US2901425A - Vacuum distillation - Google Patents

Description

5, 1959 l M. ADDlLL 2,901,425

VACUUM DISTILLATION Filed Deg. 28. 1953 9 Sheets-Sheet 1 MOVED 30083 GHddOJ.

INVENTOR.

P. M WADDILL /WW M ATTORNEYS OIL RESIDIUM FIG.

' Aug. 25, 1959 P. M. WADDILL VACUUM DISTILLATION Filed Dec. 28, 1953 9 Sheets-Sheet 2 N at INVENTOR. P. M WADDILL ATTORNEYS P. M. WADDILL VACUUM DISTILLATION' Aug. 25, 1959 Filed Dec. 28, i953 9 Sheets-$heet 3 I22 INVENTOR.

P.M.WADDILL.

FIG. .5.

ATTORNEYS Aug. 25, 1959 P. M. WADDILL 2,901,425

VACUUM DISTILLATION Filed Dec. 28, 1953 9 Sheets-Sheet 4 INVENTOR. P. M. WADDILL SMWM ATTo/ ygrs Aug. 25, 1959 P. M. WADDILL VACUUM DISTILLATION 9 Sheets-Sheet 6 Filed Dec. 28, 1953 Aug. 25, 1959 P. M. WADDlLL VACUUM DISTILLATION Filed Dec. 28. 1953 9 Sheets-Sheet 7 ut R INVENTOR. P M WADDILL.

ATTORNE S United States Patent VACUUM DISTILLATION Paul M. Waddill, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Application December 28, 1953, Serial No. 400,450

3'1 (llaims. (Cl. 208-652) This invention relates to process and apparatus for the distillation of distillable materials. In one aspect this invention relates to the vacuum distillation of oils. In one aspect this invention relates to the distillation of hydrocarbon oils. In another aspect this invention relates to the vacuum reduction of heavy hydrocarbon oils to produce clean low carbon residue distillates in higher yields and residual high softening point pitch in lower yields than have been obtained heretofore. In another aspect this invention relates to process and apparatus wherein a hydrocarbon oil is vacuum distilled in a first stage to produce a first residual pitch distillation product and wherein the said residual product is then redistilled in a second vacuum distillation stage to produce a still higher softening point pitch. In another aspect this invention relates to process and apparatus wherein a first residual pitch distillation product is redistilled in the same distillation system to produce a still higher softening point pitch together with additional distillate fractions, Without the need for heat or applied vacuum not already utilized in producing the initial residual pitch product. In another aspect this invention relates to the utilization of lower temperatures for effecting the vacuum distillation of residual oils than have been utilized heretofore. In another aspect this invention relates to a combination of process steps wherein a heavy hydrocarbon oil is vacuum reduced in a first stage and then further reduced in a econd stage, and wherein residual product of the second stage reduction is subjected to a series of steps comprising visbreaking, cracking of resulting visbroken residuum, and vacuum reduction of resulting cracking residuum, to provide a final residual high melting pitch, and for conversion of gas oil distillate recovered from the second stage residuum, to lighter product. in still another aspect this invention relates to the distillation of distillable materials under conditions providing for low pressure drop across the distillation zone under high vacuum, and is advantageously applied to the vacuum reduction of residual hydrocarbon oils to provide lower yields of higher softening point residual pitch together with concomitantly higher yields of distillate. In another aspect this inven tion relates to a vacuum distillation process in which a distillable material is partially flash vaporized and particles entrained in resulting vapors are settled from the vapors in whole or in part as desired, prior to condensing the vapor in one or more condensing steps, at least one of which is eflected in heat exchange relation of the vapors with a relatively cool liquid spray. In another aspect this invention relates to a vacuum distillation process wherein a hydrocarbon oil is partially flash vaporized, and resulting vapors are maintained at a residence time sufficient to permit settling therefrom of at least a portion of entrained particles, prior to effecting condensation of the vapors in heat exchange relation with cooler liquid spray, the latter emitted in concurrent flow relation withthe said vapors so as to achieve a lowered pressure drop across the vacuum distillation chamber. In another aspect this invention relates to apparatus comprisinga flat ring disand the like.

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posed peripherally about the inner wall of a chamber section in a substantially horizontal distillation chamber, for preventing flow of unvaporized liquid in an axial directionalong the chamber side walls from the partial flashing section to a downstream section in the distillation chamber. In another aspect this invention relates to the intro duction of feed into a flash vaporization section of a vacuum distillation chamber, in an upstream direction, from an open-end pipe, preferably against a coalescing surface such as provided by a wire rnat, so as to facilitate separation of unvaporized feed from vapors formed. In another aspect this invention relates to the vacuum distillation of a hydrocarbon oil in a single stage by partially fiash vaporizing the oil, contacting the resulting vapors with a liquid spray under temperature conditions effecting partial, or substantially no condensation of the vapors, as desired, and removal of entrainment therefrom, and then effecting substantially complete condensation of resulting vapors in heat exchange relation vith a relatively cool liquid spray, emitted against the direction of flow of vapors contacted therewith.

This application is a continuation-in-part of my copending application Serial No. 241,183, filed August 10, 1951, now abandoned.

Heretofore in the vacuum distillation of residual oils, distillate fractions having high carbon residues have been obtained, together with residual pitch or tar fractions in high yield, as for example from 507() volume percent of residue based on the total oil charged. Furthermore the distillate fractions so produced are dirty, that is, they are high carbon residue oils containing heavy carbonaceous materials present as a result of the entrainment of such materials in the vapors during the vacuum distillation. Such high carbon residue gas oils are undesirable as feed stock for various conversion processes. Furthermore when employing conventional oil reduction operations some of the gas oil components of the oil charge are lost to the distillation residue at the expense of gas oil yield.

My invention is concerned with the vacuum reduction of hydrocarbon oils particularly crude residua, for the recovery of clean gas oil fractions and for the concomitant recovery of residual pitch. My invention is advantageously applied to the further reduction of an initial residual pitch distillation product to provide a still higher softening point pitch and additional gas oil distillate product, and when desired, without the need for applying any heat or vacuum in addition to that already utilized in carrying out the initial distillation. My invention is further concerned with a method for the vacuum distillation of hydrocarbon oils so as to operate the distillation at any given pressure, at a lower temperature than utilized heretofore.

An object of my invention is to provide apparatus and process for the distillation of distillable materials. Another object of my invention is to provide for the distillation of a distill-able material, under conditions providing for low-pressure drop across the distillation zone under high vacuum. Another object of my invention is to provide for the vacuum distillation of oils. Another object is to provide for the vacuum reduction of residual hydrocarbon oils. Another object is to provide for the recovery of residual pitch from oil residua in lower yield, and having a higher softening point than has been obtained heretofore by distillation alone. Another object is to provide for the recovery of clean gas oil fractionsfrom crude oil residua in yields higher than have been obtained heretofore. Another object is to provide pitch of improved quality for use in coke production, container manufacture, as a surfacing agent, road coating,

Another object is to provide for the recovery of valuable hydrocarbons from crude oil residua.

Still another object is to provide for the vacuum distillation of a hydrocarbon oil at any given pressure level, at a temperature lower than that utilized heretofore. Still another object is to provide a process for vacuum distilling a residual hydrocarbon oil to produce an initial residual pitch of high softening point, and then for further reducing the initial pitch product in a second reduction stage. Still another object is to provide a process for vacuum distilling a residual hydrocarbon oil to produce an initial pitch residue of high softening point, and then to further reducing the initial pitch product in the same distillation system to produce a pitch residue of still higher softening point, without the need for heating or vacuum-producing means other than those employed in carrying out the initial distillation. Still another object is to provide a combination process wherein a hydrocarbon oil is vacuum reduced in two successive stages and resulting residuum product is subjected to visbreaking followed by cracking of resulting visbroken residuum and vacuum reduction of the resulting cracked residuum.

In accordance with this invention, apparatus and process are provided wherein a distillable material is partially vaporized and at least a portion of entrained particles are removed from resulting vapors, by settling same from the vapors by gravity alone, or, by contacting the vapors with a liquid spray, prior to condensing resulting vapors in one or more condensation steps, at least one of which condensation is effected by contacting the vapors in heat exchange relation with a relatively cool liquid spray; in accordance with one concept, my invention providing for introducing a distillable material into a first section of a distillation zone under flashing conditions so as to vaporize a portion of the said material, thus forming vapors containing entrained liquid particles, passing vapors from the said first section into a second and downstream section of said distillation zone and therein separating from the said vapors at least a portion of said particles entrained therein, passing vapors from said second section into a third section of said distillation zone in heat exchange flow relation therein with a spray of liquid droplets maintained at a temperature below that of the vapors contacted therewith so as to condense same, and recovering liquid product from the said distillation zone; in accordance with another concept, my invention providing an elongated chamber, preferably disposed substantially horizontally, a conduit extending into said chamber, a spray nozzle assembly in said chamber, a baflle product to the flashing step together with fresh feed to section transversely closing said chamber and adapted to deflect liquid droplets from vapors passed therethrough and disposed intermediate said spray nozzle assembly and the end of the said first conduit, and conduit means for withdrawing liquid and any uncondensed vapor from the said chamber; another concept providing means for arresting downstream flow in an axial direction of unvaporized portions of liquid along the inner periphery of a substantially horizontally disposed distillation zone, comprising a flat ring disposed around the inner periphery of the said zone disposed downstream from its feed inlet. In accordance with narrower concepts of my invention, the said separation of entrained particles from vapors can be effected by (1) passing the vapors in contact with a flow of atomized droplets as a spray, the latter spray being oriented to impinge on the entrained particles in such a manner that removal of entrainment occurs, such as passing the vapors against a flow of atomized droplets maintained at a temperature at least as high and under a momentum at least as great as that of entrained particles contacted therewith, whereby impinging droplets and impinged particles settle to provide entrainment-free vapors; (2) contacting the vapors with a spray of atomized droplets so as to condense a portion of the vapors and, concomitantly remove entrained particles with condensate from the vapors-the direction of flow of atomized droplets, contacted with vapors, being countercurrent to, concurrent with, or transverse to the direction provide a substantial proportion of requisite sensible heat in the flashing section and to reduce requisite peak feed preheat temperatures; further reduction of initial residuum product, in one or more successive stages; further reduction of initial residuum product in a second stage, in the same distillation system, without the need for supplemental heat and/or vacuum; and subjecting residuum distillation product to a series of steps comprising visbreaking, recycle cracking and vacuum reduction to provide a final high softening point residual pitch product, together with gasoline as product.

In accordance with one embodiment of my invention, illustrated with reference to the drawings as discussed hereinafter, a distillable material such as a hydrocarbon oil residuum, generally a topped crude or a residuum from a topped crude cracking operation is heated to a temperature at which very little cracking takes place, or more desirably, none at all, such as within the limits of 600-900 F. The heated liquid is discharged into a flash, or first section, of a distillation zone, which distillation zone is maintained under subatmospheric pressure, generally at an overall absolute pressure from about 0.1 to 21 mm. Hg, and often from 0.1 to 8 mm. The heated charge upon being introduced into the first section is flashed, with the highest boiling components of the charge material remaining unvaporized. These unvaporized materials comprise residual pitch, a major proportion of which settles as liquid in the first section. As is inherent in all flash vaporization operations, particularly with heavy oils, a small portion of the unvaporized material is entrained in the flashed vapors as small finely divided liquid droplets, often appearing as a fog or mist. Such an entrainment of finely divided liquid droplets is typical of that also occurring in conventional vacuum distillation procedures. In conventional processes, the entrained liquid is carried on through the distillation system and is recovered in the gas oil fractions, thereby contributing to the high carbon residues so typical of those recovered gas oil fractions. As described hereafter, my invention provides for arresting these finely divided suspended materials, and for their separate recovery from the recovered gas oil distillates. These entrained fog-like materials must be removed from the vapor containing them in order that clean distillate fractions, i.e., of low carbon residue, be recovered. This is done by passing the vapors from the flash section, i.e., the first section, into a second section of the distillation zone downstream and adjacent the first section, against an atomized oil spray, which completely blankets the path of vapor flow, maintained at substantially the Same temperature or more preferably slightly above that of the vapors contacted therewith. The atomized liquid oil droplets are ejected from the spray nozzles under conditions affording each of them at least as great and preferably a greater momentum than that of each of the liquid particles also referred to herein as droplets, entrained in the vapor. In this manner the sprayed droplets impinge against the entrained droplets, and cause the impinged droplets to settle with the impinging or sprayed droplets to the bottom of the second section. It is to be understood, however, that in the practice of this embodiment, the momentum of the sprayed inaterial need not be equal to that of the'entrained materials, as long as settling of impinged and impinging materials is eifected prior to condensing thesaid vapors, and also, that the spray may be emitted in any predetermined direction as desired, i.e., transverse to vapor flow, concurrent therewith, or countercurrent thereto. Also, if desired, spray temperature may be below that of vapors contacted therewith, so that some condensation will take place and condensate thus provided can settle from the vapors with entrainment.

Vapors, having been contacted with the spray droplets under the conditions described, are free of entrained liquid and are passed from the second section into a third section of the distillation zone downstream from the second section and adjacent to it, against a relatively cool vsecond oil spray, maintained at a temperature lower than that of the vapors contacted therewith, so as to condense at least a portion of those vapors as for example a temperature of from 3 to 500 F. below that of the contacted vapors. Condensate thus formed settles in the bottom of the third section. Settled condensate is recovered from the third section as clean distillation product. Similarly, the process is continued in as many additional downstream sections as desired, and any uncondensed portions of original charge are removed from the final section of the distillation zone as vapors.

The settled liquid, i.e., the pitch residue, in the first section is then withdrawn and is introduced at its existing temperature, i.e., with or without supplemental heating, into communication with a section of the distillation zone downstream from the first section, either into such a section or into a vacuum flash vessel directly in communication with such a downstream section. In either case the withdrawn residual liquid is further flash vaporized by virtue of the fact that the upstream or first section of the distillation Zone operates inherently at a higher pressure than any downstream section therein, because of the presence in the first section of a larger proportion of the total vapors in the distillation zone, and accordingly, a pressure drop is developed across the entire distillation zone which is generally within the limits of from about 2-15 mm. Hg absolute, sometime being as high as 15-20 mm. Hg absolute, dependent upon the specific operation.

I prefer to carry out this embodiment of my process by introducing the withdrawn residual liquid into a section of the distillation zone downstream from the initial flash section. However, the residual pitch can be passed from the first or flash section directly to a second distillation zone generally a flash vaporization vessel maintained in direct communication with a downstream portion of the initial distillation zone. As in the preceding described embodiment, the pressure in the second distillation zone is inherently lower than that in the first or flash section of the initial distillation zone.

In the copending application Serial No. 188,604, to V. C. Cavin, W. H. Acker, and P. M. Waddill, filed October 5, 1950, now abandoned, and in the co-pending application Serial No. 343,560, filed March 20, 1953, now U.S. Patent No. 2,805,981, as a continuation-in-part of the said Serial No. 188,604, of which I am one of the inventors, a vacuum distillation process is disclosed in which the initial oil charge is. partially flash vaporized and vapors are freed of entrained droplets in a second section, and then partially or completely condensed in one or more of a series of downstream zones in a manner similar to that already described above. In the process of each of these applications referred to, i.e., Serial Numbers 188,604 and 343,560, pitch residue is recovered from the first or second section as product, or can be further heated and then vacuum distilled in a separate vacuum distillation zone at a lower pressure by means of supplemental heating and vacuum producing means, separate and apart from that employed in the first distillation zone, to provide a final reduced pitch product of high softening point. As stated above, I have by one concept of this 6 invention taken advantage of the inherent pressure drop across the vacuum distillation zone so as to further flash distill the initial residual pitch residue in the same distillation system without the'need for heating or applied vacuum, other than that utilized in the initial flash distillation step.

I have provided further for conducting the flash vaporization, both in the initial flash vaporization step and in the succeeding flash vaporization step, at a temperature lower than that utilized heretofore while maintaining the pressure substantially unchanged by dispersing the feed in a finely divided state so as to charge liquid feed particles having extremely small radii of curvature. When operating in this manner flash vaporization is facilitated at a lower temperature and vapors having a density many times greater than otherwise formed are obtained, the latter resulting in decreased vapor velocities. The concomitant lower distillation temperatures eliminate the necessity for superheating the feed to attain the requisite vaporization.

For a further clarification of my invention, reference is made to the attached diagrammatic drawings. Figures 1 and 2 are diagramm'aticflow sheets illustrating various concepts of process and apparatus employed in the practice of my invention. Figure 3 shows an elevationof a baffle section that can be employed in the vacuum chamber illustrated in each of Figures 1 and 2, taken along the line 3-3 of Figure 1. Figure 4 is a side elevation of the baffle structure of Figure 3 taken along the line 4-4 of Figure 3. Figure 5 is a plan View of the baffle structure of Figure 3, taken along the line 55 of Figure 3. Figure =6 is a cross sectional view of a preferred arrangement of sprays, employed in the apparatus of Figures 1 and 2, and is taken along the line 6--6 of Figure 1. Figure 7 is a cross sectional view of an alternative form of section III in the apparatus of Figure 1. Figure 8 is illustrative of a baffle section employed in section III of the apparatus of Figure 1, alternative to the guard assembly comprising vessel 79, to prevent flow of any entrained liquid droplets into the vacuum producing system 28. Figure 9 is a plan view of the battle section of Figure 8 taken along the line 99 of Figure 8. Figure 10 is a cross sectional view of a bellowstype expansion joint for use in .the hot oil lines of the apparatus of Figures 1 and 2. Figure 11 is illustrative of other concepts of my invention in which Figures 11A, 11B and 11C show process and apparatus for carrying out the vacuum distillation of a distillable material without the need for contacting vapors, from flashing, with sprayed atomized droplets to remove entrainment therefrom prior to condensation of any vapor, i.e., specifically illustrating m'aintainingsuflicient vapor residence time so that a portion or all entrainment can settle from the vapors prior to the said condensation; and also, contacting the entrainment-containing vapor with relatively coo-l spray so that a portion of the vapor is condensed and entrainment is concomitantly settled therefrom together with resulting condensate. Figures 11A, 11B and 11C together are illustrative of another concept of multiple stage reduction of this invention, i.e., distilling a distillable material in one or both vessels (11A1or 11B), of a first-stage reduction and then subjecting first-stage residuum product to further reduction in a second stage (vessel llC). Figure 11D is illustrative of a series of steps comprising visbreaking, recycle cracking, and a final reduction, particularly applicable to further processing of residual second-stage product of the 2-stage reduction of Figures 11A, 11B and 11C. Figure ll, inclusive of Figures 11A, B, C, and D, is thus illustrative of a combination of process and apparatus for preparing a hydrocarbon oil feed and subjecting same to vacuum reduction in a plurality of separate stages, and for further processing resulting residual product in a series of visbreaking, recycle cracking and vacuum reduction steps to produce a final (high meltingrflsiduum pitch product,

together with light hydrocarbon product, particularly hydrocarbons boilingin the gasoline range. The baflle sections, i.e., adapted to deflect liquid particles entrained in vapors passed therethrough, illustrated with reference to Figures 3, 4, 5, 8 and 9 are illustrative of those that can also be employed in conjunction with apparatus of Figures 11A, 11B, 11C, and 12 and 13 discussed hereinafter. The illustrated forms of section III of Figure 1, as illustrated in Figures 1 and 7 are also illustrative of spray, dam means, and the like employed in the central chamber sections of Figures .11B and 110. Figure 12 is illustrative of still another form of central chamber section (such as section III of Figure 1, section 11b of Figure 11B and section 1110 of Figure 1 1C) that can be employed. This latter arrangement of sprays provides for concurrent flow contact of vapors with condensing spray, thereby providing for improved low pressure drop across the distillation chamber at high vacuum. Figure 13 illustrates a distillation chamber and its operation, in which entrainment in vapors from flashing is removed at least in part, by settling, and resulting vapors are condensed in concurrent flow contact with condensing sprays; the latter is also illustrated by Figure 12. Figure 13 is illustrative of one form of apparatus and process employing the spray nozzle assembly of Figure 12, as applied to a third stage reduction of a hydrocarbon oil.

Although the illustrated embodiments of my invention refer to the vacuum distillation of a residual hydrocarbon oil, it is to be understood that my invention is not limited to the distillation of such oil but is applicable to the distillation of any distillable material such as for example vegetable, animal and mineral oils, distillable organic and inorganic chemical mixtures or solutions and juices;

such as in low-temperature flash distillation of water from fruit and vegetable juices as, e.g., in the concentration of orange or other citrus juices by flashing water therefrom. It is to be understood that these drawings are diagrammatic and may be altered in many respects by those skilled in the art and yet remain within the intended scope of my invention.

Referring to Figure l, a residual hydrocarbon oil is admitted from lines 10 and 11 directly into feed accumulator 12 for charging to the distillation system.

In one embodiment, virgin petroleum crude is admitted from line 10 into crude topping tower 13, wherein a lighter crude oil fraction comprising light and heavy gas oils, gasoline, and a residual fraction are separated, the former being withdrawn from tower 13 through line 14 and the latter through line 16. Virgin topped crude in line 16 is passed to feed accumulator 12 via line 11, or preferably passed to topped crude cracking system 17 via line 18. Oil residuum cracking product is withdrawn from cracking system 17 through line 19 and is charged to feed accumulator 12 via line 11. Other cracking product in cracking system 17, is withdrawn via line 15. Accumulator 12 is maintained at about atmospheric pressure and any vapors to be vented are discharged through line 21. Steam can be admitted to accumulator 12 through line 22 tostrip out any traces of light ends and thereby reduce the load on the vacuum producing means in the distillation step to be described hereafter.

Oil charge stock such as a reduced crude, fuel oil, cracking still residue, cylinder stock, cracked topped crude or the like, as for example a residuum from topped crude cracking having a gravity within the limits of to 5 API and a viscosity at 210 F. generally above 20 SP8, is withdrawn from accumulator 12 through line 23 and is passed into feed heater 24, where it is heated to a predetermined temperature generally suitable for, vacuum distillation of same described hereinafter, such as within the limits of from 600-900 F. under a presfrom heater24 through line 26 into vacuum distillation chamber '27, the structural details of which are further described hereafter. t

Vacuum chamber 27, in a preferred embodiment, is horizontally disposed, and is heavily insulated'by external insulation means 9 and is maintained at an'absolute pressure preferably not exceeding 21 mm. Hg absolute, and often within the limits of 0.01 to 18 mm. Hg. Thedistillation pressure in chamber 27 is maintained by any desired vacuum producing means maintained in communication with the interior of chamber 27 at a downstream point described hereafter, such as a system of steam jets 28. e r

Liquid charge from line 26 is introduced into flash vaporization section I of chamber 27 from an open-end pipe or as a spray in any desired direction, or preferably as a spray through spray assembly 29 comprised of one or more spray nozzles, in a direction toward a liquid coalescing screen such as a wire mat 31, intermediate spray assembly 29 and the upstream end of closure 30, under suflicient momentum to carry the unvaporized feed droplets into the porous matted area which is of such depth that liquid is arrested therein and allowed to flow out of the matted formation by gravity. Wire mat 31 is preferably supported in the end portion 30 by support means 35. In this manner, charge emitted toward mat 31 from spray nozzle system 29 is caused to suddenly reverse its direction of flow, and separation of unvaporized portions from the vaporized portion is thereby greatly accelerated, and sprayed droplets not vaporized coalesce on mat 31'with a minimum of splashing, thereby lessening the amount of liquid entrained in vapors in section 1. Discharge of the oil feed spray in section I in this manner also causes unvaporized droplets to flow against the flow of hot vapors which facilitates further vaporization of those liquid charge droplets, thus further providing for a decreased yield in residual unvaporized charge, and for increasing the yield of clean light oil distillates.

Removal of entrained unvaporized material from the vapors is also facilitated by the impingement of the sprayed feed upon the entrained material. Important factors in the introduction of the feed appear to be (1) the distance of the sprays from the wire mat or other such surface contacted, (2) the velocity of the liquid droplets with respect to the velocity of the vapors and the entrained material therein and (3) the diameter of the sprayed droplets. The distance of the sprays from the wire mat is critical inthat the time allowed for effecting the desired vaporization is not sufficient to permit the atomized droplets to be reversed and to be re-entrained. The velocity is closely related to this distance for the same reason. Smaller diameter particles will afford a greater area and a shorter path for diffusion of the vapors or gases from the liquid droplets. Variation of one or more of these factors is utilized to obtain the best results in the operation of this system.

A portion of the unvaporized material in section I settles therein as liquid product. The portion of unvaporized material not settled as residual pitch in section I is entrained in a highly dispersed state in the vapors therein, appearing generally as a mist or a fog. Vapors from section I passed downstream from spray nozzle means 29, contain these entrained droplets which must be removed in order to produce clean, low carbon residue distillates. This is done by passing the vapors downstream in distillation zone 27 from section I into adjacent section II through perforate or baflle section 32 and against the flow of an oil spray in section II from spray nozzles 34. Perforate section 32, with dam 33 described hereafter, transversely closes shell 8. Section 32 comprises a plurality of openings disposed in at least two separate planes, each said plane extending in a longitudinal direction and preferably parallel with the other. 'Such openings in each plane are disposed from the openings in an adjacent plane, to provide as high as a percent opening between: sections I and II and to: provide further a. circuitous path" for vapor flow tlierethrough. Section 32'. in. a. preferred. embodiment; comprises a system of anglermembers as. illustrated. and described with. respect to the drawings hereafter. The requisite structure of section. 32 issuch that vapors can be passed through it and oil spray impinging upon it will not pass through it. Pressure drop across bafile 32is a fraction of a mm. Hg, generally less than about 0.5 mm. and often as low as 0.05 mm; The structure of baffle sections 42, 77 and 63, described hereafter, are similar to or can be the same as that. of section 32;

Spray nozzle assembly 34- in section II is disposed so astodeliver oil spray in. a direction toward perforate section 32. Atomized droplets of oil are delivered from spray nozzles 34. at a momentum higher than that of the entrained liquid droplets in the vapors contacted therewith and impinge against those entrained droplets whereby the atomized droplets and impinged droplets are caused to settle from the vapors as liquid in section II. The operation of the sprays 34'2 in section II is critical in obtaining the. desired results. It involves the problem of properly controlling the relative momentum of the feed vapors and the sprayed liquid droplets. In section II the liquid droplets being sprayed against the direction of vapor flow impinge upon entrained droplets in the vapor stream. When this impingement occurs there is an ex change of momentum. If the sprayed droplets have the greater momentum the direction of flow of the entrained droplets will be reversed; if the momentums of the two droplets are equal the resulting momentum will be zero and the combined droplets will tend to fall to the bottom of the vessel. If, however, the entrained droplets have the greater momentum, the direction of flow of the sprayed droplets will be reversed with a resulting increase in entrainment. The ratio of the momentum of the blanket of spray to the momentum of the vapor stream, including the entrained mist contained therein is at least 1:1. This ratio may be between 1:1 and 125:1, but is preferably at least 3:1.

The temperature of the oil spray from spray nozzles 34 is maintained at a level very nearly the same as that of vapors contacted therewith. It is important that these spray temperatures be at least as high as the vapor tern pera-tures, for oil spray temperatures lower than the vapors contacted cause some condensation of Vapors not preferred in this embodiment of my invention. In most cases in order to obtain maximum efficiency it will. be necessary to keep the temperature of the oil spray from nozzles 34 above that of the entering vapors to offset heat losses by radiation and thereby prevent condensation in section II. However, in some instances for special purposes it may be desirable to effect some condensation in section II in which case the spray temperature is adjusted accordingly. In sections in which partial condensation takes place, it is preferred to maintain the initial momentum of the sprayed dropletssulficiently high that even after absorbing momentum, through condensation of some of the vapors traveling in the opposite direction, the resulting momentum will still be at least as great or greater than that of the vapors or any liquid droplets entrained therein, otherwise excessive entrainment of condensate will occur. Oil charge to spray nozzles 34 is pro vided by withdrawing a portion of the settled liquid from the bottom of section II and recycling same to spray nozzle system Total liquid is withdrawn through line 3d via pump 37, and line 41. Se tled' liquid from section II, for recycle to spray nozzle system 34, is passed from pump 37 to spray system 34 via line 35% and heater 39, generally a steam heater. Oil in heater 39 is heated to a temperature generally of from about 15 to 30 F. above that of the vapors passed through perforate section 32. Material passed through line 41 is substantially the same material as settled liquid in section I. Ifthe temperature of oil from spray nozzles 34 is lower thanthat of vapors passed; through section; 32., some condensatefli'ay be formed and. collected with residual pitch product. in section II. In such instances it is sometimes. advantageous to recycle liquid from line 41 to section I via line 40, accumulator 12, heater 24, and line 26. When: liquid from line 41 is the same as that described hereafter as settled in section I, these two streams can be combined for further treatment to be described.

Vapors passed downstream in section II from spray nozzles 34 are free of entrained liquid and comprise vapor fractions of clean gas oils to be recovered as described hereafter. These vapors are passed from. section II into adjacent and downstream section III through perforate section 42 against. a flow of atomized oil sprayed from spray nozzles 44. Spray nozzle assembly 44is disposed in section III so as to deliver oil spray in. a direction toward perforate section 42, and is preferably thesame in design as system 34, described in more detail hereafter. Perforate section 42 with dam ring 43 transversely closes vessel 27 at a point intermediate nozzle assemblies 44 and 34. Oil from spray nozzles 44 is maintained at a. temperature lower than the temperature of vapors being passed from section I I through perforate section 42 so as to cause substantially total condensation. of those vapors upon contact therewith. The temperature of oil emitted from spray nozzles. 44 is dependent on the specificdistillation conditions employed, but is generally with the limits of 3 and 500 F. lower than that of the vapors contacted therewith. The momentum of the atomized oil droplets ejected from spray nozzles 44 is maintained greater than that of the vapors contacted therewith, whereby the atomized droplets with condensate thereon and impinged entrained droplets are caused to settle and to accumulate in the bottom of section III. Total condensate collected in the bottom of section III including that described hereafter, is withdrawn through oil outlet 46 via pump 47", and in part through lines 48 and 49, and in remaining part as required. in. spray nozzle assembly 44, and 51 described hereafter, through cooler 52, line 53 and header 54. Oil in cooler 52 is cooled to the necessary temperature lower than that of vapors passed through perforate section 42 sufficiently to provide for total condensation as described. Condensate withdrawn through line 49 is a distillate product of the process.

As described hereinabove, the operating pressure in section I is higher than that in any other section in vacuum chamber 27 for reason that most of the vapor-s present in chamber 27 are in section I. Consequently a gradual pressure drop is eliected and each section downstream from section I operates at a lower pressure than the preceding or upstream section. In this specific em bodiment illustrated, section III is in direct communication with evacuation means 28 and is under the lowermost operating pressure in the chamber. Sections IV and V are each at a lower pressure than that of section I. Settled residual pitch product from section I is withdrawn through line 56 either alone or combined with liquid from line 41 and is discharged through pump 57' and line 58 into section V which is the opposite most section in chamber 27, and operating at a pressure lower than that of section I. Liquid from line 58 is introduced into section V, which serves in this embodiment as a second flash vaporization section, as a spray through spray nozzle system 59, similar in design to spray system 29, in a direction toward (an upstream direction with respect to the path of flow), a wire mat, or coalescing means 62 similar in structure to wire mat means 3 1. Wire mat 62 is preferably supported in end closure 61 of chamber 27. Liquid charge admitted into section V is caused to suddenly reverse its direction of flow so as to minimize the amount of entrained liquid in vapors in section V in the same manner as carried out with respect to the charging operation in section I. A portion of the material in section V is unvaporized and settles therein as liquid and comprises a. higher softening point pitch product than that settledin section I. In this embodiment, this step may be effected without supplemental heating and while utilizing the inherent pressure drop through chamber 27 without the need for any supplemental pressure reducing means. Operating pressure in section V is often a fraction of a mm. Hg pressure and is as much as 15 mm. Hg absolute lower than that in section I, thereby effecting a substantial and significant flash vaporization to pro duce a higher softening point pitch in proportionately reduced yield together with an increased yield of desirable clean gas oil, the latter being suitable as charge stock to various hydrocarbon conversion process steps. The portion of unvaporized material not settled as liquid in section V is entrained in the vapors therein in a highly dispersed state, which vapors are passed from section V downstream into section IV through perforate section 63 of design similar to that of perforate sections 32 and 42, and against the flow of an oil spray in section IV from spray nozzle system 66, of design similar to that of nozzle system 34, and disposed to direct liquid spray toward section 63. Spray from nozzles 66 comprises atomized oil droplets having a momentum higher than that of entrained liquid droplets in contact therewith and impinge those entrained droplets whereby the atomized droplets and impinged droplets are caused to settle in section IV. The operation of sprays in section IV is the same as that described with respect to the operation of spray system 34 in section II. Accordingly the temperature of oil spray from spray nozzles 66 is maintained at a level very nearly the same as that of the vapors contacted therewith and preferably is at a temperature of from to 30 F. higher than the vapors contacted therewith. Settled liquid in section IV is under some conditions of operation the same as settled liquid in section V and comprises pitch of increased softening point, i.e., relative to pitch product of section I. Settled liquid is withdrawn from section IV through line 67 via pump 68, in part returned as feed to oil spray system 66 via line 69, heater 71 and line 72. Oil in heater 71 is heated to the requisite temperature described above. Remaining liquid from pump 68 is discharged through line 73 either as separate product via line 70, or combined with residual oil withdrawn from section V via pump 74 and line 76 or recycled to section V via line 58. Residual pitch withdrawn from section V and discharged through line 76, comprises the high softening point pitch product of my process. Vapors in section IV, passed downstream from spray nozzles 66, are free of entrained liquid and comprise vaporous fractions of clean gas oils to be passed into section III and are totally condensed in section III. These vapors are passed from section IV downstream through perforate section 77 simi lar in design to perforate sections 32, 42, and 63, against a flow of atomized oil sprayed from nozzles 51 in section III, intermediate spray system 44 and perforate section 77, and adapted to direct liquid spray in a direction toward section 77. Oil droplets from spray nozzles 51, maintained at a temperature sufficiently lower than that of vapors to be contacted therewith have a momentum sufiiciently high such that even after absorbing momentum from the vapors contacted the resulting momentum will still be at least as great or greater than the vapors or any liquid droplets entrained therein. Such droplets of entrained condensate are then removed by impingement of the sprayed droplets thereon, and total condensate formed settled in the bottom of section III and is withdrawn from section III together with other condensate formed as described above, through line 46, and comprising a portion of the distillate product of the process.

Although substantially total condensation is effected in section III, scrubbing means 79 is positioned intermediate vacuum pump 28 and section III in order to prevent delivery of any condensate particles directly to the vacuum pump, thereby maintaining the efficiency of the evacuation system at the desired level. Scrubbing system 79 comprises any conventional scrubbing means employing a scrubbing liquid, as for example a heavy hydrocarbon oil flowing in counter-current contact relation with the vapors to be scrubbed. Fresh absorption oil, for example, can be introduced into zone 79 through line 81 and withdrawn through line 82 via pump 83 and recirculated via line 81, or via line 80 and cooler 85. Oil can be withdrawn from the system via line 84, if desired. Vacuum producing means 28, e.g. a steam jet, communicates with section III via line 90, scrubber 79, and vacuum line 75.

With reference to Figure 1, I have illustrated one embodiment of my invention whereby the residual flash vaporization pitch product formed initially in chamber 27 can be flash vaporized in the same system without the need for supplemental heating or additional applied vacuum. It is by virtue of the inherent pressure drop through chamber 27, developed as I have described, by means of which this feature of my invention is made possible Another embodiment of my invention is illustrated with reference to Figure 2 wherein the residual pitch distillation product is withdrawn from the initial flash vaporization section and further flash vaporized in a flash vaporization zone external to the zone of the initial flash vaporization. In this embodiment the external or secondary flash vaporization step is maintained in direct communication with a downstream section of the initial distillation zone and is thereby maintained at a pressure lower than that of the initial flash vaporization. Referring to Figure 2, residual hydrocarbon feed from line 26 is introduced into flash section I of a horizontally disposed chamber 27 through spray nozzle assembly 29, similar in design to nozzle assembly 29 of Figure l and adapted to direct liquid spray in a direction towards coalescing means 31. Pressure conditions in chamber 27 are similar to those maintained in vacuum distillation chamber 27.

As described with reference to the embodiment of Figure 1, a portion of the charge is vaporized in section I. A major proportion of the unvaporized material settles in section I and comprises a high softening point residual pitch product. The portion of unvaporized material not settled in section I is passed entrained as droplets in vapors from section 1 into adjacent section II, through perforate section 32 similar in design to section 32 of Figure 1, against the flow of oil spray in section II from spray nozzles 34. Spray nozzles 34, which can be the same as those of nozzle system 34, are adapted to direct spray in a direction toward section 32. The operation in section II of chamber 27 is the same as that described above with reference to chamber 27 in section II with respect to spray temperture, momentum of the atomized droplets, and settling of entrained liquid. Settled liquid in section II is withdrawn through line 91 via pump 92 and passed in part via heater 39 to spray nozzles 34 and, in remaining part is withdrawn from the system through line 41. When the temperature of oil spray in section II is very nearly the same or not more than 30 F. higher than that of vapors contacted therewith, settled liquid in line 41 is very nearly the same as that in section I and can be combined with the latter if desired for use in a manner as described hereafter. Vapors passed downstream in section II from spray nozzles 34 are free of entrained liquid and comprise vaporous gas oil fractions. These vapors are passed from section II into adjacent and downstream section III through perforate section 42 against a flow of atomized oil sprayed in section III from spray nozzles 44, adapted to direct oil spray toward section 42. Perforate section 42' is similar in design to section 42 of Figure 1. Oil spray from nozzles 44 is maintained at a temperature lower than the temperature of vapors passed from section II through perforate section 42', preferably from 5 to F. lower so as to cool and condense a portion of those vapors. The condensate is formed in section III as described above with respect to the formation of condensate in section III in chamber 27. Condensate is withdrawn from section III through line 46 via pump 47 and passed in part to spray system 44 through cooler 52, wherein it is cooled to the oil spray temperature required in section III, and in remaining part is discharged through line 49. Uncondensed vapors free of entrained liquid are passed from section III into adjacent section IV through perforate section 93 similar in design to perforate section 42 and section 32', against a flow of oil spray emitted from spray nozzles 96 adapted to direct liquid spray against section 93, and to also disperse it in other directions throughout section IV. It is desired that in section IV the maximum condensation be offected, i.e., the condensation of all remaining condensable vapors. It is important that a sufficient amount of oil spray be discharged from spray nozzles 96 at a desired low temperature to complete the condensation of all remaining condensable vapors in contact therewith. It is often advantageous that the temperature of the oil spray from spray nozzles 96 be as low as 100 F. Total condensate formed in section IV is withdrawn through line 97 via pump 98 and recycled in part via cooler 99 to spray nozzles 96, and passed in remaining part through line 101. If desired, total condensation in section IV can be effected under these temperature conditions by positioning baflie section 93 downstream from spray nozzles 96, and then directing oil from nozzles 96, only toward baffle 93 downstream therefrom (and also toward conduit 112 as shown). In such a case, total condensate is collected upstream from baffle section 93 employing a dam in vessel 27 to prevent flow of total condensate thus formed into section III.

Settled liquid from section I is withdrawn through line 102 via pump 103 and lines 104 and 105 to secondary reduction chamber 106. Residual liquid discharged from pump 103 is passed alone or in admixture as desired with liquid from line 41 introduced into line 104- through line 107. When desired, any portion of liquid in line 104 can be withdrawn from the system directly through line 108. Secondary vacuum chamber 106 is maintained in direct communication via line 109 with the interior of at least one downstream section of distillation chamber 27'. In this manner, these latter sections in chamber 27' operating under higher vacuum than that employed in section I inherently provide for a vacuum in chamber 106 higher than that in section I of chamber 27. Accordingly, settled liquid from section I passed into chamber 106, is further flash vaporized therein without the need of supplemental pressure reduction and without further heating,

to provide further yields of gas oil fractions, and higher softening point pitch in correspondingly lower yield. Vapors formed in chamber 106 are discharged therefrom via line 109 into at least one of sections II, III or IV through lines 110, 111 or 112 respectively. Whether or not vapors are discharged into all three sections or one selected section is dependent on the particular operating conditions employed in chamber 27 which in turn affects the operating pressure in chamber 106, and the composition of vapors dischargedthrough line 109. Generally thecomposition of distillate from chamber 106 (in line 109) is the determining factor, such vaporous distillate being returned into that section of chamber 27 containing settled liquid most nearly the same in composition thereto. In any case vapors passed into either sections II, III or IV are contacted with oil spray emitted from one or more nozzles 34, 44 or 96, respectively, as the case may be, under conditions providing the same sprayvapor contacting already in progress in that section. Residual pitch product of high softening point is withdrawn as a product of the process from chamber 106 through line 113.

In this embodiment vacuum reducing means 28 is in direct communication with section IV of chamber 27,

14 section IV being the downstream-mostportion and 015- erating at the lowest pressure in chamber 27.

A preferred form of the perforate bafile sections 32, 42, 77, and 63 of Figure l and 32', 42' and 93 of Figure 2, is illustrated with reference to Figures 3, 4, and 5. As illustrated in these figures baflle section 42 comprises a plurality of parallel courses of angle irons, each said course substantially closing said chamber, angle irons in each of these said courses facing a common direction transversely across said chamber, and each angle in each course having its vertex positioned within the sides of the adjacent and preceding angle. Dam ring 43 (Figures 4 and 5) serves as a partial support for the angle iron baiifie section 42 and also to prevent channeling of vapors from section II to section III, i.e., thereby causing vapor to pass only through the circuitous path provided by baffie assembly 42. Seal rings 121 in conjunction with. fastening means 122 provide for further supporting baffle section 42. Figure 4, shows baffle section 42 to consist of. two courses of angle irons each transversely crossing chamber 27, and Figure 5 shows the relative position of angles in each course making up the baffle section 42. As illustrated in Figure 5, the angle irons in all courses face a common direction transversely across the chamber 27, and each angle in each course. has its vertex positioned within the sides of the adjacent and preceding angle. Preferably, the sides of the angles in each course are parallel with the corresponding sides of the angles in the adjacent course. Dam rings 33, 78 and 60 of Figure l, and 33', 43 and 94 of Figure 2, are preferably the same as dam ring 43 specifically illustrated in Figure 5.

Figure 6 is illustrative of one system of spray nozzles utilized in the practice of my invention. Figure 6, shows a portion of the spray nozzle assembly .34 in Figure 1 by means of which the oil spray is dispersed uniformly against the flow of vapors passing against it from bafile section 32. It is to be understood that this invention is not limited to the particular spray system illustrated, the requisite being a spray assembly capable of spraying the spray in each section in a manner so as to uniformly distribute liquid through the vapors contacted therewith and to completely blanket the path of the vapors. It is advantageous that each spray nozzle system illustrated in either chambers 27 or 27 be spaced away from the re speotive bafile section or wire mat, with which it is associated so that it is at a distance from the plane of the face of the ba-fiie or mat of from 0 to 2 feet, but preferably less than 1 foot. Although two banks of spray nozzles are shown in each location, it should be understood that one bank may be used or more than two, if desired.

Figure 7 illustrates an alternate form of section III in chamber 27. In this embodiment dam 50 is positioned so as to maintain the condensate formed as a result of contacting vapors passed through bafiie section 42 with sprayed oil from spray assembly 44, separate from condensate formed by contacting vapors passed through baffle section 77 with oil spray from nozzle assembly 51. As illustrated in Figure 7 separate distillates are withdrawn through lines 46a and 46b. In this embodiment separate oil streams are fed to the respective oil spray systems. Oil charged through spray assembly 51 is withdrawn from section III through line 46a, via pump 47a, and line 48a, and returned to sprays 51 via cooler 52a, and line 53a. Similarly, oil charged through spray assembly 44 is withdrawn from section III through line 4617 via pump 47b, and line 43b, and returned to sprays 44 via cooler 52b and line 53b. Condensate product is withdrawn from line 46a via line 49a, and through 46b via line 4%.

Figure 8 is illustrative of a baffle means alternate to guard chamber means 79 of Figure 1, for preventing the escape of any entrained liquid droplets from section III into the vacuum producing means 28. As shown in Figure 8, guard chamber or baflle section is an assembly of angle irons disposed in two separate courses (see also the plan. view of Figure 9) disposed so as to -which reduce the severity of initial entrainment.

- provide a circuitous path therethrough. In this respect the bafiie section 130 is similar in design to the baffle sections of chamber 27 and 27 described in detail with reference to Figures 3, 4, and 5, above. Vapor outlet 131 is disposed in the side of guard assembly 130 in gas tight communication with vacuum producing means 28. Liquid outlet 132 is provided in the bottom of baffle section 130. In the operation of this embodiment, uncondensed vapors in section III before reaching vacuum producing means 28 are forced to pass through the batiie section 130, thereby causing the vapors to follow a circuitous path so as to knock out any entrained droplets. Any liquid thus separated, is collected in the bottom of the section 130 for withdrawal through conduit 132. Baffle assembly 130 is preferably located centrally in section 'III. Figure 9 is a plan view (see line 9-9 of Figure 8) showing a preferred arrangement and design of the baiflies in section 130.

As is the case in operating many petroleum processes, it is important in the practice of the present invention to provide means for compensating against expansion and contraction of lines carrying hot oil streams under high vacuum. Such a compensating means is the expansion joint assembly illustrated in detail with reference to Figure 10, wherein expansion joint assembly 140 is a bellowstype expansion joint comprising sealed diaphragm 141 disposed in the hot oil line 142, line 142 being exemplary of any line in the process system illustrated in Figures 1, 2, 11A, 11B or 11C, carrying hot oil under high vacuum such as lines 56, 36, 46, 67 and others, in Figure 1, and lines 102, 91, 46, and others in Figure 2. Diaphragm 141 contains concentric support ring 143 mounted internally to prevent collapse of the diaphragm 141 due to an increase in vacuum within the piping system. Support ring 14-3 is adapted to prevent collapse of diaphragm 141 due to the force of atmospheric pressure, without interfering with the ability of the diaphragm to absorb expansion.

I generally prefer to maintain the momentum of the sprayed droplets in each of the sections of the distillation zone sufliciently higher than that of the entrained droplets contacted therewith, so that the sprayed droplets carry on through and impinge upon the aforesaid baffle section, as for example, sprayed droplets from spray system 34 against the battle section 32; however, when substantially total condensation is effected, the relative momentum of the sprayed droplets and the entrained droplets is not of primary importance. In this manner the function of the battle section is to coalesce the spray, carrying with it the coalesced entrainment, i.e. droplets entrained in the vapors contacted with the spray, causing the coalesced materials to drain to the bottom of the ba-flie section. It appears that it is the surface tension of the oil on the surface of the batlle section that prevents reentrainment of liquid into the high velocity vapor stream.

In another embodiment of my invention, a portion of settled liquid from section I is returned into section I as a spray 2% directly behind spray system 29, and sprayed droplets from spray 29, and from the said returned spray system 2% in section I, are sprayed toward wire mat coalescing means 31. In this manner, unvaporized feed portions entrained in vapors in section I formed as a result of the initial flash vaporization of feed ejected from. spray system 29, are impinged with additional sprayed droplets under conditions of momentum already described, so as to cause all such entrainment to settle in section I. If desired, total vapor from section 1, free from entrained liquid, can be condensed, thereby eliminating the need for bafile section 32, partition 33 and spray assembly 34, pro viding for a still lower pressure drop across chamber 27. Such operation is well applied at generally lower flow rates, or when other operating conditions are employed In the present embodiment, however, the temperature of liquid droplets sprayed from system 34 in section 11 (Figure 1),,

is maintained slightly lower than that of vapors contacted therewith, so as to cause partial condensation of vapors passed through baffle section 32 and settling of same in section II, and thereby for recovery of an additional distillate product fraction. Similarly, settled liquid from section V of Figure 1, and from section I of Figure 2 can be directed into these respective sections'at a point positioned behind spray means 59 and 29' respectively to provide for settling in those sections of all entrained unvaporized feed portions, and for recovery of an additional distillate fraction in the respective downstream section, or, if desired, baffle sections 63 and 32' together with spray assemblies 66 and 34' respectively can be dispensed with.

The high softening point pitch product of my invention particularly that withdrawn as settled liquid from section V of chamber 27 (Figure l), and from secondary vacuum reduction chamber 106, through line 113 (Figure 2), is sufliciently devoid of vaporizable materials that it can be used in admixture with coal to produce a coal-coke of increased mechanical strength without substantial contamination of aromatic by-products of the coal coking process. It is also characterized as being very low in materials insoluble in carbon disulfide.

In one embodiment of my invention I have provided for conducting the flash vaporization steps of my process at temperatures lower than those utilized hereinbefore without the need for reducing the pressure proportionately. The practice of this embodiment is accomplished by charging the oil feed in a sufiiciently high finely divided, or atomized state so that the liquid feed particles have an extremely small radius of curvature; the feed is atomized in the flash vaporization chamber so that the average radius of curvature of the liquid feed particles is less than 0.1 micron, preferably from 0.01 to 0.001 micron. In atomizing the feed particles in this manner, a larger amount of vaporization is eifected than would be indicated by the normal vapor pressure curve, characteristic of that feed material, and an amount of vaporization is obtained at the operating pressure level of my process comparable to that obtained when charging feed droplets of larger radius of curvature at absolute pressure as low as about 20 microns. In this embodiment, at the operating pressure, vapors in equilibrium with the atomized feed droplets will have a density often as high as 1,000 times greater than that of vapors in equilibrium with larger radius droplets at pressure as low as about 20 microns absolute pressure. Also the vapor in equilibrium with the atomized feed droplets will be approximately 250 F. cooler than indicated by the normal vapor pressure curve. Atomizing the liquid feed in this embodiment eliminates the necessity for superheating the feed to obtain vaporization, and the concomitantly increased density of the vapors results in decreased vapor velocities; and it is possible to operate the vacuum chamber while obtaining the operating advantages generally possible only at much lower pressures, while at the same time preventing the high vapor velocities that are characteristic of normal operation.

With reference to Figure 11, a hydrocarbon oil, such as a virgin petroleum crude is introduced into preheat furnace 151 via line together with steam introduced via line 153, and heated in preheater 151 to a predetermined temperature suitable for distillation described hereinafter, such as within the range of 600-900 F., and passed to vacuum steam stripper 152 together with steam from preheater 151., also heated to withln the said temperature range.

In vacuum steam stripper 152 a gasoline streamus sep arated, and discharged via overhead line 15; a side out of gas oil is separated, and withdrawn via line 156; and a bottom residuum product, generally containing some gas oil, is withdrawn via line 153. Residuum in line 158 at a temperature within the predetermined range is introduced into chamber In of elongated distillation vessel 157,

preferably disposed substantially horizontal, under flashing conditions so as to vaporize a portion of the said residuum. Residuum from line 158 is preferably introduced into section la in an upstream direction, i.e., toward end section 159 as a-spray, from nozzle assembly 150a, against a liquid coalescing surface such as that provided by a wire mat 161. Advantages of this method of feed introduction are set forth herein, with reference to Figures 1 and 2. However, feed from line 158 can be introduced into section Ia from an open end pipe against a coalescing surface; or, in lieu of a coalescing surface, from an open end pipe or as a spray, in any desired direction. Vapors formed in section Ia contain entrained liquid droplets or particles, comprising unvaporized portions of the residuum feed, which, if not removed from the vapors prior to condensation, will be present in the condensate as undesired impurities, as discussed hereinabove with reference to Figures 1 and 2. Vapors from section Ia of chamber 157 are passed through baflle section 162, which can be similar in design to battle sections of Figures 1 and 2, further illustrated with reference to Figure 3, 4 and 5; transversely closing chamber 157 and supported by darn ring 163 and adapted to deflect liquid droplets present as entrainment in vapor passed therethrough. Dam ring 163 also provides for confining liquid product in section Ia, i.e., prevents its passage into section Ila. Dam ring 163 also prevents unvaporized liquid in section la, adhering to the inner side wall of that chamber section and moving downstream, from passing into section Ila to thus contaminate liquid product therein, and causes liquid contacting same to accumulate in section Ia.

Vapors containing entrained droplets not deflected therefrom by baflie section 162 are passed against a flow of atomized droplets emitted from spray nozzle means 164, the latter spray being maintained at a temperature lower than that of vapors contacted therewith so as to effect partial condensation of same and to concomitantly cause impingement of sprayed droplets with condensate droplets and entrained particles and settling of the resulting impinging and impinged droplets in section Ila. Preferably the momentum of the atomized droplets emitted from spray 164 is at least equal to that of condensate droplets formed plus that of entrained particles contacted therewith, so that droplets of condensate and entrained particles are settled from vapors in section Ila prior to the flow of vapors from section Ila. However, if desired, the momentum of sprayed droplets from nozzle assembly 164 can be less than that of the entrained particles plus condensate droplets formed in section Ila, when section Ila is of sufficient length to permit settling of the impinged and impinging droplets prior to passage of the vapors therefrom into section Illa. Vapors, free from entrainment are passed through bafile section 166 transversely closing chamber 157, which can be similar in design to baffle section 162, and are contacted in section Illa with atomized liquid droplets emitted from spray nozzle assembly 167, the latter at a temperature sufficiently below that of the vapors contacted therewith so as to effect substantially complete vapor condensation in section Illa. Momentum conditions of the atomized droplets from spray assembly 167 are preferably such that impinging spray and impinged total condensate formed in section llla are caused to settle therein as liquid product. Vapors, free from entrained condensate are passed from section Illa through baffle section 163, transversely closing chamber 157, and which can be similar in design to baffle 162, baifle 163 serving as a deflector of any remaining liquid droplets in vapors passed therethrough. Any vapors, i.e. uncondensed in section Illa, passed through baffle section 168 into section IVa are removed via internal guard chamber 169, similar in design to haffle system 136 of Figure 8, in any event functioning as a deflector of any entrained particles that may be present in uncondensed vapors to be re- 18 moved from section IVa via line 171 and steam jets 172. Baffle system 169, which can also be referred to as a liquid-vapor separator can comprise any suitable means such as an assembly of conventional mist-extractor battles or the like.

During residence of vapors in section Ia, some entrainment settles in the bottom thereof as product together with a major portion of the unvaporized liquid charge. Liquid product settled in section la, comprises residuum product of the distillation in chamber 157 and is withdrawn from section Ia via line 173. Residuum product in line 173 can be recycled in part to section la via line 174, preheater 176 and line 158, i.e., with fresh feed thereto, or directly from line 173 to line for further preheating in 151 together with fresh feed. Residuum product can be withdrawn from the system via line 176a and can also be withdrawn via lines 173 and 177 for charging to a second stage vacuum reduction discussed hereinafter.

Condensate formed in section Ila is withdrawn via line 178 and recycled in part via cooler 179 and line 181 as feed to spray nozzle assembly. 164, thereby providing liquid product from section Ila as the source of liquid spray emitted from nozzle assembly 164. The remaining portion of liquid roduct from section Ila is withdrawn via lines 178 and 182. Total condensate formed in section Illa is withdrawn therefrom via line 183 and recycled in part via cooler 184 and line 186 to spray nozzle assembly 167 and emitted therefrom as the said spray. Thus, as in the case of section Ila, the source of droplets emitted from spray 167 is total condensate recovered in section Illa.

Although it is only a very minor amount of liquid and vapor that is passed from section Illa into section IVa, if any at all, any such liquid collected in section IVa is withdrawn via line 186a.

When desired, the use of a spray in section Ila, in chamber 157, can be dispensed with, with the concomitant advantage of lowered pressure drop across the distillation chamber 157. The separation of entrainment from vapors in section Ila is generally not as complete when the said sprays are dispensed with, although some entrainment settles in section Ila, such settling being facilitated by increasing proportionally the linear dimension of section Ila. Also, a small amount of condensation generally occurs in section Ila, in the absence of spray from nozzle assembly 164, by radiation therein. Operating in this manner, the pressure drop across chamber 157 can be lowered, although, when not employing a liquid spray in section Ila, some unsettled entrainment, i.e., particles of unvaporized feed, will be present in condensate recovered from section Illa. Although the pressure drop lowering acLieved in any specific instance is dependent upon the initial operating conditions, i.e., when employing a spray, a pressure drop lowering of up to 2 mm. Hg is often achieved when dispensing with the use of such spray.

Another fraction of hydrocarbon oil, such as petroleurn crude, is introduced via line 191 into preheater 192, wherein it is heated to a temperature in a predetermined distillation range as discussed with reference to preheating of oil from line 150, and is then withdrawn via line 191a and passed into flash chamber 193, wherein a gasoline fraction is separated, and withdrawn via overhead line 194; a gas oil fraction is separated, and withdrawn via line 196; and a residuum or bottoms fraction is separated, and is withdrawn via line 197, and passed as charged to elongated vacuum distillation chamber 198, preferably substantially horizontally disposed. A portion of charge from line 197 is introduced into chamber 198 via line 199 into end section lb, under flashing conditions that can be carried out as described relative to introduction of feed into section Ia of chamber 157, i.e. as a spray or from an open end pipe, in any desired direction, preferably upstream toward end section 201, against a coalescing surface such as wire mat 202, the latter supported by support means 203 and adapted to be moved in a longitudinal direction in section 1b. A re maining portion of charge from line 197 is introduced into the opposite end section Ib under flashing conditions as described relative to introduction of feed into section Ib. A major proportion of the unvaporized charge in sections Ib and Ib settles in each section as liquid product. Vapors from section 117 containing entrained liquid particles are passed through baffle section 207 transversely closing chamber 198 and of design similar to that of baflie section 162 of chamber 157, into central section 11b in contact therein with droplets of atomized spray emitted from nozzle means 288. The temperature of droplets emitted from nozzles 208 is sufliciently lower than that of vapors contacted therewith-so as to cause substantially complete condensation of the said vapors. The momentum of the atomized droplets is sufficiently high so as to cause impinging droplets and impinged droplets of condensate and particles of entrained unvaporized feed to settle as liquid product in central section IIb. However, if desired, the said momentum conditions may be dispensed with, it being important, in any case, that all the liquid droplets are settled in section IIb as product. Thus, in the event that the said momentum conditions are dispensed with, section IIb can advantageously be of sufficient length to permit the said settling of all liquid droplets therein.

Vapors formed in section Ib contain entrained particles of unvaporized feed and are passed through baffle section 209, the latter transversely closing chamber 198 and of design similar to baffle section 207, into section IIb, against a spray of atomized liquid droplets therein from spray nozzle assembly 211a under momentum and temperature conditions to cause substantially complete condensation of vapors contacted therewith and settling of same withentrained particles. If desired, the said momentum conditions of spray from nozzle assembly 211a can be'dispensed with, it being important, in any event, that all condensate and entrainment be settled in section IIb. Vacuum is applied to the central section, i.e., section 1112 of chamber 198 by any conventional means, as for example by steam jet means 211 connecting with section IIb via line 212, external guard chamber 213, and line 214, the latter connecting with the interior of section IIb at a point intermediate spray nozzles 208 and 211a, through internal guard chamber 216; the latter serving as a mist-extractor so as to deflect any unsettled liquid droplets from any vapors leaving section IIb, so as to prevent their flight to vacuum producing means 211, such interference with vacuum means 211 seriously impairing its vacuum producing efficiency.

A' preferred form of internal guard vessel 216 is illustrated in the drawings with reference to Figure 8, the latter specifically referring to its adaptation to apparatus of Figure l, but being also illustrative of the preferred form of internal guard chamber in section IIb of chamber 198. External guard chamber 213 comprises a spray and baffle means for condensing any residual vapors from line 214 and for arresting any liquid particles entrained therein. Liquid supplied to the spray system in external guard chamber 213 can be any heavy fraction of hydrocarbon oil, but is preferably liquid, originally withdrawn from section IIb and charged to chamber 213 via line 216a, withdrawn via line 217 and, when desired, recycled to line 216a, by means not specifically shown.

Liquid product in section Ib and Y1; in chamber 198 comprises unvaporized liquid charge and contains any condensate, such as formed in either section by means of heat radiation, and also particles of unvaporized charge initially entrained in vapors therein but settled from those vapors during the flight of same through section Ib into the central chamber section IIb-or through section I'b into section IIb.

Residuum product of distillation, present in section lb of chamber 198is withdrawn via line 218. A portion of residuum from line 218 can be recycled to section Ib together with fresh feed thereto via lines 219, 221, 222, preheater 223 and line 197. If desired, residuum product. from line 218 can be recycled via lines 219 and 224 directly to preheater 192 and sections lb or Ib. If desired, residuum product can be withdrawn from line 218 via line 226, or, via line 227 for passage to further reduction in a second stage vacuum distillation discussed hereinafter.

Residuum product from section P12 is withdrawn via line 228, and can be recycled to distillation chamber 198 via lines 229, 222, preheater 223, and line 197, or, if desired, via line 228 and preheater 192, to distillation chamber 198. Residuum from line 228 can also be with drawn from the system via line 231. If desired, residuum from line 228 can be withdrawn via line 227 and passed to a second stage vacuum distillation, for further reduction as described hereinafter. Total condensate collected in section IIb is withdrawn via line 233 and recycled in part via 234 and cooler 236 to spray assembly 208 as the source of liquid droplets emitted therefrom; is passed in part from line 233 via line 237 and cooler 238 as liquid to be emitted from spray nozzle assembly 211a; remaining condensate being withdrawn from section IIb via lines 233 and 239.

Residuum product from distillation chamber 157 or 198, or both, can be further reduced in a second-stage vacuum distillation system to provide a. still higher softening point residual pitch product and higher overall yields of gas oil distillate. Thus, residuum product from line 177, alone, or together with residuum product from line 227, is passed via line 232, preferably divided as two separate streams, and passed through preheater 233a and therein heated to a temperature within a predetermined range for the said second stage distillation such as within 600-900 F. A portion of the preheated residuum product is withdrawn from preheater 233a via line 234a and the remaining portion is withdrawn via line 236a. Residuum in line 234a is then passed into section Ic of distillation chamber 237a under flashing conditions therein, that can be carried out as described relative to introduction of feed into section 1b of chamber 198, i.e. as a spray, or from an open end pipe, in any desired direction, preferably upstream against a coalescing surface such as that provided by wire screen 239a, transversely positioned in chamber 237a intermediate the end of conduit 234a in section I0 and chamber end portion 2384'. A major portion of unvaporized charge settles as liquid in section Ic. Vapors formed in section Ic contain entrained particles of unvaporized charge and are passed into adjacent section IIc through baflle sections 238a, transversely closing chamber 237a and which can be of design similar to that of baffle section 162 of chamber 157. Vapors passed from section Ic into section are contacted in the latter section with a spray of atomized liquid droplets maintained under temperature-momentum conditions so as to effect condensation of a portion. of the said vapors contacted therewith and concomitantly cause impingement of sprayed droplets with particles of unvaporized charge and droplets of condensate, to cause settling of all liquid droplets in section IIc as liquid product. If desired, the momentum conditions can be such that the force of impinging droplets is below that causing settling of all droplets in section 110, in which case it is important that the linear dimension of section He be sufficiently great that these droplets are-substantially completely settled prior to passing of vapor from section IIc into the central section IIIc. If desired, the step of contacting vapors with spray in section 110 can be dispensed with, whereby a lower pressure drop across the chamber 237a is achieved and higher vacuum is achieved. However, in the latter event, complete settling of entrainment from vapors in section H0 is not achieved, although a substantial proportion of the said entrainment is settled by virtue of the residence time of vapors in section IIc. Vapors from section IIc are passed through baflle section 241 transversely closing chamber 237a and which can be similar in design to bathe section 162 of chamber 157, and contacted in section IIIc with a spray of atomized liquid droplets maintained at a temperature sufliciently below that of vapors contacted therewith so as to effect substantially complete vapor condensation. When dispensing with the use of a spray in section 110, condensate thus formed in section IIIc contains small proportions of feed particles entrained in vapors entering section IIIc. However, the small proportion of unvaporized charge particles present can generally be justified in view of the lower pressure drop achieved across the distillation chamber 237a and the higher vacuum resulting therefrom to provide an improved yield of gas oil'and a correspondingly lowered yield of residuum.

Operation in sections 1's and II'c is the same as that respectively in sections Ia and He and is not specifically illustrated.

Vacuum is applied to distillation chamber 237a by means of steam jets 242, connecting with the interior of section IIIc via line 243 and internal guard chamber 244, the latter being similar in design to guard chamber 216 of distillation chamber 198. Dam means 246, in combination with spray nozzle assembly in section IIIc (also illustrated with reference to Figure 7) provides for isolation of condensate fractions in section IIIc, recovered from vapors from sections IIc and 11's.

Residuum product is withdrawn from section Ic of chamber 237a via line 247 and can be withdrawn from the system via line 248, or recycled via line 249 with fresh feed to distillation chamber 237a. Residuum from section Ic of chamber 237a is withdrawn via line 251 and can be withdrawn from the system via line 252, or recycled in part, if desired, via line 253 and 232 to distillation chamber 237a. Liquid product from section IIc is withdrawn via line 254, and can be withdrawn from the system via line 256, recycled in part as liquid spray in section IIc, when desired, via line 237b, cooler 258, and line 259. Liquid product is withdrawn from section IIc of chamber 237a via line 261 and can be withdrawn from the system via line 262, and, when desired, can be passed in part via line 263, cooler 264 and line 266 to spray nozzle assembly 2410. Liquid product from lines 254 and 261 can also be each recycled to distillation chamber 237a together with fresh feed, via lines 255 and 232, and preheater 233a, these latter recycling steps being particularly advantageous when no liquid spray is employed in sections I10 and IIc.

Recycle of residuum from a vacuum distillation system with fresh feed thereto, in preferred forms, is described and claimed in the copending applications of William E. Barr and Charley H. Owen, Serial No. 351,017, filed April 24, 1953, now U.S. Patent No. 2,799,628, and Golden A. Moyer, Serial No. 316,411, filed October 23, 1952, now US. Patent No. 2,774,723.

By means of the second stage vacuum distillation of my invention, such as specifically illustrated, the softening point of the first stage residuum product can be increased by about 50 to 350 F., and the overall yield of gas distillate is correspondingly increased, thereby providing for lowered yields of residual pitch product, although of better quality, and higher yields of gas oil.

As illustrated with reference to Figure 11D, residuum product of the second stage vacuum distillation, above discussed and illustrated, is further processed in a series of steps comprising visbreaking, recycle cracking, and final vacuum reduction, to provide a final high softening point pitch product, and for recycle and reaction, substantially to extinction of gas oil fractions formed, to produce hydrocarbons boiling in the gasoline range as a chief light hydrocarbon product. Thus, residuum from lines 247 and/ or 251, together with, if desired, gas oil distillate from lines 261 and/or 254, although the last said gas oil streams are generally withdrawn from the system for other utilization, are passed via line 266a, to visbreaking Selas furnace 267, wherein it is heated to a temperature generally of about 750 to 850 F., so as to effect mild cracking of same. It is generally advantageous to pass a stream from line 266a via separator 268, to furnace 267, whereby any relatively light fractions can be withdrawn overhead and utilized as described hereinafter. Effluent from visbreaking furnace 267 is quenched at points 268a and 269 with gas oil from line 271. Steam from line 272 is also added at point 269 for control of final quench temperature. Resulting quenched furnace efiiuent at a tem perature such as from 710 to 750 F. is passed into vacuum flash chamber 27 3, maintained under about 1.0 to 10 mm. Hg from which residual product is withdrawn via line 274. Vapors from vacuum flash chamber 273 are withdrawn via overhead line 276 and passed to vacuum bubble tower 277, the latter under about 1.0 to 10 mm. Hg. Gas oil bottoms product is withdrawn from tower 277 via line 278 and is passed in part into line 271 and is withdrawn in remaining part as product via line 279. Overhead product withdrawn from vacuum bubble tower 277 comprises gasoline in line 281 and gas in line 282, separated in separator chamber 283. Residuum in line 274 if passed to a recycle cracking operation in which all gas oil product from cracking is recycled to the cracking step so that the only products are gas, gasoline, and residuum. Thus, residuum in line 274 is charged to bubble tower 284, operated under vacuum of about 10 to mm. Hg to which is also charged an aromatic gas oil from line 286, preferably a sulfur dioxide extract oil together with vapors from flash drum 287, described hereinafter, via line 288. Fractionation in bubble tower 284 provides gas as an overhead product, withdrawn via line 289 and a sidestream of gasoline withdrawn via line 291, and, a bottom gas oil stream which is charged to furnace 292, via lines 293 and 294. More severe cracking conditions are maintained in furnace 292 than were maintained in furnace 267, e.g., a cracking temperature within the range of 900 to 1100 F. under about atmospheric pressure to 50 p.s.i.g. Water is injected into the feed to furnace 292 via line 290. Furnace effluent is withdrawn via 297 and charged to flash drum 287. Residuum is withdrawn from flash drum 287 via line 298 and is charged to surge tank 299. Combined with residuum from chamber 287 in line 298 is residuum from other refinery operations, in line 301, recycled pitch from vacuum flash distillation tower 302 in line 303, and superheated steam from line 304. Vacuum is applied to surge drum 299 via vacuum jets not specifically shown through line 306 to remove the more volatile components of the feed through line 306. Residuum is withdrawn from surge tank 29.9 and passed to furnace 307, wherein it is heated to a temperature in a range suitable for vacuum reduction described hereinafter such as about 600-900 F., preferably such that little or no cracking is effected during the heating. The heated residuum from furnace 307, via line 300 is flash vaporized in vacuum distillation chamber 302, the latter maintained under high vacuum such as in the range of 0.10 to 10 mm. Hg, applied by vacuum jets via line 307a. In chamber 302, lighter hydrocarbon fractions are condensed from the flashed vapors and recovered as products via lines 308 and 309, any uncondensed vapors being removed via the jets. Residual pitch product is withdrawn from distillation chamber 302 via lines 311 and 312, and in part, when desired, via line 303 for passage together with steam and the above-described residuum fractions in line 298 for further processing in vacuum surge tank 299.

The above-described embodiment, with reference to the combined process steps of Figures 11A and/or 11B, 11C and 11D, provides a residual pitch product of high softening point, for example in the range of 2001 to 450 F., and for recycle to extinction of a major proportion of the gas oil fractions recovered during the visbreaking, cracking and vacuum reduction steps, thereby providing for gas and

Claims (2)

11. IN A VACUUM DISTILLATION PROCESS WHEREIN MATERIAL IS PARTIALLY FLASH VAPORIZED IN A FIRST ZONE AT SUBATMOSPHERIC PRESSURE, THE IMPROVEMENT WHICH COMPRISES SEPARATING AN UNVAPORIZED PORTION OF SAID MATERIAL FROM SAID VAPORS, FLOWING AN UNVAPORIZED PORTION OF SAID MATERIAL OUT TO CONTACT AND SEPARATED FROM SAID VAPORS TO A SECOND ZONE IN OPEN VAPOR COMMUNICATION WITH SAID FIRST ZONE AND FLASH REDISTILLING SAME AT A PRESSURE SUBSTANTIALLY LOWER THAN SAID SUBATMOSPHERIC PRESSURE, SO THAT A SECOND FLASH DISTILLATION IS OBTAINED IN THE SAME VACUUM DISTILLATION SYSTEM, UTILIZING PRESSURE REDUCING MEANS EMPLOYED IN MAINTAINING SAID SUBATMOSPHERIC PRESSURE, AS THE SOLE SOURCE OF VACUUM FOR SAID PARTIAL VAPORIZATION AND SAID SECOND FLASH REDISTILLING.

29. IN THE VACUUM DISTILLATION OF A HEAVY OIL THE IMPROVEMENT COMPRISING INTRODUCING LIQUID CHARGE STOCK INTO A DISTILLATION ZONE, UNDER FLASH CONDITIONS PROVIDING FOR VAPORIZATION OF A PORTION OF SAID CHARGE TO FORM VAPORS CONTAINING ENTRAINED LIQUID DROPLETS, IN A DIRECTION OPPOSITE TO THE DIRECTION OF VAPOR FLOW THEREIN AND AGAINST A LIQUID COALESCING SURFACE, UNDER CONDITIONS CAUSING VAPORS EMITTED TOWARD SAID SURFACE TO SUDDENLY CHANGE THEIR DIRECTION OF FLOW SUBSEQUENT TO CONTACTING SAID SURFACE, WHEREBY SEPARATIONS OF UNVAPORIZED AND VAPORIZED PORTIONS OF CHARGE IS FACILITATED AND ENTRAINMENT OF LIQUID IN THE VAPOR FORM IS MAINTAINED BY COALESCING OF UNVAPORIZED LIQUID DROPLETS ON SAID COALESCING SURFACE, AND DRAINING COALESCING LIQUID FROM SAID SURFACE AND COLLECTING LIQUID SO DRAINED BELOW SAID COALESCING SURFACE.

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