Structured packing

Structured packings have been established for several decades. The first generation of structured packing arose in the early 1940s. In 1953, a patented packing appeared named Panapak™, made of a wavy-form expanded metal sheet. The packing was not successful, due to maldistribution and lack of good marketing. The second generation appeared at the end of 1950's, with highly efficient wire mesh packings, such as Goodloe ™, Hyperfil ™ and Koch-Sulzer. Until the 1970s, due to their low pressure drop per theoretical stage, those packings were the most widely used in vacuum distillation. However, high cost, low capacity and high sensitivity to solids have prevented wider utilization of wire mesh packings.

Corrugated structured packings, introduced by Sulzer by the end of the 1970s, marked the third generation of structured packed columns. These packings offer high capacity, lower cost, and less sensitivity to solids, while keeping a high performance. Popularity of the packings grew in the 1980s, particularly for revamps in oil and petrochemical plants. These structured packings, made of corrugated metal sheets, had their surfaces treated, chemically or mechanically, in order to enhance their wettability. Consequently, the packings' wetted area increased, improving performance. In 1994, a new geometry was developed, and called Optiflow. Later, in 1999, an improved structure of corrugated sheet packings, the MellapackPlus, was developed based on CFD simulations and experiment. This new structure, compared with conventional Mellapak, has a lowered pressure drop and maximum useful capacity could be extended up to 50%.

Structured packing is manufactured in a wide range of sizes by varying the crimp altitude. Packing surface ranges from 50 m²/m³ (lowest efficiency, highest capacity) to 750 m²/m³ (highest efficiency, lowest capacity).

Typical applications include vacuum and atmospheric crude oil fractionators, FCC main fractionators and TEG contactors. The separation of mono-, di- and triethanolamine, conducted under vacuum, may also utilize structured packing, owing to its relatively low pressure drop. Tall oil fractionation, the process of separating fatty acids from rosin acids and pitch obtained as a by-product of the Kraft process of wood pulp manufacture, also utilizes structured packing. The packing additionally finds use in the manufacture of styrene monomer and the dehydration of glycol in natural gas processing.[2]

Structured packing also finds use in the equipment/processes below:

• Air separation[3][4]
• Cyclohexanone/Cyclohexanol separation[3]
• Xylene splitters[3]
• CO₂ absorbers[3]
• H₂S absorbers[3]
• Ethylene oxide absorbers[3]
• Acrylonitrile absorbers[3]
• Oleo Chemicals
• Fine Chemicals

Structured packing offers the following advantages as compared to the use of random packing and trays:

• Lower pressure drop[2][5]
• Higher efficiency (given the same tower height)[2][5]
• Higher capacity[2][5]
• Reduced liquid hold-up[2]

Structured packing offers the following disadvantages as compared to the use of random packing and trays:

• Cost[5]
• Greater sensitivity to maldistribution

• Packed bed
• Raschig ring
• Dixon rings
• Random column packing