US2768939A - Integrated fluid coke desulfurization process - Google Patents

Description

1956 R. B. MASON ET AL 2,768,939

INTEGRATED FLUID COKE DESULFURIZATION PROCESS Filed Sept. 15, 1954 5 N O O I w '6 m 3 N m o In 5 g 0 II (D m N 8 (0 25 N QLLO "2u E- I D 0..

Ralph B. Mason Inventors: svhfirles N.Kimberlin,Jr.

i iom F. Arey, Jr.

Attorney United States Patent INTEGRATED FLUID COKE DESULFURIZATION PROCESS Ralph B. Mason, Denham Springs, and Charles N. Kimberlin, Jr.,' and William F. Arey, Jr.," Baton Rouge, La.,

' assignors to Esso -Research and Engineering Company; a corporation of Delaware a I I Application September 13, 195a,v Serial No. 455,617

6 Claims; c1. 202-14,

I 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 containing a dense turbulent fluidized bed of hot inert solid particles, preferably coke particles. Uniform temperature exists in the coking bed. Staged reactors can be employed. 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. Product vapors are-removed from the coking vessel and sent to' a fractionator'for the recovery of gas and lightdistillates coke is transferred from the reactor to the burner vessel employing a standpipe and riser system; air being sup.-

plied to the riser for conveying the solids to the burner.

Sufficient coke or carbonaceous matter is burned in the burning vessel tobring the solids therein up to a temperature suflicient to-maintain the system in heat balance. The burner solidsare-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 may amount to approximately 15% to 30% of the coke made inthe 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 The unburned portion of the coke represents the net coke formed in the process and is withdrawn.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 process include heavy or reduced crudes vacuum bottoms, pitch, asphait, other heavy hydrocarbon petroleum residue. or mixtures thereof. Typically such 'feeds can have aninitial boiling "point ofabout 800 F; or higher, an P. I. 'grav'it y of'about 01to 20,3and a Conradson'carbon resi due'content of about 5 to 40 wt. (As -"to Conrad'so'n carbon residue see ASTM Test Dl80 52..)'1

It is preferred to operate with solidshaving a particle sizerangingbetween 100 .and 1000 microns .in diameter with'a preferred average particle. size range between 150 and 400. microns; Preferably not more than 5% has a particle size below about 75 microns, since small parti- Patented Oct. 30, 1956 cles 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 broardly 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 wt. percent or more and the coke product produced from high sulfur feeds are also high in sulfur con+ tent. In general the sulfur content of the coke product from the coking process is about 2 times the sulfur content of the residuum feed from which it is produced. The sulfur content of coke from sour residue can thus 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. percent sulfur is required. For example, low sulfur content coke is desired for the manufacture of phosphorous, for the production of calcium carbide, for lime burning in the manufacture of soda ash or other alkalies, for various metallurgical application, for the production of electrode carbon for various electrochemical applications such as. the manufacture of aluminum and the like.

The conventional methods of removing sulfur from coke from ordinary sources, such as delayed coke, with gaseous reagents have in general not been too satisfactory. The results are even poorer when 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, how ever, is laminar in structure and may comprise some 30 to 100 superposed layersfof coke. Thus, it is difficult for a reagent to penetrate more than a few outer layers. These difficulties of the coke are even further compounded because of the before-mentioned possibly higher than normal sulfur content of the fluid coke derived from high sulfur petroleum feeds.

This invention provides an improved process for lowering the sulfur concentration of fluid coke which comvated temperatures. The sulfur is thereby removed from the outer layer or layers from the coke particles as fast as it is laid down. .The build up of the sulfur to high levels which are diflicult tolower is thereby prevented as the coke isconstantly deposited on prepurified coke. A The hydrogen treatingis con-ducted non-catalyticallyat a-temperature of 1200 to 1400 F.,-preferably about 1300" F. At temperatures below about 1200 F. thev rate of sulfur removalby hydrogen is extremely slow and requires an impractically long contact time. At temperais also quite slow. Thelmaximum, rate of sulfur removal occurs at about l300 -F. The pressure in the hydrogen treating zone is. approximately the same as that in the coking zone and may be in the range of about 0 to 25 pounds per square inch gage; hydrogen partial pressure may be in the range of one to three atmospheres absolute. The treating gas should contain at least 40% and normally comprises about 50 to hydrogen with the remainder being, for the most part, methane and other light hydrocarbon gases. The superficial gas velocity in the hydrogen treating zone is sufiicient to maintain the coke in fluidized state; a velocity of 0.3 to 3.0 ft./sec., preferably 0.5 to 1.5 ft./sec., is contemplated. The contact time of the coke in the hydrogen treating zone is in the range of 1 to 20 minutes, preferably about 5 to minutes. The hydrogen can be utilized pure or in the form of hydroformer tail gas or other refinery streams but is preferably treated in the conventional manner to remove hydrogen sulfide and other sulfur-containing compounds before use.

, Itshould be emphasized that the conditions expressed are integrated with the fluid coking for fuels process and represent an ideal manner of lowering the sulfur content and recovering the sulfur in the form of useful compounds.

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

In the drawing numeral 10 represents a coking vessel constructed of suitable materials for operation at 1000 F. The temperature is maintained by the introduction of coke at about 1100 F. from line 35. A fluid bed of solid particles of 150 to 400 microns in diameter reaches an upper level indicated by numeral 60. The bed is fluidized by means of a gas such as steam entering the vessel at a temperature of 400 F. via line 63. The fluidizing gas passes upwardly through the vessel at an average velocity of 1.5 ft./sec., including the gas generated in the bed, establishing the solids at the indicated level. The fluidizing gas serves also to strip the vapors and gases from the coke which flows down through the vessel from pipe 35.

A reduced crude oil containing 3.5 weight percent sulfur to be converted, preferably preheated to a temperature not above its cracking temperature, e. g., 700 F., is introduced into the bed of hot coke particles via line 6, 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 fluidization 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 16 after passing through cyclone 65 from which solids are returned to the bed via dipleg 66. The coke formed is thus laid down in thin films on preheated cokeas described hereafter. The coke stream is withdrawn through line 64 and exclusive of recycle through lines 11 and 35 is transported by means of hydrogen gas from line 13 to hydropurifier through line 12. In purifier 20 the coke is maintained in a fluidized bed having an upper level 67 by means of hydrogen from lines 13, 54 and 55.. The temperature of the coke in purifier 20 is 1300 F. and the residence time is 5 minutes. The upward superficial velocity of hydrogen in purifier 20 is 1.0 ft./sec. and methane and a small amount of heavier hydrocarbons from the coke. The hot gases leaving the fluid bed pass through line 26 into cyclone 28 from which any entrained solids are returned to the bed via dipleg 68. The gaseous materials are taken through line 29 to condenser and separator section 40 maintained at a temperature below about 100 P. where a small amount of condensable and tarry hydrocarbons are separated and removed through line 69.

. The residual gases comprising hydrogen, hydrogen sulfide, and gaseous hydrocarbons leave through line 48, are taken to hydrogen sulfide scrubber 50 containing triethanolamine. The scrubber solution removes the hydrogen sulfide and itself can be removed through line 56 where it can be degassed and recycled. The cooled hydrogen sulfide can be compressed and sold or used for commercial enterprises.

. Other conventional means of separating hydrogen sulfide from hydrogen such as water scrubbing, caustic soda scrubbing, sodium phenolate scrubbing, tripotassiurn The hydrogen removes sulfur compounds.

phosphate scrubbing, or the like, can be employed. The hydrogen is taken overhead through line 70 and recycled through line 54 as previously described. Any venting and purging is done through line 52. Make up hydrogen is added through line 55.

The purified coke from hydropurifier 20 is withdrawn through line 22. A portion of the coke from the purifier is fed by means of line 24 to heater 30. Air is supplied via line 32. to heater 30. In the heater a portion of the carbonaceous materials, e. g., coke or materials deposited thereon, is burned to raise the temperature to a point suflicient to keepthe system in heat balance, in this case to about 1500" F. The bed of coke in vessel 30 is fluidized to a bed level 61 in much the same manner as the bed in vessel 10. Other gases or liquid fuels can be substituted in all or part for the coke burned. Similarly a transfer line burner system could be employed. Hot flue gases pass through cyclone 71 and line 38 with entrained solids being returned to the bed via dipleg 72. A portion of the heated coke is withdrawn through line 33 and passed to hydropurifier 20 as a source of heat. To obtain a temperature of 1300" F. in purifier 20.1 /2 parts of stream 33 at 1500 F. is required for 1 part of coke from line 12 at 1000 F. These ratios can be varied according to temperature requirements and heat losses in the transfer lines. The other portion of the coke stream is passed through line 34 to the coking unit.

The coke in line 34 at a temperature of 1500 F. is mixed with 1000 F. coke withdrawn from the reactor 10 by lines 64 and 11 and the mixture at a temperature of about 1100 F. is introduced into reactor 10 by line 35 as hereinbefore described.

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

CONDITIONS IN FLUID COKER REACTOR 10 Broad Preferred Range Range Temperature, fF 900-1, 500 950-1, 050 Pressure, p. s. 1. g 0-100 5-25 Superficial Velocity of g s, 0. 3-5.0 1. 5-3.0 Average Size of Coke Particles,microns 50-1, 000 -400 CONDITIONS IN TREATING ZONE 20 Broad Preferred Range Range Temperature, F 1, 200-1, 400 1, 250-1, 350 Pressure, p. s. i. g 0-100 5-25 Hydrogen Partial Pressure, Atmospheres 1 Absolute 0. 5-7 l-3 Superficial Gas Velocity, Ft./sec 0. 3-3. 0 0. 5-1. 5 Coke Residence Time, Min 1-20 5-10 CONDITIONS IN HEATER 30 Broad Preferred Range Range Temperature, r l 1, 250-1, 600 1,40o-1,500 Superficial Velocity of Fluidizin'g Gas,

Eta/sec 0.3-3.0 1.0-1. 5

The process of this invention is also applicable to the coking'of heavy hydrocarbon oils-for the production of chemicals, e; g., principally unsaturated hydrocarbons. A process of this nature is conducted with reactor temperatures ofabout 1200 to 1500 F. and heater temperatures of 1300 F. to 1600 F. Transfer line systems are preferred for both of these steps in the coking at high temperature for chemicals.

The value of treating coke in thin layers and the effect of-ternperature of treating are shown by the following data treating 100' to 400 micron particles with hydrogen at 1500 v./v./hr. In one'case solid particles of high sulfur (7%) coke were treated. In the other case the coke was deposited in a thin layer (1 to 2 microns thick) on sand: 3

Initial rate of Sulfur Removal, Lbs. of Sulfur per Ton of Coke per Minute Temperature, F.

Solid Coke Thin Layer of Coke Experience has shown that initial desulfurization rates are not maintained when the total particle is to be purified and the rate drops off tremendously after the outside Solid Par- .Thin

ticle Layer Time on H; at 1,300 F. to Reduce Sulfur to 2%. 12 hours". 5 min.

Thus the operability of the process is demonstrated.

The advantages of this invention will be apparent to those skilled in the art. Improved purification is obtained in an integrated system in that the coke is treated before it is rendered passive by excessive temperatures in the burner section. The coke is thus deposited in thin layers on prepurified coke. The loss of some of the sulfur compounds in the burner is avoided by purifymg prior to the excessive burner heating. This process works best with freshly deposited films of coke on prepurified coke as a nucleus. The purification of the coke prior to the burner section concentrates all the sulfur available as hydrogen sulfide. In addition to this gain insulfur compounds a relatively pure coke passes to the burner which minimizes the objectionable air contamination from sulfur dioxide which otherwise would be encountered.

It is to be understood that this invention is not limited to the specific examples which have been oflered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. 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 dense, turbulent, fluidized bed of coke particles maintained in a coking 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; withdrawing the coke particles from the coking zone; contacting the hot circulating coke with hydrogen in a treating zone at a temperature in the range of 1200 to 1400 F. to remove sulfur therefrom; heating a portion of the hydrogen treated circulating coke particles removed from the coking zone in a separate heating zone to increase the temperature of said particles and returning a portion of the circulating heated coke particles from the heating zone to the coking zone to supply heat thereto.

2. The process of claim 1 including the additional step of Withdrawing product coke from the hydrogen treating zone.

3. The process of claim 2 including the additional step of returning a portion of tr e circulating heated coke particles from the heating zone to the hydrogen treating zone to supply heat thereto.

4. The process of claim 3 including the additional step of recovering hydrogen sulfide from the overhead hydrogen containing gases from the hydrogen treating zone and recycling the hydrogen from the overhead gases to the hydrogen contacting step.

5. The process of claim 1 in which the hydrogen contacting step is carried out while the coke is maintained in the form of a dense turbulent fluidized bed.

6. The process of claim 5 in which the hydrogen contacting step is carried out for a period of time in the range of 1-20 minutes.

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 a1. Nov. 9, 1954 2,700,642 Mattox Jan. 25, 1955 2,721,169 Mason et a1. Oct. 18, 1955 FOREIGN PATENTS 690,791 Great Britain Apr. 29, 1953

Claims (1)

1. A PROCESS FOR COKING A HEARY 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 DENSE, TURBULENT, FLUIDIZED BED OF COKE PARTICLES MAINTAINED IN A COKING 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; WITHDRAWING THE COKE PARTICLES FROM THE COKING ZONE; CONTACTING THE HOT CIRCULATING COKE WITH HYDROGEN IN A TREATING ZONE AT A TEMPERATURE IN THE RANGE OF 1200 TO 1400* F. TO REMOVE SULFUR THEREFROM; HEATING A PORTION OF THE HYDROGEN TREATED CIRCULATING COKE PARTICLES REMOVED FROM THE COKING ZONE IN A SEPARATE HEATING ZONE TO INCREASE THE TEMPERATURE OF SAID PARTICLES AND RETURNING A PORTION OF THE CIRCULATING HEATED COKE PARTICLES FROM THE HEATING ZONE TO THE COKING ZONE TO SUPPLY HEAT THERETO.

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