US1845959A - Method of cracking petroleum hydrocarbons - Google Patents

Description

Feb, 16, 1932. w, M, CROSS 1,845,959

METHOD OF CRACKING PETROLEUM HYDROCARBONS Filed June 22, 1928 BUBBLE TOWER COOLER REA CT/ 0N CHA MBER F l/RNACE I N VEN T0 R Patented Feb. 18, 1932 lTD STATES PATENT OFFICE WAL'JEEJB. M. CROSS, OF KANSAS CITY, MISSOURI, ASSIGNOR IO GASOLINE PRODUCTS UOIVDE'ANY, INCL, OF WILMINGTON, DELAWARE, A CORPORATION OF; DELAWARE Ilv'IETHOID F CRACKING PETROLEUM HYDROCARBONS Application filed June 22,

This invention relates to improvements in a method of cracking and decomposing petroleum hydrocarbons to produce lighter from heavier boiling point products and to manufacture a motor fuel adapted for internal combustion engines.

The novelty of the invention lies primarily in the combination of steam with the hydrocarbon products after they have been raised y to a relatively high temperature and subsequent superheating of the hydrocarbons in the presence of steam to effect additional decomposition and rearrangement ofthe molecules and what is hereinafter termed as selective oxidation of the hydrocarbons in which the mixture of oil and steam is carried to a sufficiently high temperature to form earbon monoxide and hydrogen which appears to re-combine with the gumming hydrocarbons and carbonaceous material separated during the incipient decomposition of the oil, thus retarding the decomposition and accumulation of the separated polymers in tubes.

The single figure is a diagrammatic side elevational view of a type of apparatus in which the process may be carried on, with parts in section and parts broken away.

Referring to the drawings, at 1 is shown a furnace in which is positioned a heating coil an separated into two sections designated as 2 and 3. Adjacent the furnace 1 is a second furnace or superheater 4 in which is positioned a superhcating coil 5. The discharge end of the superheating coil communicates 35 with the reaction chamber 6 which ispref erably fabricated of a single ingot of forged steel. This chamberhas removable ends to facilitate cleaning and is heavily insulated to prevent heat by radiation.

At 7 is shown an evaporator connected by a transfer line 8 to the reaction chamber 6 and in this line 8 is interposed a reduction valve 9. The top of the evaporator 7 is connected by a vapor line 10 to a dephlegmating is or refluxing tower 11, preferably of a bubble 1928. Serial N0. 237,400.

type. The bottom of the evaporator is equipped with a draw-off line 11 controlled by a valve 12 automatically manipulated by a liquid level regulating device 13. The line 11 terminates in a cooling coil 14.

The dephlegmating tower has a bottom draw-off line 15 controlled by a valve 16 automatically regulated by the liquid level regulating device 17. A vapor line 18 is conneete'd to the top of the tower and terminates in a condensing coil 19 positioned in the condenser box 20. The discharge end of the coil 19 connects with a pipe 21 which communicates with a gas separator 22. This gas separator is likewise equipped with a gas relief line 23 controlled by a valve 24: and a bottom liquid withdraw line 25 regulated by a valve 26 manipulated automatically by a. liquid level regulating device 27.

In operation, oil is introduced from any convenient source through the pipe 28 and is passed through a pre-heating coil 29 positioned in thetop of the dephlegmating tower. From the coil 29 the preheated oil is directed through the line 30, is picked up by the pump 31 and charged to the upper heating coil section 2 in the furnace 1. From the upper bank of tubes the oil passes through the transfer line 32 into the lower bank of tubes 3 where additional heat is added.

At a point intermediate of the inlet and discharge of the passage of the oil through the furnace, preferably at a position designated by the pipe 33, steam is introduced and combined with the hydrocarbons passing.

the tubes 5, and this thermo-couple regulates the valve which controls the fuel supplied to the burner 34. Combustion gases, after being passed over the tubes 5, are discharged through a breeching 37 into the main furnace 1 to supplement heat applied to the tube banks 2 and 3.

After being superheated in the tubes 5, the oil is discharged into the reaction chamber where it collects in a considerable body, and in this stage the cracking which is initiated in the tubes 2, 3 and 5, is substantially consummated. The pressure maintained upon the heating tubes and reaction chamber and the apparatus up to the valve 9 ranges from 500 to 1000 pounds per square inch. Normally pressures of the order of from 600 to 700 pounds are utilized, although higher pressures are more feasible with certain types of oil.

The cracked hydrocarbon products are discharged from the opposite end of the reaction chamber 6 through the transfer line 8, pressure being reduced at the valve 9. The pressure maintained in the apparatus subsequent to the chamber 6 is normally only sufficient to overcome friction in the apparatus, but where'operation and quality of the ultimate distillate is to be improved, super-atmospher ic pressures of 200 to 250 pounds may be maintained upon the evaporating and dephlegmating stages.

In the evaporator the heavier and lighter hydrocarbons are separated by distillation, the lighter materials passing overhead through the line 10110 the refluxing tower 11.

The heavier materials accumulate in the bottom of the evaporator, and are drawn off through the pipe 11' and directed to a cooler 14:, after which they are diverted to storage or to subsequent further methods of treatment, such as in coking stills, for the separation of the free carbon and distillable fractions.

The vapors passing into the refluxing tower through the pipe 10 rise and are contacted by a wash oil flowingin a counter-current direction tothe rising vapors. The temperatures in the towers are-so controlled that the vapor passing overhead through the line 18 constitutes substantially the fractions com prising the ultimate distillate. This overhead material is drawn off through the line 18 and condensed in the condensing coil 19 after which it is collected in the gas separator 22. The gas is taken off from the separator through the line 23 and the distillate through the bottom liquid withdrawal line 25. V

Refluxing condensate accumulating in the tower 11 is withdrawn through the pipe 15, is picked up by the pump 38 and re-circulated through the line 39 to the suction side of the pump 31 by means of which it is again introduced into the system.

It has been found in actual practice in cracking hydrocarbons at temperatures in excess of 700 at pressures in excess of 500 pounds, that carbon has a tendency to collect in the transfer line between the heating tubes and the reaction chamber or in the tubes near the discharge end of the heating bank. This accumulation may necessitate shutting down the operation for cleaning at intervals, and toward the close of the run retards considerably the normal operation of the apparatus. It has been found that if steam is introduced to the heating tubes and superheated with the hydrocarbons to temperatures of the order of 1000 F. in the coil bank 5, the steam will combine with the resinous material and free carbon which is separated during the cracking of the oil to form substantially carbon monoxide and hydrogen, thus preventing the accumulation of the polymers and carbonaceous material on the tubes, and eliminating difliculties or clogging of the tubes from this source. To effect this type of operation it is advisable to maintain the temperatures in the supplementary heater 4 relatively constant, and for this purpose a thermo-couple 40 is attached to the surface of one or more of the tubes and set at a predetermined temperature. When the tube surface reaches this temperature the thermo-couple causes the diaphragm or electrical manipulating device 41 to which it is connected, to throttle the fuel control valve of the burner 34, thus automatically controlling the combustion temperature of the gases in the furnace 4:.

By maintaining these tubes at a metal temperature of around 1000 and an oil temperature of the order of 900 F., it has been found that the steam introduced through the line 33 decomposes and combines with the polymers separated out during the cracking operation.

It has also been found in actual operation that under these conditions a gasoline is produced having improved anti-detonating qualities. A mid-continent gas oil operated on in this manner had anti-detonating qualities equal to a gasoline produced from ordinary parafiin base crude gasoline when blended with 40% of benzol, so that the cracked distillate removed from a process of this character when operating on mid-continent gas oil, has substantially the characteristics of a .0% benzol blend gasoline distillate.

The particular reaction that takes place 12 is unknown, though it is thought that there is a selective oxidation created by the presence of the steam, or that the steam has a hydrogenating effect upon the polymerized material.

The process contemplates any type of operation in which steam is combined with hydrocarbons during heating, and the mixture superheated tothe extent that the constitucombined with the hydrocarbon constituents to prevent the accumulation of polymers and carbonaceous material in the heating tubes.

llt is obvious also that the elimination of deposition in the heating coils and superheating coils 5 diminishes the amount of separated polymerized material accumulating in the reaction stage.

A typical operation on mid'continent gas oil having a gravity of 32 to 33 Baum,

would be to heat the oil to a temperature of 700 to 800 F. in the heating coil and raise the temperature in the superheating coil 5 to 900 to 950 F, while temperatures in the reaction chamber would recede to from 700 to 800 l5. T he pressure, as suggested, would be in the order of 500 to 1000 pounds per square inch in the heating and reaction stages up to the reduction valve 9.

"l he oil is heated in separate zones which may be identified as a. primary heating stage and a secondary heating stage which correspond to the initial stage of heating and a stage of superheating. In the primary heating stage the oil is raised to a temperature of incipient cracking or to a degree of heat where the separation of polymerized mate.- rial is not excessively formed or formed to the extent that considerable deposition occurs in the tubes. In the secondary or superheating zone sutiicient heat is supplied so that the heat is added at a greater rate than it can be carried away by the oil passing through the tubes, and this excessive heating of the tubes or metal surrounding the circulating oil is automatically controlled so that the walls of the tubes carrying the oil shall be heated to a temperature substantially higher than the temperature of the oil, and in the neighborhood of 1000 F. or above. This excessive temperature to which the metal in the tubes in the superheating stage is raised may be defined broadly as that term perature at which the carbonaceous or gumming hydrocarbons separated during the heating will be oxidized by the constituents of the steam present with the oil to produce carbon monoxide and hydrogen.

ll claim as my invention:

1. A. process of cracking hydrocarbon oils to increase the anti-detonating properties thereof comprising the steps of heating the oil to a conversion temperature in a heating zone, subsequently supplying steam to the hydrocarbons at an intermediate stage in the heating zone, raising the temperature of the hydrocarbons after the introduction of steam sutliciently high to produce a selective oxidation of the polymers separated during heating, collecting the hydrocarbons in an enlarged body in liquid phase, and maintaining superatmospheric pressure thereon, passing the products of conversion from the enlarged body to an evaporating zone maintained at a pressure lower than that at which the conversion is carried out whereby a portion of the products of conversion will be vaporized, and then separating the lighter from the heavier vaporous fractions by fractionation.

2. A process of cracking hydrocarbon oils to increase the anti-detonating properties thereof comprising the steps of heating the oil to a conversion temperature in a heating zone, subsequently supplying steam to the hydrocarbons at an intermediate stage in the heating zone, raising the temperature of the hydrocarbons after the introduction of steam sufliciently high to produce a selective oxidation of the polymers separated during heating, collecting the hydrocarbons in an enlarged body in liquid phase and maintaining superatmospheric pressure thereon, passing the products of conversion from the enlarged body to an evaporating zone maintained at a pressure lower than that at which the conversion is carried out whereby a portion of the products of conversion will be vaporized, then separating the lighter from the heavier vaporous f actions by fractionation, and recycling the reflux condensate to the heating zone.

3. A process of cracking hydrocarbon oils to increase the anti-detonating properties thereof and retard carbon accumulations comprising the steps of heating the oil to a conversion temperature under high pressure, combining steam with the highly heated oil, further heating the oil at high temperatures and effecting a combination of the constituents of the steam and polymers separated from the oil during heating by superheating the mixture of oil and steam, affording time for completing the reaction by collecting the highly heated products of conversion in an enlarged body in a reaction zone without any substantial reduction in temperature and pressure, passing the products of conversion from the reaction zoneto a vaporizing zone maintained at reduced pressures whereby the lighter fractions will be vaporized, and sub jecting the vaporized fractions to fractionation to separate the lighter from the heavier fractions.

4;. A process of cracking hydrocarbon oils to increase the anti-detonating properties thereof and retard carbon accumulations comprising the steps of heating the oil to a conversion temperature under high pressure, combining steam with the highly heated 011, further heating the oil at high temperatures and effecting a combination of the constituents of the steam and polymers separated from the oil during heating by superheating the mixture of oil and steam, affording time for completing the reaction by collecting the highly heated products of conversion in an enlarged body in a reaction zone without any substantial reduction in temperature and pressure, passing the products of conversion from the reactlon zone to a vaporizing zone 4- p, r I 1,845,959

maintained at reduced. pressures whereby the lighter fractions will be vaporized; subjecting the vaporized fractions to fractionation to separate the lighter from the heavier fractions, preheating the oil to be treated by passing the same in; heat exchange relation with the vapors to be fractionated, mixing the preheated oil with reflux condensate from the fractionation ofthe vapors, and introducing the same into the heating zone.

WALTER M. CROSS.

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