<p>Disclosed is an apparatus and process for controlling residence time in a reaction zone by adjusting the effect of reactor volume by varying the elevation of feed introduction or the space velocity in a fluidized catalytic conversion reactor. Changing effective volume results in controllable residence time and/or space velocity. The effect of reactor volume may be changed by altering the space velocity the feed distributor elevation, diluent flow rate or the number of reaction subsections to which feed is distributed.</p>
