US1689590A - Petroleum-cracking process and apparatus - Google Patents

Description

Oct. 30, 1928.

J. J. JAKOSKY PETROLEUM CRACKING PROCESS AND APPARATUS Filed Oct. 15. 1925 esa-59a QFFICE.

Joint JAY JAKOSKY, or LOS ANGELES, CALIFORNIA.

EE'IROLEUM-GRACKING PROCESS AND APPARATUS.

Application filed flctober 15, 1925; Serial No. 62,553.

This invention relates to a method and apparatus for cracking petroleum or petroleum products by the actionof heat for the production of gasoline or other lighter productsand applies particularly to cracking processes in which the petroleum product is maintained during the cracking at such pressure that the cracking stock, that is the raw oil to be cracked, remains mainly in the liquid phase and only the cracked products are converted to the vapor phase as formed. The main object of the invention is to provide for substantially immediate removal of all gasoline or other cracked products of the desired volatility from the high temperature cracking zone as soon as formed so as to prevent recracking or further decomposition of such products, while at the same time'preventing the cracking stock from escaping from such zone and contaminating the cracked product.

One undesirable feature of cracking processes is the fact that the lighter hydrocarbons after their initial formation are sul 'ected to further heating and consequent fur ther decomposition before their exit from the cracking zone. This is especially true in cracking processes of the so-cailed tube type in which the cracking stock is passed under pressure through a tube heated to the desired temperature, the pressure being usually such that at. the prevailing temperaturethe cracking stock remains wholly or principally in the liquid phase while the lighter hydro-1 from the cracking opera- As a.

carbons resulting tion are converted to the vapor phase. general rule the more the gasoline or other light hydrocarbons formed in such process are subjected to formation the lower is the percentage of their recovery. Furthermore, certain portions of the cracking stock are cracked at lower temperatures than other portions and are therefore decomposed first, but according top-resent methods the vapors resulting from this relatively low temperature cracking are carried along with the liquid and subjected to a higher temperature before being released, resulting in their further decomposition. Ac cording to my invention I overcome these objections by substantially immediate removal from the cracking zone of all vaporized products, and I eflect such removal in such manner as to prevent entrainment of cracking stock with the vapors either in the form of a mist or l g or otherwise.

' The Uottrell electrical precipitator is prefthis purpose high temperture after their crab-1y used according to my invention to prevent such entrainment, and I take advantage of the fact that true gases or vapors are not precipitated or acted upon by the corona discharge of the precipitator while mist or liquid particles are precipitated thereby as in other Gottrell installations. However, while I prefer to use electrical precipitation for because of the high degree of separation obtainable thereby, I may also use any other well known means for precipitating a liquid from a gas. The invention consists briefly in passing the cracking stock through a retort and subjecting the same to a high temperature at a suitable pressure and continually removing from the high temperature zone the lighter cracked hydrocar bons substantially as soon as formed, such removal being preferably carried out at a plurality of points distributed lengthwise of the retort, subjecting each of the removed .portions to a separate precipitating operation to precipitate therefrom any mist or other liquid particles, returning the liquid so precipitated to the cracking zone at substantially the point at which it was removed therefrom, and withdrawing the clean vapors for recovery by condensation. I also preferably control the temperature-during the precipitating operation so as to maintain all thedesired lighter hydrocarbons in the vapor phase, cracking of the precipitated liquid on the walls ofthe precipitating apparatus. The invention consists riotonly in the above procbut also in the apparatus hereinafter'described for carrying out such process.

The accompanying drawings illustrate an apparatus suitable for carrying out my invention and referring thereto:

' Fig. 1 is a longitudinal vertical section of the cracking apparatus.

Fig.2 is an enlarged vertical section of two of'the precipitating tubes.

Fig. 3 is a vertical section on line 3-3 in Fig. 2.

Fig. 4 is a horizontal section on line 4-4 In Fig. 2. i

Fig. 5 is a partly sectional view of an 818 trically' heated retort.

The apparatus illustrated in Figs. 1 toA comprises a furnace chambenl of suitable refractory material. and provided with burner means 2 having supply means 3 and i for fuel and steam or air respectively andalso provide l with a stack 5 for exit of the combuswhile at" the same time preventing Lion gases. lVithin said furnace chamber is provided'the cracking retort which may comprise for example a horizontal tube or pipe 7 provided with inlet pipe 8 for supplying the cracking stock thereto and outlet pipe 9 for removing the uncracked residue and the unvaporized product of cracking therefrom. Such a cracking retort is similar to those now employed and the detailed construction of the same forms no essential part of this invention. Any other type of tubular cracking retort may therefore be used without departing from the invention.

In order to provide for immediate removal from the retort of the vaporized products I provide a plurality of upwardly extending vapor outlet passages distributed lengthwise of the retort T and each provided with means therein for etlecting precipitation, either electrically or otherwise, of suspended liquid particles from gas. Such Outlet means may comprise as shown, vertical tubes or pipes 10 co1nniunicating at their lower ends with tube 7 and connected at their upper ends for example by means of connecting pipes 11 to outlet manifold 12, which may conduct the vapors to any suitable condensing means for recovery thereof. In the drawings I have shown electrical precipitating means for removing entrained liquid from the vapors. Tubes 10 are closed at their upper ends as at 13 and a fine wire or rod 14 is suspended centrally within each of said tubes to act as a discharge elec- U'OClQ, said wire or rod or the lead-in wire connected thereto passing through suitable insulating means 15 secured in the top 13 of the tube and being connected to the high tension line 16. The insulating means 15 should the of such construction and should be secured to the top 13 in such manner as to be perfectgas-tight at' the pressure employed-in the operation. Suitable t-ensioning means such as weights 17 may be provided at the lower ends" of thefdischarge electrodes 14 so as to cause said discharge electrodestohang vertically and centrally within the respective tubes; The lowerends oftubes 10*are pref- ,erably somewhat enlarged, as at '19,*so as to prevent discharge from weights 17. These enlarged portions also act to a certain extent as mechanical traps for entrained liquid. The tubes 10 may be grounded as indicated at 18 so as to complete the electrical circuit hereinafter described and enable such tubes to serve as collecting electrodes. The connecting pipes 11 preferably extend, as shown, downwardly from the point of connection with the respective precipitator tubeslO to the i point of connection with the outlet manifold Y Q 12 so'as to prevent any condensate formed in such connecting tubes or in the outlet manifold 12 from draining back into the precipitator tubes and hence into the'cracking chamher.

In order to prevent cracking of material precipitated onto the collecting electrodes 10 it is desirable to maintain the temperature of such walls considerably below that of the retort, that is, low enough to prevent such cracking. On the other hand, the temperature at this point must be high enough to prevent condensation of any of the desired lighter hydrocarbons. The necessary control of the temperature may in some cases be secured b directing the heating flame in contact wit the retort tube, while placing the precipitator tubes in the upper part of the furnace chamber and out of direct contact with the flame. In other cases it may be found desirable to project the precipitator tubes outside the furnace to give the-desired reduction in temperature and in such cases the tubes may or may not be covered with suitable heat insulating material. As shown in the drawings, the temperature control in the precipitating zone may be efi'ected by placing a wall of refractory material 20 above the retort tube 7, in such manner that the precipitator tubes 10 are enclosed in a separate compartment 21 between such wall and the top wall 22 of the furnace. Openings 23 and 24 may be provided for permitting limited circulation of hot gases through compartment 21, and damper 25 may be placed in one of said openings for controlling such circulation. The upper ends of the precipitator tubes project above the top of the furnace to permit of connection to the vapor manifold 12, and such projecting portions of the tubes may be covered with suitable heat insulating material indicated at 26.

In operation the high tension line 16 is connected to any suitable source of high tension current either alternating or direct-but preferably rectified alternating high tension current, said source having its other terminal grounded and being adapted to maintain a potential difference between the discharge electrodes Hand the grounded collecting electrodes 10 of from say 15,000 to 100,000 volts, according to the spacing of the electrodes and other conditions. A silent electric discharge is thus caused to take place within the precipitator tubes 10 in the usual manner of electrical precipitator operation. The furnace and retort being heated tothe proper temperature by means of burner 2. the supply of raw oil or cracking stock which may be any oil adapted for cracking purposes, for example that commonly known as gas .oil, is supplied to the retort through inlet pipe 8. Such oil may if desired be preheated in any suitable manner before entering the retort, and may be supplied to the retort by pumping at the pressure which it is desired to maintain during the cracking operation, which pressure may be for example from one hundred to several hundred pounds per square inch.

In passing through the retort the oil is heated to the necessary temperature to effect grade and the lighter hydrocarbons formed by the resulting cracking operation are converted to the vapor phase at the existing conditions of temperature and pressure. In this connection it should be stated that the pressure to be employed depends upon the temperature which it is necessary or desirable to use to effect the desired cracking, and is in any case'suflicient to ensure that substantially all hydrocarbons of higher boiling point than those which it is desired to recover will remain in the liquid phase at the existing temperature while those hydrocarbons which it is desired to recover in the cracked product will be converted'to the vapor phase at such temperature. The hydrocarbon vapor thus formed at anypoint in the retort tube 7 rises and passes upwardly through the vertical precipitator tubes 10, the oil level being maintained at approximately the bottom of such tubes. In the sudden liberationof vapor from the liquid oil more or less liquid is carried along with the vapor in the usualmanner of entrainment of liquid by gas. Furthermore certain hydrocarbons which'are heavier than those which it is desired to recover in the cracked product may be temporarily vaporized on coming in contact with the hottest portions of the retort tube 7 and may be subsequently cooled and condensed upon reaching cooler portions of the body of oil or upon reduction in temperaturein the precipitator tubes. The material thus condensed is usually in the form of a fog or mist and such material passes out of the body of oil with the vapors or is subsequently formed in such vapors, and, if it were not for the electrical or other precipitation operation, would contaminate the cracked product. According to my invention however such mist particles together with any larger liquid particles entrained by the vapor are precipitated onto the surface of the vertical tubes 10 by the action of the electrical field in such tubes and 'the liquid thus collected drains back into the retort tube at substantially the point at which it was removed therefrom and is subjected to further cracking or passes out with the residue. Damper 25 may be so adjusted as to maintain the precipitator tubes at such tem perature as to prevent condensation of lighter hydrocarbons which it is desired to recover in the product and at the same time to prevent cracking of liquid precipitated onto the walls thereof. The hydrocarbon vapors free from suspended liquid particles pass through connecting pipe 11 to the vapor manifold 12, whence they are conducted to any suitable means for condensing and collecting the same. The residual oil, together with the nongaseous products of cracking, pass out through outlet pipe 9 to be disposed of in any suitable manner, for example by burning in burner 2 to furnish heat for the operation.

It will be seen that all vaporized products of cracking are thus released from the hot cracking zone almost immediately after their formation, so that their further heating is prevented and recracking substantially eliminated. Furthermore, the temperature of the cracking stock increases gradually in its passage through the retort, due to longer time of heating anddecreased amount of oil. 7 Those constituents of the cracking stock which are acted upon at lower temperatures are there- 'fore cracked first, and the resulting vapors are immediately removed from the retort, then those requiring higher temperatures are formed and removed, andso forth. Each portion of vapor is thus subjected to no higher temperature than is necessary to effect formation thereof, and re-cracking is therefore reduced to aminimum. In order to increase the last-mentioned eifeet I may provide, if desired, for progressively more intense heating of the retort so as to produce a steeper temperature gradient therein,'although in general the apparatus shown in the drawings will produce a considerably higher temperature at the far end of the retort (with respectto oil flow) than at the near end.

Instead of heating the retort by the combustion of fuel, any other suitable method of heating may be employed. Electrical heating may for example be employed, the combination of electrical heating and electrical precipitation being of particular. ad-

vantage in that it provides for extreme sharpness of temperature control in the retort and sharpness of liquid separation in the vapors removed" therefrom. For example as shown in Fig. 5 the retort 7 may itself be utilized as the resistor or heating element, the wires 30 and 31 for supplying the electric heating current being connected to the opposite ends of said retort in such manner that the heatingcurrent passes directly through the shell of the retort and heats the same tothe desired temperature. Furthermore in order to provide for the desired control of temperature at diiferent portions of the retort in such manner as to give the progressive increase in temperaturethroughout the retort in the direction of flow of oil therethrough, additional electric supply wires may be connected at different points in the length of the retort tube as indicated at 32, 33, and 34: so that different voltages may be maintained across different portions of the tube and different temperatures thereby obtained. A covering of refractory or insulating material may be placed around the retort tube in this case as indicated at 35, the construction ofthe retort and precipitator tubes being in other respects the same as above described.

I claim:

1. The process of cracking petroleum or petroleum products which comprises passing the material to be cracked under pressure through a retort, heating such retort to a sufficient temperature to effect cracking thereof, the pressure being such as to maintain the uncracked material substantially. wholly in the liquid phase while permitting vaporization of cracked products, removing vaporized products of such cracking at a plurality of points distributed lengthwise of said retort, subjecting each of such vaporized products to a separate electrical precipitating operation to remove liquid particles therefrom and returning the material precipitated from each of such products to the retort at substantially the point at which such product was removed and then collecting such vaporized products.

2. A process as set forth in claim 1, the temperature during each of said precipitating operations being so controlled as to maintain cracked products to be recovered in the vapor phase while permitting condensation of products of higher boiling point and preventing cracking of precipitated material.

3. The process of cracking petroleum or petroleum products which comprises heating the material to be cracked to successively higher temperatures in a heating zone so as to successively crack portions requiring increasing temperatures,while keepingsuch material undersuflicient pressure to maintain the uncracked material substantially wholly in the liquid phase while permitting vaporization of cracked products, withdrawing vaporized products of such cracking from the liquid material and from the heating zone at a plurality of points of successively higher temperatures so that said vaporized products are removed from the heating zone substantially as soon as formed and while their temperature is substantially that at which they are formed, subjecting each portion of vaporized products so removed to a separate precipitating operation to remove liquid particles therefrom, returning liquid material so prec1p1- tated from each of said portions to the heating zone-substantially at the point at which such portion was removed therefrom and then recovering said vaporized products.

4. An apparatus for petroleum crackin comprising a retort, means for passing liqui cracking stock through said retort under pressure, means for heating the material passed through such retort to successively higher temperatures in the direction of flow, means distributed lengthwise of said retort for removing vaporized products therefrom, at a plurality of points of successively higher tem: peratures, and electrical precipitating means in each of said vapor removing means.

5. An apparatus as set forth in claim 4 and comprising in addition means for controlling the temperature at each of said electrical precipitating means.

6. An apparatus for petroleum cracking comprising a retort, means for passing liquid cracking stock through said retort under pressure, means for heating material passed through such retort to successively increasing temperatures in the direction of flow, means distributed lengthwise of said retort for removing vaporized products therefrom at a plurality of points of successively higher temperatures and means in said vapor remoY-2 ing means for precipitating unvaporized material and for returning the same to the retort at substantially the point at which it was removed therefrom.

7. An apparatus for petroleum cracking comprising a retort, means for passing-liquid cracking stock through said retort under pressure, means for heating said retort to successively higher temperatures in the'direc-' tion of flow of material therethrough, means distributed lengthwise of said retort and connected thereto at portions thereof to be heated to successively higher temperatures for removing vaporized products from said retort and means in each of said vapor removing means for electrically precipitating unvaporized material from the vapors and for returning material so precipitated to the retort at the point of connection of said vapor removing means therewith.

In testimony whereof I have hereunto subscribed my name this 7th day of October, 1925.

JOHN JAY JAKOSKY.

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