Keywords: Silicon tetrafluoride gas, Void spray towers, Superphosphate, Fluorine.

The published literature on the absorption of superphosphate den gases and certain other gases in void spray towers is reviewed.

An experimental programme conducted on the plant scale and devised to determine the effect of tower height, liquor rate, liquor concentration, counter and co-current operation is described and the data interpreted in terms of simple mass transfer theory. Particular note is made of problems encountered in the analysis of den gases.

Over the range of parameters studied it is concluded that:

1. Short towers have higher efficiencies per unit sprayed volume than tall towers.

2. The efficiency of a tower is primarily dependent on the liquor rate.

3. Towers in which co-current flow exists are as efficient as counter-current towers.

4. Re-circulating liquor concentrations of up to 18-20 per cent w/w fluosilicic acid may be used without significantly affecting the absorption rate.


A G Calver and J D C Hemsley, Fisons Fertilizers Ltd, UK.

46 pages, 12 figures, 3 tables, 12 references.