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April 3, 1962 3,028,332 H. FORBES ETAL LIQUID RECOVERY FROM AN ORIGINALLY VAPOROUS MIXTURE Filed June 15, 1959 X X 52 \ r53 46 47 33 ll 50 / 49 /32 /43 TEX“. 34 45% k 55 1 INVENTORS: GODFRIED J.VAN DEN BERG HENRY FORBES HUBRECHT VAN DER MAREL THEIR ATTORNEY 3,028,332 S?ltes Patent Patented Apr. 3, 1962 1 2 3,028,332 tially separated or a fraction from that liquid obtained VAPOROUS MIXTURE Henry Forbes, Huhrecht van der Marc], and Godfried The conjoint liberation of the relatively light compo nents from the pressurized gaseous and liquid portions may, for instance, be brought about by treating the two portions together (premix or otherwise) in a distillation column with the light components being removed over, head. In this instance the gaseous portion may, if de LIQUID RECOVERY FROM AN ORIGINALLY J. van den Berg, The Hague, Netherlands, assignors to Shell 0i] Company, New York, N.Y., a corporation of Delaware 7 Filed June 15, 1959, §er. No. 820,517 Claims priority, application Netherlands Oct. 7, 1958 9 Claims. (Cl. 208-340) This invention provides an improvement in the process say in a later distillation. sired, be introduced into the distillation column on a tray 10 which is higher than the one on which the liquid portion is introduced. It is, however, often advisable to mix the two pressurized portions and then to liberate the light involving pressurization of an originally vaporous hydro components therefrom by subsequent cooling of the re carbon mixture, containing normally gaseous components, sultant mixture to promote condensation, after which to recover further liquid therefrom, which improvement permits a signi?cant reduction in the total compression 15 the mixture is passed to a separator wherein it is sepa rated into gas and liquid. The separated liquid is prefer work required for the operation. It is conventional practice in the processing of a va ably further treated in a distillation to remove additional porous hydrocarbon stream, containing normally gaseous light components therefrom, yielding a heavy liquid frac components, to pressurize the stream to increase liquid tion which may be combined with the original vaporous recovery therefrom. The stream may be ?rst cooled to 20 mixture, or it may be deemed more feasible to pass the bring about a condensation, following which the stream is separated into a gaseous portion and a liquid portion. The individual portions are then separately pressurized heavy liquid fraction to another fractionation to obtain to substantially the same elevated pressure and then re vaporous hydrocarbon stream undergoing treatment at a a still more heavier material for the recycling. Preferably, the recycled liquid portion is added to the combined for further processing. There is an economic 25 point preceding the cooling of that stream, although it may be combined with the cooled stream before its sep advantage in separately pressurizing the two portions. aration into its vaporous and liquid portion and prior to Processing schemes of this general nature are used in their separate pressurizations. re?nery gas recovery and for gasoline stabilization in The vaporous stream undergoing treatment may be the some instances. A process of this general type is described in Petroleum Re?ner, page 232, September 1949. It is an object of the invention to provide an improve ment in the process of pressurizing an original vaporous top product of a primary distillation operated at approxi~ mately atmospheric pressure. The feed to the primary distillation column may, for instance, be a hydrocarbon mixture relatively rich in light components (such as hydro hydrocarbon mixture and more particularly to provide an gen and methane) which is therefore di?icult to con improved process reducing the amount of work required in pressurization. This and other objects will become 35 dense; such hydrocarbon mixtures include the effluent from a reforming unit or from a hydrodesulfurization more apparent in the following description of the process, treatment. taken in conjunction with the drawing which is a sche In a preferred embodiment of the process the top prod matic representation of a preferred embodiment of the uct will be a gasoline range material containing lighter improved process. It has now been discovered that in the processing of a 40 components from an atmospheric primary distillation. This top product prior to cooling is combined with a re vaporous hydrocarbon stream, containing normally gas cycle heavy gasoline (naphtha), then cooled and passed eous components, to increase the liquid recovery there to a separator maintained say at 1.1 atmospheres and from, that it is advantageous to recycle a portion of the around 45° C. There the liquid and gas phases separate recovered liquid to the vaporous hydrocarbon stream un and are separately removed, pressurized and subsequently dergoing treatment. In the improved process the stream recombined, passed to a second cooler to obtain further is cooled to bring about a condensation, following which condensation, and then to a second separator maintained it is separated into a gaseous portion and a liquid portion at say, 5 atmospheres and 40° C. A gaseous stream con and the individual portions are then separately pressurized taining principally non-condensibles is removed from this to substantially the same elevated pressure. Following latter separator. The liquid recovered in this second 50 pressurization, light components are conjointly liberated separator is moved to a secondary distillation (a dc from the two pressurized portions to obtain a liquid frac butanizer) where the butane and remaining lighter com tion. A portion of this liquid fraction is returned to the ponents are distilled overhead. This column may operate vaporous hydrocarbon stream at a point preceding its at around 12 atmospheres. The liquid gasoline product separation into the gaseous and liquid portions. The re from the base of the debutanizer goes to a fractionation 55 cycling of the portion of the recovered liquid in this man column where it is separated into a top product boiling ner will signi?cantly reduce the total compression work below say 93° C. and a bottom product having the boil required for the pressurization of the two separate por ing range of approximately 93° C. to 165° C. A por tion of this bottom product is now recycled according to tions. The term pressurizing and the like is employed to mean 60 the invention to combine with the top product from the raising the pressure to which the vaporous mixture is primary distillation column at a point preferably preced under in the initial stage of the process which original ing its initial partial condensation. As a result of the pressure may be atmospheric, superatmospheric, or sub recycle the compression work to be exerted on the liquid atmospheric. The recycled or returned portion of the portion is admittedly slightly increased, but that on the recovered liquid may be a portion of the ?rst liquid ini 65 gaseous portion is greatly reduced. Since from an eco 8,028,332 3 nornic point of view it is much more attractive to pres surize a liquid instead of a gas, the practice of the process of the invention results in a considerable reduction of the 4 system. The liquid separating out in the accumulator 24 is removed via line 27 and is forced under the pressure of a pump 28 to a central section of a secondary distilla tion column 29 where it is separated into a butane-free gasoline and an overhead fraction containing butane and the two portions. lower boiling components. The secondary distillation When it is desired to change the cutting point in the column operates under a pressure of approximately 12 primary column (for instance, when a change is necessary atmospheres. The heat needed for the column is sup to the preparation of a product answering di?erent speci plied by a reboiler 30. The butane-free gasoline bottom ?cations), the quantity of the recycled liquid fraction which is combined with the primary top product should 10 product is removed from the column in a line 31 to a fractionation column 32 where it is separated into a light be accordingly varied to hold the gas-compression work gasoline discharge overhead through a line 33 and into a substantially constant, thus permitting the gas compressor total compression work required in the pressurization of heavy gasoline (naphtha) which is withdrawn through a to operate (with changes in the primary distillation cutting line 34. A reboiler 35 supplies the heat required for the points) at a capacity approaching the optimum. For instance, if the cutting point in the primary column is 15 operation of this column. The top product of the second distillation column 29 varied to take overhead a larger proportion of heavier is withdrawn through a line 37, cooled in a cooler 38 and material, the amount of recycle required will be less. It is recommended that the amount of recycle material em— collected in an accumulator 39. The accumulator is operated under a pressure of 12 atmospheres absolute ployed be such that the total quantity of debutanized gasoline removed from the secondary distillation column 20 and at a temperature of approximately 45 ° C. A portion of the liquid collecting in the accumulator is returned via remains substantially constant with variations in the cut a line 40 as re?ux to the top of the second distillation ting point of the primary column. In the instance where column. The rest of the liquid is removed from the the debutanized gasoline is passed to a subsequent frac accumulator in a line 41 and forced under the pressure tionation where it is separated into a light gasoline and a heavy gasoline product, and a portion of the heavy 25 of a pump 42 to the central section of a distillation col umn 43. In the latter column the material is separated gasoline is used as the recycle material, the quantity of into C; hydrocarbons on the one hand and lower boiling the recycle and the quantity of heavy gasoline actually components on the other. The C4 fractions are dis withdrawn as product should give a total that remains charged from the column through a bottom line 45 and substantially constant at di?erent primary cutting points. This practice will result, it will be seen, in the amount of 30 the top product is removed via an overhead line 46, to a cooler 47 and an accumulator 48. In the accumulator debutanized gasoline being maintained at substantially a liquid substantially consisting of propane separates constant volume. which is withdrawn through a line 49 and partially re The invention will now‘be further explained with refer turned through a line 50 as re?ux to the distillation ence to the accompanying drawing, which relates to the use of the process of the invention in working up a hydro 35 column 43. The pressure in the distillation column 43 and the accumulator 48 is approximately 24 atmospheres carbon oil having a relatively high content of normally absolute. The temperature in the accumulator is about gaseous components. The term gases as used herein 45° C. includes vapors. The hydrocarbon stream is introduced The uncondensed gases gathering in the accumulators through a line 10 to an atmospheric primary distillation column '12 which is operated with a cutting point at 40 39 and 48 are discharged through the lines 52 and 53, respectively, which are provided with the necessary re 165° C. to separate overhead a light fraction containing ducing valves. .gasoline and lighter components and a heavier bottom According to the present invention, a portion of the fraction composed of kerosene and gas oil. The heavy fraction is removed from the distillation column through a line 14. In the present instance circulating re?ux is ‘supplied to the column via a line 60 opening into the top naphtha fraction withdrawn through the line 34 is recycled via a line 55 to the top product line 13 at a point preced ing the cooler 15. The recycled naphtha may be mixed with the top ‘product beyond the cooler 15 at a point pre ceding the gas compressor and pump, although it is pref erably combined with the top product stream before the ‘the column through a line 13 to a partial condenser 15 and then to an accumulator 16. The accumulator is 60 ‘cooler. EXAMPLE operated under a pressure of 1.1 atmospheres absolute with a temperature of approximately 45° C. In the A crude oil is separated by distillation into a fraction cooler 15 there occurs only a partial condensation, with boiling below 350° C. and a fraction boiling above 350° the result that a partly gaseous and partly liquid product C. The former fraction is subjected to a hydrodesulfuri is collected in the accumulator. A liquid product is 55 zation treatment in which a cobalt oxide-molybdenum removed from the bottom of the accumulator through a oxide-alumina catalyst is used. After cooling the reac line 17, while the gaseous product is led through a line 18 tion product is subjected to an expansion in stages to ‘to a gas compressor 19. The liquid ?owing in line 17 is separate the bulk of the dissolved gases and vapors. compressed by a pump 21 to substantially the same pres The liquid ?nally obtained (486 tons per 1000 tons of ‘sure as the pressurized gas leaving the compressor 19 in crude oil), in which small quantities of light components line 20. The two pressurized streams combine in a line such as hydrogen, hydrogen sul?de and normally gaseous 22 which opens into a cooler 23. From the cooler the hydrocarbons are still dissolved, is then separated by dis of the column. Conventional re?uxing may be-employed. The light overhead fraction is removed from the top of ‘combined stream passes to an accumulator 2.4 which op tillation into a number of fractions with the use of the erates at a pressure of approximately 5 atmospheres and Ya temperature of say 40° C. In ‘the accumulator a partly plant shown in the above-described accompanying drawing. In the primary column 12 (for which circulating re ?ux is exclusively used again) a bottom product boil ing above 165° C. is obtained at about atmospheric distillation column 12 is impossible even at this relatively pressure (1.1 atm. abs); the feed components boiling be ‘high pressure of 5 atmospheres and relatively low tem 70 low this temperature pass overhead as primary top prod perature, because of the relatively high content of low uct (184.15 tons per 1000 tons of crude oil) and are led boiling components in the feed to the primary distilla through the line 13 and the cooler 15, where they are tion column 12. The uncondensed gases gathering in the cooled to 45° C., into the accumulator 16 where the head space of the accumulator 24 are discharged through a line 25 and a pressure, reducing valve 26 from, the 75 pressure is 1.1 atm. abs. gaseous and a partly liquid product is again collected. Complete condensation of the top product of the primary 3,028,332 5 6 The liquid and the vapor are pumped, as shown in the drawing, to the accumulator 23 where the pressure is 5 atm. abs. The temperature in this vessel is 40° C. The point of 165° C., the quantity of gas to be compressed is not more than about 34.7 tons per 1000 tons of crude oil, i.e., a quantity only slightly greater than the quan tity to be compressed at a cutting point of 185° C.; the di?erence in compressor load at the two ?nal boiling points is now not more than 2.5%. Recycling thus makes it possible to use the same (relatively small) compressor even though the cutting point in the primary column is liquid collecting in the accumulator is removed and then separated in the secondary distillation column 29 at an elevated pressure into butane-free gasoline on the one hand and butane+lighter components on the other. The top product is obtained with the use of a conventional re?ux system, as indicated in the drawing. The pressure altered, thereby improving the operational economy and and temperature, in the re?ux accumulator 39 are 12 atm. 10 also the ?exibility of the plant. In this case the recycled quantity~ of the bottom prod uct of the fractionation column 32 is equal to the differ separated in the column 43 into a bottom product con ence between the quantity of the bottom product (of col umn 32) at a primary distillation cutting point of 185' sisting of butanes, and into a more volatile top product. The top product is again obtained with the use of a con 15 C. (145.4 tons per 1000 tons of crude oil) and the quantity of bottom product at a primary cutting point ventional re?ux system, the pressure and the temperature in the re?ux accumulator 48 being 24 atm. abs. and 45° of 165° C. (118.2 tons per 1000 tons of crude oil), there being no recycling in the latter case. In other C. respectively. The condensed top product consists sub stantially of propane and is withdrawn through the line words, care is taken to ensure that the total quantity 49. 20 of bottom product (viz. the quantity to be recycled plus the quantity immediately withdrawn) is substantially con Gases not condensed in the re?ux accumulators 24, stant at the different primary cutting points. 39 and 48 are discharged through the lines 25, 52 and We claim as our invention: 53. The bottom product of the column 29 is separated 1. In the processing of a vaporous hydrocarbon stream in the column 32 into a top product boiling below 93° C. and a bottom product boiling between 93° C. and 25 containing normally gaseous components to increase the 165° C. which is withdrawn through the line 34. Part liquid recovery therefrom, wherein the stream is cooled of this bottom product (27.2 tons per 1000 tons of crude to effect a condensation, following which the stream is separated into a gaseous portion and a liquid portion and oil) is now recycled according to the invention through the individual portions are separately pressurized to sub the line 55, as a result of which the work to be done by the gas compressor 19 is considerably decreased. This is 30 stantially the same elevated pressure, the improvement comprising conjointly liberating light components from the shown in the table. abs. and 45° C. respectively. The partly lique?ed top product of the column 29 is two pressurized portions to obtain therefrom as one new Table Top Product Top Product Quantities of Gases and Primary Primary Vapors to be Compressed Distillation Distillation . by Compressor 19 Column 12 Column 12 Cutting Point In Distillation In 185° C. 165° C. 185° C. 165° C. 165° C. Column 12 Recycling 1 ________________________________ __ Quantitieszl H2 ____________ .. None None 27.2 portion a liquid fraction recovered by fractional distilla tion and returning a portion of said liquid fraction to the 35 hydrocarbon stream at a point preceding its separation into the gaseous and liquid portions, thereby signi?cantly reducing the total compression work required for the pres surizations of the two separated portions. 2. A process in accordance with claim 1 wherein said 40 returned portion comprises a vfurther heavy ‘fraction ob tained from said liquid fraction. 3. A process in accordance with claim 1 wherein the returned portion of the liquid fraction is combined with 0.005 . 0. 005 0.33 0.005 0. 326 0.005 0.326 0.005 0.326 1. 79 2. 25 6.93 17. 18 155. 67 1.673 2.007 5. 532 9. 958 14. 158 1. 69B 2.11 5. 776 10. 891 16.257 1. 670 2. 075 5. 515 9. 909 15. 160 184. 155 33. 729 37. 062 34. 660 1 In tons per 1000 tons of crude oil. the vaporous hydrocarbon stream at a point preceding 45 the cooling of said stream. 4. A process in accordance with claim 1 wherein a ?rst liberation of light components is effected by ( 1) mixing the two pressurized portions, (2) cooling the resulting mixture, and (3) thereafter separating said light compo 50 nents from the cooled mixture. 5. A process in accordance with claim 4 wherein the liquid separated ‘from the light components in step (3) of that claim is subsequently distilled at a still more ele The second data column of the table shows the quan tity of top product supplied by the primary distillation column 12 at the said ?nal boiling point of 165° C. The last two data columns of the table show the quantities of gas from this top product which are to be compressed vated pressure to separate vfurther light components there 55 from to provide a heavy liquid fraction, a portion of which is returned to the process at a point preceding the initial separation of the hydrocarbon stream. 6. A process in accordance with claim 5 wherein the heavy liquid fraction of that claim is subjected to a still the line 55 of a quantity of the bottom product from the 60 further distillation to separate another heavy liquid frac column 32 (27.2 tons per 1000 tons of crude oil). For tion which is recycled in part to the process at a point the purpose of comparison the ?rst data column of the preceding the initial separation of the hydrocarbon stream. table shows the quantity of the top product from the pri 7. A process in accordance with claim 4 ‘wherein the mary distillation column 12 formed when the cutting vaporous stream undergoing treatment is a reformed point in this distillation column is 185 ° C.; the third col naphtha and the light component separated in step (3) umn shows the quantities of gas which are to be com of claim 4 are principally normally non-condensibles in by the compressor 19, without and with recycling through l l 1 pressed in this case by' the compressor 19. When the bottom product of column 32 is not recycled cluding hydrogen and the liquid fraction of step (3) is a gasoline fraction containing butane and wherein the liquid at a cutting point of 165° C. nor at a cutting point of vfraction is passed to a ?rst distillation to separate the 185° C., the quantity of gas to be compressed by the 70 butane and light components therefrom and the resulting . debutanized gasoline fraction is subjected to a further compressor 19 is approximately 37.1 tons per 1000 tons distillation to separate a light gasoline product overhead of crude oil in the ?rst instance and approximately 33.7 from a heavy gasoline product which is returned in part tons in the second. In the ?rst case the load on the com to the vaporous stream of reformed naphtha prior to its pressor 19 is 9.9% greater than in the second. ‘When the recycling is, however, effected at a primary cutting 75 cooling and initial separation. 3,028,832 7 claim 1 is derived from a second distillation and a por 8 References Cited in the ?le of this patent 8. A process in accordance with claim 1 wherein the vaporous hydrocarbon ‘stream is the top product of a primary distillation operating at approximately at mospheric pressure and wherein said liquid fraction of UNITED STATES PATENTS 5 1,552,980 Blaise ________________ __ Sept. 8, 1925 2,175,180 Dieserud _____________ __ Oct. 10, 1939 2,895,909 Strickland ____________ __ July 21, 1959 226,724 Great Britain __________ __ I an. 1, 1925 tion of that liquid fraction is the material returned to FOREIGN PATENTS the top product of the primary distillation. ' 9. A process in accordance with claim 8 wherein, when the distillation cutting point in the primary distillation is changed, the quantity, of the ‘liquid fraction combined v10 OTHER REFERENCES Fetroleurn Re?ner, vol. 28, No. 9, 1949, pages 213, with the ‘top product is so regulated in amount that the 216, 217, 220, 22,1, 224, 225, 229, 232,233, 236, 237 total quantity of heavy components Withdrawn from the secondary distillation remains substantially constant. and 240. - Petroleum Re?ner, April 1950, pages 97 to 100.