Small diameter tower internal orifice type gravity pan distributor
1. Pan distributor is belong to column internals
Column internals play very important role in effective mass
transfer performance. So they need to be designed carefully for
both process and mechanical point. Meanwhile, the engineers put
great effort into structured packing and random packing development
in the recent years. The column internals include mist eliminators,
feed pipes, distributors, re-distributors, support plates, bed
limiters, collector trays, etc.
2. Pan distributor is a kind of orifice gravity liquid distributor
Orifice type gravity distributor usually shows as pan type. An
orifice pan distributor consists of a pan. There are circular or
rectangular risers for vapor flow and perforation for liquid flow
in the pan.Orifice type distributor can be designed to have a large
number of drip points to provide superior liquid distribution,
though it may suffer from corrosion and plugging. Orifices are
sized to maintain a minimum liquid head at desired turndown
conditions & to avoid distributor overflow during turn up
condition. Very small orifice diameters (<4mm) are avoided to
prevent fouling.
3. Pan distributor application circumstances
Column Diameter inches | Specific liquid load gpm/ft2 | System fouling tendency | Turndown ratio | Suitable type of liquid distributor |
| 10-36 | 0.3 - 2 | Low - medium | ＜10:1 | Trough type liquid distributor with sump Deck type liquid distributor with orifices on drip tubes |
| 2 - 12 | Low - medium | 2:1 | Pan type liquid distributor Trough type liquid distributor with sump |
| ＞12 | Low - medium | 2:1 | Pan type liquid distributor Trough type liquid distributor with sump Deck type liquid distributor |
| ＞36 | 0.3 - 2 | Low - medium | ＜10:1 | Trough type liquid distributor with parting box Deck type liquid distributor with orifices on drip tubes |
| 2 - 12 | Low - medium | 2:1 | Trough type liquid distributor with sump Trough type liquid distributor with parting box Deck type liquid distributor |
| ＞12 | Low - medium | 2:1 | Deck type liquid distributor Trough type liquid distributor with sump |
4. Important points in designing Pan liquid distributor:
There are some important points to be checked before finalizing the
liquid distributor design.
- Maximum and Minimum head:
Maximum liquid head is the actual liquid head on the distributor
deck at turn up condition. The overall height of the liquid
distributor (trough / riser) shall be higher than this maximum
head. Please refer to the following formula.
Riser (Trough) height = {(Maximum head) 1.10 + 25} mm
Minimum head on the distributor is always to be estimated as per
requirement at turn down condition. Liquid vortexing and
entrainment may happen at low liquid head as insufficient
resistance to orifices. Also considerable mis-distribution can
occur if minimum heads are fallen short of. So the minimum liquid
head on the distributor shall be around 35mm. Punched orifices,
instead of drilled orifices, are always recommended in the
direction of liquid flow.
- Pressure drop and open area requirement for vapor:
Sufficient gas passage area must be provided by the liquid
distributor according to gas load, to avoid liquid entrainment or
high pressure drop. A minimum of 12% open area is used when very
low open area is required for gas. The pressure drop of liquid
distributor shall not exceed a value of 20mm water column. Well, it
finally depends on gas load, liquid load and a particular service.
Flow variation will increase due to low liquid head at the time of
low liquid loads and / small column diameters. Flow variation is a
strong function of mechanical points such as plate levelness,
distributor deck flatness etc. Liquid mis-distribution and
entrainment may occur on below packed bed with excessive flow
variation. So we need to minimise the excessive flow variation. The
liquid distributor or re-distributor can allow maximum of 12% flow
variation.
5. Pan distributor production laser cutting machine
Welcome your contact with your private tower internals plan or
ideas!
