packed tower absorber
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Packed Scrubber Design
Basics
Gas-Liquid Equilibrium
Operating Line Tower Diameter and Pressure Drop
Mass Transfer and Tower Height
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In absorption processes, gaseous
contaminants are removed from a gasstream by transferring them to a liquid.
That liquid is usually water or an aqueous
solution that contains chemicals selected
to react with the absorbed contaminants.
Most systems operate with collection
efficiencies of 70 percent to over 99
percent
Packed bed systems are typically used for
highly water soluble gases such as HCl orHF or NH3
Spray towers are usually used on power
plants due to their lower pressure drop
Absorption Basics
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The most important factor affecting collection
efficiency is the solubility of the contaminantin the liquid.
Gases are more soluble in cold liquids than
in hot liquids and less soluble in liquids with
low pH.
The liquid surface area and the time
available for diffusion of the gaseous
contaminants into the liquid are also
important factors affecting performance
Solubility
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There are many equipment designs for contacting theliquid with the contaminated gas stream. The most
common ones are:
spray towers, tray towers,
packed beds, and
spray dryers.
Types of Absorbers
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Packed Scrubber Design
Basics
Gas-Liquid Equilibrium
Operating Line Tower Diameter and Pressure Drop
Mass Transfer and Tower Height
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Packed Scrubber Design
Basics
Gas-Liquid Equilibrium
Operating Line Tower Diameter and Pressure Drop
Mass Transfer and Tower Height
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Packed Scrubber Design
Basics
Gas-Liquid Equilibrium
Operating Line Tower Diameter and Pressure Drop
Mass Transfer and Tower Height
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Packed Scrubber Design
Basics
Gas-Liquid Equilibrium
Operating Line Tower Diameter and Pressure Drop
Mass Transfer and Tower Height
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Two film theory
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For a highly soluble gas such as HCl or HF in
water, m = 0. Then Nog simplifies to:
1
2
1ln ln
1O G
YN
Y
In this case, to achieve 99% removal:
1ln 4 .6
0 . 01
O GN
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(g/mole)gaspollutantofweightmolecularM
(atm)pressuresystemtotalP
)/m(minterfaceliquid-gasofareaeffectivea
Pa)-m-(moles/hphasegasonbasedtcoefficientransfer-massoverallK
)m-(g/hvelocitymasslsuperficiagasG'
(m)resistancephasegasoverallonbasedunittransferaofheightH
(m)unittransferaofheightHTU
))(P)(M(aK
G'HHTU
G
32
e
2
OG
2
OG
GeOG
OG
where
Height of a transfer unit
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D d P f
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There are several operating problems that can occur in absorption systems.
The most common of these include the following:
Inadequate liquid flow
Low inlet liquid pH
Poor gas-liquid contact
Inadequate chemical feed rate
Excessive liquid temperature
Plugged beds or mist eliminators
Corrosion
Decreased Performance
D d P f
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To determine if an adsorption system is working properly,
field personnel should observe if possible:
Outlet Gas Stream Contaminant Measurement
not likely available
Temperature Difference between the Gas Inlet and
Outlet,
Liquid Flow Rate and Liquid Pressures.
Pressure Drop, and Stack Opacity
Decreased Performance