Drum Vessels
Drum Vessels Design Rules of Thumb
- Drums are relatively small vessels to provide surge capacity or separation of entrained phases.
- Liquid drums usually are horizontal.
- Gas/liquid separators are vertical.
- Optimum length/diameter=3, but a range of 2.5-5.0 is common.
- Holdup time is 5 min half full for reflux drums, 5-10 min for a product feeding another tower.
- In drums feeding a furnace, 30 min half full is allowed.
- Knockout drums ahead of compressors should hold no less than 10 times the liquid volume passing through per minute.
- Liquid /liquid separators are designed for settling velocity of 2-3 in./min.
- Gas velocity in gas/liquid separators, V = K (PL / PV − 1)^0.5 ft / sec , with k =0.35 with mesh deentrainer, k =0.1 without mesh deentrainer.
- Entrainment removal of 99% is attained with mesh pads of 4-12 in, thickness; 6 in. thickness is popular.
- For vertical pads, the value of the coefficient in Step 9 is reduced by a factor of 2/3.
- Good performance can be expected at velocities of 30―100% of those calculated with the given k; 75% is popular.
- Disengaging spaces of 6―18 in. ahead of the pad and 12 in. above the pad are suitable.
- Cyclone separators can be designed for 95% collection of 5 µm particles, but usually only droplets greater than 50 µm need be removed.