US2780586A - Coking system and method of coking - Google Patents

Description

Feb. 5, 1957 c. K. MADER coKING SYSTEM AND METHOD oF coxING Filed March 2, 1955 ATTORNEYS United States Patent i COKING SYSTEM AND METHOD OF COKING Charles K. Mader, Sutfern, N. Y., assigner to The M. W. Kellogg Company, Jersey City, N. I., a corporation of Delaware Application March 2, 1953, Serial No. 339,776

6 Claims. (Cl. 19d-65) This invention relates generally to the coking of heavy petroleum residua, such as reduced crude or cracked tars, -to produce a relatively clear gas oil and by-products of gas, gasoline, and granulated coke. ln the past, coking has lgenerally been carried out in delayed coking drums or shell stills in a sequence of batch steps, but the present process involves coking the heavy oil by wetting the surface of a bed of coke granules maintained in a fluidlized state (i. e. a dense, turbulent suspension) by lthe upper passage of combustion gases. More particularly, this invention involves introducing dry coke granules into an upowing stream of air or other oxygen-containing gas to initiate combustion in a dilute upiiowing stream, discharging said dilute burning suspension upwardly into a dense fluidized mass of turbulent, circulating coke particles, wetting the turbulent upper surface of said dense bed with oil droplets, and overdowing said bed into a dense downwardly moving phase of coke particles in which cracking and stripping take place.

The coking operation, including combustion, contacting of coke particles with oil, maintaining the wetted coke particlesunder coking conditions for suitable residence time and recirculation of coke partices, is carried out in' a single unitary vessel, a coking reactor. Preferably, the upowing combustion steps take place in a centrally located upowing column within a vertically extended vessel, and the downllowing coking phase is contained in an annular space surrounding the upowing combustion vessel. At the lower end of the downilowing coking phase, dry coke particles re-enter the dilute upflowing combustion stream. Control for the rate of circulation of coke in this system is readily effected by `the rate of introduction of gases (air, oxygen, or oxygen-containing gases) into the upflowing dilute column. Moreover, the introduction of this gas is preferably accomplished by means of a hollow-stem valve which also serves to control the opening between the lower end of the downllowing coking phase and the uptlowing combustion phase.

Since the combustion takes place in a iluidized phase immediately underneath the surface upon which the oil is deposited, that surface is extremely turbulent and hot, much more so than would be the case in other types of tluidized coking reactors. This prevents the formation of wet-tarry crusts or lumps. The turbulent surface overflows a Weir-like partition into the adjoining (preferably annular) coking zone. The point of overflow is preferably aerated, with steam for example, so as to encourage continuous and unclotted overflow. The oil is sprayed ontoV this surface from =a point overhead by means of steam injection. `Effluent gases and ue gases are withdrawn together from a point substantially higher within the coking reactor vessel than that at which the oil is introduced; this allows for a settling zone and avoids too much carry-over of lin-e coke particles or fine droplets. However, such lines Ias are carried over are precipitated as a slurry in the eflluent fractionating tower and recycled to the incoming h-ot feed on its way to the coking reactor.

A -typical embodiment of my invention is shown in the accompanying drawing.

The coking takes place in a large coking reactor10. Coking reactor 10 is charged by introducing black oil, or the like, into the system at 11, pumping it by means of pump 12 and line 13 into absorber 14, wherein the incoming oil descends in contact with upflowing eiuent gases, thus absorbing heavier components thereof.

The warm oil is withdrawn from the bottom of absorber 14 through line 15, heated in furnace 16 to a temperature of about 900 F.; preferably, this temper- Aature should be within a range of 840 F. to 950 F. The pressure at this point is not a critical matter provided only that it is suiiiciently high to force the oil into the coking reactor 10. Ordinarily, pressures within the coking reactor will be between 20 and 50 p. s. i. g. The pressure in line 22 upstream from injection valve 23 ought to be between 50 and 100 p. s. i. g. higher than within coking reactor 10. Theoil passes `through furnace 16 in a period of about 25 seconds, preferably not less than 10 seconds and not more than 60 seconds, so that clogging of the furnace does not occur; the oil passes by way of line 17 into a -ash tower 18 in which between 20 per-cent and 70 percent of the hot oil ashes oi and is removed overhead Ithrough vapor line 19. This vapor is comprised primarily of 4gas oil of 15 to 35 API gravity and has a boiling range of 450 F. to 850 F. The remaining heavy oil is vsteam stripped Ia little by steam (about p s. i. g. and 400 F.) introduced at 20. This stripped hot oil passes through valve 21 and line 22 to an injection valve 23 mounted in the top of the coking reactor 10. Steam or gas is introduced by way of opening 24 into an annular chamber 25 within valve 23 to atomize the liquid oil. The hot oil passes down -a central pipe 26 and emerges from an opening 27 at the lower end at a rate which is controlled by valve 28. Valve 28 is controlled by a vertically reciprocable valve rod 29 by any conventional control means located above packing 30.

Oil emerging from opening 27 i-s entrained in steam or gas from annular steam -chamber 25 and sprayed out through opening 31, falling in a rain of droplets 32 upon the turbulent upper surface 33 of a turbulent mass 34 of coke lgranules suspended in upiiowing gases in 4the fluidized manner employed commonly in fluidized catalytic cracking. The method of `spraying from steam -injection valve 23 prevents the accumulating of tarry deposit on the edges of openings 28 and 31. f

Coking reactor 10 is supplied with oxygen through a novel-oxygen inlet valve 35 at the lower end of the coking reactor vessel, and with steam or gas at suitable points; coke land gaseous eluent are produced within coking reactor 10 in a manner to be described hereinafter. The coke is withdrawn through either or both of valved coke outlets 36 and 37.

Gaseous eifiuent, containing some entrained fine particles of coke, is withdrawn at the upper end of coking reactor 10 by way of line 38 and introduced into the lower end of lan effluent fractionator 39. The gases originally flashed off from hot charge oil in flash tower 18 and withdrawn through line 19 and likewise introduced into the lower end of efuent fractionator 39 and 40. Ediuent fractionator 39 is preferably operated at a pressure in a range of about l0 p; s. i. g. to 25 p. s. i. g. and with temperatures of about 700 F. to 800 F. at the lower end and 350 F. to 450 F. at the upper end. At the bottom of fractionator 39 a slurry of condensed heavy gas oil having 0 to 5 API gravity and 10 percent boiling point above 700 F., yand containing coke fines, is withdrawn as a slurry through line 41 and pumped by means o-f pump 42 and line 43 to rejoin the -hot charge oil passing through line 17 on the way from the furnace 16 to iatented Feb. 5, 1957 flashtower 18. Somewhat higher in fractionator 39, preferably atv a temperature. within the. range. of 600 F. to 650 F., a clear gas oil suitable for catalytic cracking or the like is withdrawn at 44.

It willv be. understood, of course, thattheparticular embodiment of the apparatus illustrated could be modicd without departing from the method of the` invention. For example, ash tower 18v can bei eliminated by` em-Y ploying the lower part of fractionator 3Q (substantially extended in vertical dimension below gas-oil withdrawal point 4.4)y as a hashing zone. Flashed vapors would simply rise from the lower part h39 into. the upper part. Line 17 would charge the hot oil directly into the lower ash zone sectionr of tower- 39.

iuto'coking reactor` 10. If operated in thismanner, pump 42.would, rather than pump 12, be the principal sourceY of pressure on the oil charged toA coking reactor 10.

Vapors are withdrawn overhead through line 4S, condensed (about 40. percent to 80 percent) in condenser 46, and introduced into separator drum 47 from which gasoline isV withdrawn at 48A and pumped by means of pump. 49 partly to subsequent processing by way of line- 50, and partly to the upper end of fractionator 39 by way of line 51 to serve as rellux. Uncondensed gases are taken overhead at a temperature of about 90 F. to 110 F. through line 52 and compressor 52a and introduced into the bottom of absorber 14 for recovery of some components. Water is drawn ofi through line 53.

in the process of coking` heavy oil one of the most diliicult problems is the handling of the hot tarry mass which forms as some of the oil is, heated and partially vaporized. This problem is particularly serious in any attempt to carry out coking continuouslyina uidized system. The interior of coking reactor 10 presents a simple circulatory system which is resistant to clogging by tar cake formation, etc. External transfer lines for coke particles and separate vessels for heat, etc. are eliminated. The combustion and coking processes are combined in simple vertical upilow and downow steps in which the iiow is controlled by the introduction of gases and the densities of the suspensions of coke particles. When the oil droplets 32 lirstV wet the particles ofv hot coke in turbulent surface 3 3, the most volatile components are immediately vaporized. The droplets as, they fall encounter hot upflowing eiuent gases. They leave nozzle opening 3l at a temperature of between 700 F. and 800 F. and reach turbulent surface 33 at a temperature between 800 F. and 900 F. They encounter coke particles which have a temperature of between 900 F. and l800 F. Any tendency to cake on the topof dense phase 34 is resisted by the turbulence causedV by hot upllowing combustion gases. Dense phase 34 has ya-.typical density of 25 lbs. per cu. ft. but it may be at any suitable density between l lbs. per cu. ft. and 45v lbs. perV cn. ft. The gases passing upwardly through it ow at an upward velocity of 1.8 to 3.0 ft. per sec. The-particle size may range between 20 fand 200 microns but preferably these particles have a size distribution as follows:

t Percent 0-20 u 10v 20-80 40 80+ 50 Pump 42. would deliver o il directly to line 22 forY Steam injection-` below coking vessel S5 and supporting grid 56. Coking vessel 55. and combustion chamber 57 are in this particu-v lar embodiment located concentrically within coking reactor 10 so that there is a substantial annular space 58 entirely surrounding both coking vessel 55 and combustion chamber 57. This annular space is substantially filled with a dense mass of downwardly moving coke particles. This downwardly moving mass may be turbulently fluidized by the introduction of steam or other inert gas (or in some cases, water) through aeration steam lines 59 and 60. On the other hand, it may be preferred not to aerate the downwardly moving mass of coking particles sufficiently to luidize it, instead permitting the particles to flow downwardly in a dense phasebut without being suspended or turbulent or in circulatory movement within the mass. The criteria which will determine this choice will be desired properties of the coke produced. The downwardly moving dense phase will have a density of about 30 lbs. per cu. ft., preferablyy in a range of about l5 to 45 lbs. per cu. ft.

Within annular space 53 near the lower end of coking reactor 10, most of the coke particles, somewhat augrnented by the formation of new coke, enter thelower end of combustion chamber 57 by way of an opening 61. The rate of this liow is determined in part by the.

height and density of the downliowing dense phase within annular space 58, but principally by upward or downward regulation of the large hollow-stem valve 35. ValveA 3S leaves the annular space between the'conical valve face and the valve-set periphery of opening 61. horizontal cross-sectional area of the annular space at opening 6,1 can be reduced by moving hollow-stem valve 3 5 upwardly.

In general, the downward flow of coke in the annular dense phase must be slow enough to permit hardening of the colte. A preferred range of velocities for this slowly downwardly moving dense coke is .1 to 3ft. per sec.

As soon as the recirculating coke particlesenter combustion chamber 57 they are entrained in air or oxygen moving upwardly at a velocity of 45 ft. per sec., preferably in a range of 30 to 100 ft. per sec. The particles iiow upwardly at about the same velocity and in a very dilute phase of only about 1.0 lbs. per cu. ft., preferably between 0.5 -and 6.0 lbs. per cu. ft. In the process, these coke particles begin to burn and their temperature is increased from a temperature at opening 61 of about 800 F. to l000 F. to a temperature of about 850 F. to 1500 F. as they reach perforated grid 56. These particles enterdense phase 34 and combustion continues therein so that dense phase 34 actually achieves a higher temperature than those particles passing through grid 56, usually a temperature between 900 F. and 18009 F.

Between 5 percent and 30 percent of the oil charged to the coking reactor is withdrawn as make coke by way of lineA 36. However, in case a harder and driercoke is desired, then allor part of the make coke may be withdrawn through line 37, directly from dense phasev 34. The droplets 32 deposited on turbulent surface 33 wet the surface particles and are about 40 percent to 80 percent vaporized. Substantially none lof the wetted particles find,V their way back into dense phase 34, almost all of them overflowing into the downwardly dense phase in annular space 58. At the upper surface of this latter dense phase, the. particles are still somewhat sticky and may not fiuidize very well but as they descend they bef come quite dry so that by the time they have passed steam line 59 they are more readily made owable.

A critical feature of control is the rate at which tarry oil is deposited on turbulent surface 33. This rate'V is severelylimited because agglomeration must be avoided. In most cases, an upper. preferred limit may be. lSet of notl more than 5 lbs. of tarry oil deposited foreach 100 lbs. of coke particles circulating around the coking and coke burning circuit. lt will be understood, of curse,

The,

that the ratio of reduced crude charged to theisystem will be much vlarger because this ratio of tarry oil `to each 100 lbs. of circulated coke applies only tothe heavy oil which actually reaches turbulent surface 33 after gasification of al1 those components of the reduced crude which are readily evaporated in the ashing step and during the descent of droplets from injection valve 28 to turbulent surface 33. f

The eilluentvapors in the coke process rise within the upper part of coking reactor 10, carrying with them some entrained line coke particles. These vapors are withdrawn from the uppermost part of the interior of the coking reactor 10 by way of a cyclone 62, most of the lines being precipitated and passed by way of dipleg 63 into the dense mass of downowing coke into annular space 58. The gases carrying some residual fines are Withdrawn through line 38 as described previously.

The combined etliuent gases from ash tower 18 and from coking reactor 10 are introduced into eluent fraction-ator 39 by way of lines 19 and 38 respectively; this eliiuent comprises between 5 percent and 20 percent by weight of the original black oil. Between percent and 50 percent of this'will be recovered as condensables within the system, but an uncondensed gas comprising about '70 percent V(or between about 50 percent and 90 percent of the original effluent gases) will leave the system by way of line 64 at the top of absorber 14. In addition to uncondensed effluent there will be a much larger amount of flue gases comprised of N2., CO2, CO, etc. Any gas recovery system conventionally used in rciineries and the like may be used to separate the gases leaving the coking system by way of line 64. If it is desired to reduce the load on the recovery system, it is possible to introduce oxygen instead of air for combustion at valve 35.

It will be understood that my invention is not restricted to any particular apparatus feature. For example, any inert aeration gas may be used in place of steam as an aeration and stripping medium.

Furthermore, it is possible to simultaneously carry out ilashing in both ash tower 18 and the lower zone of fractionator 39; for this purpose, the feed from furnace output line 17 would be divided between ash tower 18 and the lower region of fractionator 39. Also, recycle from fractionator 39 may be divided and partly returned to ash tower 18 and partly directly to line 22.

I claim:

1. A coking system comprised of: a vertically extended reactor vessel; a smaller vertically extended combustion vessel positioned substantially coaxially within the lower part of said reactor vessel so as to provide an annular space between the exterior of said combustion vessel and the lower interior surfaces of said reactor vessel, said combustion vessel being open at the upper end and having an opening in the lower end; horizontal grid means transversely positioned within said combustion vessel at a point intermediate the upper and lower ends thereof; a vertically reciprocable hollow-stem valve means positioned in the lower end of said reactor vessel, the upper end of said valve means projecting into said lower end of said combustion vessel and adapted to introduce uid upwardly into said combustion vessel through said hollowstem, and adapted by its vertical movement to control communication between the lower end of said annular space in said reactor vessel and the lower end of said combustion vessel; injection valve means in the upper end of said reactor vessel adapted to introduce liquids downwardly towards the upper open end of said combustion vessel; means for removing gaseous eifluent from the upper region of said reaction vessel; and conduit means for withdrawing make coke from said coking system.

2. A method for coking heavy petroleum oil in the presence of hot coke particles, which includes the steps of: maintaining a mass of hot coke particles in a coking zone in a dense iluidized liquid-like condition by passing gases upwardly through said mass at a velocity adapted to maintain it in av condition of internal turbulent circulation without entraining the lentire massin net iiow upward with said gases; spraying heated petroleum oil on the turbulent upper surface of said iluidized mass of hot coke particles to wet said particles at a rate sufficiently low to avoid agglomeration; continuously overflowing wetted coke particles from the turbulent upper surface of said uidized mass to a second dense mass maintained separate and distinct from said iirst dense mass; maintaining a vertically extended column of uptlowing particles of coke undergoing combustion in dilute suspension in oxygen-containing gas below said iirst dense uidized mass and discharging at its upper end into the bottom of said iirst dense uidized mass; and continuously owing at least part of said second dense mass into said upowing column of coke particles undergoing combustion at the lower end thereof. p

3. A method as described in claim 2 in which coke product of a desired hardness and dryness is withdrawn from the system by withdrawing a portion of the coke product from the bottom of each of said two dense phase masses. l

4. A method for coking heavy petroleum crude in the presence of hot coke particles, which includes the steps of: heating said crude petroleum oil to a temperature between 800 F. and l000 F. and introducing it into a flash zone to vaporize a substantial portion of said crude; withdrawing the remaining liquid and continuously spraying said liquid downwardly from the upper region of a coking zone onto a substantial horizontal turbulent surface of a mass of hot coke particles at a rate sutiiciently low to avoid agglomeration of the particles so wetted; maintaining said mass of hot coke particles in a coking zone in a dense lluidized liquid-like condition by passing gases upwardly through said mass at a velocity adapted to maintain it in a condition of internal turbulent circulation without entraining the entire mass in net ow upward with said gases; continuously overflowing wetted coke particles from the turbulent upper surface of said fluidized mass to a second dense mass; maintaining a vertically extended column of upowing particles of coke undergoing combustion in dilute suspension in oxygencontaining gas below said iirst dense iuidzed mass and discharging at its upper end into the bottom of said rst dense fluidized mass; continuously flowing at least part of said second dense mass into said upowing column of coke particles undergoing combustion at the lower end thereof; withdrawing coking eluent vapors from said coking zone together with residual coke particles entrained in said vapors; introducing vapor from said ash zone and said coking efuent vapors into a vertically extended fractional distillation zone, and partially condensing said vapors therein, said coking effluent vapors being introduced substantially below the upper end of said fractionation zone to scrub out coke particles with descending condensate; withdrawing condensate containing coke particles recovered by scrubbing, and introducing said condensate into said crude prior to its introduction into said llash zone.

5. A method for coking heavy petroleum oil in the presence of hot coke particles, which includes the steps of: maintaining a mass of hot coke particles in a coking zone in a dense fluidized liquid-like condition by passing gases upwardly through said mass at a velocity adapted to maintain it in a condition of internal turbulent circulation without entraining the entire mass in net llow upward with said gases; spraying heat petroleum oil on the turbulent upper surface of said uidized mass of hot coke particles to wet said particles at a rate suiciently low to avoid agglomeration; continuously overflowing wetted coke particles from the turbulent upper surface of said iluidized mass to a second dense mass maintained separate and distinct from said first dense mass; introducing an inert gas upwardly through at least part of said second dense 4mass toprevent agglomeration within itgor at its surface; maintaining a vertically extended column of -upflowing-.particles of coke undergoing combustion in Ydilute suspension in oxygen-containing gas below said rst denseuidized .massand discharging at its upp'er end'into the -bottorn of saidfrst dense vfluidized mass; and continuouslyfowing at least ypart of saidsec' ond dense mass into said upowing column of coke particles undergoing combustion at the lower end thereof.

`6. Acoking systemcomprised of: a vertically rextended reactor vessel; a smaller vertically extended combustion vessel, open atthe upper end and positioned substantially coaxially within the lower vpartof said reactor vessel so as toprovidean annular 'Space between the exterior of said combustion vessel and the lower interior surfaces of said 'reactor vessel, the lower part of said combustion vessel being reduced in horizontal crossesection to form a verticallyextended conduit having a lower end opening communicating with the bottom of said reaction vessel; gas injection meansdisposed along the edge of the upper opening of said combustion vessel; horizontal grid means transversely positioned within said combustion vessel at a point intermediately above said conduit portion; a vertically reciprocable hollow-stem valve means positioned in thelower end of said reactor vessel, the upper end of said valve means projecting into said lower end opening .of said combustion vessel and adapted to introducefluid upwardlyinto said combustion vessel through said hollow-stem, and adaptedby its vertical movement to control communication between the lower end of said annular space'in said reactor vessel and the lower end of said-combustion vessel; injection valve means in the ru pperend of said reactor vessel adapted to introduce liquids downwardly towards the upper open end of said combustion vessel; meansfor Yremoving gaseous eluent from `the upper region of said reaction vessel; and conduit means for withdrawing, make Vcoke from said ycolcing system.

References Cited in the le of this patent UNITED srATEs PATENTS 1,056,045 Murray v -v.. a .r.... Mar. 18, 1913 1,643,401 Yard etal. Y Sept. 27, 1927 825,378 Wilson Sept. v29, 1931 "'2-,f3665'055 Rollmanv Dec. 26, 1944 -2,543;884 -Weikart ....fMar. 6, 195,1 '2,58-2i'711 Nelson Jan. 15, 1952 FOREIGN PATENTS "25a-,'39s 'Great Britain May 1, 1925

Claims (1)

1. 2. A METHOD FOR COKING HEAVY PETROLEUM OIL IN THE PRESENCE OF HOT COKE PARTICLES, WHICH INCLUDES THE STEPS OF: MAINTAINING A MASS OF HOT COKE PARTICLES IN A COKING ZONE IN A DENSE FLUIDIZED LIQUID-LIKE CONDITION BY PASSING GASES UPWARDLY THROUGH SAID MASS AT A VELOCITY ADAPTED TO MAINTAIN IT IN A CONDITION OF INTERNAL TURBULENT CIRCULATION WITHOUT ENTRAINING THE ENTIRE MASS IN NET FLOW UPWARD WITH SAID GASES; SPRAYING HEATED PETROLEUM OIL ON THE TURBULENT UPPER SURFACE OF SAID FLUIDIZED MASS OF HOT COKE PARTICLES TO WET SAID PARTICLES AT A RATE SUFFICIENTLY LOW TO AVOID AGGLOMERATION; CONTINUOUSLY OVERFLOWING WETTED COKE PARTICLES FROM THE TURBULENT UPPER SURFACE OF SAID FLUIDIZED MASS TO A SECOND DENSE MASS MAINTAINED SEPARATE AND DISTINCT FROM SAID FIRST DENSE MASS; MAINTAINING A VERTICALLY EXTENDED COLUMN OF UPFLOWING PARTICLES OF COKE UNDERGOIN G COMBUSTION IN DILUTE SUSPENSION IN OXYGEN-CONTAINING GAS BELOW SAID FIRST DENSE FLUIDIZED MASS AND DISCHARGING AT ITS UPPER END INTO THE BOTTOM OF THE FIRST DENSE FLUIDIZED MASS; AND CONTINUOUSLY FLOWING AT LEAST PART OF SAID SECOND DENSE MASS INTO SAID UPFLOWING COLUMN OF COKE PARTICLES UNDERGOING COMBUSTION AT THE LOWER END THEREOF.

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