FCC YIELD SELECTIVITY IMPROVEMENTS IN HIGH CONTAINMENT RISER TERMINATION SYSTEMS

Abstract

The invention provides an improved system for separation technology intended to reduce unwanted catalyst/thermal reactions by minimizing contact of the hydrocarbons and the catalyst within the reactor.

Description

BACKGROUND OF THE INVENTION

Fluidic catalytic cracker (FCC) reactor technology has evolved over the years, continuously searching to improve yield selectivity of hydrocarbons by minimizing unwanted reactions that occur outside of the FCC riser. Most FCC reactors use a catalyst which is an extremely porous powder that reacts with the hydrocarbon mixture to capture intermetal carbon and metal. In the process, the pre-heated hydrocarbon feed mixed with hot catalyst enters the reactor through one or more risers. The riser creates a fluidized bed where a concurrent upward flow of reactant gases and catalyst particles occurs. Nearly every FCC unit employs some type of separation device connected on the end of the riser which is intended to separate the bulk of the catalyst from the hydrocarbon vapors. The technology includes riser termination devices which range from providing a physical downward deflection of the catalyst as it exits the riser to directly attaching the riser outlet to sets of cyclones. The most commonly used separation devices are vortex separation systems (VSS) and vortex disengager stripper systems (VDS). The vortex separation system includes a tube with a split head located at the riser outlet to separate the mixture. The VDS system has a stripping unit at the bottom of a rough vortex evaporation system and usually forms two stage stripping.

Gases leave the reactor through the cyclones after separation from the powdered catalyst. The gas is then passed to a fractionator for separation into the product streams. The spent catalyst is commonly sent to a regenerator unit and is regenerated by combusting carbon deposits to carbon dioxide. The regenerated catalyst is returned to the reactor for further use. Separation of the gases from the catalyst is seldom totally efficient, whereas gases and catalyst may tend to recirculate in the separation device creating conditions resulting in over cracked gases and over fouling of the catalyst. The present invention provides an improved system for the VSS/VDS technology intended to reduce unwanted catalytic/thermal reactions by minimizing contact of the hydrocarbons and the catalyst outside of the riser.

SUMMARY OF THE INVENTION

This invention reduces the amount of undesired thermal and catalytic reactions occurring in FCC reactors having high containment separation systems such as the VSS/VDS. The undesired reactions are exacerbated by hydrocarbon underflow in the separation system, resulting in increased residence time between the hydrocarbon vapors and the catalyst. It is desirable to limit the time during which the hydrocarbon vapors and catalysts are intermixed. The longer the mixing time, the more potential for lower hydrocarbon yields and greater catalyst fouling. If the catalyst is too fully entrained with hydrocarbon vapors as it exits the riser and enters the separation technology, the hydrocarbon vapor will not cleanly separate from the catalyst and will carry under with the catalyst resulting in hydrocarbon underflow to the catalyst bed, leading to unwanted thermal and catalytic reactions. The present invention mitigates these unwanted reactions and improves FCC yield by minimizing hydrocarbon underflow into the separation system. In essence, the bottom of the separation system sits in a catalyst bed that prevents hydrocarbon vapor from remixing with the catalyst in the separation system. Vent tubes provide an exit path for the hydrocarbon vapor exiting the stripper to bypass the separation system and exit the reactor via the cyclones.

The cyclone operations must be carefully monitored to ensure that cyclone inlet hydrocarbons are not dragged downward by the catalytic solids. Historically, increasing the amount of catalyst inventory contained in the reaction prevents such under flow or back flow of hydrocarbon gases. However, the structures of the present invention create an environment wherein increased hydrocarbon gas yield can be associated with lesser catalyst inventory, less catalyst entrainment into the separation system and less resultant hydrocarbon underflow.

The structure of the present invention and a resulting use of decreased catalyst inventory produces evident FCC operations with less consumed energy.

IN THE DRAWINGS

FIG. 1 is a schematic of a FCC reactor incorporating a first embodiment of the present invention.

FIG. 2 is a schematic of an FCC reactor incorporating another embodiment of the invention.

FIG. 3 is a schematic of a FCC reactor incorporating yet another embodiment of the present invention.

FIG. 4 is a graphical representation of catalyst temperature response to decreased catalyst levels in the reactor.

FIG. 5 shows the results of two test runs of the present invention.

FIG. 6 is a graph of the results of varying the catalyst bed elevation for a variety of fluidized bed density levels for the test runs of FIG. 5.

FIGS. 7a-i are product yield graphs at varying catalyst bed levels in the reactor for the test runs of FIG. 5.

FIG. 8 shows the results of a third test run of the present invention on another FCC reactor at a different location.

FIG. 9 shows the dry gas and regenerator temperature shifts at varying catalyst bed levels for the test of FIG. 8.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to FIG. 1, a schematic depicting a FCC reactor incorporating a first embodiment of the invention is shown having a lowered fluidized catalyst bed 22 maintained just above the windows 32 of the separator or VSS 14. The reactor 10 includes an inlet 12 for receiving a mixture of heated crude oil and heated catalyst. The crude and catalyst mixture travels up the riser 13 during which the catalyst and crude internet and the catalyst absorbs carbon, metals, and other deleterious materials not wanted in the hydrocarbon gases. As the entrained hydrocarbon/catalyst mixture exits the riser and enters the separator 14 the catalyst will fall downward through the separator 14 while the clean hydrocarbon stream continues to rise where it is received by cyclones 16 which serve to further separate any remaining catalyst from the hydrocarbon stream. The cleansed hydrocarbon stream then exits the reactor through outlet 18 to be transferred to separation equipment, such as a fractionator. The separated catalyst located in the cyclone flows down the dipleg 20 and is reentered into the catalyst bed 22. Any hydrocarbon gases that become entrained with the falling catalyst will reenter the fluidized catalyst bed 22 for further separation and those gases will flow upwardly as shown by flow arrows H. The catalyst bed 22 is fluidized by high pressure steam being injected in the reactor 10 through steam inlet 26. The spent catalyst will exit the reactor at exit 24 and, most commonly, will be sent to a regenerator for cleansing. The regenerated catalyst is then reentered with the crude mixture at inlet 12.

The hydrocarbon gases that become entrained with the falling catalyst enter the fluidized catalyst bed and are processed until they become cleansed hydrocarbon gases. The cleansed hydrocarbon gases will rise through the separator and will be captured by the cyclones 16.

In the prior art at FCC units, not shown, there is a common effect at the lower level of the separator 14, wherein the hydrocarbon gases and catalyst recirculate above the fluidized bed 22. This recirculation creates an inefficiency in the operation of the reactor as the catalyst and hydrocarbons continue to react, resulting in decreased hydrocarbon yield and increased catalyst fouling. Increased catalyst fouling leads to increased heat expenditure when the catalyst is sent to the regenerator for cleansing. Increased regenerator temperatures create inefficiencies in the operation of the system. The present invention seeks to solve the catalyst/hydrocarbon recirculation issues in the lower portion of the separator 14.

In the prior art, not shown, the fluidized bed 22 was maintained well above the top of the separator windows 32, preferably at 180 inches water column (“IWC”). In the FIG. 1 embodiment the fluidized bed has been lowered to approximately 150 IWC and yield has been improved as exhibited in FIGS. 4-9.

The reactor of FIG. 1 is shown having the top level of the catalyst bed 22 located directly above the windows 32 of the separator 14. Referring to FIG. 3, it can be seen that when the catalyst bed level in the reactor ranges between 130 and 160 IWC or directly above the separator 14 windows 32, the catalyst temperature being delivered from the regenerator is much lower, resulting in higher efficiencies.

Referring now to FIG. 5, the yield results from two test runs of the present invention on the same FCC reactor, for the various products produced by the catalytic cracking are shown. The yield plots on the tables show total hydrocarbon production increasing or remaining stable as the result of decreased overall cracking due to the lower bed levels for the catalyst. Delta coke is also decreased indicating more valuable product being recovered. Due to increased product recovery and decreased over cracking, the reactor operations are made more efficient.

FIG. 6 graphically represents proposed more efficient operating levels for the catalyst bed elevation, using a variety of fluidized bed density levels. The most efficient operating levels range from 125 IWC for the least dense fluidized catalyst to 170 IWC for the most dense fluidized catalyst. The catalyst bed levels are optimally located just above the VSS windows 32.

FIGS. 7a-i show the product yield graphs for the tests of FIG. 5. During the first test, the reactor outlet temperature was 970° F. compared with a reactor outlet temperature of 950° F. during the second test. The difference in reactor outlet temperature is the reason for the offsets in the yields shown in FIGS. 7a-i. Again, it can be seen that lower catalyst bed levels result in increased yield and decreased temperatures.

Referring now to FIG. 2, the FCC unit is shown having the top level of the catalyst bed 22 located below the windows 32 of the separator 14. Under proper gas flow rates and hydraulic balance, hydrocarbon gases will bypass the separator 14 and exit the reactor, lowering hydrocarbon/catalyst residence time in the separator 14.

Referring now to FIG. 3, the invention provides another alternative structure to assist in the effort to separate clean hydrocarbon gases from the fluidized catalyst efficiently. The alternative structure includes a baffle member 28 positioned immediately under the separator 14. The structure allows for the optimal level for the catalyst bed 22 to be further lowered as shown. Baffle 28 prevents any fluidized catalyst from entering the separation chamber 14. Hydrocarbon gases escape the fluidized bed after residence in the stripper 15 and fluidized bed 22 through vent tubes 30 which carry the clean hydrocarbon gases directly to the upper most region of the separator, allowing those gases to be passed to the cyclones 16.

Another example of a test run of the present invention at a different location and on a different reactor from that as shown in FIG. 5 is shown in FIG. 8. The data shown in FIG. 8 and FIG. 9 proves improved yield selectivities and the dry gas and regenerator temperature shifts associated with lower catalyst inventory. The delta yields for a 26-28% lowered catalyst inventory in the reactor shows significant improvement. In both volume percent and weight percent.

The above detailed description of the present invention is given for explanatory purposes. It will be apparent to those skilled in the art that numerous changes and modifications can be made without departing from the scope of the invention. Accordingly, the whole of the foregoing description is to be construed in an illustrative and not a limitative sense, the scope of the invention being defined solely by the appended claims.

Claims

1. A process for increasing hydrocarbon yield and decreasing coke production in an FCC reactor having a separation unit, the bottom of which is spaced from a bed of fluidized catalyst wherein the catalyst bed level in the reactor is located directly above the chamber windows of the separator unit.

2. The process of claim 1 wherein the catalyst bed level falls within the range of 125 IWC to 170 IWC.

3. The process of claim 1 wherein the catalyst bed density is 32.8 lbs/ft3 at an operating level of 125 IWC at an elevation of 164 ft.

4. The process of claim 1 wherein the catalyst bed density is 36.9 lbs/ft3 at an operating level of 140 IWC at an elevation of 164 ft.

5. The process of claim 1 wherein the catalyst bed density is 41 lbs/ft3 at an operating level of 140 IWC at an elevation of 164 ft.

6. The process of claim 1 wherein the catalyst bed density is 45.1 lbs/ft3 at an operating level of 170 IWC at an elevation of 164 ft.

7. The process of claim 1 wherein the distance between the bottom of the separation unit and the top of the catalyst bed is maximized to prevent fluidized catalyst from entering the bottom of the separator unit.

8. The process of claim 1 wherein fluidized catalyst is prevented from entering the separation unit by means of a baffle member positioned between the bottom of the separation unit and the top of the fluidized bed.

9. The process of claim 1 wherein hydrocarbon gases evacuate from the fluidized bed after residence in the catalyst through at least one vent tube which carry the clean hydrocarbon gases directly to the top region of the separator unit.

10. A process for increasing hydrocarbon yield and decreasing coke production in an FCC reactor having a separation unit comprising: a bed of fluidized catalyst which is spaced apart from the separation unit;wherein the catalyst bed level in the reactor is optimized at a location immediately above the chamber windows of the separation unit;a baffle member positioned between the separation unit and the top of the fluidized bed; andat least one vent tube which carry the clean hydrocarbon gases directly to the top region of the separator unit.

11. The process of claim 10 Wherein the optimum bed level falls within the range of 130 IWC to 160 IWC.

12. The process of claim 10 wherein the catalyst bed density is 41 lb/ft3 at an operating level of 150 IWC at an elevation of 164 ft.

13. A process for increasing hydrocarbon yield and decreasing coke production in an FCC reactor having a separation unit comprising: a bed of fluidized catalyst which is spaced apart from the separation unit;wherein the catalyst bed level in the reactor is optimized at a location immediately above the chamber windows of the separation unit;at least one vent tube which carry the clean hydrocarbon gases directly to the top region of the separator unit.

14. The Process of claim 13 wherein the optimum bed level range falls within the range of 130 IWC to 160 IWC.

15. The process of claim 13 wherein the catalyst bed density is 41 lb/ft3 at an operating level of 150 IWC at an elevation of 164 ft.