Pressure drop of structured packing in pilot column and comparison to common correlations

Abstract

Packed columns are widely used in the chemical industry such as absorption, stripping, distillation, and extraction in the production of e.g. organic chemicals, and pharmaceuticals. Pressure loss and pressure drop correlations are of special interest when it comes to the hydrodynamic properties of a column. The pressure loss across the column is of interest in the design phase when the size of the blower to drive the gas stream through the column has to be decided. The loading point and flooding point are also influenced by the pressure loss and the area of operation is determined from these points. This work examines four different correlations on pressure drop. The correlations are (i) Ergun’s equation (1952), (ii) an improved version of Ergun’s equation by Stichlmair, Bravo, and Fair (1989), (iii) an equation developed by Billet and Schultes (1999), and (iv) an equation by Rocha, Bravo, and Fair (1993). The complexity of the correlations is increasing in the mentioned order, Ergun’s equation being the simplest one. This study investigates if the more complicated correlations give better predictions to pressure drop in packed columns. This is determined by comparing the correlations to experimental data for pressure drop in a packed column with 8.2 m of structured packing using water as the liquid and atmospheric air as the gas. Seven experiments were carried out for determining the pressure drop in the column with liquid flows varying from 0 to 500 kg·h−1. At constant liquid flow, the gas flow was varied from approximately 10 to 70 kg·h−1. The pressure drop across the non-wetted column was best described by the correlation by Rocha et al. while the pressure drop for liquid flows from 100 to 500 kg·h−1 was, in general, best described by Stichlmair’s equation. For an irrigated column, the highest deviation was a predicted pressure drop 69.6% lower than measured. The best prediction was 0.1% higher than the measured. This study shows, surprisingly, that for a system of water and atmospheric air, complicated correlations on pressure drop determination do not provide better estimates than simple equations.