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Oviedo, Spain

Duelli Varela G.,University of Stuttgart | Charitos A.,University of Stuttgart | Diego M.E.,Spanish Research Council | Stavroulakis E.,University of Stuttgart | And 2 more authors.
International Journal of Greenhouse Gas Control

Calcium looping post-combustion CO2 capture process takes advantage of the reversible carbonation of CaO, during which CO2 contained in flue gas is absorbed by CaO forming CaCO3 and then is released when the reverse step of the reaction, named calcination, takes place. In the scope of the present paper, the performance of the process will be presented as recorded from experiments performed at University of Stuttgart, in the 10kWth Dual Fluidized Bed calcium looping facility under conditions closer to those expected industrially: wet flue gas in the carbonator reactor and atmospheres rich in CO2 and H2O in the regenerator reactor. The decomposition of limestone was realized under CO2 presence up to 75vol.% d.b., water vapor presence up to 35vol.%, balanced with N2 while the carbonation of CaO was carried out under 10-16vol.% CO2 and up to 10vol.% water vapor. Various temperatures were tested, i.e. between 620 and 680°C for the carbonator and 870 up to 930°C for the regenerator. Results showed that the demands in Ca to be circulated between the reactors is an increasing function of the CO2 vol.% in the regenerator and decreasing function of the presence of water during both sorbent carbonation and calcination. The carbonator CO2 capture efficiency decreases with increasing carbonator temperature and decreasing regenerator temperature. Efficiencies for both carbonator and regenerator of more than 90% were recorded for looping ratios (molCa/molCO2) less than 10 under oxyfired conditions when water vapor was present. With regard to chemical properties, the sorbent exhibited a residual activity (also referred to as average maximum carbonation conversion) almost double (~20%) in the case where water vapor was present in the carbonator and regenerator, as opposed to when water vapor was absent. However, sorbent friability was enhanced resulting in material loss up to 0.095molCa/molCO2 to be captured or 4.75wt.%/h based on the total system inventory. © 2015 Elsevier Ltd. Source

Abanades J.C.,Spanish Research Council | Arias B.,Spanish Research Council | Lyngfelt A.,Chalmers University of Technology | Mattisson T.,Chalmers University of Technology | And 5 more authors.
International Journal of Greenhouse Gas Control

In 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range of emerging CO2 capture technologies that promised to deliver lower energy penalties and cost. These included new energy conversion technologies such as chemical looping and novel capture systems based on the use of solid sorbents or membrane-based separation systems. In the last 10 years, a substantial body of scientific and technical literature on these topics has been produced from a large number of R&D projects worldwide, trying to demonstrate these concepts at increasing pilot scales, test and model the performance of key components at bench scale, investigate and develop improved functional materials, optimize the full process schemes with a view to a wide range of industrial applications, and to carry out more rigorous cost studies etc. This paper presents a general and critical review of the state of the art of these emerging CO2 capture technologies paying special attention to specific process routes that have undergone a substantial increase in technical readiness level toward the large scales required by any CO2 capture system. © 2015 Elsevier Ltd. Source

Rodriguez N.,Spanish Research Council | Alonso M.,Spanish Research Council | Abanades J.C.,Spanish Research Council
AIChE Journal

Calcium looping processes for capturing CO2 from large emissions sources are based on the use of CaO particles as sorbent in circulating fluidized-bed (CFB) reactors. A continuous flow of CaO from an oxyfired calciner is fed into the carbonator and a certain inventory of active CaO is expected to capture the CO2 in the flue gas. The circulation rate and the inventory of CaO determine the CO2 capture efficiency. Other parameters such as the average carrying capacity of the CaO circulating particles, the temperature, and the gas velocity must be taken into account. To investigate the effect of these variables on CO2 capture efficiency, we used a 6.5 m height CFB carbonator connected to a twin CFB calciner. Many stationary operating states were achieved using different operating conditions. The trends of CO2 capture efficiency measured are compared with those from a simple reactor model. This information may contribute to the future scaling up of the technology. Copyright © 2010 American Institute of Chemical Engineers (AIChE). Source

Rodriguez N.,Spanish Research Council | Alonso M.,Spanish Research Council | Abanades J.C.,Spanish Research Council
Chemical Engineering Journal

Calcium looping cycles for capturing CO2 from large emission sources will most likely use interconnected circulating fluidized bed reactors. The mass balances that govern the mixed solids in the main reactors of these systems, combined with a description of sorbent reaction and decay in activity, are used in this work to define the average activity of the material as a function of the sorbent recycling and make up flow ratios. The new formulation of the mass balances takes into account the fact that particles during carbonation and/or calcination achieve partial conversion in the respective reactors. In these conditions, average activity is shown to be a function of not only sorbent properties and make-up flow ratios, but also the internal solid circulation rates between the reactors. Explicit equations are obtained for the average activity of the circulating materials. These equations are used to discuss the effect of the key operating variables on CO2 capture efficiency. The equations proposed here for the CaCO3/CaO system may also be valid for other chemical reactor systems that use interconnected circulating fluidized beds. © 2009 Elsevier B.V. All rights reserved. Source

Diego M.E.,Spanish Research Council | Arias B.,Spanish Research Council | Abanades J.C.,Spanish Research Council
Journal of Cleaner Production

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. © 2016 Elsevier Ltd. Source

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