Integrated CO2 Capture and Utilization by Combining Calcium
Looping with CH4 Reforming Processes: A Thermodynamic and
Exergetic Approach
Published as part of Energy & Fuels virtual special issue “Recent Advances in CO2 Conversion to Chemicals and
Fuels”.

Theodoros Papalas, Andy N. Antzaras,* and Angeliki A. Lemonidou

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ABSTRACT: This study investigates a novel concept to
coproduce high-purity H2 and syngas, which couples steam
methane reforming with CaO carbonation to capture the generated
CO2 and dry reforming of methane with CaCO3 calcination to
directly utilize the captured CO2. The thermodynamic equilibrium
of the reactive calcination stage was evaluated using Aspen Plus via
a parametric analysis of various operating conditions, including the
temperature, pressure, and CH4/CaCO3 molar ratio. Introducing a
CH4 feed in the calcination stage promoted the driving force and
completion of CaCO3 decomposition at lower temperatures (∼700
°C) compared to applying an inert flow, as a result of in situ CO2
conversion. A conceptual process design was investigated that
employs a system of two moving bed reactors to produce nearly
equivalent volumetric flows of pure H2 and a syngas stream with a H2/CO molar ratio close to 1. A solar reactor was examined for
the reactive calcination step to cover the energy requirements of endothermic CaCO3 decomposition and dry reforming. The overall
exergy efficiency of the process was found equal to ∼75.9%, a value ∼4.0 and ∼8.0% higher compared to sorption-enhanced
reforming with oxy-fuel and solar calciner, respectively, without direct utilization of the captured CO2.

1. INTRODUCTION
Increasing CO2 emissions derived from the excessive use of fossil
fuels have triggered an immediate need for Carbon Capture,
Utilization, and Storage (CCUS) technologies. Calcium looping
is a promising technology for reducing the environmental
footprint of the industrial sector by separating CO2 from the flue
gas via the exothermic carbonation of CaO (eq 1). The
carbonatedmaterial can revert back to oxide form via the reverse
endothermic reaction in a separate reactor.1 Aside from
postcombustion CO2 capture, calcium looping can intensify
thermodynamically limited reactions, such as steam methane
reforming (eq 2, SMR). Conventional SMR plants without
CCUS are widely deployed at industrial scale and account for
∼50% of the worldwide production of H2,

2 a major building
block for refineries and chemical and petrochemical industries
and also an emerging energy carrier for transportation and
electricity generation. However, SMR retains severe energy
demand due to the harsh operation of the reformer (temper-
atures of 800−900 °C and pressures of 20−30 bar). Another
downside is the high carbon footprint due to the large quantities
of CO2 emitted to the atmosphere. CO2 is a byproduct of
reforming and water gas shift (eq 3, WGS) reactions and, in

addition to CO2 from combusting natural gas to cover the
energy demand of the reformer, ends up in the flue gas of the
unit.3 Coupling calcium looping and SMR has been established
as an intensified technology, called sorption-enhanced steam
methane reforming (SE-SMR). The presence of CaO enables in
situ capture of the byproduct CO2 and the shift of the system
toward a new thermodynamic equilibrium with high H2 yield
and purity in a single step while operating at lower temperatures
(600−650 °C). Moreover, heat released from carbonation is
exploited in situ for reforming, avoiding external fuel
combustion.4,5

Received: March 27, 2024
Revised: June 7, 2024
Accepted: June 7, 2024
Published: June 21, 2024

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HCaO CO CaCO , 178

kJ/mol

(s) 2(g) 3(s)
0

298 K

CO2

+ =

(1)

H

CH H O 3H CO ,

206 kJ/mol

4(g) 2 2(g) (g)

0
298 K CH4

+ +

= (2)

H

CO H O H CO ,

41 kJ/mol

(g) 2 (g) 2(g) 2(g)

0
298 K CO

+ +

= (3)

Despite the advantages of SE-SMR, the calcination is usually
conducted under a pure CO2 stream in order to not dilute the
CO2 released fromCaCO3 decomposition, forcing the reactor to
operate at harsh temperatures (≥900 °C).6,7 The group of
Farrauto has proven that using a reactive gas feed instead of CO2
in the calciner can cause the in situ conversion of captured CO2
in the presence of a suitable catalyst and drive calcination at
lower temperatures, according to Le Chatelier’s principle.8,9 An
example of reactive gas is CH4, which can react with the captured
CO2 via dry reforming of methane (eq 4, DRM). Apart from
DRM, the reverse WGS (reverse eq 3, RWGS), CH4
decomposition (eq 5), and Boudouard (eq 6) reactions may
occur and affect the quality of syngas.10

H

CH CO 2H 2CO ,

247 kJ/mol

4(g) 2(g) 2(g) (g)

0
298 K CH4

+ +

= + (4)

HCH C 2H , 75 kJ/mol4(g) (s) 2(g)
0

298 K CH4
+ = +

(5)

H2CO C CO , 171 kJ/mol(g) (s) 2(g)
0

298 K CO2
+ =

(6)

The potential of reducing the temperature of calcination has
triggered the interest for various integrated CO2 capture and
utilization processes,11,12 while calcium looping coupled with
dry reforming of methane (CaL-DRM) has already been widely
studied and applied for postcombustion CO2 capture
applications.10,13−17 A major issue of this process is the carbon
deposition in the reactive calcination stage.16−18 Although
carbon can be gasified by CO2 in the subsequent carbonation
stage, the release of CO with the CO2-stripped flue gas raises
environmental concerns,13,19 while CO2 cannot completely
gasify all carbon.16 Another problem is related to the partial
oxidation of the Ni surface during exposure under CO2 during
carbonation.15,20 Even though the formed NiO can be reduced
from CH4 in the calcination stage,13 the inadequate number of
Ni active sites in the beginning of the stage can affect the syngas
quality. Finally, the CO2 uptake of CaO displays rapid decrease
over cycles, thereby reducing the syngas production
capacity.16,17

The challenges of CaL-DRM and the aforementioned high
calcination temperatures of SE-SMR could be alleviated by
coupling the carbonation and calcination steps of calcium
looping with steam and dry-reforming of methane simulta-
neously (SMR-CaL-DRM). The proposed intensified process
can take place in two reactors using CH4 as carbonaceous feed to
produce high-purity H2 with in situ capture of CO2 and to
directly utilize the captured CO2 for syngas generation. Both H2
and syngas comprise major building blocks for the industry and
the energy sector, and they can be produced from SMR and

DRM in the presence of the same Ni-based catalyst. Conducting
SMR along with carbonation could enable carbon deposited in
the preceding calcination-DRM stage to be more efficiently
gasified from H2O compared to CO2, while the produced CO
could further react via theWGS reaction (eq 3) and produce H2.
The presence of H2O during carbonation could also lead to
higher CO2 capture activity and stability of CaO over cycles
compared to operating under dry conditions, thereby securing a
higher syngas uptake.7,21 Finally, the H2 generated during
reforming can create a strongly reducing environment and
ensure that Ni is retained in metallic form for the subsequent
reactive calcination stage.
The benefits of SMR-CaL-DRM dictate the necessity for

further study to realize the potential of this technology. A
thermodynamic analysis could indicate the optimum operating
windows for the reforming and calcination stages. Despite the
plethora of work on the thermodynamics of the reforming
stage,22−26 studies dealing with the effect of operating
conditions on calcination coupled with DRM are scarce.27,28 It
is also necessary to address whether SMR-CaL-DRM can
compete with SE-SMR in terms of energy efficiency, since
despite the lower operating temperatures, SMR-CaL-DRM
combines two highly endothermic reactions in a single stage.
Conducting an exergy analysis could provide an answer to this
question. Based on the second law of thermodynamics, an exergy
analysis accounts for the degradation of mass and energy streams
when undergoing various processes, providing a rational and
meaningful assessment of the useful energy contained in a
system.24,29,30 Zhang et al. reported a higher exergy efficiency for
sorption-enhanced biomass gasification coupled with in situ
conversion of CO2 to syngas compared to standalone sorption-
enhanced gasification.28 Such a study would be fruitful for SMR-
CaL-DRM, which has not yet been reported yet. The exergy
analysis could also explore efficient ways to cover the energy
demand of the highly endothermic calcination stage. Oxy-fuel
calciners comprise the most widely studied solution for
conventional calcium looping or the SE-SMR process. However,
cofeeding O2 with CH4 in the calciner of SMR-CaL-DRM can
decrease the selectivity toward DRM and the calcination driving
force.16,31 On the other hand, solar heating comprises a
sustainable approach to cover the energy demand,32,33 while
solar reactors have been studied for thermochemical energy
storage applications of calcium looping.34,35

In this work, Aspen Plus software is used to conduct a
thermodynamic analysis of calcination coupled with DRM,
along with a conceptual design and exergy analysis of the SMR-
CaL-DRM process. The thermodynamic analysis aims to clarify
the effect of different operating parameters, including the reactor
temperature, pressure, and CH4 to CaCO3 molar ratio, on the
efficiency of the reactive calcination stage. The process design is
conducted by simulating both the reformer and calciner as
moving bed reactors and by introducing kinetic correlations of
the literature for reactions taking place. Solar heating is
investigated as a means of covering the energy demand of the
calcination coupled with the DRM stage, and the SMR-CaL-
DRM process is evaluated from an exergetic point of view and
compared to SE-SMR with either a solar or an oxy-fuel calciner.
The results are expected to highlight the potential of SMR-CaL-
DRM and contribute to the ongoing research on integrated CO2
capture and utilization processes.

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2. METHODOLOGY
2.1. Thermodynamic Analysis. The effect of operating

conditions on the performance of the calcination/DRM stage was
evaluated via equilibrium calculations with the Aspen Plus V9
computational software. The thermophysical properties of all
substances are defined by the Peng−Robinson equation of state.
Equilibrium compositions are calculated using the RGIBBS
model, by minimizing the Gibbs free energy of introduced
components. A sensitivity analysis is performed for the
calcination/DRM stage, including a range of temperatures and
pressures for operating the reactor and different CH4/CaCO3
molar ratios for the inlet stream. Simulations are run by either
accounting or neglecting carbon formation, while the
production of compounds other than CH4, H2O, H2, CO,
CO2, CaO, CaCO3, and C is considered nonthermodynamically
favorable under the studied conditions. Table 1 summarizes all
parameters investigated. For comparison, a simulation is run
where calcination is conducted under inert flow (100 vol % N2).

The above parameters are evaluated for their effect on CaCO3
and CH4 conversions, in situ CO2 utilization, purity, andH2/CO
molar ratio of syngas. CaCO3 conversion is defined (eq 7) as the
difference between inlet and outlet molar flows of CaCO3,

divided by the inlet molar flow of CaCO3. CH4 conversion is
defined similarly (eq 8) as the difference between the inlet and
outlet molar flows of CH4, divided by the inlet molar flow of
CH4.

n n

n
CaCO conversion (%) 1003

CaCO CaCO

CaCO

3,in 3,out

3,in

= ×

(7)

n n

n
CH conversion (%) 1004

CH CH

CH

4,in 4,out

4,in

= ×
(8)

In situ CO2 utilization efficiency is defined (eq 9) as the CO2
moles that are converted to syngas. This is expressed as the
difference between the inlet molar flow of CaCO3 and outlet
molar flows of CO2 and CaCO3, divided by the inlet molar flow
of CaCO3.

n n n

n

In situ CO utilisation (%)

100

2

CaCO CaCO CO

CaCO

3,in 3,out 2,out

3,in

= ×
(9)

Syngas purity is defined (eq 10) on a dry basis as the outlet molar
flows of H2 and CO divided by the total molar flow in the outlet
stream. TheH2/COmolar ratio is also found (eq 11) by dividing
the outlet molar flows of H2 and CO.

Table 1. Range of Parameters Studied for the Calcination/
DRM Stage

temperature (°C) pressure (bar) CH4/CaCO3 molar ratio (−)

500−1000 1−25 0.1−3.5

Figure 1. Simulation flowchart prepared for the conceptual process design (streams colored in blue refer to inlet gas streams, red to outlet gas streams,
black to other gas streams, green to utility streams, and purple to solid streams circulating between the two reactors).

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n n

n n n n

Syngas purity (%) 100

H CO

H CO CH CO

2,out ,out

2,out ,out 4,out 2,out

=

×
+

+ + +
(10)

n

n
H /CO ratio ( ) 1002

H

CO

2,out

,out

= ×
(11)

2.2. Conceptual Process Design. This section describes
the methodology followed for the process design and exergy
analysis. Τhe main scenario studied (case 1) comprises the
integrated SMR-CaL-DRM process with solar calciner and it is
compared to the SE-SMR process where calcination is
performed with a solar (case 2) or an oxy-fuel heating (case
3) approach. Each process is designed for a H2 production
capacity of ∼11,000 N m3/h.

2.2.1. Process Flow Diagram. Figure 1 illustrates the flow
diagram for the three cases, with the main difference between
them being the composition of the various streams. The flow
diagram consists of the following.

• Steam generation and mixing with natural gas to form the
gas feed of the reformer by also recycling unreacted steam
condensate from the reactor outlet.

• H2 production with in situ capture of CO2 in a moving bed
reactor and transfer of saturated solids in a secondmoving
bed reactor for CaCO3 calcination to occur.

• Heat integration of the hot gas product streams for
preheating the feeds of both reformer and calciner and for
generating electricity in a heat recovery steam cycle.

• Final compression and purification of H2 by pressure
swing adsorption (PSA) and combustion of part of PSA
tail gas to generate steam and preheat the feed of calciner.

In the proposed conceptual design, fresh process water
(stream 102) is mixed with recycled water (stream 303). The
required heat for steam generation in the boiler, simulated by the
array of heat exchanger B-101 and furnace F-101, is provided by
combusting part of the PSA tail gas (stream 307) with air
(stream 106). The generated steam is then mixed with the
appropriate amount of natural gas (stream 101) to obtain a H2O
to CH4 molar ratio of 3, and the total stream is finally preheated
in two sequential heat exchangers (E-201 and E-202) by
exploiting the heat from H2 (stream 204) generated in the
reformer and gas product (stream 211) obtained from the
calciner. The preheated stream (203) is then introduced in the
reformer. Aspen Plus does not contain a built-in model to
simulate the moving bed reactor. Therefore, the reformer is
simulated with an array of three RCSTR models in series (R-
201, R-202, and R-203), which represent the top, middle, and
bottom of the reactor, respectively, with this approach having
been previously proposed for the simulation of moving bed
reactors in Aspen Plus.36 Stream 203 enters the reformer by
being introduced to RCSTR model R-201 together with a
stream (213) of solid components returning from the calciner.
The spent solids of the reformer (stream 214, exiting RCSTR

model R-203) are then fed in the calciner, which is also
simulated with an array of three RCSTR models in series (R-
204, R-205, and R-206). The solid stream is introduced to
RCSTR model R-204 along with a gas inlet flow (stream 210)
whose composition differentiates based on the studied case
(natural gas for case 1, CO2 for case 2, and natural gas and O2 for
case 3), while both gas and solid components exit the reactor

from RCSTR model R-206. The gas feedstock of the calciner
(stream 206) is initially preheated in an array of two heat
exchangers (E-203 and E-204) using the heat of the H2 and
calciner gas products (streams 205 and 212, respectively) that
remains after preheating the reformer’s feed, followed by a
furnace (F-201) that combusts part of the PSA tail gas (stream
308).
The heat-depleted H2 product (stream 301) is further cooled

using cooling water in a heat exchanger (E-301) to condense
unreacted steam, which is then separated (stream 303) in a flash
separation drum (D-301), in order to be recycled and reused.
The gas outlet of the drum (stream 304) is compressed to 25 bar
in a two-stage compressor (C-301) and the compressed gas
(stream 305) is introduced to a PSA unit to remove impurities
(CO2, unreacted CH4 and CO). The latter is simulated with a
calculator block that defines the composition and flow of the pure
H2 product (stream 306) and PSA tail gas. Most of the tail gas of
the PSA unit is used as fuel for the aforementioned preheating
purposes (steam generation and preheating of the calciner inlet
flow), while the remaining gas is flared to the atmosphere.
Regarding the gas outlet of the calciner (stream 211), after

preheating the gas feed of the reformer and the calciner in heat
exchangers E-202 and E-204, respectively, the temperature of
the stream (313) is above 400 °C. The remaining energy is used
to produce superheated steam (heat exchanger E-302), which is
expanded and cooled down in a heat recovery cycle to generate
electricity in steam turbine T-301. The heat-depleted stream
(314) is then cooled using cooling water in heat exchanger
E-304.
All simulations are conducted by considering the following

assumptions.
• Natural gas is composed of 100 vol % CH4.
• All inlet streams are delivered at 15 °C and 1 bar, while

cooling water utility is available at 20 °C and 1 bar.
• All heat exchangers are operated with counter-current

flow of hot and cold streams, with a ΔT between the hot
outlet and the cold inlet streams being 20 °C, except the
preheater of the reformer (heat exchanger E-202).

• The reformer operates at 1 bar and under a fully adiabatic
mode. The feed of the reactor is composed of H2O and
CH4 with a molar ratio of 3, while the amount of CH4 is
adequate for the CH4/CaO ratio to be equal to 1.

• The calciner operates at 1 bar and at 800 °C for case 1 and
900 °C for cases 2 and 3.

• The above description refers to a cocurrent configuration
for the moving bed reactors. Counter-current flow is also
investigated by feeding streams 214 and 215 toR-203 and
R-206, which results in their exit from R-201 and R-203.
The reactor dimensions are the same for cocurrent and
counter-current flow and are specified by accounting that
in the counter-current flow, the gas velocity should be
lower than the minimum fluidization velocity, calculated
through the correlations of Wen and Yu.37

• The solid material circulating between the two reactors is
assumed to be a bifunctional material studied in our
previous work,16 with a nominal composition of 60 wt %
CaO, 10 wt % NiO, and 30 wt % CaZrO3 (in reduced
state). The material is assumed to have a particle size
distribution between 1.8 and 3.5 mm, while similar
particle sizes have been reported before in studies with
moving bed reactors.38−40 Deactivation of the material
over consecutive cycles is considered negligible.

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• Kinetic models from the literature are applied to describe
the reactions taking place,41−45 which are presented in
detail with eqs S1−S17.

• The PSA unit attains 85% H2 separation with a purity of
99.999 vol %.46

• Compressors and turbines are isentropic with an
efficiency of 72%.

2.2.2. Exergy Analysis. The two cases studied are further
compared based on their exergetic efficiency. Standard
conditions are defined as a pressure of 1 bar and temperature
of 25 °C (T0). Exergy flow of a material stream j (Ėxj) consists of
the chemical (Ėxchem,j), physical (Ėxphys,j), kinetic (Ėxkin,j), and
potential (Ėxp,j) exergy flow terms (eq 12).29 The latter two can
be neglected since neither high velocities nor large height
differences are considered.47

Ex Ex Ex Ex Exj j j j p jchem, phys, kin, ,= + + + (12)

The chemical and physical exergy of a stream with molar flow
rate ṅj can be described by eqs 13 and 14. The standard specific
exergy of each component (εi

ο), needed for the calculation of the
chemical exergy term, is provided in Table 2. For solids,

chemical exergy is found like as they are in the gaseous phase.48

The CaZrO3 flow does not alter between the inlet and outlet
streams of reactors and does not affect the analysis outcome.

n x R T x xEx ln( )j j
i

i i
i

i ichem,
0

0= × × + × × ×
i
k
jjjjjj

y
{
zzzzzz
(13)

n h h T s sEx ( ) ( )j j j j j jphys, 0, 0 0,= × [ × ] (14)

Equations 12−14 enable the calculation of the exergy flows of
inlet (Ėxin,k) and outlet (Ėxout,k) material streams for each
equipment module k. Using this data, it is possible to find the
exergy flow destroyed (Ėxdes,k) in module k with the equations of
Table 3.
Work and heat streams also affect the exergy balance of each

module. Electricity needed and produced in the compressor and
the turbine, respectively, can be considered equivalent to work
(Ẇcomp and Ẇturb) and exergy flow. However, heat flow (Q̇s)
provided by a heating source with temperature T is associated
with exergy destruction (ĖxQ,calc), since not all heat can be used
for work (eq 15).24,30

Q
T
T

Ex 1Q ,calc s
0= × i

k
jjj y

{
zzz

(15)

Heat is required for only the solar calciners of cases 1 and 2.
Calcium looping driven by concentrated solar power has been
widely studied in the literature, in which a heliostat field directs
solar radiation toward a tower receiver, which can be the calciner
itself.48,50,51 In general, solar irradiation Q̇s depends on the
surface area A of the heliostat field and on direct normal
irradiance DNI, with the latter varying between geographic
regions and time zones. The heat received by the tower Q̇tower is a
function of Q̇s and the efficiency of the heliostat field (nhelio).
Except for heliostat losses, heat lost due to radiation or reflection
from the outer surface of the receiver and during the transfer of
heat from the outer surface to the material within the reactor can
also affect the heat exploited in the calcination/DRM stage
(Q̇calc). These losses can be accounted with the efficiency of the
tower receiver nrec.

51 Equation 16 shows the relation between all
aforementioned terms.

Q n Q n n Q

n n ADNI
calc rec tower rec helio s

rec helio

= × = × ×

= × × × (16)

The Q̇calc term can be retrieved from the Aspen Plus simulations,
while nrec and nhelio are assumed to be equal to 80 and 85%,
respectively, which are average values from the literature.48,50−53

This data allows the calculation of Q̇s and ĖxQ,calc, by defining T
to be equal to 5300 °C, the temperature of the outer surface of
the sun.47 The heliostat field area can also be estimated by
assuming an average value of 700 W/m2 for DNI.52 It should be
stressed that this study focuses on the conceptual design of the
process, while a more detailed design of the heliostat and the
reactor would be needed for realization and accurate estimation
of nrec and nhelio efficiencies, rendered out of the scope of this
work.
After finding the Ėxdes,k for each module k, the exergy

efficiency nex can be found with eq 17. The Ėxin,tot and Ėxout,total
terms refer to the total input and output exergies from material
streams and they can be found from eqs 18 and 19. Streams
contributing to the total input and output exergy flows are
marked with blue and red color in Figure 1.

n
W

W

W

W

100
Ex

Ex Ex

100
Ex Ex Ex

Ex Ex

Q

Q

Q

ex
out,tot turb

in,tot comp ,calc

in,tot comp ,calc des,tot

in,tot comp ,calc

= ×
+

+ +

= ×
+ +

+ + (17)

Ex Ex Ex Ex Ex Exin,tot 101 102 206 106 309= + + + + (18)

Ex Ex Ex Ex Exout,tot 306 315 312 109= + + + (19)

Table 2. Standard Specific Exergy for All Chemical
Compounds Used (Obtained from Refs 29,49)

chemical compound (−) standard specific exergy (MW/kmol)

CH4 833.9
CO 277.1
CO2 19.9
H2 236.1
H2O 9.5
N2 0.72
O2 3.97
CaO 127.3
CaCO3 16.3

Table 3. Exergy Balances of Individual Modules

module exergy balance

heat
exchangers

Ėxdes,k = (Ėxin,k − Ėxout,k)hot fluid + (Ėxin,k − Ėxout,k)cold fluid

furnaces Ėxdes,k = (Ėxin,k − Ėxout,k)fuel + (Ėxin,k − Ėxout,k)heated fluid

compressors Ėxdes,k = Ėxin,k + Ẇcomp − Ėxout,k
turbines Ėxdes,k = Ėxin,k − Ẇturb − Ėxout,k
steam reformer
and oxy-fuel
calciner

Ėxdes,k = (Ėxin,k − Ėxout,k)gas + (Ėxin,k − Ėxout,k)solid

solar calciner Ėxdes,k = ĖxQ,calc + (Ėxin,k − Ėxout,k)gas + (Ėxin,k − Ėxout,k)solid
mixing streams
and PSA unit

Ėxdes,k = Ėxin,k − Ėxout,k

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Figure 2. Effect of temperature on (a) CaCO3 conversion when applying pure CH4 or pureN2 gas feed and (b) CH4 conversion, in situ CO2 utilization,
purity, and H2/CO molar ratio of the produced syngas when applying pure CH4 gas feed (P = 1 bar, CH4/CaCO3 = 1, no carbon formation).

Figure 3. Effect of pressure on (a) CaCO3 conversion, (b) CH4 conversion, (c) in situ CO2 utilization, (d) purity, and (e) H2/CO molar ratio of the
produced syngas in the calcination/DRM stage (CH4/CaCO3 = 1, no carbon formation).

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3. RESULTS AND DISCUSSION
3.1. Thermodynamic Analysis. Thermodynamic calcu-

lations are conducted using the RGIBBS model of Aspen Plus in
order to find the optimum operating conditions for the
calcination/DRM stage. The section below describes the
alteration of the different performance indicators listed in eqs
7−11 as a function of the temperature, pressure, and CH4/
CaCO3 molar ratio when not accounting for carbon formation.
Separate simulations are also conducted to consider carbon as
the possible product. The main outcome of all simulations
comprises the outlet molar flow composition of the RGIBBS
model, which then allows for the calculation of the performance
indicators. The outlet molar flow composition for all simulations
run, along with the results of the thermodynamic analysis when
accounting for carbon formation, are presented in Figures S1
and S4.
Figure 2a compares the CaCO3 conversion as a function of

temperature, when exposing CaCO3 under a N2 or CH4 gas flow,
which reveals the clear advantage of the intensified calcination/
DRM stage. Applying the reactive CH4 flow leads to the in situ
consumption of CO2 via DRM (eq 4) or RWGS (reverse eq 3)
reactions. The decrease of CO2 partial pressure due to the in situ
conversion and volumetric increase caused by the DRM reaction
(eq 4) enhance the driving force of CaCO3 calcination, causing
the system to shift toward a different thermodynamic
equilibrium compared to the case where calcination is
performed under an inert gas (N2) flow. Higher temperatures
promote the calcination extent due to the endothermic nature of
the reaction. Ultimately, full CaCO3 conversion is attained at
700 °C, a much lower temperature compared to applying the N2
gas flow. It is acknowledged that a N2 gas flow is not a realistic
operation for conventional calcination compared to that using
pure CO2. For the purpose of this study, N2 is used as an inert gas
flow to clearly demonstrate the enhanced calcination driving
force when applying a reactive CH4 gas flow. It should also be
mentioned that using a pure CO2 feed would not permit
conversion of CaCO3 thermodynamically until the temperature
would exceed 900 °C,43 a difference of more than 200 °C
compared to full CaCO3 conversion under CH4 flow.
Figure 2b demonstrates the alteration of the remaining

performance indicators (CH4 conversion, in situ CO2 utilization,
syngas purity, and H2/CO molar ratio) as a function of
temperature when applying pure CH4 flow. For temperatures up
to 700 °C, where CaCO3 is incomplete and the molar ratio of
CH4 to CO2 released from calcination is substoichiometric, CH4
conversion and CO2 utilization increase exponentially with
temperature, with both being mainly dictated by the CO2
released from CaCO3 calcination. At temperatures above 700
°C, where full calcination is attained, CH4 conversion and CO2
utilization increase rates decline and are solely affected by the
extent of the DRM and RWGS reactions at the respective
temperature. It is noted that at the threshold of 700 °C, the CH4
conversion and in situ CO2 utilization exceed 70 and 80%,
respectively.
The purity of the generated syngas follows a trend similar to

that of the other performance indicators. In the temperature
range of 500−700 °C, it sharply increases from ∼5 to ∼86%,
with the remaining percentage of the gas phasemainly consisting
of unreacted CH4. For temperatures above 700 °C, where
CaCO3 conversion is equal to 100%, the system is mainly
affected by the equilibrium of DRM and RWGS. An increase in
the temperature enhances the CH4 and CO2 conversions and

thus the purity of the produced syngas. Finally, the H2/CO
molar ratio presents an inverse volcano profile versus temper-
ature, with the peak occurring at the point of complete CaCO3
calcination. As the temperature increases up to 700 °C, the ratio
of CH4 to CO2 released from CaCO3 calcination remains above
the stoichiometric value for DRM reaction. CO2 is the limiting
reactant in this range and part of it reacted with the produced H2
via the RWGS reaction toward generating CO and H2O. The
mildly endothermic RWGS seems to be favored over the
strongly endothermic DRM until reaching 700 °C. Above the
breakpoint of 700 °C, an increase of temperature led to the
expected gradual increase of the H2/CO molar ratio close to
unity, as the DRM reaction proceeded to a higher extent
compared to RWGS.
Overall, all reactions are interconnected with each other, and

the temperature of the calcination/DRM stage can highly affect
their extent and selectivity. Due to the important role of
temperature in the efficiency of the calcination/DRM stage, the
effect of other parameters is investigated at three different
temperatures, which include the breakpoint temperature for
complete calcination (700 °C), a low temperature where CaCO3
decomposition is limited (650 °C), and an elevated temperature
(800 °C), where both CaCO3 and CH4 conversions are high.
Figure 3 illustrates the effect of pressure on different

performance indicators of the calcination/DRM stage. CaCO3
conversion presents a gradual decrease with increasing pressure
at 650 and 700 °C due to the increase of partial pressure of CO2,
which is the only gaseous product of the reaction. A constant full
conversion precedes the aforementioned decrease for pressures
up to ∼6 bar at 800 °C, which is the reason for the other
performance indicators presenting two different regimes as a
function of the pressure at this temperature. The first regime is
related to full CaCO3 conversion and stoichiometric molar ratio
of CH4 to CO2 released from calcination for pressures up to ∼6
bar, while for higher pressures, the decreasing CaCO3
conversion infers a decreasing CO2 to CH4 molar ratio as well,
which affects the result.
Pressure increase has a negative effect on CH4 conversion,

given the volumetric increase inferred by the DRM reaction. At
800 °C, where complete calcination is attained, the negative
effect of pressure on CH4 conversion is milder, since the
presence of stoichiometric CO2 released from calcination
promotes the extent of the reaction. After passing the threshold
of ∼6 bar, the CH4 conversion is affected by both the negative
effect of pressure on the DRM reaction and the decreasing CO2
content, thereby leading to a more pronounced effect of
pressure, similar to 650 and 700 °C. The in situ CO2 utilization
and syngas purity follow the same trend as CH4 conversion with
increasing pressure, with unreacted CH4 being the main
impurity in the syngas.
Lastly, the pressure increase has a different effect on the H2/

COmolar ratio for the various temperatures studied, depending
on the extent of CaCO3 conversion. At 650 and 700 °C, where
CaCO3 calcination and therefore release of CO2 are largely
suppressed with increasing pressure, the H2/CO ratio is
relatively stable. The lower H2/CO molar ratio at 700 °C
compared to 650 °C could be attributed to the extent of RWGS,
which, in contrast to DRM is only affected by temperature and
not pressure changes, as it is equimolar on reactants and
products. However, as both DRM and calcination reactions are
negatively affected by the pressure increase, the lower amounts
of H2 and CO2 shift the RWGS equilibrium toward the reactants
side, leading to an increasing H2/COmolar ratio as a function of

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pressure. At 800 °C and pressures up to ∼6 bar (complete
CaCO3 calcination), the H2/CO molar ratio decreases due to
the high partial pressure of CO2, which shifts the RWGS toward
the side of the products, while DRM is inhibited by the pressure
increase. When pressures reach above ∼6 bar at 800 °C, the H2/
CO molar ratio increases due to the indirect influence of the
DRM and calcination extents on RWGS.
As CH4 is the only reactant in the gas feed of the calcination/

DRM stage, variation of the CH4/CaCO3 molar ratio can
considerably affect the efficiency of the stage (Figure 4). The
increase in the CH4 feed enhances the in situ CO2 consumption
and CaCO3 conversion, with more CO2 needing to be released
to reach the equilibrium partial pressure. Higher temperatures
require lower CH4/CaCO3 molar ratios for full CaCO3
conversion, since calcination can proceed under a higher CO2
partial pressure in the gas phase. On the other hand, CH4
conversion is initially stable as a function of the CH4/CaCO3

molar ratio when operating at either 650 or 700 °C, indicating
that the increase of the CH4 flow causes the release of an
adequate amount of CO2 from CaCO3 decomposition to retain
stable CH4 conversion. Upon reaching full CaCO3 conversion,
the molar ratio of CH4 to CO2 released from calcination is above
the stoichiometric one, leading to a gradual decrease of CH4
conversion from this point onward. At 800 °C, CH4 conversion
remains at values higher than 94% for substoichiometric molar
ratios (CH4/CaCO3 < 1) due to the high reaction temperature
and availability of CO2, which both promote the DRM.
The in situ CO2 utilization displays an increasing trend as a

function of CH4/CaCO3 molar ratio, similar to CaCO3
conversion, at 650 or 700 °C. The increase of CO2 utilization
and the stable CH4 conversion until reaching full CaCO3
conversion prove that CO2 is the limiting agent that controls
the equilibrium, resulting in the production of syngas with stable
purity and H2/CO molar ratio close to unity. After reaching full

Figure 4. Effect of CH4/CaCO3 molar ratio on (a) CaCO3 conversion, (b) CH4 conversion, (c) in situ CO2 utilization, (d) purity, and (e) H2/CO
molar ratio of the produced syngas in the calcination/DRM stage (P = 1 bar, no carbon formation).

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CaCO3 conversion, the CO2 utilization continues to slightly
increase, since the excess CH4 enhances the extent and
selectivity of DRM compared to RWGS, as also indicated by
the increase of the H2/CO molar ratio. However, excess CH4
decreases the purity of the syngas. At 800 °C and CH4/CaCO3
molar ratios lower than unity, CO2 utilization and syngas purity
are dictated by the enhancement of DRM and RWGS with
higher CH4 contents, resulting in a different increasing trend
compared to 650 and 700 °C, where the CaCO3 conversion
extent also affects the CO2 utilization. The H2/CO molar ratio
of syngas is lower at these conditions due to the presence of
unconverted CO2.
Overall, the results of the thermodynamic analysis provide the

operating conditions for successfully integrating CaCO3
calcination and DRM reactions in a single step. Full CaCO3
conversion requires a minimum temperature of ∼700 °C for
CH4/CaCO3 = 1 while attaining an in situ CO2 utilization of
∼80% toward the production of syngas with H2/COmolar ratio
close to unity. Pressure increase results in lower conversions as
neither CaCO3 calcination nor DRM are favored, indicating that
pressures close to atmospheric are the optimum operating
conditions for this integrated process. The CH4/CaCO3 molar
ratio should be appropriately adjusted for the molar ratio of inlet
CH4 to released CO2 to be close to unity. The aforementioned
results are obtained without accounting carbon as a possible
product of the thermodynamic analysis. As mentioned before,
separate simulations are run where carbon formation is
considered, with results being presented in Figures S1 and S2.
Carbon formation is promoted at low temperatures (660−680
°C) from a thermodynamics point of view, which highlights the
necessity for appropriate catalysts that can kinetically suppress
the extent of carbon formation in a potential demonstration of
the process. Given the potential to suppress carbon formation in
a real-life application of the SMR-CaL-DRM process by
operating the calcination/DRM stage at high temperatures and
by using appropriate catalysts, carbon generation is not further
studied in this work and the subsequent process design.

3.2. Process Design. Aspen Plus is then applied to propose
a conceptual design for the SMR-CaL-DRM process. A
comprehensive analysis is provided for the results from the

design of case 1 of interest, where the reforming and calcination/
DRM stages are conducted in a system of two moving bed
reactors. The integrated process is then compared to the SE-
SMR in terms of exergy efficiency. The conditions of each
stream of the flow diagram of SMR-CaL-DRM (case 1) and SE-
SMR with a solar (case 2) or an oxy-fuel calciner (case 3) are
presented in Tables S4−S6.

3.2.1. Performance of SMR-CaL-DRM in a System of Two
Moving Bed Reactors. Setting ∼11,000 Nm3/h of H2 as a
desirable production target and a H2O/CH4 molar flow ratio of
3 for operating the reformer can define the inlet volumetric flow
of the reactor. The diameter is chosen to be equal to ∼1.46 m to
avoid fluidization of the solid particles when designing the
reactor as a moving bed with counter-current flow of gas and
solids. Based on the applied kinetic correlations, the reactor has a
total volume of∼7.5 m3 (height of∼4.4 m) to attain at least 90%
CH4 conversion.
The reformer operates adiabatically, with the inlet gas

feedstock preheated at 630 °C and the solid components
circulating back from the calciner at 800 °C. Figure 5 presents
the temperature, CH4 conversion, H2 purity, and CaO
conversion profiles in the axial direction of the reformer with a
cocurrent flow of gas and solid components. The aforemen-
tioned performance indicators are calculated based on eqs S18
and S20. In the cocurrent flow (Figure 5a), where both gases and
solids enter from the top of the reactor and move downward,
CH4 conversion and CO2 capture occur simultaneously, since
the inlet CH4 comes in contact with CaO from the calciner. CO2
capture boosts the driving force of WGS and SMR, thereby
leading to ∼80% CH4 conversion and ∼90% purity of the
generated H2 at the exit of the first RCSTR model. Conversions
of CH4 and CaO continue as the gas and solid compounds
transcend the reactor, while at the bottom, ∼90% CH4 has been
consumed to produce H2 with ∼95% purity. Throughout the
reactor length, temperature ranges between 570 °C at the upper
part of the reactor, where the endothermic reforming occurs to a
higher extent, and 600 °C at the bottom.
When simulating the reformer as a moving bed with counter-

current flow (Figure 5b), solid compounds perform a downward
flow within the reactor and meet the gaseous components that

Figure 5. CH4 conversion, H2 purity, CO2 capture, and temperature profiles in the axial direction of the reformer moving bed reactor with (a)
cocurrent and (b) counter-current flow of gas and solid compounds (P = 1 bar, H2O/CH4 = 3, CH4/CaO = 1). Schematics on top of the figures display
the part of the reactor that each unit represents.

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move upward. Even though the final CH4 conversion, H2 purity,
and CaO conversion are similar to the ones attained with
cocurrent flow, the axial temperature profile inside the reactor is
broader. Gaseous CH4 enters from the bottom and comes in
contact with descending solids, which, however, under steady-
state conditions, are already in a partially carbonated form.
Therefore, SMR occurs without its heat demand being
completely covered from CaO carbonation, leading to the
decrease of temperature at ∼510 °C. Furthermore, SMR is not
intensified to a high extent, leading to lower CH4 conversion and
H2 purity compared to the cocurrent flow. As the gaseous
compounds reach higher heights, they come in contact with
more unreacted CaO. Since the extent of CaO carbonation is
higher than SMR at the upper parts of the reactor, this leads to a
temperature increase up to ∼630 °C.
The cocurrent flow of gas and solid components leads to a

more uniform temperature profile, with 30 °C difference
between the top and the bottom of the reactor and both the
gaseous and solid compounds being retrieved at ∼600 °C. The

cocurrent flow also attains an optimum coupling of SMR and
CaO carbonation. On the other hand, the counter-current flow
moving bed reactor results in a temperature difference of ∼120
°C between the top and the bottom of the reactor, the exit of the
gaseous and solid compounds at different temperatures (∼510
and ∼630 °C, respectively), and the nonefficient coupling of
SMR and CaO carbonation. The low temperature of solids and
the higher difference compared to the operating temperature of
the calcination/DRM stage (800 °C) would result in an
undesirable higher energy demand for the latter. Due the
aforementioned statements, the moving bed reactor with
cocurrent flow of gaseous and solid compounds is deemed a
more appropriate configuration for the reformer reactor. The
reformate gas undergoes cooling, while after purification, a
stream with ∼11,010 N m3/h flow and 99.999 vol % H2
composition is retrieved, reaching the production target.
Solid materials that exit the reformer comprise Ni, CaCO3,

CaZrO3, and unreacted CaO and enter the calciner with a
stream of pure CH4. The reactor is designed with a diameter of

Table 4. Main Exergy Results for the SMR-CaL-DRM and SE-SMR Processes

exergy term SMR-CaL-DRM with solar calciner (case 1) SE-SMR with solar calciner (case 2) SE-SMR with oxy-fuel calciner (case 3)

Ẇturb (MW) 0.18 0.19 0.16
Ẇcomp (MW) 2.18 2.18 2.18
ĖQ,calc (MW) 22.69 11.20 0
Ėxin,tot (MW) 64.57 35.71 43.21
Ėxout,tot (MW) 67.70 33.10 32.56
nexergy (%) 75.92 67.81 72.10
Ėxdes,tot 81.06 (MJ/kmol H2 + syngas) 124.10 (MJ/kmol H2) 99.47 (MJ/kmol H2)

Figure 6.Distribution of exergy destroyed in (a) SMR-CaL-DRM process with a solar calciner and the SE-SMR process with (b) solar or (c) oxy-fuel
calciner.

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∼1.65 m and a length of ∼4.18 m and operates isothermally at
800 °C and a cocurrent flow of gas and solid components.
Counter-current flow is not simulated for the calciner, since the
introduction of CH4 from the bottom would result in its contact
with already partially calcined material, and the substoichio-
metric molar ratio of CO2 released from calcination to CH4
would promote carbon formation. The operating temperature is
chosen based on the results of the thermodynamic analysis to
allow high CH4 and CO2 conversion toward syngas generation
(Figure 2). Cocurrent flow of solids and gas components enables
to attain 97% CH4 conversion toward syngas production with
∼12,130 N m3/h volumetric flow and H2/CO molar ratio close
to unity. The CaCO3 reaches full decomposition at the bottom
of the reactor, attaining an in situ CO2 utilization of 98%. To
perform the two endothermic reactions, a total of ∼16.3 MW or
∼116MJ per kmol of syngas produced is required for isothermal
operation at 800 °C, which would require a heliostat field of
approximately 0.04 km2. The area of the heliostat field could be
specified accurately depending on the geographic region of the
unit and the DNI value.

3.2.2. Exergy Analysis Results. The main inlet and outlet
flows considered in the exergetic analysis for the material
streams, work of compressors and turbines, and energy required
in the calciner are presented in Table 4 and compared between
the three cases. The SMR-CaL-DRM unit (case 1) is
characterized by a higher inlet exergy flow for the material
streams (Ėxin,tot), since more CH4 is required in the integrated
reactive calciner compared to the amount of CH4 needed for the
oxy-fuel calciner of case 3, while no CH4 is required for the solar
calciner of case 2. Moreover, the aforementioned requirement
for 16.30 MW of energy for operating the endothermic
calcination/DRM stage (Q̇calc) corresponds to the required
solar irradiation (Q̇s) of 23.97 MW and an inlet exergy flow of
22.69 MW (ĖxQ,calc) for case 1. The inlet exergy flow for solar
radiation is lower for case 2 since only the calcination reaction
occurs in the reactor, while no exergy flow of heat is required for
the autothermal oxy-fuel calciner (case 3). Despite the much
higher total inlet exergy flow for case 1, the retrieval of two high-
value products (high-purity H2 and syngas) results in much
higher outlet exergy flow from material streams (Ėxout,tot)
compared to both case 2 and case 3 and a slightly higher (by 8
and 4%) overall exergy efficiency of the whole process (75.92%
instead of 67.81 and 72.10%). Furthermore, the total exergy
destroyed in case 1 is equal to 81.06 MJ/kmol of high-value
products, which is ∼22.7 and ∼18.5% lower compared to the
respective exergy destruction in case 2 and case 3.
Figure 6 breaks down the contribution of different modules in

the exergy destroyed in each case. The dominant section
contributing to the exergy destruction for case 1 is the solar
calciner (≥55%) as a result of heat needed to drive the two
endothermic reactions. This is followed by the heat exchangers
(≥25%) and more specifically the boiler needed to generate the
steam for the reformer (simulated by heat exchanger B-101
coupled with furnace F-101). The remaining exergy destruction
(∼20%) is attributed to the reformer, the operation of the
compressor and turbine units, the mixing of CH4 and H2O
streams for the reformer, and the nonexploited content of the
flare gas. In case 2, the solar calciner has a lower contribution to
the total exergy destroyed since there is no significant chemical
exergy change between the inlet and outlet streams, while the
energy needed is much lower compared to the calciner of case 1.
In case 3, heat exchangers are considered the main source of
exergy destruction (∼50%), followed by the calciner whose

exergy destruction is a result of the conversion of a stream with
high chemical exergy (mixture of CH4 and O2) to a stream with
low chemical exergy (mixture of CO2 and H2O). The lower
contribution of the oxy-fuel calciner to the exergy destroyed
compared to case 1 and case 2 signifies that future research could
be focused on improving the efficiency of solar calcination and
on a more detailed design of such reactors. Nonetheless, despite
solar calciners being currently less promising compared to oxy-
fuel calciners, the slightly higher exergy efficiency of SMR-CaL-
DRM (case 1) indicates that even though two highly
endothermic reactions are coupled in a single step, reactive
calcination with solar heating can present a more attractive
option.

4. CONCLUSIONS
Coupling steam methane reforming with calcium looping can
lead to in situ removal of generated CO2 and elevated CH4
conversion toward high-purity H2 production in a single step.
Commercializing the sorption-enhanced reforming technology
relies on finding efficient methods to moderate the elevated
temperatures of calcination. This work investigated an
intensified process that integrates a reactive calciner in
sorption-enhanced reforming to in situ utilize the captured
CO2, by coupling calcination with dry reforming of methane.
With both reformer and calciner being fed with CH4, this
process coproduces high-purity H2 and syngas. The concept was
evaluated from a thermodynamics point of view, focusing on the
operation of the calcination stage, followed by a preliminary
design of the integrated process while employing a system of two
moving bed reactors. Solar heating was evaluated as a means of
covering the energy demand of the calciner by conducting an
exergy analysis to compare the proposed integrated process with
a sorption-enhanced steam methane reforming process with
either a solar or an oxy-fuel calciner. The main outcomes of this
work are presented below.

• The complete decomposition of CaCO3, along with
∼80% in situ utilization of CO2 toward syngas generation
were feasible thermodynamically at 700 °C, a milder
temperature than conventional calcination (800−900
°C). The lower operating temperature proved that the
reactive gas feed enhances the driving force of calcination.

• Cocurrent flow of gases and solids in a reformer with a
moving bed configuration enabled for the adiabatic
production of ∼11,000 N m3/h H2 at 600 °C, while an
isothermal operation of the calciner at 800 °C resulted in
the generation of similar amount of syngas (∼12,130
Nm3/h) with H2/COmolar ratio close to unity. Counter-
current flow was related to a more expanded profile of
temperature in the axial direction of the reformer.

• Solar calcination was linked with higher exergy
destruction compared to an oxy-fuel calciner. However,
the in situ conversion of CO2 toward syngas allowed for
the integrated proposed process to display an efficiency of
∼75.9%, a value ∼8 and ∼4% higher compared to the
benchmark process with the solar and oxy-fuel calciner.

The results of this work highlighted the potential of the
proposed process and intensified the interest for its experimental
demonstration in the future.

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■ ASSOCIATED CONTENT
*sı Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.energyfuels.4c01462.

Kinetic rate equations used for process design simu-
lations, results of thermodynamic analysis when account-
ing carbon formation, molar flow composition of the
outlet of the calcination/DRM stage as a function of the
temperature, pressure, and CH4/CaCO3 (PDF)

■ AUTHOR INFORMATION
Corresponding Author

Andy N. Antzaras − Department of Chemical Engineering,
Aristotle University of Thessaloniki, 54124 Thessaloniki,
Greece; orcid.org/0000-0002-7896-1392;
Email: aantzara@cheng.auth.gr

Authors
Theodoros Papalas − Department of Chemical Engineering,

Aristotle University of Thessaloniki, 54124 Thessaloniki,
Greece; Department of Chemical Engineering and
Biotechnology, University of Cambridge, CB3 0AS Cambridge,
U.K.; orcid.org/0000-0002-5122-5125

Angeliki A. Lemonidou − Department of Chemical
Engineering, Aristotle University of Thessaloniki, 54124
Thessaloniki, Greece; Chemical Process & Energy Resource
Institute, CPERI/CERTH, Thessaloniki 57001, Greece;
orcid.org/0000-0001-8376-0678

Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.energyfuels.4c01462

Funding
The open access publishing of this article is financially supported
by HEAL-Link.
Notes
The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS
The research project was supported by the Hellenic Foundation
for Research and Innovation (H.F.R.I.) under the “3rd Call for
H.F.R.I. Research Projects to support Post-Doctoral Research-
ers” (Project Number 7155). Dr. Theodoros Papalas acknowl-
edges the State Scholarship Foundation for the support of his
Ph.D. Thesis, which was cofinanced by Greece and the
European Union (European Social Fund�ESF) through the
Operational Program “Human Resources Development, Edu-
cation and Lifelong Learning” in the context of the Act
“Enhancing Human Resources Research Potential by under-
taking a Doctoral Research”, Subaction 2: IKY Scholarship
Programme for Ph.D. candidates in Greek Universities. The
authors thank Dr. Athanasios Skaltsogiannis for the fruitful
discussions for the kinetic rate equations. Finally, the authors
acknowledge the contribution of Mr. Ioannis Kazantzidis in the
conduction of the simulations of this work.

■ NOMENCLATURE
A area of heliostat field
DNI direct normal irradiance
Ėxdes,k exergy flow destroyed in module k
Ėxdes,tot total exergy flow destroyed from modules and flare gas
Ėxj exergy flow of stream j

Ėxchem,j chemical exergy flow of stream j
Ėxin,k total exergy flow of inlet material streams of module k
Ėxin,tot total input exergy flow in the case studied
Ėxkin,j kinetic exergy flow of stream j
Ėxout,k total exergy flow of outlet streams of module k
Ėxout,tot total output exergy flow in the case studied
Ėxp,j potential exergy flow of stream j
ĖxQ,calc exergy flow of heat required in the calciner
Ėxphys,j physical exergy flow of stream j
hj enthalpy of stream j
h0,j enthalpy of stream j at standard conditions
nex exergy efficiency of the studied case
nhelio efficiency of heliostat field
ṅj molar flow of stream j
ṅi,in inlet molar flow of component i
ṅi,out outlet molar flow of component i
nrec efficiency of heat transfer in the calciner
Q̇calc heat flow required for reactions occurring inside the

calciner
Q̇s heat flow provided by a heating source
Q̇tower heat flow reaching the outer surface of the calciner

receiver
P pressure
R ideal gas constant
sj entropy of stream j
s0,j entropy of stream j at standard conditions
T temperature
T0 temperature at standard conditions
Ẇcomp work of compressor
Ẇturb work of turbine
xi molar fraction of component i
εi
0 standard specific exergy of component i

■ ABBREVIATIONS
CCUS carbon capture utilization and storage
CaL-DRM calcium looping coupled with dry reforming

of methane
DRM dry reforming of methane
PSA pressure swing adsorption
RWGS reverse water gas shift
SE-SMR sorption-enhanced steam methane reforming
SMR steam methane reforming
SMR-CaL-DRM steam methane reforming coupled with

calcium looping and dry reforming of
methane

WGS water gas shift

■ REFERENCES
(1) Garcia, J. A.; Villen-Guzman, M.; Rodriguez-Maroto, J. M.; Paz-
Garcia, J. M. Technical Analysis of CO2 Capture Pathways and
Technologies. J. Environ. Chem. Eng. 2022, 10 (5), No. 108470.
(2) IEAGHG Low-Carbon Hydrogen from Natural Gas: Global
Roadmap IEAGHG Technical Report, No. 2022−07, 2022.
(3) Antzaras, A. N.; Lemonidou, A. A. Recent Advances on Materials
and Processes for Intensified Production of Blue Hydrogen. Renewable
Sustainable Energy Rev. 2022, 155, No. 111917.
(4) Harrison, D. P. Sorption-Enhanced Hydrogen Production: A
Review. Ind. Eng. Chem. Res. 2008, 47 (17), 6486−6501.
(5) Masoudi Soltani, S.; Lahiri, A.; Bahzad, H.; Clough, P.;
Gorbounov, M.; Yan, Y. Sorption-Enhanced Steam Methane
Reforming for Combined CO2 Capture and Hydrogen Production: A
State-of-the-Art Review. Carbon Capture Sci. Technol. 2021, 1,
No. 100003.

Energy & Fuels pubs.acs.org/EF Article

https://doi.org/10.1021/acs.energyfuels.4c01462
Energy Fuels 2024, 38, 11966−11979

11977

https://pubs.acs.org/doi/10.1021/acs.energyfuels.4c01462?goto=supporting-info
https://pubs.acs.org/doi/suppl/10.1021/acs.energyfuels.4c01462/suppl_file/ef4c01462_si_001.pdf
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Andy+N.+Antzaras"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://orcid.org/0000-0002-7896-1392
mailto:aantzara@cheng.auth.gr
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Theodoros+Papalas"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://orcid.org/0000-0002-5122-5125
https://pubs.acs.org/action/doSearch?field1=Contrib&text1="Angeliki+A.+Lemonidou"&field2=AllField&text2=&publication=&accessType=allContent&Earliest=&ref=pdf
https://orcid.org/0000-0001-8376-0678
https://orcid.org/0000-0001-8376-0678
https://pubs.acs.org/doi/10.1021/acs.energyfuels.4c01462?ref=pdf
https://doi.org/10.1016/j.jece.2022.108470
https://doi.org/10.1016/j.jece.2022.108470
https://doi.org/10.1016/j.rser.2021.111917
https://doi.org/10.1016/j.rser.2021.111917
https://doi.org/10.1021/ie800298z?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/ie800298z?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.ccst.2021.100003
https://doi.org/10.1016/j.ccst.2021.100003
https://doi.org/10.1016/j.ccst.2021.100003
pubs.acs.org/EF?ref=pdf
https://doi.org/10.1021/acs.energyfuels.4c01462?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as


(6) Papalas, T.; Antzaras, A. N.; Lemonidou, A. A. Evaluation of
Calcium-Based Sorbents Derived from Natural Ores and Industrial
Wastes for High-Temperature CO2 Capture. Ind. Eng. Chem. Res. 2020,
59 (21), 9926−9938.
(7) Antzara, A. N.; Arregi, A.; Heracleous, E.; Lemonidou, A. A. In-
Depth Evaluation of a ZrO2 Promoted CaO-Based CO2 Sorbent in
Fluidized Bed Reactor Tests. Chem. Eng. J. 2018, 333, 697−711.
(8) Duyar, M. S.; Wang, S.; Arellano-Treviño, M. A.; Farrauto, R. J.
CO2 Utilization with a Novel Dual Function Material (DFM) for
Capture and Catalytic Conversion to Synthetic Natural Gas: An
Update. J. CO2 Util. 2016, 15, 65−71.
(9) Arellano-Treviño, M. A.; He, Z.; Libby, M. C.; Farrauto, R. J.
Catalysts and Adsorbents for CO2 Capture and Conversion with Dual
Function Materials: Limitations of Ni-Containing DFMs for Flue Gas
Applications. J. CO2 Util. 2019, 31, 143−151.
(10) Hu, J.; Hongmanorom, P.; Chirawatkul, P.; Kawi, S. Efficient
Integration of CO2 Capture and Conversion over a Ni Supported
CeO2-Modified CaO Microsphere at Moderate Temperature. Chem.
Eng. J. 2021, 426, No. 130864.
(11) Lv, Z.; Chen, S.; Huang, X.; Qin, C. Recent Progress and
Perspective on Integrated CO2 Capture and Utilization. Curr. Opin.
Green Sustainable Chem. 2023, 40, No. 100771.
(12) Jin, B.; Wang, R.; Fu, D.; Ouyang, T.; Fan, Y.; Zhang, H.; Liang,
Z. Chemical Looping CO2 Capture and In-Situ Conversion as a
Promising Platform for Green and Low-Carbon Industry Transition:
Review and Perspective. Carbon Capture Sci. Technol. 2024, 10,
No. 100169.
(13) Sun, S.; Zhang, C.; Wang, Y.; Zhao, X.; Sun, H.; Wu, C. CO2
Capture from H2O and O2 Containing Flue Gas Integrating with Dry
Reforming Methane Using Ni-Doping CaO Dual Functional Materials.
Chem. Eng. J. 2023, 468, No. 143712.
(14) Tian, S.; Yan, F.; Zhang, Z.; Jiang, J. Calcium-Looping Reforming
of Methane Realizes in Situ CO2 Utilization with Improved Energy
Efficiency. Sci. Adv. 2019, 5 (4), 1−9.
(15) Hu, J.; Hongmanorom, P.; Galvita, V. V.; Li, Z.; Kawi, S.
Bifunctional Ni-Ca Based Material for Integrated CO2 Capture and
Conversion via Calcium-Looping Dry Reforming. Appl. Catal., B 2021,
284, No. 119734.
(16) Papalas, T.; Lypiridis, D.; Antzaras, A.; Lemonidou, A. A.
Experimental Investigation of Integrated CO2 Capture and Conversion
to Syngas via Calcium Looping Coupled with Dry Reforming of CH4.
Chem. Eng. J. 2024, 485, No. 149866.
(17) Kim, S. M.; Abdala, P. M.; Broda, M.; Hosseini, D.; Copéret, C.;
Müller, C. Integrated CO2 Capture and Conversion as an Efficient
Process for Fuels from Greenhouse Gases. ACS Catal. 2018, 8 (4),
2815−2823.
(18) Ma, X.; Cui, H.; Cheng, Z.; Zhou, Z. Application of Engineered
Natural Ores to Intermediate- and High-temperature CO2 Capture and
Conversion. AIChE J. 2023, 69 (9), No. e18146.
(19) Sun, S.; Zhang, Y.; Li, C.; Wang, Y.; Zhang, C.; Zhao, X.; Sun, H.;
Wu, C. Upgrading CO2 from Simulated Power Plant Flue Gas via
Integrated CO2 Capture and Dry Reforming of Methane Using Ni-
CaO. Sep. Purif. Technol. 2023, 308, No. 122956.
(20) Hu, J.; Hongmanorom, P.; Chen, J.; Wei, W.; Chirawatkul, P.;
Galvita, V. V.; Kawi, S. Tandem Distributing Ni into CaO Framework
for Isothermal Integration of CO2 Capture and Conversion. Chem. Eng.
J. 2023, 452 (P3), No. 139460.
(21) Donat, F.; Florin, N. H.; Anthony, E. J.; Fennell, P. S. Influence of
High-Temperature Steam on the Reactivity of CaO Sorbent for CO2
Capture. Environ. Sci. Technol. 2012, 46, 1262−1269.
(22) Wang, Y. N.; Rodrigues, A. E. Hydrogen Production from Steam
Methane Reforming Coupled with in Situ CO2 Capture: Conceptual
Parametric Study. Fuel 2005, 84 (14−15), 1778−1789.
(23) Martínez, I.; Romano, M. C.; Fernández, J. R.; Chiesa, P.;
Murillo, R.; Abanades, J. C. Process Design of a Hydrogen Production
Plant from Natural Gas with CO2 Capture Based on a Novel Ca/Cu
Chemical Loop. Appl. Energy 2014, 114, 192−208.

(24) Tzanetis, K. F.;Martavaltzi, C. S.; Lemonidou, A. A. Comparative
Exergy Analysis of Sorption Enhanced and Conventional Methane
SteamReforming. Int. J. Hydrogen Energy 2012, 37 (21), 16308−16320.
(25) Anderson, D. M.; Kottke, P. A.; Fedorov, A. G. Thermodynamic
Analysis of Hydrogen Production via Sorption-Enhanced Steam
Methane Reforming in a New Class of Variable Volume Batch-
Membrane Reactor. Int. J. Hydrogen Energy 2014, 39 (31), 17985−
17997.
(26) Antzara, A.; Heracleous, E.; Bukur, D. B.; Lemonidou, A. A.
Thermodynamic Analysis of Hydrogen Production via Chemical
Looping Steam Methane Reforming Coupled with In Situ CO2
Capture. Int. J. Greenhouse Gas Control 2015, 32, 115−128.
(27) Ebneyamini, A.; Grace, J. R.; Lim, C. J.; Ellis, N.; Elnashaie, S. S.
E. H. Simulation of Limestone Calcination for Calcium Looping:
Potential for Autothermal and Hydrogen-Producing Sorbent Regener-
ation. Ind. Eng. Chem. Res. 2019, 58 (20), 8636−8655.
(28) Zhang, C.; Li, Y.; Chu, Z.; Fang, Y. Thermodynamic Analysis of
Integrated Sorption-Enhanced Staged-Gasification of Biomass and In-
Situ CO2 Utilization byMethane Reforming Process Based on Calcium
Looping. Energy Convers. Manage. 2023, 278, No. 116710.
(29) Dincer, I.; Rosen, M. A. Exergy and Energy Analyses. In Exergy;
Elsevier, 2013; pp 21−30.
(30) Davies, W. G.; Babamohammadi, S.; Yan, Y.; Clough, P. T.;
Masoudi Soltani, S. Exergy Analysis in Intensification of Sorption-
Enhanced SteamMethane Reforming for Clean Hydrogen Production:
Comparative Study and Efficiency Optimisation. Carbon Capture Sci.
Technol. 2024, 12, No. 100202.
(31) Wei, L.; Han, R.; Xing, S.; Wang, Y.; Li, Z.; Liu, Q. Calcium-
Looping Coupling Methane Partial Oxidation and Dry Reforming
Process for Integrated CO2 Capture and Conversion: Regulable H2/
CO Molar Ratio and Excellent Coke Deposition-Resistant. Chem. Eng.
J. 2023, 474, No. 145833.
(32) Teng, L.; Xuan, Y.; Da, Y.; Sun, C.; Liu, X.; Ding, Y. Direct Solar-
Driven Reduction of Greenhouse Gases into Hydrocarbon Fuels
Incorporating Thermochemical Energy Storage via Modified Calcium
Looping. Chem. Eng. J. 2022, 440, No. 135955.
(33) Nikulshina, V.; Halmann, M.; Steinfeld, A. Coproduction of
Syngas and Lime by Combined CaCO3-Calcination and CH4-
Reforming Using a Particle-Flow Reactor Driven by Concentrated
Solar Radiation. Energy Fuels 2009, 23 (12), 6207−6212.
(34) Ortiz, C.; Valverde, J. M.; Chacartegui, R.; Perez-Maqueda, L. A.;
Giménez, P. The Calcium-Looping (CaCO3/CaO) Process for
Thermochemical Energy Storage in Concentrating Solar Power Plants.
Renewable Sustainable Energy Rev. 2019, 113, No. 109252.
(35) Teixeira, P.; Afonso, E.; Pinheiro, C. I. C. Tailoring Waste-
Derived Materials for Calcium-Looping Application in Thermochem-
ical Energy Storage Systems. J. CO2 Util. 2022, 65, No. 102180.
(36) Aspen Technology Inc. Aspen Plus Model for Moving Bed Coal
Gasifier, https://user.eng.umd.edu/~nsw/chbe446/Aspen_Plus_
Model_for_Moving_Bed_Coal_Gasifier.pdf (accessed May, 2024).
(37) Wen, C. Y.; Yu, Y. H. A Generalized Method for Predicting the
Minimum Fluidization Velocity. AIChE J. 1966, 12 (3), 610−612.
(38) Furimsky, E. Selection of Catalysts and Reactors for Hydro-
processing. Appl. Catal., A 1998, 171 (2), 177−206.
(39) Kim, K.; Park, Y. K.; Park, J.; Jung, E.; Seob, H.; Kim, H.; Lee, K.
S. Performance Comparison of Moving and Fluidized Bed Sorption
Systems for an Energy-Efficient Solid Sorbent-Based Carbon Capture
Process. Energy Procedia 2014, 63, 1151−1161.
(40) Gyngazova, M. S.; Kravtsov, A. V.; Ivanchina, E. D.; Korolenko,
M. V.; Chekantsev, N. V. Reactor Modeling and Simulation of Moving-
Bed Catalytic Reforming Process. Chem. Eng. J. 2011, 176−177, 134−
143.
(41) Xu, J.; Froment, G. F. Methane Steam Reforming, Methanation
andWater-gas Shift: I. Intrinsic Kinetics. AIChE J. 1989, 35 (1), 88−96.
(42) Scaltsoyiannes, A.; Antzaras, A.; Koilaridis, G.; Lemonidou, A.
Towards a Generalized Carbonation Kinetic Model of CaO-Based
Materials Using a Modified Random Pore Model. Chem. Eng. J. 2021,
407, No. 127207.

Energy & Fuels pubs.acs.org/EF Article

https://doi.org/10.1021/acs.energyfuels.4c01462
Energy Fuels 2024, 38, 11966−11979

11978

https://doi.org/10.1021/acs.iecr.9b06834?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.iecr.9b06834?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.iecr.9b06834?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.cej.2017.09.192
https://doi.org/10.1016/j.cej.2017.09.192
https://doi.org/10.1016/j.cej.2017.09.192
https://doi.org/10.1016/j.jcou.2016.05.003
https://doi.org/10.1016/j.jcou.2016.05.003
https://doi.org/10.1016/j.jcou.2016.05.003
https://doi.org/10.1016/j.jcou.2019.03.009
https://doi.org/10.1016/j.jcou.2019.03.009
https://doi.org/10.1016/j.jcou.2019.03.009
https://doi.org/10.1016/j.cej.2021.130864
https://doi.org/10.1016/j.cej.2021.130864
https://doi.org/10.1016/j.cej.2021.130864
https://doi.org/10.1016/j.cogsc.2023.100771
https://doi.org/10.1016/j.cogsc.2023.100771
https://doi.org/10.1016/j.ccst.2023.100169
https://doi.org/10.1016/j.ccst.2023.100169
https://doi.org/10.1016/j.ccst.2023.100169
https://doi.org/10.1016/j.cej.2023.143712
https://doi.org/10.1016/j.cej.2023.143712
https://doi.org/10.1016/j.cej.2023.143712
https://doi.org/10.1126/sciadv.aav5077
https://doi.org/10.1126/sciadv.aav5077
https://doi.org/10.1126/sciadv.aav5077
https://doi.org/10.1016/j.apcatb.2020.119734
https://doi.org/10.1016/j.apcatb.2020.119734
https://doi.org/10.1016/j.cej.2024.149866
https://doi.org/10.1016/j.cej.2024.149866
https://doi.org/10.1021/acscatal.7b03063?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acscatal.7b03063?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1002/aic.18146
https://doi.org/10.1002/aic.18146
https://doi.org/10.1002/aic.18146
https://doi.org/10.1016/j.seppur.2022.122956
https://doi.org/10.1016/j.seppur.2022.122956
https://doi.org/10.1016/j.seppur.2022.122956
https://doi.org/10.1016/j.cej.2022.139460
https://doi.org/10.1016/j.cej.2022.139460
https://doi.org/10.1021/es202679w?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/es202679w?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/es202679w?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.fuel.2005.04.005
https://doi.org/10.1016/j.fuel.2005.04.005
https://doi.org/10.1016/j.fuel.2005.04.005
https://doi.org/10.1016/j.apenergy.2013.09.026
https://doi.org/10.1016/j.apenergy.2013.09.026
https://doi.org/10.1016/j.apenergy.2013.09.026
https://doi.org/10.1016/j.ijhydene.2012.02.191
https://doi.org/10.1016/j.ijhydene.2012.02.191
https://doi.org/10.1016/j.ijhydene.2012.02.191
https://doi.org/10.1016/j.ijhydene.2014.03.127
https://doi.org/10.1016/j.ijhydene.2014.03.127
https://doi.org/10.1016/j.ijhydene.2014.03.127
https://doi.org/10.1016/j.ijhydene.2014.03.127
https://doi.org/10.1016/j.ijggc.2014.11.010
https://doi.org/10.1016/j.ijggc.2014.11.010
https://doi.org/10.1016/j.ijggc.2014.11.010
https://doi.org/10.1021/acs.iecr.9b00668?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.iecr.9b00668?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/acs.iecr.9b00668?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.enconman.2023.116710
https://doi.org/10.1016/j.enconman.2023.116710
https://doi.org/10.1016/j.enconman.2023.116710
https://doi.org/10.1016/j.enconman.2023.116710
https://doi.org/10.1016/j.ccst.2024.100202
https://doi.org/10.1016/j.ccst.2024.100202
https://doi.org/10.1016/j.ccst.2024.100202
https://doi.org/10.1016/j.cej.2023.145833
https://doi.org/10.1016/j.cej.2023.145833
https://doi.org/10.1016/j.cej.2023.145833
https://doi.org/10.1016/j.cej.2023.145833
https://doi.org/10.1016/j.cej.2022.135955
https://doi.org/10.1016/j.cej.2022.135955
https://doi.org/10.1016/j.cej.2022.135955
https://doi.org/10.1016/j.cej.2022.135955
https://doi.org/10.1021/ef9007246?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/ef9007246?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/ef9007246?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1021/ef9007246?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as
https://doi.org/10.1016/j.rser.2019.109252
https://doi.org/10.1016/j.rser.2019.109252
https://doi.org/10.1016/j.jcou.2022.102180
https://doi.org/10.1016/j.jcou.2022.102180
https://doi.org/10.1016/j.jcou.2022.102180
https://user.eng.umd.edu/%7Ensw/chbe446/Aspen_Plus_Model_for_Moving_Bed_Coal_Gasifier.pdf
https://user.eng.umd.edu/%7Ensw/chbe446/Aspen_Plus_Model_for_Moving_Bed_Coal_Gasifier.pdf
https://doi.org/10.1002/aic.690120343
https://doi.org/10.1002/aic.690120343
https://doi.org/10.1016/S0926-860X(98)00086-6
https://doi.org/10.1016/S0926-860X(98)00086-6
https://doi.org/10.1016/j.egypro.2014.11.125
https://doi.org/10.1016/j.egypro.2014.11.125
https://doi.org/10.1016/j.egypro.2014.11.125
https://doi.org/10.1016/j.cej.2011.09.128
https://doi.org/10.1016/j.cej.2011.09.128
https://doi.org/10.1002/aic.690350109
https://doi.org/10.1002/aic.690350109
https://doi.org/10.1016/j.cej.2020.127207
https://doi.org/10.1016/j.cej.2020.127207
pubs.acs.org/EF?ref=pdf
https://doi.org/10.1021/acs.energyfuels.4c01462?urlappend=%3Fref%3DPDF&jav=VoR&rel=cite-as


(43) Scaltsoyiannes, A.; Lemonidou, A. CaCO3 Decomposition for
Calcium-Looping Applications: Kinetic Modeling in a Fixed-Bed
Reactor. Chem. Eng. Sci.: X 2020, 8, No. 100071.
(44) Richardson, J. T.; Paripatyadar, S. A. Carbon Dioxide Reforming
of Methane with Supported Rhodium. Appl. Catal. 1990, 61 (1), 293−
309.
(45) de Souza-Santos, M. L. Solid Fuels Combustion and Gasification,
2nd ed.; CRC Press: Boca Raton, 2010.
(46) Sircar, S.; Golden, T. C. Pressure Swing Adsorption Technology
for Hydrogen Production. Hydrogen Syngas Prod. Purif. Technol. 2009,
414−450.
(47) Karasavvas, E.; Panopoulos, K. D.; Papadopoulou, S.; Voutetakis,
S. Energy and Exergy Analysis of the Integration of Concentrated Solar
Power with Calcium Looping for Power Production and Thermo-
chemical Energy Storage. Renewable Energy 2020, 154, 743−753.
(48) Khosravi, S.; Hossainpour, S.; Farajollahi, H.; Abolzadeh, N.
Integration of a Coal Fired Power Plant with Calcium Looping CO2
Capture and Concentrated Solar Power Generation: Energy, Exergy
and Economic Analysis. Energy 2022, 240, No. 122466.
(49) Szargut, J. Chemical Exergies of the Elements. Appl. Energy 1989,

32 (4), 269−286.
(50) Ferrario, D.; Stendardo, S.; Verda, V.; Lanzini, A. Solar-Driven
Calcium Looping System for Carbon Capture in Cement Plants:
Process Modelling and Energy Analysis. J. Cleaner Prod. 2023, 394,
No. 136367.
(51) Khosravi, S.; Neshat, E.; Saray, R. K. Thermodynamic Analysis of
a Sorption-Enhanced Gasification Process of Municipal Solid Waste,
Integrated with Concentrated Solar Power and Thermal Energy
Storage Systems for Co-Generation of Power andHydrogen. Renewable
Energy 2023, 214, 140−153.
(52) Zhai, R.; Li, C.; Qi, J.; Yang, Y. Thermodynamic Analysis of CO2
Capture by Calcium Looping Process Driven by Coal and
Concentrated Solar Power. Energy Convers. Manage. 2016, 117, 251−
263.
(53) Meier, A.; Bonaldi, E.; Cella, G. M.; Lipinski, W.; Wuillemin, D.;
Palumbo, R. Design and Experimental Investigation of a Horizontal
Rotary Reactor for the Solar Thermal Production of Lime. Energy 2004,
29 (5−6), 811−821.

Energy & Fuels pubs.acs.org/EF Article

https://doi.org/10.1021/acs.energyfuels.4c01462
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https://doi.org/10.1016/j.cesx.2020.100071
https://doi.org/10.1016/j.cesx.2020.100071
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https://doi.org/10.1016/S0166-9834(00)82152-1
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https://doi.org/10.1016/S0360-5442(03)00187-7
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pubs.acs.org/EF?ref=pdf
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