US1868466A - Distilling process and apparatus - Google Patents

Description

July .19, 1932- E. H. LESLIE E'r AL 1,868,465

DISTILLING- PROCESS AND APPARATUS Filed June'29. 1925 3 Sheets-Shee l July 19, 1932- E. H. LESLI ET AL 1,868,466

DISTILLING PROCESS AND APPARATUS Jl Jg.

FEOM PUMP 62 I JOL* ,eas/0MM( met July 19, 1932.

El H. LESLIE ET AL DISTILLING PROCESS AND APPARATUS l Filed June 29, 1925 3 Sheets-Sheet 3 CONDE/V651? Misma July 1e, 1932 Arnia oFFieE.

EUGENE E. LESLIE AND EDWIN' M. BAKER, 0F ANN ARBOR, MICHIGAN DISTILLING PROCESS AND APPARATUS Application filed June 29,

acter above mentioned. A further object 0fv the invention is to provide apparatus whereby the foregoing object may be achieved while at the same time utilizing to a -large extent previously installed refinery equipment, such as batteries of stills, by associating with' such equipment suitable fractiona-ting apparatus,

thus providing a complete apparatus system appropriate for practicing the invention at 'the lowest cost lconsistent with the accomplishment of the desired result.

While the invention is not restricted to the field of petroleum distillation, its greatest pres-ent utility is in that field. Accordingly in -explaining; the. underlying principles of the invention hereinafter, reference will be made more particularly to petroleum distillation by way of a concrete illustrative eX- ample.

In the continuous distillation of petroleum 3D as heretofore practiced, the operating equipmentis usually composed of a continuous still battery, thestills of which may or may not be fitted with'towers, dephlegmators, or in general, fractionating condensers. Assum- 40 ing the use of some form of fractionating condensers with the stills, the conventional mode'of operation has been as follows:

The incoming loil is first passed through heat exchangers and then flowed through the 45, stills in series which are suitably heated to effect continuous stage-wise distillation of the oil passing serially through the stills of the battery.l The distillation vapors, which are successively heavier from the first to the lastl still of the battery, pass from each still '3.925. Serial No. 40,421.

into its associated fractionating condenser wherein a relatively heavy portion of the vapor condenses, the condensate flowing back to the still. Vapors from the tops of the fractionating condensers pass to water-cooled condensers, and the resultant condensates are cooled separately. The distillate from the first still lof the battery (assuming crude petroleum to be the oil to be distilled) is found upon test to be almost wholly within the a0 gasoline boiling range Aas fixed by standard Navy specifications, for example. For instance, if the crude oil contains 30 per cent of gasoline, the distillate from the Yfirst still comprises commonly from 5 to 15 per cent 65. of the crude oil, depending upon the particular mode of operating the still battery. The distillate from the second still tests perhaps 90 per cent of gasoline boiling range, the other 10 per cent probably boiling somewhat 70 above 45370 F. However, this high boiling portion can be mixed into the gasoline when the light distillate from the first still is mixed with the distillate from the second still. The distillate from the second still may be 76 say 10 to l5 per cent of the total volume of crude flowing to the battery.

Usually only about orge-half to threefourths of the distillate from the third still will be found to be of gasoline boiling ran-ge, 80 and this constitutes what is known as benzine in refinery parlance. The distillate from this third still may in some cases be as much as l5 to 2O per cent of the crude oil,

especially where the distillates from the first and second stills were minimum percentages. In order to secure the gasoline content of'this distillate from the third still, it is customary to re-run the' benzine in so-called re-run stills, which stills are fireeand-steam stills, usuallyfitted with some form of dephlegmator to permit. more effective separation. The distillate from these re-run stills is of gasoline boiling range band is mixed into the gasoline product. The bottoms or unvaporlzed portion is a light kerosene.

Assuming the battery to consist of four stills, the distillate from the fourth or last still comprises the gas oil, and in some plants includes also what is the heavy end of the 10 kerosene. 'Where heavykerosenes are to be made, this fourth distillate may be re-run to recover such heavy kerosene. More usuum The prior practice above outlined is open to numerous ser1ous objections from the standpoint of the practical refiner. In the lirst pla/ce, it is impossible by this procedure to obtain from a given crude oil the maximum amount of distillate that will pass the standard specications for gasoline boiling range. Furthermore, the necessity of employing rerun stills greatly increases thev first cost of the installation and its subsequent upkeep, not to mention the large ground space occupied by said re-run stills. The system as ai whole is also thermally ineiiicient and uneconomical in operation. These and other objections are overcome by the process of the present invention and certain additional advantagesl are alsoattained, as will appear more fully from the description hereinafter'.

In contrast to prior methods of continuy ously distilling petroleum in accordance with the general 'procedure above outlined, 'the process of the present invention involves sharp fractionation of the. distillation vapor coming from each ofthe stills of a battery, in.

such manner that everything that can be in.- cluded in the gasolinel under standard speciflc'ations leaves the distilling system and is' obtained in the `gasoline condensate, while everything that should not be included as gasoline leaves the'system either in the form of residuum, or of gas-oil, kerosene, or the like, which may be withdrawn at one or more intermediate points inthe system. Stated generally, this result is achieved by conductmg the distillation vapors from all of the distilling units of the battery into a rectifying system character in the sense rthat the liquid' therein with which the distillation ,vapors countercurrently contact is provided solely by reiiuxin into the rectifying system condensate V from t e rectidvapors that leave said system. Ordinarily said rectifying system takes the form of a single column fractionator, using the term fractionator in the correct 55. technical sense by which it is sharply disltinguishied from apparatus of the fractionating condenser type. While a structurally unitary or single rectifying column or fractionator is generally the most convenient form of unitary rectifying system to employ in the practice-of the present invention, this is not a rigid requirement within the broad scope of the inventive idea here involved so long as the conditions of operation here emphasized are observed, namely, that the only which is essentially unitary in` counter-flowing liquid introduced as such into the aforesaid rectifying system shall be refluxed condensate from rectified vapors` leaving the system.

(Certain very importalltpractical advantages result from the novel procedure characterizing the invention. In the iirst place, the necessity for re-run stills is entirely eliminated, while in place of such equipment itis only necessary to install a rectifying column of which the cost is relatively very small as compared to that of a batteryof re-run stills and which occupies only a fraction ofthe ground space required by such a battery. Furthermore, as will be more `fully hereinafterpointed out, the yield of salable gasoline is substantially increased and a material economyof heat units is effected, not to mention other advantages that will appear as the description proceeds. 85`

The underlying principles of the invenf tion can be further explained to best advanl tage in connection with a detailed description of a typical practical embodiment thereof that has been found to give good results in practice. 1n this descriptiom reference will be made to the accompanying drawings which illustrate more or less diagrannnatically typical apparatus installations useful in carrying out the process. 'Referring to these drawmgsa i l Fig. 1 is a diagrammatic view in elevation of a typical plant embodying the yprinciples of the invention, wherein a single rectifying column or fractionator is associated with a battery of four stills of the ordinary pot type;

Fig. 2 is a similar view of a plant in which a battery of pipe stills isused in place of the pot stills of Fig'. 1;

Fig. 2a is a cross sectional view of one of the pipe stills; and- Fig. 3 is a similar view of another plant also embodying the broad principles of the invention in which, however, the rectifying system differs-structurally from that illustrated in Figs. 1 and 2.

Referring -iirst more particularly to Fig.

1 of the drawings, thevcru'de petroleum .or other oil to be distilled is pumped by the pump 10 through heat exchangers 11, 11", 11, 11d, in which exchangers the heat from the hot residuum leaving the system is transn ferred in part to be incomingcrude. From. v the last heat exchanger, the o1l iows b pipe 120 12 to the first of a series or battery o stills' Nos. 1, 11,111, 1V. From still No. 1, the

oil passes by pipe 13 into still No. I1, thence by pipe 14 into still No. 111, thence by pipe 15 into still No; 1V. From still No. 1V, the 125 'hot outiowing residuum exits through pipe 16 and is forced by pump 17 through the heat exchangers before mentioned, countercurrently to the incoming crude\petroleum as already described.

soA

Stills Nos. I, II, III, IV are of any suitable type or form and are set in any conventional or suitable way. In the present instance, said stills are horizontal, cylindrical stills of the pot type, supported in brick work in the usual manner with their upper exposed portions covered by heavy insulating lagging. The stills and the interconnecting piping are so arranged that the oil iows into one end of still No. I and out of the opposite end into .still No. II, then out of the opposite end of still No. II to still No. III and so on. The interconnecting piping between the stills should be of suilicient size to permit easy flow of .oil from one still to the next without undue back pressure. When normal running conditions have been established, the oil in the respective stills of the battery stands at successively lower levels, as indicated at L1, L2', L3, L4, due to corresponding differences in back pressure from the rectifying system to be described presently. Of course, if the stills themselves are set at successively lower levels, the depth of oil in each still may be the same'. In any case, the oil level in any given still should always be such'that the heating surface of the still is completely covered with oil in order that local overheating may not occur at points where the still bottom is exposed to the direct fire beneath the still.

'Ihe' vapors from each still are introduced into a suitable rectifying or fractionating -system at suitable points. In the installation illustrated in Fig..1, this rectifying or fractionating system consists of a single fractionating column, indicated generally at C,.

having an appropriate number of bubblercap sections which may be of any usual or suitable design. It is not essential that the rectifying column be of the bubbler-cap type, the essential point being that the apparatus be of such character `as to afford full opportunity for countercurrently contacting upwardly flowing vapors with downwardly flowing liquid under conditions ensuring an approximation to equilibrium conditions at all points in the rectifying system. Such conditions can be realized in certain other forms of columns, such as packed columns, for example. In general, the distillation vapors from the several stills of the battery should be introduced into the fractionating column at such respective points that the vapors introduced at any one of said points will be, as nearly as is practically possible, in equilibrium with the vapor and liquid within the column at that point when the entire battery" of stills land the column are functioning smoothly and properly in the regular course of operation.

In the present instance, it will be seen that the vapor from still No. I is almost all gasoline, although of necessity it contains a small proportion (the equilibrium proportion) of the higher boiling components of the petroleum from which the vapor was evolved. Consequently, this vapor is introduced into the column near the top but such a sufficient number of sections below the top that the small proportion of heavy oil molecules contained in this vapor will be removed by the process of countercurrent contacting within the fractionating column.

The vapor from still No. IV is the least rich in volatile constituents and is therefore introduced into the bottom section of the fractionating column C. The vapors from stills Nos. II and III are introduced at appropriate points in the column intermediate the points at which the vapors from stills Nos. I and 1V are introduced. As before stated, the general principle governing the selection of the point for introducing the vapors from any of the stills into the column is that the point selected should be such that the introduced vapors will be substantially in equilibrium with the vapor and liquid within the column at that point when the entire battery of stills and the column are functioning smoothly and properly in the regular course of operation. In any given case it will be necessary to take several factors into account and to follow the general rule that the vapors should enter the column at the point where they will be most nearly in equilibrium when the column is functioning properly.

In the present example the fractionating column consists of'sixteen bubbler-cap sections, but the number of sections may of course be varied depending upon the various factors of operation'to be taken into account. Each section is provided with a drawoff pipe 18 for liquid, which draw-off pipe is provided with a valve and trap, as indicated. These draw-off pipes enter a header 18a. Vapor from the top of the column is led by vapor pipe 19 to condenser 2O which may be of any desired form. In the present instance the condenser consists of a worm .2l arranged within a tanlrlled with coolfrom the fractionating column. As will be pointed out hereinafter, however, it is sometimes an advantage to operate this condenser in such ma er that` the lighter portions of the gasoline vapors escape condensation therein, and when this procedure is followed, such lighter vapors pass on into a second condenser 22,-yielding a light condensate which is collected in cooler 23, so-called fixed gases or normally uncondensable vapors being vented from the system at 24. The condensate produced in condenser Q0 passes from the condenser into a dividing box 25. It will be seen that the liquid enters the box at one end andthence flows through two weirs S26-27, the horizontal opening of these weirs being adjustable by manual controls S28-29, as indicated, so that the proportion of the distillate flowing through the respective Weirs may be adjusted to any desired proportion. The discharge through Weir 27 passes vthrough a cooler 30 and thence to any suitable receiving tank or other place of storage (not shown). .The discharge through 4the other Weir (26) is directed back to the top of the fractionating column and constitutes the reux to the column. This flow.

may be by gravity or, as in the case here illustrated, the discharge of Weir 26 goes to a receiving tank 31 and is pumped therefrom by pump 32/ into the top section of the column, as indicated. In the installation here shown, the feed of liquid from receiving tank 31 into the top of the fractionating column is autpmatically controlled by the level ofthe li uid in the receiving tank by oat-contro led means indicated diagrammatically at 33 and arranged to govern the actuating mechanism of the pump 32, the arrangement being such thatthe pump automatically delivers reux to the top of the fractionatin'g column at the same rate that the redux liquid runs into the receiving tank to which the suction side of the pump is connected.

The liquid condensates received in coolers 23 and 30, respectively, are usually mixed 'together and constitute the gasoline product of the plant.

, It will be seen that in the specific procedure just described, the reflux liquid returned to the top .of the fractionating column is not rich in very light gasoline vapors, these latter largely escaping condensation in condenser 20 and therefore not yielding any liquid product entering dividing box 25 from which reflux is supplied to the column. In some cases it is advantageous thus to avoid returning very light gasoline fractions to the. top of the column,.and while the process of the invention does not necessarily involve this specific procedure, it forms a desirable feature of the invention in its more specific aspects and has been found to Work Well in practice.

At 34 is indicated a small exhausting column linto which liquid. from `the bottom of the main fractionatingcolumn C may be run.

The use of this'exhausting column is optional and is dependent upon the nature of the product that it is desired to obtain from the bottom of the column. Ordinarily, the apparatus may be sorun that the liquid from the bottom of the column contains a negligible. proportion of gasoline, say less than one to three percent. If'it were desired to produce from the bottom of the column a liquid product containing no gasoline and possibly not even a lighter part of what is normally kerosene, this could be done by using the exhausting column referred to. Heat' must be sup-- plied in the form of vapor to the bottom of the exhausting column and this is done by means of a Ismall auxiliary heater.v (not Lesaaego shown). In the present example the liquid from the bottom of the main fractionating columnC -is shown entering the top section of the exhausting column 34, while the vapors lfrom the exhaustingl column leave through of the liquid leaving the bottom of the column C` liquid leavesthe' bottom of said column C'through pipe 36 which delivers it to coolerf37. In the present example this liquid may be assumed to be a gas-oil'fraction. If the kerosene can not' be included either in the gasoline or inthe gas-oil fraction, it must be Withdrawn at some intermediate point along the column. In the present instance, the kerosene fraction is Withdrawn through pipe 38 and header 18a from -that section of the column C indicated at 39. This kerosene fraction is delivered into an exhausting column 40 which contains a heating coil 4l in its base. The vapors leave the column 40 through pipe 42 and pass into condenser 43 Where condensate is formed and reiluxes through pipe 44 back to the top of the exhausting column 40;.

while the uncondensed vapors are delivered through pipe 45-to vapor-manifold 46 from which they can be directed into any desired section 'of the fractionating column C. In this way', liquids of various compositions can be removed from the column C through suitably located draw-off lines 38, 38a, 38h, 38,

and any one of the liquids so removed may be treated in an exhausting column as desired. That is, if it be found that from no section of the column can a liquid of exactly the desired composition be Withdrawn directly, this procedure can be adapted to obtain a liquid of .the composition desired. A liquid can be withdrawn from some one Section of the column C that. is of 'such composition that its` higher boiling portion. is satisfactory.

. The volatile end of 'this liquid can then be removed in an exhausting column and the vapor so formed returned to the column C at the point Where it is most nearly in equilibrium when the column is operating normally.

If desired, that portion of the auxiliary exhausting column 40 above the feed section into which liquid is delivered through pipe 38 may be omitted; The sections above this feed section perform a rectifying function, and inl somel instances would be unnecessary because it .would be immaterial Whether a portion of the heavier components in the liquid fed in throu h pipe 38 was onnot vaporized and returne to the main column C. If 130 34. -'Under such circumstances it would in most instances be desired` to remove perhaps not more than ten per cent by volume of the liquid fed to the top of column 40. Consequently the reflux ratio would be 8 or 9 to 1, which Would be ample for all requirements. v

Reference has been made hereinabove to removal of intermediate products as liquids. They may, however, be removed as vapors; and to this end the rectifying or fractionating system may be provided with oftake means whereby vapor may be lWithdrawn from' any desired section or locality. In order to avoid `complicating the drawings, such means are not illustrated here but are of sufciently Well understood character not to require special explanation. The choice as to whether a given desired product should be removed as a liquid or as a vapor depends upon Whether it is desired to have such product free from volatile components or free from heavy components and of particularly good color. In the first case, it should be removed as a liquid; in the second, as a vapor.

Itis also feasible and desirableunder some conditions to employ an auxiliary column into which vapor is introduced from the main column, but to which auxiliary column no heat is supplied in additionto that contained in the vapor itself. In such an arrangement, the auxiliary column should be provided with a reflux condenser and a certain amount of liquid should be reluxed to the top of said column, a-vapor product leaving the upper part of the column and being condensed and collected. The liquid from the base of 'this auxiliary column, which liquid may desirably be thermally equivalent to the liquid refluxed to the top of said column, may either be returned into the main column at an appropriate point Vor may be collected separately as a product.

In starting the battery intoloperation, it may be found desirable in some Acases to return the liquid from the bottom of the column C to stillvNo. III for a time. This is because normal yand regular operation of thesystem Will not be attained immediately upon starting up, and consequently gasolinein morethan the normal small amount Will be found for a time in the liquid exiting from the bottom of column C. A valved return line 47, branching from line 36 and entering line 14, is therefore provided for permitting temporary return of liquid from the bottom of column G to still No. III., It is preferable to return this liquid to still' No. III rather than to still No. IV because re-vaporization and recovery of all of the gasoline content of the returned liquid is thereby rendered more certain.

It is to lbe especially noted that the distillation vapor from each still of the battery is sharply fractionated in operating in accordance with the process of the invention. This is true even of the vapor from still No. I. The vapor from this still contains only a small amount of high-boiling hydrocarbons;

and although it vWould be possible to include these hydrocarbons in the gasoline Without making a product having an end-point above 437 F., it is undesirable to do this because,

just to the extent that these higher boiling hydrocarbons are included in the gasoline, the'average boiling point of the gasoline is raised, particularlyl in the later stages of the distillation test to which the gasoline is subjected understandard specifications. According to the present process, the greater part of the undesirably heavy hydrocarbons that formerly could bekept out of the gasoline fraction only by special means such as redistillation, can be easily excluded; While much of the gasoline formerly going into the gasoil fraction is recovered.

In one Way of operating the illustrated still battery in practicing the present process, the vapor from still No. II may correspond very closely to the benzine fraction above referred to as obtained in prior practice. In the present process, these benzine vapors are introduced into the column, as shown, several sections below the point at which the vapors from still No. I are introduced; and by .the action .of the column, this benzine vapor is fractionated in such manner that only the gasoline portion exits from the column as a vapor, While the noni-gasoline portion passes down the column 'as a liquid. The vapor from still No. III, although it contains no light gasoline, contains a moderate proportion of hydrocarbons that boil below 437 F. This is also-true of the vapor from still N0.. IV, although to a less degree. Both of these vapors are introduced into the fractionating column at the respectively lower points indicated and are similarly fractionated so that only such portion thereof as can properly be included in the gasoline exits from the top of the fractionating column. As a result of proceeding in the manner above described, re-running is completely eliminated; and in a plant Where re-run stills lform a part of the original equipment, the re-run stills may vvtherefore be entirely dispensed with or used for some other purpose. A further advantage of the novel process, already mentioned above, is the increased yield of marketable gasoline. InA actual practice it has been found that employment of the novel process in distilling a given crude, for` example, results in an increased yield of gaso line amounting to from 15g to 30 per cent of the yield obtained from the same crude disuned by the' described method df the prior mf lfuel consumption can be cut as much as per cent or more by distillation in accordance with the present invention as above described.

In addition to the advantages already mentioned, there are others possessed by the invention vthat are of material importance.

For example, the color of the gasoline product obtained is improved over that obtained 'in prior practice, and consequently less acidis' required in refining. Again, the easier control and more fiexible operation of the battery `as a whole is marked, and consequently the operating costs for labor and supervision are reduced. All these advantages attainable by the present invention result in increased rev-l enues and reduced expenses amounting to many thousands of dollars monthly in a plant of substantial size running several thousand barrels of oil daily as such plants quite commonly do.

The plant illustrated in Figs. 2 and 2a. is generally similar in mode of operation to that illustrated in Fig. 1 and may be used with equal and in some cases greater advantage in practicing the novel process. The principal difference is in the employment of pipe stills as primary vaporizers instead of4 horizontal cylindrical stills. In the present instance the prlmary vaporizing portion of the system conf sists of a battery of pipe stills which may,-for example, comprise five pipe coil units, 50,

51, 52, 53 and 54, serially related and all housed within a suitable furnace structure indicated generallyat 55, the interior of the furnace structure being divided vertically into four sections, by partition walls 56 and horizontally by apertured partition walls 57. Each section defined by the vertical furnace walls has a combustion chamber 58 at the top, from which flame and hot combustion gases pass downwardly around one of the pipe coils 51, 52, 53, 54, and thence through apertures 59 in the wall '57 and around pipe coil 50, the gases finally passing to a suitable stack -through `due 60.

The crude oil enters the system through a system of heat exchangers indicated generally at 6l and similar to that described in connection with Fig. 1; passes thence through line 62 into pipe coil 50 which is located in the lower part of the pipe still battery and fwhich therefore is subjected to the heating effect of combustion gases at a substantially lower temperature than are pipe coils 51, 52, 53 and 54. From heating coil 50, the oil is delivered through linev 63 into a 4Hash vaporaccadde sist of upper and . lower sections 65, 66, filled 7n with suitable packing, such as ring packing or the like, 'between which sections is located a distributing baffle 67 upon which the superheated oil from pipe coil 50 is delivered through line 63. ln this vaporizer the hot oil -75 is rapidly distributed over an enormously extended surface and a vapor flashed oif which approximates the equilibrium vapor of the liquid for the temperature and pressure prevailing in the vaporizer. The vapor,

thus flashed 0H, preferably scrubbed of its entrained liquid and to some extent recti'- fied in passing through the upper packed section 65, leaves the vaporizer through line 68 and is delivered thereby into the upper part of fractionating column C( which may be similar in all respects to the fractionating column C of Fig. 1. `The liquid remaining unvaporized in vaporizer 64 is withdrawn therefrom by pump 69 which forces it through pipe 70 into and through pipe coil 51 in the pipe still furnace where said oil is superheated at a substantially higher temperature than the oil in pipe coil 50. From i pipe coil 51 the superheated oil is delivered fthrough pipe 71 into a second'flash vaporizer l 72 which may be essentially similar to Vaporizer 64 already described. Vapors flashed ofi in vaporizer 72 are delivered through line 73 into a somewhat lower section of the fracf tionating column C', as shown; while separated liquid oil is drawn from vaporizer 72 through trapped line 74 by a suitable pump (not shown) and forced through the next pipe coil .in series, namely, pipe coilv 52. In adnanner similar to that already described in connection with :pipe coil 51, the oil passing through pipe coil 52 is superheated at a still higher temperature and is discharged into a third vaporizer (not shown), the vapors flashed off therein being introduced into a still lower section of the fractionating column C through vapor line 75, while the separated liquid oil passes into and through pipe coil 53 in the furnace where it isstill further superheated and then delivered linto a. fourth vaporizer (not shown). From this fourth vaporizer, the flashed-off vapors pass into the fractionating column through vapory line 76, while the separated liquidoil passes into the last pipe coil 54 ofthe battery where it isI superheated to the maximum temperature employed and then delivered to a fifth vaporizer (not shown) from which the separated vapors pass into the base of the fraccylindrical type. Furthermore, by employ-l ing vaporizers of the type illustrated at 64 and 72 in, conjunction with such pipe stills, a much cleaner separation of substantially equilibrium vapors from the superheated oil is initially obtained prior to the introduction of vapors into the fractionating column from the several still units than is possible when a system of the type illustrated in Fig. 1 is employed.l This renders satisfactory win- -ningpf the gasoline content ofthe oil more certain, but in broad principle the system shown in Figs. 2 and 2a does not fundamentally differ from that shown in Fig. 1. y j In the system illustrated in Fig. 3, a battery of four horizontal cylindrical stills is employed as in the case of the system illustrated in Fig. 1. The rectifying system, however, differs from the specific form thereof illustrated in Figs. 1 and 2 principally in that, instead of a single rectifying or fractionating column, there are employed a plurality of rectifying or fractionating units,l

one for each of the stills of the battery, which are so related structurally and functionally, however, as nevertheless to constitute a unitary rectifying system within the meaning of this expression as hereinabove defined. Thus, the vapors from stills Nos. I, II, III and IV pass into the base of rectifying units 80, 81, 82 and 83, respectively. Liquidfor countercurrent contacting with the vapors in the rectifying units passes in series through the four units in the order 80*81-82-83.

-tifying system as such is the gasoline product refiuxed from the dividing` box 25 into the top section of rectifying unit 80. The' liquid leaving the bottom of each of the rectifying units 80, 8l and 82 is led directly into the top of the next succeeding unit ofthe series, as shown; the liquid leaving the bottom -of rectifying unit 83 being, in a typical instance, a gas-oil substantially free of gasoline constituents. On the other hand. the vapors leaving the top of rectifying unit 83 are introduced into the bottom of the next preceding unit 32 in the series, and so on, the completely rectified gasoline vapors finally 'leaving the top of rectifying unit 80 and entering the condenser as shown to yield a gasoline condensate of which at least a portion is refiuxed to the top of said unit as already stated. 65 The system just described may include also The only liquid oil introduced into the recauxiliary exhausting columns of the type described in connection with the systems shown in Figs. 1 and 2, where it is desired to draw intermediate liquid products from different portions of the rectifying system in order to obtain products of certain specified characteristics.

It is also feasible to so arrange the piping connections that any one of the four'rectifying unit-s, with itscooperating still, may be cut out of the system for repairs or cleaning out, Without interfering with operation of the remaining units and stills in the manner described. Such flexibility is at times very desirable in a system of this kind.

The general mode of operation of such a system as this does not differ materially from that of the other novel systems hereinabove described; but in some situations itisconvenient to split up the rectifying system structurally into a plurality of serially related units of the character described, and by arranging the apparatus as described, it is possible to do this while observing the essential conditions of operation characterizing the invention and realizing its benefits wholly or in large measure.

In referring to conditions of operation such that introduction of counterflow liquid into the system is to be avoided at points other than that adjacent where rectified vapors leave the system, it is not intended to exclude from .the scope of the invention herein dis closed and lclaimed the case where it may be necessary or advisable, as a temporary measure or otherwise, to re-run a distillate (e. g. so-called benzine) for separation into gasoline and a heavier fraction by introducing such distillate into some appropriate point 1n the main column.

1What we claim is:

1. Distilling apparatus comprising 1n combination, a plurality of stills, connected in series for flow of liquid through the entire series, a single rectifying or fraotionating column, vapor lines arranged to conductvapors from the several stills separately into different sections of said column adjacent the top and bottom of the column and at intermediate points thereof where the vapors are respectively substantially in equilibrium with the vapor and liquid of the column, condensing means into which vapors pass from said column, means for refluxying condensate to the upper part of the colcombination, a plurality'of stillsl connected in-series for flow of liquid throu h the entire series, a single rectifying or ractionating column, vapor lines arranged to conduct vapors from the several stills separately into .diiierent sections of-said'column at points thereof where they are respectively substantially in equilibrium with the vapors and liquids of the column, condensing means into @which vapors pass from said column, means for 'reliuxing condensate to the Aupper part of said column, an auxiliary exhausting column, means for diverting liquid thereinto from a section of said fractionating column, and means for returning to said fractionating column vapor from said exhausting col-l lIIIlIl.

3. The process of distilling liquids of mixed composition which comprises passing l such a liquid serially through a plurality of suitably heated distilling chambers, conducting evolved vapors from all of said distilling chambers into a unitary rectifying system, condensing rectified vapors leaving said rectifying system, providing a rectifying counterllow "of liquid in contact with said vapors in said rectifying system by refluxing at least a part of the condensate'from said rectified vapors to said rectifying s stem at a point adjacent where said recti ed vapors leave Asaid system while avoiding introduction of counterilow liquid, as such, elsewhere into said system, the evolved vapors from 'each of said distilling chambers being introduced into that part of said rectifying system where they will be respectively substantially in equilibrium with the vapor and liquid in said system, removing from said rectifying system an intermediate fraction 40 of an approximately desired composition, ex-

hausting said fraction of-its more volatile portion to obtain a product of an exactly predetermined composition, returning said more volatile portion to the 'rectifying system at such point as to be in substantial equilibrium with the liquid and vapor in said system, and withdrawing. a desired distillation roduct from a point in the combined recti ying and condensing system. In testimony whereof we hereunto aliix our signatures,

EUGENE H. LESLIE. EDWIN M. BAKER.

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