Expedient method for altering the yield distribution from fluid catalytic cracking units

摘要

A fluid catalytic cracking unit equipped with multiple feed injection points along the length of the riser is operated such that all of the fresh feed is charged to one of different feed injection points, depending on the ratio of light distillate (gasoline) to middle distillate (light catalytic gas oil) that is desired in the product slate. When all of the fresh feed is charged to one of the upper injection points in the riser in order to increase middle distillate yield, the unconverted slurry oil (650 DEG F.+material) can be recycled to a location below the injection point of the fresh feed so as to increase conversion to middle distillate while lowering the activity of the catalyst (via coke deposition) for single pass conversion of the fresh feed. Steam in excess of levels typically employed for dispersion is used at the bottom of the riser to lift the regenerated catalyst up to the feed injection points. Other inert gases can be used in place of, or in conjunction with steam to accomplish lifting of catalyst in the riser.