Efficacy of Nanosilica Coatings in Calcium Looping Reactors.

Nanosilica coatings are considered a simple physical treatment to alleviate the effect of cohesion on powder flowability. In limestone powders, these coatings buffer the rise in cohesion at high temperatures. Here, we investigate the role of particle size in the efficiency (and resilience) of these layers. To this end, this work examines a series of four limestone powders with very sharp particle size distributions: average particle size ranged from 15 to 60 µm. All the samples were treated with nanosilica at different concentrations from 0 to 0.82 wt %. Powders were subjected to short- and long-term storage conditions in calcium looping based systems: temperatures that vary from 25 to 500 °C and moderate consolidations (up to 2 kPa). Experiments monitored powder cohesion and its ability to flow by tracking the tensile strength of different samples while fluidized freely. Fluidization profiles were also used to infer variation in packings and the internal friction of the powder bed. Interestingly, for particle sizes below 50 µm, the nanosilica treatment mitigated cohesion significantly-the more nanosilica content, the better the flowability performance. However, at high temperatures, the efficiency of nanosilica coatings declined in 60 µm samples. Scanning electron microscopy images confirmed that only 60 µm samples presented surfaces barely coated after the experiments. In conclusion, nanosilica coatings on limestone are not stable beyond the 50 µm threshold. This is a critical finding for thermochemical systems based on the calcium looping process, since larger particles can still exhibit a significant degree of cohesion at high temperatures.

Metas maternas, prácticas y consumo de alimentos predictores del índice de masa corporal en preescolares / Mother objectives, practices, and food consumption which are predictors of the body mass index in pre-school children / Metas maternas, práticas e consumo de alimentos preditores do índice de massa corporal em pré-escolares

Resumen Introducción: La obesidad es uno de los problemas de salud pública más graves del siglo XXI. Durante la etapa infantil la madre es el cuidador principal y modelador de las conductas de salud del hijo; factores como metas maternas y prácticas de alimentación determinan el índice de masa corporal en el hijo. Objetivo: Identificar si las metas y prácticas maternas de alimentación, así como el consumo de alimentos predicen el índice de masa corporal en niños preescolares. Método: Estudio descriptivo correlacional. Participaron 217 diadas (madre e hijo preescolar). Se aplicó el Cuestionario Elección de Alimentos, Cuestionario Integral de Prácticas de Alimentación y el Cuestionario de Frecuencia de Alimentos. Se midió peso y talla de las diadas, se calculó el índice de masa corporal y se obtuvo el estado nutricio. Se aplicó estadística descriptiva e inferencial a través de regresión lineal múltiple. Resultados: La meta conveniencia, el consumo de alimentos lácteos y cereales dulces, edad y el índice de masa corporal materno, contribuyeron al índice de masa corporal en el hijo preescolar, varianza explicada de 28.3%. Conclusión: Las variables estudiadas tuvieron mínima contribución al índice de masa corporal del hijo. Se recomienda realizar estudios multivariados para explicar de forma más integral el exceso de peso infantil.

Abstract Introduction: Obesity is one of the most severe public health problems of the 21st century. During childhood, the mother is the main care provider and model of the health the son´s behaviors; and thus, factors such as the mother's objectives and the food choices habits have an impact on the body mass index of the son. Objective: To identify if the objectives and food choices of the mother, as well as the specific food can predict the body mass index in pre-school children. Method: This is a descriptive and correlational study. 217 dyads (mother and pre-school son) participated. The Food Choices Questionnaire, the Integral Questionnaire on Feeding Practices and the Food Frequency Questionnaire were administered. Weight and size were measured. The body mass index was calculated and nutritional status was estimated. Descriptive and inferential statistics, including multiple linear regression, were obtained. Results: Convenience as an objective, the consumption of dairy products and sweet cereals, the age, and the mother's body mass index, had an impact on the body mass index of the son and accounted for 28.3% of the explained variance. Conclusion: The studied variables had a minimal contribution to the BMI of the sons. It is recommended to carry out multivariate studies in order to explain more integrally the excess of weight among pre-school children.

Resumo Introdução: A obesidade é um dos problemas de saúde pública mais graves do século XXI. Durante a etapa infantil a mãe é o cuidador principal e modelador das condutas de saúde do filho; fatores como metas maternas e práticas de alimentação determinam o índice de massa corporal no filho. Objetivo: Identificar se as metas e práticas maternas de alimentação, bem como o consumo de alimentos, predizem o índice de massa corporal em crianças pré-escolares. Método: Estudo descritivo correlacional. Participaram 217 díades (mãe e filho pré-escolar). Aplicou-se o Questionário Eleição de Alimentos, Questionário Integral de Práticas de Alimentação e o Questionário de Frequência de Alimentos. Mediu-se peso e tamanho das díades, calculou-se o índice de massa corporal e obteve-se o estado nutrício. Aplicou-se estatística descritiva e inferencial através de regressão lineal múltipla. Resultados: A meta conveniência, o consumo de alimentos laticínios e cereais doces, idade e o índice de massa corporal materno, contribuíram ao índice de massa corporal no filho pré-escolar, variância explicada de 28.3%. Conclusão: As variáveis estudadas tiveram mínima contribuição ao índice de massa corporal do filho. Recomenda-se realizar estudos multivariados para explicar de forma mais integral o excesso de peso infantil.

[Value of plasma C-reactive protein and lactate dehydrogenase levels in the diagnosis of intestinal obstruction in an emergency department]. / Proteína C reactiva y lactato deshidrogenasa en el diagnóstico de la obstrucción intestinal en un servicio de urgencias.

BACKGROUND: Intestinal obstruction is one of the most frequent surgical emergencies. Its diagnosis is essentially based on clinical history, physical exploration and image tests. The aim of this study was to analyze the diagnostic value of acute phase reactants in patients with benign versus malign intestinal obstruction. METHOD: Historical cohort study of 53 patients who underwent surgery because of intestinal obstruction and/or non-obstructive colorectal cancer. The patients were placed in three groups: group 1 (colorectal cancer with intestinal obstruction) (n=23), group 2 (benign intestinal obstruction)(n=10) and group 3 (non-obstructive cancer of the colon)(n=20). We determined the initial plasma values of the C-reactive protein (CRP) and the lactate dehydrogenase (LDH)enzyme. RESULTS: CRP was quantitatively higher in patients with benign intestinal obstruction (group 2) (p=0.001), while LDH was quantitatively higher in group 1 (patients with obstructive cancer). The plasma levels of LDH were significantly greater in the groups with intestinal obstruction (groups 1 and 2) than in patients without obstruction (p<0.001). Plasma levels of CRP above 11 mg/l and of LDH above 317 U/L showed an acceptable diagnostic value for differentiating patients with intestinal obstruction, with areas under the ROC curve of 80% (CI 95% = 68-92%) and 86% (CI 95%= 75-96%)respectively. Their diagnostic value for differentiating benign or malign origin is lower, with areas under the ROC curve of 56% for levels of CRP > 24 ng/l (CI 95% = 30-82%) and 52% (CI 95% = 29-74%) for levels of LDH > 359 U/L. CONCLUSION: Determination of plasma concentrations of CRP can help in the diagnosis of intestinal obstruction and indicate its benign or malign origin in emergency services.

Validation in colorectal procedures of a useful novel approach for the use of C-reactive protein in postoperative infectious complications.

AIM: Our aim was to validate a novel use of C-reactive protein (CRP) measurement to identify postoperative infectious complications in patients undergoing colorectal surgery, and to compare the predictive value in this setting against white blood cell (WBC) count and neutrophil-to-lymphocyte ratio (NLR). METHOD: This was a retrospective study of CRP, NLR and WBC measurements in patients undergoing colorectal surgery. CRP, NLR and WBC were recorded on the second postoperative day and on the day of infectious complication (patients who developed infectious complications) or within 3 days prior to discharge (subjects with no complications). The test for detecting infectious complications consisted of comparing the value of the inflammatory marker on the day on which a complication was suspected against the value recorded on the second postoperative day. The test was considered positive if a given value was higher than the registered peak at postoperative day 2. Factors influencing the postoperative peak CRP were also studied. RESULTS: A total of 254 patients were retrospectively studied. Patients whose CRP value was higher than on the second postoperative day had a diagnostic accuracy for infectious complications of up to 94.4% and sensitivity, specificity, positive predictive value and negative predictive value of up to 97.4%, 93.4%, 85.7% and 99.1%, respectively. Poorer results were observed when WBC count and NLR were used rather than CRP measurement. Multiple linear regression analysis showed that surgical procedure and approach, as well as additional resections, were independent factors for 48 h peak CRP. CONCLUSION: C-reactive protein is a better parameter than WBC count and NLR for detecting infectious complications. Our proposed methodology presents good diagnostic accuracy and performance and could potentially be used for any surgical procedure.

Relevant influence of limestone crystallinity on CO2 capture in the Ca-looping technology at realistic calcination conditions.

We analyze the role of limestone crystallinity on its CO2 capture performance when subjected to carbonation/calcination cycles at conditions mimicking the Ca-looping (CaL) technology for postcombustion CO2 capture. The behavior of raw and pretreated limestones (milled and thermally annealed) is investigated by means of thermogravimetric analysis (TGA) tests under realistic sorbent regeneration conditions, which necessarily involve high CO2 partial pressure in the calciner and quick heating rates. The pretreatments applied lead to contrasting effects on the solid crystal structure and, therefore, on its resistance to solid-state diffusion. Our results show that decarbonation at high CO2 partial pressure is notably promoted by decreasing solid crystallinity. CaO regeneration is fully achieved under high CO2 partial pressure at 900 °C in short residence times for the milled limestone whereas complete regeneration for raw limestone requires a minimum calcination temperature of about 950 °C. Such a reduction of the calcination temperature and the consequent mitigation of multicyclic capture capacity decay would serve to enhance the efficiency of the CaL technology. On the other hand, the results of our study suggest that the use of highly crystalline limestones would be detrimental since excessively high calcination temperatures should be required to attain full decarbonation at realistic conditions.

Acoustic streaming enhances the Multicyclic CO2 capture of natural limestone at Ca-looping conditions.

The Ca-Looping (CaL) process, based on the multicyclic carbonation/calcination of CaO at high temperatures, is a viable technology to achieve high CO2 capture efficiencies in both precombustion and postcombustion applications. In this paper we show an experimental study on the multicyclic CO2 capture of a natural limestone in a fixed bed at CaL conditions as affected by the application of a high-intensity acoustic field. Our results indicate that sound promotes the efficiency of CO2 sorption in the fast carbonation phase by enhancing the gas-solids mass transfer. The fundamentals of the physical mechanism responsible for this effect (acoustic streaming) as well as the technical feasibility of the proposed technique allows envisaging that sonoprocessing will be beneficial to enhance multicyclic CO2 capture in large-scale applications.

Enhancement of fast CO2 capture by a nano-SiO2/CaO composite at Ca-looping conditions.

In this paper we show the performance of a new CO(2) sorbent consisting of a dry physical mixture of a Ca-based sorbent and a SiO(2) nanostructured powder. Thermo-gravimetric analysis (TGA) performed at conditions close to the Ca-looping process demonstrate that the rate of CO(2) capture by the mixture is enhanced during the fast carbonation stage of practical interest in applications. Moreover, the residual capture capacity of the mixture is increased. SEM/EDX, physisorption, and XRD analyses indicate that there is a relevant interaction between the nanostructured SiO(2) skeleton and CaO at high temperatures, which serves to improve the efficiency of the transfer of CO(2) to small reactive pores as well as the stability of the sorbent pore structure.

Improving the gas-solids contact efficiency in a fluidized bed of CO2 adsorbent fine particles.

A modified CO(2) adsorbent is obtained by dry mixing of a Ca(OH)(2) fine powder as received with a commercial silica nanopowder. Silica nanoparticles form light agglomerates of size of the order of tens of microns, which are uniformly fluidizable. These agglomerates act as dispersants of the Ca(OH)(2) fine particles, which coat the nanoparticle agglomerates likely due to contact charging. Ca(OH)(2) particles (CO(2) adsorbent) are thus provided with a vehicle for uniform fluidization. In this way, the contact efficiency between the CO(2) adsorbent and CO(2) in the fluidized bed is greatly enhanced. Experimental results show that the improvement of Ca(OH)(2) fluidizability serves to enhance the carbonation reaction in the fluidized bed.

Magnetic field induced inversion in the effect of particle size on powder cohesiveness.

Experimental measurements are reported on the tensile yield stress of magnetofluidized beds of fine magnetic powders operated in the cross-flow configuration. In the absence of externally applied magnetic field the yield stress of the powder depends on particle size as expected, i.e., it increases as bead size is decreased. This trend is however inverted when an external magnetic field is applied. It is suggested that the average orientation of interparticle contacts relative to the direction of the field as affected by particle size plays a relevant role on the magnetic yield stress of these systems.

Magnetofluidization of fine magnetite powder.

The behavior of a fluidized bed of fine magnetite particles as affected by a cross-flow magnetic field is investigated. A distinct feature of this naturally cohesive powder, as compared to noncohesive magnetic grains usually employed in magnetofluidized beds, is that the fluidized bed displays a range of stable fluidization even in the absence of an external magnetic field. Upon application of the magnetic field, the interval of stable fluidization is extended to higher gas velocities and bed expansion is enhanced. We have measured the tensile strength as affected by application of the external magnetic field according to two different operation modes. In the H off-on operation mode, the bed is driven to bubbling in the absence of external magnetic field. Once the gas velocity is decreased below the bubbling onset and the bed has returned to stable fluidization due to natural cohesive forces, the field is applied. In the H on-on mode, the field is maintained during the whole process of bubbling and return to stable fluidization. It is found that the tensile strength of the naturally stabilized bed is not essentially changed by application of the field ( H off-on) since the magnetic field cannot alter the bed structure once the particles are jammed in the stable fluidization state. Magnetic forces within the bulk of the jammed bed are partially canceled as a result of the anisotropic nature of the dipole-dipole interaction between the particles, which gives rise to just a small increment of the tensile strength. On the other hand, when the field is held on during bubbling and transition to stable fluidization ( H on-on mode), the tensile strength is appreciably increased. This suggests the formation of particle chains when the particles are not constrained due to the dipole-dipole attractive interaction which affects the mechanical strength of the stably fluidized bed. Experimental data are analyzed in the light of theoretical models on magnetic surface stresses.

Electromechanics of fluidized beds of nanoparticles.

The electromechanical behavior of a gas-fluidized bed of insulating silica nanoparticles is investigated. When fluidized by gas, these nanoparticles form highly porous agglomerates of size of the order of hundreds of microns, which gives rise to a nonbubbling fluidization regime. Bed expansion is enhanced by an imposed alternating electric field for oscillation frequencies in the range between tens and hundreds of hertzs and field strengths of about 1 kV/cm . Nanoparticle agglomerates are naturally charged and experience forced oscillations that cause an increase of the gas flow shear on their surface. As a consequence, the agglomerate size is expected to decrease, which can explain the observed behavior. A model based on the balance between attractive and flow shear forces is presented that accounts for agglomerate size reduction as the strength of the field is increased.

Nanofluidization electrostatics.

Electrostatic charging of powders is a relevant phenomenon for a number of industrial applications. The design of new processes and the use of high resistivity materials and ultrafine powders may lead to higher charging rates and to higher levels of charge accumulation that can become a serious problem. In this work we investigate experimentally electrostatic charging in nanofluidization. The behavior of a fluidized bed of silica nanoparticles under the influence of an electrostatic field is studied. The electric field is applied in the horizontal direction and perpendicular to the gas flow. On one hand, we observe the influence of the electric field on the bulk behavior of the fluidized bed, which suffers a collapse when the electric field is turned on. For strong electric fields the stationary state of the fluidized bed reminds one of that of a spouted bed, with a solid layer adhered to the wall and a low density core region of local high gas velocity. On the other hand, and in order to gain additional insight, we look at the trajectories of nanoparticle agglomerates as affected by the electric field. This images analysis reveals that these agglomerates are horizontally deflected towards the wall as a consequence of being charged. From the analysis of agglomerate trajectories the charge per agglomerate is estimated. Using these measurements the electrostatic forces between agglomerates are calculated and compared to van der Waals attractive forces.

Novel instrument to characterize dry granular materials at low consolidations.

The performance of traditional instruments for measuring the flow properties of dry granular materials at small consolidation stresses is not fully satisfactory. Generally, commercial quick tests, as, for example, the angle repose method, do not yield intrinsic material properties. This difficulty is solved in currently available ring shear testers, in which the externally applied torque necessary for shearing the sample is measured as a function of the normal stress previously applied through an annular lid. In this article we show a novel device in which the shear stress is caused by the action of a centrifugal force on a vertical layer of unconsolidated material, which is rotated around its vertical axis. At a critical point the shear stress is large enough to drive material avalanches. From a theoretical analysis of these avalanches based on Coulomb's method of wedges, we derive the angle of internal friction and cohesion of the granular material. To illustrate the functioning of the instrument, measurements on steel, ferrite, and magnetite beads of different particle size are presented. The data obtained are used to analyze the gravity-driven avalanches of these materials in a slowly rotated drum.

Physics of compaction of fine cohesive particles.

Fluidized fractal clusters of fine particles display critical-like dynamics at the jamming transition, characterized by a power law relating consolidation stress with volume fraction increment [sigma--(c) proportional, variant(Deltaphi)(beta)]. At a critical stress clusters are disrupted and there is a crossover to a logarithmic law (Deltaphi = nu logsigma--(c)) resembling the phenomenology of soils. We measure lambda identical with- partial differentialDelta(1/phi)/ partial log(sigma--(c) proportional, variant Bo(0.2)(g), where Bo(g) is the ratio of interparticle attractive force (in the fluidlike regime) to particle weight. This law suggests that compaction is ruled by the internal packing structure of the jammed clusters at nearly zero consolidation.

Jamming threshold of dry fine powders.

We report a novel experimental study on the jamming transition of dry fine powders with controlled attractive energy and particle size. Like in attractive colloids dry fine particles experience diffusion-limited clustering in the fluidlike regime. At the jamming threshold fractal clusters crowd in a metastable state at volume fractions depending on attractive energy and close to the volume fraction of hard nonattractive spheres at jamming. Near the phase transition the stress-(volume fraction) relationship can be fitted to a critical-like functional form for a small range of applied stresses sigma approximately (phi-phi(J))(beta) as measured on foams, emulsions, and colloidal systems and predicted by numerical simulations on hard spheres.

Effect of particle size and interparticle force on the fluidization behavior of gas-fluidized beds.

Gas-fluidized powders of fine particles display a fluidlike regime in which the bed does not have a yield strength, it expands uniformly as the gas velocity is increased and macroscopic bubbles are absent. In this paper we test the extension of this fluidlike regime as a function of particle size and interparticle attractive force. Our results show that for sufficiently large particles, bubbling initiates just after the solidlike fluidized regime as it is obtained experimentally by other workers. A scaling behavior of the solid-phase pressure in the fluidlike regime and a predictive criterion for the onset of macroscopic bubbling are analyzed in the light of these results.

Experimental study on the dynamics of gas-fluidized beds.

Gas-fluidized fine powders display three regimes of fluidization: solidlike, fluidlike, and bubbling. We investigate, from both macroscopic and local measurements, the transition between these regimes. We show that the transition between the solidlike and the fluidlike regimes takes place along an interval of gas velocities in which transient active regions alternate with transient solid networks. Although in the apparently homogeneous fluidlike regime large amplitude bubbles are not perceived and the bed expands continuously with increasing gas flow, optical probe local measurements show the existence of mesoscale pseudoturbulent structures and short-lived voids, reminiscent of liquid-fluidized beds behavior, and whose characteristic temporal frequency increases with gas velocity. These mesostructures might be responsible for the fast diffusion measured in gas-fluidized beds.

Fine cohesive powders in rotating drums: Transition from rigid-plastic flow to gas-fluidized regime.

We investigate the dynamics of fine cohesive powders inside rotating drums. We show that these powders may be fluidized due to entrapment of ambient gas, and we determine the onset of fluidization. Experimental measurements on the bed expansion as a function of the rotation velocity have been performed. Drums of different diameters and fine powders of varying cohesiveness have been tested. We show that (i) fine powders transit directly from a rigid-plastic state to a gas-fluidized state in accordance with the flow regime boundaries predicted elsewhere [A. Castellanos et al., Phys. Rev. Lett. 82, 1156 (1999)], (ii) the onset of fluidization in the rotating drum is determined by the ratio of the powder kinetic energy per unit volume to its tensile strength, and (iii) once the powder is completely fluidized the average interstitial gas velocity increases proportionally to the rotation velocity. The last two results imply that the required velocity to fluidize a powder, omegaR (omega angular velocity, R radius of the drum), must increase as the square root of its tensile strength, and this has been confirmed by independent measurements and estimations.

Aggregation and sedimentation in gas-fluidized beds of cohesive powders.

We present measurements on the settling velocity of gas-fluidized beds of fine cohesive powders. In the solidlike regime (solid volume fraction straight phi>straight phi(c)) particles are static, sustained by enduring contacts. The settling is hindered by interparticle contacts and is a very slow process. In the fluidlike regime (straight phi