| abstract |
A high efficiency FCC process obtains the necessary regenerated catalyst temperature for a principally thermal cracking stage by cracking a light feedstock such as naphtha or a middle distillate in a first riser that principally performs thermal cracking and then cracks a heavy FCC feed in a second riser with a blend of catalyst from the principally thermal cracking step and recycle catalyst from the heavy feed to provide the necessary coke content on the catalyst that will produce high regenerated catalyst temperatures. The high temperature of the regenerated catalyst in the first riser provides a convenient means of cracking naphtha under high severity conditions and then using the remaining activity of the contacted catalyst for the principally catalytic reaction of the heavier feed. A separate thermal cracked product may be recovered from an intermediate blending vessel downstream of the first riser. Alternately, the thermal products such as cracked naphtha products may remain with the effluent from the second riser for separation from the heavy cracked products in a downstream separation zone. |