Carbon Capture in Molten Salts
A new process for CCS based on Ca-looping chemistry
Espen Olsena, Viktorija Tomkutea, Asbjørn Solheimb
aDep.
Mathematical Sciences and Technology, UMB, N-1432 Ås, Norway
bDep.
Energy Conversion and Materials, SINTEF Materials and Chemistry, N-0314 Oslo, Norway
Experimental
Summary
Carbon Capture in Molten Salts (CCMS) has
been demonstrated on the laboratory scale.
Absorption of CO2 from a simulated
combustion gas is shown to exhibit extremely
efficient characteristics, absorbing up to
99.97% of CO2 from a simulated flue gas in a
reactor column of 10 cm length. Desorption
proceeds to 100% so all CaO is regenerated in
reactive state overcoming the main challenge
in conventional Ca-looping. If the process
characteristics are scalable to larger scale
reactors exhibiting similar efficiency, selective
capture and release of CO2 from a wide range
of gas compostitions is possible. This opens
for a large number of applications.
A dedicated laboratory set up involving a highsensitivity FTIR gas analyzer and TGA
functionality is used. A simulated flue gas (0100% CO2 in N2) is fed to a 10 cm column of
molten salt containing CaO. The gas
composition before and after absorption is
analyzed with high accuracy
Weight
(TGA)
Gas in (MFC)
Gas out (MFM)
Gas composition
(FTIR)
Temperature
Reactor
chamber
Introduction and Theory
The Ca-looping principle1 relies on
displacement of the equilibrium described by
Eq.(1) (M denotes an alkaline-earth metal) by
thermal cycling at elevated temperatures
(650 - 1000°C). This minimizes fundamental
losses due to low temperature waste heat.
MO (s)  CO 2 (g)  MCO
3
Results
Tubular ceramic
furnace (1250°C)
Figure 2: The experimental setup, schematically depicted.
The absorption-desorption processes are monitored by
gravimetry (TGA) and mass balance by gas analysis (FTIR).
Figure 5: Repeated absorption-desorption cycling (4x,
800°C/950°C) from a simulated flue gas (N2+27% CO2) in a
chloride based absorbing liquid (CaCl2+5%CaO). The content
of CO2 in the gas emitted is shown in the bottom panel while
the mass of the reaction vessel (―) as well as temperature
(―) is shown in the top panel.
(1)
(s)
N2
N2+CO2(+ SO2)
300
200
SS
Ni
150 mm
ΔG°/[kJ/mol]
100
0
0
-100
500
1000
1500
2000
CaF2/NaF/CaO/CaCO 3
v
Temperature/°C
Mg
-200
Ca
Sr
Ba
-300
50 mm
Figure 3: Details of the reaction chamber. Outer sleeve
of steel, inner crucible and feed tube of Ni.
CaCO3-enriched molten salt
Figure 1: The Gibbs free energy of reaction (1) vs.
temperature and alkali-earth cation.
N2. H2O etc
The process is performed in FBR-reactors and
is being developed on the demonstration
scale2. The main obstacles for successful
commercial implementation is deactivation of
CaO powders by decomposition and sintering
introduced by thermal cycling.
heat
CO2
~900°C
CaO → CaCO3 + CO2
The CCMS idea: By (partly) dissolving the
active substances in a supersaturated molten
salt, highly reactive absorbing CaO is
constantly regenerated as described by
Eq.(2). (M denotes an alkaline-earth metal)
MO (diss, s)  CO 2 (g)  MCO 3 (diss, s) (2)
The CCMS project aims at:
CaCO3 → CaO+ CO2
~700°C
Flue gas
N2, CO2, etc
heat
•Establish the scientific foundation for
industrialization. Time frame: 5-10 years.
CaO- enriched molten salt
Figure 4: Schematic set up of a pilot scale reactor for
continous operation.
References:
1 Chem. Eng. Res. Des. 89, (2011), 836-855
2 www.caoling.eu
•To develop a new and patented process for
carbon capture. 3
Figure 6: The conversion efficiency of the cycling between
CaO and CaCO3 during absorption (•) and desorption (•) in
each of the cycles from Fig.5. The decarbonation of CaCO3
by forming CaO and CO2 is reaching 100% efficiency in all
the cycles while the conversion of CaO to CaCO3 during
absorption shows a rising trend with each cycle, contrary to
the loss in reactivity experienced in solid state Ca-looping.
3 Norwegian patent No. 20092083
Figure 7: Absorption with subsequent desorption of CO2
from a simulated flue gas (N2+27% CO2) in a fluoride based
liquid (NaF/CaF2/10% CaO) at 820°C. Desorption at 1150°C.
The content of CO2 in the gas emitted from the reactor (―)
and temperature (―).
Conclusions and further work
The CCMS process works as predicted from
fundamental thermodynamic modeling. 5
cycles has been completed with 100%
conversion efficiency from CaCO3 to CaO. The
present results are promising indicating the
potential for CCS from a wide variety of gas
compositions from different sources. Focus
will be now be directed towards construction
of a lab pilot reactor for continous operation