US1757843A - Process for cracking heavy hydrocarbons to produce lighter hydrocarbons and coke - Google Patents

Description

May 6, 1930. H. L. PELZER ET AL PROCESS FOR CRACKING HEAVY HY I DROCARBONS TO PRODUCE LIGHTER HYDROCARBONS AND COKE Filed Sept. 16. 1922 INVENTORS ATTORNEYS Patented May 6, 1930 UNITED STATES HARRY L. PELZER AND EUGENE PATENT OFFICE C. HERTHEL, OF CHICAGO, ILLINOIS, ASSIGNORS TO SINCLAIR REFININ G COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE PROCESS FOR CRACKING HEAVY HYDROCARZBONS TO PRODUCE LIGHTER HYDRO- CARBONS AND COKE Application filed September 16; 1922. Serial No. 588,535.

The present invention relates to improvements in the cracking or converting of higher into lower boiling hydrocarbons.

When heavy oils are subjected to cracking by distilling under pressure in externally heated stills, the heat must pass through the still walls into the oil, and the oil tends to deposit carbon on the still walls, particularly if it is not kept in active circulation. The difficulties due to carbon deposit on the heated still walls are increased with heavy oils, and particularly With certain residues which give excessive coke formation when heated in this way.

The present invention relates to an improved method for cracking heavier oils for the production of lighter oils and coke therefrom, in which the difficulties due to external heating of the still are overcome and in which the heavy oil is heated internally by the introduction therein of highly superheated gases.

The apparatus for carrying out the present invention comprises a heating coil or the like for the superheating of gases to a high temperature and a pressure still arranged so that the highly superheated gases will be discharged into the body of oil in the still to heat the same internally. The pressure still may vary in its construction and operation and the preheating means for heating the gases may likewise vary. The pressure still may be provided with appendages, such as a reflux tower, etc., while the gas which is preheated and supplied in a preheated state to the pressure still may advantageously be the permanent gas escaping from the pressure still, this gas being recycled and used repeatedly in the process.

, The process of the invention involves the preheating of the gas to a temperature considerably in excess of that required for cracking the oil in the pressure still and then introducing this highly superheated gas into the oil in the pressure still to effect heating of the same, as well as effective agitation. The gas thus utilized may in part combine with the oil or with the vapors in the pressure still, While the uncondensed gas escaping from the still can be recirculated and reheated for further use in the carrying out of the process.

The present invention adapted for use in the cracking of heavy oils and residues, such as are difficult to crack in externally heated pressure stills or which give excessive coke formation when so heated. Crude oil which partakes of the nature of residues, such as certain Mexican crudes, can be treated according to the present process. Residues produced in externally heated pressure stills can similarly be subjected to further cracking for the production of increased amounts of light oils therefrom. When these heavy oils or residues are used the cracking operation can be continued until a coke-like product is produced. The present invention accordingly makes possible the operation of the pressure still as a coke still without objectionable external heating of the charge.

Instead of treating heavy oils or residues, lighter oils of the general character of gas oils or fuel oils or other distillates can be similarly treated, and, with such oils, the crack ing operation can be continued, if desired, until only a coke-like residue remains. With such oils the present process makes possible the production of increased amounts of light oils, such as are referred to as pressure distillates, and which contain large amounts of gasoline from individual charges of oil without the necessity for stopping the operation when a thick residue is obtained.

When the gas used for heating the oil is itself a hydrocarbon gas, such as the permanent gas from the cracking process, the hydrocarbons of this gas may themselves undergo cracking to a greater or less extent, so. that the superheated asesintroduced into the pressure still may e of a higher degree of unsaturation or may otherwise vary in composition from the gases before undergoing preheating. Gases which have thus been subjected to cracking will tend to react to a greater or less extent with the oil or with the vapors in the pressure still, thus promoting the formation of increased amounts of gasolene hydrocarbons.

The pressure maintained in the pressure is particularly I still can be widely varied. One effect of the passing of a current of gas through the pressure still is to promote the vaporization of heavier hydrocarbons, and an increased pressure is needed to prevent or reduce this vaporization. When such heavy hydrocarbons are vaporized, however, they will be con.- densed and returned to the still if the operation is carried out with a reflux tower. The cracking operation can be carried out at pressures around 90 to 95 lbs., or at much lower pressures, for example, around to lbs., as well as at higher pressures considerably in excess of 100 lbs. per square inch.

The preheated gas should be under a pressure somewhat in excess of that maintained in the pressure still so as to ensure the introduction of a continuous current of the gas into the'still. The compressing of the gas to a high pressure promotesheat transfer to the gas and from the gas to the oil. .By compressing the gas to a pressure in excess of that maintained in the pressure still and forcing the gas through a preheating coil, where it is preheated to a high temperature, the preheated gas will be forced'into the pressure still by its own pressure.

The nature and advantages of the invention will be further illustrated in the following more detailed description, taken together with the accompanying drawing, which illustrates in a somewhat conventional and diagrammatic mariner an arrangement of apparatus embodying the invention and adapted for practicing the process of the invention. It is to be understood, however, that the specific disclosure is for the purpose of illustration and exemplification and that the invention is not limited thereto, but is defined in the accom anying claims.

In the rawing the pressure still is indicated at 1. The oil for the pressure still is supplied from a suitable source of supply indicated conventionally at 2 through the pipe 3, pump 4 and pipe 5. The still has a vapor outlet pipe 6 leading to a reflux tower shown conventionally at 7. The uncondensed vapors pass from the reflux tower through the pipe 8 to the condenser, shown conventionally at 9. The condensed distillate collects in the receiver 10 and is drawn off through the pipe 11 to any suitable storage receptacle indicated conventionally at 12. The uncondensed gases escape from the receiver 10 through the pipe 13 to the gasometer 14. A separate supply of gas to the gasometer is' indicated at 15 or this connection may be employed for withdrawing excess gas from the system. From the gasometer the gas is drawn through the pipe 16 to the pump 17 and is pumped through the gas receiver or equalizing tank 18 and the pipe 19 to the coil 20, where the gas is preheated and then through the pipe 21 to the bottom of the pressure still 1. The coil 20 is heated in a furnace chamber 22 heated in any suitable way, for example, by an oil or gas burner shown conventionally at 23; the outlet flue is indicated at 24. A drawoff 25 is arranged at the bottom of the pressure still. A by-pass pipe 26 with valve 27 therein connects the pipes 13 and 16. Valves 27, 28, 29, and 30 permit regulation of the flow of gas through the respective pipes.

The apparatus shown in the drawing is not intended to be shown to scale, but the showing is conventional and diagrammatic. The tanks 2 and 12 and the gasometer 14, for example, will in operation be much larger in proportion than the relative size illustrated. The gasometer may be one operating at atmospheric or at a slight pressure, or it may be one adapted to receive and hold the gas at a pressure substantially the same as that in the still. 1

Instead of circulating the gas through the gasometer, it may be directly recycled, without, release of pressure, by closing the valves 28 and 29 and opening the valve 27 in the bypass pipe 26. By opening valve 30 and either valve 29 or valves 27 and 28, additional gas can be lntroduced into the circulation, while by openlng valves 28 and 30, any excess gas can be released from the circulation.

In the operation of the apparatus the pressure st1ll is charged with the heavy oil to be cracked, and this'oil may advantageously be preheated by means not shown before it is charged into the still. The gas is su plied from the gasometer and is compressed by the pump 17 to the necessary pressure, sufliciently in excess of that maintained in the pressure still to insure the introduction of the gas into the still. The compressed gas then passes through the heating coil 20 or other eating means, where it is heated to a temperature considerably in excess of that required for cracking the oil in the pressure still. The gas may thus be heated, for example, to a temperaturearound 1,000 F. and supplied at this temperature to the pressure still. In the heating of the gas gradually up to the maximum temperature, the gas may undergo cracking to a greater or less extent, particularly if it contains considerable amounts of hydrocarbon gases which are capable of undergoing cracking at the temperature and pressure employed.

The highly superheated gases enter the pressure still and pass upwardly through the charge of oil therein. The intimate contact of the gas with the oil results in cooling of the gases and heating of the oil, and this heating is locally applied where the superheated gases come in contact with the surrounding oil. The passage of the gas through the oil also serves to keep the entire body of oil' agitated and at a uniform temperature. The passage of the gas through the still also promotes vaporization of the oil while the vaporized oil is diluted with the gas. Further reaction between the gas and the oil vapors may take place in the vapor space in the cracking still, particularly where considerable amounts of unsaturated hydrocarbons are present in the superheated gas. The heavier portions of the vapors are condensed in the reflux tower 7 and returned to the still, while the ressure distillate is condensed in the con enser 9 and received in the receiver 10.

The pressure in the still may, as above stated, vary considerably with different kinds of oil and with the nature of the product desired. The pressure may be maintained and released by a valve (not shown) arranged between the still and condenser, or by the valve between the condenser and receiver, or by the outlet valve upon the receiver, so that either the still alone or both the still and condenser may be maintained under pressure.

The permanent gas and uncondensed light vapors will be drawn off into the gasometer 14 and may be recirculated over and over again with such modification in the com osition of the gases and vapors as results rom subjecting them to superheating and to subsequent commingling with oil and oil vapors in the pressure still.

It is one advantage of the present process that it permits the carrying out of the cracking operation at a substantially uniform temperature and without exercise of ob ectionable local overheating of the still walls or of the oil, although the contact of the superheated gases with the oil gives a des1rable local heating of the oil with which the gas comes in contact, with resulting promotion of the cracking operation. The process also gives a reduced yield of coke and a coke of improved quality. A dryer coke can be produced by the present process than by theconventional coke still practice. The gas loss resulting from the crackmg operation is also low and the process canbe carried outwith recycling of the gas in the manner above described without any considerable increase in the quantity of gas circulated.

By increasing the degree of the reflux ng operation, the gasoline production can be 1ncreased and the pressure still can be operated even at low pressures with resulting cracking of the oil.

While a single heating coil 1s shown conventionally for heating the gas, yet it will understood that in practice a series of coils with an appropriate number, length and size of pipes will be used for effectlvely heating a suificient amount of the gas to the desired high temperature. It will also be understood that the preheating coils can be freed from carbon, in case of carbon deposlt therein, by burning out the carbon 1n a manner well understood in the art, and that one or more of the series of preheatin coils can be disconnected when such car on removal may be necessary.

The pressure still can be operated as a coke still and the residue run down to coke.

The process and apparatus above described can be used in the cracking of a wide variety of oils and residues for the production of gasolene or pressure distillate and coke. For example, Mexican crude oil can be directly subjected to treatment in the pressure still and'reduced to coke with the production of a pressure distillate containing gasolene.

The nature of the pressure distillate can be varied and regulated, for example, by increasing or decreasing the amount of refluxing or the temperature and pressure at which the still is operated.

While only a single embodiment of the invention is illustrated in the accompanying drawings, yet it will be understood that va-' riations and modifications can be made without departing from the spirit and scope of the invention.

We claim: 1

1. In the cracking of heavier hydrocarbon oils to produce lighter hydrocarbon oils and coke therefrom, internally heating a substantial liquid body of the heavier oil at a cracking tem erature without external application of heat y introducing directly into the liquid body of oil, at a point below the liquid level thereof and'passing upwardly therethrough, hydrocarbon gases superheated to a temperature above the cracking temperature of the oil in the liquid body and continuing the operation until the liquid body of oil is reduced to a dry coke-like residue.

2. In the cracking of heavier hydrocarbon oils to produce lighter hydrocarbon oils and coke therefrom, internally heating a substantial liquid body of the heavier oil at a cracking temperature without external application of heat by introducing directly into the liquid body of oil, at a point below the liquid level thereof and passing upwardly therethrough, hydrocarbon gases superheated to a temperature above the cracking temperature of the oil in the liquid body while maintaining the liquid body of oil under superatmospheric pressure and continuing the operation until the liquid body of oil.

is reduced to a dry coke-like residue.

3. In the cracking of heavy hydrocarbon oils and residues which have previously been subjected to cracking treatment to produce lighter hydrocarbon oils and coke therefrom, internally heating asubstantial 1i uid body of the heavy oil or residue at a crac ing temperature without external application of heat by introducing directly into the liquid body, at a point below the liquid level thereof and assing upwardly therethrough, hydrocar- Eon gases superheated to a temperature above the cracking temperature of the heavy oil or residue in the liquid body and continuing the operation until the liquid body of heavy oil or residue is reduced to a dry coke-like residue.

4. In the cracking of heavy hydrocarbon oils and residues which have previously been subjected to cracking treatment to produce lighter hydrocarbon oils and coke therefrom, internally heating a substantial liquid body of the heavy oil or residue at a cracking temperature without external application of heat by introducing directly into the liquid body, at a point below the liquid level thereof and passing upwardly therethrough,

hydrocarbon gases superheated to a temperature above the cracking temperature of the heavy oil or residue in the liquid body While maintaining the liquid body under superatmospheric pressure and continuing the operation until the liquid body of heavy oil or residue is reduced to a dry coke-like residue.

HARRY L. PELZER. EUGENE C. HERTHEL.

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