Method for vapor recovery for fluidized catalytic cracking processes

Abstract

A vapor recovery shroud of relatively small size is positioned in a large diameter catalyst disengaging vessel of a fluid catalytic cracking system so that vapor released directly from the riser reactor pipe must execute a reversal of flow direction to enter the vapor recovery shroud. At the same time catalyst and vapors from the stripper are separated by gravity and inertia in the large diameter separation vessel so that stripper vapors may also vent through the vapor recovery shroud. Vapor is vented from the vapor recovery shroud through cyclone means confined within the disengaging vessel. Preferably, the inlet to the vapor recovery shroud is located adjacent to the riser reactor outlet because this location is the most rarefied in catalyst density and provides the shortest path for hydrocarbon vapors to exit the hot separation vessel and enter a distillation system. Desirably, the vapor recovery shroud closely surrounds the primary vapor release point from the riser reactor pipe, so that essentially all the vapor must execute a 180.degree. turn to enter the vapor recovery zone. Such a position produces the combined improvements of product yield (less gas and coke, more gasoline and light cycle oil) and product quality (less ash content). These product improvements are respectively due to reduced residence time of hydrocarbon vapor with spent catalyst, which produces undesirable secondary cracking, and reduced catalyst carryover, which adds solids to the product fluids.