US2081855A - Method for increasing lubricating oil yields - Google Patents

Description

F. G. FELLOAWS METHOD FOR INCREA'SING LUBRICATING OIL YIELDS Filed Jan. 28, 1935 3 Sheets-Sheet l AO n.0@

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May 25, 1937. F. G. FELLows METHOD FOR INCREASING LUBRICATING OIL YIELDS E' Sheets-Sheet 2 Filed Jan. 28, 1955 utbhoxuk May 25, i931.

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@mwah Patented May 25, 1937 UNITED STATES METHOD FOR INCREASING LUBRICATING OIL YIELDS Fred G f. Fellows, Ponca City, Okla., assigner to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Application January 28, 1935, Serial No. 3,697

4 Claims.

My invention relates to a method for increasing lubricating oil yields.

This application is a continuation in part of my co-pending application, Serial No. 558,765, 5 led August 22, 1931, for Method and apparatus for increasing lubricating oil yields.

Oil renners rind that, at certain periods, lubricating oil demands increase While light oil demands decrease. This renders it desirable to operate reneriesior the maximum production of lubricating oils.

A distillation plant is usually designed for a crude oil having characteristics falling between certain limits. It frequently happens that the supply of crude oil having the characteristics for which a distillation plant has been designed, becomes exhausted. If a crude oil having different lcharacteristics is processed in a plant designed for another crude, the yields will be low, and if the processing conditions are attempted to be adjusted to increase these yields, other difficulties will arise, and it will be found that cracking and carbon depositions may take place. For example, a plant was designed for running Seminole Osage crude for producing cylinder stock in an atmospheric, single flash operation. Similarly, another plant was designed for producing cylinder stock from Seminole Osage crude in a two-stage atmospheric and vacuum distillation unit. In operating these units with the Serninole Osage crude, satisfactory yields were obtained, the stocks were of good character and were produced with ease. The units could be kept on stream for considerable periods without cleaning. When the supply of Seminole Osage crude was not available, it was attempted to run a Kansas Crude in the same units. Diiiiculties immediately arose. The yields were W and the stocks produced were of poor quality. Considerable difculty was encountered in that the towers coked after a short period of operation. lt will be obvious that inasmuch as crude oils vary in price it is desirable to be able to run a unit with various crudes and yet produce the desired results.

One object of my invention is to provide a method enabling refiners to secure a lubricating oil yield, when desired, from crude oils normally not adapted to give such yields.

5 Another object of my invention is to provide a charging stock from a virgin crude having a preponderance of light fractions, enabling it to be processed in units which were designed for crude oils of different characteristics.

Another object of my invention is to provide a process whereby crude oils of differing characteristics may be economically processed in order to obtain desired lubricating oil yields.

In general, my invention contemplates the building of a synthetic crude by altering the equilibrium flash vaporization temperature of the virgin crude. I accomplish this by adding to the virgin crude a percentage of topped crude having a higher equilibrium dash vaporization point, so that the resulting equilibrium flash vaporization point will allow the material which it is desired to recover, to be vaporized without causing cracking to take place, and at the same time supply sufiicient heat to the fractionating column so that sufficient reflux medium can be used to produce streams of proper specifications.

It is known that crude oils bearing a large percentage of heavy ends require a higher flash temperature in order to secure the same percentage of overhead lubricating oil products than do crude oils carrying a preponderance of light ends.

ln the prior art, United States patent to Peterkin et al., No. 1,710,240, discloses the addition of low boiling materials to crude, oils which are decient in the same, in order to obtain the carrying effect of the easily volatile, lighter ends.

United States patent to Coubrough, No. 1,911,993, dated May 30, 1933, discloses the adding oi heavy material, such as non-volatile asphalt, to the crude oil as a heat-carrying medium. Coubrough adds a heavy material of such character kthat the boiling point of the desired constituents of the crude oil is not sufciently affected. I-le mak-es no attempt to alter the equilibrium ,flash vaporization temperatures, but employs the heatcarrying material to supply heat in much the same manner as employed in a heating coil for reboiling the heaviest fraction of reflux condensate. Moreover, none of the heavy material added by Coubrough is vaporized and taken overhead.

In the accompanying drawings which' form part of the instant specication and which are to be read in conjunction therewith, and in which like reference numerals are used to indicate like parts in the various views;

Figure l is a diagrammatic View of a two-stage atmospheric and vacuum distillation unit.

Figure 2 is a diagrammatic view of an atmosr pheric, single flash lubricating oil unit. o

Figure 3 is a, graph showing curves obtained by plotting the slopes of the true boiling point curves from the 10% to the 70% over points against the percentages over at intersections between ash 55 distillation curves and true boiling point batch distillation curves.

Figure 4 is a graph showing a curve obtained by plotting the slope of the true boiling point curve from the 10% to the 70% over points against the slope of the flash distillation curve from the 10% to the 7 0% over points.

Figure 5 is a graph showing curves obtained by plotting the percentage distilled overhead against temperature degrees Fahrenheit (true boiling point curves).

The curves in Figure 6 are equilibrium flash vaporization temperature curves showing percentages obtained overhead at temperatures degrees Fahrenheit.

By the term equilibrium flash vaporization temperature is meant the temperature to which a hydrocarbon oil must be heated in order to vaporize a given percentage of oil when the heated mixture is flashed and at which temperature the flashed vapors are in equilibrium with all remaining liquid. It will be appreciated that due to the ease with which hydrocarbon oils are decomposed at high temperatures, the desired percentage cannot be obtained in some cases without cracking or decomposing certain fractions. Sometimes this difficulty may be overcome by lowering the equilibrium flash vaporization temperature below the cracking temperature by adding more volatile hydrocarbons to the charging stock, thus taking advantage of the carrying effect of the lighter ends. An example of this has been pointed out above in Peterkin et al. Patent No. 1,710,240. In other cases, however, the difficulty is not overcome in this manner, because cracking is not only a function of temperatures, but of time, as well.

By way of example, assume that I desire to distill out the lubricating oil fractions of a light crude which contains a small percentage of such fractions. In attempting to secure a yield of such products by distillation, it is discovered that the volume of the heavy or lubricating oil fractions is so small that the liquid refluxing down through the tower and being withdrawn from the side streams and the bottom of the tower has a low velocity and therefore remains in the tower for such a long period of time that cracking ensues.

The amount and nature of the hydrocarbon oil to be added to the charging stock to obtain an increased equilibrium flash vaporization temperature is determined in the following manner:

(a) The time and temperature relationship to cracking of the heavy ends which it is desired to recover, is determined in the laboratory by bomb tests.

(b) The volumetric capacity of the pipe still and flash tower is known. From this volume and the time and temperature relation to cracking, I am enabled to determine the amount and nature of oil which must be present in the charging stock to prevent cracking at varying temperatures.

(c) For co-related relationships between laboratory true boiling point curves and equilibrium flash curves, the equilibrium fiash vaporization temperature can be determined for a mixture which will satisfy (b) above, and in all cases will be higher than the equilibrium flash vaporization temperature of the original hydrocarbon oil to be distilled.

An example of such determination is as follows:

An analysis of a particular hydrocarbon oil disclosed the presence of desired heavy ends which could be used for lubricating oil production. The equilibrium flash vaporization temperature of this oil was calculated to be 705 F. when obtaining the total quantity of the desired heavy ends. It was found from laboratory bomb tests that the desired heavy ends would crack at a temperature of 700 F. or above, if subjected to such temperature for '7 minutes or more. Calculations revealed the fact that the volume of desired heavy ends will be so small that the length of time it would take for them to flow through the tower would be approximately 7 minutes. It is obvious that if this oil were processed in an attempt to recover the desired heavy ends, cracking would ensue. It was also found that the desired heavy ends would not crack at higher temperatures if the time period at which they were held at the higher temperatures were reduced. For example, it was found that cracking would not ensue if the oil was held at a temperature as high as 850 F., provided the time period during which the oil was subjected to this temperature did not exceed iive minutes. If the oil could be processed so that the desired heavy ends would remain in the tower not more than ve minutes, a temperature of 850 F. could be used without cracking. To obtain this short a time period it was necessary to increase the percentageof heavy ends from 28% to 40%. Having determined the amount of heavy ends required to increase the percentage of heavy ends in the mixture to 40%, it is necessary to determine whether or not the equilibrium flash vaporization temperatures of the blended material containing 40% of heavy ends is above the critical cracking temperature.

Figures 3, 4, 5 and 6 show the co-related relationship between laboratory true boiling point curves and equilibrium flash vaporization temperature curves. The use of these curves will be apparent from the following example.

In Figure 5 the vapor temperatures are plotted as ordinates against liquid-volume percent disn tilled as abscissze. The following data is read from the true boiling point curve of the initial stock:

F. Temperature of 70% vaporized 790 Temperature of 10% vaporized 230 Temperature of 50% vaporized y 605 The slope between the 10% and 70% points obtained as follows:

From Figure 4 it will be seen that the slope of the flash curve equals 6.6. From Figure 3, the per cent over at the intersection between the true boiling point curve and the ash curve is 35%. From Figure 5 the temperature at 35% is read as 465 F. A point on the flash curve and its slope being established, the flash curve is drawn in Figure 6.

In a similar manner, the equilibrium flash vaporization temperature curve for the blended stock is drawn. By referring to Figure 6, it will be seen that the equilibrium flash vaporization temperature for the initial stock when 72% is vaporized is 705 F. When 60% of the blended stock is vaporized, the temperature will be 825 F. f

lIt will appear from the foregoing that even tho-ugh the equilibrium flash vaporization temperature for the blended stock is higher than the equilibrium flash vaporization temperature of the virgin stock, yet cracking will be prevented in the latter case, due to the shorter time the stock is subjected to heat in the tower. This follows because there is a larger quantity of heavier ends in the mixture, and the velocity of liquid flow through the high temperature zones in the process is increased.

More particularly, referring now to Figure l, a crude oil passes from storage through line I and is pumped by pump 2 through heat exchanger 3, through line 4, through heat exchanger 5, through line 6, through heat exchanger 1, through line 8, through heat exchanger 9, through line I0, through heat exchanger I I, through line I2, through heat exchanger I3, through line I4, to mixing tank I5. Heavy crude, or a top crude containing a quantity of desired heavy ends, is pumped from line I6 by pump I1 through line I8, into the mixing tank in which it is thoroughly blended with the virgin crude. The mixture passes from the mixing tank I5 through line I9, and is pumped by pump 28, through line 2| through the convection heat bank 22 of the atmospheric tube still 23, through radiant heat bank 24, through transfer line 25, into the atmospheric fractionating tower 26. Gasoline vapors are removed overhead through line 21, passed through heat exchanger 3 and condenser 28, into separator 29. The condensate is withdrawn from the separator 29 and passes into reflux tank 38 from which reflux is pumped by pump 3| through reflux line 32. Gasoline is pumped through line 33 to storage. A kerosene cut is withdrawn through line 34 and a gas oil cut is withdrawn through line 35. 'Ihe mixture thus denuded of gasoline, kerosene and some of its gas oil is withdrawn from the bottom of atmospheric tower 26 through line 36 and is passed through convection heat bank 31 of the vacuum tube still 38. Then it passes through the radiantly heated bank 39 of the tube still 38 and through transfer line 40 to the vacuum fractionating tower 4I. A booster or vacuum jet 42 discharging into a barometric condenser 43 maintains the vacuum tower under sub-atmospheric pressure. The oil vapors are withdrawn from the vacuum tower through line 44, and pass through heat exchangers v1 and 45 to run tank 45 from which lubricating fraction A is withdrawn through line 41. A portion of this lubricating oil fraction is returned to the tower through line 48 as reflux. Lubricating fraction B is withdrawn from the tower, passed through heat exchangers 9 and 48, through line 49, to run tank 50, whence it is pumped b-y pump 5I through line 52 to storage. Similarly, lubricating oil fraction C is withdrawn from the tower through heat exchangers II and 53, and passed through line 54 to run-tank 55 whence it is pumped by pump 56 through line 51 to storage. The heaviest fraction of reflux condensate and unvaporized tar is withdrawn from the tower through line 58 by pump 59, and is passed through heat exchangers I3 and 60, through line 6I to storage.

The above operation is that which takes place during the two stage operation. To show the efficiency of my invention, I give herewith the yields obtained when running a virgin crude deficient in heavy ends and a mixture of of crude and 20% oi.' top crude containing heavy ends:

The topped crude which was added in the above example contained the following pertinent fractions:

Per cent Gas oil 5.0 Lube A 47.9 Lube B 6.6 Lube C 22.5 Tar 15.0 Loss 3.0

Total 100.0

It is to be remembered, however, that the pertinent fractions in a topped crude to be added will vary according to the degree to which it is topped, or the amount of light material removed. The pertinent fractions will also vary in topped crudes produced from different virgin crudes. The degree to which the topped crude must be reduced is predetermined by the laboratory determinations of the desired blended crude as set forth herein.

It will be observed that the yields of lubricating oil fractions A, B and C have been materially increased. Furthermore, it is found that the quality of the lubricating oil fractions is better and that there is little danger of cracking.

In the example given above, when the virgin crude was being processed, the transfer temperature from the atmospheric tube still to the atmospheric tower, that is, the temperature in line 25, was 550 F., the reduced crude passing through line 36 to the vacuum still was 30.2% of the total charge. 'I'he transfer temperature from the Vacuum tube still to the vacuum tower was 800 F.

In the case of the mixture, the transfer temperature from the atmospheric tube still to the atmospheric tower, that is, through line 25, was 500 F., and the material passing from the atmospheric tower to the vacuum tube still was 41.2% of the total charge.

Referring now to Figure 2, crude oil is charged through line I and pumped by pump 2 through condenser 3, through line 4, through heat exchanger 5, through line 6, through heat exchanger 1, through line 8, through heat exchanger 9, through line I0', -through heat exchanger II, through line I2, through heat exchanger I3, through line I4 to mixing tank I 5. Topped crude or a heavy crude rich in heavy fractions, is pumped fro-m line I6 by pump I1, through line IB to the mixing tank I5 in which it is thoroughly admixed with the preheated virgin crude.

',Ihe mixture is pumped from mixing tank I5 through line I9, through pump 20, through line 2l, `through convection heat bank 22 and radiant heat bank 24 of atmospheric tube still 23, through the transfer line 25 into the atmospheric, single flash fractionating tower 2E. Gasoline is removed overhead through line 2l' and passes through heat exchangers 3 and 28 to separator 29. Gasoline is added from separator 29 and passes into the reflux tank 3Q, from which reflux is pumped by pump 3l through reux line 32. A portion of the gasoline from separator 29 is pumped through line 33 to storage. A kerosene fraction is withdrawn from the tower through line 34, and a gas oil fraction is withdrawn from the tower through line 35. A lubricating oil fraction A is cooled and withdrawn from the tower through line A lubricating oil fraction B is withdrawn from the tower through line 52, and lubricating oil fraction C is withdrawn from the tower through line 5l'. The heaviest fraction of reflux condensate, commonly called tar, is withdrawn from the tower through line 6I.

in order to show the improved results I obtain in practice, the following table is given:

Mixture- 80 percent 7 virgin x l crude and Cru e' 20 percent topped crudo Percent Percent Gasolene 42. 35. 0 i 6.3 5. 3 20. 17.9 15. 7 21.0 2. 2 3. 0 7. 3 9. 9 5. 0 6. 7 l. O 1` 2 It will be observed that the yields of lubricating oil fractions A, B and C are increased by my invention.

In the example given just above, 20% of top crude was added to 89% of virginy crude. The transfer temperature in line 25 in the caseof the Virgin crude was 629 F. 1n the case of the blended crude, in which the equilibrium flash vaporization temperature of the mixture was higher than that of the virgin crude, the transfer temperature was 870 F.

The topped crude in the above was a bottom cut having5% of gas oil.

.T t will be seen that I have accomplished the objects of my invention. I am enabled to ernploy a given unit to obtain uniform results by way of yields and quality from charging stocks normally unadapted to be processed in the unit. A refiner is enabled to convert portions of cheap fuel oils into valuable lubricating oils.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

1. The method of increasing lubricating oil fraction yields from a crude hydrocarbon oil, including the steps of adding a topped crude ntwo lubricating oil stocks from the fractionating zone at different points therefrom, said stocks having had their equilibrium flash vaporization temperature raised by the addition of said topped crude.

2'. A method of fractionating crude oils to obf tain lubricating oil stocks, in which a crude oil is heated to vaporize a portion thereof and the heated oil and vapors fractionated in a fractionating zone, increasing lubricating oil yields without cracking the lubricating oils desired to be recovered, by raising the equilibrium flash Vaporization temperature of the oil to be distilled, by adding a hydrocarbon oil mixture containing a larger proportion of lubricating oil fractions than is contained in the oil to be dis;

tilled to reduce the carrying effect of the light, more volatile components in the oil to be distilled, and to increase the velocity of the liquid flow through the fractionating zone.

3. A process of increasing lubricating oil yields in the fractional distillation of crude hydrocarbon oils, including the steps of raising the equilibrium flash vaporization temperature of the oil to be distilled by adding thereto a sufficient quantity of topped crude containing a largerA proportion of lubricating oil fractions than is contained in the crude oil to be distilled, heating the oil of raised equilibrium flash vaporisation temperature, fractionating the heated oil in a rst fractionating Zone, removing gas oil and lower boiling reflux condensate fractions from the first fractionating zone, separately removing the residual oil from the first fractionating Zone. heating the residual oil, fractionating the residual oil in a second fractionating Zone at reduced pressure, and withdrawing at leastV two lubricating oil stocks from said second fractionating zone at different points in said fractionatingzone, said stocks having had their equilibrium flash vaporization temperatures raised by the addition of said topped oil.

4. In a process of fractionating crude oils to obtain lubricating oil stocks in which a crude oil is heated to vaporize a portion thereof, and the heated oil and vapors fractionated in a fractionating zone, the steps of admixing with the crude oil before the heating step a sufiicient quantity of topped crude containing a larger proportion of lubricating oil fractions than is contained in the on to be distilled in order to,`

raise the equilibrium flash vaporization temperature of the oil being distilled, whereby to increase the Velocity of ow in the process and to avoid substantial cracking of the desired lubricating oil fractions.

FRED G. FELLOWS.

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