US2261927A - Gasoline extraction - Google Patents

Description

Nov. 4, 1941; T1 v. MOORE ETAL GASOLINE EXTRACTION Filed May 11, 1940 W uPIJJ-FW.D DZ i-Buzz: FIG: U m TI s N Y 0 W I E H 5 M w 7 m 1 2 E 6 r 2 w 5 m O r I E E E I L C O A|l m a 2 v n s uzou zotmmommv COOLING MNJQQU MM.

INVENTORS ATTORNEY Registered Nov. 4, 1941 GASOLINE EXTRACTION Thomas V. Moore and Stuart E. Buckley, Houston, Tex., assignors to Standard Oil Development Company, a corporation of Delaware Application May 11, 1940, Serial No. 334,672

6 Claims.

The present invention is directed to a method for recovering gasoline from distillate gas at high pressure.

In a great many distillate wells the distillate is carried out of the earth in high pressure gas at pressures ranging from 1500 to about 5000 lbs/sq. in. In the operation of these wells it is desirable to recover the distillate contained in the gas without any substantial reduction in the gas pressure so that the gas may be reinjected into the producing formation. The attainment of this end presents a difi icult problem, particularly when the method of recovery employed is an absorption method because there are two distinct limitations to the use of that method. The first of these is that the practical operating pressure is limited by the vaporization of the absorption oil by reason of the phenomenon known as retrograde vaporization. The second is a temperature limitation imposed by reason of the fact that the heavier hydrocarbons in the distillate contained in the high pressure gas tend to form hydrates at low temperatures. These hydrates deposit in flow lines and valves in the form of an ice and lead to difliculties due to plugging.

The principal object of the present invention is to increase the limits of practical operating pressure and reduce the limits of practical operating temperatures in a method of the character above referred to. Primarily this is accomplished by cooling the gas containing distillate to a temperature just above that at which hydrate formation occurs, say about 65 F., at a pressme of about 1500 lbs./sq. in. for a typical gas, and without substantially reducing the pressure of the gas, scrubbing it with an absorber oil which has a strong absorption power for the heavier hydrocarbons contained in the gas, and then substantially reducing the temperature of the gas, still without any substantial reduction in its pressure, so as to condense out of it any absorber oil which it has carried over from the scrubbing step.

During the scrubbing operation, in one specific embodiment of the present invention, the temperature of .the gas is gradually reduced as the scrubbing proceeds. In a specific embodiment the final reduction in temperature of the gas is accomplished by expanding the scrubber oil, containing some fixed gases dissolved therein during the scrubbing operation, into a coil or refrigerating zone arranged above or behind the scrubbing zone, whereby a reduction in temperature will be effected by the Joulee'lhompson expan- 55 thetower are cooling coils I, 8 and 9. Any desion of said fixed gases as well. as the vaporization of readily volatile liquids contained in the menstruum.

Another specific feature of the present invention is the scrubbing of the gas after the final.

cooling step with an absorption menstruum heavier than that employed in the first scrubbing step, whereby any of the first menstruum carried over by the gas is absorbed from it by the heavier menstruum the temperature of which is simultaneously considerably reduced. This cold heavy menstruum is then used, by indirect heat exchange, to cool the lighter menstruum introduced into the first scrubbing zone.

The nature of the present invention will be more fully understood from the following detailed description of the accompanying drawing in which the single figure is a front elevation, partly in section. of one type of apparatus which may be employed for the practice of the present invention.

Referring to the drawing in detail, numeral l designates a distillate recovery tower into the bottom of which is fed, through line 2, rich wet gas recovered from a producing formation. The rate of feeding of this gas into the tower is regulated by manipulation of valve 3. The gas, before being introduced, is precooled in heat exchanger 4, where it is passed in indirect heat exchange relation, with dry gas issuing from the top of tower l'through line 5, this dry gas having undergone a cooling step as will hereinafter be described. The tempertaure to which the wet gas is cooled will be as low as possible, but above that at which the formation of hydrocarbon hydrates will occur. This, of course, will depend upon the pressure of the gas and upon the nature of the as.

Illustrative examples of suitable temperatures for different pressures are as follows:

The lower part of tower I above the inlet of line 2 is provided with interior equipment such as perforated plates 6 which, if desired, may be equipped with bubble caps of conventional design. Also if desired, this portion of the tower may be packed with inert material having a large surface, such as Raschig rings, porcelain balls, or the like. Suitably spaced in this portion of through line 2 l sired number of these cooling coils may be utilized. Preferably, these cooling coils have a progressively lower temperature. For example, if the'entrance temperature of the gas is 100 F., cooling coil 1 may be held at 80 E, coil 8 at 70 F., etc. This serves to minimize the amount of absorbent carried off by the scrubbed gas. If desired, only suflicient refrigeration may be provided by the cooling coils to compensate for the heat of absorption generated by the absorption of constituents of the gas by the menstruum. The lowermost of these coils will be preferably spaced asuiflcient distance above the inlet of line 2 to allow for the removal of a substantial portion of the heavier hydrocarbons from the gasbefore it reaches the Zone of influence of the coils.

The absorber oil is introduced into tower l above the absorption zone by line ID. This ab-.

sorber oil is preferably an oil the constituents of which have a chemical structure similar to that of the hydrocarbons the recovery of which is desired. Generally, the boiling range of this oil will be somewhat above the boiling range of the hydrocarbons to be recovered. For example, the oil may be a cut from the kerosene range or from the gas-oil range for the recovery of naphtha constituents. It is to be noted, however, that heavy naphtha may also be employed for the recovery of naphtha constituents even though its boiling range overlaps the boiling range of the constituents to'be recovered.

The rich absorption oil containing the absorbed constituents is withdrawn i'rom the bottom of the tower through line H in which it is pumped by pump I2 ,into a cooling coil l3 arranged in tower I above the absorption zone, an expansion valve It being arranged in line H ahead of said substantially dry gases are separated and pass out of the system through line I6. The residual rich absorber oil is then discharged through line I! into a fractionating tower [8 from the top of which the absorbed constituents are withdrawn through line l9 and from the bottom of which lean absorber oil is withdrawn through line It). It will be understood that tower I8 is provided with the conventional heating coils, reboilers and reflux arrangements. At this point it may be noted that when the absorption menstruum is a naphtha having a boiling range overlapping that of the naphtha to be recovered from the gas, fractionating tower I8 is operated so that a predetermined cut is recovered from the top thereof, absorbed constituent having boiling points abov this out being retained in the absorption oil.

In the specific embodiment shown the cold gases, after having passed the cooling coil l3, pass into the upper part of tower l where they are again scrubbed by a heavier absorption menstruum introduced into the top of tower I This heavier absorption menstruum will usually be a gas-oil if the main absorption menstruum is a heavy naphtha, and will be in the lubricating oil range if the main absorption menstruum is a kerosene or a light gasoil.- In the upper part of the tower there is also provided interior equipment such as baiile plates 22, or the like. This upper part of the tower is separated from the cooling zone by a plate 23 having a central opening 24 which is covered with an inverted tray 25, whereby the absorption menstruum containing any absorbed constituents collects on the top of plate 23 from which it is withdrawn from the tower throughline 28, passed through a heat exchanger 21 in which it exerts a refrigerating effect on the lean absorption oil passing through line H and discharged into a tower 28 which is operated in such a way as to cause the vaporization from the heavy menstruum of any lighter menstruum contained therein. The vapors of light menstruum are carried oil from tower 28 through line 29 and introduced into the upper part of fractionating tower 48 below the point of entry of line H. The lean heavy menstruum is withdrawn from tower 22 through line 2| and pumped by pump 30 into the top of tower I.

It will be apparent that many changes can be made in the specific operation and apparatus above described without departing from the scope of the present invention. For example, the dry gas recovered from the top of tower I through line 5 need not be pumped back into the formation from which it was derived, but may be used in other ways in which its energy can be utilized. Likewise, the refrigeration in coil l3 may be effected by any of the common refrigerating means.

The nature and objects of the present invention having been'thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

1. A method for recovering distillate from high pressure gas which comprises cooling the gas while under pressure to a temperature just above that at which the formation of hydrocarbon hydrates will occur at such pressure, contacting the cool gas with an absorption menstruum to thereby remove from the gas those constituents which would lead ,to the formation of hydrates upon further cooling of the gas and then, after the absorption step, cooling the gas still further to condense therefrom any absorption menstruum contained therein.

2. A method for recovering distillate from high pressure gas which comprises cooling the gas while under pressure to a temperature just above that at which the formation of hydrocarbon hydrates will occur at such pressure, contacting the cooled gas with an absorption menstruum, thereafter conducting said gas through a cooling zone and discharging into a closed space in said cooling zone'the rich absorption menstruum with a simultaneous reduction in the pressure on said menstruum, whereby a refrigerating effect is produced in said cooling zone to remove from the gas any absorption menstruum contained in it.

3. A method for recovering distillate from high pressure gas which comprises cooling the gas while under pressure to a temperature just above that at which the formation of hydrocarbon hydrates will occur at such pressure, contacting the cooled gas with an absorption menstruum, thereafter further cooling said gas, and finally sembbing said cooled gas with a heavier absorption menstruum than that used in the first absorption step.

4. A method according to the preceding claim in which the heavy absorption menstruum, after contact with the cooled gas. is passed into indirect heat exchange relation with the absorption menstruum used in the first absorption step prior to its introduction into said step.

5. A method for recovering distillate from high pressure gas which comprises cooling the gas while under pressure to a temperature just above that at which the formation of hydrocarbon hydrates will occur at such pressure, passing the cooled gas countercurrently to an absorption menstruum and in direct contact therewith, cooling said gas in stages while it isin contact with such said menstruum, and finally, after the gas has completed contact with said menstruum,

' said tower, a draw-oil? line for said absorption menstruum at the bottom of said tower, a cooling cooling the gas still further to condense there- 15 from any absorption menstruum contained therein.

6. An apparatus for recovering distillate from high pressure gas comprising a tower, means for introducing the high pressure gas into the bottom of said tower, means for introducing an absorption menstruum into an intermediate point in zone arranged in said tower above the point of introduction of said absorption menstruum, and means for expanding the absorption menstruum recovered from said tower into said cooling zone.

' THOMAS V. MOOHJEL STUART E. BUCKLEY.

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