Beet Juice Defecation Comparative, quantitative studies were made of a cold predefecation system and the Teatini process for purification of beet sugar juices. The studies were made first in the laboratory and then on a plant scale. Variables measured were colloids, sugar purities, color, and filtration notes. Some significant differences were found in colloid elimination, elimination of impurities, and final sugar quality between the two processes. The results of these studies should contribute to a better understanding of what takes place during purification of sugar beet juices.
GUY RORABAUGH a b
AND V.
I. MORRIS
Holly Sugar Corp., Colorado Springs, Colo. *
S
EVERAL yeais ago, this company studied two proposed schemes for reducing the amount of lime needed t o purify beet sugar diffusion juice in the manufacture of sugar. Even though neither process is now in use by the Holly Sugar Corp., the studies may contribute t o a better understanding of what takes place during purification of sugar beet juices. Conventional practice in this country at the start of this study (1937) involved the use of batch carbonation in which all the lime was added a t one time. The raw beet sugar diffusion juice was heated t o 80" t o 90" C., and pumped t o first carbonation tanks, approximately 2% lime on beets was added with agitation, and then carbon dioxide was bubbled into the tank. A precipitate of calcium carbonate was formed, which carried with it many of the impurities in the beets. After filtration, the juice was heated t o 90" t o 100" C. and further carbonated to a lower alkalinity (second carbonation). It was again filtered, treated with sulfur dioxide, and evaporated t o thick juice which was sent t o vacuum pans for crystallization of sucrose. The parallel development of continuous carbonation in combination with a Dorr thickener was adopted by almost all plants (1, I, 8). Unfortunately, the schemes described in this paper presented difficulties in settling in the Dorr thickener and were not put into practice, though they resulted in certain economies in the batch process.
tinct operations. The first is predefecation, where lime is added to some definite p H point or amount (usually from 0.20 t o 0.30y0 on beets). Second is the predefecation pause, where the above juice is held with agitation for around 2 minutes in order t o stabilize the flocculated material. Third is the main defecation, where 1.00 t o 3.00% lime on beets is added; and fourth is the carbonation, where carbon dioxide gas is added t o precipitate out
1
OPTIMUM ALKALINITY
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The two processes studied were cold predefecation and the Teatini process (9). The work was done at the Hardin, Mont., factory, a non-Steffen house, where the necessary equipment was installed for operation of both processes. I n the purification of raw beet juice, where alkaline predefecation is used the lime purification of juice is divided into four dis619
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INDUSTRIAL AND ENGINEERING CHEMISTRY
juice from beets shows them t o consist primarily of pectic substances and proteins. The Teatini process, as applied t o the beet sugar industry, attempt,sprimarily t o produce a thin juice free of colloidal materials. This object,ive is realized b y treating the raw juice direct from the diffusion battery a t a temperature 40" t o 50" C. with a quantity of milk of lime sufficient t o raise the p H and alkalinity to predetermined points, a t which practically all of bhe colloidal materials in the limed juice are coagulated into large flocs. These flocs are then aggregated and st,abilized by the addition of liquid sulfur dioxide and the temperature is raised t,o 90" C. in raw juice heat,ers, so that later dispersion and return to the colloidal state are avoided during the completion of normal carbonation and filtration processes. The theory as advanced by Teatini is that tmheliquid sulfur dioxide forms a hydrate upon its injection into t,he limed juice, and this molecule, being heavily negatively charged, attracts a large number of the lime-colloid flocs which probably carry a light posit,ive charge due t o the alkaline reaction of the mixture; this i ~ s u l t a n product t remains stable throughout the regular factory carbonation process. Another theory is that the liquid sulfur dioxide forms a calcium sulfite which, owing to the speed of reaction, is formed in an infinitely large number of extremely small crystals, which provide a nucleus for the coagulation of the previously flocculated colloidal materials. The cold alkaline predefecation process depends solely upon the use of lime and was originally developed in Europe. Many mechanical attachments and variations of adding the necessary lime have been used and developed; they differ not in basic theory, but only in details of the operation of reaching an optimum precipit,ation point in more or less uniform gradual stages between a p H of 10.8 to 11.1, followed by the addition of lime for main defecation, heating, and carbonation. I n no case, however, is a single addition of all predefecat#ion lime recommended; the reaching of the opt,imum point. of p H and alkalinity t,o give the best conditions for completing the normal carbonation process must be follow-ed by a rest period, and this rest period followed by a final heating either before or after the normal carbonabion is completed. The rest or pause period serves t o stabilize the floc. The principle is that, several successive additions of lime provide a series of different conditions, each of which is optimum for flocculation of one specific group of colloids. The quality of the raw juice in any event seems t o play a very import,ant part in juice purification. DBdek in 1939 ( 3 ) and McGinnis ( 7 ) suggested that experimental rt:sults pertaining t o the processing of sugar are valid only for the particular beets concerned.
OBJECTIVES The object of this experiment a t the Hardin plant was not to prove or disprove the value of either form of predefecation, but to compare the two processes under actual operation rather than in a series of laboratory scale tests. Considerable experimental work was necessary in the laboratory in order t o determine optimum flocculation points, color, filtration time, colloids, and temperature for bot,h processes. After this work, the tests were carried out on a plant scale. The objectives and the criteria used to judge the results were:
A reduction in the total amount of lime required for purification of raw juice Increased capacity of the first carbonation filtration station, due t o the more granular nature of the first carbonation precipitate and to the decreased amount of lime to be handled Increased capacity and decreased losses on the first carbonation Oliver filters due to the characteristics mentioned above. Increased capacity and efficiency of the evaporator station on account of the nonforming, low-viscosity, and low-lime salt characteristics of the thin juice Increased capacity of the pan and centrifugal stations due t o the absence of colloidal materials and low viscosity of the resultant sirups
Vol. 43, No. 3
Increased extraction due to higher percentage of crystallization possible where colloidal materials have been removed Improvement in final white sugar
MECHANICAL EQUIPMENT The equipment for the predefecation installation was designed t o be used for either cold predefecation or Teatini processes and was capable of being changed over from one t o the other with a minimurri loss of time. The installation was made up of two tanks, 6 feet in diameter and 8 feet 6 inches in height, including a cone bottom which sloped a t a n angle of 30" with the horizontal. Both tanks were supplied with agitators with four sets of revolving paddles and two sets of stationary deflectors, which were designed so their pitch could be changed through 90 and the travel of the juice reversed by reversing the agitator motors. The speed of the agitators was 50 r.p.m. A third tank equipped with agitators and sweeps driven a t 15 r.p.m. was used as a receiving tank, t o give the necessary retention period for the predefecated juice, and also as a supply tank for first carbonation. T h e juice from both processes was pumped through heaters by means of a horizontal centrifugal pump with capacity of 600 gallons per minute. I n order to maintain as even a temperature as possible, a return line was run t o the receiving tank from a point after the heaters and ahead of the first carbonation inlet valve. This allowed for recirculation through the heaters and back to the receiving tank when the first carbonation valve was closed and eliminated irregular temperatures. A Leeds and Northrup Microinax recorder was used for H control of both processes, but as p H was found not to be txe only controlling factor, a laboratory check of the percentage of calcium oxide in the predefecated juice and examination of the type of flocculation were found necessary to control the processes. Liquid sulfur dioxide was obtained in carload lots and stored in a tank, and was drawn into a calibrated glass vessel for discharge into the prelimed juice.
LABORATORY PROCEDURES Before either process was put in operation it was necessary t o determine the point at which the optimum flocculation of colloids took place and, in the case of Teatini, the proper dosage of liquid sulfur dioxide.
A sample of raw juice was obtained from the measuring tank and divided into ten or more 400-ml. portions, and milk of lime was added in incremental amounts t o each sample, so as to obtain an alkalinity from a minimum of 0.10 t o a maximum of 0.20 gram of calcium oxide per 100 ml.; the lime q-as added while the raw juice was well agitated and a t a rate comparable with factory scale operation. T h e samples were then all heated simultaneously t o a temperature of 90" C. and allowed t o settle for the same amount of time in glass cylinders. The settling rate, nature of the precipitate, and clarity of the supernatant liquid were noted, after which the samples were filtered and the speed of filtration and physical characteristics of the precipitate were noted. From each sample were then withdrawn the samples necessary for colorimetric determinations, determination of alkalinity, p H value, and lime salt content, and ultramicroscopic examination. ANALYTICAL METHODS Alkalinity of prelimined juice and other juices was determined on filtered juices by acidimetric titration against phenolphthalein as an indicator and expressed as grams of calcium oxide per 100 ml. Total lime including calcium carbonate was determined by acidimetric titration and expressed as grams of calcium oxide per 100 ml. Filtration rates were expressed as time in minutes t o filter 400 ml. All filtration rates mere determined under same conditions and using the same filter. Color was determined on a Stammer colorimeter and expressed as degree Stammer. Lime salts were determined by titration with standard soap solution and expressed as grams of calcium oxide per 100 Brix. Ultramicroscopic examination of the juices was used for a semiquantitative comparison. All juices were examined a t the same Brix after being filtered through highly retentive filter paper, slides were prepared clean and free from dust, and the colloid content was determined as evidenced by the Brownian movement in the field of the microscope. The arbitrary numerical values used for coinparing colloids in different juices a t a definite standard Brix of 10 were obtained by counting number of Brownian movements in a unit time and a unit volume.
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1951 Figure 1 shows the results of a number of determinations of colloids, lime salts, color, and rate of filtration plotted against alkalinity in grams of calcium oxide per 100 ml. under laboratory conditions. Because of the difficulty experienced in measuring small v o l u m e s of l i q u i d s u l f u r dioxide (of the order of 0.1 gram Of dioxide per liter of juice), the optimum amount of sulfur dioxide t o be added for the Teatini process was determined in the factory, where i t was Possible to measure a definite volume of sulfur dioxide into a calculated volume of juice. A series of determinations was made with amounts of sulfur dioxide both smaller and greater than 0.1 gram per
Table 1.
Highest Lowest Ap arent purity of cossettes Iverage Highest Lowest Av. apparent purity diffusion juice First carbonation juice Evaporator thick juice ~ v elimination . carbonation, % Av. alkalinity prelimed juice First carbonation juice Av. pH second carbonation juice Evaporator thin juice Av. filter cloth on first filtration, sq. feet/100 tons beets Av. sugar loss, lime flume, % ' on beets Av. lime salts Thin juice Blowup thick juice *v.Thin Brixjuice Thick juice Difference Total sugar traces in evaporator leg line, %
for colloids at the different a m o u n t s of s u l f u r dioxide addition, and the minimum amount of sulfur dioxide required t o set the reaction was determined. Figure 2 shows the effect of temperature on colloids and color in thin juice under laboratory conditions of raw juice prelimed t o 0.15 gram of calcium oxide per 100 ml. This curve shows t h a t both color and colloid dispersion increase as the temperature varies above or below 90" C.
FACTORY OPERATION The original plan was t o operate the Teatini process for 7 days, run for 24 hours with normal lime addition and no predefecation of any kind, and follow with a 7-day period of cold predefecation and then 24 hours without any form of predefecation before changing back t o Teatini; the cycle was t o be continued through the campaign. Because of trouble with the gas blower on the carbon dioxide system, it was impossible t o carry out this schedule and actually cold predefecation was used for 3 weeks before the second change t o Teatini. This gave a longer run on cold predefecation than on Teatini. The first Teatini run was for 7 days, and the first cold predefecation run was for 23 days. The sec* ond Teatini run was for 7 days and the second cold predefecation run was for 9 days. There was a 24-hour break between each change-over while the juice from each process cleared through the factory.
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I n operation, the Teatini method was a batch process requiring a n operator. Each tank was filled and limed, the liquid sulfur dioxide was added, and the tank was emptied. Pneumatically controlled inlet and outlet valves and hand-operated plug cocks on the lime and sulfur dioxide lines simplified the operation. The raw juice entered at the bottom of the tank and at the same time the milk of lime valve was opened. T h e measured amount of milk of lime was allowed t o flow in to the juice as it filled the tank. The orifice through which the milk of lime was discharged was of such a size that the total amount was mixed with the juice at the time the inlet valve was closed. The proper amount of liquid sulfur dioxide for the batch was drawn into a calibrated glass vessel and discharged into the relimed juice. T h e contents of the tank were then released into t f e receiving tank. This completed the cycle and the next batch was started. As a result of the laboratory work, an optimum alkalinity of 0.14 to 0.15% calciumoxide on raw juice or 0.20 to 0.22y0 calcium oxide on beets was maintained with the corresponding p H used
Results during Operation
First Teatini Period 11,936 1,705
Total beets sliced, tons Av. beets sliced, tons per day su iverage ar in cassettes' 7%
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First Cold Predefecation Period 34,328 1,635
15.97 17.0 13 7
16.39 18.4 14.2
84.8 88.5 80.9 86.0 88.1 89.0 17.0 0.14 0.091 8.7 8.7
85.3 88.6 79.3 87.0 89.5 90.2 21.5 0.14 0.078 8.8 8.8
17.89 0.02
10.87 0.02
0.009 0.010
0.013 0.011
Second Teatini Period 11,362 1,623 15.14 17.0 11.9
Second Cold Predefecation Period 13,610 1,701
Total and Weighted Averages PredefecaTeatini tion 23,298 47,938 1,664 1,653
16.21 16.7 12.9
15.67
16.05
83.9
84.5
10.38 0.02
13.10 0.02
.... ....
.... ....
....
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8 10 0.02
9.78 0.02
0.017 0.013
0.022 0.017
0.013 0.012
14.9 62.1 47.2
13.0 61.1 48.1
11.3 62.3 51.0
12.1 60.9 48.8
13.1 61.0 49.1
8.8
30.2
11.9
13.5
10.4
0.016 0.012 12.8 62.2 48.3 ,
26.0
as control. This p H varied with different batches of beets. The optimum point was checked at regular intervals but, regardless of conditions of beets or raw juice, did not vary beyond these close limits. The sulfur dioxide addition was a t the rate of 0.25 pound per ton of beets. I n the cold predefecation process, which is continuous, the raw juice entered the primary tank a t approximately the level a t which the juice circulated. The rotation of the agitators was such as to cause circulation down through the middle of the tank and out the bottom, then up through a loop to the established level in the secondary tank, where the agitation again drew the juice t o the bottom of the tank from where i t flowed over a vented loop to the receiving tank. Milk of lime of about 16y0 calcium oxide content was discharged continuously into flat plates which diffused it over the surface of the inflowing juice: 75% of the milk of lime was added to the primary tank and the other 25% t o the secondary. Addition of all the lime in the primary tank did not seem to give as satisfactory results a s adding it in two stages. The necessary pause or holdup time was achieved in the receiving tank. An alkalinity of 0.14 to 0.15% calcium oxide on raw juice or 0.20 to 0.220/, on beets was maintained with the corresponding pH a s close as possible, and every effort was made to keep the process in continuous operation, a s any shutdown of any duration was invariably apparent in the colloid count somewhere along the pro cess. Table I presents operating results during the actual operation of each process and are baet end figures. Table I1 gives sugar end and other operating results during the operation of each process and includes the 24 hours a t the end of each change-over, when no predefecation was used.
OPERATING RESULTS As the relative merits of the two processes must be judged on actual results of factory operation, accurate operating data were kept and recorded along with the laboratory data. Tons of Beets Sliced. The slicing capacity of the factory was not influenced to any great extent by either process, unless the lime addition at first carbonation was cut too low, at which point the Borden filters slowed up. The slicing average was better during the Teatini process, but this was due t o trouble with t h e carbon dioxide gas pump during the time Teatini was not in operation.
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Evaporation. I t was the opinion of the operators t h a t T o t a l and Weighted the juice boiled somewhat First First Cold Second Second Cold Averagesfaster in the evaporators durTeatini PredefecaTeatini PredefecaPredefecaPeriod tion Period Period tion Period Teatini tion ing Teatini operation, but there W h._.. ite ~ n i n-r ia t. i is only a slight difference in White pans bailed, total 69 237 61 80 130 317 Av. apparent purity white massecuite 91.4 92.4 91.7 93.1 91.6 92.6 the Brix of thin juice to evapoAv. apparent purity high green 83.3 85.2 83.2 86.9 83.3 86.7 rator thick juice in favor of Av. difterence in purity-massecuite t o high green 8.1 7.2 8.5 6.2 8.3 6.9 Teatini. The percentage of A v . boiling time white pans, hours 1.54 1.60 1.61 1.80 1.58 1.66 sugar traces in the determinaHigh raw pan d a t a High raw pans boiled, total 50 196 61 84 111 280 tions of sugar in the evapoA v . apparent purity high raw masserator leg line as determined cuite 85.5 85.7 84.5 85.3 85.0 85.5 A T . apparent purity machine sirup 74.4 76.6 75.5 77.4 75.0 76.8 by the qualitative 1-naphthol Av. difference in purity massecuite t o machine sirup 11 1 9.1 9.0 7.9 10.0 8.6 test shows that the Teatini Low raw pan d a t a juice did not foam or tend t o Low raw pans, total 17 57 19 20 36 77 cause entrainment as much Total low raw massecuite, cu. feet 22,750 72,815 23,400 24,950 46,150 97,765 A v . low raw massecuite, cu. feet per as the cold predefecation juice. ton beets 1.92 1.86 2.06 1.83 1.99 1.84 X v . apparent purity low raw masseDate on White Pan and ouite 74.6 74,7 73.9 76.4 74.3 74.9 High Raw Pan. The purity 77.87 79.08 A v . true purity loiv raw inassecuite 78.06 78,96 77.67 79.33 Av. true purity molasses 64.42 63.93 62.35 63.19 63.41 63.65 drop between the white mas.4v. difference in t r u e purity massecuite t o molasses 13.64 15.03 15.32 16.14 14,46 15.43 secuite and the high green Sugar d a t a sirup shows a decided differAv. granulated sugar ence in favor of Teatini, and Color grade .4 A+ A A+ A+ 12.1 10.2 2.9 14.0 11.1 A8+3 SOz, p.p.m. the same is true of the drop SOa, % 0.0014 0,0010 0.0016 0,0007 0.0015 0.0009 A v . ash by conductivity, % 0.0097 0,0092 0.0084 0,0064 0.0091 0.0082 in purity between the high Sugar i n molasses raw massecuite a n d t h e 2.43 2.31 2.50 2.36 2.46 2.32 yo on beets 15.45 15.87 14.46 14.08 16.63 yo on sugar in beets 15.19 machine sirup purity, even 49.40 42.20 46.49 45.23 39.16 37.20 Elimination though the massecuite purities are higher in both cases in the cold predefecated juice. During the Teatini periods certain pans showed a very high Sugar in Cossettes and Purity of Cossettes. These figures are drop in purity between the massecuite and green sirup but it in no way affected by either process, but are presented as a basis was not consistent, as a pan with a high drop in purities would of evaluating the results obtained, as they show the quality of be followed with one or more with a n average drop. This was beets sliced during each period. unexplained, but knowledge of how to obtain it consistently Purity of Diffusion Juice and First Carbonation Juice. The would be an advantage to sugar end operation. average rise in purity between the diffusion juice and purity of Low Raw Pan Data and Molasses Loss. Here the average drop f i s t carbonation juice was nearly one point higher during the in true purity between the true purity of the low raw maqsecuite cold predefecation runs than during the Teatini operation. This and that of the final molasses reversed from what the drop was in shows up as a thick juice of higher purity for cold predefecation. the white and high raw pans and the drop was higher in favor of Elimination. Elimination of impurities through first carthe predefecation process. The amount of sugar that is lost in bonation was 7.27’c higher for cold predefecation than Teatini. final molasses is extremely important and affects not only the The formula for calculation is: operational efficiency of the factory but also the economics of the 10,000 ( A - B ) process. The molasses loss in the Teatini process was higher First carbonation elimination = A (100 - B ) than in the cold predefecation process and 1.41 pounds more of A = purity of first carbonation juice sugar were lost for every 100 pounds of sugar entering the factory B = purity of diffusion juice during operation of the Teatini process than during cold predefecation. The over-all elimination of impurities was higher durAlkalinity and pH. The best filtering conditions seemed to be ing the cold predefecation periods than during the Teatini periods. evident at a higher first carbonation alkalinity for the Teatini Calculation of Elimination. Tons of impurities entering facoperation than for cold predefecation. The alkalinity of both tory - tons of impurities leaving in molabses = tons of impurities processes averaged 0.14 gram of calcium oxide per 100 ml., aleliminated. though considerable variation from this point was unavoidable at times. The p H of second carbonation was held a t a n average Tons of impurities eliminated X 100 of 8.7 during both processes. = yo elimination Tons of impurities entering factory Filtration. .4t Hardin, with Borden filters which are of the vacuum type, filtration capacity was seriously lowered by the Calcium Oxide Per Cent on Beets. The average calcium oxoperation of any form of predefecation, and filtration was not as ide on beets showed a very slight advantage for cold predefecasatisfactory under Teatini operation as with cold predefecation. tion, amounting t o 0.05% difference. The calcium oxide per The filter cloth consumption was 207, higher during Teatini cent on beets reached as low as 1.60y0during some periods of operation than during cold predefecation. All of the Borden cold predefecation operation, but this point could not be reached capacity a t first filtration was required to be in use when the during Teatini operation. Teatini process was in use, whereas only SOYc of the capacity was required for cold predefecation. RESULTS Sugar Loss in Lime Flume. The sugar loss in the lime sewer The inspection of the juices under the ultramicroscope showed a per cent on beets showed no variation in the two types of opervery marked difference in Brownian movement and type of floes. ation. The floes in the Teatini juice appeared practically circular in shape Lime Salts. The lime salts in the evaporator thin and blow-up and no sign of movement or breaking an-ay of the colloids from thick juice are slightly lower during the Teatini process. In the main floc as evidenced by the lack of Brownian movement, neither case were the lime salts excessive. Table 11.
Sugar End and Other Operating Results
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March 1951
a n d the indication was that the colloids were stable and tendency towards redispersion had been halted. I n the cold predefecation juices, the flocs were irregular in shape and occasionally one of the colloids was seen t o break away from the floc and move across the field a s shown by the Brownian movement. In almost every case a tendency toward a partial redispersion of the colloids was noted and was evidenced by the increase of colloid count in the stages from the Borden filtrate to the evaporator thick-juice stage.
, I
e
18
B
I
-C O L D P R E D E F E C A T I O N Lo
I
----TEATIN1
e
e
o
516;
6
E: 14
4
12
2
IO
0
I
HlQH
-I
0 3
\
2.
2 L
I 5
l
'9 \ \
\
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I STAGE IN PROCESS FROMRAWJUICETOLOWRAWMASSECUITE
Figure 3.
Flow of Colloids
Cold predefecation -_ - Teatini
A
IO
THIN JUICE
Y
2 PO
d
0
20
25
a
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I n the case of operation without any form of predefecation during conventional practice in 24-hour break period with only regular batch carbonation, a definite type of flocculation was observed. The flocs assumed more of a chainlike arrangement and appeared to be loosely bound together; this was borne out by the very rapid redispersion of the colloids a t the advanced points of the process. After 24 hours during the changeover from one type of defecation to the other without any type of predefecation, poor low raw side operation was noted a s evidenced by sticky, hard working, raw massecuite, and high molasses yields. Figure 3 was made up from the information gathered from daily determinations during the factory operation on each type of predefecation on the various sirups in the factory. The colloid count is the actual number of colloids visible in the ultramicroscope aa evidenced by the Brownian movement and calculated to a standard Brix or dry substance basis. Examination of this curve shows a tendency toward the redispersion of the colloidal flocs in the cold predefecation compared to t h a t in the Teatini juice. The colloids in the Bordon filtrate were nearly equal for the two processes, but showed a definite rise in the cold predefecation process a t the thin juice stagc. The rise in the colloid count of Teatini a t the thin juice stage could possibly to due to an insufficient amount of sulfur dioxide or because the amount used was not thoroughly mixed through the prelimed juice. Both processes show a marked reduction in colloids a t the thick juice stage, and no explanation of this was obvious. Practically equal colloidal counts were obtained in the blowup thick juice or sulfured thick juice, and here the colloids reached a minimum. This may be due to sulfitation, but there is no substantiation to this theory. Figure 4 shows the variation in colloid count and color in the Borden filtrate under actual operating conditions at varying alkalinitiee of the predefecated juice. The optimum conditions of alkalinity appear to be 0.15 gram of calcium oxide per 100 ml., although the color curve for Teatini does not follow the colloid curve. Figure 5 shows the variation at the thin juice stage under actual
operating conditions of color and colloids at varying alkalinities using Teatini predefecation. For predefecation in factory operation it was not possible to get a complete range of data for alkalinities from 0.13 to 0.17 and therefore a separate predefecation curve is not shown. The curves for the process were parallel, however, up t o an alkalinity of 0.15 and showed a dip at 0.15 alkalinity. Slicing capacity was in no way influenced by either process, and lime saving showed little difference between either process. Filter capacity was lessened a t Hardin by Teatini and more filter cloth per ton of beets was required when predefecation was used. Sugar losses on lime flume to the sewer were the same for both processes. Boiling time of the massecuites showed little difference, but a slight difference in favor of Teatini was found in the evaporators. Colloid elimination through the thin juice stage was more efficient during Teatini operation and color of the juice was slightly better,
* * ' 2 r + P
IO
0
I .I 3
I
I .I 4 ' ALKALINITY
,115 G R A M S C-0
16
IT
I N IOOUL
Figure 5. Variation i n Colloid Count a n d Color under Operating Conditions At thin-juice stage u s i n g Teatini predefecation
The rise in purity from the diffusion juice to the evaporator thick juice was greater during cold predefecation which resulted in higher first carbonation elimination, over-all elimination, lower molasses loss, and increased extraction in favor of cold predefecation. P a r t of these higher figures may be due to differences in beet quality during the two runs. The drop in purities from massecuite to green sirups was higher in the white and high raw pan operation during Teatini, but lower in the case of low raw massecuite to molasses. The final granulated sugar was superior during cold predefecation.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
EUROPEAN DEVELOPMENTS SUBSEQUENT TO WORK REPORTED HERE Recent work in Europe merits discussion here, as preliming and predefecation have been used very extensively and numerous systems have been devised and patented. Dkdek and Vasatko’s method (6) is used very extensively. The original system is a progressive cold wet preliming which takes place by a number of small additions of lime. Use of DBdek and Vasatko’s procedure, followed by addition of balance of the lime hot and dry or cold and wet with continuous first carbonation, has been reported by Wiklund and Lindblad (10). The above method was compared to the Dorr method of continuous defecation and carbonation using a Benning carbonator ( I O ) . Settling rates showed that the carbonation sludges from the preliming and carbonation would be hard to handle in a thickener such as a Dorr, while the sludge from the Dorr carbonation would be very satisfactory. Data are given showing that as the filtration time increases, the sedimentation velocity decreases, the volume of the precipitate increases, and the color of the thick juice decreases. Desirable physical properties of the sludge mean poor thick juice and vice versa. By the use of the Dorr continuous carbonation method a carbonation sludge with desirable physical properties was obtained, but poor, dark, thick juices were also the result. With the DBdek-T’asatko preliming and separate dry or wet main liming and continuous carbonation, good purified juices were obtained, but the sludge was such that it was impossible to handle in a thickener and continuous filters of normal size (10). The experiments by Wiklund showed that it was not practical to combine the preliming method directly with the Dorr carbonation. After considerable experimental work, both in Sweden and in Belgium, a system of preliming and defecation was worked out that gave sludges with excellent settling rates and juices light in color that were relatively stable as to color during evaporation (10). Raw juice from a preheater is mixed in the first compartment of a preliming tank with overcarbonated juice in the ratio of 1t o 1 in the next seven compartments of the preliming tank, and milk of lime is added by the DBdelr and S’asatko method, so that the alkalinity gradually increases t o about 0.25 gram of calcium oxide per 100 ml.; the juice is heated to 80” to 85” C. through a heater and then the balance of the lime is added in a liming tank, either
Vol. 43, No. 3
as dry lime or milk of lime. The alkalinity is then about 0.7 gram of calcium oxide per 100 ml.; after liming the juice is carbonated to 0.08 gram of calcium oxide per 100 ml. From this carbonation half of the juice (corresponding to total quantity of raw juice) is passed to a thickener or filters. The other half of the juice is overcarbonated t o a n alkalinity of 0.02 to 0.03 gram of calcium oxide per 100 ml. and is then recirculated to the first compartment of the preliming t,ank because it is believed t,his supplies nuclei for flocculation (10). Dkdek, of Belgium, recently (4, 5 ) gave an excellent summation of the principles of defecation on which he, Brueghel-Muller of Copenhagen, and Wiklund of Sweden, are working. BrueghelR!Iuller’s work is along the line of eliminating completely all the colloidal precipitation of nonsugars in the raw juice by t>heaction of calcium oxide. He invented a process of so-called stabilization of the colloids during preliming of the raw juice by the very slight addition of lime (about 0.02%). This stabilizat,ion is believed to be due to combination of calcium ion, pectin, and protein. Through discussions and common experiments DBdek, Brueghel-Muller, and Wiklund became a.ware that both BrueghelMuller’s and Wiklund’s methods of purification could be improved by incorporating features of the other method. Briefly, this method would combine predefecation with continuous carbonation.
ACKNOWLEDGMENT The writers wish to acknowledge the work of F. W,Kopplin for his part in these studies and also the help J. DBdek and Olaf Wiklund gave in supplying information on the recent developments and trends of purification in Europe.
LITERATURE CITED (1) Bull, A. V., U. S. Patent 1,755,165 (1930). (2) Ihid., 1,860,321 (1932). (3) Dsdek, J . , J . .fabr. sucre, 80, 63 (1939). (4) DPdek, J., personal communication, March 9, 1950. (5) DPdek, J., Socker H a n d . , 6, 50 (1950).
(6) Dsdek, J., and Vasatko, J., U. S. Patent 2,007,424 (1936). (7) McGinnis, R. A,, P r o c . Am. SOC.S u g a r Beet Technol., 5, 573 (1948). ( 8 ) Ramsey, E. R., and Bull, A. V., U. S. Patent 1,868,472 (1932). (9) Teatini, D., I b i d . , 1,988,923 (1935). (10) Wiklund, O., and Lindblad, L., Socker Handl., 9, 157-96 (1949). RECEIVED April 6 , 1950.
Reburning of Defecation Lime
Cake R. M. DANIELS AND ROBERT H. COTTON Holly Sugar Corp., Colorado S p r i n g s , Colo.
B
ECAUSE 30 t o 100 pounds of lime are used per ton of beets
in beet sugar manufacture, and good Steffen lime rock has been increasingly difficult t o obtain, especially in California, reburning of lime has been intensively studied by this company. These studies resulted in a large scale installation for reburning waste lime cake a t the -4lvarad0, Calif., plant. I n America, beet sugar factories burn lime rock in vertical kilns with coke as the fuel. The lime is used in defecation of beet diffusion juice, and carbon dioxide is employed in the carbonation process t o precipitate calcium carbonate which carries with it numerous impurities in the juice; finally, carbon dioxide is used to reduce the alkalinity of the juice before it goes to the evapora-
tors. Factories using the Steffen process use much greater amounts of lime; this is used t o recover additional sugar from molasses by precipitation of calcium saccharate. Thus, a limereburning system had t o provide adequate carbon dioxide recovery, and the objective was a carbon dioxide concentration approximating that available from a lime kiln, 30 to 35%. This was accomplished in early work by burning the lime partly by indirect heat in a muffle furnace ( I ) , thus avoiding dilution with combustion gases. Natural gas was the fuel. Figure 1 shows diagrammatically the multiple hearth furnace used in this work, referred t o as a Skinner roaster.
