71s
INDUSTRIAL A N D EI1'GIATEERISGCHEMISTRY
Vol. 22, N o . 7
contains enough iron compounds to act as catalysts. If no value were placed on the lime, t h e cost of the oxygen would vary from $5.93 to $14.11. Where a mixture of oxygen and carbon dioxide could be used, a suspension of precipitated calcium carbonate can satisfactorily be substituted for the suspension of lime. Precipitated calcium carbonate in suspension is a common bv-product of no value. This method of oxygen manufacture is particularly well adapted to small-scale production of oxygen, since the process is simple in operation and the equipment needed is relatively low in cost. I n localities where there is a local overproduction of chlorine and a demand for oxygen, the process should take care of the overproduction as it occurs. It is, of course, of particular value where chlorine is being produced as a by-product and is practically a waste product. In many localities it might be possible to dispose of the calcium chloride in solution as it comes from the settling tanks for local uses such as application to roads. The smaller laboratory apparatus may be used advantageously in laboratories where oxygen is ordinarily purchased in small cylinders for experimental use. Frequently in laboratories where oxygen is used only occasionally or in limited amounts daily, the rental charge on cylinders costs more than the oxygen used. Where the oxygen is made by this method, the rental charge on the cylinders is eliminated. If chlorine is purchased in cylinders for the exclusive purpose of producing oxygen, there would be no great advantage. The cylinder rental would be reduced because a cylinder of chlorine at the usual pressure of 120 pounds per square would be equivalent to 1.6 cylinders of oxygen of the same size a t the usual pressure of 2000 pounds per square inch. This comparison is based on a yield of oxygen of 95 per cent. However, both chlorine and oxygen are ordinarily used in the laboratory. With chlorine a t 12 cents a pound and lime a t 1 cent a pound, oxygen can be produced for 5 cents a cubic foot. This is approximately the cost in cylinders exclusive of the usual rental charge. KO credit for the calcium chloride has been allowed in making this estimate. The prices for chlorine and lime are those actually paid for these materials in small quantit ies.
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9 d. 4
Figure 6-Design
of Commercial Plant for Production of Oxygen
Tower-Absorption Coefficients 111-Absorption of Benzene by Mineral Oil' C. W. Simmons and J. D. Long LEHICHUNIVERSITY, BETHLEHEM, PA.
HE rate of solution in a n absorbing liquid of a soluble
T
gas from an inert carrier has been studied in cases where the solute obeys Henry's law and where the solute is very soluble in the extractor ( 2 ) . Here the rate of solution is expressed by the equation
sorbing liquid and where equilibrium conditions are expressed by the equation n = f(m). V h e n the solute obeys Henry's law, the rate of solution may be expressed in the form dm/dt = -K2(km - n)
where k is Henry's coefficient. dm/dt = - K f ( m ) Cantelo ( 1 ) considered a small element of volume of a dx from the botwhere m is the concentration of the gas in the carrier, expressed packed tom-er between the heights z and z either in terms of volume concentration or of partial pressures, tom of the tower and assumed a continuous process in which the velocities of the carrier and extractor were uniform. He and K Pis the dissolution coefficient. I n considering the form of f ( m ) ,Donnan and Masson (3), pointed out the functional relationships between the dissoluLewis (J), and Whitman and Keats ( 5 ) have expressed this tion coefficient and velocities of the liquid and the gas, the function of the concentration in terms of either concentrations temperature of the system, and the concentration of the solute or partial pressures in the solvent and the inert carrier. Thus in the inert carrier. For the purposes of experiment Cantelo Donnan and Masson give as a general form f ( m ) - n, where transformed the equation d m l d t = -K?(km - n) n is the concentration of the soluble component in the abinto one involving d n l d x , which upon integration between ' Received April 5 , 1930
+
I S D V S T R I A L A S D ENGIhTEERIXG CHEMISTRY
July, 1930
Figure 1-Apparatus
for D e t e r m i n i n g B e n z e n e A b s o r p t i o n by M i n e r a l Oil
the limits of concentration and height of packing gives an equation in which the dissolution coefficient may be expressed in direct experimental units. Thus for a gas which obeys Henry’s law the integral equation has the form: 1
K 2 = a(kff) + ( j M ’ - ‘Fj In
(a - M ’ ) [ f k -f).lfo+
(kM’
- .\-’I
719
ffM’’\IO)
(a -
[”’l
solvent contained no solute and hence the term iY’niay be discarded and the final equation becomes:
.\-’)I
-,e.‘
Apparatus
-0’1
velocity of inlet gas =flow ratio velocity of liquid = grams per liter of soluble component in outlet gas = grams per liter of soluble component in inlet gas = temperature of the extractor in K.; T‘ = temperature of outlet gas in ’ K. = partial pressure of soluble component = molecular weight of soluble component = vapor pressure of extractor in atmosphxes a t T w = liters of gas per hour issuing from the tower = fraction of free volume per cubic decimeter of gross volume = cross section of tower in square decimeters = height of tower in decimeters = Henry’s coefficient = vapor pressure of extractor in atmospheres a t T’ = dissolution coefficient = grams of soluble component absorbed per hour per cubic decimeter of free volume per concentration deficit from equilibrium of one gram per liter = grams per liter of soluble component in entering extractor
-
Sole-It should be noted t h a t K? will have t h e same numerical value whether metric or English units are used.
The experimental absorption tower (Figure 1) was constructed of a Pyrex glass tube 91.5 cm. long and 7.1 cm. inside diameter with the inlet and outlet fittings sealed through cork on each end of the tower with a suitable silicate cement. Tower packing approximating Raschig rings was prepared froin ’/d-inch (6-mm.1 glass tubing and added a t random t o the tower to the effective height of 73.5 cm. From an average of three methods, this packing showed a wetted free volume of 60.54 per cent of the gross effective tower volume. The ease of inspection through the glass to\yer proved valuable in controlling channeling. The petroleum wash oil or straw oil was sprayed froin a distributor placed just above the surface of the tower packing in such a way as t o prevent wall wetting. A uniform velocity of oil was maintained by supplying oil to the distributor from a constant-level oil reservoir 2 meters above the top of the tower. The oil was discharged a t the bottom of the tower through a n adjustable oil seal into a measuring tank. Temperatures of the oil were taken a t the top and bottom of the tower. The wash oil used conformed to the following specifications:
...
Olefins 18 per cent 250 c Flash point (open) Vlscosltv 146 Specific h e a t . . . . . . . . . . . . . . . . . . . . . . . . 0.6 Specific gravity. . . . . . . . . . . . . . . . 0.875 Molecular weight. . . . . . . . . . . . . . . . . . . . . . . 260 ~~
~
~~~
K h e n the solute obeys Raoult’s law, P = P X , where P, Air a t constant pressure was supplied by a compressor and is the vapor pressure of the pure solute under the conditions a receiver, and its volume measured by a wet test meter. and X i s the mol fraction in the liquid phase. Thus Henry’s After drying by passage through two calcium chloride absorpcoefficient can be evaluated from the relation: tion towers, the air was partially saturated with benzene vapor. This degree of saturation was, to a large extent, conconcentration in liquid phase 1000 R T - -k = trolled by the sensible heat of the dried air. The carrier air concentration in gas phase .2117’1P, was passed through an electric tube furnace and then through where u1 is the specific volume of the solvent and M I the ino- a benzene bubble tower. By controlling the temperature of lecular weight of the solvent. the furnace according t o the velocity of the air, the sensible This paper deals with the absorption of benzene from air heat of the carrier gas provided the latent heat of vaporizaas the inert carrier by petroleum mash oil. Therefore, the tion of a desired quantity of benzene and the temperature of form of the equation using the evaluated Henry’s coefficient, the system was unaffected. The benzolized air entered the when the solute obeys Raoult’s law, may be applied directly. bottom of the tower and was distributed at a point slightly I n the experimental application of this equation the entering above the oil outlet. The gas mixture passed contracur-
INDUSTRIAL AND ENGI,VEERIXG CHEMISTRY
720
rently to the oil up through the tower packing and was discharged a t the top of the tower. By means of a bleeding system samples of either inlet or outlet gas could be run directly to a gas-analysis apparatus without disturbing the gas circuit, and the benzene determined by burning in excess oxygen. Temperatures and pressures of the gas were taken at the top and bottom of both the benzene and absorption towers.
Vol. 22, s o . 7
particular tests were not used in the calculations until the composition of both the inlet and outlet gas had remained constant for at least 30 minutes. Results
Table I gives the results of the tests, from which it may be noted that the concentration of the solute in the inlet gas, the velocity of the absorbing oil, and the flow ratio were varied over wide ranges. The variation of K s with t he velocity of the absorbing liquid and with the flow ratio is shown graphically in Figures 2 and 3, respectively. Conclusions
(1) The experimental results indicate the validity of Cantelo’s derived equations applied to an absorption process where the solute obeys Raoult’s law, and further that the determination of an evaluated Henry’s coefficient, for a process gorerned by Raoult’s law, permits the direct application of experimental and theoretical evidence obtained in this process to fundamental equations developed for a system in which the solute obeys Henry’s law. ( 2 ) Similar to the considerations in the design and operation of absorption towers for the removal of gases which obey Henry’s law, given in Parts I and I1 ( 2 ) , the tests on the removal of gases governed by Raoult’s law indicate that the important factors are rate of flow and temperature of the absorbing liquid. (3) Figures 2 and 3 show that the rate of solution of the soluble component varies linearly with the rate of flow of the extractor and that this rate of solution decreases rapidly with increase in flow ratio until a critical flow ratio is reached, whereupon the rate of solution remains substantially constant.
K2 Figure 2-Variation
BENZENE GAS AIR Inlet Outlet
%
%
3.64 4.38 3.50 3.88 3.34 5.01 4.01 5.01 5.00 4.32 3.52 3.80 3.73 5.30 4.87 4.42 3.99
0.67 0.78 0.48 0.52 0.68 0.98 0.92 1.20 1.10 0.99 1.13 1.67 1.42 2.17 2.60 0.42 0.43
of KZ w i t h Velocity of Absorbent
Table I -Absorption of Benzene OIL TEXP.GAS TEMP. OIL Inlet
Liters /min. oc. 5.95 0 . 1 2 26.4 5.95 0 . 0 9 2 3 . 5 5.66 0.15 29.2 5.38 0.14 28.3 5.66 0.12 28.2 5.66 0.12 28.0 5.66 0.11 27.0 5.66 0.06 24.6 5.38 0.04 24.0 5.66 0 . 0 6 2 4 . 8 5 . 6 6 0 . 0 5 ’27.4 6.80 0.03 27.0 6.51 0.03 26.0 5.66 0.02 29.6 8.49 0.03 26.0 5.66 0.25 28.0 5.66 0.21 25.8
Outlet
Inlet Outlet
oc.
oc.
=e,
28.0 25.0 30.5 30.0 29.7 29.6 29.2 25.0 25.0 26.2 29.7 29.5 28.0 32.2 29.7 31.0 28.3
23.0 23.2 30.0 31.0 29.3 29.5 29.5 27.5 25.0 28.0 27.5 28.5 27.5 31.5 29.0 27.5 26.0
30.0 28.7 34.5 34.3 32.5 33.0 34.0 30.5 29.0 32.0 33.0 33.0 33.5 36.0 33.5 31.0 28.5
FLOW RATIO 50.00 66.07 36.81 40.30 47.19 46.02 51.49 94.39 134.51 94.39 113.27 234.35 191.56 246,22 308.91 22.65 26.97
Kz 0.5837 0,5909 0.8139 0.7914 0.6342 0.6140 0.6082 0.5501 0.5262 0.5951 0.4791 0.4443 0,4880 0.4592 0.4474 0.8360 0.7471
Operation
I n operating a n experimental run, a desired rate of carrier gas was indicated on the wet test meter. The air delivered from the meter contained an average of 28 per cent humidity a t 21’ C. Thus an average correction factor of 0.993 was applied to the humid volume recorded to give the dry volume used in the calculations. After thoroughly drying in calcium chloride towers, the carrier gas was heated to a required temperature in a combustion tube furnace, this temperature, in general, controlling the composition of the benzolized air on passage through the benzene tower. By means of a suitably constructed burning pipet in a gas-analysis apparatus, the benzene was determined in the inlet and outlet gases of the absorption tower. I n this burning method the diminution in volume after combustion with excess oxygen was checked against the carbon dioxide formation. From the volume of the inert carrier and the composition of the inlet and outlet gases, the volumes of the inlet and outlet gases were calculated under operating conditions. The data on any
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30 60 80 IZO 150 180 PIO 240 270 300 330
Flow Aa tio Figure 3-Variation
of K2 w i t h Flow R a t i o
(4) I n addition to the theoretical considerations, the method described has been applied to the determination of the relative efficiency of various absorbents, particularly different petroleum base stocks, for light-oil scrubbing in byproduct coke practice.
July, 1930
I N D U S T R I A L A N D ENGI,VEERISG CHEMISTRY Acknowledgment
72 1
Literature Cited
This investigat,ion was carried out under the Henry Marison Byllesby ~ ~Research~ Fellowship ~ in ~ ~ ~ i~ Grateful acknowledgment8 is also expressed for the assistance rendered by R. F.Smith.
(1) Cantelo, Chem. M e f . Eng., 33, 680 (1926). (2) Cantelo, 19, 989 .(1927) i ~ ~Simmons, l ~ Giles, ~ and Brill, ~ IND.i ENG.~CHEM.,~ (3) Donnan and Masson, J . SOL.Chem. I n d . , 39, 236T (1920). (4) Lewis, J , ENG, CHEM,, s, s25 (1916), ( 5 ) Whitman and Keats, Ibid.. 14, 186 (1922).
Heat Transfer from a Gas Stream to a Bed of Broken Solids-II’i’ C. C. Furnas NORTH CESTRAL
EXPERIMEKT STATION
OF THE
u. s. BEREAUO F
hfIhES, h\IINSEAPOLIS,I f I S S .
This paper represents a continuation of a study pubR - I S S F E R R I S G heat Schumann’s Method lished under the same title in a previous issue of Into or from a fluid dustrial and Engineering Chemistry (6). The first It is possible that the exs t r e a m t o b e d s of article reported work on beds of iron balls, while t h e perimental difficulties would broken material is one of the data for t h e present article are for materials of more have proved insurmountable most common industrial procindustrial interest-iron ores, coke, limestone, coal, had it not been for a very esses. yet quantitative inforand a typical blast-furnace charge. important theoretical paper mation on the subject is alCurves are given for the temperature history of a cold recently published by Schumost entirely lacking. As far bed of broken solids being heated by a hot fluid. A mann (21). S c h u m a n n ’ s as the author k n o w , there method of determining the coefficient of heat transmethod of attack was somehave been only two previous fer between a gas stream and a bed of particles is given. w h a t a s follows: Assume experimental studies bearing The temperature history curves of a bed are shown to that a uniform fluid stream is directly on the problem. One be applicable when there is a heat of chemical reaction. allowed t o flow through a bed was conducted by the ComEquations have been developed for the steady state in of broken solids at some unitiustion L-tilities Corporation countercurrent heat flow equipment. form temperature initially (28) and the other by the presAn illustrative problem involving a foundry cupola is lower than the temperature ent author (6). Inbothcases given, using the equations a n d experimental data preof the stream. If there is no the beds were made up of sented. uniformly sized iron balls and heat loss through the walls of the apparatus, the entire bed although the data and the relations betjveen variables are of theoretical value, they are of material will eventually arrive a t the initial temperature of the fluid. Given the thermal properties of the fluid and solid, not directly applicable to industrial apparatus. The theoretical considerations of the fundamental physics it should be possible to develop the mathematical relations of heat transfer are c.xceptionally complicated and no satis- for the temperature history of any point in the bed. factory general theory has ever been developed. However, The problem is difficult, but Schumann presents a very a very uqeful method of attack has been found along almost clever and skilful solution. The derivation is rigorously purely mat heinatical lines-mainly by methods of dimensional exact only for systems where the thermal properties are conanalysis. stant and for a noncompressible fluid and where the solid parwas probably the first to make an adequate ticles are so small that there is no temperature gradient formulation of the variables controlling heat transfer. His within the piece at any time. However, as will be shown pioneer work was later supplemented by Boussinesq ( l ) , later, it a-as found experimentally that this solution applied Susselt ( 2 1 ) . llciidams (20),Rice (24),Russell (RB), Stanton quite accurately to systems where the fluid is a gas and where (ZQ), and others. This theoretical work, coupled with a there are considerable variations in thermal properties and the mass of experiments of recent investigators, has resulted in solid pieces are large. Schumann’s mathematical procedure will not be presented a very satisfactory quantitative theory for liquids flowing here, but his computed curves are important and are given through conduits (50). However. none of these studies are directly applicable to in Figures 1 and 2. The symbols used have the following heat transfer to beds of broken solids, so in 0rdt.r to obtain definitions : quantitative information regarding the operation of blast T o = initial uniform temperature of the fluid furnaces the Bureau of Mines has found it necessary to take T , = temperature of fluid a t any point at any time T , = temperature of solid a t any point at any time up this experimental study. It is part of a general program of blast-furnace research which this bureau is conducting in the laboratory and in the field (3, 11 to I ? , 25). The method used in the previous investigation (6) was y = -k- x that of alternately measuring the temperature of the gas h, 21 stream and of the solid. Although this method Tvorked satis- where x = distance from bottom of column in centimeters factorily when the bed was made of iron balls, it mas inadet = time in seconds quate when applied to beds of iron ore and other irregular w = fluid velocity in cubic centimeters per second per square centimeter cross-sectional area of bed pieces of low thermal conductivity. f = fractional voids in bed (no units) h, = heat capacity of solid in calories per cubic centimeter 1 Recened May 10, 1930. Presented before the American Institute of per degree Chemical Engineers, Detroit, Mich , June 4 t o 6, 1930. h,= heat capacity of fluid in calories per standard cubic 2 Published b y permission of the Director, U. S. Bureau of Mines. centimeter per degree (Not subject to copyright )
T
