Natural CaO Research Articles

Tailoring waste-derived materials for Calcium-Looping application in thermochemical energy storage systems

The integration of the Ca-looping (CaL) process in concentrated solar power systems (CSP) has been identified as an interesting approach for thermochemical energy storage (TCES) systems, since the TCES material regeneration can use clean and unlimited solar energy. The CaL cyclic stability of CaCO3 is an important parameter for the large-scale implementation of this technology, but in literature little attention has been paid to the absorptivity of natural CaO precursors such as limestone and other CaCO3-based materials. The CaCO3/CaO particles are usually white, and their absorptivity is relatively low at the wavelengths that correspond to solar radiation, limiting their use in directly irradiated reactors. In this work, the heat storage density (HSD) and absorptivity of different waste resources and natural Portuguese geological materials were assessed and improved after doping with 10 or 20 wt% of “dark” inert additives. A sludge and SiC were used to increase the CaL-TCES materials absorptivity at the wavelengths of solar visible radiation and to hinder the material sintering. It is found that the doping of the CaL-TCES materials with sludge hinders the sintering of the CaO particles, and after 20 carbonation-calcination cycles the HSD of the doped material is two times higher than the corresponding value for undoped material (400–408 vs 203 kJ/kg CaCO3). However, the sludge additive has a minimal impact on the solar absorptivity of the TCES material. On the other hand, the SiC addition to a waste of marble powder (WMP-Galrão) has a positive impact with an increase of 13 % on the absorptivity of the TCES material but does not improve the HSD. The absorptivity of CaL-TCES materials is a relevant property that can be improved through the use of “dark” inert additives. These new results show that TCES materials with improved HSD can be obtained through the tailoring of marble and sludge waste-derived materials, but sludges from other sources, with higher solar absorptivity need to be evaluated. The use of wastes is relevant for the circular economy goals, and it is environmentally friendly.

Development of structural descriptors to predict dissolution rate of volcanic glasses: Molecular dynamic simulations

AbstractEstablishing the composition–structure–property relationships for amorphous materials is critical for many important natural and engineering processes, including the dissolution of highly complex volcanic glasses. In this investigation, we performed force field molecular dynamics (MD) simulations to generate detailed structural representations for 10 natural CaO–MgO–Al2O3–SiO2–TiO2–FeO–Fe2O3–Na2O–K2O glasses with compositions ranging from rhyolitic to basaltic. Based on the resulting atomic structural representations at 300 K, we have calculated the partial radial distribution functions, nearest interatomic distances and coordination number, which are consistent with the literature data on silicate‐based glasses. Based on these structural attributes and classical bond valence models, we have introduced a novel structural descriptor, that is, average metal–oxygen (M–O) bond strength parameter, which has captured the log dissolution rates of the 10 glasses at both acidic and basic conditions (based on literature data) with R2 values of ∼0.80–0.92 based on linear regression. This structural descriptor is seen to outperform several other structural descriptors also derived from MD simulation results, including the average metal oxide dissociation energy, the average self‐diffusion coefficient of all the atoms at 2000 K, and the energy barrier of self‐diffusion. Furthermore, we showed that the MD‐derived descriptors generally exhibit better predictive performance than the degree of depolymerization parameter commonly used to describe glass and mineral reactivity. The results suggest that the structural descriptors derived from MD simulations, especially the average M–O bond strength parameter, are promising structural descriptors for connecting composition with dissolution rates of highly complex natural glasses.

Glycerolysis of Palm Fatty Acid Distillate (PFAD) as Biodiesel Feedstock Using Heterogeneous Catalyst

Biodiesel is normally produced through transesterification of triglycerides with methanol in the presence of an alkaline catalyst. With the uncertain crude oil prices and competition of vegetable oils used for food purposes, alternative feedstock for biodiesel production has to be studied. In this study, palm fatty acid distillate (PFAD), a by-product of the palm oil refinery was used as a feedstock. Glycerolysis reaction was carried out from 160 to 200 °C in the presence of a natural CaO catalyst derived from raw chicken eggshell. The commercial CaO was also evaluated as a control. The results showed that the free fatty acid (FFA) was reduced from 81 to 1.5% using activated eggshell as catalyst at reaction temperature of 180 °C and catalyst dosage of 1.5 wt% while commercial CaO reduced FFA to 3.7% at reaction temperature of 200 °C and 1.5 wt% of catalyst dosage, respectively. The treated PFAD can be used for biodiesel production.

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.

Role of calcium looping conditions on the performance of natural and synthetic Ca-based materials for energy storage

In this work, the multicycle activity of natural CaO precursors (limestone and dolomite) and Ca-based composites (Ca3Al2O6/CaCO3 and ZrO2/CaCO3 mixtures) has been studied for Thermochemical Energy Storage (TCES) in Concentrated Solar Power (CSP) plants by means of the Calcium-Looping process (CaL), using two integration schemes proposed elsewhere that differ in the calcination stages. Under CSP-He conditions, calcination for CaO regeneration is performed under pure He at low temperatures (725 °C) while under CPS-CO2 conditions calcination is carried out under pure CO2 at high temperatures (950 °C). The latter avoids the use of selective membranes to separate He from CO2 even though it requires the use of more expensive materials for solar receptors. Carbonation/calcination conditions drastically affect the multicycle CO2 uptake of the materials tested. Effective multicycle conversion is higher in CSP-He tests due to the mild conditions employed for calcination, which mitigates CaO sintering. On the other hand, the harsh calcination conditions used in CSP-CO2 tests enhance sintering of CaO derived from limestone and the Ca3Al2O6/CaCO3 composite due to the low Tammann temperature of Ca3Al2O6. CaO sintering is hindered by the presence of inert oxides with high Tammann temperatures, such as ZrO2 in the ZrO2/CaCO3 composite and MgO in dolomite. Dolomite derived CaO shows high effective conversion values along the carbonation/calcination cycles when tested under both types of conditions, as compared to limestone and the composites, which suggests that the integration scheme based on CSP-CO2 conditions would be a feasible alternative to CSP-He if natural dolomite were used as CaO precursor.

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.

Carbonation of Limestone Derived CaO for Thermochemical Energy Storage: From Kinetics to Process Integration in Concentrating Solar Plants

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination–carbonation of CaCO3 stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO2 capture in fossil fuel power plants or to enhance H2 production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a...

The Ca-looping process for CO2 capture and energy storage: role of nanoparticle technology

The calcium looping (CaL) process, based on the cyclic carbonation/calcination of CaO, has come into scene in the last years with a high potential to be used in large-scale technologies aimed at mitigating global warming. In the CaL process for CO2 capture, the CO2-loaded flue gas is used to fluidize a bed of CaO particles at temperatures around ~ 650 °C. The carbonated particles are then circulated into a calciner reactor wherein the CaO solids are regenerated at temperatures near ~ 950 °C under high CO2 concentration. Calcination at such harsh conditions causes a marked sintering and loss of reactivity of the regenerated CaO. This main drawback could be however compensated from the very low cost of natural CaO precursors such as limestone or dolomite. Another emerging application of the CaL process is thermochemical energy storage (TCES) in concentrated solar power (CSP) plants. Importantly, carbonation/calcination conditions to maximize the global CaL-CSP plant efficiency could differ radically from those used for CO2 capture. Thus, carbonation could be carried out at high temperatures under high CO2 partial pressure for maximum efficiency, whereas the solids could be calcined at relatively low temperatures in the absence of CO2 to promote calcination. Our work highlights the critical role of carbonation/calcination conditions on the performance of CaO derived from natural precursors. While conditions in the CaL process for CO2 capture lead to a severe CaO deactivation with the number of cycles, the same material may exhibit a high and stable conversion at optimum CaL-CSP conditions. Moreover, the type of CaL conditions influences critically the reaction kinetics, which plays a main role on the optimization of relevant operation parameters such as the residence time in the reactors. This paper is devoted to a brief review on the latest research activity in our group concerning these issues as well as the possible role of nanoparticle technology to enhance the activity of Ca-based materials at CaL conditions for CO2 capture and energy storage.

Material development and assessment of an energy storage concept based on the CaO-looping process

The cyclic carbonation/calcination reaction of CaO is discussed as a thermochemical energy storage system. Especially the high reaction temperature enables high theoretical energetic efficiencies. A severe issue is the strong cycle-to-cycle degradation of the material due to sintering. In order to overcome this, two different approaches are studied in this work: (1) Intermediate hydration of natural CaO to regenerate the sorbent. (2) Preparation of pure CaO and CaO/Al2O3 composites with different Ca/Al molar ratios. All materials prepared are structurally and morphologically characterized and for the evaluation of the sorbents, the CO2 uptake capacity during carbonation reaction is measured over multiple cycles. Besides the successful proof of an optimized cyclic stability, the energetic efficiency and storage density of the synthesized samples is calculated and compared to the benchmark material, natural CaO. In case of storage density, values of up to 3.5 times and in case of energetic efficiency, a factor of 1.2 referred to natural CaO are obtained within the 20th cycle.

Optimizing the CSP-Calcium Looping integration for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is considered a promising technology to overcome the issues of intermittent energy generation in Concentrated Solar Power (CSP) plants and couple them with yearly electricity demand. The development of this technology could favor the commercial deployment of CSP, which is considered as a key factor for new challenges in reducing GHG emissions. Among other possibilities, using the Calcium Looping (CaL) process for TCES is an interesting choice mainly due to the low cost of natural CaO precursors such as limestone (below $10/ton) and the high energy density that can be achieved (around 3.2GJ/m3). This manuscript explores several configurations in order to maximize the performance of the CSP-CaL integration with the focus on power cycle integration in the carbonator zone. For this purpose, firstly, a discussion about the possibility of using open and closed power cycles is carried out, which leads to the conclusion that a CO2 closed cycle is more appropriate. Then, a closed regenerative CO2 Brayton cycle is analyzed in further detail and optimized by means of the pinch-analysis methodology. A main output is that high plant efficiencies (of about 45%) can be achieved using a simple closed CO2 Brayton power cycle. The optimized integration layout shows good performances at carbonator to turbine outlet pressure ratios around 3, thus allowing for a feasible integration of the power cycle in the CSP-CaL system.

Transesterification activity and characterization of natural CaO derived from waste venus clam (Tapes belcheri S.) material for enhancement of biodiesel production

In this study, waste venus clam (WVC) was used as a raw materials of catalyst to produce biodiesel from palm oil at atmospheric pressure. The thermogravimetric, surface functional group, morphology, structure, basicity, surface area and leaching properties of catalyst was studied by using TGA, FTIR, SEM, XRD, TPD-CO2, BET, and AAS respectively. The result demonstrated that CS-900 catalyst gave high amount of total basicity at about 44 times than commercial CaO catalyst which is favorable for higher catalytic activity. Further, it was evident from BET that the shells calcined in temperature range 800–900°C was exhibited enhance surface area than uncalcined shells. Under the best reaction condition (temperature 65°C, methanol/oil molar ratio 15:1, reaction time 6h, and catalyst 5wt.% of oil), a high biodiesel yield of 97% was obtained. The leaching test on synthesized biodiesel revealed that the concentration of Ca in the biodiesel was 1.214ppm which is inacceptable levels of metals as ASTM D6751 (United State) and in Europe, EN 14214 (Europe) standards. The subsequent reuse of the catalyst indicates the viability of utilizing waste shell as green catalysts for synthesis of biodiesel.

Synthesis and characterization of Fe2O3/CaO derived from Anadara Granosa for methyl ester production

In this study, the iron (III) oxide (Fe2O3) doped on natural CaO catalyst (Fe2O3/CaO) was prepared and utilized in biodiesel production from used frying oil by a single-step reaction process. The heterogeneous Fe2O3/CaO catalyst was synthesized using impregnation method; followed by calcination at 500°C. The catalyst was characterized in detail by both qualitative and quantitative methods such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), thermal gravimetric analysis (TGA), ammonia and carbon dioxide-temperature programmed desorption (NH3-TPD and CO2-TPD), and Brunauer-Emmett-Teller (BET) analyses. The operating parameters such as molar ratio of methanol, catalyst amount and reaction time were investigated in order to optimize the reaction condition for the biodiesel production. As a result, the optimum reaction parameters found were 15:1 methanol-to-oil molar ratio, 65°C reaction temperature, 3h of reaction time and 1wt.% of the Fe2O3/CaO. The reported results revealed suggestively high potential of the heterogeneous Fe2O3/CaO catalyst for direct conversion of used frying oil to biodiesel-with the possibility to reuse at least 5 reaction cycles without any reactivation process.

Utilization of a cost effective solid catalyst derived from natural white bivalve clam shell for transesterification of waste frying oil

The solid oxide CaO catalyst derived from natural white bivalve clam shells were employed to produce biodiesel via transesterification of waste frying oil (WFO). The shell materials were calcined in a muffle furnace at 900°C with an optimum time of 4h to transform calcium species in the shells into active CaO catalyst. The catalyst was characterized using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Atomic X-ray Spectrometry (EDAX). The activity of the natural CaO catalyst was compared with the commercial CaO. A high biodiesel yield of 95.84% was obtained at a methanol/oil molar ratio of 18:1, 8.0wt.% catalyst, 3h reaction time and temperature of 65°C. The biodiesel composition was determined by Gas Chromatography coupled with Mass Spectroscopy (GC–MS).

Investigation of natural CaO–MgO sorbent for CO2 capture

ABSTRACTThe cyclic CO2 capture activity of natural CaO–MgO sorbents derived from dolomite or limestone with different MgO contents has been investigated on a TGA, with the consideration of the influence of H2O during the carbonation and calcination. The scanning electron microscopy (SEM) and the brunauer emmett teller (BET) were used to characterize the fresh and used CaO–MgO sorbents. The results have indicated that the natural CaO–MgO sorbent with MgO content of 31.5%–38.7% should be good to improve the cyclic capture activity of CaO. The CaO–MgO sorbent has the best cyclic activity when H2O is present during both carbonation and calcination. H2O changes the sorbent morphology producing bigger particles and pores for the sintering during calcination but makes the sorbent have more stable surface area for the taking palace of the fast kinetic carbonation reaction. Besides, H2O decreases the product layer diffusion resistance and increases the reaction rate during the transition and the product layer diffusion control stage. After sorbent sinters during the reaction cycles, the H2O‐improving effect becomes more obvious as the MgO content increases. The results indicate the potential of the natural CaO–MgO sorbent with proper MgO content for cyclic CO2 capture in the presence H2O. Copyright © 2013 Curtin University of Technology and John Wiley &amp; Sons, Ltd.