product involves filtering a dilute aqueous solution of an acid chloride. For this service a manually operated 40-inch basket centrifugal with all wetted surfaces of Hastelloy B is used. High a n d Low Temperatures. Tubular, disk, and nozzledischarge centrifuges are commonly used for clarifying viscous or high-melting materials such as chicle, tars, and organic intermediates at temperatures up to 300 F. or higher. Jacketed or electrically heated vapor-tight casings are used. An automatic top-suspended, 48-inch basket centrifuge is separating tarry solids from an organic liquid at 450 F. under a gage pressure of '/z pound per square inch of inert gas. I t operates on a 20-minute cycle. The casing is lagged but not externally heated. The tar is normally friable and easily discharged, but O
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INDUSTRIAL AND ENGINEERING CHEMISTRY
on occasion becomes hard and tenacious. For this reason the unloader mechanism is strongly reinforced (see Figure 9). Many centrifugal separators operate at temperatures well below 0" F. One of the lowest-temperature applications is the separation at - 80" F. of xylene isomers. This is usually done in conical screen centrifugals with an internal conveyor. Sensitive, Explosive, a n d Fissionable Materials. Centrifugal separators handle a variety of sensitive and hazardous materials; in fact, because of their rapid operation and low holdup they are well suited to materials that must be separated rapidly. Filtering centrifuges have been used with solids that decompose or ignite on exposure to air, usually with a small positive pressure of inert gas maintained inside the casing. Explosive materials are routinely handled in liquid-liquid separators, both tubular and disk-type, as in the separation of spent acid and wash liquids from various nitrobodies. In Sweden, a remote-operated, liquid-liquid separator is operating on nitroglycerine. Handling fissionable materials requires special design for t\\ o reasons. First, the critical mass must not be exceeded, so that the total amount of material and its distribution in the machine are severely restricted. Second, the machine must be maintained and repaired in a "glove box," with a radiation shield between the worker and the machine at all times. ControlIed Moisture Content. A major advantage of centrifugal filters over other types of filtration equipment is that the discharged solids contain significantly less moisture. \.\'ith many materials, the moisture content of a centrifuged cake will be to l / 2 that of a cake of the same material taken from a vacuum filter or pressure filter. Coarse crystals of NaCl, ammonium sulfate, and similar materials may contain only 2 to 570 moisture after discharge. Sometimes the moisture content is 1014 enough so that no further drying is required. For example, 50-mesh crystals of nickel sulfate are centrifuged to 9770 solids and packaged directly from the separator. I n centrifuging nitrocellulose, the moisture content must also be controlled, but in another way: The discharged solids must contain not less than 2S70 moisture, for otherwise they readily decompose. Pressure and Vacuum. Sedimentation centrifuges, both high-speed and conveyor-discharge, are now available for operation at gage pressures up to 150 pounds per square inch. In high-speed clarifiers or liquid-liquid separators, the bowl
CE/APPLICATIONS solids to fall out of the machine by gravity. No unloader knife is used. Such machines are used on leafy vegetables such as spinach and cut salad mixtures and also on NaCl crystals. Automatic short-cycle machines are also available commercially in which solids are unloaded a t full basket speed. The basket is held in fixed bearings and rotates about a horizontal axis. Clearance must be allowed between the unloader knife and the filter screen so that a residual layer of solids acts as a precoat for each successive load. Degradation or “glazing” of this precoat often means that a screen rinse must be included in the oueratine This - cvcle. , rinse may be used in each cycle or only Once in each Or l o The a medium is screen, supported inside a perforated drum. Typical basket sizes range from 20 to 42 inches in inside diameter; typical cycles
Figure 8.
The entire assembly i s suspended from three vertical posts. Filtered solids are manually removed through the top o f the machine in the model shown; in some designs the basket i s unloaded b y a knife as in a top-suspended centrifugal (courtesy Tolhursf Division, American Machine and Metals, Inc.)
of a pressure unit runs full, with liquid taken off through valved lines set to maintain the desired pressure and interface position in the bowl (7). I n scroll-conveyor machines with continuous solids discharge the chief problem is the design of shaft seals to operate in the presence of liquids and solids. High-speed separators also operate under vacuum, a t pressures down to 5 mm. of H g absolute. Link-suspended filtering centrifugals have been operated under moderate vacuum, a t absolute pressures of 250 to 500 mm. of Hg; a few special machines have been built, as indicated below, for operation a t much lower absolute pressures. Frothing Liquids. Liquids which foam or froth pose serious problems for a centrifugal separator. If the frothing is not severe, the problem may be solved by providing oversize
Figure
9.
Link-suspended filtering centrifugal
High temperature centrifugal
This reinforced unloader assembly i s used to discharge tars (courfery Wesfern Sfafer Machine Co.)
casings. In high-speed clarifiers, it is possible to remove the liquid with a paring device or centripetal pump, which converts the kinetic energy of the liquid in the rotating bowl into pressure energy. The liquid is thus discharged without being sprayed or jetted into the casing. The paring device, also, acts as a pump and may discharge the liquid a t pressures up to 100 pounds per square inch. Some materials do not foam under vacuum; with others the froth breaks when brought into contact with a hot surface. For such applications jacketed separators operating under vacuum are used. Fractional Crystallization. Centrifugal filters are coming into use for the separation of isomers and other close-boiling substances by fractional crystallization. One example is the separation of xylene isomers mentioned earlier. Another is the concentration of vinegar from 175- to 235-grain material by freezing out some of the water in scraped-surface heat exchangers, followed by filtration of the ice crystals in a topsuspended 36-inch automatic basket centrifugal operating on a 12-minute cycle. A proposed process for sea-water desalting by freezing also involves separation of the ice by centrifugal filtration. OTHER APPLICATIONS. Centrifugal separators are finding some applications in processes where formerly they were used little or not at all. Sewage disposal is one example. Digested sludge is dewatered in scroll-conveyor centrifuges in several localities, including a large installation a t the Los Angeles County Sanitation Districts’ Joint Disposal Plant. Similar machines are also used on raw primary sludge prior to incineration. Another application is on flue dust from oxygen-conversion steel mills. This dust is almost unfilterable. Solidbowl, scroll-conveyor centrifuges have been used successfully, despite the large slurry volumes and slow sedimentation rate of the dust. A final highly special application is in removing dirt from gelatin solutions used in making optical filters. The solutions had a viscosity of 80 cp. a t the maximum permissible temperature. They were strongly subject to bacterial attack, foamed readily, and contained both floating and sinking solid particles. Furthermore. absolute clarity of the centrifuged solutions was necessary. The answer to this problem was a special factorymade, double-bowl vacuum centrifuge, which operates at an pressure Of mm. Of Hg. This machine has been described in detail in the literature ( 3 ) .
VOL. 53, NO. 6
JUNE 1951
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PERFORATED BASKET UNLOADER KNIFE
?\‘E
SOLIDS UISCHRRGE
CRYSTAL DISTRIBUTOR
/ UNLOADER HYDRAULIC PUMP
Figure 1 0. trifugal
L L QUID OUTLfT
FILTRATE
Horizontal automatic short-cycle filtering cen-
All steps are made at full basket speed. seconds
Cycle times range from
from 40 seconds to 3 minutes. These machines find their chief application in handling large tonnages of relatively coarse crystals such as ammonium sulfate. CONTINUOUS SOLIDS DISCHARGE.Filtering centrifugals with continuous solids discharge are available in two main types: those with cylindrical rotors and those with conical rotors. They are further differentiated according to the method of solids removal. I n all cases, every effort is made to put down a uniform layer of crystals so that washing and mother-liquor displacement will be effective. Cylindrical screen centrifugals with an internal helical conveyor are available in various sizes. The “screen” is usually the slotted wall of the centrifuge bowl. Slurry is admitted near one end of the horizontal bowl, depositing a layer of solids which is moved by the conveyor over the slotted surface to discharge slots a t the other end. During their travel the crystals may be sprayed with wash liquid. These handle relatively coarse crystals such as XaCl in the manufacture of chlorine by electrolysis. Other cylindrical screen centrifugals also turn about a horizontal axis, but the solids are moved over the filtering surface by a reciprocating pusher, which moves a n inch or so every few seconds. Solids reaching the basket lip fly off into the casing and fall out a discharge chute. They may be washed with fairly small amounts of liquid during their passage over the screen. Basket diameters range from 12l/2 to 48 inches, with nominal capacities of one to two tons per hour up to 25 tons per hour, on crystals of which 65y0 are coarser than 35 mesh. These machines handle coarse and mediumcoarse crystals, and solids which can be pushed as a sleeve over the filter surface without cracking or crumpling. Crumpling is reduced in multistage units of the same general design, in which feed admitted to a small-diameter basket where it is filtered, after which the solids
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40 to 180
Figure 1 1 . centrifugal
Reciprocating-conveyor
Slurry feed is brought up to basket speed in the rotating funnel. Deposited solids are moved over the filter screen b y the pusher and fly off the basket lip into the casing
are pushed out of the first stage into successive stages of increasing diameter. Since the travel distance in each stage is small. the cake is less likely to crack or channel than in a single-stage machine. The power required is said to be less, and washing and liquid removal are said to be more effective. Capacities range up to 44 tons per hour of coarse crystals. Conical screen centrifugals have recently found increasing application in the process industries. In these separators the feed is admitted to the small end of the cone, where most of the filtration takes place. The deposited solids are then removed by one means or another to the larqe end of the cone, being “dried” and perhaps washed on the way. After this they fly over the basket lip into the casing. Because of the design of the expanding cone, solids tend to move through the machine of their own accord. and little power is required. In the simplest machines the cone angle is slightly larger than the angle of repose of the solids and no external urging is needed to make the solids flow. I t has proved to be very difficult, however, to obtain consistently satisfactory operation from such a device, for a slight change in the angle of repose makes the machine inoperable. Its chief application has been in the dewatering of washed coal particles up to ’/4 inch in size. A similar machine, also used chiefly for coal dewatering, is a conical screen unit with a basket which oscillates on its longitudinal axis. Rotational speeds are fairly low, but capacities on coarse materials such as ‘/d-inch coal and naturally occurring potash crystals range up to 25 tons per hour in a machine 40 inches in diameter a t the large end. Power consumption is very low and the life of the filter screen is said to be very long. Conical screen machines with a differential solids conveyor have appeared only recently in most of the process
INDUSTRIAL AND ENGINEERING CHEMISTRY
continuous filtering
industries, although they have been used for coal dewatering for a number of years. The conveyor normally turns slightly faster than the bowl. Near the slurry inlet at the small end of the rotor, the conveyor often tends to hold back the slurry and prevent it from flowing too rapidly over the screen; near the discharge end the conveyor does move the solids over the screen surface. This type of separator has found the following applications : dewatering of fibrous solids: such as paper pulp and chemical fibers; removal of pulp, skins, and seeds from tomato juice, citrus juices, and fruit purees; dewatering of medium to coarse crystals (usually larger than 100 mesh); and the wet classification of crystalline solids. Capacities range from a few hundred pounds per hour on a IO-inch unit to 50-75 tons per hour of coarse crystals on a 26-inch machine.
Acknowledgment Thanks are due to a number of centrifuge manufacturers for their assistance in the preparation of this article and especially to C. M. Ambler of the Sharples Corp., E. G. Piper of the Bird Machine Co., J. A. Schneider of the Western States Co., and G. F. Wheelwright, Jr., of the DeLaval Separator Co. literature Cited (1) Ambler, C. M., Chem. Eng. Prngr. 48, 150 (1952). (2) FloFod,J. E., Chem. Eng. 62, No. 6, 217 (195 J). (3) Meyers, J. J.,Smith, A , , Smith, J. C., Chem. Eng. Prngr. 51, 415 (1955). (4) Smith, J. C., Chem. Ind. 65, 519 (1949). (5) Smith, J. C., Euclides (Madrid) 12, 1 (1952). (6) Sorochenko, A. F., Korobchanskiy, 0. A., Khim. Mashinostroenie (U.S.S.R.) 1959,No. 5, pp. 1-3. (7) Sullivan, F. E., Chem. Eng. Prngr. 52, 83-F (1956). RECEIVED for review March 15, 1961 ACCEPTED March 21, 1961 Division of Industrial and Engineering Chemistry, 139th Meeting, ACS, St. Louis, Mo., March 1961.
