To determine the amount of liquid to be vaporized by the stripping steam in the bottom of the tower, it is necessary to construct the flash curve of this liquid (called the initial bottoms). The flash curve of the reduced crude can be constructed from the flash curve of the whole crude.9 It is assumed that the initial bottom is flashed in the presence of stripping steam at the pressure existing on top of the stripping plate and at the exit temperature of liquid from this plate.
Approximately 50-60% of the crude is vaporized in the flash zone of the atmospheric tower. The unvaporized crude travels down the stripping section of the tower, containing four to six plates, and is stripped of any remaining low-boiling distillates by superheated steam at 600°F. The steam rate used is approximately 5-101b/bbl of stripped product. The flash point of the stripped product can be adjusted by varying stripping steam rate.
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