CA1091572A - Process for removing condensable components from hydrocarbon gas - Google Patents

Abstract

PROCESS FOR REMOVING CONDENSABLE
COMPONENTS FROM HYDROCARBON GAS

ABSTRACT OF THE DISCLOSURE
Improved recovery of condensable components from gas mixture and/or energy savings are obtained in a process which cools a high pressure gas mixture in order to condense it into a saturated liquid and vapor stream and recovers most of the condensable component from the saturated liquid stream by subcooling the liquid stream prior to recovering the condensable component. This improvement is especially applicable to hydrocarbon gas mixtures.

Description

'7~

BACKGROllND OF TEIE INVENTION
. . .
Field of the Invention . . . _ This invention relates to the recovery of condensable components from a hydrocarbon gas mixture particulary condensable hydrocarbons, especially ethane and propane.
Priox Art ~a,n~- processes have been tauyht for the separation Oæ gases, e.g. the separ~Ltion of nitrogen from methane, the sepaxation of methane, ethane, propane, et cetra from hydrocarbon gas streams. Some of these processes even utilize subcooling means. For example, U.S. 3,559,418 to Ho~frqan discloses th~e subcooling of the methane product prior to E~offman, U.S. 3,568,458 and U.S. 3,589,137 disclose . .
the subcooling of the liquid hydrocarbon, the hydrocarbon obtained after fractionation, so it can be used to condensè
nitrogen out of the hydrocarbon gas~ In turn, nitrogen and ~ydrocarbon vapors subcool the li~uid hydrocarbon. Tracy et .
al in U.S. 3,791,157 in teaching the separation of nitrogen from hydrocarbon gases uses the liquid phase from 'che second ~
` separation to subco~1 the feed gas, i.e. the contaminated ;
-~ naturai gasO Thùs, the liquid phase is actually heated in .~ .
the subcooler. Another use of a subcooler is disclosed by Eakin et al in IJ.S. 2,823,523.
. - .
Previously the prior art would increase recovery of a condensable component by lowering the temperature of the vapor in order to condense more of the desired h~drocarbon. -However, the lower the pressure to which the vapor is reduced~
the more recompression is required of the final residue gas prior to storage or transportation. Additionally, the ~ bm:

'''' '' , '' ' ' ' `; ' ~ ~,. ,' ~""", ' , " ' :': '' ', '` ::' '. ' ' , ''1. ' ' '' ' . :'' "

1''31r- 7~"
ability to do this is some-times limi-ted by the amount of carbon dioxide the hydrocarbon gas contains because ag the temperature is lowered it will tend to freeze creating plugging problems.
None of the prior ar1 teaches the subcooling of a pressurized, condensed saturated liquid produced in hydrocarbon recovery processes in order to increase the recovery of the desired component from the hydrocarbon gas mixture. By sub-cooling the saturated liquid, it was found that more of the component could be recovered than what is present in the liquid streamts~ that make up the liquid stream which i5 processed for.th.e recovery of the desired component.
~ lthough the.prior art teaches the subcooling of refrigerants, it does not teach the use of subcooling to reduce energy requirements of processes recovering condensable components from hydrocarbon gases. Thus, in processes utilizing vapor expanders, this technique permits a higher expander outlet pres.sure for a given recoYery of a condensable component. Ener~y sayings are realized throug~ the reduction ;.
of recompress~on horsepower due to a hlgher expander outlet pressure. An added benefit can be the aYoidance of problems caused by the freezin~ of carbon dioxide~
SUMMARY QF THE`INVENTION
Enhanced and!or more efficient recovery of condensable co~ponents from relative~y high pressure hydrocarbon gas mixture can be obtained in processes for the recovery of .
condensable components ~hich utilize low temperatures to ~:
partially conaense the gas into saturated ~apor and saturated liquid phases by subcooling the saturated liquid prior to the liquid being depressured for further processing.

.~ bm:

. ~ ;~' . ;

I'he tw~ phases can be separated with-the saturated liquid phase being subcooled and depressurcd separately from the depressuring of the vapor stream. Thereafter, -the two streams (each of which is usually tw~-phased) may be recombined. The co~densation of the desired canponent obtained, and, thus, the recovery of the c~nponent, will be greater than the ~nount of condensable ccmponent the separate liquid phases contained prior to their reccmbination. Plternatively, for a given recovery of condensable ccmponents frcm hylrocarbon gas, the low pressure section of the process can be run at higher pressures. This results in energy savings due to a reluction in the amount of recompression of the residue gas needed prior to its storage or transportation.
m is technique is applicable to a nu~ber of processes which partially condense a hydrocarbon gas mixture to create a saturated liquid phase in order to remove or recover a condensable component from the hydrocarbon gas. Examples of such processes includes straight refrigeration processes, Jc~le-Thcmpson valve expansion processes and -processes utilizing one or more expansion enginesl For example, a process to which this subcooling is beneficial is the ccmmon technique for the recovery of condensable camponents from hydrocarbon gas which involves the cooling of pressuriz~d hydracarbon gas to partially condense it. mis tWD phase muxture is then introduced into a separator ~referred to as a chiller separator) to effect a separation between the vapor and liquid phases. The vapor is fed into an expander where it is let down to a lower pressure, thereby doing w~rk, cooling and~
usually partially condensing the vapor, Thereafter, the liquid phase fram the chiller separator is recombined with the partially condensed vapor fram the .,,,~ .

.:

:': :,. ~ . .- .:
. ~ . . , . . ;:
. .:

lti 7~

expander~ The mixture of vapor ancl liquid are again separated in a low pressure separ~-tor -to a vapor phase and liquid phase.
The liquid from this separa-tor is processed, e.g., in a frac-tionation tower, to remove undesirable components. The vapor can be used to satisfy a portion o~ the process refrigeration demand, after which it is recompressed and leav~s the process as a residue gas.
Thus, the invention of the present process entails the subcooling of the condensed liquid phase of the hydrocarbon - 10 gas mixture. It is preferred that the liquid phase be sub-cooled so -that when it is depressured it is essentially the same temperature as the temperature of the vapor phase prior to recombining it with the vapor phase or prior to subjecting it to a separation process to obtain the various components of ~; the hydrocarbon gas. This improvement is particularly appli-cable in the recovery of hydrocarbon components, e.g. ethane ,, or propane, from a hydrocarbon gas mixture.

Broadly speaklng and in summary of the above, the .-: - : i present invention may be seen to provide a process for the :- ~
20 recovery of a condensable component from a pressurized gas ' ... .
mixture wherein the pressurized gas mixture is coole~ to selectively condense at least a portion of the condensable ` component to produoe a saturated vapor phase and a saturated liquid phase whlch contains the deslrable component, the im-.. , ~
~; provement comprising: (a)separating the saturated vapor phase and the saturated liquid phase into separate streams; (b) sub-cooling and then depressuring the saturated liquid stream into - a vapor and a liquid phase; (c) depressuring the saturated vapor ~ stream into a vapor and a liquid phase;(d) recombining the two ." g .. - . . . ~ : . .

~O ~1.5~

phase, depressured, subcooled liquid s-tream and the two phase, depressured vapor stream; (e) separating the recombined stream into a vapor stream and a liquid s-tream; and (E) processing ; the liquid stream of step (e) .for the recovery of the desired condensable component.
BRIEF DESCRIPTION OF THE DR WINGS
: FIG. l is a schematic representation of the process showing the recombining of the vapor and liquid phases from the ;` chiller separator;
FIG. 2 is a schematic flow sheet of the process -; showing separate processing of the vapor and liquid phases of the chiller separator; and ~
FIG. 3 is a schematic representation of Example 3. .
~:. DESCRIPTION OF T~IE PREFERRED EMBODIMENTS
This invention is useful in any process for the recovery or removal o~ condensable components from a gas mixture which is pressurized and cooled to condense at least a portion ~ of '. :

:

::
., ; , .

:~-~,'' : ' ... .
-'''. ;
;: ~
:. :
:"
:, 3~ 1 ~ 5A -, ~vg~
the desired component into a saturated liquid phase. The gas mixture can be inorganic gases, organic gases or a mixture of inorganic and organic gases. The invention is particularly useful in any process for the recovery of removal of condensable components, e.g., methane, ethane, propane, butane, from hydrocarbon gas m~tures wherein some of said component is contained in a conclensed saturated liquid phase of the hydrocarbon gas mixture and the process is conducted under conditions which cause some vaporization of the liquid phase. The invention is especially useful in the recovery of condensable hydrocarbon, e.g., ethane, propane, from hydro-carbon gas. In processes for the recovery of condensable components which utilize low temperatures to treat relatively high pressure hydrocarbon feed gas containing methane and condensable components, it was found by subcooling the essentially saturated liquid produced from a relatively high pressure separator prior to the liquid being depressured for further processing that enhanced recovery of the desired ~: .
~-~ hydrocarbon components and/or energy savings could be obtained.
Generally, in a process for the recovery of - condensable components from a hydrocarbon feed gas, the hydrocarbon feed gas having a pressure of from about 2,760 -.,:
(400 p.s.i.a.) to about 13,790 kilopascals ~2,000 p.s.i.a.) is cooled to a temperature of from about 10C to about-100C, . :
preferably from about -35 to about -75C in order to partially condense the hydrocarbon feed gas. The hydrocarbon sought to be recovered will be more concentrated in the liquid phase.
This two phase mixture is introduced into a separator, often call~d a chiller separator, in order to effect a separation between the vapo~ and the l~uid phases. The chiller separator , -6 bm:

7 ~
is opera-te~ at a tempera-ture of from about 10C to about -100C, preferably from about -35 to about -75C and at a pressure from about

2,760 (400 p.s.i.a.) to about 13,790 kilopascals (2,000 p.s.i.a.), and preferably fram about 4,137 kilopascals (600 p.s.i.a.) to about 6,895 kilopascals (1000 p.s.i.a.). The vapor is fed into one or more expansion engines, referred to as an ~pander or expanders, where as a result of the work it is doing, is lowered to a pressure of from about 515 (75 p.s.i.a.) to about 2,760 kilopascals (400 p.s.i.a.) and preferably from about 690 (100 p.sOi.a.) to about 2,070 kilopascals (300 p.s.i.a.). This causes the vapor to be caoled and usually become partially condensed. The liquid frcm the chiller separator is subcooled. It is preferred the saturated liquid be cooled so that its temperature after depressurizing will be about as cold as the temperatwre of the expander effluent. However, more or less subcooling of the saturated liquid stream prior to being depressurized will be beneficial.
In any process for the recovery of condensable ccmponents, it is kncwn by those skilled in the art that the parameters can be varied in accordance with physical properties of the desired ccmponent sought .
to be recovered. It is also kncwn by those in the æ t that a parameter or parameters can be varied in the process and this usually results in other parameters being varied elsewhere in the process. These variances are within the kncwn chemical and physical properties of the hydrocarbon gas and ccmponents being recovered. The condensed liquid phase is sukcooled to maximize the recovery of the desired ccmponent or the maximize energy savings where the amount of recovery remains constant ; or used to provide more moderate recovery parameters. Thus~ it will be obvious to one skilled in the art what the desire amount of -, - , : :
~ . :

, . ~ . . . .

7~' .
subcoolincJ will be for a given process, since it will involve a balancing of the econom~ics of a process, closeness o~
temperature approach in heat exchangers, amount and type of component being recovered, et cetera.
The refrigeration for the subcooler can be supplied by other streams produced in the process, e.g., vapors from the low pressure separator, the net overhead vapors from a demethanizer, by a deme~hanizer feed, or it can be supplied by an external source.
After the liquid from the chiller separator has been subcooled, it can be recombined with the partially condensed -`- vapor which are thereafter subjected to a low pressure - separation process~ Alternatively, the partially condensed vapor and the subcooled liquid can be subjected to individual low pressure separation processes. The invention can also be used in processes ~hich use a straight refrigeration process to recoYer desirable components from hydrocarbon gas. The subcooling ~ill benefit the recovery of the condensable `~
hydrocarbon in either of those latter two processes; however, - 20 greater benefit is seen in a process ~hich recombines the depressured subcooled liquid with an expander effluent~
The lo~ pressure separatorCs~ are operated at a pressure of from about 515 ~75 p~s.i.a.) to about 2,760 kilopascals ~4qO p.s.i.a.~ and preferably from about 6~0 - (100 p.s.i.a.¦ to about 2,070 kilopascals t300 p.s.i.a.) : .
~-~ The invention can also be illustrated by refexence ;
`~ to the figures which are illustratiYe of an ethane recoYery process. In Fiyure 1 a hydrocarbon gas feed stream is cooled in heat exchanger 1 such that a portion of i-t is condensed to produce a two phase stream consisting of a vapor and a :. , bm:

~ V'3~:i7'~
liquid. The two phase stream is introduced to a high pressure separator vessel 2 called a chiller separa-tor which separates -the vapor and liquid in-to separate s-treams 3 and 5, respectively.
The vapor is then passed to an expander 4 where it is expanded to a lower pressure in order to perform work. As a result of this expansion the Yapor is cooled and usually partially condensed. The liqu~d from the chiller separator 5 is flowed through a su~cooler 6. The subcooler 6 is cooled by a refrigerant stream 7. The subcooled chiller separator liquid is. then passed through control ~alve 8 which controls the liquid leyel in the separator 2 and also depressures the liquid to the same pressure as the vapor from expander 4. Thereafter, the chiller separator liquid 9, which is usually a t~o phase stream., is reco~bined with the partially condensed vapor from ex~ander 4. Th~s ~ixed stream 10 is flo~ed into a low pressure separator 11. The lo~ pressure separator 11 separates the h~drocarb.on mixture into a vapor stream 12 and a liquid stream ~3. Th.e ~apo.r stream 12 can be recycled to the process as a xefr~gerant, for example, in a heat exc~anger 1 or in -.
.. 20 subcooler 6. T~ereafter, t~e ~apor is~ recompressed ready . fo~ sto~a~e qr tr~ns.porta~i~on for suBsequent use. The .. condensed hxdrocarb.on l~qu~d in stream l3 is subjRcted to a urther ~ecover~ process, e.g., fract~onat~on, ~n order to - xeco.vex the eth.ane,.
. Figure 2 depicts an alternative embodiment of . Figure 1 wherein the subcooled chiller separator liquid 9 and the effluent are not recombined, but rather are subjecked to separate low pressures separations ln low pressure separators llA and llB respectively. Again, the vapor produced from these separators 12A and 12B can be recycled to ..
. ~ ~
_g_ bm:
~: . .. .. . , - . , . :

. . .
'- . ~
.- , ~; , : . ~
.. . . . . .
, .; . ~ , ~ , . .
.
.. . .

-gi'j~7~

refrigeration steps of th~ process and ultima-tely recompressed for storage or -transportation. The liquids 13A and 13B are processed for the recovery of -the desired condensed component.
The use of individual separators for these two streams allows them to be ope,rated at different pressures which may be advanta~eous with certain gas compositions, supply pressures or recover~ levels.
The invention is illust~ated by the comparaltive examples presented below. These examples are meant to be illustrative of the invention but not limiting thereof.
'EXAMPLES
.
;~ Example 1 ~, 31,689 pound moles per hour of hydrocarbon gas at a pressure o~ 5,654 kilopascals (820 p.s.i.a.~ was cooled to -64C to condense a portion of the feed gas. The two phase ~',, hydrocarbon gas was then introduced to a chiller separator ; .
- haying a temperature o~ -64C and a pressure of 5,516 kilo~ascals ~800 p.s.i.a.~. 'The stream ~as separated into ~, a, va,por stxeam and a liquid st~eam. 'The Vapor stream was $ent ~rough an expander-~here'it dld work and was reduced to a ~ressuxe of 1,0,34 ki~lop~sca~s (150 p.s.i.a.l~and a tempeXature of -116.5G. ,~he'liquid phase ~rom the chiller ~''' sepa,rato~ wa,s sent throug~ a control valve which reduced t~le ;' l,iqu;~d?s pressure to 1,034 k~lopasca~s C150 p.s.~.a.1; the ,~ 'tempera-ture of the liquid was -110,5C. The depressured chiller liquid stream was recombined with the expander ~'' effluent, resulting in a mixed stream havin~ a temperature ,' of -112.5C and a pressure of 1,034 kilopascals (150 p.sOi.a.). ~ ' , Thereafter, the stream was again separated in a low pressure ,, 30 separa-tor to vapor and liquid streams. The liquid stream was ,, -10-bm:~

,-: - :. . . . .

. ~ , . ,', ., -:: .,: ', ', ,, : .. ,. ', ' '` , . :, - ~V~ 7~
processed :Eor the recovery of ethane. Data relating to the composition of the s-treams and the amount of ethane recovered is given below in Tables 1 and 2.
Example 2 Example 2 was run exact:Ly the same as Example 1 except that the chiller separator liquid was subcooled such that when it was depressured to the expancler exhaust pressure its temperature was -116.5C prior to being recombined with the ~ expander exhaust. The resultant stream from the combining - 10 of the expander exhaust and depressured subcooled chiller liquid was at -116.5C and 1,034 kilopascals (150 p.s.i.a.).
The comparative results to Example 1 are given below `- in Tables 1 and 2.
. ................................................................. .
::
. .
':!
; ` .

.,.~ . .

:, : ' .'- ' :'`' .

.'~ , ' .
:'~' ' :
, . . .
~' ..
, --11-- ~.
~ bm:lc' ., .~ .

~, .:

,; ~ . . - . :. -O ~ O ~1 ,~ ~ . . . ~1 0 C~ ~ ~
f3 ~ ~

W r ~ . ~ N ~ _ I' ~ ., . _ _ .

~-1 ~ o ~ N tq N o ~ ~ .
O- ~`I ~ O

. I ~ O N

Cr~ N ~ ¦ -:r 1~ N ~ N N Ul . ~ . W r ¦ O ~ _ _ ~ ~ O O O ~ O

~CS , ,1" ~o 5 ~O ~D ,'' O .' . ._ ~ ,~

. . W ~ I ~a ~ N O~ ~ ~O N U~ O O ~ 1~ ~

= ¦ 11 ~1 ¦ ~ ~ J ~ O ~ O
e ¦ w rJ COu~ r 1 _I C - ¦ r~
oo ~ 3 ~

~ ¦ I
N
~' I I ~
:3 1 I I ~ u . "

~r U U U~Ur~ U' ~ s " 1o"~ ~ ~
--12-- .

: ~, . - . :: :

91~j'7~

N ,~ ~ N

N ~ O N

~```'''` ~ 3~' ' ' ' " ~ f ~ ~1 .sRa ba f9 ~a ~ ~f ?~

D, ,. `, . :~ . --13--hn 31~`i'7 Example 3 This example is described with reference to Figure 3. 34,586 pound moles per hour of hydrocarbon gas 1 at a pressure of 5,654 kilopascals (820 p.s.i,a.) was cooled in chiller train 2. In this example an intermediate separation of a small condensed amount of the inlet gas stream is made in separator 3 at -36.5C. This small intermediate separation could he done at other temperatures or not done at all without significantly affecting the value of the chiller liquid subcooler, After the intermediate separation the vapor was further cooled and partially condensed down to a temperature of -64C, This two phase hydrocarbon stream was then introduced into a chiller -separator 4 having a temperature of -64C and a pressure of ~- 5,516 kilopascals (800 p,s.i.a,), In the separator 4~ the ~ ~ .
stream was separated into a vapor stream 5 and a liquid stream 6. The vapor stream 5 was sent through an expander ~;
7 where it did work and was reduced to a pressure 1,034 kilopascals (150 p,s,i.a.~ and a temperature of ~116.5C, The liquid phase 6 from the separator 4 was sent through a control valve 8 which reduced the li~uid's pressure to 1,034 kilopascals ~150 p.s.i.a,); the temperature of the liquid was -110C. The two phase li~uid stream 9 was combined with the expander 7 effluent stream 10 to form stream 11. Stream 11 had a temperature of -112,5C and a pressure of 1,034 kilopascals (150 p,s.i,a,l, Thereafter, -stream 11 was separated in a low pressure separator 12 to a vapor stream 13 and a liquid stream 14, For refrigeration recovery the vapor stream 13 flowed through a demethanizer reflux condenser 15 and thence as stream 16 to the process .. ..
'I -1~-I bm:

,-: , - , :: ; ., : - :,, - - ~ :
~ - : . . : :: . . :

-::: - . . - : , as coolant for the initial chiller train 2 along with stream 17.
Thereafter, those vapor streams 17 (undesirable light ends frcn the fractionator) an~ 16 were sent through compression 18 to compress the vapors prior to transportation. The recompression service i5 performed using a brake-ccm~ressor dr:iven by the power developc~d by the expander plus a separate recompreC3sor. The liquid strean 14 from the low pressure separator 12 is directed through the demethanizer reflux condenser 15 and is recycled back through the process as a refrigerant 19, for example, in the chiller train 2. This liquid stream ~: 10 19 is then sent to a fractionation tGwer 20 having a reboiler 21 to recover the ethane in stre~m 22.
The data concerning the . ccnpositions of ~hese various .. streams stated in po md moles per hour is given in l'able 3 c~n~ the -: energies required for this process are given in Table 5.
TA~IE 3 (No Subcooler Us0d - Exam~le 31 Stream No.
Component 1 6 10 13 19 17 ?2 Nz 1110 349 738 1055 55 55 ~ C2 4~79 2706 919 267 4212 190 4022 j C3 1124 581 81 3 1121 1121 i-C4 52 19 1 T 52 52 . n-C4 73 22 1 T 73 73 :i i-C5 17 3 T 17 17 n-C5 14 2 T 14 14 n~C614 1 T 14 14 (T denotes trace amount, less than 0,5 pound moles per hour) ~ -15-- '. .. ' :, ' , lV'~J1.rJ~ 7 ~btal pouu~l moles~. 3458616294 15385 21957 12629 7191 5438 ~lec~ar weight 19.5019.89 17.69 16.84 24.11 16.80 33.79 Pressure kilopascals5,6545,5161,034 1,034 1,434 1,379 1,482 (p.s.i.a.)(820)(800) (150) (150) (208) (200) (215) T~nperature C 32 -64 -116.5 -112.5 -41.5 -101 -15 10Mole Percent Vaporized 100 0 81.6 100 80 100 0 Example 4 The same hydrocarbon gas as in Example 3 is subjected to the `` same type of process with the exception that the liquid produced from the dhiller separator 4 is subcool~d in a subcooler prior to going through control valve 8. Additionally, because the same amount of ethane is sought to be recovered, the low pressure separator 12 is operated at a -~ higher pressure in Example 4 than in Example 3, So stream 11 has a pressure of 1,310 kilopascals (190 p.s.i.a.) and a temperature o~ -110.5C, The bene~icial results of such an operation are given below in ~ables 4 an~ 5.
. .. ~ .
Table 4 - (Subcooler Used - Example 4) ~,~ Component 1 _ 6 _ 10 13 19 17 22 _ : CO2 138 78 47 26 112 87 25 Cl 27565 1253313608 17199 10366 10265 101 ; C2 4479 2706919 183 4296 271 4025 ..

3 1124 581 81 2 1121 1122 ic4 52 19 1 T 52 52 n-C4 73 22 1 T 73 73 n-c5 14 2 T 14 14 ~, n-C6 14 1 T 14 14 s __ ~
, -16-:::: .: ... .

- : . . . ~ . , , .: : - : .. ; :
.: .
~ - . . , ~ t~7o, Ibt~l pou~
moleY/hr. 34586 16294 15395 18425 16160 10718 5443 Mblecular ~ei~ht 19.50 19.89 17.69 16.88 22.47 16.73 33.79 Pressure kilopascals 5654 5516 1310 1310 1434 1379 1482 (p.s.i.a.) (820) (800) (190) (190) (208) (200) (215) Temperature C 32 -64 -110.5 -110.5 -48.5 -101.5 -15 Mole Percent Vaporize~ 100 0 81.9 100 as loo o .

' . ' .
,~:

:
.

. .

.

.

, .

,.......... .
: '; ` ~ ', : ' :'' ~ . .

., - , . .

, ~ . , 3 i ~ ~ ~

~i O ~D ~ ~ o ~ ~ ~ ~ ~ :

.~...... ' ~"

. . .

~`~,., ` ~ "
:`, h : ~

..... ~

~, ,, .

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the recovery of a condensable component from a pressurized gas mixture wherein the pressurized gas mixture is cooled to selectively condense at least a portion of the condensable component to produce a saturated vapor phase and a saturated liquid phase which contains the desirable component, the improvement comprising:
(a) separating the saturated vapor phase and the saturated liquid phase into separate streams;
(b) subcooling and then depressuring the saturated liquid stream into a vapor and a liquid phase;
(c) depressuring the saturated vapor stream into a vapor and a liquid phase;
(d) recombining the two phase, depressured, sub-cooled liquid stream and the two phase, depressured vapor stream;
(e) separating the recombined stream into a vapor stream and a liquid stream; and (f) processing the liquid stream of step (e) for the recovery of the desired condensable component.

2. In a process for the recovery of a condensable com-ponent from a pressurized hydrocarbon gas stream wherein the gas stream is partially condensed into a two phase saturated vapor and saturated liquid stream, separating this stream into a saturated vapor stream and a saturated liquid stream and thereafter recovering the condensable component from the saturated liquid stream, the improvement comprising:

(a) depressuring to a pressure of from about 690 to 2,070 kilopascals the saturated vapor stream into a vapor and a liquid phase;
(b) subcooling and then depressuring the saturated liquid stream into a vapor and a liquid phase to obtain a stream having about the same temperature as the depressured vapor stream of step (a);
(c) recombining the two phase, depressured, sub-cooled liquid stream and the two phase, depressured vapor stream;
(d) separating in a separator having a pressure of from about 690 to 2,070 kilopascals the recombined stream into a vapor stream and a liquid stream;
(e) processing the liquid stream of step (d) for recovery of the desired component.

3. The process of claim 1 or claim 2 wherein the vapor is depressured in an expansion engine.

4. The process of claim 1 or claim 2 wherein the vapor is depressured through a Joule-Thompson valve.

5. The process of claim 1 or claim 2 wherein the con-densable component is selected from the group consisting of ethane, propane and butane.

6. The process of claim 1 or claim 2 wherein the conden-sable component is ethane.

7. The process of claim 1 or claim 2 wherein the satur-ated liquid phase is subcooled so that when it is depressured its temperature is about as cold as the temperature of the depressured vapor steam.

8. The process of claim 1 or claim 2 wherein the satur-ated liquid phase is subcooled in order to maximize the recovery of the condensable component.

9. The process of claim 1 or claim 2 wherein the saturated liquid phase is subcooled to maximize a savings of energy requirements for the process recovering a specified amount of condensable component.

10. The process of claim 1 or claim 2 wherein the saturated liquid phase is subcooled in order to increase the recovery of the condensable component and to cause a savings in the energy requirements of the process.