US1769698A - Process for recovering natural gasoline - Google Patents

Description

-July 1, T930. w. G. LAIRDl 1,769,698

PROCESS FOR RECOVERING NATURAL GASOLINE Filed June l0, 1927 oosTER Patented Julyv l, 1930 UNITED i STATES PA'IEIWI OFFICE WILBUR G. LAIRD, OF NEW YORK, N. Y., ASSIGNOR. TO HEAT TREATING COMPANY, OF NEW YORK, N. Y., A CORPORATION- OF DELAWARE v rRocEss vnon nEcovERING NATURAL eAsoLINE Application tiled4 Tune 10,

covery of a stable natural gasoline separatefrom the lighter. hydrocarbon present in natural gas.

Various processes have been proposed in which it was an object to obtain natural gasoline by making a separation of what may be styled non-gasoline hydrocarbons from a mixture containing ethane, propane, butane, pentane, hexane; etc., the gasoline consisting mainly of butane, pentane and higher hydrocarbons while ethane, propane and some -butane constitute the non-gasoline portion. By one process, it is proposed to absorb the mixed natural gas hydrocarbons in an absorber oil under pressure, heat the oil and absorbed hydrocarbons sufficient only t9 vaporize the lighter or non-gasoline constituents from the mixture then in a'separate still drive ol3 and recover the remaining gasoline hydrocarbons while maintaining the pressure. Another process distills all of the absorbed hydrocarbons from a medium at once, subjects the vapors to cooling and pressure and then introduces them into a rectifying column from which the natural gasoline is withdrawn from the bottom as liquid and the .non-gasoline hydrocarbons are removed from the top of the column as vapor or gas.

In the former process a very poor separation of the respective classes of hydrocarbons is made because in distilling of the lighter hydrocarbons from the mixture some of the heavier ones are carried along and atthe same time the attractive force of the heavier hydrocarbons retains large amounts of the non-gasoline hydrocarbons which will be vaporized and collected with thel gasoline. This of course gives a gasoline which will have a high outage due to the subsequent 1927. -serial no. 197,784.

vapor-ization, under atmospheric conditions, of the lighter and some of the heavier constituents. This process therefore is but slightly better than the older weathering methods.

The latter process while containing certain features of advantage over the former never- A theless is very expensive in that the energy expended in compressing the gas for the absorbers is dissipated by reducing the pressure on the charged absorbing medium before distillation, after which the vapors are again compressed before being subjected to rectifl cation.

The primary object of the invention is to provide a process of recovering gasoline from natural gas in which the various steps are so correlated that the recovery of natural gasoline is achieved in a thorough and efficient manner.

Another object is to provide a process in which heat and power eiiciencies are maintained at the highest possible maximum.

A further object of the invention is to provide a process in which the disadvantages pointed out above with respect to other processes will be overcome.

Further objects and advantages of the invention will appear from the following detailed description 4taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic showing of apparatus adapted to carry out the novel process;

Fig. 2 is a vertical view partly in section of a portion' of one of the rectifying towers;

Fig. 3 is a view partly in section of the portion of theptower shown in Fig. 2, looking from the right.

` According to the process of the present invention the cold absorbing medium charged with natural gas hydrocarbons is passed from absorbers under superatmospheric pressure through a series of'heating zones where the charged medium is intensely agitated and gradually heated to a higher temperature. 90

. top oft The mixture of vapor and oil medium thus produced is then distilled under rectifying conditions and superatmospheric pressure to remove the so-called wild or more volatile hydrocarbons, the most of which may be collected and bottled. The absorbin medium now containing only the gasoline ydrocarbons is subjected to a similar treatment under normal pressure to recover the gasoline as a stable product.

Referring to Fig. 1, the wet gas to betreated is drawn through the collecting main 2 by the compressor 4 and passed through a trap 6 where any liquid formed by the compression is collected and drawn oil. The compressed gas, usually under a pressure of from 150 to 400 pounds per square inch, is passed by-a pipe 8 into the bottom of the irst of a series of absorbers 10, 12 and 14. From the absorber 10 the unabsorbed Uas passes by a pipe 16 into the bottom of absorber 12 and the unabsorbed gas from the absorber 12 passes by a pipe 18 into the bot-tom of the absorber 14. The dry gas leaves'the last absorber 14 by a valved pipe 20 by which it may be passed to any combustible gas supply system or to crackin apparatus for the' production of carbon lack.

The absorbing oil to be used in the absorbers to take up hydrocarbons from the natural gas is drawn by a pump-22 from a storage-cooler 24 and assed by means of a pipe 26 into the e last absorber` 14. From the bottom 1of 'the absorbers 14 and 12 the oil partly charged with hydrocarbons is withdrawn by a pump and suitable piping and passed respectively into the top of the absorbers 12 I and 10. By the time the oil has been vpassed through the series of absorbers counter-current to the passage of the gas ,the oil Idischarged from the bottom of the absorber 10 usually contains a substantial amount of abnatural gas hydrocarbons. This charged oil from the absorber 10 together with any liquid which may have beenv condensed by the compression and drained from the. trap 6, are conducted under pressure through a pipe 28 to a rectifying tower 30. The oil containing the absorbed hydrocarbons first enters the tower 30 throughy the uppermost of a series of heat interchange units 32 and passes through vthe units in series as indicated by the dotted line 34.

sorbe l From the lowermost unit the oil is passed 36 into the base of the tower where it 1s distributed by a distributor 38 into a body of oil maintained therein. The oil in the bottom of the tower is heated by the pipe yindirectly by a heating coil 40 to a temperature sulicient to distil from the absorbing oil all of the non-gasoline hydrocarbons regardless of whether or not some gasoline is also vaporized; The vapors produced by the distillation in the base of the column are subjected to rectification in the tower so that the gasoline is condensed and returned by the usual overflow pipes to the body of oil in the base of the tower. In passing upward through the tower the vapors pass alternately through exchangers 82. The condensate formed in passing the vapors in heat exchange with the oil in the' exchangers 32 flows back onto the next lower bubbling plate where it mingles with the condensate thereon and is subjected to rectification by the hot vapors bubbling through it.' The vapors not condensed in the tower 30 'and which rcomprise substantially all of the non-gasoline hydrocarbons are passed'by the pipe 42 into the condenserdephlegmator 44 by which the higher boiling of the non-gasoline hydrocarbons are con-i ble Aplate a valved pipe 51 is provided for passing condensednon-gasoline hydrocarbons back onto this plate. 4

The distillation and rectiication in the tower 30 is preferably carried on under a superatmospheric pressure suiciently high that the higher boiling of the non-gasoline hydrocarbon vapors passed to the condenser 44 may be condensed at normal temperatures (about F.) These hydrocarbons may comprise some butane and may be stored under pressure 1n containers (bottles), shipped and used aS fuel for motors or otherwise.

The oil collectin'g'in the base of the column 3() and which now contains only absorbed gasoline hydrocarbons is vwithdrawn bya valved pipe 52, valved by-pass 54, and a pipe 56 and passed into the lowermost heat ex- 32 from which it is passed in series through the other units 3221s indicated by the dotted line 58. From the uppermost unit 32 'the oil is passed by a valved pipe 60 Vinto a rectifying tower 62 which is the same in structure as the tower 30. The oi'l enters this tower as Iin the former case through a series of heat exchange units 64 and vis distributed into a body of oil maintained in the base of the column by a distributor 66.

The tower tained at a much higher temperature than the tower 30 so that the vapors which leave the tower by a vapor line 68 are the vaporized gasoline hydrocarbons., These vapors are passed to a condenser 70, in structure identical to condenser 44, the condensate and vapors liquid on bubbling cap plates and ethane, propane, and some' 62 may be heated and main-l being passed to a trap 72 from which gasoline -is withdrawn by the valved pipe 74 and passed to storage while the non-condensed gases resulting from the distillation may be sent by a valved pipe 76 to the dry gas line trap 72 by a valved pipe 78. The return of condensate to the upper plate may bek and preferably is controlled by the end point desired for the gasoline. The absorbing medium freed of gasoline is withdrawn from the base of the tower 62 through a valved pipe 80, by a pump 82 and passed upward through the series of heat exchange'units 64 where its heat is transferred to the oil being passed downward through theseunits. From the uppermost unit 64 the stripped and partially cooled oil is passed by a pipe 84 to the cooler 24.

The distillation in tower 62 is preferably carried out at substantially atmospheric pressure so that the gasoline as produced will exert substantially the same vapor pressure as it would under normal conditions of use or storage. With this mode of operation a valve v85 in pipe 60 is used to reduce the pressure on the oil mixture passing from the tower 3() to tower 62. However, in case it is not desired to condense and collect the light non-gasoline A hydrocarbons under pressure the tower 30 may be operated at atmospheric or other pressures, but if not `operated at a pressure y higher than that used in tower 62 the oil withdrawn by the pipe 52'will be passed through A a pump 86 instead of through the by-pass 54.

The towers 30 and 62 are each constructed alike; they comprise a plurality of bubble cap plates alternating with the heat interchan'gers 32 (tower 30). Referring to Figs. 2v and 3 it will be seen that the interchangers 32 are divided by tube sheets 90 into two end `compartments with an intermediate compartment through the latter of which extend tubes 92 connecting the two end compartments. The vapors passing up through the tower after bubbling through the liquid maintained on the vbubble trays pass by the `outlets'94 into one end compartment of the exchangers 32, through tubes 92 to the other end compartment then back into the tower proper below the bubbler plates by inlets 96. The oil introduced into the tower by the pipe 28 enters the upper exchanger 32 inside the tube sheets 90 and passes from exchanger to exchanger by the pipes 34. In each exchanger the oil enters near one end inside the tube is conducted from exchanger to exchanger by the pipes 58 lwhich connect with small headers 98 in the .end compartments of the continuous passage for the hot oil to pass in heat exchange with the oil between the tube sheets 90in all the exchangers. The oil introduced between the tube sheets 90 of the exchangers32 comprises the vapors and unvaporized oil from the preceding exchanger.

These vapors together with the vapor formed in the -oil around the tubes 92 and 100 cause intense agitationin the menstruum' containing hydrocarbons, and thereby increases the heat exchange and amount of vaporization in the exchangers. Between the bubbler plates in the tow-ers are interposed imper-forate plates 102 which force the vapors above each bubbler plate to pass through the outlets 94 into the exchanger 32 next above.

The condensate formed in the exchangers by the heat of the vapors being transferred to the `oil around the tubes 92 flows counter to the vapors through the conduits 94 and onto the bubbler plate therebelow. From each bubble cap plate the oil (condensate) not vaporized thereon by contact with the rising vapors overflows by the usual overiow pipe to Jthe next bubble cap plate below where it meets vapors of higher temperature and from the lowermost plate the unvaporized condensate overflows into the body of oil undergoing distillation in tower. y

In operating the apparatus described above it has been found desirable in some cases to pass a gas along with the oil mixtures introgas to the oil in pipe 6() for the tower 62.

In this case a valved gas line 114 containing a booster 116 delivers gas from' line 76 to the line 60.. Instead of using the relatively dry gas from the' line 50 for mixing with the oil in pipe 28 gas maybe passed by the booster 116 through a valved line 118 into the pipe line 28 for. mixing with the oil there- 1n.

posed of only four heat exchangers but this is only an example .since in actual practice' a larger number will usually bel employed particularly in the tower 30. Likewise the number of bubbler platesmay vary either as to the total number or as to the number per exchanger. A large number of bubble plates the base of the` The towers 30 and 62 are shown as coma are required where accurate separation of different boiling point hydrocarbons is required. i

Reference has been made to the agitation of the oil in the exchangers 32 and 64. In an actual construction of the apparatus the oil delivery pipes 34 may terminate below the tubes 9 2 1n the formdo'f avdistributor so that agitation is secured by the bubbles of gas or vapor rising through the liquid around the tubes. i

In order to effectively transfer `the heat Vfrom the vapors passing through'the interchangers to the advancing oil mixture a certain amount of vaporization is essential, but since the oil contains very light hydrocarbons it is evident that vaporization will occur without the return of any substantial amount of gas to reduce the partial pressure of the vapors. If no gas 1s returned the vaporized hydrocarbons as they are gradually evolved may be relied upon for agitating the oil in the exchangers 32 and 64;. The 'combined vaporization and agitation of the oil in the stills or exchangers gives a very efficient heat transfer from the hotter materials passing through the tubes 92 and 100.

By the present process it is possible to obtain a stable gasoline free of propane and lower boiling hydrocarbons which as pointed out above account forl the high outages inpordinary natural gasolines. Furthermore the vapor pressure of the final product may be regulated by controlling the amount of 5 butane retained. Ordinarily it is not desired to have the product contain substantially over 60 percent of butane. The vapor pressure at 100 F. for a natural gasoline containing 60 percent butane is 20 pounds while ,it is only 11.5 pounds for one containing 40 percent. Natural gasoline of 20 pounds pressure may be" shipped in insulated cars but for ordinary cars the pressure must not be over ten pounds.

While the invention has been described in detail with reference to the recovery of gasoline from natural gas itis evident that the process is equally applicable to the treatment of gases from coal carbonization, cracking or other stills, asoline agitators and storage tanks. There ore the expressions in the claims relative to natural gas are to' be understood as including the gases here referred to.`

Having described the4 preferred embodiment of the invention what is claimed as new is:

1. In the process of recovering gasoline hydrocarbons from natural gas containing non-gasoline hydrocarbons, in which natural gas 1s passed under superatmospheric pressure in contact with an absorbing medium whereby said medium becomessaturated with said gas, the improvement which comprises passing the said saturated medium through a series of zones of increasing temperature in a rectifying zone, then into a vapor separating zone, passing the vapors evolved from said medium and separated in said separating zone alternately through each of said zones of increasing temperature and through each of a series of bodies of condensate of said vapors whereby said vapors are partially condensed and rectified, withdrawing the nongasoline hydrocarbon vapor from the rectifying zone 'and condensing higher boiling hdrocarbons therefrom, removing the absor ing medium containing the gasoline hydrocarbons from said separating zone, and recovering the said gasoline 'hydrocarbons therefrom by distillation.

2. In the process of recovering gasoline hydrocarbons from natural gas in which both the gasoline and part of the non-gasoline hydrocarbons are absorbed in a liquid menst ruilm, the improvement, which comprises passing said menstruum containing said hydrocarbons through a series 'of heating zones of increasing temperature, intensely agitating said menstruum containing hydrocarbons l in said heating zones, passing the menstruum with the hydrocarbons into a distilling chamber where the non-gasoline hydrocarbons are vaporized therefrom, passing the vaporized hydrocarbons through said zones counter-current to and out of contact with said men` struum containing hydrocarbons, passing the menstruum containing I substantially only gasoline hydrocarbons parallel with said vapors through said zones but isolated from the other materials therein removing said menstruum from the final zone, reducing the pressure vthereon and subjecting the mixture to a rectifying distillation whereby said gasoline hydrocarbons are recovered.

3. In the process of separately recovering the gasoline and non-gasoline hydrocarbons by successive distillations from a liquid menstruum containing the same, the improvement, which comprises distilling from said menstruum the non-gasoline hydrocarbons under superatmospheric pressure, cooling the menstruum containing the gasoline hydrocarbons, reducing the pressure thereon and passing it through a series of heating zones of increasing temperatures, then into a still, distilling the gasoline from said menstruum, passing the stripped menstruum through said zones counter to and out of direct contact with said charging menstruum and rectifying the gasoline vapors by passing them alternately through bodies of condensate and in heat exchange with charging menstruum in said zones.

4. The process of recovering natural gasoline hydrocarbons from a liquid absorbing medium containing absorber gasoline and non-gasoline hydrocarbons, which comprises maintaining a series of alternating heatn and rectifying zones, passing the charg medium through said heating zones and into.

.reducing the pressure thereon and subjecting the mixture to a rectifying distillation whereby said gasoline hydrocarbons are recovered from said medium. 'f

5. In the -processof producing stable gasoline from natural gas, in which natural gas containing non-gasoline hydrocarbons is subjected to the action of an absorbing medium, the improvement which comprises passing the charged absorbing medium under superatmospheric pressure through a series of heating zones of increasing temperature whereby the absorbed non-gasoline hydrocarbon'content of said medium is vapori'zed,

. passing the vapors thus, produced-alternately through said heating zones counter to the flow of the charged medium passing therethrough and throughk bodies of condensate maintained in a rectifying zone, vremoving the vaporized non-gasoline hydrocarbons from the rectifying zone, passing the absorbing medium containing substantially only absorbed gasoline hydrocarbons through said zones counter-current to the flow of the charging medium ltherethrou-gh and effecting a vseparation of said gasoline hydrocarbons from said medium by distillation. n

6. The process of recovering stable gasoline from an absorbing medium containing absorbed natural gas hydrocarbons which comprises progressivelyheating the charged medium to a temperature suii'icient to completely vaporize the non-gasoline hydrocarbons, subjecting the vapors produced to rectifying conditions whereby the non-gasoline hydrocarbons are separated from the medium containing the gasoline, passing the medium containing the gasoline. in heat exchange with the charged medium to partially effect said progressive heating then progressively heating the medium charged with gasolinefto a temperature sufhcient to vaporize the gasoline content thereof and using the heat in the stripped absorbing mediumto partially e'ect .the latter progressive heating.

7. In the process of producing stable gasoline from natural gas, in which natural gas is subjected to the action of an absorbing menstruum whereby `a mixture of hydrocarbons is absorbed therefrom, the improvementl which comprises subjecting the menstruum containing. the absorbed hydrocarbons to distillation in a rectifying tower whereby the morevolatile of the absorbed hydrocarbons are separated therefrom, agitating'the mixture being rectified in said tower by passing a gas in a continuous cycle through said tower, passing the menstruum containing substantially only absorbed gasoline hydrocarbons from said tower into a separate distilling zone and distilling the gasoline therefrom.

8. In the production of stable gasoline from natural gas, the process, which comprises heating an absorbing menstruum containing absorbed natural gas hydrocarbons to effect the vaporization of the lower boiling constituents, subjecting the vapors to rectification under superatmospheric pressure-in a rectifying zone to separate the non-gasoline hydrocarbons from themixture, passing the menstruum containing substantially only gasoline hydrocarbons into a second rectifying zone whereby the gasoline is recovered j from said menstruum and passing a portion of the vapors remaining uncondensed from said second rectifying zone into the vapors being rectied in thefirst instance.

9. In the recovery of stable gasoline from an absorbing medium containing a mixture of absorbed hydrocarbons, the process, which comprises passing an absorbing medium containing the4 hydrocarbons into the base of a rectifying column, heating and agitating the mixture to eiect the vaporization of all hydrocarbons lower than pentane, subjecting the vapors to rectification whereby substantially all hydrocarbons lower than butaneare removed from said column, refluxing substantially all the butane and higher hydrocarbons in said column back into the medium, removing said medium from said column and distilling therefrom stable gasoline containing substantially no hydrocarbons lower than butane. i

10. In the process of producing gasoline from a mixture of hydrocarbon gases, in which said mixture is subjected to the action of an absorbing medium to take up said hydrocarbons, the improvement -*which comprises subjecting the charged medium to a primary distillation treatment to effect the removal therefrom of the low boiling hydrocarbons not desired in the gasoline product, thereafter subjecting the medium containing the desired gasoline hydrocarbons to distillation in a column still, condensing the vaporized gasoline and vrecirculating a portion of the vapors remaining uncondensed back through the materials undergoing .distillation in said still.

11. The process of recovering natural gas-` oline hydrocarbons from a liquid absorbing rmedium containing absorbed gasoline and non-gasoline hydrocarbons, which comprises passing the charged absorbing medium through a seriesof heating zones of increasing temperature in which the charged medium is heated and portions of the absorbed constituents vaporized,. passing the vaporsV formed in said zones forward and in intimate Contact with the unvaporized material, separating the vapors from the unvaporized material in a zone maintained at a predetermined temperature adapted to insure vaporization of substantially all of the non-gasoline hydrocarbons, further heating the medium containing substantially only the gasoline hydrocarbons in a separate zone to vaporize the latter, and rectifying the gasoline hydrocarbons to produce a suitable gasoline product.

In testimony whereof I afliX my signature.

WILBUR Gr. LAlilBLDQ

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