US2388102A - Distillate production - Google Patents

Description

F. S. WEST DISTILLATE PRODUCTION Filed Sept. 4, 1942 .Sus ...n- So 2 :0.2513 :95513 9.25.5 1v on 2:1 283 .SEL 2 Oct. 30, 1945.

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l Patented Oct. 3 0, `1.945

UNITED STATESv vPATl.:NT oFFicE DISTILLATE PRODUCTION Frankl S. West, Houston, Tex., assigner to The' Texas Company, tion of Delaware New York, N. Y., a corpora- Application September 4, 1942, SerialNo.l457,280

l 1 Claim.

This invention relates to aprocess for the-production of desiredliqueable hydrocarbons from the -fiuids nowed from a well tapping a high pressure formation of the distillate type: More par.`

ticularly the invention relates to a process for the production of a`distillate field, wherein desired liqueiiable hydrocarbons are recovered by a procedure involving absorption, and residual gases are returned to the same or a diierent formation for the purpose of maintaining pressures.

Various types of processes have been employed .and proposed for the production of the so-called distillate or `condensate fields. Because of the necessity for returning residual gases to-a formation for maintaining pressures, these processes have been designed in one way or another to conserve energy so as to be able to return the gases at a minimum compression cost. Some of the processes have employed an absorption step and in these cases, particularly where the absorption is carried out' at a relatively high pressure, the amountof oil which must be circulated in the processes has been recognized as being an important factor in the success of the processes. t `It is known that the hydrocarbons in adistillate formation exist substantially as a homogeneous gas phase at high pressures and temperatures. .The formation pressures may range from 3000 to 5000 pounds per square inchor higher.

, Also, so far. as known, in the typical distillate formation the conditions oi temperature and pressure are such as to be at or near the dew point for the composition of the uid, or, stated in another way, the conditions are near the dew4 any substantial reduction in pressure will cause In many fields the rate of iiow 4from the producing wells ,is such that when the reduction in l pressure due to friction is added to that resulting from the static head of the fluid in the wells, a large reduction in pressure occurs from the formation to the well-head. This, with the consequent reduction in temperature may cause the condensation at the well-head of 50 per cent to 80 per cent or even more of the llqueilable hydrocarbons in the fluid.

The material actually producedl therefore, is a mixed iluid containing a gas phase and a liquid phase, the latter apparently being in the form of small droplets or a mist. Y Ihe liquidY condensed under these conditions is composed of a large proportion of normally liquid hydrocarbons but point curve of the two-phase boundary for the fluid on the pressure-temperature plane. Thus,

(ci. 18a-114.6)

also contains a substantial proportion oi' light gases, including ethane and methane, which are not desired in the recovered liquid hydrocarbons. Incidentally, it will be understood that in'producing a distillate field the liqueiiable hydrocarbons that will be recovered will depend upon economic considerations. In some cases, the recovery process will be operated so as to recover only a part of the butanes together with the pentanes and heavier. `In other cases, the propanes may have a ready market and the process will` be designed and operated so as to recover a.

maximum amount of the propanes and heavier.

It is an object of the invention to provide an improved process for the production of distillate characterized in that an efficient recovery of desired liqueable hydrocarbons is accomplished with a minimum expenditure oi energy. v

` Other objects of the invention in part will be obvious and in part will appear hereinafter.

The present invention is particularly concerned with a process for the production of distillate wherein a substantial proportion of the liqueable hydrocarbons are condensed because of a reduction in pressure Yand temperature such as occurs due to the flow of the fluid from the formation to the plant, the remaining gases are subjected to absorption to separate additional liquefiable hydrocarbons, and the residual gases are returned to a formation, preferably after compression,

for the purpose of maintaining formation pres- 'undesired light hydrocarbons. This reduction in pressure is accomplished in, stages in which certain pressures are maintained depending upon the characteristics of the condensed liquid hydrocarbons and the liquefiable hydrocarbons which itis desired to recover. For example, where the condensed liquid hydrocarbons are separated at Y. a pressure of about 2000 `pounds per square inch the pressure on the liquids may be reduced in two stages, the pressure in the first stage being l maintained at a'point somewhere between about 400 and 1000v pounds/ per square inch and the next stage being maintained at a pressure below 100 pounds per square inch, for example, between about 40 and 80 pounds per square inch.

It has been proposed in processes of this general type to recover desired liqueflable hydrocarbons from the hydrocarbonsY vaporized in the pressure reduction steps at a relatively low pressure below 100 pounds per square inch.V In.` this case the residual gases would be obtained at such a low pressure as not to be usable for return to the formation because of the high compression costs involved.

I have discovered in accordance with the pres'- ent invention that by compressing the evolved hy drocarbons removed from the first pressure reduction stage or stages to the pressure maintained in the high pressure absorption step, and passing these evolved hydrocarbons, together with gases separated from the condensed liquid hydrocarbonsin the separation stage, through the absorption stage important advantages with4 respect to the amount of oil required to be circulated for absorption and also the precentage recovery of ,desired liquid hydrocarbons are obtained. I have also discovered that important` advantages are obtained by reducing the pressure on the enriched more fully reference should be had to the accompanying drawing which contains a ilow sheet illustrating one manner of carrying out the process of the present invention. In order to simplify the description and also in order to illustrate a preferred application thereof, the invention will be described in connection vwith the treatment of a distillate iiuid removed from a relatively high pressure fomation, of the order of 4000. to5000 pounds `per square inch, wherein the absorption is carried out at a pressure above 1500 pounds per square inch, such as between 1500 and 2500 pounds per square inch, a pressure of about 2000 pounds per square inch being typical.

Referring to the drawing, a. distillate fluid is removed from an output well A, which taps a distillate formation, and the fluid is passed through a valved line I leading to a first sepa-- rator-I2.l As discussed above, distillate fluids normally are under such conditions of temperature and pressure in the formation that the rediuc.

' tion in pressure and temperature resulting from the ow of theI fluid to the Well head is sumcient to cause the condensation 'of a substantial pro-4 portion of the liqueable hydrocarbons contained in the fluid. Thus, the material ilowing in line- I0 will consist of a gas phase containing drOP- lets of condensed hydrocarbons.

In the first separator I2 the condensed hydrocarbons are substantially entirely removed from the remaining gases. lTo aid in this, the separator I2 may be provided with bafiies or other means, not shown, adapted to accomplish this lremoval. The gases are removed from this separator through a valved line I4 leading to the lower portion of a high pressure absorber I6. Tothe gases iiowing in line-14,. additional gases .are

added from line I8, as will presently be described.

In the absorber I8 the gases come countercurrent contact with an absorption oil introduced 'through line 22 and substantially complete reabsorption oil leaving theabsorption step to a covery of remaining desired liqueable hydrocarbons is accomplished. The residual gases are removed through line 24 and are raised in pressure by means of compressor 28 to a high pressure for maintaining pressure in a formation At the raised pressure, they are passed through line 28 leading to an input well B, through which they are passed to the desired formation.

The liquid collecting in the separator I2 is removed therefrom throughvalved line 32 which leads to a second separator 34. In this embodiment of the invention, the ilrst separator may be maintainedat about the pressure of the later absorption, for example, a pressure between 1500 and 2500 pounds per square inch or higher, depending upon the well-head pressure, the pressure of absorption, and the composition of the distillate iluid. The second separator is preferably maintained at some pressure below 1000 pounds. Under these conditions hydrocarbons are evolved and are removed through valved line 38. Although these hydrocarbons contain a substantial proportion of methane and ethane they also contain considerable amounts of recoverable liqueiiable hydrocarbons. In 'accordance with the invention, these hydrocarbons are passed through line 3'8 leading to compressor 40 and the pressure on them is raised to the pressure maintained in absorber I6. At this pressure, the gases are passed through lines I8 and Il and into the absorber where the liqueiiable hydrocarbons are recovered. Also, the light gasescontained in the hydrocarbons removed in the second separator become a part of the residual gases which are economically returned, to the formation through input well B.

The liquid hydrocarbons are removed from the second separator 34 through line 42 leading to a lthird separator 44 which may be maintained at some relatively low pressure of the order of 40 to 80 pounds per square inch. The hydrocarbon vapors evolved in this separator rare `removed through valved line I8 leading to the bottom portion of a low pressure absorber ll. The liquid hydrocarbons in condition for storage vare removed from separator M through valved line 50 and passed to storage. A small proportion of these hydrocarbons may be passed .through line 52 and employed for a purpose that will be referred to later.

`The enriched absorption oil h removed from the bottom portion of high pressure absorber. through valved line Il, leading to a vent tank Il which is maintained at some pressure below 1000 pounds and preferably at about the same pressure as second separator ll. At this reduced pressure, hydrocarbon vapors are evolved in vent f tank it and are removed through valved line It.

These hydrocarbons contain a proportion of liqueilable hydrocarbons and are preferably passed through line 38 with the. hydrocarbon vapors from the second separator Il and are compressed and introduced into the bottom o! A the absorber at absorption pressure.

The remaining liquid is removed from vent tank 56 through line 00 and introduced into the bottom portion of low pressure absorber Il. Since the' pressure in the low pressure absorber maybe about .40 to pounds per square inch,

additional hydrocarbons are evolved and are' contacted with the absorption oil introduced into this absorber through line I2. Thus, in this low pressure absorber liqueflable hydrocarbons are removed from the gases released from the con-f densed liquid in the third separator M and from the gases released from the enriched absorption oil entering the bottom of the low pressure absorber. The lean gases are removedfrom the low pressure absorber through valved line 64, the

process preferably being carried out so that the amount of gases obtained at this point is not substantially greater'than the amount required for plant fuel.

The enriched absorption oil is removed from -the'lowpressure absorber through line 66 and is l passed Ainto a low pressure vent tank 61, which may be maintained at a very low pressure of the order of to 15 pounds per .square inch. `Gases may be vented from this tank through a valved line 68 and also used for fuel. The portion of the liquid-hydrocarbons which is passed through line 52 is preferably introduced irto this vent tank and used as make-up for theabsorption oil.

The enriched absorption oil is pumped through valved line B9 provided with pump 10 Vand passes ,through heat exchanger 1l and heater 12, which serve to raise the temperature of the enriched absorption oil to a sufficiently high temperature for distillation. 'I'he heated oil is introduced into a still 13 which may be maintained at a pressure of the order of about60 pounds per square inch. In this still light liqueable hydrocarbons boiling, say, below 320 F. are vaporized and removed overhead through line 14. The vapors are then'condensed in condenser 15 and passed to storage through line 16.

The oil is. removed from this still through valved line 11 and is passed into a second, lower pressure still 18. In the 'latter still the remaining absorbed hydrocarbons are largely removed from'the absorption oil, lalthough a portion of the higher boiling compounds may remain therein. The vaporized hydrocarbons are re moved overhead through line 19, condensedin condenser 88 and passed to storage through line 8|. The leanl oil is removed from the bottom of still 18 through line A82 and ispumped by means of pump 83 to heat exchanger 1I where the heat contained in the lean oil is employed for heating i material reduction the amount of absorption oil required to be circulated can be accomplished by compressing the evolved hydrocarbons in the pressure reduction stage and subjecting these to absorption in the high pressure absorber. Additional reduction in the amount of absorption Aoil required to be circulated is accomplished by also compressing the evolved hydrocarbons from `the vent tank into which the enriched absorption y oil leaving the high pressure absorber is passed.

Other features of the invention, which are preferably combined with those described, are the -introductign of the enriched absorption oil from the high pressure vent tank into the low pressure absorber, the absorption of thel evolved hydrocarbons from the low pressure separator in the low pressure absorber, and the use of a portion of the condensed hydrocarbons as make-up for the absorption oil. In connection with the use of a portion of the hydrocarbons condensed due to the reductionin pressure as the absorption oil, itis pointed out that these hydrocarbons constitute the heavier liqueflable hydrocarbons contained in the distillate uid and are higher boiling than the bulk of the liqueablehydrocarbons present in the gas phase of the fluid.

the enriched oil going to the stills, while the lean y oil is partially cooled to absorption temperature.

The lean oil is then passed through line 84 and is cooled in cooler 85 to the temperature desired for absorption; for example, to a temperature below 100 F. A portion of this oil passes through line 82 into the upper portion of the low pressure absorber as described above,A while the remain- 4der is raised to the pressure existing in the highpressure absorber by means of Pump 86, and at this pressure is passed `.through line 22 leading into the high pressure absorber.

In order to avoid the accumulation of tarry materials and other impurities in the absorption oil, avportion of the oil lmaybe removed periodically or continuously from the lean oil flowing in line 82 `through line 81. This line leads to areclamation system 88 where impurities are removed from the oil. The cleaned increment of oilA is then returned to the process through line 89.

The process described above is particularly valuable in cases where the rst separator and the high pressure vabsorber are maintained at y pressures of about '1500 to 2500 pounds per square inch, especially 2000 to 2500 pounds per square inch' or higher, and it is desirable to maintain a stage of reduced pressure on the condensed liquid of from 400 to r100 pounds per square inch. Under these conditions it hasbeen found that a appended claim.

The process described can be employed eiliciently for therecovery of liqueable hydrocarbons from a distillate fluid having the composition shown in the following table: y i

come

Methane 0. 74056 Ethane- 0. 073737 Propane 0. 046921 Ischnrrmn Q 009764 n-Bifen 0. 019817 Isopentane 0. 007244 n-Pentane. 0. 007564 Hexanes and heavier .1 0. 081557 Carbon dioxide 0. 006824 This duid apparently exists as a homogeneous phase at a pressure of about 4700 poundsper f square inch in the formation, and may be produced lat a pressure of about 2200 pounds per square inch at the well-head. lin` the treatment of this fluid, the first separator and high pressureabsorber may be maintained at about 2000 pounds per square inch, the second separator and the enriched oil vent tank at about 400 to 700 pounds per square inch, and the, third separator and the low pressure absorber at about 40 to 80 pounds per square inch.` Under these conditions,

liqueflable hydrocarbons are recovered efficiently with a circulation of a minimum amount of absorption oil and return to the formation of a. maximum amount of light hydrocarbons at low compression costs. Also, the liquid hydrocarbons of the invention, as hereinbefore set forth, may bevmade without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in fgthe I claim:

A process of recovering liqueiiable hydrocarbons from distillate well iiuids produced at a high wellhead pressure and temperature such that the fluids are composed of a liquid phase and a gas phase, which comprises separating `said liquid phase and said gas phase at an elevated pressure of about 2000 pounds per square inch, reducing the pressure on said liquid phase in successive stages maintained at about 40d to '100 pounds per square inch and about 40 to 80 pounds per square inch to evolve hydrocarbon vapors comprising liqueiiable hydrocarbons in each stage, and produce a liquid fraction, compressing the hydrocarbon vapors evolved in said stage at about 400 to 700 lpounds per square inch to a pressure of about 2000 pounds per square inchpassing said compressed vapors and the gases constituting the gas phase into contact under l'absorption conditions with an absorption oil composed of hydrocarbons of saidc liquid fraction ata pressure of about 2000 pounds per square inch to absorb liquefiable hydrocarbons therefrom and produce an enriched absorption oil, reducing the pressure on the enriched absorption oil in successive stages maintained at about 400 to '100 pounds per square inch and about 40 to 80 pounds per square inch to evolve hydrocarbon vapors comprising liqueilable hydrocarbons in each stage, `compressing the vapors evolved in the stage maintained at about 400 to 700 pounds per square inch to a pressure of about 2000 pounds per square inch, contacting the last-mentioned vapors with said absorption oil under absorption conditions to remove liquefiable hydrocarbons therefrom, con--` tacting the vapors evolved from said liquidyfraction and from said enriched absorption oil in said stages maintained at about 40 to 80 pounds per square inch with an absorption oil under absorption conditions at a pressure of about 40 to 80 pounds per square inch to absorb liqueilable hydrocarbons from said vapors and produce an en-v riched absorption oil, and 1recovering absorbed hydrocarbons from said enriched absorption oil.

y v FRANK s. Wrisr,

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