Sorbent Deactivation Research Articles

Tailoring solar-assisted calcium looping for polyethylene terephthalate (PET) steam gasification: Combined effect of carbonation and calcination temperatures on process performance

The solar-assisted calcium looping process has gained more and more interest in recent years. It allows both the capture of CO2 and the storage of solar energy during sorbent regeneration, removing the request of auxiliary fuels for heat supply. The effect of carbonation or calcination temperatures on calcium looping performance has been widely studied but mainly based on individual factors. This study investigated the combined effect of carbonation and calcination temperatures on sorbent deactivation and solar energy carrying capacity of a solar-assisted calcium looping process (10 calcination‑carbonation cycles) in a directly irradiated fluidized bed, to obtain the optimized operating temperatures with conceptual reference to the integration with polyethylene terephthalate (PET) steam gasification. The investigated carbonation and calcination temperatures were 600–700 °C and 800–900 °C, respectively, while the inlet CO2 concentration during carbonation was set at 10%v following previous results on PET steam gasification. The experimental results showed that increasing the calcination temperatures promoted the deactivation, while the carbonation temperature had a negligible effect. Fitting parameters of deactivation models were obtained by varying carbonation and calcination temperatures and performed well in process prediction, which broadens the application of these models at different operating temperatures. The best optimized condition of the solar-assisted calcium looping process for maximal averaged carbonation degree and energy carrying capacity was at carbonation temperature of 600 °C and calcination temperature of 800 °C. However, considering hydrogen yield and heat transfer to gasification, the second-best set (carbonation temperature of 650 °C and calcination temperature of 850 °C) would be preferable for the PET steam gasification process. The results of process optimization for all temperature combinations were provided, so that the required condition can be accordingly chosen also for the integration of other processes with solar-assisted calcium looping.

Deactivation Patterns of Potassium-Based γ-Alumina Dry Sorbents for CO2 Capture

Gamma-alumina (γ-Al2O3) is an essential support material in dry sorbents used to capture CO2 from flue gas. This study explores the deactivation of potassium-based γ-Al2O3 sorbents due to by-products such as KAl(CO3)(OH)2 during CO2 capture. We synthesized sorbents with K2CO3 loadings of 5, 10, 20, and 30 wt% and subjected them to repeated capture and regeneration cycles. The results show significant variations in the deactivation degree: the sorbent with 5 wt% K2CO3 exhibited a 100% deactivation rate, while the 30 wt% variant showed a markedly reduced rate of 44.6%. These findings highlight the impact of the formation of KAl(CO3)(OH)2 at the interface between K2CO3 and γ-Al2O3 on sorbent deactivation. An equation that can be used to predict the final CO2 capture capacity based on the ratio of active material to support was proposed using these results.

Precision Calcination Mechanism of CaCO3 to High‐Porosity Nanoscale CaO CO2 Sorbent Revealed by Direct In Situ Observations

AbstractDeploying energy storage and carbon capture at scale is hindered by the substantial endothermic penalty of decomposing CaCO3 to CaO and CO2, and the rapid loss of CO2 absorption capacity by CaO sorbent particles due to sintering at the high requisite decomposition temperatures. The decomposition reaction mechanism underlying sorbent deactivation remains unclear at the atomic level and nanoscale due to past reliance on postmortem characterization methods with insufficient spatial and temporal resolution. Thus, elucidating the important CaCO3 decomposition reaction pathway requires direct observation by time‐resolved (sub‐)nanoscale methods. Here, chemical and structural dynamics during the decomposition of CaCO3 nanoparticles to nanoporous CaO particles comprising high‐surface‐area CaO nanocrystallites are examined. Comparing in situ transmission electron microscopy (TEM) and synchrotron X‐ray diffraction experiments gives key insights into the dynamics of nanoparticle calcination, involving anisotropic CaCO3 thermal distortion before conversion to thermally dilated energetically stable CaO crystallites. Time‐resolved TEM uncovered a novel CaO formation mechanism involving heterogeneous nucleation at extended CaCO3 defects followed by sweeping reaction front motion across the initial CaCO3 particle. These observations clarify longstanding, yet incomplete, reaction mechanisms and kinetic models lacking accurate information about (sub‐)nanoscale dynamics, while also demonstrating calcination of CaCO3 without sintering through rapid heating and precise temperature control.

Contributions of CO2, O2, and H2O to the Oxidative Stability of Solid Amine Direct Air Capture Sorbents at Intermediate Temperature.

Aminopolymer-based sorbents are preferred materials for extraction of CO2 from ambient air [direct air capture (DAC) of CO2] owing to their high CO2 adsorption capacity and selectivity at ultra-dilute conditions. While those adsorptive properties are important, the stability of a sorbent is a key element in developing high-performing, cost-effective, and long-lasting sorbents that can be deployed at scale. Along with process upsets, environmental components such as CO2, O2, and H2O may contribute to long-term sorbent instability. As such, unraveling the complex effects of such atmospheric components on the sorbent lifetime as they appear in the environment is a critical step to understanding sorbent deactivation mechanisms and designing more effective sorbents and processes. Here, a poly(ethylenimine) (PEI)/Al2O3 sorbent is assessed over continuous and cyclic dry and humid conditions to determine the effect of the copresence of CO2 and O2 on stability at an intermediate temperature of 70 °C. Thermogravimetric and elemental analyses in combination with in situ horizontal attenuated total reflection infrared (HATR-IR) spectroscopy are performed to measure the extent of deactivation, elemental content, and molecular level changes in the sorbent due to deactivation. The thermal/thermogravimetric analysis results reveal that incorporating CO2 with O2 accelerates sorbent deactivation using these sorbents in dry and humid conditions compared to that using CO2-free air in similar conditions. The in situ HATR-IR spectroscopy results of PEI/Al2O3 sorbent deactivation under a CO2-air environment show the formation of primary amine species in higher quantity (compared to that in conditions without O2 or CO2), which arises due to the C-N bond cleavage at secondary amines due to oxidative degradation. We hypothesize that the formation of bound CO2 species such as carbamic acids catalyzes C-N cleavage reactions in the oxidative degradation pathway by shuttling protons, resulting in a low activation energy barrier for degradation, as probed by metadynamics simulations. In the cyclic experiment after 30 cycles, results show a gradual loss in stability (dry: 29%, humid: 52%) under CO2-containing air (0.04% CO2/21% O2 balance N2). However, the loss in capacity during cyclic studies is significantly less than that during continuous deactivation, as expected.

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.

Tailoring lattice oxygen triggered NiO/Ca9Co12O28 catalysts for sorption-enhanced renewable hydrogen production

Sorption-enhanced steam reforming of ethanol shows potential of supplying high-quality hydrogen with in situ CO2 capture, but suffers from sorbent deactivation. This paper describers the design of functionalized xNiO/Ca9Co12O28 materials, whose phases can be segregated once triggered by the lattice oxygen consumption via NiO/Ca9Co12O28-O2-→Ni-Co+CaO, thus acting as the catalytic sorbent. Their superiorities are demonstrated in: (i) low-temperature activation via lattice oxygen induction; (ii) recyclability via lattice oxygen replenishment; iii) high-quality hydrogen actuation via in situ CO2 adsorption. Hydrogen concentration of 95.56 vol% and near-complete ethanol conversion can be achieved. Moreover, stability across 50 repeated cycles without obvious reduction in catalytic reforming and CO2 adsorption is demonstrated. In situ XRD studies demonstrate the formation of the Ni-Co alloy and the reorganization of the catalytic sorbent. The adsorption energies of ethanol on the surface of Ni(111), Co(111), and Ni-Co(111) were studied by DFT calculations, reaffirming the higher catalytic activity of Ni-Co alloys.

Dynamic Monte Carlo reactor modeling of calcium looping with sorbent purge and utilization decay

This work presents a new dynamic modelling approach for calcium looping systems that allows explicit sorbent deactivation and purge/makeup. These are common in plant operations, but often neglected in modelling. This model adopts a Monte Carlo approach, tracking merely 100 particles between the carbonator and the calciner for 60 reaction cycles with the particle residence time in each reactor determined stochastically. The simulated results agree well with the experimental data in both the transient and steady-state stages. This model provides a promising approach to predicting the dynamic behaviour of calcium looping systems under relatively realistic conditions at low computational cost. The stochastic description of a multiphase reactor via the Monte Carlo process can be widely adapted in various scenarios.

H2S-Selective Catalytic Oxidation to Sulfur over Iron Oxide Sorbent Supported on Semi-Coke

Iron oxides modified by semi-coke sorbents (referred to as FeSC) were prepared by the hydrothermal impregnation method and were used for the selective catalytic oxidation of H₂S to sulfur. The physicochemical properties of samples were characterized by Brunauer–Emmett–Teller analysis, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry (TG), and X-ray photoelectron spectroscopy. The results showed that iron oxide could be highly loaded on semi-coke with a microporous structure and high specific surface area. Fe₂O₃ was considered the only major active component on the surface of the sorbent. Fe7SC stably maintained the catalytic performance at 180 °C with the longest breakthrough time and highest release sulfur capacity. There was no benefit to desulfurization with excess oxygen in the feed gas. Through further analysis by TG, elemental sulfur was confirmed to be the main product of the catalytic oxidation of H₂S. Besides, a possible mechanism of H₂S selective catalytic oxidation over sorbent was proposed, in which the key step was the oxidation of FeS into S⁰ and Fe³⁺ by O₂. Moreover, sorbent deactivation was mainly caused by pore structure blockage by the sulfur product.

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.

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.

Ni-Zn-based nanocomposite loaded on cordierite mullite ceramic for syngas desulfurization: Performance evaluation and regeneration studies

A series of Ni-Zn-based nanocomposites with various Ni:Zn mol ratios was prepared using a facile hydrothermal-calcination method. The Ni-Zn-based nanocomposites were characterized using XRD, FESEM, EDX and N2 adsorption, indicating that all the Ni-Zn-based nanocomposites consisted of hierarchical nanostructure. The Ni-Zn-based nanocomposites were used as sorbents for desulfurization of simulated syngas. It was found that the optimum Ni:Zn mol ratio for preparing highly-regenerable sorbent was 2:5 and hence, this ratio was used to prepare the Ni-Zn-based nanocomposite loaded on cordierite mullite honeycomb (NiZn-28-HC). The characterization study revealed that the immobilized Ni-Zn-based nanostructure consisted of seaweed-like morphology with 10 µm thickness. After 5 desulfurization-regeneration cycles, the NiZn-28-HC demonstrated only a minor loss in the desulfurization performance. Investigation of the surface chemical states using XPS revealed that the marginal sorbent deactivation during repeated desulfurization-regeneration cycles was mainly due to the formation of sulfate. The influence of HCl on the desulfurization-regeneration cycle was also studied, showing that the presence of HCl can inhibit the desulfurization process due to competition reaction with sulfur compounds for sorption onto the sorbent active sites. However, it was found that HCl up to 50 ppmv has no significant influence on the performance and regenerability of the sorbent. The results indicated that the NiZn-28-HC is a promising sorbent with high reactivity and stability for syngas desulfurization.

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.

Facile synthesis of silica aerogel supported K2CO3 sorbents with enhanced CO2 capture capacity for ultra-dilute flue gas treatment

Silica aerogel supported K2CO3 sorbents with different K2CO3 loadings were synthesized by sol-gel and wet impregnation processes. The sorbents were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM) techniques. CO2 capture performances of the sorbents were tested in a simulated ultra-dilute flue gas stream of 1.0%CO2 and 2.0%H2O at 20 °C, using a fixed-bed reactor coupled with an online infrared gas analyzer. Sorbent regeneration performances of the samples were evaluated in a pure N2 atmosphere at 200 °C with a heating rate of 10 °C/min. CO2 capture capacity and K2CO3 utilization efficiency increased first and then decreased with the increase in K2CO3 loading. The desired sorbent with 20 wt% K2CO3 was screened for investigating the effects of acid impurities. The presence of 500 ppm SO2 and 500 ppm NO in the simulated flue gas stream was found to adversely affect the CO2 capture, sorbent regeneration and multiple cyclic performances. Detailed mechanisms of the irreversible sorbent deactivation process were discussed. SO2 could be chemically absorbed by K2CO3 under a moist condition to form byproduct of K2SO3·H2O, and the byproduct was stable and would be accumulated in the sorbent during the repeated cycles. This further attenuated the physical properties and K2CO3 utilization efficiency of the sorbent. These results would lay a solid foundation for further application of the sorbent in ultra-dilute flue gas treatment.

Biomass derived wood ash with amine modification for post-combustion CO2 capture

Large quantities of wood ashes derived from biomass materials combustion potentially threaten the ecological environment. Recycling of the wood ashes as solid sorbents for pollutants control is an economical and environmentally friendly route. In this work, waste wood ashes (WAs) were modified with tetraethylenepentamine (TEPA), monoethanolamine (MEA), diethanolamine (DEA), polyethyleneimine (PEI), and diethylenetriamine (DETA) to synthesize solid sorbents with enhanced CO2 capture performances. CO2 capture behaviors of the synthesized sorbents were tested under 60°C, 5.0%CO2+5%H2O using a fixed-bed reactor, and sorbent regeneration behaviors were evaluated under 120°C, 10°C/min and 100%N2. The sorbent synthesized of ashes collected from straw-fired power plants modified with TEPA (TEPA-WA-1) is identified as the optimum candidate with superior capability for CO2 capture and sorbent regeneration. CO2 capture capacity of TEPA-WA-1 increases first and then decreases with the increase of amine loading. Sufficient amine loading can provide substantive active sites for enhanced CO2 chemisorption, whereas excessive loading will cause particle aggregation and pore structure blockage and affect its CO2 capture capacity adversely. The maximum CO2 capture capacity of 2.02mmol CO2/g is obtained with an amine loading of 45wt.%. The desired sorbent is demonstrated to be stable during 10 cyclic operations. Moreover, the presence of acid impurities (SO2 and NO2) exerts negative effect on the cyclic CO2 capture and sorbent regeneration performances of the synthesized sorbent. It is mainly attributed to sorbent deactivation induced by the formation of byproducts and weakened physical properties for the sorbent exposed in acid impurities.

Effectiveness of CO2 Capture by Calcium Looping with Regenerated Calcium Sorbents – Last Step Calcination

The Ca looping process offers many advantages over the other CO2 capture technologies, such as a relatively small decrease in power plant efficiency and a potential for is further reduction. However, calcium sorbents in the consecutive cycles of adsorption and regeneration by calcination undergo deactivation, which is a considerable drawback of this technology. The depletion of sorbent reactivity is due to sintering, which causes changes in the sorbent's porous and crystal structure, whereby its reacting surface area decreases.The approaches to reducing sorbent deactivation (sorption capacity loss) include thermal preactivation, reactivation by hydration and/or the production of synthetic sorbents and doping.This paper studies three methods of regenerating deactivated sorbents. The sorbents underwent deactivation after working in the calcium looping of 10 calcination/carbonation cycles at respectively 900°C and 650°C. The first regeneration method consisted in hydration with water in controlled time and temperature conditions. The second regeneration method consisted in hydration with steam in controlled time and temperature conditions. The third method – 2-stage regeneration – besides water or steam hydration, included a second stage consisting in the controlled exposition of the sorbent to a CO2 enriched atmosphere. In all the methods the regeneration of the spent sorbent was conducted after the final calcination process. After regeneration the sorbent was subjected to 24 calcination/carbonation cycles in similar conditions as before regeneration.This study compares the three methods of regeneration in terms of the CO2 capture efficiency of the regenerated sorbent. The sorbents collected after the looping tests and after each regeneration step were analysed by mercury porosimetry, X-ray diffraction and scanning electron microscopy to determine the interdependences between the sorbents’ physicochemical properties and their CO2 capture capacity.The investigations showed that: 1) an improvement in CO2 capture capacity in the calcium looping process was achieved by applying both water/steam hydration and 2-stage regeneration after 10 calcination/carbonation cycles), 2) the size of CaO crystallites increased during looping cycles and decreased as a result of the 2-stage regeneration, 3) the sorbent's pore and particle structure showed significant changes after the reactivation, which may explain the increase in its CO2 capture capacity.The regeneration and CO2 sorption capacity of deactivated sorbent can be effected by radically changing the process temperature and simultaneously feeding saturated steam and then washing the sorbent with a gas with a high CO2 content. The novelty of this idea consists in the fact that the desired regeneration effects can be achieved by changing the regeneration parameters and only slight modifying the structure of the regenerators.

Efficacious means for inhibiting the deactivation of K 2 CO 3 /AC for low-concentration CO 2 removal in the presence of SO 2 and NO 2

Abstract K 2 CO 3 supported on activated carbon (K 2 CO 3 /AC) shows promise as a potential candidate for removing low-concentration CO 2 from environmental control and life support systems (ECLSS). However, K 2 CO 3 /AC would suffer a decreased CO 2 sorption capacity due to sorbent deactivation in acid impurities such as SO 2 and NO 2 . To solve this problem, water vapor pretreatment, KOH addition and polyethyleneimine (PEI) modification were proposed as efficacious means for improving its CO 2 sorption capacity and mitigating the sorbent deactivation in these acid impurities. CO 2 sorption performances of the pretreated and modified sorbents were evaluated in a fixed-bed reactor under simulated ECLSS conditions of 20 °C, 1.0% CO 2 , 2.0% H 2 O, 30 ppm SO 2 , 20 ppm NO 2 and balanced N 2 . The mechanisms for sorbent deactivation inhibition by water vapor pretreatment, KOH addition and PEI modification were revealed by N 2 adsorption-desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FT-IR). Effects of water vapor pretreatment duration, KOH addition and PEI loading on sorbent deactivation inhibition performances were demonstrated. Furthermore, the long-term working stabilities of the pretreated and modified sorbents in impurities were evaluated. The results will provide fundamental support on practical application of K 2 CO 3 /AC for low-concentration CO 2 removal in ECLSS.

Understanding the deactivation of K2CO3/AC for low-concentration CO2 removal in the presence of trace SO2 and NO2

Efficient removal of low-concentration CO2 from manned closed systems including space-crafts and submarines is critically significant for fulfilling the requirement for long-term space or deep sea explorations therein. K2CO3 supported on activated carbon (K2CO3/AC) shows promise in these low-concentration CO2 removal applications, with respect to minimizing the system mass and volume. However, the undesirable trace impurities of SO2 and NO2 in these systems are expected to degrade the CO2 sorption efficiency of K2CO3/AC. In this work, K2CO3/AC is synthesized with wet impregnation method. CO2 sorption capacity, sorbent regeneration behaviors and multiple cycle performances of K2CO3/AC in the presence of trace SO2 and NO2 are evaluated with a modified fixed-bed reactor system. The sorbent is characterized by N2 adsorption–desorption, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDX) as well as elemental analysis (EA), to enable detailed mechanisms for sorbent deactivation in these impurities being fully understood.

Role of precalcination and regeneration conditions on postcombustion CO2 capture in the Ca-looping technology

The Ca-looping (CaL) technology is already recognized as a potentially viable method to capture CO2 from postcombustion gas in coal fired power plants. In this process, CO2 is chemisorbed by CaO solid particles derived from precalcination of cheap and widely available natural limestone. The partially carbonated solids are regenerated by calcination under high CO2 concentration. Novel CaL concepts are proposed to further improve the efficiency of the technology such as the introduction of a recarbonation reactor in between the carbonation and calcination stages to mitigate the progressive deactivation of the regenerated CaO. Process simulations aimed at retrieving optimum design parameters and operating conditions to scale-up the technology yield results critically dependent on the multicyclic sorbent performance. Nevertheless, technical limitations usually preclude lab-scale tests from mimicking realistic CaL conditions necessarily involving high CO2 concentration for sorbent regeneration and quick transitions between carbonation and calcination. In this work, a lab-scale experimental analysis is reported on the CaO multicyclic conversion at CaL conditions closely resembling those to be expected in practice. The results presented evidence a relevant role of precalcination conditions. Precalcination in air leads to a strongly adverse effect on the activity of the sorbent regenerated under high CO2 concentration, which is further hindered if a recarbonation stage is introduced. On the other hand, sorbent deactivation is mitigated if precalcination is carried out at conditions similar to those used for sorbent regeneration. In this case, recarbonation helps lessening the loss of multicyclic conversion, which is further enhanced by the synergistic combination with heat pretreatment. Moreover, the present study shows that the kinetics of carbonation is strongly dependent on precalcination and regeneration conditions. The diffusion controlled carbonation phase and recarbonation are intensified if the sorbent is precalcined and regenerated under high CO2 concentration whereas the reaction controlled carbonation phase is notably hampered.

Alstom's Regenerative Calcium Cycle - Norcem Derisking Study: Risk Mitigation in the Development of a 2nd Generation CCS Technology.

Alstom is a pioneer and industrial leader in the development of post combustion CCS technologies. Alstom's Regenerative Calcium Cycle (RCC) is a 2nd generation post combustion CCS technology utilizing a calcination/ carbonation loop to capture CO2 from flue gas at high temperatures. The CO2 capture cycle is driven by introducing heat required to regenerate sorbent at 900 °C (4.0 GJ/t CO2, chemically bound CO2) the regenerated sorbent is then used for CO2 capture from flue gas where the exothermic heat of the reverse reaction (-4.0 GJ/t CO2 captured) is recovered in a power cycle. Due to the option of using natural sorbent materials (limestone), RCC also provides attractive integration opportunities with industrial processes such as cement production. Recently indirectly fired RCC calcination concepts also open the door for game changing performance gains using natural or even synthetic materials. However, the wide range of performance variability characteristic of natural sorbents contributes to uncertainty in defining process performance. Reliable sorbent deactivation models, which describe both cyclic and chemical deactivation, in combination with mechanistic reactor models which predict gas and solids phase conversions are required to lower the uncertainty associated with new reactor concepts and larger geometries required for commercialization for retrofit power-plant flue gas or for integrated solutions for the cement industry. Parallel to RCC process development, Alstom is currently executing a “Derisking” or risk-mitigation study for Norcem, a Norwegian cement producer, who seeks to take a leading position in the development of technologies for CO2-capture from cement production facilities. Norcem is currently heading up a project on behalf of the European cement industry (partners are Norcem, HeidelbergCement and the European Cement Research Academy) investigating various technological options at the pilot scale. In relation to this project, Alstom's RCC technology was selected with the objective to define process performance and the associated uncertainty. Pilot testing was conducted at the Institute of Combustion and Power Plant Technology at the University of Stuttgart (IFK) planned by Alstom focusing on the validation of process models and less the targeting of pilot plant performance, which is often limited by reactor geometries. This paper discusses the characterization of sorbent performance and the gap between the performance expected from thermo- gravimetric analysis (TGA) and that realized during steady state pilot testing under representative operating conditions. Operational stability, material balance closure and the confirmation of sorbent attrition characteristics from pilot testing are also discussed and steady-state operational data, gained from pilot testing are applied to initialize mechanistic process models which allow prediction of reactor performance for larger more efficient designs.

Dry Regenerable Metal Oxide Sorbents for SO2 Removal from Flue Gases. 3. Long-Term Durability

The modified expanding grain model, presented in the part-2 of this series of papers, is extended to describe the sorbent behavior in a long-term cyclic process using the experimental data obtained in a 25-cycle sulfation/regeneration test. The model extension uses one adjustable parameter to describe the changes in the diffusional resistances occurring within the sorbent particle to predict the behavior of the sorbent undergoing an extended cyclic process. The model suggests that during the cyclic process, because of the cracks and fissures developing within the product layer of the grain, the product layer porosity and the product layer diffusivity of the grain as well as the tortuosity parameter gradually increase, resulting in lower intergrain diffusivity and lower overall sorbent reactivity. The model was used to predict the long-term performance of the sorbent to estimate the fresh sorbent makeup rate in the regenerative copper-oxide process. The results indicate that the sorbent makeup rate generally correspond to a useful sorbent life of higher than two years, but is highly sensitive to the slope of the extrapolation line for the sorbent deactivation.