Method for reducing fouling of coker furnaces

1. A method for reducing furnace fouling in a delayed coking process for producing anode or fuel grade coke wherein at least one coker feed is supplied to a delayed coking unit comprised of a coker furnace, at least two coke drums and a coker fractionator comprising

(a) increasing the aromaticity of the feed to produce a modified stream by combining with the feed upstream of the coker furnace a hydrotreated aromatic gas oil wherein the hydrotreated aromatic gas oil is formed from an unhydrotreated aromatic gas oil in a hydrotreater wherein the hydrotreater has a hydrotreater product and a hydrotreater feed, and wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about X % according to the formula

X =( A %)−[(0.02)·(hydrogen uptake in a hydrotreater)]

where X is as least about 20% as measured by 13C NMR based on the total carbon content of the hydrotreated aromatic gas oil and A is the aromaticity of a unhydrotreated aromatic gas oil as measured by 13C NMR and is at least about 40%, where hydrogen uptake is [ρ·659.5·(Δ hydrogen content (wt %) of the hydrotreater product and the hydrotreater feed)] and where ρ is the density (grams/cc) of the hydrotreater feed;

(b) introducing the modified stream into the coker furnace;

(c) heating the modified stream to a coking temperature in the coker furnace to produce a heated modified stream; and

(d) transferring the heated modified stream from the coker furnace to a coke drum.

2. The method of claim 1 wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about 50% as measured by as measured by 13C NMR based on the total carbon content.

3. The method of claim 1 wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about 60% as measured by as measured by 13C NMR based on the total carbon content.

4. The method of claim 1 wherein step (a) is carried out such that the amount of the hydrotreated aromatic gas oil is between about 1 wt % up to about 50 wt % of the modified stream.

5. The method of claim 1 wherein step (a) is carried out such that the hydrotreated aromatic gas oil is between about 20 wt % to about 40 wt % of the weight of the modified stream.

6. The method of claim 1 wherein the hydrotreated aromatic gas oil has a boiling point in a range of about 650 to about 1,000° F.

7. The method of claim 1 wherein the hydrotreated aromatic gas oil has a boiling point in a range of about 750 to about 850° F.

8. The method of claim 1 wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about 30% as measured by as measured by 13C NMR based on the total carbon content.

9. The method of claim 8 wherein the hydrogen uptake of the hydrotreated aromatic gas oil is at least about 150 SCFB.

10. The method of claim 8 wherein the hydrogen uptake of the hydrotreated aromatic gas oil is at least about 500 SCFB.

11. The method of claim 8 wherein the hydrogen uptake of the hydrotreated aromatic gas oil is at least about 1000 SCFB.

12. The method of claim 1 wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about 40% as measured by as measured by 13C NMR based on the total carbon content.

13. A method for reducing furnace fouling in a delayed coking process wherein at least one coker feed is supplied to a delayed coking unit comprised of a coker furnace, at least two coke drums and a coker fractionator comprising

(a) supplying the feed to the bottom of the fractionator to produce an overhead stream, a bottoms stream and at least one intermediate stream from the fractionator;

(b) increasing the aromaticity of the bottoms stream to produce a modified stream by combining with the bottoms stream upstream of the coker furnace a hydrotreated aromatic gas oil wherein the hydrotreated aromatic gas oil is formed from an unhydrotreated aromatic gas oil in a hydrotreater wherein the hydrotreater has a hydrotreater product and a hydrotreater feed, and wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about X % according to the formula

X =( A %)−[(0.02)·(hydrogen uptake in a hydrotreater)]

where X is as least about 20% as measured by 13C NMR based on the total carbon content of the hydrotreated aromatic gas oil and A is the aromaticity of a unhydrotreated aromatic gas oil as measured by 13C NMR and is at least about 40%, where hydrogen uptake is [ρ659.5·(Δ hydrogen content (wt %) of the hydrotreater product and the hydrotreater feed)] and where ρ is the density (grams/cc) of the hydrotreater feed;

(c) introducing the modified stream into the coker furnace;

(d) heating the modified stream to a coking temperature in the coker furnace to produce a heated modified stream; and

(e) transferring the heated modified stream from the coker furnace to a coke drum.

14. The method of claim 13 further comprising the step of adding at least a portion of at least one intermediate stream to the bottoms stream.

15. The method of claim 14 wherein the at least one intermediate stream is selected from the group consisting of a light coker gas oil stream, a heavy coker gas oil stream, and combinations thereof exiting the fractionator.

16. The method of claim 14 wherein at least a portion the at least one intermediate stream is hydrotreated.

17. A method for reducing furnace fouling in a delayed coking process for producing anode or fuel grade coke wherein at least one coker feed is supplied to a delayed coking unit comprised of a coker furnace, at least two coke drums and a coker fractionator comprising

(a) supplying the feed to the coker furnace without first passing the feed through the fractionator,

(b) increasing the aromaticity of the feed to produce a modified stream by combining with the feed upstream of the coker furnace a hydrotreated aromatic gas oil, wherein the hydrotreated aromatic gas oil is formed from an unhydrotreated aromatic gas oil in a hydrotreater wherein the hydrotreater has a hydrotreater product and a hydrotreater feed, and wherein the hydrotreated aromatic gas oil has an aromatic carbon content of at least about X % according to the formula

X =( A %)−[(0.02)·(hydrogen uptake in a hydrotreater)]

where X is as least about 20% as measured by 13C NMR based on the total carbon content of the hydrotreated aromatic gas oil and A is the aromaticity of a unhydrotreated aromatic gas oil as measured by 13C NMR and is at least about 40%, where hydrogen uptake is [ρ659.5·(Δ hydrogen content (wt %) of the hydrotreater product and the hydrotreater feed)] and where ρ is the density (grams/cc) of the hydrotreater feed;

(c) introducing the modified stream into the coker furnace;

(d) heating the modified stream to a coking temperature in the coker furnace to produce a heated modified stream; and

(e) transferring the heated modified stream from the coker furnace to a coke drum.

18. The method of claim 17 further comprising the step of combining with the feed upstream of the coker furnace at least a portion of at least one intermediate stream exiting the fractionator.

19. The method of claim 18 wherein the at least one intermediate stream is selected from the group consisting of a light coker gas oil stream, a heavy coker gas oil stream, and combinations thereof exiting the fractionator.

20. The method of claim 18 wherein at least a portion the at least one intermediate stream is hydrotreated.