Column Internals-Absorption-Lecture Slides, Slides of Technical Writing

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Process Mass & MomentumProcess

Mass & MomentumTransfer

AbsorptionAbsorption Dr Muhammad Tayyeb JavedDCME-PIEASDCME PIEASdocsity.com

Column Internals Column^ should^ be^ mounted

truly^ vertically^ to^ help uniform liquid distribution^ Packing Support „ o carry the weight of the wet packing „ ree passage of the gas and liquid „ oorly designed plate will give high

∆ P and can cause local flooding „ ide spaced grids are used to increase flow area; withlayers of larger size packing stacked on the grid tosupport the small size random packing „„ he best design of P S is one in which gas inlets areprovided above the level where liquid leaves the bed „ hese^ designs^ have^

a^ low^ pressure^ drop

and^ no hese^ designs^ have^

a^ low^ pressure^ drop

and^ no tendency to flooding PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Liquid Distributors „ In^ the^ orifice^

type^ the^ liquid

flows through holes in the plate and the gasthrough short stand pipes „ The gas pipes should be sized to givesufficient^ area^

for^ gas^ flow^

without creating a significant pressure drop „ Must be correctly sized for a particularduty „ Should not be used where there is any risk of the holes plugging PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Liquid Distributors „ In^ the^ weir^ type

the^ liquid^ flows

over „^ In^ the^ weir^ type

the^ liquid^ flows

over notched weirs in the gas stand pipes „ This type can be designed to cope with awider range of liquid flow rates than thewider range of liquid flow rates than thesimpler orifice type „ For larger liquid flow rates, vapour flowwill be restrictedwill be restricted PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Liquid Distributors „^ Pipe^ manifold

distributor^ can

be^ used when the liquid is fed to the column underpressure and the flow rate is reasonablyt^ tconstant „ The distribution pipes and orifices shouldbe sized to give an even flow from eachl^ telement

Perforated RingType Distributoryp^ High gas rates and relatively small liquid ratesare encountered with minimum pressure dropFor larger size towers For^ larger^ size^ towers PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Liquid Redistributors „^ If^ the^ tower

is^ high,^ re-distributing plates^ are necessary „^ To^ collect^ liquid

that^ has migrated to the column wallsd^ di t ib^ t^ it

l and redistribute it evenly overpacking „ These^ plates^ are

needed^ at intervals^ of^ about

2 5^ to^3 intervals^ of^ about

2.5^ to^3 column diameters for Raschigrings „ 5-10 column dia for Pall rings

g „^ Not more than 6 m apart „^ For larger columns weight ofpacking is also a factorp^ g PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Hold Down Plates „ A hold down plate is often placed at the topto^ minimize^ movement

and^ breakage

of packing caused by surges in flow rates „ The top layer of packing may be fluidized „ Ceramic packing may breakupPl^ ti^ ki^

b^ bl^ t^

f^ l „^ Plastic packing may be blown out of column „^ Used with ceramic packing to weigh downthe top layers and prevent fluidization „^ Bed-limiters are sometimes used with plasticpacking to prevent bed expansion „^ Lighter^ construction

&^ are^ fixed^

to^ the „^ Lighter^ construction

&^ are^ fixed^

to^ the column walls „ Openings^ in^ hold-down

plates^ and^ bed- limiters should be of proper sizelimiters should be of proper size PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Installing Packings^ „^ Ceramic^ &^

metal^ packings

are^ normally^

dumped^ into^ the column^ “wet”,^

to^ ensure^ a^ truly

random^ distribution

and

prevent damage to the packing „ If the column must be packed dry, the packing can be loweredinto the column in buckets or other containers „ Ceramic packings should not be dropped from a height of more„ Ceramic packings should not be dropped from a height of morethan half a meter Liquid Hold-up „ Liquid held up in the packing under operating conditions „ To calculate the total load carried by the packing support „ Depend on liquid rate and, to some extent, on gas flow rate „ As a rough guide, a value of about 25 % of the packing weightcan be taken for ceramic packings

can^ be^ taken^ for

ceramic^ packings PMMT^

Dr. M. T. Javed, DCME, PIEAS

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Wetting Rate „^ For low liquid rates, wetting rate should be checkedMake sure it is above minimum recommended by the„^ Make^ sure^ it

is^ above^ minimum

recommended

by^ the

packing manufacturer

PMMT^

Dr. M. T. Javed, DCME, PIEAS

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