ISO 27927:2025
(Main)Carbon dioxide capture — Key performance parameters and characterization methods of absorption liquids for post-combustion CO2 capture
Carbon dioxide capture — Key performance parameters and characterization methods of absorption liquids for post-combustion CO2 capture
This document provides definitions, guidelines and supportive information for the key performance parameters and their characterization methods of absorption liquids used in post-combustion CO2 capture. It covers common methodologies to measure and calculate specific key performance parameters of the absorption liquids. The absorption liquids for post-combustion CO2 capture covered by this document are chemically reactive liquids, such as amine solutions, potassium carbonate solutions, aqueous ammonia, amino-acid salt solutions and mixtures of these reactants. Other absorption liquids based on different principles for CO2 capture are not covered. The key performance parameters considered in this document relate to the design and operation of absorption liquid-based post-combustion CO2 capture processes, as well as equipment such as absorber and desorber columns, reboilers and other heat exchangers. The key performance parameters are: — primary parameters, such as rich and lean CO2 loading, absorbent concentration, absorption capacity, heat of absorption, absorption rate and absorbent volatility; — secondary parameters, such as cyclic loading, that are directly derived from the primary parameters, or combined with other physical measurements, as in the case for the absorbent loss rate. In addition, physical and chemical properties such as density, viscosity, pH, thermal conductivity and specific heat capacity are described. These properties are essential for understanding the key performance parameters of the absorption liquids. This document also: — establishes key performance parameters (see REF Section_sec_4 \r \h Clause 4 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E000000530065006300740069006F006E005F007300650063005F0034000000 ), physical and chemical properties of absorption liquids, and their calculation methods, and provides a common way of reporting them; — specifies the general requirements for the absorption liquid characterization in laboratory measurement and field testing (see REF Section_sec_5 \r \h Clause 5); — provides the requirements for the instrumentation to be installed or used, and guidelines for the characterization methods (see REF Section_sec_6 \r \h Clause 6 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000E000000530065006300740069006F006E005F007300650063005F0036000000 ); — provides information on the characterization methods of absorption liquids, describing all stages of test preparation, set-up and execution (see Annexes A to I), as well as guidance on sampling absorption liquids. NOTE While key performance parameters of absorption liquids are important process indicators for post-combustion CO2 capture, factors such as process design, equipment design and manufacturing, economics and safety are also considered for a comprehensive evaluation of post-combustion CO2 capture technology. The document does not provide guidelines for benchmarking or comparing absorption liquids for post-combustion capture processes, nor does it offer methods to assess different technologies or projects, or specify methodologies for process engineering design. Additionally, the document is not intended to compel technology owners to disclose any intellectual properties related to their proprietary absorption liquids. The document does not cover all available and emerging characterization methods for the key performance parameters considered in this document.
Captage du dioxyde de carbone — Paramètres clés de performance et méthodes de caractérisation des liquides d'absorption pour le captage du CO2 post-combustion
General Information
Standards Content (Sample)
International
Standard
ISO 27927
First edition
Carbon dioxide capture — Key
2025-09
performance parameters and
characterization methods of
absorption liquids for post-
combustion CO capture
Captage du dioxyde de carbone — Paramètres clés de
performance et méthodes de caractérisation des liquides
d'absorption pour le captage du CO post-combustion
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 2
3 Terms, definitions, abbreviated terms and symbols . 2
3.1 Terms and definitions .2
3.2 Abbreviated terms .6
3.3 Symbols .6
4 Evaluation of performance parameters . 8
4.1 General .8
4.2 Primary performance parameters .9
4.2.1 Rich and lean CO loading .9
4.2.2 Absorbent concentration .10
4.2.3 CO absorption capacity .11
4.2.4 Heat of absorption .11
4.2.5 Absorption rate. 12
4.2.6 Absorbent volatility . 13
4.3 Secondary performance parameters . 13
4.3.1 Cyclic loading . 13
4.3.2 Absorbent loss rate. 13
4.4 Physical and chemical properties .14
5 General for the characterization of absorption liquids . 14
5.1 Laboratory measurements and field testing .14
5.2 General requirement . 15
6 Instrument and characterization methods .16
6.1 General .16
6.2 Instrument classification .16
6.3 Calibration of instrument .16
6.4 Evaluation of measurement uncertainty .16
6.5 Competence in characterization methods .17
Annex A (informative) Methods for sampling absorption liquids used in post-combustion CO
capture demonstration system .18
Annex B (informative) Summary for the characterization methods of primary performance
parameters of absorption liquids used in post-combustion CO capture .22
Annex C (informative) Characterization methods for evaluating carbon dioxide loading .24
Annex D (informative) Characterization methods for evaluating absorbent concentration .30
Annex E (informative) Characterization methods for evaluating CO absorption capacity .40
Annex F (informative) Characterization methods for evaluating heat of absorption .46
Annex G (informative) Characterization methods for evaluating absorption rate .50
Annex H (informative) Characterization methods for evaluating absorbent volatility .58
Annex I (informative) Characterization methods for evaluating physical and chemical
properties of absorption liquids .66
Bibliography .68
iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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This document was prepared by Technical Committee ISO/TC 265, Carbon dioxide capture, transportation
and geological storage.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Carbon dioxide capture and storage (CCS) is a suite of technologies to reduce carbon dioxide (CO )
emissions into the atmosphere, as a central aspect of reducing overall greenhouse gas emissions that are
causing climate change. CCS is widely recognized to play a crucial role in achieving deep and large-scale
decarbonization in a short time frame in the power and industrial sectors. Among several CO capture
pathways, post-combustion CO capture (PCC) is the most mature and viable, capable of reducing CO
2 2
emissions from combustion processes in the energy-related and industrial sectors. Chemical absorption
using reactive liquids is a proven technology and has been widely developed in numerous PCC facilities.
Various absorption liquids, such as amines, potassium carbonate, aqueous ammonia solutions, amino-acid
salt solutions and mixtures of these reactants, have been adopted for PCC applications.
The performance of absorption liquids is one of the key factors influencing the cost and the energy
consumption in a PCC process, thereby influencing its commercial application and its net greenhouse gas
impact. Understanding the key performance parameters and physical and chemical properties of absorption
liquid is essential, not only for screening of promising absorption liquids, but also for process engineering
design and evaluating PCC plant performance during operation.
Specifically, accurate monitoring of CO loading and absorbent concentration in the absorption liquid
will guide parametric measurement, optimization, commissioning and operation of the PCC plant.
Understanding the absorption capacity helps in selecting the appropriate absorption liquid for CO capture,
and optimizing the process conditions using information from vapour-liquid equilibria. A larger cyclic
loading of CO in the absorption liquid means that less absorption liquid needs to be circulated, leading
to lower energy consumption for pumping, heating and cooling. Absorbent volatility is one of the factors
leading to absorbent loss. The heat of absorption of CO is a primary factor influencing the energy required
for regenerating absorption liquids. The viscosity of absorption liquids can affect absorber flooding, and
electricity consumption for pumping. A higher viscosity of the absorption liquid also reduces the heat
transfer coefficient for the heat exchanger, meaning more heat exchanger area is required to achieve the
same heat duty. It also decreases the absorption and mass transfer between gas and liquid. The absorption
rate of absorption liquids impacts the capital costs of the PCC process. A higher absorption rate of the
absorption liquids enables a shorter packing height in CO capture, which reduces the sizes of the absorber
and desorber. The density and viscosity are physical and chemical properties of absorption liquids. The
thermal conductivity and specific heat capacity are important thermophysical properties to understand the
heat transfer process in absorption liquid-based CO capture process.
Given the large and diverse impact of absorption liquids on various aspects of PCC plant performance, an
ISO standard for evaluating and characterizing the key performance parameters of absorption liquids is
required and that would complement the standards for CO capture, ISO 27919-1 and ISO 27919-2. Previously,
ISO 27919-1 was developed as a guideline for measuring, evaluating and reporting the performance of
a PCC plant integrated into a power plant. It provides a general methodology for calculating specific key
performance indicators for the PCC process within the entire power system. ISO 27919-2 was developed
to specify an evaluation procedure to ensure and maintain the stable performance of the PCC process
integrated into a power plant during operation, from a commissioning perspective.
The measurement and evaluation of the key physical and chemical characteristics of absorption liquids,
as defined in this document, are essential. This will benefit technology developers for the subsequent PCC
process design, optimization, performance monitoring and plant operation.
v
International Standard ISO 27927:2025(en)
Carbon dioxide capture — Key performance parameters and
characterization methods of absorption liquids for post-
combustion CO capture
1 Scope
This document provides definitions, guidelines and supportive information for the key performance
parameters and their characterization methods of absorption liquids used in post-combustion CO capture.
It covers common methodologies to measure and calculate specific key performance parameters of the
absorption liquids.
The absorption liquids for post-combustion CO capture covered by this document are chemically reactive
liquids, such as amine solutions, potassium carbonate solutions, aqueous ammonia, amino-acid salt solutions
and mixtures of these reactants. Other absorption liquids based on different principles for CO capture are
not covered.
The key performance parameters considered in this document relate to the design and operation of
absorption liquid-based post-combustion CO capture processes, as well as equipment such as absorber and
desorber columns, reboilers and other heat exchangers.
The key performance parameters are:
— primary parameters, such as rich and lean CO loading, absorbent concentration, absorption capacity,
heat of absorption, absorption rate and absorbent volatility;
— secondary parameters, such as cyclic loading, that are directly derived from the primary parameters, or
combined with other physical measurements, as in the case for the absorbent loss rate.
In addition, physical and chemical properties such as density, viscosity, pH, thermal conductivity and
specific heat capacity are described. These properties are essential for understanding the key performance
parameters of the absorption liquids.
This document also:
— establishes key performance parameters (see Clause 4), physical and chemical properties of absorption
liquids, and their calculation methods, and provides a common way of reporting them;
— specifies the general requirements for the absorption liquid characterization in laboratory measurement
and field testing (see Clause 5);
— provides the requirements for the instrumentation to be installed or used, and guidelines for the
characterization methods (see Clause 6);
— provides information on the characterization methods of absorption liquids, describing all stages of
test preparation, set-up and execution (see Annexes A to I), as well as guidance on sampling absorption
liquids.
NOTE While key performance parameters of absorption liquids are important process indicators for post-
combustion CO capture, factors such as process design, equipment design and manufacturing, economics and safety
are also considered for a comprehensive evaluation of post-combustion CO capture technology.
The document does not provide guidelines for benchmarking or comparing absorption liquids for post-
combustion capture processes, nor does it offer methods to assess different technologies or projects, or
specify methodologies for process engineering design. Additionally, the document is not intended to compel
technology owners to disclose any intellectual properties related to their proprietary absorption liquids.
The document does not cover all available and emerging characterization methods for the key performance
parameters considered in this document.
2 Normative references
There are no normative references in this document.
3 Terms, definitions, abbreviated terms and symbols
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
absorbent
substance able to take up liquid or gas
Note 1 to entry: the absorbent for post-combustion CO capture is the substance able to take up CO mainly through
2 2
chemical reactions in liquid solution.
[SOURCE: ISO 27919-1:2018, 3.1.1, modified — "absorb" has been replaced with "take up" in the definition
and Note 1 to entry has been added.]
3.1.2
absorbent concentration
amount of absorbent (3.1.1) present in a specific amount of absorption liquid, excluding water or other non-
reactive substances in the absorption liquid
Note 1 to entry: Absorbent concentration may be expressed in units of kilograms of absorbent per kilogram of
−1 −1
absorption liquid (kg·kg ), or moles of absorbent per litre of absorption liquid (mol·l ).
3.1.3
absorbent loss rate
speed at which the absorbent (3.1.1), excluding water or other non-reactive substances in the absorption
liquids, that is lost from the CO capture process due to factors such as evaporation, leaks and degradation
3.1.4
absorption liquid
liquid that is capable of removing carbon dioxide gas from the feed gas in a gas-liquid absorption process
Note 1 to entry: The absorption liquid contains both the absorbent (3.1.1) and solvent; the solvent can be water or
other non-reactive substances.
3.1.5
absorption rate
mass transfer rate
speed at which the absorption process proceeds
Note 1 to entry: The absorption rate is quantified by the absorption rate coefficient or mass transfer coefficient, which
is a proportionality factor in the rate law of chemical kinetics that relates to the concentration or partial pressure of
gas phase species.
Note 2 to entry: The absorption rate can be expressed as the liquid-side mass transfer concentration driving force in
−1 −2 −1
the unit of mol·s ·m ·Pa .
3.1.6
accuracy
accuracy of measurement
measurement accuracy
closeness of agreement between a measured quantity value and a true quantity value of a measurand
[SOURCE: ISO/IEC Guide 99:2007, 2.13, modified — "accuracy" has become the preferred term.]
3.1.7
alkalinity
capacity of aqueous media to react with hydrogen ions
[SOURCE: ISO 6707-1:2020, 3.7.3.62]
3.1.8
carbon dioxide capture and storage
CCS
process consisting of the separation of CO from industrial and energy-related sources, transportation and
injection into a geological formation, resulting in long term isolation from the atmosphere
Note 1 to entry: CCS is often referred to as carbon capture and storage. This terminology is not encouraged because it
is inaccurate: the objective is the capture of carbon dioxide and not the capture of carbon. Tree plantation is another
form of carbon capture that does not describe precisely the physical process of removing CO from industrial emission
sources.
Note 2 to entry: The term “sequestration” is also used alternatively to “storage”. The term “storage” is preferred since
“sequestration” is more generic and can also refer to biological processes (absorption of carbon by living organisms).
Note 3 to entry: Long term means the minimum period necessary for geological storage of CO to be considered an
effective and environmentally safe climate change mitigation option.
Note 4 to entry: The term carbon dioxide capture, utilization (or use) and storage (CCUS) includes the concept that
isolation from the atmosphere can be associated with a beneficial outcome. CCUS is embodied within the definition
of CCS to the extent that long term isolation of the CO occurs through storage within geological formations. CCU is
carbon capture and utilization (or use) without storage within geological formations.
Note 5 to entry: CCS should also ensure long term isolation of CO from oceans, lakes, potable water supplies and other
natural resources.
[SOURCE: ISO 27917:2017, 3.1.1]
3.1.9
carbon dioxide loading
CO loading
quantity of carbon dioxide absorbed in a specific amount of absorption liquids
Note 1 to entry: Carbon dioxide loading may be expressed in units of moles of CO per mole of absorbent (3.1.1)
−1 −1
(mol·mol ) or moles of CO per kilogram of absorption liquid (mol·kg ).
3.1.10
CO absorption capacity
maximum quantity of carbon dioxide absorbed in a specific amount of absorption liquids in a vapor liquid
equilibrium state, under a certain temperature and CO partial pressure
3.1.11
CO flux
rate of CO absorption (3.1.13) or mass transfer per unit area, which is linked to the concentration or partial
pressure driving force for absorption or mass transfer
−1 −2
Note 1 to entry: CO flux is expressed in mol·s ·m .
3.1.12
chemical absorption
process in which CO is absorbed by chemical reaction
[SOURCE: ISO 27919-1:2018, 3.1.8]
3.1.13
CO absorption
process through which CO is separated from the feed gas through contact with absorption liquids
3.1.14
CO desorption
process through which absorption liquids release CO after changing the conditions of the liquid (e.g.
temperature, pressure)
3.1.15
cyclic loading
net quantity of CO produced from a complete absorption and desorption cycle in a specific amount of
absorption liquids
Note 1 to entry: The value of cyclic loading equals to the CO loading (3.1.9) after absorption minus the CO loading
2 2
after desorption.
−1
Note 2 to entry: Cyclic loading may be expressed in units of moles of CO per mole of absorbent (3.1.1) (mol·mol ) or
−1
moles of CO per kilogram of absorption liquid (mol·kg ).
3.1.16
mass density
ρ
common density (mass per unit volume)
−3 −3
Note 1 to entry: The unit of the mass density is kg·m (or g·cm ).
[SOURCE: ISO 16413:2020, 3.1.19]
3.1.17
dynamic viscosity
viscosity
η
ratio between the applied shear stress and rate of shear of a liquid
Note 1 to entry: It is a measure of the resistance to flow or deformation of a liquid.
Note 2 to entry: The term dynamic viscosity is also used in a different context to denote a frequency-dependent
quantity in which shear stress and shear rate have a sinusoidal time dependence.
Note 3 to entry: Dynamic viscosity is expressed in pascal multiplied by seconds (Pa⋅s).
[SOURCE: ISO 3104:2023, 3.2, modified — Note 3 to entry has been replaced.]
3.1.18
heat of absorption
change of enthalpy in absorption liquids resulting from the absorption process
−1 −1
Note 1 to entry: The heat of absorption is often expressed in kJ·mol CO , or kJ·kg CO .
2 2
3.1.19
lean liquid
absorption liquid with a lower carbon dioxide loading (3.1.9) after the carbon dioxide desorption process
3.1.20
measurement uncertainty
uncertainty of measurement
uncertainty
non-negative parameter characterizing the dispersion of the quantity values being attributed to a
measurand, based on the information used
Note 1 to entry: Measurement uncertainty includes components arising from systematic effects, such as components
associated with corrections and the assigned quantity values of physical properties, as well as the definitional
uncertainty. Sometimes estimated systematic effects are not corrected for; associated measurement uncertainty
components are incorporated.
Note 2 to entry: The parameter may be, for example, a standard deviation called standard measurement uncertainty
(or a specified multiple of it), or the half-width of an interval, having a stated coverage probability.
Note 3 to entry: Measurement uncertainty comprises, in general, many components. Some of these may be evaluated
by Type A evaluation of measurement uncertainty from the statistical distribution of the quantity values from a series
of measurements and can be characterized by standard deviations. The other components, which may be evaluated
by Type B evaluation of measurement uncertainty, can also be characterized by standard deviations, evaluated from
probability density functions based on experience or other information.
Note 4 to entry: In general, for a given set of information, it is understood that the measurement uncertainty is
associated with a stated quantity value attributed to the measurand. A modification of this value results in a
modification of the associated uncertainty.
Note 5 to entry: “Type A evaluation of measurement uncertainty” is an evaluation of a component of measurement
uncertainty by a statistical analysis of measured quantity values obtained under defined measurement conditions.
“Type B evaluation of measurement uncertainty” is an evaluation of a component of measurement uncertainty
determined by means other than a Type A evaluation of measurement uncertainty”.
[SOURCE: ISO/IEC Guide 99:2007, 2.26, modified — “measurement standards” has been changed to “physical
properties” in Note 1 to entry and Note 5 to entry has been added.]
3.1.21
partial pressure
pressure due to a specified component of a gaseous mixture
Note 1 to entry: Partial pressure is expressed in pascal (Pa).
[SOURCE: ISO 3529-1:2019, 3.1.5, modified — Note 1 to entry has been added.]
3.1.22
pH
measure of the activity of the hydrogen ion
Note 1 to entry: Essentially, pH is a measure of acidity or alkalinity (3.1.7).
[SOURCE: ISO/IEEE 11073-10422:2017, 3.1.17, modified — the definition has been split into the definition
and Note 1 to entry.]
3.1.23
rich liquid
absorption liquid with a higher carbon dioxide loading (3.1.9) after the carbon dioxide absorption process
3.1.24
specific heat capacity
amount of energy required to raise 1 kg of material by the temperature of 1 K
−1 −1
Note 1 to entry: The specific heat capacity is expressed in J·kg ·K .
3.1.25
thermal conductivity
quotient of the amount of heat flow per unit of time through a unit of surface area perpendicular to the heat
flow in a solid material, divided by the temperature difference per unit length (temperature gradient)
−1 −1
Note 1 to entry: The SI unit of thermal conductivity is W·m ·K .
[SOURCE: ISO 4825-1:2023, 3.3]
3.1.26
volatility
tendency of a substance to evaporate
Note 1 to entry: The volatility of an absorbent (3.1.1) is often expressed as the Henry’s law constant which represents
the vapor-liquid partition of the absorbent in terms of the ratio of the vapor pressure to its liquid mole fraction at a
given temperature.
Note 2 to entry: Volatility is expressed in pascal (Pa).
3.2 Abbreviated terms
CCS carbon dioxide capture and storage
PCC post-combustion CO capture
3.3 Symbols
The following mathematical symbols are preparatory for revising variables and formulae in Clause 4 based
on the ISO directives and relevant standards.
−1
α
Carbon dioxide loading per mole of absorbent mol·mol
−1
α′
Carbon dioxide loading per kilogram of absorption liquid mol·kg
−1
α Carbon dioxide loading per mole of absorbent of the lean absorption liquid mol·mol
lean
Carbon dioxide loading per kilogram of absorption liquid of the lean absorption
′
−1
mol·kg
α
lean
liquid
−1
α Carbon dioxide loading per mole of absorbent of the rich absorption liquid mol·mol
rich
Carbon dioxide loading per kilogram of absorption liquid of the rich absorption
′
−1
mol·kg
α
rich
liquid
−1
Δα
Cyclic loading of CO per mole of absorbent mol·mol
−1
′
Δα
Cyclic loading of CO per kilogram of absorption liquid mol·kg
−1 −1
c
Specific heat capacity J·kg ·K
p
−3
ρ
Density kg·m
η Dynamic viscosity Pa·s
−1 −1
λ Thermal conductivity W·m ·K
γ
Absorbent activity coefficient at the reference state of infinite dilution of absor-
abs
—
bent in absorption liquid
−1
γ
Absorbent loss rate kg·tonne
lossrate
−1
C Absorbent concentration in molar mol·l
abs
′
−1
Absorbent concentration in mass fraction kg·kg
C
abs
2 −1
D Diffusion coefficient of CO in absorption liquid m ·s
CO2
d
Hydraulic diameter of the mass transfer measurement device m
h
−1
ΔH
Heat of absorption kJ·mol CO
−1
′
ΔΗ Heat of absorption kJ·kg CO
H
Henry’s law volatility constant Pa
abs
−1 −2 −1
k Gas-side mass transfer coefficient mol·s ·m ·Pa
g
′
−1 −2 −1
Liquid-side mass transfer coefficient mol·s ·m ·Pa
k
g
−1 −2 −1
K
Overall mass transfer coefficient mol·s ·m ·Pa
G
m Mass of absorbent in absorption liquid kg
abs
m
Mass of absorption liquid kg
l
l
Mass of CO absorbed in absorption liquid kg
m
CO2
l
m Mass of CO absorbed at equilibrium kg
CO2()eq
m
Mass of CO produced tonne
CO2
m Mass of absorbent in absorption liquid after a period of PCC operation kg
final
m
Mass of absorbent in absorption liquid at the start of measurement in PCC operation kg
initial
−1 −2
N CO flux mol·s ·m
CO2
l
Amount of moles of CO absorbed in liquid phase mol
n
CO2
l
Amount of moles of CO absorbed in liquid phase in the lean absorption liquid mol
n
CO2lean
l
Amount of moles of CO absorbed in liquid phase in the rich absorption liquid mol
n
CO2rich
l
n Amount of moles of CO absorbed in liquid phase at equilibrium mol
CO2()eq
n
Total amount of moles of absorbent in absorption liquid mol
abs
P Partial pressure of an absorbent in vapour phase Pa
abs
P
CO partial pressure in the gas phase Pa
CO ,g
*
Equilibrium CO partial pressure of the absorption liquid Pa
P
CO2
Q
Amount of heat produced in the absorption liquid in the CO absorption process kJ
−1 −1
R Universal gas constant J·K ·mol
S Sherwood number —
h
T Temperature K
V Volume of absorption liquid without CO absorbed l
l 2
x
Mole fraction of unreacted absorbents in absorption liquid —
abs
−1
X Absorption capacity in moles per kilogram of absorption liquid mol·kg
−1
′
X
Absorption capacity in kilograms per kilogram of absorption liquid kg·kg
4 Evaluation of performance parameters
4.1 General
Clause 4 provides the key performance parameters of absorption liquids used in PCC applications.
The key performance parameters of absorption liquids are as follows.
a) The primary performance parameters are those derived directly from measurements:
— rich and lean CO loading;
— absorbent concentration;
— absorption capacity;
— heat of absorption;
— absorption rate;
— absorbent volatility.
b) The secondary performance parameters are those derived from primary parameters:
— cyclic loading;
— absorbent loss rate.
c) The primary and secondary parameters are essential for characterizing absorption liquids used in PCC.
Characterization of the absorption liquid also includes the following physical and chemical properties,
which are dependent on CO loading and absorbent concentration:
— density;
— viscosity;
— specific heat capacity;
— thermal conductivity;
— pH.
A block diagram demonstrating the key performance parameters and properties considered in this work and
their application is shown in Figure 1. The parameters are used in research and development in laboratories,
and field testing at PCC plants.
Field testing demonstrates both the long-term performance of absorption liquids within the PCC process
and ultimately validates a novel CO capture technology utilizing these absorption liquids. Monitoring the
following parameters and properties are useful in field testing:
— rich and lean CO loading;
— absorbent concentration;
— absorbent volatility;
— cyclic loading;
— absorbent loss rate;
— pH;
— density;
— viscosity.
Key
impact
defined scope
parameter measured only through laboratory measurement
parameter measured through both laboratory measurement and field testing
Figure 1 — Block diagram of key performance parameters of absorption liquids considered in this
document (in the solid frame)
NOTE The rectangular block with grey fill indicates parameters that can be measured through both the laboratory
measurement and field testing. The oval block with grey fill indicates parameters that can be measured solely through
the laboratory measurement. Long term operation usually refers to field testing campaigns lasting a minimum period
of 1 000 hours.
4.2 Primary performance parameters
4.2.1 Rich and lean CO loading
−1
The carbon dioxide loading (CO loading) α [mol·mol ], is defined as the ratio of moles of all CO absorbed
2 2
to the moles of absorbent in absorption liquid:
l
n
CO2
α = (1)
n
abs
where
l
is the total number of moles of CO absorbed in a specific amount of absorption liquid [mol];
n
CO2
n
is total number of moles of absorbent in a specific amount of absorption liquid [mol].
abs
When information about the composition and concentration of the absorption liquid is unknown or
−1
undisclosed, the CO loading can also be expressed as α′ [mol·kg ], which is the ratio of moles of all CO
2 2
absorbed to the mass of the absorption liquid. This mass includes both the absorbent and solvent, such as
water or other non-reactive substances.
l
n
CO2
′
α = (2)
m
l
where m is the mass of absorption liquid [kg].
l
When complete information on an absorption liquid, including its composition and concentration, is
difficult to obtain, the alkalinity of the absorption liquid can serve as an alternative indicator of absorbent
concentration. This approach is introduced in Clause D.2.
′
−1 −1
The rich CO loading α [mol·mol ] or α [mol·kg ] is defined as the CO loading after the CO
2 rich rich 2 2
absorption process. In the laboratory measurement, and field testing at a PCC plant as shown in Figure A.1,
the rich CO loading can be obtained from the measurement of a liquid sample taken at the solvent stream
flowing out from the absorber bottom:
l
n
CO2rich
α = (3)
rich
n
abs
l
n
′ CO2rich
α = (4)
rich
m
l
l
where n is the total number of moles of CO absorbed in a specific amount of absorption liquid after
CO2rich 2
CO absorption [mol].
′
−1 −1
The lean CO loading α [mol·mol ] or α [mol·kg ] is defined as the CO loading after the CO
2 lean lean 2 2
desorption process. In the laboratory measurement, and field testing at a PCC plant, as shown in Figure A.1,
the lean CO loading is obtained from the measurement of a liquid sample taken at the solvent stream flowing
out from the desorber bottom:
l
n
CO2lean
α = (5)
lean
n
abs
l
n
′ CO2lean
α = (6)
lean
m
l
l
where n is the total number of moles of CO absorbed in a specific amount of absorption liquid after
CO2lean 2
CO desorption [mol].
See Annex A for additional information on the sampling of absorption liquid for rich and lean CO loading
measurements. The characterization methods for evaluating rich, lean and other CO loadings are provided
in Annex C for further information.
4.2.2 Absorbent concentration
The absorbent concentration is a key parameter monitored during the commissioning and operation of PCC
plants. The absorbent concentration can be expressed in terms of molar concentration or mass fraction.
−1
The absorbent concentration in molarity C [mol·l ], is defined as the ratio of moles of absorbent to the
abs
volume of absorption liquid, which includes both the absorbent and solvent, such as water or other non-
reactive substances:
n
abs
C = (7)
abs
V
l
where V is the volume of absorption liquid without CO absorbed [l].
l 2
′
−1
The absorbent concentration in mass fraction C [kg·kg ], is defined as the ratio of mass of absorbent to
abs
the mass of absorption liquid:
m
′ abs
C = (8)
abs
m
l
where m is the mass of absorbent in absorption liquid [kg].
abs
In addition, see Annex A for information on the sampling of absorption liquid for absorbent concentration
measurement. Annex D provides absorbent concentration characterization methods, including the
alkalinity method, total organic carbon method, ion chromatography and liquid chromatography with mass
spectrometry.
4.2.3 CO absorption capacity
−1
The CO absorption capacity X [mol·kg ] of absorption liquids refers to the moles of CO absorbed in a
2 2
certain mass of absorption liquid, under conditions of CO partial pressure and temperature, when gas and
liquid phases reach equilibrium:
l
n
CO2()eq
X = (9)
m
l
l
where n is the number of moles of CO absorbed in the liquid phase when the gas and liquid phases
CO2()eq
reach equilibrium [mol].
−1
The absorption capacity can also be expressed as X ′ [kg·kg ] absorption liquid:
l
m
CO2 eq
()
X′= (10)
m
l
l
where m is the mass of CO absorbed in absorption liquid when the gas and liquid phases reach
CO2()eq
equilibrium [kg].
The characterization method using a vapour-liquid equilibrium apparatus in the laboratory for measuring
CO absorption capacity is provided in Annex E for further information.
4.2.4 Heat of absorption
−1 −1
′
The heat of absorption ΔH (kJ·mol ) or ΔH (kJ·kg ), is the total amount of heat produced per unit of CO
absorbed during the CO absorption reaction. The value of heat of absorption can vary depending on the CO
2 2
loading.
Q
−=ΔH ×0,044 (11)
l
m
CO2
Q
′
−=ΔH (12)
l
m
CO2
where
Q is the amount of heat produced in absorption liquid in the CO absorption process [kJ];
l
is the mass of CO absorbed in absorption liquid [kg].
m
CO2
The characterization methods for evaluating the heat of absorption are provided in Annex F for further
information.
4.2.5 Absorption rate
The absorption rate of CO in the absorption liquid can be represented by the liquid-side mass transfer
′
−1 −2 −1
coefficient k [mol·s ·m ·Pa ], which represent the liquid-side mass transfer concentration driving force.
g
′
The value of k can vary under different CO loadings and temperatures. It relates to the overall mass
g 2
transfer coefficient K and gas-side mass transfer coefficient k as follows:
G g
11 1
=− (13)
′
Kk
k
Gg
g
where
K
is the overall mass transfer coefficient, which incorporates the processes of physical and chemical
G
−1 −2 −1
absorption of CO in absorption liquid [mol·s ·m ·Pa ];
k
is the gas-side mass transfer coefficient, representing gas-side mass transfer concentration driving
g
−1 −2 −1
force [mol·s ·m ·Pa ].
N
CO2
K = (14)
G
*
PP−
()
CO22,gCO
logm ean
where
−1 −2
N
is the CO flux [mol·s ·m ];
CO2
P
is the CO partial pressure in the gas phase [Pa];
CO2,g
*
is the equilibrium CO partial pressure in the absorption liquid at the measured temperature and
P
CO2
CO gas phase pressure conditions [Pa].
k is calculated using:
g
SD×
hCO2
k = (15)
g
RT××d
h
where
S
is the Sherwood number;
h
2 −1
D
is the diffusion coefficient of CO in absorption liquid [m ·s ];
CO2
−1 −1
R is the universal gas constant [J·K ·mol ];
T is the temperature [K];
d
is the hydraulic diameter of the mass transfer measurement device [m].
h
′
The characterization methods for evaluating k are provided in Annex G for further information.
g
4.2.6 Absorbent volatility
The absorbent volatility describes the tendency for the absorbent to evaporate from the absorption liquid at
a given temperature. It is determined by the vapour-liquid partitioning of the absorbent. The Henry’s Law
volatility constant ( H , expressed in Pa) is a primary indicator of absorbent volatility, which is referenced
abs
to the state of infinite dilution of absorbent in absorption liquid. H is expressed as the ratio of absorbent
abs
vapour pressure to the unreacted absorbent mole fraction in the absorption liquid. The Henry’s law constant
is referenced to the state of infinite dilution of absorbent in absorption liquid at a given temperature:
P
abs
H = (16)
abs
x ×γ
absabs
where
P
is the vapour pressure of absorbent over absorption liquid at a given temperature [Pa];
abs
x
is the mole fraction of unreacted absorbents in absorption liquid, typically present in a dilute
abs
concentration;
γ
is the absorbent activity coefficient defined at the reference state of infinite dilution of absorbent
abs
in absorption liquid.
NOTE The activity coefficient used in Formula (16) to account for the deviation of a mixture of chemical
substances from the ideal behaviour can be found in ISO 80000-9.
At dilute absorbent concentrations, the absorbent activity coefficient is close to unity. Therefore, the Henry’s
Law volatility constant can be evaluated as follows:
P
abs
lim H = (17)
abs
x
x →0
abs abs
The characterization methods for evaluating H are provided in Annex H for further information.
abs
4.3 Secondary performance parameters
4.3.1 Cyclic loading
−1
The cyclic loading of CO in absorptio
...
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