CaO Particles Research Articles

Calcium particle films promote artificial shading and photoprotection in leaves of American grapevines (Vitis labrusca L.)

Other materials with potential for the production of particle films for agriculture, besides the traditional use of kaolin, can present solar radiation reflection properties and promising results for temperature reduction and mitigate effects of climate change and adverse conditions on grapevine cultivation. The objective of this work was to verify the hypothesis that CaO and CaCO3 particles films could promote shading effects, influence on chlorophyll content, temperature and energetic metabolism of photosynthesis during the establishment of two American grapevine cultivars (Vitis labrusca L.) cv. Early Isabella and cv. Bordô (Ives) during the dry and hot summer in Northeast Brazil. The results showed that the films were efficient to provide artificial shading and to increase chlorophyll content (chl a, chl b and total chl) and to reduce chl a/b ratio. The temperature of the leaves (Tleaf) was significantly reduced in plants with films, which also provided greater efficiency to control the energy absorption and the electrons fluxes energized by the photosystems and the electron transport chain, especially for 'Bordô'. The results also lead to the need for additional studies to adapt the concentrations to the cultivars and of interactions between leaves and materials. Beneficial and promising effects for stress mitigation on grapevine cultivars were verified in this study, although it was also verified that the cultivar 'Early Isabella' presented better adaptation to the local climatic conditions.

Grain refinement of pure magnesium by the addition of calcium carbonate

The effect of CaCO3 addition on grain refinement of pure magnesium was studied in the present work. Results show that remarkable grain refinement in pure magnesium was achieved with the addition of CaCO3 because of the formation of in situ CaO particles, which can act as effective heterogeneous nuclei for magnesium grains. With the addition of 0.2 wt% CaCO3, the average grain size of pure magnesium was significantly reduced from 3860 μm to 240 μm, and further addition only resulted in negligible refinement. After 10 min of holding, the pure magnesium with the addition of 0.2 wt% CaO3 indicated a very fine equiaxed grain structure across the entire section, which was somewhat retained for holding time up to 120 min.

Effect of Flow-pattern Reconstruction on Combustion Efficiency and Pollutant Emission in CFB Boiler

The effect of flow-pattern reconstruction on combustion efficiency and pollutant emission in CFB boilers was investigated with a 1-D CFB combustion model. The results from the 1-D model agree well with the field test data. It was found that, the mass fraction of fine coal particles should be increased at lower bed pressure drop to achieve flow-pattern optimization. As the bed pressure drop decreases, the carbon content decreases first and then increases, both in fly and bottom ash. The change of bed pressure drop is the main factor in the influence of flow-pattern optimization on SO2 emission. The higher the bed pressure drop is, the lower the SO2 emission concentration is. Bed pressure drop and coal size distribution are the chief factors of NOx emission concentration in flow-pattern optimization. With the decrease in bed pressure drop and increase in mass fraction of fine particles, NOx emission concentration decreases first and then increases. SO2 emission concentration can be decreased below 100 mg/m3 by increasing Ca/S, while the original emission concentration of NOx increases. Therefore, other assistant adjustments are also needed to achieve flow pattern optimization, such as the secondary air proportion and CaO particle size distribution.

Physiological parameters of cowpea treated with CaO-based particle film and subjected to water restriction

Abstract: The objective of this work was to evaluate the effects of CaO-based particle film on the physiological parameters of cowpea (Vigna unguiculata) subjected to water restriction. Plants were subjected to two levels of soil moisture and three concentrations of the film, as follows: control, without film + 100% crop evapotranspiration (ETc); without film + 50% ETc; 5% CaO + 50% ETc; 10% CaO + 50% ETc; 5% CaO + 100% ETc; and 10% CaO + 100% ETc. Plants treated with 50% ETc remained stable with the application of 10% CaO particle film and showed high photosynthetic assimilation of CO2 (32 μmol m-2 s-1), moderate transpiration (5.6 mmol m-2 s-1), maintenance of chlorophyll content, and greater intrinsic water-use efficiency (IWUE, 226.65 μmol mol-1) and instantaneous water-use efficiency (6.06 μmol mmol-1) than plants of the other treatments. Control plants and plants at 5% CaO + 50% ETc showed, respectively, photosynthetic assimilation of CO2 at 15.34 and 15.94 μmol m-2 s-1, transpiration at 3.51 and 3.45 mmol m-2 s-1, and IWUE at 177.7 and 198.9 μmol mol-1. The CaO-based particle film is effective in protecting bean plants subjected to water restriction.

Preparation of CaO-containing carbon pellet from recycling of carbide slag: Effects of temperature and H3PO4

CaO-containing carbon pellets (CCCP) was prepared by mixing carbide slag (Ca(OH)2) and powdered char to produce CaC2, achieving the recycling of carbide slag during CaC2 production process. The thermal strength of CCCP was the focus of most attention when employing arc furnaces as reactors for CaC2 production in industry. To improve the thermal strength of CCCP, H3PO4 was used as a binder in this study. The results indicated that Ca3(PO4)2 reacted by H3PO4 and Ca(OH)2 could help refine the average particle sizes of CaO, resulted in a relatively uniform pore diameter distribution of CCCP with low porosity, therefore improving the thermal strength of CCCP. When H3PO4 content was more than 8 wt%, some over-sintering and melting structure for CaO particles appear, and thus resulting in the decrease in thermal strength of CCCP. The experimental results show that CCCP with 3% H3PO4 has the best thermal strength at 1100 °C. The non-isothermal shrinkage kinetics of CCCP indicated that the addition of 3% H3PO4 reduced the apparent activation energy of sintering reactions and accelerated the sintering of CaO particles in CCCP. Furthermore, the addition of H3PO4 has a positive effect on the formation of CaO sintered necks, enhancing the strength of CCCP.

High-performance and low-cost macroporous calcium oxide based materials for thermochemical energy storage in concentrated solar power plants

High energy density, cycling stability, low cost and scalability are the main features required for thermochemical energy storage systems to achieve a feasible integration in Concentrating Solar Power plants (CSP). While no system has been found to fully satisfy all these requirements, the reversible CaO/CaCO3 carbonation reaction (CaL) is one of the most promising since CaO natural precursors are affordable and earth-abundant. However, CaO particles progressively deactivate due to sintering-induced morphological changes during repeated carbonation and calcinations cycles. In this work, we have prepared acicular calcium and magnesium acetate precursors using a simple, cost-effective and easily scalable technique that requires just the natural minerals and acetic acid, thereby avoiding expensive reactants and environmentally unfriendly solvents. Upon thermal decomposition, these precursors yield a stable porous structure comprised of well dispersed MgO nanoparticles coating the CaO/CaCO3 grains that is resistant to pore-plugging and sintering while at the same time exhibits high long term effective conversion. Process simulations show that the employment of these materials could significantly improve the overall CSP-CaL efficiency at the industrial level.

Effects of calcium particle films and natural shading on ecophysiological parameters of conilon coffee

Conilon coffee (Coffea canephora Pierre ex A. Froehner) is an important agricultural crop in Brazil due to its high economic value. This plant species is sensitive to the effects of high levels of solar radiation and temperature, which could limit its wide cultivation in the Brazilian Northeast region. However, management practices such as shading could increase the feasibility of its cultivation. This study aimed to evaluate the effects of different shading methods and the use of calcium particle films on the conilon coffee ecophysiological parameters in the coastal flatland the State of Sergipe, Brazil. The field experiment was carried out as randomized block design with four treatments: i) Natural shading (intercropping coffee and banana plants), ii) Artificial shading with 10% w/v CaCO3 particle films; iii) Artificial shading with 20% w/v CaO particle films; and iv) and control (without shading), and four replicates. Measurements were performed 7, 21 and 35 days after film application at 9:00 h and 12:00 h. Individual parameters, gas exchange efficiency, chlorophyll a fluorescence and maintenance of film coverage on leaves were evaluated. Artificial shading with particle films promoted greater physiological stability of the coffee plants during diurnal meteorological oscillations as compared to the control, resulting in higher rates of liquid photosynthesis (A), better control on stomatal conductance (gs) and transpiration (E). Improvement was also observed in the plant water use efficiency (WUE and IWUE) and in the reduction of leaf temperature. Calcium particle films were more efficient in providing protection to the photosystems and improving photochemical efficiency and energy conversion for photophosphorylation than natural shading. However, the results were more pronounced at 21 days after film application and more persistent for treatment with 20% CaO film. Therefore, calcium particle films are useful tools to alleviate coffee plants stress under adverse climate conditions.

Development KCl/CaO as a catalyst for biodiesel production by tri‐component coupling transesterification

In this research, the optimized experimental conditions to obtain CaO supported KCl (KCl/CaO) as an efficient heterogeneous basic catalyst to produce no‐glycerol biodiesel using tri‐component (canola oil, dimethyl carbonate [DMC], and methanol) coupling transesterification was established. The solid base catalyst was prepared by wet impregnation of CaO in KCl solution and calcination subsequently, which greatly improved the reaction efficiency with high biodiesel yield of 96.4% at only 2 h. The KCl/CaO was characterized by techniques, such as BET surface area, XRD, CO2‐TPD, and SEM. Then, it was observed that the KCl introduced not only differed from CaO particles in the surface area and number of basic sites but also changed its base strength significantly. To obtain an improvement in conversion of canola oil, the influence on the catalytic performance of several kinetic parameters, such as mass ratio of catalyst to oil, reaction time, and molar ratio of methanol/oil/DMC were evaluated separately.Novelty or Significance: In this work, it was found that the catalytic performance of CaO‐based catalyst to coupling transesterification for no‐glycerol biodiesel production can be greatly improved by modifying CaO with KCl. As a result, the time to obtain as high as 96.4% yield of biodiesel over KCl/CaO can be greatly shortened from 5 to 2 h compared with common CaO. © 2018 American Institute of Chemical Engineers Environ Prog, 38: 647–653, 2019

Carbonation of Fine CaO Particles in a Drop Tube Reactor

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 re...

Carbonation of Fine CaO Particles in a Drop Tube Reactor

Carbonation of Fine CaO Particles in a Drop Tube Reactor

Effect of CaCl2 on Microstructure of Calciothermic Reduction Products of Ti2O3 to Prepare Porous Titanium

The compound CaCl2 plays a significant role in the process of direct calciothermic reduction of Ti2O3 to prepare porous titanium. In this paper, the effect of CaCl2 on reduction products by calciothermic reduction of Ti2O3 was investigated. Results show that the distribution of CaCl2 in reduction preform influences particle size and morphology differences in reduction products both on the surface and the inside. The CaCl2 is transferred to the surface of the Ti2O3 preform due to its volatilization before and throughout reduction. The content of CaCl2 in the surface zone of Ti2O3 preform is significantly higher than that in the interior during the reduction process, contributing to the formation of large Ti particles with a smooth shape on the surface, and small Ti particles with inherited morphology of Ti2O3 inside. More CaCl2 causes the aggregation of Ti particles to form large Ti particles which are advantageous as they connect and form a more solid porous titanium structure. The presence of a small amount of CaCl2 in the interior also results in the coexistence of small Ti and CaO particles, forming a loose structure with uniform distribution.

Highly efficient treatment of real benzene dye intermediate wastewater by simple limestone and lime neutralization-coagulation with improved Fenton oxidation.

Multistage Fenton oxidation is a favored method for the treatment of benzene dye intermediate (BDI) wastewater, but the pH adjustments required after each stage of the Fenton process with a simple way is still a challenge. Limestone pretreatment and lime neutralization-coagulation were used to solve the problem in multistage Fenton process. First, we determined the optimal conditions of Fenton oxidation using the Box-Behnken response surface method. Limestone pretreatment before the multistage Fenton process allowed for simultaneous pH adjustment and 14.15% COD removal. Most notably, the lime cream neutralization-coagulation process effectively adjusted the pH after each stage of the Fenton process. The optimum CaO particle size, lime mass fraction, mixing time, and stirring speed were determined by orthogonal tests. COD removal (89.23%) was obtained when lime cream neutralization-coagulation was applied to the three-staged Fenton process, while only 58.57% COD removal was obtained by the unadjusted single-staged Fenton process. The COD and wastewater color were reduced from 10,600mg/L and 12,200 multiples to 495mg/L and 20 multiples, respectively, using the adjusted process. This improved method provides a promising cost-effective way to efficiently treat real BDI wastewater.

Development of Ca/KIT-6 adsorbents for high temperature CO2 capture

The incorporation of CaO into an inert porous solid support has been identified as an effective approach to improve the stability of adsorbents for CO2 capture. In this work, we focus on enhancing the capacity of carbon capture and cyclic stability of CaO by impregnating CaO particles into a three-dimensional mesoporous silica (KIT-6) support. At a low CaO loading, the three-dimensional mesoporous support was filled with CaO nano-particles. The further increase of CaO loading resulted in the aggregation of CaO particles on the external surface of the support material, as identified by electron microscopy analysis. These CaO/KIT-6 adsorbents show excellent high-temperature CO2 carbonation/calcination stability over multiple cycles of CaO carbonation and calcination. The enhancement of the performance of carbon capture is attributed to the interaction between CaO and the silica skeleton of KIT-6 through the formation of interfacial CaSiO3 and Ca2SiO4 which enhanced the resistance of CaO sintering.

Effect of the Carbonation Temperature on the CO2 Carrying Capacity of CaO

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 effe...

Introduction of chemically bonded zirconium oxide in CaO-based high-temperature CO2 sorbents for enhanced cyclic sorption

In this study, ZrO2 is introduced in a new form to reduce sintering and enhance the cyclic stability of CaO-based sorbents. Such a material has potential for high-temperature CO2 capture applications. Two Zr-modified CaO materials having a Ca/Zr molar ratio of 30 are prepared using the solid-state and citrate sol-gel methods. The solid-state method yields a physical mixture of CaO and ZrO2, while the citrate sol-gel method induces chemical bonding between ZrO2 and the CaO surface to form CaZrO3. The CO2 sorption uptake was significantly increased in both unmodified CaO and ZrO2-containing CaO [77.3 wt% (17.6 mol kg−1) and 73.2 wt% (16.6 mol kg−1), respectively, at 650 °C and 1 bar] when the citrate sol-gel method was used. The CaO having the chemically bonded ZrO2 reveals significantly enhanced cyclic stabilities, with an extremely high CO2 sorption uptake of 70.5 wt% (16.0 mol kg−1) on average during 10 cycles. On the other hand, the CaO containing the physically mixed ZrO2 reveals an average cyclic CO2 sorption uptake of only 37.2 wt% (8.5 mol kg−1). The chemically bonded ZrO2 is expected to be well scattered on the CaO surface and effectively cover the sorbent, resulting in the reduction of thermal sintering. In addition to cyclic stability, CO2 sorption kinetics of CaO-based sorbents can be enhanced through the citrate sol-gel method, which is resulted from the significantly reduced size of CaO particles.

The mOxy-CaL Process: Integration of Membrane Separation, Partial Oxy-combustion and Calcium Looping for CO2 Capture

CO2 capture and storage (CCS) is considered as a key strategy in the short to medium term to mitigate global warming. The Calcium-Looping process, based on the reversible carbonation/calcination of CaO particles, is a promising technology for post-combustion CO2 capture because of the low cost and non-toxicity of natural CaO precursors and the minor energy penalty on the power plant in comparison with amines capture based technologies (4-9 % compared to 8-12 %). Another interesting process to reduce CO2 emissions in power plants is oxy-combustion, which is based on replacing the air used for combustion by a highly concentrated (~95 % v/v) O2 stream. This work proposes a novel process (mOxy-CaL) for post-combustion CO2 capture based on the integration of membrane separation, partial oxy-combustion and the Calcium-Looping process. An oxygen-enriched air stream, which is obtained from air separation by using highly permeable polymeric membranes, is used to carry out partial oxy-combustion. The flue gas exiting partial oxy-combustion shows a CO2 concentration of ~30 % v/v (higher than 15 % v/v typical in coal power plants). After that, the flue gas is passed to the CaL process where the CO2 reacts with CaO solids according to the carbonation reaction. Thermogravimetric analysis show that the multicycle CaO conversion is enhanced as the CO2 concentration in the flue gas stream is increased. Process simulations show that the mOxy-CaL process has a high CO2 capture efficiency (~95%) with lower energy consumption per kg of CO2 avoided than previously proposed post-combustion CO2 capture technologies. Moreover, the overall system size is significantly lower that state-of-the-art CaL systems, which allows for an important reduction in the capital cost of the technology.

Residual bubble volume formed behind a sphere plunging into liquid bath (meniscus breakdown with finite velocity of sphere penetration)

The residual bubble formed from spherical particles plunging into a liquid bath has an important effect on the performance of CaO particles used for the desulfurization of melted iron. Previous work has theoretically estimated the residual bubble volume resulting from quasi-static sphere immersion by applying the energy minimization principle to the gas–liquid interface meniscus at its rupture [Katoh et al., “Residual bubble formed behind a sphere plunging into liquid bath (in Japanese),” Jpn. J. Multiphase Flow 28, 547–553 (2015)]. Here, we propose a method to theoretically estimate the residual bubble volume for sphere penetration with a finite velocity from 0.05 to 30 mm/s into a liquid bath. To do so, the meniscus rupture at the sphere’s critical depth was calculated via a dynamic equation in which the energy gradient along the sphere surface was considered as the driving force to move the triple-phase contact line. The bubble volume was then estimated by calculating the system energy at the meniscus breakpoint and by using the principle of minimum energy. The model results were verified experimentally for a variety of liquids, showing that the proposed model can be used for estimation of the residual bubble volume.

Recovery of phosphate and dissolved organic matter from aqueous solution using a novel CaO-MgO hybrid carbon composite and its feasibility in phosphorus recycling

Metal oxide-Carbon composites have been developed tailoring towards specific functionalities for removing pollutants from contaminated environmental systems. In this study, we synthesized a novel CaO-MgO hybrid carbon composite for removal of phosphate and humate by co-pyrolysis of dolomite and sawdust at various temperatures. Increasing of pyrolysis temperature to 900 °C generated a composite rich in carbon, CaO and MgO particles. Phosphate and humate can be removed efficiently by the synthesized composite with the initial solution in the range of pH 3.0–11.0. The phosphate adsorption was best fitted by pseudo-second-order kinetic model, while the humate adsorption followed the pseudo-second-order and the intra-particle diffusion kinetic models. The maximum adsorption capabilities quantified by the Langmuir isotherm model were up to 207 mg phosphorus (or 621 mg phosphate) and 469 mg humate per one-gram composite used, respectively. Characterization of composites after adsorption revealed the contributions of phosphate crystal deposition and electrostatic attraction on the phosphate uptake and involvement of π − π interaction in the humate adsorption. The prepared composite has great potential for recovering phosphorus from wastewater, and the phosphate sorbed composite can be employed as a promising phosphorus slow-releasing fertilizer for improving plant growth.

Ductile damage mechanism under shear-dominated loading: In-situ tomography experiments on dual phase steel and localization analysis

The nucleation, evolution and coalescence of voids is the well-established mechanism leading to ductile fracture under tension-dominated loading conditions. From a theoretical point of view, the same mechanism also applies to shear-dominated loading conditions. Here, an attempt is made to provide for the first time tomographic evidence of damage nucleation and evolution under shear-dominated loading in a modern engineering material. Monotonic experiments are performed on a flat double gage section smiley-shear specimen on the laminography stage of a synchrotron X-ray line. Based on fifteen scans of the entire gage section μm3, the mesostructural evolution inside a ferrite-bainite steel (FB600) is imaged in 3D up to the instant of specimen fracture. It is found that the as-received material includes a volume fraction of about 0.015% CaO particles. Upon mechanical loading at stress triaxialities evolving from 0 to 0.3, the ductile matrix detaches from these second phase particles, creating a prolate void space whose principal axis is aligned with the principal direction of the applied macroscopic field of deformation. The void space continues to grow while developing micro-crack like features. A large deformation analysis is performed on a representative volume element of the particle-matrix mesostructure replicating the experimental observations of void growth in an approximate manner. Furthermore, the simulation results suggest that a porosity as low as 0.05% is already sufficient to cause the ductile failure under shear-dominated loading through the formation of a band of localized plastic deformation at the mesoscale.

Performance of synthetic CaO-based sorbent pellets for CO2 capture and kinetic analysis

Three powdery CaO-based sorbents were synthesized respectively from calcium acetate and three different inert support precursors. Based on these sorbent powder, sorbent pellets without and with pore forming material (cellulose) were fabricated using an extrusion-spheronization method. Cyclic CO2 sorption performance of all powdery sorbents and sorbent pellets were tested in a TGA. It was found that introduction of inert supports was beneficial for enhancing the CO2 capture capacity of CaO. For sorbent powder, sintering was retarded due to high thermal stability of inert supports and good dispersion of CaO particles among inert supports, resulting in better performance of synthetic sorbent than calcined CaCO3. However, CO2 uptake of sorbent pellets deteriorated dramatically owing to damage of pore structure caused in the extrusion process. Cn and Xn was even lower than 0.1 g CO2/g sorbent and 20% for sorbent pellets during the 25th cycle. Adding cellulose was found to be effective for promoting the CO2 sorption capacity of sorbents which was mainly ascribed to enlarged specific surface area and pore volume during cellulose burning. Two kinetic models were used to understand the mechanism of the carbonation reaction and the models were proven to be feasible for analyzing the chemical reaction controlled stage and diffusion controlled stage in the carbonation process. Reaction rate constants obtained from kinetic calculation can also be used to explain the different performance between different types of sorbents.