Spent catalyst regeneration with internal and external regenerated-catalyst recycle means

#The field of art to which this invention pertains is catalyst regeneration apparatus. More specifically, the present invention relates to a regeneration apparatus which is applicable for use in regenerating fluidizable catalytic cracking catalysts which have become spent by the deposition of coke on the catalyts in a hydrocarbon reaction zone.

#In most regeneration processes presently employed the oxidation of coke from spent catalyst is done in a single-vessel regeneration apparatus containing one or more dense-phase beds of catalyst located in the bottom of the apparatus with a large dilute-phase disengaging space positioned above and in connection with the dense bed. In this type of regeneration process the dense-phase bed of catalyst is maintained in the bottom portion of the apparatus by limiting the superficial velocity of the incoming fresh regeneration gas to the transport velocity, that is, the velocity above which large amounts of catalyst would be carried out of the dense bed to the disengaging space. Typical velocities are therefore less than about 3 feet per second with 1.5 to 2.5 being the usual range. Provisions are made for recovering and returning to the dense bed any catalyst entrained in the flue gas effluent passing from the dense bed. This is generally carried out by passing this effluent flue gas containing entrained catalyt through separation means such as cyclone separation devices located in the disengaging space and returning separated catalyst to the same dense bed. Average residence time of the catalyst within the apparatus per pass through the apparatus is generally in the two to five minute range with 2 to 3 minutes being the more common, while the residence time of gas is generally withn the range of 10 to 20 seconds. All of the regenerated catalyst is returned directly from the regeneration apparatus to the hydrocarbon reaction zone without additional passes through any part of the regeneration apparatus.

#It is also general refinery practice to operate conventional regeneration apparatus in a manner to essentially preclude afterburning anywhere within the regeneration apparatus. The term "afterburning" as used herein and as generally understood by those skilled in the art shall mean the uncontrolled, unintentional, and generally incomplete oxidation of CO to CO.sub.2. Generally, afterburning occurs during periods of unsteady state operations or process "upsets". This prevention of significant afterburning is generally done by controlling the oxygen-containing gas stream introduced to such regeneration apparatus directly responsive to a rather small predetermined temperature differential between the flue gas outlet or the disengaging space and the dense bed of the regeneration apparatus. Excess oxygen within the regeneration apparatus is thus minimized thereby severely limiting CO afterburning to only that amount characterized by the small temperature differential.

#Having thus described the apparatus of my invention in brief general terms, reference is now made to the drawing depicting the side view of one embodiment of my apparatus. The drawing also indicates to those skilled in the art how an existing single-vessel regeneration apparatus of the type in common use at the present time might be modified to construct the apparatus of my invention.

#While the invention will be described in connection with a preferred embodiment, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. It will also be understood that the drawing is only shown in such detail as is necessary for an understanding of the invention and that various items such as minor valves, bleed and dispersion steam lines, expansion joints, instrumentation, and other control means have been omitted for the sake of simplicity.

#The drawing shows the apparatus of my invention which basically comprises as the largest components a spent-catalyst receiving chamber 1, a regenerated-catalyst receiving chamber 2, and a transfer conduit 3.