sustainability
Article
Improving the Carbon Capture Efficiency for Gas Power Plants
through Amine-Based Absorbents
Saman Hasan *, Abubakar Jibrin Abbas and Ghasem Ghavami Nasr
School of Science, Engineering and Environment, University of Salford, Manchester M5 4WT, UK;
a.j.abbas@salford.ac.uk (A.J.A.); g.g.nasr@salford.ac.uk (G.G.N.)
* Correspondence: saman.hussein@ymail.com or s.h.hasan@edu.salford.ac.uk
Citation: Hasan, S.; Abbas, A.J.; Nasr,
G.G. Improving the Carbon Capture
Abstract: Environmental concern for our planet has changed significantly over time due to climate
change, caused by an increasing population and the subsequent demand for electricity, and thus
increased power generation. Considering that natural gas is regarded as a promising fuel for
such a purpose, the need to integrate carbon capture technologies in such plants is becoming a
necessity, if gas power plants are to be aligned with the reduction of CO2 in the atmosphere, through
understanding the capturing efficacy of different absorbents under different operating conditions.
Therefore, this study provided for the first time the comparison of available absorbents in relation
to amine solvents (MEA, DEA, and DEA) CO2 removal efficiency, cost, and recirculation rate to
achieve Climate change action through caron capture without causing absorbent disintegration.
The study analyzed Flue under different amine-based solvent solutions (monoethanolamine (MEA),
diethanolamine (DEA), and methyldiethanolamine (MDEA)), in order to compare their potential for
CO2 reduction under different operating conditions and costs. This was simulated using ProMax
5.0 software modeled as a simple absorber tower to absorb CO2 from flue gas. Furthermore, MEA,
DEA, and MDEA adsorbents were used with a temperature of 38 ◦ C and their concentration varied
from 10 to 15%. Circulation rates of 200–300 m3 /h were used for each concentration and solvent.
The findings deduced that MEA is a promising solvent compared to DEA and MDEA in terms of
the highest CO2 captured; however, it is limited at the top outlet for clean flue gas, which contained
3.6295% of CO2 and less than half a percent of DEA and MDEA, but this can be addressed either by
increasing the concentration to 15% or increasing the MEA circulation rate to 300 m3 /h.
Efficiency for Gas Power Plants
through Amine-Based Absorbents.
Sustainability 2021, 13, 72.
https://dx.doi.org/10.3390/
Keywords: process technology description of different amine solvents; amine-based chemical solvent
using monoethanolamine (MEA); degradation of MEA and other solvents; diethanolamine (DEA)
solvent; methyldiethanolamine (MDEA)
su13010072
Received: 23 October 2020
Accepted: 17 December 2020
Published: 23 December 2020
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Copyright: © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This
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Creative Commons Attribution (CC BY)
license (https://creativecommons.org/
licenses/by/4.0/).
1. Introduction
A considerable amount of attention has been focused on our planet due to the conceivable outcomes of climate change, which is a result of the energy generated from fossil
fuel emissions and greenhouse gases such as CO2 . Therefore, the number of CO2 capture
technologies has increased significantly due to their flexibility and design, efficacious cost,
and proficient application [1,2]. In addition, flue gas is released into the environment from
diverse industries, including power generation, the petrochemical industry, and refinery
gases [3]. The definition of flue gas is a blend of combustion products, including carbon
dioxide, particulates, water vapor, heavy metals, and acidic gases, generated from indirect
(gasification and pyrolysis) intermediate synthesis gas or the oxidation of radial distribution
functions (RDF) or generated directly (incineration) [4,5]. In this research, we will examine
which of the chemical solvents of monoethanolamine (MEA), diethanolamine (DEA), and
methyldiethanolamine (MDEA) are best able to produce good, low-cost outcomes; low
amine degradation; and losses to remove or capture CO2 from flue gases. Carbone dioxide
must be separated from the gases and other vapors by using absorption technology, which
Sustainability 2021, 13, 72. https://dx.doi.org/10.3390/su13010072
https://www.mdpi.com/journal/sustainability
Sustainability 2021, 13, 72
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is used to remove carbon dioxide from flue gases by employing liquid solvents (e.g., MEA,
MDEA, DEA, etc.) for this purpose. This was conducted in this study by a simulation
program (ProMax) and there were two scenarios employed to compare amine solvents
from previous study [6]. Currently, chemical solvents using absorption process consider
use the technology of the post-combustion CO2 capture technologies, considered one of
the best technology for capturing CO2 , in addition to pre-combustion capture that has been
used to remove CO2 and H2 S from natural gas components in a refinery [5–7].
This study also presents trade-off option of CO2 capture versus amine recirculation
required and cost for amine solvents (MEA, DEA, and MDEA). Therefore, the most significant problem which must be determined and considered is the percentage of oxygen
in the flue gas, which is affected by caused degrade of the amine solvents. These solvents
cause oxidative degradation and should prevent it and limit it to around 5 to 10 ppm [8].
Additionally, as a UK report, the highest emission came from power generation, which
is shown in Table 1. Therefore, choosing a power generation station represents the best
source of CO2 . The total emission of CO2 by power stations in the UK annually given in
a British petroleum (BP) report is 65.2 million tons, which is a huge number, as shown in
Table 1 [5].
Table 1. Greenhouse gas emissions in 1990–2018 in the UK on an annual basis (CO2 in million tons).
Years
1990
1995
2000
2005
2010
2015
2017
2018
Energy supply
from power
stations
242.1
210.3
204.0
219.1
197.3
137.6
106.0
98.3
203.0
163.0
158.7
173.1
157.3
104.1
72.4
65.2
2. Theory (Literature Review)
2.1. Background
There are two significant points that should be considered before capture CO2 ,
which are
(a)
(b)
How to deal with the huge amount of carbon dioxide from fossil fuels formed
during combustion;
How to grip impurities of the stream in flue gas.
The impurities in flue gas may contain sulfur and nitrogen oxides, particulate matter,
and water vapor. The combustion of the fuel source will produce various amounts of impurities and changes, depending upon the fuel source. It is crucial to know the fundamental
mechanisms behind CO2 and to prevent impurities and the formation of impurities during
the combustion of fossil fuel [9]. The common reactions taking place during combustion
can be applied to any fuel for CO2 formation, as follows in Equations (1) and (2) [9]:
C + 0.5O2 → CO
(1)
This is uncompleted combustion,
C + O2 → CO2
(2)
This is a complete combustion.
It should be noted that, when using natural gas instead of coal, the emissions of
carbon dioxide will be significantly reduced and the coal will emit more nitrogen and
sulfur dioxide because it will contain more impurities, rather than natural gas. Acid rain
is caused by nitrogen and sulfur oxides, which are the main contributors to its formation.
There is an advantage of employing some technologies for capturing CO2 , such as oxycombustion, chemical looping combustion, and pre-combustion, which is the creation of
an environment for combustion without impurity precursors, such as H2 , S, N, and N2 .
However, there are certain amounts of inherent nitrogen and sulfur in fuel, so complete
Sustainability 2021, 13, 72
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impurity removal is not possible, and it cannot be considered as a perfect fuel. In addition,
this impurity of combustion depends on the process that is used to treat the fuel before
use in burning. In common cases of CO2 capture, the impurities are removed from flue
gas before capture is applied. Finding ways to handle the large quantity of CO2 produced
by burning fuel in power stations, whatever the source of fuel, is a big challenge [9]. In
the different power plants in Hebei Province, China, as shown in Table 2, the raw coal had
a high emission value of about 900 to 1000 g per KW/h, which is double the amount of
oil and gas that was emitted. Moreover, it needs excess oxygen more than other fuels to
complete combustion, which is considered a challenge when using chemical solvents to
capture CO2 , increasing the degradation when amine solution is used [10,11]. However,
the consumption of fuel per KW/h for oil and natural gas represents less than one third
of the consumption of raw coal required to generate power. Currently, commercial CO2
capture systems have a maximum capacity of about 800 t/d CO2 , which means that the
capture process emits approximately ten times less than that in a power plant. Therefore, it
is appropriate to begin discussing the various CO2 capture approaches and their associated
technologies, such as post-combustion, pre-combustion, oxy combustion, and chemical
looping combustion [7,9,10,12,13].
Table 2. The emission of flue gases from different power plans in Hebei Province, China.
Fuel
Type
Fuel per
KilowattHour
PM2.5
(mg/m3 )
SO2
Emission
(mg/m3 )
CO2
Emission
(g)
NOx
Emission
(mg/m3 )
Coal
290–340
g
20–30
50–200
900–1000
100–200
Oil
80–90 g
20–30
50–100
400–450
100–200
Natural
gas
70–80 g
5–20
35–50
400–450
100–150
CO
O2 %
Emission
1800–
2000
1800–
2000
1800–
2000
9
3.5
3.5
On the other hand, rather than the amount of CO2 emitted into the atmosphere by
many industries, the chemical and the physical properties of the CO2 should be studied
to learn about it and how it behaves. Therefore, Table 3 illustrates the physical and
chemical properties of CO2 [14], and Table 1 shows the properties of CO2 that used in
amine absorption come out from ProMax in Appendix A.
2.2. Process Technology Description of Different Amines
Amine processing includes two major processes of absorption and separation. When
the CO2 is absorbed by a lean amine aqueous solution solvent through an absorption
process, the equipment used is called an absorber. In addition, the process in which
the CO2 is separated from aqueous solution by applying heat is called a separation or
regeneration process, and the equipment employed is called a regenerator or stripper [15].
Moreover, the treatment occurs at an absorber at high pressure and at a low temperature,
while at the stripper, there is a low pressure and high temperature between 100 and
120 ◦ C [13,16]. There are some arguments about the stripping temperature, which varies
between 120 and 150 ◦ C [8,17], 95 and 135 ◦ C [18], and 120 and 140 ◦ C [15]. Therefore, the
system includes heat, a cooling source, and a compressor to raise the pressure of flue gas
before it enters the absorber. Furthermore, the system includes a pump to circulate the lean
solution and rich amine [13,15,16]. In absorption, the following steps occur [19]:
(a)
(b)
(c)
(d)
CO2 dissolves into the absorbent;
A low temperature is required to ensure a high rapport for the absorption of CO2 ;
The distribution of CO2 will occur between the gas–liquid interface and the bulk gas;
The CO2 will react with the amine in the solution.
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Table 3. The physical and chemical properties of CO2.
Property
Value and Unit
Molecular weight
Critical density (ρc)
Critical pressure (Pc)
Critical temperature (Tc)
Triple point pressure
Triple point at 5.1 atm (518 kPa)
Sublimation point at 1 atm (101.3 kPa)
Gas density at 0 ◦ C and 1 atm (101.3 kPa)
Liquid density at 0 ◦ C and 1 atm (101.3 kPa)
25 ◦ C and 1 atm CO2 (101.3 kPa)
Solid density
Specific volume at 1 atm and 21 ◦ C
Latent heat of vaporization at the triple point
(−78.5 ◦ C)
At 0 ◦ C
231.3 J/g
Viscosity at 25 ◦ C and 1 atm CO2 (101.3 kPa)
Solubility in water at 0 ◦ C and 1 atm (101.3 kPa)
44.01 g/mol
0.468 g/cm3 or 468 g/L or 468 kg/m
72.85 atm (7383 kPa)
31.04 ◦ C
5.185 bar
−56.5 ◦ C
−78.5 ◦ C
1.976 g/L
928 g/L
0.712 v/v
1560 g/L
0.546 m3 /kg
25 ◦ C and 1 atm (101.3 kPa)
0.3346 g CO2 /100 g-H2 O or 1.713 mL
CO2 /mL-H2 O at 0 ◦ C
0.1449 g CO2 /100 g-H2 O or 0.759 mL CO2 /mL-H2 O
at 25 ◦ C
Heat of formation at 25 ◦ C, ∆H gas
353.4 J/g
0.015 cP (mPas)
0.1372−393.5 kJ/mol
The flue gas results from burning fossil fuel in power stations and represents approximately 3–20% of gas emitted. It is fed into an absorption column, needed to cool the
temperature of flue gas to below 50 ◦ C or about 47–50 ◦ C, due to the high temperatures
of the exhaust gas of power generations [17]. After the flue gas has been cooled by an
exchanger, such as cooling water and a fan cooler, it will enter the absorption tower or
so-called absorber column and pass through it from bottom to top, in which approximately
86–90 vol.% of the CO2 is absorbed by solvent [5,13,15,20] and amine absorbs the carbon
dioxide at 40–75 ◦ C [18]. In addition, the absorbent or solvent enters the column from the
top side of the tower and moves down to the bottom. In the meantime, the flue gas which
contains acid gas will react with the solvent and usually has a temperature of nearly 40 ◦ C.
Through this process, lean amine is converted into rich amine, which means that CO2 is
absorbed by aqueous amine solution. Secondly, heat is released as a result of the absorbed
CO2 and the temperature of the solvent is increased due to the exothermic reaction, which
is a kind of reversible reaction. At the bottom of the absorber, the CO2 -rich stream will
be collected at a required level, to prevent untreated gas from escaping from the desorber
tower and, for safety reasons, to prevent the stripper tower caps and trays from being
damaged due to the high differential pressure between the regenerator and absorber.
The purified gas emitted out into the atmosphere is washed by water at the top of
the absorber to cool the top of the tower, prevent evaporation of the amine solution, and
mitigate the loss of solvent [9,13,15,17]. Furthermore, the loading is varied from 0.1 to
0.45 mol CO2 /mol amine, depending on the lean and rich solvent (generally, lean and
rich solvent CO2 loading of 0.1-0.2 mol CO2 /mol MEA and 0.4–0.5 mol CO2 /mol MEA,
respectively) and on several other factors, which are
a.
b.
c.
The increasing or decreasing amine flow rate;
The increasing/decreasing concentration of amine, considering the factors of corrosion that are caused by amine and the amount of CO2 that will be absorbed;
The loading is defined as the total amount of CO2 absorbed by amine and can be
described as in Equations (3) and (4) [16,21]:
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Loading =
Moles of all CO carrying species
Moles of all MEA carrying species
Loading =
Moles of all CO carrying species
Moles of all MEA+ carrying species−
[MEA] + [MEA ] + [MEACOO ]
Loading =
+
] + [MEA
] +−[2MEACOO− ] −
[CO[2MEA
]+[HCO
3 ]+[CO3 ]+[ MEACOO ]
Loading =
(3)
(3)
(4)
(4)
[CO 2 ] + [HCO 3 ] + [CO 3 −2 ] + [MEACOO−
The absorber column or tower includes trays and is different, depending on the solThe absorber
column orprocess
tower includes
trays1and
is different,
depending
on the
vent used
for the capturing
[15]. Figure
illustrates
the different
types
of solvent
amine
used
for
the
capturing
process
[15].
Figure
1
illustrates
the
different
types
of
amine
aqueous
aqueous solutions with the number of trays used in each solvent [15].
solutions with the number of trays used in each solvent [15].
Figure1.1.Number
Numberof
oftrays
traysrequired
requiredfor
forCO
CO22absorption
absorptionininan
anamine’s
amine’saqueous
aqueoussolution.
solution.
Figure
Therich
richamine
amine solution
solution leaves
leaves via
to
The
via the
the bottom
bottom of
ofthe
theabsorber,
absorber,which
whichisisthen
thenheated
heated
◦ C across the amine–amine exchanger (lean/rich amine heat exchanger). It is
about
100
to about 100 °C across the amine–amine exchanger (lean/rich amine heat exchanger). It is
fedtotothe
thetop
topside
sideofofaastripping
strippingcolumn
columnor
orregenerator,
regenerator,in
inorder
orderto
tominimize
minimizethe
theheating
heating
fed
energycost
costof
ofthe
therich
richsolution,
solution,which
whichisisrequired
requiredbefore
beforeititenters
entersthe
thestripper
stripperto
toavoid
avoid
energy
widely
different
temperatures
between
the
solvent
and
regenerator.
The
flow
that
happens
widely different temperatures between the solvent and regenerator. The flow that hapbetween
the absorber
and stripper
occurs
due to
thetodifferent
pressures
between
them,
pens
between
the absorber
and stripper
occurs
due
the different
pressures
between
which
is
quite
high,
being
about
15–20
times
greater
than
the
regenerator
pressure
[21].
In
them, which is quite high, being about 15–20 times greater than the regenerator pressure
the desorption column, the following occur [19]:
[21]. In the desorption column, the following occur [19]:
(a) To ensure a lower relationship for the absorption of CO2 , the temperature be should
(a) To
beensure
high; a lower relationship for the absorption of CO2, the temperature be should
be
high;
(b) To ensure that CO2 will be released, chemical equilibria should occur;
(b)
ensure
that CO
2 will be released, chemical equilibria should occur;
(c) To
The
desorption
process
is endothermic; therefore, to maintain the high temperature,
(c) The
desorption
process
is
endothermic;
heat must be applied to the
absorbent. therefore, to maintain the high temperature,
heat must be applied to the absorbent.
Where further heated, a supply at the bottom of the stripper is required to increase the
◦ C aby
temperature
to 120–140
using at
a steam
reboiler
is generated
for this
purpose
Where further
heated,
supply
the bottom
of which
the stripper
is required
to increase
or the
power plant
will become
The operating
pressure
for a stripper
is nearly
the
temperature
to 120–140
°C byexhausted.
using a steam
reboiler which
is generated
for this
pur1.5–2orbar
and
it is formed
of abecome
packed exhausted.
column which
a kettle reboiler
The rich
pose
the
power
plant will
Thehas
operating
pressure[5,15,21].
for a stripper
is
solution
or stable
product
that formed
in the absorber
and thehas
COa2kettle
, whichreboiler
was absorbed
by
nearly
1.5–2
bar and
it is formed
of a packed
column which
[5,15,21].
the solvent,
will be
at the regenerator
then, COand
be CO
released
fromwas
the
The
rich solution
orrecovered
stable product
that formedcolumn;
in the absorber
2, which
2 willthe
◦ C, due to the equilibrium
absorbent
inside
the
stripper
at
a
high
temperature
of
100–120
absorbed by the solvent, will be recovered at the regenerator column; then, CO2 will be
isothermfrom
andthe
loading
(mole
of CO
of amine)
transfer
from higher
(rich°C,
amine)
released
absorbent
inside
the
stripper
at a high
temperature
of 100–120
due
2/ mole
lower
loading isotherm
(lean amine
amine
had
taken
the CO
is why
the
2 ); that
totothe
equilibrium
andmeans
loading
(molethat
of CO
2/mole
ofoff
amine)
transfer
from
higher
solvent-recovering energy cost is high. The lean solution at the bottom of the regenerator
Sustainability 2021, 13, x FOR PEER REVIEW
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(rich amine) to lower loading (lean amine means amine that had taken off the CO2); that
6 of 27
is why the solvent-recovering energy cost is high. The lean solution at the bottom of the
regenerator is circulated back to the absorption tower after passing through the heat exchanger
and cooler
[13,15,16].
The gas
consisting
of a mixture
of the
water
vapor
and CO
2
is circulated
back to
the absorption
tower
after passing
through
heat
exchanger
and
with
some
evaporated
amine
travels
out
of
the
top
of
the
stripper
and
enters
a
cooler
to
cooler [13,15,16]. The gas consisting of a mixture of water vapor and CO2 with some
2 from
condensate
cool
it. Then, amine
it is fed
into aout
flash
drum
thestripper
acid gas,
which
is aCO
evaporated
travels
of the
topand
of the
and
enters
cooler
to cool
it. Then,
water,
and
amine
are
physically
separated,
no
matter
the
kind
of
amine.
Finally,
2 is
it is fed into a flash drum and the acid gas, which is CO2 from condensate water, andCO
amine
compressed
and
transported
for
sequestration.
Figure
2
shows
a
schematic
diagram
of
the
are physically separated, no matter the kind of amine. Finally, CO2 is compressed and
[8,17]. a schematic diagram of the amine-based
amine-based
absorptionFigure
process
transportedchemical
for sequestration.
2 shows
chemical absorption process [8,17].
Figure 2. Schematic diagram of the chemical absorption process used for capturing CO2 with solvent process regeneration.
Figure 2. Schematic diagram of the chemical absorption process used for capturing CO2 with
solvent process regeneration.
2.3.
2.3.Amine-Based
Amine-BasedChemical
ChemicalSolvent
SolventUsing
UsingMonoethanolamine
Monoethanolamine(MEA)
(MEA)
Amines
and where
whereone
oneorormore
morehydrogen
hydrogen
atAminesare
areofficially
officiallyderivatives
derivatives of
of ammonia,
ammonia, and
atoms
oms
have
been
displaced
by
an
organic
substituent,
such
as
an
alkyl
group,
these
amines
have been displaced by an organic substituent, such as an alkyl group, these amines
called
calledalkylamines
alkylamines[22].
[22].MEA
MEAisisone
oneofofthe
themost
mostimportant
importantabsorption
absorptionliquids
liquidsand
andisisthe
the
least
expensive.
It
can
be
produced
in
large
quantities
from
ethylene
oxide
and
ammonia
least expensive. It can be produced in large quantities from ethylene oxide and ammonia
reactions.
reactions.The
TheAcid
AcidDissociation
DissociationConstant
Constant(pKa)
(pKa)isisclose
closetotoa aprimary
primaryamine.
amine.Therefore,
Therefore,itit
has
2, with
anan
overhasa avery
verygood
goodviscosity
viscosityand
andananexcellent
excellentaverage
averagerate
rateofofabsorption
absorptionofofCO
CO
,
with
over2
average
amino group
groupisisthe
theperfect
perfect
group
absorbing
2
averagenormalized
normalizedability
ability [19].
[19]. An amino
group
forfor
absorbing
COCO
2 and
and
provides
enough
alkalinity.
is commonly
dissolved
so that
2 chemically
reacts
provides
enough
alkalinity.
It isItcommonly
dissolved
so that
CO2CO
chemically
reacts
with
with
alkanolamines.
ofmost
the most
crucial
advantages
of alkanolamines
that, struc-at
alkanolamines.
OneOne
of the
crucial
advantages
of alkanolamines
is that,isstructurally,
turally,
at least
one hydroxyl
group is contained
in them.
to help
this, to
it raise
can help
to raise
least one
hydroxyl
group is contained
in them. Due
to this,Due
it can
the solubility
the
in aqueous
solutions
the vapor
pressure
[10]. Monoethanolain solubility
aqueous solutions
and
mitigateand
themitigate
vapor pressure
[10].
Monoethanolamine
(MEA)
is considered
of the most
general
alkanolamine
groups andgroups
is widely
It has
mine
(MEA) is one
considered
one of
the most
general alkanolamine
andused.
is widely
beenItused
for over
years
and
H
S
from
natural
gas
and
flue
gas
[23].
used.
has been
used75for
overto
75remove
years toCO
remove
CO
2
and
H
2
S
from
natural
gas
and
flue
2
2
Due
to Due
MEAtohaving
a high-water
solubility,
high cyclic
and considerable
kinetic
gas
[23].
MEA having
a high-water
solubility,
highcapacity,
cyclic capacity,
and considerarates
of absorption-stripping
at a low CO
it is considered
to be a standard
it is considered
to be
ble
kinetic
rates of absorption-stripping
at 2a concentration,
low CO2 concentration,
sorbent
[8].
a standard sorbent [8].
Thecapacities
capacitiesofofchemical
chemicaland
andphysical
physical
MEA
absorption
are
affected
the
pressure,
The
MEA
absorption
are
affected
byby
the
pressure,
temperature,concentration
concentrationofofaqueous
aqueousMEA,
MEA,and
andpresence
presenceofofadditional
additionalgases,
gases,which
which
temperature,
meansimpurities
impurities[22].
[22].The
Theweight
weight%%concentration
concentrationofofmonoethanolamine
monoethanolaminevaries
variesfrom
from1515
means
35%,depending
dependingon
onthe
theprocess
processand
and0.45
0.45CO
CO22moles/mole
moles/moleamine
amine(324
(324ggCO
CO2/kg
MEA),
2 /kg
toto35%,
MEA),
so the lean and rich amine solvent loading can vary from 0.242 to 0.484 CO2 moles/mole
amine, respectively [2,9,22]. However, others have reported that monoethanolamine can
remove around 90% and 30 wt.% MEA solution with optimum lean amine solvent loading
Sustainability 2021, 13, 72
so the lean and rich amine solvent loading can vary from 0.242 to 0.484 CO2 moles/mole
amine, respectively [2,9,22]. However, others have reported that monoethanolamine can
remove around 90% and 30 wt.% MEA solution with optimum lean amine solvent loading
7 of 27
of nearly 0.32–0.33 mol CO2/mol MEA and a requirement of thermal energy of 3.45 GJ/ton
CO2 [2]. Figure 3 [24] shows the chemical structure of primary amine and Table 4 illustrates
the typical
characteristics
of MEA
amineand
solvents
for MEAof
and
other amines
used
CO2
of nearly
0.32–0.33
mol CO2 /mol
a requirement
thermal
energy of
3.45for
GJ/ton
absorption
[8,15,16,24,25].
CO2 [2]. Figure 3 [24] shows the chemical structure of primary amine and Table 4 illustrates
the typical characteristics of amine solvents for MEA and other amines used for CO2
absorption [8,15,16,24,25].
◦ C.
Figure
Figure3.3.The
Theoxidation
oxidationrate
rateofofgeneral
generalamines
amineswith
withcycling
cyclingfrom
from55
55to
to120
120°C.
There are two major amine technologies used to treat flue gas. Kerr-McGee/ABB
Table 4. Typical characteristics of amine solvents employed for monoethanolamine (MEA) and other amines used for CO2
Lummus Crest was the first commercial technology, developed by Mitsubishi Heavy
absorption.
Industries with the Kansai Electric Power Company in the 1990s. This technology is
operated with
cogenerationDiglycolamine
systems and boilers
that have a range
of fire fuels. The
Monoethanolamine
Diethanolamine
Methyldiethanolami
Diisopropanolamin
Amine
concentration of(DEA)
aqueous amine solution
15–20%. However,e in
this process,
(MEA)
(DGA) MEA is about
ne (MDEA)
(DIPA)
the flue gas should contain limited sulfur dioxide, as well as tolerate a reasonable amount
Typical
of oxygen. Furthermore, in 1978, the first Kerr-McGee/ABB Lummus Crest technology
Concentration
13–20
25–30recovered CO
50–60
in Trona (California)
a production value20–40
of 800 t/day
2 from flue gas, with
range
35–55
15–25
20–40
50–65 are the low amine losses, low heat required for
of CO2 . The most
crucial advantages
recommended
regeneration, and low amine degradation due to the additives and inhibitors used in
(wt.%)
this technology [15].
Solvent loading
technology is the0.35
Fluor process, which
was developed by 0.45
Fluor Daniel
0.3 The second0.3–0.7
0.45
(mole/mole)
from Dow Chemical in 1989. Using a 30 wt.% of MEA solvent, the Kerr-McGee/ABB
Heat of
Lummus Crest process uses additives and inhibitors to prevent equipment corrosion and
regeneration
2degradation. The Fluor
1.5 Daniel process
2 has mainly been1.3
1.5 gases and
used to remove exhaust
(MJ/kg CO2)
has been employed in more than 20 plants worldwide. For example, in Lubbock, Texas, the
t/day
of CO2C
. This
technology
can recover
between
Chemical formula
7NO has a capacity
C4H11rate
NO2of aboutC41200
H11NO
2
5H13NO
2
C6H15NO
2
C2Hplant
85
and
95%
of
CO
from
flue
gas,
with
the
purity
reaching
99.95%
[15,19,21].
The
two
most
2269
Boiling point (°C)
171
221
247
249
fundamental reactions of amines are shown in Equations (5) and (6) [22,26,27]:
Molecular weight
61.08
105
105
119.16
133
(g/mol)
RNH2 + CO2 + H2 O ↔ RNH3 + HCO3
(5)
There are two major 2RNH
amine 2technologies
used
to treat flue gas. Kerr-McGee/ABB
+ CO2 ↔ RNH
(6)
3 + RNHCOO
Lummus Crest was the first commercial technology, developed by Mitsubishi Heavy InFinally,
temperature
which
causes
the MEA
become
to thermal
degradustries
with the
the
Kansai Electric
Power
Company
in to
the
1990s. exposed
This technology
is oper◦ C and is considered one of the main drawbacks in comparison to oxidation,
dation
is
120
ated with cogeneration systems and boilers that have a range of fire fuels. The concentraso inhibitors
should
used to MEA
avoidisit about
[20]. 15–20%. However, in this process, the flue
tion
of aqueous
aminebesolution
Sustainability 2021, 13, 72
8 of 27
Table 4. Typical characteristics of amine solvents employed for monoethanolamine (MEA) and other amines used for CO2
absorption.
Amine
Monoethanolamine Diethanolamine
(MEA)
(DEA)
Diglycolamine
(DGA)
Methyldiethanolamine Diisopropanolamine
(MDEA)
(DIPA)
Typical
Concentration
range
recommended
(wt.%)
13–20
15–25
25–30
20–40
50–60
50–65
35–55
20–40
Solvent
loading
(mole/mole)
0.3
0.3–0.7
0.35
0.45
0.45
Heat of
regeneration
(MJ/kg CO2 )
2
1.5
2
1.3
1.5
Chemical
formula
C2 H7 NO
C4 H11 NO2
C4 H11 NO2
C5 H13 NO2
C6 H15 NO2
Boiling point
(◦ C)
171
269
221
247
249
Molecular
weight (g/mol)
61.08
105
105
119.16
133
2.4. Degradation of MEA and Other Solvents
The MEA degradation rate is nearly 1.5 kg/ton CO2 whatever the type of degradation [2,20]; therefore, degradation has several types, and two major types will now
be discussed.
A.
Oxidative degradation
Oxidation degradation occurs because of flue gas containing oxygen in the absorber
tower. Neither a high temperature nor CO2 is required for oxidative degradation. This
is a major issue for capturing CO2 in the flue gas, and the concentration of oxygen varies
between 3 and 5% in the gas stream. It mainly occurs in the absorber, at 40–70 ◦ C [8]. In
addition, according to a study conducted at the University of Texas, the degradation can be
controlled by the mass transfer of oxygen under industry conditions, where the degradation
rate is nearly 0.29–0.73 kg of MEA/ton of CO2 . Furthermore, loss of the solvent and the
formation of heat-stable salts are also caused by oxidative degradation, and to prevent this,
inhibitors are added to the system [21,23]. The products, such as aldehydes, organic acids,
and ammonia, are formed by an oxidative degradation chain of amine solvent starting
with MEA. In the second step, the acids are formed (heat-stable salts), leading to mitigation
of the capacity rate of the absorption of CO2 by the solvent. These acids react with the
absorbent MEA, leading to the production of amide compounds [8,23]. Table 5 shows the
oxidative degradation compounds formed from MEA [8,23].
Table 5. The formation of compounds from the oxidative degradation of MEA.
Solvent
Compounds
MEA
inorganic compounds (NH3 , NO2 − , NO3 − )
Organic acids (HCOO− , CH3 COO− , HOCH2 COO− , (C2 O4 )2 − )
Amides (oxamides, HEF, formamides,)
cyclic compounds (HEPO-3, HEPO-2, HEI, HEP, DMPz)
Aldehydes (CH3 CHO, HOCH2 CHO, CH2 O)
Amines (MAE, methylamines, BHEEDA, MEA-urea)
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Diethanolamine is formed by oxidizing primary and tertiary amines; however, a
Diethanolamine
is isis
formed
and
tertiary
amines;
however,
aa
Diethanolamine
formed
byoxidizing
oxidizingprimary
primaryand
and
tertiary
amines;
however,
Diethanolamine
formedby
oxidizing
primary
tertiary
amines;
however,
a large
large amount
of diethanolamine
isby
also
produced
by oxidizing
MDEA,
as shown
in Figure
Diethanolamine
is
formed
by
oxidizing
primary
and
tertiary
amines;
however,
a
large
amount
of
diethanolamine
is
also
produced
by
oxidizing
MDEA,
as
shown
in
Figure
large
amount
of
diethanolamine
is
also
produced
by
oxidizing
MDEA,
as
shown
in
Figure
amount of diethanolamine is also produced by oxidizing MDEA, as shown in Figure 3 [19].
3 [19].
3 large
[19].
3 [19].amount of diethanolamine is also produced by oxidizing MDEA, as shown in Figure
B. B. Thermal
Thermal degradation
degradation of
of MEA
MEA and
and other
other solvents
solvents (polymerization
(polymerization of
of Carbamate):
Carbamate):
B.3B.[19].
Thermal
and
solvents
(polymerization
ofofCarbamate):
Thermaldegradation
degradationofofMEA
MEA
andother
other
solvents
(polymerization
Carbamate):
Polderman
was
the
first
person
to
propose
the
mechanism
of
the
polymerization
Polderman
was
the
first
person
to
propose
the
mechanism
of
the
polymerization
ofof
B. Polderman
Thermal
degradation
ofperson
MEA
and
other
solvents
(polymerization
of
Carbamate):of
was
totopropose
the
ofofthe
polymerization
Polderman
wasthe
thefirst
first
person
propose
themechanism
mechanism
the
polymerization
of
carbamate
of
MEA
in
1955
[28].
The
polymerization
of
carbamate
occurs
in
the
stripper
carbamate of MEA in 1955 [28]. The polymerization of carbamate occurs in the stripper
Polderman
was
first
person
to
propose
the of
mechanism
ofoccurs
the
polymerization
of
carbamate
ofof
in
1955
[28].
The
polymerization
ininthe
carbamate
MEA
inthe
1955
[28].
The
polymerization
ofcarbamate
carbamate
occurs
thestripper
stripper
column
aMEA
high
temperature
and
over
long period
period
column
at at
a high
temperature
and
over
aalong
of time
time [21].
[21]. The
The thermal
thermaldegradation
degradacarbamate
of
MEA
in
1955
[28].
The
polymerization
of
carbamate
occurs
in
the
stripper
column
at
a
high
temperature
and
over
a
long
period
of
time
[21].
The
thermal
degradacolumn
at
a
high
temperature
and
over
a
long
period
of
time
[21].
The
thermal
degradaincreases
when
thethe
temperature
is increased
in the
column,
where
the degradation
tion
increases
when
temperature
is increased
in stripper
the stripper
column,
where
the degcolumn
a high
temperature
andbeover
a long period
of
time
[21].
Theof
thermal
degrada◦C
tion
increases
when
the
temperature
is
ininthe
stripper
column,
where
tion
increases
when
the
temperature
isincreased
increased
the
stripper
column,
wherethe
thedegdegrate
of at
MEA
any
solvent
will
2.5–6%
week
at
aweek
temperature
about
135
[16].
radation
rate oforMEA
or any solvent
will beper
2.5–6%
per
at a temperature
of about
tion
increases
when
the
temperature
is
increased
in
the
stripper
column,
where
the
degradation
rate
of
MEA
or
any
solvent
will
be
2.5–6%
per
week
at
a
temperature
of
about
radation
rate
of
MEA
or
any
solvent
will
be
2.5–6%
per
week
at
a
temperature
of
about
The
polymerization
of
carbamate
causes
an
increased
amine
solution
viscosity,
loss
of
car135 °C [16]. The polymerization of carbamate causes an increased amine solution viscosradation
rate
ofpolymerization
MEA
or any
solvent
will be causes
2.5–6%
per
week
at amine
a amine
temperature
of
about
135
°C°C[16].
The
ofofcarbamate
solution
viscos135
[16].
The
polymerization
carbamate
causesan
anincreased
increased
solution
viscosbon
dioxide’s
absorption
capacity,
increased
corrosion,
and
foaming
[28].
The
mechanism
ity, loss of carbon dioxide’s absorption capacity, increased corrosion, and foaming [28].
135
°C
The polymerization
of carbamate
causes
an increased
amine
solution
viscosity,
ofofcarbon
dioxide’s
absorption
capacity,
increased
corrosion,
and
foaming
[28].
ity,
loss[16].
carbon
dioxide’s
absorption
capacity,
increased
corrosion,
and
foaming
[28].
ofloss
degradation
as
follows.
The
mechanism
ofisdegradation
is as follows.
ity,
loss
of carbon
dioxide’s
absorption
capacity,
increased
corrosion,
and
foaming
[28].
The
of
isat
asthe
follows.
Themechanism
mechanism
ofdegradation
degradation
is
as
follows.
First,
the
reaction
occurs
absorber
with
CO
,
and
CO
associates
with
MEA
2
First, the reaction occurs at the absorber with CO2, 2and CO2 associates
with MEA to to
The
mechanism
of
degradation
is
as
follows.
First,
the
reaction
occurs
at
the
absorber
with
CO
2
,
and
CO
2
associates
with
First,
the
reaction
occurs
at
the
absorber
with
CO
2
,
and
CO
2
associates
withMEA
MEAtoto
form
carbamate
MEA,
shown
Equation
[28]:
form
carbamate
of of
MEA,
asas
shown
in in
Equation
(7)(7)
[28]:
First,
the reaction
occurs
at the
absorber
with
CO
form
ofof
MEA,
asasshown
inin
Equation
(7)(7)
[28]:
formcarbamate
carbamate
MEA,
shown
Equation
[28]:2, and CO2 associates with MEA to
form carbamate of MEA, as shown in Equation (7) [28]:
(7)(7)
(7)(7)
(7)
Then,
at at
thethe
stripper,
thethe
reaction
is is
generally
reversed;
however,
forfor
some
statuses,
Then,
stripper,
reaction
generally
reversed;
however,
some
statuses,
Then,
atatthe
the
is isgenerally
reversed;
however,
for
statuses,
Then,
thestripper,
stripper,
thereaction
reaction
generally
reversed;
however,
forsome
some
statuses,
2-oxazolidone
will
form
due
to
the
cyclizing
of
MEA
carbamate,
and
this
reaction
type
is
2-oxazolidone
will
form
due
to
the
cyclizing
of
MEA
carbamate,
and
this
reaction
type
Then, at will
the
stripper,
the
reaction
is generally
reversed;
however,
for
some statuses,
2-oxazolidone
form
toto
the
ofofMEA
carbamate,
and
reaction
type
is isis
2-oxazolidone
will
formdue
due
thecyclizing
cyclizing
MEA
carbamate,
andthis
this
reaction
type
also
reversible,
as
shown
in
Equation
(8)
below
[8]:
also
reversible,
asshown
shown
inEquation
Equation
(8)
below
[8]: carbamate, and this reaction type is
2-oxazolidone
will
form
due
to
the cyclizing
of[8]:
MEA
also
reversible,
as
shown
in
Equation
(8)(8)
below
also
reversible,
as
in
below
[8]:
also reversible, as shown in Equation (8) below [8]:
(8)
(8)
(8)(8)
(8)
Furthermore, the 2-oxazolidone will react with one mole of monoethanolamine to
Furthermore,
the
2-oxazolidone
will
react
with
one
mole
ofofmonoethanolamine
toto
Furthermore,
the
2-oxazolidone
will
react
with
one
mole
Furthermore,
the
2-oxazolidone
will
react
with
one
mole
ofmonoethanolamine
monoethanolamine
form 1-(2-hydroxyethyl)-2-imidazolidone
and
is referred
to as
HEIA.
Equation (9) showsto
Furthermore,
the
2-oxazolidone
will
react
with
one
mole
of
monoethanolamine
to
form
and
is isreferred
totoas
Equation
(9)(9)
shows
form1-(2-hydroxyethyl)-2-imidazolidone
1-(2-hydroxyethyl)-2-imidazolidone
and
Equation
shows
1-(2-hydroxyethyl)-2-imidazolidone
and
isreferred
referred
toasHEIA.
asHEIA.
HEIA.
Equation
(9)
shows
theform
reaction
[29]:
form
1-(2-hydroxyethyl)-2-imidazolidone
and is referred to as HEIA. Equation (9) shows
the
reaction
[29]:
the
reaction
[29]:
the
reaction
[29]:
the reaction [29]:
(9)
(9)(9)
(9)
(9)
After that, the HEIA will react with water (hydrolyze) to form HEEDA, which is NAfter
Afterthat,
that,the
theHEIA
HEIAwill
willreact
reactwith
withwater
water(hydrolyze)
(hydrolyze)totoform
formHEEDA,
HEEDA,which
whichis isN-N(2-hydroxyethyl)-ethylenediamine,
as illustrated
in (hydrolyze)
Equation (10)to[28]:
After that, the HEIA will react
with water
form HEEDA, which is
After that, the HEIA will reactaswith
water (hydrolyze)
to
form
HEEDA, which is N(2-hydroxyethyl)-ethylenediamine,
ininEquation
(10)
[28]:
(2-hydroxyethyl)-ethylenediamine,
asillustrated
illustrated
Equation
(10)
[28]:
N-(2-hydroxyethyl)-ethylenediamine, as illustrated in Equation (10) [28]:
(2-hydroxyethyl)-ethylenediamine, as illustrated in Equation (10) [28]:
(10)
(10)
(10)
(10)
(10)
These four types (HEEDA, dihydroxy ethyl urea, 2-oxazolidone, and HEIA) of forThese
Thesefour
fourtypes
types(HEEDA,
(HEEDA,dihydroxy
dihydroxyethyl
ethylurea,
urea,2-oxazolidone,
2-oxazolidone,and
andHEIA)
HEIA)ofofforformation are the major products of thermal degradation [29].
These
four
types
(HEEDA,
dihydroxy
ethyl
urea,
2-oxazolidone,
and
HEIA)
of
formation
are
the
major
products
of
thermal
degradation
[29].
mation
are
the
major
products
of
thermal
degradation
[29].
These four types (HEEDA, dihydroxy ethyl urea, 2-oxazolidone, and HEIA) of formamation
arethe
themajor
major
products
thermaldegradation
degradation[29].
[29].
tion
are
products
ofofthermal
2.5.
Diethanolamine
DEA
Solvent
2.5.
Diethanolamine
Solvent
2.5.
DiethanolamineDEA
DEA
Solvent
DEA is often used
an
abbreviation for diethanolamine, and it is an organic compo2.5. DEA
Diethanolamine
DEA
Solvent
DEAis isoften
oftenused
usedananabbreviation
abbreviationfor
fordiethanolamine,
diethanolamine,and
andit itis isananorganic
organiccompocomponent that has both a Dialcohol and a secondary amine. In addition, a Dialcohol contains
DEA
is both
often
an abbreviation
for diethanolamine,
and it aisaDialcohol
an
organic
component
and
amine.
contains
nentthat
thathas
has
bothaused
aDialcohol
Dialcohol
anda asecondary
secondary
amine.InInaddition,
addition,
Dialcohol
contains
nent that has both a Dialcohol and a secondary amine. In addition, a Dialcohol contains
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two hydroxyl groups in its molecule [19,30]. Diethanolamine, like other alkanol amines,
rules as a weak base [24].
DEA is an inexpensive solvent due to its wide use in many industries, and it is espe2.5.
Diethanolamine
DEA Solvent
cially
used for removing
CO2 and H2S in natural gas that has rapidly reacted, where the
selectively
highused
(between
other and acid
gases), and for and
the reversible
reaction
process
DEA isisoften
an abbreviation
for diethanolamine,
it is an organic
component
that
both a column.
Dialcohol
and a secondary
amine. Inconditions
addition, can
a Dialcohol
two
at thehas
absorber
Furthermore,
the operation
be a low contains
heat reaction
hydroxyl
groups
its2)molecule
alkanol
amines, rules
(around 70
kJ/molinCO
and low [19,30].
pressureDiethanolamine,
[30]. One of the like
mostother
common
disadvantages
is
as
weak base
theapresence
of [24].
SO2 and O2 in flue gas, causing solvent degradation (which should be less
is anThe
inexpensive
solvent
wide the
useoxidation
in many of
industries,
it to
is
than DEA
10 ppm).
presence of
O2 in due
flue to
gasitscauses
DEA andand
leads
especially
used for removing
COconcentration
natural
gas that hasvaries,
rapidly
reacted, where
increased degradation
[10]. The
diethanolamine
depending
on the
2 and H2 S in of
the
selectively
high
(between
other and
acid gases),
for the reversible
reaction
process
amount
of COis
2 to
absorb.
In approved
industries,
theand
concentration
has been
shown
to be
at
the
absorber
column.
Furthermore,
the
operation
conditions
can
be
a
low
heat
reaction
between 25 and 35% and lean amine (DEA) loading is set at 0.1 mol CO2/mol DEA [30],
(around
CO2 )ofand
low pressure loading
[30]. One
disadvantages
whereas 70
thekJ/mol
rich amine
diethanolamine
is of
0.4the
molmost
CO2common
/mol DEA,
as illustrated
is
presence
in the
Figure
4 [5]. of SO2 and O2 in flue gas, causing solvent degradation (which should be
less than
10 ppm).
presence of
of O
causes
of that
DEAofand
leads
to
2 in flue gasof
However,
theThe
mechanism
degradation
DEAthe
is aoxidation
similar to
MEA
[28].
increased
degradation
[10]. The
concentration
of diethanolamine
varies, depending
on the
Consequently,
the products
produced
after degradation
are Tris-hydroxyethyl
ethyleneamount
CO2 THEED,
to absorb.
In approved industries,
the (bis-HEP),
concentration
hasBis-(hydroxyethyl)
been shown to be
diamineof
called
Bis-hydroxyethyl
piperazine
MEA,
between
25
and
35%
and
lean
amine
(DEA)
loading
is
set
at
0.1
mol
CO
[30],
2 /mol
glycine (Bicine), and polymers. Polymers are products produced when the
DEADEA
molecule
whereas
the
rich
amine
of
diethanolamine
loading
is
0.4
mol
CO
/mol
DEA,
as
illustrated
reacts with THEED (ethylenediamines). Furthermore, the MEA 2product is obtained when
in
4 [5].
theFigure
DEA molecule
degrades in the presence of oxygen [31].
Figure 4.
4. The
different types
types of
of amine
amine with
with the
the capacity
capacity to
to absorb
absorb CO
CO2..
Figure
The different
2
2.6. Methyldiethanolamine
MDEA
However, the mechanism
of degradation of DEA is a similar to that of MEA [28]. Consequently,
theisproducts
produced
degradation are Tris-hydroxyethyl
ethylenediamine
MEDA
an abbreviation
ofafter
N-methyldiethanol-amine
and the chemical
formula of
called
THEED,
Bis-hydroxyethyl
piperazine
(bis-HEP),
MEA,
glycine
it is C5H
13NO2 [15].
MDEA is considered
a chemical
solvent,
soBis-(hydroxyethyl)
the chemical solvents
have
(Bicine),
and
polymers.
Polymers
are
products
produced
when
the
DEA
molecule
reacts
a characteristic during the absorption process, which is that the acid gas component in the
with
THEED
(ethylenediamines).
MEA can
product
obtained
thea
solvent
is bonded
chemically [32].Furthermore,
The density ofthe
MDEA
rangeis from
1 to when
1.149 at
DEA
molecule
degrades
in
the
presence
of
oxygen
[31].
temperature roughly between 298 and 363.15 K with a concentration percentage between
23.8 and 60 wt.% [3]. MDEA can degrade at 119–129 °C [8]. Some of the advantages of
2.6. Methyldiethanolamine MDEA
MDEA are the need for only a low energy for regeneration due to the acidic gas reaction
MEDA
an abbreviation
N-methyldiethanol-amine
and the
of it
having
a lowis enthalpy
and theofhigh
capacity for the absorption
of chemical
CO2 [10].formula
In addition,
is
C
H
NO
[15].
MDEA
is
considered
a
chemical
solvent,
so
the
chemical
solvents
have
a
5
13
2
the solution has a lower vapor pressure and corrosiveness, with a good chemical and thercharacteristic
during
the
absorption
process,
which
is
that
the
acid
gas
component
in
the
mal stability. On the other hand, there are some drawbacks, including the slow reaction
solvent
is bonded
chemically
[32]. The density
MDEA
range fromof1 carbon
to 1.149dioxat a
with carbon
dioxide
and low absorption
capacityofwhen
thecan
concentration
temperature
roughly
between
298
and
363.15
K
with
a
concentration
percentage
between
ide is low [4].
◦ C [8]. Some of the advantages of
23.8 and
60 wt.%
[3]. MDEA
can degrade
119–129
MDEA
has several
advantages
which at
make
it a very
popular solvent, including the
MDEA
for onlyrequires
a low energy
for regeneration
duewith
to the
gas reaction
fact thatare
it isthe
lessneed
aggressive,
a low heat
for the reaction
COacidic
2, is less corrosive,
having a low enthalpy and the high capacity for the absorption of CO2 [10]. In addition, the
solution has a lower vapor pressure and corrosiveness, with a good chemical and thermal
stability. On the other hand, there are some drawbacks, including the slow reaction with
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carbon dioxide and low absorption capacity when the concentration of carbon dioxide
is low [4].
MDEA
severalconcentrations,
advantages which
a very popular
including
the fact
can be
used has
in higher
has make
loweritcirculation
rates,solvent,
and is easier
to regenerthat
it is less aggressive, requires a low heat for the reaction with CO2 , is less corrosive, can
ate [24].
be used
higher
concentrations,
hasoperating
lower circulation
and
is easier
to regenerate
[24].
Theinmajor
determinate
for the
cost andrates,
capital
cost
is the circulation
rate
of
The
major
determinate
for
the
operating
cost
and
capital
cost
is
the
circulation
rate
the solvent, which is roughly proportional to the amount of acid gas to be removed. The
of
the solvent,
which is
roughly
proportional
to the in
amount
acid
gas toand,
be removed.
process
of gasification
and
flue gas
treatment shown
Figureof
5 is
common
as in the
The
process
of
gasification
and
flue
gas
treatment
shown
in
Figure
5
is
common
and,
MEA process, the lean MDEA enters the absorber and reacts with acid gas to absorb some
as
in the
the lean
MDEAMDEA
enterswith
the absorber
reacts
withthan
acid carbon
gas to
of the
COMEA
2 and process,
H2S, whereas
bonding
H2S takesand
place
quicker
absorb
of bottom
the CO2ofand
MDEA
with H2 Sand
takes
placethe
quicker
2 S, whereas
dioxide.some
At the
theHabsorber,
the bonding
rich stream
is pre-heated
enters
stripthan
carbon
dioxide.
At
the
bottom
of
the
absorber,
the
rich
stream
is
pre-heated
and
per/regenerator to regenerate the solvent by using the reboiler to break the bond of chementers
the
stripper/regenerator
to
regenerate
the
solvent
by
using
the
reboiler
to
break
the
ically reacted substances. The component of acid gas will be cooled through the cooler
bond
of
chemically
reacted
substances.
The
component
of
acid
gas
will
be
cooled
through
when exiting the top of the stripper column to condensate out the water for recycling purthe
cooler
poses
[32]. when exiting the top of the stripper column to condensate out the water for
recycling purposes [32].
Figure
Figure 5.
5. A
A flowsheet
flowsheet of
of the
the typical
typical methyldiethanolamine
methyldiethanolamine (MDEA)
(MDEA) process.
process.
The degradation of MDEA will produce several products, which include dimers
The degradation of MDEA will produce several products, which include dimers
(degradation of DIPA-OX to diamines (“dimers”)), polymers (dimer reacts with a DIPA
(degradation of DIPA-OX to diamines (“dimers”)), polymers (dimer reacts with a DIPA
molecule), Monoisopropanolamine (MIPA) (occurs when oxygen reacts with a DIPA
molecule), Monoisopropanolamine (MIPA) (occurs when oxygen reacts with a DIPA molmolecule), Triisopropanolamine (TIPA) (produced when amine degrades in the presence
ecule), Triisopropanolamine (TIPA) (produced when amine degrades in the presence of
of oxygen in the flue gases to produce simpler amines, whilst these simpler amines will
oxygen in the flue gases to produce simpler amines, whilst these simpler amines will react
react with other base amines to produce complex amines), and others, such as DIPA and
with other base amines to produce complex amines), and others, such as DIPA and 1,11,1-Dioxidetetrahydrothiophene (Sulfolane) [31].
Dioxidetetrahydrothiophene (Sulfolane) [31].
In 2008, Bedel assumed that there were several degradation pathways for MDEA,
In 2008, Bedel assumed that there were several degradation pathways for MDEA,
including hydrolysis, elimination reactions, disproportionation, and hemolytic splitting.
including hydrolysis, elimination reactions, disproportionation, and hemolytic splitting.
Amino acid hydrolysis occurs in extrapolated conditions of a stripper and at a high temperAminowhich
acid hydrolysis
occurs
in extrapolated
conditions
of a stripper
at a highoftemature,
is a reasonable
reason
for degradation
[28]. Under
normaland
conditions
the
perature, which
is a reasonable
reason
fordegradation
degradationof
[28].
Under
normalthe
conditions
of
regenerator,
the common
pathway
for the
MDEA
involves
reaction of
the
regenerator,
the
common
pathway
for
the
degradation
of
MDEA
involves
the
reaction
disproportionation, sometimes referred to as alkanolamine “scrambling”. Therefore, one
of disproportionation,
sometimes referred
to as alkanolamine
Therefore,
molecule
of dimethylethanolamine
and triethanolamine
is formed“scrambling”.
by replacing the
methyl
one
molecule
of
dimethylethanolamine
and
triethanolamine
is
formed
by
replacing
the
group in the MDEA molecule with another molecule of the ethanol group [8,28]. In this
methyl group in the MDEA molecule with another molecule of the ethanol group [8,28].
In this process, a methyl group can be replaced with a hydrogen to form DEA, and this
reaction can continue for amine degradation by the polymerization of carbamate [8,15,19].
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process, a methyl group can be replaced with a hydrogen to form DEA, and this reaction
can continue for amine degradation by the polymerization of carbamate [8,15,19].
2.7. Comparative Amines Solvent
Table 6 shows the comparatives of amine solvent, such as MEA, DEA, and MDEA as a
rate, heat, and capacity of absorption, with the stability of solvent [19].
Table 6. Characterization properties of the solvents for popular amine solvents.
Absorbent
Methyldiethanolamine
(MDEA)
Diethanolamine
(DEA)
Monoethanolamine
(MEA)
Rate of
Absorption
Absorption
Capacity CO2
Stability of
Solvent
Heat of
Absorption
Low
High
High
Medium
Medium
Medium
Medium
High
High
Medium
Low
High
3. Material and Method
This section highlights the framework involves in specifying the variables for solving
absorber column using Promax, which was developed using a typical composition of the
Flue gas from gas-powered power plant plants as obtained in Table 7.
Table 7. Flue gas feed compositions in mole%.
Compositions
Mole Percent (%)
N2
CO2
H2 O
O2
77
21
1.99
0.01
The Amine Sweetening Peng Robinson (PR) was employed as the most compatible
thermodynamic equation to handle the components listed in Table 7, when combined
with Amine absorbent. The process was then followed by specifying the components in
the Flue gas, followed by column convergence using MEA. This was then repeated at
300 m3 /h as well as changing the absorbent type. The procedure shown in Figure 6, was
used to simulate amine solvents MEA, DEA, and MDEA, in order to capture the carbon
dioxide from flue gas, utilizing amine concentrations of 10% and 15% for all solvents and
circulation rates of 200 and 300 m3 /h. In addition, the flue gas flow rate, compositions,
temperature, and pressure of the flue gas and amine solvents was kept constant through
all scenarios, having 20 trays and a 0.5 pressure drop from the bottom to top column.
The flue gas that feed to the absorber had the following specifications: Temperature of
32 ◦ C; pressure of 30 bar; and CO2 representing 21% of the total components.
Assumptions of steady state model whereby feed composition and materials flows remained the same during the convergence iterations were made, a 20 trays absorber column
typical for Amine absorber columns. The limitation of this study is that it focused on typical
natural gas-powered plant alone without consideration to fuel-switch between natural
gas and other fuels such as Diesel etc., this was to ensure constant flue gas composition
from the plant. Other limitations include steady-state analysis considered compared to
the transient operations where plant start-up and shut-down generate different flue gas
composition. Figure 7 is a schematic diagram of the simple absorber tower used in an
amine sweetening system.
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Figure 6. The flow chart of a ProMax simulation.
Tables
7 and
show
thetocompositions
flue
feed andspecifications:
amine solvent,Temperature
respectively,
The
flue
gas 8that
feed
the absorber of
had
thegas
following
in 32
mole
of
°C;percentage.
pressure of 30 bar; and CO2 representing 21% of the total components.
Assumptions of steady state model whereby feed composition and materials flows
Table 8. Amine-based
solutionthe
solvents
in percent.
remained
the same during
convergence
iterations were made, a 20 trays absorber column typical for Amine absorber columns. The limitation of this study is that it focused on
Composition of Amine
Mole Percent (%)
typical natural gas-powered plant alone without consideration to fuel-switch between
Amine
DEA fuels
and MDEA)
10 was to ensure constant 15
natural
gas(MEA,
and other
such as Diesel etc., this
flue gas comH2 O
90
85
position from the plant. Other limitations include steady-state analysis considered compared to the transient operations where plant start-up and shut-down generate different
With
regard to the
amine-based
solution
flow rate,
two
different
flow tower
rates were
flue gas
composition.
Figure
7 is a schematic
diagram
of the
simple
absorber
used
3
chosen,
which
were 200system.
and 300 m /h for each scenario. The first scenario was a 10%
in
an amine
sweetening
amine concentration of each amine solvent (MEA, DEA, and MDEA) with amine circulation
rates of 200 and 300 cubic meters, and the second one was a 15% amine concentration with
200 and 300 m3 /h. In this chapter, we will investigate the comparison of amine solvents
(MEA, DEA, and MDEA) using the ProMax program. This program calculated and solved
the process that occurred in the absorber tower and the outcome with an acceptable result.
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Figure 7. A schematic diagram of the simple absorber tower used in an amine sweetening system.
There
two scenarios
thissimple
process,
which
wasused
conducted
by simulations,
and
Figure
7. Aare
schematic
diagramfor
of the
absorber
tower
in an amine
sweetening system.
some constants did not change during all scenarios:
Tables 7 tower
and 8 had
show20the
compositions
of flue
solvent,ofrespec1.
Absorber
trays
with 29.5 and
30 gas
bar feed
at theand
topamine
and bottom
the
tively,
in mole
percentage.
tower
pressure;
2.
The amine circulation temperature was 38 ◦ C, with a pressure of 33 bar;
8. flue
Amine-based
3. Table
The
gas flow solution
rate wassolvents
76,000 in
m3percent.
/h and temperature were 32 ◦ C, with a pressure
of 30
bar.
Composition
of Amine
Mole Percent (%)
The other
values
changed
in the two scenarios:
Amine
(MEA,
DEA
and MDEA)
10
15
3
The amine circulation
rate was changed from 200
of
1.
H2O
90 to 300 m /h with a concentration
85
10% for all flow rates, and 15%.
With regard to the amine-based solution flow rate, two different flow rates were cho4. sen,
Results
which were 200 and 300 m3/h for each scenario. The first scenario was a 10% amine
4.1.
The
First Scenario
concentration
of each amine solvent (MEA, DEA, and MDEA) with amine circulation rates
Theand
first300
scenario
for amine
MEA,
a concentration
of 200
cubic meters,
andsolvents
the second
oneDEA,
was aand
15%MDEA
amine is
concentration
withof
200
10%
of300
each
with
a change
theinvestigate
circulationthe
each
time, that of
which
means
that(MEA,
200,
and
m3solvent
/h. In this
chapter,
we in
will
comparison
amine
solvents
300
m3 /h
that
done by
simulations
of ProMax
were
conducted
a value
of solved
200 andthe
DEA,
and
MDEA)
using
the ProMax
program.
This
program with
calculated
and
3 /h.
300
m
process that occurred in the absorber tower and the outcome with an acceptable result.
There are two scenarios for this process, which was conducted by simulations, and
4.1.1. MEA with a Concentration of 10%
some constants did not change during all scenarios:
MEA with a Circulation Rate of 200 m3 /h
1.
Absorber tower had 20 trays with 29.5 and 30 bar at the top and bottom of the tower
The whole process that was conducted by ProMax is shown in Figure 8, demonstrating
pressure;
that the resulting products were clean flue gas and rich amine.
2.
The amine circulation temperature was 38 °C, with a pressure of 33 bar;
3.
The flue gas flow rate was 76,000 m3/h and temperature were 32 °C, with a pressure
of 30 bar.
The other values changed in the two scenarios:
m /h.
4.1.1. MEA with a Concentration of 10%
MEA with a Circulation Rate of 200 m3/h
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The whole process that was conducted by ProMax is shown in Figure 8, demonstrat15 of 27
ing that the resulting products were clean flue gas and rich amine.
3 /h
3/h simulated by ProMax. “*” means
Figure8.8.Absorption
Absorptionprocess
processusing
usingMEA
MEAsolvent
solventwith
witha a10%
10%concentration
concentration
and
200
Figure
and
200
mm
simulated by ProMax. “*” means
theresults
resultsthat
thatcome
comeout
outfrom
frombottom
bottomand
andtop
topofofabsorber
absorberare
arementioned
mentionedininthe
theTable
Table
the
9. 9.
MEA with
Circulation
Rate
of 300
/h
of theaabsorber
tower
results
aftermcalculated
by ProMax for amine (MEA, DEA, and
Table 9. The A summary outcome
3
MDEA) with an amine circulation rate
of 200
and 300
m was
/h and
with a concentration
and 15%
for each
Thefrom
whole
process
that
conducted
by ProMaxofis10%,
shown
in Figure
9,solvent.
demonstrat3
Amine Con. wt.%
Amine
Feed
200 m3 /h
ing that the resulting products were clean flue gas and rich amine.
10%
Outcome from
Absorber Tower
CO2 % in clean flue gas
N2 % in clean flue gas
Temp. of bottom
absorber (◦ C)
CO2 % in clean flue gas
300
m3 /h
N2 % in clean flue gas
Temp. of bottom
absorber (◦ C)
15%
MEA
DEA
MDEA
MEA
DEA
MDEA
3.6295
95.466
8.1355
91.29
8.4559
91.278
0.0000032862
99.782
5.5612
93.911
8.2545
91.51
84.551
75.133
73.127
100.75
83.177
75.639
0.0038358
3.7518
6.9516 × 10−7
0.00036247
4.305
99.768
96.01
99.782
99.782
95.468
77.21
69.249
83.495
80.638
69.137
2.9564 ×
10−6
99.768
78.95
MEA with a Circulation Rate of 300 m3 /h
The whole process that was conducted by ProMax is shown in Figure 9, demonstrating
that the resulting products were clean flue gas and rich amine.
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16 of 28
Figure
9. Absorption
process
using
MEA
solvent
witha a10%
10%concentration
concentrationand
and 300
300 m
m33/h
Figure
9. Absorption
process
using
MEA
solvent
with
/hsimulated
simulatedbybyProMax.
ProMax.
Figure 9. Absorption process using MEA solvent with a 10% concentration and 300 m3/h simulated by ProMax.
4.1.2. DEA with a Concentration of 10%
4.1.2. DEA with a Concentration of 10%
3/h
DEA
Circulation
Rate of 200
4.1.2.with
DEAa with
a Concentration
ofm
10%
3 /h
DEA with
a
Circulation
Rate
of
200
m
solvent Rate
with of
a circulation
DEAUsing
with DEA
a Circulation
200 m3/h rate of 200 m3/h and 10% concentration proUsing
DEA
solvent
with
a circulation
rate of 200 m33/h and 10% concentration produced
the
results
shown
in
Figure
10.
Using DEA solvent with a circulation
rate of 200 m /h and 10% concentration produced
thethe
results
shown
inin
Figure
10.
duced
results
shown
Figure
10.
Figure 10. Absorption process using DEA solvent with a 10% concentration and 200 m3/h simulated by ProMax.
3/h simulated by ProMax.
3 /h
Figure
10. Absorption
process
using
DEA
solvent
with
a 10%
concentrationand
and200
200mm
Figure
10. Absorption
process
using
DEA
solvent
with
a 10%
concentration
simulated by ProMax.
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17 of
1727
of 28
3/h
DEA
with
a Circulation
Rate
ofof
300
m3m/h
DEA
with
a Circulation
Rate
300
DEA with a Circulation Rate of 300 m3/h
3/h
Using
solvent
with
a circulation
rate
of of
300300
m3m
/h
and
UsingDEA
DEA
solvent
with
a circulation
rate
and10%
10%concentration
concentrationpropro3/h and 10% concentration proUsing
DEA
solvent
with
a
circulation
rate
of
300
m
duced
the
results
shown
in
Figure
11.
duced the results shown in Figure 11.
duced the results shown in Figure 11.
Figure
11.11.
Absorption
process
using
DEA
solvent
with
a 10%
concentration
andand
300300
m3m
/h3/h
simulated
byby
ProMax.
Figure
Absorption
process
using
DEA
solvent
with
a 10%
concentration
simulated
ProMax.
Figure 11. Absorption process using DEA solvent with a 10% concentration and 300 m3/h simulated by ProMax.
4.1.3. MDEA with a Concentration of 10%
4.1.3.
MDEA
with
a Concentration
of of
10%
4.1.3.
MDEA
with
a Concentration
10%
MDEA with a Circulation Rate of 200 3m3/h
3/h
MDEA
with
a Circulation
Rate
of of
200200
mm
/h
MDEA
with
a Circulation
Rate
Using MDEA solvent with a circulation rate of 200 m3/h
and 10% concentration proUsing MDEA
solvent
with aacirculation
rate
m33/h
/hand
and10%
10%
concentration
MDEA
solvent
rate of
of 200 m
concentration
producedUsing
the results
shown
in with
Figure circulation
12.
produced
the
results
shown
in
Figure
12.
duced the results shown in Figure 12.
Figure 12. Absorption process using MDEA solvent with a 10% concentration and 200 m3/h simulated by ProMax.
Figure
Absorption
process
using
MDEA
solvent
with
a 10%
concentration
m3/h
simulated
ProMax.
Figure
12. 12.
Absorption
process
using
MDEA
solvent
with
a 10%
concentration
andand
200200
m3 /h
simulated
byby
ProMax.
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2827
MDEA with a Circulation Rate of 300 m3 /h
3
MDEA with a Circulation Rate of 300 m /h
3 /h and 10% concentration
Using
MDEA
solvent
rateofof300
300
Using
MDEA
solventwith
withaa circulation
circulation rate
m3m
/h and
10% concentration proproduced
shownininFigure
Figure13.
13.
duced the
the results
results shown
FigureFigure
13. MDEA
solvent
withwith
a circulation
raterate
of 500
m3m
/h3/hand
byProMax.
ProMax.
13. MDEA
solvent
a circulation
of 500
and10%
10%concentration
concentration simulated
simulated by
4.2. Second Scenario
4.2. Second Scenario
The second scenario for amine solvents MEA, DEA, and MDEA is was a concentraTheofsecond
for amine
MEA,
DEA, and
MDEA
is was
a concentration
tion
10% ofscenario
each solvent
with asolvents
change the
circulation
each
time, that
which
means that
of 10%
of each were
solvent
with a by
change
theatcirculation
each
time,
that which
means that
simulations
conducted
ProMax
200 and, 300
m3/h
that done
by simulations
of
3
simulations
ProMax. were conducted by ProMax at 200 and, 300 m /h that done by simulations of
ProMax.
4.2.1. MEA with a Concentration of 15%
4.2.1.MEA
MEA
with
a Concentration
15%
with
a Circulation
Rate ofof
200
m3/h
MEA with
a Circulation
Ratewith
of 200
m3 /h
Using
MEA solvent
a circulation
rate of 200 m3/h and 15% concentration proSustainability 2021, 13, x FOR PEER REVIEW
duced
results
shown
in Figure
14.
Usingthe
MEA
solvent
with
a circulation
19 ofpro28
rate of 200 m3 /h and 15% concentration
duced the results shown in Figure 14.
Figure 14. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.
Figure 14. MEA solvent with a circulation rate of 300 m3 /h and 15% concentration simulated by ProMax.
MEA with a Circulation Rate of 300 m3/h
Using MEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 15.
Sustainability 2021, 13, 72
19 of 27
Figure 14. MEA solvent with a circulation rate of 300 m3/h and 15% concentration simulated by ProMax.
3/h
MEA
with
a Circulation
Rate
of of
300
m3m
/h
MEA
with
a Circulation
Rate
300
Using
MEA
solvent
with
a circulation
rate
of of
300300
m3m
/h3/hand
15%
concentration
proUsing
MEA
solvent
with
a circulation
rate
and
15%
concentration
produced
the
results
shown
in
Figure
15.
duced the results shown in Figure 15.
Figure
MEA
solvent
with
a circulation
of 300
and
15%
concentration
simulated
ProMax.
Figure
15.15.
MEA
solvent
with
a circulation
raterate
of 300
m3 m
/h3/h
and
15%
concentration
simulated
byby
ProMax.
4.2.2. DEA with a Concentration of 15%
4.2.2. DEA with a Concentration of 15%
DEA with a Circulation Rate of 200 m3/h
DEA with a Circulation Rate of 200 m3 /h
Using DEA solvent with a circulation rate of 200 3m3/h and 15% concentration proUsing
solvent
with
a circulation
rate of 200 m /h and 15% concentration20
proSustainability 2021, 13, x FOR PEER REVIEW
of 28
duced theDEA
results
shown
in Figure
16.
duced the results shown in Figure 16.
3/hand
Figure
16.16.
DEA
solvent
with
a circulation
rate
of of
200
m3m
/h
Figure
DEA
solvent
with
a circulation
rate
200
and15%
15%concentration
concentrationsimulated
simulatedby
byProMax.
ProMax.
DEA with a Circulation Rate of 300 m3/h
Using DEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 17.
Sustainability 2021, 13, 72
20 of 27
Figure 16. DEA solvent with a circulation rate of 200 m3/h and 15% concentration simulated by ProMax.
3
DEA
3/h
DEAwith
withaaCirculation
CirculationRate
Rateofof300
300mm/h
3
Using
DEA
solvent
with
a
circulation
3/h and
Using DEA solvent with a circulationrate
rateofof300
300mm/h
and15%
15%concentration
concentrationproproduced the results shown in Figure 17.
duced the results shown in Figure 17.
3 /h
3/hand
Figure
Figure17.
17.DEA
DEAsolvent
solventwith
witha acirculation
circulationrate
rateofof300
300mm
and15%
15%concentration
concentrationsimulated
simulatedby
byProMax.
ProMax.
4.2.3. MDEA with a Concentration of 15%
4.2.3. MDEA with a Concentration of 15%
MDEA with a Circulation Rate of 200 m3/h
MDEA with a Circulation Rate of 200 m3 /h
Using MDEA solvent with a circulation rate of 200 m3/h and 15% concentration proUsing MDEA solvent with a circulation rate of 200 m3 /h and 15% concentration
Sustainability 2021, 13, x FOR PEER REVIEW
21 of 28
duced the results show in Figure 18.
produced the results show in Figure 18.
3/h and 15% concentration simulated by ProMax.
3 /h
Figure18.
18.MDEA
MDEAsolvent
solventwith
witha acirculation
circulationrate
rateofof200
200mm
Figure
and 15% concentration simulated by ProMax.
MDEA with a Circulation Rate of 300 m3/h
Using MDEA solvent with a circulation rate of 300 m3/h and 15% concentration produced the results shown in Figure 19.
Sustainability 2021, 13, 72
21 of 27
Figure 18. MDEA solvent with a circulation rate of 200 m /h and 15% concentration simulated by ProMax.
3
MDEA
with
a Circulation
Rate
of 300
m3m
/h3/h
MDEA
with
a Circulation
Rate
of 300
Using
MDEA
solvent
/hand
and15%
15%concentration
concentration
Using
MDEA
solventwith
witha acirculation
circulationrate
rateof
of 300
300 m33/h
proproduced
the
results
shown
in
Figure
19.
duced the results shown in Figure 19.
Figure
19. 19.
MDEA
solvent
with
a circulation
raterate
of 300
m3 /h
15%
concentration
simulated
by by
ProMax.
Figure
MDEA
solvent
with
a circulation
of 300
m3and
/h and
15%
concentration
simulated
ProMax.
A summary
of the
results
obtained
from
simulations
of ProMax
was
compiled
from
A summary
of the
results
obtained
from
simulations
of ProMax
was
compiled
from
Figures
8–19
and
is
shown
in
Table
9,
demonstrating
that
the
MEA
solvent
is
the
best
Figures 8–19 and is shown in Table 9, demonstrating that the MEA solvent is the
best
solvent
in comparison
to DEA
andand
MDEA,
whilst
MDEA
is the
worst
one.
solvent
in comparison
to DEA
MDEA,
whilst
MDEA
is the
worst
one.
From the aforementioned results presented in Table 9, when using the 200 m3 /h
circulation rate with 10% concentration of amine, the CO2 % from clean flue gas is 3.6295%
for MEA, while that for DEA is 8.1355%. Additionally, that of MDEA is the highest percent,
with a value of 8.4559%. Furthermore, at 15%, with the same flow rate mentioned above,
DEA and MDEA have the highest percentage values of 5.5612% and 8.2545%, respectively,
whilst MEA has a value of 3.2862 × 10−6 %. These mean that the concentration is directly
proportional to the flow rate and inversely proportional to CO2 in the clean flue gas.
However, at 200m3 /h with 10% concentration, the CO2 in the clean flue gas for MEA is
2.9564 × 10−6 %, while for DEA and MDEA is 0.0038358% and 3.7518%, respectively. At
15% concentration of amine with a circulation rate of 300m3/h, the percentage of CO2
in the clean flue gas for MEA, DEA, and MDEA is 6.9516 × 10−7 %, 0.00036247%, and
4.305%. It has been noted that the percentage of CO2 in the clean flue gas for MEA and
DEA decreased, while for MDEA, at 15% with 300 m3 /h circulation rate increased. This is
because MDEA has different operating condition and it works efficiently from 50 to 60 bars.
Another reason is that at this flow (300 m3 /h) of circulation rate is critical flow and the
mass transfer in this flow is false for MDEA. That is the reason why CO2 % in clean gas
flue increased rather than to decreased. As shown in Table 4 the typical concentration
should the MDEA be work is 35–55%. Therefore, considering these results, MEA is the best
amongst them. Figures 20 and 21 illustrate the CO2 percent in clean flow gas at 200 and
300 m3 /h for MEA, DEA and MDEA at 10 and 15% concentration of amines.
Sustainability 2021, 13, 72
MDEA has different operating condition and it works efficiently from 50 to 60 bars. Another reason is that at this flow (300 m3/h) of circulation rate is critical flow and the mass
transfer in this flow is false for MDEA. That is the reason why CO2 % in clean gas flue
increased rather than to decreased. As shown in Table 4 the typical concentration should
the MDEA be work is 35–55%. Therefore, considering these results, MEA is the best
22 of 27
amongst them. Figures 20 and 21 illustrate the CO2 percent in clean flow gas at 200
and
300 m3/h for MEA, DEA and MDEA at 10 and 15% concentration of amines.
Amine recirculastion rate of 200m 3 /hr
9
8.1355
8.4559
8.2545
% CO2 IN CLEAN FLUE GAS
8
7
5.5612
6
5
4
3.6295
3
2
1
3.29E-06
0
Amine concentration 10%
Amine concentration 15%
AMINE CONCENTRATION
Sustainability 2021, 13, x FOR PEER REVIEW
MEA
DEA
23 of 28
MDEA
Figure 20. The CO2 % in clean flue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 200 m33 /h.
Figure 20. The CO2% in clean flue gas with concentration of amine solvents (MEA, DEA, and MDEA) at 200 m /h.
Amine recirculation rate of 300m3/hr
5.00
4.305
%CO2 IN CLEAN FLUE GAS
4.50
3.7518
4.00
3.50
3.00
2.50
2.00
1.50
6.95E-07
2.96E-06
0.0038358
0.00036247
1.00
0.50
0.00
MEA
DEA
MDEA
AMINE CONCENTRATION
Amine concentration 10%
Amine concentration 15%
and MDEA)
MDEA) at
at 300
300 m
m33/h.
Figure 21.
21. The
Figure
The CO
CO22%
% in
in clean
clean flue
flue gas
gas with
with concentration
concentration of
of amine
amine solvents
solvents (MEA,
(MEA, DEA,
DEA, and
/h.
4.3. The Cost of Amine
4.3. The
Costout
of Amine
To find
which solvent costs the least, each one’s price was estimated by performfind out which
solvent
costs the
each one’s
estimated
by performing
ing a To
calculation.
The result
shows
thatleast,
the MEA
is theprice
bestwas
solvent.
The prices
were as
a
calculation.
The
result
shows
that
the
MEA
is
the
best
solvent.
The
prices
were
as
follows:
follows:
(a)
(b)
(c)
(d)
GBP 1121/ton for monoethanolamine (MEA) [33];
DEA GBP 1039/ton [33];
MDEA unknown?
To calculate the price, there should be a specific gravity for amine to convert the cubic
meters to tons, as shown in Equations (11) and (12);
3
3
Sustainability 2021, 13, 72
23 of 27
(a)
(b)
(c)
(d)
(e)
GBP 1121/ton for monoethanolamine (MEA) [33];
DEA GBP 1039/ton [33];
MDEA unknown?
To calculate the price, there should be a specific gravity for amine to convert the cubic
meters to tons, as shown in Equations (11) and (12);
Specific gravity of MEA = 1.01531, density = 1015.31 kg/m3 = 1.01531 t/m3 (ProMax program):
Total MEA ton = Amine feed × Amine concentration% × Density (ton/m3 ) = ton (11)
Total cost = Total MEA ton × GBP/ton = GBP
(12)
Therefore, by using Equations (11) and (12), the cost was calculated and is shown for
MEA in Table 10 and for DEA in Table 11.
Table 10. The total weight of amine (MEA) in tons, with the total cost in GBP.
MEA Solution m3 /h
10% = Net MEA Tons from
Solution
Total Cost GBP
(GBP 1121/ton)
200
300
20.3062
30.4593
22,763.25
34,144.88
Table 11. The total weight of DEA in ton with total cost in GBP.
(a)
DEA Solution m3 /h
10% = Net DEA Tons from
Solution
Total Cost GBP
(GBP 1039/ton)
200
300
20.8718
31.3077
21,685.8002
32,528.7003
Specific gravity of DEA = 1.04359, density = 1043.59 kg/m3 = 1.04359 t/m3 (ProMax program).
The capital cost for CO2 capture facility is USD 223 million and capture cost (USD/tonne
CO2 ) ranges between USD $36–70 for MEA for a typical gas-powered power plant integrated with Carbon capture using MEA shown in Table 12 [19,34].
Table 12. The cost of MEA for one a real company for post capture of CO2 .
Study
[19,34]
Industrial source
CO2 capture technology
CO2 capture efficiency (%)
CO2 captured (Mt CO2 /y)
Project life (years)
Currency
Cost year
External power plant or fuel
Capital cost for capture facility (millionUSD)
Capture cost (USD/tonne CO2 avoided)
Combined stack gas
PCC MEA
90
1.04
20
US
2007
Natural gas
223
36–70
5. Conclusions
From the present study, the following conclusions can be drawn:
1.
From the results of Table 9, it can be concluded that
•
At 10% concentration and feed of 200 m3 /h of amine solvents, the outcome
obtained cannot be chosen for capture because the CO2 % in flue gas for each
Sustainability 2021, 13, 72
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•
•
•
2.
Based on the results in Tables 10 and 11, the following comparison can be drawn:
•
•
3.
MEA, DEA and MDEA are 3.6295%, 8.1355%, and 8.4559%, respectively, and
these values are not enough. With these percentages obtained my target was
not achieved neither of other of other researchers because to use capture process
there should be clear from CO2 % in clean flue gas as aforementioned is not
acceptable (the percentage of carbon dioxide) as sustainable for power plants,
even the temperature at the bottom of the absorber is quite good but the purity of
nitrogen is not qualified to be utilized to other purposes such as food processes.
MEA produces a good outcome at 200 m3 /h with a 15% concentration in comparison to DEA and MDEA, with their values being 3.2862 × 10−6 , 5.5612, and
8.2545, respectively, but the temperature of the rich amine is still high, so it is
recommended that cooling is induced by increasing the flow rate or decreasing
the concentration of amine;
Likewise, the MEA has perfect significant results at a 300 m3 /h amine circulation
rate at a 10% concentration, reducing the temperature to 78.95 ◦ C, whereas the
temperature was 100.75 ◦ C at 15%. A good result of 77.21 ◦ C was obtained for
0.0038358% of CO2 in the top outlet of the tower and 99.768% nitrogen for both
MEA and DEA and 96.01% for MDEA, with 3.7518% CO2 in clean flue gas, which
is still high, however, the other significant advantages of capturing CO2 is that
the gained nitrogen, with a purity 99.68%, can be used for other purposes;
For MDEA, the bad result means that the operating condition needs to be
changed, which changes the pressure to 50 or 60 bar. This will produce good
results but will be costly.
For MEA at 200 and 300 m3 /h, the total weight in tons was equal to 20.3062 and
30.4593, with a total cost of GBP 22,763.25 and 34,144.88, respectively;
for DEA at 200 and 300 m3 /h, the total weight in tons was equal to 20.8718 and
31.3077, with a total cost of GBP 21,685.8002 and 32,528.7003, respectively.
Finally, from the results of the comparison, MEA was proven to be the best solvent
investigated in this study, rather than DEA and MDEA; however, the DEA was
slightly cheaper than MEA, but the result was an enormously different comparison
with MEA.
Author Contributions: S.H. conducted the study simulation and data analysis, A.J.A. supervised
the overall research, contributed to paper development and editing, G.G.N. conducted review and
made changes to the manuscript. All authors have read and agreed to the published version of the
manuscript.
Funding: This research was fully funded by CNOOC Iraq Limited.
Conflicts of Interest: The authors declare no conflict of interest.
Abbreviations
BP
IPCC
CCS
CO2
COS
SO2
NOX
O2
N2
H2 O
British Petroleum
Intergovernmental on climate change
Carbon capture and storage
Carbon dioxide
Carbonyl sulfide
Sulfur dioxide
Nitrogen oxides (x = 1, 2, 3)
Oxygen
Nitrogen
Water or (vapor water)
Sustainability 2021, 13, 72
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H2 S
PM
RDF
MEA
DEA
DGA
MDEA
DIPA
TIPA
Gt
Mt
MPa
Ppm
PCC
Hydrogen sulfide
Particulate matter
Radial distribution functions
Monoethanolamine
Diethanolamine
Diglycolamine
Methyldiethanolamine
Diisopropanolamine
Triisopropanolamine
Gigatons
Million tons
Megapascal (unit of pressure)
Part per million
Post-combustion capture
Appendix A
pKa: This is one method that can be used to indicate the strength of acid. pKa = −log10Ka
means pKa is a negative logarithm of the Ka value. In addition, a higher pKa value indicates a
weaker acid, and a lower value of pKa means a stronger acid, and the latter means that the acid is
fully dissociated in water.
Dimers: A structure implicates two similar or identical units. These units may be associated by
noncovalent forces or covalent bonding [31].
Rich amine: An amine solution that has held or absorbed the acid gas CO2 from the flue gas
during the absorption process.
Lean amine: An amine solution that does not contain any acid gas CO2 and this means that,
before the absorption processes, the amine undergoes the regeneration process, which removes all
acid gas, producing a lean amine.
Table 1. The properties of CO2 that used in amine absorption come out from ProMax simulation program.
Properties
Temperature
Pressure
Mole fraction vapor
Mole fraction light liquid
Mole fraction heavy liquid
Molecular weight
Mass density
Molar flow
Mass flow
Vapor volumetric flow
Liquid volumetric flow
Normal vapor volumetric flow
Std vapor volumetric flow
Std liquid volumetric flow
Compressibility
Specific gravity
API gravity
Enthalpy
Mass enthalpy
Mass Cp
Ideal gas Cp, Cv ratio
Dynamic viscosity
Kinematic viscosity
Thermal conductivity
Surface tension
Net ideal gas heating value
Net liquid heating value
Gross ideal gas heating value
Gross heating value
Units
Vapor
◦C
32
30
100
0
0
44.0095
65.0285
2272.24
100,000
1537.79
1537.79
50,929.8
53726.7
121.773
0.827261
1.51953
barg
%
%
%
Kg/kmol
Kg/m3
Kmol/h
Kg/h
m3 /h
m3 /h
Nm3 /h
m3 /h
m3 /h
KJ/h
kJ/kg
kJ/(kg ◦ C)
cP
cSt
W/(m ◦ C)
dyn/cm
MJ/m3
MJ/kg
MJ/m3
MJ/kg
−8.96706 × 108
−8967.06
1.08707
1.28541
0.0166239
0.25564
0.0198344
0
−0.17659
0
0.17659
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26 of 27
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