| 摘要 |
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 which results in a fast, efficient separation of reactive hydrocarbons from spent catalyst. At the same time vapors from the stripper and catalyst are separated by gravity and inertia in the large diameter separation vessel so that stripper vapors 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 rarefield 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 DEG 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 solid content and fractionator bottoms). These product improvements are respectively due to reduced residence time of hydrocarbon vapor with spent catalyst, which produces undesirable secondary cracking, and reduces catalyst entrainment and carryover with the hydrocarbon vapor, which adds solids to the product fluids.
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