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The attrition of CaO-based solids operating in calcium looping (CaL) post-combustion CO 2 capture systems is an important factor to consider when limestones are selected as sorbent precursors. In this work, four commercial natural limestones with similar chemical compositions but with very different mechanical properties were tested in a 30kWth calcium looping pilot plant. The main attrition mechanisms that act upon the limestones (i.e. fragmentation, decrepitation and abrasion) were identified on the basis of the evolution of their particle size distributions during the start-up and the first calcination of each batch. Great differences in the performance of the selected limestones were observed, which confirms the suitability of the experimental procedure employed for sorbent screening purposes in these high-velocity, high-temperature pilot plants. Several attrition indexes reported in the literature were tested to conclude that the Total Particle Generated Index (TPGI) and the Maximum Diameter of Particles Generated (MDPG) indexes are the most useful for quantifying attrition phenomena and rank limestones. [ABSTRACT FROM AUTHOR]

The Calcium Looping (CaL) process is a promising technology for post-combustion CO 2 capture from fossil-fired power plants and carbon intense industry. Within a CaL system, a limestone based sorbent stream is forced to circulation between two interconnected circulating fluidized bed (CFB) reactors. The main part of the CO 2 , contained in the flue gas stream is absorbed by CaO within the carbonator, whereas it is released during regeneration in the oxy-fired calciner. The feasibility of this technology was proven by numerous experimental investigations in semi-industrial scale. The next step in the development of this technology is expected to be a demonstration plant in the scale of approximately 20 MW th . The focus of this paper is the determination of the heat and mass balances and the assessment of the operability of a newly designed 20 MW th CaL demonstration plant. The investigations are based on a steady-state process model, which has been validated by experimental data from 1 MW th pilot tests. The aspect of solid entrainment during part load operation are addressed. In the present design case, a stable operation of the demonstration plant at 40 % equivalent carbonator load is feasible without additional flue gas recirculation. [ABSTRACT FROM AUTHOR]

The Calcium-Looping process is a promising thermochemical energy storage method based on the multicycle calcination-carbonation of CaCO 3 -CaO to be used in concentrated solar power plants. When solar energy is available, the CaCO 3 solids are calcined at high temperature to produce CaO and CO 2 , which are stored for subsequent utilization. When power is needed, these reaction by-products are fed into a carbonator reactor where energy is released from the exothermic carbonation reaction. In comparison with currently commercial energy storage systems, such as solar salts, the Calcium-Looping process presents several benefits such as the feasibility to work at significantly higher power cycle temperatures, a higher energy storage density and the possibility to store energy in the medium-long term. The present manuscript analyzes a number of novel Calcium-Looping configurations for energy storage combined with CO 2 cycles in a solar tower plant. The high overall efficiencies achieved (32–44%, defined as the ratio of net electric power production to net solar thermal power entering the calciner) indicate a potential interest for the integration of the Calcium-Looping process in Concentrating Solar Power Plants, although major technological challenges related to the design of the solar receiver and of the high temperature solids handling devices remain to be faced. [ABSTRACT FROM AUTHOR]

Carbide slag, as a kind of typical industrial waste, was proposed as a CO2 sorbent in the calcium looping process. The CO2 capture performance of carbide slag was investigated in a bubbling fluidized bed reactor (BFBR) under fluidization conditions. A surface reaction‐controlled kinetic model was employed to describe the carbonation kinetics of carbide slag during the chemical reaction‐controlled stage. The results show that the values of k, tcrcs, and Xu, which respectively denote the reaction rate constant, duration time, and final carbonation conversion in the chemical reaction‐controlled stage, decrease with the cycle number, due to the sintering of the sorbents. The microstructure of calcined carbide slag leads to higher CO2 diffusion resistance in carbide slag than that in limestone, causing lower k and longer tcrcs compared with limestone. The larger BET areas and pore areas of calcined carbide slag provide additional surface for the reaction of CaO and CO2. Therefore, the Xu values of carbide slag are higher than those of limestone after 5 cycles. Reaction conditions have a significant effect on the carbonation process of carbide slag. 850–900 °C is the optimum temperature range for the calcination of carbide slag. The gas‐solid transfer is strengthened at a higher fluidization number, enhancing the CO2 capture of carbide slag. The pores of the larger particles are more easily blocked due to the formation of CaCO3 layer, and the Xu of the carbide slag with a larger particle size is lower. [ABSTRACT FROM AUTHOR]

Experimental investigations were carried out to determine the intrinsic kinetic parameters of the carbonation reaction of limestone (CaCO3) in a calcium looping (CL) process for (1) dilute carbon dioxide conditions (1 vol % CO2 in air) and (2) dilute methane conditions (1 vol % CH4 in air). The random pore model (RPM) was applied to estimate the gas‐solid heterogeneous kinetic parameters and further used to study the effects of bed temperature, fluidizing velocity and inventory size on carbon dioxide capture and methane combustion. Experiments were conducted in a single lab‐scale bubbling fluidized bed reactor on calcined limestone at a range of temperatures (450–600°C) and inventory sizes (8–16 g). The activation energy determined for the carbonation reaction in dilute CO2 and dilute CH4 conditions were found to be 25.7 × 103 kJ/kmol and 22.3 × 103 kJ/kmol, respectively. These values were compared with the conventional calcium looping process (12–15% CO2 in flue gas). © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1312–1318, 2018 [ABSTRACT FROM AUTHOR]

Calcium looping (CaL) is an emerging CO 2 capture technology that uses high temperature circulating fluidized beds, CFB, with CaO particles as functional material and that can be retrofitted to existing power plants. Its similarity to existing CFB combustion technology has made it possible to demonstrate its feasibility at MW scale and to obtain an accurate estimation of its energy efficiency and cost. This work analyzes a novel CaL system that incorporates recent developments tested at large pilot scale, where the calciner operates under an oxygen-rich atmosphere and the sorbent is reactivated by recarbonation allowing a reduction in the thermal input needed in the calciner. It has been shown that, when this 2nd generation CaL system is coupled to existing large sources of flue gases and biomass is used as fuel in the calciner, the full system becomes carbon-negative, with CO 2 emissions as low as −245.3 kg CO2 /MWhe since the biomass source is carbon-neutral. The net electric efficiencies achieved for the entire system including CO 2 capture are higher than 33%. Moreover, the total investment required for this CaL system can be reduced by more than 30% compared to conventional CaL systems due to the reduced footprint of the calciner-related equipment when the calciner is fired with pure oxygen. [ABSTRACT FROM AUTHOR]

Calcium looping (CaL) for post-combustion CO 2 capture is an emerging technology that has developed rapidly due to its similarities with existing circulating fluidized bed combustion boilers. This work presents an alternative calciner configuration as it is applied in La Pereda CaL pilot plant, the aim of which is to minimize or altogether eliminate the need to recycle CO 2 during the oxy-fuel combustion of coal in the calciner. The strategy underlying this configuration is to reduce the heat demand in the calciner, and hence the energy penalty of the whole CaL system. After undergoing several modifications, the pilot was able to operate under O 2 -rich conditions in a series of experiments with a coal thermal input of up to 2.0 MW th in the calciner and 75 O 2 % v in the oxidant. No hot spots were detected in the calciner reactor in these conditions due to the thermal ballast effect produced by the circulating solids from the carbonator. This new operation mode in the calciner in no way undermined the performance of the carbonator and CO 2 capture efficiencies close to the maximum limit permitted by the equilibrium were achieved during the experimental campaigns. In short, the results of this work indicate that it may well be possible to operate the calciner of a CaL system using pure oxygen. [ABSTRACT FROM AUTHOR]

The utilisation of coal as fuel for the production of energy will grow parallel with the increase of the cost of oil in the next years. This paper aims to investigate the integration between two clean coal technologies: Calcium Looping (CaL) process and Molten Carbonate Fuel Cell (MCFC) in order to produce a high CO 2 concentrated stream. The main goal of this work is to find out the optimum working point of a system using CaL and MCFC technologies, coupled together, to produce decarbonised energy from coal as a primary energy source. The integrated system of CaL with MCFC presented in this paper, is fed with a raw syngas coming from coal gasification [1]. The raw syngas is decarbonised using calcium oxide as solid sorbent in the first reactor of CaL (carbonator), subsequently the clean syngas flowing out of the carbonator is used as anodic fuel for an MCFC. The thermal regeneration of solid sorbents occurs burning methane with air producing a CO2 reach gas, that feeds the cathodic compartment of MCFC. This configuration allows to concentrate the CO2 from cathode side to anode side of the MCFC, using internal electrochemical reactions of the cell, producing electric power at the same time. This work has been structured to tackle the coupling of CaL with MCFC using a combined numerical and experimental approach. Thus the investigation of the possible integration has been carried out starting with a lumped model simulating the whole calcium looping process. The model was used to investigate the behaviour of the CaL system when varying the amount of solid sorbent used in the process. Data coming from the model in terms of gas composition flowing out from CaL reactors were subsequently validated experimentally simulating different operating conditions in a MCFC single cell (81 cm2). Performance of the MCFC was monitored with polarisation curves and power density curves, aiming to integrate experimentally the electric behaviour of the whole system, in order to have a first validation of the two systems working together. [ABSTRACT FROM AUTHOR]

The experimental characterization of sorbents for Calcium Looping (Ca-L) processes is generally accomplished by thermogravimetric analysis or by using single fluidized bed bench scale reactors. These methods may present limitations, the most significant being the poor ability to reproduce the thermal history that sorbent particles experience in a real Ca-L plant. This limitation may severely affect the correct evaluation of the sorbent behavior in terms of CO 2 capture capacity and attrition. In this study, a purposely developed experimental apparatus is applied for Ca-based sorbent testing under conditions that simulate a realistic thermal history of the sorbent. The apparatus consists of two identical lab-scale bubbling beds (Twin Beds - TB) operated batchwise as the calciner and the carbonator, respectively. The reactors are connected to each other via a rapid solids pneumatic transfer line, designed so as to enable rapid and selective transfer of the sorbent from one reactor to the other at the end of each calcination/carbonation stage. The two beds consist mostly of coarse-grained silica sand, acting as a thermal ballast, to which sorbent samples to be characterized are added. The TB apparatus has been used to investigate the effect of the thermal history on the performance of two limestones, in terms of CO 2 capture capacity and attrition tendency, upon multiple calcination/carbonation cycles under the typical operating conditions of the Ca-L process. The results have been compared with those obtained for the same sorbents carried out in a single lab-scale fluidized bed reactor (SB) and under the same operating conditions. The comparison showed that the CO 2 capture capacity in the TB system is larger than that found in SB tests for both sorbents. On the contrary, the absence of strong thermal shocks in the TB experiments leads in general to a decrease of the attrition tendency, with a reversal in terms of generated fines between calcination and carbonation stages. Indeed, the generation rate of fines measured in the TB tests during carbonation is smaller than that measured in the corresponding calcination stage, which is opposite to what was found during the tests in the SB device. These findings indicate that the sorbent thermal history plays a non-negligible role on its CO 2 capture performance in Ca-L. [ABSTRACT FROM AUTHOR]

Calcium (or carbonate) looping (CaL) is a high-temperature process to capture CO 2 from industrial installation using CaO-based materials as the sorbent. A large number of natural and synthetic CaO-based sorbents for CO 2 capture have been developed and investigated in the laboratory by cycling the material between a low-temperature carbonation stage and a high-temperature calcination stage. We demonstrate the importance of the exact experimental protocol chosen to transition from the carbonation to the calcination step by varying the CO 2 concentration and the heating rate while keeping the conditions during the actual carbonation (650 °C, 15 vol.% CO 2 ) and calcination (950 °C, 80 vol.% CO 2 ) stages constant. The experiments were performed in a thermogravimetric analyser, the equipment most frequently used in investigations of the cyclic CO 2 uptake, using a natural limestone as the sorbent. Our results show that the reaction conditions under which the CaCO 3 is decomposed to CaO determines the cyclic performance of the sorbent, whereas the effect of the CO 2 concentration during the set calcination stage (which usually begins after most of the CaCO 3 has been converted to CaO) appears to be insignificant. Higher heating rates facilitate a higher cyclic CO 2 uptake because the carbonate phase, known to be prone to sintering, is exposed to higher temperatures for a shorter time. The reaction conditions during the transition period crucially affect the CO 2 uptake determined in laboratory tests and hence need to be reported in full detail, yet this is currently hardly the case. Otherwise it is unclear whether differences in the CO 2 uptake of different CO 2 sorbents are due to modifications of the material or variations in the testing protocol. [ABSTRACT FROM AUTHOR]

The application of an ethanol pre-treatment step on biomass-templated calcium looping sorbents resulting in an improved pore structure for cyclic CO 2 capture was investigated. Three ethanol solutions of varying concentrations were used with an improved pore and particle structure, and thermogravimetric analyser CO 2 carrying capacity arising with the 70 vol% ethanol solution. The extent of attrition of these sorbents was tested within a fluidised bed reactor and compared against an untreated sorbent and a limestone base case. It found that despite the ethanol-treated sorbents displaying an admirable CO 2 carrying capacity within the thermogravimetric analyser even under realistic post-combustion conditions, this was not translated equivalently in the fluidised bed. Attrition and elutriation of the biomass-templated sorbents was a significant issue and the ethanol pre-treatment step appeared to worsen the situation due to the roughened surface and mechanically weaker structure. [ABSTRACT FROM AUTHOR]

Carbon capture and storage is expected to play a key role in decarbonisation of the power and industrial sectors, with calcium looping (CaL) being regarded as a well-developed technology that can reduce energy and economic penalties associated with mature technologies. Nevertheless, retrofits of CaL to coal-fired power plants result in net efficiency penalties of 5–8% points. The state-of-the-art CaL configurations assume that, similarly to oxy-fuel combustion systems, CO 2 needs to be recycled to moderate the temperatures in the calciner. This study aims to assess the feasibility of CaL with no CO 2 recirculation to the calciner via pilot plant testing and techno-economic analysis. The results collected during the experimental trials indicated that the temperatures inside of the calciner were within 930–950 °C, which were within the commonly reported operating temperature range of that reactor. Furthermore, the techno-economic analysis of the CaL retrofit to a conventional 580 MW el coal-fired power plant indicated that operation of CaL without CO 2 recirculation will have a negligible effect on the net thermal efficiency of the entire system. Nevertheless, reduction in the size of the system resulted in a 21.7% reduction in the specific capital cost, and thus a 14.3% and 27.4% reduction in the levelised cost of electricity and cost of CO 2 avoided, respectively. Therefore, CaL with no CO 2 recirculation can be considered as a technically and economically feasible option to reduce the economic penalty associated with this emerging technology. [ABSTRACT FROM AUTHOR]

Calcium looping, basing on sorption/desorption cycles, is a novel and promising approach to capture CO 2 from flue gas of power plant. In the desorption process, sulfation inevitably occurs accompanying the dominant calcination of sorbents due to the in-situ combustion of coal, and it demonstrates an interesting and representative consecutive multi-reaction mode which is different from the typical sulfation patterns. Unfortunately, the process is still lack of good understanding and accurate simulation. Here, we report our work on the development of a particle model involving the consecutive reactions, geometrical evolution, and mass/heat transfer. Then, the interactive behaviours, and effects of reaction conditions and particle parameters on the temporal and spatial changes in particle-grain geometry, the successive conversion of CaCO 3 , CaO and CaSO 4 are studied. It shows that the model developed could get a more precise simulation than the conventionally used separate calcination/sulfation assumption, and clearly identify the interaction between calcination and sulfation. Furthermore, it is observed that gas concentrations, size of the particle and its grains generate the most pronounced impacts on the consecutive reactions under the conditions of calcium looping. [ABSTRACT FROM AUTHOR]

Calcium looping process is well considered as one of the most promising technologies for trapping CO 2 from flue gas. But the drastic decay of CO 2 capture capacity and the severe attrition of the CaO-based sorbents are the two main obstacles for the calcium looping process. In order to enhance the CO 2 capture capacity and the anti-attrition property of the CaO-based sorbents, an extrusion-spherization method was proposed by biomass templating method to manufacture spherical sorbents. In addition, the effects of three components of biomass, lignin, cellulose and hemicellulose in the spherical sorbents on the cyclic CO 2 capture capacity were investigated in details. The CO 2 capture performance of the sorbents and pyrolysis of three biomass components were test by a simultaneous thermal analyzer (STA), and the attrition resistance properties of the sorbents were examined by a friability tester (FT). The microstructure of the sorbents was measured by N 2 adsorption/desorption measures, an X-ray diffraction apparatus (XRD) and a field emission scanning electron microscope apparatus (FESEM). Results showed that cellulose and hemicellulose templating processes were beneficial to the CO 2 capture performance of the sorbents, whereas lignin was detrimental. The BET surface area of the molded sorbents increased drastically when templated with cellulose or hemicellulose. The binder effect of the three components on the modeled sorbents followed the order: lignin > cellulose > hemicellulose. Extrusion-spherization process is a promising technology to manufacture spherical tough sorbents. Considering the effect of CO 2 capture capacity and the attrition resistance property, the optimal templating component of biomass is cellulose. [ABSTRACT FROM AUTHOR]

This work reports the Calcium-Looping (CaL) multicycle performance under energy storage and CO 2 capture conditions of different Al-composites prepared by milling mixtures of nanoalumina and natural limestone powders. The micro- and nanostructure of the composites have been analyzed by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy as affected by the type of CaL conditions employed, either for energy storage in Concentrated Solar Power (CSP) plants or for post-combustion CO 2 capture. Two types of calcium aluminates are formed under these diverse CaL conditions. A calcium aluminate with ratio Ca/Al < 1 (Ca 4 Al 6 O 13 ) is formed under CaL-CSP conditions, which helps stabilize the CaO microstructure and mitigate pore-plugging. On the other hand, a crystalline phase Ca 3 Al 2 O 6 is formed (Ca/Al > 1) under CaL-CO 2 capture conditions presumably due to the higher calcination temperature, which withdraws from the sorbent a relatively higher amount of active Ca. Moreover, the addition of nano-alumina, and the consequent generation of calcium aluminate, affects in a diverse way the microstructure and morphology of the CaO particles as depending on the CaL application, which critically modifies the performance of the composites. [ABSTRACT FROM AUTHOR]

Carbonate looping, based on the reversible gas–solid reaction of CaO with CO 2 , is considered as a promising alternative to amine scrubbing for post-combustion CO 2 capture. Solid sorbents suffer however from degradation, mainly due to thermal sintering and elutriation of fine particles due to enhanced attrition rates in fluidized-bed reactors. In this work, a previously developed synthetic Zr-promoted CaO-based CO 2 sorbent was tested in a fluidized bed reactor unit to determine its performance in cyclic CO 2 capture over various operating conditions, relevant to industrial application. The material exhibited very high carbonation conversion (60–85%) during pre-breakthrough under all investigated conditions, with more than 75% CO 2 removal. The addition of steam in both the carbonation and calcination steps resulted, not only in higher conversions, but also in significantly enhanced cyclic stability. Deactivation was less than 16% after 20 consecutive cycles. The performance of the sorbent was further tested under lower temperature difference between carbonation (680 °C) and calcination (750 °C), a scheme more favourable for utilizing the heat generated by the highly exothermic carbonation reaction for the thermal demands of the calciner in the actual process. The material displayed similar carbonation conversion, but inferior performance in terms of stability. Advanced post-reaction characterization with in-situ XRD revealed that even though the sintering effect was more limited due to the lower calcination temperature, calcination of CaCO 3 was incomplete, rendering a small fraction of the sorbent inactive for CO 2 capture. Under severe calcination conditions (920 °C and 80 vol% CO 2 concentration) the sorbent maintained more than 70% of its initial sorption capacity (7.1 mol of CO 2 /kg of sorbent after 20 cycles), a value more than 5 times higher compared to natural limestone. [ABSTRACT FROM AUTHOR]

[Display omitted] • MgO promotes Ni-CaO to achieve an efficient and stable calcium chemical dual looping. • 720 °C is the optimum temperature for CaLDRM and CaLODRM reactions. • The synergy of MgO and POM reduces CO pollution in the capture stage due to coke deposition oxidized by CO 2. • Oxygen facilitates the elimination of coke deposition and enhances the resistance of the material to coke deposition. • Obtain H 2 /CO syngas with a regulated ratio. Calcium-looping dry reforming of methane (CaLDRM) implemented on Ni-CaO dual-functional materials (DFMs) is a promising solution to achieve integrated CO 2 capture and conversion. However, the sintering and coke deposition of DFMs and the difficulty of adjusting the H 2 /CO ratio in syngas limit the application of CaLDRM. In this work, partial oxidation of methane (POM) reaction was introduced into the CaLDRM process to form a novel Calcium-looping partial oxidation and dry reforming of methane process (CaLODRM) that relies on the developed MgO-modified Ni-CaO DFMs. The effects of different POM to DRM ratios on the reactivity and stability of MgO-modified Ni-CaO were investigated. The results demonstrated that the introduction of POM improved the resistance of the material to coke deposition and allowed the molar ratio of H 2 /CO in the product to be freely regulated between 1.1 and 1.43. When the DRM to POM ratio is 1:1, the coke deposition of Ni-CaMg after 10 CaLODRM cycles was only 0.0120 g coke /g material , which is less than half of the CaLDRM. Therefore, combining POM with CaLDRM is beneficial for producing syngas that meets different industrial needs and thus have good prospects for industrial applications. [ABSTRACT FROM AUTHOR]

• Two configurations of calcium looping for a cement plant are analyzed. • Replacing oxyfuel combustion with electrification and thermal energy storage. • The proposed system reduces the energy consumption for CO 2 capture. • The CO 2 avoidance cost achieves 58.2 $/t-CO 2 at a production rate of 3000t-clinker/day. • The price of renewable electricity dominates the operation cost. Decarbonization of the cement industry is an important goal in the carbon neutralization vision. Calcium looping is a promising decarbonization method in the cement industry due to the well-established solid management system and the direct utilization of deactivated sorbent in cement manufacturing. Oxyfuel combustion is often used in the calcium looping to obtain high-purity CO 2 , yet results in large capital expenditures on the air separation unit and high electricity and fuel consumption. In this work, we propose an electrified calcium looping process which uses electric heating from renewables and thermal energy storage to replace fossil fuels. The CO 2 generated in the calciner is directly separated with CO 2 as the heat transfer fluid. The proposed process in a cement plant is assessed in the energy, environment, and economic aspects with both tail-end configuration and integrated configuration. Compared to conventional oxyfuel-based calcium looping, electrified calcination can reduce the primary energy consumption in cement manufacturing from 7458.0 MJ/t-clinker to 6484.0 MJ/t-clinker in the tail-end configuration and from 5320.9 MJ/t-clinker to 4996.6 MJ/t-clinker in the integrated configuration, at a CO 2 capture efficiency of 90%. The reduced fuel consumption decreases CO 2 emissions and capital expenditures for the CO 2 capture system. Replacing oxyfuel with electrification and thermal energy storage brings only a limited reduction in the cost of CO 2 avoidance in the integrated configuration, and the economic benefits can be significantly improved with lower-priced renewable energy. This work provides insights into the applications of cost-effective renewable energy, electric heating, and thermal energy storage in calcium looping-based industrial decarbonization. [ABSTRACT FROM AUTHOR]

Cyclic adsorption by using of bio-waste eggshell particles as a cheap, accessible and environmentally friendly CaCO 3 source has been considered as one of the important methods to decrease or remove CO 2 from the flue gas. However, deactivation of eggshell particles and CO 2 capture capacity decaying with increasing the cycle's number remained as an important challenge. Using metal nitrates as one of the modification methods has been proposed by the researchers to overcome this problem. Current study investigates the influence of three metal nitrates of Al, La and Mg added to the eggshell particles via successive incipient wetness impregnation (SIWI) method to improve their adsorption performance. The TGA results at the end of the 20th carbonation/calcination cycle revealed a meaningful relationship between CaO molar conversion of eggshell modified with metal nitrates and their crystallite size as well as the surface area of the sorbents, so that the smaller the crystal size and the larger the surface area, the higher the molar conversion of CaO could be achieved. Due to the highest conversion obtained for Mg-containing sample, the effect of different weight percentages of this additive was also investigated. Results showed that 5 wt% MgO contained eggshell particles could be reported as the most outstanding sample for its improved molar conversion, capture capacity at the end of 20th carbonation/calcination cycle and BET surface area, which were 30.18%, 0.23 gr CO 2 /gr adsorbent and 3.5 m2/g while the corresponding amounts for raw eggshell were 17.26%, 0.11 gr CO 2 /gr adsorbent and 1.63 m2/g, respectively. [Display omitted] • SIWI method was used to obtain the novel metal containing Ca-based sorbents. • Three kinds of metal nitrates (Al, La and Mg) was added to the eggshell particles. • Prepared adsorbents were subjected to calcination/carbonation cycles in TGA. • Magnesium nitrate led to a sorbent with fluffier structure and higher porosity. • Effect of MgO weight percentages on CO 2 capture capacity was considered. [ABSTRACT FROM AUTHOR]

The calcium looping technology is one of the most promising technologies for capturing and storing CO 2. This technology has been evaluated with a variety of sorbents and conditions in previous works, but the inlet CO 2 -ladden gas has typically been a flue gas from combustion, which typically has a composition of 10–20% CO 2 and 80–90% N 2. On the other side, the performance of the calcium looping process for CO 2 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% CO 2 , 60% CH 4) 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 CO 2 -capture performance of calcium looping improves when using biogas as inlet CO 2 -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 CH 4 to CO 2 ratio tested is not remarkable, showing that the potentialities of the process in this aspect can be adapted to several biogas producing feedstocks. • Study of calcium looping process for biogas upgrading. • Higher CO 2 -capture for biogas than for combustion flue gas. • Sorbent storage at ambient temperature within cycles does not affect conversion. • The impact of the CH 4 -to-CO 2 ratios tested is not remarkable.". [ABSTRACT FROM AUTHOR]

A composite CaO-based sorbent/catalyst (Fe/CaO-CA, CA stands for Ca 12 Al 14 O 33) with good cyclic CO 2 uptake characteristics, mechanical stability and tar reforming performance for the carbon-negative biomass calcium looping gasification (CLG) technology is prepared by mechanical mixing method. Different synthesis parameters regarding cyclic CO 2 capture and Fe/CaO-CA's mechanical strength have been investigated. Different reaction conditions, such as low carbonation temperature, high calcination temperature, long cycles, and large particle size, were also investigated using a thermogravimetric analyzer. Results showed Fe/CaO-CA performed better in mechanical strength and carbonation when it was prepared by calcination at 750 °C for 4 h. In the carbonation temperature range from 650 °C to 850 °C, 750 °C was more favourable to promote CO 2 capture during cyclic reactions. Fe/CaO-CA still exhibited promising CO 2 uptake characteristics under severe calcination conditions, including high CO 2 partial pressure, high temperature and long-term response up to 40 cycles. Additionally, the effect of Fe/CaO-CA on tar removal enhancement was also studied via the reforming of 1-methyl naphthalene (1-MN) by using a self-designed fixed-bed reactor. Fe/CaO-CA presented the maximum 1-MN conversion and the highest H 2 yield (0.15 mol h−1 g−1) compared to the other three candidate samples (CaO, CaO-CA and Fe/CaO). Furthermore, Fe/CaO-CA showed the largest CO 2 uptake capacity and the least amount of coke deposition during tar reforming. [Display omitted] • A composite sorbent/catalyst is prepared by mechanical mixing. • The material works well in CO 2 uptake, mechanical strength and tar reforming. • Effects of synthesis variables on CO 2 capture and mechanical strength are analyzed. • The cyclic CO 2 capture performance is evaluated especially under harsh conditions. • H 2 yield was increased by enhancing tar reforming and coke inhibition. [ABSTRACT FROM AUTHOR]

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.

A novel calcium looping (CaL) process integrated with a spent bleaching clay (SBC) treatment is proposed whereby fuels and/or heat from regeneration of SBC provide extra energy for the calcination process, in addition, the regenerated SBC can be used to synthesize enhanced CaO-based sorbents. Different kinds of composite samples were prepared with the regenerated SBC and/or aluminate cement at various doping ratios via a pelletization process. All pellets were subjected to thermogravimetic analyzer tests employing severe reaction conditions to determine the optimal doping ratios and regeneration method for the SBC based sorbents. These results demonstrate that pellets containing combustible components showed higher CO 2 uptakes, due to the improved pore structure, which was verified by N 2 adsorption measurements. The as-prepared sorbent “L-10PC” (90 wt.% CaO/10 wt.% pyrolytic SBC) achieved a final CO 2 uptake of 0.164 g(CO 2 ) g(calcined sorbent) −1 after 20 cycles, which was 67.3% higher than that of natural limestone particle. A new larnite (Ca 2 SiO 4 ) phase was detected by X-ray diffraction analysis, however the weak diffraction peak associated with it indicated a low content of larnite in the pellets, which produced a smaller effect on performance compared to cement. A synergistic effect was achieved for a sample designated as “L-5PC-10CA” (85 wt.% CaO/5 wt.% pyrolytic SBC /10 wt.% cement), which resulted in the highest final uptake of 0.208 g(CO 2 ) g(calcined sorbent) −1 after 20 cycles. Considering the simplicity of pyrolysis regeneration process and the excellent capture capability of pellets doped by pyrolytic SBC, the proposed system integrating CaL with SBC pyrolysis treatment appears to offer particular promise for further development. [ABSTRACT FROM AUTHOR]

Calcium looping CO 2 capture is a promising technology to reduce CO 2 emissions from cement production. Coal has been seen as a logical choice of fuel to drive the calcium looping process as coal is already the primary fuel used to produce cement. This study assesses the impact of using different fuels, namely coal, natural gas, woody biomass and a fuel mix (50% coal, 25% biomass and 25% animal meal), on the environmental performance of tail-end calcium looping applied to the clinker production at a cement plant in North-western Europe. Process modelling was applied to determine the impact of the different fuels on the mass and energy balance of the process which were subsequently used to carry out a life cycle assessment to evaluate the environmental performance of the different systems. Using natural gas, biomass or a fuel mix instead of coal in a tail-end calcium looping process can improve the efficiency of the process, as it decreases fuel, limestone and electricity consumption. Consequently, while coal-fired calcium looping can reduce the global warming potential (life cycle CO 2 emissions) of clinker production by 75%, the use of natural gas further decreases these emissions (reduction of 86%) and biomass use could results in an almost carbon neutral (reduction of 95% in the fuel mix case) or net negative process (−104% reduction in the biomass case). Furthermore, replacing coal with natural gas or biomass reduces most other environmental impact categories as well, mostly due to avoided impacts from coal production. The level of improvement strongly depends on whether spent sorbent can be utilized in clinker production, and to what extent sequestered biogenic CO 2 can reduce global warming potential. Overall, the results illustrate the potential of using alternative fuels to improve the environmental performance of tail-end calcium looping in the cement industry. [ABSTRACT FROM AUTHOR]

An ever more environmentally conscious society demands the use of green, sustainable and high-efficiency renewable energy resources. However, large-scale energy storage remains a challenge for a deep penetration of power produced from renewables into the grid. The Calcium-Looping (CaL) process, based on the reversible carbonation/calcination of CaO, is a promising technology for thermochemical energy storage (TCES) in Concentrated Solar Power (CSP) plants. Natural limestone to be used as CaO precursor is cheap, non-toxic and abundant. Nevertheless, recent works have shown that carbonation of CaO derived limestone at optimum conditions for TCES is limited by pore-plugging, which leads to severe deactivation for large enough particles to be employed in practice. In our work, we have synthesized inexpensive CaO/SiO 2 composites by means of a biotemplate method using rice husk as support. The morphological and compositional features of the biomorphic materials synthesized help improve the CaO multicycle activity under optimum CSP storage conditions and for particles sufficiently large to be managed in practical processes. [ABSTRACT FROM AUTHOR]