US2846374A

US2846374A - Fluid coking with preparation of seed coke

Info

Publication number: US2846374A
Application number: US427499A
Authority: US
Inventors: Charles E Jahnig
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1954-05-04
Filing date: 1954-05-04
Publication date: 1958-08-05
Anticipated expiration: 1975-08-05

Description

Aug. 5, 1958 c. E. JAHNIG FLUID coKING WITH PREPARATION oF SEED coma:

Filed May 4, 1954 Charles E. Jahmg Inventor By CW` Afforney FLUID COKING WITH PREPARATION F SEED COKE Charles E. .lahnig, Rumson, N. J., assigner to Esso Research and Engineering Company, a corporation of Delaware Application May 4, 1954, Serial No. 427,499

4 claims. (ci. 19e-ss) This invention relates to improvements in the coking of heavy hydrocarbon oils where a coking charge stock is contacted at coking temperatures with coke particles maintained in the form of a dense turbulent fluidized bed. More particularly it relates to an integrated process of this nature wherein seed coke is prepared and utig in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. ln the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel. A stream of coke is transferred from the reactor to the burnervessel employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the iburner. Sucient coke or carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature sufcient to maintain the system in heat balance.- The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is burned for this purpose. This amounts to approximately to 30% of the coke made in the process. The unburned portion of the coke represents the net coke formed in the process. This coke is preferably withdrawn from the burner, normally cooled and sent to storage.

Heavy hydrocarbon oil feeds suitable for the coking process are heavy or reduced crudes, vacuum bottoms, pitch, asphalt, other heavy hydrocarbon residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F., an A. P. I. gravity of about 0 to 20, e. g., 1.9, and a Conradson carbon residue content of about 5 to 40 wt. percent. (For Conradson carbon residue test see ASTM test D 189-52.)

It is preferred to operate with solids having an average particle size ranging between 100 and 1000 microns in diameter with a preferred particle size range between 150 and 400 microns. Preferably not more than 5% has a particle size below 'about 75 microns, since small particles tend to agglomerate or are swept out of the system with the gases.

A more complete description of this technique of fluid solids coking can be obtained by referenceto copending application entitled, Fluid Coking of Heavy Hydrocar- In a typical operation the y);

2,846,374 Patented Aug. 5, 1958 Z; bons and Apparatus Therefor, Serial No. 375,088, led August 19, 1953, by Pfeier et al. The method of fluid solids circulation described above is well known in the prior art. Solids handling technique is described broadly in Packie Patent 2,589,124, issued March 1l, 1952.

Because only a part of the coke deposited is burned to supply heat, the coke particles grow in size during the process, and must be withdrawn as product. In order to counteract the growth process and to maintain a constant particle size coke inventory, fine coke must be added continuously to serve as growth seeds The seeds required can be supplied either by grinding withdrawn coke in external equipment or by devices in the unit itself. The number of seed particles required is equal to the number of coke particles withdrawn as product. However, because the seed coke is much smaller in diameter than the average of the withdrawn coke, the weight of seed required is only a small percentage of the weight of coke withdrawn. For example, if the seed coke size is 100 microns, and the product coke averages 200 microns diameter, the weight of seeds required will be 12.5% of the weight of net product coke withdrawn. If micron seed coke were used,the percentage would fall to slightly over 5 wt. percent on withdrawn coke. Seed coke particles typically have a size distribution predominantly of 75 to 150 microns in diameter.

Equipment, including grinding equipment, for making seed coke can increase the cost of a iiuid coking unit by 10% or more. It is therefore desirable to be able to supply seed coke economically to the process.

This invention provides an improved integrated fluid coking process wherein seed coke is prepared and utilized therein. The method comprises broadly atomizing a heavy hydrocarbon oil in a drying zone and countercurrently contacting the small atomized oil droplets with hot flue gas from the coke heating or combustion zone. The size of the atomized oil droplets, and the velocity of the ue gas is controlled. This results in a product of dried coke seed particles which are then returned to the coking zone for utilization in the precess. Specic modifications are discussed in further detail hereafter.

This invention will be better understood by reference to an example in the flow diagram shown in the drawing.

In the drawing the numeral l is a coking vessel constructed of suitable materials for .operation at 950 F. A bed of coke particles fed to the ybed at a sufficient temperature, e. g., 1125 F. to establish the required bed temperature of 950 F. is made up of suitable particles of 75 to 800 microns. The bed of solid particles reaches an upper level indicated by the numeral 5. The bed is uidized by means of a gas such as steam entering the vessel at the bottom thereof via pipe 3. The iluidizing gas passes upwardly through the vessel at a velocity of l ft./sec. establishing the solids at the indicated level. The lluidizing gas serves also to strip the vapors and gases from the coke which flows down through the vessel from pipe 9 to pipe S, as will be later related.

A reduced crudeoil, to be converted having a Conradson carbon residue of l0 wt. percent, is preferably preheated to a temperaure not above its cracking temperature, e. g., 700 F. lt is introduced into the bed of hot coke particles via line 2, preferably at a plurality of points in the system. The oil upon contacting the hot particles undergoes decomposition and the vapors resulting therefrom assist in the uidization of the solids in the bed and add to its general mobility and turbulent state. The product vapors pass upwardly through the bed and are removed from the coking vessel via line 4 after passing through cyclone 6 from which solids are returned to the bed via dipleg 7.

A stream of solid particles is removed from the coking vessel via line S and transported with the assistance of air u or other free oxygen-containing gas into an external heating zone or burner vessel 10. A transfer line heater could be used as an alternative. Air is supplied via line 11 with the assistance of pump 12. In the burner aportion of the carbonaceous materials, e. g., coke or materials deposited thereon, is burned to raise'the temperature to a point sufficient to supply the heat to the endothermic reaction occurring in the coking vessel 1. The ,temperature of the burner solids is usually 100 F. to 300 F. higher than that of the solids in the coking vessel, e. g., 175 F. in this example. The bed of coke is fluidized in vessel in much the same manner as the bed in vessel 1. The solids are iluidized by the incoming air and resulting combustion gases and are maintained at a level indicated bythe numeral 13. Hot ue gases ata temperature of i125" F. and containing CO2, CO, N2 and any unused O2 leave the hot bed, pass through cyclone 14 and line 16. Any entrained solids are returned to the bed via dippipe 15. A portion of the hot solids are continually removed from burner 10 via line 9 and introduced into vessel 1 at one or more points in order to maintain heat balance in the system. Product coke is withdrawn through line 17.

A high boiling oil, e. g., atmospheric or preferably vacuum residuum, asphalt, tar, etc., having a Conradson carbon residue of 3() wt. percent, first preheated to a temperature of 700 F. is fed through line 19 into nozzle spray head located in an upper portion of drier 26. The amount of oil fed will normally amount to about 10 volume percent of the oil feed to reactor 1. The spray head converts the oil stream into droplets of a diameter such that the coke formed will be of the desired particle size. The drops can have a diameter in the range of 150 to 600 microns. These droplets are countercurrently contacted with hot flue gas at a temperature of 1125 F. taken from

lines

16 and 18. In some cases it will be desirable to heat the ilue gas in line 18 to a higher temperature and this can be done by adding air and burning the CO content or extraneous feed in an auxiliary burner to increase the temperature to say 1500Z500 F. Heat can later be recovered from the gases in a waste heat boiler. The droplets also scrub out tine coke kparticles from the iiue gas and thus help in the problem of disposing of these nes. The flue gas is at a velocity of l-4 ft/sec. This countercurrent contacting results in the conversion of 'the droplets to dry coke seed particles. These seed particles are then withdrawn from drier 26 through line and returned to the bed 5 in Coker 1. A transporting gas such as steam may be used for this purpose. The withdrawn seed has an average diameter of about 75-150 microns.

Product gases consisting of flue gases and cracked oil products together with tine particles of coke and oil drops entrained out of spray drier 26 are withdrawn through L line 21 into wet cyclone 22. Preferably these gases are scrubbed by contacting with pitch feed added through line 28. This scrubs the coke lines and small drops out of the gases. The scrubbing liquid is recovered in cyclone 2:2 and returned to the spray drier 26 via line 19, or to Coker 1 via line 2. This also serves to preheat the ieavy oil added via line 28. The product gases are withdrawn overhead through line 24 from the wet cyclone and the liquid scrubbing oil slurry withdrawn through dipleg E3. The pitch separated can be recycled back to line 19 for further atomization. It may be necessary to keep the wet cyclone hot so that the pitch will flow.

it will be noted that tine coke particles that would be too tine for use in the coker are recycled as a slurry to the spray drier until their size is increased to the desirable range. Similarly, oil spray which is too line is so recycled, and only oil drops of optimum size are allowed to fa'll down into the hotter drying Vzone of vessel 26. This effect can be regulated by means of the gas Velocity in drier 26 according to well known laws. The spray 4 may be formed by a nozzle, spinning disc or other conventional means.

Hot coke can be withdrawn from heater 10 as an additional heat transfer and drying medium to drier 26. The hot coke from the heater is then preferably discharged in an annular curtain in the periphery of the drier and thus serves to maintain the proper temperature in the drier. The coarser coke particles then collect at the bottom of the drier and serve to even further dry the seed particles. it is not necessary to separate the seed particles, since the entire coke stream from drier 26 can be returned to the Coker. In this case a relatively large amount of dry coke particles may entrain out of drier 26 depending on the gas velocity, in which case oil will not be added at 28 and cyclone 2.2 will operate dry instead of wet.

The feed to the Coker and the drier can be the same. lf two different types of heavy hydrocarbon oils are available, it is preferable to utilize the one of higher Conradson carbon as feed to the drier. Also it is advantageous to feed a slurry stream to drier 26, as for example the heavy recycle from the coker fractionator.

Oil products in gases leaving line 24 may be recovered as desired. This recovery can be facilitated by recycling tail gas from the recovery system to the spray drier. Light hydrocarbons in the gas may serve as fuel for maintaining the proper drier temperature. If desired coke particles can be Withdrawn from the spray drier via line 3@ for other uses.

ln order to express this information more fully the following conditions of operation of the various components are set forth below:

CONDITIONS IN FLUID OOKER 1 Broad Range Preferred Range Temperature, F S50i, 200 9004, 000 Pressure, atmospheres 1-10 l. 2 Superficial Velocity,7 of Fluidizing Gas, Ft./

see O. 2-20 0. -l. 0 Average Size of Coke Particles, mierons 1h04, 000 0400 OONDlTIONS IN BURNER 10 Temperature, F 1, 050-1, 600 1. 1004, 200 Superficial Velocity of Fluidizing Gas, ft./

sec 1-5 2-4 CONDITIONS IN SPRAY DRIER 26 Temperature of Flue Gas, F 1, 00072, 500 1, 2G02. ODD Velocity of Flue Gas, ftJsee 0. 5-8 1-4 Size of Feed Droplets Diameter, mierons 10D-1. OGD 1250-600 Average Particle Size of Seed Coke Make,

microns 50 -ZiCU 'Z5-150 Feed to Briar/Feed to Coker, Vol. Percent" 5-30 7-15 The arrangement just described is highly flexible. It makes it possible to replace vlarge product coke .particles with an equivalent number of small seed particles at so constant and regular a `rate as to keep the total number of particles, the particle size distribution, and the total solids inventory substantially constant at all times.

Other advantages of the process of this invention include savings in equipment and efficient heat balance.

Itis to'be understood that this invention is not limited to the specitir, examples which have been offered merely as illustrations and that modifications may be made without departing .from .the spirit of .the invention.

lWhatis claimed is:

1. In a process for coking a heavy hydrocarbon oil which comprises the steps of contacting a heavy oil cokng charge stock ata coking temperature with a body of coke particles maintained in the form of a dense turbu lent fluidized bed in a reaction zone; removing product vapors from .the reaction zone; circulating the coke through an extraneous heating zone, wherein a portion of the coke particles are burned, and sent back to the reaction zone to supply heat thereto; the improvement which comprises atomizing a heavy hydrocarbon oil having a higher Conradson carbon residue than the charge stock and in an amount of rfrom 7 to l5 volume percent based on the charge stock into a drying zone to produce small oil droplets having a ydiameter in the range of 150 to 600 microns; countercurrently contacting the atomized oil droplets with hot ue gas from the extraneous heating zone at a temperature in the range of 1000 to 2500 F. and having a velocity of 1 to 4 ft./sec. whereby coke seed particles having a diameter size distribution of predominantly 75 to 150 microns are formed; withdrawing the coke seed particles from the drying zone and sending the coke seed particles to the reaction zone.

2. The process of claim l including the additional step of withdrawing gas and entrained oil particles overhead from the drying zone; separating the oil from the gas and returning the oil as additional feed to the drying zone.

3. The process of claim 1 including the additional step of circulating a portion of the coke particles from the heating zone to the drying zone to supply additional heat thereto.

4. In a process for coking of a heavy hydrocarbon oil which comprises the steps of contacting a heavy oil coking charge stock at a coking temperature with a body of coke particles maintained in the form of a dense turbulent tluidized 'bed in a reaction zone; removing product vapors from the reaction zone; circulating the coke through an extraneous heating zone, wherein a portion of the coke particles are burned, and sent back to the reaction zone to supply heat thereto; the improvement which comprises atomizing a heavy hydrocarbon oil having a higher Conradson carbon residue than the charge to the reaction zone into a drying zone to produce small oil droplets having a diameter in the range of 150-600 microns; countercurrently contactingthe atomized oil dropletswith hot flue gas from the heating zone at a temperature in the range of 1200-2000 F. and having a velocity in the range of 1-4 ft./sec. whereby nes are removed fromv the ue gas and coke seed particles having a diameter size distribution of predominantly -100 microns are formed; withdrawing gas, coke nes and entrained oil particles overhead from the drying zone; scrubbing this overhead fraction with additional higher Conradson carbon residue oil to scrub out the oil particles and fines, the volume percent of the total oil fed to the drying zone and for scrubbing to the oil charge to the reactor being in the range of 7-15 volume percent; separating resultant oil lines slurry from the gas; returning the oil `slurry as additional feed to the drying zone; withdrawing the coke seed particles from the drying zone and sending them to the reaction zone.

References Cited `in the file of this patent UNITED STATES PATENTS 2,436,166 Blaming Feb. 17, 194s 2,443,714 Arveson June 22, 1948 2,598,058 Hunter May 27, 1952 2,719,115 Russell Sept. 27, 1955 2,742,403 Nicholson et al Apr. 17, 1956 FOREIGN PATENTS 1,057,092 France OCt. 28, 1953

Claims

1. IN A PROCESS FOR COKING A HEAVY HYDROCARBON OIL WHICH COMPRISES THE STEPS OF CONTACTING A HEAVY OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF COKE PARTICLES MAINTAINED IN THE FORM OF A DENSE TURBULENT FLUIDIZED BED IN A REACTION ZONE; REMOVING PRODUCT VAPORS FROM THE REACTION ZONE; CIRCULATING THE COKE THROUGH AN EXTRANEOUS HEATING ZONE, WHEREIN A PORTION OF THE COKE PARTICLES ARE BURNED, AND SENT BACK TO THE REACTION ZONE TO SUPPLY HEAT THERETO; THE IMPROVEMENT WHICH COMPRISES ATOMIZING A HEAVY HYDROCARBON OIL HAVING A HIGHER CONRADSON CARBON RESIDUE THAN THE CHARGE STOCK AND IN AN AMOUNT OF FROM 7 TO 15 VOLUME PERCENT BASED ON THE CHARGE STOCK INTO A DRYING ZONE TO PRODUCE SMALL OIL DROPLETS HAVING A DIAMETER IN THE RANGE OF 150 TO 600 MICRONS; COUNTERCURRENTLY CONTACTING THE ATOMIZED OIL DROPLETS WITH HOT FLUE GAS FROM THE EXTRANEOUS HEATING ZONE AT A TEMPERATURE IN THE RANGE OF 1000* TO 2500* F. AND HAVING A VELOCITY OF 1 TO 4 FT./SEC. WHEREBY COKE SEED PARTICLES HAVING A DIAMETER SIZE DISTRIBUTION OF PREDOMINANTLY 75 TO 150 MICRONS ARE FORMED; WITHDRAWING THE COKE SEED PARTICLES FROM THE DRYING ZONE AND SENDING THE COKE SEED PARTICLES TO THE REACTION ZONE.