The Economic Cost of Pressure Drop

Packing performance can be assessed in terms of mass transfer but can also be assessed in terms of the power needed to push the gas through the tower. A more open tower with lower pressure drop will offer greater production capacity or less power consumption or less acid mist or a combination of all three. For the 2000 TPD case chosen, the overall plant pressure drop typically will be around 220" W.C.

(atmospheric pressure is 406.8" W.C.). The pressure saving from high performance packing in one tower would amount to around 70 kW for a pressure drop saving of 5" W.C. This is worth between fifty and sixty thousand dollars per year based on $0.10/kW hr. For standard packing, around 3300 ft³ would be needed to fill the tower which, with an allowance for settling, would cost around sixty thousand dollars. The HP^TM saddle will sell for a premium cost due to its more expensive manufacturing process and structured packing will cost still more. With the HP^TM saddle, the power saving would pay for the extra packing cost in less than a year. A second important issue is the fact that, by using HP^TM packing, in a tower repack case, additional acid production will become possible, not only because of its inherent lower pressure drop, but also because of its low breakage during installation. In one 13 ft acid tower with a bottom chimney screen, less than half a bucket of packing chips were collected during the first annual turn-around.