Liquid Distributors and Redistributors in Metal and Plastic

The efficiency of a packed bed is above all dependent upon an even, uniform distribution of liquid. If a packed bed does not operate satisfactorily, this is often due to faulty design or incorrect installation of the distribution system.

The most important criteria in the selection of a liquid distributor are the liquid flow rate and the properties of the liquid itself, such as:

fouling

foaming tendency

density

viscosity

surface tension

Depending on the process used, the most frequent irrigation rates range from

B = 2 m³/m²/h in the case of vacuum rectification to
B = 300 m³/m²/h in the case of high-pressure absorption.

When looking at these factors, it becomes clear that no one single distributor model^ is suitable for all requirements.

The basic version of the distributors, standardized as far as possible, must therefore be varied in accordance with the design liquid flow and the minimum and maximum flow. Normally, our liquid distributors have a standard liquid level of 25 mm and approximately 100 distribution points per m² of column cross-section under minimum load. The rate of flow in the troughs of the distributor should be not more than 1 m/s or usually below 0.5 m/s.

Perforated troughs or weirs with slits or triangular incisions are typical. Besides a sufficient number of distribution points, it is important that these are distributed as uniformly as possible over the cross-sectional area of the column. A larger number of distribution points is often found in columns with systematic mass transfer packings, such as RALU PAK 250 YC or RASCHIG-SUPER-PAK, since greater mass transfer efficiency is usually required in such cases.

In principle, trough distributors with weirs permit a greater operating range between maximum and minimum liquid rate than distributors with submerged orifices.

Compared to orifice type distributors, however, trough distributors with rectangular weirs are three times, and those with triangular weirs five times as sensitive to deviations in liquid level in the trough. Consequently, if care is not taken over the installation, the weir type distributor may, in practice, be less satisfactory than orifice type distributors even at full design flow. For this reason, we only supply weir type distributors if this is expressly desired. If the incoming liquids contain solid particles which may block an orifice type distributor, however, they are a useful alternative.

Liquid distributors are available in the following materials:

carbon steel

various stainless steels

special alloys, such as Monel, Hastelloy, titanium, nickel etc.

thermoplastic materials such as polypropylene, polyethylene, PVC or polyvinylidene fluoride (PVDF).

Standard material thicknesses:

3 mm for carbon steel

2 mm for stainless steels and special alloys

6 mm for thermoplastic materials

Slight deviations for the various materials are possible.

In the case of distributors made of plastics, we require details concerning the composition of the liquids and the maximum operating temperature for design purposes.

If the feed contains solids, small discharge holes in particular tend to become blocked. If, owing to small liquid loads, small downcomer holes are provided for, despite solid particles contained in the liquid, the tendency towards contamination can be reduced by covering up the holes.

Both standard and high quality liquid distributors are available.

Standard liquid distributors can be used in a liquid load range of between 2 m³/m²/h and 80 m³/m²/h and in some cases even up to 125 m³/m²/h. Their design is usually determined by a large number of earlier versions, and this means short design and production times as well as low costs. Standard liquid distributors are described in the following.

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