US2938852A - Coking process - Google Patents

Description

May 31, 1960 w. F. woLFF Erm.

coxmc PRocsss Filed sept. 2o, 195e CGKING PROCESS William F. Wolfi, Park Forest, and Philip Hill, Lansing, lll., assignors to Standard Oil Company, Chicago, lll., a corporation of Indiana Filed Sept. 20, 1956, Ser. No. 610,921

2 Claims. (Cl. 208-48) This invention relates to the coking of hydrocarbon oils and in particular it concerns a coking process in which coke is easily removed from the coking zone.

in the coking of hydrocarbon oils such as petroleum the most diticult problem has always been the removal ot coke produced from the coking chamber. Basically, the process has been carried out by introducing the liquid petroleum fraction into a coking chamber and subjecting it to a high temperature to produce coke or distillates and coke. When the operation was completed the chamber was opened and it was necessary to drill out the coke formed therein. Various methods were devised for removing the solid coke, for example, coiled chains were placed within the coking chamber prior to the coking operation so that when the chamber was full of coke it could be dislodged by forcibly removing the chain which tore loose a substantial amount of the coke which had formed about it. Another advance in removing coke from the coke chamber was to blast it out with high pressure hydraulic jets.

An object of this invention is to provide a process for coking petroleum which is characterized by its simplicity for removing coke from the coking zone while minimizing or eliminating the costly mechanical means of decoking usually associated therewith. Another object is to provide a coking process for reduced crude especially for metals contaminated reduced crudes which produces a demetallated oil highly advantageous as a charging stock for catalytic cracking while minimizing the amount of coke formed which is characterized by easy removal of coke from the coking zone and the recovery of coke therefrom generally of a small particle size. Other objects and advantages of the invention will be apparent from the detailed description thereof.

According to the invention, heated reduced crude is introduced directly into a tixed bed of water soluble salt particles e.g, rock salt which are contained in a coking zone. The particles of the water soluble salt preferably have a minimum cross sectional diameter greater than about 1A: inch and may be in the form of lumps having a cross sectional diameter of 6 to l2 inches. The reduced crude is coked in the coking zone under the usual conditions comprising a temperature between about 700 and 1200 F. for a time suflicient to eiect partial or complete conversion of the reduced crude to coke and vaporous products. The reduced crude is preferably continuously introduced into the coking zone and the hydrocarbon products continuously withdrawn therefrom. Coke is formed on and among the void spaces of the salt particles. After completion of the coking operation when coke fills the void spaces between the salt particles, the introduction of reduced crude is discontinued. Thereafter water is introduced into the bed of salt particles and coke, and after cooling of the bed, the Water dissolves the salt particles and the coke particles become dislodged and are easily removed from the coking vessel. Since the distribution of salt particles prevents the formation of large lumps of coke, the coke which is thus 2,938,852 Patented May 3l, 1960 ice produced is generally of the small and usually regular size which does not require breaking up or crushing prior to its use elsewhere.

In a preferred species of this invention the coking procedure described above is practiced upon a reduced crude having an undesirably high metals content to prepare therefrom a demetallated highly satisfactory catalytic cracking charge stock. In this modilication the coking operation is carried out under mild coking conditions comprising a temperature between about 750 and 950 F., a space velocity between about 5 and 500 volumes of charged reduced crude per hour per volume of free space in the coking zone, and the coking is carried out so that the amount of coke formed is not more than about twice (preferably about the same amount) the Ramsbottom carbon content of the reduced crude charged. Both liquid and hydrocarbon vapors are removed from the coking zone. In the mild coking op eration the yields of coke, gas, and gasoline are minimized and this enables catalytic cracking of a maximum portion of the reduced crude and thus the production of maximum amounts of catalytic gasoline of high octane number.

The invention will be more clearly understood by referring to the attached drawing which illustrates in simplitied form the coking process of this invention. The embodiment of the invention illustrated herein describes a mild coking operation for producing demetallated catalytic cracking charge stocks from the reduced crude with a minimum formation of coke. However, the invention may also be satisfactorily used in the more severe conventional coking operation wherein from 5 to 25% of the reduced crude is converted to coke along with the formation of hydrocarbon distillates.

Reduced crude, which may be a 5 to 75% reduced crude having a metals content varying between 5 and 500 ppm. or even higher, is passed from source 11 by way of line 12 into furnace 13 wherein it is heated to a temperature between about 700 and l200 F., herein about 800 F. Ihe heated reduced crude is then passed by way of line 14 through valved manifolding lines 16, 17, 18 and 19 at space points directly into the bed of rock salt particles contained in coking drum 21. Coking drum 21 is a vertical vessel having a supporting grid 22 with large openings of the order of 6 to l2 inches. Large particles of rock salt are packed on top of the grid and vessel 21 is filled with rock salt particles of a smaller size e.g. 1A to l inch cross sectional diameter to a level such that a substantial amount of free space exists above the bed of rock salt. While the water soluble salt particles employed in the embodiment shown herein is commercially available cheap rock salt, other water soluble salts which remain solid at the coking temperatures used can be employed. For example, such salts as Na2S04, Nazcog, K2SO4, Kgcog, MgSO4, Algso and the like can be used.

The mild coking of the reduced crude is carried out at a temperature usually between about 750 and 950 F. employing a space velocity between about 5 and 500 volumes of reduced crude charged per hour per volume of free space in the coking zone, higher space velocities being employed with the higher temperatures. Pressures ranging from subatmospheric to 500 p.s.i. or higher may be employed, somewhat lower temperatures being used with the low pressures. By the term mild coking is meant coking the reduced crude to such an ement that the amount of coke formed is not more than about twice the carbon residue of the reduced crude as measured by its Ramsbottom carbon content. This latter measurement is a measure of the amount of carbonaceous residue which would be formed by distilling a reduced crude 3 and it provides an indication of its coke forming propensity. ASTM D S24-52T describes the procedurefor determining the Ramsbottom coke. The amount of coke which 'is allowed to be formed in the mild coking step is usually -not more than the Ramsbottom carbon content of the reduced crude and is preferably slightly less. Under such conditions a minimum amount of coke, gas and gasoline are formed together with maximum amounts of demetallated charging stock for catalytic cracking. lIn the embodiment shown herein, a 52% reduced crude is mildly coked at about 800 F. and a space velocity of about 50 Volumes of reduced crude charged/ hour/volume of free space in the coking zone. Under such conditions approximately 2.5 weight percent-coke, 20 s.c.f./ bbl. of gas and 2.5 weight percent of gasoline are formed. The hydrocarbon vapors released and formed during the coking operation are removed from coking drum 21 andV passed by way of line 23 into line 24. Liquid hydrocarbons which trickle down through -the bed of salt particles are recoveerd from the bottom of coking drum 21 and passed by way of line 26 into line 23. After the coking reaction hasv been carried out in vessel -21 until it is time to remove coke therefrom, the ow of reduced crude through the manifolding lines into coking drum 21 is discontinued and reduced crude is then passed by way of valved line 14 through manifolding lines 27, 28, 29 and 31 into the bed of rock salt particles contained in coking drum 32. Coking drum 32 is thus being used while coke is being removed from coking drum 21. Obviously more coking drums can be employed, either in Series or in parallel. Coking drum 32 is the same as coking drum 21, having a bottom supporting grid 33 upon which the large salt particles are packed with progressively smaller sized rock salt particles placed thereabove. Hydrocarbon vapors are removed from coking drum 32 and passed by way of line 34 into line 23. Liquid hydrocarbons are removed from below grid 33 and passed by way of line 36 into line 24. The vaporous and liquid products are then passed by way of line 24 into cooler 37 wherein their temperature is reduced e.g. to about 400-500 F. They are then passed by way of line 38 into flash drum 39 wherein Xed gases and gasoline boiling range hydrocarbons are flashed and removed overhead by Way of line 41 and a liquid hydrocarbon phase is removed as a bottoms and passed by way of line 42 to catalytic cracking. This bottoms stream comprises about 95% of the reduced crude charged to the coking lstep andV approximately 90% of the metals have been removed therefrom by the coking operation. 4It is a highly satisfactory charging stock for catalytic cracking, much superior to the reduced crude whose metals content would cause rapid deactivation of the cracking catalyst with the formation of much larger amounts of coke and gas with lesser yields of gasoline. It has been found to our surprise that this demetallated reduced crude has not picked up salt during the coking operation. vI-Evperiments have shown that the demetal- -lated reduced crude contains less than 1 part per million of sodium and that the coking operation has removed approximately 90% of the metals originally present in the reduced crude.

In conducting the operation, reduced crude is charged to the coking drum until the amount of coke formed therein substantially fills the void space in the bed of salt particles. At this time, or even prior to this time as desired, the flow of reduced crude is discontinued and coke is removed from the coking drum. The particular time at which theriiow of reduced crude is discontinued in order to remove coke may also be governed by the rise in Vthe pressure drop through the bed of packed salt particles. lf the pressure drop becomes inordinately great, it is Vusually desirable to discontinue coking in -the bed coking drum and remove the coke vrtlllere'fron'i. Generally, reduced crudes should not be introduced for a length of time such that large amounts o-f coke are deposited above the top of the bed of salt particles, for it is much more diicult to dislodge the coke formed thereabove. After discontinuing the ow of reduced crude, the bottom plate 43 of coking drum 21 is removed. Water is passedfrom source 44 by way of valved line 46 and then through manifolding lines 47, 48, 49 and 51 into coking drum 21. Steam which is formed is removed overhead by way of line 52, together with hydrocarbons stripped from the bed of rock salt and coke, and the heat and hydrocarbons from the stream recovered. After the bed of coke and rock salt has cooled so that all of the water introduced is not vaporized, water dissolves rock salt as it trickles down through the bed of rock salt. The water passes through the opening in the bottom of coking drum 21 and carries coke particles into hopper 53. Hopper 53 has openings in its bottom which permit water to pass through. The salt contaminated water may either be processed to recover the salt therefrom or it can be passed to sewers by way of line 54 as is shown herein. Coke particles are removed from hopper S3 by way of screw conveyor 56. The coke is then passed to storage by way of line 57. As the water is introduced intorcoking drum 21, it continues to dissolve rock salt and the particles of coke tumble down through the vessel, through the holes in grid 22, and then into hopper 53 until substantially all of the coke particles are removed. Higher velocity jets of water may be used to assist in removing the more stubbornly held coke particles. These more stubbornly attached particles are rather readily removed, however, since they exist as a honey-combed mass due to the presence of the salt particles during the coking operation.

After the coke has been removed from coking drum 21, particles of rock salt are packed therein in the fashion previously described and the vessel is -then made ready for return on stream. The ilow of reduced crude to coking drum 32 is discontinued at the proper time and the coke is then removed from this latter coking drum in the manner described above. Bottom closure 58 of coking drum 32 is opened. Water is passed from source 59 by way of valved line 60, through manifolding lines 61, 62, 63 and 64 into coking drum 32. Steam and residual amounts of hydrocarbons are vaporized from the bed of salt particles and coke and are removed from coking drum 32 overhead by way of line 66. Use ismade of the heat contained in this stream and the hydrocarbons therein are recovered. Water together with dissolved salt and rock particles pass through'grid 33 through the bottom of coking drum 32 into hopper 67. The water is removed from hopper 67 -through the openings in the bottom and passed to the sewers by way of line 68. `Coke particles are removed from hopper 67 by means of screw conveyor 69 and are then passed to storage by way of line 71.

Y While the invention has been described with reference to a certain specific example, the invention is not to be considered as limited thereto but includes within its scope such modications and variations as would occur to one skilled in this art.

' What is claimed is:

1. A process of producing coke in a vessel in a form readily removable from said vessel which process comprises introducing hot reduced crude into said vessel, said vessel having contained therein a fixed bed of watersoluble salt particles having a minimum cross sectional diameter of at least about 1A inch, said salt particles being solid at the temperatures hereinafter set forth, holding said reduced crude at conditions of temperatures in the region of about 700 to 1200 F. for a residence time sufficient to produce coke, said coke being deposited in voids between said salt particles, removing from said vessel at least one of hydrocarbon vapors and liquid hydrocarbons, discontinuing the introduction of reduced crude linto said vessel before said voidsl are"'entirelyv` 5 filled with coke, thereafter introducing water into said vessel to dissolve said salt particles and to leave in said vessel a porous honeycombed mass of coke, and removing water and lumps of coke from said vessel.

2. The method of claim 1, wherein the water-soluble 5 salt is rock salt.

References Cited inthe le of this patent UNITED STATES PATENTS 1,450,327 smith Apr. s, 1923 1 6 Darlington Apr. 12, 1932 McAfee Oct. 9, 1934` Morrell Nov. 13, 1934 Atwell June 16, 1936 Mattox Jan. 25, 1955 Adams et al. Sept. 18, 1956 De Rosset Feb. 12, 1957

Claims (1)

1. A PROCESS OF PRODUCING COKE IN A VESSEL IN A FORM READILY REMOVABLE FROM SAID VESSEL WHICH PROCESS COMPRISES INTRODUCING HOT REDUCED CRUDE INTO SAID VESSEL, SAID VESSEL HAVING CONTAINED THEREIN A FIXED BRED OF WATERSOLUBLE SALT PARTICLES HAVING A MINIMUM CROSS SECTIONAL DIAMETER OF AT LEAST ABOUT 1/4 INC. SAID SALT PARTICLES BEING SOLID AT THE TEMPERATURE HEREINAFTER SET FORTH, HOLDING SAID REDUCED CRUDE AT CONDITIONS OF TEMPERATURES IN THE REGION OF ABOUT 700 TO 1200*F. FOR A RESIDENCE TIME SUFFICIENT TO PRODUCE COKE, SAID COKE BEING DEPOSITED IN VOIDS BETWEEN SAID SALT PARTICLES, REMOVING FROM SAID VESSEL AT LEAST ONE OF HYDROCARBON VAPORS AND LIQUID HYDROCARBONS, DISCONTINUING THE INTRODUCTION OF REDUCED CRUDE INTO SAID VESSEL BEFORE SAID VOIDS ARE ENTIRELY

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