US3592762A

US3592762A - Method for detecting coke build-up in fluid coker outlets and method for removing said coke

Info

Publication number: US3592762A
Application number: US842211A
Authority: US
Inventors: Don E Blaser; William E Heck
Original assignee: Exxon Research and Engineering Co
Current assignee: Phillips Petroleum Co; ExxonMobil Technology and Engineering Co
Priority date: 1969-07-16
Filing date: 1969-07-16
Publication date: 1971-07-13
Anticipated expiration: 1988-07-13
Also published as: CA936819A; JPS506001B1

Abstract

COKE BUILD UP IN A CYCLONE OUTLET IN A FLUID COKING PROCESS IS DETECTED BY MEASURING THE PRESSURE DIFFERENTIAL BETWEEN THE INLET TO THE CYCLONE AND THE DIPLEG OF THE SAME CYCLONE. WHEN THE PRESSURE DIFFERENTIAL THUS MEASURED EXCEEDS A PREDETERMINED POINT, TH E INSTRUMENTATION IS CUT OFF AND A FLUIDIZING GAS IS INTRODUCED TO THE DIPLEG TO INCREASE COKE FLOW THROUGH THE CYCLONE OUTLET AND SCOUR OFF THE COKE DEPOSITED THEREON.

Description

July 13, 1971 BLASER ETAL 3,592,762

METHOD FOR DETECTING COKE BUILD-UP IN FLUID COKER OUTLETS AND METHOD FOR REMOVING SAID COKE Filed July 16, 1969 2 Sheets-Sheet 1 9 .CONVERS|ON VWSCRUBBER I PRODUCTS I 3 CYCLONE /0UTLETS FLUIDIZING GAS HEATED 'RESIDUAL COKE OIL FIG. I.

GAS INVENTORS N E. al Asr r H K COOL COKE BY ATTORNEY July 13, 1971 BLASER ETIAL 3,592,762

METHOD FOR DETECTING COKE BUILD-UP IN FLUID COKER OUTLETS AND METHOD FOR REMOVING SAID COKE Filed July 16, 1969 2 Sheets-Sheet 2 CYCLONE OUTLETS CONVERSION PFODUCTS GAS - RESIDUAL OIL GAS INVENTORS DON E. BLASER United States Patent Int. Cl. (110g 9/32 US. Cl. 208-127 7 Claims ABSTRACT OF THE DISCLOSURE Coke build up in a cyclone outlet in a fluid coking process is detected by measuring the pressure differential between the inlet to the cyclone and the dipleg of the same cyclone. When the pressure differential thus measured exceeds a predetermined point, the instrumentation is cut off and a fluidizing gas is introduced to the dipleg to increase coke flow through the cyclone outlet and scour off the coke deposited thereon.

BACKGROUND OF THE INVENTION This invention relates to the coking of heavy oils in a fluidized solids system. More particularly it relates to a method for detecting coke build up in individual fluid coker reactor cyclone gas outlets and to means for scouring the coke so built up.

Experience has shown that coke deposits in the cyclones can be removed onstream by raising the dense bed level, thereby partially flooding the cyclones and causing a high carryover of coke particles from the cyclone through the cyclone outlet, thereby scouring the deposited coke from the cyclone outlet. This procedure is not recommended for two reasons. The cyclone outlet which is least coked is eroded before the cyclone outlet which is most coked is cleaned. There is also a danger of increasing the carryover of coke to the extent that the slurry system is plugged.

SUMMARY OF THE INVENTION It has now been found that any given cyclone in which coke has built up in the outlet can be determined and the coke scoured free. The differential pressure between the cyclone inlet and the dipleg or body is measured. The cyclone in which coke has preferentially built up will have a lower pressure drop than the other cyclones. The pres sure differential indicator is blocked off and a fluidizing gas such as natural gas, nitrogen or steam is admitted to the dipleg of the offending cyclone whereby the amount of coke discharged with the vapor through the cyclone outlet is increased so as to scour the coke from the outlet.

The offending cyclone can also be located by measuring the differential pressure between the cyclone outlet or scrubber and the cyclone body or dipleg top. In this case the greater pressure differential indicates the coked outlet. If desired both methods can be employed simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS Reference to the attached drawings will serve to make this invention clear. FIG. 1 illustrates a preferred modification of this invention and FIG. 2 illustrates an alternate embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Illustrated by FIG. 1 is a fluid coking vessel 1 for pyrolytically converting heavy oils. A fluid bed of solids, e.g. coke of 40 to 1000 microns in size, having an upper level L is maintained in the vessel by admitting a fluidizing gas, e.g. steam, to the base of the vessel by line 2 in amounts sufficient to obtain superficial fluidizing gas velocities in the coker 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 3 in amounts suflicient to maintain a coking temperature in the range of 900 to 1200 F. 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 4 and is circulated to an external heating zone to be reheated.

The feed, e.g. a residual oil, is injected into the coker via line 5. Vaporous conversion products are passed through a plurality of cyclones 6 to remove entrained solids which return to the coker through diplegs 7. The solids-free vapors leave the cyclones through lines 8 and pass into scrubber 9 and are removed overhead therefrom through line 10.

To detect the onset of coke build-up in the cyclone outlets a pressure tap 11 is connected to the coker at point A near the inlets 12 of the cyclones and

other pressure taps

13a and 13b are connected to each cyclone dipleg 7 at point B. These taps connect with a pressure differential indicating means 15. The pressure drop between point A, the cyclone inlet, and point B, the cycle dipleg, will show which cyclone outlet is severely coked when the difference in pressure drop between the cyclones reaches a predetermined point. After it has been determined that a cyclone outlet is coking the pressure differential indicator is blocked off and a fluidizing gas such as natural gas is admitted to the dipleg of that cyclone through line 16. This results in disrupting the flow of coke through the dipleg and causing it to be carried out with the coker gas flowing through line 8 thus scouring the deposited coke from the cyclone outlet.

FIG. 2 is identical with FIG. 1 except that line 11 is connected to vessel 1 at a point C adjacent the cyclone outlets. In this manner the differential pressure between the cyclone outlet and the top of the cyclone dipleg is measured. In this case the greater pressure differential indicates the coked outlet.

In the third embodiment FIG. 1 and FIG. 2 are combined and pressure taps are used at points A, B and C simultaneously.

EXAMPLE A fluid coker contains 300 tons of particulate coke of a particle size in a range of 40 to 800 microns, 250 microns median particle size. The bed was maintained at a temperature of 950 F. Natural gas was admitted to the base of the vessel in amounts sufficient to maintain a superficial fluidizing gas velocity of 1.5 ft./sec. The fluid bed had a total height of 63 ft. The pressure at the inlet to the cyclones was 12 p.s.i.g. A pressure tap (point B) was located in the cyclone dipleg 3.0 ft. above the bottom and a corresponding pressure tap (point A) was located on the coker at a point near the cyclone inlets. A third .pressure tap (point C) was located at a point near the cyclone outlets.

A residual oil of a gravity of 42 API, an initial boiling point of 1000 F. and a 24 wt. percent Conradson carbon was injected into the fluid bed at a rate of 0.5 lbs./ lb. of solids. Solids, heated to a temperature of 1125 F. were supplied to the coker at a rate of 26 tons/min. to maintain coking temperature.

Upon injection of the feed the pressure differential between points A and B was 0.5 psi. while that between points B and C was 1.8 psi.

It has been found empirically for this particular coking apparatus and these coking conditions that if the difference in pressure diflerential between the various cyclones is greater than 0.1 psi, then the outlet of the cyclone with the lower pressure differential is preferentially coked. When this happens the pressure differential indicator is blocked off and natural gas is introduced to the dipleg of the offending cyclone where the coke entrained in the outlet gas is increased to such an extent that the coke is scoured from the outlet.

Modifications of this invention will be apparent to those skilled in the art. For example, it may be desirable to have all or a part of the pressure measuring means located within the coking vessel 1. More than one measuring means can be used to determine the pressure drop in each cyclone.

In summary it can be seen that this invention proposes a method for detecting when a cyclone outlet to a coking vessel is coking up. This method comprises measuring the pressure drop between the inlet to each cyclone in a coking vessel and the dipleg of that cyclone. With this arrangement a change in the pressure differential obtained is indicative of increased coking in the outlet of the particular cyclone involved. The outlet is then scoured free of coke by admitting natural gas to the dipleg so as to increase the amount of coke in the outlet gas, causing the deposited coke in the outlet to be scoured out.

The nature of the present invention having thus been fully described and illustrated and specific examples of the same given, what is claimed as new, useful and unobvious and desired to be secured by Letters Patent is:

1. An improved process for coking heavy oils at coking temperature with a coking bed of fluidized solids whereby said heavy oil is converted into vapors and residue most of which residue is deposited on said solids, which comprises passing said vapors containing finely divided solids and the remaining residue through a plurality of gas-solids separation zones to remove the solids therefrom, each of said separators having a vapor inlet, a vapor outlet and a column for returning solid to said fluid bed, withdrawing the vapors and residue from said gas-solids separation zone through the said vapor outlet whereby coke builds up on said outlet, and returning the solids to said fluidized bed through said column, maintaining a pressure differential indicating means connected to said column and said vapor inlet, determining the pressure differential between the said inlefand said column, blocking off said pressure differential indicating means from the column of any individual gas-separating means when the said pressure differential decreases below a predetermined amount and introducing a fluidizing gas into said column whereby coke is entrained in said vapor and acts to scour deposited coke from said vapor outlet.

2. An improved process for coking heavy oils at coking temperature with a coking bed of fluidized solids whereby said heavy oil is converted into vapors and residue most of which residue is deposited on said solids, which comprises passing said vapors containing finely divided solids and the remaining residue through a plurality of gassolids separation zones to remove the solids therefrom, each of said separators having a vapor inlet, a vapor outlet and a column for returning solid to said fluid bed, withdrawing the vapors and residue from said gas-solids separation zone through the said vapor outlet whereby coke builds up on said outlet, and returning the solids to said fluidized bed through said column, maintaining a pressure differential indicating means connected to said column and said vapor outlet, determining the pressure differential between the said outlet and the said column, blocking off said pressure differential indicating means from the column of any individual gas-separating means when the said pressure differential increases above a predetermined amount and introducing a fluidizing gas into said column whereby coke is entrained in said vapor and acts to scour deposited coke from said vapor outlet.

3. An improved process for coking heavy oils at coking temperature with a coking bed of fluidized solids whereby said heavy oil is converted into vapors and residue most of which residue is deposited on said solids, which comprises passing said vapors containing finely divided solids and the remaining residue through a plurality of gas- 4 1 solids separation zones to remove the solids therefrom, each of said separators having a vapor inlet, a vapor outlet and a column for returning solid to said fluid bed, withdrawing the vapors and residue from said gas-solids separation zone through the said vapor outlet whereby coke builds up on said outlet, and returning the solids to said fluidized bed through said column, maintaining pressure differential indicating means connected to said column and said vapor inlet and to said column and said vapor outlet, determining the pressure differentials between the said inlet and said column and said outlet and said column, blocking off said pressure differential indicating means from the column of any individual gas-separating means when the said pressure differential between the said inlet and the said column decreases below a predetermined amount and when the said pressure differential between the said outlet and the said column increases above a predetermined amount and introducing a fluidizing gas into said column whereby coke is entrained in said vapor and acts to scour deposited coke from said vapor outlet.

4. A coking apparatus comprising a vessel, a fluid bed of solid particles in said vessel, means for introducing feed to be coked into said fluid bed, means for introducing fluidizing gas into said vessel, means in said vessel for separating vaporous conversion products from entrained particles coming from said fluid bed, said last named means having inlets for admitting said vapors containing entrained particles means for returning solids to said fluid bed and outlets for solid-free vapors, and means for determining the pressure differential betwen said inlets and said means for returning solids to said fluid bed.

5-. A coking apparatus comprising a vessel, a fluid bed of solid particles in said vessel, means for introducing feed to be coked into said fluid bed, means for introducing fluidizing gas into said vessel, means in said vessel for separating vaporous conversion products from entrained particles coming from said fluid bed, said last named means having inlets for admitting said vapors containing entrained particles means for returning solids to said fluid bed and outlets for solid-free vapors, and means for determining the pressure differential between said outlets and said means for returning solids to said fluid bed.

6. A coking apparatus comprising a vessel, a fluid bed of solid particles in said vessel, means for introducing feed to be coked into said fluid bed, means for introducing fluidizing gas into said vessel, cyclones in said vessel having inlets for admitting vapors containing entrained solids, outlet for removing vapors free from solids, and diplegs extending into said fluid bed for returning solid particles to said fluid bed and means for determining the pressure differential between said inlets and said diplegs.

7. A coking apparatus comprising a vessel, a fluid bed of solid particles in said vessel, means for introducing feed to be coked into said fluid bed, means for introducing fluidizing gas into said vessel, cyclones in said vessel having inlets for admitting vapors containing entrained solids, outlet for removing vapors free from solids, and diplegs extending into said fluid bed for returning solid particles to said fluid bed and means for determining the pressure differential between said inlets and said diplegs and between said outlets and said diplegs.

References Cited UNITED STATES PATENTS 2,549,117 4/1951 Nelson 208-48 2,763,601 9/1956 Martin et a1. 208-48 2,906,792 9/1959 Kilpatrick 208-48 2,943,993 7/1960 Sykes 208--48 HERBERT LEVINE, Primary Examiner U35. C1.X.R. 20848; 23284