Holddowns, packing

As indicated above, packed column internals include hqiiid distributors, packing support plates, redistributors (as needed), and holddown plates (to prevent movement of packing under flow conditions). Costs of these internals for columns with random packing are given in Fig. 14-80, based on early 1976 prices, and a Marshall and Swift cost index of 460. 

FIG. 14-80 Cost of internal devices for columns containing dumped packings, a) Holddown plates and support plates, (h) Redistributors, (c) Liquid distributors. [Pikulik and Diaz, Cbem. Eng., 84(21), 106 (Oct. 10, 1977).]... 

As a result, the tower flooded above the holddown plate. To fix this problem, the packing holddown was dropped 15 in below the chimney, orifice plate, distributor. As a result, the tower fractionated properly. 

Possible restrictions to vapor flow, from the packing grid support, or holddown... 

No. of trays Tray spacing, in Packed height, ft Allowance for distributor, ft Allowance for support ar holddown, ft Total height ft Bottom section ... 

Packed columns, c/s column with c/s Raschig rings including support trays, holddown plates, distributor and redistributor trays including column with some nozzles but no access holes. FOB cost 28000 at the product of (column height, m) (diameter, m) = 2.8 with n = 0.65 for the range 0.5-2.8 m and n = 0.9 for the range 2.8-85. L-i-M = 2.9. L/M = 0. 4. 

Packed Towers Better Than Trays 133 11.2.3 Packing Holddowns... 

This logic would also apply to packed towers. However, designing for a strong bed limiter (i.e., packing a holddown grid) would largely avoid this sort of failure. 

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