Shashi report

Shashikumar A N CO2 emission capture in cement industry by Calcium Looping technology
2016
Dr. M. Mahadeva Swamy,Professor,
Dept of Environmental Engineering, SJCE. Page 1
CHAPTER 1
INTRODUCTION
1.1 General
Global cement production reached 4 billion tonnes in 2013 and has been following a
rising trend for decades, as cement consumption is intimately linked to economic development.
Consequently, CO2 emissions from the cement industry exceeded 2 billion tonnes in 2011, which
represents about 5% of the total man-made greenhouse gas emissions. The main source of CO2
emissions during cement production (over 60% of the total amount in highly efficient plants) is
the calcination of limestone required to generate CaO. The remaining emissions come from fuel
combustion in the precalciner and the kiln and indirect emissions linked to the substantial use of
electricity in the process, usually produced also from fossil sources. The Ca-looping (CaL)
technology has recently emerged as a potentially feasible process for post combustion CO2
capture. As a main advantage over other technologies it stands the low cost, wide availability and
harmlessness towards the environment of natural limestone to be used as CaO precursor for CO2
capture. The increasing concentration of CO2 in the atmosphere is believed to be the major
contributor to climate change. Carbon Capture and storage (CCS) has been proposed as a
promising approach to reduce CO2 emissions from fossil fuel fired stationary Sources (such as
power stations, cement industry and hydrogen production facilities). The first step in the CCS
approach is the capture/separation of CO2, which is a critical step with respect to the technical
feasibility and cost. The conventional CaL and CLC processes led to the proposal of a novel
combined CaL/CLC looping process where regeneration of CaO-based sorbent in CaL can be
accomplished by means of the reduction of the fuel in CLC. This is the main advantage of
combining CaL with CLC, where no addition fuel will be burnt to provide the required heat for
CaCO3 calcination. It is of paramount importance to characterize it at realistic conditions in order
to extract from simulations useful information for the optimum design and operational
parameters to scale-up the technology.

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1. 2 Carbon dioxide capture by calcination looping process
Calcium Looping (CaL) stands out as a promising option for cement plants. The basis of
calcium looping technology is the reversible reaction between CO2 and CaO that generates
CaCO3 in the interior of the carbonator reactor at 650 C. The decomposition of CaCO3 takes
place in a second reactor, namely the calciner, at temperatures of around 900 C. In the most
standard configuration in a power plant, the calciner operates under oxyfired conditions, which
produces a concentrated stream of CO2 suitable for purification, compression and permanent
storage (Diego et al., 2016).
The CaL technology is being demonstrated in large-scale pilot plants (up to 1.7MWt)
showing efficient and sustainable CO2 capture. A typical run commences by precalcining the
initial inventory of limestone in air after which the calciner is set to oxy-combustion mode and
the circulation of solids in the loop is started. Burning fuel with pure oxygen (oxy-combustion)
ensures a high CO2 concentration in the gas exiting the calciner and a sufficiently high
temperature (close to 950 oC) to achieve complete CaO regeneration in short residence times.
However, oxycombustion imposes an energy penalty (due to the consumption of fuel and
oxygen) and generates additional CO2. Moreover, the carbonation activity of CaO regenerated at
high temperature and under high CO2 concentration suffers a marked drop, which is particularly
intense along the first cycles. Other causes of decay of the sorbent capture capacity are
irreversible sulphation due to SO2 (present in the flue gas and produced in the calciner by oxy-
combustion) and the loss of fine particles generated by attrition. It is thus necessary to feed the
calciner periodically with a makeup flow of fresh limestone to compensate for sorbent
deactivation.(Valverde et al., (2015) As opposed to the sorbent derived from calcination of the
initial limestone inventory, CaO derived from the makeup flow is obtained by calcination in a
high CO2 partial pressure environment.
Another naturally occurring mineral that can be used as CaO precursor is dolomite (CaMg
(CO3)2), which is also abundantly available at low price. According to process simulations. The
efficiency of the CaL technology is extraordinarily dependent upon the sorbent capture
performance. (Ridha et al., 2015)

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The CaL cycle provides a number of benefits when coupled with fuel gasification or
reforming as precombustion capture process. The heat released in the carbonation reaction is
used to run the endothermic in-situ steam reforming or the gasification reactions, leading to an
overall auto thermic reaction. Another benefit derived from the presence of CaO is the shifting of
the equilibrium to greater hydrogen yields. The subsequent calcination of the CaCO3 to
regenerate the sorbent is however a significant problem still to be solved for precombustion CO2
capture systems. The high temperature heat demanded in the calcination stage and the transfer
mechanism is in practice quite problematic. Different configurations have been adopted to
integrate the CaL process in a precombustion process for enhanced hydrogen production and
minimize the energy penalty associated to sorbent regeneration. (Konstantinos atsoios et al.,
2015) The basic configuration includes the application of oxycombustion of a solid fuel in the
calciner itself to provide the energy required. Several studies have been focused in the
integration of this CaL basic configuration with steam reforming of gaseous fuels (sorption
enhanced reforming, CaL-SER) and solid fuel gasification.
The CaL technology may be also integrated with other industrial processes leading not only to a
reduction of the CO2 emissions but also to an improvement of the operation of those processes.
This is the case of the concentrated solar power (CSP) generation and the paper and cement
industries. There are two ways in which CSP may be integrated with the CaL cycle. (Anette
mathisen et al., 2014). CaL cycle is based on reversible reaction between calcium oxide and
carbon dioxide. CO2 produced by fuel combustion in the boiler is captured in the carbonator to
form CaCO3. The entrained solids are transported into the calciner, where the sorbent
regeneration by thermal decomposition of calcium carbonate takes place. A further relevant
aspect of the CaL technology that would contribute to improve the industrial competitiveness of
the process is the minimization of energy penalties. Different schemes of the CaL process were
originally proposed to match the need and supply of energy stream within the loop. Need for an
oxygen separation plant while ensuring a high overall CO2 efficiency. This is achieved by
employing two calcium chemical loops

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1.3 Carbon dioxide capture in cement industry
The efficient capture of CO2 evolving from the kiln flue gas in existing and new built
cement plants, without significant modifications to the upstream cement process scheme, will
require the deployment of post-combustion technologies. The main CCS post-combustion
technologies considered for the cement industry are amine scrubbing, chilled ammonia scrubbing
and emerging concepts based on the use of membrane separation processes and calcium looping
technology. The CaL process requires a continuous make-up flow of fresh limestone to
counteract the deactivation of lime with the number of carbonation/calcination cycles while a
corresponding purge is also extracted from the calciner. The calcined purge is obviously a
potential material to be fed to the kiln of a cement plant.
In stand-alone calcium looping systems for cement plants (no synergy with the power
plant), the most attractive configuration is when the CaCO3 contained in the raw meal is
decomposed in an oxy-fired calciner, delivering a constant flow of CaO to the kiln, while the flue
gas that exits the rotary kiln is directed to the carbonator for CO2 capture. As a result, a very high
overall CO2 capture efficiency can be attained. A variant of this configuration arises when no
carbonator is present and only the CO2 evolving from fuel combustion and calcination in the
oxy-fired precalciner is captured, resulting in lower values of CO2 capture efficiency.
The integration of the cement industry and the CaL technology has been broadly studied
since the production of cement is one of the industrial sectors with the biggest carbon footprint
and makes use also of limestone as a raw material for the clinker manufacture. Moreover, the
CaL retrofitting capacity makes this integration a promising combination not only for future
designs but also for existing cement plants. Different degrees of integration may be achieved
depending on the aspects coming into play: (i) Most proposed schemes focus on the integration
of mass flows; the CO2 generated in the cement plant is captured in the CaL cycle and the purged
sorbent is directed to the cement plant to feed the precalciner or the rotary kiln. (ii) In other
studies, the heat flows are also involved. The whole system comprises a power plant and a
cement plant, from which the CO2 is captured, the CaL process, and a steam cycle to make use of
the surplus energy from the capture system and the cement plant.

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The concept of integrating the CaL technology with the cement industry for CO2 capture
has been investigated in several theoretical studies. There is a general consensus that CaL
process seems to be the most appropriate technology for CO2 capture in cement industry since:
1. Cement industry is already familiar with the management (handling, storage, feeding,
etc.) of CaO-bearing materials.
2. Has a low cost of fresh limestone that is required for the enhancement of the circulating
solids capture ability.
3. It allows for potential utilization of the purge CaO for the cement production as it is the
chemically compatible with cement raw meal.
4. There is room for recovery of the waste heat that is dissipated from the CO2 capture unit.

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1.4 Scope of the Seminar
Limiting the fossil carbon dioxide emissions from human activities e.g. energy
production and other energy-intensive industrial sectors are major challenges of science and
technology today. Several methods to capture and store CO2 resulted from the energy production
have been proposed The key issue in developing and large scale deployment of carbon capture
technologies is the high energy and cost penalties for CO2 capture. One promising method of
CO2 capture is to use a cyclic calcination, carbonation reaction (calcium looping process). This
carbon capture method exhibits low energy penalty (in the range of 6e8 net electricity percentage
points) compared to gas-liquid absorption using alkanol amines which has an energy penalty of
at least 10 net electricity percentage points. The main reason for low energy penalty of calcium
looping process is due to the high running temperature of the CaL cycle (in the range of 500-900
0C) which make possible to generate high pressure steam with positive influence on overall plant
energy efficiency. The reduction of the energy demand in the CaL process has attracted the
attention of many researchers. In general, these works could be divided in two main options to
minimize the capture energy penalty. On one hand, we find some works aimed at reducing the
energy requirements of the capture cycle within the loop. On the other, there are studies whose
main goal is to recover the energy of the capture system by retrofitting the existing power plant
or by defining a new power plant that produces additional power. The power plants are operated
in a dynamic (load-following) Scenario according to the grid demand. This operation scenario is
likely to be intensified in the future by the greater integration of highly time-irregular renewable
energy sources (e.g. wind and Solar). Usually, the power plant is operated at full capacity during
the day and part-load or even shut down during the night. For power plants equipped with carbon
capture, the load following operation of the power block will affect also the post-combustion
CO2 capture unit. Another naturally occurring mineral that can be used as CaO precursor is
dolomite which is also abundantly available at low price. Arguably, the irreversible
decomposition of MgCO3 would enhance the surface area of the calcined sorbent, which should
favor the CaO reactivity in the fast phase controlled by carbonation on the surface of the solids.
Moreover, the presence of MgO in calcined dolomite is expected to increase the thermal stability
of the sorbent and help mitigating the loss of CaO carbonation reactivity, which is generally
attributed to its superior resistance to sintering at high calcination temperatures.

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1.5 Objectives
The main objective of the paper is to know carbon dioxide capture by calcium looping process in
cement. The specific objective objectives are as follows:
1. To know the CO2 capture efficiency at calcium looping condition.
2. To know the performance of dolomite and lime stone in calcium looping process.

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CHAPTER 2
LITERATURE REVIEW
2.1 General
Calcium looping process for cement plants, based on a reactor configuration that uses a double
calcium chemical loop for CO2 capture and the calcination of CaCO3. The low cost and wide
availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the
Ca-looping technology for post combustion CO2 capture as already demonstrated by 1Mwt scale
pilot projects. A major focus of studies oriented towards further improving the efficiency of the
CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO
as the number of carbonation/calcination cycles is increased. Combined Ca looping and chemical
looping combustion cycles were the most susceptible to fragmentation, indicating the low
mechanical strength of these pellets (Perejón et al., 2016). The Calcium Looping technology, based
on the multicyclic carbonation/calcination of CaO in gas–solid fluidized bed reactors at high
temperature, has emerged in the last years as a potentially low cost technology for CO2 capture.
The most important benefit of the high temperature CaL cycles is the possibility of using high
temperature streams that could reduce significantly, the energy penalty associated to CO2
capture. The application of the CaL technology in precombustion capture systems and energy
integration, and the coupling of the CaL technology with other industrial processes are also
described. In particular, the CaL technology has a significant potential to be a feasible CO2
capture system for cement plants. A precise knowledge of the multicyclic CO2 capture behaviour
of the sorbent at the CaL conditions to be expected in practice is of great relevance in order to
predict a realistic capture efficiency and energy penalty from process simulations.
Cement sector is currently responsible for approximately 5% of the global CO2 emissions.
CO2 originates principally from the raw meal calcination stage and conventional fuel (e.g. coal)
combustion for the thermal needs of the process. Carbon capture and storage (CCS) is among the
examined technologies for mitigating CO2 emissions generated in a cement plant. A very
competitive technology for CO2 capture from flue gases appears to be Calcium Looping (CaL).

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The process is realized in a dual fluidized bed system where CO2 is absorbed by CaO in the first
reactor (carbonator), and the produced CaCO3 is regenerated in the second oxy – fired reactor
(calciner). Among various carbon capture options, calcium looping (CaL) seems to be a
promising method to reduce both energy and cost penalties for post-combustion CO2 capture
compared to gaseliquid applications. In addition, assessment of dynamic performances of power
plants with carbon capture is of great importance, in the context of actual energy sector, CO2 is
captured by reacting with CaO and the carbonator, where the CO2 is released and the sorbent is
regenerated. Detailed Mathematic models for both CaL cycle reactors were developed and
simulated in dynamic conditions similar to the power plant cycling (Valverde et al., 2015).

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2.2 Performance of dolomite and limestone in carbon dioxide capture
Diego et al. (2016) demonstrated a new calcium looping process configuration for cement
plants that avoids the need for oxy-fired calcination has been analysed. This process scheme
makes use of a double calcium chemical loop for CO2 capture and a number of preheating
cyclonic stages to reduce the overall energy demand in the calciner. The CO2 capture efficiency
of the most complete configuration is estimated to be 94%, which corresponds to 92% of CO2
avoided. The overall energy consumption associated to this configuration is 7.5 GJth/t cement, as
against 4.0-4.4 GJth/t cement which is typical of a reference cement plant. Nevertheless, a proper
integration of the high-temperature energy streams available from the process allows the energy
requirements of the system to be satisfied, and even leads to an exportable surplus 25 MWe.
Therefore, the net overall increase in heat consumption by the process attributable to the CO2
capture system amounts to just 1.1 GJth/t cement. CO2 evolving from the calcination process and
also makes use of suspension preheaters to reduce the process energy consumption was
investigated. In this case, a CO2 capture efficiency of 58% and 53% CO2 avoided was achieved
with an increase in the system thermal demand of just 0.3 GJth/t cement. Additionally, a
preliminary economic analysis revealed that the cost of cement increases by 43 and 15%. This
enhanced performance was explained by the well-developed porosity in the mixed pellets.
Interestingly, copper oxide in cycled pellets was found to consist of 45% Cu2O and 55% CuO,
indicating that CuO reduction is partially irreversible and loss of oxidation capacity of copper
oxide is possible. The choice of a calciner temperature has a noticeable effect on the heat and
mass balances in the system, as shown in figure 2.1, which depicts the change in the combustor
heat requirements (Qcomb) as a function of the calciner temperature for different CO2 capture
efficiencies in the arbonator (Ecarb). It is in figure 2.2, a lower carbonation conversion of the
solids, Xcarb, favours an increase in the solid circulation flow between reactors and hence, in the
energy requirements of the calciner. The direct contact of the stream of carbonated solids with
the high-temperature gases (air combustor flue gas and highly concentrated CO2 leaving the
calciner) generated in the process as shown in figure 2.3.

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Fig 2.1 Effect of the calciner temperature on the combustor energy
(Source: Diego et al., 2016)
Fig 2.2 Effect of the overall CO2 capture efficiency
(Source: Diego et al., 2016)

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Fig 2.3 Scheme of the CO2 capture system proposed for the cement
plant (Source: Diego et al., 2016)

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Valverde et al. (2015) depicted that natural dolomite can be an advantageous alternative to
limestone as sorbent precursor for post combustion CO2 capture by means of the CaL
technology. TGA tests carried out under realistic sorbent regeneration conditions (high CO2
concentration, high temperature and quick transitions between carbonation and calcination
stages) show that the capture capacity of limestone derived CaO is critically influenced by
precalcination conditions and an intermediate recarbonation stage. The capture capacity of CaO
derived from precalcining limestone in air suffers a drastic drop in the first cycles. Moreover, the
introduction of a recarbonation stage, which is intended in practice to minimize the need for a
makeup flow of fresh limestone fed to the calciner, would actually have an adverse effect on the
capture capacity of the sorbent derived from precalcining the initial inventory of limestone in air.
SEM analysis of CaO derived from limestone precalcined in air and regenerated under high CO2
concentration/ high temperature show that it suffers marked sintering. The multicyclic stability
of CaO may be enhanced if precalcination is carried out under the same conditions as those used
for regeneration, which leads also to a favourable effect of recarbonation. On the other hand, the
behaviour of the sorbent derived from dolomite is quite insensitive to either recalcination or
recarbonation conditions and shows a neatly higher capture capacity as compared to limestone at
realistic calcination conditions. The predictability of dolomite behaviour, regardless of
precalcination and recarbonation conditions, can be a further advantage over the strong
dependence of limestone performance on these conditions, which may vary uncontrollably in any
modification of the process. Figure 2.4 shows multicyclic capture capacity results from carb/cal
tests in which dolomite and limestone samples were precalcined in air and regenerated either in
air at 8500 C as shown in figure 2.4 (a) or under 70 % CO2 at 9500 C represented in figure 2.4 (b)
respectively. In this case, limestone suffers a drastic drop of its capture capacity after
regeneration and it falls below 0.05 in just 10 cycles. In contrast, dolomite deactivates at a much
lower rate. As a result, the capture capacity of dolomite is twice that of limestone after 20 cycles.
The effect of recarbonation on the performance of both sorbents precalcined in air and
regenerated under high CO2 concentration

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Fig 2.4 (a) CO2 capture capacity as a function of cycle number for limestone
(Source:Valverde et al.,2015)
Fig. 2.4 (b) CO2 capture capacity as a function of cycle number for dolomite
(Source: Valverde et al., 2015)

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Ridha et al. (2015) investigated the CO2 capture performance of combined CaL/CLC
processes over consecutive redox cycles Three groups of CaO/CuO-based pellets were prepared
following different synthesis procedures to examine the effect of pellet structure and composition
on CO2 performance in a fixed bed reactor. Characterization results showed that mixed CaO-
based pellets and CuO-based pellets exhibited nearly 2 times higher surface area and pore
volume than those for integrated CaO/CuO-based pellets (core-in-shell and homogenous). This
suggests that incorporating CuO in the CaO-based pellets reduced the porosity of the final pellets
significantly. In the first cycle, the mixed pellets exhibited the highest CO2 uptake of 0.11 g
CO2/g bed corresponds to a CaO conversion of 32.1 %) which was 69 % and 64 % higher than
those of core-in-shell and homogeneous pellets, respectively. After 11 cycles, the CO2 uptake of
mixed pellets declined to 0.07 g/g (corresponds to a conversion of 19%), but was still higher by
77 % and 84 % than those obtained with core-in-shell and homogeneous pellets, respectively.
This enhanced performance was explained by the well-developed porosity in the mixed pellets.
Interestingly, copper oxide in cycled pellets was found to consist of 45 % Cu2O and 55 % CuO,
indicating that CuO reduction is partially irreversible and loss of oxidation capacity of copper
oxide is possible. Despite the fact that all pellets in this work were prepared with 10 % binder,
core-in-shell pellets were the most susceptible to fragmentation compared to the mixed and
homogenous pellets. These results suggest that a bed of mixed CaO-based pellets and CuO-based
pellets appears to be more promising than a bed of integrated CaO/CuO-based pellets for
combined calcium-looping and chemical- looping combustion processes with CO2 capture.
Furthermore, the mixed pellets are easier to reduce with better quality control than integrated
pellets. In figure 2.5 (a), CO2 uptake is presented in terms of specific CO2 capture per gram of
loaded pellets. It can be seen that CO2 uptake decreased with increasing number of cycles in a
similar fashion for all groups of pellets. Carbonation conversion of CaO is presented in figure 2.5
(b). In the first cycle, MX-bed, CS-bed and HM-bed achieved conversions of 32.1 %, 19.3 % and
19.9 %, which declined to 19 %, 10.9 %, and 10.5 % after 11 cycles, respectively.

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/
Fig 2.5(a) CO2 capture capacity; conversion
(Source: Ridha et al., 2015)
Fig 2.5 (b) CO2 capture capacity; specific capture

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Table 1.1 The pellet specifications
Table 1.2 Physical properties of pellets
Pellets BET surface area
(m2/g)
BJH pore volume
(cm3/g)
Av. pore diameter
(nm)
CS 6.9 0.031 9.12
HM 7.5 0.028 9.11
MX 14.1 0.068 10.88
Pellets Lime (wt. %) CuO (wt. %) Cement (wt. %) Size (lm)
Core-in-shell 64 26 10 250-600
Homogeneous 64 26 10 250-600
CuO-based - 90 10 250-425
CaO-based 90 - 10 425-600

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Perejon et al. (2016) concluded that reaction kinetics and CO2 capture capacity of Ca-based
sorbents are usually evaluated by means of thermo gravimetric analysis (TGA) lab-scale tests.
Realistic CaL conditions to be expected in practice involve: (i) short residence times (on the
order of a few minutes), (ii) low CO2 concentration (about 15% in volume) for carbonation at
Temperatures around 650 oC, (iii) high temperature and high CO2 concentration in the calciner
for sorbent regeneration and recalcination of the makeup flow of solids (temperatures above 930
oC and CO2 % vol of at least 70% in volume, respectively) and (iv) very fast transitions between
the carbonation and calcination stages. Ace in two well differentiated phases (figure 2.6). In a
first fast carbonation stage, CO2 is chemisorbed on the available free surface of the CaO particles
until a thin layer of CaCO3 (40–50 nm thick) is formed. Carbonation continues in a second
relatively slower stage characterized by diffusion through the solid CaCO3 layer. It is usually
believed that most of carbonation taking place in residence times of a few minutes occurs in the
fast carbonation Stage, which is driven by the reaction kinetics. However, TGA tests carried out
under calcination environments of high CO2 Partial pressure show otherwise. As may be seen in
figure 2.6 Carbonation in the solid-state controlled diffusion phase (XD as compared to XK in
the fast phase) represents a significant contribution to the overall carbonation. CaO conversion
is` defined as the ratio of mass of CaO converted in each carbonation stage to the mass of CaO
initially present in the sorbent after calcination. TGA tests show that the CaO multicyclic
conversion in short residence times can be described by the following expression
Where N is the cycle number, X1 is CaO conversion in the first cycle, k is the deactivation
constant and Xr is the residual conversion, which is asymptotically approached after a large
number of cycles. Figure 2.7 also shows the effect of introducing a recarbonation stage aimed at
reactivating the sorbent. In carb/recarb/cal cycles, 3 min of recarbonation in 10% air and 90%
CO2 (vol/vol) at 800 oC were introduced between the carbonation and the calcination stages.

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Fig 2.6 Time evolution of sorbent weight % during a carbonation
(Source: Perejon et al., 2016)

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Fig 2.7 CaO conversionat the end of the carbonationstage
(Source: Perejon et al., 2016)

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Atsonios et al. (2015) investigated the CaL process with an existing cement plant for CO2
capture was investigated. Various technical aspects were taken into consideration in the
simulation analysis such as the specifications of CO2 stream for transport and storage and the
purge material quality with respect to utilization to the clinker process, substituting part of the
raw materials feedstock. Process simulation on the integrated system, i.e. cement plant with CO2
capture, revealed the importance of fuel composition that is employed in the calciner on the
system operation and performance. When fuels with high S content like petcoke and oil are used,
the formed CaSO4 tends to accumulate in the loop, increasing the demand for fresh (make-up)
limestone (>0.15 kmol CaCO3/ kmol CO2) and at the same time deteriorating the purge CaO
quality. Additionally, in such a case, high SO3 content is observed, a fact that decreases
considerably the purge CaO utilization rate in the clinker process. From this comparative
assessment, low S coal was proven as the most suitable fuel for the calciner contributing to the
8% reduction of raw limestone consumption, because of spent CaO utilization. In such a concept,
the net electricity that is produced and can be provided to the grid is estimated to be around to
426.66 kW h/t clinker. The economic analysis reveals CaL process and MEA scrubbing are
almost comparable in financial terms, while CaL has an advantage over MEA owed to lower
OPEX, mainly attributed to credits gained from the electricity selling. On the other hand, MEA
has a lower CAPEX. However, high CO2 avoidance cost in both technologies (68.75 €/tCO2 and
71.06 €/tCO2 for CaL and MEA, respectively) keeps them away from industrial implementation.
The sensitivity analysis for the examination of the effect of the bed material heater and the steam
cycle characteristics on the system performance reveals that the decrease of fuel consumption in
the CaL system has slightly more beneficial impacts on the cost reduction of avoided CO2 than
the increase of steam cycle efficiency. CaL process has the potential for technical improvements
in order to become more competitive by the adoption of novel concepts with lower equipment
cost. A far as the impact on fuel type on the clinker process and the produced emissions are
concerned, the main results are summarized in table 1.3. The specific operational values are
selected to be presented in normalized format respect to the clinker production, since the vast
majority of CO2 emitted originates during the clinker production. The main results from the
economic assessment are presented in table 1.4.

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Table 1.3 Main results on clinker process for using different fuel type
(Source: Atsonios et al., 2015)

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Table 1.4 Comparison of CaL and MEA for retrofitting CO2 capture in cement plant
(Source: Atsonios et al., 2015)

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Cormos et al. (2015) investigated that the differences between the pilot plant data and the
simulation results were very small, which indicates that the real process is adequately described
by the mathematical model. Temperature and composition profiles within both CFB reactors are
predicted successfully illustrating the predictive capabilities of the model (for instance R for
mass balance is about 0.96). The CO2 capture sorbent capacity is a key issue to be evaluated, this
parameter is rapidly decrease with the number of cycles. The operational conditions to improve
the performance were also evaluated e.g. smaller superficial gas velocities gives a higher
carbonation degree. As the results suggest, the most part (at least 90 %) of the reactions take
place in the dense region, which decrease with increasing of gas velocity. The dynamic
behaviour of CaL cycle during the load following operation of the power plant was studied by
incorporating the ramp, step and sinusoidal input changes. As main changing parameter with
load following, the flue gas flow rate was used. The effect of the disturbance propagates with
delay for solid phase by comparison with gas phase. The ramp perturbation does not destabilize
the process as a step change. The simulation results, in case of sinusoidal input change, shows
that the solid flow rate and the CO2 capture rate reach a minimum value when the flue gas flow
rate was at its maximum rate. The insight obtained from the dynamic simulation results are
particular useful for design an advanced control scheme and for evaluation of various operation
conditions for CaL cycle optimization. The cooling loads for the proper operation of the
cryogenic system are obtained by an external Refrigeration System. The main parameters for the
PCU are summarized in table 1.5. The entrained solids are transported into the calciner, where
the sorbent regeneration by thermal decomposition of calcium carbonate takes place. The
one-dimensional dynamic model considers the following phenomena:
1) Sorbent deactivation with the number of recirculation cycles (N),
2) CO2 equilibrium concentration which influences the carbon capture rate and sorbent
regeneration capacity,
3) Heat transfer within the fluidized beds between the solid and gaseous phases.
To simplify the complex mathematical description of CaL cycle, the following assumptions were
made: perfectly spherical solid particles with permanent macroscopic structure and constant
diameter were considered; 1-D hydrodynamic model based on literature sources; pseudo-
homogenous system was assumed within the elementary segments of both CFD reactors.

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Table 1.5 Process parameters for the PCU
(Source: Cormos et al., 2015)

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2.3 GENERAL OBSERVATION
A new calcium looping process configuration for cement plants that avoids the need for oxy-
fired calcination has been analyzed. This process scheme makes use of a double calcium
chemical loop for CO2 capture and a number of preheating cyclonic stages to reduce the overall
energy demand in the calciner. The CO2 capture efficiency of the most complete configuration is
estimated to be 94 %, which corresponds to 92 % of CO2 avoided (Diego et al., 2016). Net
electricity production is estimated to be around to 426.66 kWh per ton clinker. CaL and MEA
scrubbing are almost comparable in financial terms. Combined CaL–CLC system in a fixed bed
reactor is a feasible process. Mixed pellets exhibited the highest CO2 uptakes of 0.11 g CO2/g
bed in the first cycle. The reduction of CuO to Cu2O is partially irreversible. Among all pellets,
mixed pellets are the most promising for CaL–CLC combined cycles (Ridha et al., 2015). The
Calcium Looping (CaL) technology is a potentially low cost and highly efficient post
combustion CO2 capture technology. Energy integration and sorbent behavior play a relevant
role on the process. The industrial competitiveness of the process depends critically on the
minimization of energy penalties. It may be used in pre combustion capture systems and other
industrial processes such as cement production. Sorbent deactivation must be assessed under
realistic conditions involving high CO2 concentration in the calciner (Perejón et al., 2016).
Development of dynamic model for the CO2 capture using calcium looping (CaL) process.
Evaluation of CaL cycle dynamic behavior and model validation vs. experimental data.
Evaluation of CO2 removal capacity during a ramp, step and sinusoidal input tests. The CO2
capture performance of dolomite is studied at realistic calcium-looping conditions. Dolomite has
a superior capture performance as compared to limestone. MgO grains in decomposed dolomite
serve as a thermally stable support for CaO. Full de-carbonation of dolomite is achieved at lower
calcination temperatures as compared to limestone (Cormos et al., 2015). The improved stability
provided by the inert MgO skeleton would serve to significantly enhance the multicyclic CaO
conversion and sorbent capture capacity at realistic CaL conditions for post combustion CO2
capture. An additional potential advantage brought about by the use of dolomite would be its
much faster decomposition under CO2 as compared to limestone, which would allow reducing
notably the temperature of the calciner that imposes the main energy penalty to the technology.

2016
CHAPTER 3
DISCUSSIONS
Many investigations reported that CO2 emissions from the cement industry exceeded about 2
billion tonnes and global cement production reached 4 billion tonnes in 2013 and has been
following a rising trend for decades, as cement consumption is intimately linked to economic
development, which represents about 5 % of the total man-made greenhouse gas emissions. The
main source of CO2 emissions during cement production is the calcination of limestone required
to generate CaO. The remaining emissions come from fuel combustion in the precalciner and the
kiln and indirect emissions linked to the substantial use of electricity in the process, usually
produced also from fossil sources. The increasing concentration of CO2 in the atmosphere is
believed to be the major contributor to climate change. Carbon capture and storage has been
proposed as a promising approach to reduce CO2 emissions from fossil fuel fired stationary
sources. There are many technologies available to minimize CO2 emissions by CO2 capture.
From the economical point of view calcium looping for post combustion process found to be
more effective. Limestone was extensively used for the CO2 capture as sorbent. Recently natural
dolomite is also used in chemical looping for post combustion process. Since CaO sintering is
mitigated in the dolomite derived sorbent, sulphation would be presumably minimized by the use
of dolomite as compared to limestone. Moreover, the possibility of lowering down the calciner
temperature would allow decreasing the generation of SO2 in this reactor, which would serve to
further mitigate deactivation of the sorbent as caused by sulphation thus allowing for a reduction
of the makeup of fresh solids to counterbalance the purge flow of the solids deactivated.
Moreover, as seen in our work, the capture capacity of dolomite is substantially higher than that
of limestone for the initial solids inventory precalcined in air, which would allow further
decreasing the amount of purged solids while the capture efficiency is kept at a high level,
Process optimization is required to reduce CO2 emissions from the cement industry. It is
observed that, the performance of dolomite subjected toordinary carb/calc cycle is similar to that
of limestone subjected to carb/recarb/calc cycles the economical benefit of using dolomite
instead of limestone.

2016
REFERENCES
1. Ana-Maria Cormos and Abel Simon. (2015), “Assessment of CO2 capture by calcium
looping (CaL) process in a flexible power plant operation scenario”, Applied Thermal
Engineering , Vol 134, pp 319–327.
2. Anette Mathisena , Maria M. Skinnemoenb and Lars O. NordbYanjie. (2014),
“Evaluating CO2 capture technologies for retrofit in cement plant”, Energy Procedia, Vol
63. pp 6484–6491.
3. Antonio Perejón , Luis M. Romeo , Yolanda Lara , Pilar Lisbona , Ana Martínez and
Jose Manuel Valverde. (2016), “The Calcium-Looping technology for CO2 capture: On
the important roles of energy integration and sorbent behavior”, Applied Energy, Vol.
162, pp 787–807.
4. J.M. Valverde, P.E. Sanchez Jimenez and L.A. Perez-Maqueda. (2015), “Ca-looping for
postcombustion CO2 capture: A comparative analysis on the performances of dolomite
and limestone”, Applied Energy, Vol.138, pp 202–215.
5. Firas N. Ridha , Dennis Lu , Arturo Macchi and Robin W. Hughes . (2015), “Combined
calcium looping and chemical looping combustion cycles with CaO–CuO pellets in a
fixed bed reactor”, Fuel, Vol 153, pp 202–209.
6. M.E. Diego, B. Arias, J.C and Abanades (2016), “Analysis of a double calcium loop
process configuration for CO2 capture in cement plants”, Bioresource Technology,
Vol.117, pp 110–121.
7. K. Atsonios , P. Grammelis , S.K. Antiohos , N. Nikolopoulos and Em. Kakaras. (2015),
“Integration of calcium looping technology in existing cement plant for CO2 capture:
Process modeling and technical considerations”, Fuel, Vol. 153, pp 210-223.
8. Konstantinos Atsonios, Myrto Zeneli, Aristeidis Nikolopoulos, Nikos Nikolopoulos,
Panagiotis Grammelis and Emmanuel Kakaras. (2015), “Calcium looping process
simulation based on an advanced thermodynamic model combined with CFD analysis”,
Fuel, Vol. 153, pp 310–381.

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