US2608516A

US2608516A - Combination high and low pressure absorption process

Info

Publication number: US2608516A
Application number: US69163A
Authority: US
Inventors: Alvin J Miller
Original assignee: Phillips Petroleum Co
Current assignee: Phillips Petroleum Co
Priority date: 1949-01-04
Filing date: 1949-01-04
Publication date: 1952-08-26
Anticipated expiration: 1969-08-26

Description

A. J. MILLER Aug. 26, 1952 COMBINATION HIGH AND LOW PRESSURE ABSORPTION PROCESS Filed Jan. 4, 1949 KMJOOUJ mmwZmOZOU m30-mmm lean oil enters the top of this vessel through a line 43 and rich absorption oil leaves the bottom of the vessel through a pipe 24. Residue gas from this vessel flows through an overhead gas line 23 for such disposal as desired. This saturator vessel 9 is for all practical purposes an absorber vessel and maybe of similar size and of similar construction as absorber vessel 8.

An additional quantity of raw natural gas from line I is passed into a line 3 and is compressed by compressor 4 to a pressure of about 600 pounds per square inch absolute. I

The low pressure absorption andY saturator'V Vessels are described as operating under gauge pressures While the high pressure absorber yIIJ is described as operating under absolute pressure.

Hence, all pressures describing operating conditions in the low pressure portions of the system are gauge pressures and, the pressures `in the high pressure portion of my system are absolute pressures.-

..This compressed gas from line 3 passes into a Separator vessel 5 in which any condensate vformed by the compression is separated from the .compressed gas. This condensate may be removed from the yseparator through a line S for such disposal as desired The vapor phase from this separator passes through a line 'I into the lower portion of a high pressure absorber III. T he saturated absorption oil from saturator 3 is passed through pipe 24 and under the influence .of a pump 25 is introduced into the top of the highpressure absorber as absorption oil. If desired, a cooler 29 may be used to cool the absorptionoil prior to its introduction into the high pressure absorber. This cooling may be necessary or atleast desirable since absorption is ordinarily accompanied by evolution of heat and accordingly the absorption oil leaving the bottom of saturator 9 will have a higher temperature than that conducive to good high pressure absorber operation. f High pressure residue gas leaves the top of the high pressure absorber through a line 26 kfor such disposal as` desired as, for example, it may flow directly into a utility pipe line or into a pressure storage vessel prior to pipe line use.- The enriched highvpressure absorption oil is removed from the absorber through a pipe 27 and is Vpassed through a pressure reducing valve .32 into a ash tank II. The amount of pressure reduction occurring through valve 32 is intended to be such that at least the major portion oi the methane absorbed under the high pressure lconditions in absorber I0 is flashed from the liquid and may be removed through a vapor line 28. The ash tank bottoms is passed through a line r3I into the line 34 and therein is combined with the rich absorption oil from the lowpressure absorber 8. This combined absorption oil stream is then passed through line 34 and is heated somewhat in exchanger 33 and is further heatedl in heater 35 prior to passage through a line 35 into .the top of a conventional stripper still I2. Steam may be added to or introduced into the bottom of this stripper still through a pipe 31 to assist in removing the absorbed hydrocarbons from the absorption oil. Steam and stripped hydrocarbons lleave the still through the overhead vapor line` 4 4. This overhead vaporous material is cooled in condenser I3 and the cooled material passed on through a line into a make tank I4`.n In this make tank, condensed water settles to the bottom and may be withdrawn'through a water drawo line 46 while liquid hydrocarbons may be removed through a line 52 and passed under influence of a pump 5I through a cooler 53 and on through a line 54 into a high pressure accumulator I5. Uncondensed vapors from the make tank I4 are removed through a line lII'I and are compressed by a compressor 48 and added to the liquid hydrocarbons prior to cooling in cooler 53. `An unstabilized natural gasoline product is then removed from the accumulator through a line 5'I for such disposal as desired. The uncondensed gases may be removed from this accumulatornthrough aline 5E for such disposal as desired.

The stripper still bottoms is removed from the still I2 through a line 38 and is passed through exchanger 33 in indirect heat exchange with the rich absorption oil flowing through line 34. This Vstill bottoms flows on through line 38 and is further cooled in cooler 4I and the stream of cooled oil is then divided and a portion flows through pipe 42 into the low pressure absorber 8 as lean oil and the remaining portion ows through a line 43`into the low pressure saturator y9 as lean oil. Y

In actual operation of such aV system, the flash tank vapors owing through line 28 maybe, if desired, compressedand added to the compressed gas flowing throughline 'I prior to introduction pf the Yl-attergas into the high pressure absorber In a similar manner, the vented gases'froin .the high pressure accumulator I5 may likewise be compressed Vand added to the'high pressure gas in line 'I. In this manner of operation, the methane content of the'flash tank and accumulator vapors will ultimately iind its Away into the high pressure residue gas flowing through line 26 while some ethane and higher boiling hydrocarbons will ultimately nd their Way into the natural gasoline product' flowing Vthrough line The low pressure absorber'B may be operated under about 50 pounds per square inchv gauge pressure while the saturator 9 may be operated at a slightly lower pressure as, for example; about 45 pounds. The temperature of the lean oil used in the absorber 8 and saturator 9 may enter these vesselsl at about atmospheric temperature.A l'Ihe high pressure absorber I0 may be operatedgt about 600 poundsV per square inch absolute'. This absorber may also be operated at about atmospheric temperature. It Will be Vunderstood, however, that these absorbers and saturators need not be operated specicallyat atmospheric temperature Aand under the pressures stated, but these pressures and temperatures may be varied somewhat as will be dictated byl the pressures of the available natural gas or gases.

and by the available temperature of the plant.

for extraction of desired hydrocarbons from the gases.

Hydrocarbon gases pumped into utility pipeY lines frequent times Yare sold on minimum B. t. u specications and one particular advantage of my inventionis that I am able to produce a high pressure residue gas suitable for utility pipe line purposes and having a high minimum B. t. u. conV tent and at the same time I am able to extract large? themes .0f essere .that aan. he.. cb-

tained in conventional processes. In order to il-A` lustrate quantitatively theseadvantages, Tables lean oil saturationland with'flean'oil'fsaturation. m .5.

Referringgto thedata, vit willbe notedthatlnider 1 the heading Residuegasf the column headed With leancoil saturation-"venows thatthereare producedfabouti 350,692 cubic feet. more: high pressure residue-z` gas than' when-the lean` oilto 152Go the high. pressure. absorber. was.y not.. saturated with low*pressureresiduem gas constituents: In addition, under Vthe subheadin'gf Gross heating' value it will be further: noted that' when lean" oil saturation was used a higher-yield of higher 20 B. t. u. value residue gas was obtained.

B. t. u. valuewas `11'2'111 percubic foot; Without lean oil saturation, the smaller volume of high pressure residue gaslad'a heating value of 1113.3 25 B. t. u. percubic` foot. This; diierencein heating value is 13.8. B., tr u.. per 4cubic*foot-Lbui. when. itis considered that.350,692`rrior`e cubicfleet of. gas were produced havingthei-higher'Bs tiu. value Upon reference to'theVA heading Absorbed constituentsiv whichaareactually the constituents i absorbed by; the: absorption .oils and.. produced .as gasoline, it will. be seenthat. there. is.. a conside erably higher yield of gasoline With my process. 35i

than..in-theconventionalprocess- Withieanoil.. saturationthere is .produced slightly over 369,000A gallons of "gasoline in comparison to 339,000 gallons when the lean oilto the high pressure absorberf wasvnot .previously treated. as herein dise closed... Thisdiiference 30,000 gallons `of .gasoiline for each approximate. 65,000,000 of high4 pressure gas treated. From another pointof View.,

this ..increased..` gasolineizlyield. amountsto. zthree; 45 tank! cars. of gasoline.:V

Conventional gasoline: tankcars hold. approximately 10000iga11onsfofir lidilidatfi()o High. pressure absorption with* andwtwutl sat uration of asorptionoil. (64,931,253 S. C. F. wet gas feed to high pressure absorber in each feed to'zmy process, of the: lean oilfand of several intermediate streams, ofrich absorptionoils, rese:r idue gases and gasoline products.` The circled??? numerals on the drawing are the stream numbers; for identificationin Table II. then theprocessofmy invention hasereal.' value. 30.

The term MSO as used in Tables II and AIII andthroughout thespeciiication andclaims is a short-- ened form of fmineralseal oil."" Mineral seal oi-lst'.h used for absorptionof hydrocafmms. from'.- gases are usually oilshaving-a boiling-rangefsirnilar to." that of kerosene or somewhat higher.

Table III shows lthe compositionof the-severalc streams including` the. raw gas, high pressure separator bottoms (compression condensate), separator.gas,which gas .isfed to a conventional highv pressure' absorber,l and residue gas, lean oil, and'A rich-"oil compositions fora-conventional high pressure .absorption operation. Aseparate". drawing showing these process'stages is not given.; since. it is` believedN that vsince thisV operation ina-` yolves only compression, cooling, separation. of; gasand liquid, and a high pressure absorbemja separate drawing; is noti necessary. The stream.` compositions shown in Table IIllaregiven` directly;4 under theco1umn headings which are believedto be s'efhexplanatory'. TheV second column which is headed"S'eparator gas is the gaszseparated from the compression condensate of the vvthirdH column and .thiszcondensateresults from'therooling of `the.compressedgastof column 1. Therdatai. off Tables IIandr III. are.` based'` ont theaprocessng; off64",93 1,253'stand`ar-d rcubic-ff eet offhigh pressures gasoflthe composition given inrtlierst f'xolumn.` of 'Tables II: Aand III. It sh'ould belnoted'thatfthe residue" gas as stream'V 9" from' the high pressure absorberof my pro-cess 'is-oi fgreater'yolume" 350,692 cubic feet than the" highpressuregas' produced by the conventonal'high'-.pressurepromf high pressure gas Wasincreasedzby this.35016922r cubic ,feet Withoutthe compression of". any. addi;l tional gasbyusing theprocessof my invention..

s It` should be further. noted .that while.therea.is;`

vreservoir is depleted, the pressure falls. vnatural gas from this source is usually drier,

TABLE 11,15,u

s000111 N--. V(1) 3) (4) (e) Y 7) Component Mols Percent Mols Percent Mols Percent Mols Percent Mols Percent Y n* 9' 3. 00' 4. 87 0. 01 3, 553. 10 Y' 3. 19 3, 547. 88 3. 30 0.01.V .t 0. 70 7. 88 0.02 822. 31 0.74 813. 96 0. 76 0. 02 0. 10 5. 88 0. 01 112. 72 0. 10 106. 21 0. l0 0. 01 63. 74 415. 77 1. 05 75, 179. 23 67. 48' 74, 737. 93 69. 42 1.041 17.34 717. 93 1. 82 19, 847. 14- 17. 81 19, 102. 08 17. 74 1. 75 8. 06 1, 108. 47 2. 81 S, 450. 61 7. 58 7, 410. 09 6. 88 2. 44 v 1. 04 322. 97 0. 82 910. 46 0. 82 634. 83 0. 59 1 0.65 3. 11 1, 345. 65 3. 41 2, 342. 78 2. 10 1, 295. 79 1. 20 2. 46 1. 00 1, 028. 85 2. 60 157. 14 0. 14 13. 36 0. 01 0.34 `0. 94 l, 066. 89 2. 70 47. 94 Y 0. 04 0. 55 0. 00 0. 11 i). 56 663. 75 v 1. 68 0. 40 0.00 0.00 0.00 0. 00 0. 41 486. 26 1. 23 0. 00 0 00 0. 0 0 0. 00 32,329.53 81.84 r 91.17 T. 4],*( )'t8.1.. 118, '599. 00 100.0()- 39, 504. 70 100. 00 111, 423. 83 100 00 107, 662 68 100. 00 100.00

s110010 N0-.. (s)v 9) 10) 11) 2) v(a) Y Component Mols Percent Mols Percent Mols Percent Mols Percent Mols p Mols 83. 49 0. l1 94. 95 0. 07 171. 93 0. 10 8. 94 0. 10 7, 994. 96 l0. 45 106, 737. 26 77. 23 114, 290. 92 66. 38 993. 71 11. 44 10, 118. 37 13. 22 20, 968. 95 15. 17 30, 342. 26 17. 62 1, 020. 08 11. 74 1l, 081. 75 14. 48 3, 037. 67 2. 20 13, 078. 90 7. 60 1, 498. 98 17. 25 1, 516. 1. 98 237. 48 0. 17 1, 478. 10 0. 86 402. 92 4. 64 4, 473. 34 5. 84 643. 72 0. 46 4, 070. 07 2. 36 1, 554.89 17. 89 1, 066. 22 1. 39 37. 21 0. O3 959. 65 0. 56 849. 02 9. 77 829. 63 1. O8 9. 95 0. 00 792. 19 O. 46 907. 96 10. 45 250. 07 0. 33 0. 03 0. 00 249. 70 0. 15 763. 15 8. 78

81. 16 0. 11 0. 00 0.00 81. 16 0. 04 660. 7. 60 K 38,807.44 50.71 ...vu- 32,329.53 3 807.59 VVTotal... 76, 533. 68 100. 004 138, 212. 85 100 00 172, 177 94 100. 00 8, 689. 06 100. 00 32, 329. 53 38,1807. 59

TABLE III Compression Sep# Compression f 1 f RaW Gas Mater Gas condensate HP R1eh Oil l PIP Resldue Gas Lean Q11 M01 M01 M01 M01 M01 M01 Mols percent Mols percent Mols percent M015 percent Mols percent M015 percent 5, 426. 0l 3. 00 5, 414. 24 3. 14 11. 77 0. 14 78. 40 0. 1l v 5, 335. 84 3. 89 1, 266. 07 0. 70 1, 248. S2 0. 73 17. 25 0. 20 121. 14 0. 16 1, 127. 68

31, 362. 34 17. 34 30, 342. 26 17. 62 1, 020. 08 11. 74 8, 650. 88 11. 74 21, 691. 38 14, 577. 88 8. 06 13, 078. 90 7. 60 1, 498. 98 17. 25 10, 345. 41 14. 04 2, 733. 49 1, 881. 02 1.04 1, 478. 10 0. 86 402. 92 4. 64 `1, 477. 36 2. 01 0. 74 5, 624. 96 3. 11 4, 070. 07 2. 36 1, 554. 89 17. 89 4, 070. 07 5. 52 0. 00 1, 808. 67 1. 00V f 959. 65 0. 56 849.02 9. 77 959. 65 l. 30 0. 00 l, 700. 15 0'. 94' 792. 19 0. 46 907. 96 10. 45 792. 19 1. 07 0. 00 A1, 012. 85 o, 56 249. 7o 0. 15 763. 15 s. 7s 249. 7o o. 34 v 11.01) 741, 55 (l. 41 81. 16 0. 04 660. 39 7. 60 8l. 16 0. l1 0.00 38,807. 44 52.66 38,807.44 100.00 180, 867. 00 100. O0 1.72, 177.194 100. 00 n 8, 689.06 100.00 73, 696. 45 100. 00 137, 288 93 100. 00 38, 807. 44 100. 00

Natural gasoline and LPG fractions are extracted' from a Wide variety of natural gases by well known absorption processes. The natural gas may be produced along with crude oil in which case'the gas is available from a gas-oil separator or from the casinghead of thewell. Usually such a natural gas contains a relatively great percentage of heavier or high boiling hydi'ocarbon constituents and is available under relatively 10W pressures ranging from near atmospheric to or 100 pounds per square inch. Natural gas may also originate from a gas cap from which only 'gas is being produced under relatively high. pressures initially; but as the The that is, contains less higher boiling hydrocarbon constituents. A typical low pressure gas from a source such as noted above may be passed to a low pressure absorber such as absorber 8 wherein substantially all of the natural gasoline hydrocabons together with a portion 0f the LPG-hy` drocarbons are extracted by absorption in an absorption oil. Usually it will be desiral'ole to circulatesuicient absorption oil to extract all of the pentane vand heavier hydrocarbons. The residuev gasy from such a low pressure absorber contains substantial .quantities of. propane and butane which are valuable hydrocarbons for LPG markets. Nevertheless, it is not economically feasibleA to extract te@ meier porti@ 0f these.

butane content does not enhance its value.V Inv fact if the residue fuel gas is to be used as fuel i foi` gas engines, it is usually preferable that the f paneand butane'cententlbei reduced -so as -to lower the B. t. u. value. k ,i Wlthf 1the#advent?ef` thelutilityfpipe lines lorthe transmission ofifesidue gas-f-rom the`gas`fields Etodomestic #aridi-*industrial lmark'ets *located fseverallhundred miles distant, "itfhasbecome necessary to substantially increase fthe pressure fon tlfiefgaswhich'lis' to besotransmitted. In rn'anycased-l. it hasbeen necessary'ftocmpress a i low pressurefgasWhich-maybeavailable at'pressures below l'gpoundsup to pressures' ranging -trom-SOO to 1000I5po'unds. In'a-fewcases, the natural gas is naturally availablefat sufficiently ."liigh pressures to permit injection intoa -utility `pipe lllnewithout compression. In eithercase -fafresidudgasmarketed-toa utilityp'ipe linemust havelasspec-ifled caloric value. In other words, the B. t. u. value of the residue gas so marketed must not fallbel'w a certain 'specified minimum which is usually setby contract. Itis well known that the compression of gas toipressu'res in the order of 600l `pounds-and -above is an expensive operation'a'nd,"therefore, any means for reducing the 'amount of gas which must be compressed irepresentsa valuableimprovement. The process rflmy invention provides "a `means for transferifrin'g constituents from -a low `pressure pgas Sto a fhi-ghpressure residue gas without compression. Furthermora Amy process provides a means for extracting substantialquantities'oi butane and propane whichare actually being wasted in` W pressure `fuel gases and]transferring` a .portion -of these constituents to a' high pressure `re`siduegas so as to increase its caloric value and/or its volume. The low pressure absorber may actually be a part of a complete gasoline plant located at some distance from the high pressure plant in which case the low pressure residue is passed to the saturator in the high pressure plant or the lean absorption oil from the high pressure plant is passed to a saturator in the low pressure plant. In either case, selected constituents free of undesirable diluents, such as nitrogen and carbon dioxide. are absorbed from the low pressure gas and are transferred in the oil passing to the high pressure absorber and thus these selected constituents may be used to increase the volume and/or the calorific Value of the high pressure residue gas Without incurring any compression cost.

In the specific application of my process as discussed hereinabove, all of the gas available to the gasoline plant is at a relatively low pressure. A sufIicient quantity of this gas to supply fuel and lease needs is processed through the low pressure absorber and only the quantity needed for the high pressure pipe line sale is compressed. It is well known that the volume of gas initially compressed for processing in the high pressure absorber is subject to shrinkage due to extraction of hydrocarbons in the absorber. Such shrinkage requires the compression of an additional quantity of gas in order to supply a specified volume to a utility pipe line. A portion of this compression cost may be eliminated by transferring a selected portion of the low pressure residue gas to the high pressure residue by the process of my invention. In this particular application, the low pressure absorber was operating under a pressure of 50 pounds p. s. i. g. and was processing about 41 million cubic feet of natural gas with a lean oil circulation of 1 million gallons per day and an absorber pressure of 50 pounds per square inch. The high pressure absorber was processing about 68.5 million cubic sorber.

invention, it was possible to transfer about'lljrOO'O` cubic feet per day of low pressure residuali-constituents to the high pressure residue an'dthereby increase the calorific value :by 13.81%.` t. u.1'p`er cubic "foot -andsimultaneously increase' the overall recovery of natural'gasoline` and .LPGv constituents by 30,000gallons perday. `Had Vitbeen unnecessary to Aincrease :the caloriiic value,` the volume `of the high pressure-'residue could have been increased-'and `the B. t. u.value held 'con- `stant and the recovery-or yield of condensa-ble -hydrocarbons increased still' further.

-Fromthe foregoing, it should be apparent that my process'isespecially advantageous Vwhere both high-and l'ow `pressure-'wet gas streams 'are-,avail- Aable toV a natural zgasoline `plant :er wheref itfris `necessary lto:` compress a substantiall `duantityoi.'

lovvrpressure gas fory marketing through'a utility pipe line ona Kspecied minimumB. t. iu; basls.

fMy process may be` employed advantageously lIto `accomplishvthefollowingresults: i -2`5V (l) The volume of boththe high'zpressurefresidue gas andnthe. recovered condensable'hydrocarbons may be increased and' the caloriilc i value of the high pressure residue gas increasedlwith'- out increasing the -low 'pressure and 't-h'e hig pressure wetgasfeeds to theplant. f' V(2) The wetgas feed stream may beimain- Vtained constant and fa" higher extraction of condensable 'hydrocarbens, such 'asf propane and 'buitane, may be eiected by increasing oil circula.- tion to the high pressure absorber to the extent necessary to maintain the calorific value of the high pressure gas at a predetermined level.

(3) The Volume of high pressure gas processed can be reduced and the caloriiic value maintained at a predetermined level without appreciably effecting the recovery of condensable hydrocarbons.

(4) The volume of low pressure gas processed can be increased and the volume of high pressure gas decreased While still maintaining a predetermined caloriiic value for the high pressure residue.

The gas volumes, temperatures and pressures given herein are given merely as exemplary and it is not intended that these conditions be limiting an any way. For example, the 10W pressure absorber may be operated at 10, 25, 65 or 100 pounds per square inch as Well as at *.50 pounds as described. In addition, the high pressure absorber may be operated at other pressures than the 600 pounds stated. The high pressure absorber should, however, be operated at a pressure considerably higher than the low pressure ab- 'Ihe process has little advantage when the ratio of pressures, that is, high pressure-tolow pressure, is less than 2, and the advantage increases as the ratio increases. It is possible, of course, for the ratio to be increased up to the order of 40:1. A preferable ratio of pressures lies between about 6:1 to 20:1.

The saturator Will usually be operated at a Apressure some lower than that of the low pressure absorber on account of the pressure drop of the low pressure residue gas in transit from the low pressure absorber to the saturator.

Many valves, pumps, meters, controllers and other auxiliary apparatus are not shown on the drawing nor described in the specification for purposes of simplicity. That such auxiliary apparatus is necessary in the operation of such a process is understood by those skilled in the art. It

will be'obvious to those skilled in the art that many `Vtlliations and alterations of my process may be made and yetremain within the intended spirit and scope oimy invention.

without compressing as a gas said gaseous constituents, which comprises absorbing a portion of said gaseous constituents from a rst stream of said natural gas at a rst superatmospheric pressure with a rst stream of a liquid lean absorption oil in a yfirst absorption step to produce a rst residue gas, absorbing an additional portion of said gaseous constituents from said rst residue gas at substantially no greater pressure than said rsty pressure'with a second stream of the same liquid lean absorption oil in a second absorption step to produce a second residue gas and a partly presaturated liquid absorption oil, pumping said presaturated liquid from saidiirst pressure to a second superatmospheric pressure which is at least twice said iirst pressure, and absorbing a portion voi' said gaseous constituents from a second stream of that portion of the same said natural gas that remains gaseous at said second pressure with said presaturated liquid in a third absorption step to produce a third residue gas,

whereby said third residue gas contains more propane and Vheavier constituents than if said lean oil were employed inplace of said presatu- L n rated liquid. I 1, 2. The combination of claim 1 in which-,the resulting rich absorption oils from the iirstv and third absorption steps are fractionated to produce said lean obsorption oil which is recycled to said first and second absorption steps. 3. The combination of claim 2 in which the rich absorption oil from the third absorption step is flashed byl lowering its pressure before said fractionation, and the vapors from said flashing step are compressed and recycled to said third absorption step. Y

4. The combination of claim 2 in which vapors from the distillate of said fractionation are compressed and recycled to said third absorption step.

ALVIN J.- MILLER.

REFERENCES CITED y The following references are of record vin. the

le of this patent: a

UNITED STATES PATENTS OTHER REFERENCES McCullough et al., Petroleum Processing, Apr. 1948, vol. 3, pages 307-310.

Claims

1. THE PROCESS OF TREATING A RAW WET NATURAL GAS CONTAINING PROPANE AND HEAVIER CONSTITUENTS TO TRANSFER GASEOUS CONSTITUENTS CONSISTING OF PROPANE AND HEAVIER FROM A LOW PRESSURE RESIDUE GAS STREAM TO A HIGH PRESSURE RESIDUE GAS STREAM, WITHOUT COMPRESSING AS A GAS SAID GASEOUS CONSTITUENTS, WHICH COMPRISES ABSORBING A PORTION OF SAID GASEOUS CONSTITUENTS FROM A FIRST STREAM OF SAID NATURAL GAS AT A FIRST SUPERATMOSPHERIC PRESSURE WITH A FIRST STREAM OF A LIQUID LEAN ABSORPTION OIL IN A FIRST ABSORPTION STEP TO PRODUCE A FIRST RESIDUE GAS, ABSORBING AN ADDITIONAL PORTION OF SAID GASEOUS CONSTITUENTS FROM SAID FIRST RESIDUE GAS AT SUBSTANTIALLY NO GREATER PRESSURE THAN SAID FIRST PRESSURE WITH A SECOND STREAM OF THE SAME LIQUID LEAN ABSORPTION OIL IN A SECOND ABSORPTION STEP TO PRODUCE A SECOND RESIDUE GAS AND A PARTLY PRESATURATED LIQUID ABSORPTION OIL, PUMPING SAID PRESATURATED LIQUID FROM SAID FIRST PRESSURE TO A SECOND SUPERATMOSPHERIC PRESSURE WHICH IS AT LEAST TWICE SAID FIRST PRESSURE, AND ABSORBING A PORTION OF SAID GASEOUS CONSTITUENTS FROM A SECOND STREAM OF THAT PORTION OF THE SAME SAID NATURAL GAS THAT REMAINS GASEOUS AT SAID SECOND PRESSURE WITH SAID PRESATURATED LIQUID IN A THIRD ABSORPTION STEP TO PRODUCE A THIRD RESIDUE GAS, WHEREBY SAID THIRD RESIDUE GAS CONTAINS MORE PROPANE AND HEAVIER CONSTITUENTS THAN IF SAID LEAN OIL WERE EMPLOYED IN PLACE OF SAID PRESATURATED LIQUID.