INDUSTRIAL A N D ENGINEERING CHEMISTRY
1148
Vol. 20, No. 11
Automatic Control of the Carbonation Process in Beet-Sugar Manufacture’ R. T. Balch and J. C. Keane CARBOHYDRATE DIVISION, BUREAUOF CHEMISTRY AND SOILS, WASHIKGTON, D. C.
A n automatic control of the second carbonation this method to beet-sugarprocess in the manufacture of beet sugar based on the years there has been a house control is very limited reaction (pH) of the juice has been shown to be pracdecided improvement owing to high alkalinities or ticable. If sulfur dioxide could be delivered to the in the technology of b e e t the presence of sulfur dioxide sulfitation station under as constant conditions as the sugar manufacture. Contriband sulfites in many of the carbon dioxide is delivered to the carbonation station, u t i n g t o this improvement factory liquors. Since colorian automatic control employing similar equipment are many factors which are metric methods are the simwould be as successful. The control functions on resulting in a more efficient plest for d e t e r m i n i n g p H electrometric principles whereby the e. m. f. produced operation of the clarification values, although g e n e r a 11y between the tungsten and calomel electrodes immersed processes, particularly a t the unsuitable for first or second in the juice, which varies in proportion to the pH of the second carbonation and sulcarbonation, they have rejuice, causes the electric motor that is connected to the fitation stations. cently been found to be of gas valve to operate indirectly through a system of reOne of the functions of the much value and have been lays. The supervision required, principally for changsecond c a r b o n a t i o n i s t o widely adopted in controlling ing and caring for the electrodes, is believed to be more e l i m i n a t e as completely as the sulfitation of thin juice than compensated by the advantages of the control. Dossible the lime which is not a n d sugar-end products. precipitated at the first carSuch applications of coloribonation station. With proper control of the second carbona- metric pH inetliods to beet-sugar manufacture were described tion process the amount of lime entering the subsequent by Balch‘ in 1925. processes can be held to the minimum, under which conditions Being desirous of finding a suitable method for controlling the scaling of heating surfaces is materially lessened. One of the steps in the important factory process automatically, the results is that many factories are now compelled to clean particularly second carbonation, the writers directed their attheir evaporators only half the number of times formerly re- tention to the use of tungsten electrodes*in combination with quired during a campaign, in spite of the fact that their daily a recording potentiometer. The preliminary experiments slicing capacity has in many instances been considerably in- with tungsten electrodes in second carbonation juice, made by creased. In the sugar end of the factory easier boiling mas- Balchs in 1924, indicated possibilities. This work was consecuites and the production of a better grade of sugar have tinued by Dawson and Keane‘ in 1925,who recorded continualso resulted from the improved control. ously for long periods of time the reaction of second carbonaThe proper point to which the gassing of juice a t the second tion juice with wholly satisfactory results. The task, then, to carbonation station should be carried is reached when the pre- be accomplished was to determine whether an automatic concipitation of calcium carbonate is just completed. The time- trol of second carbonation and sulfitation processes based on honored titration method has formed the basis of controlling electrometric principles employing tungsten electrodes the reaction of the juice at the second carbonation and sul- would be feasible. By automatic control is meant the fitation stations and of sugar-end products until recently, c o n t i n u o u s addition when hydrogen-ion concentration or pH methods (colorimet- of the correct amount ric) are being applied with advantage.2 of gas (carbon dioxide One of the first studies relating hydrogen-ion concentration or sulfur dioxide) to the values with beet-sugar factory operation was undertaken by juice, governed autoPaine, Sibley, and Keane* in 1923. An electrometric method matically by the reacemploying a double hydrogen electrode was used and found to tion (pH) of the juice. be impracticable for factory control purposes on account of the Success with s i m i l a r time consumed in obtaining equilibrium between hydrogen gas equipment for the autoand the liquid of which the pH was being determined. Daw- matic control of cane son and Keane4 in 1925-7 obtained much more satisfactory j u i c e defecationlo by results with the hydrogen electrode, using Dawson’s modi- means of lime led the fication of Aten and van GinnekenV apparatus. Although authors to believe that satisfactory for laboratory tests, this equipment was believed it could be adapted to to be too complicated for controlling factory operations. A t h e p u r p o s e in quesmore ideal method for pH measurements is by means of the t ion. quinhydrone electrode,G but unfortunately the application of
URIXG the past few
D
1 Presented under the title “Automatic Control of Carbonation and Sulfitation Processes in Beet Sugar Manufacture” before the Division of Sugar Chemistry at the 75th Meeting of the American Chemical Society, St. Louis,Mo., April 16 to 19, 1928. 9 Zisch, Facts About Sugar, 21, 706 (1926). Ibid., 30, 778 (1925). 4 Unpublished report of Carbohydrate Division, Bureau of Chemistry and Soils. * 2. Vn.dcut. Zucknind., 76,260(1925). DawsOn, Sugar, 38,211,262,310,369(1926).
*
’
7 Sugar, 37, 587 (1925). I B a y l i s , IND. END. CXEM., 15, 852 (1923); Parker, Ibid., 17, 737 (1925); 19, 660 (1927). * Unpublished report of Carbohydrate Division, Bu- . reau of Chemistry and Soils. I* Balch and Paine, IND. ENO.CHEW.,30, 348 (1928).
Figure 1-Flow
Chamber
Xovember, 1928
INDUSTRIAL A N D ENGINEERING CHEMISTIZY
In previous investigations relating to the pH of second earbonation juice no definite optimum value was found; the pH value required for complete precipitation of lime with carbon dioxide is apparently dependent upon such factors as the conditions of the beets and t.he character of their non-sugars, and iipon factory operation of preceding processes. I n view of this fact: an arrangcment, was made wherehy the control could
Fiaure 2-Facory ~ ~ s n g e m e of n rElecrrodesand @towchamber
1119
in proportion to the pH of the juice under continuous and standardized conditions. This feature makes them valuable for control work but requires facilities for checking the pH of the values recorded and in determining the control pointi. e., the pII value a t which it iS desirable to cany the juice. This may possibly he accomplished by use of indicators, but Dawson's modification of Aten and van Ginneken's hydrogen electrode in conjunction wit.h a portable potentiometer is
ida sohltion of trisodium phosphate, before being placed in1 a bath of a saturated solution of the phosphate for a period of approximately 2 days. After this treatment the electrodes were ready for service. Eight electrodes were used in following this method of rotation and treatment. RECORDER AND CO~VROLLEI~ -The recording p o t e n t i o m cter'3 with controlling device is an adaptation of an i n strument that has been on the market for a number of years. The recent dovelopments, exp e r i m e n t a l in character, include the arrangement for temperature compensation of the recorded values and improved ineans for eontroliing the reversing motor'3 which operates, in this instance, the gas valve. The details of the reversing
lie made t,o operate at any desired pN value within the customary range. Description of Equipment
ELECTRODES A X D JDICE
CUIBER-AS in other systems for determining hydrogen-ion concentrations e l e c t r o m o t r i cally, the b a i c principle is tlic production of an electromotirc force between two electrodes in direct proportion to the pH the juice. The elect.rodes used in this study were (1) the usrri~l s t a n d a r d saturated calomel half cell, contact with the jnice being made through a poroos cup filled with potassium chlor i d e , c o n s t i t u t i n g the salt. Fipure 3 --Reveraiefl Motor and Gear Reducer bridge, and ( 2 ) the bare tmigsten wire clrctrodr. The electrodes were suitably arranged in :Lglass fiow c h a i i i b c ~(Figure ~~ 1) through which a continuous .sample iii juice was passed over the tungsten electrodes and salt bridge. A temperature compensator,'z the purpose of diicii was to correct autoniatically for the changes in pH cawed by temperature fluctuations, was also inserted in the flow chamber. The ia.ctory arrangement of this equipment (and eirculat.ing juice pomp) is shown in Figure 2. Since a satisfactory eont,rol must necessarily depend upon the behavior of the elcctrodes, consider&& attention was p-iven them under v:trying conditions. The calomel electrode ?\-:IS found to nieed but little attention to keep it in proper ronditioni-namely, a biveekly Bushing out with a saturated potassium chloride solution and a n infrequent repkcement of the calomel lost by dissolution and flushing. The porous clay cup constituting the salt bridge was cleaned and refilled with Fieure 4-ExPerimenra1 lnetaEia'ion Of .wofor and Recorderpotassium chloride solution and crystals as needed, x~hicliwas Confrdier nbont every 6 to 12 hours. Although tungsten electrodes are not suitable for ordinary motor and the gear reducer are shown in Figure 3," and the intermittent pH measurements, they respond sensitively and experimentnl installation of the motor and recorder-controller I*
Parker, I n . ENO.C S S ~ .17, , 637 (I@%). Developed by The Leedr & Noorthrup Cornpang, Philadelphia, Pa.. for
use with t h d r reroxidins potentiometer.
I8
The authors acknowledge with appreciation the loan of thir equipThe k e d s & Northrup Company. Photograph kindly furnirked I>>- T h e J.ceda & XoFthiup Company.
meat by 8'
1150
Vel. 20, No. 11
INDUSTRIAL A N D ENGINEERING CHEMISTRY
carbonation juice pump (juice going to the second presses). Since the temperature of the juice at this point was from 85’ to 90”C., a cooling apparatus was used to cool the juice to approximately 30‘ C., for a t this temperature the pH can he measured more conveniently. The cooling apparatus consisted of a 3/rinch (9.5-mm.) juice line, surrounded by a water jacket 1inch (2.54 em.) in diameter, 20 feet (6 meters) long. The water flowed countercurrent to the juice. This arrangement for sampling the juice was entirely satisfactory for recording the reaction of the juice sample, but for control work the lag between the time of carbon dioxide addition and time of sampling was too great to obtain as accurate a control as was desired. The factory arrangement for gassing the juice at the second carbonation station was to allow the fist press liquor to flow continuously into a double-compartment tank. In the first compartment the mein portion of the g a i n g took place. After a certain level was reached, the juice overflowed into the second compartment and any further gassing required was accomplished here before the juice was pumped to the second presses. Improvement was made in the automatic control by taking the sample directly from the first compartment, thereby shortening the time lag, and doing all the gassing in the one tank. Since gravity flow was not possible, a small motordriven centrifugal pump was used to circulate the juice from the tank throueh the cooline anoaratus and cell containine the .. electrodes. To insure continuous operation and to obtain a strictly representative samplc of juice. wh~chis very important, I
~
Figure 5-Details of Recorder
in the factory is shown in Figure 4. The control used in this investigation is termed the “anbicipatory” type, in contrast to the “intermittent” type used by Balch and Paine in their study of automatic control of cane juice defecation. The anticipatory coutrol acts in such a manner that the gas valve is gradually opened when t,he reaction of the solution is above the desired pH and still going higher and is gradually closed when the pH is too low and stiil going lower. The mechanism for producing a control of this type consists of a mercury snitch containing four contacts io series with the contacts of two other switches, which arc closed according to the direction the recording carriage is moving. The mercury switch is adjusted so as to be in a horizontal position when the reaction of the juice is at the desired pH v a l ~ c . ’ ~Figures 5 and 614 show the details of the recorder and controlling switches. The range of the recorder was 7.0 to 11.0 pH. JUICE SAMPLInG-During the first part of this investigation the sample juice was taken from the air vent of the second 18 Brief description furnished by H. C. Parker. of The k e d s & Northrug Company. in a persend communication t o the authors.
’?
n
Figure 7-Carbonstion
Tanks in Beet-Sugar Factory
an over-capacity pump was used and only a portion of tho juice circulated by the pump was sent through the cell by means of a by-pass but with sufficient pressure to replace rapidly the juice in the cell. Also, the capacity of the cooling apparatus was designed to maintain a temperature of 30” to 35” C . ,even with a rapid circulation of juice. Discussion of Results
Figure 6-Details of CDntrDller
In Figure 8 the curves represent the pH while the addition of carbon dioxide a t the second carbonation station is being automatically controlled. The maintenance of the juice reaction within narrow limits shows conclusively, it is believed, the practicability and efficiency of automatic control of the type herein described, in spite of the fact that the ideal conditions could not he attained in this experimental installation. Other Considerations which aid automatic control are the
INDUSTRIAL AND ENGINEERING CHEMISTRY
Kovember, 1928
maintenance of a constant level of juice in the carbonation tanks and of a gas of fairly constant pressure. A certain amount of latitude is possible without seriously affecting the c o n t r o l , provided the fluctuations are not too pronounded. The carbonation tanks (Figure 7) should be covered and equipped with a foam stack to prevent juice losses due to foaming. This would occur if the juice level is too high in the tank of juice being gassed, or if, for some reason, excessive foaming took place. I n view of the fact that the control of sulfitation processes, particularly of thin juice going to the evaporators, is likewise of primary importance. the behavior of the tungsten electrodes in this type of juice was also tested. An automatic control was not attempted owing to the variability in the composition and pressure of the sulfur dioxide-air mixture. The reaction of the juice was recorded, however, and the results obtained agreed very well with colorimetric and hydrogen electrode pH tests on the same material. This indicates, therefore, the possibility of utilizing similar equipment for an automatic control of sulfuring thin juice, provided arrangements are made for de-
1151
HOURS Figure 8-Facsimile of pH Record
livering sulfur dioxide under more constant conditions than are ordinarily present.
Wood Separators for Lead Storage Batteries' Relation of Life Characteristics to Cell Design C. A. Robak HORTEN, NORVAY
HEETS of wood are used to a large extent as separators in lead storage batteries, alone or together with perforated hard-rubber sheets. I n the former case the wood sheets are grooved in the direction of the grain, in the latter case smooth mood sheets are used together with ribbed hard-rubber separators, the object of the ribs being to provide some free space for the circulation of the electrolyte. In both cases it is common practice to place a flat side of the wood next to the negative and the ribs of the wood or hardrubber against the positive plates. One reason for this practice is that the oxidizing character of the positive plate material tends to destroy the wood substance and reduce the mechanical strength of the wood separators. To determine to what extent the wood separators are actually being destroyed in Q storage battery under ordinary working conditions, and particularly to make clear how great the difference is betliTeen the positive and the negative plates in this respect the following experiments were carried out,
S
Description of Batteries
Two complete 42-cell batteries were built from pasted plates of the dimensions 145 X 220 X 3.5 mm., the insulation consisting of two smooth sheets of rotary-cut aspen veneer with horizontal grains which were treated with alkaline and sulfuric acid solutions to remove acetic acid and other impurities. No free space was left between the plates, the separators lying close to the surface of both the positive and the negative plates. One battery was installed in a large electric truck, the other in an electric coupe. The batteries worked fairly well. 1
Received March 23, 1928.
Charging and Discharging The truck was in use more than 300 days during a period of approximately 2 years. The battery was charged 290 times. An average of 50 per cent of the 3-hour capacity was taken out each time. The charging was carried out a t a moderate rate, 1.2 to 0.5 times the IO-hour discharge rate, but with considerable overcharging, the excess being usually 20 per cent and often more than 25 per cent of the amount discharged. The service conditions were hard. The truck wheels were provided with rings of compact rubber which on the bad roads would naturally shorten the life of the battery. The coup6 was used almost every day for nearly 3 years. This battery was charged 738 times, the ampere-hours taken out each time averaging about 25 per cent of the 3-hour capacity. The charging was usually commenced a t the 3-hour rate, the current being reduced to half or less when the point of common gassing was reached. The battery was much overcharged, the excess being usually 25 to 30 per cent and often 50 to 100 per cent of the discharge. The total distance driven was 4900 miles on bad roads in a hilly country. During all this time the separators worked well in both of the batteries and mere still in a good condition when removed for replacement of the positive plates. The separators next to the negative plates looked perfectly sound, but some of those next to the positives showed some slight signs of wear. The mechanical strength of the used separators was examined. Separators from Truck Battery Test pieces were cut along the fiber direction from the central and end parts of the separators. The pieces were
