Mapping of the range of operational conditions for Cu-, Fe-, and Ni-based oxygen carriers in chemical-looping combustion

Available online September 14, 2006.- El pdf del artículo es la versión post-printChemical-looping combustion (CLC) is a two-step combustion process that produces a pure CO2 stream, ready for compression and sequestration. A CLC system is composed by two reactors, an air and a fuel reactor, and an oxygen carrier (OC) circulating between the reactors, which transfers the oxygen necessary for the fuel combustion from the air to the fuel. This system can be designed similar to a circulating fluidised bed, but with the addition of a bubbling fluidised bed on the return side. A mapping of the range of operational conditions, design values, and OC characteristics is presented for the most usual metal oxides (CuO, Fe2O3, and NiO) and different fuel gases (CH4, H2, and CO). The pressure operation of a CLC system is also considered. Moreover, a comparison of the possible use of three high reactive OCs (Cu10Al-I, Fe45Al-FG, Ni40Al-FG) previously characterised is carried out. It was found that the circulation rates and the solids inventories are linked, and the possible operating conditions are closely dependent on the reactivity of the OCs. The operational limits of the solids circulation rates, given by the mass and heat balances in the system, were defined for the different type of OCs. Moreover, a plot to calculate the solids inventories in a CLC system, valid for any type of OC and fuel gas, is proposed. The minimum solids inventories depended on the fuel gas used, and followed the order CH4 > CO > H2. Values of minimum solids inventories in a range from 40 to 133 kg / MWf were found for the OCs used in this work, excepting for the reaction of Fe45Al-FG with CH4, which needs a higher amount of solids because of its low reactivity. From the economic analysis carried out it was found the cost of the OC particles does not represent any limitation to the development of the CLC technology. © 2006 Elsevier Ltd. All rights reserved.This work was carried out with financial support from the European Coal and Steel Community (Project 7220-PR/125), and the Spanish Ministry of Education and Science (Project CTQ2004- 04034).Peer Reviewe

Kinetic and morphological differentiation of Ettringites in plain and blended Portland cements using Metakaolin and the ASTM C 452-68 test. Part I: kinetic differentiation.

22 pages, 3 figures, 5 tables.[ES] En esta Parte I de la investigación, se han logrado verifi- car mediante el ensayo ASTM C 452-68, los resultados obtenidos en anteriores investigaciones realizadas con DRX y SEM y el ensayo Le Chatelier-Ansttet. Para ello, a 10 cementos Portland –6 CPO y 4 CPRS– se les añadió 20%, 30% y 40% de metakaolín (MK). Tanto los 10 CP como los 30 de sus mezclas con metakaolín (MK), se ensayaron durante 2 años, mediante dicho método ASTM C 452-68, y a sus probetas no sólo se les determinó su incremento porcentual de longitud, ∆L(%), sino además, el contenido de sulfatos de sus aguas de conservación. Otras determinaciones complementarias fueron: análisis químico de los materiales cementiceos utilizados y pro- piedades específicas de algunos cementos ensayados. Los resultados experimentales, ∆L(%) frente al tiempo, han confirmado de nuevo que la velocidad de formación de la ettringita de origen alúmina reactiva, Al2O3 r-, de las puzolanas, tiene que ser considerablemente mayor que la velocidad de formación de la ettringita de origen C3A de los CP, lo que ha sido verificado por la evolución durante todo el ensayo, del contenido de sulfatos de las aguas de conservación de las probetas. Debido a ello, se ha pro- puesto denominar a ambos tipos de ettringitas, ettringita de rápida formación, ett-rf, y ettringita de lenta forma- ción, ett-lf, respectivamente.[EN] In this first part of the study, the results obtained in prior research with XRD and SEM, as well as the Le Chatelier- Ansttet test were confirmed with the ASTM C 452-68 test. To this end, 20%, 30% and 40% metakaolin (MK) was added to ten Portland cements, six OPCs and four SRPCs. Both the ten plain PCs and the 30 metakaolin (MK) blends were tested for two years under ASTM C 452-68 specifications, determining not only the percentage increase in length, ΔL(%), of the specimens, but also the sulphate content in the curing water. Other parameters studied included: chemical analysis of the cementitious materials used and specific properties of some of the cements tested. The experimental results, ΔL(%) versus time, re-confirmed that the formation rate of ettringite from the reactive alumina, Al2O3 r-, present in the pozzolan must be substantially higher than the formation rate of ettringite from the C3A present in the PC. This was verified by the variation of the sulphate content in the specimen curing water throughout the test. In light of those findings, in this article these two types of ettringite are denominated rapid forming ettringite or ett-rf, and slow forming ettringite or ett-lf.Peer reviewe

Synthesis and Internal Structure of Finite-Size DNA–Gold Nanoparticle Assemblies

Spatially defined networks of 15 nm-sized DNA-functionalized gold nanoparticles (DNA–AuNPs) were studied using dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), as well as optical extinction spectroscopy (OES). We use a combination of these techniques with Monte Carlo simulations of pair-distance distribution function (PDDF) curves and generalized Mie theory simulations as well as in situ-transmission electron microscopy (in situ-TEM) to analyze the internal structure of the finite-size assemblies. The DLS data show that monodisperse, spherical networks with hydrodynamic radii of ca. 30 nm are found for reaction mixtures of complementarily functionalized DNA–AuNPs between 1:15 and 1:20. Different interparticle distances within these assemblies are identified and quantified. By controlling the network morphology through selection of the reaction mixture, center-shell geometries are obtained. The number of shell-AuNPs surrounding each center-AuNP is determined from the SAXS data and Monte Carlo simulations. This number is quantified to be ca. 10, with the exact number depending on the linking DNA double strand. The optical spectra of the networks are found to be consistent with the structural properties. The structural information gained here enables a quantitative description of optical and other physical properties, which is expected to prove useful for the construction and application of such systems, for example, in drug release, gene regulation, or external-stimuli-responsive materials