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CO2 capture technologies are required to address intermittent sources of CO2, such as the natural gas combined cycle (NGCC) used for backup power applications. The high reactivity of Ca(OH)2 powder facilitates the design of low cost carbonators to capture diluted CO2 (typically below 4%v in NGCC flue gases) as CaCO3. By storing CaCO3 and Ca(OH)2 it is possible to decouple the CO2 capture step in the carbonator from the oxy-calciner/hydrator block in which Ca(OH)2 is regenerated and CO2 extracted. This facilitates the integration of CO2 capture elements in backup power systems. Simulations of the completely integrated backup power plant with and without capture indicated that for a NGCC capacity factor (CF) of 0.1, the thermal capacity of the oxy-calciner was just 2% of the gross power output of the NGCC gas turbine. Capture efficiencies of 90% can be reached without modifying the operating conditions of the gas power plant, while achieving a global efficiency of 38% for the system with CO2 capture. A basic economic analysis indicated that the proposed scheme would lead to a cost of CO2 avoided of approximately 200 $ per tCO2, making it suitable for retrofitting natural gas-based power plants.

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.

The share of renewables in the energy sector is increasing, and energy storage and backup power combustion systems to cover the periods of time with low renewable energy production are becoming increasingly needed. Flexible calcium looping configurations based on the storage of solids are a promising alternative to capture the CO2 produced in such backup combustion systems. The use of Ca(OH)2 instead of CaO is better suited to these applications due to the faster reaction kinetics and higher carbonation conversions as Ca(OH)2 in powder form can achieve conversions of up to 0.7 in just a few seconds at temperatures of 550-650 °C. To take advantage of these fast reaction kinetics, compact carbonator reactors with short gas-solid contact times (i.e., a few seconds) can be designed. However, the low enthalpy of the carbonation reaction of Ca(OH)2 makes it challenging to find the optimum conditions which maximize the CO2 capture efficiency. In this work, a basic entrained reactor with recent experimental reaction kinetics has been used to determine suitable operational windows for this kind of carbonator. CO2 capture efficiencies above 90% can be achieved for flue gases with low CO2 concentrations (4%v CO2) when they are fed into the carbonator at temperatures of around 500-600 °C while maintaining low F Ca/F CO2 ratios (<2) and feeding the sorbent at ambient temperature. When capturing from a flue gas with a higher CO2 concentration (14%v CO2), the sorbent needs to be fed at higher temperatures to effectively capture CO2 in short contact times (i.e., 6 s).

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.

Existing power-to-X-to-power (PtXtP) systems re-emit CO2 when X is a synthetic carbonaceous fuel, as it is uneconomical to capture the CO2 during the brief periods of operation when back-up power is produced by burning X with air. This work presents a new strategy to re-capture such CO2 by using as sorbent a large flow of stored Ca(OH)2, which is produced from a reservoir of CaCO3. This approach can bring to zero or even negative values the carbon footprints, in particular when the pure CO2 evolved from the CaCO3 calciner is recycled to the Power-to-fuel subsystem or stored permanently. The capture process decouples the CO2 capture and the sorbent regeneration steps by using an two intermediate storage systems of Ca(OH)2 and CaCO3. This allows to reduce the capacity of the elements related with the sorbent regeneration and the investment cost, thus minimizing the economic penalty. A basic analysis using information available related to commercial technologies for Calcium Looping and PtXtP systems yields round-trip efficiencies of 0.253 and avoided CO2 cost around 60 $/tCO2.

CO2 capture efficiencies in post-combustion Calcium looping (CaL) systems are usually reported to be around 0.90, mainly due to the operation of the carbonator at temperatures around 650 ºC and the restrictions imposed by the CO2-CaO equilibrium. This work analyzes a solution to increase the CO2 capture efficiencies, by reducing the temperature in the solid entrainment upper part of the circulating fluidized carbonator. To overcome known CaO conversion limits in such region, an additional small flow of Ca(OH)2 is fed to the cooled solid entrainment region of the carbonator. Thus, the dense bed, where most of the CO2 is captured, is operated at standard conditions but the full CaL process includes a small hydrator to treat a small fraction of the purge of CaO-rich solids and to provide the necessary flow of Ca(OH)2. A second approach also discussed in this work involves similar actions but carried out after the carbonator cyclone, where the cooling is facilitated by the absence of the circulating solids. In this case, the flue gas leaving the CFB carbonator is put in contact with Ca(OH)2 in a second carbonation entrainment zone. These two CaL configurations can reach CO2 capture efficiencies of 0.99. Experimental work characterizing the fast carbonation kinetics of Ca(OH)2 powders in the entrainment zones has been completed. Mass and energy balances have been solved to discuss feasible process configurations. Net energy efficiencies of 0.342 and 0.345 have been estimated for the two CaL configurations, which result into a decrease of only 0.021 and 0.018 net points respect to a standard CaL system with a CO2 capture efficiency of 0.90.

This invention discloses a calcination process to produce high purity CO2 from solids containing CaCO3 which operates cyclically and continuously on the solids, arranged in a packed or a moving bed, and wherein each cycle comprises a first step where the combustion at atmospheric pressure of a fuel in the bed of solids containing CaCO3 heats them up to 800-900ºC and a second step wherein a vacuum pressure between 0.05 and 0.5 atm is applied to extract pure CO2 from the solids containing CaCO3 while cooling them by 30-200ºC. Said combustion can be carried out directly with air, oxygen enriched air or O2/CO2 mixtures when the process is applied to the calcination of a continuous flow of limestone in a moving bed shaft kiln. The process is also applied to calcine CaCO3 formed in reversible calcium looping processes comprising a carbonation reaction step to form CaCO3 from CaO.

A method to capture CO2 from the flue gases emitted intermittently from a power plant burning a synthetic fuel in power-to-fuel-to-power systems is disclosed. The method is characterized by arranging a reservoir of Ca(OH)2 (21) to feed a flow of such solids (1) to a countercurrent carbonator (22) located in the flue gas path (2) of the power plant, separating the resulting carbonated solids (3) from the CO2 depleted-gas (4), storing the carbonated solids (3) in a reservoir of CaCO3 (24) while the power plant is operating, calcining (in 25) a steady flow of carbonated solids (5) to produce CaO solids (6) and CO2 (14) when the power plant is not operating, hydrating (in 27) the resulting CaO solids (6) with water (8) to replenish the reservoir of Ca(OH)2 (21) and feeding the CO2 (14, 7) to the power-to-fuel system (100) to manufacture (in 32) and store (in 33) the synthetic fuel burned when the power plant is operating.

[EN] The disclosure relates to a method to capture CO2 from the flue gases emitted intermittently from a power plant burning a synthetic fuel in power-to-fuel-to-power systems. The method comprises arranging a reservoir of Ca(OH)2 to feed a flow of such solids to a countercurrent carbonator located in the flue gas path of the power plant, separating the resulting carbonated solids from the CO2 depleted-gas, storing the carbonated solids in a reservoir of CaCO3 while the power plant is operating, calcining a steady flow of carbonated solids to produce CaO solids and CO2 when the power plant is not operating, hydrating the resulting CaO solids with water to replenish the reservoir of Ca(OH)2 and feeding the CO2 to the power-to-fuel system to manufacture and store the synthetic fuel burned when the power plant is operating., [FR] La divulgation concerne un procédé de capture de CO2 des gaz de combustion émis par intermittence à partir d'une centrale électrique brûlant un combustible synthétique dans des systèmes de puissance électrique-combustible-puissance électrique. Le procédé comprend les étapes consistant à disposer un réservoir de Ca(OH)2 pour acheminer un flux de ces solides vers un carbonateur à contre-courant situé dans le trajet des gaz de combustion de la centrale électrique, à séparer les solides carbonatés ainsi obtenus du gaz appauvri en CO2, à stocker les solides carbonatés dans un réservoir de CaCO3 pendant que la centrale électrique est en fonctionnement, à calciner un flux constant de solides carbonés pour produire des solides de CaO et du CO2 lorsque la centrale électrique n'est pas en fonctionnement, à hydrater les solides de CaO ainsi obtenus avec de l'eau pour remplir le réservoir de Ca(OH)2 et à alimenter en CO2 le système d'alimentation électrique pour fabriquer et stocker le combustible synthétique brûlé lorsque la centrale électrique est en fonctionnement.

The CO2 capture from back-up power plants by making use of calcium looping systems combined with large piles of Ca-solids has been studied in this work. A flexible CO2 capture system based on a concept described in a previous work has been integrated into an existing power plant by including a small oxy-fired calciner (that represents just 8% of the total thermal capacity) to steadily regenerate the sorbent and a carbonator reactor following the back-up power plant operation periods to capture 90% of the CO2 as CaCO3 and two large piles of rich CaO and CaCO3 solids stored at modest temperatures. When the back-up plant enters into operation, the calcined solids are brought into contact with the flue gases in the carbonator reactor; meanwhile, the oxy-calciner operates continuously at a steady state. In order to improve the flexibility of the CO2 capture system and to minimize the increase of CO2 capture costs associated with the additional new equipment used only during the brief back-up periods, we propose using the steam cycle of the existing power plant to recover a large fraction of the heat available from the streams leaving the carbonator. This makes it possible to maintain the electrical power output but reducing the thermal input to the power plant by 12% and thus the size of the associated CO2 capture equipment. To generate the auxiliary power required for the oxy-calciner block, a small steam cycle is designed by integrating the waste heat from the streams leaving this reactor. By solving the mass and heat balances and proposing a feasible thermal integration scheme by using Aspen Hysys, it has been calculated that the CO2 emitted by long-amortized power plants operated as back-up can be captured with a net efficiency of 28%.

The attrition of CaO-based solids operating in calcium looping (CaL) post-combustion CO2 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.

Calcium looping (CaL) is an emerging CO2 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 CO2 emissions as low as −245.3 kgCO2/MWhe since the biomass source is carbon-neutral. The net electric efficiencies achieved for the entire system including CO2 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.

The calcium looping technology using entrained flow reactors seems particularly suited for integration in cement plants due to the fine particle diameters and high gas velocities that are characteristic of these plants. However, there is little experimental information available in the literature on the carbonation performance of fine CaO-based particles with a few seconds of gas/solid contact times. In this work, the carbonation of calcium oxide has been experimentally investigated in a 6 m long and 0.1 m internal diameter drop tube reactor. Carbonation tests between 600 and 700 °C using sorbents with different CO2 sorption capacities have been carried out. The effect of the carbon dioxide and steam on the extent of the carbonation reaction has been evaluated. The experimental results can be described by means of a simple plug flow reactor model with a modest axial dispersion, and they enable the determination of the kinetics parameters for the carbonation of CaO particles in these emerging carbonator reactors.

The calcium looping process based on the CaO/CaCO3 carbonation/calcination cycle has been proven to be an efficient CO2 capture technology. Most of the experimental work describing the behavior of the CaO particles has been performed under carbonation reference conditions of 650 °C and 10–15% vol CO2. Although, process schemes recently proposed have pointed out the practical benefits of operating the carbonator reactor at lower temperatures, on the assumption that these would lead to higher CO2 capture efficiencies. However, there is a lack of correlations for estimating the evolution of the carrying capacity along cycling at temperatures below 650 °C. Therefore, in this work the carrying capacity of a high purity natural Ca-material used as reference has been studied in a selected range of representative carbonation temperatures (450–725 °C). The parameters on the CaO deactivation curve that is widely employed have been readjusted to accord with a more general decay model that takes into account the effect of the carbonation temperature on the thickness of the CaCO3 product layer that marks the end of the fast kinetically controlled regime.

Calcium looping (CaL) for post-combustion CO2 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 CO2 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 O2-rich conditions in a series of experiments with a coal thermal input of up to 2.0 MWth in the calciner and 75 O2%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 CO2 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.

Calcium Looping (CaL) is a technology that makes use of CaO to capture CO from industrial flue gas sources in a carbonator, after which the CO is released in a concentrated form in an oxyfired calciner. The CO carrying capacity of the particles circulating between the carbonator and calciner is a key variable, as it is intimately linked to CO capture efficiency in the carbonator reactor. Therefore, the ability to predict dynamic changes in the CO carrying capacity of the sorbent is required to understand the dynamic performance of CaL systems. This work investigates the dynamic evolution of the average CO carrying capacity of the sorbent (X) during transient scenarios in a large CaL pilot plant. Several experimental campaigns with extensive solids sampling and analyses were carried out to analyse the evolution of X with time when the make-up flow fed into the calciner is modified (between 0–2.7 kmol CaCO/h). Variations in X were tracked and the observed trends were interpreted using two residence time distribution models of different complexity. The main characteristics and limitations of each model are discussed in this study. The choice between the two modelling approaches developed in this work depends on the input information available and the degree of accuracy required for each specific application.

This work analyses the performance of a Calcium Looping (CaL) carbonator reactor that captures CO from a power plant operating under large load changes. Several experimental campaigns have been conducted in La Pereda 1.7 MW CaL pilot plant where the carbonator inlet flue gas velocity varied between 2.0 and 5.3 m/s, leading to large changes in the particles entrainment rate and the solids inventory. These tests showed that CaL systems using circulating fluidized bed reactors are highly flexible. Modest gas velocities translate into high CO capture efficiencies because circulation rates equivalent to CaO/CO molar ratios ~10–12 can still be maintained, while carbonator solids inventories are relatively large. Under high carbonator gas velocities, a sorbent with high CO carrying capacity is necessary to guarantee high CO capture efficiencies. In these conditions, the recirculation of a fraction of the exiting particles towards the bottom of the carbonator proved to be useful for moderating the solids circulation rate between reactors, increasing the particles residence time in the carbonator and sustaining high CO capture efficiencies. For load increases, staging the flue gas entering the carbonator helped to sustain high CO capture efficiencies thanks to maintaining the solids inventory at the bottom of the reactor.

Post-combustion calcium looping is an emerging capture technology that uses CaO particles as CO2 sorbent. This work analyses the average maximum CO2 carrying capacity of the sorbent (Xave) in a continuous large-scale calcium looping (CaL) pilot plant, which is believed to adequately represent the lifetime of CaO particles in larger CaL systems based on the regeneration of CaO by oxyfuel combustion in the calciner. The CO2 carrying capacity is a key variable in designing the CO2 capture carbonator reactor and for optimizing the performance of the system. Several experimental campaigns have been carried out in La Pereda 1.7 MWth pilot plant both under oxy-fired and air-fired combustion conditions, in which the evolution of Xave with time has been measured under a wide range of conditions in the calciner. A methodology based on a closure of mass and particle population balances has been used to estimate Xave. Closure of the sulphur balance was found to be very accurate as an internal calibration tool to quantify the make-up flow of limestone that effectively participates in the CO2 capture process in any given set of conditions. When the calciner reactor was operated in conditions far from the equilibrium of CO2 on CaO, a good agreement was found between the experimental Xave values and those calculated from population mass balances which account for the number of carbonation-calcination cycles of each particle. However, a CO2 carrying capacity lower than expected was observed in some tests in oxy-combustion mode when the calciner was operating close to equilibrium. Departure from ideal sorbent behavior and more intense deactivation was found to increase with longer residence times in the calciner (∼3 min). This deactivating effect may be due to the effective increase in the number of carbonation-calcination cycles of the particles, caused by switching between carbonating and calcining conditions inside the calciner when the reactor operates close to equilibrium. The r

Actualización del monográfico sobre captura del CO2 publicado por PTECO2 en 2014. Una vez superada la crisis financiera y con el horizonte de cumplir el Acuerdo de París, existen novedades suficientes que justifican dicha reedición: En una etapa donde las emisiones de CO2 debidas a la producción energética con combustibles fósiles parecen en proceso de desaparición irreversible, se debe incidir en las tecnologías que apunten hacia las emisiones de otras industrias, como el cemento, la siderurgia y la industria química, con sus particularidades. El enorme crecimiento que los usos del CO2 han venido mostrando en los últimos años también supone una importante diferencia en cuanto a los procesos de captura. Ya no se trata de una visión en la que simplemente se captura el dióxido de carbono, sino que se realiza para darle un uso a este gas, con lo que esto supone. Nuestro punto de vista no se limita al entorno nacional, sino que pretendemos dar también una visión global de la situación.

This work analyses a novel calcium looping process for cement plants, based on a reactor configuration that uses a double calcium chemical loop for CO2 capture and the calcination of CaCO3. This novel scheme employs a number of state-of-the-art cyclonic preheaters, where the solids exiting the carbonator reactor are overheated by being brought into direct contact with high-temperature gas streams before they enter the calciner. This reduces the energy demand in the calciner, which is fed by solids from a second calcium solid loop where solids are overheated by an external air-fired combustor, thereby transferring the heat required for CaCO3 calcination and avoiding the need for oxy-fired combustion. Two different process schemes, with different ranges of capture efficiency and complexity, emerge when considering the option of feeding the flue gases from the new air-fired combustor to the carbonator. The results of the energy and mass balances performed on the proposed schemes reveal that as much as 94% of the total amount of CO2 generated can be captured (equivalent to 92% CO2 avoided) with an increase in the overall process heat demand of just 1.1 GJth/tcement. Moreover, this value could be as low as 0.3 GJth/tcement if a second configuration is used to capture only the CO2 derived from the calcination of the CaCO3 in the raw meal of the cement plant, resulting in a CO2 capture efficiency of 58%. A preliminary economic analysis of both configurations indicates that the cost of cement increases from 74 $/tcement typical of a reference cement plant to 106 and 85 $/tcement, respectively, while the calculated avoided costs are of the order of 42 and 27 $/tCO2 avoided, respectively. The results obtained show that the configurations proposed could be feasible and competitive within certain operating windows that are discussed in this work.

Postcombustion CO2 capture systems that use CaO as a regenerable CO2 sorbent in two interconnected circulating fluidized beds (CFBs) are rapidly developing at increasing scale. The properties of the circulating materials, the reactor geometries and operating conditions (gas velocities and temperature ranges) are remarkably similar to those present in existing large scale circulating fluidized bed combustors, CFBCs. In this work a fluid-dynamic model published for CFBCs is adopted and applied to the study of the interconnected twin reactor calcium looping (CaL) system. The model was used to find operating windows that will allow the CaL system to be applied on a large scale. It was found that when operating at high gas velocities (4-5m/s) in the carbonator, unacceptably high solids circulation rates might be present when high bed inventories are in place to achieve large CO2 capture efficiencies. An additional loop to allow the internal circulation of the excess solids can be quantified with the help of the model used in this work. © 2012 Elsevier B.V.

Experiments to test the concept of biomass combustion with in situ CO2 capture by CaO have been conducted in a 30 kW interconnected fluidized-bed test facility. The CO2 capture efficiency in a combustor–carbonator reactor was measured over a range of operating conditions, using three biomass feeds (olive pits, saw dust, and pellets). Overall CO2 capture efficiencies higher than 80% were achieved with sufficiently high solids circulation rates of CaO and solids inventories in the combustor–carbonator. Emissions of CO and CH4 were detected during the experiments, possibly because of pulse feeding and/or an inappropriate air/fuel mixture. The application of a simple reactor model for combining biomass combustion and CO2 capture allows an effectiveness factor of 0.74 to be derived for all of the experiments. This could be valuable for scaling-up purposes.

A calcium looping (CaL) process is a carbon capture technology which utilizes calcium oxide to remove carbon dioxide from the flue gas of a power plant. Like most capture technologies, CaL process has a high energy demand, which reduces power plant efficiency. The energy penalty and the operating and capital costs of the unit can be reduced by increasing the concentration of O2 in the oxidant flow to calciner. In this study, a calciner has been studied with a three dimensional, steady-state, CFB process model. First, the model was validated by test data of the calciner in la Pereda CaL pilot. Next, a 3D model was created for a 200 MWth commercial scale calciner, in which the inlet oxygen concentration was increased up to 75% to map the potentials of improving the heat balance of the system and to investigate how the calciner operates in these conditions. Based on the simulations, the CaL process is feasible even at very high inlet oxygen concentration.

This poster presents the first experimental results obtained from a 30 kWth Calcium Looping test facility upgraded to work at conditions closer to those expected in a calcium looping system retrofitted to a cement plant. The main modification in the facility is the use of a second recycle of fine solids (<40 micron) collected in the secondary cylones located after the main calcium loop for CO2 capture. This allowed the operation of the main calcium loop using finer particle size distributions (dp50 around 60-75 micron), which should generate solid purges more suitable to be processed in clinker ovens. High CO2 capture efficiencies have been achieved in preliminary experiments with high make-up flow of limestone and high CO2 concentrations. Further experimental work and modeling activities for an adequate interpretation of results are ongoing within the CEMCAP H2020 project.

This paper provides a review of the experimental results obtained from a 1.7 MWth Calcium Looping (CaL) postcombustion pilot plant located in La Pereda, Spain under two EU projects carried out in the pilot: CaOling (2009–2013), ReCaL (2012-2015). Recent modifications to the pilot and the results of an ongoing third project, CaO2 (2014-2017) are also discussed. The experimental results obtained so far demonstrate the viability of CaL as a competitive CO2 capture technology at conditions close to those expected in large scale system. There is also potential for further improving efficiency and reducing costs as new innovations are implemented in order to sustain the activity of the sorbent or to operate with very high concentrations of O2 in the calciner, which will lead to process schemes that can be considered as 2nd generation CaL technology.

This paper analyses a CO2 capture system based on calcium looping, designed for power plants that operate with very low capacity factors and large load fluctuations, including shut-down and start-up periods. This can be achieved by decoupling the operation of the carbonator and calciner reactors and connecting them to piles filled with CaO or CaCO3. When the power plant enters into operation, calcined solids are fed into the carbonator to provide the necessary flow of CaO for capturing CO2 and storing the carbonated solids. An oxy-CFB calciner designed to have a modest thermal capacity and operate continuously refills the CaO pile. Mass and energy balances of the entire system, combined with state-of-the-art performance criteria for reactor design, have been solved to identify suitable operating windows. An analysis of the effect of the CaO reactivity of the material stored in the piles indicates that temperatures of around 500–600 °C in the carbonator are compatible with the storage of solids at low temperature (<250 °C). This, together with the low inherent cost of the material, allows large piles of stored material. Electricity costs between 0.13–0.15 $ per kWhe are possible for the system proposed in contrast to standard CaL systems where the cost would increase to above 0.19 $ per kWhe when forced to operate at low capacity. The proposed concept could be integrated into existing power plants operating as back-ups in renewable energy systems in preference to other CO2 capture technologies that are heavily penalized when forced to operate under low capacity factors.

Calcium looping technology has a high potential for capturing CO2 in cement plants as the CaO-rich purge from the calciner can be used to replace a sizable fraction of the CaCO3 used as feedstock. Integrating the CaL process into the cement plant requires the carbonator reactor to operate under new conditions (i.e., a higher carbonator CO2 load, a more active sorbent, smaller particle sizes). This work analyzes the impact of some of the new CaL operating conditions on the performance of the carbonator in a retrofitted 30 kWth testing facility as there is little experimental information available nowadays. A wide range of sorbent activities has been tested, including those corresponding to very large makeup flows of limestone that would be characteristic of CaL applications in cement plants. The results have been interpreted using a basic reactor carbonator model that required little modification of previous versions developed for power plants.

Sistema para el almacenamiento de energía a gran escala en un sistema de generación de potencia eléctrica que comprende: i) un combustor de lecho fluidizado circulante (40, 52) con una primera tubería (1,18) para suministrar un combustible y una segunda tubería (2, 19) para suministrar un comburente a través de un distribuidor de gas, estando conectado el combustor de lecho fluidizado circulante (40, 52) a ii) un primer ciclón (41, 53) para separar el gas de escape caliente (12, 22) resultante y la corriente de sólidos caliente circulante (11, 23) al combustor de lecho fluidizado circulante (40, 52), iii) un primer dispositivo (44, 55) para dividir las corrientes de sólido descendentes por gravedad del primer ciclón (41, 53), dirigiendo los sólidos desde el primer ciclón (41, 53) a) hacia el combustor de lecho fluidizado circulante (40, 52) a través de una tercera tubería (3, 21), b) hacia un silo de mayor temperatura (43, 58) que recibe los sólidos de mayor temperatura a través de una cuarta tubería (4,24), dirigiendo los sólidos del silo de mayor temperatura (43, 58) a un primer intercambiador de calor de lecho fluidizado (42, 61), y c) hacia un silo de menor temperatura (47, 57) para almacenar los sólidos de menor temperatura de un segundo intercambiador de calor de lecho fluidizado (45, 56), estando conectado el silo de menor temperatura (47, 57) con el segundo intercambiador de calor de lecho fluidizado (45, 56) mediante una quinta tubería (5, 30) y estando conectado con el combustor de lecho fluidizado circulante (40, 52) mediante una sexta tubería (6, 31), y iv) un primer dispositivo de control de sólido (48, 60) para controlar la alimentación de los sólidos de mayor temperatura desde el silo de mayor temperatura (43, 58), y v) un segundo dispositivo de control (49, 62) para controlar la alimentación de los sólidos de menor temperatura desde el silo de menor temperatura (47, 57) al combustor de lecho fluidizado circulante (40, 52).

This invention relates to a system and a method for large scale energy storage in power generation systems using circulating fluidized bed combustors wherein the system can be further interconnected with another reactor that captures CO2 with CaO, thereby enhancing the energy storage density in the system by using the enthalpy of the reversible reaction of CO2 with CaO, wherein the system and the method of this invention are characterized by a large flexibility between periods of maximum power output and complementary periods of low power output, wherein at maximum power output, a circulation of solids from a high temperature silo to a low temperature silo is established through the system of the invention and at minimum power output, part of the thermal energy released in the circulating fluidized bed combustor is used to heat up solids from the low temperature silo and store them in the high temperature silo.

Postcombustion CO2 capture by Calcium Looping (CaL) has been successfully carried out for more than 700 hours in a 1.7 MWth continuous pilot facility in La Pereda (Spain). The pilot is equipped with two interconnected circulating fluidized bed reactors: a CO2 carbonator, where CaCO3 is formed when CO2 is captured from a combustion flue gas in contact with fine particles of CaO, and an oxy-fired calciner, where a highly concentrated stream of CO2 is generated by decomposing the CaCO3 formed in the carbonator. CaL is a technology that has the potential to achieve a substantial reduction in the cost of CO2 capture because of the capability to recover waste heat and generate more power from the additional fuel fired in the calciner. However, one of the weaknesses of CaL systems is the rapid deactivation of the sorbent. The EU “ReCaL” project (http://recal-project.eu/) aims to develop a robust and simple reactivation process to stabilize sorbent activity in CaL systems, based on the thermodynamic and kinetic ability of the sorbent to increase its CaCO3 conversion under enhanced carbonation conditions. This paper presents a first attempt to demonstrate the concept at the scale of the La Pereda 1.7 MWth pilot plant. It describes the redesign and retrofitting exercise conducted in the pilot and discusses the initial experimental results achieved when one of the loop seals is used as “recarbonator” reactor (putting a small flow of pure CO2 in contact with partially carbonated particles arriving from the carbonator). The findings of this study suggest that recarbonation could be responsible for about 100% increase in the average CO2 carrying capacity of the material used in the CO2 capture step taking place in the carbonator. This could allow CaL systems to operate with very low limestone make-up flow requirements, making this emerging capture technology more competitive.

This paper presents a power plant concept based on an oxy-fired circulating fluidized bed combustor (oxy-CFBC) combined with thermal energy storage on a large scale. The concept exploits to full advantage the large circulation flows of high temperature solids that are characteristic of these systems. Two solid storage silos (one for high temperature and the other for low temperature solids) connected to the oxy-fired CFBC allow variability in power output without the need to modify the fuel firing rate and/or the mass flow of O2 to the combustor. During the periods of high power demand the system can deliver additional thermal power by extracting heat from a series of fluidized bed heat exchangers fed with solids from the high temperature silo. Likewise, during period of low power demand, the thermal power output can be reduced by using the energy released in the combustor to heat up the low temperature solids on their way from the low temperature silo to the oxy-CFBC and storing them in the high temperature silo located below the cyclone. A preliminary economic analysis of two designs indicates that this highly flexible system could make this type of power plant more competitive in the electricity markets where fossil fuels with CCS will be required to respond to a large variability in power output.

[EN] CO2 emission levels have experienced a sharp increase in recent years mainly due to the use of fossil fuels to meet the increasing global energy demand. This phenomenon has promoted changes in the behaviour of the climate system and has contributed to what is known as climate change. This is the main reason why we need options that allow CO2 emissions to be reduced to levels that are assumable and compatible with the climate system. However, all predictions clearly indicate that fossil fuel consumption will increase over the next few decades, and this will entail a substantial increase in CO2 atmospheric concentration unless other measures are adopted. One of the alternatives proposed for the short and medium term consists in decoupling CO2 emissions from fossil fuels usage by developing CO2 capture processes. The objective of these processes is to separate the CO2 present in the gas streams produced in large stationary emission sources for its permanent storage. To this end, CO2 capture by means of carbonation-calcination cycles is one of the proposed technologies and constitutes the subject of study of the present Doctoral Thesis. The work conducted for this Thesis has been focused on the development of the CO2 capture technology at high temperature using CaO as sorbent in some of its main process routes as a step towards its implementation at industrial scale. For this purpose, several pilot-scale experimental tests were carried out, as well as studies related to the modeling of the reactors involved in the system and the incorporation of improvements to the process. Specifically, this dissertation consists of the two sections outlined below. The first section comprises the experimental tests performed at a postcombustion CO2 capture pilot plant which uses real flue gases from an industrial power plant and also includes the experimental campaigns carried out in a pilot plant of simultaneous combustion and in situ CO2 capture. The results obtained under diffe, [ES] Los niveles de emisión de CO2 han experimentado un gran incremento en los últimos años debido principalmente al empleo de combustibles fósiles para satisfacer el crecimiento de la demanda energética global. Esto ha provocado cambios en las tendencias del sistema climático, contribuyendo de este modo a lo que hoy se conoce como cambio climático. Es por ello que necesitamos disponer de opciones que permitan reducir las emisiones de CO2 hasta alcanzar niveles compatibles con cambios asumibles del sistema climático. Sin embargo, todas las previsiones apuntan indudablemente a un mayor consumo de combustibles fósiles en las próximas décadas, lo que supondría, en ausencia de otras medidas, un incremento sustancial en las concentraciones de CO2 en la atmósfera. Una de las alternativas que se plantea a corto y medio plazo consiste en desacoplar las emisiones de CO2 del empleo de combustibles fósiles por medio del desarrollo de los procesos de captura de CO2. El objetivo de estos procesos es separar el CO2 de las corrientes gaseosas generadas en grandes focos de emisión estacionarios para proceder a su confinamiento permanente. En este sentido, una de las tecnologías propuestas es la captura de CO2 mediante ciclos de carbonatación-calcinación, que constituye el objeto de estudio de la presente Tesis Doctoral. El trabajo realizado durante esta Tesis se ha centrado en el desarrollo de la tecnología de captura de CO2 a alta temperatura empleando CaO como sorbente en algunas de sus principales rutas de proceso con el objetivo de avanzar hacia su implantación a escala industrial. Para ello se han llevado a cabo estudios experimentales a escala de planta piloto, así como trabajos de modelado de los reactores involucrados en el sistema e implementación de mejoras en el proceso. En concreto, esta memoria se ha estructurado en las dos secciones que se indican a continuación. La primera sección comprende el trabajo experimental llevado a cabo en una planta piloto de captura de CO2

This work deals with the modeling and design of a novel bubbling fluidized bed reactor that aims to improve the CO2 carrying capacity of CaO particles in CO2 capture systems by calcium looping (CaL). Inside the new reactor (the recarbonator) the particles that arrive from the carbonator of the CaL system react with a concentrated stream of CO2, thereby increasing their carbonate content up to a certain value, which can be predicted by means of the model proposed. The recarbonator model presented in this work is based on the Kunii and Levenspiel model for bubbling bed reactors of fine particles. The reduction in the gas volume due to the reaction of CO2 with CaO is taken into account by dividing the recarbonator into a number of reactor elements where the bubble properties are recalculated, whereas the solids are perfectly mixed throughout the bed. The model has been used to test the conceptual design of a CaL system that incorporates an additional recarbonator reactor to more than double the residual CO2 carrying capacity of the sorbent (from 0.07 to 0.16). In a reference design case of a 1000 MWth coal-fired power plant it was found that the recarbonator cross section needs to be between 80 and 100 m2 (about 40–50% the area of the carbonator reactor), the solid inventories around 1200–1500 kg/m2, and the inlet CO2 gas velocities between 0.6 and 0.9 m/s. This set of operating and design windows predicts an increase in the carbonate content of the particles in the recarbonator of around 0.02, which has been shown to be sufficient to sustain the increased average CO2 carrying capacity of the sorbent.

[EN] Postcombustion CO2 capture by calcium looping (CaL) is being rapidly developed for coal combustion applications. This work discusses the impact of the accumulation of CaSO4 and other inert solids on CO2 capture efficiency and the overall CaL process performance. Several process configurations are considered, and the mass and energy balances and an updated carbonator reactor model are solved for each configuration. The minimum fresh sorbent requirements for sustaining a certain level of CO2 capture efficiency are quantified as well as the effects of an increase in the make-up flow. It was found that the main effect on the CaL process is produced by the sulfur present in the coal fed to the calciner and in the flue gas entering the carbonator. For a typical set of operating conditions it was calculated that the deactivating effect caused by an increase of 0.5% in the sulfur content with respect to a reference coal (low ash content) fed to the calciner is similar to the effect caused by the accumulation of inerts when using a coal with 15% more ash.

La presente invención se encuadra dentro del campo de obtención de energía a partir combustibles carbonosos con captura de dióxido de carbono para su uso o almacenamiento permanente y en concreto se refiere a dispositivos y procedimientos que hacen posible la captura mejorada de CO2 mediante CaO en procesos de calcinación-carbonatación debido al uso de un recarbonatador donde se pone en contacto a los sólidos parcialmente carbonatados provenientes del carbonatador con CO2 altamente concentrado; de modo que la fracción de carbonato en los sólidos aumente ligeramente por encima de la capacidad de captura efectiva de CO2 en el carbonatador y dicho aumento compense la pérdida de capacidad de captura de CO2 que experimentan dichos sólidos en el siguiente ciclo de calcinación-carbonatación, frenando así el proceso de desactivación en un valor de capacidad de captura de CO2 del sorbente más alto.

[EN] The present invention is included within the field of energy production from carbonaceous fuels with capture of carbón dioxide for its use or permanent storage and in particular relates to devices and methods which enable the improved capture of C02 by CaO in calcination-carbonation processes due to the use of a recarbonator(l) where the partially carbonated solids from the carbonator(2) are brought into contad: with highly concentrated C02(13); so that the fraction of carbonate in the solids increases slightly above the effective C02 carrying capacity in the carbonator and said increase compensates the loss of effective. C02 carrying capacity that said solids undergo in the following calcination-carbonation cycle, thus checking the deactivation process in a higher valué of C02 carrying capacity of the sorbent., [ES] La presente invención se encuadra dentro del campo de obtención de energía a partir combustibles carbonosos con captura de dióxido de carbono para su uso o almacenamiento permanente y en concreto se refiere a dispositivos y procedimientos que hacen posible la captura mejorada de CO2 mediante CaO en procesos de calcinación-carbonatación debido al uso de un recarbonatador donde se pone en contacto a los sólidos parcialmente carbonatados provemientes del carbonatador con CO2 altamente concentrado; de modo que la fraccion de carbonato en los sólidos aumente ligeramente por encima de la capacidad de captura efectiva de CO2 en el carbonatador y dicho aumento compense la pérdida de capacidad de captura de CO2 que experimentan dichos sólidos en el siguiente ciclo de calcinación-carbonatación, frenando así el proceso de desactivación en un valor de capacidad de captura de CO2 del sorbente más alto.