US3803023A

US3803023A - Steam gasification of coke

Info

Publication number: US3803023A
Application number: US00264056A
Authority: US
Inventors: G Hamner
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1970-06-09
Filing date: 1972-04-19
Publication date: 1974-04-09
Anticipated expiration: 1991-04-09

Abstract

A heavy carbonaceous material having a Conradson carbon residue of at least 5 wt. % is coked in the presence of an alkali metal compound to produce an active surface carbon containing the alkali metal compound. The coke is then partially gasified to produce a hydrogen-containing gas and the remaining coke is recycled to the coking zone as seed coke therein.

Description

O United States Patent 11 1 1111 3,803,023 Hamner Apr. 9, 1974 STEAM GASIFICATION ()F COKE 2,600,430 6/!952 Rihlcn 2011/54 I 3,475,323 Ill/I969 Stuckey et all. 208/127 [75] lnvemor- Ham", Baton R F 3,172,840 3/1965 Paterson 208/79 [73] Assigneer Esso Research and Engineering Company [22] Filed: 19, 1972 Primary Eraminer-Herbert Levine [21] Appl. No.: 264,056

Related US. Application Data [63] Continuation-impart of Ser. No. 45,096, June 9, [57] ABSTRACT 1970, abandoned.

521 US. Cl 208/46, 48/197 R, 208/127, A heavy carbonaceous material having a Conradson 208/131 carbon residue of at least 5 wt. 7: is coked in the pres- 51 1111.01 ClOg 9/32 alkali metal Compound to Produce an [58] Field of Search 208/127, 131, 46; "vesurface Carbon comaining the alkali metal 48/197 R pound. The coke is then partially gasified to produce a hydrogen-containing gas and the remaining coke is re- [56] References Cited cycled to the coking zone as seed coke therein.

UNITED STATES PATENTS 3,179,584 4/1965 Hamner et al. 208/127 22 Claims, 1 Drawing Figure CRACKED PRODUCTS HYDROGEN FEED i i 110T COKE I? 13 l -STEAM COKE BURNER GASIFIER 5fihl COKE, s 10 ZONE AIR 20 I'RECYCLE com; [\4 FLUlDlZlNG GAS 1 STEAM GASIFICATION OF COKE RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 45,096, filed June 9, 1970 by Glen P. l-Iamner now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a combination coking and steam gasification process to produce a hydrogencontaining gas and a method of preparing an alkali metal promoted coke for use in the steam gasification process.

The use of alkali metal compounds in coking hydrocarbon oils to increase the hydrogen content of a coker gaseous product is known (see US. Pat. No. 3,179,584). Alkali metal compounds are also known to increase hydrogen production when solid carbonaceous material is steam gasified.

It has now been found that a hydrogen containing gas can be produced at high gasification rates at temperatures between l,O and l,500 F. and that liquid coker products having a reduced heavy metal content can be obtained by a combination coking and gasification process wherein an alkali metal containing coke product produced in a coking zone is subsequently steam treated in a separate gasification zone and the resulting partially gasified alkali metal containing coke is recycled to the coking zone as seed coke on which additional coke is deposited.

It has also been found that a particularly effective method for incorporating the alkali metal compound in the coke is to coke a hydrocarbon feedstock in the presence of an alkali metal compound.

Further advantages of this invention will become apparent from the ensuing description of the invention.

SUMMARY OF THE INVENTION In accordance with one embodiment of the invention, there is provided a method of preparing an alkali metal-containing coke for use in the steam gasification process which comprises (a) mixing a heavy carbonaceous material having a Conradson carbon residue of at least 5 wt. with an alkali metal compound and coking the mixture in a coking zone maintained at a temperature between about 750 and l,l50 F. and at a pressure between about 5 and 150 psig to produce vaporous products and coke containing alkali metal compound; (b) passing at least a portion of said coke containing alkali metal compound to a separate gasification zone maintained at a temperature between about l,000 and l,500 F. to contact steam introduced into said gasification zone and thereby convert at least a portion of said coke to gaseous products and to obtain a partially gasified coke containing alkali metal com- 1 pound; (c) passing said partially gasified coke containing alkali. metal compound to the coking .zone of step (a); and (d) coking an additional portion of said heavy carbonaceous material in said coking zone whereby a portion of said additional heavy carbonaceous material is converted to additional coke and said additional coke deposits on the partially gasified coke containing alkali metal compound.

In accordance with another embodiment of the invention, there is provided a process for steam gasifying coke which comprises (a) mixing a heavy carbonaceous material having a Conradson carbon residue of at least 5 wt. with an alkali metal compound and coking the mixture in a coking zone maintained at a temperature between about 750 and l,l50 F. and at a pressure between about 5 and psig to produce a vaporous product and coke containing alkali metal compound; (b) passing at least a portion of said coke containing alkali metal compound to a separate gasification zone maintained at a temperature between about l,000 and l,500 F. to contact steam introduced in said gasification zone and thereby convert at least a portion of said coke to a gaseous product and to obtain a partially gasified coke containing alkali metal compound; (c) passing said partially gasified coke containing alkali metal compound to the coking zone of step (a); (d) coking an additional portion of said heavy carbonaceous material in said coking zone whereby a portion of said additional heavy carbonaceous material'is converted to additional vaporous product and to additional coke which deposits on the partially gasified coke containing alkali metal compound; and (e) recovering the additional vaporous product.

Furthermore, the coke coated partially gasified coke containing alkali metal compound resulting from step (d) may be passed to the steam gasification zone to gasify a portion of the coke and the resulting steam treated coke containing alkali metal compound may be returned to the coking zone to deposit additional coke on the coke containing alkali metal compound product for use in the steam gasification zone.

In accordance with'a preferred embodiment of the invention, the gaseous product of the gasiflcation zone is a high purity hydrogen-containing gas.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic representation of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a high Conradson carbon and preferablyahigh metal content feedstock to which has been added an alkali metal compound is introduced into the upper portion of catalytic coking zone 1 by line 2 onto a fluidized bed of coke particles 3 maintained at a temperature of 750l,l50 F. and under a pressure ranging from about 5 to 150 psig. Suitable alkali metal compounds include any compounds soluble or dispersible in the feed such as the hydroxide, carbonate, sulfide or silicate or organic salts such as phthalate, oxalate, acetate, etc. of potassium, sodium, lithium, rubidium and cesium. The preferred catalysts are the alkali metal carbonates and silicates. The carbonate may be added as such to the feed or an alkali metal compound which is more soluble than the carbonate and convertible to the corresponding carbonate under the operating conditions and in the presence of the reaction products, such as CO produced in the reaction zone can be initially mixed with the feed. If sulfur is present, some alkali metal sulfide may also be formed. Furthermore, any alkali metal silicate formed as a result of the corrosive effect of the alkali metal compound on the refractory lining of the reactor may also be present as effective catalyst. A preferred catalyst is therefore the alkali metal silicate since it will not react with the refractory lining of the reactor;

wt. or higher Conradson carbon and boiling above about 900 to l,200 F. However, any stock having a Conradson carbon above may be 'used. The particles of coke are maintained as a fluid bed by the upward passage of a fluidizing gas such as steam which enters the lower portion of coking zone 1 through line 4. The contact of the heavy feed and the coke results in the feed being converted to lower boiling vaporous hydrocarbons and to coke containing an alkali metal compound. The resulting coked alkali metal compound is deposited on the coke particles in the fluid bed along with the metals in the feed. The vaporous hydrocarbons v and steam are removed through line 5 while the fluidized coked alkali metal compound containing coke particles descend in bed 3 and are withdrawn from the lower portion of coking zone 1 through line 8 and are introduced into the top of coke burner 9 wherein part of the coke is oxidized to produce carbon oxides by means of an oxygen-containing gas such as air introduced through line 10 with a resultant rise in temperature of the coke to at least l,250 F. and under preferred operating conditions to 1,350 to l,500 F. The temperature at which the reaction in the oxidation zone is effected may be controlled by regulating the quantity of oxygen-containing gas, by regulating the temperature of the oxygen-containing gas and by regulating the amount of coke present in the burner. The amount of oxygen in the oxygen-containing gas may be regulated by blending inert gaseous material, such as steam, nitrogen or flue gas, with the air or oxygen used. if desired the amount of coke burned may be controlled by the introduction of liquid or gaseous fuel to be burned instead of the coke.

A portion of the heated coke in burner 9 may be returned to coking zone 1 by line 6 to control the temperature therein. Nitrogen, excess air, oxygen and other gases are removed from coke burner 9 through line 1 1. Care must be made to insure that all nitrogen is removed since it is highly desirable to prevent the introduction of any nitrogen into the gasifier 7.

The remaining heated coked alkali metal compound containing coke particles arewithdrawn from burner 9 through line 12 and supplied to the top of gasifier 7 where the particles drop into fluidized bed 13 supplying heat thereto and maintaining the temperature therein between 1906 and 1,560" F., preferably between l',l00 and l,400 F. However, whenever desired, coke 1 may be withdrawn through line 14. The reactions in the gasifier may be, effected at substantially atmospheric pressure and pressures up to. 150 psig, if desired, al-

though it is preferable to operate at substantially atmospheric pressure in order to prevent the saturating effect of hydrogen on any volatile conversion products ig the g as i fier. St earn for fluidizing bed 13 and for gas- STEAM GASIFICATION 0F BAGHAQUERO'DELAYEDQOKE WITH POTASSIUM HYDROXIDE 4 ifying the coke is introduced through

lines

17 and 18.

It is highly important that no nitrogen be present in the gasifier. Hence care must be maintained to remove it prior to the introduction of the coked alkali metal compound containing coke to the gasifier. The presence of nitrogen will contaminate the synthesis gas product, requiring an extra costly step for its removal.

The partially gasificd coke particles containing the gasifying zone 7 and are withdrawn through line 19 and returned to coking zone 1 through line 20 as seed coke therein.

It is important to remember that the presence of the alkali metal compound in the gasifier enables the gasification to take place at a much lower temperature. When this partially gasified coke of increased surface area known as seed coke, is recycled, the resulting coke, though not increased in yield, gives increased gas yields on subsequent gasification. This gas contains over twice as much CO which is easily removed, about half as much CO and less than half as much methane. It also results in a reduction in metals content of the liquid coker products which in turn improves any subsequent, hydrotreating operation on these liquid products. Catalytic seed coke (increased in surface area) gives reduced gas make and increased distillate in the coking zone 1 operation.

While the above process has been described in connection with a fluid type process, it is obvious, of course that other techniques may be used. For example, the coke may be'laid down with the alkali metal catalyst in a delayed coking operation. The coke containing alkali metal catalyst would then be removed from the coking drum, ground and transferred to a gasifier. To make the process continuous two coking drums are used. While coking is taking place in one, coke is being removed from the other. Delayed coking is carried out above 650 F. preferably between 850 and l,000 F. and at a pressure between about 5 and 150 psig. v

The following examples are presented as specific illustrations of the present invention. All quantities are expressed in the specification and claims on a weight basis unless stated otherwise.

EXAMPLE 1 Bachaquero vacuum residuum withand without 5 wt. of potassium hydroxide was edited in a laboratory 1- inch diameter vycorre'actor at a temperature of 950 F., 10 psig for 2 hours to obtain 8-10 gram samples of coke. The temperature was then raised to 1,200 F. for 15 minutes to remove the last traces of the heavy oil fraction. The resulting coke containing the alkali metal component or not was ground to mesh and 8 gram samples'were gasified with steam at different temperatures. The following data were obtained.

(Excess steam with 8-gram sample) 1 None None 1 1 1,175 1, '170 1, 370 1, 350 1, 350 1st 3d 1st 2d 4th 1st 2d 1 3d 118 134 .010 0T3 046 .062 624 0. it .085 0 54 1 All coke gasifled.

cation step. The results are set forth below.

3,803,023 V 6 g The above data show that the base coke without a STEAM SIF CAT ON OF COKE FROM RUN B AND RUN c catalyst promoter gave low gasification rates. With potassium hydroxide promoted coke, the gasification ratel (l250F., I hour, I W/W/Slcam to Carbon, Atmospheric Pressure) (20 Gram Coke Charge) 13 at 1,1 80 F. was equivalent to that for the unpromoted; gga z- Run B n C coke at l ,3 70 F. Atthe higher temperature l ,350? F.) 5 (Catalytic Nomcatalyfic the gasification rate for the first hour with potassium- Gasifled Gasified Recycle Recycle Coke) coke mixture increased tenfold. By the third hour all Coke) the promoted coke had been gasified. At the lower temperatures the carbon monoxide concentration was lower for the promoted than for the unpromoted coke.

. Dry Gas Yield, SCF 0.157 0.04!

Dry Gas Composition, Mol.

EXAMPLE 2 Y H,

The experlment of Example 1 was repeated except C 2 L9 4.9 that potassium silicate was used as the alkali metal 0.4 0.8

compound promoter. The following data were obtained: The above data show that the use of recycled seed coke in the coking step results in a drastic reduction of the metals content of the liquid products from coking.

STEAM GASlFlCATlON 0F BACHAQUERO DELAYED COKE Catalytic Seed k y Operation) g increased WITH POTASSlUM SILICATE distillate yield with a corresponding reduction in gas (Excess steam with 8 gram sample) make and coke production when compared to corre- Run No. 8 spondmg non-catalytic recycle systems. The gasrfica- 9 tion of the coke prepared with the use of alkali metal Gasificatron Conditions promoted partially gasified coke as seed coke gives a e p 1345 fourfold increase in steam gasification rate. The gase- "9" 15 j ous product contains half as much CO and-less than Gas Rate, SCF/Hr. 0.06 half as much methane. Gas Composition, Mol. v 3O EXAMPLE 4 H 74.0 r C0 6.8 The liquid product obtained in the coking Run B of g 17 Example 3 was subjected to a hydrotreating step using a cobalt sulfide-molybdenum sulfide catalyst on silica stabilized alumina. The following results were ob- The above data show that potassium silicate is an efi 7 fective promoter giving a high yield of hydrogenl- HYDROTREATING 0F COKER DEMETALLIZED (74%). LIQUID PRODUCT Run Number D EXAMPLE 3 Coke Liquid Coking Run B Product Source The experiment of Example 1 was repeated except Hydrotreating Conditions (1 that residuum feed without additional alkali metal coma d k d the of rt. d Temperature, F. 650 poun was co e in presence pa la y gasi 1e prcssumpslg 400 coke containing alkali metal compound from a previ- /Hr. 1

Gas Rate, SCF H /bbl. 2000 ous steam gasification run. The quantity of partially gasified recycle coke was 10 wt. based on residuum Hydrotreatcd Li quid Feed-Coking Run B feed. The coking results from this operation were com- Produc Llqu'd Pmdm pared with those obtained without the addition of the seed coke and with the results obtained when using partially gasified coke from an operation in which no alkali v GmmY' Sulfur, Wt. 71 0.2 [.7 metal compound was used in the coking or coke gasifi- (l) Co Mo on silica stabiliied alumina catalyst.

COKING OF RESIDUA WITH l0% RECYCLE GASIFIED COKE Y (Bachaquero Residua. 400 F. Run A B (l Recycle coke from catalytic gasificalion, K CO as promoter. surface area of 250 square meter per gram. (2) Recycle cake from non-catalytic gasification, surface area of 230 square meters per gram.

The results from the above run show that hydrodesulfurization of the liquid products obtained using seed coke during the coking step resulted in a drastic reduction in the sulfur content of these products. The removal of low molecular weight metal components from the coker distillate improves the catalytic activity maintenance of the hydrodesulfurization catalyst since such metals bring about deactivation of conventional alumina base catalysts normally employed for hydrodesulfurization.

What is claimed is:

1. A method of preparing a coke containing an alkali metalv compound for use in a steam gasification process which comprises:

a. mixing a heavy mineral oil having a Conradson carbon residue of at least wt. with an alkali metal compound and coking the mixture in a coking zone maintained at a temperature between about 750 and l,l50 F. and at apressure between about 5 and 150 psig to produce vaporous products and coke containing an alkali metal compound;

b. passing at least a portion of said coke containing the alkali metal compound to a separate gasification zone maintained at a temperature between about l,0OO and l,500 F. to contact steam introduced into said gasification zone'and therebyconvert at least a portion of said coke to gaseous products and to obtain a partially gasified coke containing the alkali metal compound;

alkali metal compound to the coking zone of step (a) as a separate stream from said mineral oil, and

. coking an additional portion of said heavy mineral oil in said coking zone whereby a portion of said additonal heavy mineral oil is converted to additional coke and said additional coke deposits on the partially gasified coke containing the alkali metal compound.

2. The process of claim 1, wherein said gasification zone is maintained at a temperature between about l,lO0 and 1,400" F.

3. The process of claim 1, wherein said gasification zone is maintained at a pressure between about 0 and ISOpsigL- passing said partially gasified coke containing the 9 4. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium silicate.

5. The process of claim 1, wherein the alkali metal 1 compound mixed with'said heavy mineral oil is potassium carbonate.

6. The process'of claiml, wherein the alkali metal compound mixed with said heavy mineral oil is potassium hydroxide.

7. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium sulfide.

' maintained at a temperature between about 750 and l,l50 F. and at a pressure between about 5 and psig to produce a vaporous product and coke containing an alkali metal compound;

b. passing at least a portion of said coke containing the alkali metal compound to a separate gasification zone maintained at a temperature between about 1,000 and 1,500 F. to contact steam introduced into said gasification zone and thereby convert at least a portion of said coke to a gaseous product and to obtain a partially gasified coke containing an alkali metal compound;

c. passing said partially gasified coke containing the alkali metal compound directly to the coking zone of step (a) as a separate stream from said mineral oil;

d. coking an additional portion of said heavy mineral oil in said coking zone whereby a portion of said additional heavy mineral oil is converted to additional vaporous product and to additional coke which deposits on the partially gasified coke containing the alkali metal compound, and

e. recovering the additional vaporous product.

10. The process of claim 9, wherein a portion of the coke containing alkali metal compound of step (d) is passed to the gasification zone of step (b) to convert a portion of the coke to additional gaseous product.

11. The process of claim 9, wherein said additional vaporous product comprises normally liquid hydrocarbon products having a reduced heavy metals content.

12. The process of claim 10, wherein said additional gaseous product is a hydrogen-containing gas.

13. The process of claim 9, wherein said gasification zone is maintained at a temperature between l,l00 and 1,400 F.

14. The process of claim 9, wherein said gasification zone is maintained at a pressure between 0 and 150 15. The process of claim 9, wherein a portion of the coke containing alkali metal compound is passed from the coking zone to a heating zone maintained at a temperature of at least about 1 ,250 F. and a portion of the heated coke containing alkali metal compound is recycled to the coking zone to provide a portion of the heat needed in the coking zone.

16. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium silicate. t

1.7. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium hydroxide.

18. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium carbonate.

19. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium sulfide.

20. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is cesium carbonate.

21. The process of claim 9, wherein said coking zone is a fluid coking zone.

22. The process of claim 9, wherein said coking zone is a delayed coking zone.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 Dated Agril 9, 1974 Inventor s) Glen P Hamner It is certified thet error appears in the above-identified patent and that said Letters Patent are hereby ccutrected as shown below:

On top page of the patent change "Filed: April. l9, 1972" to read "Filed: June 19, 1972--.

Signed andv sealed this 3rd day of September 1974.

(SEAL) Attest:

c. MARSHALL DANN MCCOY M. GIBSON JR.

Commissioner of Patents Attesting Officer FORM PC4050 (1M9) Q USCOMM-DC wan-pan ".5. GOVERNMENT PRINTING OFFICE 1 IQ. O-JI-Jl

Claims

2. The process of claim 1, wherein said gasification zone is maintained at a temperature between about 1,100* and 1,400* F.
3. The process of claim 1, wherein said gasification zone is maintained at a pressure between about 0 and 150 psig.
4. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium silicate.
5. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium carbonate.
6. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium hydroxide.
7. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is potassium sulfide.
8. The process of claim 1, wherein the alkali metal compound mixed with said heavy mineral oil is cesium carbonate.
9. A catalytic process for steam gasifying coke, which comprises: a. mixing a heavy mineral oil having a Conradson carbon residue of at least 5 wt. % with an alkali metal compound and coking the mixture in a coking zone maintained at a temperature between about 750* and 1,150* F. and at a pressure between about 5 and 150 psig to produce a vaporous product and coke containing an alkali metal compound; b. passing at least a portion of said coke containing the alkali metal compound to a separate gasification zone maintained at a temperature between about 1,000* and 1,500* F. to contact steam introduced into said gasification zone and thereby convert at least a portion of said coke to a gaseous product and to obtain a partially gasified coke containing an alkali metal compound; c. passing said partially gasified coke containing the alkali metal compound directly to the coking zone of step (a) as a separate stream from said mineral oil; d. coking an additional portion of said heavy mineral oil in said coking zone whereby a portion of said additional heavy mineral oil is converted to additional vaporous product and to additional coke which deposits on the partially gasified coke containing the alkali metal compound, and e. recovering the additional vaporous product.
10. The process of claim 9, wherein a portion of the coke containing alkali metal compound of step (d) is passed to the gasification zone of step (b) to convert a portion of the coke to additional gaseous product.
11. The process of claim 9, wherein said additional vaporous product comprises normally liquid hydrocarbon products having a reduced heavy metals content.
12. The process of claim 10, wherein said additional gaseous product is a hydrogen-containing gas.
13. The process of claim 9, wherein said gasification zone is maintained at a temperature between 1,100* and 1,400* F.
14. The process of claim 9, wherein said gasification zone is maintained at a pressure between 0 and 150 psig.
15. The process of claim 9, wherein a portion of the coke containing alkali metal compound is passed from the coking zone to a heating zone maintained at a temperature of at least about 1,250* F. and a portion of the heated coke containing alkali metal compound is recycled to the coking zone to provide a portion of the heat needed in the coking zone.
16. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium silicate.
17. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium hydroxide.
18. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is potassium carbonate.
19. The process of claim 9, wherein the alkali metal compound Mixed with said heavy mineral oil is potassium sulfide.
20. The process of claim 9, wherein the alkali metal compound mixed with said heavy mineral oil is cesium carbonate.
21. The process of claim 9, wherein said coking zone is a fluid coking zone.
22. The process of claim 9, wherein said coking zone is a delayed coking zone.