Industrial & Engineering Chemistry Volume 45 Issue 1 1953 Pigford, R. L. -- Absorption and Humidification

7/26/2019 Industrial & Engineering Chemistry Volume 45 Issue 1 1953 Pigford, R. L. -- Absorption and Humidification

1/5

ABSORPTION A

HUMIDIFICATI

ms

R

L.

PIGFORD

UNIVERSITY

OF

DELAWARE NEWARK,

DEL.

r*

Impor tant progress in gas absorpt ion has been made in the f ields of phase equi l ibr ia, especial ly

for hyd rocarbon systems, and i n s tudies

of

packed towers.

O n ly a few papers have appeared

in the pract ical ly m ore important f ield of t ray-tower performance.

CCURATE and reliable methods of correlating and predicting

phase equilibrium data for gas-liquid systems must be made

& Available before general design procedures

for

gas-liquid con-

tact ing equipment can be developed. Although generalized meth-

ods for estimating gas solubility are not yet available for com-

pounds which differ chemically from the solvent, there has been

substant ial progress in the last few years on methods of esti-

mating phase distribution constants for hydrocarbon systems.

Methods for estimating equilibrium vaporization constants

for light hydrocarbons have been described previously by Bene-

dict, Webb, and Rubin

5 )

ased on an equation of stat e fitted

to

P-TI-T data on pure hydrocarbons. The calculations are rathe r

tedious but the results have been shown to be in bet ter agreement

with existing vapor-liquid equilibrium data tha n many less funda-

mental methods th at have been popular for many years. The

Benedict equation has now been used to calculate th e fugacities of

the hydrocarbons, methane through heptan e, in gas

or

liquid

mixtures and the resulting values of

K

have been correlated

graphically with temperature, pressure,

and composition-ex-

pressed by the molal average normal boiling point of the mix-

ture-by Benedict, Webb, Rubin , and Friend

(6).

Sample

chart s are given in the published article and the complete collec-

tion of c harts for the seven hydrocarbons a t pressures up to

3000

pounds per square inch can be purchased from the

hl.

W. Kellogg

Co.

of

New York City.

As an example of the success of the correlation, the est imated

K values were shown to agree with the data of Webber 37) for

hydrocarbon solubilities in an absorption oil, a t pressures up to

2000

pounds per square inch, the average absolute deviation for

methane being only

7.7%.

The charts published by t he Kellogg

Co. are concluded to bereliable except ( a )when better t han 5%

accuracy is required,

( b )

when the pressure is within 50 pounds

per square inch of the tru e critical pressure of either phase, c )

when the characterization fac tor of either phase is less than

11.4

( d )

when either phase contains more than 30% of a polar com-

pound,

or ( e )

when extensive extrapolation is required beyond

the range of the char ts.

An alternative method of expressing methane solubili ties was

also proposed by Organick and Brown 27) who employed an

empirical relationship based on critical pressures for methane

binary systems, t he correlating pressure

for

any mixture of paraf-

fin hydrocarbons, binary or complex, being defined in terms of

three other variables: the equilibrium pressure, functions of the

equilibrium vapor, and liquid-phase compositions. The liquid

phase is assigned an equivalent molecular weight which is a func-

tion of its boiling point for paraffinic and olefinic compounds and

is also a function of the characterization factor for naphthenics,

aromatics, and other nonparafis of high molecular weight.

Experimental data agreed with values indicated by the correla-

tion in all ranges of t emperature and pressure, within the experi-

mental uncertainty.

Solubilities of methane, ethylene, and isobutane in high-molec-

*

ular-weight paraffinic, naphthenic

and aromatic compounds and in

two complex hydrocarbon absorption oils were de termined

experimentally by Solomon

(36)

and were compared with the

predictions of Benedict, Webb, Rubin, and Friend (6) based on

the Kellogg equation of state. The predictions were made fo

mixtures of paraffin hydrocarbons. It

was found tha t the experi

mental and predicted values agreed if the Watson characteriza-

tion factor ( K ) f the whole liquid phase was greater than about

13

but for smaller K-factors the equilibrium vaporization constants

were larger by a factor as large as 2.4 and 1.9 for methane an d

ethylene, respectively, in

a

liquid having

K

=

10.

The correc

tion charts proposed by Solomon are consistent with the previous

data of Kirkbride and Bertetti (88) and Webber 37) .

A discussion of t he paper by Solomon

(36)

presented by Organ

ick showed that the empirical methods described

in

his pape

with Brown

27)

were nearly

as

effective as the modified Kellogg

procedure described by Solomon.

New data on the methane-isopentane system were published

by Amick, Johnson, and Dodge

2 ) .

Arnold

(3 )

discussed

vaporization equilibria of methane a t high pressures, sunlmariz

ing existing data.

Winn (40) ublished a nomographic repre

sentation of hydrocarbon vapor-liquid equilibria.

Baldwin and Daniel

( 4 )

described experimental measurements

of gas solubility in viscous liquids. Bunsen solubility coefficient

determined by their method for air oxygen and nitrogen in water

were shown to be consistent with reliable data already existing

and new values of gas solubility were reported for permanen

gases in light hydrocarbons.

EQUIPMENT PERFORMANCE

Packed

Towers.

Ergun 14) eviewed data from severa

sources on pressure drop across random packings and compared

them with an equation proposed previously by Ergun and Orning

(16). Only single-phase flow, either liquid or gaseous, through

the solid packing was considered.

As a result it was found th at the equation

represents the

640

experimental points, including data for Ra

schig rings and Berl saddles, with remarkable accuracy, as shown

by Figure 1. The left-hand side of the equation is the friction

factor defined as th e ratio of, the head loss, due to friction, to t h

value of a velocity head based on the tru e fluid velocity,

U / E

between the packing. The first term on the right is caused by

viscous shear an d the second represents the effect of changes i

fluid direction and of flow channel area. In the limit where th

first term predominates, the equation is identical with that o

Kozeny

(28)

nd Carman IO),while at high Reynolds number

the equation reduces to th at of Burke a nd Plummer

(8).

Th

effect

of

free space, e, is in agreement w ith the authors own dat

taken a t various bed expansions using the same solid particles

19


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20

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.

45,

No.

t

100

8

6

4

3

2

0

8

6

4

3

2

B u r k e

8a P l u m

__

R e

- E

Figure

1 .

Fric t ion

Factors

for Single-phase

Flow through

Packed Beds

7 4 )

In a second article Ergun

( 1 4 )

attempted to correlate data on

mass transfer from irregular shapes of packing pieces into liquid

or gaseous streams flowing through the equipment. Following

Osborne Reynolds' suggestion that the coefficients a and

a ,

s

well as

b

and b , be taken proportional to each other in

R = au u2

(2 )

( 3 )

for

the fluid resistance, R, and the mass transfer rate,

w,

as

a

function of fluid velocity, u, nd driving force,

AC,

Ergun con-

cluded tha t a new mass transfer factor, J , should be defined by an

equation equivalent to

w

= a AC +

b

p

u

AC

J

B e ( p c / p D , ) ( k ~ P / G ~ i ) 4)

Assuming th at th e factor of proportionality between a and a "

is the same as that between

b

and

b ,

Ergun concluded too that

J f k ( 5 )

with

fk

being given by Equation 1. Although this equation was

moderately successful

for

the correlation of data on mass trans-

fer

in

solid-liquid systems, the friction factor was 5 to

100

times

greater than

J

for solid-gas sys te m. This reviewer believes

th at this large discrepancy may be due more to the inadequacy of

the theory than to experimental errors in the various sets of

literature data.

Even for a shape as simple as a cylinder mounted

transverse to the fluid stream the form drag (excess fluid pres-

sure on the front face, caused by detachment of the boundary

layer) forms

a

large pa rt of the total frictional drag but contrib-

utes nothing t o mass transfer,

It

seems quite improper to as-

sume that b is the same fraction of

b

as

a

is of a; to do so neg-

lects the fact t ha t the frictional effect of changes in fluid direc-

tion for flow through tortuous channels causes more pressure drop

tha n it does mass transfer.

A

somewhat similar comparison of fluid friction and mas

transfer in packed columns was reported by Ranz

(SO),

mh

showed that drag coefficients and mass transfer coefficients fo

single, isolated spheres could be used to estimate the pressur

drop and mass transfer coefficients for beds of spheres throug

which gases flow. In each case the superficial fluid velocity ha

to be multiplied by a factor of about

10

in order to arrive at t h

right individual drag coefficient or a single-sphere mass-transfe

coefficient. Th at the factor was nearly the same for friction an

for mass transfer indicates tha t the form-drag effect is not greatl

different around single spheres and in beds

of

spheres.

Pratt

WQ)

reviewed existing data on absorption, vaporiza

tion, and distillation for packed columns and concluded that th

gas phase mass-transfer coefficients could be expressed by a

equation suggested by friction a nd mass transfer effects in wetted

wall columns

The value of

i c ~

s based on the tota l exposed surface

of

the pack

ing; the equivalent diameter, Deq , is defined as four times th

free space divided by the periphery

of

the packing;

L

in cubi

feet per hour per foot is based on th e same periphery, and is ca

culated by dividing the superficial liquid mass velocity (mass pe

unit t ime per unit area) by the product of th e liquid density an

the periphery in feet per square foot of column cross section

For random packings the to tal packing perimeter per square foo

of

column cross section is assumed equal to the exposed packin

surface per unit of packed volume.

The factor,

tu,

is represented graphically

in

the paper and in

creases roughly linearly from zero

t o

unity

as

the liquid rate in

creases from zero to th e minimum effective liquid ra te for max

mum wetting of the packing

(M.E.L.R.).

The 1LI.E.L.R. is


3/5

January 1953 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

21

*

characteristic of the system, as indicated in Table I ;

a

and

vary with the packing, as shown in Table 11.

Differences in the M.E.L.R. in different liquid-gas systems

were suggested to be related to the heat of absorption of the

solute gas, possibly because the heat released a t th e interface and

th e resulting influence on interfacial properties may have affected

the tendency of t he liquid to sp read over the packing.

Table

1

Va l u e s o f M i n i mu m E f fec t i v e L i q u i d R a te f o r Ma x i mu m

W e t t i n g o f Pa c k in g

or

W e t te d - W a l l C o l u mn Ac c o r d i n g t o P ra tt 29)

Liquid System

M.E.L.R.,

Cu. Ft./(Hr.) (Ft.)

Wate r Vaoorization of water 0.7a

Wate r Abiorption of ethyl alcohol

1.0

Wate r Absorption of ammonia 1 . 7

Kerosene Absorption of organic vapors

< O

.26

Distillation 0.6-0.7

?c

a For regular packings with good distribution this may be as low as

0.4 cu. ft./(hr.)lft.)

Table

II.

Constants in Equatio n 6 Recomm ended by Prat t 29)

Packing

Type Size, inches Mode of installation

eoa

Drip-point grids No. 6897 Continuous flue 0.032 0.146

Drip- oint grids No. 6295 Continuous or crossed flue 0 .067 0.0 61

W?o$grids

7/g X

4

X 1/4

Continuous

or

crossed

flue

0.152

0

Triple spiral tiles

3

Continuous flue >0.034 0.068

Triple spiral t les

3

Staggered flue 0.046 0.120

Single s iral trles Stag ered flue 0.048 0.038

Berl saJdies 0. 5

to

1.5 Ranjom 0.072 0

Rasehig ring8 0,3 75 o 2 Random 0.123 0

Sherwood an d Holloway

(989,

from observed total resistance.

a Based on subt rac tio n of liquid film resistance, est imated from da ta of

The question of wetted and effective areas of packing was fur-

ther investigated by Shulman and DeGouff 34)who employed

a

new and clever experimental technique. They studied vaporiza-

tion of Raschig rings cas t from naphthalene into air with water

flowing through th e packing. Since the naphthalene was in-

soluble in water, vaporization into the a ir occurred only from the

portions of th e packing th at were dry. Measurements of rates of

absorption of carbon dioxide from water agreed closely with pre-

vious, generally accepted data, showing that the liquid distri-

bution was satisfactory. Rates of naphthalene vaporization with

the packing completely dry agreed very closely with the data of

Taecker and Hougen

36)

or vaporization of water, af ter a cor-

rection had been applied by assuming

k~

proportional to

DyZ/*.

By

measuring the reduction in naphthalene vaporization rate

when the packing

was

irrigated the fraction of total packing sur-

face area that was wetted could be calculated, leading to the re-

sults shown in Figure 2.

by the gas flow rat e and by th e liquid %ow rate. The dips in the

curves are more pronounced a t th e lowest liquid rate, suggesting

that the minimum is caused by the

fac t

th at the liquid layer

on

the packing is thin enough for the gas to blow it

o f f

easily. The

gas-liquid interfacial area t ha t is effective in countercurrent trans-

fer processes is generally greater tha n the wetted packing area, as

Shulman and DeGouff 34) ound when they compared their cor-

rected naphthalene vaporization rate coefficients with Fellingers

(16)

oefficients for ammonia absorption (corrected for liquid-

film resistance). Presumably the drops and spray surface formed

inside the packing are responsible for the excess of gas-liquid in-

terfacial area over liquid-solid interface, the ratio

of

the two being

as large as 1.4 n some circumstances.

Procedures for the design of commercial gas absorbers in which

gas-film resistance predominates were reviewed by Williamson

39). New data were reported on the effect of different kinds of

liquid distributors on packing performance and on liquid entrain-

ment. Table I11 shows the variation of performance of a tower

filled with 3-inch rings stacked 8 feet deep at L

=

2200 pounds

per hour per square foot and a t a gas velocity

of 4

feet per second.

As may be seen in the figure, the wetted area is influenced both

Tab le

Ill.

E f fe c t o f M e t h o d of L i q u i d D i s t r i b u t i o n

on

Relat ive

Packing Performance 39)

Relative

Packing

Type

of

Distributor Performance

Trough distributor,

1

inch wide troughs evenly spaced a t 4.5

inches 100

Vertical pipe discharging downward o nto packing, qne distribu-

tion point per 2.25 square fee t of tower cross section 16

Vertical pi e disoharging downward

9

inches above flat target

p la te l a 8

on

packing, one distribution point per 2.25 square

feet

of

tower cross section 76

Vertical pipe discharging dortnward above 18 inches deep layer

Outlet 9 inches above packing, one distribution point per

Outlet a t top level of packing, one distribution p oint per 2.25

Outlet 6 inches above packing, one. distribution point per

of random packing

2.25 square fee t of tower cross section

square fe et of tower cross seotion

0.56 square foot of tower cross section

63

5 9

120

~~

The tower was used to cool water by evaporation into air, and

85

to

90 of

the total mass transfer resistance was estimated

t o

be

in the gas phase.

Liquid entrainment was found to be less than 0.1 pound per

1000 pounds of air with 2-inch serrated wood-grid packing and

was considerably greater with 3-inch random ring packing. With

the latter, a trough-type distributor gave much less entrainment

than a splash-type distributor made from a pipe discharging onto

the top of the packing.

Mass and heat transfer in a 6-inch square tower filled with 1 X

l/*-inch carbon grids was studied extensively by Norman M)

who reported over-all coefficients for ammonia absorpt ion in

water and for evaporative cooling of water. The results were

ex-

pressed by the formula

(7)

O G=

p(G/lOOO)O.*

feet

0, or HOG t

G

= 1000 f t .

L,

lb./(hr.)(sq.

f t . )

Water cooling

NH3

absorption

930

1400

1640

1870

2100-2810

2900

1.88

. . .

1.57

1.53

. . .

The carbon grid packing was found to be more efficient than

the common 1-inch ring packing as indicated b y t he following com-

parison based on operation a t L / G

=

1.

Pressure Drop,

Inch

HzO

Capacity

G

= L ,

Per Figure

of

lb./ hr.) HOG, Transfer Merit,

Packing (sq.

f t . )

f t . Unit G I H o Q

Carbon grid

2500 1.75

0.19 1430

1-Inch rings

500 1 . 6 0 .48 310

The grid packing can be used at a higher gas velocity without

flooding and without a large friction

loss.

The high allowable

velocity and small height of a transfer unit results in

a

compara-

tively small packed volume for scrubbing a given quantity of gas.

Norman (86) lso studied the spreading flow of water an d

kerosene over a grid element, introducing the liquid a t a single

point on the top edge of the element. Glass, stoneware, and

bright metal surfaces could be wetted uniformly when they were

perfectly clean, but the slightest contamination caused the film

to break down. Wood and rusted iron surfaces were easily

wetted b ut slight surface irregularities interfered with t he liquid

flow an d made it difficult to obtain reproducible results. Finally

it was found th at certain types of carbon provided an ideal

sur-

face which could be wetted uniformly without the need for clean-

ing, and gave reproducible results even after considerable han-

dling and exposure to the atmosphere. The water films spread

1-Inch rings 700 1 .6 0.96 435


4/5

22 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. 45, No.

L

IO

G GAS RATE LB./ HR.) SQ.FT,)

Figure 2.

Effect of

Gas

R at e on W et t ed A rea of Packed Gas

Absorber

3 4 )

more rapidly and completely when the liquid rate was high and

when the liquid stream was allowed to fall

0.25

or 0.50 inch ont o

the top edge of t he packing tha n when it did not fall freely a t all.

Water and kerosene behaved alike.

Table IV. Constants in Dal l -and-Prat t Equat ion for Flooding

V e l o c i t y

Values of Dimensionless Constants,

C2

and

p

M > iMorit io s1

< M o ri t i a a l

___-

Type of Packing cz

P

Mcritiosl Cz

P

Random Raschig rings

0.64 -0 .20

0 . 4 7 0 . 3 3 - 0 . 3 6

Stacked Raechig rings , , , 0 . 7 2 - 0 . 3 6

Random Berl saddles 0.69

- 0 2 0

0 . 2 5

0 .42

- 0 . 3 6

Random wire helices . . . , , 0 .24 -0 .44

Extensive and accurate data on mass and heat, transfer coef-

ficients for air-wat-r contact in a 21.5-inch square tower filled

wiCh 1.5-inch Berl saddles were reported b y Hensel and Treybal

(20). Some of their conclusions were similar to those reached

earlier by McAdams, Pohlenz, as d St. John

34):

the psychro-

metric ratio was generally higher than the humid heat, probably

because the effective area for hea t transfer was as much as twice

th at for mass transfer; and the dynamic equilibrium temperature

of t he recirculated water was sometimes as much as

6' F.

above

the adiabatic saturation temperature of the entering air. The

transfer coefficients increased very rapidly with increasing gas

velocity as the loading point was reached.

A

comprehensive review of existing data on flooding velocities

in packed columns was made by Dell and Pratt ( 1 2 ) along lines

suggested by Bert etti 7 )and by their own earlier paper on flood-

ing phenomena for two-phase liquid-liquid flow in packed ex-

tractors

( I S ) .

Based on the idea that the frictional effects re-

sponsible for flooding are friction of the gas and liquid against the

packing and not against each other, the following equation was

found to correlate several sets of publ ished da ta for packing

larger than 0.25 inch, except for 0.50-inch packings when use

with very viscous liquids.

1

+ M

= C2Y

(8

where A

=

~ G / ~ L ) ~ ~ ~ ~ ~ L / ~ C L , ) ~ . ~ ~

/G)0.64

1 =

vGza/gLea)(PG/PLj(a~Q/8Q

The authors point out that the values

of

CZ

Table

I V )

vary

from one packing to another in t he same direction as the variation

of fluid friction for these packings; flow through stacked ring

occurs with the lowest pressure drop, followed in turn by Ber

saddles and random rings.

The change in

p

a t a critical value of

M

is thought to be associated with

a

transition in t he type qf flow i

one phase.

Measurements of liquid and gas-phase resist

ances on small bubble trays have been described previously by

Gerster, Colburn, Bonnet, and Carmody

(29).

These measure

ments have now been extended by Gerster, Bonnet, and Hess 18

who have shown th at the resistance in each phase is affected by

the dens ity of the foam and by the liquid time of contact as i

flows

across th e tray . Tests of oxygen stripping efficiencies on

large tray section having

a

liquid f l o ~ ath about 5 feet lon

were found to agree with an extrapolation of similar data from

small-tray measurements.

When the long tray was operated a

high horizontal liquid velocities, causing a variation in liquid

depth and a nonuniform distribution of air flow through the dif

ferent caps, the liquid-film resistance was increased, apparently

because only

a

few

of

th e caps were bubbling.

Tray

Towers.

A I R OUT

I

WATER IN

-

-

,

,,

AS-TO-LIQUIDURFAC: ~

HEAT EXCHANGER

COOLING

TOWER

-

WATER OUT

Figure 3 . Use of Au xi l iar eat Exchanger to Produce Water

Colder than

Air k ?-Bulb

Temperature (7)

New data on foam densities and point cJfficiencies

for

air-wate

contact on perforated trays weie published by West, Gilbert , and

Shimizu

(58).

The gas-phase resistance was determined by th

wet-bulb humidification of air and the liquid-phase resistance by

absorption and desorption of carbon dioxide. Th e correlation o

the data w s attempted by a method similar to that proposed by

Geddes

(179,

based on the assumption of transient diffusion

through stagnan t liquid and gas near the interface

of

a completel

formed bubble. (The mass transfer during the period of bubble

formation was not included. The theory requirm value of the

time of contact between gas and liquid, which was taken a s the

time required for the bubble to rise a distance eqLal to its diam

eter, thus assuming that the liquid at the interface is contin-

uously replaced from the stagnant

pool

where th e bubble enter$

The effective bubble diameter that should be used with the

theory to account for the observed tr ay efficiencies was computed

using observed values of foam density

to

estimate contact time


5/5

January 1953 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 2

The resulting values range from about 0.33 to 0.55 inch for ab-

sorption, desorption, and humidification and a re roughly inde-

pendent of the gas and liquid rates and the initial liquid depth.

The average value of 0.50 inch agreed very closely with equivalent

bubble diameters calculated by West

t al. (88)

rom the data of

Gerster, Colburn, Bonnet, and Carmody (19) or bubble-cap

plates, These equivalent diameters were larger tha n the center-

to-center distance between adjacent holes in the perforated tray .

Using these bubble diameters without correction

for

physical

properties, bubble-tray efficiencies were predicted for methanol-

water rectification and for furfural extractive distillat ion of bu-

tane-butene with disappointing results. The predicted efficiencies

Cross and Ryder

( 1 1 )

found

that

the formation of gas bubbles

at submerged orifices is strongly affected by l iquid surface tension

when the gas rate is low. Thus, th e depression of the gas-liquid

interface below the tops

of

the slots of a bubble cap cannot be

calculated from the hydrodynamic weir formula alone, as was

suggested by Rogers and Thiele

(3 )

n 1934. Below a critical

gas flow rate, th e slot opening is nearly constant a nd independent

of the gas flow. For water this critical opening ranges from about

2

inches for very narrow slots (ca. 0.01 inch +$e)

to

about 0.20

inch for

slots

wider than abou t an inch.

were substantially different from those of Gerster

et

al. f8).

II

ABSORPTION PROCESSES

Commercial practices in the removal of carbon dioxide and

carbon monoxide from coke oven gas and natural gas by absorp-

tion were described by Yeandle and Klein

( 4 1 ) .

Carbon dioxide

is removed by scrubbing the gas with a n amine solution or with

water under pressure and carbon monoxide is taken out with

copper ammonium formate or acetate. A unique process for

removing carbon monoxide, methane, argon and acetylene

from hydrogen was also described.

It

involves scrubbing the

hydrogen-rich gas with liquid nitrogen from an ai r liquefaction

plant, followed by flashing a part of the liquid effluent to purge

th e system of th e dissolved gases.

Severe corrosion of carbon-steel tubes of a reboiler handling a

30 volume yoaqueous solution of monoet,hanolamine containing

small amounts of dissolved carbon dioxide and hydrogen sulfide was

reported (9). The boiling solution was heated by oil

at

500

F.

If this temperature was reduced to 370 F. or if hydrogen sulfide

was absen t th e corrosion was very much reduced. Th e discussion

of

this paper brought out t ha t corrosion is generally less severe in

absorption plants using both ethylene glycol and ethanolamine,

even though t he boiling point of these solutions is higher than tha t

of the

aqueous solution of ethanolamine alone.

COOLING TOWERS

A novel method of using a cooling tower in conjunction with

auxiliary surface-type heat exchangers t o produce cold water

at

a

temperature lower than t he wetrbulb temperatu re of th e evail-

able air was described b y Agnon and Young

1 ) .

I n

its

simplest

air by transferring heat t o cool the water, which is then recycled

to the tower,

as

shown by Figure

3.

In a

typical example, proc-

ess water was cooled from 78 to 67

F.

using air having a wet-

bulb temperature of

69

F. (which was reduced to

62

F. in the

air

cooler). The quanti ty of water circulated through the cooling

tower was 2.5 times the ra te of supply of fresh water. In

an

ex-

tension of the same idea, the cool, saturated air leaving the cool-

ing tower can be used to cool the fresh air, and in the same ex-

ample,

the

water flow through the tower would be reduced in thi s

method of operation to

1.43

times the water feed rate.

6

version their process employs a hea t exchanger for precooling th e

NOMENCLATURE

a

D ,

= specifie surface of d ry packing, square feet per cubic foot

= diameter of

a

sphere having the same ratio of surface to

of packed volume

volume

as

a piece of packing, feet

go =

standard gravitational conversion factor, (lb. mass)(ft.)

=

local gravitational acceleration,

f t . b . 2

? =

superficial mass velocity of gas, lb./(hr.)(sq . it .)

HOG heigh t of an over-all gas-film transfer unit, feet

L =

superficial

mass

velocity of liquid, lb./(hr.)(sq. ft.)

N R ~

D,G/p

=

Reynolds number for flow through packed be

VQ

= superficial velocity

of gas, feet

per hour

U =

superficial velocity, fe et per hour

Z =

depth of bed, feet

e

= fraction free space in d ry packing

jw

=

viscosity

of

gas, lb./(ft.)(hr.)

p~ =

viscosity of liquid, lb./(ft.)(hr.)

p

=

fluid density lb./cu.

f t .

PQ

=

gas density ib. cu. f t .

p~

=

liquid density, i ./cu.

f t .

(Ib. force)(hr.Z)

REFERENCES

1)

Agnon,

S.,

and Young, ChiaYung,

Heating, Piping A ~ To n d

(2) Amick, E. H.,

Jr.,

Johnson, W.

B.,

and Dodge, B.

F.,

Chem

(3) Arnold, J. H., Ibid.,

No.

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2 ,

161-

(5)

Benedict, M., Webb, G. B.,

and

Rubin,

L

C.,

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334 (1940); 10, 747 (1942); Chem. E w . Progr., 47, 419

(6) Benedict, M., Webb, G. B., Rubin, L. C., and Friend, Leo

Chem. Eng Progr., 47, 571-8, 609-20

(December

1951).

(7)

Bertetti,

J.

W.,

Trans. Am. I nst. Chem. Engrs.,

38, 1023 (1942

8)

Burke,

S.

P., and Plummer, W. B.,

IND.

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0, 119

(9)

Carlson, E.

C.,

Davis, G. R., and Hujsak, K.

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(10) Carman, P.

C.,

Trans.Jnst. Chem. Engrs., 15, 150 (1937).

(11)

Cross,

C. A., and Ryder,

H.,

J . AppZ. Chem., 2, 51-60 (Febru

(12) Dell,

F.

R., and Pratt, H. R. C., Ibid., 2,429-35 (August 1952

(13)

Dell,

F.

R.

and Pratt,

H.

R. C.,

Trans. Inst. Chem. Engrs.,

29

(14)

Ergun,

S., Chem. Eng. Progr., 48, 227-36 (1952).

(15) Ergun, S., and Orning,

A.

A.,

IND.

NG.CHEM., 1,1179 (1949

(16) Fellinger, L. L., Sc.D. thesis, Mass. Inst. Technol., 1941.

(17)

Geddes,

R.

L.,

Trans. Am. Inst. Chem. Engrs., 42, 79 (1946).

(18)

Gerster,

J .

A., Bonnet, W. E., and Hess,

I.

Chem.

Eng. Progr

(19)

Gerster,

J.

A., Colburn, A. P., Bonnet, W. E., and Carmody

(20)

Hensel, S., and Treybal, R. E.,

IbicE.,

48,

362-9 (1952).

(21) Hughes,

H.

E., and Maloney,

J.

O.,

Ibid.,

48, 192-200 (1952)

(22)

Kirkbride,

C.

G., and Bertetti, J. W.,

IND.

NG. CHEM.,

5

ary

1952).

89 (1951).

47, 223-7, 621-7 (December 1952).

T.

W.,

Ibid., 45, 716-24 (1949).

1242 (1943).

(23) Kozeny, J.. Sitzber. Akad. Wiss Wien. Math.-naturw. Klass

Abt. IIa , 136, 271 (1927).

Eng. Prop., 45, 241 (1949).

(24) McAdams, W. H., Pohlenz,

J.

B., and St. John,

R.

C., Chem

(25)

Norman, W.

S., Trans.

Inst.

Chem. Engrs.,

26,

81 (1948).

(26) Ibid.,

29,

226-39 (1951).

(27) Organick,

E.

I., and Brown,

G.

G., Chem. Eng. Progr., Sym

(28)

Plewes,

A.

C., and Klsssen,

J., Can. J . Technol., 29, 322-3

(29) Pratt,

H.

R. C., Trans. Inst. Chem. Engrs.,

29,

195-214 (1951

(30) Ranz, W. E., Chem. Eng. Proor., 48, 247-53 (1952).

(31) Ranz, W. E., and Marshall, W. R., Jr., Ibid., 48, 141-6, 173-8

(32)

Rogers,

M.

C., and Thiele, E. W.,

IND.

NG. CHEM.,

26, 82

posium

Ser., No. 2 ,

48, 97 (1952).

(July 1951).

1952).

(1934).

(33) Shkrwodd,

T.

K., and Holloway,

F.

A. L., Trans. Am.

Ins

(34)

Shulman, H. L., and DeGouff.

J. J..

Jr..

IND.

NG.CHEM..

4

Chem. Engrs., 36, 39 (1940).

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1915-22 (1952).

93-8 (1952).

1949).

(1940).

(35) Solomon, E., Chem. E w . Prog., Symposium Ser., No. 3, 48

(36) Taecker, R. G., and Hougen, 0. A.,

Chem.

Eng. Progr., 45, 18

(37) Webber, C.

E.,

Am. Inst. Mining Met. Engrs., Tech. Pub.

125

(38)

West,

F. B.,

Gilbert,

W.

D., and Shimizu,

T.,

IND. NG.CHEM

(39) Williamson, G. f . , Trans.

Ins t .

Chem. Engrs.,

29,

215-25 (1951

(40)

Winn, F. W.,

Chem. Eng. Progr., Symposium Ser., 48, 121-3

44, 2470-8 (1952).

(1952).

---- -

(41) Yeandle, Wd W., and Klein,

(3. F.

Chem. Eng. Progr., 48, 344

52 (1952).

Documents

Industrial & Engineering Chemistry Volume 45 Issue 1 1953 Pigford, R. L. -- Absorption and Humidification