10
 roduction o FIG I-Showing typical high-pressure absorber installation. N TURAL gasoline is in the peculiar posilion of being at the same time a raw material and a fin- ished product. It is seldom heard of in retail trans- actions involving petroleum products, because it is usu- ally first blended with other fractions to produce motor and aviation fuels, in which it finds its principal outlet. In this case it may be considered a raw material. How- ever, it is nsually produced to such stringent specifica- tions that little if any further processing is necessary after it leaves the natural gasoline plant. In this sense it may be considered a finished product. The importance of natural gasoline is evident from the fact that in California the production of this mate- rial in recent years has amounted to about one-fifth the net production of refinery gasoline. The ratio in the United States has been smaller, but still it averaged one gallon of natural to about ten gallons of net refinery gasoline prior to the war and has now reached one gallon in six as a result of the increased demand for the volatile natural gasoline fractions in aviation fuel. N TUR L G SOLINE y ROBERT B BOWM N fuel purposes. Either it has had the gasoline extracted from it, or it was originally produced without an appre- ciahle amount of gasoline i n it. Dry gas is often ob- tained from gas wells which produce no oil, such as those in the Rio Vista. But~onwillow and other fields in California. The nredominant constituent of drv eras from wells is methane. Also present in dry gases discharged from natural gasoline plants are ethane, propane and some butane. Propane, isobutane and normal butane are in. termediate between dry gas and natural gasoline and are becoming increasingly important a i raw materials for various products. Originally they were disposed of prin- cipally as liquefied petroleum gases, but isobutane has become so much more valuable as a raw material in aviation gasoline that it has been virtually eliminated from this service. Bv direct combination with butvlenes produced in refinery operations, isobutane yields prod- uct high in isooctane content that is one o the principal base stocks for aviation fuels. Much normal butane is converted to isobnhme to increase this source material. Also normal butane is dehydrogenated to butadiene, an important ingredient in synthetic rubber manufacture. Natural gasoline is composed principally of isopentane and heavier hydrocarbons, with varying amounts of nor- mal butane depending upon specifications. A small amount of isohutane is usually present because of the difficulty of entirely eliminating this constituent. At the present time natural gasoline plants are generally oper- ated to recover substantially all of the isohutane and heavier fractions from the inlet gas. Table is a compilation of compositions of typical wet gases, dry gases, liquefied petroleum gases and natu- ral gasolines. This table serves to indicate the distrihu- tion of the various hydrocarbons in these materials. All hydrocarbons heavier than butane are grouped as pen- tanes +). This is because an attempt is made always extract all of these constituents and include them in tural gasoline. Information on the actual amounts of h one present is in general of little importance. It will he noted that in the case of wet cases. comuo.

Propiedades de La Gasolina Natural

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  roductiono

FIG I-Showing typical high-pressure abso rber

installation.

N

TURAL gasoline is in the peculiar posilion of

being at the same t ime a raw material and a fin-

ished product. I t is seldom heard of in retai l t rans-

actions involving petroleum products, because it is

usu-

ally first blended with other fractions to produce motor

and aviation fuels, in which it finds its principal outlet.

In this case it may be considered a raw material. How-

ever, i t is nsual ly produced to such stringent specifica-

tions that little if any further processing is necessary

after i t leaves the natu ral gasol ine plant . In this sense

it may be considered a finished product.

The importance of natural gasol ine is evident from

the fact that in California the production of this mate-

rial i n recent years has amounted to about one-fifth the

net produ ction of refinery gasoline. The ratio in the

United States has been smaller, but still it averaged one

gallon of natur al to about ten gallons of net refinery

gasoline prior to the war an d has now reached one gal lon

in six as a result of the increased demand for the volatile

natural gasol ine fract ions in aviation fuel.

N TUR L

G SOLINE

y ROBERT B BOWM N

fuel purposes. Either it has had the gasoline extracted

from it, or it was originally produced without an appre-

ciahle amount of gasoline

i n

it . Dry gas is often ob-

tained from gas wells which produce no oil, such as

those in the R io Vista. But~ onw illow an d other fields

in California.

The nredominant constituent of drv eras from wells

is methane. Also present

in

dry gases discharged from

natural gasol ine plants ar e ethane, propane and some

butane. Propane, isobutane and norm al butane are in.

termediate between dry gas and natural gasol ine and are

becoming increasingly imp ortant a i raw materials f or

various products . Original ly they were disposed of prin-

cipally as liquefied petroleum gases, but isobutane has

become so much more valuable as a raw material in

aviation gasoline that it has been virtually eliminated

from this service. Bv direct combination with butvlenes

produce d in refinery operations, isobutane yields prod -

uct high in isooctane content that is one

o

the principal

base stocks for aviation fuels. Much normal butane is

converted to isobnhme to increase this source material.

Also normal butane is dehydrogenated to butadiene, an

important ingredient in synthet ic rubber manufacture.

Natural gasol ine is composed principal ly of

isopentane

and heavier hydrocarbons, with varying amounts of nor-

mal butane depending upon specificat ions. A small

amount of isohutane is usually present because of the

difficulty of entirely eliminating this constituent. At the

present t ime natural gasol ine plants are general ly oper-

ated to recover substantially all of the isohutane and

heavier fractions from the inlet gas.

Table is a compilation of compositions of typical

wet gases, dry gases, liquefied petroleum gases and natu-

ral gasolines. Th is table serves to indicate the distrihu-

tion of the various hydrocarbons in these materials. All

hydrocarbons heavier than butane a re grouped as pen-

tanes +). This is because an attempt is made always

extract all of these constituents and include them in

tural gasoline. Informa tion on the actual amounts of

h one present is in general of little importance.

It will he noted tha t in th e case of wet cases. comuo.

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TABLE I-TYPICAL COMPOSITIONS OF NATURAL GASES LIQUEFIED GASES AND NATURAL GASOLINES

W E T G A S E S F R O M K E T TL E M A N H I L L S

Type of Ga s Hi gh Pressure Gas

Component

Methane

Ethane

Propane

Isobut ane

N-Butane

Pentanes

4-

Vapor

75 57

10 87

7 38

1 09

2 74

2 35

--

100 00

DRY

G A S E S

Low Pressure Ga s Tank Vapors

Vapor Gal./m.c.f. Vapor Gal./m.c.f.

69 57 19 83

11 46 14 95

8 88 2 45 26 98 7 37

1 58 0 51 6 26 2 03

4 02 1 26 17 04 5 36

4 49 1 72 14 94 5 79

100 00 100 00

Source

Discharge Gas from

Kett leman Hi l ls Natural

Gasoline Plants

W e l l G a s f r o m

Buttonwillow Gas Field

W e l l G a s f r o m

McDonald Is land F ield

Component

Carbon dioxide

Nitrogen

Methane

Ethane

Propane

Isobut ane

N-Butane

Pentanes +

Vapor

0 05

-.-.-...

87 75

8 33

3 65

0 15

0 05

0 02

100 00

Vapor

0 5

....---.

99 3

0 2

L IQ UEF IED G ASES

Commercial Butane

Commercial

N a m e

Propane

( W i n t e r G r a d e ) ( S um m er G r a d e )

Component

Ethane

2 5 1iq.

2 5 liq.

2 0

iq,

Propane

97 0

45 0 30 0

Isobutane

0 5

1 0 1 0

N-Butane

51 5 67 0

100 00 100 00 100 00

N A T U R A L G A S O L I N E S

Source Kettle man Hills

I

Southern California

Reid Vapor Press. 16 Ibs. 24 Ibs

16

Ibs 24 Ibs.

Component

Isobutane

0 8 iq. 2 0 iq.

1 0 1iq. 2 5 iq

N-Butane 11 7

33 5 14 0

30 7

Pentanes

-

87 5

64 5 85 0

66 8

100 0 100 0 100 0 100 0

lected at lo places in the lines, particularly if cooling

due to luiv atmospheric temperatures had occurred. At

that time, which ^as prior to

t h e

development of the

automobile. light liquid hjdrocdrbona such as what is

now called natural gasoline had no commercial value.

In

fact, exen in refineries gasoline fraction;; er e dis-

carded from crude oil because kerosene was the lightest

product

or

bhich there bas a ready market. The vola-

tile liquid sparating from natural gas was therefore

first

recognized as a nuisance because it not only 'was

valueless, but caiided restrictions in t he flov~ of gas

tliruugli the lines and created a tire hazard -when it

v d s

drained off'.

About the beginning of the present century, gasoline

began to assume value because of the birth

of

the auto-

mobile industry. More of this material was saved in the

refineries and some attention was given to the liquid

which separated from

vet

gases. Ah early as 1904., g a o -

1i11ebecame of sufficient importance to justify consider-

ing means for extracting from natural gas more of the

volatile liquid fractions than were separatingfrom

na tu

ral causes in p s lines.

JUNE

1945

Page

5

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G S TO

?At-F-S LINE

R E T U R N

V A P O R ?

ACCUMULATOR

TC CCIMPPESOR

D IA G RA M I - A

COMPRESSION

T Y P E

N A T U R A L

GASOLINE

PLANT

DRY GAS

7

SALES L 1NF

DIAGf~ AMI -E5

ABSORPTION

TYPE

NATURAL

GASOLINE PLANT

DIAGRAM 1-A Above)-Flow chart of a typical compression ty pe natural gasoline plant.

DIAGRAM

I-B Below)-

Flow chart of absorption-type natural gasoline plant.

4

COMPRESSION

METHOD

O F

EXTRACTION

I t i s a fundamenta l pr inc iple tha t condensat ion i s

in-

duced either fly a

decrease in tem pera ture o r hv an

increase in pressure below the range where the retro-

gr ad e phenomena occur . Therefore . the f irs t method

t r ied in a t tempt ing to obta in more gasol ine f rac t ions was

to compress the gas and cool i t . then separa te the con-

densed l iquid in an acrumnla tor .

iugram

- A i s a s im-

plified

f low sheet for a na tura l gasol in e plant of the

so-ca l led compression type . The l iquid f ro m the acr-u-

mula to r was d rawn off in to tanks and the uncondensed

portion of the gas was delivered to fuel l ines. Wh en

high pressures were used. a large quantity of ethane and

propane was re ta ined

in

the l iquid and an exceedingly

volati le or wild gasolin e was obtaine d. I t was par-

i ial lc stabil ized h wi thdrawing vapors f rom the t anks

and re turning them lo the intake to the compressor . I n

passing again through the process of compression an d

cool ing. some

of

the l ightest components of the vapors

fa i led to condense an d were re jec ted into the fue l l ines.

The pr inc ipa l weakness

o

the compression process

was its inefficiency. Excessive1 high pressures or very

low temperatures were required lo recover suhstari i ial l

a l l of the pentanes and heavier f ra c t ions which could

ho

included in finished ga-soline. Also. the quali ty of the

product was poor because i t conta ined a la rge amount of

the hydrocarbons such as methane . e than e

and

propane .

which are not proper1

y

designated as na tura l gasol ine

In sp ite of these weaknesses. however. an d

in

the absenc

of

a

wel l -developed bet te r process, the numb er of ?om

pression- type na tura l gasol ine plants ra pid ly grew, unt i

in 1912 there were 250.

i n

1916 there were 550. and in

1 9 2 1 t h e r e w e r e

865

Nevertheless, since 1921 the nurri

her has dec l ined and the compression process has given

way a lmost comple te ly to the oi l absorpt ion process.

B.

OIL

ABSORPTION PROCESS

Th e oil abso rpt ion process consist s basica l ly of br ing

i~i

wet gas

i n

contact with an oil . whereupon the oi

absorb s the gasol in e f rom the gas. Th e apt ion of the oi

may

be

pic tured as tha t of

a

sponge drawing into i t se l

the gasol ine f rac t ions. After contac t ing the gas. the oi

is heated and contacted with steam to drive off the all

sorbed frac t ions.

w hich are then condensed as na tura

gasoline.

Diagram -R is a simplified flow sheet

of

a na tu ra

gasol ine plant of the oi l absorpt ion type . Th e individua

i tems of equipment ar e cl isrussed more ful ly la ter . Th

princ ipa l fea ture? of the process are as fol lows:

Wet gas f rom the f ie ld i s f i rs t compressed and then

cooled before it i s in t roduced into the absorber . I t then

passes upwards counter-current ly to a descending st ream

of oi l. an d out a t the top in to fuel l ines.

age

ENGINEERING

AND

SCIENCE

MONTHL

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The oil possesses the important property of preferen-

tially absorbing the heaviest hydrocarbons from the gas.

This so-called selective feature is an advantage of the

oil absorption method over the compression method of

extracting natural gasoline. The separation between

heavy and light fractions in an absorber is, however,

by no means a sharp one. When enough oil is circulated

to absorb all the hydrocarbons which are desired in fin.

ished gasoline, some of the lighter ones are also ex-

tracted, but the separation is much sharper than when

compression and cooling alone are employed.

The contacted sponge, or rich oil as it is called,

leaves the absorber at the bottom and is heated before it

passes into a stripper. Here steam is introduced to act

as a carrier to remove the gasoline fractions from the

o i l The lean or stripped sponge leaves the bottom of

the stripper and is cooled before being circulated again

into the absorber.

The steam and gasoline fractions are carried overhead

from the stripper and are then cooled. The steam con-

denses and is drawn off a s water from the bottom of the

separator. The heaviest gasoline fractions also condense

and form a liquid layer on top of the water in the sep-

arator, whence they are drawn off t o the storage tank.

The uncondensed vapors are then subjected to a step

similar to the compression type of natural gasoline plant.

They are first compressed and cooled, then the condensed

portion is conducted to the storage tank, atld the portion

still in the vapor form is recycled to the absorber to

recover any residual gasoline fractions.

A

comparison of Diagrams

1 A

Q n d 1 B will indicate

that compression still plays an important role in the oil

absorption process. However, the use of oil makes pos-

sible the recovery of substantially all the gasoline from

wet gas at ordinary temperatures and reasonable operat-

ing pressures. The efficiency and economy of the oil ab-

sorption process have made it the predominant method

of operation now employed in the natural gasoline in*

dustry.

C OTHER METHODS OF EXTRACTION

In addition to the compression and oil absorption

processes, two other methods of extracting natural gaso-

line have received consideration; namely, 1) charcoal

absorption and 2) refrigeration. Neither method has

been extensively employed in the past, but future devel-

opments could bring either

or

both of them into prom-

inence.

TYPICAL PRESENT DAY

PL NT

Diugrmn I1 is a flow sheet of a modern gasoline plant

such as is operated at Kettleman Hills. Basically, this

flow sheet is similar to

Diagram

1 B.

Among the prin.

cipal elements are the absorber, the stripper, the sepa-

rator, and the vapor compressor, all of which appear in

Diagram.

1 B. The only additional major feature is the

rectifier or stabilizer in which specifications of the final

product are controlled. However, the stabilizer is a

single unit only when all the recovered hydrocarbons

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AT LEFT:

FI G. 2-Typical high-pressur

natural gasoline plant locate

at Kettleman Hills Calif.

ar e delivered fro m the plant as a mixture to be fur the r rately. Th e miscellaneous accumula tors, coolers, ven

separated t

a refinery. In many cases batteries of rec- tanks, etc., ar e all essential, hu t they play relatively

tifiers are located in the field, and propane, isobutane, minor roles in the process and are shcnvn onl y fo r th

normal butane, and natural gasoline are produced sepa-

purpose of completeness.

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A

TIIK ABSORBER

High pressures and

l o b tern

peratures are favorable to ab-

sorptioii because the} make

possible the complete extrac-

tion of the desirable gasoline

fraction at relative]} low rates

of

oil circulation. The operat-

ing pressure employ ed deptwds

upon the pressure at which gas

is available from tlie ^ells aud

tile pressure at which it must

he

delivered

to

fuel lines after

gasoline has been extracted

from it.

A

pressure of

35

poun& per square inch ahead

is approximately the minimum

at which an absorption plant

can be eronomicalh installed

a n d

operated. If wet gas is

produced at

a

lower pressure

i n

the field, general practice is

to compress it to at least 35

hounds

per

square inch allcad

of the absorpt ion step. If gas

is available in the field i i t a

pressure above 35 pounds per

square inch, or if deliverj to

fuel lines at higher pressures) is

required, the absorption step

is

conducted at the greater of

these two pressures.

At

Kettle-

man Hills, conditions are such

that absorber operating pres-

sure is maintained at about

425

pounds per square

inch.

Some

gas is available in the field at

this pressure, but most of the

field gas. all crude oil tank \a-

imrs and vapors originating

within the plant require com-

pression ahead

of

the ahsorp-

tion step.

An

absorber is a vertical cvl

TABLE 11-PRODUCTION OF NATURAL A N D REFINERY GASOLINE

(All Fi gures

in

Gal lons per Day]

YEAR

NATURAL GASOLINE

UNITED

STATES

TOTAL

CALIFORNIA

REFINERY GASOLINE*

UNITED

STATES

Includes atraight run gasoline cracked gasoline ;ind nature1 yasoline blended

Information incomplete.

indrical column such as those illustrated in

Figure 1

This picture s h o ~ s group of eight units arranged in

two rows of four each.

In

the early dajs of the absorp-

tion process, the columns were filled with wooden grids.

wire coils or sometimes even haling ^ti re to promote in -

timate contact between oil and gas. At the present time,

Lul~bleplates or trajs are used almost exclusively for

this purpose.

The use of bubble plates makes possible the absorption

of

gasoline fractions at low oil rates.

t the same time

tlie selectivity of the process is improved; that is, less

of tlie undesirable frac tions is absorbed by the oil wliile

the desirable fractions ar e Leing recovered. Alisorhers

generally contain from 16 to 24 bubble plates.

B. THE STRIPPER

Stripping is the reverse of absorption. High pressure

a n d

lev\

temperature are favorable to absorption, but low

pressure and high temperature ar e favorable to stripping.

Also. steam is admitted into the Lottom of the stripper

to act as a carrier in removing absorbed fractions from

the oil. Thus

n

an absorber, gasoline fractions are re-

moved from a b e t ¡a; in contacting tlie gas vi i tl i a "lean"

sponge iinckr conditions of high pressure and lo^ ifin -

JUN

945

TOTAL

CALIFORNIA

peraturc, mhile in a stripper, gasoline fractions are rp-

mm ed from a "rich" sponge

1 ~

oiitacting it ivith

a dq

gas (steam) under conditions

of

o w

pressure and high

temperature.

The rich sponge leaking the absorber, after first bein"

w e d y reducing its 13rehssure o remove a portioi1 of

the undesirable fractions which are unav oi dab1y picked

up

in the absorber, is heated before it

is

introduced into

tlie stripp er. The first step in the heating is by transfer

from

hot

lean oil returning to the absorber from the-

bottom of the stripper. The rich oil is again rented, then

heated by indi rect contact ivith steam in a preheater.

Rich oil is introduced about midday between top

a n d

bottom of the stripper. Steam and stripped vapors pass

upwards through the column,

a n d

the oil passes

down

wards over bubble trays. The steam and vapors pass

overhead from the column, then through cooling coils

into a separator. Here, as was shown previously. the

steam is removed as water, and a portion of the gasuliin

fractions is condensed. Some of these gasoline fraction<-

are returned as reflux to the top of the stripper to %as11

hack

ail

of the light fractions) of the oil itself \\Iiic11

might tend to be carried overhead by the steam. The

remaining gasoline fractions from the separator are c o n

d ~ i e i e d o the rectifier, ~ h i c hs described later.

a g e

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In Dhgrf im

11

some of the st r ipper ref lux is shown

to

he suppl ied by condensed mater ia l or iginat ing: e lse-

where in the plant . Any l iquid is sui table which is s im-

i lar in composi t ion to the separ a tor gasol ine . Use of rna-

ter ia l a l read y condensecl e lsewhe re in the plant reduces

the load on the s t r i pp e r vapor condens ing sys tem.

Th e most f avorab le s t r i ppe r ope ra t ing p re ssure is o f

the order of

5

p u n d s p er s q u a r e i nc h ga u ge . A t t h is

pressure i t i s usual ly impossible to condense a11 the

abso rbed frac t ions that have been removed fr om the oi l .

Th e uncondensed port ion is therefo re subjected to com-

pression and cool ing in the plant vapor system.

C. PLANT VAPOR SYSTEM

The uncondensed vapors f rom the sepa ra to r a re f i r s t

compressed to a pressure of about

8

p u n d s p e r s q u a r e

inch gaug e ancl are then cooled to remove ad di t ional

gasol ine frac t ions. which ore in turn del ivered to the rec-

t i fier . Even a t this pressure som e of the gasol ine frac-

t i ons fa i l t o condense . The remain ins ; vapors a r e t he re -

fore subjected to addi t ional compression and co ol ing and

ar e f inal ly conducted into the absorber . In some cases

a separa te absorpt ion step opera ted a t low pressure i s

employed for processing; uncondensed separa tor vapors.

This procedure i s ca l led reabsorpt ion.

D

THE RECTIFIER

I t has been m ent ioned that th e absor pt ion process.

whi le represent ing an improvement over the compression

process for ext rac t ing natura l gasol ine . i s s t i l l unable

to pick u p al l of the desi rab le hyd rocarb ons wi thout a t

the same t ime recovering a port ion of those not desi rable

in finished gasoline. It is the fun ctio n of a rectifier to

mak e the requ i red sepa ra t ion . The nature of the rec t i f ier

insta l la t ion depends upon a number of fac tors, such as

the type of fac i l i t ies avai lab le fo r transp ort ing f inished

products. the demand for l iquefied pet roleum gases in

the vic ini ty of the plant . e tc . W he re a pipel ine out le t

to a ref inery is avai lable . of ten th e composi te f inal pro d-

uct i s shipped as a whole and separa t ion into individual

products such as propane. i sobutane. normal butane . and

natura l gasol ine i s made in the ref inery that receives the

mix ture .

I n

t i l ls case the rectifier installation at the

natura l gasol ine plant comprises only one frac t ionat ing

uni t wi th the simple funrt ion of removing methane.

e thane. and excess p ropane f rom the mix ture . When . fo r

example . l iquefied gases are produced local ly or f lexibi l -

i ty i n the disposal of f inished prod ucts i s desi red. a ser ies

of f rac t iona t ing ro lumns i s employed to m ake the sepa -

ra t ion.

Th e opera t ion of the individual f ra c t ionat in g o r rec-

t i fying uni ts i s s imi lar and wi l l be i l lust ra ted hy a de-

srr ipt inn of a single-uni t system. [n this rase the con-

densed hydroca rbons f rom the sepa ra to r and va r ious

accumulators are col lec ted in a so-cal led mixing or surge

tank. f rom whir- li they a re pum ped throu gh

a

heat ex-

rha nge r into the rect if ier . Th e mixtu re is des igna ted a<

raw prod uct. Th e rectifier consists essen tially of three

uni ts , comprising a column. a ref lux system. and a ket t le

o r rehoi ler . Th e raw product i s int roduced into the

rolurnn about midw ay between top and bot tom. When

i t enters the column. i t separa tes into two part s: a vap or

port ion which r ises towards the top. and a l iquid port ion

wbi rh t r ave l s downwards .

s in the case of abs orber s

and s t r i ppers . t he re a re a nu mber o f bub ble - rap t r ays

or pla tes in the column. usual ly between

24

a n d 30

These t rays a r e so des igned tha t t he l i qu id a nd v apor

may t ravel countercurrent ly to each other and wi l l he

brought into int imate contact on each t ray. T he ket tle

o r rehol ler i s the source of ascend ing vapor f rom the

bot tom of the column and the ref lux system is the source

of descending l iquid from the top of the column. Th e

contact between vapor and l iquid on each t ray resul ts in

an interchange of the var ious ronst i tuents. the l ighte

hydroca rbons t end ing to f ind the i r way upw ards in t he

vapor s t r eam and

the

heavier ones tending to f ind thei

way downw ards in the l iquid st ream. Th e final resul

is tha t the product removed from the ket t le conta in

essent ia l ly only those frac t ions which are desi red to he

re ta ined. At the same t ime. the undesi rable frac t ion

a re re j ec t ed ove rhead wi thou t

ca r ry ing any des i rab l

f rac t ions wi th t hem.

In the case of a mul t iple-u ni t insta l la t ion a common

pract ice i s to make the f i rst uni t a depropanizer in which

prop ane a nd l i gh t e r f r ac t ions a r e removed ove rhead anc

isobutane and heavier f rac t ions are re ta ined in the hot

tom product . Th e second uni t i s a debutanizer , th e fee

to which is the bot tom product f r om th e f irst uni t . I n

t he second un i t a l l i sobu tane and a s m uch of t he norm a

butan e as i s not desi red in the f inished gasol ine are re

moved ove rhead and the bo t tom p roduc t i s na tu ra l gaso

line. 4

thi rd u ni t processes the overhead mater ia l f rom

the f i r s t un i t and p roduces commerc i a l p ropane a s

bo t tom produc t . four th un i t p rocesses t he bu tanes n ix

ture from the second uni t . separa t ing i t into i sobutanc

and norm a l bu tane . Th e p r inc ipa l d i ffe rences i n t h

un it s a re ope ra t ing p re ssure s and t empera tu re s and th

number o f bubble t r ays i n each one .

The

number o

bubble t r ays i s a func t ion o f t he ea se o f sepa ra t ion (d i f

fere nce in boi1in ;oints) ancl the efficiency of se pa rat ion

desi red. Th e column makin g the separa t ion between iso

bu tane and norma l bu tane gene ra lly con ta ins abou t twic

as many t rays a s t he o the rs .

T h e f lo w sheet represented by Diagram

If

is show

princip al ly as an i l lust ra t ion many modif ica t ions of

a re employed . For example. i ns t ead o f hav ing absorbe r

ope ra t ed a t on ly one p r e s w e . two o r t h ree p ressure

may b e uti l ized. I f a substant ia l quant i ty of gas a t low

pressure were required local ly for fuel purposes. an ab

sorbe r migh t he ope ra t ed a t a pressure of the order o

l

pounds per sq ua re inch. in which c ase hot oi l ven

tank. vapor uni t acrumulator and low pressure f ie ld gase

might he processed in it.

Again. i t might l ie found ex

pedient to conduct a port ion of the absorpt ion step a

a pressure of 15 pounds pe r squa re i nch . i n w hich cas

the intake gas would comprise cold oi l vent tank an

in t e rmedia t e accumula to r vapors .

st i l l fur ther modif i

ca t ion is to conduct the comp ression of

l o w

pressure ari

vacuum field gases ahead of the gasoline plant. a nd de

l iver a l l gas to the plant in a sing le high pressure l ine.

The hot oi l vent tank might he e l iminated and a so

called rich oil rectifier he used i n i ts place. [n this case

gasoline rontent of the rejected vapors conlrl be kep

low eriougti to omit fur the r processing. At the sam e time

l ight f rac t ions might be e l imin ated to the extent tha t th

ent i re remaining gasol ine frac t ions rould be cot idrnsec

and del ivered di rec t ly to the rec t i f ier wi thout se t t inp u

a vapor recycle.

T l i e s t r i pp ing s t ep may be conducted in two stage

instead of one as indicated on

D k g r ~ m 1.

I n m a n

plants the l ightest f rac t ions are f i rst removed from th

oi l in a pr imary st r ipper and this step is fol lowed I)

removal of the heavier f rac t ions in a seconda ry s t r i ppe

which is opera ted a t a low er pressure . Varia t ions

the rectifying step have already been fliscussecL

Figure i s a genera l view of the abso rpt ion. s t r ipp in

and rect i f ica t ion systems a t a high pressure natura l paso

Page 1

ENGINEERING

ND

SCIENCE

MONTHL

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line plant. It shows the compact arrangement of equip-

ment.

1 . :OMPRESSORS

As 1 noted previous ), compressors pla) an im-

portant role in the operation of tin absorption-tfijt: natu-

ral gasoline plant. They are employed to boost field gas

and vapors

to

absorber operating prehsure and to pro-

cess plant vapors. At Kettleman Hills, where dry gas

mnst be delivered to sales lines at a pressure of about

25 pounds per square inch, this pressure, as was stated

previouslj become;? the most fav orable absorption pres-

sure. Compressors ar e required t o boost much of Itlie

field gas to this final pressu re. The) ar e also employ ed

to raise the pressure of gas utilized in producing wells

by the gas-lift method. At the present time the total

iinestmeiit in compression facilities at Kettleman Hills

far outweighs the value of the actual gaso line extraction

equipment represented

h y

the oil circulating and process-

ing qstems and the rectifiers.

Comprei-3ors ha\ e undergone an interesting develop-

ment. Original1 they were steam-driv en because the in-

tmial combustiou engine liad not been developed to a

sufficient degree of dependability to justify its adoption .

Steam-driven units

\\

ere subject to tu o major disadvan-

tages. Fir~t,liey were inefficient an d required a s fuel a

verj large (luaiitity

of

salable gas. I n the second place,

i+a ter with a sufficient degree of purity for boiler opera-

tioil was frequentlj not available at places where natural

gasoline plants were located. Expensive treating equip-

ment w a ~hen required. With the rapid development

of the gasoline-driven automobile engines,

a

parallel

improvement in gas-engine driven compression equip-

ment occurred.

By

1920, practically all of the steam-

driven equipment had been displaced.

The first .method of transmitting- the power of the

engine to the compressor was by means of a belt. Most

of the par11 natural gasoline plants consisted of a row

of engines 011 one side of a wide room and a row

o f

compressors on the other side. The engines were placed

hell akva) from t he compressors as a safegua rd against

explosions in the engine rooms.

In

some cases t h e en-

gines

a n d

compressors were even put in separate rooms.

and the belts vsere run through separate holes in the side-

v\ alls or partitions.

Belted units were hulk) and were expensive to main-

lain. Rapid improvements in gas engines soon greatly

reduced the fire hazard, and direct-connected gas-engine

driven units were soon recognized as practical and safe.

Die direct drive is much more efficient than the belted

drive and has man) less moving parts to keep in rep air.

Also, it is economical from the standpoint of space re-

quirements. which are often an important consideration

in natural gasoli~~elant design and construction.

The firat direct-drikeii units were horizontal, with the

power cylinders in alignment t11 the rompressor c l-

indrrs . They were comparative1 slow -speed, operating

usuallj at

22

r.p.m. or less, am3 had high poi+er

out-

puts per cyl inder. The result vÃ̂a that immense concrete

foundations were required to ahsorh the large horizontal

thrust uhic11 was developed.

Ear h in the 19-'30's, so-called angl e- t\pe units were

introduced. These ar e constructed with vertical power

i nders a nd horizontal compressor cy linders. The

power output per cy linder has beell reduced, and the

rpeed and number of cjlinders has been increased to

provide a high total power output in a compact and

efficient unit. A tjpical unit has a I - t j p e arrangement

of eight power e>linders. Four compressor c\linders are

arranged horizontallj and operate from the same crank-

shaft as the

power

cjliiiders. The pokver output

is 300-

JUNE 945

horsepower per unit.

Angle-t) pe equipment can he in-

stal led fo r about tit o-third s of tht* cost of tlie horizontal

units, and is proportionately more economical in main-

tenance costs and apace requirements.

Gas-engine driven compressors are available in units

having well over 1,000 horsepower each. However, these

are practicable only in service on large dry-gas trans-

mission lines where comparatively

steady volumes are

handled. For natural gasoline plant service. smaller units

possess greater flexibility and can be readily installed o r

rernov ed to meet cha iigi~ig fiel conditions.

PLANT CONTROL

Th e most important basis for control over plant oper-

ation is what is known as the Absorption Factor, which

was originally developed by Kremser and presented in

a paper before tlie California Natural Gasoline Associa-

tion in 1930. The original form of the absorption factor

equation was as f'ollows:

PC

4

3 156

-

M

Equation

1 )

P

wherein absorpt ion factor,

= specific gravity of sponge.

M molecular weight of sponge,

P

= absorber pressure, pounds per square

inch absolute,

gallons of sponge per m.c.f. of gas. and

p ^

vapor pressure in pounds per square inch

absolute of constituent for which the fac-

tor is computed.

TABLE Ill NUMBER OF NATURAL GASOLINE PLANTS

YEAR

UNITED

STATES

TOTAL

CALIFORNIA

Page

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This equation quantita tively rel ate s the

variables in abso rber operation. A change

which increases the numerical value of the

factor increases; the efficiency of extraction.

The ra t io D M in the equation takes into

consideration the nature of the absorbent

r s o n g stock.

Thus an oil which has

a

high density but low molecular weight is

the preferred type of sponge. Other condi-

tions remaining the same, the absorption

factor i s directly proportionate

t o

the abso-

lute operating pressure or to th e o i l ra te.

Th e influence of temperature i s introduced

in the te rm

p

Th e importance of op erating

i t low temperatures is evident when it is

realized how rapidly the vapor pressure of

a

substance increases with

a

rise i n tem-

perature.

At th e present time most natural

gaso-

line plants are operated t o recover substan.

tia lly all the isobutane from intake gas.

Thus n isobutane absorption factor i3

w a l l y the basis fo r opera ting contro l .

Since plant capacity is

a

function pri,

marily of th e ability to circulate sponge

stock once the operating

pressure

has been

established, the absorption factor presents

a

simple means for comparing the sizes of

plants that will effect different extents of

recovery of light fractions. Befo re but ane s

were in demand, natural gasoline plants

were operated for substantially complete

isopentane recovery. In the norm al, range

of operating temperatures

(70 -100

F.)

the isopentane absorp t ion fac to r i s a l~ ou

three and one-half times the isohutane fa*

tor fo r a given set of conditions. Th us to

ALUMINUM MAGNESIUM CASTINGS tract

a

given proportion

o

the available

so butane

requires thc circulation of abont

three

and one-half times

s

much oil as to

ex trac t the s a m e proportion of the i.w-

New facilities, greater capacities and highly trained personnel are

pentane.

perform ing production records at Kinney Aluminum fo r many types

iagram H I talien f rom the Kremser pa.

per, is

a

correlation between the absorption

of western manufacturers requiring variety of aluminum alloy and

factor, th e number of theoretical plates in

n absorber and the efficiency of extraction ,

magnesium castings-sand an d permanent mold.

The importance of having an adequate

number of trays is obvious when it is noted

Kinney's modern heat treating department, mold shop, chemical

how rapidly at a given absorption facto

and X-ray laboratories within

the

pl nt assure high quality in the fin-

the efficiency of extraction increases s t h e

number of trays is increased. Likewise, it

ished product. T he Quality Control over alloys and processes and the

will be noted that a given efficiency of ex

traction can lie maintained with a mate-

craftsmanship of our workers combine to produce castings which have

rially lower absorption factor a nd attend ant

made this foun dry on eof the largest in the West.

plant investment and operating cost if ade-

quate trays are used . I t must he empha-

This experience and know-how are at your service. Call aK inn ey

i that the number of trays

is

based on

.oretically perfect performance. For

ac

engineering representative for further details, or write.

conditions the efficiency may

be

much

er. In this case the performance would

K I N N EY I N D U S T R I E S

based on the line corresponding to the

mber of theoretical trays times the plate

K m N E Y I R O N W OR KS 525 East 49th Street

ciency. T hu s the performance of a

24

Meehanite Metal nd Grey Iro n Castings

y absorber having a plate efficiency of

T H E K I N N E Y C O M P A N Y-

275

Nort h Avenue 19

per cent would he represented by the

Production machine work, igs, dies and fixtures

e of Diagram I11 corresponding to 12

V E R N O N P A T T E R N W O R K S

323

East 27th Street

eoretical plates. As

a

matter of interest,

Wood and Metal Patterns

t will be noted th at

100

per cent extraction

KINNEYN G I N E E R I N G C O M P A N Y

950

So. Boyle Ave.

uld be obtained at a factor of 1.0 in an

Engineers and Fabricators of A ircraft Parts

r e a n g an infinite number of

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  ickingup

ern on the

overseas mail

fly

Nothing is quite so precious

to

a fighting man as a letter from

a loved one back home-noth-

ing more miserable han "sweat-

ing out" mail call-for the letter

that doesn't come.

Picking up mail "on the fly"

at small stations, as shown

here, is one way Southern Paci-

fic and other railroads see to i t

that your letters are handled

quickly

Another example of fast, effi-

cient mail service was Southern

Pacific's handling of Christmas

mail to the men overseas.

All mail to the Pacific fight-

ing fronts is first routed t o

Army and Fleet Post Offices in

San Francisco. During the last

Christmas season,

2,931

car-

loads of overseas mail rolled

into Oakland and San Fran-

cisco rail terminals

If

the mail

bags in these cars were placed

end to end they would have

formed a continuous column

Page

2

from. San Francisco to Seattle.

To get this unprecedented

volume of mail through on time

-loading, transporting, switch-

ing, handling, and trucking

problems were worked out well

in advance. Many solid trains

of ma il were run across th e

country- thousands of freight

cars were "drafted" for mail

service.

Everything possible was

done to assure your fighting

man a letter or package from

home on Christmas.

We want you to know that

mail for fighting men comes

first with us. It is never put

aside for other traffic.You know

how letters help the morale of

men and women at the front.

So, won't you write more let-

ters? Whether it's V-mail or

regular mail, write often.

Â

The friendly

Southern Pacific

Natural

Gasoline

Continued f r om age

72

t ion factor becomes a s t r ipp ing fac to r

applic able to control l ins the operation in

which the absorbed fractions ar e re inrn ed

f rom the r ich sponge c to rk . Q\ a n a p p r o

priate

change in units . the equation

becomes

wherein

S

s t r ipp ing fac to r . and

f f

pounds of s team per gallon

of oil.

A

s imi la r app roach cou ld he made to

the performance of a rectif ier or fractionat-

ing column. The section of the column

above the feed cou ld be cons ide red a s an

absorber and that below the feed

a s a

stripper. Reflux in the upper section

serves a Fponge stock. a n d Tapors from

the reboiler serve as the s tr ipping mediurr

in th e lower section.

ST TISTICS

Tab le is a summary of the average

daily production of natural gasoline a n d

refinery gasoline in California and the

Un i ted S ta te " fo r the yea rs 1Q11 t o 1943

Th e f igurea for ref inery gacoline include

the natural gasoline which has been

blended in to the product.

Prodnrtion of natural gasoline i n the

United State" is

now

sl ightly more than

per cent of the

ent ire outpul of refinery

gasoline.

I n

California . the ra t io is a lmos

the same. Prio r to the present war, the

ratio in California wac appreciably highe

than in the Un i ted S ta te s a s a whole

However, in the concertefl effort to increas

the production of l ight fractions for use

in

aviation gasoline i t was possible to

expand p roduc t ion a t a much fa s te r r a t

e lsewhere than in (a l i for nia . California i

now the source of abo ut

15

per rent of

the to ta l natural gasoline produced in the

United States . hut in a number o f p rewa

years the perce ntage was about double that

Tab le HI represent'; t h ~ umber

o

nat ura l gasoline plar* opera ted in the

Un i ted S ta te s and i n California in the

years from 1911 to 1943. Th e to tal numb e

in the U n i ted S ta te= i s shown to ha je

inc rea~ efi rapidly from 176 in 1911 to a

peak of 1.191 in 1919. From that t ime

unti l 1930. with the exception

of

one year

t h e numher s tayed i n ex r f = o f 1 ,000 bu

cuh-:equently there has been a decline.

T he rela ti te ly s ta t ic posit ion of the

num

her

of

plant? i n the 1920'1- was due to th

fact that as fac t a s

I I P M

ones were hililt

there was an elimination of small unit '

which hecame unprofitahlc to operate. Also

with the inception of the oil abcr~rptio

p r o c m . t h e r e w e r c

m a n y

t-uses where

P rw plant of tilie type looh the plar

of ~ e i e r a l m a ll c o i q i ~ r f - ~ s i o nlant". Tli

decline

q i i ~ ~

^30 1 i : i ~ been in

a

l a rg

~~~~~~~~~e

r lne to ron ~ tn ic t i on r~ f io in t ly

ow-ned plant's

in

view fipId1 whirl1 a r e ro

opera ti t-1)

I f ^

P I O J I P ~ J

t \ the

T

a r i o u ~ i

u p e r a to i s . T J I F r r w l t I I E I Q bepn a

tmu

to ftawl" - a cnml le r iu i rn h~ rnf plants wi t

l a r a r r

indivirliial cilparitiw.

n

recent yearc

l i p j ~ r ~ ~ ~ ~ a l ~ l yi i ~ - ~ e w n t hf

the

en t i r

num ber of plant s in the L'nitwf Sta tec ha

w e n o p ~ iting in California .

f l ip ah rue s t i i t iq t i< ~ re he lieve( l tn ind i

cate .

i n

turn . the in iportan rp of natura

g a ~ ( ~ l i n rn relation to

t r

I-ntire ort pn t o

motor a n d a\ia t ion gasolinr-

a n d

the i rn

pctr tance of (a l ifo inia i l l the natural paso

l i n e i n d i i ~ t r v

of

the Lniter state^.

ENGINEERING ND SCIENCE MONTHL