Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Reexamination Certificate
1999-10-28
2002-12-10
Knode, Marian C. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
C422S141000, C422S144000, C422S145000, C422S147000, C422S187000, C208S046000, C208S055000, C208S106000, C208S108000, C208S113000
Reexamination Certificate
active
06491875
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to processes and apparatus for the regeneration of particulate catalysts in a dense phase transport mode and separation of particulate catalyst from the gas stream.
BACKGROUND OF THE INVENTION
Contact between catalyst particles and gaseous reactants routinely occur in reaction vessels for production of chemicals, the conversion of hydrocarbons, or the rejuvenation of catalyst. Typically process arrangements retain the catalyst. in a fixed bed, as a semicontinuously moving bed or in a fluidized state. An increasing number of reaction arrangements are practiced or proposed for the fluidized transport and contacting of particulate catalyst with gas streams. Such processes include catalytic cracking of hydrocarbons, dehydrogenation processes, and olefin production from methanol.
In a fluidized system, catalyst particles are transported like a fluid by passing gas or vapor through the particles at a sufficient velocity to eliminate friction between the catalyst particles and to produce a desired regime of fluid behavior with the solid particles. Fluidized catalyst systems are most useful for processes that have rapid catalyst deactivation. Most of these processes rapidly lay coke down on the catalyst as a by-product of the reaction. Coke deactivates the catalyst. The fluidized transport provides the necessary high circulation of solids between a reaction zone that generates the coke and a regeneration zone that removes coke from the catalyst. High catalyst circulation, also referred to as catalyst mass flux, is a key to controlling the accumulation of coke on the catalyst. Conventional regeneration operations oxidatively combust coke from the surface of the catalyst to reduce the coke levels before returning the catalyst to the reaction zone.
The fluidized catalytic cracking of hydrocarbons is the most familiar example of a fluidized catalytic reaction system. In the FCC process, large hydrocarbon molecules associated with a heavy hydrocarbon feed are cracked, thereby producing lighter hydrocarbons. These lighter hydrocarbons are recovered as products, primarily gasoline, and can be used directly or further processed to raise the octane barrel yield relative to the heavy hydrocarbon feed. The FCC process is carried out by contacting the starting material—whether it be vacuum gas oil, reduced crude, or another source of relatively high boiling hydrocarbons—with a catalyst made up of a finely divided or particulate solid material. Contact of the oil with hot fluidized catalyst catalyzes the cracking reaction. During the cracking reaction, coke deposits on the catalyst. Coke is comprised of hydrogen and carbon and can include other materials in trace quantities such as sulfur and metals that enter the process with the starting material. Coke interferes with the catalytic activity of the catalyst by blocking active sites on the catalyst surface where the cracking reactions take place.
The basic equipment or apparatus for the fluidized catalytic cracking of hydrocarbons has been in existence since the early 1940's. The basic components of the FCC process include a reactor, a regenerator, and a catalyst stripper. The reactor includes a reaction zone where the hydrocarbon feed is contacted with a particulate catalyst and a separation zone where product vapors from the cracking reaction are separated from the catalyst. Further product separation takes place in a catalyst stripper that receives catalyst from the separation zone and removes entrained hydrocarbons from the catalyst by countercurrent contact with steam or another stripping medium. The stripping medium displaces hydrocarbon vapor from the interstitial space between catalyst particles and from the internal pore volume of the catalyst particles. Catalyst is traditionally transferred from the stripper to a regenerator for purposes of removing the coke by oxidation with an oxygen-containing gas. An inventory of catalyst having a reduced coke content relative to the catalyst in the stripper, hereinafter referred to as regenerated catalyst, is collected in the regeneration zone for return to the reaction zone.
Oxidizing the coke from the catalyst surface releases a large amount of heat, a portion of which escapes the regenerator with gaseous products of coke oxidation generally referred to as flue gas. The balance of the heat leaves the regenerator with the regenerated catalyst. The fluidized catalyst is continuously circulated from the reaction zone to the regeneration zone and then is circulated again to the reaction zone. The fluidized catalyst, as well as providing a catalytic function, acts as a vehicle for the transfer of heat from the regeneration zone to the reaction zone. Catalyst exiting the reaction zone is spoken of as being spent, i.e., partially deactivated by the deposition of coke upon the catalyst. Specific details of the various contact zones, regeneration zones, and stripping zones along with arrangements for conveying the catalyst between the various zones are well known to those skilled in the art.
The rate of conversion of the feedstock within the reaction zone is controlled by regulation of the temperature of the catalyst, activity of the catalyst, quantity of the catalyst (i.e., catalyst-to-oil ratio) and contact time between the catalyst and feedstock. The most common method of regulating the reaction temperature is by regulating the rate of circulation of catalyst from the regeneration zone to the reaction zone which simultaneously produces a variation in the catalyst-to-oil ratio as the reaction temperatures change. That is, if it is desired to increase the conversion rate, an increase in the rate of flow of circulating fluid catalyst from the regenerator to the reactor is effected. As a result, the rate of catalyst circulation through the regeneration zone varies throughout the routine operation of the process.
Separate and distinct separation systems are used to separate gases from particles on both the reaction and regeneration sides of the process. Each system will use a two-stage separation with a first initial disengagement stage that separates most of the particles from the gas and a secondary separation stage that further reduces the particulate levels in the gas stream.
After particulate removal, the cracked hydrocarbons of the FCC reaction are recovered in vapor form and transferred to product recovery facilities. These facilities normally comprise a main column for cooling the hydrocarbon vapor from the reactor and recovering a series of heavy cracked fractions which usually include bottom materials, cycle oil, and heavy gasoline. Lighter materials from the main column enter a concentration section for further separation into additional product streams. The heaviest fraction of the separated hydrocarbon vapors will contain any residual particulate material that enters with the incoming vapors. Thus, particulate material that is not recovered by the separation systems of the reactor may still be readily recovered downstream in the heaviest hydrocarbon fractions.
Following separation of particulate material in the regeneration zone, flue gases undergo appropriate treatment for removal of pollutants such as sulfur and nitrogen compounds and particulate material and are then discharged to the atmosphere. Therefore, recovering as much particulate material as possible from the flue gas is especially important on the regenerator side of the process to avoid discharge of particulate material to the atmosphere and to reduce downstream treatment costs for the flue gas. The minimization of catalyst particle carryover has become of increasing concern due to environmental restrictions on the discharge of particulate materials. Consequently, all commercially practiced separation systems for regenerators rely exclusively on a two-stage cyclone system for removing the fine particles of entrained catalyst from the gases before the gases exit the system. As a result, a firmly entrenched practice has evolved wherein two stages of cyclone separators are used
Knode Marian C.
Paschall James C.
Rudnick Douglas W.
Tolomei John G.
UOP LLC
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