Vertical Three-phase Separators Vapor Space
Allowable mass velocity, based on the full cross section of the vessel (not the circular space inside the shroud) is Gc from Equation 300-1, multiplied by a derating factor. That factor is 0.5 for hot separators in residuum desulfurizer and vacuum residuum desulfurizer plants, 0.7 for other high pressure separators in hydroprocessing plants, and 0.9 for other separators and knockout drums at pressures above 800 psig. Vessel diameter, Dimension “D” in Figure 300-7, is at least that which corresponds to the allowable mass velocity just determined. The diameter may be larger if liquid surge requirements would require an L/D ratio greater than 3.
The head is hemispherical. The vapor outlet nozzle is in the head. The demister, if used, is mounted on a baffle ring at the tangent line. The width of the ring (crosssectional area left for vapor flow through the demister) is determined by Equation 300-3. The baffle ring is at least 2 feet 0 inches above the shroud. If there is no demister, then an outlet baffle is placed on the centerline as in Figure 300-8.
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