US2793172A - Integrated fluid coke desulfurization process - Google Patents

Description

May 21, 1957 B. 1. SMITH EIAL I 2,793,1 7 2 INTEGRATED FLUID coma DESULFURIZATION PROCESS Filed July '25, 1954 BROOK 1. SMITH FRED w. BANES INVENTORS JOSEPH F. NELSON Kim ATTOFNEY INTEGRATED FLUID COKE DESULFURIZATION PROCESS Brook I. Smith, Elizabeth, and Fred W. Banes and Joseph F. Nelson, Westfield, N. 1., assignors to Esso Research and Engineering Company, a corporation of Delaware Application July 23, 1954, Serial No. 445,436

5 Claims. (Cl. 202-14) This invention relates toimprovements in the coking of heavy petroleum oils containing a high percentage of sulfur wherein the 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 the sulfur is continuously removed from the circulating coke particles.

There has recently been developed an improved process known as the fluid coking process for the production of coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking 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 containinga dense turbulent fluidized bed of hot inert solid particles;

preferably coke particles. Uniform temperature exists in'. I I v V in general, not'been too satisfactory. The results are 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;

V 2,793,172 latented May 21, 1957 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.

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 11, 1952.

Fluid coking has its greatest utility in upgrading the quality of low grade petroleum vacuum residua and pitches from highly asphaltic and sour crudes. Such residua frequently contain high concentrations of sulfur,

i. e.; 3 percent or more, and the coke products produced from these high sulfur feeds are also high in sulfur content.- In general, the sulfur content of the coke prodnot from the fluid coking process is about 2 times the content of the residuum feed from which it is produced. The sulfur content of coke from sour residua may range from 5% to 8% sulfur or more. The high sulfur content of the coke product poses a major problem in its eflicient utilization. For most non-fuel or premium fuel uses a low sulfur content coke, below about 3 wt.

. in the manufacture of soda ash or other alkalis, for vari- Ous metallurgical application, for the production of elec- Product vapors are removed from the coking vessel and 4 sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually re-' turned 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.

The heat for carrying out the endothermic coking reaction is generated in the heater or burnervessel. A stream of coke is transferred from the reactor to the burner vessel or heating zone employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. ceous matter, or added fuel such as natural gas or. torch oil is burned in the burning vessel to bring the solids therein up to a temperature suflicient 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, or an equivalent amount of other carbonaceous material such as fuel oil, natural gas, etc. is burned for this purpose.

in the process. The unburned portion of the coke represents the net coke formed in the process and is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process are heavy crudes, atmospheric and vacuum crude oil bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F. or higher, an A. P. I. gravity of about 0'' to 20, and a Conradson carbon residue content of about 5 to 40 .wt. percent. (As to Conradson carbon residue see ASTM test D-l80-52). x

It is preferred to operate with solids having a particle size range of 75 to 1000 microns in diameter with a preferred average particle size between 150 and 400 microns.

Sufficient coke or carbona.-.

trode for'various electrochemical applications such as the manufacture of aluminum and the like.

*"The" conventional methods of removing sulfur from coke from ordinary sources with gaseous reagents have,

even 'poor'erwhen these procedures are applied to fluid coke. Delayed coke is more porous than fluid coke and the interstices are more connected and larger than in fluid coke. A'treating gas consequently 'has relatively easy access ''to the-sulfur. Fluid coke, on the other hand, is laminar in structure and may comprise some 30 to 100 superposed layers of coke. Thus, it is diflicult for a reagent to penetrate more. than a few outer layers. These difliculties of the fluid coke are even further compounded because of the beforementioned possibly higher than norremoving the sulfur as it is laid down and before it be- This may amount to approximately 15% to 30% of the coke madecomes chemically more resistant to this removal and before it has been covered by succeeding layers of coke. The method comprises continuously contacting at least a portion of the hot circulating coke from the coke burningstep with a gaseous sulfur removing reagent. The sulfur is. thereby removed from the outer layer or layers from the coke particles as fast as it is laid down. The buildup of the sulfur to high levels which are diflicult to lower is thereby prevented.

The gaseous sulfur removing agents that can be utilized comprise those known in the art, such as steam, air, carbon dioxide, carbon monoxide, hydrogen, chlorine, coke oven: gas, producer gas, ammonia and normally gaseous hydrocarbons such as methane. Hydrogen is preferred and can be utilized pure or in the form of hydroformer gas orother refinery streams. Suflicient hydrogen is used in order to provide a minimum hydrogen partial pressure of about mm. Hg in the efliuent gas from the treating zone. Preferably the hydrogen or other gas partial pressure is one atmosphere or higher. It is also preferred that the partial pressure of hydrogen sulfide in the efliuent gas not exceed about 300 mm. Hg.

-'--'Iheconditions at which the gaseous reagents are utilized, are supplied in detail below. It should be emphasized however, that these conditions are integrated 3 with the fluid coking process and represent an ideal mannet of lowering the sulfur content.

This invention will be better understood by reference to an example and the flow diagram shown in the w nsc In the drawing the nnmeral l is a coking vessel constructed of suitable materials for operation at QSQf F. -A bed of coke particles preheated to a sufiicient temperature, e. g., 1150 F. to establish the required bed tempcrature of 950 F., is made up of suitable particles of 150-40Q rnicrons. Thebedof solid particles reaches an upper level indicated by the numeral 5. The bed is fluidized by means ofa gassuch as steam at a -tempera- We b ?.F- rin heves's tat est pi s Pe fion v ribs 4: The find ngs. se r d y oi shi t s l. ta ay asa a q a th n. c u n h a s f i st sdu dished ab s n e s id latffl a isatefi 1W I 9 flq i i s a rve @1 9 to. s r t e .t nq jied as .irq s s cak which flows down through the vessel from pipe 20 as will belatcrrelated. H A I p A reduced rude oil, containing 4 3 wt. percent sulfur, to be converted is preferably preheated to a temp'erature notahove its cracking temperature, e. g., 700 F. It is introduced into the bedof hot coke particles via line' 2, preferably at a plurality of points in the system. The oil upon contacting the hotparticles undergoes decomposition and the vapors resulting therefrom assist in the fluidization of theisglids in the bed and a dd to its general mobility and turbulent state. I The 7 product vapors pass hpward lygthrough bed and tire removed from the cdking vessel via 1in'e:4 after passin'g throngh cyclone 6. from which solids are returned to the bed viadipleg']. v I. h H

A' sneam f vsolid particles is removed from the col:- ing v'slsel'yiailine hand transported. transfer line heatericoiild he used'a s 'an .alternative. Air is supplied via lin'q ll to urner lfl. in the burner a portion of h' ih s.'m iii teUs "cbke 9 na q eposited a reement-raga to raise the temperature to a point slifiicient it o supply the heat to the endothermic reaction occurring in the coking vessel 1. The temperatune of thebiiriier so 'ds is' usually 100 to 300 F. higher than thatfof theI-solids iii, the coking vesseh'e. g., 200-F. eracmanyimy in this eiample. The bediof coke fluidized. in vessellloin much the same manner as the bed in 'vessel 1. The solids are fluidized by the incomingair and resulting combustion gases and are mainat ai 'lvelindicatedbythe numeral 13. Hotiflue gases pass through ;1e 14 and line 16. Any entrained'solids hre returned tothe pea via dip-pipe 1s. The hot circulating solids are continuously removed from burner via line 9 to treating zone 21.

The circulating coke is fluidized by hydrogen tail gas from a hydroformer operation which enters through line 23. The temperature of the treating'bed'which hasan upper level24is essentially that of the coke leaving the burner or 1150 F. A portion of the coke is removed from treating zone 21 through line 17 as product coke. Sulfur-containing gas, to fuel or to sulfur recovery, is withdrawn through line 22 and can be recirculated after treating. The'residence timein treating zone 21 is about 10 minutes. About 200 standard cubic feet of hydrogen per ton of circulating coke are utilized in order to insure a minimum'h'ydrogen partial pressure of 100 mm. Hg in the efliuent; in this case v825 mm. in the efiiuent leaving through line 22. The hydrogen sulfide content of the efllucnt' gas corresponds to a partial pressure of about 250mm.Hg. V

The desu'lfurized coke product withdrawn from line 17 can be calcined elsewhere if desired largely'to increase thejdensity and lower the volatile content. The remander of the coke in treating vessel 21 is recycled to the coker reactor through line 20 in order to main- 4 tain heat balance in the system. Fluidizing gas such as steam is introduced through line 18.

In another embodiment a portion of the circulating coke bypasses the treating zone. The residual portion is raised to a higher temperature in an auxiliary heating zone and this portion is then treated in the treating zone. The product coke is withdrawn and the remainder circulated back to the coker.

The burner and treater can be combined if desired in a single vessel. A series of superimposed beds of coke particles is set up thereih. The burning is conducted in the upper beds and the treating with the sulfur removing gaseous agents in the lowermost beds as the coke particles descend.

The treatment with the gaseous reagent can also be in the form of a fixed or moving bed.

The following example further shows the advantage of this invention.

EXAMPLE in an experiment coke was deposited on sand in the form of a superposed layer (-1). Other coke particles were prepared in the conventional manner, i. e., 'built up entirely of coke ('II). The diameter of both types of particles were the same and averaged about 300'microns. The sulfur content of the coke was also similar, 7 weight percent.

Both types of particles were treated with equivalent amounts of hydrogen under equivalent :conditions at 1500 F. The sulfur content'in. thescoke-ofl was reduced to 2.6 weight percent whereas thesulfur content of II was reduced to only 6.3 weight percent. This demonstrates the advantages of treating surfacelayers of coke as formed rather thanpermittinga 'relatively impervious barrier to' be formed. j

-In orderto express this information more-fully the following conditions of operation of the various 'co mponents including those in which the"fluid coke isprepared are set forth below.

Conditions in 'flilid coker reactor] ,Broad Preferred Range Range Temperature, F 850-1; 200 '900-1, 000 Pressure, Atmospheres 1-10 1. 5-2 Superficial Velocity of Fluidizing Gas, FtJsec. 0.2-2.- 0 0. 5-1. 5 Particle Size Range of Coke Particles, microns 751','000 -400 Conditions in treating'zbne 21 (with hydrogen) The process of this invention is also applicable to the higher temperature coking for chemicals which conventionally is conducted at about ll50to 1-500-F. Under those circumstances the temperatures in the beating and treating zone are correspondingly raised.

The advantages of the process of 'thisinvention will be apparent to those skilled in the art. The sulfur content is 'rnaintained'at acceptable levels byan integrated easily controlled process.

--It-is to'be understood thatthis-invention-is-not-limited to the specific examples which have been offered merely as illustrations and that modifications may be made with out departing from the spirit of the invention.

What is claimed is:

1. In a process for coking a heavy petroleum oil containing a high concentration of sulfur by the steps of contacting the heavy petroleum 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, wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles; removing product vapors from the coking zone; heating of the circulating coke particles removed from the coking zone in a separate heating zone to increase the temperature of said particles; returning of the circulating heated coke particles from the heating zone to the coking zone to supply heat thereto, and wherein the fluid coke product particles normally contain a high percentage of sulfur, the improvement which comprises continuously contacting of the hot circulating coke particles from the heating step to the coking step with a gaseous sulfur removing reagent at a temperature in the range of l050 to 1600 F. whereby sulfur is continuously removed from the circulating coke particles and their sulfur content lowered.

2. The process of claim 1 in which the heavy petroleum oil contains at least 3 weight percent sulfur.

3. A process for coking a heavy petroleum oil containing a high concentration of sulfur which comprises the steps of contacting the heavy petroleum 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, wherein the oil is converted to product vapors and carbonaceous solids are continuously deposited on the coke particles; removing product vapors from the coking zone; burning circulating coke particles removed from the coking zone in a burning zone to increase the particle temperature; contacting the circulating coke particles from the burning step while in the form of a dense turbulent fluidized bed in the treating zone with a gaseous sulfur removing reagent at a temperature in the range of 1050 to 1600 F. to continuously remove sulfur therefrom; withdrawing a portion of the treated coke as product and recirculating the remainder to the coking step.

4. The process of claim 3 in which the reagent is hydrogen.

5. The process of claim 4 in which maximum partial pressure of evolved hydrogen sulfide from the treating zone is 300 mm. Hg.

References Cited in the file of this patent UNITED STATES PATENTS 2,595,366 Odell et a1 May 6, 1952 2,694,035 Smith et al Nov. 9, 1954

Claims (1)

1. IN A PROCESS FOR COKING A HEAVY PETROLEUM OIL CONTAINING A HIGH CONCENTRATAION OF SULFUR BY THE STEPS OF CONTACTING THE HEAVY PETROLEUM OIL COKING CHARGE STOCK AT A COKING TEMPERATURE WITH A BODY OF COKE PARTICLES MAINTAINED IN THE FORM OF A DENSE TURBULTENT FLUIDIZED BED IN A REACTION ZONE, WHEREIN THE OIL IS CONVERTED TO PRODUCT VAPORS AND CARBONACEOUS SLIDS ARE CONTINUOUSLY DEPOSITED ON THE COKE PARTICLES; REMOVING PRODUCT VAPORS FROM THE COKING ZONE; HEATING OF THE CIRCULATING COKE PARTICLES REMOVED FROM THE COKING ZONE IN A SEPARATE HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID PARTICLES; RETURNING OF THE CIRCULATING HEATED COKE PARICLES FROM THE HEATING ZONE TO THE COKING ZONE TO SUPPLY HEAT THERETO, AND WHEREIN THE FLUID COKE PRODUCT PARTICLES NORMALLY CONTAIN A HIGH PERCENTAGE OF SULFUR, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY CONTACTING OF THE NOT CIRCULATING COKE PARTICLES FROM THE HEATING STEP TO THE COKING STEP WITH A GASEOUS SULFUR REMOVING REAGENT AT A TEMPERATURE IN THE RANGE OF 1050* TO 1600*F. WHEREBY SULFUR IS CONTINUOUSLY REMOVED FROM THE CIRCULATING COKE PARTICLES AND THEIR SULFUR CONTENT LOWERED.

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