process column internals part ii packed column rev 1

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    Tower packings can be divided into two distinct categories: random (or dumped) and structured (or ordered) packing.

    Random packing consists of individual pieces which are dumped into the tower where they are oriented randomly.

    Structured packing is usually in modular form (blocks or sections), and the modules are designed and placed in a tower with specific orientations




    Shaped cylindrically with solid walls and open ends

    Manufactured in metal, carbon, plastic, and ceramic.

    Carbon Raschig rings are still used in extremely corrosive, non-oxidizing environments.


    Commonly used in refinery and petrochemical applications.

    Available in metal and plastic under various trade names. "Pall Ring" , "Ballast Ring" and "Flexiring".

    Modifed metal Pall rings which provide slightly better performance are available under the trade names "HyPak" , "Ballast-Plus Ring" , and "K-Pac" .

  • Plastic Pall rings are primarily used in low temperature, low pressure systems.


    Saddles are available in plastic and ceramic.

    Trade names "Intalox Saddles" and "Flexisaddles".

    Ceramic saddle is thick, providing a low void fraction. This causes a higher pressure drop and lower capacity relative to other types of packings.

    Properly designed tower bottoms strainers are needed to protect pumps from damage.

    For these reasons, the ceramic saddles are not preferred for most refinery and petrochemical applications despite their relatively low cost.


    Designed to compete against the Pall ring in efficiency, pressure drop, and capacity.

    Examples of these packings are the Miniring , IMTP etc. In certain applications, some proprietary packings can offer a significant advantage over the Pall ring.

    Particularly in retrofit situations where modest incremental improvement in a tower's efficiency, pressure drop, or capacity can make or break justification for a project.

    The main disadvantage of the proprietary packings compared to Pall rings can be the cost.

  • Raschig Rings Random Packing

  • Pall Rings Random Packing.

  • Saddles Random Packing.

  • Proprietary Random Packing.

  • STRUCTURED PACKING Types are the corrugated and grid types.

    Structured packings can be used in any service random packings are used.

    They generally provide higher mass transfer efficiencies, lower pressure drops, and higher capacities than random packings.

    Major drawback is cost.


    Vertically oriented corrugated layers.

    The angled corrugations of adjacent layers are reversed relative to one another.

    Most commonly manufactured in metal.

    Available under the trade names Flexipac , Gempac , Intalox and Max-Pak.

  • GRID

    Lowest pressure drop and highest capcity of any packing.

    Very high resistance to fouling because of its open design.

    This open design also provides a very low specific surface area, which in turn reduces the mass transfer provided by the vapor-liquid interface on the packing surface.

    Primarily used for heat transfer services, where it is quite effective.

  • Corrugated Structured Packing.

  • Intalox Grid Structured Packing.

  • INTERNALS : Packing Support , Liquid

    Distributors, Bed Limiters/Hold Downs, Flashing

    Feed Galleries

    Packing may perform poorly if the internals aren't designed for good liquid and vapor distribution.


    Bar type, grid type and the gas injection type.

    Packing support, support the weight of the packed bed while providing little resistance to the flow of vapor and liquid.

    Maintaining a high open area, yet not so open that the packing is not retained.

    Gas injection support

    Most commonly used in random packing applications.

    Hump" design can provide an open area that exceeds 100% of the tower CSA when metal and approximately 80% for other materials.

  • Grid type support

    Most commonly used to support structured packing

    Commonly consists of parallel bars braced with crosspieces.

    The modular or block form of the structured packing allows the bars in the grid to be spaced far apart, which provides a very high open area.

    Bar type supports

    Consisting of thick parallel bars, are primarily made of and used for ceramics, glass, and graphite.

    Lowest open area of all supports

    In some very corrosive environments, they may be the only economically viable option.


    Weir type and orifice type.

    Weir types are designed for gravity flow of liquid over a weir.

    Orifice types are designed for gravity or forced flow of liquid.

    From a mechanical standpoint, the trough, tubular, and plate distributors are the most common.

    Orifice Flow

    A gravity-flow orifice distributor normally provides accurate and uniform flow control.

    The flow is controlled by the liquid head above the orifice.

    Maintain a uniform flow over the cross-section of a tower even when slightly out-of-level.

    Main drawback is plugging.

  • The forced-flow orifice distributor's effectiveness depends much on the distribution header and orifice pressure drops.

    Perforated pipe type distributors are primarily used to distribute a tower liquid inlet stream onto multipass trays or large packed bed liquid distributors.

    Used where the distribution requirements are not stringent.

    Weir Flow

    Used in high liquid flow and dirty or fouling systems

    Modelled by using the Francis formula.

    A slightly out-of-level distributor can result in substantial maldistribution.

    Designs with narrow rectangular weirs and high liquid levels over the weirs can provide good distribution.

    Weir flow distributors are less prone to plugging.

  • Plate Type

    Control liquid flow using weirs, orifices, or a combination of both.

    Consists of a plate with risers for vapor flow.

    Attached to a support ring that is welded to the tower wall.

    Often preferred for flashing feeds because it can save tower height and is relatively inexpensive.

    Trough Type

    Control liquid flow using weirs, orifices, or a combination of both.

    Consist of a header trough that distributes into lateral troughs.

    Supported either by a support ring or rest on a distributor support grid which rests directly on top of the packing.

    Provide a high open area, and the vapor pressure drop is negligible.

    Reliable in dirty or fouling services.

  • Tubular Type

    Employ both gravity and forced orifice flow.

    The gravity flow tubular distributor consists of a vertical feed box, horizontal main header (pipe or closed channel), and lateral pipes. Feed enters at the top of the feed box in which the liquid level is maintained.

    Designed to provide high turndown and low liquid residence time relative to trough types

    Highly susceptible to plugging.

    The forced flow tubular distributors have no feed box, and the liquid feed enters through a main pipe header, and flows through orifices in lateral pipes.

    The two main types are ladder and spray.


    The function of bed limiters and holddown plates is to prevent the packing from being displaced from the bed.

    In extreme cases, random packing can be blown into the liquid distributor and even into the tower overhead line.

    These plates are an open type of grid placed above the packed bed which retains the packing and allows passage of vapor and liquid.

    A bed limiter is attached to the support ring or clips, whereas a holddown plate rests on the packing.

    Sometimes the bed limiter is integral with the liquid distributor.

    They are rarely used with structured packing, which is less likely to become displaced, unless there are serious uplift concerns (resulting from process upsets).

    Bed limiters and holdown plates are available in metal, FRP, plastic, ceramic, and graphite materials.

  • Bed Limiter for Structured Packing

    Bed Limiter for Random Packing


    Flashing Feed Gallery is used to disengage the vapor phase from a two-phase feed.

    It consists of two plates: an upper gallery, which is 50% open for vapor disengagement, and a lower plate for liquid distribution.

    Each plate requires a separate support ring.

    The two-phase feed is fed to the upper gallery where the vapor disengages from the liquid.

    Inlet Deflector Baffle is typically used in front of the feed nozzle to deflect the feed around the tower wall.

    Holes in the bottom of the upper gallery transfer the liquid to the lower plate where the liquid is distributed over the packing.

    Flashing Feed Distributor is fabricated in sections for passage through column manways.

  • Flashing Feed Gallery

  • Manufacturers and catalogues

    Major Manufacturers in the field of Column internals and their web address (Refer website for their products,

    catalogues and design softwares ) are as follows :

    Sulzer Chemtech : (also taken over Nutter)

    Montz : http://www.montz.

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