packed columns

20
Politecnico di Milano Chemical Processes and Technologies (8 CFU) Dipartimento CMIC “G. Natta” Prof.ssa Laura Annamaria Pellegrini – AA 2014/ 2015 Contacting of vapor and liquid phases on trays is either in countercurrent flow or with cross flow of liquid against vapor flow upward. The spacing of trays is determined partly by the necessity of limiting carryover of entrainment from one tray to another, and is thus related to the vapor velocity and the diameter of the vessel. For reasons of accessibility of trays to periodic servicing, however, their spacing commonly is 20-24 in. Then workmen can go up or down the tower through removable sections of the trays and have enough room to work in. For the same reason, tray diameters are restricted to a minimum of 30 in. Tray columns

Upload: -

Post on 19-Dec-2015

123 views

Category:

Documents


5 download

DESCRIPTION

Distillation

TRANSCRIPT

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Contacting of vapor and liquid phases on

    trays is either in countercurrent flow or with

    cross flow of liquid against vapor flow

    upward. The spacing of trays is determined

    partly by the necessity of limiting carryover of

    entrainment from one tray to another, and is

    thus related to the vapor velocity and the

    diameter of the vessel. For reasons of

    accessibility of trays to periodic servicing,

    however, their spacing commonly is 20-24 in.

    Then workmen can go up or down the tower

    through removable sections of the trays and

    have enough room to work in. For the same

    reason, tray diameters are restricted to a

    minimum of 30 in.

    Tray columns

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Sieve traysA liquid level is maintained with an overflow weir while the vapor comes up through the perforated floor atsufficient velocity to keep most of the liquid from weeping through.

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Valve traysA valve tray has openings commonly from 1 to 2 inches in diameter. Each hole is fitted with a valveconsisting of a cap that overlaps the hole, with legs or a cage to limit vertical rise while maintaining thevalve cap in a horizontal orientation. Without vapor flow, each valve covers a hole. As vapor rateincreases, the valve rises, providing a larger opening for vapor to flow and to create a froth.

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Bubble-cap traysA bubble-cap tray consists of a cap, 3 to 6inches in diameter, mounted over and above aconcentric riser, 2 to 3 inches in diameter. Thecap has rectangular or triangular slots cutaround its side. The vapor flows up through thetray opening into the riser, turns around, andpasses out through the slots and into the liquid,forming a froth.

    Three types of tray openings for passage of vapor up into liquid: (a) perforation; (b) valve cap; (c) bubble cap; (d) tray with valve caps

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    The broad classes of packings for vapor-liquid contacting are either random or structured. The former aresmall, hollow structures with large surface per unit volumes that are usually randomly dumped into thetower. Structured packings are normally layers of elements fabricated form expanded metal, sheet metal,and are stacked into the tower very carefully.

    Packed columns

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    random packings

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    structured packings

    Mellapak Sulzer structured packing

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    The corrugated metal sheets of structured packings are arranged in a crisscross relationship to create flowchannels for the vapor phase. The intersections of the corrugated sheets create mixing points for the liquidand vapor phases. Structured packings offer excellent capacity and low pressure drop per theoreticalstage.

    Wire gauze structured packing

    FLEXIPAC S Koch-glitsch structured packing

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Design and variants of Sulzer columns

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Design of packed columns

    Once known the number of theoretical trays, the height of the packing can be determined as:

    where: HETP = height equivalent to a theoretical plateN = number of theoretical plates

    H HETP N=

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Comparison between trays and packed columns

    In general, other conditions being equal, the packed columns are more advantageous for small size

    (under 1 m in diameter), while tray columns for large diameters. In addition :

    1)at constant gas flow rate, the pressure drop is lower in packed columns ;

    2)packed towers are less expensive and simpler to be constructed in case of corrosive fluids;

    3)the retained liquid is lower in packed columns;

    1)tray columns are lighter;

    2)packed columns cannot be realized with large diameters because of the bad liquid distribution;

    3)tray columns can be cleaned more easily;

    4)tray column are more flexible to changes in fowrates.

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

  • Politecnico di Milano Chemical Processes and Technologies (8 CFU)Dipartimento CMIC G. Natta Prof.ssa Laura Annamaria Pellegrini AA 2014/ 2015

    Diapositiva numero 1Diapositiva numero 2Diapositiva numero 3Diapositiva numero 4Diapositiva numero 5Diapositiva numero 6Diapositiva numero 7Diapositiva numero 8Diapositiva numero 9Diapositiva numero 10Diapositiva numero 11structured packingsDiapositiva numero 13Diapositiva numero 14Diapositiva numero 15Design and variants of Sulzer columnsDesign of packed columnsComparison between trays and packed columnsDiapositiva numero 19Diapositiva numero 20