US2847365A - Coking process and apparatus - Google Patents

Description

Aug.'12, 1958 *B. v. MOLSTEDT 2,847,365

COKING PROCESS AND APPARATUS Filed April 21, 1954 COKER PRODUCTS T0 FRACTIONATOR BYRON V.HOLSTEDT I N VENTOR ATTORNEY COKTNG PROCESS AND APPARATUS Byron V. Molstedt, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of Delaware Application April 21, 1954, Serial No. 424,611

4 Claims. (Cl. 196-55) This invention relates to an improved apparatus for carrying out a hydrocarbon oil fluid coking process. Specifically, the invention is concerned with an improved coking system wherein the coking reactor is provided with an auxiliary section at the bottom thereof to serve as a trap for large coke particles or coke agglomerates which are rejected from the coke circulation system.

Recently it has been proposed to coke hydrocarbon oils such as petroleum residua by injecting them into a coking vessel containing a fluidized bed of high temperature finely divided solids, e. g. coke, sand, spent catalyst and the like. In the coking vessel, the oil undergoes pyrolysis in the fluidized bed, evolving lighter hydrocarbons and depositing'carbonaceous residue on the solid particles. The necessary heat for the pyrolysis is supplied by circulating a stream of the, fluidized solids through an external heater, generally a combustion zone, and back to the coking vessel. The solids, which have had carbon deposited on them during the coking, are partially combusted in the heater.

In established processes employing the fluidized solids technique, for example, catalytic cracking, the catalyst particles circulating between the reactor andthe regenerator are relatively small in size and the growth of such particles during the cracking operation due to deposited carbon is relatively minor. Thereis little or no tendency of the catalyst particles to increase in size to such a degree that their bulk interferes with their circulation in the system.

In a petroleum oil fluid coking process this is not the case. It is preferred'to operate in the fluid coking process with solids having an average particle size ranging between 75 and 500 microns in' diameter and more preferably in the range of 150. to'300 microns indiameter. Asthe coking operationproceeds, the particles tend to grow rapidly by deposition thereon of coke formed in the process. If the particle growth during the pyrolysis is excessive and the particles reach sizes greatly above the cited limits, without being removed, erratic and interrupted flow occurs in the solids circulation system.

Furthermore, during the coking process coke deposits of appreciable size are apt to form on the reactor walls and on other internal surfaces in the vessel. They eventually become dislodged and fall into the fluidized bed and finally find their way into the circulating solids system, causing difiiculty.

Abnormalperiods of coking operation also give rise to theformation of coke agglomerates. Removal of these agglomerates is essential to the smooth uninterrupted-fluid coking process.

According tothe present invention, means are provided for preventing agglomerates and large size particles exceeding a predetermined size decided upon for proper 'fluidization and solids transfer from invading the solids transfer lines and means are provided permitting the accumulation of agglomerates and large size particles so rejected in a separate confined compartment in the reactor from which they can be continuously or intermittently 2,847,365 Patented Aug. 12, 1.958

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removed. The removal of oversize particles and their rejection from the solids transfer system are attained by providing restraining means, e. g., a cage or screening, over the inlet to the solids withdrawal well in the fluid coking vessel to prevent large particles from enteringthe transfer lines, and permitting the particles so excluded to fall into a lower tr-apwhere, by dense phase elutriation, they settle into a quiescent state and are removed.

An object of the present invention is to improve the operability of a hydrocarbon oil fluid coking process. Specifically, an object of this invention is to provide a means for removing oversized'particulate coke from a fluid coking system in order to prevent erratic andinterrupted flow in the solids circulation system.

The invention will be more readily understood by reference to the accompanying figure which shows one-form of novel apparatus for carrying out the present invention.

Referring, to the figure, vessel A is a coking vessel constructed of suitable material for operations at tempera tures in the range of 900 F. to 1600 F. or higher. The vessel A has alower tapered stripping section S, a bulged center portion C and a top section D of reducedcrosssectional area which includes a cyclone separation system 3. The bottom portion of the stripping section is used to form an agglomerate trap T.

The stripping section contains a pipe 7 for the" withdrawal of solids therefrom and the opening of 'the pipe is covered with a wire cage 8, screen or other restraining device. The cage is preferably welded cover the inlet to the solids transfer pipe. The screen or cage is soconstructed as to permit flow therethrough of solid particles up to a predetermined maximumsize, while preventing the entrance into the pipe of particles above the predetermined size.

The coking vessel contains a bed of high temperature coke particles 2 in the coking and stripping section which solids are fluidized by means of a gas such as steam or other inert gas entering at the bottom of the stripping section via pipe 4. The solids are maintainedin the bed at a height indicated by the letter L.

The fluidizing gases'serve'to strip vapors and gases from the coke or solid particles which flow downwardly in the stripping zone. Product vapors are removed from the vessel via line 5 after passing through a cyclone" system 3and are sent to a fractionator for the recovery'of gas, gasoline, gas oil and heavier products. Entrained solids removed by the cyclone are returned to the bed via dipleg 6.

Hydrocarbon oil or other hydrocarbonaceous material to be converted, preheated to a temperature not above its cracking temperature, usually not above 750 F., isinjected into the bed of solid particles, preferably at a plurality of points in the coking vessel both circumferentially and vertically. The vapors resulting from' the decomposition of the hydrocarbon oil after'contactwiththehot solids assist in the fluidiz-ation of the solids in the'coking bed and add to its mobility and general turbulent state:

The solids in the bed move continually downwardly from the coker to the stripping section and are removed from the stripping section after passage through screen 8 via standpipe' 7. Any coke agglomerates of undesirably large: particles are deflected by the screen 8 and fall downwardly into the agglomerate trap T. -In the trap, the large heavy agglomerates settle out through the mobilized bed of smaller particles and concentrate in a relatively quiescent mass at the bottom of the trap.

Aeration gas is admitted to the bottom of the trap by line 17, in amounts sufiicient to mobilize the particles. The superficial gas velocity used in this zone will be near or at the minimum fluidization velocities of the material, i. e., 0.1 to 2.5 ft./sec. In this manner, the finer solids in the trap.

It is not, however, necessary to provide a restricted section in the stripping area as a trap for the oversized material. The trap section may be the same diameter as the stripper, or in the case when an external stripper or elutriator is used, a trap section may be of the same diameter as the reactor and form the reactor bottom. By increasing the cross-sectional area of the trap, larger amounts of aerating gas may be used to mobilize the collective material and then may pass upwardly to serve as fluidizing gas for the main coking bed.

The segregation or separation of the rejected coarse material from the fines may be enhanced, of course, by providing baififles, vanes or packing in the upper portion of the trap.

In order to maintain the necessary temperature of about 900 to 1600 F. in the coking vessel, a stream of solid particles containing adsorbed or deposited carbonaceous material is removed from the coking vessel via standpipe 7 and with the assistance of fiuidizing gas such as air entering through taps t are conveyed to burner vessel 10 being introduced at a point in the lower section thereof. Air or oxygen introduced via line 11 at the bottom portion of the vessel is employed to burn some of the coke on the solid particles and thereby raise their temperature to a point suflicient to supply the heat for the endothermic coking reaction occurring in the coking vessel A.

The hot solid particles at the temperature of approximately 100 'F. to 300 F. higher than the coking temperature of vessel A are removed from the vessel 10 by means of overflow into standpipe 12, said overflow being situated preferably at a point near the upper level of the fluid bed. The hot solids descend the standpipe 12 and with the assistance of fluidizing gases injected via taps t at spaced intervals are returned to the coking section of vessel A.

In the burner 10 the solids are maintained in the fluidized state at a bed level L in very much the same manner as the solids in the coking vessel A. Combustion gases are removed from the burner by line 15 after passing through cyclone 13. Entrained particles are returned to the bed by dipleg 14.

The coking process will, of course, produce a net amount of coke. The net coke product of the process may be removed from the burner via line 16 besides by line 9.

It is to be understood that alternate conduit arrangements for transferring the solids may be used and be within the scope of this invention. As an example, the burner or combustion zone can operate on the transfer line reactor principle, the upflowprinciple, or the gravitating bed principle. The coking vessel can be supplied with solids and solids removed therefrom in a manner similar to that shown for the heater, i. e., conduit 7 may extend upwardly to the fluid bed level L and serve as an overflow standpipe and the high temperature solids may be introduced into the lower portions of the vessel.

It will be observed from the described process that a segregation Zone in the coking vessel has been properly located for the collection and withdrawal of large coke formations formed during the coking operation. Circulating coke is withdrawn from a well fluidized zone either in the reactor or stripper at a point above the trap through a screen or cage designed to prevent the entrance into the circulating system of agglomerated particles larger than a particular chosen size. In this manner large pieces of coke or other agglomerates which are potential sources of circulation difiiculty are continually removed from the solids circulation system, thereby prevently disruption of the continuous coking process.

What is claimed is:

1. Apparatus for the coking of heavy hydrocarbon oil comprising a coking vessel containing a coking section and a stripping section and a trap at the base of said stripping section for the collection of large size solid particles, a burner vessel, means for introducing a heavy hydrocarbon oil into said coking section, means for introducing stripping gas into said stripping section, means for removing conversion products from said coking vessel, outlet conduit means for conveying solids from said stripping section to said burner vessel, means for conveying solids from said burner vessel to said coking vessel, a screen in said stripping section at the entrance of said outlet conduit means for preventing flow of solid particles greater than a predetermined size from said stripping section of said coking vessel to said burner vessel, means for collecting and aerating large particles rejected from circulation to said burner vessel in said trap, said trap being located at the base of said stripping section and below the location of said screening means, and means for removing said large particles from said trap.

2. In a process wherein a petroleum oil is subjected to pyrolysis by contact with a fluidized mass of high temperature particulate coke in a coking vessel, vapors are removed overhead as product, a portion of said mass is continuously circulated to an external heating zone tion and circulation of the solids in said process comprising circulating only particulate coke below a predetermined size from said coking vessel to said external heating zone and back to supply said heat, collecting in the base of said coking vessel oversized particles above said predetermined size as a mobilized mass fluidized at minimum fluidization gas velocities in the range of 0.1 to 2.5 ft./sec. and withdrawing said oversize particles from said system as product.

3. In a system wherein heavy petroleum oils are subjected to pyrolysis in a coking vessel, wherein product vapors are removed overhead and wherein conduit means are provided for circulating particulate coke from said coking vessel to a heating vessel and back, the improvement comprising restraining means in said coking vessel at the entrance of said conduit means for preventing flow restraining means permitting the collection of coke particles above said predetermined size, means for aerating at minimum fluidizing gas velocities the particles so collected and conduit means for withdrawing particles so collected.

4. An improved hydrocarbon oil fluid coking process which comprises contacting an oil with a dense turbulent bed of fluidized solids maintained at a coking temperature in a coking zone to produce vapors and coke which is deposited on said solids, removing said vapors overhead as product, circulating only solids below a predetermined maximum size from said dense turbulent bed to an external heating zone and rejecting coarse particles above said predetermined maximum size from circulation to said heating zone, returning heated solids from said heating zone to said dense turbulent bed to maintain said coking temperature, collecting said rejected coarse particles in a segregation zone comprising a quiescent but mobilized mass of solids in the bottom portion of said coking zone, said mass being aerated at superficial gas velocities in the range of 0.1 to 2.5 ft./sec. whereby said coarse particles settle therethrough to the bottom portion of the mass, and removing said coarse particles as References Cited in the file of this patent UNITED STATES PATENTS Degnen et a1. July 21, 1942 6 Hemrninger Nov. 7, 1944 Hunter May 27, 1952 Leifer Dec. 1, 1953 Watson May 3, 1955 Galbreath et a1. Mar. 20, 1956 Weber July 17, 1956

Claims (2)

1. 2. IN A PROCESS WHEREIN A PETROLEUM OIL IS SUBJECTED TO PYROLYSIS BY CONTACT WITH A FLUIDIZED MASS OF HIGH TEMPERATURE PARTICULAR COKE IN A COKING VESSEL, VAPORS ARE REMOVED OVERHEAD AS PRODUCT, A PORTION OF SAID MASS IS CONTINUOUSLY CIRCULATED TO AN EXTERNAL HEATING ZONE AND BACK TO SUPPLY THE NECESSARY HEAT FOR THE PYROLYSIS AND THE EXCESS COKE PRODUCED BY THE PYROLYSIS IS REMOVED AS PRODUCT, AN IMPROVED METHOD FOR PREVENTING THE ACCUMULATION OF OVERSIZED PARTICLES THAT DISRUPT FLUIDIZATION AND CIRCULATION OF THE SOLIDS IN SAID PROCESS COMPRISING CIRCULATING ONLY PARTICULATE COKE BELOW A PREDETERMINED SIZE FROM SAID COKING VESSEL TO SAID EXTERNAL HEATING ZONE AND BACK TO SUPPLYA SAID HEAT, COLLECTING IN THE BASE OF SAID COKING VESSEL OVERSIZED PARTICLES ABOVE SAID PREDETERMINED SIZE AS A MOBILIZED MASS FLUIDIZED AT MINIMUM FLUIDIZATION GAS VELOCITIES IN THE RANGE OF 0.1 TO 2.5 FT./SEC. AND WITHDRAWING SAID OVERSIZE PARTICLES FROM SAID SYSTEM AS PRODUCT.
2. 3. IN A SYSTEM WHEREIN HEAVY PETROLEUM OILS ARE SUBJECTED TO PYROLYSIS IN A COKING VESSEL, WHEREIN PRODUCT VAPORS ARE REMOVED OVERHEAD AND WHEREIN CONDUIT MEANS ARE PROVIDED FOR CIRCULATING PARTICULATE COKE FROM SAID COKING VESSEL TO A HEATING VESSEL AND BACK, THE IMPROVEMENT COMPRISING RESTRAINING MEANS IN SAID COKING VESSEL AT THE ENTRANCE OF SAID CONDUIT MEANS FOR PREVENTING FLOW OF SOLID PARTICLES GREATER THAN A PREDETERMINED SIZE FROM SAID COKING VESSEL TO SAID HEATING VESSEL, A TRAP LOCATED IN THE LOWER PORTION OF SAID COKING VESSEL BELOW SAID RESTRAINING MEANS PERMITTING THE COLLECTION OF COKE PARTICLES ABOVE SAID PREDETERMINED SIZE, MEANS FOR AERATING AT MINIMUM FLUIDIZING GAS VELOCITIES THE PARTICLES SO COLLECTED AND CONDUIT MEANS FOR WITHDRAWING PARTICLES SO COLLECTED.

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