US2085422A - Method of distilling oils - Google Patents

Description

June 29, 1937. F. L. FAST METHOD DISTILLING OILS Filed Deo. 4, 1955 patented June 29, '1937 METHOD F DISTILLING OILS Fred L. Fast, Woodbury, N.

cony-Vacuum Oil Company, New York, N. Y., a corporation J., assignor to So- Incorporated, of New York Application December 4, 1935, Serial No. 52,755 4 Claims. '(Cl. 19d- 73) This invention relates' to methods of distillatiiclin of the heavier fractions of crude petroleum o s.

.Considerable difilculty is encountered in obtaining full yields of the heavier viscous distillates, particularly from crudes of a mixed base or asphaltic base nature in which the oils heavier than those whose recovery is desired are of an asphaltic nature. Batch fractional distillation, by shell stills or other methods taking narrow vapor cuts at increasing temperature levels are objectionable, even when carried out under vacuum, because of the combination of temperature and time elements of sucha nature as to lead to serious decomposition of the desired fractions. Flash distillations, with or without steaming, at atmospheric pressure or under vacuum, are effective insofar as they are able to reduce ex'posure to conditions which promote decomposition, but since the heat for the vaporization vof desired constituents must come from the sensible heat of the flash stream, vaporization occurs in a region of rapidly falling temperature, and dangerously high heat levels are necessary to attain good recovery,

in damage to the stock distilled, even under high vacuum and/or in the presence of considerable steam. It has been proposed to accomplish the supply of sufficient heat at a sufficiently high level to give desired vaporization by recirculation of residuum through the heater in company with the charge. Even this has not been able to accomplish the desired purpose in some instances, and resort has been had to adding a light volatile material of the nature of gas oil or kerosene to the charge oil entering the heater in order to take advantage of its carrying effect in the subsequent vaporlzation. The addition of this material adds to the heat load necessary to accom- 0 plish a given distillation, and its separation and recovery calls for additional fractionation and condensing equipment. The object of this invention is to reduce the .temperature level which must be carried to accomplish a desired vaporization of heavy distillates, without including in the charge of oil to be heated a carrier material of nature widely diering from that which it is desired to recover in the particular distillation step. A further ob- 5ject is to obtain a proper additional carrying effeet of vapors lighter than the heaviest oil'recovered as distillate, without introducing to the distillation system an oil which is foreign in nature to the oils handled therein, and without the these heat levels often resulting` expenditure of additional heat to create those lighter vapors.

It is a feature of this invention that an oil comprising a long residuum, i. e. containing some gas oils, light and heavy lubricants, and whatever asphaltic residual matter is present in the crude, is first subjected to ash distillation to remove the greater portion of the desired material as vapors. The remainder, stripped of the greater proportion of vaporizable fractions, but at a lowered temperature due to the loss of heat absorbed by vaporization of the lighter fractions, is circulated through a heater to regain temperature and vaporized in such a way that advantage is taken of the carrying effect of the vapors previously formed. The reheated oil, now carrying a much smaller proportiony of vaporizable to nonvaporizable material, will not lose as much temperature onI flashing as the original mixture. The higher temperature thus prevailing is vconducive to the vaporization of fractions of higher boiling point than vaporizable by the iirst ashing.

It is a further feature of this invention that the sensible heat carried by the residue of this second vaporization step is further used to impart heat to the cooler residue of the rst vaporization step, which heat is imparted and dissipated with a minimum time element, thereby securing maximum vaporization with high heat economy and a minimum of decomposition.

It is a further feature of this invention that the final temperature of the residue of the second flashing step may be controlled by controlling the proportionof vaporizable to non-vaporizable materials present in the stream before the secondary vaporization occurs. f It is a further feature of this invention that vapors of similar nature, destined for commingling in the same final product, but originating in separate vaporization operations, are so handled that they may be fractionated and condensed together, resulting vin marked economies of equipment for a given recovery of distillate.

Other features of the invention consist of certain novel modes of operation hereinafter described and particularly defined in the claims.

4This invention is herein described as being.

.pertinent to the recovery of heavy lubricating stock from the asphaltic residue of a mixed base crude. It is not limited to such use, but may be used for the separation of oils of high boiling point whether the residue be asphaltic or not, as Well as for other uses hereinafter pointed out. The vaporization steps of this invention may A be carried out at atmospheric pressure, or under mum temperature with less vacuum and/or steam. With set limits of temperature and of vacuum and/or steam, it will permit the recovery of greater amounts of distillate for a given heat input.

This invention, as directed to the recovery of heavy lubricating oil distillates, is operated upon topped crude oil. That is, the charging stock to the distillation process is a crude oil from which gasoline, kerosene, and more or less` gas oil have already been removed by a process of distillation as a step in preparation for the process of. this invention. This topped crude, if `from a mixed base oil, to which this invention is most applicable, will contain, in addition to the light and heavy lubricants ,which are desired, an asphaltic material to be rejected as residue and more or less gas oil lighter than the desired lubricant fractions. It may contain only the amount of gas oil normally recovered with and considered a part of the wax distillate cut, or it may contain more than that amount if desirable for its carrying effect in flash vaporization.

In ,orderl that this invention may be more thoroughly understood, reference is made to the drawing which is attached to and made a part of this specification. 'I'he single gure of this drawing shows in diagrammatic form an apparatus suitably equipped for carrying out this invention.

In the drawing, I designates a furnace or pipe still heater, and 2 the lower portion of a fractlonating tower. Topped crude oil charge, under pump pressure, enters the furnace I through inlet 3 and passes through convection coils and roof coils 5, to leave through transfer line S, entering fractionating tower 2 in ash chamber l. If desired a back pressure may be held upon the heating coil by control of'valve 8. Upon entry of the heated topped crude to the ash chamber l, a considerable portion, determined by the temperature in transfer line 6 and the nature of the charge, will vaporize, and rise through chimney 9 past drawoi` plate I0, to continue upward through tower 2. Unvaporized residue will pass downward through bailles ii to storage space I2, into which steam is led through pipe I3. This steam in passing through the oil in I2 and upward in contact with the oil passing baiiies II, will exert a stripping action thereon. This much of the operation is substantially identical withprior practice. As explained, due to conditions of heat drop in chamber 'I and across baiiles Il, it is dificult to get complete vaporization of heavy lubricant fractions, even with the aid of steam from i3, without unduly high temperatures in transfer line 6.

In practice according to this invention, no attemptis made to get complete vaporization by means of high heat level in transfer line 6. Instead, residue from I2 is withdrawn through pipe I4 by pump I5, forced through coils I6 placed on the walls of the combustion chamber of the furnace I, and delivered through transfer line AIl to Hash plate I 8 located in tower 2 above flash chamber l. If desired back pressure may be held on this heating cycle by control of valve I9. Ailditional vaporization will take place on flash plate i8, and the oil not thereon vaporized will drop through one or more stripping plates 2W, where it is contacted with light vapors from the rst vaporization, collect on drawoff plate I and pass through tube 2I and over bales II to storage space I2. The operation of this cycle is so conducted that the amount handled by pump I5 and heated per unit of time is much greater than the amount of residue from crude unvaporized in lduring the same unit, of time. That is, there is a continuous circulation of completely Istripped asphaltic residue through I5, I6, I'l, I8,

20, I0, 2|, I2 to which is added a small amount of fresh incompletely stripped residue from chamber ll.

The present invention is an advance over prior practice in several very important respects.

Heavy oil fed to ash plate I8 contains enough heat storage medium so that such vaporization as occurs there is without substantial lowering of temperature. Heavy oil leaving flash plate I8 is at a high temperature, and is immediately contacted, at stripping plate 20, with light vapors and steam from ash chamber I, and by them further stripped. The stripping action so accomplished is of suiiicient magnitude so that for a certain temperature in transfer line I'I, a much lower proportion of heat-carrying medium will give an equivalent vaporization, or with the same proportion of heat carrier, a lower temperature maybe used. At thev temperature levels necessary for vaporization of oils of this nature, even small differences of temperature are of major importance.

As a second feature of very considerable economic importance, all vapors pass together into the upper portion of tower l2, which is equipped with fractionation equipment of any 'type'suit'' able, the functioning of which has nothing to do with this invention, and which is here omitted for simplicity.

'I'he heavy, unvaporized hot oil from ash plate i8, after passing through and being stripped on stripping plate 20, collects on drawo plate ill. 'I'hat portion of it which is desired to be recovered as residuum is drawn through pipe 22 for removal from the system. Ii' desired, thisv oil may be further concentrated by use of a stripping tower of the usual sort 23, from which nal tar product is withdrawn to storage through pipe 24. The oil passing from drawoi `plate ID through pipe 2l has a further very useful duty to perform. It is at a much higher temperature than the residue from ash chamber 1, and is immediately mixed with that residue, and passes with it over baffles Il in contact with steam from i3. In this manner, arsource of heat at a usefulhigh level is available for the stripping of the otherwise rapidly cooling residue from flash chamberV l. And, most important, that heat is available at a level which will not cause decomposition of valuable constituents in the residue from ash chamber 1.

Taken together, the new concepts present in.

'following steps: heating maximum temperature limitation combined with a requirement for maximum yields. As an example of one such application, the finishing distillation of treated pressure distillate may be noted.

I claim:

l. The method of distilling an oil susceptible to decomposition -eiects above a certain temperature to obtain therefrom a full yield of uncracked distillate products which comprises the the oilv in a confined stream to a temperature near, but substantially below its cracking temperature level, passing it to a vaporizing step and separating vapors from liquid oil, mixing the liquid oil with a hydrocarbon heat carrier which is at a higher temperature still below the cracking temperature level of constituents the mixture with steam to cause vaporization of a further portion of the liquid oil, heating the mixture in a second confined heating stream to a temperature close to the cracking temperature level of constituents of the first oil, passing the heated mixture to a vaporizing step to separate vapors and leave a residuum, contacting the residuum with vapors and steam from the rst va porization to effect removal of a final portion of vapor therefrom, removing a portion of residue from the system, and mixing the remainder with liquid oil from the rst vaporization as a heat carrier therefor.

2. The method of claim 1 in which the vaporization and stripping steps are conducted under reduced pressure.

3. The method of claim 1 in which the proof the first oil, contactingv portion of heat-carrying residue added to liquid oil from the first vaporization is suihciently great so that no substantial drop in temperature occurs during the second vaporization. Y

4. The method of recovering a full yield of un cracked lubricating distillate from a mixed base crude oil without subjecting the oil to temperatures suiliciently great to cause substantial loss of the lubricant oil fraction by decomposition which comprises the following steps: heating a long residuum in a confined stream to a temperature sulcient to cause vaporization of a substantial portion of the lubricant distillate, flashing the heated oil to separate vapors from liquid oil, admixing the liquid oil with asphalt which is at a higher temperature, contacting the mixture with steam to vaporize further lubricating distillate, heating the mixture in a second co'nfined stream to a temperature high enough to vaporize substantially all the remaining lubricating distillate, this temperature being higher than that of preceding heatings, but not suciently high to bring about substantial cracking of unvaporized constituents of the long residuum, dashing the heated mixture to separate lubricating distillate vapors and a residual asphalt, contacting the residual asphalt with vapors and steam from the rst vaporization to insure complete stripping of lubricating distillate therefrom, removing a portion of the asphalt from the system, and mixing the remainder with the liquid oil from the rst vaporization as a heat carrier therefor.

FRED L. FAST.A

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