Process for withdrawing catalyst particles from a reaction zone

Claim 1

A process for progressively withdrawing catalyst from a catalyst bed contained in a substantially vertical, elongate and cylindrical reaction zone during the catalytic treatment therein of a fluid charge, said catalytic treatment comprising: (a) progressively circulating the catalyst downwardly through the reaction zone, counter-currently with said charge, while maintaining said catalyst in the reaction zone by support means of a shape adapted to correspond substantially to a section of the reaction zone, said support means being provided at the lower part of the reaction zone, (b) periodically or continually fluidizing the lower part of the catalyst bed and progressively discharging the catalyst from the reaction zone through at least one withdrawal duct extending from the lower part of the reaction zone, and (c) upwardly circulating the fluid charge formed of a liquid and a gas, by first introducing the major part of the charge in the lower part of the reaction zone, by injecting the major part of the gaseous phase of the charge into the catalyst bed through a plurality of holes provided in said support means and by introducing a major part of the liquid phase of the charge into the catalyst bed through a plurality of substantially vertical pipes, the lower end of each pipe dipping from the bottom of the reaction zone into said liquid charge and the upper end of each pipe opening above said support means, the process for withdrawing the catalyst particles comprising: moving at least a portion of the catalyst said particles through at least one flared zone shaped as an inverted cone or a pyramid, whose vertical axis substantially coincides with the axis of a substantially vertical withdrawing duct, said flared zone being discontinuous and formed of a plurality of elongate and narrow members each shaped as a substantially triangular or trapezoidal strip, the axes of the strips of a given flared zone substantially converging towards the substantially vertical axis of a given withdrawing duct, so as to induce, inside the one or more flared zones, the motion of the catalyst particles towards at least one of said withdrawing ducts, and an angle (α) being about from 30°-70°, said angle α being defined as the angle of the axis of one of said withdrawing ducts with either (i) a generatrix of the cone frustrum when the flared zone is frustroconical or (ii) with one edge of the pyramid when the flared zone is pyramidal, in order to orient the assembly of catalyst particles towards a withdrawing duct and to move towards a withdrawing duct the catalyst particles which have passed below said flared zone, between said strips, and thus to prevent accumulations of particles which might be formed between said support means and said strips, fluidizing the catalyst particles in the lower part of the reaction zone and above the support means by injecting through said catalyst bed support means the liquid and gaseous charge, the pressure drop for the gases, through the support means ranging from 0.1 to 1.5 kgf/cm 2 , each of said ducts for introducing the liquid phase being substantially discontinuous over at least a portion of said duct dipping into the liquid at the bottom of the reactor.