2. ABSORPTION COLUMN
IRIS BUSTAMANTE PÁJARO*
ANGIE CASTILLO GUEVARA*
ALVARO JOSE GARCÍA PADILLA *
KARIANA ANDREA MORENO SADDER*
9th SEMESTER
CHEMICAL ENGINEERING PROGRAM
UNIVERSITY OF CARTAGENA
2
UNIT OPERATIONS LAB II
UNITOPERATION:ABSORPTION
3. 3
UNITOPERATION:ABSORPTION
OUTLINE
1. Introduction
2. Theoretical foundations
3. Applications
4. Limitations
5. Current researches
6. Objectives & Methodology
7. Results & Discussion
8. Conclusion
Acknowledgements
ABSORPTION COLUMN: FOUNDATIONS, APPLICATIONS AND
SCIENTIFIC PROGRESS
"Good, better, best. Never let it rest. 'Til your good is better and your better is best." - St. Jerome
4. 4
UNITOPERATION:ABSORPTION
INTRODUCTION
UNIT OPERATION
ABSORPTION
It’s the removal of a solute
(component) from its gaseous
mixture using a solvent.
Importance:
Gas absorption processes are widely used in the industry, mainly for
environmental regulations of gaseous emissions.
Chemical engineer, job duties:
Design, simulate, develop & operate absorption unit, where mass transfer
phenomena take place.
Shreve’s et al., 1955; Ocon Tojo et al., 2001; Wang et al., 2014; Geankoplis, 1993
Important unit operation encountered in both CPIs and PCIs
5. 5
UNITOPERATION:ABSORPTION
MAIN TYPES
Types of absorption extensively applied in laboratory and industrial
processes
CHEMICAL ABSORPTION
Amine processes
Carbonate processes
PHYSICAL ABSORPTION
Selexol
Purisol
Rectisol, sulfinol
Only physical and is limited by the
formation of solution of the gas in
the liquid
Absorption follows incipient
chemical reaction
Chattopadhyay et al., 2007
6. 6
UNITOPERATION:ABSORPTION
THEORETICAL FOUNDATIONS
Chemical solventsPhysical solvents
Chattopadhyay et al., 2007
• MEA
• DGA
• DEA
• MDEA
• Dimetil de polietilenglicol
• Metanol
• NMP
• Propilencarbonato
ELECTION OF THE SOLVENT
High selectivity
High solubility
Low volatility
Low viscosity
Water is the solvent most
commonly used.
7. 7
UNITOPERATION:ABSORPTION
DISTILLATION-ABSORPTION
Chattopadhyay et al., 2007
DISTILLATION ABSORPTION
Stripping vapor is generated by the
partial evaporation of the liquid.
The liquid is always well below its
boiling point.
Simultaneous molecular diffusion
in both directions.
Diffusion is chiefly unidirectional.
The radio of the liq flowrate to the
gas flowrate is minor.
The radio of the liq flowrate to the
gas flowrate is greater tan
distillation.
The primary objective is to involve
separation of solutes from each
other to any important extent.
The primary objective is only solute
recovery or solute removal.
Table 1. Comparison between distillation and absorption process
8. 8
UNITOPERATION:ABSORPTION
CONVENTIONAL COLUMNS
Bruinsma et al., 2012; Li et al., 2017
PACKED TOWER ADVANTAGES
DISADVANTAGES
Source: Copyright Tri-Mer Corporation, Owosso
Superior contact between gases and liquid
that promote high mass transfer rate.
Low capital, operating, and maintenance
cost.
Channeling, which must be controlled by
redistributing liquid
Cannot handle extremely high or low flow
rates
9. 9
UNITOPERATION:ABSORPTION
CONVENTIONAL COLUMNS
Ensure a large area of contact between fluids
Encourage the mass transfer of one or more
components from one fluid to another
What causes pressure drop in a packed tower?
The packing of the column
For absorption, the tower should be designed using about 50-70% of the
gas flood velocity with the high value used in high flow parameters
PACKAGE
The fluid velocity
Chattopadhyay et al., 2007
11. 11
UNITOPERATION:ABSORPTION
CONVENTIONAL COLUMNS
DESIGN OF A PACKED ABSORPTION COLUMN
Balance around the dotted line
𝐿2 , 𝑥2
Operating line
𝑉, 𝑦
𝑉2 , 𝑦2
𝐿, 𝑥
𝐿1 , 𝑥1𝑉1 , 𝑦1
𝐿´
𝑥2
1 − 𝑥2
+ 𝑉´
𝑦1
1 − 𝑦1
= 𝐿´
𝑥1
1 − 𝑥1
+ 𝑉´
𝑦2
1 − 𝑦2
𝐿´
𝑥
1 − 𝑥
+ 𝑉´
𝑦1
1 − 𝑦1
= 𝐿´
𝑥1
1 − 𝑥1
+ 𝑉´
𝑦
1 − 𝑦
Total matter balance for component A
𝑑𝑧𝑧
Geankoplis, 1993
12. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
WETTED WALL COLUMN
H.A. Rodríguez et al. 2013; Bruinsma et al., 2012; Li et al., 2017
10
Source: H.A.Rodríguez et al. 2013
ADVANTAGES
DISADVANTAGES
Can neutralize corrosive gas
Can be used in a multi-staged
configuration
Complex design
High maintenance costs
13. 13
UNITOPERATION:ABSORPTION
CONVENTIONAL COLUMNS
Li et al., 2017
TRAY TOWER ADVANTAGES
DISADVANTAGES
Source: Copyright Tri-Mer Corporation, Owosso
Can handle high or low liquid flow rates
cost effectively.
Easily customized to specific requirements
such as operations requiring much heat
Higher pressure drops than packed
columns
Slow reaction rate processes
Plugging and fouling may occur
15. 15
UNITOPERATION:ABSORPTION
CONVENTIONAL COLUMNS
𝑦1
𝑦2
0
𝑥2 𝑥1
Operating line
Balance line
Molarfraction,y
Molar fraction, x
𝑦2
𝑦1
0
Balance line
Operating line
Figure 1. Location of operation lines: a) for absorption of A from V to the current L, and b) for
rectification of A from L to the current V
a) b)
Molarfraction,y
Molar fraction, x
𝑥1 𝑥2
19. 19
UNITOPERATION:ABSORPTION
LIMITATIONS
Chattopadhyay et al., 2007; Narimani et al., 2017; Hassan et al., 2016
ABSORPTION
DISADVANTAGE
Low biodegradation of absorbents
Nagging problems of corrosion
Source: www.encyclopedia.che.engin.umich.edu
Much energy-intensive for the
regeneration of solvents
20. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Removal efficiency of SO2 for various absorbents. Source: Rahmani et al, 2015.
Solubility study in a flask with pressure
and temperature indicators.
Rahmani et al., 2015
Amino acid salt
Sodium based
buffer solutions
Sterically
hindered
amines
Amide
21. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Variations of removal efficiency of SO2 with temperature.
Source: Rahmani et al, 2015.
Operational behavior of absorbents in
packed column
Rahmani et al., 2015
Why packed colum?
High efficiency, high capacity, low pressure drop
𝑆𝑂2 inlet
concentration
𝐿/𝐺 ratio
Temperature Removal
Removal
Range: 0.007 − 0.008
22. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Variations of 𝐾 𝐺 𝑎 𝑉 with: a) partial pressure, b)temperature. Source: Xu et al., 2016
Determination of 𝐾 𝐺 𝑎 𝑉 considering
different operational parameterXu et al., 2016
Solvent: DEEAGas:𝐶𝑂2
a
24. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Removal of CO2 and or 𝐾 𝐺 𝑎 versus liquid flow rate. Source: Xu et al, 2017.
New configuration of spray towerXiaomei Wu et al., 2017
Dual-nozzle opposed impinging spray
MEA
Gas
Solvent
Diameter-varying
CO2
25. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Schematic diagram of wetted-wire column (a) cropped view
(b) side view . Source: Abouali et al, 2017.
Abouali et al., 2016 Simulation in MATLAB
Absorption system:
CO2-MEA
Fast reaction and gas
phase mass transfer
resistance
Overall mass
transfer coefficient
Gas absorption
rate
Efficiency of
column
26. UNITOPERATION:ABSORPTION
CURRENT RESEARCHES
10
Comparison between the predicted values and experimental data, presented by Migita et
al., .Source: Abouali et al, 2017.
Abouali et al., 2016 Comparison with experimental data
Migita et al., 2005
Uchiyama et al., 2003
Multi-wetted-wire column
One wetted-wire column
28. UNITOPERATION:ABSORPTION
RESULTS & DISCUSSION
28
There isn’t important fluctuations in the pH of water through the time.
0
1
2
3
4
5
6
7
0 5 10 15 20
pH
Time (min)
pH of the liquid versus time
Series1
Series2
3 SCFH
5 SCFH
Variation of the pH of the water at the outlet of the absorption column with respect to the time for
the carbon dioxide flow of 3 and 5 SCFH. Source: Authors.
29. UNITOPERATION:ABSORPTION
RESULTS & DISCUSSION
29
Standard deviation
dispersion measure
Percentage increase in water
acidity
Van Ness, 2007
𝜎 = 𝑖=1
𝑛
(𝑝𝐻𝑖 − 𝑝𝐻)2
𝑛
Average deviation
dispersion measure
𝑝𝐻 =
1
𝑛
𝑖=1
𝑛
𝑝𝐻𝑖
% cambio pH =
𝑝𝐻 𝑓𝑖𝑛𝑎𝑙 − 𝑝𝐻𝑖𝑛𝑖𝑐𝑖𝑎𝑙
𝑝𝐻𝑖𝑛𝑖𝑐𝑖𝑎𝑙
∙ 100
30. UNITOPERATION:ABSRPTION
RESULTS & DISCUSSION
30
Average, standard deviation and % change of pH of the liquid at the outlet of the
absorption column for carbon dioxide flow of 3 and 5 SCFH
Flujo de CO2
(SCFH)
pH
promedio
Desviación
estándar (𝝈)
% Cambio de pH
3 5.14 ±0.046 -13.18
5 4.97 ±0.064 -16.04
Little dispersion of data. Decrease in pH
Increased absorption at
high flow rates.
31. 31
UNITOPERATION:ABSORPTION
RESULTS & DISCUSSION
CALCULATION OF THE DIAMETER OF
A PACKED TOWER
The value of the abscissa is calculated.
For a given pressure drop it reads the
ordinates a value for a given expression.
For a given packing factor, the capacity factor
is cleared.
The surface velocity and the gas flow rate are
determined.
The area is found from the ratio of liquid flow
rate and liquid velocity.
The diameter of the tower is calculated
Calderon & Luna, 2007
35. UNITOPERATION:ABSORPTION
CONCLUSION
35
Absorption column. Source: www. spanish.alibaba.com
Absorption is the one of the most
commonly used separation techniques
for the gas cleaning purpose for
removal of various gases like H2S, CO2,
SO2 and ammonia.
Design of the column involves
estimation of diameter of the column
and height of the packing required for
specified separation.
An optimum transfer of mass between
the liquid and gaseous phase in contact
guarantees a better performance of the
absorption column