US1856471A - Method of and apparatus for oil distillation - Google Patents

Description

May 3, 1932.

F. DE'NIG METHOD OF AND APPARATUS FOR OIL DISTILLATION Fil'ed March 5, 1951 IN VENTOR. #ad Dawg BY Q A T'gRNZ Y.

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Patented May 3, 1932 rATss artnr ortica FRED DENIG, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO THE KOPPERS COMPANY, vA CORPORATION OF DELAWARE METHOD'OF AND .APPARATUS FOR OIL DISTILLATION Application filed March 3,

My invention relates to the distillation ot hydrocarbon oil for the separation of constituents thereof in relatively uncontaminated form. lt has an especial relation to the distillation oi hydrocarbon oil such, for eX- ample, as that recovered from coal. gas and consisting largely of a mixture ofA benzol, toluol and Xylols, for the recovery therefrom of such constituents in relatively uncontaminated form. My invention may, however, be employed in the distillation of other analogous oils. y

In the methods and apparatus of the prior art, intermittent distillation of crudelight oil of the character described above is necessarily accompanied by frequent regulation throughout the course of the distillation in accordance with the nature of the principal constituent being separated at any one time.

In intermittent distillation operations of this character, the various constituents are volatilized in the order of their respective boiling points, the constituents having the lowest boiling points being volatilized first. Dueto the varying temperatures at which these constituents condense. it has been necessary in the past to provide dephlegmation apparatus therefor which is capable of temperature regulation according to the condensation temperatures of the various constituents, the volatilization of which varies throughout the course of distillation.

Such dephlegmation has been accomplished in the past by subjecting the vapors evolved during the distillation operation to indirect contact with a cooling fluid such, for example, as water,r to effect a partial condensation, and the temperature regulation has een effected by varying the amount or temperature of water delivered to the dephlegmating apparatus.

Dephlegmation of this character has two other disadvantages. In the first place, the amount of condensate collected in the de phlegmator and returned as reflux to the dis- 1931. Serial No. 519,745.

tilling apparatus is necessarily only a fraction of the total condensate evolved, and is usually much less in amount than the amount of material which is permitted to leave the dephlegmator. Any attempt to increase the amount of condensate in the dephlegmator inevitably causes a material lengthening of the distillation process.

In. the'second place, it necessarily follows from a consideration of the natureI of the 1 partial condensation taking place in a dephlegmator of this type that the refluxed liquid differs somewhat from the vapors evolved, being in, fact of somewhat lower volatility.

Consequently, both the amount and nature of the reiiuxed liquid in a process ofthe character indicated above leave much to be desired, and even with large fractionating apparatus, have made it difficult or impossible in the past to obtain pure products (that is, commercially pure benzol, toluol and the like) within a reasonable time.

Furthermore, in such prior processes, it hasbeen diliicult or impossible to avoid the production of large amounts of intermediate fractions, which cause considerable loss of time and necessitates 11e-distillation.

An object of the present invention is to provide a method of and apparatus for distillation of hydrocarbon oil oit the character described, in which the regulation of fractionating or dephlegmating'temperature required throughout the course oi the distillation operation is self-controlled according to the constitution of the vapors being evolved at any time.

My invention has for other kobjects such other operative advantages and results as may hereinafter be found to obtain.

In the copending application of Joseph Van Ackeren, Serial No. 480.647, iiled September 9, 1930, there is described and claimed an intermittent distillation operation and apparatus therefor' in which the oil to be disl bell-and-tray sections,

Y effected-by withdrawing a .2G flux oil from the rectifying column and com- Y heat fromthe vapors passing rectifying column at substantially the'sameY tilled is maintained throughout the distillation at its boiling point in the usual manner and the vapors thereby evolved from the oil are conducted through a rectifying column such, forexample, as a series of conventional passing through the same in countercurrent with a suitably proportioned flow of reflux oil.

Reflux oil is introduced to the rectifying column at a point sufficiently removed from the heating vessel to accomplish an adequate rectification of the vapors, and prior to such introduction is subjected to an through the time.

Inthe aforesaid copending application of Joseph Van Aclreren, this heat exchange is portion of the reiningling the thus withdrawn reflux oil (which issues from the column at a temperature substantially equal to that of the vapors passing therethrough)V with Vay quantity of fresh reflux oil and then returning the mixs ture to the rectifyingeolumn at a point above the point of withdrawal of said portion of the reflux oil. yThe fresh reflux oil preferably consists of a portion of condensate obtainedY by cooling the rectified vapors issuing from the top of the rectifying column.l

. In this manner there is accomplished a self-regulation of the temperature and nature of the reflux oil, whereby an exceptionally efficient rectification is made possible without the usual necessity for'frequent regula- A Y tion throughout the course ofthe distillation operation as the temperatures of distillation increase. Y .l

According to my present invention, an exchange of heat between the vapors produced in the distillation and the reflux oil is accomplished lay-dividing the stream of rectified vapors issuing from the top of the rectifying column into two portions, one of which is immediately subjected to acooling operation sufficient to condense all condensible constituents of the same, thecondensate being then subjectedto indirect heat exchange with the remaining portion of the vapors andvreturned to the stillr as reflux oil,

Y, while the remaining portion of the vapors,

after such heat exchange withthe condensate .obtained from the first-mentioned portion, is

condensed in the-'usual manner.

Inthis manner, the increase of temperature of the vapors in the rectifying column causes a corresponding increase in the teinperatureof the reflux oil added to the same and-in spite of the change of temperature y throughout the operation, no regulation on the part of the operator is required, the processand apparatus beingto this extent selfregulated.

`Moreover, it is possiblein thisinanner to exchange of 'and is preferably overcome the disadvantages of the usual type of dephlegmation operation, in which the reflux oil returned to the columnnecessarily differs from the constituent being volatilized. It will be obvious that according to my invention, the reflux oil added at any time is substantially identical with the principal constituent being recovered at the same time.

1n order that my invention may be clearly set forth andunderstood, I now describe, with reference to the accompanying drawing, a preferred form in which it is accomplished and embodied. ln this drawing,

rlChe single figure is amore or less diagrammatic view, partly in elevation and partly in vertical section, of apparatus for distilling Vhydrocarbon oilin accordance with the presrihe rectifying column 2 is. in the present instance shown as comprising a plurality of bell-'a-nd-tray sections of conventional type located directly over vthe still tanlr 1 or is iii any event so connected therewith as to Vreceive therefromV Vvapors evolved during the distillation of'a hydrocarbon oil.

Each bell-and-tray sectionis provided with a suitable number of bells located over vapor uptakes 11, land one or more liquid downflow pipes 12 so disposed as to provide a liquid seal for the bells 10. A

Vapors are withdrawn from the top of the rectifying column 2 through a vapor conduit 15 having branches 16 and 17 with valves 18 and 19, respectively. s

The vapor branch conduit 16 communicates with the condenser 3 which is of the usual indirect type and isprovided with cooling water inlet and outlet conduits 21 and 22, respectively. The condenser y3 is also provided with an outlet conduit 23 which serves to remove non-condensible constituents of the vapors passing through the condenser 3 and communicates atV its lower portion with a conduit 24 which serves to remove oils condensed from the vapors passing through the condenser 3. l

The conduit 24 communicates with the l vapor-to-oil heat exchanger 5 which in turn f nica-tes with a vapor space within the heat exchanger 5 which in turn 'communicates 'ends with a condensate line 29 Vjected to a Vvided with a cooling through a vapor conduit 26 with coils 27 located within the condenser 4, which is prowater supply conduit 28 and an overflow conduit 29 so disposed as to keep the coils 27 immersed in cooling water in the condenser 4.

Vrlhe coils 2'? communicate at their lower leading through suitable connections to a plurality of receiving tanks 31.

The vapor space within the vapor-to-oil heat exchanger also communicates through a sealed conduit 33 with the condensate line 29. In the operation of the method ofthe present invention, the still tank l is charged with a suitable quantity of the oil to be distilled and heat is supplied, at first through the indirect steam coils 6 and later through the direct steam coils 7 when necessary, to maintain the oil at its boiling point and thus to effect a continuous vaporization of constituents of the oil, the removal and recovery of which in uncontaminated form are desired.

lThe vapors evolved during the distillation and which vary throughout the course of the distillation from the vapors of the lowest boiling constituent of the oil to the vapors of the highest boiling constituent of which recovery is contemplated, pass upward through the rectifying column 2 and are subcountercurrent flow of reflux oil introduced through the conduit 25 to the rectifying column 2.

.2 as reflux.

By,v reason of such contact, vapors are stripped of their higherboiling constituents so that except during the inevitably immediate periods, said vapors are rectiiied to contain substantially only the lowest boiling constituent of the vapors present in the system at any time, while any of said low boiling` constituent may in spite of such rectilication be present in the reflux oil is caused to be revolatilized in the absence of the condensation of higher boiling constituents of the vapors. In this manner what may be described as a double rectifying action is `ac complished.

Upon issuing from the rectifying column 2, a portion of the rectiiied vapors enters the condenser 3 where they are subjected to indirect contact with a flow of cooling water of such temperature and in such quantity as to eti'ect a condensation of substantially all of the condensible constituents thereof.

rlhe condensate thereby secured, and which is substantially identical in constitution with the vapors issuing from the rectifying column 2 is then subjected to an exchange of heat from the remaining portion of the vapors issuing from the rectiiying column 2 and is then returned to the rectifying column It will be obvious that reflux oil yobtained in this manner approximates both in temperature and constitution the vapors within the rectifying column 2 at the point of introduction of the reflux oil and that any changes in temperature or constitution of the reflux oil will effect a corresponding change in the nature and temperature of the reflux oil so that an extremely el'iicient rectiiication is made possible. f

The condensate obtained from the condenser 4 is delivered to the receiving tanks 3l in the usual manner in accordance with the nature of such condensate.

That is to say, so long as the condensate consists of substantially pure benzol it is delivered to one of the tanks 31 set apart for the purpose ot receiving the same and when the condensate begins to show signs of contamination with toluol which is the next highest boiling constituent of the mixture being distilled, it is delivered to another of the tanks 3l set apart for the purpose of receiving the intermediate condensate. Subsequently, upon substantially complete disappearance of benzol from the condensate, the latter is then delivered to still another of the tanks 3l set apart for the purpose of receiving toluol and so on throughout the distillation.

According to the present invention, the amounts of intermediate distillates obtained may be considerably reduced in comparison with the amounts of distillates obtained according to methods now generally employed and this constitutes an advantage of the present invention. However', such intermediates are conveniently disposed of by introducing them together with quantities of crude oil to be distilled in the following or quent distillation operation.

Moreover, the valves 18 and 19- are regulated by the operator to maintain a proper balance between the reiux oil and the vapors removed for condensation in accordance with the requirements of the particular oil being distilled.

Such operation is well within the skill ot the ordinary operator and it is ordinarily possible for such an operator to so regulate these valves at the beginning ot the distillation that no further regulation during the course of the distillation operation is required.

It will therefore be obvious that my invention dispenses with the tedious requirements oi regulation of a dephlegmating operation that have been necessary in the past and akes provi sion for a self-regulation of the temperature and nature of the reflux oil.

Where it is desirable, however, to reduce the amount of intermediate condensate obtained, the present procedure may be modilied in accordance with that described and claimed in the aforesaid copending application of Joseph Van Ackeren. According to this method, all of the distillate evolved from the column is returned thereto as reflux during the periods in which it is impossible to any subseavoid the production of an intermediate condensate.

'n "To illustrate this modification of the present process, it may be assumed that at a given time the distillation operation is produc-ing substantially flux being returned to theV rectifying column consists'also of substantially uncontaminated benzol. `When the amount of benzol'in the vapors Within the rectifying column 2 fails to such a point that the condensate begins to showcontamination with Vtoluol, the next higher boiling constituent, the valve 19 Ais closed and' all of the vapors issuing from the top of the column 2 are subjected to condensation in the condenser 3 and the condensate being then recirculated as reflux.

Since the vapors leaving the top of the column during thisl period areY necessarily richer in benzene (the most volatile constitui ent now present) and the liquid in the top of the column, the reflux returned to the column will 'also be richer in benzene than the liquid with which it mixes. For this reason, benzene'willbe caused to be concentrated in rectified form in the uppermost trays;

When this condition is established, the

valve -19 is reopenedvand thevalve 18 closedk until the rectified'benzol in the upper part of the rectifying column passes over the condenser 4. After av short period, it becomesvimpossible to prev-ent the collection of an intermediate benzol in toluolfraction and the Y valve 18 is then opened, the valve 19 remain- Y ingV open.

The intermediate fraction obtained during the time the valve 18 is closed -is delivered tothe intermediate receiver selected forgthe collection of this material.

.condensate then changes sharply to substantially pureftoluol `and is delivered 'tothe appropriate receiver.

A similar operation may be performed,Y

when so desired, during each of the interniediate periods inevitably encountered during the course of the'distillation. After all of the highest'boiling fraction-which it is possible'to obtain in satisfactorily pure form has been driven over, the Idistillation is ended.

`The intermediates then recovered during the distillation are then mixed with a fresh batch of oil for rcdistillation in the manner indi-V f cated hereinabove. Y In this instanceit v1s necessaryzto continue to deliver the condensate to the intermediate receiving tank f-or -a short time after the resumption of normal operation in order to prevent the introduction vinto the toluol receiver of such small amounts of benzol as uncontaminated benzol, the re- Vexchanging' means 'modification in detailrand is therefore not limited to such illustrative examples but may bey variously employed and practiced within the scope ofthe claims hereinafter made.,

1 claim as myinvention:

1. ln a method of distilling hydrocarbon oil of the class described, the improvement which comprises charging a batch of the oil into. a vessel, applying heat thereto to maintain the oil at its boiling point, conducting" vaporsy thereby Yevolved through a rectifying column, withdrawing rectified vapors from said column, cooling a portion thereof. to condense the same, subjecting the condensate thereby obtained to heat exchange with' ane other portion of saidv vapors, and then returning the thereby heatedv condensate to ,said rectifying column as reliux. Y

' 2. Apparatus forV distilling hydrocarbon oil of the class described which4 includesa vessel adapted to receive a batch of-said oil, means for applying heat thereto to maintain the oil at its boiling point,va rectifying column adapted to receive lthereby evolved vapors therefrom, means'for withdrawing rectified vapors from vsaid column, Va condenser located inthe pathv of a portionof said rectified vapors, means Vfor Asubjecting the condensate obtained therein to heat exchange with the remaining portion of said f rectified vapors, and means for returning the thereby heated condensate fromsaid heat to said rectifying column as reflux.

s. The nieuwe of ,draining ma@ iight 0urecovered from a gas and comprising a mixture of atleast tw-o constituents having dif- A ferent boiling points, which comprises;

charging a batch of said oil into a vessel;

applying heat thereto to maintain Ythe oil at its boiling point; conducting vapors thereby evolved through a rectifying column; withdrawing vapors from said column; during such time as said vapors contain substantially separating said vapors into two portions, cooling one portion to condense the saine, subjecting the condensate thereby obtained to heat exchangewith said other portion, and then returning said thereby heated condensate to said rectifying column as reflux, and separately condensing the other portion of said vapors; when saidvapors commence to include considerable amounts of the higherboiling constituent, condensing all of the vapors withdrawn from said column and returning the condensate t-o said column as reflux, whilefcontinuing 'the distillation, until the vapors of the lower-boiling constituent remaining in said column are caused to bel said vapors no longer contain a substantialN only the lower-boiling constituent',"

ary, 1931.

FRED DENIG.

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