Calcium Looping Technology Research Articles

Process simulation and techno-economic analysis of CO2 capture by coupling calcium looping with concentrated solar power in coal-fired power plant

The calcium looping (CaL) cycle is an effective high-temperature CO2 capture technology, its primary energy consumption arises from the calcination process, which limits the development of CaL technology. Utilizing concentrated solar power (CSP) instead of combustion for the calcination process in the CaL cycle can significantly reduce the energy penalty associated with CO2 capture of coal-fired power plants. Currently, the application of coupling CaL with concentrated solar power (CaL-CSP) systems in coal-fired power plants is still in its infancy, and there is limited research on its thermal performance and techno-economic analysis. In this study, a process simulation model of a 660 MW supercritical coal-fired power plant is developed as a reference. Subsequently, four different heat transfer routes are integrated into the design of CaL-CSP systems. The results indicate that the coupled power plant achieves a CO2 capture rate of 90 % compared to the reference coal-fired power plant, and reduces annual CO2 emissions by 93 % to only 58.2 g CO2/kWh. The CO2 capture energy penalty is 0.24 MJ/kg CO2. A sensitivity analysis of power generation cost reveals that if the cost of solar concentrator components is halved, the power generation cost will decrease to just 25 % higher than the reference power plant. Given the rapid advancements in CSP technology, this reduction is likely to be realized soon. Moreover, with the increase in carbon taxes and carbon prices, the power generation cost is expected to further decrease.

High-Entropy Fluorite Oxide-Modified CaO-Based Sorbent Pellets for Enhanced High-Temperature CO2 Capture.

The calcium looping technology employing CaO-based sorbents is pivotal for capturing CO2 from flue gas. However, the intrinsic low thermodynamic stability of CaO-based sorbents and the requisite molding step induce severe sintering issues, diminishing their cyclic stability. Herein, a high-entropy fluorite oxide (HEFO) inert stabilizer premised on entropy stabilization and synergistic effect strategies is introduced. HEFO-modified, CaO-based sorbent pellets are synthesized via a rapid cigarette butt-assisted combustion process (15 min) combined with the graphite molding method. Post-multiple cycles, their CO2 capture capacity reaches 0.373g g-1, which is 2.6-fold superior to that of pure CaO, demonstrating markedly enhanced anti-sintering properties. First, the subtle morphological and crystallographic modifications suggest that the inherent entropy stability of HEFO imparts robust thermal resistance. Concurrently, the disordered structure of single-phase HEFO exhibits a high affinity for CaO, resulting in an interface binding energy of -1.83eV, in sharp contrast to the -0.112eV of pure CaO, thereby restricting CaO migration. Additionally, the multi-element synergistic effect of HEFO reduces the energy barrier by 0.15eV, leading to a 40% and 140% increase in carbonation and calcination rates, respectively. This work presents highly efficient and rapidly synthesized CaO-based sorbent pellets, showcasing promising potential for industrial application.

Infusion of Fly Ash/MgO in CaO-based sorbent for high-temperature CO2 capture: Precursor selection and its effect on uptake kinetics

Calcium Looping Technology for high-temperature CO2 capture suffers from a gradual decline of uptake capacity over repeated cycles caused by the sintering-induced agglomeration of CaO particles. The latter is typically inhibited by infusing inert into the sorbent to disperse CaO grains. In this respect, current work investigates the infusion of inerts like Fly ash (FA) and Magnesium salt in CaO-based sorbent through sol-gel combustion, assessing sorbent performance under harsh conditions: carbonation at 650 °C for 30 min and calcination at 950 °C for 15 min under a CO2 (100%) atmosphere. The study includes (i) in-depth characterization of various sorbents: both unsupported and modified with inert, synthesized using inorganic (InOP) and organometallic (OMP) precursors for different fuel-to-metal oxide molar ratios (MR = 2 and 3), (ii) thermogravimetric analysis for evaluating uptake kinetics based on carbonation conversion (XCBN) and cyclic stability and (iii) kinetic modeling to evaluate rate parameters. Kinetic analysis after a single cycle revealed the highest XCBN (78%) for unsupported InOP (MR = 2 and 3) and OMP (MR = 2) among thermally pre-treated sorbents. MgO-modified InOP (MR = 2) performed better (XCBN = 66%) than its OMP counterpart, while both MgO-modified sorbents (MR = 3) performed similarly (XCBN = 66%). Cyclic stability studies conducted for 30 cycles established higher stability of FA-modified OMP with lower deterioration by 13.47% (XCBN = 22.60%) than unsupported OMP by 62.99% (XCBN = 15.06%). Overall, the results showcase FA infusion in OMP as a viable route to develop stable modified CaO-sorbents with considerable carbonation conversion.

Insight into Dynamic Characteristics of Concentrated Solar Power Systems with Calcium Looping Based on ZnO–Na2SO4 Co‐Doped CaO Composites

Concentrated solar power (CSP) integrated with calcium looping (CaL) technology has garnered significant interest as a solution to mitigate the issue of intermittency in solar power production. However, the deactivation of CaO‐based materials during cycling limits the application of CaL technology on a large scale. Herein, the dynamic characteristics of the CSP‐CaL system indirectly integrated with the s–CO2 Brayton cycle using CaO–ZnO–Na2SO4 composites are studied. Energy analysis shows that the energy storage density varies from 1328.13 to 1232.03 J g−1, and its average value increases by 32.0%. Round‐trip efficiency of the system varies from 40.0% to 39.5%, and its average value increases by 22.6%. Exergy analysis shows that the co‐doping of ZnO and Na2SO4 into CaO enhances the exergy efficiency of the calciner and the heat exchange network, but reduces the exergy efficiency of the carbonator. Exergy round‐trip efficiency of the CSP‐CaL system has slightly decreased from 44.0% to 43.4%, with an average increase of 22.8%. Techno‐economic analysis shows that the levelized cost of electricity for different sizes of CSP‐CaL systems using CaO–ZnO–Na2SO4 ranges from 176.44 to 153.70 $ MWh−1. Therefore, the CaO–ZnO–Na2SO4 composite shows promising prospects for application in solar thermal power generation.

Techno-economic assessment of solar photovoltaic electrification and calcium looping technology as decarbonisation pathways of alumina industry

Aluminium industry stands out as a significant source of CO2 emissions, due partially to the high energy demand of the alumina extraction stage. Accordingly, this study explores the implementation of direct resistive heating of mid-temperature processes in alumina production as an alternative to decrease CO2 emissions. Additionally, two different strategies are evaluated to decarbonize alumina industry: the generation of renewable electricity through solar photovoltaic panels and the integration of a CO2 capture plant based on calcium looping technology. This work comprehends the modelling and sizing of these plants and the assessment of their economic performance through the calculation of their Net Present Value and their respective payback periods. The integration of both strategies into an alumina refinery model reveals that electrification of low and mid-temperature processes yields a 15 % reduction in CO2 direct emissions, whereas calcium looping demonstrates the potential to capture 97 % of emissions with a 7 % energy penalty. Also, economic assessments indicate substantial potential for improvement through in-site electricity generation via solar photovoltaic panels, exhibiting a payback time of 4.5 years. Conversely, the feasibility of a calcium-looping plant is hindered by high capital expenses, necessitating a longer payback period of 19–24 years. Sensitivity analyses underscore the suitability of in-site renewable electricity generation, whereas carbon emission taxes emerge as crucial in incentivizing carbon-neutral processes, with thresholds around 95–125 €/tonne of CO2. Despite potential deviations from real industrial settings, this study provides evidence for environmentally friendly strategies in alumina production that demonstrate limited adverse effects on economic performance.

The key role played by mesoporous alumina as binder for obtaining ultra-hard CaO based pellets for thermochemical heat storage leveraging the CaO/CaCO3 cycle

The synthesis of CaO-based pellets with high energy storage and suitable mechanical resistance after prolonged cycling is pivotal for the successful implementation of the Calcium looping (CaL) technology for energy storage in CSP plants. In this work, CaO-based spherical pellets (CAA) were prepared made up of 60 wt % Ca(OH)2 and varying ratios (0–40 wt %) of commercial γ-Al2O3 and mesoporous γ-Al2O3 (m-Al2O3). They were tested in TG in several CO2 carbonation/decarbonation cycles (15 and 50 for selected pellets) and their respective average crushing strengths measured. After 15 cycles, the optimum pellet CAA 20-20 (60 wt % Ca(OH)2/20 wt % γ-Al2O3/20 wt % m-Al2O3) exhibits a remarkable energy storage density of 1030 kJ/kg with a superb crushing strength of ∼29 N. This was ascribed to the enhanced formation of the calcium aluminate mayenite (Ca12Al14O33), since the high BET surface area (384 m2 g−1) of mesoporous γ-Al2O3 promotes the interaction with calcium oxide. Additionally, CAA 20-20 showed meaningful porosity that favored CO2 mass transport. Interestingly, after 50 cycles, the optimum CAA 20-20 pellet maintained a high carbonation yield (0.46), representing an 84 % of the initial value and corresponding to an energy storage density of ∼873 kJ/kg. Additionally, the optimum CAA 20-20 pellet was coated with an external layer of Al-MCM-41 silica that augmented its crushing strength up to 37 N, with a concurrent slight abatement in the carbonation yield and energy storage density after 50 cycles (0.43 and ∼824 kJ/kg). Consequently, both uncoated and coated CAA 20-20 pellet are promising for the successful implementation of CaL in CSP plants.

Biogas upgrading through calcium looping: Experimental validation and study of CO2 capture

The calcium looping technology is one of the most promising technologies for capturing and storing CO2. This technology has been evaluated with a variety of sorbents and conditions in previous works, but the inlet CO2-ladden gas has typically been a flue gas from combustion, which typically has a composition of 10–20% CO2 and 80–90% N2. On the other side, the performance of the calcium looping process for CO2 capture of other gases (i.e., biogas or gases resulting from hydrothermal carbonization) remains largely unstudied. In this work, this knowledge gap is assessed through evaluating the performance of the calcium looping process for biogas (synthesized as 40% CO2, 60% CH4) in terms of carbonation conversion. This experimental study investigates the impact of: (1) using an inlet gas composition representative for biogas instead of combustion flue gas; (2) different biogas compositions; (3) the carbonation temperature; (4) the cooling-down and heating-up of the sorbent material between the reactor and ambient temperatures within cycles; (5) the atmosphere composition during calcination; and (6) the solids particle size. The main result obtained is that the overall CO2-capture performance of calcium looping improves when using biogas as inlet CO2-ladden gas, in comparison with combustion flue gas. One main contribution to this improved performance is shown to be the presence of secondary reactions (i.e., dry reforming, methanation). The impact of the CH4 to CO2 ratio tested is not remarkable, showing that the potentialities of the process in this aspect can be adapted to several biogas producing feedstocks.

Experimental analysis on calcination and carbonation process in calcium looping for CO2 capture: study case of cement plants in Indonesia

AbstractCarbon dioxide (CO2) is the main contributor to greenhouse gases that affect global warming. The industrial sector is the third largest producer of CO2 and the cement industry is one of the industries that consistently produces the most significant CO2 emissions. The cement industry produces 5–8% of global CO2 emissions. Several methods for reducing specific CO2 emissions have been reported in the cement industry, including calcium looping, which uses the reversible reaction between calcination [calcium carbonate (CaCO3) decomposition] and carbonation [CO2 capture by calcium oxide (CaO)]. This work investigates calcium looping employing limestone obtained directly from several cement factories in Indonesia to observe the carbon-absorption characteristics of limestone from different mining locations. The experiment was carried out using a tube furnace equipped with a controlled atmospheric condition that functions as a calciner and a carbonator. X-ray diffraction and scanning electron microscopy with energy-dispersive x-ray spectroscopy characterization were conducted to analyse the changes in the experimental samples. The results demonstrated that the reactor configuration was capable of performing the calcination process, which converted CaCO3 to calcium hydroxide [Ca(OH)2], as well as the carbonation process, which captured carbon and converted it back to CaCO3. Parametric analysis was performed on both reactions, including pressure, temperature, duration, particle size and reaction atmosphere. The results show that the limestone obtained from all sites can be used as the sorbents for the calcium-looping process with an average reactivity of 59.01%. Limestone from cement plants in various parts of Indonesia has the potential to be used as carbon sorbents in calcium-looping technology. With a similar CO2 concentration as the flue gas of 16.67%, the experimental results show that Bayah limestone has the maximum reactivity, as shown by the highest carbon-content addition of 12.15 wt% and has the highest CO2-capture capability up to >75% per mole of Ca(OH)2 as a sorbent. Similar levels of the ability to capture CO2 per mole of Ca(OH)2 can be found in other limestones, ranging from 14.85% to 34.07%. The results show a promising performance of raw limestones from different mining sites, allowing further study and observation of the possibility of CO2 emission reduction in the sustainable cement-production process.

Limestone Calcination Kinetics in Microfluidized Bed Thermogravimetric Analysis (MFB-TGA) for Calcium Looping

Limestone calcination is an important part of calcium looping (CaL) technology and is critical to the design and operation optimization of fluidized bed reactors. However, obtaining a method of measuring the fast calcination kinetics in a fluidizing environment with isothermal conditions is still a challenge in the field of calcium looping. We address this challenge in this work and develop a new method of obtaining limestone calcination kinetics by injecting limestone particles into the hot fluidizing sands in a microfluidized bed thermogravimetric analysis (MFB-TGA) with a mass measurement resolution of 1 mg. The calcination characteristics of limestone are investigated at different particle sizes (150–1250 μm), temperatures (750–920 °C), and CO2 concentrations (0–30 vol.%). The experimental data measured from MFB-TGA were analyzed using a detailed model including surface reaction and intraparticle and external diffusion. The results show that the kinetics of limestone calcination measured by MFB-TGA are faster than those measured via regular TGA. This particle-injecting method of MFB-TGA provides a new experimental idea for measuring fast calcination kinetics occurring inside fluidized bed reactors and provides guidance on the application of CaL technology.

Environmental impact assessment of post-combustion CO2 capture technologies applied to cement production plants

Decarbonizing the cement manufacturing sector presents an interesting and pressing challenge as it is one of the largest energy consumers in industry (i.e., 7%), emitting considerable amounts of anthropogenic carbon dioxide (i.e., 7%). This paper performs a technical and environmental assessment of decarbonisation of cement production through process modelling and simulation, thermal integration analysis, and Life Cycle Assessment (LCA). Integration of three post-combustion capture methods for a conventional cement plant with an annual productivity of one million tons and a carbon capture rate of 90% is evaluated in comparison to the reference case without carbon capture and storage (CCS). Mass and energy balances derived from simulations are used for the assessment of three innovative capture systems: reactive gas-liquid absorption using Methyl-Di-Ethanol-Amine, reactive gas-solid adsorption using calcium looping (CaL) technology and membrane separation. For the LCA study, a “cradle-to-gate” approach is carried out using GaBi software, according to the ReCiPe impact assessment method. The general conclusion is that integrating the CCS methods into the cement production process leads to a decrease in global warming potential (GWP) in the range of 69.91%–76.74%. Of the CCS technologies analysed, CaL technically outperforms the others as it requires 34% less coal and provides 1.6 times higher gross energy efficiency. From an environmental perspective, CaL integration ranks first, with the lowest scores in six of the nine impact categories and a GWP reduction of 76.74% compared to the baseline scenario without CCS.

The Nanofibrous CaO Sorbent for CO2 Capture.

The nanofibrous CaO sorbent for high-temperature CO2 capture was fabricated by the calcination of electrospun composite filaments containing calcium acetylacetonate and polyacrylonitrile as a calcium-oxide precursor and a binder polymer, respectively. The calcination was carried out in air to prevent PAN carbonization and to obtain pure CaO nanofibers. The resulting mats of CaO nanofibers with the average diameter of 130 nm were characterized by a specific surface area of 31 m2/g, a CO2-uptake capacity of 16.4 mmol/g at the carbonation temperature of 618 °C, a hardness of 1.87 MPa, and the indentation Young’s modulus of 786 MPa. The low decarbonation temperature makes the fabricated sorbent promising, for example, for the calcium-looping technology of CO2 removal from the hot exhaust gases of fossil-fueled power plants.

Improved performance of modified CaO-Al2O3 based pellets for CO2 capture under realistic Ca-looping conditions

Calcium looping (CaL) technology implementation under realistic conditions is limited due to some problems related with sorbents' deactivation at high temperatures, being the incorporation of inert additives or supports identified as a promising alternative to overcome these issues. In this work, alumina was incorporated to CaO-based pellets containing limestone and waste marble powder (WMP) as Ca source by extrusion followed by calcination at 800 °C and granulation, using different CaO/Al2O3 ratios (50/50, 60/40 and 70/30) and Methocell™ as pore forming agent. Sorbents were tested in a laboratory scale fixed and fluidized bed reactor. The carbonation was carried out with 25% of CO2 at 700 °C, while the calcination was performed under realistic industrial conditions (70 – 80% of CO2 at 930 °C), foreseeing the subsequent CO2 utilization. During the CaL tests calcium aluminates (CaAl2O4 and Ca3Al2O6) were formed, reducing the amount of CaO available for capture (31–42% of free CaO) but improving the sorbents’ CO2 capture performance due to the role of these inert compounds as structural supports and the increase of sorbents’ surface area. The high amount of calcium aluminate support (58–69%) improved the mechanical resistance of the sorbents, with reduced fragmentation and abrasion problems during the fluidization. For both reactors, the highest CaO conversion was achieved for 60/40 CaO/Al2O3 based pellets. Considering the pure WMP sorbent as reference, the total amount of CO2 captured after 10 cycles by 60/40 CaO/Al2O3 based pellets (g CO2/g CaO) increased 93% and 135%, in the fixed and fluidized bed reactors, respectively.

The effect of BeO on heat transfer and durability of nano-CaO-based CO2 adsorbents.

The solution of decreasing the decomposition temperature of CaCO3 and the development of the durability of the CaO-based CO2 adsorbent are the key issues in reducing the energy consumption and cost of CO2 capture in calcium looping technology. In this work, BeO with high thermal conductivity was chosen as a dopant of the adsorbent to increase the thermal conductivity properties and decomposition properties of CaCO3. The endothermic rate of the nano-CaO-BeO/Al2O3 adsorbent with 15.6 wt% BeO dopant increased by 12.3% compared with that of the nano-CaO/Al2O3 adsorbent at 720 °C, leading to an increase of 10.1% of CaCO3 decomposition rate. The enhancement of the decomposition rate of the nano-CaO-BeO/Al2O3 adsorbent was significant to lower the regeneration temperature by 50 °C compared with that of the nano-CaO/Al2O3 adsorbent under calcium looping conditions, which made the total average deactivation rate decrease by 21.0% and made the total residual stable carbonation conversion increase by 27.0% in infinite calcium looping cycles. Strengthening the heat transfer inside the adsorbent material can effectively decrease the regeneration temperature, so as to improve the sorption durability.

Techno-economic analysis of a 660 MWe supercritical coal power plant in India retrofitted with calcium looping (CaL) based CO2 capture system

The current study deals with techno-economic analysis of a 660 MWe supercritical coal powerplant in India retrofitted with calcium looping (CaL) based CO2 capture system. Process simulation and thermodynamic analysis are performed using Aspen Plus software, followed by a detailed economic analysis. Performance parameters of calcium looping system are evaluated for Indian high ash (HA) coal as fuel for sorbent regeneration, followed by sensitivity analysis, then compared on a techno-economic basis with different fuel varieties such as South African coal, woody biomass, rice husk and also with other CCS technologies such as MEA and Oxycombustion. Among different fuel varieties, using South African coal results in lowest energy penalty (6.14% points), using biomass based fuels leads to negative emissions and low CO2 avoided cost, using Indian HA coal results in lowest LCOE (93.7 €/MWhnet). Energy penalty of CaL system (8.63% points) is lower than MEA (9.32% points), but slightly higher than Oxycombustion (8.04% points). However, net power output of CaL system (∼870 MWe) is 45% more than existing powerplant (∼601 MWe) and 94% and 81% more than MEA (∼449 MWe) and Oxycombustion (∼482 MWe). Comparison of CCS technologies for same net power output (870 MWe) clearly shows that CaL has the lowest LCOE and CO2 avoided cost. Existing coal power plants in India (having space availability), if retrofitted with calcium looping could achieve the twin goals of decarbonisation as well as an increase in electricity generation capacity. Hence, the calcium looping technology should be explored in detail for further technology development.

Decarbonization of Fossil Energy-intensive Industrial Processes Using Innovative Calcium Looping Technology

Mitigation of fossil carbon dioxide emissions from the main industrial sectors is a key element in the fight against global warming and climate change. In this respect, the main fossil energy-intensive processes (e.g., heat and power generation, cement, iron and steel, chemical applications etc.) are to be decarbonized for the future low-carbon economy. This paper is evaluating the post-combustion carbon capture based on innovative Calcium Looping (CaL) technology to be applied for decarbonization of various fossil-based industrial applications e.g., power generation, cement, iron and steel production. As illustrative cases, relevant industrial size systems are considered (e.g., 1,000 MW power plants, 4 Mt/year steel mills, 1 Mt/year cement plants). As benchmarks, similar processes without carbon capture as well as ones using chemical gas-liquid absorption for carbon capture are considered to assess the energy penalty for decarbonization. The decarbonized systems have 90 % carbon capture rate. As assessment tools a wide range of process systems engineering elements are used as follow: mathematical modelling and simulation using ChemCAD software, model validation based on experimental data, thermal integration analysis using pinch method for optimization of overall energy efficiency, technical and environmental evaluation to quantify the key performance indicators. As the results show, the innovative calcium looping technology for post-combustion carbon capture has significant advantages in comparison to the chemical gas-liquid absorption in term of higher overall plant energy efficiency (by about 2 net energy efficiency percentage points), lower CO2 capture energy penalty (7 - 8 vs. 10 net energy efficiency percentage points), reduced specific CO2 emissions etc.

Utilization of biomass to promote calcium‐based sorbents for CO2capture

AbstractTo promote and maintain the reactivity of calcium‐based sorbents for CO2capture is essential for calcium looping technology. Biomass together with cement was doped with calcium‐based sorbents pellets to promote the reactivity and enhance the sintering resistance for CO2capture. The influence of parameters, such as biomass types, addition, pretreatments, precursors, and cement amounts on CO2capture performance of sorbents are determined and an optimized process is developed for sorbents pellets making. Biomass such as coconut shell doped with calcium‐based sorbents present promising enhancement in CO2capture capacity. Sorbents doped with pretreated biomass exhibit excellent CO2capture performance with a carbonation conversion of 0.6 and 0.73 after 10 cycles, respectively. The microstructures of the sorbents characterized by N2physisorption/desorption and the phase structure determined byin situX‐ray diffraction (XRD) are investigated as a supplement for mechanism study. The release of volatiles and pyrolysis of biomass char in sorbents are the main causes for microstructure improvement for sorbents. The formations of CaAl2O4, CaAl4O7and Ca12Al14O33in sorbents during the carbonation/calcination cycles account for the enhancement of the sorbents’ sintering resistance. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

Preparation of CaO-SiO<sub>2</sub> Adsorbent for Potential CO<sub>2</sub> Capture via Dry Mixing Method

Calcium-looping technology is defined as one of the most desirable methods of carbon capture, utilization and storage (CCUS). However, because of sintering, rapid deactivation of CaO-sorbents is currently a major barrier to this technology. The stability of calcium based sorbent may be enhance by incorporating them with inert support materials such as MgO, Al2O2, ZrO2 and SiO2. For this study, calcium based sorbent has been incorporate with silica obtained from rice husk ash. CaO-SiO2 sorbents are prepared using physical dry mixing method which is much simpler compared to other available methods. The prepared CaO-SiO2 sorbents were then characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). New crystalline phase, larnite (Ca2SiO4) was detected in XRD patterns and this phase possess good chemical durability and may help to prevent sintering effect of calcium based sorbents and enhance their cyclic capability. CaO-SiO2 sorbent calcined at 700 oC with different grinding times have highest intensity of XRD peak at (104) with element of calcite. Sorbents with different weight composition of CaCO3-RHA were observed to have different surface morphology. SEM images of the sorbent (90wt% CaCO3-RHA) before calcination showed bigger particle size with irregular shape and more porosity. Then, SEM analysis was conducted for samples with different grinding times after calcination. CaO-SiO2 sorbents with 20minutes grinding time exhibited small size of particles with some porosity. Besides that, the particles are well distributed without agglomeration occured. The CaO-SiO2 sorbent calcined at 700 oC sorbents were tested for 20 consecutive carbonation and calcination cycles using Thermogravimetric Analysis (TGA). CaO-SiO2 sorbent treated with 700 oC calcination temperature and 20 minutes of grinding shows better cyclic CO2 sorption capacity.

Comparison of the Properties of Natural Sorbents for the Calcium Looping Process.

Capturing CO2 from industrial processes may be one of the main ways to control global temperature increases. One of the proposed methods is the calcium looping technology (CaL). The aim of this research was to assess the sequestration capacity of selected carbonate rocks, serpentinite, and basalt using a TGA-DSC analysis, thus simulating the CaL process. The highest degrees of conversion were obtained for limestones, lower degrees were obtained for magnesite and serpentinite, and the lowest were obtained for basalt. The decrease in the conversion rate, along with the subsequent CaL cycles, was most intense for the sorbents with the highest values. Thermally pretreated limestone samples demonstrated different degrees of conversion, which were the highest for the calcium-carbonate-rich limestones. The cumulative carbonation of the pretreated samples was more than twice as low as that of the raw ones. The thermal pretreatment was effective for the examined rocks.

Techno-Economic Analyses of the CaO/CaCO3 Post-Combustion CO2 Capture From NGCC Power Plants

Calcium looping is a post-combustion technology that enables CO2 capture from the flue gases of industrial processes. While considerable studies have been performed at various levels from fundamental reaction kinetics to the overall plant efficiency, research work on techno-economic analyses of the calcium looping processes is quite limited, particularly for the Natural Gas Combined Cycle (NGCC). Earlier work has shown that theoretically, a high thermal efficiency can be obtained when integrating calcium looping in the NGCC using advanced process configurations and a synthetic CaO sorbent. This paper presents an investigation of calcium looping capture for the NGCC through a techno-economic study. One simple and one advanced calcium looping processes for CO2 capture from NGCC are evaluated. Detailed sizing of non-conventional equipment such as the carbonator/calciner and the solid-solid heat exchanger are performed for cost analyses. The study shows that the CO2 avoided cost is 86–95 €/tCO2, avoided, which is considerably more expensive than the reference amine (MEA) capture system (49 €/tCO2, avoided). The calcium looping processes considered have thus been found not to be competitive with the reference MEA process for CO2 capture from NGCC with the inputs assumed in this work. Significant improvements would be required, for example, in terms of equipment capital cost, plant efficiency and sorbent annual cost in order to be make the calcium looping technology more attractive for capturing CO2 from NGCC plants.

Calcium Looping Technology Demonstration in Industrial Environment: Status of the CLEANKER Pilot Plant

Calcium Looping (CaL) is recognized as one of the most promising emerging technology for CO2 capture in cement plants. The highly integrated Calcium Looping process configuration enables CO2 capture with an efficiency target over 90% and high-energy efficiency. The core activity of the CLEANKER project is the design, construction and operation of a CaL demonstration system including the entrained-flow carbonator (the CO2 absorber) and the entrained-flow oxyfuel calciner (the sorbent regenerator). This demonstration system, connected to the Buzzi Unicem kiln of the Vernasca cement plant (Italy), will capture the CO2 from a portion of the flue gases of the kiln, using as CO2 sorbent the same raw meal that is used for clinker production. The CLEANKER implementation plan spans four years and half, from October 2017 to March 2022 (an extension of six months has been requested due to the pandemic situation). The first two years have been devoted to the (i) detailed design of the CaL demonstration system, the (ii) characterization of raw meals as CO2 sorbents and the (iii) erection of the demonstrator. The pilot plant has been commissioned in October 2020 and then will be demonstrated by means of several short and long steady-state tests (during spring and summer 2021), with the aim of optimizing the operational parameters governing the CO2 capture process and of bringing the integrated CaL technology at TRL7. The pilot plant and the conventional kiln operations will be deeply integrated: the CaL calciner will be fed by the same kind of raw meal used in the kiln for producing clinker, whereas the carbonator will treat the effluents coming from the cement plant. The CaL calciner will be fired in a recirculated oxy-fuel combustion mode, where a heavy fuel oil will be burnt with oxygen and a fraction of the CO2-rich exhausts will be recirculated to control the oxidant composition. Before being recycled to the CaL calciner inlet, this CO2-rich stream will be properly cooled in a regenerative riser-cyclone stage, designed to preheat the fresh raw meal-based sorbent fed to the pilot, minimizing the additional fuel supplied to run the calcium looping process. In the carbonator, the amount of sorbent (FCa/FCO2) will be tuned either by increasing the raw meal exchanged with the CaL calciner or by internally recycling a fraction of sorbent from the carbonator outlet to the inlet. First short campaigns will be carried out by specialized Buzzi Unicem operators (assisted by CLEANKER partners such as, Politecnico di Milano, Laboratorio Energia e Ambiente Piacenza, IKN, University of Stuttgart and VDZ) to test the process performances as a function of the type of raw meal, the amount of sorbent (solid to gas ratio in the carbonator) and the carbonation/calcination operating temperatures. The experimental activity will prove the stability and the effectiveness of the process by running over hundreds of hours the optimal experimental configuration, capable of achieving a constant carbon capture rate higher than 90%. Besides the continuous monitoring of process temperatures, flow rates and gas compositions, the experimental campaigns will be supported by post-processing sorbent analysis, in order to evaluate the capture capacity of the raw meal and the extent of side reactions. Test results will be exploited to validate simulation models and to improve the future scale-up and the design of an industrial size CaL plant.