US2199759A - Manufacture of coke - Google Patents

Description

May 7, 1940. H. G. SCHNETZLER MANUFACTURE OF COKE Filed June I6, 1937 HARRY G. SCHNETZLER m), ,4 WM

ATTORNEY Patented May 7, 1940 MANUFACTURE OF COKE Harry G. Schne'tzler, Neodesha, Kansaassignor to Standard Oil Company; Chicago, 111., a cornotation of Indiana .8 Claims.

This invention relates to the coking of hydrocarbon oils and contemplates a process in which hydrocarbon oil is subjected to a prolonged digestion to thereby greatly increase the yield of lump coke. -In accordance with the invention, hydrocarbon oil is subjected to a coking temperature to eflect conversion into a coke residue and the coke residue is digested underits contained heat.

My invention is concerned with a process in which the oil to be coked is heated in a heating coil or zone of restricted cross sectional area and discharged into an enlarged chamber in which the oil is maintained at a coking temperature to efiect coking. I have discovered that if the material in the coking chamber be digested for a prolonged time beyond the period when any substantial quantity of distillate is formed the yield of lump coke is thereby greatly increased. In ordinary coking practice it has been the custom to cool down the coked mass as rapidly as possible as soon as the flow of distillate has ceased in order to remove the coke. In accordance with my invention, the yield of lump coke may be materially increased, and the hardness of the coke product increased, by maintaining the coke at an elevated temperature for a considerable period beyond that at which the flow of distillate has substantially stopped.

In accordance with the invention a petroleum oil such as reduced crude is passed through a heating coil wherein the oil is raised to a temperature adequate to support a coking reaction upon being discharged into an enlarged coking chamber. The heat imparted to the mass in the coking chamber by the entering stream of hot oil operates to effect the coking of the mass in the coking chamber. The vapors and gases evolved are withdrawn from the coking chamber while the liquid constituents are retained and converted into a solid coke residue. A continuous stream of hot oil from the heating coil is passed into the coking chamber until the desired quantity of liquid has been introduced whereupon the introduction of heated oil is discontinued. The evolution of condensable vapors continues for a time after the introduction of heated oil has ceased. If the mass in the coking chamber is permitted to remain, at an elevated temperature, a reaction will continue for a considerable time, the presence of the reaction being indicated by the evolution of a relatively small quantity of fixed gas.

In order to more fully disclose the invention, reference will now be had to the accompanying drawing, which is a diagrammatic sectional elevation of an apparatus adapted for the practice of the invention.

In the drawing, i represents a furnace in which is mounted a heating coil I l to which the coil 22.

Application June 16, 1937, Serial No. 148,441

charging stock is introduced by p mp A conv nient number of coking drums as l3a, I31) and l3c are shown. The heated oil is transferred from the heating coil ll through a, transfer line H having a ring manifold l5 through which the heated oil may be constantly circulated and diverted to the desired coking drum through one of the branch lines l5a, I51), and I50. The drums are provided with bottom manways l6a, 16b and I60 for the removal of the coke. The drums may be conveniently equipped with coke-removal apparatus (not shown) which may consist of cables supported on wires stretched across the interior of the drum on hooks welded to the sides of the drums. The drums should be heavily insulated against heat loss. The drums are equipped with vapor lines Ila, Nb and He respectively, manifolded to a common vapor line i8 extending to a fractionating tower l9. A branch vapor line 2!! isprovided, having branches 20a, 20b and 200 to the respective coking drums, to providefor the passage of hot vapors from a coking drum in operation to another drum for the purpose of;

preheating the latter preparatory to the introduction of the heated oil from the heating coil thereinto. A vapor line H extends to a condenser Acondensate line 23 is provided for withdrawing reflux condensate from the fractionating tower. The coking drums are equipped with blow-down lines 25a, 26b, and 240 manifolded to a gas line 25 extending to a blow-down tank 26. e

The invention is particularly adapted for the treatment of heavy petroleum stocks, such asreduced crude, to cheat a reduction of the heavy stock to coke and produce, in addition to gasoline,

a relatively large yield of condensate of the nature of gas oil suitable for charging stock to a cracking operation for conversion into gasoline. In practicing the invention with this end in view, the reduced crude is charged by the pump i2 to the heating coil ii whereinit is heated to'a temperature of about 870 F.-940F., and discharged thence into a coking drum for conversion into coke. During the time that the heated oil from the coil is being discharged into a given coking drum and for a comparatively short time after the hot oil stream has been diverted to another coke drum, the operation is accompanied with the production of distillate, the evolved vapors being subjected to fractionation in the tower is, the overhead vapors therefrom being condensed in coil 22 and the reflux condensate, which is suitable for charging stock to a cracking operation, being withdrawn from the tower l9 through the line 23. In a relatively short time after the stream of hot oil from the heating coil has been diverted from a given coking drum, and

as soon as the flow of distillate has substantially in the gas line of such drum, as in line 24a, MD, or 240, is opened to permit the flow of gas to the blow-down tank 26.

The mass in the coking drum is permitted to digest with retained heat for a period of time approximating at least 18 hours and preferably about 24 hours or even longer. At the beginning of the digestion period the temperature in the coking drum will be about 800 F.-850 F. The heat is largely retained during the digestion. At the end of the digestion the inner portions of the coke mass may be at temperatures approximating 800 F., and although portions near the outer surface may have dropped to about 500 F.-600 F. the average temperature may be in excess of 700 F. v a

The coking operation is advantageously carried on under atmospheric pressure or moderate superatmospheric pressures, suchas pounds, although the use of higher pressuresis not precluded in the practice of the invention. During the digestion period there is, as stated, a relatively small evolution of gas which fiows through the line 25 to the blow-down tank '26. In the early part of the digestion period the evolved gas may contain a very small proportion of waxy condensables. Upon washing the gas with water in the blowdown tower 26 a small quantity of wax slop is separated from the gas. The amount of condensables thus formed will be less than one percent of the charge to the coking drum. During the greater portion of the digestion period only a light gas is evolved.

During the digestion period it is advisable for safety purposes to introduce a very small quantity of steam into the coking drum from which the heated oil stream has been diverted in order to prevent the possibility of air getting into the coking drum from the blow-down tank. ,Thus, for example, assuming that drum l,3a has been charged with hot oil from the heating coil to the extent desired and that the hot oil stream has been diverted to one or the other cokingdrums, a very small quantity of steam may be admitted into the branch transfer line I5a. This procedure will serve to insure that air does not enter the coking drum l3a. from the blow-down tower 26. The quantity of steam introduced, however, should be insumcient to produce any material amount of cooling of the coke mass in the' coking drum. After the coke in the coking drum has been thus digested for the required length of time the coke mass may be steamed with a relatively large quantity Q steam and washed with water. The coke is then pulled from the bottom manway.

If desired, a portion or all of the reflux condensate withdrawn through line 23 may be cycled to the heating coil l i, or lighter and heavier cuts of reflux condensate may be made in the fractionating tower, with the heavy out being cycled to the cracking coil II and the lighter cuts subjected to cracking in another unit. The cycling of condensate to the heating coil will normally effect an increase in the gasoline yield due primarily to the cracking of the cycle condensate in the cracking coil. It is advantageous, however, to operate without recycling condensate, or at least to only cycle a heavy cut of condensate, so that the large yield of gas oil stock, and particularly the lighter gas oil constituents, produced in the process may be subjected to cracking in a separate cracking unit under conditions better suited for the production of a gasoline of higher anti-knock quality.

In a typical operation in accordance with the invention using coking drums having a diameter of about 16 feet and a length of about 30 feet, reduced crude petroleum is charged through the heating coil II and thence to one of the coking drums, as I311, for a period of about 36 hours. The reduced crude is delivered to the coking drum at a temperature approximating 900 F. The evolved vapors pass through branch line Ila and vapor line l8 to the fractionating tower IS, the overhead vapors from which are condensed in condenser coil 22 and the heavier reflux condensate from which is withdrawn through line 23. -During the latter portion of the 36 hour period, for example for about 7-12 hours, the vapors from the drum .l3a may be diverted into another drum, as through branch line I lb into drum 13b, thence through branch line 20b and line 20 to the fractionating tower, the withdrawal of distillate and reflux condensate being continued. In this way drum l3b may be preheated ready to receive the stream of hot oil from the heating coil II, when the stream is diverted from the drum l3a. At the end of the 36 hour period the oil stream from the heating coil is diverted from the drum l3a into drum I 317, the

flow of vapors from drum I311. being then restored to the direct passage to the fractionating tower through lines I10. and 18. In about an'hour after the discontinuance of charging into drum I311,

the production of distillate from this drum will have practically ceased, at which time the vapor line l'la is closed and the gas line 24a is opened to permit the passage of gas through line 25 into the blow-down tank 26. This operation is continued for some 23 hours or.until about 24 hours from the time when the heated oil stream was diverted from drum l3a, thus permitting the desired reactions to occur in the coke mass in the drum l3a; At the end of the 24 hour period steam at the rate of about 12,000 to 15,000 pounds per hour is introduced into the coking drum l3a for a period of about 15 minutes, after which water at the rate of about gallons per minute is introduced for another 15 minute period. The coke is then ready to be pulled through the bottom manway 16a.

In comparing the yield of lump coke produced by the practice of my invention with the yield produced in prior methods in which heavy oil was passed through 'a heating coil and delivered into an insulated coking drum for coking, the yield of lump coke is taken as the proportion, of total coke produced, obtainable over a 3 inch grizzly. In the prior practice the usual amount of lump coke, as thus determined, was about 15 percent and only occasionally was it possible to obtain as high a yield as 25 percent. In practicing my invention, the yield of lump coke is very materially increased, the following examples being representative of the yields of coke produced by the practice of the invention:

In the last example given in the table the reduced crude was charged to the heating coil at a rate of 90 to 100 barrels per hour, and delivered into the transfer line at a temperature of 910 F. while air at the rate of 250-300 cubic feet per minute was admitted into the transfer line operating to raise the temperature about 20 F.

While I have described a particular embodiment of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof which will be obvious to one skilled in the art, may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. The method of coking hydrocarbon oils that comprises maintaining a mass of hydrocarbons at av coking temperature with resultant evolution of condensable vapors in an enlarged coking chamber insulated against heat loss, heating a confined stream of hydrocarbon oil in an elongated passageway of restricted cross sectional area to a cracking temperature and delivering into the enlarged coking chamber the resultant heated stream of hydrocarbon oil at a temperature sufiicient to maintain the mass in the coking chamber at a coking temperature, discontinuing the delivery of said heated stream of hydrocarbon oil to the coking chamber while retaining the residual constituents therein under their contained heat with the continued evolution of conin the coke mass increasing the yield of lump coke,

as measured by the lump coke obtainable over a three-inch grizzly.

2. The method of coking hydrocarbon oil that comprises maintaining'a mass of hydrocarbons in a coking zone at a coking temperature with resultant evolution ofcondensable vapors and conversion into a coke residue and continuing the maintenance of a coking temperature in the coking zone until such time as the evolution of condensable vapors from the coking zone has substantially ceased, 'and then digesting the entire mass of resultant coke residue under its contained heat, without the application of either sub stantial cooling or heating thereto, for an extended periodof time beyond that at which such evolution of condensable vapors from the coking zone has'substantially ceased to there y eflect such reaction in the coke mass that up ards of approximately 40% of the total coke," product, upon removal fromthe coking zone, will consist of lump coke of the sizes obtainable over a threeinch grizzly.

3. The method of coking hydrocarbon oil that comprises maintaining amass of hydrocarbons in a coking zone at a coking temperature with resultant evolution of condensable vapors and conversion into a coke residue and continuing the maintenance of a coking temperature in the coking zone until such time as the evolution of condensable vapors from the coking zone has substantially ceased, then digesting the entire mass of resultant coke residue under its contained heat,

without the application of either substantial cooling or heating thereto, for a period of upwards of 18 hours beyond that at which such evolution of condensable vapors has substantially ceased to thereby eflect reaction in the coke mass materially increasing the yield of lump coke, as measured by the lump coke obtainable over a three-inch grizzly.

l 4. The method of coking hydrocarbon oil that comprises maintaining a mass of hydrocarbons in a coking zone at a coking temperature with resultant evolution of condensable vapors and conversion into a coke residue and continuing the maintenance of a coking temperature in the coking zone until such time as the evolution of condensable vapors from the coking zone has sub- .fect reaction in the coke mass materially increasing the yield of lump coke, as measured by the lump coke obtainable over a three-inch -grizzly.

,5. The method of coking hydrocarbon oil that comprises maintaining a mass of hydrocarbons in a coking zone at acoking temperature with resultant evolution of condensable vapors, delivering into the cokingzone a continuous stream of hydrocarbons heated suificiently to maintain the mass therein at a coking temperature, discontinuing the delivery of the stream of heated hydrocarbons into the coking zone, maintaining the mass in the coking zone at a coking temperature under its contained heat after discontinuing the delivery of the stream of heated hydrocarbons thereto until such time as the evolution of condensable vapors has substantially ceased, then digesting the entire mass of resultant coke residue under its contained heat, without the application of either substantial cooling or heating thereto, for an extended period of time beyond that at which such evolution of condensable vapors has substantially ceased to thereby efiect reaction in the coke mass materially increasing the yield of lump coke, as measured by the lump coke obtainable over a three-inch grizzly.

6. The method of coking hydrocarbon oil that comprises maintaining a mass of hydrocarbons in a coking zone at a coking temperature with resultant evolution of condensable vapors, delivering into the coking zone a continuous stream of hydrocarbons heated sufliciently to maintain the mass therein at a, coking temperature, discontinuing the delivery of the stream of heated hydrocarbons into the coking-zone, maintaining the mass in the coking zone at a coking temperature under its contained heat after discontinuing the delivery of the stream of heated hydrocarbons thereto until such time as the evolution of condensable vapors has substantially ceased, then digesting the entire mass of resultant coke residue under its contained heat, without the application 4 of either substantial cooling or heating thereto,

moval from the coking zone, will consist of lump- 1 coke of the sizes obtainable over a three-inch grizzly.

7. The method of coking hydrocarbon oil that comprises maintaining a mass of hydrocarbons in a coking zone at a coking temperature with resultant evolution of condensable vapors, delivering into the coking zone a continuous stream of hydrocarbons heated sufiiciently to maintain the mass therein at a coking temperature, discontinuing the delivery of the stream of heated by drocarbons into the coking zone, maintaining the mass in the coking zone at a coking temperature under its contained heat after discontinuing the delivery of the stream of heated hydrocarbons thereto until such time as the evolution of con: densable vapors has substantially ceased, then digesting the entire mass of resultant coke residue while largely retaining its contained heat and maintaining the bulk of the coke mass at temperaturesapproximating 700 F.-800 F. for an extended period of time beyond that at which such evolution of condensable vapors has substantially ceased to thereby effect reaction in the coke mass materially increasing the yield of lump coke, as measured by the lump coke obtainable over a three-inch grizzly.

8. The method of coking hydrocarbon oil that comprises heating a confined stream of hydrocarbon oil in an elongatedpassageway of restricted cross-sectional area to a temperature within the range of 870 F.-940 F., continuously passing the heated stream of hydrocarbon oil into an enlarged coking chamber insulated against heat loss to maintain a mass of hydrocarbons therein at a coking temperature with resultant evolution of condensable vapors, discontinuing the delivery of the heated stream of hydrocarbon oil into the coking chamber while continuing the maintenance of the mass therein at a coking temperature until such time as the evolution of condensable vapors has substantially ceased, then digesting the entire mass of resultant coke residue in thecoking chamber while largely retaining its contained heat and maintaining the bulk of the coke mass therein at temperatures of the order of 700 F.-800 F. for an extended period of time beyond that at which such evolution of condensable vapors from the coking chamber has substantially ceased to thereby effect reaction in the coke mass materially increasing the yield of lump coke, as measured by the lump coke obtainable over a threeinch grizzly.

HARRY G. SCHNE'IZLER.

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