(109d) Random Packing Surface Area Influence On Hydraulic-Efficiency Performance: Challenging Conventional Wisdom

It is well known that the surface area of random packings directly influences their hydraulic-efficiency performance. In particular the lower the surface area, the higher the throughput capacity combined with lower pressure drop but at the expense of a decreased theoretical stage count (high HETP). The converse is true as the surface area increases. These heuristics were validated following a 2 year research program at FRI in the mid 1980's, in which four Second Generation Pall Rings were tested.

Nowadays there are numerous third generation ring-saddle hybrids and the first fourth generation random packing (the Raschig Super-Ring) available on the market. Such advancements in packing geometries raise the question of whether the above mentioned heuristic still applies. It was put to the test by comparing test results obtained from the SRP 430mm ID Distillation Pilot column of four random packings spanning three generations.

The recently tested Raschig Super-Ring No. 0.5 of Surface Area 250 m2/m3 was compared against two Second Generation 25 and 50 mm Pall Rings (207 and 102 m2/m3 surface areas) and a Third Generation 40 mm Ring-Saddle of Surface Area 170 m2/m3. The data presented will show that the relative high surface area Raschig Super-Ring No. 0.5 exhibits higher capacities combined with as good as or lower pressure drops compared to the lower surface area Second and third Generation types with much better efficiencies. On the whole the fluid dynamic behaviour within the packing element and not just surface area alone should be considered when evaluating the performance of random packings.