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Granulation is an effective method to mitigate the issue of CaO-based sorbent elutriation in the calcium looping process. To further enhance CO2 capture performance of CaO-based pellets, pore-formi...

Loss-in-capacity of carbide slag in CO2 capture restricts the development of industrial wastes in calcium looping technology. In this work, a novel Mn/Mg-copromoted carbide slag was prepared using carbide slag, dolomite and trace Mn(NO3)2 additive. Experimental tests were carried out in the fixed-bed reactor to evaluate how the preparation and the reaction conditions influenced the CO2 capture performance of Mn/Mg-copromoted carbide slag during calcination/carbonation cycles. Results show that MgO diminishes the sintering of synthetic sorbents. The optimal Mn/Mg-copromoted carbide slag (mass ratio of CaO:MgO:MnO2 = 89:10:1) exhibits the highest CO2 capture capacity of 0.52 g/g after 10 cycles under the severe calcination condition (100 % CO2, 950 °C) and the wet carbonation condition (15 % CO2/20 % steam/N2), which is 1.7 times as high as that of untreated carbide slag. MnO2 positively affects the slow carbonation stage by enhancing the electron transfer between CaO and CO2. Observations of the morphology of Mn/Mg-copromoted carbide slag indicate that the stabilized CO2 capture performance is mainly attributed to porous structure, MgO as the skeleton and MnO2 as an electron-transfer promoter.

In this work, a CaO/CeO2 composite was used in a process that coupled the calcium looping for CO2 capture and CaO/H2O thermochemical heat storage. A four fixed-bed reactor system was used to invest...

The high-temperature attrition behavior of nano CaO-based CO2-reactive adsorbents was studied during multiple calcium looping (CaL) processes with a carbonation temperature of 600 °C and a calcination temperature of 800 °C using a fluidized bed reactor. The effect of the cyclic run number and the presence of steam on attrition were analyzed under a given fluidization number. The features of the hot attrition revealed that the attrition of the adsorbents occurred mainly in the first 15 cycles, and the maximum average single attrition loss reached about 3.6% in the first five cycles. With the CaL run number increasing, the average single attrition loss decreased, was basically stable below 0.5% between 20 and 60 cycles, and was less than 0.2% during 60–90 cycles. Moreover, because of the presence of steam, the attrition loss increased by about 8.9% in the calcination stage while attrition loss only increased by 2.8% in the carbonation stage. The particle size distribution, scanning electron microscopy, and energy-dispersive spectrometry tests showed that the attrition was mainly due to the surface flaking, and the high-temperature steam made adsorbent particles more prone to cracking. Additionally, attrition mainly occurred in the calcium-rich area, which was the weak point of the mechanical strength of the adsorbents.

In this study, an in situ weighting system was used to study the thermal behavior of dried municipal sludge (MS) in the flue gas exiting from calcium‐looping (Ca‐L) process. The results showed that mass loss peak, initial decomposition temperature, and decomposition complete temperature moved to high‐temperature zone with increased heating rate. However, they moved to low‐temperature zone at higher O2 and CO2 concentrations. Apparent activation energy (E) and preexponential factor (A) increased with the increase of heating rate and O2 concentration and decreased with the increase of CO2 concentration. The heating rate has the greatest effect on the thermal decomposition of dried MS. With the heating rate increasing, the maximum mass loss peak occurred from 301 to 493°C, the corresponding E and A increased from 36.14 to 45.69 kJ mol−1 and from 29.58 to 321.4 min, respectively. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

The aim of this work is to prepare the nano-CaO–CaTiO3 adsorbents with both high CO2 sorption capacity and high durability. A series of nano-CaO–CaTiO3 adsorbents with different CaTiO3 grain sizes ...

Lime mud, a kind of industrial waste that produced in paper mill, was proposed as CO2 sorbent in calcium looping process. The carbonation performance of the lime mud was investigated in a dual‐fixed bed reactor (DFR) and a thermogravimetric analyzer (TGA). The carbonation kinetics of the lime mud in the chemical reaction controlled stage was analyzed by a surface reaction‐controlled kinetic model. The results show that the lime mud presents much poorer carbonation performance during the chemical reaction controlled stage compared with the limestone, mainly due to the high content of chlorine in the lime mud. A prewash treatment process was used to decrease the chlorine content to mitigate the sintering of the lime mud when calcined at high temperature. After prewash treatment, the prewashed lime mud shows much higher CO2 capture capacity during the chemical reaction controlled stage compared with the lime mud. A prolonged carbonation process successfully further enhances the microstructure and improves the carbonation performance of the prewashed lime mud in the chemical reaction controlled stage. The lime mud can be effectively used as CO2 sorbent in calcium looping process after prewash treatment and the following prolonged carbonation treatment.

This paper investigates the equilibrium performance of CaO hydration and CaCO3/Ca(OH)2 co-calcination in calcium-looping processes. A novel lime hydration configuration is proposed, introducing saturated steam as the reactivating reagent and direct-heat-removal medium. The proposed hydrator generates a substantial amount of superheated steam, used elsewhere as required. The slaked lime and limestone are calcined simultaneously in a methane-concentrated oxy-fuel calciner. The equilibrium performance of the co-calciner is studied at different reactor temperatures, operating pressures, solid/gas feed ratios and feed compositions. A correlation is proposed which estimates the required gaseous feed composition for autothermal, coke-free and complete sorbent regeneration using this novel technology.

The calcium looping (CaL) process is a promising second-generation carbon capture technology for post-combustion CO2 capture from power and industrial plants. The CO2 in a flue gas stream is captured by means of the reversible carbonation reaction. The CaL process is based on two coupled circulating fluidized bed reactors (carbonator and calciner) using natural limestone as sorbent. Until now, remarkable progress has been made in terms of long-term CaL pilot testing and evaluation in various test rigs. Mainly fossil fuels have been applied as supplementary heat source in the calciner. This work presents first results from long-term pilot testing of the CaL process in the 1 MWth CaL pilot plant at Technische Universitat Darmstadt, firing solid recovered fuels under real oxy-fuel conditions in the calciner. The flue gas to be decarbonized in the carbonator was supplied by on-site combustion of pulverized lignite or natural gas. The CO2 concentration in the resulting flue gas stream to be decarbonized in the carbonator was adjusted according to typical values of waste-to-energy plants. During the experimental campaigns, two types of solid recovered fuel were investigated. The lower heating value of the SRF was approximately 21 MJ/kg for the first and approximately 16 MJ/kg for the second type. Overall, the plant was operated over 230 h in interconnected CFB mode, while firing SRF. The process evaluation is based on a simplified reactor model, which is typically applied in the field of CaL technology. It was experimentally proven that carbonator CO2 absorption rates close to the theoretical maximum are feasible while firing SRF in the calciner. Furthermore, it was found that accumulation and distribution of coarse SRF ash fraction in the solid looping system are a key challenge to be addressed in the design stage and operation of a SRF-fired CaL system.

The calcium looping (CaL), which applies carbonation/calcination cyclic reactions of a CaO sorbent, has received extensive attention for postcombustion CO2 capture. However, as the number of cyclic reactions increased, the capture efficiency of regenerated CaO decreased rapidly. Sodium doping was proposed for modification of a CaO sorbent, but there was little research on whether sodium doping had a good effect on different kinds of sorbents. In this paper, three different kinds of calcium-based sorbents, i.e., CaCO3, dolomite, and SG-CaO, were modified by NaBr to explore the effect of sodium on CO2 capture performance. The results showed that the modification effects of sodium on three kinds of precursors were different. For CaCO3, the modification effect of sodium doping was the best. After 50 cycles, the sorption capacity of CaO/NaBr was over 3.5 times that of an unmodified sorbent; for dolomite, sodium had a moderate effect during initial cycles and then showed obvious improvement in the stability of the sorbent, the sorption capacity of the modified dolomite increased by over 30% after 50 cycles; for the SG-CaO, sodium had a negative effect, the sorption capacity of the modified sorbent decreased by about 30% after 50 cycles. When the atmosphere contained SO2, the doping of an alkali metal also showed a certain effect.

Limestone can be used to generate a sorbent suitable for CO2 capture via the reversible carbonation of CaO, in a process often referred to as calcium looping. This sorbent loses reactivity to CO2 upon cycles of carbonation and calcination (the reverse of carbonation). Several methods of improving sorbent performance have previously been investigated, including by generating synthetic sorbents or simple doping. Here, we demonstrate, for the first time, that sorbent performance can be enhanced by simple doping with seawater. This effect is consistent across five different limestones investigated and can be enhanced by steam addition. This would be a simple and inexpensive method for improving sorbent performance in calcium looping processes. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

It is important and urgent to overcome the intermittent nature of solar energy as a green substitute for fossil-based electricity. Concentrated solar power plants with thermochemical energy storage...

The calcium looping (CaL) process is a promising CO2 capture technology, which uses CaO-based sorbents by employing a reversible reaction between CaO and CO2, generally named as carbonation and cal...

Calcium looping is one of the most promising technologies for large-scale CO2 capture, while CaO-based materials suffer from the deactivation in CO2 capture capacity in the multiple carbonation/cal...

Biomass combustion with in situ CO2 capture via the calcium looping cycle is a novel process for the production of low- (or even negative-) carbon heat and power. Both processes can take place in t...

In this work, the SO2 removal performances of the aluminum- and the magnesium-modified carbide slags fabricated by the combustion synthesis from CO2 capture cycles at the calcium looping conditions were investigated in a thermogravimetric analyzer and a dual fixed-bed reactor. The effects of sulfation temperature, number of CO2 capture cycles and calcination condition on the SO2 removal performances of Al- and Mg-modified carbide slags experienced the multiple CO2 capture cycles were studied. The sulfation temperature in the range of 800–950 °C shows a little effect on SO2 removal capacities of Al- and Mg-modified carbide slags experienced the multiple CO2 capture cycles. As the number of CO2 capture cycles increases, the sulfation conversions of the original and modified carbide slags decrease rapidly. However, Al- and Mg-modified carbide slags possess obviously higher SO2 removal capacity and cyclic stability than original carbide slag due to the good supports Ca3Al2O6 and MgO, respectively. And the larger surface areas and volumes of pores in 5–20 nm in diameter of Al- and Mg-modified carbide slags promote the higher SO2 removal capacity than original carbide slag. The modified carbide slag shows higher sintering resistance in high concentration of steam calcination condition during the CO2 capture cycles, compared with high concentration of CO2 calcination condition. Therefore, Al- and Mg-modified carbide slags from CO2 capture cycles based on calcium looping calcined under high steam concentration achieve SO2 removal capacities.

A simultaneous NOx/SO2 removal system using bio-char and CaO combined with calcium looping process for CO2 capture was proposed. The simultaneous NO/SO2 removal performance of coconut shell char/CaO experienced CO2 capture cycles was investigated in a fluidized bed reactor. The effects of reaction temperature, mass ratio of CaO to coconut shell coke, CaO particle size and number of CO2 capture cycles from calcium looping process were discussed. The NO removal efficiency of char is improved under the catalysis of CaO. The reaction temperature plays an important role in the simultaneous NO/SO2 removal. Coconut shell char/CaO achieve the highest NO and SO2 removal efficiencies at 825 oC, which are 98% and 100%, respectively. The mass ratio of CaO to coconut shell char of 60: 100 is a good choice for the simultaneous NO/SO2 removal. Smaller CaO particle size contributes to higher NO and SO2 removal efficiencies of coconut shell char/CaO. The NO and SO2 removal efficiencies of coconut shell char and cycled CaO from calcium looping declined slightly with the number of CO2 capture cycles. In addition, the Ca-based materials balance in process of simultaneous NOx/SO2 removal combined with calcium looping is given. The novel simultaneous NO/SO2 removal method using bio-char and cycled CaO from calcium looping process appears promising.

An iron-calcium hybrid catalyst/absorbent (Ca–Al–Fe) is developed by a two-step sol-gel method to enhance tar conversion, cyclic CO2 capture and mechanical strength of absorbent for hydrogen production in calcium looping gasification. The developed catalyst/absorbent consists of CaO and brownmillerite (Ca2Fe2O5) with mayenite (Ca12Al14O33) as inert support. Comparing with three candidate absorbents without Ca2Fe2O5 or Ca12Al14O33, cyclic carbonation reactivity and mechanical strength of Ca–Al–Fe are largely promoted. Meanwhile, Ca–Al–Fe approaches the maximum conversion rate of 1-methyl naphthalene (1-MN) with enhanced hydrogen yield around 0.15 mol/(h·g) under reforming conditions of present study. Ca–Al–Fe also shows the largest CO2 absorption and lowest coke deposition. Influences of operation variables on 1-MN reforming are evaluated and recommended conditions can be iron to CaO mass ratio of 10%, reaction temperature of 800 °C and steam to carbon in 1-MN mole ratio of 2.0. Ca–Al–Fe hybrid catalyst/absorbent presents good potential to be applied in future.

The O2/CO2 coal combustion provides enough heat for the decomposition of calcium carbonate in the regenerator reactor of Calcium-looping (Ca-L) process. In this study, the dried sewage sl...

Calcium looping (CaL) process offers a promising option to boost the energy efficiency and dispatchability in concentrated solar power (CSP) plants. Backed by ample experience on lime and cement industry, the CaL integration in CSP plants could be not only a feasible and reliable technology for energy storage but also a low-cost choice based on the abundance and cheap price of limestone (CaCO3). However, to date, there is no deep fundamental understanding about how different conditions through the pipes and in storage silos affect the flowability of the granular medium. This is a critical issue, therefore, concerning the ease with which the granular medium is transported, fluidized or stored. Our present work challenges the status quo on the granular-based energy storage systems in which many central questions about powder dynamics through the circuit have been dodged. To deeply explore and figure out optimal settings, we have investigated the potential side effects that changes in temperature and consolidations can induce in the powder flowability. In so doing, we analyze the variation of the tensile strength of the powder while it is being fluidized in a wide range of temperatures and consolidations. The powder, CaCO3 with a particle size around 50 μm, was chosen to mimic the actual conditions in CaL-CSP pilot plants (currently under development). The results show a severe impact on cohesion when the CaCO3 granular medium is exposed at different temperatures ranging from ambient to 500 °C, and consolidation stresses up to 2 kPa. With cohesion increasing up until an order of magnitude in this range of relatively low consolidations, it is a foregone conclusion that those changes uncover a scenario that has not been brought up so far.

The thermochemical energy storage based on Calcium looping (CaL) process shows great potential for the application in the 3rd generation Concentrated Solar Power (CSP) compared to other high-Temperature heat storage schemes. However, due to the inherent low solar absorptance of CaCO3, the surface heating mode is widely adopted in the conventional CaL-CSP system, which causes large thermal resistance and severe radiative heat loss. Herein, we propose achieving direct solar absorption in the CaL-CSP system through enhancing the CaCO3’s ability to capture thermal energy from the concentrated solar irradiation. Efforts are devoted to design and fabricate a modified CaL material by doping CaCO3 with some materials with high solar absorptance. In order to obtain a highly stable CaL, the cyclic performance of the composite material is investigated and optimized. The calcium gluconate ((Ca(C6H11O7)2)) was used as the precursor while fabricating the porous CaCO3, and the Mn–Fe oxides were doped into CaCO3 through two different doping processes. The experimental results indicate that the proposed material obtains the solar absorptance of ∼90%. The heat release efficiency (equal to carbonation activity) remains over 92% in 60 cycles, which is much higher than that of the commercial CaCO3 powder (20% after 60 cycles). The proposed calcium-based thermochemical energy storage material is expected to dramatically improve both the solar utilization efficiency and cyclic stability of the integrated CaL-CSP system.

Negative-emission technologies are largely investigated to better control atmospheric carbon dioxide concentration driving global warming. Calcium looping has been proposed in literature for direct air capture, but a comprehensive system analysis is still missing. Methanation of carbon dioxide can represent an alternative to geological storage, widely investigated within the power-to-gas framework. In this study, an integrated process considering the catalytic methanation of the concentrated carbon dioxide stream after capture from ambient air by a pure hydrogen stream from water electrolysis was proposed and numerically investigated. The system relies on packed bed reactors and uses calcium oxide as sorbent, and a nickel-based catalyst for methanation. A comprehensive study on the overall system performance was carried out, assuming a carbon dioxide capture target of 100 t y−1. Model computations suggest that roughly 50-in-parallel reactors, 0.5 m diameter each, are required for a continuous operation. The overall energy demand of the integrated process ranges within 344–370 GJ tCH4−1, or 215–293 GJ tCH4−1 if neglecting the humidifier. The methanation process requires 3-in-series reactors and can yield a continuous gas stream with a flow rate of 5 kg h−1 and a methane molar fraction of nearly 91%. If this stream is exploited for heat generation, a return of energy index of 16%, or 23% if neglecting the humidifier, is foreseen. The proposed process stems as viable solution towards a circular carbon economy.

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).

Submitted by KELY REGINA MAXIMO VIEIRA (kely.maximo@unesp.br) on 2022-07-12T16:38:22Z No. of bitstreams: 1 Vieira, Kely R.M._Tese_UNESP_2022.docx: 11558545 bytes, checksum: 775aad86fe2834edf2d98e5a41f2343d (MD5) Approved for entry into archive by Luciana Máximo (luciana.maximo@unesp.br) on 2022-07-14T18:04:06Z (GMT) No. of bitstreams: 1 vieira_krmv_dr_guara.docx: 11558545 bytes, checksum: 775aad86fe2834edf2d98e5a41f2343d (MD5) Made available in DSpace on 2022-07-14T18:04:06Z (GMT). No. of bitstreams: 1 vieira_krmv_dr_guara.docx: 11558545 bytes, checksum: 775aad86fe2834edf2d98e5a41f2343d (MD5) Previous issue date: 2022-03-21 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Reducing anthropogenic emissions of greenhouse gases in the atmosphere, mainly carbon dioxide (CO2), from the burning of fuels for energy generation is an urgent challenge to reverse the negative consequences of climate change. Carbon capture and storage (CCS) technologies are essential for mitigating the effects of climate change caused by CO2 emissions into the atmosphere. The application based on the reversible calcination/carbonation reactions of calcium-based materials, called Calcium Looping (CaL), is currently a promising technology. In the present study, thermogravimetric analyses (TGA) are applied to study the calcination/carbonation process. Two Brazilian limestones (calcitic and dolomitic) as CO2 sorbents were used. The experimental design was applied, and the variables that affect the conversion in the reactions were assessed. Sorbent treatments by hydration and acidification methods were assessed to minimize the deactivation of the sorbent material. The results obtained demonstrate variations between the two sorbents studied and different results after the treatments used. Hydrated limestones present better CO2 conversion than untreated limestones, driving the study and investigation to improve Brazilian natural limestones in CaL cycles for CO2 capture. A diminuição das emissões antrópicas de gases do efeito estufa na atmosfera, principalmente do dióxido de carbono (CO2) a partir da queima de combustíveis para a geração de energia, é um desafio urgente para reverter as consequências negativas provenientes das mudanças climáticas. As tecnologias de captura e sequestro de carbono (CCS - Carbon capture and storage) são essenciais para a mitigação dos efeitos das alterações climáticas causadas pelas emissões de CO2 na atmosfera. A aplicação baseada nas reações reversíveis de calcinação/carbonatação de materiais a base de cálcio, denominado por Calcium Looping (CaL), é atualmente uma promissora tecnologia. No presente estudo realiza-se a aplicação da termogravimetria (TGA) no estudo do processo de calcinação/carbonatação utilizando dois calcários brasileiros (calcítico e dolomítico) como sorventes de CO2. Utiliza-se o planejamento experimental, considerando-se as variáveis que afetam a conversão nas reações, bem como a inserção de tratamentos por métodos de hidratação e acidificação, para minimizar a desativação do material sorvente. Os resultados obtidos demonstram variações entre os dois sorventes estudados, bem como resultados distintos após os tratamentos empregados. Os calcários hidratados apresentam melhores conversão de CO2, que os calcários sem tratamento, impulsionando o estudo e investigação para melhoramento de calcários naturais brasileiros em ciclos de CaL para captura de CO2. CAPES - 001 FAPESP: 19/16966-8

Steam injection has been proposed to attenuate the decay of CaO reactivity during calcium looping (CaL) under operating conditions compatible with carbon capture and storage. However, it is yet unknown whether the perceived advantages granted by steam hold under the distinct operating conditions required for the integration of the CaL process as a thermochemical energy storage system in Concentrating Solar Power Plants (CaL-CSP). Here, we study the influence of steam in conditions compatible with a CaL-CSP scheme and assess its impact when injected only during one stage; either calcination or carbonation, and also when it is present throughout the entire loop. The results presented here demonstrate that steam boosts the CaO multicycle performance in a CO2 closed loop to attain residual conversion values similar to those achieved at moderate temperatures under inert gas. Moreover, it is found that the enhancement in multicycle activity is more pronounced for larger particles., This work has been supported by the Spanish Government Agency Ministerio de Economía y Competitividad-FEDER (contracts CTQ2017- 83602-C2-1-R and -2-R) and Junta de Andalucía and Universidad de Sevilla (Programa Operativo FEDER Andalucía 2014–2020, projects P18-FR-1087 and US-1262507). We acknowledge the funding received by the European Union's Horizon 2020 research and innovation programme under grant agreement No. 727348, project SOCRATCES. Financial support received from Junta de Andalucía-Consejería de Economía, Conocimiento, Empresas y Universidad via a postdoctoral fellowship with reference DOC_00044 is also acknowledged.

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.

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.

Thermochemical energy storage (TCES) has attracted interest in the last years due to the possibility of attaining high energy densities, seasonal storage capacity and greater efficiencies than currently commercial thermal energy storage systems using molten salts. This work analyses the potential of an ultra-high temperature TCES system based on the SrCO3/SrO system. The process relies upon the reversible decomposition of SrCO3 into SrO and CO2. As proposed in previous works for the integration of the Ca-Looping process to store energy in CSP plants, both the calcination (endothermic) and carbonation (exothermic) reactions are carried out in a closed CO2 loop. At these conditions, the required temperature to attain full calcination in short residence times is around 1400 ◦C whereas carbonation takes place at about 1200 ◦C. Using this process, the energy density potentially achievable by the storage material is very high (around 2000 MJ/m3 ) while the ultra-high carbonation temperature would improve thermoelectric efficiency. The enhancement of the multicycle performance of the SrCO3/SrO system using refractory additives is also explored. Even though current commercial CSP plants with tower technology cannot yet operate at these ultra-high temperatures, recent advances in the development of high-temperature solar receivers could allow operation at 1400 ◦C in the medium term. Finally, a conceptual model of the integration of the SrCO3/SrO system in a CSP plant supports higher overall efficiency and energy density, but lower solar-to-electric efficiency due to thermal losses., This work has been supported by the Spanish Government Agency Ministerio de Economía, Industria y Competitividad, the Agencia Estatal de Investigación and FEDER (contracts CTQ2017-83602- C2-1-R and -2- R) and Junta de Andalucía-Consejería de Conocimiento, Investigación y Universidad-Fondo Europeo de Desarrollo Regional (FEDER) (Programa Operativo FEDER Andalucía 2014–2020, projects P18-FR-1087 and US1262507). We also acknowledge the funding received by the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 727348, project SOCRATCES.

En este trabajo revisamos el estado de desarrollo de distintos procesos de captura de CO2 que hacen uso de reacciones reversibles de carbonatación/calcinación a altas temperaturas, especialmente en aquéllos en los que el Instituto de Ciencia y Tecnología del Carbono (INCAR-CSIC) ha generado propiedad industrial. El mayor nivel de desarrollo se ha alcanzado en el proyecto TRL7 de La Pereda CO2, pero las centrales térmicas están en rápido declive en Europa y las prioridades se dirigen a la descarbonización de sectores industriales difíciles de electrificar con energías renovables. Se repasan las nuevas líneas de desarrollo de estas tecnologías en el grupo de captura de CO2 del INCAR. En concreto, se ilustran, con algunos proyectos vigentes, las grandes posibilidades de integración térmica y de materiales que ofrecen la captura de CO2 a alta temperatura con CaO, incluyendo nuevas aplicaciones en el sector del acero, el cementero y el de la cal, e incluso la captura de CO2 directa del aire por carbonatación pasiva de Ca(OH)2., El trabajo de nuestro grupo de investigación se realiza principalmente gracias a la financiación obtenida a través de proyectos de I+D europeos (FP6, FP7, h2020, RFCS), con aportación adicional de proyectos obtenidos en convocatorias públicas de concurrencia competitiva en los Planes Regionales y Nacionales de Investigación y, en el periodo 2021-2022, con Fondos de Recuperación del CSIC (RECUPERA: “PTI+ Alta tecnología clave en la transición en el ciclo energético”).

The present document describes the potential retrofit of an existing cement plant with carbon capture technologies applied in two sequential steps. The pathway proposed consists in a first retrofit through partial oxyfuel followed by the integrated calcium looping (CaL) technology. This kind of applications may represent a promising strategy for the decarbonization route in the cement sector without introducing chemical solvents or special components, in particular for existing cement kilns that may need to be revamped. The cement plant selected for this study is the 0.5 Mtcem/y Colleferro facility owned by Italcementi-HeidelbergCement. This study analyses the mass & energy balances of the partial oxyfuel, and the integrated CaL process retrofitted to the existing cement plant. The results of the two CCS technologies are then compared in terms of CO2 emission reduction and energy consumption with the reference plant without CO2 capture. The scope of this analysis is to evaluate the impact of carbon capture technologies on the cement production process. The process simulation software Aspen Plus V10.0® has been employed to develop the model for the three different plant configurations (i.e., the base case w/o carbon capture, the partial oxyfuel mode, and the integrated CaL). The base case has been validated using field measurements coming directly from the Colleferro plant. From this process flow model, the two CCS technologies have been developed according to the specific process requirements. Results show that a maximum reduction in CO2 emissions of 92.4% is possible with the integrated CaL, while the partial oxyfuel enables to capture 71.7% of the CO2 generated in the plant.

This study explores the effect of steam addition during carbonation on the multicyclic performance of limestone under calcium looping conditions compatible with (i) CO2 capture from postcombustion gases (CCS) and with (ii) thermochemical energy storage (TCES). Steam injection has been proposed to improve the CO2 uptake capacity of CaO-based sorbents when the calcination and carbonation loops are carried out in CCS conditions: at moderate carbonation temperatures (∼650 °C) under low CO2 concentration (typically ∼15% at atmospheric pressure). However, the recent proposal of calcium-looping as a TCES system for integration into concentrated solar power (CSP) plants has aroused interest in higher carbonation temperatures (∼800−850 °C) in pure CO2. Here, we show that steam benefits the multicyclic behavior in the milder conditions required for CCS. However, at the more aggressive conditions required in TCES, steam essentially has a neutral net effect as the CO2 uptake promoted by the reduced CO2 partial pressure but also is offset by the substantial steam-promoted mineralization in the high temperature range. Finally, we also demonstrate that the carbonation rate depends exclusively on the partial pressure of CO2, regardless of the diluting gas employed.

Thermochemical energy storage (TCES) has attracted interest in the last years due to the possibility of attaining high energy densities, seasonal storage capacity and greater efficiencies than currently commercial thermal energy storage systems using molten salts. This work analyses the potential of an ultra-high temperature TCES system based on the SrCO3/SrO system. The process relies upon the reversible decomposition of SrCO3 into SrO and CO2. As proposed in previous works for the integration of the Ca-Looping process to store energy in CSP plants, both the calcination (endothermic) and carbonation (exothermic) reactions are carried out in a closed CO2 loop. At these conditions, the required temperature to attain full calcination in short residence times is around 1400 °C whereas carbonation takes place at about 1200 °C. Using this process, the energy density potentially achievable by the storage material is very high (around 2000 MJ/m3) while the ultra-high carbonation temperature would improve thermoelectric efficiency. The enhancement of the multicycle performance of the SrCO3/SrO system using refractory additives is also explored. Even though current commercial CSP plants with tower technology cannot yet operate at these ultra-high temperatures, recent advances in the development of high-temperature solar receivers could allow operation at 1400 °C in the medium term. Finally, a conceptual model of the integration of the SrCO3/SrO system in a CSP plant supports higher overall efficiency and energy density, but lower solar-to-electric efficiency due to thermal losses. España Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigació and FEDER (contracts CTQ2017-83602- C2-1-R and -2- R) Junta de Andalucía Consejería de Conocimiento, Investigación y Universidad-Fondo Europeo de Desarrollo Regional (FEDER) (Programa Operativo FEDER Andalucía 2014–2020, projects P18-FR-1087 and US- 1262507) European Union’s Horizon 2020 research and innovation programme under grant agreement No. 727348, project SOCRATCES

Steam injection has been proposed to attenuate the decay of CaO reactivity during calcium looping (CaL) under operating conditions compatible with carbon capture and storage. However, it is yet unknown whether the perceived advantages granted by steam hold under the distinct operating conditions required for the integration of the CaL process as a thermochemical energy storage system in Concentrating Solar Power Plants (CaL-CSP). Here, we study the influence of steam in conditions compatible with a CaL-CSP scheme and assess its impact when injected only during one stage; either calcination or carbonation, and also when it is present throughout the entire loop. The results presented here demonstrate that steam boosts the CaO multicycle performance in a CO2 closed loop to attain residual conversion values similar to those achieved at moderate temperatures under inert gas. Moreover, it is found that the enhancement in multicycle activity is more pronounced for larger particles. España Ministerio de Economía y Competitividad-FEDER (contracts CTQ2017- 83602-C2-1-R and -2-R) Junta de Andalucía and Universidad de Sevilla (Programa Operativo FEDER Andalucía 2014–2020, projects P18-FR-1087 and US-1262507)

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 (2partial 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 analysed by applying a simple kinetic model, able to properly describe the fast (under kinetic control) and slow (under diffusion control) stage of the 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–1has 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.

Η χημική ανάδραση CaO (Calcium Looping - CaL) βασίζεται στην αντιστρεπτή αντίδραση του CaO με το CO2 και στην εφαρμογή της με κυκλικό τρόπο. Περιβαλλοντικές εφαρμογές της χημικής ανάδρασης αποτελούν -μεταξύ άλλων- ο διαχωρισμός του CO2 από απαέρια καύσης και η θερμοχημική αποθήκευση της ηλιακής ενέργειας στα συγκεντρωτικά ηλιακά πάρκα. Στην παρούσα διατριβή γίνεται μελέτη των κινητικών των αντιδράσεων, του μηχανισμού διάσπασης του CaCO3 καθώς και της απενεργοποίησης του CaO σε διαδοχικούς κύκλους ρόφησης. Τα πειράματα για την κινητική μελέτη της διάσπασης του CaCO3 πραγματοποιήθηκαν σε αντιδραστήρα σταθερής κλίνης σε θερμοκρασίες 825-885°C και μερικές πιέσεις CO2 έως 0.6 atm, χρησιμοποιώντας ασβεστόλιθο υψηλής περιεκτικότητας σε CaCO3. Βρέθηκε μια μη-γραμμική εξάρτηση του ειδικού ρυθμού από την PCO2 η οποία περιγράφηκε μέσω ενός μοντέλου τύπου Langmuir. Οι κινητικές παράμετροι που υπολογίστηκαν είναι σε συμφωνία με τιμές που έχουν αναφερθεί προηγουμένως, ενώ το κινητικό μοντέλο επικυρώθηκε με πειραματικά δεδομένα από τη βιβλιογραφία. Ο μηχανισμός της αντίδρασης μελετήθηκε με πειράματα ισοτοπικής εναλλαγής και θερμοπρογραμματιζόμενης εκρόφησης CO2 (TPD). Ισοτοπική εναλλαγή CO2 με σημαντικό ρυθμό παρατηρήθηκε για θερμοκρασίες άνω των 450°C. Η ρόφηση συνεχίζει να εξελίσσεται και κατά τη διάρκεια της αντίδρασης διάσπασης μέσω ειδών CaO που βρίσκονται στην περιοχή του αντιδρώντος CaCO3 και όχι στη φάση του παραγόμενου προϊόντος CaO. Επιπλέον, από τα πειράματα CO2-TPD, εντοπίστηκε ποσότητα CO2 που ισοδυναμεί με 2.75 μονοστρωματικές καλύψεις χημειοροφημένου CO2 να εκροφάται πριν από την έναρξη της αντίδραση διάσπασης, υποδηλώνοντας το σχηματισμό κενών πλεγματικών θέσεων CO2 ως ενδιάμεσο είδος. Η κινητική της αντιδρασης ρόφησης μελετήθηκε επίσης, σε θερμοκρασίες 670-820°C και μερικές πιέσεις CO2 μεταξύ 0.1 and 1.2 atm, χρησιμομοποιώντας τέσσερα ροφητικά υλικά με διαφορετική περιεκτικότητα και είδος αδρανούς φάσης. Ο μετρούμενος ρυθμός της αντίδρασης ήταν πολύ υψηλός σε όλες τις συνθήκες, με το αρχικό γρήγορο στάδιο της αντίδρασης ρόφησης να ολοκληρώνεται σε λίγα δευτερόλεπτα. Για την κινητική μοντελοποίηση της αντίδρασης όλων των ροφητικών υλικών, το μοντέλο των τυχαίων πόρων τροποποιήθηκε επιτυχώς ώστε να λαμβάνει υπόψιν και την παρουσία της αδρανούς φάσης. Ο ειδικός ρυθμός της αντίδρασης βρέθηκε να εξαρτάται γραμμικά από τη μερική πίεση του CO2 στην αέρια φάση, ενώ οι κινητικές παράμετροι που υπολογίστηκαν είναι σε συμφωνία με τις τιμές της βιβλιογραφίας. Τέλος, η απενεργοποίηση του CaO σε διαδοχικούς κύκλους μελετήθηκε πειραματικά και υπολογιστικά. Εκτός από την πυροσυσσωμάτωση του CaO, αλλαγές που λαμβάνουν χώρα κατά τους κύκλους ρόφησης/εκρόφησης παρατηρήθηκε ότι εντείνουν την απενεργοποίηση του υλικού. Πιο συγκεκριμένα, πειράματα in-situ XRD αποκάλυψαν ότι μετά από κάθε στάδιο αναγέννησης το μέγεθος του κρυσταλλιτών του CaO αυξάνεται οδηγώντας στη σταδιακή μείωση του πορώδους και της ειδικής επιφάνειας, και κατά συνέπεια της ροφητικής ικανότητας του υλικού με τους κύκλους. Με βάση αυτά τα πειραματικά ευρήματα αναπτύχθηκε για πρώτη φορά ένα μη εμπειρικό μοντέλο, ικανό να προβλέψει τη ροφητική ικανότητα του CaO με τους κύκλους υπό διαφορετικές συνθήκες. Τα αποτελέσματα της παρούσας διατριβής αναμένεται να συνεισφέρουν στην κατανόηση των υπό μελέτη αντιδράσεων από θεμελιώδη άποψη, καθώς επίσης στην «ωρίμανση» της διεργασίας χημικής ανάδρασης του CaO για περιβαλλοντικές εφαρμογές., Calcium looping (CaL) is based on the reversible reaction of CaO with CO2 and its application in cycling mode. Environmental applications of CaL are –among others– the CO2 capture from flue gases and the thermochemical storage of solar energy in concentrated solar power (CSP) plants. In this thesis the kinetics of the reactions, the mechanism of CaCO3 decomposition, as well as the deactivation of CaO under cycling conditions are investigated. The kinetics of calcination reaction were studied experimentally in a fixed-bed reactor apparatus under conditions of temperature in the range 825-885°C and CO2 partial pressure up to 0.6 atm. The material used was limestone composed of almost pure CaCO3. A nonlinear relation was found between the specific rate of reaction and PCO2 which was described through a Langmuir-type equation. The kinetic parameters calculated from the kinetic study were within the range among other previously reported, while the kinetic model was also successfully validated with experimental data from the literature. The mechanism of the reaction was investigated via isotopic exchange and temperature programmed desorption (TPD) experiments. Isotopic exchange with significant rate was detected at temperatures higher than 450°C. During decomposition, sorption continues to take place on CaO species located in CaCO3 regions and not in the phase of CaO product. Additionally, from CO2–TPD experiments, a quantity of CO2 equivalent to 2.75 monolayers was measured to be desorbed prior to the onset of decomposition, implying the formation of CO2 vacancies on the surface of calcite as intermediate species. The kinetics of carbonation were also studied in the present thesis, at temperatures in the range of 670-820°C and under CO2 partial pressures between 0.1 and 1.2 atm. Four sorbent materials were used containing different type and weight percentage of inert phase as stabilizing agent. The measured rates were high in all conditions, with the initial fast regime of carbonation being completed in a few seconds. For the kinetic modeling of all sorbent materials, the RPM was successfully modified in order to take into account the existence of the stabilizing agent apart from CaO phase. The specific rate of reaction exhibited linear relation to the CO2 partial pressure in the gas phase, while the calculated kinetic parameters we found to be in agreement with the literature. Finally, the deactivation of CaO subjected to successive cycles was experimentally and numerically investigated as well. Apart from CaO sintering, structural changes during cycling were found to enhance the deactivation. More specifically, in-situ XRD experiments revealed that after each calcination step, the average CaO crystal size was increasing leading to a gradual loss of porosity and surface area, and consequently of sorption capacity with cycles. A non-empirical deactivation model was developed for the first time based on these experimental findings, able to predict the sorption capacity of CaO with cycles under different conditions. The results of the present thesis are anticipated to contribute in understanding the studied reactions from a fundamental aspect, as well as in increasing the readiness level of the CaL process for environmental applications.

In this work, a Calcium Looping (CaL) configuration for cement plants using two interconnected circulating fluidized bed (CFB) reactors integrated into the clinker production process, is investigated. In the proposed system, the oxy-fired CFB calciner has a dual task: (i) calcining the finer fraction of the raw meal to feed the rotary kiln of the plant and (ii) calcining the coarser fed raw meal fraction, so as to recirculate part of it to the carbonator to capture CO2 from the flue gases of the kiln. Such arrangement also exploits the known tendency of limestone materials to experience intense attrition and fragmentation under the severe calcination conditions in the oxyfired CFB calciner, so that the calciner also performs the task of an auxiliary mill. The techno-economic study conducted in this work has been carried out by analysing different levels of fragmentation of the raw material, consistent with experimental results from the TRL7 la Pereda CaL pilot plant. Two different configurations were analysed: the first, in which limestone with a larger particle size than the correctives is fed, to be used in CFB reactors; the second, in which no separation of limestone from other solid species is possible and all raw meal is used as CO2-sorbent in the CaL system. The benefits of this approach are confirmed by the estimated specific primary energy consumption for CO2 avoided (SPECCA) of 2.8-3.0 MJLHV/kgCO2 when pure limestone is used in the carbonator and of 3.5-4.6 MJLHV/kgCO2 when the raw meal is used as sorbent. The economic analysis indicates the competitiveness of the novel proposed process compared to other CaL systems, resulting in a cost of CO2 avoided (CCA) between 49.2 to 57.9 €/tCO2, excluding costs for CO2 transport and storage., This research has received funding from the Spanish Ministry of Economy and Competitiveness (PTI+ TransEner TRE2021-03-005).

On May 11th, 2019, atmospheric CO2 levels reached 415 ppm, a number 40% higher than the maximum level ever reached in the 800 000 years prior to the Industrial Revolution. This rise can be directly attributed to human activity, and has been linked to global temperature increase and climate change. Net CO2 emissions continue to rise as economies grow, and in 2018 global emissions reached 37.1 Gt. In order to reach the climate targets identified in the 2015 Paris Agreement, some scientists estimate that the world will need to attain net-zero anthropogenic greenhouse gas (GHG) emissions by 2050. Achieving this goal will require deployment of multiple technologies across multiple sectors. Of particular importance will be reducing or eliminating emissions associated to energy production via combustion of fossil fuels, which account for over 80% of CO2 emissions in G20 countries. One method of achieving this is to displace fossil fuel electricity generation with renewable source generation. Canada currently has 12 GW of installed wind capacity, and although it is the country���s fastest-growing source of renewable electricity, widespread deployment is inhibited by technical challenges including the time variability and geographic dispersion of sources. A potential solution to overcome the challenges facing integration of renewables is grid-scale energy storage. Many storage technologies currently exist at various levels of maturity. Although currently low on the development scale, thermochemical energy storage (TCES) has gained significant interest due to its potential to offer low-cost, short- or long-term storage of high-temperature heat using non-toxic, abundant materials. Several recent works have focused on the potential to pair the calcium looping (CaL) process, which exploits the reversible calcination of calcium carbonate, with concentrated solar power (CSP). This would enable CSP to provide continuous power to the grid while receiving discontinuous solar input, and recent projects have predicted storage cycle efficiencies in the range of 38-46%. As an extension of the work done 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. A process simulation of the proposed system shows that it is capable of offering comparable storage cycle efficiencies, with the overall efficiency being strongly dependent on the residual conversion of calcium oxide in the carbonator as well as on the efficiencies of the power cycles employed to discharge the stored energy. In addition to the technical challenges that may come with this type of system, social and economic barriers may arise due to the fact that it will require large-scale storage of CO2, mining of natural limestone, and potentially large and complex facilities. All of these challenges must be considered and addressed in order to achieve deployment of this technology within Canada and around the world.

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.