Process for catalytic cracking two integrated cracking zones of different degrees of severity followed by a cooling zone

Process for fluidized-bed catalytic cracking of a hydrocarbon feedstock in a rising reaction zone (1) or riser comprising the introduction (14) of a regenerated catalyst at the lower portion of the riser, the injection of the feedstock above the introduction of the catalyst, injection (5) of a fluidization gas of the catalyst at the base of the riser, whereby the reaction zone comprises in its lower portion an inner tubular zone (2) that is essentially coaxial in which a portion of the regenerated catalyst is circulated with a transport fluid that is introduced at the lower end of the tublar zone;

• and the remaining portion of the catalyst and the feedstock are circulated in an annular zone that is defined between the tubular zone and the fraction zone, whereby the process is characterized in that said portion of catalyst and the transport fluid are circulated in the tubular zone under more severe conditions of temperature and/or catalyst to transport fluid mass ratio than the conditions of temperature and/or catalyst to feedstock mass ratio that prevail in the annular zone, whereby a first flow that exits from the tubular zone and a second flow that exits from the annular zone are mixed, and the mixture that is obtained that contains the catalyst is cooled by injection (13) of an inert and vaporizable fluid at or above the injection of the feedstock;
• and the cooled mixture is cracked in the upper portion of the reaction zone wherein the upper of the tubular zone is located above the zone for injecting the feedstock and below the zone for injecting the inert fluid.