US2140276A - Continuous coking of hydrocarbon oils - Google Patents

Description

Dec. 13, 1938. J. G. ALTI-1ER CONTINUOUS COKING OF' HYDROCARBON OILS Filed Nov. 18, 1936 NNNQN iN @MANN @Wk kmmx NNW

Patented Dec. 13, `193s UNITED STATES PATENT OFFICE i 2,140,216 coN'rrNUoUs coxnsor mnocAanoN Application November 18, 1936, Serial No. 111,376

10 Claims.

'I'his invention particularly refers to an im-A proved process and apparatus for the continuous coking of liquid or semi-liquid hydrocarbons and particularly heavy residual liquids resulting from 5 the pyrolitic conversion of lower boiling hydrocarbon oils.

I have previously disclosed, in my co-pending application Serial No. 745,257 flled September 24, 1934, a process and apparatus for the continuous coking of heavy hydrocarbon oils wherein the heat required for such coking is supplied to the oil by passing the same through a fluid conduit preferably disposed in a special type of furnace designed to employ high rates of heat transferand quickly heat the oil to a temperature adequate to effect its subsequent reduction to coke without allowing it suiilcient time in said uid conduit to permit any substantial formation and deposition of coke therein. In this previously disclosed process the highly heated products from said fluid conduit are continuously supplied to a coking zone wherein they are reduced t a substantially solid coke-like residue without additional heating, the coking zone preferably employing a continuous conveyor or similar structure whereon the coke-like residue is allowed to accumulate in a relatively thin layer and wherefrom it is continuously removed.

In my co-pending application Serial No. 71,896, filed March 31, 1936, I have disclosed an operation wherein heavy oil to be coked is heatediin the manner above described, the heated products Separated into vaporous and heavy liquid components or pitch-like residue and the latter supplied to the surface of a continuous conveyor disposed in a coking zone wherein they are reduced to coke by supplyingheat directly to the exposed surface of the bed of material accumulated on the conveyor, the resultant coke being continuously removed from the conveyor.

The process of the present invention is similar in many respects to the two processes above outlined, combining advantageous features of each with each other and with additional features, not previously disclosed, in a novel and cooperative manner. This process embodies the steps of quickly heating heavy oil to be coked to a high cracking temperature under non-coking conditions in a fluid conduit, separation of the resultant heated products, preferably at relatively lowpressure, into vaporous components and a heavy Apitch-like residual liquid, reduction of the latter to a bed of coke-like residue on the surface of a continuous conveyor, without additional heating, followed by the application of additional heat to the upper or exposed surface of the bed of cokelike material on the conveyor, removal of the coke bed from the conveyor, preferably in the form'of relatively small lumps, to expose additional surfaces of the coke mass, further heating of the removed coke to produce a coke of more uniform volatility, and recovery of the resultant products.

I have found that, in continuous coking systems, in general, wherein a bed of 'coke is allowed to accumulate either upon (1) a heated surface or (2) upon a surface which is not directly heated but whereon the exposed surface of the material undergoing coking is subjected to direct heating, the volatility of the resultant coke and its phys- 'ical structure will vary considerably from top to bottom of the coke bed, particularly in case the latter is over some.two or three inches, at the most, in thickness.

In the improved process of the present invention I am able to produce a cokeproduct of lqw volatility and of substantially uniform volatility and structure. This is accomplished in a continuous operation and without the excessively strict limitations with respect to the` thickness of the coke bed formed on the conveyor necessitated by other continuous 'coking operations ofthe same general type but which do not employ the sentlal steps of the present process in combination. Particular attention is directed to the fact that all or substantially all of the heat required for the initial reduction of the heavy oil to coke-like residue is contained in the oil entering the coking zone. This feature in itself insures amore uniform grade of coke than could ordinarily be obtained by supplying heat from an external 35 source to the upper or lower surface, or both, of an unpreheated heavy oil. Furthermore, by removing the accumulated bed of coke from the conveyor, preferably in the form of relatively small lumps, new surfaces of the coke are exposed and, by subjecting the mass to further heating, volatiles entrapped in the porous substructure of the coke bed accumulated on the conveyor are released and the coke is thereby more uniformly devolatilized.

Depending upon the specific nature of the oil subjected to treatment in the present process and upon the desired nature of the products it will not be necessary, in all cases, to employ all of the various steps herein provided. The invention also provides for certain alternative methods of treatment which may be selected to suit requirements and are not to be considered equivalent.

One specic embodiment of the invention comprises quickly heating an oil of high coke-formf ing characteristics to a high cracking temperature at substantial superatmospheric pressure and under non-coking conditions in a heating coil, introducing the highly heated products into a reduced pressure vaporizing zone wherefrorn the resultant vaporous products'areremoved and recovered, supplying the resultant non-vaporous residue, in the form of a heavy pitch-like material, onto the moving surface of a continuous conveyor disposed within a coking zone, causing reduction of said non-vaporous residue to coke-like material without additional heating in the initial stages of the coking operation, subsequently supplying additional heat to the exposed upper surface of the bed of coke-like material accumulated on the conveyor, continuously removing the resultant accumulated coke from the conveyor in the form of lumps and accumulating a substantial mass of the latter, passing hot combustion gases from the coking zone zone through said mass of accumulated coke to reduce its volatile content and recovering the resulting devolatilized coke.

rThe accompanying diagrammatic drawing illustrates a sectional elevation of one specic form of apparatus embodying the features of the invention. v

Referring to the drawing, the apparatus consists essentially of a heating. Zone I, a vaporizing' and separating zone 2, a primary coking and primary devolatilizing zone 4 and a final devolatilizing zone 5 through which the material undergoing treatment is passed in the sequence given.

The heating zone I comprises a furnace structure 6 which, in the particular case here illustrated, is of the type now generally known in the cracking industry as an equinux furnace. This type of furnace has a centrally disposed vertical bank 'I of horizontally disposed tubes 8 arranged, in this particular case, in two Vertical rows in staggered formation. rlube bank I is disposed between and divides the main body of the furnace into combustion and heating' zones 9 and I0 to each of which independently regulated amounts of combustible fuel and air are supplied by means of suitable burners l l through firing ports I2 in the roof of the furnace. The flames and hot combustion gases resulting from the combustion of fuel in zones 9 and I@ are preferably directed at an angle toward the side Walls of the furnace structure and passed downwardly thereover to be removed from the lower portion of the furnace through heating Zone I3 wherein a separate tube bank i4 may be disposed.

The heavy high coke-forming oil or other hydrocarbon fluid to be reduced to coke is supplied by well known means, such as a pump, not illustrated, from any suitable source to the lower row of tubes in bank I4 and passes in series through the adjacent tubes in each row and through the adjacent rows of tubes in a general upward direction to be transferred from the uppermost row of tubes in bank I4 to the lowermost tube of bank 1. The fluid undergoing heating thence passes in series through adjacent tubes v The fluid passing through tube bank l' is subjected to high rates of heating primarily by radiant heat supplied directly to the tubes of this bank fromv the flames and hot combustion andere gases in zones Si and i@ of the furnace and from the hot refractory furnace walls. By exposing opposite sides of each tube of this bank to direct radiation in this rmanner the average rate of heating obtained in this zone may be maintained near the maximum allowable rate, whereby the uid undergoing treatment is quickly raised to the desired high temperature without allowing it to remain in the heating coil for a sumcient length of time to permit any substantial formation and deposition of coke in this zone. Tube bank ifi is subjected to milder heating conditions, the upper rows of this bank being exposed to radiant heat from the hot refractory walls of the furnace and the hot combustion gases and the entire bank being subjected to heating by directy contact with the hot combustion gases passing from zones 9 and i0 of the furnace to a suitable fiue and stack, not illustrated. Tube bank I 4 may be eliminated, whenl desired, but is advantageous as a means of reducing the tem'- perature of the combustion gases leaving the furnace and 'thereby increasing its thermal ediciency. Other forms of tube bank il' may, of course, also be employed within the scope ofthe invention and the possible modifications include a single row of tubes or, when desired, two or more rows of tubes connected either in crisscross arrangement, as illustrated, or in sequence or the various rows of tube bank 'l may, when desired, be connected in parallel.

The invention is, of course, not limited to the use of an equinux type furnace although thisV porous components and heavy pitch-like residua To assist this separation I preferably employ a spray arrangement or spreader device, one form of which is indicated at i1, whereby the highly heated nuids discharged from line l5 are directed against the walls of the lower portion of the separating zone, the heavy pitch-like residue flowing downwardly thereover to be discharged from the lower end of this zone onto the upper surface I8 of conveyor belt I9 while the vaporous products pass upwardly through zone 2 to be directed from the upper portion thereof through line 2 0 and valve 2! to suitable condensing and collecting equipment of any desired form, not illustrated.

Suitable means such as, for example, bailies,

' perforated pans, bubble trays, packing or the like,

or any desired combination of such means, not illustrated, may be employed, when desired, in the upper portion of vaporizing and separating zone 2 for the purpose of assisting removal of entrained or dissolved heavy liquid particles from the vapors prior to condensation of the latter and, when desired, the vaporous products from zone f2 may be subjected to fractionation for the separation of their relatively low-boiling and high-boiling components in a separate fractionating Zone, not illustrated, or in an extension of zone 2.

In the particular case here illustrated the prithe conveyor preferably being of the type employing a sectional belt composed of any suitable metal or metallic alloy capable of withstanding the relatively high temperatures to which it is subjected and preferably having anged edges 23 for retaining thereon a substantial bed of the material undergoing coking. The inlet end of .the conveyor is located in primary coking zone 3 and the discharge end in zone 4 and preferably zones 3 and 4 are divided by means of a suitable partition, one form of which is indicated at 24.

The heavy pitch-like residuesupplied to the inlet end of conveyor I9 from separating zone 2 e is reduced to a bed of coke-like residuel on that portion of the lconveyor passing through Zone 3 without supplying additional heat thereto and the resultant bed of coke-like material then passes on the moving conveyor into zone 4 wherein additional heat is supplied to the upper surface of the bed primarilyby radiation from the heated refractory roof 25 of this zone and from the iiames of hot gases resulting from combustion therein.

In the particular case here illustrated a suitable burner or air injector 26 is provided through which air or a mixture of combustible fuel and air is supplied to zone 4, and, when desired, the vaporous hydrocarbons evolved from the pitch?. like residue undergoing coking in zone 3 may be directed through opening 21 in partition 24 Iby the injector action of the materials discharged from the device 26 whereby said vapors are admixed with sufficient air to cause their total or partial combustion in zone 4.v Preferably the combustible materials supplied to zone 4 are directed at an angle toward the inclined roof 25 of this zone in such a manner that the flames and hot combustion gases will sweep the roof and heat it to a highly radiant condition. Damper 43 is provided for regulating the iiow of vaporous products from zone 3 into zone 4 through firing port 21. v

In zone 4 the coke, and particularly that adjacent the exposed surface of the bed, is subjected to devolatilization by means of the heat supplied thereto and the resultant coke bed is I removed from the discharge endof the conveyor, preferably in the form of lumps which pass from zone 4 into the nal devolatilizing z'one 5, wherein an appreciable mass of coke is allowed to temporarily accumulate. A suitable scraper or the like such as indicated, for example, at 28 may be provided for the purpose of shearing the accumulated coke from the surface of the conveyor and,

when desired, water or steam jets may be directed by well known means, not illustrated, onto the surface of the coke or onto the conveyor belt near the discharge end of the conveyor to assist in breaking the same therefrom. The coke mass accumulated in zone 5 is subjected to further devolatiliza-tion by further heating the same and this final devolatilizing step is rendered particularly efiicient by virtue of the fact that the coke mass is in the form of a multiplicity of relatively small lumps and vtherefore has a much greater exposed surface than the bed of coke on the conveyor. Heating of the coke mass in zone 5 may be accomplished by one or a combination of several methods. ne method comprises passing the hot combustion gases from zone 4 downwardly through the mass of coke in zone 5 and, when desired, additional air or additional air and combustible fuel may be admixed with the hot combustion gases prior to their passage through zone 5 by means of one or a plurality of suitable burners or air injectors 29.

fuel supplied to zone 4 when incomplete combus-` tion is employed in the latter zone. Provision is also made for supplying additional air directly to zone 5 and into the mass of coke accumulated therein at any desired point or plurality of points in this zone by means of header 30 and tuyres 3l. When desired, by supplying a suiiicient quantity of` additional air to zone 5, either through injector 29 or tuyres 3|, or both, partial combustion of the coke mass and the volatile hydrocarbons evolved therefrom in this zone may be accomplished. The combustion gases are discharged from the lowei portion of zone 5 through ue 32 to a suitable stack 33 and the devolatilized coke passes through a suitable discharge port 34 into a quenching tank 35 wherein a suitable liquid level may be maintained to seal the discharge end of zone 5 and wherein a suitable conveyor 3B may be disposed for removing the quenched coke.

In some cases the combustion gases discharged from zone 5 will comprise a mixture of combustion gases and unburned hydrocarbons resembling producer gas, in which case this material may be recovered for use as fuel within the system or for any other desired purpose by directing the same from stack 33 through iue 3 1, controlledby damper 38 to a suitable fan or blower, not illustrated, Wherefrom it may be supplied to storage'or to zones I, 4 or 5- of the system or elsewhere, as desired. In such cases the fan or blower, not illustrated, may serve as a means of maintaining subatmospheric pressure in preceding portions 'of the system such as zone 5 or zones 4 and 5. When the gaseous products from zone 5 are not recovereda suitable air inlet device such asillustrated, for example, at 39 may be employed in stack 33 to induce sufficient draftfor maintaining subatmospheric pressure in zone 5 or zones 4 and 5.

Preferably heavy tars and pitch-like material are removed from the gaseous products discharged from zone 5 by means of a suitable water spray 40 positioned in the lower portion of stack 33 which serves to scrub out or condense the heavy l pheric pressure of the order of 50 to 150 pounds,

or more, per square inch is employed in the heating coil. As previously mentioned, the time element in this zone is sufficiently short to obviate any substantial formation and deposition of coke in the heating coil and communicating lines. Any desired pressure ranging from subatmospheric to a superatmos'pheric pressure no greater than that employed at the outlet from the heating coil may be utilized in the succeeding vaporizing and separating zone and in the primary coking zone and preferably the primary coking .zone is operated at a slightly higher pressure than that employed in the secondary coking and primary devolatilizing zone whereby any leakage of gases through partition 24 will be in the direction of the latter zone and the vaporous hydrocarbons evolved inv the primary coking zone will not be contaminated by combustion gases, a major portion of said vaporous hydrocarbons passing from the primary cking zone to the vaporizing and separating zone when damper 43 is closed.

The devolatilizing zones are preferably operated at substantially atmospheric or subatmospheric pressure, although low superatmospheric pressures-may be employed therein, when desired. The average temperature of the material undergoing coking in the primary coking zone will, of course, vary depending upon the temperature employed at the outlet from the heating coil and may range, for example, from 800 to 1000 F., or thereabouts. Preferably suiiicient additional heat is supplied to the coke bed in the secondary coking and primary devolatilizing Zone to maintain the exposed surface of the coke bed near the discharge end of the conveyor at a temperature of the order of 1000 to 1100 F., or more, and the mass 'of coke accumulated in the nal devolatilizing zone is preferably maintained at substantially the same or a higher temperature.

As a specific example of the operation of the process of the invention, a heavy residual oil of high coke-forming characteristics resulting from pyrolytic conversion of lower boiling hydrocarbon oils is supplied from a cracking system to the heating zone of the present process wherein it is quickly heated to an outlet temperature of approximately 1000 F. at a superatmospheric pressure of about pounds per square inch. The heated products arevdischarged at substantially atmospheric pressure into the lower portion of the vaporizing and separating zone wherefrom their vaporous components are recovered and the non-vaporous pitch-like residue is discharged onto the surface of the conveyor in the primary coking zone at a temperature of approximately 970 F. The conveyor is moved at a sufficiently slow rate to permit the heavy pitch-like residue sufficient time in the coking zone for the evolution of a major portion of its vaporizable components leaving a bed of coke-like residue on the conveyor.v A major portion of the vapors evolved in the primary coking zone are directed therefrom to the vaporizing and separating zone but a small portion of these materials pass through the ports in the partition dividing the primary coking zone from the secondary coking and primary devolatilizing zone, in which latter zone they serve as fuel. The vaporizing and separating zone and the primary coking zone are operated at substantially atmospheric pressure and a slight subatmospheric pressure is employed in the succeeding portions of the system. The bed of coke on the conveyor leave's the primary coking zone at a temperature of approximately-920 F. andv the exposed surface of the bed is heated in the secondary coking and primary devolatilizing zone to a temperature of approximately 1100 F. by the partial combustion of fuel adjacent the roof of this zone. The partially burned gases from the secondary coking and primary devolatilizing zone enter the mass of coke accumulated in the nal devolatilizing zone admixed with a small amount uniform quality. In addition about 25 per cent by volume of the charging stock is recovered as liquid hydrocarbons, theremainder being chargeable to uncondensed gases and loss.

I claimv as my invention:

l. A process for the continuous coking of hydrocarbon oil, which comprises heating the oil at substantial superatmospheric pressure and under y non-coking conditions to a temperature adequate to effect its subsequent reduction to coke-like residue, separating vaporizable components ofv the resultant heated products from the nonvaporous fluid residue, discharging the latter onto the moving surface cfa continuous conveyor,v causing the further evolution of vapors and reduction of uid residue to coke-like residue, in the form of a bed on said surface of the conveyor, without additional heating, subsequently passing the bed of coke-like material on said surface of the conveyor through a zone in the coking Stage wherein it is subjected to additional heating and further devolatilized by heat supplied directly to the exposed surface of said coke bed, removing the resultant coke from the conveyor in the form l of lumps following the last mentioned stage of due, in the form of a bed on said surface of the conveyor, without additional heating, subsel quently passing the bed of coke-like material on said surface of the conveyor through a zone in the coking stage wherein it is subjected to additional heating and further devolatilized by heat supplied directly to the exposed surface of said coke bed, breaking the coke bed into a multiplicity -of pieces whereby to expose the additional surfaces of the coke, continuing heating of the new- Vly exposed surfaces of the coke to effect further devolatilization thereof, and recovering the resultant products. v

3. A process for the continuous coking of hydrocarbon oil, which comprises heating the oil at substantial superatmospheric pressure and under non-Coking conditions to a temperature adequate to effect its subsequent reduction to coke-like residue, separating vaporizable components oil the resultant heated products from the nonvap'orous duid residue, discharging the latter onto the moving surface of a continuous conveyor, causing the further evolution of vapors and reduction of the fluid residue to coke-like residue, in the form of a bed on said surface of the conveyor', without additional heating, subsequently f passing the bed of coke-like material on said surface ofthe conveyor through a zone in the coking stage wherein it is subjected to additional heating and further devolatilized by heat supplied directly to the exposed surface of the coke bed, breaking the coke bed into a multiplicity of pieces whereby to expose the additional surfaces of the coke, accumulating a mass of the brolen coke, passing hot combustion gases through said mass in contact with the newly exposed surfaces of the coke pieces whereby to additionally dev mentioned zone of the coking stage.

5. A process such as defined in claimv 3 wherein the hot combustion gases passed through said accumulated mass of coke are derived, in part, from the combustion of fuel in the previously mentioned zone of the coking stage and, in part, by the addition of fresh increments of hotter combustion gases.

6. A process such as defined in claim 3 wherein heat supplied to said exposed surface of the bed of coke on the conveyor is derived by the incomplete combustion of hydrocarbons in that zone of the coking stage wherein the heating of said surface is effected and wherein incompletely burned products of said combustion are mixed with additional ,air and passed through said coke mass to effect their further combustion and further heating of the coke mass.

7. A process such as defined in claim 3 wherein at least a portion of the heat supplied to said exposed surface of the coke bed on the conveyor is derived from the, combustion ofy volatile hydrocarbons evolved in the same/,zone of the coking stage.

8. A process such as dened in claim 3 wherein at least a portion of the heat supplied to said exposed surface of the coke bed on the conveyor is derived from the combustion of volatile hydrocarbons evolved from the material undergoing coking in the preceding stageof the operation.

9. An apparatus for the continuous coking of fluid hydrocarbons, which comprises, in` combination, a coking and devolatilizing oven, said oven being divided into a primary coking zone, a secondary coking and primary devolatiiizing zone and a final devolatilizing zone, a continuous conveyor disposed within the two first mentioned zones, means for supplying the fluid hydrocarbon to be coked onto the surface of said conveyor in the primary coking zone in highly heated state, whereby to accumulate a bed of coke-like residue on said surface,v means for removing from the primary coking zone vaporous products evolved from the fluid hydrocarbons undergoing coking therein, means for supplying additional heat to the exposed surface of said bed of cokelike residue on the conveyor'in the secondary coking and primary devolatilizing zone, means for removing the resultant coke from the con#- veyor in the latter zone, means for supplying the removed coke to the final devolatilizing zone and accumulating a. substantial mass of the same therein, means for passing hot combustion gases from the secondary coking and primary devolatilizing zone through said mass of coke in the final devolatllizing zone and means for recovering the devolatilized coke from the latter zone.

l0. An apparatus for the continuous coking of fluid hydrocarbons comprising, in combination, a primary coking chamber, a secondary coking and primary devolatilizing chamber and a final devolatilizing chamber, means for supplying the fluid hydrocarbon to be coked into the primary coking chamber lin highly heated state and accumulating a bed of coke-like residue therein, means for transferring said bed of coke-like residue into the secondary coking and primary devolatilizing chamber, means for heating the exposed surface of the coke bed in the latter chamber, means for transferring the coke from thesecondary coking and devolatilizing chamber to the nal devolatilizing chamber, means for accumulating a substantial mass of said coke in the Vlatter zone, means for supplying additional heat to said coke mass and means for removing the devolatilized coke from the final devolatilizing zone.

JOSEPH G. ALTFI'ER,

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