How to calculate the pressure drop of structured packing column

The calculation methods of pressure drop of structured packing column mainly include the following:

Kister general association graph method

This is a method widely used in industry, through the flow parameter FP and flux parameter Y to establish a correlation graph, directly look up the graph to obtain the value of pressure drop. FP= (G/ρG) ^0.5 / (L/ρL) ^0.5, Y= (G/ρG) ^0.5 * μL^0.25. The method is suitable for different liquid phase loads and packing types, and the error is usually within 10%-20%.

Billet model

Applicable to the calculation of pressure drop in the constant liquid holdup area, the formula is:

Δ p/H = C

one

⋅FP

C

2

+C

3

⋅FP

C

4

Among them, C1-C4 is the characteristic constant of packing, which needs to be determined by regression of experimental data. The prediction accuracy of this model is higher near the flooding point 24.

The FP-Z formula

The general pressure drop correlation formula is:

Δ p/H = a ⋅ mu

L

0.5

⋅ rho

G

0.5

⋅U

G

1.8

⋅U

L

- 0.5

Constants a, b, m need to be determined according to the type of packing. For example, the calculation of quench tower pressure drop in sulfur recovery unit adopts this method, and the error is about 15%.

Experimental formulas for specific packings

Such as Lu Lisheng formula (dry packing pressure drop), Bravo formula (wet packing pressure drop correction), etc., need to be combined with the experimental data provided by the packing manufacturer. For example, the pressure drop curve of Mellapak packing is divided into dry and wet sections, the straight section before the load point, and the pressure drop rises sharply after the load point.

Design Suggestions:

The operating gas velocity is usually 50%-80% of the liquid flooding gas velocity, and the liquid flooding gas velocity 19 is calculated by the Bain-Haugen formula.

The height of the packing layer is recommended to be calculated in sections (15-20 meters per section), and the total packing layer height is determined by the equal plate height method.

In practical engineering, it is recommended to use the Kister correlation diagram or the general pressure drop formula in preference, taking into account the effects of liquid phase load, surface tension and viscosity.