June. 1927
I S D C S T R I A L A Y D E S G I S E E R I S G CHEMISTRY
shoulder which necessitate? slip, and by the change in area of the inflated tire when it deflects t o carry the load. The amount of work will depend on tread design with its effect on the amount of slip, on the coefficient of friction between the rubber and road surface, on the stress-strain relationship, and on the mechanical efficiency of the rubber. I t is obvious that if the coefficient of friction could be reduced to zero slipping would take place but no work would be done. If the coefficient of friction could be made infinitely great, no slipping would occur and no work woulrl tie done on the surface, but the stress due to the strain resulting in the rubber would be stored in the rubber in a reversible manner. Under normal conditioni both slip and strain in the rubber result. -4ny point on the tread of a tire a t the time of coming into contact with the road will slip unl il the pressure against the road increases t o a definite value, which depends upon the existing coefficient of friction and the stress-strain
677
relationship of the rubber, after which energy is stored in the rubber due to the strain imposed. .Is the rolling motion of the tire proceeds until the point of the tread is about to leave the road, any energy stored in the> rubber due to strain will be available to cause slip and do work on the surface of the rubber. Many of these factorb are extremely variable under road conditions and tend to be minimized by dusty or wet roads which reduce the friction. TT'hile the work done on the rear tires due to driving force and on the front tires due to steering thrust must be constant for any tread stock, the work due t o rolling, camber, and toe-in will vary with the road conditions and tread compound. While the present development of the abrasion machine makes possible a comparison of the abrasion resistance of any compound, it should not be expected to replace actual road tests in the selection of a tire tread,
Evaporation of Sulfite Waste Liquor' By W. L. Badger CHE\IICIL
EKCJSEERIV?DEPARTMENT, UNIVERSITY O F
XfICHIGAK, . h N
ARBOR,~ I I C H .
OJ disposal of waste sugte liquors by considering the design of suitable ecapnl-ating equipment. Apparatus f o r large experiments are described and the data obtaintdfrom their operation are discussed.
T/ii.i paper deal.r aith the problem
HE problem of the dispo.al of oulfite waste liquors, though not especially acute a t present, promises t o be more serious in the near future, owing to the increasing stringency of stream pollution laws. Although the ultimate solution of this problem must involve finding some new uses for the material, it is obvious that, whatever these uses may be, the first step will undoubtedly be an evaporation of the liquor. This will be particularly true in those cases where the only possible disposal of the wastes will be t o burn them. Consequently, since all recovery proceqses are based on a preliminary evaporation, the first step in the general problem will be to design suitable evaporating equipment. The difficulties met in attempts t o evaporate sulfite liquor are threefold: (1) The extreme viscoqity of the solution; ( 2 ) the very serious scale-forming tendencies of the liquor; and ( 3 ) , the corrosive nature of unneutralized liquors. The third item was not considered in this investigation. It is now generally accepted that the velocity with which a liquid will be moved past the heating surface is by far the most important factor in determining the capacity of an evaporator. I n the ordinary el-aporator, whether of the vertical tube or horizontal tube type. this circulation is accomplished by natural convection and by the evolution of steam bubbles. Obviously, as the liquid becomes more riscous, the circulation produced by both of these means rapidly decreases, with the result that it is vwy difficult to concentrate this liquid to high densities without using either excessively large evaporators or very large temperature differences. Since the cost of the disposal of sulfite liquor must be held to very low figures. and since the principal cost of evaporation is the cost of steam, it follows that an evaporator of the largest possible number of effects is desirable. This, however, results in a small temperature drop per effect, which, as has been shown above, makes operation exceed-
T
' Received March
14 1927 Presented before the Division of Industrial dnd Engineering Chemistry at the 73rd Meeting of the American Chemical Society, Richmond, Va , April 11 to 16, 1927.
ingly difficult or impossible. This line of reasoning, therefore, leads to the conclusion that a satisfactory evaporator must employ some means of artificial circulation. ~ I E C H A XOF ISM SCALEFORhIATIOS-It is now generally accepted that the cause of scale formation iq the presence in solution of a substance with an inverted solubility curvethat is, one whose solubility decreases with increasing temperature. Calcium sulfate is such a substance, and its presence in sulfite liquors gives them their scale-forming tendencies. Xext the heating surface there is a stagnant film of liquid whose temperature is higher than that of the bulk of the liquid. If a substance with an inverted solubility curx-e is present when the solution is concentrated, the solution will become saturated with respect to this substance in the stagnant film before the bulk of it is saturated. Therefore, the substance with an inverted solubility curve will be precipitated first in the stagnant film and will continue t o deposit in this film, producing a characteristic compact scale. If there is present in the liquid other solid material in a finely divided state, this solid material is very apt to be included in the scale, increasing the rate a t which it forms. Without the presence of a substance whose solubility curve is inverted, no true scale can form. If this explanation is correct, anything which decreases the thickness of this stagnant film or which brings into contact with the stagnant film particles which could act as nuclei, and therefore start the crystallization, should diminish the formation of scale, although it mould seem that such a method could not completely prevent scale but merely decrease its rate of formation. Therefore, both the viscosity of the liquid and its tendency to form scale lead to the same conclusionnamely, that some form of artificial circulation is desirable. Apparatus
One of the evaporators of this laboratory was modified to carry out these ideas. A diagram of the experimental apparatus is shown in Figure 1. The shell of the evaporator was of cast iron, 30 inches I. D. and 12 feet high. It was
(37%
I-VDCSTRIAL A N D ELYGISEERI.1'G CHEMISTRY
closed a t the bottom with a 60-degree cone. A number of heating units were made, each 5 inches in diameter, 5te-m 4 feet long, and closed at each end by a tube sheet. Between these tube sheets in each unit were expanded eight nickel tubes '/s inch 0. D., 3/4 inch I. D. The shell of the unit was surrounded by an outer jacket of sheet iron, welded on. The a n n u l a r s p a c e between this shell and the wall of the unit was filled with Sil-0Cel powder. Suitable connections w e r e made for r e m o v i n g condensate, for measuring steam pressure, and for venting noncondensed gases. The baskets were so a r r a n g e d t h a t any number of them could be assembled end to end, thus giving totaI tube lengths of multiples of 4 feet. I n these tests two such units were so assembled as to give an equivalent length of 8 feet. Steam was int r o d u c e d i n t o the center of the top tube sheet and a steam connection was made between the two units through the intermeCourtesy Trans. Am. Ins!. Chem. Eng. diate tube sheets. A Figure 1-Experimental Evaporating liquor d i s t r i b u t i o n Apparatus chamber was attached to the bottom tube sheet, and this was connected through the shell of the evaporator to a pump in such a way that liquid could be drawn out of the machine, pumped into this liquor-distributing chamber, and from the chamber pass up through the tubes. Since the liquor issued from the tubes a t the top a t very high velocities, a deflector was placed above the top unit to throw this spray against the walls of the machine. A
Calculations
The most important figure to be obtained from these tcsts was the heat transfer coefficient, which is expressed as B. t. u. transmitted per square foot of heating surface per degree Fahrenheit temperature difference per hour. The total amount of heat transferred was determined by collecting the condensate in calibrated drip receivers. The receivers were insulated, and no correction was made for radiation from the relatively short pipe lines between the basket and these receivers. Steam temperature was calculated from
Vol. 19. KO.6
the steam pressure inside the baskets. This pressure mas measured by a mercury manometer and the temperature calculated from the steam tables. I n the same way the boiling point of the liquid was calculated from the steam tables, using the pressure in the vapor space as measured by a mercury manometer. This boiling point was not corrected for the elevation of boiling point of sulfite liquor, since Moore2 has shown that this elevation is very small. The temperature drop was taken as the difference between steam and liquor temperatures determined as above and is therefore the "apparent" temperature drop, and the coefficients calculated from it will therefore be "apparent" coefficients. An orifice was calibrated with liquor of various densities at the actual temperatures a t which they were handled. The results of these calibrations were calculated in terms of entrance velocities in the heating tubes in feet per second. A mercury manometer had one arm connected to the liquordistributing chamber and the other arm connected to the vapor space of the evaporator. Its reading, therefore, gave the pressure drop which occurred in the tubes. This pressure drop is the principal resistance which must be overcome by the circulating pump and is, therefore, a measure of the power consumed in the operation. A tank car of neutralized sulfite liquor was supplied by the Hammermill Paper Company. It was desired to control the operation of the evaporator by specific gravity determinations and the only data available on the relation between specific gravity and concentration a t different temperatures are those given by Moore* (Figure 2). Since there is considerable variation in the composition of the liquor from one mill to another, it was not certain that Moore's figures would apply to this liquor. A sample was evaporated in the laboratory to different concentrations and for each of these samples specific gravity and total solids were determined. These figures were compared with Moore's data with the following results : PER CENTSOLIDS SPECIFIC GRAVITYSPECIFIC GRAVITY (Detd.) (Detd.) (Moore)
The checks are sufficiently good, with the exception of one sample, to justify the use of Figure 2 for this work. At the end of these experiments the concentrations were carried so high that they came outside the range of Moore's data and their values had to be estimated. All concentrations above 50 per cent solids, therefore. may be more or less in error. It was desired to duplicate in these experiments the ccncentration of this liquor to 50 per cent solids in a quadrupleeffect evaporator operated with forward feed, assuming that the exhaust steam would be a t 240' F. (approximately 10 pounds gage) and the vacuum, 26.5 inches on a 30-inch barometer. From Moore's data i t was estimated that the boiling point elevations in the four effects would be 0", l o , lo, and 3" F., respectively. This would leave a total temperature drop of 115' F., which, it was assumed, would be divided between the effects to give temperature drops of 22", 23', 25", and 45' F., respectively. The conditions in the four effects under these assumptions would be as follows: O
Steam to first effect Boiling point, first effect Vapor from first effect Boiling point, second effect Vapor from second effect 2
F.
240 218
218 (2 lbs. gage) 195 194 (9-inch vacuum)
Trans. A m . Z n s f . Chem. Eng., 16, Pt. 11, 248 (1923)
I-YDCSTRIAL - 4 5 0 ESGIA\TSEERILYGCHEMISTRY
June, 1927
F. Eoiling point, third effect J'apor from third effect 13oiliny: point, f o u r t h effect l-apor from fourth effect
1611 168 (18-inch vacuum) 123
120 (26.5-inch v a c u u m )
The conditions actually maintained \\-ere as follows: 0
Steam Vapor Steam Vapor Steam Yapor Steam Vaoor
P.
2.3 1
to firsi effect
211
from first effect io second effect from second effect to third effect from third effect to fourth effert from fourth effect
2 14 1'34
192 167 175 1:31
In other words, the test conditions correspond reasonably well with the assumption, except that we did not carry quite so high a vacuum nor could we carry quite so much steam pressure on the first effect as we desired.
3
0
I2 8
0
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conditions, the steam and boiling point were changed t o correspond t o second effect conditions. The partly concentrated liquor produced in first effect operation was fed into the machine and concentration continued until the desired second effect density was reached. After this, thick liquor was pumped out and more liquor fed, using thin liquor if the length of operation was sufficient to use all the thick liquor produced in the previous effect. I n the same way, third and fourth effect runs were made. A summary of the data for all these runs is given in Table I. iifter this, without cleaning, there was a return to first effect operation, using a fresh lot of thin liquor and the first three effects were run through a second time exactly a5 described above. I n this second set of experiments the fourth effect was run with a steam temperature of 247" F. and a boiling point of 211" F. in order to reproduce the conditions that would exist if thin liquor were fed to the second effect of a quadrupleeffect evaporator, the feed passing then t o the third and fourth effect, pumped from the fourth to the first, and finished t o thick liquor in the first effect. It has been explained that the yiscosity of the liquor is one important source of difficulty. Since viscosity decreases rapidly with increasing temperature, it is obT-ious that finishing with thick liquor a t a high temperature should result in a n increased capacity of the eraporator because of the decreased viscosity of the liquid. I n these runs concentration was carried to about 60 per cent solids. This concentration was not exceeded merely because of conditions of the work and not because the machine failed to perform. All the work was done on day shift only. When the evaporator was left with the 60 per cent solution in it overnight, the material in the pipe lines became so hard that it took considerable time the next day to thaw out these lines and get the apparatus running. So much time Tvas lost, and the liquor was so diluted that the rest of the day's operation merely served to get back to about BO per cent solids again. There is no way of telling from this experiment the limiting concentration that would be practical in the machine.
m
Temperature Degrees C e n i i g r a d c
Figure 2-Relation between Specific Gravil y a n d Concentration (Moore)
The total solid content of the thin liquor was about 7 . 5 per cent. On the assumption of an approximately equal distribution of evaporation between the four effects, this would give, for 1400 the concentration leaving each effect, the I X O following: I2[ 0 11CO
PERCENT SOLIDS First efiect 10 Second effect 15
PER CENT
loco
S01,IDS
Third effect Fourth effect
21
9c 0
.50
800
I( 0
Operation
6C 0 6C 0 4c 0
The machine was filled with thin liquor to JC 0 the desired level, steam and boiling point 2c 0 adjusted to the desired conditions, and evapoIC0 ration continued, thin liquor being fed as 0 4 8 became necessary, until the concentration Figure reached the limit for that effect. After that, thick liquor was pumped out of the machine and thin liquor fed to maintain concentration amxoximatelv constant. During this operat'ik actual "runs were made fo; the determination of heat transfer coefficients. A run lasted 20 minutes, during which time the amount of condensate was measured and all temperatures and pressures read a t frequent intervals. The data for each run were calculated in duplicate. These runs followed each other a t short intervals. The total time of operation was recorded each day and the figures in Table I indicate the total time the machine had been in operation. After a number of runs had been made under first effect
I2
3-Heat
I6
20
24 28 32 Percent Total So1 d,
36
40
44
48
52
58
60
Transfer Coefficients in Evaporating Sulfite Liquor 0-First series. .-Second series
Results
The results of these tests are reproduced in Figure 3. There are several interesting features, but the most important one is that in the second set of runs, where the evaporator had been in operation upwards of 60 hours, the coefficients obtained are fully as high as the first time over when t h e evaporator was clean. After this work was completed and the evaporator dismantled, the tubes were examined. There was a T-ery thin, black deposit which may have been nickel
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1-01. 19, KO. 6
of Sulfite L i q u o r i n Forced C i r c u l a t i o n Evaporator (Summary of D a t a ) FIRSTEFFECT SECOND EFFECT THIRDEFFECT Total time of operation up to end of first series 7 hours 10 min. 20 hours 00 min. 26 hours 55 min. Total time of operation up t o end of second series 73 hours 5 5 min. 87 hours 25 min. 100 hours 20 min. Number of test runs averaged 13 24 23 Average per cent total solids 9.8 14.7 21.4 Table I-Evaporation
Average steam temperature, F. Average vapor temperature, F. Average temperature drop, O F. Average velocity, feet per second Average pressure drop, feet Hz0 Average coefficient (B. t. u. per square foot per hour per a First series of runs, under fourth effect conditions. b Second series, finishing a t atmospheric pressure.
F.)
230.79 210.67 20.12 11.5 14.75 i34.5
sulfide, but the surface of the tubes was smooth and metallic to the touch and nothing that can by any stretch of the imagination be called scale was present. The principal result of these experiments may therefore be stated as follows: I n these tests, a t the end of approximately 150 hours of operation, no scale had been formed in this evaporator. Considering the performance of ordinary evaporators on this liquid, this result is so remarkable that it stands out as the principal feature of the test. The next most important item is obviously the very high value of the coefficients. The reason for the low values in the first effect cannot even be guessed. It could not have been due to scale formation by the raw liquor, because the second effect operation certainly would not have dissolved such scale and first effect operation the second time over
214 0.5 194.10 19.90 7.9 15.23
192.59
167,25 25.31 7.1 19.05 723
989
FOURTH EFFECT 63 hours 05 min. 148 hours 00 min. 60a 35b 39.9 50.3 175.17 246.76 130.94 210.92 44.53 35.84 9.4 7.6 22.64 24.00 346 337
checked these results. The results are more erratic in the first three effects than could be desired. This variation is undoubtedly due to irregularities in rate of feed and rate of drawing off thick liquor. The concentration in each run was based on a single determination of specific gravity and may not always have reflected the average density throughout the run. Even allowing for the wide fluctuations in the data, the curve still shows a coefficient several times as high as could be obtained in either a standard vertical or standard horizontal tube evaporator, even when clean. Acknowledgment
The writer wishes to acknowledge his indebtedness to the Swenson Evaporator Company, who made all the arrangements for the experimental work and financed it throughout.
An All-Glass Distilling Tube without Constriction’ By Howard J. Lucas CILIFORSIA ISSTITCTE O F TECHSOLOGY, PASADENA, CALIF.
T
HE usual distilling tube is constricted near the bottom
a t the very place where maximum capacity is needed. Peters and Baker2 overcome this difficulty by putting a wire through two small holes in the wall near the bottom of the tube and placing upon this an openwork ball of wire t o act as support for the column of 5-mm. glass rings. The presence of copper is objectionable when acids or substances ha\ ing oxidizing properties such as nitrotoluene are being distilled. The accompanying diagram (Figure l , a) shows the construction of a tube composed entirely of glass and having a t the bottom a capacity only slightly less than the rest of the tube. Three or four indentations in the wall, all a t the same lerel as shown b in b, support a hollow-glass nipple, c. Enough holes a r e b l o w n in the upper half of the nipple to take care of decreased capacity resulting from the closing of openings by the glass rings above resting against them. It is evident that C the decrease in the capac1 Received
0
2
Figure 1
March 14,1927.
T H I SJ O U R N A L , 18, 69
(1926).
ity of the tube a t the level of the indentationcorresponds to the cross-sectional area of the
indentations and of the wall of the nipple. I t is probable that this decrease is not much greater than that resulting from the presence of the glass rings higher up. This type of tube is useful TT here liquids of high boiling point are being distilled and where the run-back is large. The distillation of rt mixture of nitrotoluenes through a column of glass rings 5 X 5 mm. can be accomplished without troublesome holdup in the column and with a fair separation of the ortho isomer in one distillation. A modified Pim’s chlorinating apparatus4 is shown in Figure 2. This has given satisfactory results in the chlorination of toluene to benzyl chloride when filled with a 20-cm. column of glass rings 5 X 5 mm.
G
‘J
7\
Y Figure 2
Martin, “Industrial and Manufacturing Chemistry,” Vol. I , p. 366b, Crosby Lockwood and Son, London, 1915.
Celanese Corporation Doubles Capacity of Maryland Plant -The Celanese Corporation of America, formerly the American Cellulose and Chemical Manufacturing Company, Ltd., which recently changed its name and increased its capital stock by $5,500,000, plans t o award contracts a t once for the erection of buildings t o house machinery which will double the capacity of the maximum output of the present plant a t Amcelle, Md., a suburb of Cumberland, Md., a t a cost of about 965,000,000. A contract has already been awarded to the Cumberland Contracting Company to build a new road to the main plant, 26 feet wide. A new brick office building will be erected and another artesian well is being drilled. It is understood that the Baltimore and Ohio Railroad will build a subway under its fill to connect two sides of the plant.
