packed columns vs plate columns

7/23/2019 Packed Columns vs Plate Columns

http://slidepdf.com/reader/full/packed-columns-vs-plate-columns 1/8

Packed Columns vs. Plate Columns

The difference in cost between plate and packed columns is not too great, although packing’s are generally more

expensive than plates.

In addition, the difference in column height is not usually significant if the flow rates are such that efficiencies are

near maximum.

Conditions favouring packed columns:• small-diameter columns (less than .!m"

• more choices in materials of construction for packings especially in corrosive service (e.g. plastic, ceramic,

metal alloys"

• lower pressure drop (important in vacuum distillation"

• less li#uid entrainment $ low li#uid hold-up, especially suitable for thermally sensitive material

• foaming li#uids can be handled more readily (less agitation of li#uid by the vapour"

Conditions favouring plate columns:

• variable li#uid and%or vapour loads• low li#uid rates $ large number of stages and%or diameter

• high li#uid residence time

• dirty service (plate columns are easier to clean"

• presence of thermal or mechanical stress due to large temperature changes which might lead to cracked

packings

• exotherms re#uiring cooling coils inside column

&s a rule of thumb, plates are always used in columns of large diameters and towers that have more than ' to

stages.

)acked columns offers narrower operating range than cross-current columns*

• For too low liquid flow rate* the wetting of the packing material may not be adeguate.

• For too high liquid flow rate* the treatment in plate columns is often more economic.

+oreover,

• If solid particles are present in the liquid* the cleaning of a packing section is much too complicated and

expensive compared with the plate discharge.

• Working under stressed conditions of temperature variations and pressure* the packing elements are

easily breakable.owever packed column are the best options when*

• Costs* packed column tends are less expensive than plate column for small column diameter (.! m".

• Corrosive chemicals handling* cheap ceramic packing material, or other chemicals resistant packingelement can be easily used.

• For foaming liquid* handling of foaming li#uid in packed column is more appropriate because of the

relatively low degree of agitation by the gas.



PAC!" C#$%&' F#( )A* A+*#(P,I#' -"I$%,! **,!&*/

as absorption can be carried out in a packed column. /e will look at both column diameter and packed height in

this 0ection.The 1igure below showed a typical gas-li#uid flow in a packed column. 2lick here for more information

of packings.

http://www.separationprocesses.com/Absorption/Fig130.htm

http://www.separationprocesses.com/Operations/POT_Chp02f.htm


http://www.separationprocesses.com/Operations/POT_Chp02f.htm



3etermination of column diameter involves the analysis of pressure drop across the packed bed.

&s for packed height, the design used in the early days was based on the 4T) method. This was largely replaced

by the +ethod of Transfer 5nits.

Comparison between number of theoretical tra0s1 2!,P and &ethod of ,ransfer %nits

The 6umber of Transfer 5nits (6T5" and eight of Transfer 5nits (T5" such as 67, 7 should not be confusedwith the number of theoretical trays (6", and the height e#uivalent to theoretical plate (4T)" respectively./hen the

operating line and e#uilibrium line are straight and parallel* ',% 3 ' 8 and 2,% 3 2!,P

7therwise, the 6T5 can be greater than or less than 6 as shown in the 1igure below*

When the operating line is straight but not parallel, we have the following relationships:

where is the Absorption Factor.

http://www.separationprocesses.com/Absorption/GA_Chp04a.htm

http://www.separationprocesses.com/Absorption/GA_Chp04b.htm

http://www.separationprocesses.com/Absorption/GA_Chp04c.htm




http://www.separationprocesses.com/Absorption/GA_Chp04a.htm

http://www.separationprocesses.com/Absorption/GA_Chp04b.htm

http://www.separationprocesses.com/Absorption/GA_Chp04c.htm


packed columns vs plate columns

Documents