Feed Pipe Plus Trough Liquid Distributor Tower Internals

Design service available feed pipe plus trough liquid distributor

1. Liquid Distributor type English Units:

When we need to select a liquid distributor, we need to consider the tower diameter, flow rate, turndown ratio, available height (in case of revamp) and fouling resistance.

2. Trough liquid distributor structure:

Orifice trough type distributors consist of parallel troughs with perforated holes in the bottom for liquid flow. Vapor rises in the space between the troughs. The troughs are often interconnected by cross channels (called as parting box), which help equalize the liquid level in different troughs. This trough type liquid distributors provide more open area for vapor flow and is easier to support.

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. Important points in designing trough 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:

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.

4. Trough liquid distributor characteristics:

Liquid distributor is the most important column internal from a process point of view. It is required to distribute liquid uniformly at the top of packing tower. Meanwhile a liquid distributor much have sufficient gas passage area to avoid high pressure drop or liquid entrainment.

• Uniform liquid distribution;
• Resistance to fouling;
• Proper trundown capabitity;
• Low gas pressure drop;
• Minimum height;
• Higher cross-mixing capabity.

5. Trough liquid distributor production

Welcome your contact with your private tower internals plan or ideas!