964
IKDUSTRIAL AND EKGIKEERING CHEMISTRY
as possible the maximum concentration of hydrocyanic gas in the tented space. The above method is satisfactory during the warmer part of the season. However, on cool nights when hydrocyanic acid is evaporated less quickly, there is a tendency for some liquid to fall t o the ground or to condense on the ground or on the lower foliage of the tree or on cover crops which may be growing in the orchard. For these reasons the vaporizer is used to a large and increasing extent, The vaporizer is drawn through the orchard by a horse or may be motor-mounted. This is a two-wheeled, rubbertired vehicle on which are mounted a water boiler heated by an oil burner with the necessary small oil supply tank and connections. The water boiler contains a copper coil which acts as a vaporizer for the liquid hydrocyanic acid. At a convenient point is mouhted a measuring device somewhat similar to that on the atomizing machines. Provision is made for placing two 100-pound shipping drums of liquid hydrocyanic acid on the vehicle and for connecting them to the measuring pump. The latter forces the liquid through the copper coil in the water boiler where it is converted almost instantaneously into a warm vapor which then passes through a length of special, flexible hose which is placed under the edge of the tent. The boiler is operated a t a pressure
Vol. 25, No. 9
of 20 pounds gage, and, after a tree has been “shot,” the hose is flushed out with a small amount of steam from the boiler before being withdrawn from under the tent. This is to prevent unnecessary exposure to hydrocyanic acid escaping slowly from the hose while the vaporizer is being taken from tree to tree. Figure 5 shows a row of trees being fumigated with a vaporizer.
ACRNOWLE DGMENT Acknowledgment is made to the following men of the Pacific R. & H. Chemical Corporation: F. S. Pratt for his many helpful suggestions, D. IC.Eldred for much of the data used, and C. 5. Marvin for the photographs. LITERATURE CITED (1) Bredig and Teichmann, Z. Elektrochem., 31, 449-54 (1925). 48,299 (1926). (2) Pwry, J. H., and Porter, Frank, J. Am. Chem. SOC., (3) Sinoaako, H . , Hara, R.. and Mitsukuri, S.. Bull. Chem. SOC. Japan, 1, 59 (1926). (4) Walker, Mark, and Eldred, D. N., IXD. ESG. CHEM.,17, 1074 (1925). ( 5 ) Walker, hIark, and Marvin, C. J., Ibid., 18, 139 (1926).
RECEIVED June 16, 1933. Presented before the Meeting of the American Institute of Chemical Engineers, Chicago, Ill., June 14 t o 16, 1933.
Rotary Vacuum Filtration of Crystal Sugar CHARLESA. GODEFROY, Community Center Club, Crockett, Calif.
A theoretical method for determining the eficiency of the rotary vacuum filter in the purging of crystal sugar is given. taining substance is the ratio of the sucrose to the total investigation to determine the suitability of the solids; the yield is a measure of the efficiency in the sucrose rotary vacuum filter for the purging of crystal sugar. extraction process and may be expressed in several different This investigation has taken the form of actual operation manners. In this work yield is expressed as pounds of tests and, although the data obtained have indicated that the sucrose in finished product per 100 pounds of massecuite use of the rotary vacuum filter in the purging of sugar might solids. I n any type of filtration process the purity of the finished be feasible in all but the lowest grades, no installations for this purpose have as yet been made. However, the possi- sugar may be raised to practically any desired value but a t bilities of the rotary vacuum filter in this field have not so the expense of the yield. This is evident from the fact that far been thoroughly determined, owing mainly to the com- an increase in washing, either by water or high-purity sirup, plicated nature of the factors determining the efficiency raises the finished product purity and lowers the yield. By of the process and also to the high cost of actual operation use of the rotary vacuum filter in series with countercurrent w a s h i n g , the question arises as to the tests. ~~~JJL-CMK% ;” $ optimum n u m b e r of filters to be used; I n this article the subject is treated for, the greater the number, the greater theoretically by use of a schematic pro&GLL JUGRR will be the resultant efficiency in purgcedure which i l l u s t r a t e s the actions hzz !u ing. However, in increasing the number occurring throughout various stage sysDRUM of stages, the increase in purging efficiency tems with countercurrent washing. By JMU JCfflP~ for each succeeding stage grows less; and use of the schematic procedure g i v e n , flNIsHED f/liRRit as the number of stages is increased inactual results may be determined for the PROVUCT S/RUP definitely, there is a maximum value for processing by rotary vacuum filtration the purging efficiencywhich is approached. of any given massecuite under g i v e n -m I nAss I n this article the relative magnitudes of operating conditions w i t h the aid of LQZL JUU purging efficiency for various stage perwashing data secured from laboratory M//JJI f o r m a n c e are illustrated by yield us. tests. f / lTRAIC purity curves in various and infinite stage OPERATINGEFFICIESCY operation for a typical low-grade sugar PRODUCT FYTRAAT~ under typical operating conditions. I n the purging of crystal sugar from The general operating scheme appliits m a s s e c u i t e , the efficiency of the cable for rotary vacuum filtration of crystal o p e r a t i o n is d e t e r m i n e d by (1) the PRODWCi sugar is shown in Figure 1. I n operation, f i n i s h e d p r o d u c t purity and (2) the yield. The purity of a s u c r o s e - c o n FIGCRE1. OPERATINGDIAGRAMS as illustrated in the single-stage diagram,
URlKG the past few years there has been considerable
mbj
@ &
September, 1933
I N D U S T R I A L -4II' D E N G I N E E R I N G C H E M I S T R Y
the massecuite flows first into a iningler where it is diluted with part of the filtrate sirup to lower its consistency and to give good workability. The use of this sirup as a diluent also gives greater efficiency in operation owing to a quantity of higher purity wash liquor going through the cake and subsequently raising the purity of the mixed liquor in the feed. The greater the amount of this recirculated sirup used, the greater will be the purging efficiency; however, as the amount is raised, the beneficial effect of each succeeding amount grows
__
,_WASH ........IW, . I
-
965
of sirup recirculated, ( 2 ) temperatures in system, ( 3 ) amount of wash used, (4) moisture in sugar cake after drainage, and ( 5 ) percentage of total wash used that remains in cake after drainage. Strictly speaking, the moisture in cake after drainage and the percentage wash remaining after drainage are, in part, functions of the massecuite characteristics. However, since these two factors are dependent upon numerous complex fundamental factors, it is much more logical to term them operation characteristics and to determine their values by laboratory test data. For use in the simultaneous equations the nomenclature is as follows on a basis of 100 pounds of massecuite solids: P = purity of substance, sucrose/total solids Y = sucrose crystals in mass, % of total solids M = moisture in sugar cake after drainage, % K = sirup solids recirculated, lb. T = temp. of sugar cake, O C. E = wash solids remaining in cake, % of total P = dissolved solids in cake after drainage, lb. W = wash solids, lb. Q = massecuite solids, 100 lb. R = filtrate sirup solids, lb. s = finished product solids, lb.
The factor F , denoting the dissolved solids in the sugar cake on drum after drainage, is a function of the percentage sucrose crystals ( Y ) and of the temperature (2') and moisture ( M ) of the sugar cake. For a temperature range of 50" to 70" C. the following relation holds true very closely for pure sucrose solutions and is used in the calculations of this work with negligible error: F = (Y)
less so that it is practical to use only approximately tlie saine weight of recirculated solids as massecuite solids. This gives a feed of good workability and the beneficial effect of using more diluting liquor is too small to be of any consequence. As the drum rotates, the section immersed in the feed contained in the shell is coated with sucrose crystals as the feed liquor is drawn through the driim screen by vacuum. When any given portion of the sucrose cake reaches the wash a t top of drum, the excess liquor has been drained off and that remaining is determined by the temperature and moisture content and is dependent upon a large number of complicated factors, most of which are dependent upon the properties of the massecuite. As the sugar passes under the wash, which here is taken as a saturated solution of the finished product, the liquor in the cake is displaced in a complex manner by the wash liquor to a degree varying with the amount of ash used. It is by varying the amount of this wash liquor that the yield 1's. purity curve mav be established for a given set of conditions. I n obtaining the yield us. product purity curve for a massecuite of any given characteristics, the method used involves the establishing of simultaneous equations throughout the system in order to tie up the numerous factors affecting operation. The properties of the massecuite are then substituted into the equations along with certain operating characteristics as desired and others determined by laboratory test data.
0.075
(go -44
)
- 1.075 - 0.0447T
Factor E , denoting percentage of total wadi solids remaining in cake after drainage, must be determined by laboratory test data. To determine accurately the char-
570
-
44
46
46
50
52
54
YlElD-7. (2)
FIGURE3. YIELDus. PRODPURITYFOR LOW-GRADE SUGAR
UCT
acteristics of processing crystal sugar by the rotary vacuum filter, the effect of grain and liquor characteristics on factor E must be established. This has not as yet been attempted. I n establishing E for use in obtaining the graphs in this article, the following empirical equation was devised from test data on typical low-grade sugar:
F-LCTORS DETERMINISG OPERATIOS The factors determining operation may be broken up into two classes: (I) massecuite characteristics and (11) operation characteristics. Under massecuite Characteristics the factors are: (1) purity of massecuite, ( 2 ) percentage sucrose crystals, (3) temperature, and (4) character of sucrose crystals. Under operation characteristics the factors are' (1) amount
+ 0.04477'
E =
I-
1
I n order to obtain a clear conception of the actions occurring throughout a given system, the solids flow diagrams (Figure 2) are used. These diagrams also furnish a basis on
IN D U S T 1%IA 1,
966
ANU
E N G 1 N E E 1%L N G C E1 E M I
xirich to establish the necessary sii~iultanc~~ns eqnntions. The various 1Jart.S of Figure 2 represent sections of the systems wherein changes in purity of liquor are taking place. Section A shows tire inside of the druiii; section B gives the mingier and siieli portion of the system; atid sectimi C rcpreseiits that portion (if tlie system iirtderg~ingwashiiig
SO
In thcse fomiolas purity ( P ) is in the fractional form and the subscripts denote tho substance undar consideration eit.lier directly or indirectly. In illustration, the sy~nholP s denotes the puiity of tlie finislied product, and tiiesymlnd PIRdcnotes the purity of the liquor leaving the section I B , In applying the foregoing procedure to determine the effect of iiumher of stages 0x1 tlie purging efficiency, the following typical mtssccuite and operation characteristics are assumed and the wash (CV) is varied for various stage uperations:
+E
Pq=
,M T
0.90
Y = 50.0
+6
NUnBlR 2 O f S,WGcJ J
+~--
03
F1r;utrs 4. 13FFsa.r OF h"M*,,.:n OF
ST.M;ESON YIELD
Fur cstihlisliirig tlre relations arnong the various factors in n = stage performance, simultaneous eqiiations are ob-
tained from tlre following:
Vul. 25, No. 9
= 6.5 = 65.0
K
= 100.0
From the calculations 8s indicated, I'igure 3 sliows the manner in wliich the yield varies with the product purity in varions stage operatim. Figure 4 was derived from v a i n ~ s taken from INgurc 3 in order to bring out mare clearly the effect of nuinber of stages on ourcine . ., .~ efficiency. FRXCI Figure 4 the ~~ptiniuio number of stages for a given product purity Itlay be rleterirlirled when operation, arid sllgttl. reljr,,ccsaing are knoTpn,
1. Sucrose balance on section A in each stage 2. Sucrose balance on section B in each stage 3. Sucrose bslance on section C in nth stage
Iii iilust.ration of the equations used to determine tlw finishid prraluct picity (Ps) and the filtrate sisiip purity ( P R )from which the yield (Z) is calcnlated, the fidlowingm c those used in single stage:
Derived from +Q
y
sucr~iseb:ilance ou
I*,
(
p + (rv) ,F ;o)]p,Ig +
(K Derived Iron,
SllCIOSe
&?Po+ K P x
f
balanco
= Y
Q
appEcation of the theory given is tile deterininatioii (w)(W)psof ,knottier the effect of moisture in cake after drainage on the yield for
f i" -
y -
fi')r'n ('1
I",
Oil
+ (IC + Q - Y)P,,
(2)
Derived froin S I I C ~ O S ~bdn~reaurr IC
y i-
[.- (w)
(&)I
=
[
+
("1
EO)] (3)
Yield formula, (4)
a &en nrrrduct nuritv. This was calculated and is illustrated in Figwe 5 for single-stage operation. Tliese curves arc of narticular iutercst as thev illustrate tlie effect of varvine " .,drainage (as determined by the cake moisture content) on the yield, otlrer factors remaining constant; and, while drainage is t l i e greatest problem in the use of tho rotary vacuum filter on crystal sugar, there are no specific data on the effect of the fundamental factors determining the degree of drainage. In rendering this theoretical treatise, bhe author believes that the schernatic procedure given can be used to advantage in any futiire investigations to determine the feasibility of the rotary vacunm filter-or similar equipment in the processing of crystal sugar. II
I
.
I
