Search

Abstract The impregnated layer solution combustion synthesis (SCS) technique was employed to synthesize CaO-based sorbents supported by inert stabilizers so as to improve the cyclic CO2 uptake stability. Four different inert stabilizers were evaluated for their impact on the cyclic CO2 uptake stability of sorbents. It found that the Mg-based inert stabilizer significantly outperforms the other three in improving cyclic CO2 sorption capabilities of sorbents synthesized by the impregnated layer SCS method. Moreover, MgO-supported sorbent pellets were prepared via graphite hydrophobic layer-assisted casting, with the magnesia load within the pellets being regulated between 15 and 45 wt %. It is the addition of MgO stabilizer that significantly improves the performance of CaO-based sorbents, with the improvements being notably more pronounced at higher MgO loads. The calcium-based sorbent pellets containing 45 wt % MgO show extremely stable CO2 sorption performance; after 17 cycles, the carbonation conversion rate is 73.6%, about three times the rate of pellets without MgO loading. The uniform dispersion of MgO inert stabilizer inside pellets improves high-temperature sintering resistance and, concurrently, enhances the mechanical property. Furthermore, the use of waste cigarette butts as impregnated layer templates, rather than other organic additives, will significantly reduce the cost of synthesizing MgO-supported CaO-based sorbents. Graphical Abstract

The calcium looping integrated with the chemical looping combustion (CaL-CLC) process is an efficient and cost-effective CO2 capture technology that avoids the energy-intensive air separation unit in the calcium looping (CaL) process. However, in these CaL-CLC and CaL system integration schemes, the carbonation heat is utilized for steam generation, resulting a significant temperature difference and considerable irreversible loss. To prevent temperature mismatch, this paper proposes a novel Ca-Cu looping post-combustion CO2 capture method with thermochemical recuperation based on steam methane reforming. Additionally, a novel system integrated with turbine exhaust heat recovery is introduced to effectively reduce carbon emissions from flue gas. Results show that the proposed system has superior performance compared to the reference system based on the Ca-Cu looping method. The specific primary energy consumption for CO2 avoidance decreased from 2.40 MJLHV/kg CO2 in the reference system to 2.02 MJLHV/kg CO2. Exergy analysis indicates that a total of 3.0 % reduction in exergy destruction can be achieved in chemical reaction processes and heat recovery processes, contributing to the superior performance of the proposed system. Furthermore, the effects of key operating parameters indicate that cascaded turbine exhaust recovery is essential for improving the thermodynamic efficiency of the proposed system. Overall, recovering the mid-temperature carbonation heat via thermochemical regeneration and integrating with exhaust heat recovery contribute to reducing SPECCA, thus providing a promising low-energy-consumption alternative for CO2 capture.

This review aims to provide a comprehensive overview of sorption-enhanced gasification (SEG) with CaO, highlighting its potential as an efficient and sustainable energy conversion technology. SEG integrates dual bed steam gasification with in situ CO2 removal using CaO, efficiently converting solid carbonaceous fuels such as biomass and low-rank coal into hydrogen-rich (up to 80 vol% H2), low-carbon and tar, medium calorific value and nitrogen-free syngas that can be adapted for various downstream applications. The review details the working principle, operating conditions and reaction mechanisms of SEG, emphasizing how these factors influence product distribution. Calcium sorbents are central to the SEG process, so their reactions, catalytic activity and limitations are discussed in this review. Pilot-scale tests are examined to underscore process engineering advancements as well as to highlight scale-up challenges that currently limit the technology to TRL 5–6. Unsustainable long-term sorbent performance and energy penalties from sorbent regeneration and CO2 capture still need to be addressed through scalable and cost-effective material development and process engineering. This review discusses various process intensification concepts as potential solutions to the inherent shortcomings of SEG. Process systems analyses examined indicate the potential of SEG in hydrogen, synthetic fuel and electricity production, positioning it as a promising technology for decentralized sustainable energy conversion. Furthermore, the review explores the sustainable repurposing and disposal of spent solids to foster circular economies. Overall, this comprehensive review provides crucial insights to further leverage and advance the SEG process, offering a platform for future research and development.

The calcium looping (CaL) process stands out as a promising technology for carbon dioxide (CO2) capture, which exhibits two essential phases: carbonation and calcination. CaL process has several advantages over conventional systems such as availability of abundant and low cost CaO sorbents, reduced environmental impact, lower greenhouse emissions and energy requirements. CaL offers easy and innovative schemes to integrate renewable energy such as concentrated solar power, oxy-fuel and chemical looping process and steam dilution to further enhance the overall efficiency of the system. The review first focuses on summarizing the characteristics and operational parameters of these process integrated CaL facilities while highlighting key experimental findings. The examination of innovative sorbent materials utilized within integrated CaL processes has been addressed, emphasizing pathways directed towards enhancing reaction efficacy, energy conservation, and holistic sustainability attained via process integration and intensification. Meanwhile, strategies to overcome the limitation of CaL process in terms of rapid sintering of sorbent particles over time have also been discussed. Further, the approaches for integrating CaL into industrial plants such as power, cement and steel plants have been identified and compared to realize significant reduction of energy penalty compared to conventional system. The impact of multivariate latent variable (LV) modeling on the integrated CaL process has been examined. Based on the review, CaL showed equivalent or better performance in reducing CO2 emissions (global warming potential or climate change impact indicator) in comparison to alternative scenarios.

CaO-based materials have attracted considerable interest because of their potential roles in thermochemical CO2 capture via the calcium looping (CaL) process. The steel manufacturing sector inevitably generates substantial amounts of slag as a by-product, posing environmental issues such as soil contamination if left untreated. Despite its abundance and low cost, steel slag, which contains 20–60 % CaO, has not been extensively researched for its potential in the CaL process. This study introduces ladle furnace slag (LFS) as an optimal CaO-rich material for developing mesoporous composites to improve CO2 sequestration in the CaL process. Using an autoclave reactor/muffle furnace setup, we conducted a parametric investigation on operational variables including reaction time, temperature, pressure, and liquid-solid ratio and determined the kinetics of carbonation/calcination reaction of CaL process. Our findings reveal that the CO2 capture performance of modified LFS surpassed that of the bare LFS, achieving a CO2 uptake of 7.55 ± 0.01 g per g of sorbent over 20 cycles. Additionally, the modified LFS exhibited the capability to undergo a minimum of 20 regeneration cycles, reaching steady state after the 15th cycle with minimal variation of 0.01 g per g of sorbent. The enhanced stability was linked mainly due to the presence of ceramics such as Al2O3 and Fe2O3 in ratios of 1:5 and 1:6.5 respectively, with respect to CaO, achieved through acid etching. Such mineralogical transformation of the modified LFS improved its resistance towards sintering while ensuring 100 % recycling of metals in the LFS. Therefore, this study highlights the sustainable utilization of LFS as a valuable and efficient sorbent for CO2 capture, showcasing its potential for repurposing in environmental applications.

The cement industry is exceptionally energy-intensive and a major global carbon emitter, with CO2 primarily arising from the calcination of carbonate raw meal and the combustion of fossil fuels. This study proposes a novel process integrating calcium looping and dry reforming of methane (CaL-DRM) based on an “in-situ carbon capture and conversion” strategy to enhance the energy efficiency and decarbonization in the cement production process. Models for both conventional cement production process model and the CaL-DRM processes were developed using Aspen Plus to compare the mass flow and process energy balances of conventional cement production with the CaL-DRM process. The modelling results were validated by the cement plant operating data and published results. Sensitivity analyses were performed to optimize key production parameters, including CH4/O2 = 1.37 and CaCO3/CH4 = 0.5, which resulted in the highest conversion efficiencies of CO₂ and CH₄. Subsequently, the optimization of the tertiary air volume and the proportion of hot raw meal entering the carbonator was carried out. The optimal tertiary air volume was found to be less than 28529 Nm³/h, and 13% of the hot raw meal was directed to the carbonator. With these conditions, the process thermal efficiency can be increased from 58 % to 86 %. CO2 emissions were analyzed at key stages of cement production process, focusing on fuel combustion and carbonate decomposition at the calciner and rotary kiln, with a comparison of the conventional method and the CaL-DRM process to quantify emissions at each stage. The results indicate that 852.3 kg CO₂ per ton of cement clinker can be converted to produce 1680 kg of syngas per ton of cement clinker along with cement clinker. Additionally, up to 62.5 kg CO₂ per ton of cement clinker can be captured by the carbonator, reducing the CO₂ volume fraction in flue gas from 23.29 % to 0.24 %, thus eliminating the need for subsequent CO₂ purification and transport. These findings demonstrate the significant potential of this novel method for sustainable development in the cement 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 presence of water vapour has been proven to stimulate carbonation for the calcium looping process, while its effect mechanism during the slow reaction stage still lacks insight understanding at the atomic level, where H2O molecules may interact with the product layer to affect the transportation of CO2. This study tried to reveal the role of water vapour on CO2 mobility on the calcite surface through density functional theoretical (DFT) calculation. H2O molecule has higher adherence to calcite surface than CO2, and it can react with CO3 to generate HCO3− and OH− ions. Then, the formed OH− ion above the surface layer can adsorb CO2. Moreover, H2O can also react with O2− defect to form OH− ions, and the OH ion at the deeper position can still adsorb CO2 through a two-step process with remarkable energy barriers. However, the formation of HCO3− can degrade the energy barriers to CO2 release from the calcite surface, owning to the weaker CO bond. Two directions of CO2 movement between anions were involved in this investigation, including crossing through the surface layer to the second layer and the movement inside the surface layer, where the higher mobility of CO2 from HCO3− to O2− ion occurs in both movement directions. For the case inside the surface layer, the movement from O2− ion to HCO3− has a higher energy barrier, indicating that the stimulation by H2O is a one-way effect, and the enhancement by H2O for CO2 mobility is caused by the reaction with CO32− other than O2− ion.

CO2 emissions have posed numerous global challenges, leading to an increasing consensus on the need for carbon neutrality in future development. CO2 capture and energy storage technologies represent a critical step in the carbon neutrality journey. Calcium looping (CaL), a promising technology for both CO2 capture and energy storage, holds significant potential in future carbon neutral technology strategies. In this paper, a comprehensive review of the application of CaL in CO2 capture and thermochemical heat storage (TCHS) is offered to inform further advancements in this field. Firstly, a brief overview and analysis of the fundamental technical routes and principles underlying of CaL for CO2 capture and TCHS are provided. Then, the research progress in the development of CaL-integrated systems for CO2 capture and TCHS is subsequently reviewed, with the existing limitations and outlining future prospects for further development highlighted. Additionally, a comprehensive summary of the proposed improvements in the performance of calcium-based materials is presented, focusing on enhancing carbonation reactivity in the multiple cycles and improving sunlight absorption performance of calcium-based materials. Finally, based on the current status of CaL development, insights and perspectives on potential avenues for further technological advancement are offered. Solar-driven CaL is a promising avenue for future CaL development, calling for greater research efforts on optimizing relevant equipment and enhancing calcium-based materials for sunlight-driven CaL systems. In addition, the CO2 in-situ conversion in the calcination stage of CaL is also a great potential direction for technological evolution.

In this paper, the enhancement of thermochemical energy storage by alkali metal chloride salts-doped Ca-based sorbents is revealed by experiments and DFT calculations. The results indicate that NaCl and KCl doping increases the reaction rate and cycle stability. Compared to CaO, the conversion of NaCl-CaO and KCl-CaO after one cycle is increased by 59.1% and 61.9%, respectively. This enhancement originates from the oxygen vacancies generated by Na2O and K2O and the significantly increased surface area by CaCl2 as well as the sintering delay. The synergistic effect between Na2O, K2O, and CaCl2 increases the reaction rate of calcium-based materials. Meanwhile, the penetration of low-viscosity molten NaCl and KCl into the calcium-based materials successfully segregates the CaO grains and allows the calcium-based material to maintain the porous structure after 80 cycles, thus exhibiting a high effective conversion rate. In addition, the KCl-CaO composites show the best combined performance in terms of effective conversion and averaged thermal energy density. This work paves the way for the application of chloride salts-doped calcium-based materials.

Given the gradual nature of the energy transition, retrofitting coal-fired power plants with carbon capture technology is crucial. The calcium looping (CaL) process is a promising solution, with challenges like absorbent deactivation and reduced thermal efficiency mitigated by absorbent reactivation and heat recovery systems. This study evaluated the techno-economic feasibility of integrating a novel wet extraction and precipitation process for absorbent reactivation within a solar-assisted CaL system, alongside an existing coal power plant. The process incorporated a secondary steam cycle and an ammonia absorption chiller for enhanced heat recovery and district cooling. The integrated project could increase daily power generation by 50% and reduce CO2 emissions from 820.4 g/kWh to 54.5 g/kWh. Over its lifespan, the reactivation facility could reduce limestone extraction by 21 Mt with 90% capture efficiency. With a levelized cost of electricity (LCOE) of 116.1 €/MWh and breakeven electricity selling price (BESP) of 56.6 €/MWh, the system demonstrated promising commercial viability, with the reactor and concentrated solar heating (CSH) system making up over 60% of investment costs. CSH cost and solar abundance were identified as key factors, indicating potential feasibility even in higher latitude regions. At CO2 revenues of 150 €/t, a stand-alone capture project can break even based solely on CO2 sales, demonstrating its potential for expansion to other areas. A case study highlighted the benefits of integrating absorbent reactivation and an ammonia absorption chiller, improving both economics and carbon capture efficiency. The study also confirmed the viability of solar-assisted projects in high-latitude regions, with optimistic future CO2 revenues and advancements in carbon capture technology enhancing feasibility.

In this study, synthetic CaCO3 materials were utilized as precursors for CaO-based CO2 sorbents. The investigation examined how various operating parameters—such as synthesis temperature (ST), stirring rate (SR), and surfactant percentage (SP)—impact the properties of the adsorbents. Samples were firstly characterized by X-ray diffraction and Scanning Electron Microscopy (SEM), which revealed that the prevalence of calcite or aragonite crystal phases in the synthetic CaCO3 precursors can be tuned by adequately choosing the dose of surfactant (Triton-X100®), so that it can be used as a crystal habit and growth modifier. The calcination process applied to the CaCO3 precursors leads to the formation of partially sinterized cubic crystals of CaO, accompanied by minor quantities (< 5 %) of additional compounds like Ca(OH)2 or CaSO4. Specific surface area (SBET) and porosity were determined by measuring the N2 adsorption isotherms. A CaCO3 sample with an unprecedented value of SBET as large as 116 m2/g was prepared operating under optimal conditions. SBET and pore volumes were successfully correlated with the CO2 uptake capacity of the samples. SBET is more influential for experiments carried out under diluted CO2 atmosphere. When pure CO2 is used, the influence of meso- and micropore volumes (Vme and Vmi) is clearly predominant, which suggests that in this latter case diffusion through the porous texture of the samples plays a more remarkable role. A double-way approach through Response Surface Methodology (RSM) and the use of Artificial Neural Networks (ANNs) has been used to analyze the CO2 uptake capacity of the samples. Within the operational interval, excellent results were obtained for pure and diluted CO2 flow, and RSM and ANNs have demonstrated to be a very efficient tool to correlate the behavior of the CaO-based materials as CO2 sorbents with the surface area and pore volumes of the samples. Valuable information on (i) the importance of the different factors under study; (ii) their influence on the surface and porosity of the CaO-derived sorbents; and (iii) the subsequent CO2 capture performance of the sorbents has been obtained. The results suggest that four parameters have a statistically significant influence on CO2 uptake. These parameters are SR, the square of SR, its interaction with SP, and the square of SP. Additionally, the study assessed the stability of the CaO-based sorbents over 11 consecutive calcination-carbonation cycles. By adequately choosing the synthesis strategy and conditions, an almost negligible shrinkage effect can be achieved, resulting in a more sustained uptake capacity throughout the cycles.

Waste eggshells have been investigated as biomineralised CO2 sorbents for the calcium looping cycle due to their high Ca content, low cost, availability, and high CO2 uptake. This work investigates a novel heat-pre-treatment using eggshells as raw material. The eggshells were simultaneously calcined and thermally pre-treated via microwave heating using different powers and times whilst maintaining the same input energy in a single mode cavity reactor. The calcined eggshells were characterised using standard characterisation techniques such as TGA and isotherms of N2 adsorption at 77 K. The dielectric properties were measured using the cavity perturbation technique at 2.45 GHz. Numerical electromagnetic simulations were performed using COMSOL Multiphysics and results were used to optimise the experimental setup. The treated materials were subjected to carbonation/calcination cycles in order to assess their suitability as a calcium-looping sorbent. The sorbent that exhibited a more stable CO2 uptake was the one treated at the highest power (800 W) 4.5 mmol CO2/g sorbent after 20 cycles under mild calcination conditions. Adsorbents prepared at 400, 600 and 800 W displayed similar CO2 uptake after 20 cycles when the calcination conditions were under more realistic conditions.

Global CO2 concentration rapidly increases over the past few centuries, particularly in recent decades, and the greenhouse effect is sharply accelerated by the increase of CO2 emissions. CO2 emissions are mainly produced from fossil fuel combustion, in particular coal-fired power plants. Calcium looping, i.e. the carbonation/calcination cycles of CaO, is one of the most promising CO2 capture technologies for coal-fired power plant. At the same time, coal-fired power plants are also one of the main sources of NOx emissions. CO can be used as a reducing agent for NO due to its low cost and low toxicity. CaO is a suitable catalyst for NO reduction by CO. The combustion of biomass is used to provide the required energy for the decomposition of CaCO3 in the calciner. Few unburned char and CaO flow into the carbonator, where the unburned char reacts with O2 in the flue gas to generate CO. Thus, the simultaneous NO removal and CO2 capture in the carbonator of the calcium looping process can be realized. However, the reaction mechanism of the effect of CaO on NO removal by CO in the carbonation stage is unclear. The mechanism of NO reduction with CO catalyzed by CaO in the carbonation stage is investigated by the density functional theory (DFT) calculations. The structural, adsorption, and reaction path parameters, including atomic layout, bond length, adsorption energy, and energy barrier of CO and NO molecules on the CaO (100) surface, are determined. The optimal adsorption sites of CO and NO molecules on the CaO (100) surface are O-top sites, and the adsorption energies are −0.35 and −0.79 eV, respectively. The CO and NO adsorption energies on the CaO (100) surface in the presence of CO2 are −0.36 and −0.20 eV, respectively. The co-adsorption of CO and NO molecules appears feasible on the CaO (100) surface, while CO2 exhibits obvious inhibition for the co-adsorption. The reaction path of NO reduction by CO on the CaO (100) surface undergoes two elementary reaction stages: CO2 formation and adsorption, and N2 generation. Finally, one N2 molecule and three \begin{document}${\rm{CO}}_3^{2-} $\end{document} ions are formed, with a total energy barrier of 11.08 eV. CO2 formation and adsorption (R→IM1→IM2) are the rate-determining steps of the whole reaction process.

Poor CO2 capture stability and serious elutriation are the issues commonly occur when limestone circulating in the fluidized bed-based Calcium Looping (CaL) system. Hence, three types of coal fly ash-bound (CFA-bound) limestone-derived sorbents were synthesized via mixing the limestone, calcined lime and hydrated lime with coal fly ash, respectively. The generated ternary Ca-Al-O and Ca-Si-O phases offer structural stability for CFA-bound limestone-derived sorbents and improve their cyclic CO2 capture performance. Moreover, extrusion-spheronization method was adopted to produce CFA-bound limestone and hydrated lime sorbent pellets to synergistically enhance cyclic CO2 capture capability and mechanical properties. It is found that hydrated lime is superior to limestone as the calcium precursor to prepare CaO-based sorbent pellets due to its desirable pore structure and high binding force. Therefore, the CFA-bound hydrated lime pellets containing 15 wt % of fly ash (HL/CFA15-P) exhibits a high carbonation conversion of 40 % after 17 cycles, which is nearly 1.4 times that of limestone pellets. The discrepancy on carbonation conversion between the two sorbent pellets is enlarged to ∼1.6 times after 100 cycles, which is calculated using a semi-empirical equation. Moreover, HL/CFA15-P exhibits outstanding mechanical property, whose compressive strength reaches 6±1.7 MPa, which is comparable to the cement-bound CaO-based sorbent pellets.

Concentrating solar power (CSP) technology with thermal energy storage (TES) could contribute to achieving a net zero emissions scenario by 2050. Calcium looping (CaL) is one of the potential TES processes for the future generation of CSP plants coupled with highly efficient power cycles. Research on CaL as a system for thermochemical energy storage (TCES) has focused on efficiency enhancement based on hybridization with other renewable technologies. This work proposes a novel solid management system to improve the efficiency of a CaL TCES system. The inclusion of a solid–solid separation unit after the carbonation step could lead to energy and size savings. The role of segregation between carbonated and calcined material on plant requirements is assessed, given the experimental evidence on the potential classification between more and less carbonated particles. The results show lower energy (up to 12%) and size (up to 76%) demands when the circulation of less carbonated material through the CaL TCES system diminishes. Moreover, under a classification effectiveness of 100%, the retrieval energy could increase by 32%, and the stored energy is enhanced by five times. The present work can be a proper tool to set the design and size of a CaL TCES system with a partial separation of the carbonated material.

CaO-based materials are potential candidates for thermochemical energy storage in calcium looping (CaL) due to their low-cost and large theoretical heat storage capacity. The harsh energy storage mode can circumvent adopting the membrane separation techniques with uncertain availability, contributing to improve the practicability of CaL. Nevertheless, the high calcination temperature and CO2 partial pressure involved in harsh energy storage mode adversely affect the cyclic stability of CaO-based materials. Therefore, comparison investigation on cyclic stability of CaO-based composites with inert supports for energy storage under harsh mode (950 °C, pure CO2) was conducted. The single Zr-supported, CaO-based composite possesses the highest energy release density of 1.42 MJ/kg after 19 cycles, which is markedly higher than that of the single Al- or Zr/Al-supported CaO-based composites. The Fe/Mn-doped, Zr-supported CaO-based composites were further prepared aiming to achieve direct solar absorption in the CaL. Although the binary Fe/Mn ions doping causes the decreased energy release density due to consumption of active CaO, the optical adsorption capability is significantly enhanced. The dark composite with a molar ratio of Ca/Zr:Fe:Mn = 100:4:8 exhibits the highest spectral absorbance of 74.2%, which is approximately 5.8 times that of white Zr-supported CaO-based composite. It also possesses excellent energy storage/release stability with a low average energy release density loss of 0.005 MJ/kg per cycle during 19 cycles.

This research work deals with the application of the calcium looping concept for thermochemical energy storage. Experiments were carried out in a lab-scale fluidised bed reactor, which was electrically heated. An Italian limestone (98.5% CaCO3, 420–590 μm) was present in the bed alone, or in combination with silica sand/silicon carbide (this last material was chosen as per its high absorption capacity in the solar spectrum). Calcium looping tests (20 calcination/carbonation cycles) were carried out under operating conditions resembling the “closed-loop” scheme (calcination at 950 °C, carbonation at 850 °C, fluidising atmosphere composed of pure CO2 in both cases). Carbonation degree, particle size distribution, and particle bulk density were measured as cycles progressed, together with the application of a model equation to relate carbonation degree to the number of cycles. Mutual relationships between the nature of the bed material and possible interactions, the degree of CaO carbonation, the generation of fragments, and changes in particle density and porosity are critically discussed. An investigation of the segregation behaviour of the bed material has been carried out through tests in a devoted fluidisation column, equipped with a needle-type capacitive probe (to measure solid concentration).

Numerous carbon capture, utilization, and storage (CCUS) technologies are under development to reduce CO2 emissions. To evaluate the status of a CCUS technology under development and identify potential gaps for further advancement, we have established a new technology assessment framework and are developing a decision-making tool, the technology development matrix (TDM), starting with available carbon capture technology (CCT) data. TDM is a data inventory system and screening tool. As a screening tool, it can be used for resource allocation decisions in research, development, and deployment (RD&D) by academia, government, and industry. It shares data with techno-economic analysis (TEA) and life-cycle assessment (LCA) tools as an inventory system. By using available data, this TDM framework has been demonstrated on amine-based (monoethanolamine) absorption post-combustion CO2 capture, for pulverized coal (PC) power plant flue gas, as the best available technology (BAT) for comparison. Three groups of promising post-combustion CCTs under development are presented as Alternative Technology (Alt Tech) case studies, including membrane, solid adsorption, and calcium-based chemical looping. By using available data, preliminary analysis enabled technology benchmarking and highlighted knowledge, data, and technology gaps, all providing potential future RD&D focus.

The calcium-looping process, relying on the reversible calcination/carbonation of CaCO3, is one of the most promising solution to perform thermochemical energy storage (TCES) for concentrating solar power (CSP) plants. Indeed, CaO precursors such as limestone can rely on the high energy density, low cost, large availability and nontoxicity. In this work, the study of the sound-assisted carbonation of fine CaO particles (< 50 μm) for TCES-CSP has been furthered. In particular, a kinetic study has been performed to analyze the effect of the particular carbonation conditions to be used in TCES-CSP applications, i.e. involving carbonation under high CO2 partial pressure and at high temperature. All the experimental tests have been performed in a lab-scale sound-assisted fluidized bed reactor applying high intensity acoustic field with proper frequency (150 dB–120 Hz). The carbonation kinetics has been analyzed by applying a simple kinetic model, able to properly describe the fast (under kinetic control) and slow (under diffusion control) stage of the reaction. In particular, the reaction rate, the intrinsic carbonation kinetic constant and the characteristic product layer thickness have been evaluated, also highlighting their dependence on the temperature between 800 and 845 °C; a value of 49 kJ mol−1 has been obtained for the activation energy. Finally, a good agreement between the conversion-time profiles, evaluated from the applied kinetic models, and the experimental data has been obtained.

Using traditional Chinese medicine residue biomass as the raw material and industrial limestone as a carbon absorbent, this paper investigates the production of hydrogen-rich synthesis gas in a pilot-scale calcium looping dual fluidized bed (DFB) system. The study focuses on analyzing the distribution characteristics of temperature and pressure, as well as the operation and control methods of the DFB system. The effects of reaction temperature, material layer height (residence time), water vapor/biomass ratio (S/B), and calcium/carbon molar ratio (Ca/C) on gasification products are examined. The experimental results demonstrate that as the temperature (600–700 °C), S/B ratio (0.5–1.5), Ca/C ratio (0–0.6), and other parameters increase, the gas composition shows a gradual increase in the volume content of H2, a gradual decrease in the volume content of CO, and an initial increase and subsequent decrease in the volume content of CH4. Within the range of operating conditions in this study, the optimal conditions for producing hydrogen-rich gas are 700 °C, an S/B ratio of 1.5, and a Ca/C ratio of 0.6. Furthermore, increasing the height of the material layer in the gasification furnace (residence time) enhances the absorption of CO2 by the calcium absorbents, thus promoting an increase in the volume content of H2 and the carbon conversion rate in the gas.

The Calcium-Looping (CaL) process has emerged in the last years as a promising technology to face two key challenges within the future energy scenario: energy storage in renewable energy-based plants and CO2 capture from fossil fuel combustion. Based on the multicycle calcination-carbonation reaction of CaCO3 for both thermochemical energy storage and post-combustion CO2 capture applications, the operating conditions for each application may involve remarkably different characteristics regarding kinetics, heat transfer and material multicycle activity performance. The novelty and urgency of developing these applications demand an important effort to overcome serious issues, most of them related to gas-solids reactions and material handling. This work reviews the latest results from international research projects including a critical assessment of the technology needed to scale up the process. A set of equipment and methods already proved as well as those requiring further demonstration are discussed. An emphasis is put on critical equipment such as gas-solids reactors for both calcination and carbonation, power block integration, gas and solids conveying systems and auxiliary equipment for both energy storage and CO2 capture CaL applications.

Cement industry is estimated to account for ~6–7% of anthropogenic CO2 emissions globally. Therefore, the identification of innovative solutions for their mitigation is both a priority and a challenge. The integration of carbon capture and storage technologies into the industrial production process is considered among the most viable solutions for this purpose, and calcium looping (CaL) represents one of the most promising. A key research challenge points to maximize process efficiencies and minimize production cost to decouple cement production from carbon emissions. The carbon capture process proposed in this work is a looping system where CO2 is absorbed by calcium oxide (CaO) in the first reactor (carbonator) and the calcium carbonate (CaCO3) produced is regenerated in an oxy-fired calciner. During calcination, CO2 is released from the sorbents, purified, compressed, and then made available for geological storage. In this study, greenhouse gas (GHG) emissions related to two cement production systems with CaL carbon capture are evaluated: the tail-end CaL carbon capture and the integrated CaL carbon capture. The carbon footprint is complemented with the assessment of the resources depletion mineral and elements and the demand of primary energy. An eco-design approach was pursued by carrying out a life cycle assessment to identify the environmental hotspots and which CaL integration approach presents a higher potential for cement industry decarbonization. The results of the analysis were compared with a conventional cement production process. The results show that the GHG emissions may be reduced by 74% with a tail-end approach and 71% when the CaL is fully integrated into the cement production process. When a future perspective, with higher penetration of renewable energy resources into the electricity sector, was modeled, the results showed that CaL integrated into the clinker production process is more promising in terms of reduction of the carbon footprint, rather than the tail-end solutions. Primary energy consumption from non-renewables is substantially impacted by CaL, with the integrated CaL configuration showing to be a more efficient solution because of less primary energy consumption (coal).

The calcium looping (CaL) process, which exploits the reversible calcination of calcium carbonate, has been proposed as a solution to the challenges facing deployment of concentrated solar power (CSP). As an extension of the work undertaken to date, this project proposes a novel configuration of the CSP-CaL process which may offer advantages over other proposed configurations, including a reduction in process equipment requirements, elimination of pressure differentials between vessels, and a reduction in compression duty during the energy discharge period. The results obtained through process simulation indicate that the proposed process can achieve round-trip efficiencies in the range of 32–46% and energy storage densities in the range of 0.3–1.0 GJ/m3. These parameters are strongly dependent on the residual conversion of the CaO sorbent as well as the efficiency of the power cycles used to remove heat on the carbonator side of the process.

Global warming might be mitigated if emissions were interrupted through carbon capture technologies, as there is a significant amount of comprehensive studies on them. An outline of the main gaps and trends of a technology is critical for further development. In this context, this study provides an overview of calcium looping carbon capture processes that have proven their potential and commercial viability. A bibliometric analysis is conducted on both Scopus and Web of Science database by seeking the keywords “calcium looping”, “co2 capture”, and “fluidized bed” in titles, abstracts, and keywords. Word selection was based on a list of relevant papers on the topic. These items of data have been processed and analyzed based on the number of publications and citations by emphasizing recent publication evolution, journal influence, the use of specific keywords, and co-citation. Results reveal that the European Union (EU) leads the rankings on the topic, followed by Canada. Keyword choice might have affected the number of citations. Recent studies used limestone as a sorbent and a dual fluidized bed reactor with a calciner or resistance depending on its size. Most studies are focused on technology scale-up. Although scale-up seems to be a priority, multiple studies are designed to assess the effect of steam generation and SO2 on the process.

Biomass gasification is an attractive technology and one of the pathways for producing hydrogen. Due to the variable seasons and low calorific value of biomass, the addition of coal in the gasifier is suggested because coal has a high calorific value and carbon-to-hydrogen ratio. In general, the gaseous product obtained in gasification always contains a high amount of carbon dioxide, therefore, the co-gasification of biomass and coal should integrate with the calcium looping carbon dioxide capture process to provide purified hydrogen. In this work, the model of the co-gasification of biomass and coal integrated with the calcium looping carbon dioxide capture process was developed through an Aspen Plus simulator. The developed model was used to analyze the performance of this process. The sensitivity analysis demonstrated that increasing the gasification temperature, steam-to-feed (S/F) ratio, calcium oxide-to-feed (CaO/F) ratio, and regenerator temperature could improve hydrogen production. Next, further optimization was performed to identify the optimal operating condition that maximizes hydrogen production. The results showed that the optimal operating temperature of the gasifier is 700 °C with an S/F mass ratio of 2 and coal to biomass (C/B) mass ratio of 0.75:0.25. However, the carbonator and regenerator temperatures should be 450 °C and 950 °C, respectively, with a CaO/F mass ratio of 3. Under these operating conditions, the maximum H2 content and H2 yield can be provided as 99.59%vol. (dry basis) and 92.38 g hydrogen/kg biomass feeding. The other results revealed that the energy efficiency and carbon capture efficiency of this process are 42.86% and 99.99%, respectively, and that the specific emission of released CO2 is 80.77 g CO2/MJ.

The calcium looping process has been considered as a promising technology for capturing CO2 from the flue gas, but the decay of CaO-based sorbent, which was caused by the sintering process and the poisoning of SO2, was the major obstacle for its application in industry. In this work, NaBr modification was proposed to enhance the cyclic CO2 capture capacity of the CaO-based sorbents, and the effect of SO2 on the cyclic CO2 capture capacity of the NaBr modified CaO-based sorbents was well studied. The enhancing mechanism of cyclic CO2 capture capacity of the modified CaO-based sorbents was analyzed by X-ray diffraction, field emission scanning electron microscopy, N2 physisorption, and fractal dimensions. The result showed that the SO2 in the flue gas inactivated the CO2 capture activity of the sorbents over the cycles, but the NaBr modification not only enhanced the SO2 capture capacity but also improved the cyclic CO2 capture capacity of the sorbents. The specific surface area and BJH cumulative pore volumes of the sorbents decayed rapidly over the repeated cycles, but the fractal dimensions (D) of the NaBr modified sorbents were still larger than that of unmodified reference sorbent. The “NaBr/CaO” captured 15 grams of CO2 per gram of sorbent over the 50 cycles, which was 2.2 times that of “CaO, AR”. Hence, NaBr modification would be a promising strategy to boost the CO2 capture capacity of the CaO-based sorbent in the calcium looping process that contributes to the carbon neutralization scenarios.

Coupling solar thermal energy with the hybrid TC/CG-ES (thermochemical/compressed gas energy storage) is a breakthrough option used to overcome the main challenge of solar energy, i.e., intermittent resource and low density. This paper proposes an innovative storage system that improves the competitiveness of solar thermal energy technologies compared to conventional fossil-based power plants, potentially leading to deep decarbonization of the energy and industrial sectors. This study uses thermochemical energy storage based on the calcium looping (CaL) process and takes advantage of a number of factors: high energy density (2 GJ/m3), absence of heat loss (seasonal storage), high operation temperature (high efficiency of the power plant), and use of cheap and environmentally friendly reactant feedstock (CaO/CaCO3). This work deals with the integration of the solar CaL storage system with an unconventional supercritical CO2 (s-CO2) Brayton cycle. We analyze different s-CO2 Brayton cycle layouts suitable for direct integration with the storage system. Energy integration via pinch analysis methodology is applied to the whole system to optimize the internal heat recovery and increase the efficiency of the system. A parametric study highlights how the integration of solar CaL with an intercooling Brayton cycle shows better results than the combination with the Rankine cycle that we investigated previously, resulting in net and global system efficiencies equal to 39.5 and 51.5%. Instead, the new calculated net and global system efficiencies are 44.4 and 57.0%, respectively, for TC-CG-ES coupled with the Brayton power cycle.

We report on the design of a modular, high-temperature thermochemical energy storage system based on endothermic-exothermic reversible gas-solid reactions for application in concentrated solar power and industrial thermal processes. It consists of an array of tubular reactors, each containing an annular packed bed subjected to radial flow, and integrated in series with a thermocline-based sensible thermal energy storage. The calcination-carbonation of limestone, CaCO3 ↔ CaO + CO2, is selected as the reversible thermochemical reaction for the experimental demonstration. Synthetized 4.2 mm-mean size agglomerates and 2 mm-mean size granules of CaO with 42 %wt sintering-inhibitor MgO support attained reaction extents of up to 84.0% for agglomerates and 31.9% for granules, and good cycling stability in pressure-swing and temperature-swing thermogravimetric runs. A lab-scale reactor prototype is fabricated and tested with both formulations for 80 consecutive carbonation-calcination cycles at ambient pressure using a temperature-swing mode between 830°C and 930°C. The reactor exhibited stable cyclic operation and low pressure drop, and yielded specific gravimetric and volumetric heat storage capacities of 866 kJ/kg and 322 MJ/m3 for agglomerates, respectively, and 450 kJ/kg and 134 MJ/m3 for granules, respectively.

CO2 capture by CaO in molten salts is a variant of calcium looping in which the active substances (CaO/CaCO3) are dissolved or in a slurry with inorganic molten salts. One of the main advantages is the nonexistence of degradation in the reactivity between the active material and CO2. Previous research has revealed good absorption and desorption characteristics with CaO contents up to 20 wt% in eutectic CaF2-CaCl2. The hypothesis is that the formed CaCO3 continuously dissolves in the melt, leaving highly reactive CaO readily available for the incoming CO2. In the present study, the CaO content is increased to 40 wt%, and the absorption characteristics is investigated with focus on the sorption capacity and CO2 removal rate. The chemical system is also evaluated experimentally with regards to viscosity and solubility of the formed CaCO3 during CO2 absorption, with the aim of determining chemical upscaling limitations. The results show that the practical CaO content limit is 30 wt%, in which a sorption capacity of 20 g CO2/100 g sorbent is observed, without any deterioration of the reaction kinetics. For 40 wt% CaO, the sorption capacity is higher, but on the expense of the CO2 removal rate and CaO conversion. This is attributed to a significant increase in viscosity and the solubility limit of CaCO3 being exceeded.

A novel CaO-based material supported with Ca3Al2O6 and Dy2O3 was found to show excellent performance as a thermochemical energy storage material for use in solar thermal power plants. It retains a carbonation conversion capacity of 82.7% for a period of 40 cycles, as well as exothermic heats of reaction of 582.2 kJ kg−1, up to seven times greater than other materials found in the literature. The improved performance was attributed to the greater prevention of sintering and retention of high surface area by the addition of two inert supports: Ca3Al2O6 and Dy2O3. Long-term effectiveness of the novel material was also evaluated by using a sintering model. It retains an energy storage utilization of 6.2 kg kWh−1 after 30 years of cycling, while commercial limestone would require 81 tons kWh−1 equivalent. Limestone requires replacement every six thermal cycles, making it impractical for real thermochemical energy storage implementation. The extra cost associated with the addition of supports in this CaO-based material is justified by the long-term durability, which would imply a reduction in the overall capital and operational expenditure of the plant.

In order to obtain the cheap waste calcium-based sorbent, three wasted CaCO3 precursors, namely carbide slag, chicken eggshells, and analytical reagent-grade calcium carbonate, were selected and prepared at 700 °C to form calcium-based sorbents for CO2 capture. TGA was used to test the CO2 uptake performance of each calcium-based sorbent in 20 cycles. To identify the decay mechanism of CO2 uptake with an increasing number of cycles, all calcium-based sorbents were characterized by using XRF, XRD, and N2 adsorption. The specific surface area of calcium-based sorbents was used to redefine the formula of cyclic carbonation reactivity decay. The carbonation conversion rate of three calcium-based sorbents exhibited a decreasing trend as the cycle number increased. Chicken eggshells exhibited the most significant decrease rate (over 50% compared with Cycle 1), while carbide slag and analytical reagent-grade calcium carbonate showed a flat linear decline trend. The specific surface area of the samples was used to calculate carbonation conversion for an infinite number of cycles. The carbonation conversion rates of three calcium-based sorbents were estimated to decrease to 0.2898, 0.1455, and 0.3438 mol/mol, respectively, after 100 cycles.

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.

Carbon dioxide-abated hydrogen can be synthesised via various processes, one of which is sorption enhanced steam methane reforming (SE-SMR), which produces separated streams of high purity H2 and CO2. Properties of hydrogen and the sorbent material hinder the ability to rapidly upscale SE-SMR, therefore the use of artificial intelligence models is useful in order to assist scale up. Advantages of a data driven soft-sensor model over thermodynamic simulations, is the ability to obtain real time information dependent on actual process conditions. In this study, two soft sensor models have been developed and used to predict and estimate variables that would otherwise be difficult direct measured. Both artificial neural networks and the random forest models were developed as soft sensor prediction models. They were shown to provide good predictions for gas concentrations in the reformer and regenerator reactors of the SE-SMR process using temperature, pressure, steam to carbon ratio and sorbent to carbon ratio as input process features. Both models were very accurate with high R2 values, all above 98%. However, the random forest model was more precise in the predictions, with consistently higher R2 values and lower mean absolute error (0.002-0.014) compared to the neural network model (0.005-0.024).

A novel configuration of the Ca-Cu looping process based on dynamically operated packed-bed reactors is proposed to convert blast furnace gas (BFG) into H2/N2 and highly concentrated CO2, accompanied by a large amount of high-temperature heat. Preliminary energy and mass balances of the process reveal that around 30% of the BFG can be upgraded via calcium assisted water gas shift (WGS) if only BFG is used as reducing gas in the reduction/calcination stage. A higher amount of H2/N2 can be produced by using other steel mill off gases, such as coke oven gas (COG) or basic oxygen furnace gas (BOFG), or natural gas in the regeneration of the CO2 sorbent. This decarbonized fuel gas could be used for onsite power generation or to obtain sponge iron by a Direct Reduced Iron (DRI) process, increasing the overall capacity of the steel plant. Energy efficiencies higher than 75% have been calculated, reaching maximum values around 88% in case of using natural as fuel gas for the sorbent regeneration stage. Low values for the specific energy consumption of around 1.5 MJLHV/kgCO2 and CO2 capture efficiencies higher than 95% support the further development of the proposed Ca-Cu looping process.

This study investigated the effect of HCl in biomass gasification producer gas on the CO2 capture efficiency and contaminants removal efficiency by CaO-Fe2O3 based sorbent material in the calcium looping process. Experiments were conducted in a fixed bed reactor to capture CO2 from the producer gas with the combined contaminants of HCl at 200 ppmv, H2S at 230 ppmv, and NH3 at 2300 ppmv. The results show that with presence of HCl in the feeding gas, sorbent reactivity for CO2 capture and contaminants removal was enhanced. The maximum CO2 capture was achieved at carbonation temperatures of 680 °C, with efficiencies of 93%, 92%, and 87%, respectively, for three carbonation-calcination cycles. At this carbonation temperature, the average contaminant removal efficiencies were 92.7% for HCl, 99% for NH3, and 94.7% for H2S. The outlet contaminant concentrations during the calcination process were also examined which is useful for CO2 reuse. The pore structure change of the used sorbent material suggests that the HCl in the feeding gas contributes to high CO2 capture efficiency and contaminants removal simultaneously.

The growing demand for the reduction of anthropogenic CO2 emissions has stimulated the development of CO2 capture methods. One of the best capture methods comprises the calcium looping process, which incorporates calcium-based sorbents during the calcination and carbonation cycles. Czatkowice limestone may be considered to be a prospective chemical sorbent for the calcium looping process because of its formation characteristics. This paper addresses the thermogravimetric studies conducted under varying conditions of temperature and various concentrations of CO2 during the carbonation cycles. Moreover, a kinetic analysis of the carbonation stage was performed for the calcined sample at varying temperatures. The kinetic parameters for calcination and diffusion were determined. In addition, there was an increase in the concentration of CO2 with an increased carbonation conversion. The research results demonstrate that in further cycles of carbonation/calcination, the calcium sorbent reaches a higher rate of carbonation conversion with increased levels of CO2.

Cycling high temperature CO2 capture using CaO–based solid sorbents, known as the calcium looping (CaL) process, is gaining considerable scientific and industrial interest due to the high theoretical sorbent capacity (0.78 gCO2/gCaO), the low specific cost, and the negligible environmental impact of the employed materials. In this work, we investigated the self–combustion synthesis of CaO–CaZrO3 sorbents with different CaO contents (40, 60, and 80 wt%) for use in the CaL process. CaZrO3 was used as a spacer to avoid CaO grains sintering at high temperature and to reduce the diffusional resistances of CO2 migrating towards the inner grains of the synthetic sorbent. Samples were characterized by X–ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM) analyses. The reaction between CO2 and CaO (i.e., carbonation) was carried out in 20 vol% CO2 at 650 °C and calcination (i.e., decomposition of CaCO3 to CaO and CO2) at 900 °C in pure Ar or with 85 vol% CO2 using a thermogravimetric analyzer (thermogravimetric/differential thermal analysis (TG–DTA)). The most stable sorbent was with 40 wt% of CaO showing a CO2 uptake of up to 0.31 g CO2/gsorbent and 0.26 g CO2/gsorbent operating under mild and severe conditions, respectively. The experimental data corroborated the prediction of the shrinking core spherical model in the first phase of the carbonation. A maximum reaction rate of 0.12–0.13 min−1 was evaluated in the first cycle under mild and severe conditions of regeneration.

The increase of capital investments and operation and maintenance (O&M) costs represents a current limitation to the diffusion of carbon capture systems for the clean combustion of fossil fuels. However, post-combustion systems, such as calcium looping (CaL), for CO2 capture from flue gas are the most attractive carbon capture systems since they can be installed at new plants and retrofitted into existing power plants. This work investigates the pros and cons of employing a calcium looping system for CO2 capture and also as a desulphurization unit. A preliminary techno-economic analysis was carried out comparing a base case consisting of a coal-based power plant of about 550MWe with a desulphurization unit (Case 1), the same plant but with a CaL system added for CO2 capture (Case 2), or the same plant but with a CaL system for simultaneous capture of CO2 and SO2 and the removal of the desulphurization unit (Case 3). Case 2 resulted in a 67% increase of capital investment with respect to the benchmark case, while the increase was lower (48%) in Case 3. In terms of O&M costs, the most important item was represented by the yearly maintenance cost of the desulphurization unit. In fact, in Case 3, a reduction of O&M costs of about 8% was observed with respect to Case 2.

The calcium carbonate looping cycle is an important reaction system for processes such as thermochemical energy storage and carbon capture technologies, which can be used to lower greenhouse gas emissions associated with the energy industry. Kinetic analysis of the reactions involved (calcination and carbonation) can be used to determine kinetic parameters (activation energy, pre-exponential factor, and the reaction model), which is useful to translate laboratory-scale studies to large-scale reactor conditions. A variety of methods are available and there is a lack of consensus on the kinetic parameters in published literature. In this paper, the calcination of synthesized CaCO3 is modeled using model-fitting methods under two different experimental atmospheres, including 100% CO2, which realistically reflects reactor conditions and is relatively unstudied kinetically. Results are compared with similar studies and model-free methods using a detailed, comparative methodology that has not been carried out previously. Under N2, an activation energy of 204 kJ mol−1 is obtained with the R2 (contracting area) geometric model, which is consistent with various model-fitting and isoconversional analyses. For experiments under CO2, much higher activation energies (up to 1220 kJ mol−1 with a first-order reaction model) are obtained, which has also been observed previously. The carbonation of synthesized CaO is modeled using an intrinsic chemical reaction rate model and an apparent model. Activation energies of 17.45 kJ mol−1 and 59.95 kJ mol−1 are obtained for the kinetic and diffusion control regions, respectively, which are on the lower bounds of literature results. The experimental conditions, material properties, and the kinetic method are found to strongly influence the kinetic parameters, and recommendations are provided for the analysis of both reactions.

Reaction kinetics is an important field of study in chemical engineering to translate laboratory-scale studies to large-scale reactor conditions. The procedures used to determine kinetic parameters (activation energy, pre-exponential factor and the reaction model) include model-fitting, model-free and generalized methods, which have been extensively used in published literature to model solid-gas reactions. A comprehensive review of kinetic analysis methods will be presented using the example of carbonate looping, an important process applied to thermochemical energy storage and carbon capture technologies. The kinetic parameters obtained by different methods for both the calcination and carbonation reactions are compared. The experimental conditions, material properties and the kinetic method are found to strongly influence the kinetic parameters and recommendations are provided for the analysis of both reactions. Of the methods, isoconversional techniques are encouraged to arrive at non-mechanistic parameters for calcination, while for carbonation, material characterization is recommended before choosing a specific kinetic analysis method.

Calcium looping is a promising technology to capture CO2 from the process of coal-fired power generation and gasification of coal/biomass for hydrogen production. The decay of CO2 capture activities of calcium-based sorbents is one of the main problems holding back the development of the technology. Taking carbide slag as a main raw material and Ca12Al14O33 as a support, highly active CO2 sorbents were prepared using the hydrothermal template method in this work. The effects of support ratio, cycle number, and reaction conditions were evaluated. The results show that Ca12Al14O33 generated effectively improves the cyclic stability of CO2 capture by synthetic sorbents. When the Al2O3 addition is 5%, or the Ca12Al14O33 content is 10%, the synthetic sorbent possesses the highest cyclic CO2 capture performance. Under harsh calcination conditions, the CO2 capture capacity of the synthetic sorbent after 30 cycles is 0.29 g/g, which is 80% higher than that of carbide slag. The superiority of the synthetic sorbent on the CO2 capture kinetics mainly reflects at the diffusion-controlled stage. The cumulative pore volume of the synthetic sorbent within the range of 10−100 nm is 2.4 times as high as that of calcined carbide slag. The structure of the synthetic sorbent reduces the CO2 diffusion resistance, and thus leads to better CO2 capture performance and reaction rate.

A technical evaluation of CO2 capture technologies when retrofitted to a cement plant is performed. The investigated technologies are the oxyfuel process, the chilled ammonia process, membrane-assisted CO2 liquefaction, and the calcium looping process with tail-end and integrated configurations. For comparison, absorption with monoethanolamine (MEA) is used as reference technology. The focus of the evaluation is on emission abatement, energy performance, and retrofitability. All the investigated technologies perform better than the reference both in terms of emission abatement and energy consumption. The equivalent CO2 avoided are 73⁻90%, while it is 64% for MEA, considering the average EU-28 electricity mix. The specific primary energy consumption for CO2 avoided is 1.63⁻4.07 MJ/kg CO2, compared to 7.08 MJ/kg CO2 for MEA. The calcium looping technologies have the highest emission abatement potential, while the oxyfuel process has the best energy performance. When it comes to retrofitability, the post-combustion technologies show significant advantages compared to the oxyfuel and to the integrated calcium looping technologies. Furthermore, the performance of the individual technologies shows strong dependencies on site-specific and plant-specific factors. Therefore, rather than identifying one single best technology, it is emphasized that CO2 capture in the cement industry should be performed with a portfolio of capture technologies, where the preferred choice for each specific plant depends on local factors.

This paper presents an assessment of the cost performance of CO2 capture technologies when retrofitted to a cement plant: MEA-based absorption, oxyfuel, chilled ammonia-based absorption (Chilled Ammonia Process), membrane-assisted CO2 liquefaction, and calcium looping. While the technical basis for this study is presented in Part 1 of this paper series, this work presents a comprehensive techno-economic analysis of these CO2 capture technologies based on a capital and operating costs evaluation for retrofit in a cement plant. The cost of the cement plant product, clinker, is shown to increase with 49 to 92% compared to the cost of clinker without capture. The cost of CO2 avoided is between 42 €/tCO2 (for the oxyfuel-based capture process) and 84 €/tCO2 (for the membrane-based assisted liquefaction capture process), while the reference MEA-based absorption capture technology has a cost of 80 €/tCO2. Notably, the cost figures depend strongly on factors such as steam source, electricity mix, electricity price, fuel price and plant-specific characteristics. Hence, this confirms the conclusion of the technical evaluation in Part 1 that for final selection of CO2 capture technology at a specific plant, a plant-specific techno-economic evaluation should be performed, also considering more practical considerations.

This study examined the effect of Carbon Capture and Storage units on the environmental, energy and economic performance of the Brazilian electric grid. Four scenarios were established considering the coupling of Calcium Looping (CaL) processes to capture CO2 emitted from thermoelectric using coal and natural gas: S1: the current condition of the Brazilian grid; S2 and S3: Brazilian grid with CaL applied individually to coal (TEC) and gas (TGN) operated thermoelectric; and S4: CaL is simultaneously coupled to both sources. Global warming potential (GWP) expressed the environmental dimension, Primary Energy Demand (PED) was the energy indicator and Levelised Cost of Energy described the economic range. Attributional Life Cycle Assessment for generation of 1.0 MWh was applied in the analysis. None of the scenarios accumulated the best indexes in all dimensions. Regarding GWP, S4 totals the positive effects of using CaL to reduce CO2 from TEC and TGN, but the CH4 emissions increased due to its energy requirements. As for PED, S1 and S2 are similar and presented higher performances than S3 and S4. The price of natural gas compromises the use of CaL in TGN. A combined verification of the three analysis dimensions, proved that S2 was the best option of the series due to the homogeneity of its indices. The installation of CaL in TECs and TGNs was effective to capture and store CO2 emissions, but the costs of this system should be reduced and its energy efficiency still needs to be improved.