Industrial & Engineering Chemistry Volume 38 Issue 1 1946 Carlson, Harrison C. -- Absorption and Humidification

8/10/2019 Industrial & Engineering Chemistry Volume 38 Issue 1 1946 Carlson, Harrison C. -- Absorption and Humidification.

1/4

H a r r i s o n C. C a rl s o n w a s b o r n i n N e w t o n , M a s r . , i n 7913. H e s t u d i ed c h e m i c al e n g i n e e r i n g

a t t h e M a s sa c h u s et t s I n s t i tu t e o f T e c h n o l o g y , r ec e i v i n g t h e d e g r e e s o f b a c h e l o r o f s c ie n ce

i n 7934 a n d m a s t e r o f s c i e n c e i n 7935. Since 7935 h e h a s b e e n e m p l o y e d a t t h e Ex-

p e r i m e n t a l S t a t i o n o f E /. d u P o n t d e Ne m o u r s & C o m p a n y , In c ., a t W i l m i n g t o n , D e l .

A f t e r a y e a r as s em i w o rk s o p er a t o r i n t h e A m m o n i a D e p a r t m e n t , h e d i d r e se ar c h i n f l u i d

f l o w , h e a t t r a n s fe r , v a p o r - l i q u i d e q u i l i b r i a , a n d d i s t i l l a t i o n i n t h e Ch e m i c a l En g i n e e r i n g

a n d M e t a l l u r g i c a l L a b o r at o r y o f t h e En g i n e er i n g D e p a r t m e n t . R e c en t l y m o st o f hi s w o r k

has

b e e n i n d e s i g n o f a b s o r p ti o n a n d d i s t i ll a t io n e q u i p m e n t . W i t h A. P. C o l b u r n h e

w r o t e a p a p e r o n t h e v a p o r - l i q u i d e q u i l i b r i a o f n o n i d e a l s ol u ti o ns w h i c h a p p e a r e d i n t h e

M a y ,

1942,

i s s u e o f I n d u s t r i a l a n d E n g i n e e r i n g C h e m i s t r y , p a g e s

581

t o

589.

H e i s

a m e m b e r o f t h e A m e r i c a n C h e m i c a l S o c i e t y a n d S i g m a X i , a n d i s a l i c e n s ed e n g i n e e r .

D

Harr ison C Carlson

HE

advances in this field are reviewed here from October,

1943, to November, 1945. Arnold

2)

derived an equation

T or the u nsteady-st ate evaporation of a liquid from a plane

surface int o an infinite volume of inert gas free from convection.

The derivation assumes that the inert gas docs not diffuse into

the liquid and t ha t th e partial pressure of th e evaporating liquid

a t th e interface is constant with time. Th e development is based

on the Maxwell-Stefan differential equation, so that it is ap-

plicable to large an d small concentrations of the diffusing gas

where the previously used integration of the Fick law was true

only for low concentrations. Arnold used the equa tion to calcu-

late t he diffusion constants of liquids

at

the bottom of a vertical

tub e filled with air, from measurements

of

the ra te of air displace-

ment from the top.

Sheiwood and Gilliland measured the rates of evaporation of

liquids wetting the wall of

a

vertical tube with

a

countercurrent

air stream. With the air in viscous flow, they found tha t the

experimental data were fitted by a theory for a constant air

velocity across the tube rather than the parabolic distribution

expected in viscous flow. Boelter 5) dapted an equation previ-

ously derived for heat transfe r to this case of diffusion. He indi-

cated that evaporation of the high-molecular-weight organic

liquid increased th e density nea r the wall and induced a convec-

tion current which increased the velocity near the wall and de-

creased it near the center. This deformed the parabolic velocity

distribution t o one nearly uniform across th e tube. Considera-

tion of free convection in correlating absorption in packed towers

might be equally fruitful.

Tiller and Tour

33)

gave

a

clear exposition of the elemcnts

of the calculus of finite differences and showed the appl icability

of difference equations to chemical engineering. Equa tions for

the absorption in an isothermal plate column are derived with

the material balance expressed in mole ratios, and the equi-

librium curve with either the mole rat io in the liquid proportional

to that in th e gas

or

th e mole fraction in th e liquid proportional

to that in the gas. Th e calculus of finite differences offers the

means of finding the solutions to difference equations which are

too

involved to be solved by inspection.

Natt a and Mattei

( 2 1 )

discussed the calculation of the numbcr

of theoretical plates and the amount of solvent and reflux neces-

sary to separate a bina ry gaseous mixture completely by a process

known in this country as extractive distillation. The y trea ted

the case of a nonvolatile solvent in a n isothermal column, with

the solubilities

of

the

gases

smd1

and without mutual influence

If the operating line is drawn wi th th e composition on a solven

free basis, it will be curved if the solubilities differ. Xa tt a an

Mattei obtained a straight operating line by expressing the com

positions in solubility equivalents.

If

the solubilities follow

Henry's law, yy rnlzl and y:

m2x2

he solubility equivalen

in the gas of mole fraction yl would be ylml/(ylm~ yPmJ

Kat ta and Matte i pointed out the advantage of a packed colum

over a plate column for this type of separation employing hig

ratios of liquid to gas. For the separa tion of gaseous hydrocar

bons with an unspecified solvent, the height of a theo retical plat

in a column packed with l/2- or 1-inch Raschig rings was 4 ee

at gas velocities of

0.5

to

1.0

ft./sec.

Tour

and Lerman 34) derived a theoretical equation for th

spreading of a liquid in a packed tower, distributed from an are

source rather t han the point source used in their previous paper

Da ta on the flow of water through packed columns without any

countercurrent gas flow were used to evaluate c onstants charac

teristic of the packings. Observation

of

packed columns b

Bain and Hougen 3) and Schoenborn and Dougherty 37

revealed t ha t the gas flow played a n importa nt par t in distribut

ing the liquid in a fashion which has yet to be analyzed mathe

matically.

Goff and Gratch (9) presented tables

of

the humidity, specifi

volume, enthalpy, and entropy of dr y and saturat ed air and o

liquid water or ice in equilibrium for a to tal pressure of 1 atmos

phere and in the temperatur e range 60' to

+200

O

F.

Devia

tions from the perfect gas law were taken into account in th

calculation

of

these reliable and useful tables.

critical review of the available data

o n

the thermodynami

properties of ai r and water and their mixtures.

In measuring humidity under conditions where the wet-bulb

tempera ture was below the freezing point of water , Wile 37

suggested using a thermometer graduated to 0.1

.

and previ

ously coated with a film of ice rath er th an using a wick wet wit

liquid water. Wile reviewed the adiabatic saturati on and di

fusional theories of the wet-bulb hygrometer t o arrive

at

a recom

mended air velocity of 5 ft./sec. to make radiation to the ther

mometer negligible.

Th e problem of selecting

a

refrigerated coil to cool and dc

humidify air was treated from different approaches by Siege

50)

and Boehmer 4 ) . Siegel assumed a complicated functio

of the dry-bulb and dew-point tempera ture s of the inlet and outle

The article gave

14

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

Vol. 38,

No.


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air to calculate an average surface temperature.

For no de-

humidification, the surface temperature becomes the dew point.

The method depends on obtaining three tests on

a

coil dehumidi-

fying air to calculate the heat transfer coefficients on the air and

refrigerant sides.

Boehmer

4 )

worked from the equivalent by-

pass theory, which assumes that

part of

the air is unchanged

in temperature and humidity by the coil and the other fraction

is

cooled to the refrigerant temperature.

Boehmer pointed out

the effects of installing too large

or

two small coils on the humid-

ity and temperature of the refrigerated space, but did not com-

pare the predicted conditions with those observed, as did Siegel.

Both of these approaches are empirical and limited to the case of

dehumidifying air at atmospheric pressure. A more funda-

mental approach to the problem was given by Colburn and

Drew (6).

LIMITING

GAS VELO ITIESN

COLUMNS.

Knowledge of the

effect of the physical properties of fluids on flooding velocities of

tower packings has

and Schoenborn and

ured the flooding vel

hydrogen, and carbon dioxide. The liquid rates in th

column were varied

from

250

to

21,000 lb./(hr.)(sq. ft.)

Schoenborn and Dougherty measured the flooding velocity and

pressure drop in the flooding range with air flowing countercur-

rent to water or one of two oils, having viscosities up to 38 centi-

poises when the tower was packed with

l / h - I/ -, or

I-inch Raschig

rings or / -inch Berl saddles. The liquid rate in the 8-inch tower

was varied from 400 to 20,00Olb./(hr.)(sq.

ft.).

They found that

the gas velocity at flooding

was

inversely proportional to the

liquid viscosity raised to a power between 0.33 for Ija-inch rings

and

0.15

for 1-inch rings.

Bain and Hougen checked the conclu-

sion of previous investigators, using smaller towers, that the gas

density raised to the 0.5 power is the proper correction on the gas

velocity, Both investigations found that the oils channeled in

the packing even though given an initially uniform distribution.

From the abstract of an article by Zhavoronkov

89)

of which

the original does not seem to be available in this country, it is

impossible to tell whether new data on pressure drop and fiood-

ing velocity have ,been measured.

Schutt

98)

reported difficulty from foaming

of

an absorption

oil, whi+ decreased the gas-handling capacity

to

one-fourth of

that of a nonfoaming medium.

The absorption oil was

a

pyroly-

sis product, which circulated in a closed cycle and foamed worse

as

the oil became more aromatic. Tests indicated that the plate

efficiency decreased

as

the gas velocity increased. Observation

of the foaming in a glass apparatus showed tha t the pyrolysis

absorption oil foamed worse than

a

paraffinic oil.

RATES F

ABSORPTION.

Cooper, Fernstrom, and Miller

( 7 )

measured the rate of absorption

of

oxygen in aqueous sodium

sulfite solutions in tanks between

6

and

96

inches in diameter with

vaned-disk or flat-paddle agitators. Absorption coefficients

were measured

for a

range of gas velocities, liquid depths, and

power inputs up to 3000 ft.-lb./(min.)(gu. ft.). The absorption

coefficient was found

to

increase with the power input raised to

the

0.95

power and with the superficial gas velocity raised to the

0.67

power. The increase

of

the absorption coefficient based

on the unaerated volume of the liquid with the gas velocity is

probably related to the increase in volume of the aerated solu-

tion, which Foust, Mack, and Rushton

(8)

found

to

increme with

the 0.53 power of the gas velocity.

The absorption coefficients and power requirements may be

compared with those for

a

packed tower for oxygen transfer to

water without chemical reaction. The highest coefficient meas-

ured by

Cooper,

Fernstrom, and Miller

7)

with the driving force

expressed in mole fraction of oxygen in the liquid was 5260 lb.

mole/(hr.)(cu. ft.)(

Az)

with

a

power input

of

330 ft.-lb./min. to

a vaned disk in a 0.5-inch

jar.

Molstad, McKinney, and Abbey

80) reported

a

coefficient of 380 lb. mole/(hr.) (cu. ft.)

A x )

for

oxygen stripping with a liquor rate of 11,000 lb./(hr.) (sq. ft.)

on

a grid tile. With the vaned-disk absorber, the power required

was 330 ft.-lb./min. for agitation and 150 ft.-lb./min. to force the

gas through. In a packed tower to absorb oxygen a t the same

rate, the power would be about 1500 ft.-lb./min. for pumping the

liquid and a negligible amount for gas resistance. The agitated

tank has a slight advantage in size and power over the packed

tower, but i t is limited to gas velocities below 0.2 ft./sec., which

is approximately the rate of rise of gas bubbles in

a

liquid.

Groes

and Simmons 10)measured the rates of absorption of

benzene, trichloroethylene, and chloroform from air by kerosene

in

a

12-inch tower packed with 1-inch Berl saddles. Over-all

heights of gas-film transfer units of 2.5 to 5 feet were obtained at

gas rates between

15

and 70 lb./(hr.)(sq.

ft.),

which are too low

to be

of

commercial interest.

Molstad, McKinney, and Abbey

( 0)

reported

a

large amount

orption

of

ammonia from air by water and on

gen from water by air with a 15-inch square

1-inch rings, 1-inch saddles, 3-inch spiral

d grids,

or

sevBra1 styles and

ar-

tile. For the absorption of am-

from 100 to 11001b./(hr.)(sq. ft.)

at a constant liquor rate of 3000 lb./(hr.)(sq. ft.), and the water

rate was varied from 1800

to

18,000 lb./(hr.)(sq.

ft.)

at

a

con-

stant gas rate of

500

lb./(hr.)(sq. ft.). With these high ratios

of liquid to gas, more than 85% of the resistance was in the

gas

film. The height of a transfer unit for ammonia absorption

was in the range 0.8 to 3.0 feet on the over-all gas film basis.

The absorption coefficient for ammonia was found to vary with

the gas rate raised to

a

power varying from 0.4 to 0.9, with the

higher exponents for the smaller pacltings. Molstad

t

al. used

the pressure drop per transfer unit as

a

guide to show that the

large packings with low pressure drops result in lower column

and power costs than the small packings.

Scheibel and Othmer ( 6) measured rates of absorption and de-

sorption in water

of

acetone, methyl ethyl ketone, methyl iso-

butyl ketone,

and

methyl n-amyl ketone borne by

air.

The

tower was

4

nches in diameter and packed with 0.3-inch glass

Raschig rings for a total height of 74 inches, but divided for

sampling in the middle. The authors attempted to separate the

over-all Coefficients nto gas and liquid film coefficients, and pro-

posed

a

general equation for the over-all coefficients for any s y ~ -

tern on 0.3- and 1-inch rings. The correlation is unusual, since

they conclude that the separate film coefficients

are

proportional

to the first power

of

the diffusion coefficient times the

0.8

power

of the flow rate. Having the diffusivity enter to the first power is

characteristic of laminar flow, and the 0.8 power if the flow rate is

usually found for turbulent flow. Previous experiments

on

evaporating liquids in packed towers indicated that the diffusivity

entered to the 0.17 power, The height of an over-sll transfer

unit on the liquid film basis for the absorption of acetone was

between

3

and 6 feet.

Walthall, Miller, and Striplin (36) studied the absorptlon

of

SUI-

fur dioxide and oxygen in water containing 0.03% Mn++ o

pro-

duce 30% sulfuric acid. When the gases were bubbled through

a

porous plate in the solution, the addition of

1

aluminum sulfate

improved the gas dispersion and rate

of

absorption. Iron salts,

grease, and carbon dioxide inhibited the catalytic effect of l fn++,

but the addition

of

0.0001 Alkanol

overcame the grease dif-

ficulty. As the porous plate plugged d t h dust, the

sulfur

dioxide

was absorbed

in

an 18-inch tower packed with

15

feet

of

1-inch

glass rings, and oxidized in an external tank by air and ozone

bubbled through a porou8 carbon plate. Several absorption CO-

efficients for sulfur dioxide in the packed tower

are

presented

graphically.

Lichtenstein (18) reviewed the theory and performance of

mechanical-draft water cooling towers from the designers

viewpoint.

The

case of calculation

Continued

on

page 33)

January, 1946 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 15


3/4


4/4

dioxide in the tail gases of a sulfuric acid plant to sulfur and arn-

monium sulfate, by absorbing it in an ammonia solution and

heating the mixture of ammonium salts. Thau 88) and Ilowat

18) eviewed the numerous processes for removing hydrogen

sulfide from industrial gases. Descriptions of plants removing

hydrogen sulfide with a sodium carbonate solution, ethanolamine,

and the Thylox process were given by McFnddin IQ),by Phil-

lips

64),

and anonymously

1 ) .

Larlre

(17')

has given operating

data on the absorption of naphthalene in oil from coke oven gas,

an d reviewed the typ es of absorbeis used for a very low ratio of

oil to gas. Oppelt and Munz

(2 )

reported laboratory experi-

ment s on the increase in viscosity and asphalt content of ab-

sorption oil caused by bubbling oxygen and hydrogen sulfide

through the oil at temperatures encountered in absorption and

stripping. Kirkbride and Bcrte tti 16) measured equilibrium

constants for methane, ethane, propane, butane, and pentane in

paraffinic, naphthenic , and aroma tic bbsorption oils at a bout 85

F.

and

at

pressures from

125

to

3000

lb./sq. in. Th e three types

of

oils were compared for removing pentane from a natural gas

with regard to oil circulation, methane absorption, and loss of oil

in the outlet gas.

CONCLUSION.he published papers on absorption and

humidification represent only a small fraction of the advances

in the field, Many

of

the d ata on the design and performance of

absorption equipment

in

industry are never published.

It

is

unfortunat e that secrecy, inability to conduct tests on plant units,

and t he failure of management t o understand

how

little is really

understood a bout diffusional processes have limited th e published

material.

LITERATURE CITED

Anonymous, Ind. Heating, 11, 410-14 (1944).

Arnold, J. H.,

Trans. Am. Inst. Chem. Engra.,

40, 361-78

Bain, W.

A.,

Jr., and Hougen,

0. A , ,

Ib id . ,

40,

29-49, 389407

Boehmer, A . P., Refrig . Eng. ,

50,

329-37 (1945).

Boelter, L. M. K., Trans. Am. Inst. Chem. Engrs., 39, 557-64

Colburn,

A.

P., and Drew, T. B.,

Ibid.,

33, 197-215 (1937).

Cooper, C. M., Fernstrom, G. A , , and Miller, S. A., IND. XG.

Foust, H. C., Mack, D. E., and Rushton, J . H., Ibid., 36, 517-22

Goff,

J.

A . ,

and Gratch,

S., Heating Piping A ir Conditioning,

17,

Gross,

W.

F., and Simmons,

C.

W.,

Trans. Am. Inst. Chem.

Hickox, G. H., Proc. Am. SOC.Civil Engrs., 70, 1297-1327

Howat,

D.

D., Chem. Age (London),49, 75-8,99-105 (1943).

Hull. R. H.. Petroleum Refiner. 24. 353-6 (1945).

(1944).

(1944).

(1943).

CHEM., 6, 504-9 (1944).

(1944).

334-48 (1945),

Engrs . , 40, 12 14 1 (1944).

(1944).

Ibid.,

0, 243-9, 265-9, 285-8 (1944).

Hutchison, W. K.. and Spivey, E.,

S O C .

Chem. Ind ., Chem. Eng.

Kirkbride, C. G., and Bertetti,

J. W ., IND.

NQ.CHEM., 5,

Group Proc., 24, 14-29 (1942).

1242-9 (1943).

Larke, R. H., Gas World, Coking Sect., 118, 17-20 (1943).

Lichtenstein,

J.,

Trans. Am.

SOC.

Mech. Engrs., 65, 779-87

McFaddin, D. E., Petroleum Reliner, 23, 347-9 (1944).

Molstad, M. C., McKinney,

J.

F., and Abbey,

R.

G., Trans. Am .

Natta, G., and Mattei,

G.

F.,

Chem. Tech.,

46, 201-4 (1943).

Oppelt,

W .,

and Munz, W., Oel u. Kohle, 39, 95-7 (1943).

Pasguill, F.,

Proc. Roy. SOC.

London),

A182

5-95 (1943).

Phillips, H. L., Natl. Petroleum News, 36, R16-18 (1944).

Russell, G.

F.,

Petroleum R~fi ner , 4, 139-42 (1945).

Scheibel, E. G., and Othmer,

D.

F,, Trans. Am . Inst. Chem.

Schoenborn, E. M., and Dougherty,

W.

J., Ibid., 40, 51-77,

Schutt, H. C., Petroleum Refinsr , 24, 249-53 (1945) .

Sharpley, B. F., and Boelter, L. M. K., IND.

NQ.

CHEM.,30,

Siegel, L. G.,

Heating Piping

Air

Conditioning,

17, 90-6, 104

Sutton, W . G. L.,

Proc. Roy.SOC.

London),A182,48-75 (1943).

Thau,

E. A, , OeZ u .

Kohle, 40, 08-20 (1944).

(1943).

Inst . Chem.

Engrs.,

39, 605-62 (1943) .

E ~ Q ~ s . ,0, 611-53 (1944).

389-92,402-7 (1944).

1125-31 (1938).

(1945).

Tiller, F. A l . arid Tour, It. S., Tram. Am. I n s t . Chem. Engrs , 40

Tour, R. S. and Lerman, F., Ibid . , 40, 79-103 (1944).

Wade, S. H., SO C. hem. Ind. , Chem.

Eng.

Group Proc., 24, 1-13

Walthall, J. H., Miller, P., and Striplin, M. M., Jr., Trans. Am

Wile, D. D., Refrig. Eng.,

48, 291-301 (1944).

Woolam, C. 9. nd Jackson, A . , Chem. Trade

J.,

116, 325-0

Zhavoronkov. N. M., himicheshaua Prom., 1944, No. 1 , 4-14

317-32 (1944).

(1942).

Inst. Chem. E ~ Q T S . ,1, 53-140 (194 5).

343-4 (1945).

No 2 , 12-19; Chem. A b s . , 38, 3514, 4839 (1944).

FLUID DYNAMICS

C O N T I F U E D

F R O V PAQE ?

small ones, some control systems employed a condensate valve

only; this expedient pu t full steam pressure on the reboiler and

forced the single valve to dissipate all of the pressure differenc

between the steam and condensate systems except that los

through pressure drop in condensate lines. Operating experienc

forced modification of many such oversimplified installation

where the phenomenon of the critical pressure rat io discussed

in the previous paragraph

tvas

encountered.

The flow problems where very low pressure drops for vapor

liquid mixtures are controlling are typified by the design

of

oncc

through or natural-circulating-type vertical reboilers, employed

in connection with high-pressure fractionation of normallv

gaseous liquids. Such operations are carried out under pressur

and temperatur e conditions approaching the critical, i n which case

the difference between vapor and liquid density becomes very

small. Since the vertical position provides increased drivinq

force over the horizontal in inducing circulation, it is preferred

Reliable data on the characteristics

of

such systems are not alway

available, and the allowable margin of error ma y bc exceeded

unless

a

detailed analysis is made.

BIBLIOGRAPHY

1)

Allen,

Petroleum Refiner ,

23, 93-8 (July, 1944).

(2) Anonymous, Ibid., 24, 128 (May, 1945).

(3) Anonymous, Proc. Am. Petroleum

Inst.,

111, 20 (1939).

(4) Anonymous, Natl . Patroleurn

N e w s ,

33, R403-6 (1941).

(5) Bain and Hougen, Trans. Am. Inst.

Chem. Engr s . , 40, 29-49

(58) Benjamin and Miller, Trans. Am. SOC.M e c h . Engrs.,

1942

(1944).

657-69.

(6)

Binder, Product Eng.,

15, 466-7 (1944).

7) Boelter and Kepner, IND.

ENG.

CHEM.,

1, 426-34 (1939).

(8) Chenicek, Natl. Petyoleum News, 36,

R678-82 (1944).

(9) Evering, Fragen, and Weems, 021

Gas

J . , 43, 77 (Oct. 28, 1944

(10) Fowler and Brown, Trans. Am. Inst. Chem. Engrs., 39, 491

(11) Frey, Chem. &

M e t

Eng.,

50

126-8 (Nov., 1943).

(12) Gerhold, Iverson, Nebeck, and Kewman, Trans. Am. Inst

(13) Gradishar, Faith, and Hedrick, Ibid., 39, 201-22 (1 943).

(14) Hankins, Engineering, 157, 158-60, 177-80 (1944).

(15)

Lobo, Friend, Skaperdas

et

al.,

IND.

NG.

CHEM.,

4, 821-3

(16) Murphree, Brown, Fischer, Gohr, and Sweeney, b i d . , 35,768-73

(17)

Murphree, Brown, Gohr, Jahnig, Martin, and Tyson. Trans

(18) Murphree, Fischer, Gohr, Sweeney, and Brown, Proc. Am

(19) Newton, Dunbam, and Simpson,

Trans. Am. Inst. Chem

(20) Shoenborn and Dougherty,

Ibid.,

40, 51-77 (194 4).

(21) Simpson, Oil Gas J . 44, 88-90 (May 12, 1945).

(22) Simpson, Evans, Hornberg, and Payne, Proc. Am. Petroleum

(23)

Simpson, Evans, Hornberg, and Payne,

I b id . ,

111,

24 (1943).

(24) Watson, IND. NG.CHEX., 5, 3984 00 (1943).

(1943).

Chem. Engrs., 39, 793 (1943).

(1942).

(1943).

Am. Inst. Chem. Engrs., 41, 19-33 (1945).

Petroleum Inst.,

111,

24 (1943).

Engrs., 41, 215-32 (1945).

Inst.,

111, 23 (1942).

I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 38, No.

Documents

Industrial & Engineering Chemistry Volume 38 Issue 1 1946 Carlson, Harrison C. -- Absorption and Humidification