US2959535A - Fluid coking recycle operation - Google Patents

Description

Nov. 8, 1960 J. w. BROWN ETAL 2,959,535

FLUID COKING RECYCLE OPERATION Filed Jan. 10, 1958 James W. Brown Warren K. Lewis, Jr. lnvemors By 6M Attorney maintain the system in heat balance.

United States Patent O FLUID COKING RECYCLE OPERATION James W. Brown, The Hague, Netherlands, and Warren K. Lewis, Jr., Elizabeth, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Jan. 10, 1958, Ser. No. 708,149

3 Claims. (Cl. 208-95) The present invention relates to an improved method 20f increasing conversion and reducing recycle rates in the More particularly it relates to a vention but will be described for completeness. The fluid coking process unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing fluidized particles, e.g. a dense,

turbulent, fluidized bed or transfer line. A staged reactor can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Efllu- .ent vapors are removed from the coking vessel and sent to a scrubber-fractionator for the recovery of gas oil and lighter 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. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

' becomes necessary, increasing equipment sizes.

therefore desirable to improve this recycle operation.v

The heat for carrying out the endothermic coking refluid bed or transfer line burner, employing a standpipe and riser system; air being supp-lied to the riser for conveying the solids to the burner. Sufficient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature suificient to The burner so'ids are maintained at a higher temperature than the solids in the reactor. Coke, equivalent to about 5%, based on the feed, is burned for this purpose. This may amount to approximately 15% to 30% of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is Withdrawn and the remaining portion recycled to the reactor to supply heat thereto.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and vacuum bottoms from crude, pitch, asphalt, other heavy hydro-' carbon petroleum residua or mixtures thereof. Typically such feeds have an initial boiling point of about .700 F. or higher, an A.P.I. gravity of about 0 to 20,

and a Con-radson carbon residue content of aboutZ to the coking reactor.

.increase the average boiling point.

2,959,535 Patented Nov. 8,

40 wt. percent. (As to Conradson carbon residue see A.S.T.M. Test D-189-41.)

It is preferred to operate with solids having a-particle size ranging between and 1000 microns in diameter with a preferred particle size range between and 400 microns. Preferably not more than 5% has a particle sizebelow about 75 microns, since small particles tend to agglomerate or are swept out of the system with the gases. While coke is the preferred particulate solid, other inert particulate solids such as spent catalyst, pumice, sand, kieselguhr, Carborundurn, and alumina can be employed.

The product vapors from the coking are sent to a scrubber-fractionation zone. In the scrubber-fractiona tion zone several fractions are separated; a low boiling fraction, i.e., having a maximum boiling point of 425 F. a gas oil fraction having an end point of about 1000 F. or lower; and a heavy residual bottoms condensate fraction boiling predominantly at a higher temperature.

It is normally desired to recycle a residual bottoms fraction boiling. above about 1000 F. In practice, how.-

residual bottoms fraction. A low .cut point may also be desired where there is limited catalytic crack-ing capacity for cracking the heavy coker gas oil. The resulting bottoms fraction, because of its low boiling point, immediately flashes upon entering the coking reaction vessel thus undergoing virtually no conversion in the liquid phase. Because of this low conversion a high recycle rate It is tacting the residual bottoms fraction with an oxygen con- 'taining gas at a temperature below its cracking temperature, i.e., one in the range of 450 to 700 F. in an oxidation zone, preferably extraneous. The oil is thus oxidized to a combined oxygen content of about 2 to 6 wt. percent. This oxidation increases the average molecular weight and average boiling point. The oxidized bottoms fraction is then fed to the coker. Further details follow.

The recycle fraction is treated as stated previously with an oxygen containing gas. Because of cost considerations air is preferred. Pressure and oxygen concentration can be varied also to produce a smooth operation.

The oxidation treatment is carried out while the oil is in the liquid phase, preferably in a reactor extraneousto Excess gas is vented from the ox.-

dizer. The use of the extraneous reactor with the vent- .ing of the oxygen containing gas results in the sending of the oxidized oil to the fluid coker free of extraneous gas.

.In' this manner product degradation and dilution are avoided. Coking in the pretreating oxidizing step is avoided by staying below cracking temperatures.

It has been found that the water producedduring this stocks, temperatures and air-to-feed ratios. Corresponding decrease in the hydrogen content of the feed is less .than 0.3 wt. percent, which is not enough to decrease the quality of the stock as a coker feed significantly.

There is no need to oxidize the fresh feed to. the coker because this usually consists of material boiling almost entirely above 1000 F. Such material is high boiling enough so that relatively little of it will flash off at typical coker temperatures of 950 to 1000" F. and thus good conversion per pass is obtained without doing anythingto However, itgmay occasionally be desirable to feed lower boiling stocks,

down through the vessel to the heater.

dominantly above about 850 F. atmospheric. nominal cut point will be predominantly in the range tional fraction in the gas oil boiling range. has an 850 F. end point and is withdrawn as a side Such as catalytic cracking cycle stock, to the coker. In this case, the low boiling part of the fresh feed may be advantageously oxidized prior to coking.

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

In the drawing the numeral 1 is a coking vessel constructed of suitable materials for operation at 950 F. A bed of coke particles preheated to a suflicient temperature, e.g., 1125 F., to establish the required bed temperature of 950 F. is made up of suitable particles of 150 to 400 microns. The bed of solid particles reaches an upper level indicated by the numeral 5. Cyclone 4 is located at the upper portion of the disperse phase; several stages of cyclones can, of course, be used. The

bed is fluidized by means of a gas such as stripping steam entering the vessel at the stripping portion near the bottom thereof via pipe 3. The fluidizing gas plus vapors from the coking reaction pass upwardly through the vessel at a velocity of 1 ft./sec. establishing the solids atthe indicated level. The fluidizing gas serves also to strip the vapors and gases from the coke which flows A stream of solid particles is removed from the coking vessel via line 8 and transferred to the heater not shown.

A reduced crude oil to be converted is introduced into 'the bed of hot coke particles via line 2, but preferably at aplurality of points in the system. The oil upon contacting the hot particles undergoes decomposition and the vapors resulting therefrom assist in the fluidization of-the solids in the bed and add to its general mobility and turbulent state. The product vapors leave through cyclone 4 and line 6. The solids separated are returned to the bed through dipleg 12. Hot coke solids at a temperature of about 100 to 300 F. higher than the coker, e.g. 1125 F., are recycled from the heater not shown through line 9.

through line 14. The condensation is conducted so as to obtain a heavy residue fraction condensate boiling pre- The of 850 to 950 F. and the quenching temperature accordingly adjusted. A liquid drawoff is provided to remove the bottoms boiling above about 850 F. through line Vapors remaining uncondensed in the bottom scrubbing section of the tower pass upwardly through a series of bubble cap trays located in the top of the tower where they are subjected to fractionation to take off an addi- This gas oil stream through line 20. The low boiling products, i.e., the gases and hydrocarbons boiling to 425 F. and thus including naphtha, are removed overhead through line 11.

The residual bottoms fraction withdrawn through line 13 is sent into tower 19 wherein its is oxidized by treatmentwith air while the fraction is in the liquid phase. Air is injected through line 16 and excess gas vented through line 17. The temperature of the treatment utilized is 550 -F. and the oil is thus oxidized to a combined oxygen content of 4 wt. percent. Cracking is thereby avoided. The thus oxidized fraction, free of extraneous gas, is fed through line 18 into the fluid bed in coker 1.

follo'wing example.

4 Example A fluid coker is operated as shown. In column I are listed results that are obtained in conventional operation. Column II shows results that are obtained when oxidizing the recycle as taught herein, e.g., at a temperature of 550 F. to a combined oxygen content of 4 wt. percent.

COKING SOUTH LOUISIANAREElIDUUM, RECYCLING T0 EXTINCTION OF l015 F.+

I II

Treatment of Feed:

Fresh None None Recycle None Oxidized Coking Conditions:

Temperature, F.- 955 955 Pressure, p.s.t.g..- 10 10 Fresh Feed Rate, w.lhr./W.- 0.3 0.3 Wt. Percent Steam Dlluent on FF ll 11 Total Feed/Fresh Feed, Vol. Ratio l. 75 1.27 Products, Available Yields on Fresh Feed, Wt.

Percent:

Gas, 0; and lighter 7. 6 7. 7 Cl 1. 3 1. 3 15. 0 14. 8 58.7 57.2 17.4 19.0

4 vol. percent on crude.

It should be noted that oxidizing the recycle decreases considerably the total feed to the coker and concomitantly the load to the scrubber with little change in yields.

The advantages of this invention will be apparent to those skilled in the art. Increased conversion in the liquid phase is obtained with decreased recycle rates and consequent savings in equipment requirements. It makes it possible to economically obtain a lower end point on the gas oil product, if such is desired.

The conditions usually encountered in a fluidcokcr for fuels are also listed below for completeness.

CONDITIONS IN FLUID COKER REACTOR It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of theinvention.

What is claimed is:

1. In a process for coking a heavy hydrocarbonoil charge stock by contacting the oil charge stock at a coking temperature with fluidized coke particles in a coking zone at a temperature in the range of about 900 F. to 1200 F. wherein the oil is converted to product vapors and carbonaceous material is continuously deposited on the coke particles, passing product vapors from the coking zone to a scrubbing-fractionation zone, fractionating the product vapors in the scrubbing-fractionation zone to separate a heavy residual bottoms fraction to be recycled to the coking zone from more volatile gas oil and lighter fractions, sending a portion of the coke particles from the coking zone to a heating zone to increase the temperature of the particles and returning a portion of the heated particles from the heating zone to the coking zone, the improvement for increasing conversion perpass and for increasing the average boiling point of said recycle heavy residual bottoms fraction when the initialboillng point-ofsaid recycle heavy residual bottoms fraction is between about 850 F. and 950 F. which comprises contacting said recycle heavy residual bottoms fraction in the liquid phase with air at a temperature below its cracking temperature and in the range of about 550 F. to 700 F. in an oxidation zone to oxidize said recycle heavy bottoms fraction to a combined oxygen content of about 4 to 6 wt. percent and feeding the entire oxidized fraction substantially free of extraneous air to the coking zone.

2. A process as defined in claim 1 wherein the temperature in said oxidation zone is about 550 F. and the combined oxygen content of said oxidized recycle heavy residual bottoms fraction is about 4% by weight and the total oil feed to the coking zone including oxidized recycle heavy residual bottoms and the load on the scrubbing fractionation zone are decreased for substantially the same yield of products.

3. The process of claim 1 in which said recycle heavy residual bottoms fraction is segregated into a lower boiling fraction boiling below about 1000 F. and a higher boiling fraction boiling above about 1000 F. and only said lower boiling fraction is oxidized with air in said oxidation zone before being recycledto said coking zone, the higher boiling fraction being recycled directly to said coking zone without any oxidizing treatment.

References Cited in the file of this patent UNITED STATES PATENTS 2,527,575 Roetheli Oct. 31, 1950 2,587,703 Deanesly Mar. 4, 1952 2,776,799 Spitz et a1 Jan. 8, 1957 2,789,942 Cooper et a1. Apr. 23, 1957 2,862,867 Rehner et a1. Dec. 2, 1958 2,905,615 Arey Sept. 22, 1959

Claims (1)

1. IN A PROCESS FOR COKING A HEAVY HYDROCARBON OIL CHARGE STOCK BY CONTACTING THE OIL CHARGE STOCK AT A COKING TEMPERATURE WITH FLUIDIZED COKE PARTICLES IN A COKING ZONE AT A TEMPERATURE IN THE RANGE OF ABOUT 900*F. TO 1200* F. WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS MATERIAL IS CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES, PASSING PRODUCT VAPORS FROM THE COKING ZONE TO A SCRUBBING-FRACTIONATION ZONE, FRACTIONATING THE PRODUCT VAPORS IN THE SCRUBBING-FRACTIONATION ZONE TO SEPARATE A HEAVY RESIDUAL BOTTOMS FRACTION TO BE RECYCLED TO THE COKING ZONE FROM MORE VOLATILE GAS OIL AND LIGHTER FRACTIONS, SENDING A PORTION OF THE COKE PARTICLES FROM THE COKING ZONE TO A HEATING ZONE TO INCREASE THE TEMPERATURE OF THE PARTICLES AND RETURNING A PORTION OF THE HEATED PARTICLES FROM THE HEATING ZONE TO THE COKING ZONE, THE IMPROVEMENT FOR INCREASING CONVERSION PER PASS AND FOR INCREASING THE AVERAGE BOILING POINT OF SAID RECYCLE HEAVY RESIDUAL BOTTOMS FRACTION WHEN THE INITIAL BOILING POINT OF SAID RECYCLE HEAVY RESIDUAL BOTTOMS FRACTION IS BETWEEN ABOUT 850*F. AND 950*F. WHICH COMPRISES CONTACTING SAID RECYCLE HEAVY RESIDUAL BOTTOMS FRACTION IN THE LIQUID PHASE WITH AIR AT A TEMPERATURE BELOW ITS CRACKING TEMPERATURE AND IN THE RANGE OF ABOUT 550*F. TO 700*F. IN AN OXIDATION ZONE TO OXIDIZE SAID RECYCLE HEAVY BOTTOMS FRACTION TO A COMBINED OXYGEN CONTENT OF ABOUT 4 TO 6 WT. PERCENT AND FEEDING THE ENTIRE OXIDIZED FRACTION SUBSTANTIALLY FREE OF EXTRANEOUS AIR TO THE COKING ZONE.

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