US2366055A

US2366055A - Coking process

Info

Publication number: US2366055A
Application number: US379397A
Authority: US
Inventors: Walter F Rollman
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1941-02-18
Filing date: 1941-02-18
Publication date: 1944-12-26
Anticipated expiration: 1961-12-26

Description

Dec' 26, 1944- w. F. ROLLMAN 2,366,055

COKING PROCESS Filed Feb. 1a, 1941 cox/wc ZONE if mail: A TER nzynvc D nu coMBas non zo NE products including coke.

Patented Dee. 26, 1944 como PRocEss l Walter F. Rollman, Cranford, N. J., assigner to Standard Oil Develo ration of Delaware pment Company, a corpo- Appucauon February 1s, 1941,'seria1No. 379,397

' (ci. 2oz-s) 7 claims.

The present invention relates to improvements in the art of treating hydrocarbon oils and, more particularly it relates to a method of coking heavyl residual petroleum oils, such as topped or reduced crude .petroleum oils, to secure quantities of hydrocarbons boiling within the gas oil range, to-

' gether with some gasoline, normally gaseous 'hydrocarbons and coke.

A great deal of research and experimentation has been carried out by the oil industry directed toward improving coking operations. Heretofore, and in many instances at the present time, after, a crude petroleumoil has been topped to remove' by distillation constituents boiling up to i. say 825 F.850 F., the residual oil, often called reduced crude, is subjected to a pyrolytic treatment such as coking or viscosity reducing in order' to obtain additional quantities of gas oil, that is, hydrocarbon oils boiling Within the range of say from 400 F.850 F., which gas oil may be used as a charging stock for a thermal or, preferably,

catalytic cracking operation to produce a gasoline of high octane number. In so far as the cokin'g operation is concerned, the practice has been to preheat the oil to coking temperatures in say a tube furnace and thereafter to ldischarge the pre- 'heated oil into a coking retort or drum, preferably heat insulated, in which drum the oil undergoes conversion to form gas oil, gasoline and other Insuch an operation, the coke formed unavoidably deposits as a solid clinging to the bottom and side walls of the drum, which is eventually nearly filled so that periodically the operation must be discontinued to remove the coke. The first step in decoking a drum of the kind referred to above is to discontinue the oil feed and permit the kdrum to stand for a time,

stream operation While the other or others are being decoked.

The Vpresent invention is directed. toward a process for coking continuously and broadly `contemplates so manipulating the coking` operation as to cause the formation of a hard, dry, freeflowing granular coke which is non-adherentand which therefore may be continuously -removed from the -coking drum thus obviating the necessity of discontinuing the coking operation to remove large quantities of coke. I accomplish this result by providing a, coking drum containing three distinct sections as follows: (1) a topfeed introduction section operating slightly below normal coking temperatures into which section the oil is sprayed; (2) `a 'coking section; and (3) a coke drying section maintained at' a, high temperature by the introductiony of` air and fuel gas.

The present invention will be best understood by reference to the accompanying drawing in which Fig, I shows. schematically a form and arrangement of apparatus elements in which the present invention may -be carried into effect; and

say 24 hours, for the purpose of drying and hardening the contained coke. At the end of this time hydrocarbon vapors are displaced out of the coking drum by means of steam, the drum is cooled with water, opened, and the coke removed. There are'several methods in use for the removal of coke from the coking drum, namely, pulling out a cable which was strung spider-web fashionv in the drum `prior to thel operation; drilling and knocking out the coke with a kind of revolving hammer;l or removing the coke by means of very high pressure streams Aof water emitted from a revolving nozzle head pushed t through a hole drilled in the coke. The decoking of a drum is, therefore, a laborious and time-consuming opera- Ation when practiced intermittently as indicated above. It also requires additional equipment, be-

cause the usual practiceis to employ two or more drums of which ldrums one or` more is in on- Fig. II shows an Aenlarged modification of the equipment employed in discharging the oil into the coking drum. Throughout the several views similar reference characters refer to similar parts.

Referring in detail to the drawing, a heavy hydrocarbon topped crude oil or reduced crude is discharged into the system through line l and thence discharged into a preheater- 3, and thence discharged through line 5 into a coil 6 disposed in a furnace setting 8 where the oil is heated to a temperature of say 800 -F.-950 F. The oil thus heated in coil 6 -is Withdrawn from said coil through line I0 and discharged into a spray head I4 located in the upper` section of a vertical coking drum I 6 where the oil is formed into small droplets and thereafter discharged into the interi`or of said drum. The oil discharged into the drum is at a .temperature such that it will not readily form coke on the inlet spray head but isV thereafter heated to coking temperatures in a manner which will be presently explained. The

spray head is, as stated, employed to convert the f y oil stream into particles directed straight downwardly, in preference to a nozzle, because of the tendency of a nozzle to. direct some of the oil against the wall and to produce some mist; which would entrain out of the drum. The upper or feed zoneis provided with a cooling jacket 20 through which is circulated water or any other suitable coolant for the purpose of keeping this feed zone, and, more particularly, the feed spray head at a temperature slightly Vbelow that at 6 or 8 feet'.

venting the accumulation of coke on the oil feed spray head. Any other suitable method may be employed to prevent overheating the spray head or oil in contact with it. For example, the inner wall ofy the'feed zone may be covered with an insulating material to reduce radiation of heat from the walls in this section to the spray head: or the feed zone may be separated from the remainder of the coking drum by means of a heat insulating gasket to prevent the4 metallic conduction of heat through the walls to the feed zone. In any case, the feed zone section need be no longer than is necessary to thus insure that the spray head is not exposed to excessive temperatures. I

The finely divided oil particles fall through a stripping and/or coking zone S heated to some extent by rising combustion gases formed in a manner which will subsequently be explained., Experience in the study'of continuous coking has shown'that if the oil is preheated substantially to coking temperature; and is nely divided, in. a hot coking drum conversion to coke is completed very quickly and consequently the coking zone need not be excessively long, e. g., it may be say 25 to 100 feet. However, it is not necessary to produce an absolutely dry coke in the coking zone, and consequently the small quantity of tacky material remaining after the initial rapid ashing and cracking, which produces very little useful products and is 'the most `namely, normally gaseous hydrocarbons, and hydrocarbons in the gasoline and gas oil boiling range, and would also introducev an undesirable quantity of oxygenated bodies into these products. As a further precaution against getting excess oxygen into the coking zone extraneous gas is introduced through line 35 into perforated ring 36' located at or near the topl of the drying section, which gas will be consumed by the excess oxygen that may remain in the drum at this point.V However, it is known that the presence of some oxygen in the coking drum has l the effect of increasing the octane number of the gasoline produced in the'coking operation and consequently it Ymay be preferable to perinit some oxygen to enter the stripping and coking section, although obviously the amount of 5 d5, thus reducing the quantity of iixedgases refractory fraction of the charging material, need not be completelycokedin the coking zone. This is' an important advantage in that it materially shortens the length of the coking zone required. Oil vapors and some combustion gases are taken off at. the top of the coking zone through line 26 and these may be conducted to fractionating lequipment to separate and recover desired fracthe coking Zone through the drying Zone D where they are completely dried and, if desired, partially burned to produce heat which may be utilized in the operation in section S. The drying zone D vis maintained at a very high temperature, say 1050 F. to 1800 F., by the cornbustion of gas introduced through line 2d vinto a ring burner Siilocated as shown near the bottom of the drying section, and since reaction takes place very quicklyat these conditions, this section may be fairly short, say not more than The air necessary to support the combustion is introduced through line 32 into a perforated ring member 38 similar in construction toring 30. The air and combustion gas discharged respectively into the coking drum through

lines

32 and 28 may ordinarily be at room temperature. A supply of excess air over that required to consume the extraneous combustible gas is discharge through line 32 into the coking drum, the purpose of the excess 'air being to facilitate drying by burning off any tacky material which may remain on the coke particles at this point, and also for the purpose of burning some of the coke, which thus supplies part of the necessary heat of coking.

destroy valuable products of the coking plo'cess,`

which must subsequently be handled by the fractionating equipment attached to the unitaria also reducing the tendency of oil and coke particles to entrain out of the coke drum because of excessive gas velocities in the stripping and coking section. The sensible heat of the combustion gases, however, m'ay be used to heat the stripping section of the coking drum by passing them through a jacket (not shown) surrounding this section of the drum, but heat transmission from gases in a jacket of this type to falling particles in the drum is poor, and the slight advantage ofthe jacket does not usually warrant the expense of installing it. .In any case, much of the sensible heat of the iiue gases is recovered by heat exchangers with the oil feed by indirect contact and, consequently, only a small fired preheater coil li is required. If the coking process is so operatedthat the flue gases 4g; contain hydrocarbons, they may be burned by in- ,5f and'vapor velocities because of the comparatively 7 troducing air at or near the point Where the gases enter the heat exchanger 3, that is to say through line 43, andy the sensibleheat thus released rnay be at least in part recovered. in heat exchanger 3. lThe gases passed thru heat exchanger 3 may be Withdrawn from the heat exchanger thru line M Desirable lengths of the several sections of the coking drum have been considered above in the discussion of the respective sections. The relative order of increasing diameter of the three sections of the coking drum should be, (l) feed section,

(2) stripping and coking section, and (3) drying section. The feed section should be as narrow as possible consistent with avoiding the contact of oil lfeed with the Walls, to prevent hot vapors from the stripping section from sweeping up into the feed section and consequently overheating and causing the formation of coke onv the feed spray head. The diameter of the stripping and coking section is such that the fallingparticles are not likely to deiiect suiciently to come into contact with the walls, and vapor velocities are not sufllcient to entrain oil or coke particles out of the drunuyet the diameter of this section must not be so great thatI vapor contact time and consequently destructive cracking in this section is.

excessive. In order to avoid excessive turbulence large volume of.l gases present, the diameter of Some of the hot gaseous prod-" the drying section is greater than that, of the stripping and coking section.

and coking of theoil feed. Under the conditions n stated, the coke formed in the process is in the form of hard, dry pellets or buckshot which is free-flowing, and this material collects in the' bottom of the coking drum ,and may be with;

drawn through star feeder 50 and delivered to storage. Y

Referring in `detail to Figure 11, the spray head consists as shown of a plurality of downwardly.

l projecting nozzles 55 tapering to an'orlce of,

frequent shutdowns to remove coke from the coking drumi. Th'e coking drum itself `consists of three sections, namely, a feed section, a stripping section, and a coke drying section.l As indicated, the feed stock is discharged into the upper section," namely, the feed section, at a temperature slightly below` normal coking temperatures; and in order to prevent coking in the feed section, especially on the feed spray head, this section is maintained slightly below coking temperature by means of water or any other suitable coolant circulated through a cooling jacket. The additional heat requiredto cause rapid vand complete coking of the oil particlesis preferably supplied by burning a gas such as CO, hydrogemjhydrocarbon gases or the like,V in thefdrying section'. It is also preferable to cause some limited combustion of the coke produced in the lower part of the stripping section in order to further facilitate drying and coking of the partially coked particles. In some cases it is desirable to maintain an excess of oxygen in the drying section and permit part of` it to escape to the coking section, since it has a stripping and coking section, withdrawing a tacky coke from the saidy coking and stripping section, and discharging it into a drying section Vwhere it is heated by combustion gases to temperatures suiiiciently high to cause the formation of hard, dry pellets of coke, recovering hydrocarbon vapors from the upper section of the lcoking zone and pelleted coke from the bottom of the coking section.

2. The process set forth in claim `l in which the oilis preheated to a temperature within the range of from about 800 F. to 950 F., the temperature in the stripping and coking Irone is from about 850 F. to 1200 F., the temperature in the drying zone is from about 1 050 F. to 1800 F.,lthe pressure inthe coking drum is from 0 to 100 1bs'./sq;in. gauge'pressure and the feed rate of oil Vtdj-.t-he drum is determined by the tendency of the-oil or coke particles to be entrained in the vapors egressing from the coking zone.

3. The.. process set forth in claim l in which the oil is-preheated to. about 825 F., the tem- 4 perature in the coking and stripping zone is about 1000 F., the temperature inthe drying zone is about o1400 F., the pressure in the coking zone is about 5 Ibis/sq. in. gauge and the feed rate of oil to the coking zone is about 0.6 volume of cold oil per zone` volume per hour.

4. The process set forth in claim 1 in which -the drying section is`heated by means of com- I oil-,'-a vertical shell having a feed inlet zone, a

' coking'- zone, and `a coke-'gdrying zone, cooling meansin. said feed inletzone, means in said coking zonefor removing oil va'pors. means in the bottom of said drying z/one for introducing a hot f inert gas thereinto, means in the top of said in said head for introducing oil to be coked, coolbeen found that'smaltquantities -of oxygen in the coking zone improve the octane level of the gasoline produced. l j

As for a range of conditions, the charging oil in' line I0 should be at a temperature of from 800 F.950 F. and discharged into the feed section at-` this temperature. The pressure maintained in the drum "shouldV` be from atmospheric to 100 lbs/sq. in. gauge. The temperature in the drying section should be from 1050 F.1800 F. for best results. Oil feed rate is limited only by the-tendency of oil to entrain out of the coking drum or deflect to the sides.v l

Many modifications of my invention may be made without departing from the spirit thereof. `WhatI claim is: l l

1. A continuous process for coking heavy resdual hydrocarbon oils which comprises prevheating the oil to coking temperatures, atomiz- .ing the preheated oil into an-elongated vertical coking zone, cooling said oil during said atomii zation to prevent premature coking, permitting the atomized oil soI formed to descend through ing means adjacent said oil-introducing means, means in said drying and combustion zone for passing a current of hot gas upwardly through saidshell, means in said collector ring for removing'most of said gases being passed through said shaft, means near the top of lsaid shell for with-` drawing oil vapors vand the remainder of said gases. passing upwardly through said shell, and means in thelbottoin of said shell ,for removing '7. A coking tower for residual oils comprising v'a vertical tubularshell having a head at its upper end and an expanded section near the middle portion thereof, means in said headfor introducing the oil to be coked,V cooling means adja-l panded section for removing most of said hot gases, and means in the lower portion of said shell for burning a portion of the coke formed so as to dry the remainder of said coke, and means for withdrawing Idry coke from the bottom of said shell.

WALTER?. ROLLIIIIAN.v