What is Random Packing and How Is It Used in Process Plants?
Random packing is one of the 3 primary devices used in mass and heat transfer applications. (The other 2 devices are structured packing and trays.) Like the other 2 devices, the primary purpose of random packing is to create surface area for vapor/liquid contact so that Mother Nature (and Father Thermodynamics) can produce chemical separation. Chemical separation includes distillation, absorption and stripping.
How is Random Packing Applied in Process Plants?
In most chemical separation (aka mass transfer) processes, vapor is driven upward in the column by heat and pressure while liquid falls downward under the force of gravity. There are 3 primary components in the selection of a random packing (or any other mass transfer device) and they are capacity/pressure drop, efficiency and $’s. The larger the random packing, the higher the capacity, but at a cost of lower efficiency. The smaller the packing, the higher the efficiency but at a cost of lower capacity and higher cost. The design engineer must select the appropriate packing that provides the most economical balance capacity and efficiency.
Raschig Ring Packing – This first generation of random packing is characterized as having the same height as its diameter. Since the Raschig Ring Packing has relatively low capacity, low efficiency and high costs (in metal), its applications are generally limited to corrosive applications where the material of construction is ceramic or carbon/graphite. When fabricated in metal, the material must be thicker since the Raschig Ring does not have any internal support like the “fingers” within the Pall Ring Packing.
Pall Ring Packing – Think of Pall Ring Packing as Raschig Rings with windows and/or fingers. The development of Pall Rings was a huge advancement in random packing. By punching tabs in the wall of the ring, it created internal drip points that increased capacity and efficiency by 50% to 80% over the Raschig Ring Packing. Like the Raschig Ring Packing, Pall Rings are characterized by having the same height as its diameter. Pall Rings are often used in absorption and distillation services.
High Performance Saddle-Ring – Saddle Ring Packing may replace Pall Rings to deliver better efficiency and capacity in the same bed height and diameter. This 3rd generation of random packing was developed with a focus to create a low aspect ratio packing; i.e. having a height less than the nominal diameter of the packing. The low aspect ratio packing promotes an advantageous installation of the packed bed because the Saddle Ring settles in a way that orients more flat surfaces parallel to vapor and liquid traffic. The result is increased capacity while maintaining an effective surface area for vapor/liquid contact. These “rings” deliver higher capacity and efficiency than the Pall Ring packing. Applications include use in atmospheric and high-pressure distillation, sour water stripping, demethanizers, deethanizers, acid gas removal, quench towers, and main fractionators.
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