CaO Particles Research Articles

Multiscale model for steam enhancement effect on the carbonation of CaO particle

A multiscale model including scales at the surface, grain, and particle was developed to understand the steam enhancement mechanism on the carbonation of CaO particle. The interaction of H2O with CaO occurring at the surface scale exhibited an enhancement effect on the product layer diffusion at the grain scale, while the grain growth due to the product layer diffusion at the grain scale exhibited an important effect on the pore structure and intraparticle gas diffusion at the particle scale. The developed multiscale model was validated with the experimental data, and the effect of steam addition on carbonation performance was discussed. The effect of steam on CaO carbonation at higher temperatures (600 ~ 700 °C) was much less significant than that at lower temperatures (400 ~ 500 °C), due to the pore plugging phenomenon. In addition, the controlling step of the carbonation in the presence of steam was analyzed. Calculated results show that the external gas diffusion resistance is small enough during the reaction process. The controlling step of the carbonation at 400 °C is the chemical reaction step, while the controlling step of the carbonation at 700 °C is the intraparticle gas diffusion step.

Efficient production of biodiesel by using a highly active calcium oxide prepared in presence of pectin as heterogeneous catalyst

The cation binding ability of pectin was explored for the preparation of a highly active CaO catalyst for soybean oil transesterification. The catalyst was prepared by the precipitation method using Na2CO3 and Ca(NO3)2 in the presence of pectin followed by calcination. The best catalyst, CaP-600, was prepared at 600 °C and was characterized by FTIR, TGA, BET, CO2-TPD and powder X-ray diffraction (PXRD). CaP-600 was characterized as CaO containing carbonaceous materials left from pectin combustion. At only 1 wt% CaP-600 loading, biodiesel conversion reaches 99% after 4 h with a methanol:oil = 7:1 M ratio. Importantly, the calcium content in the produced biodiesel was only 0.7 ppm, which implies a satisfactory compliance with the ASTM D6751 and EN 14,214 standards. To the best of our knowledge, this is the best CaO catalyst reported for biodiesel production in terms of efficiency and amount of calcium leached. For comparison, CaO prepared in the absence of pectin showed poor catalytic activity in the optimized reaction conditions, demonstrating that the presence of the biopolymer prior to the calcination step is crucial for the catalytic performance of the CaO particles. Possible rationales for the biopolymer role are discussed.

Possibility of Calcium Oxide from Natural Limestone Including Impurities for Chemical Heat Pump

Improving energy recycle is an important way to save energy resources and preserve the global environment. Chemical heat pump (CHP) is a technology for saving energy, which utilizes chemical reactions to store thermal energy such as waste heat and solar heat, then release it to provide heat for heating/cooling/refrigeration. For a practical CHP, it is necessary to find cheaper and more stable supply materials. In order to evaluate the possibility of calcium oxide from natural Ofunato natural limestone including impurities, we compare Ofunato limestone with Kawara natural limestone and Garou natural limestone from Japan. These calcium oxides worked as a reactant for CaO/H2O/Ca(OH)2 CHP by repeated hydration/dehydration reaction cycle experiments in a thermogravimetric analyzer. As a result, Ofunato CaO exhibits a high hydration reaction rate after decarbonization at 1223 K for 5 h. The reactivity increased by the repeated hydration reaction although the first hydration rate was low. Furthermore, the sintering of impurities in Ofunato limestone occur easier than that in Kawara limestone with lower impurities. The impurities adhered to the surface of the CaO particle to make specific surface area of CaO particle smaller, which could inhibit hydration reaction of CaO particle. Even if Ofunato limestone contains some impurities, it can be utilized as a raw material for chemical heat pumps.

Numerical modelling of multiphase FLOW and calcination process in an industrial calciner with fuel of heavy oil

In a calciner for cement production, limestone (CaCO3) particles are decomposed into quicklime (CaO) and carbon dioxide (CO2) during the calcination process. The complex flow and temperature distribution caused by fuel combustion and calcination reaction of limestone are essential to calciner performance. This paper presents a method by coupling the calcination model and combustion into multiphase flow simulation. In this approach, flue gases, CaCO3, and CaO particles are defined as multiple continuous phases, and heavy oil droplets are defined as discrete phase. This simulation is based on the Euler multiphase model for continuous phase and discrete phase model for the oil phase.The transport of heat, mass, momentum, species and energy among these different phases are calculated by solving the governing equations of each phase with phase-interacting coefficients and models. To verify the accuracy of this modeling approach, numerical predictions were compared with measurement data collected from cement production lines, which yielded satisfactory results. This modeling approach can help optimize calciner design, performance, and process parameters in actual industrial applications.

Fabricating an effective calcium zirconate layer over the calcia grains via binder-jet 3D-printing for improving the properties of calcia ceramic cores

To improve the formability and properties of calcia (CaO) based ceramic core, the binder-jet 3D-printing was performed to fabricate porous CaO/caicium zirconate (CaZrO3) ceramic core composites with two nanozirconia addition methods. The effects of the nanozirconia addition method and additive amount on the properties of the 3D-printed CaO/CaZrO3 bodies were investigated. The dimensional accuracy, surface roughness, relative density, bending strength, and hydration resistance of CaO/CaZrO3 bodies printed with a nanozirconia suspension binder for deposition in the CaO powder layer were better than those of CaO/CaZrO3 bodies printed in the traditional manner of directly mixing nanozirconia in the CaO powder. Application of the nanozirconia suspension uniformly capped nanozirconia particles on the surfaces of the CaO particles and filled the pores of the CaO powder layer, which afforded denser and more uniform green bodies. After sintering at 1500 °C, the ZrO2 formed thicker and denser CaZrO3 layers with the CaO over the CaO grain surfaces, which improved the strength and hydration resistance of the sintered CaO/CaZrO3 ceramic core bodies, and certainly reduced their collapsibility.

Inducible regulation of spherical CaO particle for the recycling of carbide slag

Various factors affecting the high temperature compressive strength (TCS) for the carbide slag-based CaO pellets were systematically examined both experimentally and theoretically. It showed that the spherical CaO particles with microstructure can enhance the TCS of the pellets, and the higher the spheroidization of the particles, the higher the TCS. Inducing H3BO3 can lead to a low-temperature nucleation of CaO particle, inhibit the growth of CaO grain, and thus form spherical CaO particles. The TCS of CaO pellet from Ca(OH)2 was optimized with the response surface methodology with a highest value of 37.4 MPa. For the CaO pellet from the carbide slag, the TCS under optimal conditions was 39.67 MPa. However, it was found out that an excess of H3BO3 inducer in the CaO pellets from the carbide slag could produce eutectic calcium borate with a low melting point, resulting in a decreased TCS.

Calcium-looping for thermochemical energy storage in concentrating solar power applications: Evaluation of the effect of acoustic perturbation on the fluidized bed carbonation

In the framework of thermochemical energy storage (TCES) in concentrating solar power (CSP) plants, the calcium-looping (CaL) process, carried out in fluidized bed reactors, is receiving increasing research interest due to the high energy density and the extremely low price, nontoxicity, and wide availability of natural CaO precursors. One of the main open challenges in CaL is represented by finding solutions to the progressive decline in the CaO carbonation conversion with the number of cycles, which is due to the sorbent deactivation caused by sintering and pore-plugging. In this framework, the reduction of the CaO particles size has been reported to improve the carbonation conversion and, therefore, the achievable energy density, by maximizing the availability of the sorbent surface exposed to the gaseous phase and hindering the natural loss of CaO mutlicyclic activity. However, the use of fine particles in fluidized bed reactors is challenging due to agglomeration, channeling and plugging phenomena. In this work, the possibility to use a fine natural limestone (<50 μm) for CaL at TCES-CSP conditions in a fluidized bed reactor has been investigated for the first time. In particular, sound-assisted fluidization has been proposed as technique to allow the use of such fine particles in fluidized bed reactors, thus overcoming the strict limitation posed by particle size applicable in ordinary fluidized bed reactors. Ordinary and sound-assisted cyclic CaL tests at CSP-TCES operating conditions have been performed in a lab-scale fluidized bed reactor in order to study the influence of the application of high intensity acoustic fields on the carbonation performances. The effect of sound parameters (SPL and frequency) has also been highlighted.

Effect of Vanadium and Titanium on Desulfurization of CaO Slag in Liquid Iron

The possibility of vanadium and titanium participating in the CaO desulfurization reaction has been evaluated. The desulfurization products of CaO which were added to liquid iron containing vanadium–titanium in lab conditions were observed. At the early stage of adding CaO, titanium and sulfur ware agglomerated on the surface of CaO particles. The particles were composed of CaO, TiO2, and CaS. However, vanadium oxide was not detected. It was proposed that the titanium rather than the vanadium could react with CaO and sulfur. The desulfurization kinetics experiment showed that the high titanium content in liquid iron reduced desulfurization velocity, while vanadium had little effect on the desulfurization. The reason for this was that the TiO2 which surrounded the CaO particle impeded the mass transfer of sulfur. The vanadium and titanium had a little influence on the final sulfur content of CaO desulfurization. The theoretical discussion of these phenomena was carried out. The controlling reaction of final sulfur content was (CaO) + [S] + [C] = (CaS) + CO(g).

Mg-promoted Ni-CaO microsphere as bi-functional catalyst for hydrogen production from sorption-enhanced steam reforming of glycerol

The sorption-enhanced steam reforming (SESR) process provides a simple way to produce high-purity hydrogen. And a key requirement for SESR is the availability of high cyclic stability of sorbent due to the rapid decline of sorption capacity caused by the sorbent sintering. Herein, we report a facile one-pot hydrothermal synthesis method by using in situ generated carbon microspheres as templates to prepare porous Ni-CaO-MgO bi-functional catalyst. The catalyst possessed MgO-stabilized, Ni and CaO microspheres featuring highly porous structure, which provided sufficient void space for volume variations and reduced the contact between CaO particles which was beneficial to improving the stability. Meanwhile, the uniformly distributed MgO had been found to reduce the particle size of CaO and stabilize the structure of bi-functional catalyst to ensure a stable CO2 uptake. 10Ni-CM7 as the best performing material only required 8.1 wt% MgO, showing 40% loss in sorption-enhanced effect after 10 cycles of repeated SESRG-desorption, where CaO utilization kept 59.1% exceeding the commercial CaO by ~109%.

Pinning Effect of Oxide Particles on Grain Boundaries of a Low Aluminum Non‐oriented Electrical Steel

In this article the pinning effect of oxide particles on grain boundaries of a low aluminum non‐oriented electrical steel is studied. According to their locations and morphologies in annealed steel samples, oxide particles are classified into three types: globular ones at grain boundaries, globular ones in the interior of grains, and chain‐like ones pinning at grain boundaries. The chemical composition of oxide particles shows a significant influence on the probability pinning at grain boundaries. The elongation ratio of oxide particles becomes larger with the decrease in their viscosity that is determined by the chemical composition and temperature and is calculated using FactSage. Based on the thermodynamic analysis, small particles forming during solidification have more content of SiO2 due to the reaction between the dissolved oxygen and silicon in the steel. Particles of large size and large elongation ratio show larger pinning force on the grain growth. Removing large SiO2–Al2O3–MnO–CaO particles as far as possible, and controlling the composition of oxide particles to achieve larger viscosity than the steel matrix, will retard their elongation during the hot‐rolling process so that the magnetic properties of the steel are improved.

Insights and utility of cycling-induced thermal deformation of calcium-based microporous material as post-combustion CO2 sorbents

On the quest of finding ideal sorbent for post-combustion CO2 capture, calcium-based sorbent seems to have the potential, but often it cannot sustain its reactivity, especially after repeated cycle of sorption. This work aims to unravel the controlling factors in carbonation reaction and thermal-induced deformation of skeleton pore network that limits the CO2 absorptivity of calcium-based sorbent. Through precise measurement of CO2 absorption activity using TGA/DSC and a series of characterization, this study paves the way for the development of next-generation CaO sorbent that has high CO2 uptake capacity and thermal stability. Key findings include CaO particles with severe point defects contribute to fast CO2 absorption activity. The transformation from CaCO3 phase to CaO phase from organic precursor is 4 times higher than the inorganic precursor. Decomposition of calcium formate is thermally stable regardless of calcination temperature. Citrate-based structure precursor is able to produce homogeneous nanosized CaO particle. Shifting of reaction controlling regime from fast carbonation reaction to diffusion limited stage happened at Thiele modulus of 1.35. Lastly, first stage of fast carbonation reaction will take place at CaO sorbent’s surface with proximate zero activation energy and second stage of slow carbonation reaction is controlled by high activation energy of ion diffusion behavior in CaCO3 ionic crystals at product diffusion layer. Future research direction can focus on reproducing long periodical citrate-like structural precursor using sol-gel method to mimic the behavior of calcium formate and calcium citrate to form nano-sized CaO particles with thermally stable crystal structure.

Development of CaO-based adsorbents loaded on charcoal for CO2 capture at high temperature

CaO-based adsorbents have the potential to be used for CO2 capture at high temperature. However, CaO-based adsorbents exhibit a sharp decay in CO2 uptake capacity over multiple cycles, owing to the sintering of CaO particles. In this paper, a series of charcoal supported CaO-based adsorbents were developed to improve the CO2 capture performance of CaO using three different methods: physical mixing, wet impregnation and sol-gel method. The influences on CO2 capture of CaO loading and carbonation temperature are also included. The morphology and structural properties of the adsorbent were investigated by means of electron microscopy, nitrogen adsorption and XRD. It is found that the novel sorbent with an optimal mass ratio of CaO to charcoal of 4:1 prepared by the sol-gel method exhibits an initial capture capacity of 15.1 mmol g−1 and maintains a capacity of 8.0 mmol g−1 after 15 cycles of carbonation (600 °C) and calcination (650 °C), around 60% higher than that of sol-gel CaO. The CaC-4 possesses a porous stucture with a high surface area of 63.6 m2·g−1 and a pore volume of 0.166 cm3·g−1, making CO2 diffusion easier. The XRD analysis displays that crystalline size (26 nm) of the CaO phase in CaC-4 is much smaller than that of the reference bulk CaO (96 nm), reflecting that charcoal can effectively inhibit the growth of CaO crystalline. Furthermore, the introduction of charcoal derived from biomass pyrolysis will improve the economic viability of the CO2 capture process.

Immobilization of calcium oxide onto polyacrylonitrile (PAN) fibers as a heterogeneous catalyst for biodiesel production

We describe the design, creation, and usage of a CaO catalyst immobilized onto polymeric mats for environmentally-friendly biodiesel production. The polyacrylonitrile (PAN) fiber mats were prepared by electrohydrodynamic processing (EHD), commonly known as electrospinning or electrospraying, in which immobilized CaO particles were either physically entrapped on the fibers or chemically bound onto the fiber surface by a dopamine linkage. These two catalyst materials were later successfully used in the transesterification of fresh canola oil into biodiesel. Mechanically entrapped CaO particles in the PAN fibers were able to be re-used up to six times in the conversion of triglycerides into biodiesel, while the chemically immobilized catalyst was found impossible to reuse. The use of EHD processing allows us to create an easily separable, reusable catalyst that could be commonly used in transesterification reactions.

Enhancement of sintering resistance of CaO-based sorbents using industrial waste resources for Ca-looping in the cement industry

Keeping a high stability and CO2 capture capacity of CaO-based sorbents during the Ca-looping process is still a challenge. The main goal and the innovative idea addressed in this study consists of investigating if solid industrial waste resources such as a coal fly ash (CFA) and a spent Fluid Catalytic Cracking (SFCC) catalyst, can be used as particle spacers to improve the sintering resistance of two CaO-based sorbents. These two inert industrial waste materials are used in the present work for increasing the CaO particles separation and consequently, reducing their coalescence and hindering severe sintering at the high Ca-looping temperatures. There are currently no studies in the literature on the use of industrial SFCC wastes in blends with CaO based sorbents acting as CaO particles spacer with the objective of reducing the Ca-looping sorbents deactivation along the cycles of carbonation-calcination.Despite the mineralogical and textural differences between the CFA and SFCC catalyst industrial wastes, the tests carried out in a fixed bed laboratory reactor showed that the addition of a small fraction of waste to the CaO sorbent (c.a. 10%) seems to be an interesting option to improve the CO2 capture technology efficiency. During the Ca-looping, the volume and stability of sorbent mesopores is essential to achieve higher and stable carbonation conversion values, and since the CFA and SFCC increase the SBET, they contribute to enhance the sintering resistance.The innovative results presented in this study show that the industrial CFA and SFCC wastes have potential to be an economically attractive option thus contributing to reduce the cost of the Ca-looping cycle CO2 capture process, as well as to minimize the adverse environmental impacts of the high volume of industrial wastes generated.

3-6-1 CaO粒子によるタール改質実証試験

3-6-1 CaO粒子によるタール改質実証試験

Modification of inclusions by Al and Ca in ferrosilicon during alloying process of 18Cr–8Ni stainless steels

ABSTRACTIn the current study, the modification behaviours of the SiO2–MnO inclusions by the additions of three types of ferrosilicon including low Al and Ca ferrosilicon, high Al ferrosilicon, and high Ca ferrosilicon were investigated by the lab experiment and thermodynamic calculation. The SiO2–MnO inclusions change little after the low Al and Ca ferrosilicon addition. The high Al ferrosilicon significantly promotes the formation of Al2O3-rich inclusions in 18Cr–8Ni stainless steels. The high Ca ferrosilicon can modify SiO2–MnO inclusions to larger Al2O3–SiO2–CaO particles, indicating that the source of large Al2O3–SiO2–CaO inclusions in the molten steel is not only the entrapment or emulsification of the slag but also the modification of inclusions by Ca in the ferrosilicon. Thermodynamic calculated results have a similar tendency with observed experimental results. The low Al and Ca ferrosilicon is suggested to be used for alloying process in the ladle furnace.

Different catalytic action of ion-exchanged calcium in steam and CO2 gasification and its effects on the evolution of char structure and reactivity

The catalytic action of ion-exchanged calcium (Ca) in steam and CO2 gasification of coal char was examined. Its effects on pore structure and reactivity of char were also investigated. The char was prepared from a low rank coal that was first demineralized and then loaded with Ca by ion-exchanging. It was gasified at 900 °C in steam or CO2 on a specially designed thermogravimetric reactor (TGR). Partially-gasified chars were extracted at different time intervals and subject to analyses by X-ray diffraction (XRD), nitrogen adsorption measurement and scanning electron microscopy (SEM). The results show that, in steam gasification, the Ca evolves predominantly into CaO particles. They are highly dispersed on the char surface and seen to attack the char by a typical channeling mode. In contrast, the Ca is transformed into both CaO and CaCO3 in CO2 gasification. These Ca-containing compounds undergo significant sintering and form a mixture layer on the char surface. The catalytic action of Ca can be appropriately described by a surface recession mode. These differences are responsible for the evolution of char structure and reactivity. The channeling action of Ca in steam gasification results in a higher surface area and pore volume. The highly dispersed CaO particles more efficiently catalyze the reactions at the early stage of gasification. In CO2, the char possesses a less developed pore structure. The catalysts are in close contact with carbon at the later stage of CO2 gasification and the char remains a higher specific reactivity.

Preparation of Y₂O₃ Coated CaO Ceramic Cores with Anti-Hydration Performance and High-Interface Stability Against Interface Reaction of Ti-6Al-4V Alloys.

In this study, we describe a novel method for preparing Y₂O₃@CaO ceramic cores with anti-hydration performance and high-interface stability against interface reaction of Ti-6Al-4V alloys. The effect of Y₂O₃ coating on microstructure, mechanical, anti-hydration properties of ceramic cores and interface reaction with Ti-6Al-4V alloys was studied. The results show that the surface charge of Y₂O₃ and CaO are opposite at the pH value of 13, which might result in an electrostatic force and become the main driving force of Y₂O₃ particles absorb on the surface of CaO particles. The Y₂O₃ coating improved the anti-hydration properties of the CaO-based ceramic cores after sintering at 1450 °C. Meanwhile, the flexural strength improved from 11.2 to 18.8 MPa. At last, the interaction between the ceramic cores and Ti-6Al-4V metal were studied by centrifugal investment casting. Y₂O₃ coating can effectively reduce the interface reaction and the thickness of the interaction layer in the casting was less than 10 μm. The results suggest that the Y₂O₃@CaO ceramic with anti-hydration performance provide excellent mechanical and high-interface stability against interface reaction of Ti-6Al-4V alloys.

In-situ capturing of fluorine with CaO for accelerated defluorination roasting of lepidolite in a fluidized bed reactor

In-situ capturing of fluorine (F) with CaO in a fluidized bed reactor is proposed to accelerate the defluorination reaction and to improve the lithium extraction from lepidolite ore. Compared to the roasting process without addition of CaO, the Li extraction efficiency is improved by ca. 15 percentage points in the present of CaO during the roasting reaction. And more than 91% of the fluorides volatilized from the lepidolite are captured by CaO particles in the fluidized bed reactor and are converted to CaF2. The formation of CaF2 on the surface of CaO particle is attributed to the generated HF from the lepidolite particles. The in-situ capturing of HF by addition of CaO changes the thermodynamic equilibrium state that benefits the defluorination reaction. Therefore, the in-situ capturing of fluorine with CaO in fluidized bed reactor is a promising method for the de-fluorinate and for the lithium extraction for versatile applications.

Mesoporous electronegative nanocomposites of SBA-15 with CaO–CeO2 for polycarbonate depolymerization

The depolymerization of polycarbonate (PC) into bisphenol A (BPA) is performed by defective xCaO/Ce-SBA-15 nanocomposite assisted by plasma treatment. For such composite catalyst, CaO and CeO2 particles are finely encapsulated into the tubular SBA-15 without leaching or aggregation occurring. Abundant oxygen vacancies are generated from the doping of Ca and Ce atoms into the lattice of SBA-15 composite via the plasma surface engineering, entrusting strong basic sites to such mesoporous composite. The interface interaction between Ca and Ce with defective dimensional support materials predominated to generate maximum basic sites is of critical importance in tailoring the BPA yield. CaO/Ce-SBA-15 with rich oxygen vacancies and rough surface creates rich basic sites to achieve the high efficiency of PC alcoholysis and durable repeated cycles. Meanwhile, the synergistic catalysis between CaO and CeO2 is achieved, while SBA-15 with smaller disordered pores and fine connectivity between adjacent large pore channels enables a good dispersity of such xCaO/Ce-SBA-15 composite and finely prevents the leaching of Ca and Ce particles. Additionally, the high-density defects from the substitution of Ce by Ca and Si atoms as well as the plasma treatment play active basic sites during PC adsorption and activation. Such graft also leads SBA-15 itself becoming a solid base. Hence, the superior of PC depolymerization and superior durability are obtained due to the composition synergistic effects and rich abundant basic sites. It is noted that the abundant Ca on ceria surface provides affluent electrons, which makes decreased Ce valence in CeO2 subsurface and elevation of basic sites. This work explores the generation of tunable basic sites for SBA-15 and is instructive for fabricating desirable multicomponent catalysts composed of bifunctional non-novel catalyst for heterogeneous catalysis with rich surface oxygen vacancies.