Residence surge vessels

For surge vessels, allow 2 min liquid residence time for drawoff, use 15 min for reflux use 5 min provided this allows sufficient time for controllers to function. Total volume = 1.3 X holdup if the holdup volume is > 3 m . 

For vaporAiquid separators there is often a liquid residence (holdup) time required for process surge. Tables 1, 2, and 3 give various rules of thumb for approximate work. The vessel design method in this chapter under the Vapor/Liquid Calculation Method heading blends the required liquid surge with the required vapor space to obtain the total separator volume. Finally, a check is made to see if the provided liquid surge allow s time for any entrained water to settle. 

Operating pressure and temperature constrain practical size of vessel. Design codes for pressure vessels vary slightly with the country. In general, for operating pressures >10 MPa, vessel volume usually <1 m Pressure decreases as temperatures exceed 250°C. For temperatures above 350°C, consider carbon/molybdenum, and for temperatures >500°C, consider austenitic steels. Corrosion allowance 1.5 mm for corrosion rates 0.08 mm/a 3 mm for rates 0.09 to 0.3 nun/a 4.5 nun for 0.31 to 0.4 mm/a 6 mm for >0.4 mm/a. If pressure <400 kPa, use L/D of 2 to 3 1. For pressures >400 kPa, use L/D of 4 to 5 1. For surge, allow 2-min liquid residence time for draw-off, use 15 min for reflux, use 5 min, provided this allows sufficient time for controllers to function. Total volume = 1.3 X holdup if the holdup volume is >3 m ... 

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