Mineral oils: processes and products – Chemical conversion of hydrocarbons – Cracking
Patent
1998-08-19
2000-08-08
Griffin, Walter D.
Mineral oils: processes and products
Chemical conversion of hydrocarbons
Cracking
20812001, 208153, 422139, 422144, 422145, C10G 1114, B01J 818
Patent
active
060997206
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a fluid catalytic cracking (FCC) process for a hydrocarbon feed in a reaction zone where the feed circulates from top to bottom (dropper).
One of the major problems encountered by the refiner is that of optimizing the production of gasoline along with increased production of light C.sub.3 olefins. Technological modifications to riser FCC units consist of reducing the residence time in the catalytic zone to bring such values to less than 0.5 s, essentially by an increase in the rate of circulation of the feed and the catalyst. Combined with an increase in the reaction temperature, such a reduction in the residence time encourages primary cracking reactions to the detriment of consecutive hydrogen transfer and secondary cracking reactions.
In a further technological modification along the same lines, back-mixing, which is a characteristic of riser units, is reduced by using a dropping co-current of gas and catalyst. In this type of flow the radial concentration and flow rate profiles are "flatter", and so approach "piston" flow which is well known to encourage gasoline selectivity and to reduce secondary cracking reactions.
The major problem with this type of reactor concerns the intimate contact between the hot regenerated catalyst and the hydrocarbon feed.
U.S. Pat. No. 4,919,898 describes the formation of a falling curtain of catalyst from rectangular openings provided in a bed pressurized by steam. Such a bed is regulated by the pressure difference between the vessel containing the pressurized bed and a chamber for mixing catalyst and feed downstream of the bed.
That patent also describes injection of the feed in the direction of the valve forming the curtain.
Operating a pressurization system on an industrial scale is difficult because there is a very large variation in flow rate for a very small pressure variation, which can result in an unstable solid flow rate and can thus be deleterious to the selectivity towards the desired products.
U.S. Pat. No. 5,296,131 also describes an annular curtain of downward flowing catalyst. At least part of the feed is injected towards the bottom through a radial opening under the seat of a cone shaped plug valve against the upper part of the reactor.
The prior art is also illustrated by European patent application EP-A-0 209 442 which describes the presence of a valve downstream of a first fluidization ring which disturbs the fluidization conditions to cause defluidization leading to the production of a volumetric mass corresponding to a loos packed bed.
The invention aims to overcome the disadvantages of the prior art.
It has been observed that by conditioning the density of the catalyst, causing it to move in suitable geometric forms and by optimizing the zone for injecting the feed into the reaction zone, the selectivity of the cracking reaction is substantially improved.
More precisely, the invention provides a process for the fluidized bed catalytic cracking of a petroleum feed to lighter effluents in a catalytic cracking zone comprising a reaction zone or dropper, into an upper end of which, termed the injection zone, regenerated catalyst from at least one regeneration zone is introduced, the catalyst is shaped by means of a shaping means having a constriction, the catalyst is brought into contact with the feed, a downward flowing mixture of catalyst and feed is formed, and at least the majority of the feed is vaporized in said injection zone, said feed is cracked to obtain lighter effluents, the effluents are separated from the used catalyst in a separation zone at the lower end of the dropper, the effluents are recovered and the used catalyst is recycled to the regeneration zone, the process being characterized in that the regenerated catalyst from the regeneration zone is caused to flow in a dense fluidized bed catalyst conditioning zone upstream of the injection zone, the conditioning zone comprising a gas disengagement zone, the fluidization rate by a fluidization gas being in the range 0.1 to 30 cm/s, the throughput of catalyst flowi
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Bonifay Regis
Courteheuse Gerard
Del Pozo Mariano
Gauthier Thierry
Pontier Renaud
Griffin Walter D.
Institut Francais du Pe'trole
Preisch Nadine
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