Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
156
DYNAMIC SIMULATION OF SWEETENING
PROCESS OF NATURAL GAS T. Abbas, M. Ghauri, Z. Rashid, M. Shahid
Abstract — Natural gas is incomparable to other
energy sources in economics amenity and in environmental
interests. Carbon dioxide (CO2), hydrogen sulphide (H2S)
and other impurities are found in natural gas stream that
concern the quality and performance of gas. In order to
reduce their concentration less than 2 % to meet the
contractual specification, amine sweetening process is
used. In this paper, simulation study and modeling of
equipment for gas sweetening plant with di-ethanolamine
(DEA) has been investigated on HYSYS in “DYNAMIC
STATE”. The aim of this study is to design, optimize the
sweetening process and study of absorber design in both
steady and dynamic state. Simulation results show that in
dynamic mode the absorption of CO2 is constant
throughout the process.
Key Words — Natural Gas, Amine Process,
Simulation, Modeling, CO2, H2S.
I. INTRODUCTION
Discovery and utilization of coal has tremendous
effects in industrial development on this planet earth.
That is why the nineteenth century was known as a
century of coal and with the help of this fossil fuel
industrial revolution in Europe took place as this
provided the electricity to the entire Europe. As a
matter of fact, the twentieth century was called the
century of oil, the major energy source to support the
expansion of global economy. Natural gas took over
the position of coal as the number two energy source
behind oil in the late twentieth century. This boom of
global expansion is because of numerous factors,
including development of new markets, substitution
of coal as fuel for providing space and industrial
utilities requirement, use of natural gas in making
petrochemicals and fertilizers, and strong demand for
low-sulfur fuels [1,2].
Natural gas mainly consists of large quantity of
methane along with heavier hydrocarbons such as
higher alkanes and alkenes; moreover in the raw state
it often contains a considerable amount of non
hydrocarbons, such as nitrogen and the acid gases
(carbon dioxide and hydrogen sulfide).A natural gas
stream is approximately two mole percent (mol%)
sour. It means for every 100 kgmoles of gas 2
kgmoles of hydrogen sulfide (H2S) are present in it
[3]. As a matter of fact, H2S and CO2 are corrosive in
aqueous solution. Furthermore, they are very toxic in
nature and have very low heating value. Due to these
facts, sales gas is required to be sweetened to contain
no more than a quarter grain H2S per 100 standard
cubic feet (4 parts per million) and to have a heating
value of no less than 920 to 980 Btu/SCF, depending
on the contract [4].
There are quite a few treating processes available for
removal of acid gases from natural gas, including
Chemical solvents, Physical solvents, Adsorption
Processes Hybrid solvents and Physical separation
[5].
In the past few years, amine solvents for the removal
of acid gases have received increased attentions. In
this process the acidic components react with an
alkanol-amine absorption liquid via an exothermic,
reversible reaction in a gas/liquid contactor. In a
following process step the acidic components are
removed from the solvent in a regenerator, usually at
low pressure and/or high temperature [6]. Mono-
ethanol amine (MEA), di-ethanol amine (DEA), di-
isopropanol amine (DIPA) and N-methyl di-ethanol
amine (MDEA) are widely accepted alkanol amines
for industrial operations [7].
In the present paper, the use of amine di-
ethanolamine (DEA) has been investigated for a
variety of cases using a process simulation program
HYSYS in dynamic state.
II. AMINE PROCESS
The low operating cost and flexibility of tailoring
solvent composition to suit gas compositions make
this process one of the most widely used [8].
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
157
Sour gas is firstly fed into a unit, scrubber, for the
removal of entrained liquid phase, water and liquid
hydrocarbons. The gas then enters the bottom of
absorption tower most of the sweet gas exits at the
top of tower.The regenerated amine usually called
lean amine enters at the top of this tower and the two
streams are contacted counter-currently. In this
tower, CO2 and H2S are absorbed with the chemical
reaction into the amine phase. The exit amine
solution, loaded with CO2 and H2S is called rich
amine. This stream is flashed, filtered and then fed to
the top of a stripper to recover the amine and acid
gases are stripped and exit at the top of the tower.
The refluxed water helps in steam stripping the rich
amine solution. The regenerated amine is recycled
back to the top of the absorption tower as shown in
figure 1.
Table.1 Comparison of Amine solvents [10]
Solvent MEA DEA DIPA
Ch.Formula. RNH2 R2NH R`NH
Mol.wt 61 105 133
Amine type Primary Secondary Secondary
Vap.Pressue 100oF(mm
Hg) 1.05 0.058 0.01
Freezing Point oF. 15 20 16
Loading (mol Acid-
gas/mol amine)
0.35 0.5 0.7
H2S/CO2 selectivity 1 1 2
Solvent conc.(wt%) 15-20 20-35 30-40
Acid gas (mol/m) 0.3-0.4 0.5-0.6 0.3-0.4
Circulation
(gal/mole acid gas)
100-
165
60-125 --------
Steam rate(lb/gal) 1-1.2 0.9-1.1 ------
Reboiler temperature oF 240 245 255
Heat of reaction(Btu/lb
acid gas, H2S)
620 630 0
Among the amines shown in the above table 1, the
most common, less expensive, easy to install and
operate absorbent is Di-ethanolamine (DEA). It is a
comprehensive substitute of MEA and becoming the
most widely used gas sweetening solvent. It is a
secondary amine with lower reactivity and less
corrosive than MEA. Moreover, it reacts with COS
and CS2 and the product can be regenerated. It is less
volatile hydrocarbon and possesses low heat of
reaction than MEA. It means DEA is easy in
processing and easy to regenerate [8].
The basic reactions with CO2 and H2S are [8,9]
2���� + ��� ⇔ ������� 1
H2S reacts with MEA, DEA, or MDEA to form
hydrogen sulfide and protonated amine.
������� + ��� ⇔ 2������� 2
2���� + �� ⟺ ��� ������� 3
Based on above reactions, 1.7 lbs of DEA can be
used to react with the same amount of acid gas as 1.0
lb of MEA. Because of its lower corrosive nature,
higher strength upto 35% (wt) of DEA can be used.
Loading up to 0.65 mol of acid gas per mole of DEA
can cause fewer operational problems than MEA
because the elimination of the degradation products
and the absence of a reclaimer. DEA is weaker than
MEA so that Corrosion is less in a process where
DEA is used instead of MEA. Foaming is reduced
due to absence of degradation and corrosion products
[8].
III. Simulation and Modeling
The simulation model is developed on Aspentech
HYSYS 7.1.The type of fluid package selected is
Amine Package.DEA used as an aqueous absorbent
to absorb H2S and CO2 from sour gas streams. Before
entering the contractor, the sour gas is passed through
an inlet separator where entrained droplets of liquid
are removed from the gas stream. Specification of
sour gas is shown in table 2.
Table 2. Inlet sour gas and amine specifications
Parameters Values
Inlet gas flow rate 1245 kgmole/hr
Inlet liquid flow rate 1886 kgmole/hr
Inlet gas temperature 86 oF
Inlet liquid Temperature 99 oF
Amine concentration 28%
Gas in pressure 998 psia
L. Amine in pressure 995 psia
H2S in sour gas 2.5 mole%
CO2 in sour gas 4.13 mole %
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
158
Figure 1. Process Flow Sheet.
The whole process is modeled and simulated in
dynamic state as shown in figure (1) in order to get
the best absorption results, to avoid foaming, to meet
the sweet gas specification which may be result of
poor contact of sour gas and solvent. In order to
avoid all these problems controller loops are used
that after regular interval of time check the
composition of streams and take the action to get
exact required sweet gas specification all the times.
IV. Results and Discussion
The aim of the study is to investigate the effect of
using diethanolamine (DEA)) on the natural gas
treatment process using the process simulation
program HYSYS in dynamic state.
Temperature profile
It can be observed that in figure (2, steady state) and
figure (3, dynamic state) the temperature continues to
increase. This may be explained as follows. As the
liquid flows down the tower, it continues to absorb
acid gas. This absorption is accompanied by a heat of
reaction, which causes the temperature of the liquid
to continue to rise. The temperature drop at the
bottom of the tower results from the cold gas entering
the bottom and contacting the hot liquid flowing
downwards. The cold gas absorbs heat from the hot
liquid causing its temperature to decrease. This
results in a temperature profile at bottom of the
tower.
No. of Stages
0 5 10 15 20 25
Te
mp
era
ture
[o
C ]
30
35
40
45
50
55
60
65
70
Figure 2. Temperature Profile Vs No. of Stages (steady state).
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
159
No. of Stages
0 5 10 15 20 25
Tem
pera
ture
[oC]
30
40
50
60
70
80
Figure 3. Temperature Profile Vs No. of Stages (dynamic state)
Absorption of CO2 and H2S
The absorption of CO2 and H2S on different stages of
absorber with 20 trays can be observed in figure (4).
The sweet gas has composition of CO2 and H2S in
mole fraction are 0.0000004 and 0.0000001
respectively with net molar flow in MMSCFD for
both liquid and vapor phases in absorber as shown in
figure(5). The whole process is simulated in dynamic
mode, sweet gas with constant composition of CO2
and H2S is obtained, the strip chart covering the
complete simulation results of CO2 and H2S is shown
in figure (6)
No.of Stages
0 5 10 15 20 25
Mo
le F
ract
ion
Ab
sorb
ed
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
No.of Stages vs CO2 Absorbed
No.of Stages vs H2S Aborbed
Figure 4. Mole Fraction of CO2 and H2S absorbed
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
160
No. of Stages
0 5 10 15 20 25
Net M
ola
r F
low
[M
MS
CF
D]
22
24
26
28
30
32
34
36
38
40
42
No.of Stages vs Vapor Molar Flow
No.of Stages vs Liquid Molar Flow
Figure 5. Molar Flow in absorber
Strip Chart of Simulation Results
Strip chart of simulation model shows the constant
result of sweetening process. The integrator runs
from 0 to 20 minutes, CO2 concentration in sweet gas
is regularly observed. In figure (6) it can be seen that
CO2 concentration is 0.000000 (mole fraction) with
same flow rate of DEA to absorber throughout the
process.
Figure 6: Strip chart of Simulation Results
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
Conclusion
The principle investigation was directed to study the
effect of using diethanolamine (DEA), as solvent on
the gas treatment process using the software HYSYS
In all cases, DEA was the best result in the absorption
processes of CO2 and H2Sfrom the natural g
dynamic state The simulation result show that, by
using of the 1886(kg mole /h) DEA with T=99
P=995 (psia) were the best result in the absorption
processes of CO2 (0.0000004, mole fraction) and H
(0.0000001, mole fraction) without any fluctu
throughout the dynamic process.
REFERENCES
[1] Vadud.A.S. “Natural gas desulfurization.Slovenska Technicka
Univerzita V Bratislave”, 2009.
[2] Ikoku,C.U, Natural Gas Production Engineering.
John Weley & Sons, Krieger Publishing Company.,
13. ISBN: 0-89464-639-7.
[3] Abdel-Al. H.K., Aggour. M., and Fahim M.A, Petroleum and
gas Field Processing , Marcel Dekker, Inc., 2003, pp 269
ISBN: 0-8247-0962-4.
BIOGRAPHIES
Engr. Tauqeer Abbas is Research Associate in
the department of “Environmental and Energy
Engineering” at COMSATS Institute of
Information Technology Vehari
Born in 1988-Pakistan. He holds is B.Sc
degree in the field of Chemical Engineering
from COMSATS Institute of Information
Technology, Lahore, Pakistan. His area of
interest is Energy Conservation, Modeling and Simulation of
Separation Processes. He is an active member of Proces
Engineering Group of Biomass Conversion Research Center, CIIT,
Lahore, Pakistan. He is quite energetic and young researcher,
always ready to accept challenges. His email id is
Dr. Moinuddin Ghauri is Associate Professor
in Chemical Engineering Department at
COMSATS Institute of Information
Technology Lahore-Campus
in 1963-Pakistan. He holds Ph.D. in the field
of Chemical Engineering, Energy and
Environment Conservation from the
University of Sheffield, UK. Energy and
Environment is his focus area. He has exposure of working with
leading National, Multinational and European instituti
author of twenty technical teaching-learning resources for
Environmental Control Technology and modules for Chemical
Technology at technical education Pakistan. He is creative by
nature and loves creative and challenging assignments.
INSERT
Canadian Journal on Chemical Engineering & Technology Vol. 2 No. 9, December 2011
161
The principle investigation was directed to study the
effect of using diethanolamine (DEA), as solvent on
process using the software HYSYS.
In all cases, DEA was the best result in the absorption
Sfrom the natural gas in
The simulation result show that, by
using of the 1886(kg mole /h) DEA with T=99 oF and
P=995 (psia) were the best result in the absorption
(0.0000004, mole fraction) and H2S
(0.0000001, mole fraction) without any fluctuation
Slovenska Technicka
[2] Ikoku,C.U, Natural Gas Production Engineering.,New York:
Krieger Publishing Company., 1984. pp 12-
Al. H.K., Aggour. M., and Fahim M.A, Petroleum and
, 2003, pp 269-271.
[4] Mackenzie. D. H., Prambil .F.C., Daniels. C.A., and Bullin
J.A, “ Design and operation of selective sweetening Plant using
MDEA”, Energy Progress., pp 31-36. 1987.
[5] Sohbi.B., Meakaff.M., Emtir.M., and Elgarni M, “The using of
mixing amines in an industrial gas sweetening plant”,
Academy of Science, Engineering and Technology
,2007.
[6] Huttenhuis.P.J.G., Agrawal.N.J., Hogendoorn.J.A., and
Versteeg. G.F, “Gas solubility of H2S and CO
solutions of N-methyl diethanol amine”, Journal of Petroleum
Science and Engineering., vol.55, pp.122-
DOI:10.1016/j.petrol.2006.04.01.
[7] Zare Aliabad.H, Mirazei S,“Removal of CO2 and H2S using
Aqueous Alkanolamine solusions”, World Academy of Science,
Engineering and Technology.,vol.49, pp.1
[8] Abdel-Al.H.K., Aggour.M., and Fahim.M.A., Petroleum and
gas Field Processing ” Marcel Dekker, Inc., 2003.pp. 281
ISBN: 0-8247-0962-4.
[9]Danckwerts.P.V, “The reaction of CO2 with ethanolamines”,
Chem.Eng.Sci.vol.,34,pp.443-446. 1979.
2509(79)85087-3.
[10] Abdel-Al. H.K., Aggour. M., and Fahim M.A., Petroleum and
gas Field Processing , Marcel Dekker, Inc.
ISBN: 0-8247-0962-4.
Engr. Tauqeer Abbas is Research Associate in
the department of “Environmental and Energy
Engineering” at COMSATS Institute of
Information Technology Vehari-Pakistan.
He holds is B.Sc
degree in the field of Chemical Engineering
from COMSATS Institute of Information
Technology, Lahore, Pakistan. His area of
interest is Energy Conservation, Modeling and Simulation of
Separation Processes. He is an active member of Process System
Engineering Group of Biomass Conversion Research Center, CIIT,
Lahore, Pakistan. He is quite energetic and young researcher,
His email id is
Dr. Moinuddin Ghauri is Associate Professor
Chemical Engineering Department at
COMSATS Institute of Information
Campus, Pakistan. Born
He holds Ph.D. in the field
of Chemical Engineering, Energy and
Environment Conservation from the
University of Sheffield, UK. Energy and
is his focus area. He has exposure of working with
leading National, Multinational and European institutions. He is
learning resources for
Environmental Control Technology and modules for Chemical
. He is creative by
nature and loves creative and challenging assignments.
Engr. Zeeshan Rashid is Lecturer in Chemical
Engineering Department at COMSATS
Institute of Information Technology Lahore
Campus, Pakistan. Born in 1985
did his M.S from University of Teesside, U.K
in Process Manufacturi
area of research is Modeling and
and process design. He worked as Process Technologist in Aker
Solution Pvt Limited, UK.
Dr. Muhammad Shahid is Assistant Professor
in the department of “Environmental
Energy Engineering” at COMSATS Institute
of Information Technology Vehari
He is Ph.D. from INP
France in the field of “Soil & Environmental
Sciences”. His area of interest includes
Environmental Toxicology, Soil Science and
Green Energy. His doctoral thesis has been awarded “
Escande” award by INP-ENSAT. He has several publications in
the field of Soil & Environmental Sciences in high impact factor
journals.
INSERT
[4] Mackenzie. D. H., Prambil .F.C., Daniels. C.A., and Bullin
Design and operation of selective sweetening Plant using
36. 1987.
[5] Sohbi.B., Meakaff.M., Emtir.M., and Elgarni M, “The using of
mixing amines in an industrial gas sweetening plant”, World
and Technology.,vol. 31,pp 1-2.
] Huttenhuis.P.J.G., Agrawal.N.J., Hogendoorn.J.A., and
S and CO2 in aqueous
Journal of Petroleum
-134. 2007.
] Zare Aliabad.H, Mirazei S,“Removal of CO2 and H2S using
World Academy of Science,
.,vol.49, pp.1-2. 2009.
Fahim.M.A., Petroleum and
gas Field Processing ” Marcel Dekker, Inc., 2003.pp. 281-282.
“The reaction of CO2 with ethanolamines”,
446. 1979. DOI:10.1016/0009-
Al. H.K., Aggour. M., and Fahim M.A., Petroleum and
Marcel Dekker, Inc., 2003. pp 280-281.
Engr. Zeeshan Rashid is Lecturer in Chemical
Engineering Department at COMSATS
Institute of Information Technology Lahore-
Born in 1985- Pakistan. He
did his M.S from University of Teesside, U.K
Process Manufacturing Engineering. His
Modeling and Simulation
He worked as Process Technologist in Aker
Dr. Muhammad Shahid is Assistant Professor
in the department of “Environmental and
Energy Engineering” at COMSATS Institute
of Information Technology Vehari-Pakistan.
He is Ph.D. from INP-ENSAT, Toulouse-
France in the field of “Soil & Environmental
Sciences”. His area of interest includes
Environmental Toxicology, Soil Science and
een Energy. His doctoral thesis has been awarded “Léoplod
ENSAT. He has several publications in
the field of Soil & Environmental Sciences in high impact factor