US1717002A - Process and apparatus for the vacuum distillation of hydrocarbons - Google Patents

Description

June 11, 1929. c, LACK 1,717,002

PROCESS AND APPARATUS FOR THE VACUUM DISTILLATION OF HYDROCARBONS Filed Feb. 2, 1924 VAcuMN PUMP Patented June 11,109,29.

UNITED STATES- ,PATENT OFFICE.

JHN c. Breek, or DESTREHAN, LouIsIANA.

Application led February One of the advantages is the reduced temperatures ait which the distillates will distill,`

that is to say, their boiling points are reduced, and this becomes more marked as the vacuum is increased as, for instance, in the l5 lubricating oil -fractions the nornral boiling points may be reduced as much asy 150o F. or more when a vacuum of 24 to 2G inches of mercury below atmospheric. pressure is maintained on the oils under distillation.

The Vdirect electv of the lowered boilingr y point is very evident When it is considered that the valuable lubricating oils have a normal boilingpoint of well 'over 600o F. and as high as Z50o F. andover and by distilling .under vsuliicient vacuum such oils Will distill at approximately 600o F., this fact has a very important bearing on the quality and yield of the lubricating fractions for the reason that they will crack very readily When' heated to a temperature of 625 F. and over and Avery rapidly indeed at 700 F. to 725 F., the effect of such crackin is to produce lon.7 boiling low viscosity pro ucts andcarbonaceous material with resulting loss of yield of the desirable higlrviscosity high boilingr point foils. AFrom this it Will be seenthat if the teniperature of the distilling oilis kept at around G00o F. or under that, practically no cracking and consequent lossof the lubricating oils will result. This is equally true in distilling for residual products such as when making high boiling point or in the manufacture of asphalt.

The effect of the vacuum is to reduce the Vapor pressure of the oils and under high vacuum the yield of lubricating fractions may be increased to as much as double or more,

compared to distillation under substantially the normal pressurelof the atmosphere. It is well-known in the art that the cracking point of an oil is not always correspondingly reducedy with the lowering of its boiling point, for example, an oil having a boiling point of 725 degrees F. may start to slightly crack at 650 degrees F., While at 725 degrees F. the

reduced distillates- 2, 192A.l serial 110.590,20.

velocity of the cracking reaction would be very materially increased. Therefore, if the vapor pressure is sufliciently reduced to lower the boiling point to approximately 600 degrees F., substantially nocracking will take place and a distillate would berecovered without any substantial alterations due to cracking, thereby increasing the yield vof high. boiling stock suoli as lubricating oil, from a given amount of petroleum oil.

`Heretofore the usual practice in the manufactureof lubricating yoil distillates and residual 'products under vacuum where the batch method is employed is to introduce the oil to be distilled or reduced into a cylindrical still or in a series of stills in the continuous method), the stills being set over a lire box for direct heating, this type of construction, however, has several very serious drawbacks. Vespecially when largecapacity is required. In vacuumy distillation in cylindrical stills itis essential to heavily bracey the shell against a collapsing pressure and especially so the bottom or ire sheet which is subject to high heat with resultant softening of the steel and collapsing of the bottom will take place unless thoroughly braced, but bracing the bottoln presents the difficulty of additional metal in the fire sheet Wherever the bracing occurs with consequent overheating of the plate at that point and eventually burning of the steel. This action is hastened by the accumulation of carbonaceous material between the bracing members andl the shell and which'is diliicult to keep clean due to Furthermore,a still of this type requires frequent shutdowns for cleaning, due to accumu-` lations of coke building up'n. the braces'and bottom steam lines which result in hot spots which, if allowed to persist, would cause distortion of the fire sheet and possible rupture,

' requiring renewal of the plate. Also a still of the abovetype is very largely limited in itsy capacity to produce distillates by the amount of its heating surface, whereas, in the type to be later;described, the heating surface may be greatly extended, practically to any amount desired withinthe limitsof the evaporator and condensing equipment, thereby effecting a Very great saving m first cost of. construction and in subsequent op; eration.

I am aware that stillsof somewhat similar design and construction are used in the crackthe close proximity of the shell and braces.

U. n n

ing of 011s to produce gasoline or naphtha 4'the atmosphere, furthermore,

` 'and apparatus is new in the art to which it require internal bracing if used. The brac-` bracing of the shell, the

applies.

In the accompanying drawing I have indicated an advantageous form of apparatus, the drawing in part being diagrammatic.

Referring to the drawing, 1 represents a still or evaporator which may be constructed -iii a' horizontal or vertical position. I prefer lthe horizontal position when thermal circulation ,is used or when ejector circulation is used; it is also applicable toA pump circulation, but when the llatter is used, I prefer the Vertical type as it lends itself to easier operation. The shell of the still or evaporator .is

braced with circular or longitudinal bracesI ora combination of both, but for convenience of drawing, I show outside circumferential heads are concave, the latter may be convex if desired, but would ing is designated as 3 in the drawing and is lshown as an I-beam. This'bracing may be 4used either on the outside of the stillas shown or on the inside. I prefer the outside bracing as this permits a clear inside shell' easily kept clean and accessible, and is more easily and cheaply constructed.N This typp of construction is one of the advantagesjof my apparatus, as outside bracing would not be practical on a shell fired still. The vertical type of evaporator could be either circumferentially or vertically braced, depending upon engineering expedient. 10 on the drawing is a tray to facilitate evaporation, but which is not essential to the process, in the vertical type this tray wouldbe displaced by perforated trays downover which the incoming 'oi'l would percolate.' 41 designates a bottom perforated steam line and 42 a top steam supply inlet pipe. The steam supplying these steam ylines is preferably superheated, but is not necesprocessas any dry steam 4 are suspension connecthe evaporator in place. to which the drop sarily essential to the supply is suiicient. tions for holding 5 are flanged connections pipes 6 are connected. 7 is an ejector, either of the liquid jet type, steam or gas type. 8 is a heating coil made up of tubes in series. 9 shows the d'scharge pipes from the heating coil 8 which discharges onto the trayV 10; 11 is the furnace for heating the coil 8 12 is`an arch to cause the proper flow of combustion gases. 13is the stack to carry away thel products` of. combustion. 14 is the vapor line connecting lthe still to the tower 16; 15 is a separating chamber fitted with a tight bottom 37, and a top hooded opening 35. v 36 isa bafiiing material and may be tile or stone, or it can be fitted with baffle plates or trays; this is immaterial. 17 is a vapor pipe connecting the tower 16 to the condenser 18. 19 is a lookbox. 2O is a pipe connecting the look-box 19 to the auxiliary separator or receiver 21, 22 is a vacuum connection from the separator 21 to the lower portion of the tower 16 below th'e diaphragm 37. and which is designated 38. 23 is a vacuum pipe and is connected to the vacuum pump 47. 24 is a connection from pipe 23 to the receiver. 38 and is tted with a valve 24 The pipe 25 connects the lower portion of the top section of the fractionating tower 16 through the pipe 44 to the lower section of the fractionating tower designated by the numeral 38, passing through a cooler 26 controlled by a valve 25. 27 is a runback pipe from the separator 15 to the evaporator 1 and is fitted with a trap 27'; 28 is a pump for discharging separator 21 through pipe 49 and valve 49 and discharges through pipe 33 and valve 33 to tank 34. 29 is a pump connected to the receiver 38 through pipe 39 and valve 39 and discharges through pipe 3() and valve 30 to the top of the/tower 16 and into a spray 40. rlhe pump 29 is also fitted with a discharge pipe 31 and valve 31 into tank 32 or into other tanks as, for instance, tank 32.

In the drawing the apparatus is shown for batch operation and is chosen for its simplicity. Substantially the same construction, however, can be used for continuous operation by installingthe usual cross-over. connections usual in that method of operation, for instance, the continuous flow lines would be connected from bne evaporator to the other and lthe charging oil would be fed into the first evaporator. Also the drawing shows the circulation of the oil through the tubes-to be actuated by a steam pump 7. This can be replaced by the substitution of a pump takin T suction on the drop leg 6 and dischargln into the heating tubes at the point- 4where ejector 7 is shown. The heating coil or element` is shown in the drawing as a i single continuous coil and is'so shown for simplicity. However, the heating element may be madeupy of agroup of such heating coils in multiple, thereby proyiding `a very largeheating surface. In fact it may be made .double the heating surface of a shell still of equal charging capacity. .Another advantage of the tubular heating element vfor vacuum distillation is lthe small size `of the tubes which are suiiciently strong in themselves to withstand the collapsing pressure of the vacuum Without any internal bracing as is the case where ylarge shell type fire stills are employed. Pump- 28 has a branch connection 43 'and valve 43 discharging into pipe 30 so that the condensate from condenser 18 may be cirtions again being vaporized to again pass over into condenser 18, the increment inrv this condensate being discharged into tank 34.

\ There is also a connection 44 and valve 44 to permit the towery condensate to run back to the still 1 if\so desired. Ifmore than one still is used in al series of stills, then this ,connection 44 may also connect to the next still in advance, thereby obtaining a redistillation' o't' the primary distillate. This` is often found desirable. 45 is ai'esiduum drawotll connection and46 is a charging line with a valve 46. 47 is a vacuum pump with a connection 48 to the vacuum header 23.

Having now described my apparatus, I will describe its operation in the manufacture of parah'ine distillate.

The crude parafline distillate carrying stock is charged into the evaporator 1 to its` normal charging capa-city, say, eight hundred to one thousand barrels or more, the oil iills the heating coil or element 8 through the drop pipes 6. Heat is now, applied to the coils in the furnace 11; the oil in the coils becomes heated and, due to its lessened' density, will rise through the 'tubes 9 and discharge onto the tray 10. `Fresh oil downtlowing through the pipes 6 will take its place andA thus thermal circulation will be created. This 'anbe continued for some time or until the oil in the evaporator has attained a telnperature above the boiling point of water, steam or other propelling medium may now be turned into'the ejector 7 and morerapid circulation w'ill result and also more apid heating of the oil. I prefer to use steam in the ejector, as it is easy to apply, will serve to promote distillation in the ewiporator, and has the advantage ot condensing out in .the coil 18, thereby reducing the volume ot gases to be handled by thevacumn pump as would be the case if permanent gases were to be used for this purpose.

If there are any low boiling fractions present in the oil, they will begin to distill over passing out of t-he still through vapor pipe 14 into the separator 15, tower 1G, vapor pipe 17, and condenser 18 to the look-box 19, rundown line 20, separator 21, Athence by pump 28 and discharged for disposal elsewhere. lVhen the temperature has reached 350 F., in the evaporator, then the valve 24 v t paratus for vacuum d1st1llation, what` I in pipe 24 may be gradually opened, so that the air, gases and vapors in the system may be exhausted through the pipe 23 connected to the vacuum pump 47 through pipe 48. This will result in increased vaporization of the oil in the evaporator. More heat continually/ applied and the heavier or so called paratiine fractions will nowcommence to vaporize. If these were allowed to pass.

through the tower 1G and be condensed in condenser l18 along with the steam used incirculation and evapo ation, then a heavy diflicultly separated emulsion would. result.

boiling .point and high viscosity distillates in the tower 16 from whence they run to the receiver 38 to be pumped away or partially recirculated, In this way, the lighter distillates and the 'steam are permitted to pass over 'f into t-he :ondenser 18 and separately disposed of. By this procedure, the heavier high boiling point and higher viscosity oils are separated at a temperature above the boiling point of water from the lower boiling point oils and from the. water which remains in the iorm of steam. These lighter oils and steam form the residual vapors that pass into the condenser 18 and from there independently disposed of as previously described. In this man ner, the tower condensate is a clean practically water-tree distillate, the water being separately condensed and disposed of, thereby eliminating the troublesomeen'mlsions, as will be the result il one single condensate is made from an unseparated vapor, and which is condensed in one operation.

The circulation ot' the tower condensate may be so regulated that it will eliminate the rerunning or reducing operation by permitting the lighter low viscosity low-boiling pointoils to pass over to the condenser 18, and condensing out the heavier high yboiling high viscosity oils desired-in a reduced distillate.

This equipment is equally well adapted for reducing paratline distillates where'the residual productin the evaporator'is the (lesii-able fraction and by proper handling ol the injection oil in the tower, an intermediate paralline distillate may be obtained therefrom and 'the lighter lractions'and the water vapor will p ass over into the condenser 18. This type of still is well adapted to the manufacture of asphalt and at the same time also called parafltine distillate may be produced in the tower 1G, the asphalt remainil'lg in the evaporator as a residual product.

Having now described my process and apclaim as new and useful is:

1. A process for the production under reduced pressure of a. reduced lubricating oil stock, and the separation of an intermediate distillate and lower boiling hydrocarbons andI water, from a mixture otl the same, wherein the reducing and distillingoperation is eli'ected under aA partial vacuum greater' than 24 inches ofmercury, which comprises, circulating the mixture of hydrocarbons through heating tubes ,and an' evaporator, heating a portion of said hydrocarbons to a vaporizing temperature and introducing steam therein, maintaining a reduced pressure on the evaporator suicient to prevent decomposing or cracking .of the hydrocarbons, vaporizing thel'ower boiling hydro# carbons and passing the same together with the int-roduced steam into a ractionating tower, under reduced pressure, contacting bons, and separately condensing and collecting said lower boilingAJ hydrocarbons and water.

2: An apparatus for the vacuum distillation of oil,whicl1 comprises, a coiladapted said evaporator ofsuflicient strength to withstand a reduced atmospheric pressure greater than Q4 inches of mercury Without the employment of internal bracing, a fractionating tower connected to said evaporator, means for cyclicly circulating oil through said fractionating tower, a cooler connected to the lower portion of said fractionating tower, a condenser connected to the upper portion of said ractionating tower and means for producing a vacuum in said distillation, fractionation and condensing system.

In testimony whereof I hereunto aiix my signature.

JOHN c. BLACK. v

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