US2086951A - Apparatus for conditioning mixtures of granular solids and liquid for centrifuging - Google Patents

Description

.Iuly 13, 1937. G. E. STEVENS APPARATUS FOR CONDITIONING MIXTURES OF GRANULAR SOLIDS AND LIQUID FOR CENTRIFUGING Original Filed April l. 1952 3 sheets-sheet `1 NDD WQfy L INVENTOR. G. e van s ATTORNEY.

July 13, 1937. G. E. STEVENS 2,086,951

` 'APPARATUS FOR CONDITIONING MIXTURES OF GRANULAR V SOLIDS `AND LIQUID FOR CENTRIFUGING original Filed April 1, 1952 s sheetssheet 2 L I X@ Q s N s u Ns f5 V Lg Q Y INVENTOR. 6.5.5even5 BY Y 1 n (I l ATTORNEY.

July 13, 1937. a E. STEVENS 2,086,951

` APPARATUS FQR CONDITIONING MIXTURES GRANULAR SOLIDS AND LIQUID FOR GENTRIF'UGING:`

Original Filed ApriLl.' 19:52 3 sheets-sheet :s r

ATTORNEY.

i Patented July 13, 1937` l Y 7 UNITED STATES PATENT i OFI-ICE APPARATUS FOB CONDITIONING MIX- TURES OF GRANULAR SOLIDS AND LIQ FOR CENTRIFUGING l George E. Stevens, Scottsbluff, Nebr., assignor to Western States Machine Company, Salt Lake City, Utah, a corporation of Utah y Original applications April 1, 1932, Serial No. Y 602,621, and May 12, 1934, Serial No. 725,404.

l Divided and this application December 4. 1934,

Serial No. '156,003

5 claims. (ci. 12v-i7) I This invention relateslto apparatus for condihighly supersaturated and ready for further tioning mixtures of granular solids and liquid for treatmentin a, crystallizer. The object of this i A centrifuging, such as sugar massecuites and `further treatment is to cause the greatest possible i i i magmas, `and is intended to solve certain probprecipitation of sugar from solution into solid i 5 lems that have long been a source of much trouble grains or crystals of as nearlyuniiorm' size as 5 l and heavy loss in the manufacture of sugar and practicable. The crystallizers are `substantially l similar materials. horizontal drums provided with internal `stirrers 1 For purposes of illustration the invention is through which coolwater is circulated in" order l described as applied to the manufacture of sugar gradually to cool the low grade massecuite from l in beet factories,` although it is' equally advanthe vacuum pan and cause additional crystals to 10 `tageous in the production of cane sugar. In the be Vprecipitated therefrom. i i usual beet factory, after the sugar-containing Treatment in the crystallizers is usually con- Juice extracted from sliced sugar beetshas been tinued over a period of from 40 to 60 hoursvin subjected to boiling, filtering, and concentration order toobtain the optimum yield of sugar. 1It l5 and crystallization in a vacuum pan, the mass ofV results in the production of massecuite which is 15 sugar grains mingled with a considerable amount "verystiff and viscous due not only to the precipiof mother liquor (which t mixture y is termed a tation of sugar crystals but to the congelation oi massecuite) is subjected to centrifuging and colloidal constituents which tendl tobecome set washing in centrifugalsof the ltering type in or non-fluid at low temperatures. order to obtain relatively pure sugar 4grains and For proper centrifuglng massecuite must ow 20 to collect the `mother liquor separately. `A batreadily enough to permit it to build up quickly in tery or group of several centrifugal machines is an evenring around the inside of the centrifugal o usually arranged below a common overhead mixbasket and to permit proper separation of mother lng tank which supplies charges of massecuite to `liquor and sugar grains. Two of the important the centrifugals through discharge chutes, or factors aiecting the uidity of the massecuite are 25 goosenecks, leading from the bottom of the its liquid content andits temperature. YThe lack tank. A t t of fluidity characterizing low grade massecuite The centrifugally extracted syrup or mother from a crystallizer has always been a source of liquor, called green liquor, and the wash syrup much trouble to the sugarmaker. If he chills produced by thepassage of wash water "through the massecuite to'the low temperatures that are 30 sugar in a. centrifugal are conducted to separate necessary to recover the maximum amount of storage tanks, 4while the sugar grains retained sugarrb'y crystallization. a Stiff and ViSeouS mass in the centrifugal are discharged therefrom, cori-V iS obtained Which Cannot be centrifuged Satisveyed to a granulator for drying, and subse- `-factori1y; if he drops the massecuite from the` quently packaged. The green liquors and wash crystallizer while still fairly hot a great deal of 35 SYI'uDS Still `contain a largelenough sugar content the available crystal formation is sacriced and in solution to make its recovery a valuable and t0 e Corresponding extent Sugar iS left in Solution important item in sugar manufacture, and the and 10st in the nalmolaSSeS.

40 recovery of part of this dissolved sugar consti- For many years DaSt Various attempts to Solve 4o tutes what is known as the .raw side" operation this problem have been made. Heat jacketing of in sugar manufactureA as distinguished from the themixlng tenlv for the Purpose 0f Circulating hot white side operation briefly referred to above. Water alongthe bottom of the tank has been tried. In` beet sugar manufacture, centrifugally exbut without success `because the conduction of tracted liquorsy that hold in solution much less heat to the mass of material in thetank is so than'i)` percent. of dry matter are not considered slow that the temperature cannot be raised sub- 45 worth reprocessing andare usually sold as final stantially unless the heating fluid is hot enough to molasses for cattle feed .or the like.` In cane melt and redissolve and even caramelize the sugar manufacture the liquors may be reworked sugarv contacting the jacketed portion of the tank, economically down to a dry substance content of thus involving a much greater loss than gain. 50

` vabout 40 percent. In each case when further re- Partial reheating of the cooled massecuite in the covery of sugar from low grade liquors is made crystallizer by circulating hot water through the the sugar-containing liquors or syrups are subcrystallizer'cooling device also has been tried, but Jected to filtration. evaporation, and boiling in `this gained no advantage-quite the contrary, in

vacuum pans until the resulting massecuite is fact-because to achieve any appreciable reheat- 56 ing high temperatures must be used for a considerable period of time, and the entire mass of material must be heated, with unavoidable remelting and possibly caramelization of sugar, before the batch can be run off through the centrifugals. Moreover, this practice permits the massecuite to cool during passage from the crystallizers to the centrifugals, which may occupy a period of more than an hour for some of the charges withdrawn from the mixing tank, and cooling destroys any advantage that might have been realized from the preceding reheating operation.

Another expedient frequently tried out in prior practice is to add hot molasses or syrup to the massecuite in the mixing tank. This not only causes redissolution and melting of sugar grain but also adds heavily to the work imposed upon the centrifugals so that additional centrifugal apparatus and operatorsI are required, thus entailing a heavy'extra expense for which there is no compensating advantage. The most satisfactory expedient, and the one commonly used prior to the present invention, is to add cold water to the massecuite in the mixing tank. The cold water increases fluidity without remelting or caramelizing the sugar grains, but it redissolves a large amount of sugar and adds materially to the volume of material that must be run through the centrifugals.

The present invention solves this heretofore unsolved problem by providing improved apparatus for conditioning massecuites, magmas and like mixtures just before introduction into centrifugals,-apparatus which operatesin such manner as substantially to eliminate remelting, cara-melization and redissolution of the sugar grain while at the same time conditioning the material for easy and relatively quick centrifuging without increasing the volume of material to be centrifuged.

The improved apparatus in general comprises a mixing tank having in the bottom portion thereof a movable heat-transferring stirrer which is maintained at a proper temperature by the circulation of hot liquid therethrough and which is arranged to impart dry heat to a regulated stream of massecuite in an amount sufficient to render the massecuite fluent and in optimum condition for centrifuging.

The heat-transferring stirrer of the invention preferably presents effective heat-conducting surface of not less than one square foot for each cubic foot of the portion of material being stirred by it in the bottom portion of the mixing tank. In the embodiment of the invention illustrated in the drawings as the preferred form for use in the conditioning of massecuite dropped from crystallizers, the stirrer is constructed as a rotatable heating coil, with convolutions of the coil arranged to keep uniform the consistency of material adjacent thereto, and means are provided for delivering massecuite to the coil in a stream substantially equal to the flow of messecuite through the discharge chutes of the tank into the centrifugals. Thus the massecuite is continuously and uniformly conditioned and then centrifuged, until the entire supply of massecuite in the tank is exhausted.

The present application is divisional of my copending application, Serial No. 725,404, led May 12, 1934, and is also divisional of my co-pending application, Serial No. 602,621, led April 1, 1932. Subject matter shown and described but not claimed in this application, has been claimed in the aforementioned applications.

In the accompanying drawings, which illustrate preferred embodiments of the invention for the conditioning of low grade sugar massecuites,

Figure 1 represents a diagrammatic side elevation of a sugar plant arrangement system including crystallizcrs, the improved hot minglers and centrifugals,

Figure 2, a diagrammatic end view thereof,

Figure 3 represents a fragmentary vertical cross sectional view of a hot mingler tank of the type diagrammatically illustrated in Figure 1,

Figure 4, a section along the line 4-4, Figure 3,

Figure 5, a section along the line 5-5, Figure 3,

Figure 6, an enlarged fragmentary side view of a spiral coil of a hot mingler of the type shown in Figure 3, the coil functioning as the heating and stirring element for reducing the viscosity of the massecuite,

Figure 7, a sectional view of a modification of the tank and coil arrangement, and

Figure 8 is a section taken along the line 8--8, Figure 7.

In the drawings, in the several views of which like parts have been similarly designated, the crystallizers indicated by the reference numeral 9 are shown in an elevated position and are provided with outlets IO through which material passes by gravity into a hot mingler tank I2, the o lower portion of which has convergent front and rear walls. Extending transversely of the tank I2 is a deck I3 provided with openings I4, controlled by gates I5 in operative connection with levers I6.

Extending through the tank is a hollow shaft I'I carrying a pulley I8, which may be connected with any suitable driving element (not shown) to rotate the shaft. Spiral coils I9 and 20 eccentrically placed on the shaft are in fluid-conducting connection therewith, and it willbe observed that the coils are staggered as to their direction of Winding, the coils I9 winding to the left, and the coils 20 winding to the right. This staggered arrangement prevents the massecuite from ow- 4 crease the effective heating surface, add, to the r agitating action of the coils as well as providing bracing elements therefor.

The circulating system for the above apparatus comprises a storage* tank 23 which receives boiling waterfrom a conveniently located boiler or other source, by means of a conduit 24. A temperature regulator 25 thermostatically adjusts a valve 26 and thereby regulates the supply of hot water to the tank 23 in accordance with a predetermined temperature of the water in the tank. The tank is provided with an overflow outlet 21.

Water from tank 23 is circulated through the heating coils I9 and 2|] by means of a duplex pump 28, operatively connected with a motor 29. The water is drawn from tank 23 through a pipe 30 and then passes through a conduit 3| into the hollow shaft I'I. After circulating through the coils, the water enters return conduit 32 and again enters tank 23.

In carrying out the present invention, the massecuite is dropped from the crystallizers onto the deck I3 of the hot mingler tank I2, and the rate at which the massecuite passes through the openings may be regulated by adjustment of the gates I5 through the medium of levers I6. The

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massecuite on entering the tank I2 is at once subjected to the action lof the coils I9 and 20.

Since one of the dominant features of the present invention is to reduce the viscosity of the massecuite without dissolving any appreciable amounttof sugar, `the time during which the massecuite is subjected to the action .of the moving coils, and the temperature to which the massecuite is heated must be carefully. controlled,

The area of the moving heating surface is taken as a constant, and then the time factor is adjusted, depending upon the temperature of the massecuite entering the hot mingler tank, the density of the massecuite, the rate of movement of the heat transferring surface and the temperature of the circulating medium.

'Ihe present invention departs from the prior art in providing for a relatively large heating surface, preferably a moving heating surface, for contacting massecuite just before it. enters a centrifugal and while it is not desired to be limited to any specific ratio of heating surface to volume of massecuite, satisfactory results are obtained by providing at least one square foot of moving heating surface per cubic foot of massecuite when it is desired to `have a, relatively low temperature difference between the heating ,medium and the massecuite. t b

In other words, the ratio of heating surface to volume of massecuite must be adjusted, together with the temperature difference `so that` the massecuite can pass through the hot mingler and be reheatedto a suitable temperature in a relatively short time. Thus, little re-dissolving of crystals is encountered, while at the `same `time the viscosity of the massecuite is reduced to a point where it can be readily spun in the centrifugals. b b b In accordance with the present invention, there is employed a heating medium at a temperature only slightly higher than the final temperature "of the heated massecuite. `Although water` is the preferred heating medium, other fiuids may be used. It is of considerable importance to use a moving` heating surfacehaving a temperature from 50 to 65C. or slightlyhigher than theheated massecuite, since temperatures of C. to 55 C. ar `the highest that massecuite can be reheate without dissolving an appreciable portion of the sugar crystals. By `the continuous contact of the moving heating surfaces and their agitationl of the material, the temperature of vthe massecuite body being subjected to the moving surfaces can be raised a number of degrees C. in

, a time interval of only a few minutes.

The heating; coils I9 and 20 are preferably maintained at a temperature varying between C. and C., when the temperature' of the massecuite entering the hot mingler tank I2 is about 30s C. The massecuite is then heated to a temperature varying between 40 C. and 50'."v C., by the continuous application of dry heat.

Under the-"conditions above set forth, it takes approximately one and five-tenths seconds to" raise the temperature of one hundred pounds of massecuite 1 C., and approximately twenty-two seconds `to raise one hundred pounds of massecuite 15. C., orl a range of five to ten minutes to raise 'one ton oftV massecuite 15 C.,` `The time factor depends upon the temperature of the massecuite enteringthe tank, the density of the massecuite, the. temperaturel of the circulating heating fluid, the rate of movement of the heating` surfaceand the square feet of moving heating surface, the latter remaining a constant.

tion of the material is another factor influencing the beneficial results. The material upon dischargingfrom the hot mingler'tank can be readily spun in the centrifugals, and since it isin an ,undiluted condition an increase of at least 15 to 20 per cent in centrifugal capacity results from 4 the treatment.

The above explanation `discloses that there is a correlation ofl three factors, namely, the time factor, the ratio of effective heating surface to the volume of massecuite in the tank, and a low temperature difference between the re-heated massecuite and the heating medium.

In an actual operation, 124,360 pounds of heating fluid at a temperature of 60 C. were required each hour to transmit the necessary heat to the massecuite. Stated differently, approximately 450,000 Bft. u. per hour were required to heat 30,000 pounds of low grade beet sugar massecuite passing through the hot mingler tank per hour. Using water at a temperature of 60 C., 1040 B.,t. u. were required per square foot'of moving heating surface. 40B.` t. u. per degree difference in temperature per square foot of heating surface per hour gave satisfactory results.

When the crystallizers 9 are ready to drop, the auxiliary mechanism of the system is started and the temperature regulator 25 adjusted to the desired temperature. Hot water-is then circulated through the system, including the coils I9 and 20 until the system is well heated. The crystallizer 9 is then opened and the massecuite is allowed to flow onto the deck I3 in the hot mingler tank I2. After the deck I3 is well covered, all the gates I5 are opened a notch or two and the massecuite is distributed over the coils I9 and 20.

. tice is employed.

Massecuite passing through goosenecks 22 drops directly into centrifugals 33. While a gravity ow system has been illustrated, it is to be understood that the hot mingler tank is adapted for use-in any type of factory arrangement, and when the crystallizers 9 are disposed at a lower elevation than the centrifugals 33 and the mat terial pumped to the centrifugals, the tank may be installed adjacent the centrifugals at any convenient point between the crystallizers and the centrifugals without impairing its efficiency.

` In the modification illustrated in Figures 7 ACf) and 8, massecuite dropped from the crystallizers 9 is directed onto a chute 34 supported on the upper edge of tank i2.

A primary heating and agitating element 35 and a secondary heating and agitating element 36 of the system are disposed one above the other in the tank l2, which, in the operation, is a part of the secondary element.

The primary element comprises a tank 31, the walls of which are doubled to provide a water jacket 38. In the lower part of the tank, a shaft 39 of a rotary agitator 40 extends lengthwise thereof substantially in the axis of the circle of the rounded bottom of the tank.

The shaft 39 is mounted in bearings 4| and 42, three of which are supported on cross beams 43 adjacent the ends of the tank, and one of which is at a median point of the tank, supported on a cross beam 44. The portions 45 of the shaft extending through the bearings 4I and through the ends of the tank, are hollow and con-` nected with the body part 39 of the shaft by means of flanged couplings 46.

Tubular stirrers 41 on thehaft, of U-shaped form, have arms 48 which project radially from the shaft in connection with its hollow end-portions 45. These rotating stirrers operate to simultaneously agitate and heat the material in the tank in the manner hereinbefore described. Stufnng boxes 49 are provided at the ends of the shaft to provide a fluid-tight connection between the pipes of the fluid circulating system and the hollow portion 45,0f the shaft.

The main parts of the U-shaped stirrers, extending parallel to the shaft, are provided with scrapers 50, to wipe the surface of the tank at the inside of its jacket, for the purpose of presenting a clean surface for the ready transference of heat from the heating-fluid in the jacket to the material in the tank. The scrapers also aid in preventing any overheating of massecuite by reason of its remaining too long in contact with the water-jacketed surfaces.

The arms 40 are preferably arranged in pairs of unequal lengths, so that the parts of the stirrers extending parallel to the shaft, are at unequal distances from the axis of rotation of the same. In this manner, the stirring and heating element covers a wide area in its rotary movement and thoroughly agitates and heats the material Within said area, by the movement of the stirrers in intersecting zones.

An agitator constructed similarly to that of the first described heating-element has its axis of rotation coincident with the axis of the circular bottom portion of the tank l2. The agitator, like that of the heating element 35 comprises a shaft 5I, the end portions of which are supported in bearings on cross beams 52.

U-shaped tubular radial stirrers 53 are connected with the hollow end portions of the shaft 5| in a circulating system of the same character as that previously described. Scrapers 54 on the body parts of the stirrers, extending lengthwise of the tank, in parallel relation to the shaft, are provided to wipe the surface of the lower portion of the tank, the wall of which is doubled to provide a water jacket 55.

The tank 31 of the primary heatingelement has an overflow 56, the level of which may be varied by adjustment of a vertically movable gate 51. The gate has to this end a screwthreaded stem 58 projecting through an opening of a. support 5S erected upon the edge of the tank, and it is provided with a nut 60 bearing upon the support.

It will be understood that water circulation through the Water jackets 38 and 55 and through the stirrers 41 and 53, is effected in the same system as that disclosed in Figure 1, each of the aforementioned elements being provided withinlet and outlet connections in a manner well known in the art. The circulation of the heating fluid through the jackets and agitators is effected at a predetermined and automatically regulated temperature.

Likewise, if desired, each element may be provided with its own circulating system and subject to individual temperature control.

When massecuite is fed from the crystallizers onto the chute 34, it enters the primary element and is at once subjected to agitation by the rotary stirrers 41.

The rotary movement of the agitator 41 keeps the material in the tank 31 in motion while it is being heated by the hot water constantly circulated through the agitator and through the jacket of the tank. The Scrapers wipe the heating surface of the tank to constantly present a clean surface. It will be understood thatthe temperatures of the heating mediums are only slightly higher than the temperature of the entering massecuite to avoid a harmful increase in the temperature of the material.

The heated massecuite overflows from the primary tank 31 into tank I2 across the properly adjusted gate 51, and is then subjected to a second heating influence combined with an agltation action, by the heating fluid constantly circulated through agitator 53 and the jacket 55 and by the rotary movement of the agitator. The temperature of the heating mediums is preferably higher at this stage of the treatment, but only slightly in excess of the temperatures of the massecuite passing through the goosenecks 22.

It is to be understood that whenever it is desired to regulate the rate of discharge from the tank, the goosenecks may be valve-controlled.

In the preferred form of the present invention, there is no need to dilute the massecuite during or after crystallization, the treatment by means of moving contact with dry heat Within the body of massecuite being sufficient to readily reduce the viscosity of the massecuite, even though abnormally low temperatures have been used in the crystallizer's.

Since there is no increase in volume and a decrease in viscosity, the centrifugals operate at maximum capacity and with an improved yield of sugar per cycle, and the sugar obtained from the centrifugals may be of higher quality. These results mean substantial increases in the elficiency of sugar faqtory operation.

It is desired to point out that a dual action is effected in the heating operation. The massecuite moves through the coils or stirrers on its way from inlet to outlet, and at the same time the coils and stirrers are moved through the massecuite. In this way a relatively large volume of massecuite contacts each heating surface in a given period of time.

An example of the effectiveness of apparatus constructed in accordance with this invention in commercial operation is furnished by the following record from oneof the beet sugar factories in which it has been installed. This factory during its last campaign had an average of 44 crystal lizer hours for each 1150 cubic feet, or 107,000 pounds, of massecuite, during which period of time the temperature of the massecuite was lowered from C. to 30 C. It spun 22,379 tons of raw massecuite in 66.65 slicing days, or an average of 335.8 tons per day, or approximately 14 tons per hour.

` fterthe operatlonof the mingler became con-` tinuous at-the start oi:` the campaign, the masse-l cuite flowed through the gates in the deck ofthe i mixingtank as rapidlyas it` was drawnoi` into s reached the goosenecks it had been raised from C. to 44 C., in the average time'of about seven minutes, which was the average timeof one spin-` ning ycycle of the centifugals. Water `at s an average temperature of- 57` C. was used to maintain the temperature ofthe mingler.`

the material The, average `dry substance of entering the crystallizer was 90.0, andthe average `dry` substance ,leaving the' crystallizer was 89.8. Small amounts of lcold Water were introducedinto the massecuite in the crystallizers,

which accounts `for the `fractional difference in dry substance. There was no dilution of the `massecuite after leaving the crystallizers, and the percentage of dry substance, or density, of themassecuite as spun was the same as when leaving Raw massecuite contains gums, colloids, etc.,

f which upon cooling tend to jelliiy and become Very viscuous or semi-solid. i; Dry heat and agitation has the propertypf breaking up this` viscosity and rendering the material more uent, `much more so than the addition of cold water or For this reason, the apparatus of `my invention permitsthe boiling of lower purity raw pans to obtain the lowest possible molasses purity, since the subsequent treatment inthe mixer of the resulting toughf massecuite readily s conditions it for effective treatment in the centrifugals. ,l

It is to be understood that variations in the l construction and arrangement in the elements of the `system and the parts of the apparatus ineluded therein may be 'made within the scopez of the invention. Also it is to be understood that if Scrapers of the type shownin Figures 'l and 8 are desired, in la device of the type illustrated in Figure 3, they may be mounted on the coils I9 and 20, l i

While the foregoing description has pointed out that the hot mingler is particularly adapted for the treatment of massecuite passing from the crystallizers to the centriiugals,` it is to be understood that the apparatus may be effectively employed in other treatments in the sugar man-` ufacturing process and elsewhere, as at the affini ation station of a sugar refinery and in the conditioning of massecuites which pass from a vacuum pan to centriiugals without intermediate treatment in crystallizers.

For example, it maybe used to great advantage in connection with the white mixer for controlling the temperature and viscosity of white massecute after it is dropped from a Vacuum pan and during the centrifuging of the entire batch of massecuite. As a result of such treatment a bettercontrol ofthe ash and moisture content in the white sugar is obtained, and sugar of a more uniformy quality and better color is thereby produced. The continuous, `uniform high uidity of massecuite conditioned in this manner greatly increases the capacity of the centriiugals without loss of sugar grain by dissolution, caramelization or remelting.

The foregoing data as to temperatures, etc., relate to actual operations on the raw side of a beet sugar factory. Since white cane sugar massecuite, for example, is capable of withstanding lhigher temperatures` without injury than low grade massecuite, it will be understood by sugar engineersand operators that the temperatures `used in :conditioning this and other mixtures of granular solids, such as sugar, and liquids, such as syrup, may be varied in accordance with qualities of the mixture to be centrifuged. i i i What I claim and desire to secure by Letters Patent is:

lower portion of the tank from the upper portion thereof, controllable gates for regulating the iiow of` material from the upper to the lower portion of the tank, means for circulating i hot iiuid through said stirrer, and means for maintaining the uid circulating through the stirrer at a temperature not `materially above the nal temperature of the conditioned material adjacent the delivery passages, the circulating means havingcapacity to supply alarge enough flow of hot fluid to impart a uniform temperature to successive portions of the material flowing past the stirrer without substantial drop in temperature of the fluid so circulating.

of sugar `grains and syrup, the combination of a mixing tank forming a receptacle for the mixture to be conditioned and centrifuged, the bottom portion of the tank having outlet passages for delivering the conditioned material directly to individual centrifugals, an internally heated tubular stirrer revolubly mounted in the lower portion of the tank adjacent said outlet passages, means for forcing, a circulation of hot fluid through said stirrer while it is revolving, means for maintaining the hot fluid supply at a temperature not harmiully above the maximum temperature to be imparted to the mixture near the outlet passages, the hot fluid circulating means and stirrer being dimensioned to maintain a 4flow of hot fluid of large enough volume to transfer the required heat to the portion of the mixture being stirred without substantial drop in the temperature of the hot fluid passing through the stirrer.

3. In an apparatus for conditioning a mixture of sugar grains and syrup,- the combination with a mixing tank forming a receptacle for the mix- 2. In an apparatus for conditioning a mixture sioned to expose at least one square foot of heattransferring surface for each cubic foot of that portion of the mixture being stirred by it at a time, and means for continuously circulating through the stirrer a supply of hot uid at a predetermined temperature not harmfully above the maximum temperature mixture.

to be imparted to the 4. In a sugar centrifugal apparatus comprising a centrifugal separator and a mixing tank whose discharge outlet leads directly to the centrifugal, a partition partly dividing said tank into i communicating compartments, a tubular internally heated stirrer revolubly mounted in each compartment for heating in successive stages a stream of massecuite flowing through the compartments into successive contact with the stir- 0 rers therein, means for forcing a continuous flow of hot fluid through said tubular stirrers, and

means for maintaining the temperature of the` hot fluid owing through the stirrers not harmfully above the maximum temperature which it 5 is desired to impart to the massecuite as it enters the discharge outlet.

5. Apparatus for conditioning a mixture of v sugar grains and syrup for immediate centrifuging comprising, in combination, a mixing tank l0 forming a receptacle for mixture to be conditloned and centrifuged, the bottom portion of the tank having outlet passages for delivering the conditioned material directly to individual centrifugals, an internally lheated tubular stirrer providing at least one square foot of heating surface for each cubic foot of mixture being stirred revolubly mounted in the lower portion of the tank adjacent said outlet passages, means for forcing a circulation of hot fluid through said stirrer While it is revolving, means for maintaining'the hot iiuid supply at a temperature not harmfully above the maximum temperature to be imparted to the mixture near the outlet passages, the hot uid circulating means and stirrer being dimensioned to maintain a ow of hot iiuid of large enough volume to transfer the required heat to the portion of the mixture being stirred Without substantial drop in the temperature of the iluid passing through the stirrer.

GEORGE E. STEVENS.

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