Carbonation Calcination Cycles Research Articles

Modelling of a calcium-looping fluidized bed reactor system for carbon dioxide removal from flue gas

Abstract Calcium-looping process was simulated by solution of one-dimensional mass and energy balance equations for both interconnected fluidized bed reactors. Kinetics for the carbonator and calciner were derived from literature sources and were revised to include the effects of sulphation. The degree of apparent carbonation was compared to the actual level of carbon dioxide removal through a series of sensitivity analyses. It has been found that carbonation decreases with an increase in temperature. Sulphation increases with an increase in temperature. The activity of calcium oxide decreases with an increase in carbonation–calcination cycles. Neglecting the effect of sulphation during the design of the calcium-looping system leads to overestimation of active calcium particles that will react with carbon dioxide.

Catalytic gasification of wet municipal solid waste with HfO2 promoted Ni-CaO catalyst for H2-rich syngas production

Catalytic gasification, coupled with in-situ CO2 capture over Ni-CaO catalyst, is considered to be an effective approach for H2-rich and tar-free syngas production. However, the poor stability of Ni-CaO based catalyst raises a question regarding its large scale application. In this study, HfO2 was used as a stabilizer and promoter for the Ni-CaO catalyst system. The stability of catalyst was evaluated through cyclic carbonation-calcination test with a thermogravimetric analyzer. The results showed that HfO2 incorporated catalysts performed better stability towards cyclic CO2 capture. The effect of different HfO2 additions in catalyst, catalyst to municipal solid waste (C/MSW) ratio, gasification temperature, and moisture content (MC) of MSW was investigated on syngas composition, H2 yield, dry gas yield (DGY) and product distribution (syngas, tar and char). The results indicated that H2 yield was improved from 212 mL/g (without catalyst) to 442 mL/g with Ni-CaO (NC) catalyst and further improved with the application of HfO2 promoted catalysts (Ni-CaO-HfO2). The catalyst with 20% HfO2 (NCH-20) exhibited maximum H2 yield of 597 mL/g. Moreover, a significant reduction in tar content from 8.79 wt% (without catalyst), 3.19 wt% (with Ni-CaO) to 2.81 wt% (with NCH-20) was also recorded with HfO2 promoted catalysts.

Effects of CaCl2 on cyclic carbonation-calcination kinetics of CaO-based composite for potential application to solar thermochemical energy storage

The calcium looping (CaL) process is a promising thermochemical energy storage option for concentrated solar power systems due to its great advantages of high energy density and low material cost. However, CaO-based sorbents often suffer from continuous degradation in their reversibility due to the formation of a passivation layer and evolution of a sintering effect. In this work, we focused on the effects of CaCl2 as an additive to CaO sorbents with the aim to enhance reversibility by addressing the mass-transfer issue. A variety of CaO-based sorbents with CaCl2 were synthesized, characterized, and examined their reaction patterns during cyclic carbonation-calcination. The experimental results show that the addition of CaCl2 enhances the rate of the carbonation reaction, based on enhanced reactant diffusion. The CaCl2 causes reduction of surface area; however, the addition of MgO effectively delays sintering. Therefore, CaO-based sorbents with CaCl2 and MgO achieved high reversibility with enhanced durability.

Synthesis and Formation Mechanism of Limestone-Derived Porous Rod Hierarchical Ca-based Metal-Organic Framework for Efficient CO2 Capture.

Limestone is a relatively abundant and low-cost material used for producing calcium oxide as a CO2 adsorbent. However, the CO2 capture capacity of limestone decreases rapidly after multiple carbonation/calcination cycles. To improve the CO2 capture performance, we developed a process using limestone to transform the material into a rod Ca-based metal–organic framework (Ca-MOF) via a hydrothermal process with the assistance of acetic acid and terephthalic acid (H2BDC). The structural formation of rod Ca-MOF may result from the (200) face-oriented attachment growth of Ca-MOF sheets. Upon heat treatment, a highly stable porous rod network with a calcined Ca-MOF-O structure was generated with a pore distribution of 50–100 nm, which allowed the rapid diffusion of CO2 into the interior of the sorbent and enhanced the CO2 capture capacity with high multiple carbonation–calcination cycle stability compared to limestone alone at the intermediate temperature of 450 °C. The CO2 capture capacity of the calcined porous Ca-MOF-O network reached 52 wt% with a CO2 capture stability of 80% after 10 cycles. The above results demonstrated that rod Ca-MOF can be synthesized from a limestone precursor to form a porous network structure as a CO2 capture sorbent to improve CO2 capture performance at an intermediate temperature, thus suggesting its potential in environmental applications.

The Zr-Doped CaO CO2 Sorbent Fabricated by Wet High-Energy Milling

We fabricated the Zr-doped CaO sorbent for high-temperature CO2 capture by the wet high-energy co-milling of calcium carbonate and natural zirconium dioxide (baddeleyite) for the first time. The morphology of the material was examined by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction. Its CO2 uptake capacity was determined using thermogravimetric analysis. After 50 carbonation–calcination cycles, the Zr-doped CaO sorbent characterized by a high enough CO2 uptake capacity of 8.6 mmol/g and unchanged microstructure due to CaZrO3 nanoparticles uniformly distributed in the CaO matrix to prevent CaCO3 sintering under carbonation. The proposed easy-to-implement CaO-based sorbents fabrication technique is promising for industrial application.

CO2 capture from waste-to-energy plants: Techno-economic assessment of novel integration concepts of calcium looping technology

In Waste-to-Energy (WtE) plants, municipal solid waste (MSW) is combusted while power and/or heat are produced. This approach will largely remain as a promising option to handle the MSW capacities in the future. Due to the organic waste fractions present in MSW, net negative CO2 emissions are feasible when integrating carbon capture and storage (CCS) processes into WtE plants. The calcium looping (CaL) process represents one option to capture CO2 from WtE plant exhaust gases. Hereby, CO2 is separated by a circulating limestone-based sorbent being exposed to cyclic carbonation-calcination reaction regimes. Within this study, a techno-economic analysis of a CaL retrofit on a generic 60 MWth WtE plant is conducted. The analysis considerers three different types of supplementary fuel for the CaL process, namely coal, natural gas (NG) and solid recovered fuel (SRF). Based on a detailed process model, economic key performance indicators were calculated by means of a bottom-up approach. Additionally, different heat integration concepts were proposed and assessed. The techno-economic results are discussed in comparison to a benchmark MEA scrubbing process. It was found that levelized cost of electricity increases quite significantly, which leads to cost of CO2 avoidance in the range of 119 EUR/tCO2,av (CaL-SRF) up to 288 EUR/tCO2,av (MEA). It is important to note, that the supply of negative CO2 emissions from a CCS equipped WtE plant enables a cost-efficient solution to at the same time treat MSW in a carbon neutral way while clean heat and/or power as well as negative CO2 emissions are delivered.

Multi-Metals CaMgAl Metal-Organic Framework as CaO-based Sorbent to Achieve Highly CO2 Capture Capacity and Cyclic Performance.

In this study, Ca-based multi-metals metal-organic framework (CaMgAl-MOF) has been designed as precursor material for carbon dioxide (CO2) capture to enhance the CO2 capture capacity and stability during multiple carbonation-calcination cycles. The CaMgAl-MOFs were constructed from self-assembly of metal ions and organic ligands through hydrothermal process to make metal ions uniformly distributed through the whole structure. Upon heat treatment at 600 °C, the Ca-based multi-metals CaMgAl-MOF would gradually transform to CaO and MgO nanoparticles along with the amorphous aluminum oxide distributed in the CaO matrix. XRD, Fourier transform infrared (FTIR), and SEM were used to identify the structure and characterize the morphology. The CO2 capture capacity and multiple carbonation-calcination cyclic tests of calcined Ca-based metal-organic framework (MOF) (attached with O and indicated as Ca-MOF-O) were performed by thermal gravimetric analysis (TGA). The single metal component calcined Ca-MOF sorbent have the highest CO2 capture capacity up to 72 wt.%, but a lower stability of 61% due to severe particle aggregation. In contrast, a higher Ca-rich MOF oxide sorbent with tailoring the Mg/Al ratios, Ca0.97Mg0.025Al0.005-MOF-O, showed the best performance, not only having the high stability of ~97%, but also maintaining the highest capacity of 71 wt.%. The concept of using Ca-based MOF materials combined with mixed-metal ions for CO2 capture showed a potential route for achieving efficient multiple carbonation-calcination CO2 cycles.

Enhanced hydrogen production via catalytic toluene reforming with in situ carbon dioxide capture: Effects of a hybrid iron-calcium composite prepared by impregnation

Calcium looping gasification (CLG) can produce hydrogen-rich syngas with in situ carbon dioxide capture. It is challenging to enhance tar reforming performance and to simultaneously promote cyclic carbonation reactivity and mechanical strength of CaO-based absorbent for biomass gasification. A hybrid iron-calcium absorbent (Ca-Al-Fe) is prepared via a two-step impregnation method and compared with two conventional absorbents (Ca and Ca-Al). Results showed that chemical components of Ca-Al-Fe were CaO, mayenite (Ca12Al14O33) and brownmillerite (Ca2Fe2O5). Ca12Al14O33 was beneficial in hindering sintering and enhancing mechanical strength of the hybrid absorbent. After 10 carbonation-calcination cycles, conversion of CaO in Ca-Al-Fe increased from 43.6% of initial carbonation to 56% of the final cycle. Mechanical strength of Ca-Al-Fe was elevated to 101 N which was much higher than that of conventional CaO (39.4 N). Ca2Fe2O5 was observed to have a catalytic effect on the reforming of biomass tar model component (toluene). Comparing with Ca and Ca-Al, the adoption of Ca-Al-Fe resulted in much higher yield and concentration of hydrogen in reforming gas as well as less residue tar and deposited coke. To further understand performance of the hybrid absorbent at various reaction conditions, influences of mass ratio of iron to CaO (Fe/CaO), reforming temperature (T), mole ratio of steam to carbon in toluene (S/C), absorbent granulation were evaluated on properties of the reforming gas as well as the liquid and solid residue after toluene reforming. For future deployment of CLG, potential reaction conditions were recommended as Fe/CaO 10%, 700℃ and S/C 2.0 in present study. Based on the reforming liquid residue analyses by gas chromatography-mass spectrometer (GC–MS), potential toluene reaction routes were evaluated which revealed that Ca-Al-Fe favored deep dehydrogenation during toluene reforming.

Modeling the deactivation of CaO-based sorbents during multiple Ca-looping cycles for CO2 post-combustion capture

A novel model is presented for the estimation of natural CaO-based sorbents carbonation reactivity decay during Calcium Looping carbonation-calcination cycles. The model consists of a cyclic framework of two sub-models, the Overlapping Grain Model and the novel proposed modified Rate Theory for the Pore Size Distribution model. The model was implemented in gPROMS ModelBuilder® and parameter estimation was used for model validation using experimental data from three CaO-based sorbent precursors. The carbonation profile for the three sorbents was simulated with average deviations under 5%. The calcination sub-model predicted the evolution of total porous volume and total surface area for the calcination and sintering of dolomite, with an error of 3%. The cyclic framework successfully predicted the carbonation behavior of dolomite for 20 carbonation-calcination cycles. The model can be used for other CaO-based sorbents and the flexible modular structure allows the integration of other modules or approaches.

Thermochemical energy storage via isothermal carbonation-calcination cycles of MgO-stabilized SrO in the range of 1000–1100 °C

The reversible gas-solid thermochemical reaction between CO2 and SrO to form SrCO3 is considered for storing high-temperature heat delivered by concentrated solar energy systems. To maintain cycling stability, MgO-stabilized SrO-based materials were synthetized with various precursors and support contents by the co-precipitation, sol–gel, wet-mixing and dry-mixing production methods. Samples were analysed by thermogravimetry over multiple consecutive carbonation-calcination cycles in the range of 1000–1100 °C. The best performance was obtained by using the wet-mixing method with strontium acetate hemihydrate and porous magnesium oxide as precursors: the formulation with 40 wt% SrO featured stable chemical conversion over 100 consecutive carbonation-calcination cycles at 1000 °C and yielded gravimetric energy density of 0.81 MJ/kg.

Iron oxides as efficient sorbents for CO2 capture

Carbon dioxide capture/release reactions using magnetite, Fe3O4, and hematite, Fe2O3, as sorbents were studied. Kinetics of mechanically activated chemical reactions between iron oxides and CO2 was investigated as a function of CO2 pressure and planetary ball mill process parameters. It was found that complete carbonation of iron oxides can be accomplished at room temperature and elevated CO2 pressure (10–30bar). Siderite calcination was studied in vacuum and argon atmospheres. FeCO3 can be decomposed at 367°C yielding magnetite, carbon and/or iron. This mixture can reversibly re-absorb carbon dioxide in multiple carbonation–calcination cycles. These results suggest that siderite or iron oxides are prospective and efficient reversible sorbents for CO2 capture.

Eggshell as a potential CO2 sorbent in the calcium looping gasification of biomass

This work presents an investigation into the potential use of eggshell as a CO2 sorbent in the calcium looping gasification of biomass to enhance carbon negativity. Calcination reaction was studied in a quartz wool matrix reactor and a thermogravimetric analyser coupled with a Fourier transform infrared spectroscopy. The resulting sorbent was characterised with a scanning electron microscope, colourimeter, inductively coupled plasma optical emission spectroscopy, and nitrogen sorption analyser. The pore structures of the samples are of Type II isotherm. Results show that increasing the calcination temperature enhances decomposition and improves the calcium content and specific surface area of the sorbent. As compared to nitrogen, calcination in a CO2 environment is not effective due to the increased CO2 partial pressure. Samples with low particle size displayed higher carbonation conversion. Increasing the carbonation temperature to an extent enhances the carbonation conversion. The carbonation conversion by the sorbent in multiple calcination-carbonation cycles was also studied. Initial CO2 uptake by the sorbent was highly encouraging. A conversion of 76.41% was realized after the first cycle, but due to sintering and attrition, the conversion reduced with increasing cycle. The sorbent exhibited a low conversion of 18% after the seventh cycle and this corresponds to a decay extent of 76.65%.

Sustainable Use of Natural Geological Materials and Marble Wastes as Promising Calcium Looping Sorbents for CO2 Capture in the Cement Industry: Comparative Study

The present work focuses on the comparative study of the Calcium looping CO2 capture capacity and stability along 10 or 20 calcination-carbonation cycles, of three different marble powder wastes (MW) and two calcite samples (one from West Bank and another provided by CIMPOR) using a gas mixture with a /sub>CO2 concentration of 25% to mimic the real flue gases CO2 concentration in the cement industry. Very high initial carbonation (first cycle) conversions were obtained using the MW sorbents tested, which is a very interesting and promising result when compared with the initial carbonation conversions of the natural calcite sorbent currently used in industry as raw material for the cement production. For the Calcium-looping conditions used, the MW sorbent tested on the fixed bed reactor unit exhibits better cyclic stability with a lower sorbent deactivation with the number of cycles than the natural calcite resource used for the cement production. The presence of 5% of steam in the feed gas mixture with air atmosphere leads to significant differences on the sorbents cyclic performance when comparing with the results obtained for the standard calcination conditions. For both MW and calcite sorbent samples selected and tested on the fixed bed rector unit in the presence of steam, a lower CaO carbonation conversion is observed along the first 7 cycles, but a higher cyclic stability reaching a CaO conversion plateau, with a lower deactivation after 20 cycles, when comparing with the results for the standard calcination conditions. An improved sorbent stability for Ca-looping CO2 capture was observed during the carbonation-calcination cycles in the presence of steam which could allow reducing the make-up of CaO frequency along the time and the costs associated. The selection of suitable marble wastes as CaO-based sorbents, the improvement of their performance and the incorporation of exhausted sorbents in the clinker, can contribute to reducing the CO2 footprint of cement production and avoid the production of wastes associated to the marble producers.

Evaluation of the effect of inert support on the carbonation reaction of synthetic CaO-based CO2 sorbents

Calcium oxide has been proved to be a suitable sorbent for high temperature CO2 capture processes based on the cyclic carbonation-calcination reaction. In this work several synthetic sorbents have been prepared with CaO contents between 40 and 95% wt. on to two different inert supports MgO and Ca12Al14O33. The effect of CaO content and inert nature on materials CO2 carrying capacity and reactivity towards carbonation reaction has been assessed. The materials have been texturally characterised. A complete kinetic study has been performed and the Random Pore Model has been applied to determine the intrinsic rate parameters for the carbonation reaction. Suitable particles for operation in fixed bed reactor have been produced from some selected powdered materials, and a complete particle reaction model that incorporate the intrinsic kinetic data has been developed and validated.

Self-activation of CaO/Ca3Al2O6 sorbents by thermally pretreated in CO2 atmosphere

CaO/Ca3Al2O6 sorbents have been proved to be a promising sorbent for CO2 sorption. However, the sorbents still suffer from low CO2 sorption capacity. In this work, self-activation was generated via thermally pretreating CaO/Ca3Al2O6 sorbents in CO2 atmosphere at various temperatures to enhance the CO2 sorption capacity of CaO/Ca3Al2O6 sorbents. Results showed that the thermally pretreated temperature plays an overwhelming role in the CO2 sorption capacity and stability of the CaO/Ca3Al2O6 sorbents. Superior CO2 sorption capacity (8.01 mmol g−1 for C9A1-650 at 500 °C) is achieved, which is 72% higher than that of C9A1 (no pretreatment sample). After 50 carbonation-calcination cycles, the CO2 sorption capacity of C9A1-650 still remained 20% higher than that of C9A1. The high CO2 sorption capacity is ascribed to the smaller CaO grain size (37.1 nm) and the higher surface area (13.1 m2 g−1), resulting from the self-activation process. Meanwhile, the CO2 cyclic sorption stability is due to the small original surface free energy. Furthermore, the C9A1-650 sorbent is employed to use in sorption enhanced methane steam reforming process. It provides a H2 concentration of 98.9% and CH4 conversion of 98.7%, presenting greatly potential in practical application.

A study on the CO2 capture and attrition performance of construction and demolition waste

CaO-based sorbent deactivation is one of challenges to develop CaO-based chemical looping technology. The replacement of non-renewable natural or expensive synthetic CaO-based sorbents with cheap and environmental CaO-based waste sorbents is an effective way to overcome this challenge. As high CaO content, construction and demolition waste (CDW) has ability to capture CO2. Due to the rapid development of cities, a great deal of CDW is produced every year. According to the characteristics of CDW, six components were selected in this paper. From the initial CO2 carrying capacity, hydrated limestone had the highest initial CO2 carrying capacity, about 0.592 g CO2/g sorbent in TGA and 0.414 g CO2/g sorbent in fluidized bed system, followed by limestone, cement-based limestone, hydrated cement, cement-based sand, cement raw and sand. For multiple carbonation-calcination cycles, cement played a positive role in maintaining high cyclic CO2 carrying capture. Hydration degree and free lime content increased with the increase of hydration time, which improved the CO2 capture performance of CDW. For cement-based sorbents, evidence from this study suggested that extending hydration time played a positive role in improving the attrition resistance and maintaining the initial specific surface area in fluidized bed system.

CO2 Uptake Potential of Ca-Based Air Pollution Control Residues over Repeated Carbonation–Calcination Cycles

The operation of dry processes for acid gas removal from flue gas in waste-to-energy plants based on the use of calcium hydroxide as a solid sorbent generates a solid waste stream containing fly ash, unreacted calcium hydroxide, and the products of its reaction with acid pollutants in the flue gas (HCl and SO2). To date, the fate of the solid waste stream is to be put into a landfill in the absence of commercially viable recycling approaches. The present study investigates the potential of these residues as CO2 sorbents in the calcium looping process. Samples collected in different waste-to-energy plants were tested over multiple carbonation–calcination cycles, comparing their performance to that of limestone. Although inferior, the CO2 sorption capacity of the residues resulted in values comparable to that of limestone and that steadily increased for a significant number of cycles. This peculiar behavior was attributed to the presence of a chlorinated phase, which enhances the CO2 uptake in the diffusion...

A Solar Reactor Design for Research on Calcium Oxide-Based Carbon Dioxide Capture

An engineering design for a novel 1-kW solar-driven reactor to capture carbon dioxide via the calcium oxide-based two-step carbonation–calcination cycle has been completed. The reactor consists of a downward-facing cylindrical dual cavity. The inner cavity serves as the radiation receiver, while the outer cavity is the reaction chamber that contains a packed- or fluidized-bed of reacting particles. Several aspects have been incorporated in this reactor design, including high flexibility, mechanical rigidity and simplicity, high-temperature and thermal shock resistance, accommodation of thermal expansion, low convective heat losses, uniform gas distribution inside the reaction chamber, and simple reactor assembly. The final reactor design is presented, and the reactor assembly is illustrated.

Modeling of carbonation reaction for CaO-based limestone with CO2 in multitudinous calcination-carbonation cycles

In the cyclic carbonation-calcination reaction processes, CaO-based solid sorbents have been substantiated to be the effective sorbents for CO2 capture at high temperature. The carbonation reaction has been depicted the carbonation reaction by several kinetic models. Some kinetic models are capable to calculate the intrinsic carbonation rate in the cyclic carbonation-calcination reaction, but the mathematic equation of those models is basically complicated. In this work, a modified model was proposed to delineate the carbonation reaction in multitudinous carbonation-calcination cycles, and was qualified to characterize the whole progression of carbonation reaction in highly cycled particles. The sharp corner is inexistent simultaneously. Additionally, the mathematic equation of this model is apparent simplified. The disconnected pore size distribution is expressed by the log-normal function, and the time evolution of pore structure was also discussed.

Development of Synthetic Ca-based CO2 Sorbents for Sorption Enhanced Reforming Coupled to Ca/Cu Chemical Loop

Sorption Enhanced Reforming (SER) is a very promising option that allows H2 production coupled with capturing CO2 by sorption. The present research work focus in the sorbent point of view and several synthetic materials with a high CO2 absorption capacity and chemically and mechanically stable during multi-cyclic operation (at least 40 calcination-carbonation cycles and 100 cycles in some cases) under the typical SER process conditions have been developed. Two different synthesis routes (co-precipitation and mechanical mixing) have been followed trying to evaluate the effect of two different inert supports (magnesium oxide and mayenite) on the evolution of the CO2 carrying capacity of the materials. Also, sorbents have been synthesized with different morphologies (powder and particles) and sizes (from 100 microns up to 2mm) in order to test their reactivity and mechanical suitability for large scale reactor system operation. Synthetic dolomite with a molar CaO/MgO ratio of 2:1 synthesized by co-precipitation method exhibited very stable performance for 100 consecutive carbonation/calcination cycles and a residual CO2 carrying capacity of 0.29 grCO2/grcalcinedsorbent. Also a very promising result has been obtained for this sorbent mixed with a commercial catalyst in a preliminary SER experiment that yield a H2 production of 92% vol. (d.b.).