Ca-based Sorbents Research Articles

Aluminum-enhanced Ca-based CO2 sorbents: Core-shell assembly and the impact of stabilizer precursors

Lately, Ca-based sorbents with a core–shell structure have been effectively produced to augment the sorbent’s capabilities. However, modifying the pristine core of Ca-based pellets with a core–shell structure notably influences the performance of the synthesized sorbent, and research in this domain remains scarce. Here, two categories of Al-stabilized, Ca-based pristine cores were produced using Ca(OH)2 mixed with Al-based stabilizer precursors of insoluble aluminum oxide and soluble aluminum nitrate, respectively, through the extrusion-spheronization technique. Due to the impact of mechanical extrusion, soluble aluminum nitrate can accumulate in-homogeneously in the Ca-based pristine core, leading to its expansion and rupture during the high-temperature calcination stage because of the decomposition of aluminum nitrate. The oxide-form aluminum stabilizer precursor can be uniformly distributed throughout the Ca-based pristine core pellets, demonstrating notably superior cyclic CO2 sorption capability and mechanical strength. The Al-fortified, core–shell structured Ca-based sorbent pellets demonstrated a peak CaO carbonation conversion rate of 54.8 % after 100 cycles when the Ca:Al molar ratio was precisely set to 85:15, which is about 2.1 times higher compared to the core–shell Ca-based sorbent pellets composed of a pure CaO core. This is primarily due to the formation of an evenly distributed inert Ca12Al14O33 within the pristine core, which effectively reduces high-temperature sintering. Hence, core–shell Ca-based sorbent pellet assembled with an Al-stabilized pristine core, could be a promising candidate for application in the CaL process for CO2 capture.

Integrated CO2 Capture and Dry Reforming of CH4 to Syngas: A Review.

Integrating carbon capture with dry reforming of methane offers a promising approach to addressing greenhouse gas emissions while producing valuable syngas. This review examines the complexities and progress made in this integrated process, wherein catalysts play a critical role in adsorbing carbon dioxide and facilitating the conversion of methane to syngas. The chemical process entails the concurrent capture of CO2 emissions and their usage in dry reforming, a reaction in which CH4 interacts with CO2 to generate syngas, an essential precursor for various industrial applications. The dual-functional materials can adsorb carbon dioxide and actively reform to an end-use application. The much-studied Ca-based sorbents exhibit a theoretical carbon capture capacity of 17.8 mmol g-1. However, during practical exploration of these materials as a dual-functional catalyst for integrated carbon capture and the dry reforming of methane, the uptake reduces to ∼13 mmol g-1 carbon capacity with 96.5 and 96% conversions of CO2 and CH4, respectively. Therefore, a thorough analysis of the complex relationship between CO2 capture and CH4 reforming catalysis is attempted herein based on various reported materials. Design concepts, structural optimization, and performance evaluation analysis of the dual-functional materials reveal their importance in carbon capture and reformation technology. Additionally, this review covers the field difficulties, future perspectives, and attractive commercial implementation predictions. This scrutiny illustrates the significance of dual-functional materials for sustainable energy production and environmental protection.

Insights into chromium removal mechanism by Ca-based sorbents from flue gas

Chromium is a typical toxic pollution in sewage sludge incineration flue gas. Cr removal from flue gas is a challenge due to the high toxicity and valence variability of chromium. Ca-based sorbents, including CG-CaO, CA-CaO, and CCi-CaO, were developed for Cr capture by calcining calcium D-gluconate monohydrate, calcium acetate hydrate, and calcium citrate tetrahydrate, respectively. CG-CaO, CA-CaO, and CCi-CaO exhibit better Cr removal performance than traditional CaO. CA-CaO shows superior Cr adsorption ability due to the large BET surface area and pore volume. The Cr adsorption efficiency of CA-CaO is up to 94.79 % at 1000 °C. XRD and XPS results reveal that the adsorbed Cr contains Cr(III) and Cr(VI), and exists in the form of CaCr2O4 and CaCrO4. Cr adsorption on Ca-based sorbents is mainly controlled by adsorption and oxidation mechanism. The adsorption process of Cr on different Ca-based sorbents was described by four typical adsorption kinetic models. For CaO and CG-CaO, pseudo-first order model and Elovich model are suitable for the description of Cr adsorption. For CA-CaO and CCi-CaO, pseudo-second order model, Elovich model and Weber and Morris model fit well with the experimental values of Cr adsorption, suggesting that Cr adsorption on CA-CaO and CCi-CaO is controlled by a combined mechanism of chemisorption and intraparticle diffusion. The saturated adsorption capacity of CaO, CG-CaO, CA-CaO and CCi-CaO are evaluated to be 39.77, 48.98, 102.22 and 104.52 mg/g, respectively. The effects of incineration flue gas components on Cr adsorption were also explored. O2 shows no obvious influence on Cr adsorption over CA-CaO. HCl, SO2, NO and CO2 can inhibit Cr adsorption because of the competitive adsorption, and the inhibitory effect of SO2 is the strongest.

First principle-based rate equation theory for the carbonation kinetics of CaO with CO2 in calcium looping

Calcium oxide (CaO), a CO2 sorbent and key ingredient in the process of making cement, exhibits excellent potential for carbon capture, utilization, and storage (CCUS) applications through calcium looping and integrated carbon capture and utilization, owing to its outstanding kinetic properties and high recyclability. From a fundamental standpoint, it is important to establish a comprehensive and precise carbonation kinetic model for CaO. In the present study, a density functional theory (DFT)-based rate equation was developed to predict the gas–solid reaction kinetics of CaO carbonation with CO2 in calcium looping. The reaction pathway of CaO carbonation, including surface reactions and structural transformations, was obtained by a transition state search of DFT calculations, and the transition state theory was used to calculate the reaction rate constants. The nucleation model was implemented in the mean-field surface reaction model to describe the nucleation of the CaCO3 product at the gas–solid interface. A grain model was developed to couple the surface reaction and CO2 diffusion through the product layer. The developed theory was validated using a wide range of experimental data, and the negative activation energy of CaO carbonation close to equilibrium was accurately predicted. The developed first principle-based rate equation provides a detailed theoretical framework for predicting CaO performance and optimizing the microstructure of Ca-based sorbents.

New insights into stabilizing mechanism of Ca9Al6O18 stabilizing Ca-based sorbents for CO2 cyclic capture under mild conditions

New insights into stabilizing mechanism of Ca9Al6O18 stabilizing Ca-based sorbents for CO2 cyclic capture under mild conditions

Evaluation of Ca-Based Sorbents for Gaseous HCl Emissions Adsorption

The problem of acid gas exhaust emissions treatment has not been fully resolved at present. Dry adsorption of acid gases with alkaline sorbents is currently being investigated, to improve solid sorbents. In this study, 5 types of hydrated lime were characterised and tested. The sorption capacities were measured by means of a system consisting of a feed line (HCl/N2), a thermostatic reactor and a water absorber. The physical characteristics of sorbent samples were also compared. Analyses conducted with scanning electronic microscopy revealed that sample C1 showed uniform particle distribution. Samples C2 and C3 showed the co-presence of fine and coarse particles. Sample C4 showed very fine particles with agglomeration phenomena. In sample C5, fibrous elements were found. Energy dispersive spectrometry (EDS) analyses showed a similar composition of the samples, with the exception of the presence of Mg in some of them. After 30 min of testing, the following differences in sorption capacities with respect to C1 (3.59 mg g−1) were found: C2, −20%; C3, −13%; C4, −17%; C5, −3%. Higher sorption capacities were associated with more uniform particle size distributions. Conversely, agglomeration of fine particles may have adversely affected the performance of sorbents.

Desulfurization in co-firing of sewage sludge and wooden biomass in a bubbling fluidized bed combustor under air and oxy-fuel conditions

This work presents results of an experimental investigation of a direct addition of Ca-based sorbent for SO2 capture in a bubbling fluidized bed combustion. The fuel of interest was secondary biomass represented by a dried sewage sludge, which was mixed with primary biomass represented by wooden pellets in a weight ratio of 30:70. The performance of this SO2 capture approach is compared in air and oxy-fuel combustion conditions, since the different gas environment in the bed significantly affects the SO2 capture process. The experiments were carried out in an experimental bubbling fluidized bed combustor with a power load of about 30 kW.Sewage sludge is typical for its high ash content and has sufficient dimensions and attrition resistance to create the fluidized bed without the support of external bed materials. However, it typically consists of S-containing organic substances, resulting in the presence of SOX in the off-gas. A reference case was initially conducted without any sorbent addition in order to investigate the effect of sulfur self-retention in the fuel ash. The sulfur retention in the ash reached almost 45 % in air- and up to 55 % under oxy-combustion.In the next phase, the performance of Ca-based sorbents in sulfur capture was evaluated. The sorbents were represented by two types of limestone with diverse CaCO3 content produced at different locations. The experiments were carried out with three Ca/S mole ratios (1.5, 3, and 4.5). The effect of the fluidized bed temperature was also investigated as the most important parameter.The SO2 capture ratio (used as a performance indicator) was calculated based on emission factors, due to the different specific volumes of flue gas in the air and oxy-fuel modes. The results show in general a significantly higher SO2 capture ratio under oxy-fuel conditions. The differences are more significant in lower Ca/S ratios, where the SO2 capture ratio increased from 46 % under air conditions to 75 % under oxy-fuel for Ca/S = 1.5. In the case of the highest Ca/S ratio examined (Ca/S = 4.5), the increase in SO2 capture was from 90 % to 95 %.

Analysis of the behaviour of limestone sorbents for sorption-enhanced gasification in dual interconnected fluidised bed reactor

Sorption-Enhanced Gasification (SEG) is a promising technology based on the use of Ca-based sorbents (like limestone) to selectively remove CO2 from the gasification environment, for production of hydrogen rich syngas. This process benefits from the extensive understanding of “calcium looping”, a post-combustion technique aimed at removing CO2 from flue gas. Calcium looping is most typically carried out in Dual Interconnected Fluidised Bed (DIFB) reactors. The correct design of sorbent looping processes in DIFB reactors must consider: 1) sorbent deactivation (i.e., decay of CO2 capture performance) over repeated cycling; 2) the loss of sorbent material due to elutriation, that may be enhanced by attrition and fragmentation. The aim of this study is to investigate six different commercial limestones in terms of sorbent performance and attrition/fragmentation tendency under simulated SEG conditions.The experimental campaign was carried out in a lab-scale DIFB reactor, electrically heated. The six sorbents were limestones coming from different parts of Europe. A synthetic gas including air, CO2 and N2 was used to simulate SEG conditions. A “test” consisted of ten complete cycles of calcination/carbonation. Calcination was performed at 850 °C, fluidising the bed with a stream of 10 % CO2 (balance air) to simulate oxidising conditions typical of the combustor-calciner. In the carbonation stage, the temperature was kept at 650 °C and the CO2 concentration was set at 10 % (balance nitrogen) to account for reducing conditions typical of the gasifier-carbonator.During each carbonation stage, the CO2 concentration at the exhaust was continuously monitored to calculate the CO2 specific capture performance. The sorbent attrition rate was determined by working out the mass of fines elutriated at the exhaust and collected in filters, for each calcination and carbonation stage. After a test, each exhaust sorbent sample was sieve-analysed to obtain the particle size distribution and the fraction of generated fragments. Moreover, the characterisation was extended by carrying out, in an ex situ apparatus, impact fragmentation tests on samples preprocessed in DIFB.Results were critically analysed in the light of the adopted operating conditions, by also including: (a) a fitting equation of conversion data, able to give indications on the sorbent resistance to sintering; (b) a carbonation reaction model, that allowed the estimation of the decrease in the sorbent specific surface area as long as the number of cycles increases.

Findings on the use of a Ca-based sorbent as an oxygen carrier precursor in a Chemical Looping Combustion unit

Limestone Chemical Looping Combustion (L-CLCTM) is a novel process to burn sulfurous fuels with intrinsic desulfurization and CO2 capture. L-CLCTM is based on using calcium-based sorbents as precursors for CaSO4 formation, which is used as an oxygen carrier. Its principle lies in the in-situ sulfur retention process performed in fluidized bed combustors burning solid fuels with high sulfur content. The target redox pair for the oxygen transference to the fuel is CaSO4/CaS. In this research work, experimental tests burning CH4, syngas and H2 with a moderate H2S concentration were conducted in a continuous CLC unit. This experimental campaign is first in a kind as there is hardly information about the CaSO4/CaS pair for the L-CLCTM process. High combustion efficiencies were achieved at moderate temperatures (800–850 °C) when burning H2 and syngas (∼96–99 %). Likewise, low CH4 combustion efficiency (∼59 %) was found even operating at a temperature as high as 945 °C. Additionally, experimental tests at different Ca/S molar ratios were performed. They revealed that it was possible to reach suitable sulfur retention values (∼82 %) by using a Ca/S molar ratio of 2.25. This value resulted in a very feasible ratio since it is commonly used in fluidized bed combustors.

Transient simulation of biomass combustion in a circulating fluidized bed riser

Interest in circulating fluidized bed (CFB) boilers as a power generation technology has sky-rocketed in recent years because of several advantages this technology offers over conventional boilers, such as increased gas-solid mixing, which results in higher combustion efficiency and the ability to use lower rank fuels. CFB combustors are operated at lower temperatures than conventional thermal power generation combustors, thus reducing NOx emissions, while SO2 emissions can be conveniently controlled through the addition of Ca-based sulfur sorbents within the combustor.This paper summarizes the modeling effort on a 50 kWth CFB combustor designed, built, and operated at CanmetENERGY in Ottawa, Canada. The numerical model employs the multiphase particle-in-cell (PIC) approach in the open-source Multiphase Flow with Interphase eXchanges (MFiX) Software Suite. The MFiX-PIC model parameters for the simulation are tuned against cold-flow experiments from CanmetENERGY using olivine sand as the inert bed material. It is shown that for the relatively coarse fluid meshes and large parcel sizes necessitated by the scale of the simulation, filter size dependent corrections to the drag law must be incorporated to ensure accuracy of the simulation results.The validated cold flow model is extended to simulate reacting flow with torrefied hardwood as the feedstock and to validate the combustion reaction scheme. The species concentrations at the riser outlet are compared against CanmetENERGY's experiments and show satisfactory agreement. The simulations demonstrate the ability of MFiX-PIC to accurately capture both the physics and chemistry of a CFB combustor at bench scales, which can be further extended to pilot- and industrial-scale systems.

Lab-scale experimental demonstration of Ca[sbnd]Cu chemical looping for hydrogen production and in-situ CO2 capture from a steel-mill

In the present work, a lab-scale packed bed reactor has been used to decarbonize mixtures of inlet gases simulating the typical composition of blast furnace gases (BFG) and convert them to H2-rich streams by means of the CaCu chemical looping concept. The reactor was packed with 355 g of Cu-based oxygen carrier (OC) supported on Al2O3 and natural Ca-based sorbent. The three main reaction stages; namely (i) Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH), (ii) Cu oxidation and (iii) Regeneration of carbonated Ca-based sorbent were examined. In CASOH stage, BFG is converted into H2-rich stream (17% by vol.) under the experimental conditions of 600 °C, 5.0 bar and S/CO molar ratio of 2.0. A controlled oxidation causes a mere 3.5% of CaCO3 to decompose during the Cu-oxidation stage. This resulted in a nearly pure N2 stream at 600 °C and 5.0 bar operating conditions. During the regeneration stage, BFG and mixture of BFG and CH4 is used as a reducing fuel. To ensure the amount of heat needed for the decomposition of CaCO3 during the reduction of CuO, a 1.4 CuO/CaCO3 molar ratio has been used. It resulted in 46% CO2 in N2 at the end of the reduction/calcination stage.

Effect of steam addition during calcination on CO2 capture performance and strength of bio-templated Ca-based pellets

Enormous efforts have been devoted to improving the cyclic reactivity of the Ca-based sorbent for cyclic CO2 capture. Steam reactivation is one of the most promising technologies to regenerate the CO2 capture performance of the Ca-based sorbent remarkably. However, the strength of the pellets during the steam reactivation process is insufficiently investigated. This study examined the influences of steam addition during calcination on the CO2 capture capacity and mechanical strength of the bio-templated sorbent over multiple carbonation-calcination cycles. A CO2 uptake of 0.31 g/g was achieved after 20 cycles by adding 30 % steam into the calcination atmosphere, which is 2.2 times higher than the cycles without steam injection. After the long-term test up to 100 cycles with 30 % steam in the calcination environment, a 6-fold increase in the average crushing force of the pellets was observed. The enhancement of the mechanical strength was attributed to the synergy effect of thermal sintering and atmosphere-induced sintering. Generally, steam addition during calcination demonstrated great potential in retaining CO2 capture capacity and improving the mechanical strength of the bio-templated sorbent.

Assessment of the Applicability of Ca-Based Sorbents for Arsenic Removal from Flue Gases

Arsenic is one of the most hazardous compounds released into the atmosphere from coal conversion processes. One possibility to limit its amount in the flue gas is to inject dusty sorbents directly into the flue gas duct. The aim of this study was to analyze the removal efficiency of gaseous forms of As on selected Ca-based materials, with a focus on sorbents based on waste materials versus traditionally used sorbents. Coal combustion byproducts, waste (such as filter cake, fly ash, and gypsum), sedimentary rocks (dolomite and limestone), and chemical reagents like Ca(OH)2, Fe2O3, and Mg(OH)2 were examined in the quartz retort in a heated furnace where the temperature of the sorbent bed was 120 °C. The source of Asgas was the direct combustion of coal at 1200 °C. Among the tested materials, calcined limestone, calcined dolomite, Fe2O3, Mg(OH)2, and Ca(OH)2 were the most effective (removal efficiency: 85–98%). In the case of waste materials, the highest efficiency was obtained for filter cakes. However, because of their high content of toxic elements, they could be used as sorbent only after thermal preparation at 250 °C. Furthermore, the analyses showed that an increased Ca concentration in the sorbent may promote Asgas adsorption more than the development of the sorption surface area.

Improved removal of selenium by calcite-derived CaO with porosity and anti-sintering in presence of acid gas

Ca-based sorbent injected into furnace is a promising technology for control emission of selenium. As commercially available CaO was easy to sintering under actual furnace temperature or in presence of CO2/SO2, calcite-derived CaO on removal of Se were tested by a gas-solid reaction system, which was designed to simulate process of gaseous trace elements in flue gas fast contacting with injected minerals, showing a simple, economical and practical method to improve anti-sintering. Results showed conspicuous superiority of calcite-derived CaO for its porosity and anti-sintering. Capture efficiency at 700–800 °C could reach to 80% basically, even to 90% as maximum, and chemisorption was dominance for capture by analysis of thermal desorption. Both CO2 and SO2 could affect capture, while their effects mechanisms on Se capture were quite different. The impact of CO2 depended on the adsorption temperature. Below 700 °C, existence of CO2 could inhibit Se capture due to formed CaCO3, so Se capture was suggested at above 700 °C after considering both capture efficiency and leachability. Effects of SO2 was relevant to content of CaSO4 formed. Se retention was promoted as low content of CaSO4 formed, but capture was inhibited by thickened product layer as high content formed.

Ca-based sorbents as precursors of oxygen carriers in chemical looping combustion of sulfurous fuels

Limestone Chemical Looping Combustion process (LCL-C™) patented by Alstom Power Inc. proposes the formation of a CaSO4 oxygen carrier via sulfur retention process when supplying a Ca-based sorbent together with sulfurous fuels in the fuel reactor. In the present research work, four Ca-based sorbents, three limestones and one dolomite with different physico-chemical characteristics, have been evaluated as oxygen carrier precursors during consecutive redox cycles by thermogravimetric analysis. 5% H2 and 3000 vppm H2S (N2 to balance) and 10% O2 (N2 to balance) were selected as reducing and oxidizing gases, respectively. Additionally, an anhydrite ore has also been studied for comparison purpose. Results from SEM-EDX characterization of the sorbent particles revealed the existence of three different sulfation patterns: (1) uniform distribution, (2) core–shell structure and (3) high sulfur content with high limitation to be converted into CaSO4. All sorbents exhibited high oxygen transport capacity (Roc = 13.3–20.8%), except for the material showing pattern (3) (Roc = 2.6%). Likewise, the materials presented high reactivity with rate index values ranged between 11.0 and 18.8%/min. Therefore, the Ca-based sorbents herein assessed can be considered suitable precursors for the formation of CaSO4 based oxygen carriers to be used in CLC systems burning sulfurous fuels.

Effect of calcium-based sorbents on the reduction of chlorinated contaminants during municipal solid waste thermal treatment.

Chlorinated contaminants are a cause of significant concern in the development of municipal solid waste (MSW) thermal treatment techniques. This study investigates the efficacy of two calcium (Ca)-based in-furnace additives, calcium oxide (CaO), and calcined dolomite (CD), at reducing the levels of chlorinated contaminants during MSW thermal treatment. The results reveal that Ca-based additives could effectively reduce the chlorine (Cl) content by more than 76.8% and 37.3% in the gas and tar phases, respectively. The total concentration and the international total equivalent (I-TEQ) value of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-p-furans (PCDD/Fs) were significantly higher under the incineration condition than pyrolysis and gasification conditions. Adding CaO could reduce the total concentration and the I-TEQ value of PCDD/Fs by more than 43.4% and 36.7%, respectively. The reduction effect on PCDD/Fs was more significant in the gaseous phase and the tar phase than the solid phase. CD was more effective than CaO at reducing the chlorinated contaminants, including hydrogen chloride, Cl in the tar phase, and PCDD/Fs. Thus, adding Ca-based sorbents in the furnace during MSW pyrolysis and gasification can effectively reduce PCDD/Fs generation. Based on the experimental results, the mechanism of Ca-based sorbents on the high-temperature homogeneous reaction of PCDD/Fs formation was analysed.

Performance study on Ca-based sorbents for sequential CO2 and SO2 capture in a bubbling fluidised bed

High temperature CO2 and SO2 sequential capture in a bubbling fluidised bed was investigated using a natural limestone and synthetic composite pellets. Calcination was conducted under oxy-combustion conditions, while carbonation and sulphation occurred in an air-combustion atmosphere. The goal of sequential capture of CO2/SO2 is to desulphurise the flue gas first, followed by cyclic carbonation and calcination. Here, fresh sorbent is first used in the cyclic calcination/carbonation process and then the spent sorbent is sent for sulphation.The pellet carrying capacity is 0.29 g CO2/g sorbents for the first cycle, while that of natural limestone is about 0.45 g CO2/g sorbents. The carrying capacity first fell and then finally plateaued around 0.10 and 0.12 g CO2/g sorbents for limestone and pellets respectively. The SO2 carrying capacity for limestone and pellets after 20 cycles of CO2 capture was 0.17 and 0.22 g SO2/g sorbents respectively. This indicates that the sorbent spent in CO2 capture can be effectively reused for SO2 removal. Abrasion was observed to be the main mode of attrition, but some agglomeration was also found with increasing number of cycles and this may be a concern in the use of Ca-based sorbent for CO2 or SO2 fluidised bed capture.

Experimental demonstration of the Ca-Cu looping process

• A proof-of-concept of the Ca-Cu process has been carried out at larger scale. • Each process step has been studied separately for different operating pressures. • An increase in pressure negatively influences the sorption-enhanced reforming step. • H2 in the product stream higher than 90 vol% on dry basis has been obtained. In this work an experimental proof-of-concept of the Ca-Cu process has been carried out. The Ca-Cu process combines sorption-enhanced steam reforming of methane with a Ca-based sorbent with chemical looping of a Cu-based oxygen carrier to provide the energy for the sorbent regeneration. Each process step has been studied separately for different operating pressures and inlet gas compositions, and addition complete cycles (including all three consecutive process steps, viz. the sorption-enhanced reforming step, oxidation step and regeneration step) have been performed to evaluate the technical feasibility of the complete process. The pressure influences the sorption-enhanced reforming step negatively, while the steam-to-carbon ratio does not influence the average outlet H 2 (dry) fraction. When increasing the inlet O 2 concentration during the oxidation step, the amount of CO 2 released increases, whereas increasing the pressure decreases the amount of CO 2 released. In the regeneration step, increasing the H 2 fraction in the feed increases the amount of sorbent that is regenerated, reaching 70 wt% of the sorbent in the bed with 60 vol% H 2 in the feed. More than 285 complete cycles were performed, the solids were still chemically performing well, and the results were still reproducible. Simulations with a pseudo-homogeneous reactor model were performed for all the separate steps. The model does not describe the experimental data well, which was attributed to problems with the packing of the bed at the bottom of the reactor (solids maldistribution), which was confirmed after opening the reactor after the experimental campaign. The problems with the packing of the bed was caused by problems with the chemical–mechanical stability of the oxygen carrier, which became a powder after the experiments due to the high mechanical stresses it was exposed to.

Experimental and density functional theory study of the synergistic effect between steam and SO2 on CO2 capture of calcium-based sorbents

Calcium looping is a fast-developing second generation CO2 capture technology. In practical looping of Ca-based sorbents, steam and SO2 are naturally present in the flue gas subjected to CO2 capture, due to the combustion of fossil fuels. Until now, the single effect of steam or SO2 has been reported to have a significant impact on the CO2 capture of sorbents. However, there are few studies on the synergistic effect of steam and SO2 on the CO2 sorption characteristics of sorbents, and it is poorly understood. In this study, experiments and DFT calculation are employed to clearly understand the synergistic effect of steam and SO2 on the carbonation behaviors of sorbents. Tests were first performed under typical calcium looping (CaL) conditions with and without the presence of steam and SO2 during the carbonation process. Results indicated that the enhancement of steam on the sulfation is obviously stronger than that on the carbonation as the CaL cycles increased, which is then verified by a series of characterization methods. According to quantitative analysis through DFT calculation, the adsorption energy of SO2 on CaO (100) surface was found to be more than that of CO2 in the presence of steam, indicating the preferential adsorption of SO2 in the presence of H2O molecules on the CaO (100) surface. Therefore, the experimental results were verified and the competitive adsorption mechanism of SO2 and CO2 in the presence of steam during the carbonation process was further understood from microscopic aspect.

Aqueous mineral carbonation of oil shale mine waste (limestone): A feasibility study to develop a CO2 capture sorbent

The development of a Ca-based CO2 capture sorbent from a limestone-rich mine waste via aqueous mineral carbonation was first time evaluated. Aqueous carbonation of calcined oil shale mine waste rock was conducted at the laboratory scale at ambient temperature and atmospheric gas pressure using CO2 gas mixture simulated the average exhaust gas composition of a fossil fuel power generation plant. The dissolution and carbonation of calcium were found to be optimal at 2.5% pulp density and were found to proceed faster during the initial 5–10 min. The overall aqueous carbonation efficiency was estimated at ≥89%. The carbonation process resulted in the production of pure calcite, whereas a mixture of Ca and Mg carbonates was found in the reaction residue. The CO2 uptake capacity (∼80 wt%) of the developed Ca-based sorbent was promising and revealed that it can be used for direct CO2 capture.