Hydrocarbon Processing - October 2021 - 50

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sorption within the column. This provides a useful guideline for
the dosage of promoters to be used during industrial operations.
Rigorous modeling with proprietary feature. Distillation
and absorption are typically simulated with equilibrium stages,
which is often not true in practice.12
To account for the deviation
from the equilibrium, tray efficiency is used in the simulation.
However, selection of efficiency is an empirical choice,
and the prediction methods for efficiency are often unreliable.
In packed columns, HETP is used in place of the theoretical
stage, which is also difficult to predict accurately.
In contrast, the rate-based distillation model simultaneously
calculates mass and heat transfer rate, and accounts for the multicomponent
interactions between diffusing species. It includes
the well-known and accepted industry correlations to estimate
the mass coefficients, liquid holdup and interfacial areas, as well
as the heat transfer coefficients.
In Version 10 of the proprietary softwarea
, the Chilton and
Colburn method13
is normally used for heat transfer coefficients.
The model calculates heat transfer coefficients from the
binary mass transfer coefficients. In this study, this correlation
is selected for all the cases to calculate the heat transfer coefficients.
The Billet 93 method14
is typically used for the liquid
holdup calculation for random packings. The interfacial areas
are calculated with the methods that are consistent with the
correlations for mass transfer coefficients. This is where most
process engineers may become confounded, as there are several
options available for calculating mass transfer coefficients.
To help others use the rate-based column modeling, this
study explores the different mass transfer correlation methods
for the random packings employed in the specific model of the
TABLE 1. Method comparison of random packings with CO2
Correlation
methods
Billet 93
Brf 82
Onda 68
Mass transfer
correlation
Billet 93
Bravo and Fair
(1982)
Onda 68
Hanley Im10 Hanley Im10
Heat transfer
correlation
proprietary software used to simulate these methodsc
be used in random packed beds:
1. Billet 93
2. Brf 92 or Brf 82
3. Onda 68
4. Hanley Im10.
For detailed description of these correlations, please refer to the
original publications.14-17
Rigorous model performance. The correlations used for
mass transfer coefficients have been explored in rate-based
column modelingc
simulate the CO2
. The rate-based models are created to
absorbers, using K2
. The correlations
for structured packings are excluded, as the validation
data is not collected for the structured packings in this study.
The modelc
has four options for mass transfer correlations to
CO3 aqueous solvent of
both CATACARB and Benfield processes. The simulated results
are compared with the reported operation data collected.
The comparison is summarized in TABLE 1 and TABLE 2 for the
random packingsd
.
Recommendations. Based on the model performancec
dom packingsd
are recommended for typical CO2
for ran,
the Brf 82 or Onda 68 mass transfer correlations
removal processes, as both
provide consistent predictions as compared to the reported data.
The consistent behavior of these two models are expected, as
the Brf 82/Brf 92 is developed based on the Onda model. The
purpose of this study is to provide insight on the selection of
correlations for mass transfer coefficients when using rate-based
modelinga
for columns. A far-reaching evaluation of these mass
transfer correlations requires more industry data to explore.
absorber of the CATACARB process
Interfacial
area method
Chilton and Colbum Billet 93
Chilton and Colbum Billet 93
Chilton and Colbum Billet 93
Chilton and Colbum Billet 93
TABLE 2. Method comparison of random packings with CO2
Correlation
methods
Billet 93
Brf 82
Onda 68
Mass transfer
correlation
Billet 93
Bravo and Fair
(1982)
Onda 68
Hanley Im10 Hanley Im10
Heat transfer
correlation
Liquid holdup
method
Billet 93
Billet 93
Billet 93
Billet 93
Predicted
CO2
content
in overhead
0.99 mol%
0.86 mol%
0.85 mol%
0.92 mol%
absorber of the Benfield process
Interfacial
area method
Chilton and Colbum Billet 93
Chilton and Colbum Bravo and Fair
(1982)
Chilton and Colbum Onda 68
Chilton and Colbum Hanley Im10
50 OCTOBER 2021 | HydrocarbonProcessing.com
Liquid holdup
method
Billet 93
Billet 93
Billet 93
Billet 93
Predicted
CO2
content
in overhead
0.11 mol%
0.106 mol%
0.108 mol%
0.14 mol%
Reported
CO2
content
in overhead
0.1 mol%
0.1 mol%
0.1 mol%
0.1 mol%
Note
CL = 1.38
CV = 0.42
No option for liquid
holdup method
No option for liquid
holdup method
No option for liquid
holdup method
Reported
CO2
content
in overhead
0.8 mol%
0.8 mol%
0.8 mol%
0.8 mol%
Note
CL = 1.38
CV = 0.42
No option for liquid
holdup method
No option for liquid
holdup method
No option for liquid
holdup method
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