US2468750A - Method of separating hydrocarbons - Google Patents

Description

May 3, 1949. G. 1 GUDENRATH METHOD OF SEPARATING HYDROCARBONS 3 Sheets-Sheet 1 Filed May 12, 1945 IN V EN TOR.

M HZ 3 Sheets-Sheet 2 May 3, 1949- G. l.. GUDENRATH METHOD OF SEPARATING HYDROCARBONS Filed may 12, 1945 N .ma

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May f3, 1949. G. l.. GUDENRATH METHOD OF SEPARATING HYDROCARBONS 5 Sheets-Sheet 3 Filed May l2, 1945 do .5E

k mi WN do rui mm do 5mi. n .zo mu r|| llll IIIIIIIIL Patented May 3, 1949 UNITED sTATEs PATENT oFFicE- 2,468,750 METHOD or SEPARATING nYnRocARBoNs l George Louis Gudenrath, Houston, Tex., assignor to Hudson Engineering Corporation, Houston, Tex., a corporation of Texas Application May 12, 1945, serial No. 593,490

4 Claims.

A higher carbon atoms to the molecule, then raise the pressure of the remaining gas to the original well pressure and pump or cycle it back through the well into the rock formation.

At high pressures great difculty is encountered in separating methane from the other constituents Without leaving a relatively high percentage of ethane, propane and some butane in the gas after it has passed through the absorption system. Further the absorption oil often retains a relatively large amount of methane some of which is condensed with the heavier hydrocarbons and becomes a part of the hydrocarbon distillate to be fractioned. The partial pressure of methane makes the fractionation complicated and quite expensive. Ethane and propane are valuable products and it is desirable to recover them from a gas mixture containing a higher percentage of methane.

Most natural gas contains natural gasoline and is treated in absorption plants for the recovery of ethane, propane, butanes, pentanes and gasoline. Also the gases from petroleum distillation plants and oil cracking plants are treated in absorption and distillation units to separate the hydrocarbons containing C2 and higher carbon atoms to the molecule for the manufacture of fuel and chemical products.

The primary object of the present invention is to providea method of improving the selectivity of the recovery of heavier and more desirable hydrocarbons from gas with respect to the lighter less desirable hydrocarbons, such as methane or hydrocarbons having a high vapor pressure.

A further object of the present invention is to provide a method of effectively absorbing the hydrocarbons having more than one carbon atom to the molecule out of natural gas and effectively separating the methane from the absorption oil and the other absorbed hydrocarbons. v

Another object of the invention is to provide a method of absorbing hydrocarbons from gas and separating methane from the heavier hydrocarbons and menstruum without heating the absorbing menstruum or hydrocarbon'mixture.

A further object of the invention is to provide a method of absorbing hydrocarbons from gas in an oil menstruum while separating methane from the rich menstruum and obtaining the maximum recovery of ethane, and heavier hydrocarbons.

With these and other objects in View the invention consists in the method of absorbing hydrocarbons from gas in an absorption menstruum and separating methane therefrom, whichV is hereinafter described and particularly defined in the appended claims.

The various features of the invention are i1-` lustrated in the accompanying drawings in which Figure 1 is a diagrammatic flow sheet of an apparatus particularly adapted for absorbing the hydrocarbons from high pressure gas obtained in a recycling system in which condensateis recovered from the gas before the hydrocarbons of Figure 1 is adapted wherein the absorption can be effected in two diiTerent pressure stages.

Figure 3 is a diagrammatic ow sheet of an apparatus wherein the hydrocarbons may be absorbed in a menstruum under a pressure which is as low or lower than the pressure under which the menstruum may be distilled to separate the absorbed hydrocarbons and at the same time eliciently separating the methane from the menstruum and separated hydrocarbons; and

Figure 4 is a diagrammatic view of an apparatus in which a method of absorbing hydrocarbons simultaneously from a lean gas and a rich gas may be carried out while effectively separating methane from the absorbing menstruum and the separated hydrocarbons.

Throughout the specification and claims the hydrocarbons are referred to as C1, C2 and higher is introduced into the top of the tower through a line I8. The volume and temperature of the absorption oil is such that when the gas which may be at the high pressure existing at the well,

In absorbing the C2 and higher hydrocarbons the absorption oil becomes saturated with methane. It is important therefore that the methane be separated because methane is troublesome during the rich oil distillation and also during the fractionation to separate the individual hydrocarbons.

When the gas is being treated under high pressures from 1000 to 3000 lbs. per square inch, it is dimcult to reduce the pressure of the gas in a single stage and still effectively separate the methane and recover the C2 and higher hydrocarbons. Accordingly the rich oil from the bottom of absorption tower I6 passes through an expansion valve 24 and ilows through a line 26 into a ash tank 28. The hydrocarbon vapors which are separated in the tank 28 are composed of C1, C2 and higher hydrocarbons and flow through a line 38 into the lower portion of a reabsorption tower 32 and pass upwardly through a body of absorption oil which is introduced into the top of the reabsorber through a line 34. In the reabsorber substantially all of the C2 and higher hydrocarbons are absorbed in the oil and methane passes out through a line 36 and pressure reducing valve 38.

' Simultaneously with this operation the condensate from the separator I2 flows through a pressure reducing valve 48 and line 42 into a flash tank 44 where lower boiling hydrocarbon vapors are released. These vapors ow through a line 45 and join with the vapors in line 30 to pass into the bottom of the reabsorption tower 32.

The rich oil from the flash tank 28, which is saturated at its pressure with methane, passes through a line 46 and is introduced into the bottom of an absorption section of an absorber and concentrator tower 48. The pressure on the rich oil is reduced through a valve 58 so that the oil expands to relase C1, C2 and some heavier hydrocarbon vapors. The C2 and heavier hydrocarbon vapors are absorbed in an absorption oil which passes downwardly through the tower 48 after being introduced through a line 52.

Simultaneously with the introduction of rich oil from the tank 28 condensate from the tank 44 passes through a pressure reducing valve 54 and line 56 into an expansion tank 58 wherein the pressure is reduced to the pressure or slightly higher pressure than the pressure existing in the tower 48. The pressure existing in the tower 48 is comparatively low, that is for example from 50 to 200 lbs., and is such that the methane may be effectively removed from the absorption oil in the tower before the rich oil from the tower 48 is passed to a still for removing absorbed hydrocarbons from the rich oil. Rich oil leaves the bottom of reabsorber 32 through an'expansion valve 51 and iiows into the tower 48 through the line 46. The vapors separated in the tank 58 pass through a. line 68 to join with the rich oil passing through the line 46 and flow into the bottom of the absorption section of tower 48. The vapors from the rich oil and condensate pass upwardly through the tower 48 where substantially all the C2 and higher hydrocarbons are absorbed and substantially all the methane passes out from the top of the tower through a line 62 and` valve 64.

Since the rich oil and vapors introduced through the lines 46 and 68 may contain some methane it is important to remove this methane from the rich oil before the rich oil leaves the tower 48. To accomplish this the rich oil leaving the absorption section of tower 48 passes downwardly through a stripping section located below the inlet of the line 60. Near the bottom of the concentrating section hydrocarbon vapors con-v taining some C1 and substantial quantities of Czand higher hydrocarbons are introduced through a line 66. These vapors pass upwardly through the absorption oil and displace methane in this absorption oil with C2 and higher hydrocarbons and carry the methane upwardly through the tower 48. By the time the rich oll reaches the bottom of the stripper section at the bottom of the tower 48 substantially all of the methane has been removed. This rich oil is then drawn out through a pump 68 and circulated through a line 10 and heat interchanger 12 into a lich oil heater 14. The rich oil is heated to a suiliciently high temperature to vaporize the C2 and higher hydro'- carbons which are to be recovered and this rich oil is passed through a line 16 and flashed into the midportion of a rich oil rectifying still 18.

The rich oil rectifying still is preferably a bubble cap still which will permit the C2 land higher hydrocarbons to pass overhead and cut through a line 88 while causing the absorption oil to pass downwardly through the still. The C2 and higher hydrocarbons pass from the vapor line to a condenser 82 and the condensate is cllected in an accumulator 84. Part of the condensed hydrocarbons is circulated by pump 86 and line 88 up to the top of the still 18 to act as reflux. A

slightly higher pressure is maintained in the still 18 and accumulator 84 than is maintained in the absorber 48 to assist in separating C2 and higher boiling hydrocarbons from the absorption oil and to force C2 and higher boiling hydrocarbon vapors through the line |82 and into the tower 48.

When the condensate is flashed in the chamber 58 substantial amounts of the lower boiling hydrocarbons are removed therefrom and the remaining condensate passes from the tank through a line 98 up to the top of the bubble cap contactar at the top of the accumulator 84 to join the body of C2 and higher hydrocarbons in the accumulator. From the accumulator the hydrocarbon distillate may be removed through pump 92 and pass through a line to a. fractionating still where the individual hydrocarbons may be fractionally separated.

When the desired C2 and higher hydrocarbons are removed from the rich oil it becomes a lean oil which is Withdrawn from the bottom of the still 18 through a line 94 and passed through the heat exchanger 12, then through a cooler 96 from which it is carried by means of a pump 98 and forced through a line ill into the lines I8, 34 and 52 to supply lean absorption oil to the towers i6, 32 and 48,' respectively.

In the operation of the rectiiying still 18 some hydrocarbon vapors are formed and are separated from the distillate in the accumulator 84. These vapors which may contain a small amount of C1 but are composed principally of C2 and higher hydrocarbons, pass `outwardly through the contacter countercurrent to the condensate to a line |02 and constitute the vapors which are passed into the bottom of the stripping sectlon of tower 48 for the purpose of separating substantially all of the methane from the hydrocarbons passing through the contactor and tower 48.

In Figure 2 is illustrated an apparatus which is used for absorbing and separating hydrocarbons from a gas which may be under a lower pressure than the pressure of the gas which might be treated in the apparatus illustrated in Figure 1. 'This pressure may, for example, be from 200 to 600 lbs. per square inch. In this apparatus gas is introduced through a line |0 into an absorber I6 and passes upwardly through absorption oil introduced through a line I8. Methane separated from the gas passes out through a line 20 and valve 22. Rich oil from the bottom of the absorber I6 passes out through valve 24 and line 26, and flows through an inlet line 60 into the bottom of the absorption section of a combined absorber and concentrating tower 48. Condensate from the gas is drawn in through a line 42 and is flashed into a ash tank 44. The flashing operation removes substantially all of the C1 to C4 hydrocarbons, which vapors pass through a line 60 and join with the rich oil owing through. the line 26 into the tower 48. The distillate remaining in the tank 44, consisting of substantially all heavier hydrocarbons, is passed through a line 45 to the top of the bubble cap contactor tower on the top of the accumulator 84. In the bubble cap section the condensate is further distilled by the light vapors passing up through the section from the accumulator to remove lighter hydrocarbons.

The vapors released from the rich oil from absorber I6 by pressure reduction, and vapor from tank 44 pass upwardly through the tower where the C2 and higher hydrocarbons are absorbed and methane is released through a line 62 and valve 64. Lean absorber oil is introduced into the tower 48 through a line 52 and passes downwardly through the tower and a. stripping section. Near the bottom of the stripping or concentration section hydrocarbon vapors are introduced through a line 66 which vapors are composed principally of C2 and heavier hydrocarbons to displace the methane in the absorption oil and vapors passing through the tower 48. Rich oil which consists of a mixture of the enriched oil introduced through the line 52 and the rich oil from the absorber I6 pass out from the bottom of the tower 48 to a pump 68 and pass through a line `|0 and heat interchanger |2 into a rich oil heater '|4. The rich oil is distilled in a rectifying still 'I8 in the same manner as that described in connection with the distillation of rich oil in the apparatus of Figure 1. The distillate which accumulates in accumulator 84 may be passed through a pump 92 to a fractionating still to separate the individual hydrocarbons. Vapors composed principally of C2 and heavier hydrocarbons pass from the top of the accumulator 84 through a contactor to a line |02 into the inlet 68 for the purpose of displacing methane from the condensate and the absorption oil in the tower 48.

It is emphasized that the return of the C2 and higher hydrocarbons into the bottom of the combined absorber and concentrator acts Yto concentrate the propane and butane constituents which are recovered from the gas and at the same time displace the methane from the absorption oil. With most of the gasoline treating lhydrocarbons while separating the methane.

systems a substantial portion of propane and butane is removed with the methane from the absorbers, but with the apparatus and method herein described, a higher percentage of propane and butane may be recovered. Tests which have been made in the eld show that an average of ten to fifteen percent (and in some cases as high as fifty-eight percent) more ethane can be recovered than with the processes commonly in use. Further, an average of from three to ve percent (and in some cases more than eleven percent) more propane may be recovered than with the processes commonly used.

In Figure 3 is illustrated an apparatus which is well adapted for treating a gas for example of 50 to 400 lbs. for the recovery of C2 and higher In this case the gas introduced through line |0 flows into the bottom of an absorbing section of a combined absorber and concentrator tower 48. Lean oil is introduced into the top of the tower throug'h a line 52 and rich oil is removed from the bottom of the tower through a pump |04 by which it is forced through a heat interchanger `|2 and rich oil heater '|4. The absorption oil flows down through the tower 48 below the gas inlet and passes through a stripping section counter-current to a stream of hydrocarbon vapors introduced through an inlet 66 which are supplied to the inlet through a line |02. The rich oil is distilled in a still 18. The C2 and higher hydrocarbons are accumulated in accumulator 84. The vapors from the still and accumulator pass out through the line |02.

In Figure 4 is illustrated a type of combined absorber and concentrator which is well adapted for the purpose of treating two sources of gas, such as a lean natural gas and a rich natural gas, in order to recover the C2 and higher hydrocarbons and separate methane therefrom. The lean gas which is composed principally of methane and a relatively small amount of C2 and higher hydrocarbons is introduced into a combined absorber and concentrator |05 through a line |06 at the bottom of an absorber section of the tower |05. At the same time rich gas, which contains a smaller amount of methane and a relatively larger proportion of C2 and higher hydrocarbons than is contained in the lean gas, is introduced through a line |08 near the bottom of the stripping section of the tower |05. This gas passes upwardly through the stripping section to displace the methane and to concentrate the percentage of C2 and higher hydrocarbons in the rich oil passing downwardly through the tower |05. The methane is removed from the top of the tower through line ||0 and valve ||2 and rich oil is drawn out through a pump I4 by which it may be circulated through a line H6 to pass into an absorber and concentrator 48 to be treated in the tower 48 and still '|8, in the same manner that has been described in connection with the treatment of rich oil in Figures 1, 2 and 3.

The common practice for treating different types of natural gas which contain different amounts of C2 and higher hydrocarbons is to mix the gases and pass them into the bottom of an absorption tower. Comparative results in which an operation is carried out in which a lean and rich gas are mixed and passed through the bottom of the tower and the treatment of the same gas in the apparatus, such as illustrated in Figure 4, has shown the composition of the rich oil from the two types of operation:

Gases mixed Mixture Rich as, Leen gas, Rich oil, M01 24 M01/24 ,{ajg M01/24 Hr. Hr. H Hr.

C1 1, 125 23, 301 24, 427 759 C: 467 2, 676 2, 143 524 01-.. 494 1, 633 2, 127 1,077 104 89 311 400 380 N04 72 316 388 385 ICI. 14 91 105 105 NCI 10 74 84 84 C|+ 2 94 96 96 Lean Oil 7. 866

Total 2. 274 28, 496 30 770 11. 276

Gas separate as shown in Figure 4 An important feature of the present invention resides in the separation of methane from other hydrocarbons in the gas and the concentrations of light constituents, such as propane and butane, in the hydrocarbons being absorbed from the gas. For each mol of methane removed from a fractionator feed approximately fteen mols of propane or ve mois of ethane can be added to the vapor without changing the vapor pressure of the fractionator feed. It will be seen, therefore, how important it is to remove even small quantities of methane and to replace it with ethane and higher hydrocarbons thus materially increasing the recovery of the C2 and higher hydrocarbons.

It will be noted also that the methane is eilectively separated from the other hydrocarbons of the gas and from the absorption oil without the use of heat or stripping steam. The stripping of methane, from an absorption oil at low temperatures is much more selective than when treating an absorption oil which has been heated.

Furthermore the use of the combined absorber and concentrator permits the stripping of the methane from the absorption oil and gas without as many pressure reducing stages or reabsorbers as is customarily used for this purpose in commercial practice.

Tests have shown, furthermore, that a lesser amount (up to ten percent less) of lean oil is required for absorbing the hydrocarbons from gas with the present invention than with the most eflicient absorption system which has heretofore been used.

Although the combined absorber and concentrator 48 has been illustrated and described as a. single tower, it is obvious that the combined unit could be made up as absorber unit and a separate stripping unit wherein the gas would ow upwardly and the oil would ow downwardly first through the absorber unit and then through the stripping unit.

In the claims reference is made to the removal of C1 hydrocarbons from the top of the absorber and concentrator. It is to be understood that hydrogen and non-condensible gases, such as C0, CO2 and nitrogen, will be removed with the methane if they are present. It is also to be understood that in commercial operatior of absorption and distillation equipment it is not practicable to separate all methane from the heavier hydrocarbons without leaving a small amount of hydrocarbons, such as ethane and propane with the methane. With the present invention the amount of C2 and Cs hydrocarbons leaving the absorbers with the methane is comparatively a very small amount.

The C2 and heavier hydrocarbons introduced into the base of the stripper, as referred to in the claims, are vapors recovered from the distillation of a hydrocarbon mixture, said mixture having previously had the methane separated therefrom. The still 18 and accumulator 84 generally contain small amounts of methane and are operated so as to pass C2 and heavier hydrocarbons from the accumulator and up through the bubble cap section to remove C1 and other xed gas from the condensate and hydrocarbon distillate in the accumulator. These C2 and heavier hydrocarbons may therefore contain a comparatively small amount of methane and fixed gas in it which will be separated in the absorber and concentrator 48.

The preferred form of the invention having been thus described, what is claimed as new is:

1. The method of separating C2 and higher hydrocarbons from high pressure gas comprising separating a condensate by retrograde condensation from the gas, passing the uncondensed gas into the bottom of an absorption tower and upwardly through an absorption oil passing down through the tower, removing substantially only Ci hydrocarbon from the top of the tower, removing a rich oil from the bottom of the tower, reducing the pressure on the rich oil and passing it into the bottom of an absorption section of a second tower, passing absorption oil downwardly through the second tower to /join the rich oil from the first absorption tower, passing the resulting mixture of absorption oils downwardly through a stripping section of the second tower, introducing near the bottom of the stripping section hydrocarbon vapors composed principally of C2 and higher hydrocarbons and passing the vapors upwardly through the tower, removing substantially only C1 hydrocarbon from the top of the second tower, ashing the condensate with pressure reduction down to the pressure existing in the second absorption tower, passing vapors released from the condensate by the flashing operation into the second tower with the rich oil from the iirst tower, removing the rich oil mixture from the stripping section and distilling it to recover C2 and higher hydrocarbons overhead, partially condensing said overhead to produce a distillate and a lower boiling point vaporous fraction, passing said vaporous fraction into contact with the ashed unvaporized condensate to displace low boiling hydrocarbons therefrom and to obtain said vapors composed principally of C2 and higher hydrocarbons which are introduced into the stripping section of the second tower.

2. The method of separating Cz and higher hydrocarbons from high pressure gas comprising: separating a condensate by retrograde condensation from the gas, passing the uncondensed gas into the bottom of an absorption tower and upwardly through an absorption oil passing down through the tower, removing substantially only C1 hydrocarbon from the top of the tower, removing a rich oil from the bottom of the tower,

flashing the rich oil under reduced pressure in an expansion chamber, separating vapors formed by the ashing and passing them through an absorption oil of an intermediate absorption stage under the pressure prevailing in the expansion chamber, removing C1 hydrocarbon from the intermediate absorption stage, passing rich oil from the expansion chamber under reduced pressure into the bottom of an absorption section of a third tower, passing rich oil from the intermediate stage under the pressure prevailing in the third tower into the rich oil from the expansion chamber owing into the third tower, passing absorption oil downwardly through the third tower to join the rich oil from the expension chamber and intermediate stage, passing the resulting mixture of absorption oils downwardly through a stripping section of the third tower, introducing near the bottom of the stripping section hydrocarbon vapors composed principally of C2 and higher hydrocarbons and passing the vapors upwardly through the tower, removing substantially only C1 hydrocarbon from the top of the third tower, ashing the condensate with pressure reduction down to the pressure existing in the third tower, passing vapors released from the condensate by the flashing operation into the third tower with the flashed rich oil from the rst tower, removing the rich oil mixture from the stripping section and distilling it to recover C2 and higher hydrocarbons overhead, partially condensing said overhead to produce a distillate and a lower boiling vaporous fraction, passing said vaporous fraction into contact with the ashed condensate to displace low boiling hydrocarbons therefrom and obtain said vapors composed principally of C2 and higher hydrocarbons which are introduced into the stripping section of the second tower.

3. The method of separating C2 and higher hydrocarbons from high pressure gas comprising: separating a condensate by retrograde condensation from the gas, passing the uncondensed gas into the bottom of an absorption tower and upwardly through an absorption oil passing down through the tower, removing substantially only C1 hydrocarbon from the top of the tower, removing a rich oil from the bottom of the tower, ashing the rich oil into reduced pressure in an expansion chamber, separating vapors formed by the ashing and passing them through an absorption oil in an intermediate absorption stage under the pressure prevailing in the expansion chamber, removing C1 hydrocarbon from the intermediate absorption stage, passing rich oil from the expansion chamber under a reduced pressure into the bottom of an absorption section of a third tower, passing rich oil from the intermediate stage under the pressure prevailing in the third tower into the rich oil from the expansion chamber entering the second tower, flashing the condensate with pressure reduction to the pressure existing in the intermediate stage, separating vapors from the flashed condensate and passing them through the absorption oil of the intermediate stage, again reducing the pressure on the condensate to the pressure in the third tower to vaporize lighter constituents in the condensate, passing the vapors of lighter constituents into the bottom of the absorption section of the third tower, passing absorptionr oll downwardly through the i therefrom,

through a stripping section of the third tower, introducing near the bottom of the stripping section hydrocarbon vapors composed principally of C2 and higher hydrocarbons and passing the vapors upwardly through the tower, removing substantially only C1 hydrocarbon from the top of the third tower, removing rich oil mixture from the stripping section, and distilling it to recover Cz and higher hydrocarbons overhead, partially condensing said overhead to produce a distillate and a lower boiling vaporous fraction, passing said vaporous fraction into contact with the flashed condensate from the second ashing operation to displace low boiling hydrocarbons therefrom and obtain said vapors composed principally of C2 and higher hydrocarbons which are introduced into the stripping section of the said third tower.

4. A process of recovering C2 and higher hydrocarbons from high pressure gas containing methane comprising: separating a hydrocarbon condensate from the gas by retrograde condensation, passing the remaining gas through an absorber to absorb C2 and higher hydrocarbons in an absorption oil, withdrawing methane from the absorber, reducing the pressure of the enriched absorption oil and passing it into an intermediate portion of a second absorber having absorption oil passing therethrough, withdrawing methane from the top of the second absorber, flashing the condensate with pressure reduction to the pressure prevailing in the second absorber to release low boiling hydrocarbon gas and vapors introducing the released gas and vapors into said second absorber at an intermediate portion thereof, rectifying rich oil withdrawn from the bottom of the second absorber to recover C2 and higher hydrocarbons overhead, partially condensing said overhead to produce distillate and a low boiling vaporous fraction, passing said vaporous fraction directly into contact with the ashed condensate to displace low boiling hydrocarbons therefrom, mixing the scrubbed condensate directly with said distillate and introducing said low boiling vaporous fraction into the bottom of said second absorber and passing it upwardly therethrough.

GEORGE LOUIS GUDENRATH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,789,470 Loomis Jan. 20, 1931 1,953,043 Cole et al Mar. 27, 1934 2,217,429 Balcar Oct. 8, 1940 2,237,386 Carney Apr. 8, 1941 2,249,885 Carney July 22, 1941 2,250,716 Legatski July 29, 1941 2,265,845 Kuhl Dec. 9, 1941 2,288,453 Hill June 30, 1942 2,290,957 Hachmuth July 28, 1942 2,337,254 Legatski et al Dec. 21, 1943 2,345,934 Gregory Apr. 4, 1944 2,386,057 Noble Oct. 2, 1945 2,388,732 Finsterbusch Nov. 13, 1945 2,409,691 Noble Oct. 22, 1946 2,413,503 Katz Dec. 31, 1946 OTHER REFERENCES Harts: "Oil and Gas Journal. Oct. 29. 1942, pages 59 to 61. 196-8.

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