US2363963A - Oil cracking process - Google Patents

Description

.NOW 28, 1944- a c. HERTHEL 2,363,963

OIL CRACKING PROCESS Filed Feb. 12,A 1927 INVENTOR Eugene C//edcl ATTORNEYS Patented Nov. 28, 1944 OIL CRACKING PROCESS Eugene C. Herthel, Chicago, lll., assignor to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application February 12, 1927, Serial No. 167,716

6 Claims.

This invention relates to improvements in the cracking of heavier oils such as gas oil in pressure stills for the production of lighter oils such as gasoline, motor spirit or pressure distillate therefrom. The invention comprises an improved process which can .be continued for a prolonger period of time before it is necessary to shut down for cleaning purposes.

In the crackingv of heavier petroleum oils in pressure stills for the production of gasoline or pressure distillate therefrom'there are formed during the cracking operation certain constituents of an asphaltic or pitch-like character. With continuation of the cracking operation, the amount of such constituents increases and there is a tendency for a deposit of carbon or coke to form on the heated surfaces of the'still, thus necessitating the shutting down of the still for cleaning purposes between successive runs. The shutting down of a pressure still, the Withdrawal of the charge therefrom, the cleaning of the still, the recharging of the still and the preliminary heating of the still to bring the fresh charge up to cracking conditions. all require time, and the total amount of timevso required in'ordinary commercial operations means a corresponding reduction in the proportion of the time when the still is operating for carrying out the desired cracking operation. Y

According to the present invention, the'deposition of pitch or-carbon on the heating surfaces of the pressure still is prevented or greatly reduced so that overheating or danger of failure of the heating surfaces can be effectively prevented, and the time of operation of a single run can be prolonged, with correspondingly greater con-V a tinuity of operation, less loss of time, and greater production per still vper day.

When a pressure still is charged with gas` oil or other charging stock vto be subjected to cracking, and when the charge is heated to an appropriate cracking temperature, Ythe cracking takes place ina gradual andv progressive manner.

The lighter constituentsproduced by the crack` i ing operation, whichv go to makeup the pressure".`

distillate, are removed from the stillprogressivelyf` A during the cracking operation. other -consumf ents, such as heavier hydrocarbons formed by- I charge during the early portion' of the run, and

they may remain completely in solution during the early portion of the run. With gradual and progressive cracking of the charge, however, the.

amount of such asphaltic or pitch-like constituents gradually and progressively increases until sooner or later the amount of such constituents increases beyond the saturationpoint. Furthermore, certain of `these constituents, which appear to be relatively 'small in amount as compared with the total amount oi the pitch-like constituentsformed, appear to be of a diierent character and to have an increased tendency to deposit on the heating surfacesof the still. Furthermore, as the charge becomes supersaturated with the lessvobjectionable pitch-like constituents, there is an increased danger of deposit of pitch or carbon on the'heating surfaces of the still, with corresponding danger of overheating and failure of the heated surfaces if the still is not shut down at more or less frequent intervals toV remove this deposit.

Among the constituents produced by the cracking operation which seem to be particularly ob`- jectionable are certain sulphur-containing compounds. In charging stock which contains sulphur. certain of the sulphur compounds appear to undergo cracking to form sulphur-containing constituents, probably of `an asphalt-like character, which are particularly objectionable.

Analyses of the carbon deposit on the heated tubes of a cracking still indicate that certainof these, sulphur-containing constituents have a preferential afilnityfor the heated surfaces, or tend to separate out on such surfaces, to give va deposit containing both iron and sulphur in proportions approximating those ofiron sulphide. It may be lalso that asphalt-like constituents of a colloidal character, or even colloidal carbon, formed vas a result of the., cracking operation,

"tend-to separateV out on the heated surfaces of the still'in a preferential manner.

I have found that the length of time during vwhichf-the` ,operation of a pressure still can be vcIackingoperatiDn. Bymaintaining a quantity of fllersearth in lintimate admixture with the stillicharge and by introducing fresh feed and run can 'be substantially prolonged.

` lThe nely divided fullers earth does not remove from the still charge all of the pitch-likeV constituents, but it has a selective action upon certain of these constituents and apparently re- Y moves those constituents which are particularly objectionable from the standpoint of forming a carbon deposit on the heated surfaces of the still This selective action may be a selective absorption of colloidal carbon or precipitated asphalt-like constituents, or sulphur-containing constituents, etc. Whatever the explanation of the action of the fullers earth may be, it has an important protective effect in preventing objectionable carbon deposit. The fullers earth also apparently has a selec'tive desulphurizing action upon the pressure still charge, selectively removing therefrom` certain ofthe objectionable sulphur-containing constituents of the charge. It is probable, also, that certain of the constituents of an asphalt-like character produced by the cracking operation and which tend to vseparate out from the charge as 'suspended particles are removed from the circulating charge by the selective adsorbent action of the fullers earth.

In addition to the selective action of the fullers earth upon the charge, the pitch content of the charge is regulated by the introduction of fresh feed and the withdrawal of pitch-laden tar, so that the content of the charge as a whole is maintained below the point which would cause objectionable carbon deposit on the heated surfaces of the still. 1 I

Accordingly, in the process of the present invention, both the nature and the amount of the asphaltic or pitch-like constituents in the charge are regulated, certain of these constituents being selectively removed by the absorbent action 'of the finely divided fullers earth, the content of remaining constituents in the charge being regulated and controlled by the withdrawal of pitchladen tar and the introduction of fresh feed during the cracking operation.

The entire body of oil charged into the pressure still, for example, gas oil, serves to hold in solution the pitch-like constituents that are formed. In the process of the present invention, however, only the pitch-like constituents which are not removed by the fullers earth remain to be held in solution ln the charge.

In its broader aspect, the improved process of the invention canl be carried out in stills of different construction, but whatever the type of still, the nely divided fullers earth is admixed with the still charge-and yrapid circulation of the oil is maintained over the heated surfaces to prevent segregation and accumulation of the earth thereon and to insure the maintenance of an intimate admixture of the fullers earth with the oil while contacting with the heated surfaces of thestill.

The improved process of the present invention is particularly advantageous in the cracking of oils in tubular cracking stills, or so-called extent, of the fullers earth with the more objectionable pitch-like constituents absorbed therein and the separating earth may be allowed to accumulate to be withdrawn from time to time, or it may be withdrawn continuously as desired, together with a sufiicient quantity of the pitch-laden tar to maintain the concentration of the still charge belowthe saturation point.

The oil circulating through the heating tubes in contact with the heated tube walls accordingly is intimately admixed with finely divided fullers earth which selectively absorbs the more objectionable constituents of the cracking reaction as they are formed and while they are therefore in their most active state.

The invention will be further described and illustrated in connection with the accompanying drawing which shows, in a somewhat conventional and diagrammatic manner, one form of tubular pressure StiILadapted for the practice of the process of the invention, but it is intended and will be understood that the invention is not limited to the specific construction and operation so described.

The apparatus shown comprises a furnaceA structure I having a rebox 2, a vertical throat or uptake 3, a heating nue 4 and stack flue '5. The heating ue I isvprovided with baiiles B and 1, and a 'battery of tubes 8 extends vertically therethrough and 'is provided withupper and lower headers 9 and I0 respectively. Connection Il is provided whereby a. portion of the cooled products of combustion may be returned to ues underneath the rebox 2 at the base of the throat 3 whereby the fresh hot products of combustion from the burner I2 may be somewhat diluted by the recirculated waste heating gases, thus div r ranged with its long axis vertical and with its bottom thereof to a level substantially above the top of the .heating element 8 dividing the lower portion of the tank I3 into a receiving or separating chamber I5 and an exhaust or supply tube stills, in which the oil is circulated from and to a bulk supply drum through a battery of heating tubes.

In such an appa atus finely divided fullers earth admixed wi fresh `feed may be introduced into and intimately admixed with the oil circulating from the bulk supplyl tank to the heating element and the velocity of circulation Y maintained sufliciently high to insure the conchamber I 6. The receiving compartment I5 is connected to the manifold I 'I of the top header 9 by a suitable return ow pipe I8. The supply compartment I 6 is connected to the manifold I 3 of the lower header I0 by circulating lines 20 and 22 and circulating pump 2I. A manhole 23 is provided for cleaning out the compartment I5 when required. The pipe 24 having a valve 25 is connected yto the lowest point oi.' the bottom of compartment I5 for charging the still A bafiles 28 which may be of the type commonly o ascaocs employed in reilux towers. .The vapor line 23 leading to the condenser is connected directly to the upper end oi' the tank. 'I'he lowermost baffle 23' is so disposed as to discharge any liquid thereon into the supply compartment I3. A valved line 30 and spray head 3l 'are provided for the introduction of fresh charging stock into the upper end of the reflux tower. The vapor line 23, condenser 32 and receiving drum 33, with itsgas release line 34 and distillate draw-off 35, may be of the type commonly employed in connection with cracking stills. A

' pressure regulating valve 36 in line 29 between the reflux tower and the condenser may be employed for controlling and reducing the pressure in the still and reflux tower independently of the pressure in the condenser or the pressure may be reduced and regulated by suitable valves arranged beyond the condenser. Connection 31 is provided for the introduction of fresh charging stock with finely divided fullers earth admixed therewith to the circulating connection 22. Valved connections 38, 39 and 40 are provided for withdrawing pitch-laden tar and fullers earth with the constituents absorbed therein from various levels in the lower portion oi' the receiving chamber I5.

VBriefly, the operation of the illustrated apparatus in accordance with the present invention is as follows: The oil is circulated from the supply compartment I3 in the tank I3 through the heating tubes 8 and thence back to the separating compartment I by means of the pump 2 I, thevaporized oil collecting in the upper portion of the tank I3 and being subjected to reflux condensation therein, and resulting vapors passing through vapor line 23 and condenser 32 to the receiver 33, the liquid distillate being drawn olf through connection 35 and uncondensed gases through connection 3l. Feed oil may be introduced through connection 34; Feed oil may be introduced through connection 30 into the head of drum I3 to regulate the reiiuxing operation and through connection 21 into the circulating line 22. Reflux condensate, admixed with any feed oil introduced through connection 3U is returned to the heating element through-compartment I6. The pressure within the cracking system may be controlled by valve 33 or by control of the withdrawal'of liquid distillate and uncondensed gases from the receiver 33. Condensation may be eilected at atmospheric'pressure, or at some predetermined intermediate pressure above atmosphericpressure, or at substantially stili pressure. The fresh oil introduced through connection 31r` contains intimately admixed therewith finely `divided fullers earth and this oil-earth mixture is preferably introduced in the form of a jet, and circulation is maintained by pump 2| at such velocity as to insure the mixture of the fullers earth and oil and prevent settling while passing through the heating element. fhe earth or part of the earth may also be supplied to the operation in intimate admixture with oil introduced through pipe 30. The volume oi' oil maintained in the system during normal operation is such as to keep the separating chamber I5 filled to the top thereof and overflowing into the supply chainber I3 and to keep suilicient oil in the supply chamber I6 to properly maintain the circulation. The exact level of the oil in compartment IB-is not important provided it is sufficient to main'- tain the proper circulation, but may advantageously be maintained considerably below that in the receiving chamber I5, as shown in the drawing, so that oil flowing from compartment I3 to compartment IB passes in a thin sheet'or iilm down the `partition I I which is heated by the oil in the receiving chamber I3 thereby promoting the release of gas and vapors.

The oil from the return pipe I8 is discharged into receiving chamber I3 below the level of the oil therein but at a considerable distance above the bottom of the chamber. The upward movement of the oil in the chamber I 5 is relatively slow, due to the relatively large cross section of the column of oil in this chamber as compared to that of the oil stream entering it, thus affording a very favorable condition for the separation of the suspended fullers earth with the constituents absorbed therein and of any additional carbon or tarry matter formed in the passage of the oil through the heating tubes 3. That portion of the chamber I5 below the connection I8 oilers a quiescent zone in which the fullers earth, carbon and heavier tarry products separating from the circulating oil may settle out and be withdrawn intermittently or continuously during the operation of the still through the draw-off line 40. The oil entering the chamber I5 is thus substantially freed from the heavy matter formed during the cracking operation and the more objectionable sulphurcontaining constituents absorbed by the fullers earth, and only relatively clean 'oil overflows into the supply chamber I6 to be again recirculated through the heating element.

In the event of stoppage of the tar draw-oil line l0. connections 33 and 39 arranged to withdraw oil from higher levels in compartment I5 may be utilized and the run continued. The drum I3 may be constructed of sufficient size to permit operation to be continued for a. relatively long time without withdrawing tar, the 'heavy tarryoonstituents and fullers earth accumulating in the lower portion of compartment I5 from which they may be removed through a manhole 23 at the end of the run. Thus even when operating semi-continuously only substantially clean oil is recirculated through the heating tubes, the heavier tarry constituents as Well as the more objectionable sulphur containing constituents absorbed by the fullers earth being separated from the circulating oil and deposited in the settling chamber.

The amount of earth employed will depend upon several factors, in any particular case, these factors including for example the character of the oil subjected to the cracking operation, the degree to which it is cracked or converted into lighter oil, andthe rate at which the cracking operation is carried out. In the cracking of gas oil or gas oil character stocks for the production of gasoline, or a gasoline containing pressure distillate, for example, using pressures in the neighborhood of pounds per square inch to 125 pounds per square inch or upward, the amount of earth may vary from about 11n pound per barrel or somewhat less up to as much as 2 pounds per barrel or somewhat more on the total quantity of oil supplied to the operation.. In general, it is advantageousto supply the nelydivided fullers earth to the operation in amounts of about 1/2 pound per barrel of the fresh oil introduced or somewhat less. While relatively coarse grades of fullers earth, for example 30 mesh or coarser can be employed in carrying out the invention, it is advantageous to use the finer grades of earth, for example 5,0 or 60 mesh or ner. 'The earth may be admixed with the oil or with part of the oil supplied t the cracking operation in any convenient manner. Onev advantageous method is to maintain in a suitable agitator a relatively concentrated sluny of earth in oil. suchas part of the charging stock, and to pump this slurry at a rate appropriate to maintain the amount oi' earth introduced at the desired value into charging stock on its Way to the pressure still.

I claim:

1 In the cracking of heavy hydrocarbon oils for the production of lighter hydrocarbon oils therefrom by distillation under pressure, the lm provement comprising circulating the oil through a heating zone and heating it therein to a cracking temperature; maintaining nely divided fullers earth in intimate admixture with theoil while passing through'the heating zone, separat--I ing suspended fullers earth from the circulating oil after it leaves the heating zone, and after such i for the production of lighter hydrocarbon oils therefrom by distillation under pressure, the improvement comprising circulating the oil through a heating zone and heating it therein to a cracking temperature, maintaining finely divided fullers earth in intimate admixture with the o'il while passing through the heated zone, separating suspended fullers earth from the circulating oil after it leaves the heating zone, withdrawing separated earth and associated material during the operation and after such separation recirculating oil therefrom through the heating zone.

3. In the cracking of heavy hydrocarbon oils for the production of lighter hydrocarbon oils therefrom by distillation under pressure, the improvement comprising circulating a stream of the oil from a bulk supply through a heating zone and back to the Ibulk supply, heating the oil to a cracking temperature in the heating zone, introducing finely divided fullers earth into the oil circulating from the bulk supply to the heating zone at a point between the bulk supply and.

intimate admixture therewith during passagel 50 through the heating zone.

4. In the cracking of heavy hydrocarbon oils for the production of lighter hydrocarbon oils therefrom by distillation under pressure. the improvement comprising circulating a stream of the oil from a, bulk supply through a heating zone and back to the bulk supply, heating the oil therein to a cracking temperatureinr the heating zone, supplying fresh oil to the oil circulating from the bulk supply to the heating zone at a point v between the bulk supply and the heating zone. introducing nely divided fuller's earth in admixture with fresh oil so supplied to oil circuing finely divided fullers earth with oil enter-A ing said heating tubes and circulating the oil and fullers earth through said heating tubes at a rate adequate to maintain the fullers earthin intimate admixture with the oil and to prevent segregation of the fullers earth during its entire passage through said heating tubes.

6. In a system for cracking high boiling hydrox carbon oils for the production of lower boiling hydrocarbon oils therefrom wherein the' oil is heated to a cracking temperature by circulating it through heating tubes, the improvement which comprises admixing nely divided fullers earth 'with oil entering said heating tubes, vcirculating the oil and fullers earth through said heating tubes at a rate adequate to maintain the fullers earth in intimate admixture with the oil and to prevent segregation of the fullers earth during its entire passage through 'said heating tubes, adding a mixture of fresh oil and fresh iinely dividedfullers earth to the cracking system and discharging residual voil and spent finely divided i'ullersl earth from said cracking system during i the operation of said cracking system.

yEUcniiNE c. HER'I'HEL.

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