US3816084A

US3816084A - Cokeless coker with recycle of coke from gasifier to heater

Info

Publication number: US3816084A
Application number: US00250321A
Authority: US
Inventors: J Moser; W Metrailer
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1970-04-16
Filing date: 1972-05-04
Publication date: 1974-06-11
Anticipated expiration: 1991-06-11

Abstract

In a fluid coking process in which coke from the coker is passed to a heater and then to a gasifier and in which part of the heat for the heater is supplied by the gases from the gasifier, ungasified coke from the bottom of the gasifier is conveyed through a riser to the heater to supply additional heat and thence back to the coker whereby strength of the coke is increased by fresh coke deposition and in which all the oxygen is injected into the lower gasifier bed thereby eliminating possibility of oxygen breakthrough. The same results can be accomplished by passing the coke from the gasifier directly back to the coke reactor and eliminating the coke stream from the upper heater bed to the reactor.

Description

United States Patent [191 Moser, Jr. etal.

[ 1 June 11, 1974 [75] lnventors: John F. Moser, Jr.; William 'J.

Metrailer, both of Baton Rouge, La.

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

[22] Filed: May 4, 1972 [21] Appl. No.: 250,321

Related US. Application Data [631 Continuation-impart of Ser. No. 28,998, April 16,

I970, abandoned. v

52 us. Cl 48/206, 48/63, 201/25, 201/31, 201/44, 208/127 [51] Int. Cl. Cl0j 3/00, ClOb 49/10 [58] Field of Search ..201/15,'16,14,13,17, 201/31, 44, 21-24, 25; 208/127; 48/206, 63, 197, 203, 202

[56] References Cited 1 UNITED STATES PATENTS Roctheliimf; 208/127 2,543,795 3/1951 2,588,075 3/1952 2,600,430 6/1952 2,657,986 ll/l953 2,657,987 11/1953 scRuaBER FRACTIONATOR\ RESIDUUM 1 r FEED STEAM 4/1954 Garbo et a1 48/206 2,702,267 2/1955 Keith 208/127 2,741,549 4/1956 Russell 208/8 2,793,172 5/1957 I Smith et a1 208/97 2,917,451 12/1959 Leffer 208/81 3,158,566 11/1964 Tyson 208/127 3,542,532 1 1/1970 Johnson et 211....

3,661,543 5/1972 Saxton 48/206 Primary ExaminerNorman Yudkoff Assistant Examiner-David Edwards 57 ABSTRACT In a fluid coking process in which coke from the coker is passed to a heater and then to a gasifier and in which part of the heat for the heater is supplied by the gases from the gasifier, un'gasified coke from the bottom of the gasifier is conveyed through a riser to the heater to supply additional heat and thence back to the coker whereby strength of the coke is increased by fresh cokedeposition and in which all the oxygen is injected into the lower gasifier bed thereby eliminating possibility of oxygen breakthrough. The same results can be accomplished by passing the coke from the gasifier directly back to the coke reactor and eliminating thgcoke stream from the upper heater bed to the reactor.

' 17 Claims, 2 Drawing Figures RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 28,998 filed Apr. 16, 1970, now abandoned.

BACKGROUND OF THE INVENTION In conventional fluid coking, the carbonaceous feed is injected into a bed of fluid coke where it is cracked to vapors and coke. The vapors pass through a cyclone to a scrubber/fractionator where they are fractionated to gas, naphtha and oil products, and a heavy stream which is recycled to the coking reactor. A circulating stream of coke is stripped in the bottom zone of the reactor and transferred to a coke burner where sufficient air is injected for burning part of the coke and heating the remainder sufficiently to satisfy the heat requirements of the coking reactor when the unburned hot coke is recycled thereto. Net coke above that consumed in the burner is withdrawn as product coke.

Carbonaceous feeds suitable for the coking process include heavy hydrocarbon oil crudes, atmospheric and vacuum bottoms, pitch, asphalt, bitumen from coal, tar sands or. shale, other heavy hydrocarbon residua and mixtures thereof. Typically such feeds have an A.P.l. gravity of about to and a Conradson carbon content of about 5 to 40 weight percent (as to Conradson carbon residue, Sec. A.S.T.M. Test-D-l89-65).

Unfortunately, the market for this coke has been limited with the result that attempts have been made to increase its value by subsequent treatment such as high temperature calcining and briquetting. Alternatively,

the coke can be converted to an H and CO rich gas in a subsequent processing step by reaction with steam and an oxygen-containing gas. None of these subsequent coke processing steps has been found to be economically attractive for general use.

Furthermore, when processing typical petroleum residuum in a conventional fluid coker, the combustion products from the burner have an undesirably high S0 content which is an atmospheric pollutant.

The above two problems low market value of the.

product coke, and atmospheric pollution from the burner have limited the use of fluid coking which is otherwise a superior residuum conversion process.

These two problems have been overcome by providing an integrated gasifier-heater assembly in which the heater is placed on top of the gasifier and is operated .at a lower temperature with part of the oxygen for burning the coke being introduced into the bottom of the gasifier and all of the gas from the gasifier being passed through the heater. This process is described in Ser. No. 880,219 filed Nov. 26, 1969, now US; Pat. No. 3,66l,543.

SUMMARY OF THE INVENTION ifier to the heater. This coke together with the gases from the gasifier supply all the necessary heat needed in the heater and no additional air or oxygen needs to be added to the heater.

In an alternate embodiment the coke from the bottom of the gasifier goes directly to the coke reactor and the coke stream from the upper bed to the reactor is eliminated. This embodiment has the same advantage as the first embodiment instrengthening the coke to prevent its attrition.

Both of these embodiments permit the eventual re turn of partially gasified coke particles to the reactor whe're fresh coke is deposited on the coke and gives added strength thereto preventing its attrition and loss as fines. This also permits the injection of all the oxygen into the higher temperature gasification bed and thereby eliminates the possibility of oxygen breakthrough into the fuel gas which could create a dangerous situation.

The gas product from the heater is rich in H and CO and is an attractive feed gas for manufacturing a concentrated H stream via the well-known water-gas-shift reaction, or for other chemical processes. It is also a good quality fuel. For most purposes the gases will require further treatment to remove sulfur which is primarily in the form of H 5 and readily removable by available processes such as the Stretford process, and to remove the ash which has been released from the gasified coke. Valuable by-products, sulfur and metalsrich ash, are recoverable from the gas treating facilities.

This improved fluid coking process can be operated to gasify all the coke produced in the coking reactor, or any desired portion of the coke product can be withdrawn.

BRIEF REFERENCE TO THE DRAWINGS The invention will be better understood by reference to the accompanying drawing in which FIG. 1 represents in diagrammatic form one embodiment of the invention in which coke from the gasifier is passed to the heater and in which FIG. 2 represents another embodiment in which the coke from the gasifier is passed directly to the reactor and thecoke stream from the heater to the reactor is eliminated.

PREFERRED EMBODIMENTS Referring now to FIG. 1, a carbonaceous material having a Conradson carbon of about l5 percent, such as heavy residuum boiling 1050F.+, is passed into coking zone 1 by line 2, manifold 3 and multiple feed nozzles represented by lines 4, 5, 6, 7 and 8 onto a fluidized bed of solids, e.g., coke of 40 to 1000 microns in size, having an upper level L. Carbonaceous feeds suitable for the present invention are heavy or reduced crudes, atmospheric bottoms, vacuum bottoms, pitch, asphalt, bitumen, other heavy hydrocarbon residua and mixtures thereof. Typically, such feeds may have an A.P.I. gravity of about 0 to 20 and have a Conradson carbon residue of at least about 5 weight percent to about 40 weight percent, preferably above about 7 weight percent. A fluidizing gas, e.g., steam, is admitted to the base of the vessel through line 9 in amounts sufficient to obtain superficial fiuidizing gas velocities in the range of 0.5 to 4 ft./sec. Coke at a temperature to 300 F. above the coking temperature is admitted to the coker by line in amounts sufficient to maintain a coking temperature in the range of 900 to 1200F. The pressure in the coker is maintained in the range of about 10 to 150 lbs. per square inch gauge (psig), preferably in the range of about 10 to 100 psig, more preferably at a pressure not greater than 45 psig, most preferably at a pressure in the range of about 10 to 25 psig. The lower portion of the coker serves as a stripping zone to remove occluded hydrocarbons from the coke. Coke is-withdrawn from this stripping zone by line 11 and is circulated to heater l2. Conversion products are passed through cyclone 13 to remove entrained solids which are returned to the coker through dipleg 14. The vapors leave the cyclone through line 15 and pass into scrubber-fractionator 16 where they are fractionated to gas leaving by line 17, naphtha by line 18 and gas oil by line 19. A heavy stream is removed through line 20, a portion of which is circulated through conventional heat removal exchangers and returned to scrubber as pumparound by line 21; another portion is recycled to the coker by line 22. A small amount of fine solid particles which pass through the reactor cyclone is returned to the coker reactor with this recycle stream.

In heater 12, stripped coke from the reactor (commonly called cold coke) is introduced by line 11 to a fluid bed of hot coke having a level L. The bed is partially heated by fuel gas passing upward through disc and donut distributor 23 and egg crate baffle 24. Supplementary heat is supplied by coke circulating in line 33. Hot coke is removed from the fluidized bed in heater 12 and recycled to the coker by line 10 to supply heat thereto. Another portion is removed from heater 12 by line 25 and passed to a bed of fluidized coke having a level L in gasifier 27. The coke introduced to the fluidized bed in the gasifier 27 is contacted with steam introduced by line 28 and air or oxygen by line 29. The pressure in the gasifier is maintained at a level not greater than 150 lbs. per square inch gauge (psig), preferably not greater than about 60 psig, more preferably not greater than about 45 psig. The temperature of the bed in the gasifier is maintained at a level in the range of about l4002800F., preferably at a temperature greater than about 1600F., more preferably at a temperature in the range of about 1700 to l900F., most preferably at a temperature in the range of about 1800 to 1850F., by preheating the inlet air, steam, oxygen stream, and/or varying the steam and air or oxygen ratio according to the well known equilibrium relationships in the gasifier 27, where the following reactions take place:

bon to form CO. At high temperatures, equilibrium favors drawing equation (3) to the right to form CO. Low pressure also favors this reaction. Thus, equilibrium would favor very high CO/CO ratios at temperatures 6 greater than about 1600F. and low pressures in the gasifier. Steam will also gasify coke as represented by equation (4). This reaction is slightly endothermic and The g ases formed by the above reactions pass upwardly through the gasifier and into the heater by way of the narrow neck portion 30. The gases leave heater 1. t ou h sys qn hsrssn satrai d P Pa cles are returned to the gasifier. Additional inert fluid izing gas may be admitted to the heater by header 31. The gases then leave by exit 34 and have the following typical composition when air is used for gasification:

Including Excluding H O H H O H S H 6.8 H 0 2.9 CO 19.9 20.6 CO; 7.9 8.2 N, 61.9 64.4 H S Net heating value on a dry basis is 84.6 BTU/SCF. When oxygen is used for gasiflcation, a typical composition of the gas is:

M017: Mol.%

Including Excluding H 8 H 0 H 8 H 0 H 24.2 30.9 H O 20.0 CO 34.2 43.6 CO 19.8 25.3 2 0.1 0.2 H 5 1.7

Net heating value on dry basis is 224 BTU/SCF. Small quantities of cracked hydrocarbon materials 'will also be present in the product gases and will increase the heating value of the product gases. The quantity and compositions will vary somewhat depending on the coker reactor feed and on reaction and stripping conditions.

Coke from the bottom of gasifier 27 is passed by line 33 to the heater at a point just above grid 24.

Riser 33 permits the return of partially gasified coke to the upper bed in heater 12 and aids in controlling the temperature in the heater 12. The coke is passed subsequently to reactor 1 where fresh coke is deposited in the pores generated in the gasifier. Ihis gives added strength to the particle and prevents its attrition and loss of fines into the fuel gas or productrecovery system. Line 34 is provided for withdrawing solids from the gasifier whenever desired.

Referring now to FIG. 2, this drawing is identical with FIG. 1 except that line 133 takes the coke directly from the bottom of the gasifier to the top of the bed in coker l and line 10 of FIG. 1 is eliminated. The same advantages are obtained by this embodiment as are obtained by the embodiment of FIG. 1.

While the process has been described with respect to the circulation of coke as the fluidized medium used in the process, it is to be understood that a captive bed of fluidized inert particles, such as alundum or mullite, may be used in the gasifier 27. This can be advantageous for systems in which substantial quantities of very fine about ;L) particles of foreigh solids are released in the gasifier such that very low velocities would be required in order to maintain a stable fluidized bed. Such a captive bed can be fluidized readily without significant entrainment of the captive bed particles at superficial velocities substantially higher than the entrainment velocity of fine particles released from the coke. Such a captive bed provides a well mixed reaction zone in the gasifier in which the carbon can be burned and the foreign solids released without causing severe fluidization problems. Some equilibrium concentration of the fine particles are retained in the gasifier bed, thus providing sufficient residence time for complete gasification of the carbon before thebulk of the particles are entrained by the exit gases. The hot gasifier products, including entrained solid particles,

pass through a heat exchange bed similar to the bed described in connection with heater 12. This type of process would be preferable when processing feeds containing much higher solids than are normally present in petroleum residuum, e.g., bitumen from coal, tar sands or shale which may contain -20 percent inert solids. The solids, such as fine and, metal oxides, or the like, contained in the bitumen are released in the captive bed in the gasifier and being smaller than the coke are more easily entrained out and carried upwardly through the heat exchange bed. These fine particles will also pass through the conventional cyclones in the heater vessel but can be recovered by a downstream electrical precipitator.

What we claim is:

I. In an integrated fluid coking-gasification process for the production of coke and a gaseous stream containing H and CO, which comprises:

a. reacting carbonaceous material having a Conradson carbon content of at least 5 wt. percent in a fluid coking zone operating at temperatures between 900F. and 1200F. to form coke;

b. introducing at least a portion of said coke into a heating zone operating at a temperature 100 to 300F. greater than said fluid coking zone temperature to heat said coke;

c. recycling a first portion of the heated coke from said heating zone to said fluid coking zone to provide heat to said fluid coking zone and introducing a second portion of said heated coke to a gasifying zone operating at a temperature greater than the temperature of said heating zone;

d. reacting said second portion of coke in said gasifying zone with steam and an oxygen-containing gas to produce a hot gaseous stream containing H and CO;

e. introducing said hot gaseous stream containing H and CO and entrained coke into said heating zone, and

f. recovering from said heating zone the resulting cooled gaseous stream containing H and CO,

the improvement which comprises: passing a sufficient amount of additional coke from said gasifying zone to said heating zone such that said hot gaseous stream and entrained coke and said additional coke provide all of the heat requirements of said heating zone, coke being the only volatilizable normally solid carbonaceous material introduced into said heating zone.

2. A process according to claim 1 wherein said gasifying zone is operated at temperatures greater than about l600F.

3. A process according to claim 1 wherein said fluid coking zone, said heating zone and said gasifying zone are operated at a pressure not greater than about 150 psig.

4. A process according to claim 1 wherein said gasifying zone is operated at a pressure not greater than about 60 psig.

5. The process according to claim 1, wherein said gasifying zone is operated at a pressure not greater than about 45 psig.

6. A process according to claim 1 wherein said hot H and CO containing gaseous stream is at a temperature greater than about l600F.

7. A process according to claim 1 wherein an inert fluidizing gas may be introduced to said heating zone in addition to said hot H and CO containing gaseous streams.

8. A process according to claim 1, wherein said carbonaceous material is a heavy petroleum oil residuum having a Conradson carbon content of at least about 7 weight percent.

9. The process of claim 1, wherein said heating zone also contains an inert solid.

10. In an integrated fluid coking-gasification process for the production of coke and a gaseous stream containing H and CO, which comprises:

a. reacting a carbonaceous material having a Conradson carbon content of at least 5 wt. percent in a fluid coking zone operating at a temperature between 900F. and l200F. to form coke;

b. introducing at least a portion of said coke into a heating zone operating at a temperature to 300F. greater than said fluid coking zone temperature to heat said coke;

c. introducing a portion of the resulting heated coke to a gasifying zone operating at a temperature greater than said temperature of said heating zone;

d. reacting said heated coke portion in said gasifying zone with steam and an oxygen-containing gas to produce a hot gaseous stream containing H and CO, whereby the remaining coke is heated to the operating temperature of said gasifying zone,

the improvement which comprises:

e. passing said hot gaseous stream containing H and CO and entrained coke to said heating zone to provide all of the heat requirements of said heating zone, coke being the only volatilizable normally solid carbonaceous material introduced into said heating zone,

f. recovering the resulting cooled gaseous stream containing H and CO from said heating zone, and

g. passing a portion of the remaining heated coke of step (d) directly from said gasifying zone to said fluid coking zone to provide heat to said fluid coking zone.

11. The process of claim 10, wherein said heating zone additionally contains an inert solid.

12. A process according to claim 10, wherein said gasifying zone is operated at temperatures greater than about 1600F.

13. A process according to claim 10 wherein said fluid coking zone,- said heating zone and said gasifying zone are operated at a pressure not greater than about 150 psig.

14. The process according to claim 10, wherein said gasifying zone is operated at a pressure not greater than about 60 psig.

15. The process according to claim 10, wherein said stream.

Claims

2. A process according to claim 1 wherein said gasifying zone is operated at temperatures greater than about 1600*F.
3. A process according to claim 1 wherein said fluid coking zone, said heating zone and said gasifying zone are operated at a pressure not greater than about 150 psig.
4. A process according to claim 1 wherein said gasifying zone is operated at a pressure not greater than about 60 psig.
5. The process according to claim 1, wherein said gasifying zone is operated at a pressure not greater than about 45 psig.
6. A process according to claim 1 wherein said hot H2 and CO containing gaseous stream is at a temperature greater than about 1600*F.
7. A process according to claim 1 wherein an inert fluidizing gas may be introduced to said heating zone in addition to said hot H2 and CO containing gaseous streams.
8. A process according to claim 1, wherein said carbonaceous material is a heavy petroleum oil residuum having a Conradson carbon content of at least about 7 weight percent.
9. The process of claim 1, wherein said heating zone also Contains an inert solid.
10. In an integrated fluid coking-gasification process for the production of coke and a gaseous stream containing H2 and CO, which comprises: a. reacting a carbonaceous material having a Conradson carbon content of at least 5 wt. percent in a fluid coking zone operating at a temperature between 900*F. and 1200*F. to form coke; b. introducing at least a portion of said coke into a heating zone operating at a temperature 100* to 300*F. greater than said fluid coking zone temperature to heat said coke; c. introducing a portion of the resulting heated coke to a gasifying zone operating at a temperature greater than said temperature of said heating zone; d. reacting said heated coke portion in said gasifying zone with steam and an oxygen-containing gas to produce a hot gaseous stream containing H2 and CO, whereby the remaining coke is heated to the operating temperature of said gasifying zone, the improvement which comprises: e. passing said hot gaseous stream containing H2 and CO and entrained coke to said heating zone to provide all of the heat requirements of said heating zone, coke being the only volatilizable normally solid carbonaceous material introduced into said heating zone, f. recovering the resulting cooled gaseous stream containing H2 and CO from said heating zone, and g. passing a portion of the remaining heated coke of step (d) directly from said gasifying zone to said fluid coking zone to provide heat to said fluid coking zone.
11. The process of claim 10, wherein said heating zone additionally contains an inert solid.
12. A process according to claim 10, wherein said gasifying zone is operated at temperatures greater than about 1600*F.
13. A process according to claim 10 wherein said fluid coking zone, said heating zone and said gasifying zone are operated at a pressure not greater than about 150 psig.
14. The process according to claim 10, wherein said gasifying zone is operated at a pressure not greater than about 60 psig.
15. The process according to claim 10, wherein said gasifying zone is operated at a pressure not greater than about 45 psig.
16. A process according to claim 10 wherein said hot H2 and CO containing gaseous stream is at temperatures greater than about 1600*F.
17. A process according to claim 10 wherein an inert fluidizing gas may be introduced to said heating zone in addition to said hot H2 and CO containing gaseous stream.