US1768521A - Absorption of gasoline from natural gas - Google Patents

Description

Jim; 24, 1936.

E. E. AYRES, JR.

ABSORPTION 0F GASOLINE FROM NATURAL GAS Filed July 9, 1925 2 Sheets-Sheet 1,

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June 24, 1930. E. E. AYRES, JR 1,753,521

ABSORPTION 0F GASOLINE FROM NATURAL GAS Filed Jul 9, 1925 2 Sheets-Sheet 2 %&

.tane. Later steps in Patented June 24, 1930..

UNITED STATES PATENT OFFICE EUGENE 'E. AYRES, J'R OF SWARTHMORE, PENNSYLVANIA, ASSIGNOR TO B. A. S. COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF DELAWARE ABSORPTION OF GASOLINE FROM- NATURAL GAS Application filed July 9,

My invention relates to a method and an apparatus for the practice thereof, for the a sorption of. gasoline from natural gas. It

has for its ob] ect increasing the yield of gasoline, reducing the quantity of oil required for absorption purposes, and reducing the anjpimt of power required for the pumps and st' s.

The first step in the manufacture of gasoline from natural gas has, as its aim, the separation of the gas into two parts, namely, (1) hydrocarbons whose boiling points are lower than the normal butane and which constitute the-tail gases (e. g. methane, ethane, propane, and isobutane), and (2) hydrocarbons whose boiling "points are higher than isobutane and which constitute the liquid fraction (e. g. normal butane, pentanes, hexanes) This objective is never completely attained, for, in practice, the"tail gases always contain some of the higher boiling hydrocarbons, and the liquid fraction always contains dissolved gases, notably propane and isobuthe manufacture of gasoline from natural gas relate to the sepa-' ration from the gasoline of such objectionable constituents as the propane and isobutane above referred to.

My present invention has to do with an im provement in the first stage of manufacture 1 whereby the tail gases will be more completely freed from gasoline hydrocarbons,

"has been to thus increasing the gross yield of gasoline from natural gas. It relates more particularly to an improvement in oil absorption methods whereby an increased absorption efficiency is obtained without recourse to the usual expensive expedients.

The absorptive medium heretofore most used has beena menstruum of mineral-seal oil, and while it is in connection with the use of this particular absorptive medium that I describe my present invention, I do'not intend that my invention shall be limited to its ex elusive use.

' The method usually employed bring the medium into contact with the gas flow the gas and the inenstruum counter-current in a suitable tower. The oil is admitted at the top; the gas is admitted atabsorptive 1925. Serial 170, 12,392.

the bottom, thus the leancst gas is in contact with the freshest oil, and absorption efliciency is limited only by conditions of equilibrium between menstruum and gas. It has been found that an increase of pressure during the period of absorption will increase the absorptive power of the oil, but with the increase of absorptive power, there is an increase in the proportion of undesirable highly volatile substances absorbed by the oil, with resulting the gasoline afterwards distilled from the oil. An increase of pressure, however, has the advantage that less circulation of'oilis required with resulting saving in oil handling equipment. The above factors have resulted in practice in the general use of about 30 lbs. pressure in the, absorber towers.

It has also been found that a decrease oftemperature of the oil increases the absorptive efliciency thereof, with corresponding de crease in the losses of valuable gasoline hy- 1n counter-current absorbers for natural gas wildness in y the oil entering at the top of the tower, encounters a gas from which the heavier constituents have already been removed further down in the tower. Accordingly the fresh oil takes up the li hter constituents, for the most-part butane. ur: ther down in the tower the oil encounters a gas composed in greater proportion of heavier constituents such, for example, as pentane. The oil, in absorbing pentane, re-

leases a certain amount of butane which was absorbed higher up in the tower and unless this butane is recaptured nearer the top of the tower it is lost, As the oil approaches the bottom of the tower it begins to encounter gas containing in addition to butane and pentane larger and larger percentages of hexane and heavier substances. In absorbing hexane and heavier substances, for

which the oil has the greatest alfinity, a considerable quantity of the'lighter substances (butane and pentane) are liberated. These liberated gases must be recaptured higher in the tower or they will be lost with the tail gases.

In any simple counter-current absorption system it is impossible to avoid losses in gross production by this tendency of one hydrocarbon to displace another, no matter how favorable all pertinent conditions may be made.

An object of my invention' is the reduction of these losses that are inherent in simple so counter-current absorption.

In accordance with my invention, I introduce oil which has been thoroughly stripped (i. e. absorbed hydrocarbons thoroughly removed) into the top of one of a pair of absorber towers, which I will refer to as the second absorber. I introduce the gasoline bearing gas at the foot of the other (or first) absorber and flow it in succession throughthetwo absorbers. ThoughI flowthe oil counter-current with respect to the direction of flow of the gas, I do not pipe it directly from the second absorber to the first but in the interval I partially strip it to remove certain of the gases which it' has absorbed in the second absorber.

The

oil upon, entering the second absorber encounters therein gas which has alreadybeen in contact with the oil in the first absorber. From this gas has already been re-' 'moved those heavier constituents for which line.

mineral-seal oil has the greatest afiinity (hexane and heavier). The oil therefore absorbs the lighter constituents such as pentane and butane which are equally valuable in gaso- Because of the fact that the oil en tering the second absorber is thoroughly stripped, it is of suflicient absorptive capacity to 'take up successfully these lighter constituents. It is not necessary to use thoroughly stripped oil in the first absorber because at that point it is unnecessary to remove all of the gasoline hydrocarbons. The

\ oil entering the first absorber need, therefore,

be only partially stripped. This may be effectually accomplished merely bylreducing the pressure at which the oil was maintained in the absorber (usually about 30 lbs.)' to atmospheric pressure and then advantageously to about 2O inches vacuum, Without raising the temperature. This sufficently strips the oil to make it a useful absorptive medium when introduced into the first absorber where the richer gas does not require a medium of such high absorptive 5 capacity. "The oil emerging from the first absorber is saturated with those heavier.

hydrocarbons for which it has the greatest selective capacity. The oil taken from the first absorber is therefore the only oil which need be operated upon by the distillation apparatus. I vent this oil to atmospheric pressure before the oil is operated upon 'by the usual distilling apparatus.

Among the principal advantages which follow fro-m'the use of my invention is the securing of a higher gross yield of gasoline,

' Fig. 1 shows diagrammatically a simplified form of my invention in which but two absorbers are used; and

Fig. 2 shows diagrammatically a system in which three absorbers are provided.

Referring to Fig. 1, two absorbers 1 and 2 are arranged so that gas enters through pipe 4 near the foot of absorber 1, is removed from a point 5 near the top of absorber 1 by the pipe 6 and introduced at the point 7 near the foot of the absorber 2 and is finally vented from a point near the top of absorber 2 through the pipe 8. Well stripped oil is introduced through the pipe 9 at a pressure of about thirty pounds to the top of absorber 2 and in passage through absorber 2 takes up the residue of the valuable gasoline hydrocarbons remaining in the gas which enters that absorber. The oil, containing these hydrocarbons is removed from absorber 2 by the pipe 10 and introduced to the chamber 3 where it is ventedIto-atmospheric pressure. Su'ch gases as evolve are removed by the pipe 11 to the condensation plant to be treated in the later steps of the manufacture of gasoline. The effect of the release of pressure in chamber 3 is to strip the oil in that chamber with merely a moderate degree of thoroughness. Inasmuch, however, as the oil is now to be used for the absorption of hydrocarbons in absorber 1 for which it has the highest degree of selective absorption capacity, it is not necessary that this stripping be made more thorough. The oil thus stripped is removed from the chamber 3 by the-pipe 12 and restored to a pressure of 30 lbs. by the pump 13. It is then delivered by the pipe 14 to the top of absorber 1 where it comes at once into con-' tact with gas'rich in the heavier hydrocarbons. Conditions of flow in the absorber 1 are so arranged that the oil as it leaves the foot of absorber 1 will contain the highest possible percentage of gasoline hydrocarbons, without regard for absorption efiiciency, since the gases discharging from absorber 1 may be erm1tted to contain gasoline hydrocarbons in view of thefact that they are to be passed through absorber 2. The oil issuing from absorber 1' is conveyed by the pipe 15 to the chamber 19 where. it is vented to atmospheric pressure and the evolved gases are conveyed through the pipe 20 to the condensation system. The oil is then removed at substantially atmospheric pressure from the chamber 19 and is conveyed through the pipe 21 to the heater 16, the still 17 and the cooler 18. Va-

ors driven off from the absorption medium in still 17 are passed from the still 17 to the condensation system through pipe 49 while the oil isthen restored by the pump 13 to a pressure of 30 lbs. and passed through pipe 9 to repeat the above cycle.

Referring to Fig. 2 of the drawings, gas is 7 introduced into absorber 22 through the pipe 25 near the foot thereof; it is removed from absorber 22 by pipe 26 and introduced at the point 27 to absorber 28; it is removed from absorber 28 at the point 29 and conveyed'by the pipe 30 to a point 31 near the foot of absorber 32; and the tail gases are discharged from a point near the top of absorber 32 through the pipe 33. A thoroughly stripped portion of the main current of oil, at t irty pounds pressure, is introduced at the point 42 through the pipe 41 to absorber 32. This oil is removed from absorber 32 by the pipe 48 and is flowed into the chamber 23, where the pressure is reduced to atmospheric pressure, evolved gases being removed to the condensation system by pipe 45.. The effect of this evolution of gas is to produce an oil sufficiently well stripped for introduction into absorber 22, where the gas is richest in heavy hydrocarbons. Accordingly, I convey the oil from chamber 23 through the pipe 24 to the pump 51 where a pressure of 30 lbs. is restored. Thence the oil is conveyed by the pipes 52 and 53 to the top 54 of absorber 22.

In absorber 22 the flow of gas and oil is so arranged thatthe oilissuing from the foot of absorber 22 contains the highest percentage of gasoline thatit will absorb. This oil is removed through pipe 55 to chamber 56,

' where it is vented to atmospheric pressure and the evolved gases are removed by the pipe 43 to the condensing plant. The oil then flows through pipe 57 to a heater 58, thence by the pipe 59 to a still 60. The gasoline hydrocarbons here stripped from the oil are carried by the pipe 79 to the condensing system. The main flow of oil now passes throughthe pipe 34 tothe cooler 35, thence to be carried to absorber 28. A small part of the current of oil flowing out of the still 60, however, is

shunted through the pipe 36 to an additional distilling or stripping unit composed of the heater 37, the still 38, and the cooler pressure.

40. The gasoline hydrocarbons stripped from the oil in the still-38 are carried by the pipe 50 to the condensing system. 'This shunt stream is restored by the pump 46 to a' pressure of 30 lbs. and is fed through the' pipe 41 to absorber 32 to repeat the cycle above set forth. The main stream of oil, not subjected to thecombined stripping effect of stills 60 and38, but merely stripped as well as may be by the useof the single still 60, is restored by the pump 47 to a pressure of thirty pounds and is fed through the pipe 61 to ablation results in the eifervescence of more :ind introduced to the condensing plant. The

oil now passes through the pipe 68 to the pump 69, where it is restored to a pressure of 30 lbs. and is passed-through pipe 70 to a as which is drawn off through the pipe 67 junction with the above-mentioned shunt stream, whence both proceed through the pipe 53 to resume the cycle above described.

In the form of my invention illustrated by Figure 2, therefore, I employ in conjunction with three absorbers a system in which 011 1s stripped with three degrees of thoroughness.

The oil entering the top of absorber 32 is the most thoroughly stripped; that entering the top of absorber 28 is stripped with moderate thoroughness; that entering the top of absorber 22 is poorly stripped. The poorly stripped oil is composed in part of oil which has been through the third absorber and has merely been strippedby venting to atmospheric pressure, and in-part of oil which has been through the second absorber'but has been stripped by venting to atmospheric pressure and in addition by subjection to vacuum. The medium quality of oil, entering the top of absorber 28, has been stripped by the combined action of venting to atmospheric pressure in tank'56 and heating and distilling and pooling in the still 60 and adjacent apparatus. The best stripped oil, entering the top of absorber 32, has been stripped by the successive eflects of venting to atmospheric pressure (tank 56), distilling (still 60), and additional forced distilling at higher temperatures in still 38. Thus, by rearranging somewhat the essential elements contained in the form of apparatus shown in Figure 1, a system" employing three absorbers can be utilized. 1 Similarly, systems can be arranged to employ any number of absorbers, using the princirearranging to aslight extent the piping diagrams shown herewith. I

The advantages derived from the practice of my invention as set forth above are many. One important advantage is that the' heat distillation plant, whereby gasoline hydrocarbons are stripped from the oil, is required to handle an oil from which a considerable part of the lighter gasoline, hydrocarbons have already been stripped by the pressure reduction accompanying the ventin of gases in connection with each absorber, and may therefore be of less capacity. One of the methods of stripping gasoline from'char ed oil, is to flow a current of the lighter by 0- carbons such as propane through the hot 'oil in the still. If this method of distillation or stripping be utilized, it will be found that the relatively high concentration of heavier gasoline hydrocarbons-in the charged oil will require the recirculation of a relatively small quantity of gas in order efl'ec tually to strip the oil. A similar result fol: lows if steam be used. With the decreased volume of gas or steam thus required, the size of the distilling apparatus maybe cor-' respondingly reduced. A further advantage substances are in a large measure recovered from the oil before they are driven out and lost due to the absorption of the heavier hydrocarbons such as hexane, for which the oil has a selective aflinity.

My improved process can be arranged to operate with any of the known forms of mechanical absorbers or centrifugal scrubbers. If such a form of apparatus be used, my process isin no wise changed. An advantage to be gained in the use of centrifugalscrubbers is that the oil and gas are brought into more intimate contact with each other and thus there is a relative freedom from channeling. Particularly in the case of the use of centrifugal scrubbers, I can operate scrubber 1 to discharge oil containmg about 10% of absorbed gasoline, a percentage which is regarded as wastefully' inefiicient in present methods of absorption. I am enabled to vdo this, however, because my second and third absorbers prevent loss of gasoline hydrocarbons.

1 While I have described my invention more particularly in connection with its specific application to the absorption of gasoline hydrocarbons from natural gas by means of an" oleaginous absorptive medium at. a pressure of 30 lbs. in absorber towers, I desire that I shall not be limited to such a particular ap-.

plication thereof, but intend that the invention shall include such modifications and changesas fall within the appended claims.

In this connection is as desirable to provide heating coils in chambersin which the pres sure on the oil is reduced after the oil leaves the absorbers, i. ,e. chambers 3, 19, 23, 56, 64 andj66, to prevent reduction .of the tempera-tureof the oil.

What I claim as new and desire to secure by Letters Patent of the United States is 1. As a step in the process of deriving gasoline from naturalgas by absorption under pressure, reducing the pressure of the absorptive medium between stages of absorption under ressure and thereafter returning the liquid directly to an earlier stage of absorption.

2. In a multistage counter current process of absorbing-gasoline from natural gas by a liquid absorptive medium, contacting absorptive medium with only natural gas having relatively lowcontent of gasoline-hydrocarbons, partially stripping the absorptive medium and passing the partially stripped medium directly into contact with natural gas having relatively high content of gasoline hy-'" drocarbons.

3. In a multistage process of absorbing gasoline from natural gas by a liquid absorptive medium under pressure, contacting absorptive medium with only natural gas having relatively low content of gasoline hydrocarbons, removing the absorptive medium from contact with the gas and reducing the pressure thereon, restoring the pressure on the absorptive medium and passing the same directly to contact with natural gas having I a relatively high content of gasoline hydrocarbons.

4. In amultistage process of absorbing gasoline from natural. gas by a liquid absorptive medium under super-atmospheric pressure, contacting absorptive medium with natural gas having relatively low content of gasoline hydrocarbons, removing the absorptive medium from contact with the gas and subjecting it'to a sub-atmospheric pressure, restoring the super-atmospheric pressure on the absorptive medium and passing the same directly to contact with natural gas having a' aelatively high content of gasoline hydrocarons. c

5. In a multi-stage process of absorbing gasoline from natural gas by a liquid absorptive 'medium under pressure, removing the absorptive medium from contact with the gas before absorption is complete, then partially stripping a part of the medium by single distillation and more completely stripping another part of the mediumby multiple distillation, and contacting said partsrespectively with bodies of natural gas having relatively higher and lower content of gasoline hydrocarbons.

6. In multi-stage absorption of gasoline from natural gas the process which comprises passing the gas through successive absorption passing the gas through successive absorption stages, contacting oil with gas passing through a laterabsorption stage, then subjecting the oil to a partial stripping operation, contacting the partially stripped oil with gas passing through an earlier absorptive stage, and then subjecting the oil passing from said earlier absorption stage to a more complete stripping operation. a

8. In amulti-stage process of absorbing gasoline from natural gas by aliquid absorptive medium under pressure, removing the absorptive medium from contact with the gas before absorption isv complete,.stripping part thereof partially, and part thereof more completely, and returning said parts into contact with gas of difierent gasoline hydrocarbon content.

9. In the process of separation of vapors by absorption wherein the vapors flow counter-current to a menstruum that flows in a closed cycle and is subjected to a thorough strippin operation at some point of its cycle of flow, 51c stepcomprising withdrawing the menstruum-from contact with the vapors at an intermediate point of the counterfiow thereof, less thoroughly stripping the menstruum, returning it to counter flow relation from natural gas by absorption, means for with the va ors at an intermediate point of the counter ow, and completing said counterourrent flow.

'10. In apparatus for the separation of vapors byabsorption, a plurality of absorbers connected for the passage of vapors successively therethrough, means for thoroughlystripping absorptive medium passing from an earlier one of said absorbers, means for passing the absorptive medium so stripped into a later one of said absorbers, means for less throughly stripping absorptive medium passing from said later absorber, and means for passing the less thoroughly stripped absorptive medium into said earlier absorber.

11. In apparatus for deriving gasoline contacting .oil with gas lean in gasoline hystripping the diverted part, returning said part to contact with natural gas having relatively lean content of gasoline hydrocarbons and returning the remainder to contact with gasoline having a relatively high content of gasoline hydrocarbons.

13. In apparatus for deriving gasoline from natural gas by absorption, means for contacting natural gas with oil-previously used to absorb gasoline and from which the gasoline has been partially stripped, means for contacting oil with the residual gas passing from said first named contacting means, means for receiving the oil from said second mentioned contacting means and partially stripping the same, means for delivering the partially stripped oil directly to said first named contacting means and means for thoroughly stripping the oil obtained from said first mentioned contacting means and delivering the same directly to said second named contacting means. 1

14. In a process of separating gases, the steps comprising passing the gases through successive absorption stages, contacting oil with gas passing through a later absorption stage, then subjecting the oil to a partial stripping operatiomand then passing the partial- 1y stripped oil directly into contact with gas passing through an earlier absorption stage.

15. In a process of separating gases, the steps comprising passing the gases through successive absorption stages, contacting oil with gas passing through an intermediate absorption stage, then subjecting the oil to a partial stripping operation, passing thepartially stripped oil into contact with gas passing through an earlier absorption stage, then partially stripping and returning to said intermediate stage a part of the oil from said earlier stage, and more completely stripping and passing to a later stage a part of the oil passing from said earlier stage.

In testimony whereof, I have signed my drocarbons, means for partially stripping oil passing from contact with the lean gas, and means for passing the partially stripped oi'. directly tjo contact with gas rich in gasoline hydrocarbons.

12. In a multiple stage counter current process of absorbing gasoline hydrocarbons from natural gas in a liquid absorption medium, subjecting the absorptive medium to a strippin operation, diverting a part of the flow of-the. absorption medium, additionally

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