US1882568A - Method of distilling - Google Patents

Description

ocr. 11,1932. w. T. HALL 1,882,568

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w. T. HALL METHOD OF DISTILLING Filed June 18, 1928 2 Sheets-Sheet 2 mw KAS* INI/ElyToR.`

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Patented can, 1932 UmuD-STATES PATENT OFFICE WALTER T. HALL, OF GLENGOE, ILLINOIS, ASSIGNOR TO E. B. BADGER @c SONS COM- YANY, F BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS METHOD 0F Application'iled Iune 1B,

My invention relates to the control of the amount of vapor formed in vaporizers and/or fractionating columns. More specifically my invention relates to a method of controlling the amount of vapor formed in the vaporizers and/or fractionating columns of apparatus for the distillation or refining of hydrocarbon oils.

lt is a primary object of my invention to control in an eective and economical manner the amount of vapor formed in Vaporizers and/or fractionating columns. Another object of my invention is to utilize one source of heat for maintainingthe desired quantity of vapor formation in the vaporizers and/ or fractionating columns of a distillation system of the type in which a liquid fraction is withdrawn from one such distillation unit, heated to a higher temperature, and then introduced into a succeeding distillation unit Where a further distillation takes place.

A. further object of my invention is to maintain at a suitable point in a distillingA system a temperature sumcient to evaporate any Water carried in the oil before the oil is brought into contact With a highly heated metallic heating surface.

Other objects and advantages of my invention Will be apparent from the following description, taken in conjunction with the accompanying drawings, which form a part of this specification, and in which:

Figure 1 is a diagrammatic illustration of a distilling apparatus embodying my invention; and

Figure 2 is a diagrammatic representation of a cracking plant embodying my invention.

In Figure l l have illustrated my invention as applied to a system for the refining of crude-petroleum of the type in which a plurality of successively heavier c uts are taken od in succeeding distillation units, the

' residue from one unit being reheated before being introduced into the next unit., n a system of this character, crude oil is delivered to the first distillation unit of the series Where a light fraction is distilled from the oil under treatment. The bottoms from DISTILLING 1928. Serial No. 286,221.v

this first unit are withdrawn, heated to ahigher temperature, and then delivered to a second distillation unit Where a somewhat heavier fraction than that separated in the first unit is taken overhead. In such systems, it is customary initially to heat the oil before its introduction into the first unit by means of suitablevheat exchangers. 'It is known that ,for a given pressure, the yield and quality of the products of a vaporizer and/or fractionating column is governed by the amount of vapor formed therein, and that this amount depends upon the temperature of the material or materials fed thereto. It is frequently found, however, that it is impossible to raise the oil to the necessary temperature for thedegree of vaporization desired in the first distillation unit by means of such heat exchangers than the feed in sufiicient amount to raise the mixture to the desired temperature, this hotter oil being obtained from any suitable subsequent point in the system. The necessary temperature for effecting the desired amount of vaporization in the first unit is thus easily obtained, without requiring the use of an additionalheater, In a preferred embodiment of my invention, l return to the first distillation unit a regulable portion of the bottoms which have been Withdrawn therefrom and heated to ahigher temperature preparatory to their introduction into the'second unit.

Referring more articularly to Figure l, the oil to be distilled, is supplied through pipe -10 to heat exchanger 11, and is then passed through lpipe 12 to the fractionating column 13, which is provided with a plurality of trays 14 having bubble caps of the usual type. The material vaporized in the column 13 is taken overhead through pipe 15 and condensed in condenser 16. The'bottoms remaining in the column 13 are drawn off through line 17 by pump 18, and forced through pipe still 19, where they are heated to the temperature neccssary for the distillation of the next fraction to be separated. The heated oil from the pipe still 19 is conducted through the outlet pipe 20- to the fractionating column 21. The column 21 is provided with a plurality of bubble trays 22, and the vapors are drawn olf through overhead pipe 23 to a. condenser 24 from which the condensate is taken to storage. The bottoms from the column 21 are drawn oli' through pipe 25 and passed through the heat exchanger 11 where they.

serve to preheat the incoming stock. From the heat exchanger 11 the cooled bottoms from the column 21 may be conducted through thepipe 26 to storage.

The liquid to be distilled is preferably supplied to the fraction ating columns 13 and 21 considerably above the bottoms thereof, the lower portions of the columns serving as stripping sections to which steam may be supplied if desired through the pipes 27 and 28, respectively. Provision is made by the pipes 29 and 30 having valves 31 and 32, respectively, for returning a portion of the condensate from the condensers 16 and 24 to the tops of the fractionating lcolumns 13 and 21, respectively, to provide the necessary reflux. An intermediate fraction may be, if desired, withdrawn from one of the plates of the fractionating column 13 by means of the line 33, and introduced into the fractionating column 21 at a lower level through the trap 34. An

v intermediate fraction may be also drawn olf from the fractionating column 21 through the line 35 and passed through the cooler 36 to storage through the pipe 37.

For the purposes of illustration, it maybe assumed that the oil is heated in the pipe still 19 to a temperature of 57 5 F. and that the heat exchanger 11 serves to reheat the feed material to a temperature o approximately' 200 F. Furthermore, it must be assumed that this temperature of 200 F. is insufficient to secure the desired degree of vaporization in the fractionating column 13, and that it is desired to operate this column with a temperature of 340 F. at the vaporizer section. `It will be noted that we have available at the exit from pipe still 19 a source of heated oil, heated to a temperature far in excess of the required temperature in column 13. I utilize this source of heat to raise the temperature of the feed material supplied to column 13 by conducting a portion of the heated oil from the pipe still 19 through the line 40, which is connected to the outlet pipe 20, to the column 13. I may deliver the heated oil from the `line .40 to any point in the column 13 or to anyipoint in the pipe 12, and I control the amount of heated oil returned through the piper@ by means of theyalve 41.

A throttle valve 42 is located in the pipe 20 beyond the connection of the pipe 40 thereto, and serves to produce enough back ressure to/cause the oil to flow through the p1pe 40 in sukch quantity as the setting of the valve 41 will permit. By properly proportioning the amount of hot oil supplied through the pipe 40 to the amount of feed stock suppliedV through the pipe 12, I m-ay maintain the'desired resultant temperature of the mixture in the column 13. 'l

In a preferred 'embodiment of in invention, I operate the column 13 at suc a temperature that any water present in the feed is evaporated and taken off overhead through the pipe 15. In this manner the Water is removed from the feed before it is brought into contact with any highly heated metallic heating surface which is apt to become overheated, or in the specific embodiment illustrated, before the oil is introduced into the pipe still 19. This has the advantage of crystallizing any salts which may be dissolved in the Water by removing the water in which they are dissolved, thus leaving the salts suspended in the oil in a crystalline state. In this condition,the salts will not deposit upon the metallic heating surfaces, and local overheating and deterioration of the heating tubes of the pipe still, which might be'caused by such deposits, are thus avoided. The metallic heating surfaces in the heat exchanger 11 may be highly heated in the ordinary sense, that is to say, they may be at a temperature hi her than the boiling point of water, but t ey are nevertheless not highly heated metallic surfaces in the sense in which I am now employing that term. I t will be readily understood that the heating surfaces ofthe heat exchanger 11 are incapable of being seriously overheated,

since they are supplied with heat only from the hot liquid oil withdrawn from the colunm 21, and that therefore salt deposits in the heat exchanger are relatively unimportant. The pipe still' 19, on the other hand, is heated by hot products of combustion which, in the radiant heat section, are at a much higher temperature than the desired outlet temperature of the oil. Overheatin is thus an everpresent danger. I have use the term highlyl heated metallic surface in the claims, t erefore, to mean a metallic surface heated to hi h temperature, Whether by combustion or ot erwise, in such manner as to be subject to possible overheating.

As described above, the resultant temperature in the column 13 is a function of the amount of material returned from the pipe still 19 through the line 40, and: this amount is determined by the setting of the valve 41. I may operate the valve 41 manually in accordance with the temperature existing in the column 13 as shown by\any suitable temperature indicator. Preferablyyhowever, I

control the valve 4I automatically by means thereof. The thermostatic. device 43is conliti nected to the valve 41 and serves to open or close the valve as the temperature in the column 13 falls below or rises above the desired temperature. lThe construction of such thermostatic devices and the necessary mechanismfor operating the valve in accordance therewith is well known in the art and need not be described in detail, since any suitable device for accomplishing this purpose may be used.

It will be apparent that the load on the heater 19 is varied as the quantity of heated bottoms returned through the pipe varies. I therefore locate a thermostatic device 44 in the pipe 20 in such manneras to be responsive to the temperature of the oil flowing therethrough, and utilize this thermostatic device tol control the supply of fuel tothe heater 19 through the fuel supply pipe 45 by means of a valve 46. Any suitable type of standard thermostatic control may be used for this purpose, or the control may be manual if so desired. The thermostat 44 is preferably located at some pointin the line 20 beyond the throttle valve 42, or it may be placed in the column 21.

I have shown the heated bottoms from the column 21 as passing throu h the heat exchanger 11 for the purpose o preheating the feed material suppliedto column 13. While I preferably employ the heat exchanger 11, its use is not essential, and it will bel obvious that other means of preheating may be used if desired, or, in fact, all preheating may be eliminated from the system.

I preferably employ a pipe still as shown at 19 for the purpose of heating the bottoms from the column 13 before their introduction into the column 21, but any other heating means such as a shell still maybe utilized if desired. Furthermore, the return i e 40 need not be connected to the outlet ofthe heater 19, but oil may be drawn from the v heating means for return to the column 13 before it has completely passed through the heater. This may readily be done in the case of a pipe still by connecting the return pipe 40 to any one of the heating tubes instead of to the exit pipe 20 as shown. Moreover, my invention is not vlimited to returning the heated bottoms from the heater 19. I may if desired return a portion of the bottoms from column 21, or, where more units are employed, I may return heated lmaterial from any suitable point further along in the system. Moreover, I am not limited to the further heating and distillation of the bot- `toms from the column 13. I may Withdraw the bottoms from the column 13 to storage, and supply to the heater 19 and the column 21 la liquid fraction from any one of the plates of column 13.

Figure 2 of the drawings illustrates` the application of my invention to a cracking unit similar to the well known Dubbs type, comprising a fractionating column, a pipe still for heating the oil to a cracking temperature, a combined vaporizer and reaction chamber, and the customary auxiliary apparatus. The fractionating column is used for thedouble purpose of preheating the feed material and refining the pressure distillate vaporized in the vaporizer or reaction chamber of the cracking system proper. The feed material is introduced into the fractionating column near the top thereof, and the charging stock for the crackingstill is withdrawn from the bottom of the fractionating column,

the feed material und the condensed heavier portions of the cracking vapors withdrawn from the reaction chamber. According to this embodiment of my invention, I control the amount of vapor formed in the fractionating column by introducing thereto, together with the feed material and the cracked vapors, a regulable portion of'oil at a higher temperature than that of the feed material, this hotter oil being obtained from any suitable subsequent point in thesystem, and preferably from some point in the pipe still.

Y It will be apparent to those skilled in the art that the general principles underlying the two specific embodiments of my invention illustrated in Figures l and 2 arethe same, and l pipe 50 into a fractionating column 51, which is illustrated as being of the disc and doughnut type, although any other suitable type of column may be employed. The feed material is preferably introduced near the top of the column 51 and is preheated and may be partially vaporized, in a manner to be described hereinafter, in passing downwardly through the column. The unvaporized material is drawn oil' from the bottom of the column through the pipe 52, and is picked up by a pump 53 and forced through the heating coils of a pipe still 54, where it is heated to acracking temperature. The heated oil is discharged from the pipe still through the transfer line 55 having a regulating valve 56 into a combined vaporizer and reaction chamber 57. The coke formed during the cracking reaction largely deposits in the chamber 57, and the lighter constituents of the cracked oil are drawn olf overhead through the va r line 58 having a pressure reducing valve 59. Tla'heavy liquid residue remaining in the vaporizer chamber 57 is dra-wn a`valve 61.

Thevapor line 58 discharges into' the column 51 at an intermediate point thereof below the point at which the feed pipe discharges into the tower, and the vapors pass upwardly through the tower in counter-current to the downward flow of the feed Ina.- -teriaL The heavier constituents of the cracked vapors, such as gasoil, are condensed in the tower 51 by giving up their heat to the feed material supplied through the pipe 50, and the heat thus imparted to the feed material serves to vaporize any lighter constituents thereof.

The lighter vapors are taken overhead from the column 5l through the vapor line 62, are

-condensed in the condenser 63, and the condensate is drawnoi` through the pipe 64. A portion of the condensate may be introduced into the xtop of the column to serve as reflux through'the trap 65 having a valve 66. a

It frequently happens in such a system that the heat of the cracked vapors introduced into the fractionating column through the pipe 58 is insufficient to raise the lfeed material to the desired temperature and to secure the desired extent of vaporization thereof. Such a condition would result also in excessive condensation ofthe lighter constituents of the cracked vapors, and the charging stock for the pipe still 54 Withdrawn through the pipe 52 would contain a large proportion of comparatively light material. The presence of such light constituents in the material drawn off through the pipe 52 is a well recognized disadvantage,,principally because the further cracking of these constituents which takes place in their subsequent treatment results in the formation of a large amount of non-condensible gas, thus increasing the losses due to the cracking operation. To maintain the optimum temperature in the column 51, therefore, I return heated oil from the pipe still 54 to the column in such quantity as to maintain the desired temperature therein. For this purpose I connect a return pipe 70 provided with a valve 71 between a point in the pipe still 54 at which the oil has reached a suicientlv high temperature for the purpose intended, andthe column 51. In the specific embodiment illustrated, I have chosen as the ppint in the pipe still 54 the junction between the convection heat section and the radiant heat section thereof.

According to my invention, the valve 7l is preferably automatically regulated by a thermostatic device`72, located in the column 51. By this means the valve 71 may be opened or closed in accordance with the temperature existing in the column so that the desired temperature will be maintained therein.

In order still more thoroughly to strip the stock withdrawn throughthe pipe 52 of all olf through a line having lighter constituents, steam may if desired be introduced into the bottom of the tower 51 plied to the burner 76 in accordance with the temperature existing in the transfer line 55 at a point beyond the valve 56. For this purpose I employ a thermostatic device 79 located inthe pipe 55 and electrically connected to the valve 7 8 to automatically regulate the same, whereby the desired temperature may be automatically maintained in the line 55. i

The thermostatic devices 72 and 79 and the associated automatic valves 71 and 78 ma be of any desired type, and inasmuch as suc devices are well known in the art they will not be described in detail.

It will be apparent from the foregoing description that the feed material is rst preheated and partially vaporized in the column 5l, the unvaporized residue is then heated to a higher, in this case a cracking temperature, and next distilled under .cracking conditions of temperature and pressure from the vaporizer 57. As described in connection with Figure 1, my invention consists in returning a regulable portion of the highly heated material from a subsequent point in the system to the first vaporizing column to control the temperature in said first column. It will be noted that in the construction shown in Figure 2', the vapors formed in the second vaporizer are introduced into the first va orizer n stead of being separately condensed as in Figure y1, but this variation has no effect upon lie application of the principles of my inven- It will be apparent that instead of employing two fractionating columns as shown in Figure 1, or a fractionating column and a vaporizeres shown in Figure 2, I may employ any combination of vaporizers, fractionating columns,or combined vaporizers and fractionating columns. In the claim I have used the term distillation unit to mean a va-porizer, a. fractionating column, a va orizer-fractionating column, or any piece o equipment that is adapted to separate a'iiuidinto gaseous and liquid components. l

Althou h I have described my invention in considera le detail, it will be a parent to those skilled in the art that many clian es and modifications may be made Without a ecting the spirit of my invention, and I desire to be limited, therefore, only b l the prior art and the scope of the appende claim.

I claim:

The method of controlling the amount of vapor formed in a distillation unit from water-containing hydrocarbon oil which comprises introducing such oil into a distillation unit without first exposing it to any highlyheated metallic surface, separating said oil into a plurality of fractions, withdrawing and heating a substantially water-free liquid fraction, returning a regulable portion of said heated fraction to said distillation unit, further heating the remainder of said fraction, and introducing said remainder into a second distillation unit, said returned portion being' of the same character as the remainder of said heated fraction.

In testimony whereof, I have signed my name to this specifica-tion this 13th day of June 1928.

WALTER T. HALL.

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