US1956856A - Process for converting hydrocarbon oils - Google Patents

Description

y 1934- R. c. cooK PROCESS FOR CONVERTING HYDROCARBON OILS Original Filed Aug. 19, 1929 3M2 f? 2 653 r Patented May 1, 1934 UNITED STATES PATENT; OFFICE Ralph C. Cook, Burlington, Wis., Universal Oil Products Company,

assignor to Chicago, 111.,

a corporation of South Dakota Application August 19, 1929, Serial No. 386,770 Renewed June 7, 1933 3 Claims. (Cl. 196-66) This invention relates to an improvement in the treatment of hydrocarbon oils for the production, by thermo-decomposition, of lighter products therefrom. In the heating of hydro- 5 carbon oils to temperatures within the cracking range in a pipe still under relatively high pressures, a common practice is to reduce this pressure, or release it altogether, prior to introducing the heated oil to an expansion zone of lower pressure. In many instances coking takes place following this reduction in pressure, thus rendering the process inoperative after a relatively short period of time. An expedient frequently used to prevent objectionable coking is to introduce a cooling medium into conductive relationship with the heated oil, prior to discharging the heated oil into the lower pressure zone, which cooling medium may comprise a cooler oil, such as a crude, reduced crude, distillate being treated,

cooled residuum, or the like.

The purpose of this expedient is to arrest the cracking taking place at high temperatures so that decomposition to coke will not be brought about. This procedure has the disadvantage that the lowering of temperature as a result of the lowering of pressure prevents the vaporization of a certain percentage of the lighter constituents which then remain in the residual product which is usually removed from the system as fuel oil, and has a relatively low economical value; if this distillate ccud be recovered without the objectionable feature of coking the lines, and also of overcracking the residual oil in the expansion zone, as normally occurs where the cooling expedient is not utilized, a relatively large percentage of distillate would be available for further processing to yield higher percentages of more valuable materials, such as distillates within the so-called gasoline boiling range.

In the event that, by following this procedure, the residual oil is too viscous for use or ready sale, it can then be blended with a much smaller quantity of a light refractory distillate which is difiicult to crack into gasoline-like material. In other words, a residual oil representing approximately 50% of the crude oil may have the desired characteristics as to viscosity andB. S. (bottom still) content when processed by the use of cooling oil introduced at or near the point of reduction of pressure. If cooling oil is not introduced, approximately based on the raw material charged, may be recovered; the balance going into more valuable distillates, but normally this residual material will have a high B. S. content due to overcracking at the temperatures pre vailing in the process, and will also have too high a viscosity for satisfactory use or sale.

As a salient feature of my invention, I have discovered that by using, as a cooling medium. an incondensible hydrocarbon gas, usually obtained from the cracking process itself, I am able to cool the heated oil at or near the point of reduction in pressure, and, at the same time obtain as much, or more, vaporization than would normally occur were the oil not cooled and the cooling gas not admitted. At the same time the residual oil will not be overcracked, since its temperature will have been reduced below that at which undesired excess decomposition takes place. This results from the fact that, due to the high partial pressure of the cooling gas introduced, it will carry with it out of the residual oil a large proportion of the more volatile constituents which would not vaporize alone at the temperature prevailing.

Referring now to the single figure in the drawing, which illustrates a diagrammatic side elevational View of apparatus in which the process of my invention may be carried out, raw oil is introduced through line 1, pump 2, valve 3 and line 4 to an upper portion of a combination fractionating tower and expansion drum where it will aid in fractionation, and at the same time be preheated. The preheated raw oil and reflux condensate passes down to the bottom of the fractionating section and is withdrawn by line 6 to the suction side of pump '7 for passage through coil 8, disposed in a conventional furnace 9. The heated oil passes out through transfer line 10 and valve 11 by which means the high pressure maintained on the heating coil may be reduced. Adjacent the point of reduction in pressure through valve 11, cool non-condensible hydrocarbon gas may be introduced through line 12 and, by means of valves 13, the heated hydrocarbon mass passing through the transfer line may be cooled to a desired temperature. The introduction of this gas may take place either before, after, or simultaneous with reduction in pressure by means of valve 11.

The cooled transfer fluid and fixed gas enter the expansion section of combination tower 5, the vapors rising therethrough into the fractionating section for condensation and rectification. This section may be made up in accordance with any conventional design, although preferably of bubble plate design. The fractionated vapors will pass through line 14, controlled by valve 15, to condenser 16, finally passing to receiver 17, at

which point separation of the non-condensible gas from the condensed distillate occurs. The former may be removed through line 18 and valve 19, while the latter may be withdrawn through line 20 and valve 21.

To control the temperature at the top of tower 5 to produce a proper quality distillate, a portion of the distillate from receiver 17 may be returned through valves 27, pump 28 and line 29 to spray coil 30 located in the top of the tower.

Residual oil will be withdrawn from the system through line 22 and valve 23, and may be blended if too viscous by a side stream from tower 5 selectively withdrawn through any one or all of valves 24 and line 25. It will be found that the quantity of the side stream withdrawn will be relatively much less than the'additional vapors recovered from the residual oil in the expansion section of combination tower 5, allowing a much larger yield of more valuable products, such as gasoline, and a lower yield of products of less value, such as fuel oil. The blended fuel oil will then pass through line 26 to storage or may be withdrawn for other uses.

In one specific embodiment of the invention, the incondensible gas produced in the cracking process and being released from receiver 17 through line 18 and valve 19 may be diverted through line 31, controlled by valve 32, and through cooler; 33 to the line 12. In this event valve 34 in line 18 would be closed. While I have shown the return of incondensible gas made in the cracking process for cooling purposes, it is to be understood that the invention in its broad concept contemplates the utilization of cool noncondensible hydrocarbon gas brought into contact with the oil in the expansion section of tower 5, and broadly includes the use of such cool noncondensible gas either prior to or subsequent to discharge of the heated hydrocarbon mass from line 10 into the expansion section of tower 5.

As an example of the advantages of my invention, three runs were made under substantially the same conditions on the same stock, maintaining the production of the same quality of distillate, transfer temperatures and pressur s being the same. These conditions are as follows:

Stock-44 Baum gravity Mid-Continent reduced fuel.

Run 1-(No cooling) Pressure Resi distillate due Percent 55 Percent 10 Gravity A P l 56 Gravity A. P. I 13 I. B. R... 98 Viscosity at 122 F 800 End Point... 435 B. S 1.7

tinued.

Ran 2-( C'ooling in transfer line by raw oil to maintain temperature in flash combination tower 5 at 800 F.)

Pressure Residistillate due -10 Percent '55 57 Gravity A. P. I 15 102 Viscosity at 122 F 250 434 B. S 1.6

Ran 3-(C'00Zing transfer line by non-condensibZe hydrocarbon gas to maintain flash section of tower 5 at 800 F.)

By blending with a small portion of side stream from tower 5, estimated to have been about 10%, the characteristics of the blended fuel oil were as follows:

Gravity A. P. I 12.2 Viscosity 260 B. S 1.5

By an analysis of the results of the above runs it will be readily seen that by the improvement which I have devised, a much larger yield of gasoline is recoverable with a lower yield of fuel oil which has suitable characteristics for satisfactory sale and use.

I claim as my invention:

1. In a hydrocarbon oil cracking process of the character wherein the oil is passed in a restricted stream through a heating zone and heated therein to cracking temperature under suiiicient superatmospheric pressure to retain a substantial portion thereof in the liquid phase. the heated oil subsequently passed through a restricted transfer line in which the pressure thereon is reduced, and the oil then discharged into a vapor separating zone wherein it is distilled by the pressure reduction; the method of preventing coking of said transfer line and of increasing the extent of distillation in said separating zone which comprises introducing into said transfer line adjacent the point of pressure reduction a cool incondensible hydrocarbon gas in amount sufficient to lower the temperature of the heated oil to below that of substantial carbon formation.

2. In a hydrocarbon oil, cracking process of the character wherein the oil is passed in a restricted stream through a heating zone and heated therein to cracking temperature under suficient superatmospheric pressure to retain a substantial portion thereof in the liquid phase, the heated oil subsequently passed through a restricted transfer line in which the pressure thereon is reduced, and the oil then discharged into a vapor separating zone wherein'it is distilled by the pressure reduction; the method of preventing coking of said transfer line and of increasing the extent of distillation in said separating zone which comprises introducing into said transfer line adjacent the point of pressure reduction a cool incondensible hydrocarbon gas in amount suificient to lower the temperature of the heated oil to below that of substantial carbon formation, removing theevolved vapors from said separating zone and subjecting the same to dephlegmation to condense heavier fractions thereof, returning such condensed heavier fractions to the process for retreatment, finally condensing the dephlegmated vapors and separating the resultant con densate from the fixed gases produced by the cracking, cooling a substantial portion of said fixed gases and then utilizing the same as said cool incondensible hydrocarbon gas.

3. In a hydrocarbon oil cracking process of the character wherein the oil is passed in a restricted stream through a heating zone and heated therein to cracking temperature under sufiicient superatmospheric pressure to retain a sub- RALPH C. COOK.

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