FCC spent catalyst distributor

Details FCC spent catalyst distributor FCC spent catalyst distributor

2000-11-21

2004-10-26

Silverman, Stanley S. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Regenerating or rehabilitating catalyst or sorbent

Gas or vapor treating

C502S034000, C502S039000

Reexamination Certificate

active

06809054

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the dispersing of fluidized solids into a vessel. More specifically, this invention relates to a method and apparatus for distributing a stream of spent fluidized cracking catalyst particles into a regenerator for carbon removal.
2. Description of the Prior Art
There are a number of continuous cyclical processes employing fluidized solid techniques in which carbonaceous materials are deposited on the solids in a contacting zone and the solids are conveyed during the course of the cycle to another zone where carbon deposits are at least partially removed by combustion in an oxygen-containing medium. The solids from the latter zone are subsequently withdrawn and reintroduced in whole or in part to the contacting zone.
One of the more important processes of this nature is the fluid catalytic cracking (FCC) process for the conversion of relatively high boiling point hydrocarbons to lighter boiling hydrocarbons in the heating oil or gasoline (or lighter) range. In the FCC process, hydrocarbon feed is contacted in one or more reaction zones with a particulate cracking catalyst maintained in a fluidized state under conditions suitable for the conversion of hydrocarbons. The heavy hydrocarbons in the feed crack to lighter hydrocarbons. During cracking carbonaceous hydrocarbons or “coke” deposit on the catalyst to yield “coked” or “spent” catalyst. The cracked products are then separated from the coked catalyst. The coked catalyst is then stripped of volatiles, usually by steam, and then is regenerated in a catalyst regenerator. In the regenerator, the coke is burned from the catalyst with oxygen containing gas, usually air. Flue gas formed by burning the coke in the regenerator may be treated for removal of particulates and conversion of carbon monoxide, after which the flue gas is normally discharged into the atmosphere.
Emphasis on the environmental importance of reduced NO
x
formation in flue gas has prompted much work in various areas. NO
x
, or oxides of nitrogen, comes mainly from the oxidation of nitrogen compounds in the hydrocarbon feed, with perhaps some slight additional nitrogen fixation, or conversion to NO
x
of nitrogen in regenerator air.
Although all FCC regenerators produce some NO
x
, the problem is more severe in bubbling bed regenerators, as opposed to high efficiency regenerators. High efficiency regenerators burn most of the coke in a fast-fluidized bed coke combustor. Such regenerators have few poorly fluidized regions. Bubbling bed regenerators may have poorly fluidized regions and will have large bubbles of air passing through the bed, leading to localized areas of high oxygen concentration. Although the reasons for the different NO
x
emissions in these two types of regenerators are perhaps not completely understood, all agree that NO
x
emissions are usually significantly higher, frequently twice as high, from bubbling bed regenerators.
One area of work on NO
x
reduction pertains to flue gas treatment methods that are isolated from the FCC process unit. With flue gas treatment, it is known to react NO
x
in flue gas with NH
3
. NH
3
is a selective reducing agent, which does not react rapidly with the excess oxygen, which may be present in the flue gas. Two types of NH
3
processes have evolved—thermal and catalytic. Thermal processes, such as the Exxon Thermal DENOX process, generally operate as homogeneous gas-phase processes at very high temperatures, typically around 840° to 1040° C. The catalytic systems that have been developed operate at much lower temperatures, typically at 150° to 450° C. These temperatures are typical of flue gas streams. Unfortunately, the catalysts used in these processes are readily fouled, or the process equipment plugged, by catalyst fines that are an integral part of FCC regenerator flue gas. U.S. Pat. No. 521,389 and U.S. Pat. No. 434,147 disclose adding NH
3
to NO
x
-containing flue gas to catalytically reduce the NO
x
to nitrogen. U.S. Pat. No. 5,015,362 taught reducing NO
x
emissions by contacting flue gas with sponge coke or coal, and a catalyst effective for promoting reduction of NO
x
in the presence of such carbonaceous substances.
Flue gas treatment methods are effective, but the capital and operating costs are high. Therefore, the alternative areas within the FCC process unit itself should be examined, which include feed treatment, catalytic approaches, and process approaches.
First, some refiners now go to the expense of hydrotreating feed. This is usually done more to meet sulfur specifications in various cracked products, or a SO
x
limitation in regenerator flue gas rather than a NO
x
limitation. Hydrotreating will reduce to some extent the nitrogen compounds in FCC feed, and this will help reduce the NO
x
emissions from the regenerator. Again, there is typically a high cost for this procedure and it can usually only be justified for sulfur removal.
Second, there are catalytic approaches to NO
x
control. These approaches are generally directed at special catalysts which promote CO afterburning, but which do not promote formation of as much NO
x
. U.S. Pat. Nos. 4,300,997 and 4,350,615 are both directed to use of a Pd—Ru CO-combustion promoter. The bimetallic CO combustion promoter is reported to do an adequate job of converting CO to CO
2
, while minimizing the formation of NO
x
. U.S. Pat. No. 4,199,435 suggests steam treating a conventional metallic CO combustion promoter to decrease NO
x
formation without impairing too much the CO combustion activity of the promoter. U.S. Pat. No. 4,235,704 indicates too much CO combustion promoter causes NO
x
formation, and calls for monitoring the NO
x
content of the flue gases, and adjusting the concentration of CO combustion promoter in the regenerator based on the amount of NO
x
in the flue gas. As an alternative to adding less CO combustion promoter, the patent suggests deactivating it in place, by adding something to deactivate the Pt, such as lead, antimony, arsenic, tin or bismuth. U.S. Pat. No. 5,002,654 taught the effectiveness of a zinc-based additive in reducing NO
x
. Relatively small amounts of zinc oxides impregnated on a separate support having little or no cracking activity produced an additive which could circulate with the FCC equilibrium catalyst and reduce NO
x
emissions from FCC regenerators. U.S. Pat. No. 4,988,432 taught the effectiveness of an antimony-based additive at reducing NO
x.
However, many refiners are reluctant to add additional metals to their FCC units out of environmental concerns. One concern is that some additives, such as zinc, may vaporize under some conditions experienced in FCC units. Many refiners are concerned about adding antimony to their FCC catalyst inventory. Such additives would also add to the cost of the FCC process and would dilute the FCC equilibrium catalyst to some extent.
Thirdly and finally, there are process approaches. Process modifications are suggested in U.S. Pat. Nos. 4,413,573 and 4,325,833 directed to two-and three-stage FCC regenerators, which reduce NO
x
emissions. U.S. Pat. No. 4,313,848 teaches countercurrent regeneration of spent FCC catalyst, without backmixing, to minimize NO
x
emissions. U.S. Pat. No. 4,309,309 teaches adding a vaporizable fuel to the upper portion of a FCC regenerator to minimize NO
x
emissions. Oxides of nitrogen formed in the lower portion of the regenerator are reduced in the reducing atmosphere generated by burning fuel in the upper portion of the regenerator. U.S. Pat. No. 4,542,114 minimized the volume of flue gas by using oxygen rather than air in the FCC regenerator, with consequent reduction in the amount of flue gas produced.
In U.S. Pat. No. 4,828,680, NO
x
emissions from a FCC unit were reduced by adding sponge coke or coal to the circulating inventory of cracking catalyst. The carbonaceous particles selectively absorbed metal contaminants in the feed and reduced NO
x
emissions in certain instances. Many refiners are reluctant to add coal or coke to their FCC u

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