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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
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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